This article presents research results relating to the potential for waste utilization in the form of polymer optical fiber (POF) scraps. This material is difficult to recycle due to its diverse construction. Three different volumes of POF were used in concrete in these tests: 1%, 2%, and 3%. The experimental studies investigated the basic properties of the concrete, the elastic and dynamic moduli, as well as deformation and deflection of reinforced beams. The microstructures, including the interfacial transition zones (ITZs), were recorded and analyzed using a scanning electron microscope. It was observed that 180 freezing–thawing cycles reduced the concrete frost resistance containing 3% POFs by half compared to the control concrete. The resistance to salt crystallization of this concrete decreased by about 55%. POFs have significant effects on the splitting tensile and flexural strengths compared to the compressive strength. The control beams were destroyed during the four-point static bending tests at half the force applied to the beams that were reinforced with POFs. Concrete is the most widely used construction material in the world. It is predicted that demand for concrete will increase by 12%–23% by 2050 compared to 2014 ,7. One oFiber-reinforced concretes (FRC) have a number of advantages, including: greater compressive strength in the early stages of maturation than ordinary concrete ; greaterThese materials also have high abrasion resistance and durability, comparable to that of plain concrete. The disadvantages of fiber composites are the relatively high cost of the fibers , deterioOptical fibers (OF) are made of two basic coaxial layers, i.e., the core, which is a transmission medium in which light moves, and the surrounding jacket. Most often, the core is made of quartz glass or a plastic with similar parameters, while the coat is made of a polymer with a refractive index less than the core factor. The entire fiber is surrounded by an outer protective jacket . SeveralTo the best of our knowledge, in the literature there are no examples of the use of POFs for dispersed reinforcement in concrete and reinforced concrete structures. Therefore, this study focused on the evaluation of the modification of concrete by POFs. The aim of this work was POF recycling through their usage as a supplementary material for concrete. This reduces the amount of waste stored and increases the tensile strength of concrete. The quality of the obtained concretes supplemented with plastic optical fibers was evaluated within the investigation of their physical and mechanical properties, such as their bulk density, open porosity, flexural tensile strength, compressive strength, splitting tensile strength, static and dynamic modulus of elasticity, frost and salt resistance, and other properties.Thus, by considering the economic and ecological aspects of the decrease in e-waste, its application in the technology of concrete production is a reasonable choice for reinforcing concrete.In order to determine the influence of plastic optical fibers (POF)  from e-waste on the physical and mechanical properties of concrete, four mixtures of concrete were developed, the compositions of which are presented in 3, specific surface of 4049 cm2/g, compressive strength after 2 days of 31 MPa and after 28 days of 60.5 MPa, initial setting of 190 min, loss on ignition of 5.0% by weight of cement. The chemical ingredients of the cement are presented in The Portland cement CEM I 42.5R (Cemex Poland), tested according to PN-EN 196-1:2016-07 : specifi3, water absorption after 24 h = 0.01%, static modulus of elasticity = 10,000 MPa, tensile strength = 720 MPa.Plastic optical fibers (POFs) originated from the manufacturing plants located in Lublin, Poland (LSN). They consist of approximately 60% polyethylene and 40% copper cables. Thin fibers were obtained after removing the thick plastic cable jacket a. The PO3, water absorption = 2.7%, resistance to fragmentation = 25, compressive strength = 190 MPa, elastic modulus = 6750 MPa, resistance to wear = 2.Coarse aggregate–river gravel with 2–8 mm and 8–16 mm granulation. The gravel aggregate was characterized by the following properties: apparent density = 2625 kg/m3, bulk density of 1650 kg/m3, absorptivity of 0.4%, and mineral dust content of 0.4%.Fine aggregate–quartz sand with 0–2 mm granulation and specific density of 2650 kg/mAn efficient superplasticizer based on Glenium® SKY 591 polycarboxylate ethers was used at the amount of 0.70% in relation to the weight of cement in order to obtain the same workability in all the concrete mixtures.The following ingredients were used to prepare the mixture:The experimental methods used to determine various hardened concrete properties are presented in The concrete cube samples measuring 150 × 150 × 150 mm, 100 × 100 × 500 mm, and concrete cylinders (150 mm in diameter and 300 mm in height) were prepared according to EN 196-1:2016-07 . The devFour series of concrete samples  measuring150 × 150 × 150 mm  and 100 Testing of the static and dynamic modulus of elasticity was carried out on cylinders (150 mm in diameter and 300 mm in height). The dynamic modulus of elasticity of the tested samples was examined with the dynamic method utilizing the resonance frequency measurements generated by the C311-R frequency counter. Testing was conducted using the approximate output voltage at the level of 1 V.DME is the dynamic modulus of elasticity, measured in GPa; L is the length of the specimen, measured in m; n is the frequency, measured in kHz; and ρ is the apparent density, measured in kg/m3.The investigation involved installing an accelerometer on a silicone-coated concrete cylinder, which was then connected to the data acquisition system. During the test, a steel ball with a small diameter was employed as a source of impact. The steel ball was dropped onto the cylinder, while the vertical motion was measured using the accelerometer. The relevant data were acquired by means of computer software and the data acquisition system. This enabled the acquisition of amplitude–frequency and amplitude–time graphs. On the basis of the former graph, the peak value was obtained, indicating the resonant frequency of the composite specimen. The formula (1) below  was usedThe morphology of the concrete with the addition of optical fibers was determined using scanning microscopy (SEM)  equipped with a chemical composition analysis system based on EDAX X-ray energy dispersion. The samples for SEM testing in the form of a powder were glued onto the carbon holder using carbon glue . Then, the preparations were sprayed with a carbon layer about 50 nm thick in a sprayer to achieve conductivity on the sample surface.The deformation and deflection examination of the concrete in the reinforced concrete model (with the dimensions of 2000 × 250 × 350) were conducted using each type of concrete (C0–C3). The beams were reinforced by 2 Ø 6 mm rods in the top and 2 Ø 12 mm rods in the bottom made of BSt500S steel, with a yield point Re = 500 MPa, while the stirrups were made of ribbed Ø 8 mm steel. The schematic view of the beam reinforcements is presented in Four-point bending tests were performed after 28 days on a MTS 809  axial–torsional testing system machine, in accordance with ASTM C 78 . The tesThe control beams were made using the C0 concrete based on natural aggregate. Three beams were made for each concrete. The load was applied using a 2000 N capacity hydraulic jack at a rate of approximately 3 mm/min. Additionally, continuous measurement of displacement was carried out using the dial indicators and indirectly by means of highly accurate laser readings. The midspan deflection was measured using a laser optical displacement (LOD) device. The loads and strain readings were captured using the System 5000 data logger . The deflections of beams were read at upper and lower levels, while their values at the upper, compressed, and lower tensile levels were read every 5 kN. The force–deflection relationship is presented in From the data presented in In the case of the mostly POF-supplemented C3 sample, the increase of open porosity equaled 14.8% and water absorption equaled 55.1% compared to the reference C0 sample. The results for water absorptivity indicate the increased porosity of the mixtures due to the application of fibers, especially steel ones, which was demonstrated by other researchers  in studiThe surfaces of POFs have hydrophobic properties, meaning they do not absorb water or interfere with the hydration reaction of concrete . HoweverThe mechanical data for particular concrete compositions are presented in As shown in Kim et al.  tested sThe most important goal of the optical fiber cable addition to concrete was to assess the potential of using the recycled fibers as dispersed reinforcement for concrete and to change the nature of the material operation at loading points. This effect is visible in the comparison of bending tests on the beams with the addition of the optical fiber cable and concrete without reinforcement.Studies have shown a significant effect of fibers on the ductility of concrete by changing the nature of its performance from fragile to quasi-plastic. The fibers evenly dispersed in the concrete bridge its discontinuous structure, which results from the microcracks or scratches in the matrix. In the case of the non-reinforced concrete, a large concentration of stress is observed within the crack, which negatively affects the strength of this zone. The presence of the fibers allows the transmission of forces resulting from loads from one side of the crack to the other, which significantly reduces the stress concentration on the edge of the scratch. This phenomenon limits the transformation of microscratches into larger cracks, preserving the integrity of the concrete element with POFs after scratching. Unlike ordinary concrete, POF concrete does not behave in the same way as a brittle material, but exhibits quasi-plastic properties. Therefore, it seems that optical fiber cables are most effective after the brittle matrix breaks, similarly to steel fibers. According to Naaman and Reinhardt , the obs3), Grzymski and Musiał [The use of steel fibers increases both the compressive and flexural strength, as demonstrated by many authors ,74,75. Ud Musiał  observedd Musiał ,79,80.As can be seen in the research of Kalpana and Tayu , who stuIn the case of both static and dynamic moduli of elasticity, the addition of POF decreases their value. For the static modulus of elasticity, the decrease equals 15.6%, while for the dynamic modulus this amounts to 15.2% compared to the reference C0 sample.R2 = 0.929) and relatively low errors in the intercept. It is essential to point out that the amount of fibers had an influence on the data.On the basis of the test results, the dependencies and associations between the different concretes with and without POF properties were proposed. The graph in 2. The high determination coefficient equal to 0.997 indicates that the data have been matched by the best R2 value. A high determination coefficient value indicates that the flexural tensile strength has a strong association with the splitting tensile strength. There is a clear grouping of the results depending on the quantity of fibers in the concrete, which was also shown in the relationships between the compressive, splitting tensile, and flexural tensile strengths  and low errors in the intercept.R2 = 0.973). During the salt crystallization resistance test, the mass loss reached 79.0% in the case of the C3 sample as compared to C0. In turn, no deterioration was observed in the ultra-high-performance concrete with steel and polypropylene fibers after the salt crystallization test [An interesting relationship can be observed for the changes in water absorption of a material and mass loss after the salt crystallization test. The diagram presented in ion test .The frost and salt resistance values are considered to be the main elements in the assessment of the concrete durability. When the pores in the concrete are almost completely saturated, freezing can cause severe cracks and damage to the concrete ,65. In tIn our research the frost resistance features decrease (loss mass increases) together with POF supplementation . In the 2 formula. The high determination coefficient R2 equal to 0.942 indicates that the data were properly fitted. A higher correlation coefficient value indicates that the compressive strength has a strong relationship with frost durability. Together with the decrease of the compressive strength, the mass loss increases after the F-T test, which can be confirmed by the research of other scientists [This can be described by the second-order polynomial model, which can be presented in the form of y = 36.261 − 1.419x + 0.014xientists ,65,84.The main purpose of the fiber addition to the concrete is to change the nature of the material performance at a load causing tensile stress. This effect on the reinforced concrete and concrete beams without reinforcement is visible in the comparison of bending tests. When the tensile strength is achieved, a crack appears in the concrete beam that causes the destruction of the sample. After the cracking, the fiber-reinforced concrete beam goes into extra-elastic operation phase due to the cooperation of the fibers, allowing for further load transfer .The POF supplementation influenced the value of the tensile strains in the tested beams made of POF concretes. As shown in In the case of compressive strain, the values of the beams manufactured from the supplemented concrete (C1–C3) were comparable to those of the traditional concrete (C0). For the smallest loading force (5 kN), the standard beam compression strain is the lowest. Together with the loading force increase, all strains are higher and the C0 concrete beam reaches slightly higher strain values. Interestingly, after reaching the value of 35 kN of loading force, the C0 beam was damaged, while C1–C3 beams still performed, reaching significantly higher compression strain values equal to 11.2% (C1), 10.1% (C2), and finally 8.78% (C3).Finally, based on the test results shown in According to Pająk and Ponikowski , the addThe analyses carried out by Stachniewicz et al.  during aIn general, the fibers have little effect on the compressive strength value under static conditions. A clear effect of the fibers on the post-peak parameters of the concrete was noticed. The fibers delay the appearance of the microcracks and fill the macrocracks. Under static conditions, the microcracks slowly spread into macrocracks . HoweverMost of a concrete’s properties, such as strength, liquid and gas permeability, or frost resistance, depend on its structure. These features result directly from its composition and the arrangement of the elements in the structure of the material. Therefore, the areas between POFs, aggregates, and grout grains and phases occurring in concrete were investigated.2 crystals [The concrete morphology and elemental composition analysis performed with a scanning electron microscope and the EDS analysis indicate mainly calcium, aluminum, silicon, and iron oxides are present in the concrete. Due to its dominant share, the C–S–H phase, which is a component of cement slurry hydration products, constitutes an important component of the cement slurry . The concrystals , which hSimilar observations were made by Barnat-Hunek et al.  in mortaThere are slight microcracks in the cement matrix due to the excellent perforation of the ITZ bond between the mortar. However, a crack with a width of about 25 µm that does not occur at the contact of the fiber with the matrix but in the matrix itself can be seen at a distance of about 100 µm. Its appearance may be due to the fibers being pulled out of the concrete matrix during the destruction and not due to the fibers breaking or to the matrix shrinking during maturation . A similEttringite crystals were observed near POF and between sulfate ions, which are formed during the reaction between hydrated calcium aluminates and calcium hydroxide and are a product of cement hydration. The crystals are over 5 µm long, which overgrow and intertwine to form the clusters . The preThe observations made using the scanning microscope indicate the compact and solid structure of the grout and its very good adhesion to the fine aggregate–sand mixture . The pasThe industrial POFs used in this study could be an economical and environmentally friendly solution. This study was performed to determine the effects of the addition of POFs on the physical and mechanical properties, as well as on the freezing–thawing and salt crystallization resistance of concrete. -POFs cause higher concrete porosity, lowering compressive strength, as well as the static and dynamic moduli, in turn lowering the durability. The SEM studies showed that this is connected with the ITZ structure, located between the POF and the matrix.-The increased volume of free pores in the concrete reinforced with POFs decreased the mass after the frost and salt crystallization test. It was observed that 180 freezing–thawing cycles caused a doubling of the concrete frost resistance with the addition of 3% volume POFs compared to the control concrete. The resistance to salt crystallization of C3 decreased by 55%. This was due to the increased porosity and absorptivity of concretes reinforced with POFs.-The deflection values for the beams with 3% POFs were 25% lower than in the beams with 1% POFs. The control beams were destroyed at half the force (20 kN) compared to the beams with POFs.-Microstructure studies illustrated that adding optical fibers to concrete considerably changes the microstructure. The presence of an increased amount of ettringite in the ITZ structure of the fiber-reinforced concrete can weaken the adhesion of the grout to the POFs; the microcracks are visible in this zone together with a larger number of pores, which decrease some of the strength parameters.-POFs have a significant effect on the splitting tensile and flexural strengths as compared to the compressive strength. Thus, considering economic and ecological aspects of decreasing e-waste, its application in concrete production to reinforce concrete is a reasonable choice.-Practical limitations in the application of concrete reinforced with POFs result from the fact that the frost resistance decreases with increasing POF content. Therefore, elements made of POF concrete should be used indoors. The second limitation is the decreased compressive strength, which to some extent is compensated for by the increase in splitting tensile and flexural strengths. Therefore, this concrete should rather be used in elements exposed to bending and tensile forces, rather than in elements exposed to compressive forces, such as columns or walls.Through the analysis of the examination results, the following conclusions can be drawn:


The total days of therapy per 100 patient days declined from 47.0 to 42.2 days (p = 0.035). The rate of patients receiving postoperative therapy decreased from 56.8% to 45.2% (p = 0.002), comparing both periods. There was a significant decline in the rate of inappropriate indications  as well as a significant change from broad-spectrum to narrow-spectrum antibiotic use  for postoperative therapy. The significant decline in antibiotic use did not affect either clinical outcomes or the rate of postoperative wound complications. Conclusions: Postoperative antibiotic use for intra-abdominal infections could be significantly reduced by antimicrobial stewardship interventions. The identification of inappropriate indications remains a key target for antimicrobial stewardship programs.Background: The aim of this study was to assess the impact of antimicrobial stewardship interventions on surgical antibiotic prescription behavior in the management of non-elective surgical intra-abdominal infections, focusing on postoperative antibiotic use, including the appropriateness of indications. Methods: A single-center quality improvement study with retrospective evaluation of the impact of antimicrobial stewardship measures on optimizing antibacterial use in intra-abdominal infections requiring emergency surgery was performed. The study was conducted in a tertiary hospital in Germany from January 1, 2016, to January 30, 2020, three years after putting a set of antimicrobial stewardship standards into effect. Results: 767 patients were analyzed ( Antimicrobial resistance (AMR) has become a global health threat and affects us all in a way no one could have imagined when the discovery of penicillin in 1928 caught public attention [With the emergence of antimicrobial resistance, antimicrobial stewardship programs (ASPs) started evolving, aiming to combat this menace and promote the rational use of antibiotics. By reducing the adverse events and infections caused by multidrug-resistant bacteria (MDR), ASPs strive to optimize patient management and improve patient outcomes, globally supported by government policy interventions ,3. In 20This quality improvement study encompassed a period of 3 years (2016–2018) and was retrospectively conducted in a 1500-bed-sized tertiary hospital in Germany, with an in-hospital ASP officially launched in 2015, gradually reaching out to all departments including the department of general surgery by 2018.The effects of the implementation of a local ASP on the management of IAIs were examined by a retrospective cohort analysis. The years 2016 and 2017 are referred to as the “baseline period” , and the year 2018, as the “ASP period”.The primary endpoint was defined as the total days on antibiotic therapy for intra-abdominal infections. The secondary endpoints included the appropriateness (indication and documentation) of the postoperative antibiotic therapy (PAT), the empiric selection of antibiotics and the frequency of antibiotic changes.All patients ≥ 18 years old undergoing emergency abdominal surgery with suspected IAIs between 01.01.2016 and 31.12.2018 were included with the following selection criteria: diagnosis of peritonitis (ICD-10 K65.0–K65.9), acute cholecystitis , acute appendicitis (ICD-10 K35.2–K35.8), acute diverticulitis (ICD-10 K57.2–K57.22), intestinal perforation  or obstructive ileus (ICD-10 K56.5-K56.7). Patients with the following criteria were excluded from analysis: acute pancreatitis, acute mesenteric ischemia, acute leukemia, end-stage malignant disease in palliative care, an ASA score > IV, or an extra-abdominal infectious focus requiring antimicrobial therapy before and after surgery.All data were retrieved from the hospital information system and were transferred into a pseudonymous database with multiple variables containing the baseline patient characteristics ; pre-, peri- and postoperative antibiotic therapy ; surgical therapy ; and postoperative 30-day outcomes . The severity of peritonitis was staged according to the Mannheim Peritonitis Index (MPI) . Sepsis Pseudomonas aerugionsa and Enterobacterales is alarming [Pseudomonas aeruginosa to meropenem and the latter’s high utilization in the hospital and general surgical units, AMS strived to reduce its usage. Antibiotics belonging to the fluoroquinolones (FQs) and third-generation cephalosporins are linked to a rising prevalence of resistance amongst Enterobacterales too  and share potent side effects such as C. difficile infections [E. coli to FQs such as ciprofloxacin (CIP) made the AMS committee finally promote a drastic change in our hospital’s general antibiotic policy, also affecting the department of general surgery.The university hospital of Würzburg (UKW) officially launched an ASP in July 2015 complying with national and international guidelines on the implementation of ASPs in hospitals ,18. An afections . Our antAll statistical analyses were performed using IBM SPSS Statistics, version 26 . Descriptive data are reported as means with standard deviations, unless otherwise noted. Comparisons between the analyzed timeframes were performed using chi-square, Fisher’s exact or Mann–Whitney U tests, in accordance with the data scale and distribution. The level of statistical significance was 0.05 (two-sided). The UKW participates in one of the national surveillance projects on antibiotic consumption (ADKA-if-DGI), and antimicrobial use (RDD/100PD) data were provided by its twice-yearly-released surveillance report.n = 495 during the baseline period; n = 272 during the ASP period). The preoperative patient characteristics are provided in A total of 767 patients were analyzed (p = 0.02) was noted in the ASP period, decreasing the days of therapy per 100 patient days (DOT/100PD) from 47.0 to 42.2 (p = 0.035). Details on the perioperative prescription of antibiotics and AMS assessments are provided in An overall reduction in the total days on antibiotic therapy (ABT) from a mean of 6.1 days to 4.8 days (p = 0.002) in the ASP period. In addition, the postoperative empiric antibiotic therapy (EAT) significantly changed during the study, with fewer FQs and third-generation cephalosporins, and more first-generation cephalosporins (p = 0.08) was observed. During the subgroup analysis of indications for surgery, only PAT in cholecystitis was significantly shortened . Interestingly, the number of switches during ABT significantly decreased in the ASP period  postoperative antibiotic therapy, shortened treatment durations (not significant) and an influence on the choice of antibiotics, with the use of more narrow-spectrum antibiotics.Details of the postoperative outcomes and complications are provided in Enterobacterales to the named antibiotics. The data, when compared with the pre-implementation period, showed a significant reduction in targeted antibiotic use, with a sustained improvement in prescribing quality [This quality improvement study analyzed the impact of antimicrobial stewardship measures on the prescribing culture for antibiotics for surgical intra-abdominal infections and took a closer look at the quantity and quality of postoperatively prescribed antibiotics. Antimicrobial therapy for uncomplicated surgical IAIs with no signs of perforation or established infection is seen as prophylactic and not empiric; in consequence, the duration is restricted to a maximum of 24 h. Complicated IAIs with localized or diffuse peritonitis prompt empiric antibiotic therapy and are principally driven by the bacterial flora of the gastrointestinal tract, but without adequate source control, the most potent antibiotics will be administered to no avail . Popovsk quality . The hig quality , yet no  quality . In our  quality ,29. To a quality ,30. Sart quality ; on the  quality . The pro quality . Our stu quality ,35 and t quality .The study has some limitations: it was single centered and the retrospective analysis incorporated a heterogeneous patient sample with uncomplicated and complicated IAIs, either community or hospital acquired. This study does not provide recommendations for IAIs but demonstrates the general potential of ASPs for a rational prescription of antimicrobials in IAIs overall. Although an improvement of patients’ outcomes could not be demonstrated, the findings provide assurance that less antibiotic consumption is not associated with an impairment of patients’ outcomes either. This quality improvement study highlights, altogether, the power of ASPs for optimizing antimicrobial use. The clinical efficacy in the postoperative usage of narrow-spectrum antibiotics such as cefazolin underlines the paramount effect of surgical source control and warrants further studies clarifying the usefulness of the extended continuation of antibiotics in surgical IAIs for reducing postoperative infectious complications.


Fingerprints have been proposed as a promising new matrix for drug testing. In previous work it has been shown that a fingerprint can be used to distinguish between drug users and nonusers. Herein, we look at the possibility of using a fingerprint to distinguish between dermal contact and administration of heroin. Fingerprint samples were collected from (i) 10 patients attending a drug rehabilitation clinic, (ii) 50 nondrug users and (iii) participants who touched 2 mg street heroin, before and after various hand cleaning procedures. Oral fluid was also taken from the patients. All samples were analyzed using a liquid chromatography—high resolution mass spectrometry method validated in previous work for heroin and 6-AM. The HRMS data were analyzed retrospectively for morphine, codeine, 6-acetylcodeine and noscapine. Heroin and 6-AM were detected in all fingerprint samples produced from contact with heroin, even after hand washing. In contrast, morphine, acetylcodeine and noscapine were successfully removed after hand washing. In patient samples, the detection of morphine, noscapine and acetylcodeine  gave a closer agreement to patient testimony on whether they had recently used heroin than the detection of heroin and 6-AM alone. This research highlights the importance of washing hands prior to donating a fingerprint sample to distinguish recent contact with heroin from heroin use. The detection of illicit drugs in fingerprint samples has been widely reported, and there is a growing body of evidence to support the concept that the detection of drug compounds and their metabolites in fingerprint samples can be used to show that a donor has either consumed or handled illicit drugs , 19, or For forensic applications, knowledge that a fingermark has been deposited by someone who has either touched or ingested illicit drugs may help law enforcement authorities to gain a profile of an unknown suspect, perhaps if the fingermark is smudged or the offender is not listed on the fingerprint database , 21. In Conversely for clinical drug testing applications, situations may arise in which the testing authority must ensure that administration of a drug can be distinguished from dermal contact  from one geographic location and so is unlikely to be universally applicable, as highlighted by a recent letter to Clinical Chemistry  it may be necessary to distinguish administration of a substance from recent contact In previous publications , 9, 11, In this study, we explore differences in fingerprints produced after direct and indirect contact with street heroin, following hand washing and wiping. We compare this with fingerprint samples (10 donors) collected from patients at a drug rehabilitation clinic and a population (50 donors) of nondrug users. All samples were analyzed using the liquid chromatography (LC–MS) method of our previous work that was validated for heroin and 6-monoacetylmorphine (6-AM) , 26. The9 and 6-acetylmorphine-d3 (6-AM-d3)) were prepared from certified reference materials (Cerilliant). Optima™ LC–MS grade solvents (methanol (MeOH), dichloromethane (DCM), acetonitrile (ACN) and water (H2O) were used to prepare all solutions and solvent mixtures (Fischer Scientific). Formic acid was added to the mobile phase at 0.1% (v/v) (Fisher Scientific).Drug standards , heroin-dHeroin seized by Irish police and stored at Forensic Science Ireland (FSI) was used for the drug contact experiments. A sample from the drug seizure had been previously analyzed by FSI’s standard analysis protocol using gas chromatography–mass spectrometry (GC–MS) and had been found to have a heroin purity of 11% . The proFingerprints were collected on 2 × 2 cm squares of Whatman 1-Chr grade chromatography paper, with a single fingerprint collected per sample. Fingerprint samples were collected using kitchen scales (Sainsbury’s Color) to measure the pressure applied during collection .A favorable ethical opinion for collection and analysis of samples was received from the National Research Ethics Service (NRES—REC reference: 14/LO/0346). Sample collection was carried out in accordance to the relevant guidelines, and informed consent was taken from all participants.n = 10) seeking treatment at drug rehabilitation clinics and testified taking either heroin or cocaine in the last 24 hours. A fingerprint was collected from each finger of the right hand. Participants were instructed to wash their hands thoroughly with soap and water and then wear nitrile gloves for 10 minutes to induce sweating. This was followed by removal of the gloves and finally depositing fingerprint samples. The same process was used to collect fingerprint samples from the right thumb and right index finger from 50 participants who testified not to be drug users.Fingerprints were collected from individuals  collection device. Analysis of the oral fluid samples was carried out at Claritest . Claritest screening uses immunoassay testing followed by liquid chromatography–tandem mass spectrometry (LC–MS-MS) quantitation if screening is positive .n = 3) were asked to wear nitrile gloves for 10 minutes before fingerprint samples were collected.An additional group of participants, who testified to be non-drug users participated in an experiment to generate fingerprints after contact with heroin. Four scenarios were devised to test for the presence of heroin and its metabolites in fingerprints after dermal contact with the parent drug, as illustrated in In Scenario 4, a first volunteer touched 2 mg heroin, and hands were shaken with participants 1 and 2. Fingerprint samples were then collected from participants 1 and 2. Another set of fingerprint samples was collected from participants 1 and 2 after washing hands with soap and water and after wearing gloves for 10 minutes, to evaluate the presence of drugs after secondary transfer and hand washing. Samples were given unique identifiers referring to the scenario number  and participant number  such as S1P1.2O/ACN + 0.1% formic acid + 50 ng/mL heroin-d9 and 6-monoacetylmorphine-d3, before being vortexed and transferred to a 300 μL glass micro-insert vial, with 5 μL injected onto an LC–MS-MS system.The fingerprint samples were placed in a 2 mL Eppendorf microcentrifuge tube, with 1.5 mL of 10% DCM in MeOH. The tube was then centrifuged for 2 minutes . The solvent extract was evaporated to dryness under a stream of nitrogen at room temperature (20°C) and reconstituted in 100 μL of a solution containing 95:5 H2O:ACN (0.1% formic acid), increasing to 80:20 ACN:H2O (0.1% formic acid) over 2 minutes, constant for 0.5 minutes before returning to the initial mobile phase composition. The samples were introduced to a Thermo Scientific™ Q-Exactive Plus Orbitrap™ mass spectrometer using the standard electrospray interface with a capillary temperature of 320°C, spray voltage 3 kV and S-lens RF level set at 50%. Positive mass spectra were acquired in full scan mode within a range of m/z 50–500 at a mass resolution of 70,000 at m/z 200 (AGC target 106 ions and maximum inject time of 200 ms).Chromatographic separation was performed on a Thermo Scientific™ Ultimate3000 UHPLC system. Separation was performed on a Kinetex XB-C18 column  operated at 30°C at a flow rate of 0.25 mL/min. Gradient analysis was performed with an initial mobile phase of 95:5 HR2 = 0.9995 in a range 500 pg–10 ng. Although a matrix effect  for both heroin and 6-AM was observed in the presence of a fingerprint, it varied less than 5% between fingerprint donors.Our previous publication  and comparison with samples extracted from blank paper. Extracted ion chromatograms were then produced for relevant analytes. The retention time and accurate monoisotopic masses  has not been reported before. This finding shows that it is imperative that hands are cleaned prior to obtaining fingerprint samples if there is a need to make a distinction between heroin contact and heroin administration, particularly since it was not possible to find a ratio of parent drug:metabolite that could be used to distinguish the two donor groups.The detection of drug The data from Scenario 4 show that the hand washing procedure adopted here is sufficient to remove residues incorporated in fingerprints through secondary transfer. This supports our previous observation that shaking hands with a drug user did not return a positive fingerprint test result for heroin, provided hands were washed prior to giving a fingerprint sample .The patient data show that all patients in Group 1a  donated at least one fingerprint containing traces of morphine, in addition to the expected heroin and 6-AM. Acetylcodeine and noscapine were less frequently detected than the other analytes. For the patients in Group 1b  morphine, acetylcodeine or noscapine were also detected in 2 out of 3 patients. As in previous work, we attribute this discrepancy between fingerprints and oral fluid to be due to a difference in detection window , showing good agreement between oral fluid, fingerprint and patient testimony. In contrast, heroin and 6-AM were detected in the fingerprints of one of these patients , presumably through dermal contact with the substance or a contaminated surface. This result is consistent with the results of the contact residue experiment presented in either administration or recent contact with heroin. Morphine can be used to confirm that heroin has been ingested rather than touched, but future work is needed to confirm whether morphine and heroin administration can be distinguished from one another.While these data appear to show a suitable strategy for distinguishing between contact and administration of heroin, the patient in Group 3 shows that there is an alternative interpretation for a fingerprint containing all the analytes considered here. The patient in Group 3 testified taking morphine only. This is corroborated by the oral fluid result, and the detection of morphine in the fingerprints collected from this patient. However, for this patient, heroin and 6-AM were also detected, alongside acetylcodeine and noscapine. One possible explanation for this observation is that the patient’s testimony was incorrect, or that the traces thought to be relevant to heroin use originate from a previous heroin dose. An alternative explanation is that it is known that noscapine and codeine as well as other co-extracted alkaloids are present in street morphine (including a compound tentatively identified as acetylcodeine)  deliberate contact and (ii) administration of heroin. Due to the fact that both heroin and its main metabolite (6-acetylmorphine) were not removed by hand washing after contact with heroin, the detection of these substances in fingerprint may not only be indicative of heroin administration. On the other hand, the detection of morphine, acetylcodeine and noscapine could be removed through hand washing and were detected in a significant percentage of the samples collected from patients at a drug rehabilitation clinic that testified taking heroin. Thus, if there is a question about the source of heroin found in a fingerprint, future studies should explore whether detection of morphine, acetylcodeine or noscapine can assist with the interpretation.jat-19-2870-File008_bkz088Click here for additional data file.


In this paper, the significance of application-oriented fundamental research on concrete and reinforced concrete structures for progress regarding practical applications to structural design is addressed based on four examples. They were treated in a joint research project of Vienna University of Technology and Tongji University. The first topic refers to sudden heating or cooling of concrete structures, the second one to high-dynamic strength of specimens made of cementitious materials, the third one to structural analysis of segmental tunnel rings used in mechanized tunneling, and the fourth one to serviceability and ultimate limit states of concrete hinges used in integral bridge construction. The first two topics deal with exceptional load cases. Results from the fundamental research call for improvements of state-of-the-art simulation approaches used in civil engineering design. The last two topics refer to reinforced concrete hinges used in mechanized tunneling and integral bridge construction, respectively. Integrative research has led to progress regarding the verification of serviceability and ultimate limit states. In all four examples, results from fundamental research are used to scrutinize state-of-the-art approaches used in practical structural design of civil engineering structures. This allows for identifying interesting directions for the future development of design guidelines and standards. This paper is focused on four examples of fundamental research carried out in the field of engineering mechanics of concrete and reinforced concrete structures. The problems concerned were treated in a recently completed research project, called “Bridging the Gap by Means of Multiscale Structural Analyses” . This prSudden heating or cooling is the topic of the first example. A multiscale poromechanics model was used to explain why the macroscopic thermal expansion coefficient of mature cement paste is a nonlinear function of the internal relative humidity . At the The high-dynamic strength of cementitious materials is the topic of the second example. Fundamental research in this area is based on the theory of propagation of stress waves and cracks through linear-elastic, isotropic media. An engineering-mechanics approach was used to develop a model for the high-dynamic compressive and tensile strength of specimens made of cement pastes, mortars, and concretes , 6–8. HeStructural analysis of real-scale tests of segmental tunnel rings is the topic of the third example. Bearing capacity tests were analyzed with the help of transfer relations in the form of analytical solutions of the first-order theory of thin circular arches. In the developed hybrid analysis method, transfer relations and measured relative rotations of neighboring segments were combined , 10. HerRecommendations for verification of serviceability and ultimate limit states of reinforced concrete hinges are the topic of the fourth example. An engineering-mechanics model was established to determine acceptable relative rotations as a function of the normal force transmitted across the neck , 12. TheThe main aim of the present paper is to use results from fundamental research in the civil engineering science as the basis for scrutinizing state-of-the-art approaches used in practical structural design of civil engineering structures. This allows for identifying interesting directions for the future development of design guidelines and standards.The paper is structured as follows: one section each is dedicated to the aforementioned four examples, see Sects. Concrete structures, such as pavement plates made of plain concrete and tunnel segments made of reinforced concrete, are generally subjected to recurrent cycles of temperature and relative humidity. They may have to sustain exceptional loadings, such as sudden heating in case of fire disasters, or sudden cooling in case of hail showers. The resulting thermomechanical loading may lead to damage of these structures. Thus, it is a threat to their long-term durability and safety.RH of the material, because the thermal expansion coefficient of the cement paste is an asymmetrical bell-shaped function of RH, see Fig. The thermal expansion coefficient of concrete governs the thermal deformations and stresses of concrete structures subjected to thermal loading. This coefficient is a nonlinear function of the internal relative humidity At the structural scale of pavement plates, heat conduction mainly concerns the thickness direction. When it comes to transient heat conduction, the temperature and the associated thermal eigenstrains are time dependent. Their distributions over the thickness of a plate are nonlinear. However, there still exist state-of-the-art guidelines for quantification of thermal stresses of pavement plates recommending the assumption of a linear distribution of the temperature along the thickness of the plate, see, e.g., . This prThis Subsection is organized in three parts. At first, a thermoporoelastic multiscale material model is used to provide insight into the question why thermal expansion coefficients of cementitious materials depend on the internal relative humidity. Subsequently, a structural analysis of a pavement plate subjected to solar heating followed by a suddenly starting hail shower is discussed. Finally, methods available for top-down quantification of stresses experienced by the concrete constituents  are briefly summarized.Concrete is a hierarchically organized microheterogeneous material, see Fig. Subsequent homogenization of the four matrix-inclusion composites in Fig. r following exponential distributions:gpor stands for gel pores and cpor for capillary pores. The characteristic radius p(r), referring to individual pores with radius r, over pores of all sizes [r of the pores,t denotes the thickness of the layer of water adsorbed to the surface of the pores. The Kelvin radius R, the absolute temperature T, and the molar volume of water The solid constituents, i.e., the solid hydrates (shyd), the unhydrated clinker grains (clin), and the aggregates (agg), are considered to be isotropic. Thus, their elastic stiffness can be described based on their bulk and shear moduli . The gelentclass1pt{minima nm, see ,5\documeentclass1pt{minimaentclass1pt{minimaentclass1pt{minimaentclass1pt{minimak. Bottom-up homogenization of the RVEs in Fig. e scheme . Under cand the solid hydrates release water. This results in a redistribution of water within the partially saturated pore network and in an increase of the Kelvin radius. Consequently, the internal relative humidity increases and the average effective pore underpressures decrease [and the solid hydrates take up water, the Kelvin radius decreases, the internal relative humidity decreases, the average effective pore underpressures increase, and this manifests itself macroscopically as an additional poromechanical contribution to the macroscopic shrinkage of the cement paste. As regards the experimental validation of the described phenomena, the water uptake/release characteristics of the hydrates were observed recently based on proton nuclear magnetic resonance relaxometry tests of cement paste subjected to temperature changes [The described multiscale model allows for explaining the thermal expansion behavior of cement paste Fig. , based oentclass1pt{minima changes .Fig. 3SpThe homogenized thermomechanical properties of concrete  are usedolutions , providiThe thermal stresses of the pavement plate are quantified using the theory of thin plates . It is bj on the total strain of material phase k. The average microscopic stresses of the cement paste and of the aggregates follow from the phase-specific versions of the generalized Hooke’s law: Multiscale structural analysis continues with quantifying the average microscopic strains of the cement paste and of the aggregates, based on their thermal eigenstrains and the macroscopic strain of concrete relation :12\documxpansion . This raxpansion , 24 for Results from fundamental research provide an interesting view on a durability issue. The described multiscale poromechanics model allows for identification of the water uptake or release process of hydration products when cooled down or heated up. This nanoscopic material phenomenon governs the strong dependence of the macroscopic thermal expansion coefficient of the cement paste on its internal relative humidity. Within the regime of intermediate relative humidity, the thermal expansion coefficient of the cement paste is much larger than that of the aggregates, which gives rise to self-equilibrated internal stresses, as the temperature is changing, see  for detaThe temperature inside pavement plates subjected to transient heat conduction is distributed nonlinearly in the thickness direction. State-of-the-art guidelines for quantification of thermal stresses of pavement plates recommend the assumption of an “equivalent” linear distribution of the temperature along the thickness of the plate, see, e.g., . The preImportant infrastructure must not only withstand regular service loads but also exceptional loads. Such infrastructure includes, but is not restricted to, schools, hospitals, power plants, tunnels, and bridges subjected to impact and blast loads. These dynamic loads may result, e.g., from cars accidentally crashing into engineering structures, or from detonation of so-called Improvised Explosive Devices. This provided the motivation for fundamental scientific research regarding the high-dynamic strength of specimens made of cementitious materials.Split Hopkinson Pressure Bars represent a popular test equipment for the experimental determination of high-dynamic strength values. As for high-dynamic compression tests, the setup consists of the serial arrangement of a striker bar, an incident bar, a cylindrical specimen, a transmitter bar, and an adsorber, see Fig. x denotes the position and t the time variable. Regarding quantification of the maximum tensile stress experienced by the specimen, different evaluation procedures are used, see, e.g., [As for high-dynamic tension tests, the setup of a Split Hopkinson Pressure Bar is limited to a striker bar, an incident bar, and a specimen, see Fig. e, e.g., , 29. Thee, e.g.,  and concThe high-dynamic strength loss, see, e.g., [gain can be modeled, rate-dependent material properties are introduced, see, e.g., [In order to explain the high-dynamic strength gain, many models accounting for rate-dependent material properties and/or inertial confinement were proposed. Rate-dependent models are based on the assumption that the mechanical properties of cementitious materials depend on the loading rate, see, e.g., , 31 for e, e.g., . In ordee, e.g., . The disAlso for high-dynamic loading, cracking will start when the quasi-static strength of the material is reached.Cracks are assumed to propagate at a speed that is virtually equal to the velocity of shear waves.High-dynamic strengthening occurs during the failure process, lasting from the start of crack propagation to disintegration of the specimen.The model of Fischer et al. [An engineering-mechanics model for the high-dynamic strength was developed by Fischer et al.  for compr et al.  for highE denotes Young’s modulus, The conceptual simplicity of the described model allowed for deriving the following analytical expression for the DIF :15\documE, h of the specimen. Thus, the upper bound for h, see Fig.  If the first crack nucleates at one of the interfaces between the specimen and the load plates, the propagating crack edge has to travel along the total axial length h/2. Thus, the lower bound for h/2, see Fig.  If the crack nucleates at the center of the specimen, two crack edges are propagating simultaneously. Each of them has to cover a distance equal to Consequently, realistic values of The input quantities n denotes the number of high-dynamic tests included in the analyzed test series. The corresponding analyses focused on results from three testing campaigns of cylinders, made of cement paste, mortar, and concrete, respectively, illustrated as points in Fig. E, A check was made whether or not high-dynamic strength values from complete testing campaigns can be reproduced, based on Eq.  and on oatisfies . In moreg to Eq.  and the nter Eq.  as known74h, see  and Fig.74h, see , suggestAn engineering-mechanics model for the high-dynamic tensile strength was developed by Binder et al. . It reprg to Eq.  reaches The described elasto-brittle modeling approach allowed for explaining high-dynamic compression and tension tests. It was corroborated in the framework of five different testing campaigns, carried out in five different laboratories by five different teams of experimenters, using cylindrical specimens made of cement paste, mortar, and concrete.The design of dynamically loaded structures is a challenging task. Main difficulties are the specification of the design loads and the investigation of the load-carrying behavior. Concerning the latter, practitioners prefer static to dynamic simulations. In order to account for the dynamic nature of the underlying problem, static analyses are based on increased loads and increased values of material strength. The latter are obtained by multiplying the quasi-static strength with DIF values depending on the loading rate. DIF formulae, published in the Model Code 2010 , enjoy gRecent fundamental research has led to a significantly better insight into high-dynamic strength tests of specimens of cementitious materials. Also under high-dynamic loading, cracking will start when the quasi-static strength is reached. This implies that a structure will be damaged if the dynamic stress exceeds the quasi-static strength, no matter how fast the stress is increased, and no matter how short the stress pulse lasts. In addition, the five examples illustrated in Fig. Based on the improved understanding of high-dynamic strength tests, quasi-static design approaches for dynamic problems can be scrutinized as follows. Quasi-static design calculations are to be based on the quasi-static strength of cementitious materials. The calculations are realistic provided that the stresses remain smaller than the strength. If the calculated stresses reach the quasi-static strength, the analyzed structure will be damaged at least locally. In order to gain realistic insight into the structural damage, dynamic analysis appears to be indispensable.The linings of tunnels, excavated by boring machines, consist of segmental rings. The individual rings are assembled by precast segments. Hence, these rings contain segment-to-segment interfacial joints. The mechanical behavior of the joints is nontrivial, because of (i) nonlinearities resulting from bending-induced partial segment-from-segment separation, (ii) nonlinearities in consequence of the load-dependent material behavior of concrete and of the existence of steel bolts connecting neighboring segments, and (iii) the time-dependent viscoelastic material behavior of concrete. This renders structural analysis of segmental tunnel rings challenging.Early analytical models for structural analysis of segmental tunnel rings were restricted to closed rings, without explicit consideration of the joints, see, e.g., , 37. In Lee et al.  are pionA series of real-scale bearing capacity tests of segmental tunnel rings, see, e.g., , 43 and and the measured relative rotations at the segment-to-segment interfaces are used as input. The second type of structural analysis refers to a classical analysis of a segmental tunnel ring subjected to ground pressure. The analysis is classical because the external loading is used as input, whereas the relative rotations at the segment-to-segment interfaces are computed as functions of the bending moments and normal forces transmitted across these interfaces. Both types of analysis are based on transfer relations, discussed next.Two types of structural analysis of segmental tunnel rings are discussed in the following. The first type refers to the hybrid analysis of a real-scale test in which a segmental tunnel ring was subjected to 24 point loads. The analysis is hybrid because the external loading i”), i.e., at u and v stand for the radial and tangential component, respectively, of the displacement of the axis of the ring; M, N, and V denote the bending moment, the axial force, and the shear force, respectively; The mathematical expressions for the nonzero elements of the transfer matrix read as [Analytical methods for structural analysis of segmental tunnels, based on transfer relations, were developed by Zhang et al. . These rA specific mode of such analysis is a hybrid mode. In the given context, it refers to re-analysis of a real-scale bearing capacity test, carried out at Tongji University, see Fig. Load case I refers to the point loads. The relative rotation angles are set equal to zero. Thus, the corresponding structural analysis is one of a closed ring without joints, subjected to point loads. In this part of the hybrid analysis, bending-induced tensile cracking of the segments is considered. The segments are subdivided into elements, the characteristic size of which is equal to the distance of neighboring cracks. The elements contain a central crack band and two adjacent undamaged zones, see Fig. Load case II refers to the relative rotation angles at the joints. They are estimated from monitoring data, recorded during the test. The estimation is based on the Bernoulli-Euler hypothesis. Since the validity of this hypothesis is questionable for neck-like joints, the estimated relative rotation angles are post-processed such as to refer to rigid-body displacements of the segments. This includes symmetrization and adding the smallest possible increments such that rigid-body displacements are obtained, see  for detaThe simulated convergences agree well with the experimental results, see Fig. In general, measured relative rotation angles at the segment-to-segment interfaces are not available. Thus, the described hybrid method of analysis of segmental tunnels is not applicable. As a remedy, one needs to resort to a classical mode of analysis of such tunnels. To this end, linear transfer relations are combined with a nonlinear interface law. The latter allows for computing the relative rotation angles at segment-to-segment interfaces as a function of the bending moments and the normal forces transmitted across these interfaces. The used interface law accounts for (i) bending-induced partial segment-from-segment separation, (ii) compressive crushing of the concrete, and (iii) tensile yielding of the steel bolts connecting neighboring segments. Both the developed interface model and the corresponding method for structural analysis of segmental tunnel rings were validated by comparing computed results with measurements from independent bearing capacity tests of bolted joints and of a segmental tunnel ring, see .In the following, two segmental tunnel rings subjected to ground pressure Fig.  are anala. In this case, K must be larger than 0.54. Otherwise the transfer of compressive forces across the unreinforced interfaces of the segments is not sufficient to provide the normal force and the bending moment required for overall structural equilibrium, i.e., the structure is kinematically independent of the intensity of the ground pressure. In the interval K, both the serviceability limit and the bearing capacity increase. The discussion continues with the results obtained for the ring with bolted interfaces, see Fig. A sensitivity analysis with respect to the coefficient of lateral ground pressure is performed in the intervalIn order to assess the safety of segmental tunnel linings in service, it is highly desirable to estimate their internal forces and the external ground pressure acting on their inaccessible outer surface. Typically, the convergences of the linings are known. They serve as input for this assessment. The reported hybrid analysis has shown that the convergences of the investigated segmental tunnel ring are governed by rigid-body displacements of the segments. Hence, there is no unique solution for the internal forces and the external ground pressure, if only the convergences are known. In this case, it is impossible to estimate the loading of segmental tunnel linings.In tunnel engineering, serviceability limit states (SLS) and ultimate limit states (ULS) of segmental tunnels are typically related to the convergences. If an SLS is surpassed, the convergences may have a negative effect on the traffic in the tunnel, if an ULS is surpassed, they do have such a negative effect, because the clear diameter of the cross-section is reduced beyond a tolerable limit. The described fundamental research has shown that both the convergences and the bearing capacity of segmental tunnel rings are governed by the mechanical behavior of the joints. Hence, it is indispensable to account for their behavior. As regards the prediction of the convergences and the bearing capacity of segmental tunnel rings, the mechanical behavior of the reinforced concrete segments is less important, and the segments may be modeled as linear-elastic. However, consideration of cracking of the segments is of great importance when it comes to the durability assessment of segmental tunnel rings.The reported fundamental research has clarified the role of the interfacial bolts in the structural behavior of segmental tunnel rings. Such bolts result in a significant increase in the serviceability limit of segmental tunnel rings and in the bearing capacity of such rings in case of markedly anisotropic external loading.Bridges and tunnels must reach the end of their estimated service life in order to ensure the sustainability of public investments into traffic infrastructure. The long-term durability of reinforced concrete bridges is strongly affected by the performance of structural hinges. They must be durable, because their repair or replacement frequently represents a great challenge. Moreover, the associated temporary loss of serviceability may result in large costs.Integral bridge construction is an interesting approach. The idea is to build monolithic structures, where beams, columns, and the abutments are connected by means of so-called concrete hinges. They are either unreinforced or just marginally reinforced necks in reinforced concrete bridges. Proposed by Freyssinet in the 1920s, they became quite popular in Europe in the 1960s. Pioneering design guidelines were developed by Leonhardt and Reimann in 1965, see . HoweverDevelopment of such guidelines and their application to a recently built integral bridge in Austria are the topics of this part of the present work. Figure In the past, the structural performance of reinforced concrete hinges was, in general, investigated experimentally, using a test protocol consisting of two steps. At first, a specific compressive normal force was applied and kept constant thereafter. This was followed by imposing a relative rotation, which was also kept constant thereafter. The first type of loading resulted in creep of concrete and the second one in stress relaxation. This form of viscoelastic behavior of concrete provided the motivation to carry out eccentric compression tests and to perform Finite Element (FE) simulations with state-of-the-art software, in order to gain detailed insight into the structural behavior of reinforced concrete hinges. Because the aforementioned design guidelines of Leonhardt and Reimann do not account explicitly for reinforcement bars that cross the neck centrically, an extension of these guidelines was needed.N. Multiplication by the eccentricity e delivered the bending moment Combined experimental and theoretical research was carried out in order to study the structural behavior of reinforced concrete hinges , 52. TheThe test results for regular service loads have shown that the magnitude of material creep of concrete is similar to the one of structural creep of reinforced concrete hinges under centric compression. Structural creep under eccentric compression, however, has turned out to be significantly larger. This is a consequence of the strong interaction between this form of creep and cracking . BendingAs for the bearing capacity tests, the eccentricity of the normal force was set equal to one-third of the width of the neck. According to the guidelines of Leonhardt and Reimann, for this eccentricity, bending-induced tensile macrocracking will extend across one half of the initial cross-section of the neck. Along the remaining compressed ligament, the guidelines suggest a triangular stress distribution, with a vanishing normal stress at the centerline of the neck and the maximum compressive stress at its outer edge. Following this conceptual approach and setting the maximum compressive normal stress equal to the measured uniaxial compressive strength of concrete, i.e., to Results from the FE simulations have shown that triaxial compressive stress states are activated in the region of the neck . Figure There is yet another important mechanism that enables concrete hinges to sustain large ultimate loads and to fail in a very ductile fashion. To show this, stress states at the surface of the notch, on the compressed side of the throat, are investigated. Because it is a free surface, a plane stress state prevails. A biaxial compressive stress state is the only possible stress state. The biaxial compressive strength is only slightly larger than the uniaxial compressive strength. This implies that the concrete located at the surface of the notch, on the compressed side of the throat, starts to fail rather early in a bearing capacity test of a concrete hinge. Despite this local material failure, the surface layer stays in place and, thus, does not spall. This enables the building-up of triaxial stress states inside the concrete hinges . Thus, tE, of the tensile strength, E, The performed numerical simulations are a good example for modern multiscale structural analysis. The first three-dimensional FE simulations were based on default input values, derived from the known Young’s modulus and the compressive strength of the concrete. The obtained numerical results overestimated both the initial stiffness and the bearing capacity of the tested concrete hinges. This confirmed one of Leonhard’s expectations that the steel rebars constrain the free autogeneous shrinkage of concrete. It promotes shrinkage-induced damage of concrete. In a classical setting, this would have called for fitting of Young’s modulus, concrete , it was Combined experimental-theoretical research has resulted in increased scientific understanding of the structural performance of reinforced concrete hinges. This provided the motivation to develop design guidelines for reinforced concrete hinges. An important aspect of these guidelines is the specification of the limit of tolerable relative rotations as a function of the compressive normal force transmitted across the neck. This is required for both serviceability and ultimate limit states of reinforced concrete hinges.F, was estimated on the basis of regulations from the Eurocode 2 [An engineering-mechanics model was the basis for the development of new design guidelines for reinforced concrete hinges in integral bridge construction. The Bernoulli–Euler hypothesis was used to describe displacement and strain states in the region of the neck. It was combined with linear-elastic and ideally plastic stress–strain relationships for concrete in compression and steel in tension. The triaxial-to-uniaxial compressive strength factor, rocode 2 , see aboBesides application of the described model to integral bridge construction, it was also used for the analysis of bearing capacity tests of segmental tunnel rings. Moreover, it was applied to quantification of the behavior of segment-to-segment interfaces. These interfaces are bolted concrete hinges, see Sect. ab represents the cross-sectional area of the neck, see also Fig. As for integral bridge construction, analytical formulae for verification of serviceability and ultimate limits of reinforced concrete hinges were derived , 12. Thereads as 22\documeLE reads 23\documeIn the operating condition “tensile macrocracking beyond one half of the width of the neck, resulting in tensile loading of the reinforcement,” the mathematical formulation of the SLE reads 24\documeLE reads 26\documementclasspt{minimaM is directly proportional to the normal force N. Thus, the relation between the relative rotation M is affine to the relation between Graphs, illustrating the test data, see Fig. Combined experimental-theoretical research has enabled the development of new design guidelines for verification of serviceability and ultimate limit states of reinforced concrete hinges. Fundamental research has served its ultimate purpose to promote progress in civil engineering design. This was achieved in the framework of interdisciplinary research, carried out in the fields of integral bridge construction and mechanized tunneling, respectively.The new design guidelines explicitly account for the crossing steel rebars which run across the neck. The rebars provide the required position stability in case bending-induced macrocracking extends beyond one half of the width of the neck.There are interesting similarities and differences regarding serviceability and ultimate limit states of concrete hinges in the construction of integral bridges and of segmental tunnel rings. Serviceability limit states of concrete hinges in integral bridge construction are associated with elastic limits of concrete and/or steel. Serviceability limit states of segmental tunnel rings, in turn, are related to convergences that have grown so large that the traffic running through the tunnel is negatively affected, because the clear diameter of the cross-section is reduced beyond a tolerable limit. In such cases, it is almost certain that several interfaces of segments have already become plastic hinges . From thScientific research, both fundamental and applied, provides answers to open questions. Consequently, state-of-the-art models are to be scrutinized regularly. If possible, they must be improved. In the present paper, results from fundamental research in the field of engineering mechanics of concrete and reinforced concrete structures were presented. Implications on engineering design were discussed.In the regime of intermediate internal relative humidities, the thermal expansion of the cement paste is virtually twice as large as the one of customary aggregates. Thus, temperature changes result in considerable self-equilibrated internal stresses.Concrete infrastructures exposed to the open air undergo daily cycles of internal stresses. The mentioned self-equilibrated internal stresses are the source of a fatigue problem. It puts at risk on the long-term integrity of the microstructure of concrete and, thus, the long-term durability of the material.Exceptional loading in terms of sudden heating or cooling presents another serious load case. Sudden changes of temperature result in transient heat conduction. This is associated with time-dependent and spatially nonlinear temperature fields. Thus, also the thermal eigenstrains are distributed in a spatially nonlinear fashion. The linear part results in an eigenstrain and an eigencurvature of the midplane of plates or the axis of beams. The nonlinear part is associated with an eigendistortion of the generators of plates or the cross-sections of beams. The eigendistortion is prevented, however, because of Kirchhoff’s normal hypothesis. Thus, spatially nonlinear mechanical strains, i.e., stress-related strains, are activated. When added to the thermal eigenstrains, they yield linear total strains in the thickness direction of plates. This is compatible with Kirchhoff’s normal hypothesis. As for engineering design, the following conclusions are drawn:When engineering structures are subjected to transient heat conduction, thermal stresses are inevitably activated, no matter whether the structure is supported in a statically determinate or indeterminate fashion.The thermal eigenstresses are distributed nonlinearly along the generators of plates (or within the cross-section of beams). They neither contribute to the membrane forces  nor to the bending moments. Thus, it is impossible to define equivalent linear temperature fields, notwithstanding that this is still a very popular approach, because it is recommended by state-of-the-art guidelines such as .Exceptional loading in terms of high-dynamic compression or tension is another important problem. Results from fundamental scientific research suggest that cracking starts, also under high-dynamic loading, when the quasi-static strength of the material is reached. Cracks propagate at a speed which is virtually equal to the velocity of shear waves. High-dynamic strengthening occurs during the failure process, lasting from the initiation of crack propagation to disintegration of the specimen. The duration of the failure process depends on the size of the investigated structure. Thus, DIF values, obtained from tests carried out with a Split Hopkinson Pressure Bar, are structural properties of the tested specimens rather than material properties. As for engineering design, the following conclusions are drawn:Engineering structures made of concrete will be damaged provided that the dynamic stress exceeds the quasi-static strength, no matter how fast the stress is increased and how short the stress pulse lasts. Hence, conventional quasi-static analysis allows for identifying whether or not the structure will be damaged. The extent of the local damage, however, cannot be assessed.As for quantifying the local damage resulting from high-dynamic loading, it is indispensable to carry out dynamic simulations, to explicitly account for a realistic speed of crack propagation, and to use advanced models that are capable of predicting realistic directions of crack propagation also in case of multiaxial types of loading. This calls for a change of paradigm in civil engineering design.Hybrid and classical simulation methods are well-suited for structural analysis of real-scale bearing capacity tests of segmental tunnel rings used in mechanized tunneling. Both types of analysis reported in this work were based on transfer relations, representing analytical solutions of the first-order theory of thin circular arches. Externally imposed loading was used as known input. As for the “hybrid” analysis, measured relative rotations at the interfaces between the segments also entered the analysis as known input. As for the “classical” analysis, however, interface laws had to be used in order to predict the relative rotations resulting from the bending moments and the normal forces transmitted across the interfaces between the segments. The simulations provided valuable insight into the structural behavior of segmental tunnel rings. As for engineering design, the following conclusions are drawn:Tunnel convergences are governed by rigid-body displacements of the tunnel segments. Thus, it is impossible to estimate the loading of segmental tunnel linings, based on measured convergences.The bearing capacity of segmental tunnel rings is associated with the development of a kinematic mechanism. It is characterized by the development of plastic hinges at four segment-to-segment interfaces. Bolted interfaces, representing reinforced concrete hinges, significantly increase the bearing capacity of segmental tunnel rings subjected to strongly anisotropic external loading.Reinforced concrete hinges represent necks in reinforced concrete structures. Because of the throat, three-dimensional compressive stress states are activated in the region of the neck. The resulting confinement significantly increases the strength and the ductility of concrete. The triaxial compressive strength can be estimated based on regulations for partially loaded areas. New recommendations were elaborated for verification of serviceability and ultimate limit states of reinforced concrete hinges. Because the reinforcement was explicitly accounted for, the tolerable limits of the relative rotations are larger than those according to the guidelines of Leonhardt and Reimann. As for engineering design, the following conclusions are drawn.In order to ensure the position stability of unreinforced concrete hinges, bending-induced tensile macrocracking must be limited to one half of the width of the neck. This limitation can be discarded provided that tensile forces in centrically crossing steel rebars can stabilize the concrete hinge, even when tensile macrocracking extends beyond one half of the width of the neck.Elastic limits of concrete in compression and/or of steel in tension represent serviceability limit states of reinforced concrete hinges. Ultimate limit states refer to the situation that concrete reaches its ultimate limit strain in compression and/or steel attains its ultimate limit strain in tension.There are interesting similarities as well as differences regarding serviceability and ultimate limit states of concrete hinges in integral bridge construction, on the one hand, and segmental tunnel rings in mechanized tunneling, on the other hand.Serviceability limit states of concrete hinges in integral bridge construction are associated with elastic limits of concrete and/or steel. Serviceability limit states of segmental tunnel rings, however, are associated with large convergences. This may have a negative effect on the traffic in the tunnel, because the clear diameter of the cross-section may be reduced beyond a tolerable limit. In such cases, it is very likely that several interfaces between the segments have already developed plastic hinges.From the viewpoint of integral bridge construction, already the development of the first plastic hinge signals an ultimate limit state. This underlines that different types of structures may be associated with different kinds of serviceability and ultimate limit states.Finally, it is emphasized that the described fundamental research activities were carried out within an Austro-Chinese research project, bringing together researchers from Vienna University of Technology and from Tongji University, in Shanghai. The common language of the engineering sciences and the strong joint motivation to carry out fundamental research have not only led to valuable insight into important phenomena and processes governing the mechanical behavior of concrete and reinforced concrete structures, but also contributed to the advancement of civil engineering design.Recurrent cycles of temperature and relative humidity are important load cases for assessing the long-term durability of concrete and reinforced concrete structures. A multiscale poromechanics model allowed for top-down identification of a formerly unknown material phenomenon. Nanoscopic calcium-silicate-hydrates release water upon heating and take up water upon cooling in a quasi-instantaneous and reversible fashion. The corresponding changes of the internal relative humidity result in changes of the effective pore underpressures. This explains why the thermal expansion of the cement paste is a function of the internal relative humidity and why the thermal expansion in the range of intermediate relative humidities is virtually twice as large as in fully saturated or fully dried states. As for engineering design, the following conclusions are drawn:


This paper presents double shear tests performed to investigate factors influencing the bond behavior between basalt fiber-reinforced polymer (BFRP), glass fiber-reinforced polymer (GFRP) laminate, and concrete blocks. In detail, thirty-six twin concrete blocks strengthened with the aforementioned FRP types were tested to evaluate the influence of FRP length, width, and thickness, and their bonding behavior. The 2D-DIC  technique and several strain gauges bonded along the laminate were used to measure the strain distributions of the FRP-to-concrete interface. The failure mode, ultimate load, load–slip, strain distribution, and bond–slip relationships between the laminates and concrete were analyzed. Furthermore, bond–slip curves were compared with some other existing literature models. The results from the experiment showed that the ultimate load, peak bond stress, and slip increased with the increase in the BFRP and GFRP laminates length, width, and thickness. The values of peak shear stress and the corresponding maximum shear slip were significantly different because of the above-mentioned factors’ influence on them. The bond interface that contributes to the bearing of the shear load may grow to an extent and later shift from the loaded end when debonding progresses. Finally, the fractured surfaces of the failed FRP laminates were examined using scanning electron microscope (SEM), revealing that FRP rupture, debonding in concrete, and debonding in an adhesive–concrete interface were the main failure types. The wide use of externally bonded fiber-reinforced polymer (FRP) laminates (FRP sheets or FRP plates) for the strengthening, retrofitting, and repairing of ailing reinforced concrete structures has gradually become a popular area of current research in the recent decade ,2. This The external wrapping or bonding of FRP laminates has proven to be an effective and popular method for the rehabilitation, strengthening, and retrofitting of reinforced concrete (RC) structures in both shear and flexure . The effThe tensile force in the laminate declines gradually toward the fixed end of the laminate in the tensile experiment. When the loads are higher, the tensile force tends to increase within the initial bond region. Once the bond strength has been achieved, debonding starts to propagate, bond strength extents further from initial bond region, and thus, the effective bond region moves to different locations. As a result, only a portion of the bond becomes active, and the bond strength may not always increase with increasing length. In this case, it is impossible to reach the ultimate tensile strength of the laminate. The explanation above is the major distinction between the externally bonded reinforcement and internal reinforcement in which the ultimate tensile strength of the reinforcement could be reached with a considerably longer anchoring length. Moreover, the majority of current research studies concentrate on predicting the ultimate load as well as the effective bond length . MeanwhiCurrently, a significant number of studies reported that the effects of the bond between concrete and FRP laminates on the failure of adhesively bonded joints are predicted mostly by analyzing a number of factors that can affect their relationship. These factors include the concrete compressive and tensile strengths, FRP bond length and width, adhesive properties, FRP axial stiffness and thickness composition, FRP and concrete width ratio, type of FRP sheets, and surface preparation. Therefore, as a consequence, the mechanical behavior of the interface between the concrete and FRP laminates has to be understood and revealed. Zheng et al.  experimeStudying the mechanical performance of concrete structures strengthened with basalt fiber (BFRP) and glass fiber (GFRP) composites is a prominent area of current research with many important aspects that needs to be addressed. This paper investigates the factors that influence the performance of the bond between the FRP laminate and concrete interface through double shear testing. The main parameters analyzed in this paper were FRP bond length, FRP width, and FRP thickness. To achieve this, two kinds of FRP  were used for the preparation of FRP laminates. Then, the specimens were strengthened with the different laminates to cover a wide range of FRP axial rigidities. Ncorr, an open-source 2D-DIC Matlab program, as well as the conventional strain-measuring device  were employed to measure the strains distribution over the surface of the laminate. Of these, 36 double shear specimens were instrumented to examine the effects of factors on the bond interface with respect to the failure mode, the ultimate load, load–slip, the variation in axial strain distribution, and the shear stress distribution, through which the bond–slip relationship of FRP laminate–concrete interfaces was documented and studied.The raw materials used during casting of the concrete blocks include Portland cement with a grade of 42.5 per the Chinese standard code , and wasTwo FRP types  were used as the reinforcement material in this study with thicknesses of 0.42, 0.41, 0.81, and 0.83 mm. BFRP and GFRP tensile specimens were fabricated in accordance with ASTM D3039 for their mechanical properties [Double shear specimens have been used to analyze the influence of FRP bond length, width, and thickness on the bond behavior between FRP and concrete. It should be noted that the interface usually tends to refer to the interfacial part of the FRP and concrete joint, such as the FRP sheet, adhesive, and a thin layer of concrete underneath the adhesive. The materials mentioned in In order to ensure maximum possible bonding, the top surfaces of the concrete blocks were grounded using a mechanical abrasive grinder. The dirt and loose particles were eliminated using a vacuum cleaner, as shown in Strains on the double shear specimen surface were also measured utilizing the digital image correlation (DIC) method and compared with that of the conventional strain-measuring device . Deformations and strains have been determined by measuring the displacements via successive images on a textured surface. To achieve this, the surface of the specimen was sprinkled evenly with white paint. Then, a speckle pattern was produced using a black paint mist. Digital images were captured by using a Canon DSLR camera with 25 megapixels (3872 × 2592 pixels), which was placed perpendicular to the face of the specimen. The surface of the specimen was lighted with two normal white lights to achieve a uniform light intensity on the surfaces of specimens under testing. Images of each specimen undergoing deformation were automatically taken at a regular interval using a remote control. Ncorr, an open-source 2D-DIC MATLAB software package, was employed to process the recorded digital images and to calculate the strains and deformations of specimens. Ncorr is a recognized open-source software package that has implemented many DIC algorithms; more improvements and modifications have recently been proposed as well. The application of this software package has already been tested and verified by a large number of studies .The key test results obtained through the double shear testing between the BFRP/GFRP laminate and concrete substrate are highlighted below. To further investigate the damage mechanisms of the interface between FRP and concrete, the fracture surfaces of specimens were examined using scanning electron microscope (SEM) to detect the changes in the interface between the fiber, matrix, and aggregates. The failed samples from the bond test were extracted from the width center of the debonded laminates at different locations. Samples were examined to distinguish the changes in failure modes, and the result is shown in The ultimate load, average ultimate load, as well as the failure mechanism are summarized in The effects of bonding length on the ultimate load obtained from specimens with three distinct lengths  are plotted in The impact of FRP width on the ultimate load was evaluated by comparing the results of three different FRP widths  for a given FRP bond length, as shown in The findings on the ultimate load of specimens of various FRP thicknesses are shown in The effect of three distinct bonding lengths of 150, 200, and 250 mm on the load–slip curves are plotted in yyε in FRP laminate at different loading. The dashed lines indicate the boundary of the FRP laminate. The strain in the BFRP laminate was nearly 35 mm as soon as the load moved to point A. With the increase in the load to point B, the strain further distributed 60 mm along the length of the FRP laminate. The magnitude of strain also increased quickly, and a large strain gradient emerged close to the loading end. The region of the peak strain gradient moved along with the length of the FRP laminate with the increase of load. At point C, the range of strain gradient was expanded to almost 80 mm. It can be seen at point D that the strain gradient slowly moved to the other end of the bonded joint, and the span increased to approximately to 120 mm, signifying a progressive debonding propagation between the FRP laminate and the concrete substrate as the slip at the loaded end increased.The strain contours in the BFRP and GFRP laminates were obtained from Ncorr, an open-source 2D-DIC MATLAB software package, to analyze the characteristics of strain distributions during a double shear test. FRP strain distributions across the length of the bonded interface were used to determine the behavior of the FRP-to-concrete bonding interface ,47. Figuiτ is the average bond shear stress between BFRP or GFRP laminates and concrete at position i; iε and εi−1 are the strain values measured from the positions i and i−1 strain gauges; ft is the thickness of the BFRP/GFRP laminate; fE is the elastic modulus of the BFRP/GFRP laminate; and Δx is the distance between strain gauges (i) and (i−1). The local slip can be expressed as:is is the local slip within the bond interface at position i; ε0 is the strain at the free end of BFRP/GFRP laminates; and jε is the strain of the FRP laminate measured by the jth gauge.The shear stress distribution along the bonding length of BFRP and GFRP laminates was calculated in relation to the strain distribution shown in The distribution of shear stress along the length of the FRP laminate for double shear specimens is presented in The bond–slip curves of the double shear specimens have been acquired through the use of Equations (1) and (2) plotted in τ means the shear stress, (MPa); maxτ means the peak shear stress, (MPa); s means the local slip value (mm); s0 means the slip at the peak shear stress maxτ (mm); and n is the constant that determines the shape  of the bond–slip curves based on experimental results. maxτ and s0 values were derived directly from the experimental data. The results of regression coefficient (n) as well as the corresponding least squared (R2) have been listed in n increased from 1.83 to 2.66, indicating that these values have no clear relationship to FRP type. The inflection point seen for maximum shear stress (maxτ) shows a tendency to increase when the bond width increases. The expected results of the Popovics’s equation are in agreement with the experimental data having the highest correlation coefficient.Numerous researchers ,50 have The behavior of the bond stress–slip curves of FRP-to-concrete bonding interface for double shear specimens  were also compared to several other bond–slip models ,55,56,57maxτ of Dai’s model is approaching 7 MPa, which is much higher than the model of Lu, which is a little above 3 MPa. It is important to note that the model suggested by Nakaba et al. [maxτ is nearly identical to the average value of the other bond stress–slip models other than Neubauer and Rostásy.As illustrated in a et al.  has beena et al.  model prThe failure mode of BFRP/GFRP–concrete samples from the double shear testing has been attributed mostly to the state of the bonding surface of the concrete block. If the bonding surface of concrete consisted of aggregate and mortar, several debonding modes, such as debonding in concrete, debonding at an adhesive–concrete interface, and debonding at the adhesive–FRP laminate interface can happen. Even though the ultimate load is affected by the characteristics of FRP, concrete, and adhesive, their impact on the bond behavior comparative to one another remains variable and uncertain. In addition, the main debonding mode of samples failure has been associated with the distribution density of aggregate within the bonding surface of FRP and concrete.FRP width has a significant impact on the bonding behavior of the BFRP laminate–concrete interface. An increase in FRP width results in improving the maximum load-carrying capacity with higher stiffness and greater ductility. This may be because shear stresses are distributed over a larger bonded area.The thickness of FRP laminate has the same influence on the interfacial behavior of BFRP and GFRP samples significantly. Increasing the thickness to double layers of FRP sheet greatly increase the bonding interface of the load-bearing capacity. With the increase in FRP thickness and slip, the ultimate load increased significantly until failure. However, GFRP specimens recorded lower debonding load compared with BFRP specimens.The bond length has a distinct influence on the bond behavior. Increasing the length of BFRP laminate above 200 mm results in higher load capacity of the interface between FRP laminate–concrete. The slip can get enhanced with the increasing bond length when the length is less than the maximum effective bonding length.The values of peak shear stress and the corresponding maximum shear slip were significantly different because of the various factors’ influences on them.An experimental study on the mechanical properties and the factors that influence the performance of the bond between basalt fiber (BFRP) and glass fiber (GFRP) laminates strengthened concrete is discussed. A 2D-DIC  procedure was also utilized for calculating strains on the surface of FRP–concrete test specimens in addition to the strains recorded by the conventional strain-measuring device (strain gauge). Thirty-six twin specimens were prepared and were subjected to the double shear loading, with testing parameters such as bond length, width, and thickness. Variations in failure mode, load–slip relationship, strain distribution in FRP laminate, shear stress distribution, and shear stress and slip were measured and analyzed in detail. The results from the experiments can be used to draw the following conclusions: