Antibiotics, as antimicrobial drugs, have been widely applied as human and veterinary medicines. Recently, many antibiotics have been detected in the environments due to their mass production, widespread use, but a lack of adequate treatment processes. The environmental occurrence of antibiotics has received worldwide attention due to their potential harm to the ecosystem and human health. Research status of antibiotics in the environment field is presented by bibliometrics. Herein, we provided a comprehensive overview on the following important issues: (1) occurrence of antibiotics in different environmental compartments, such as wastewater, surface water, and soil; (2) toxicity of antibiotics toward non-target organisms, including aquatic and terrestrial organisms; (3) current treatment technologies for the degradation and removal of antibiotics, including adsorption, hydrolysis, photodegradation and oxidation, and biodegradation. It was found that macrolides, fluoroquinolones, tetracyclines, and sulfonamides were most frequently detected in the environment. Compared to surface and groundwaters, wastewater contained a high concentration of antibiotic residues. Both antibiotics and their metabolites exhibited toxicity to non-target organisms, especially aquatic organisms . Fluoroquinolones, tetracyclines, and sulfonamides can be removed through abiotic process, such as adsorption, photodegradation, and oxidation. Fluoroquinolones and sulfonamides can directly undergo biodegradation. Further studies on the chronic effects of antibiotics at environmentally relevant concentrations on the ecosystem were urgently needed to fully understand the hazards of antibiotics and help the government to establish the permissible limits. Biodegradation is a promising technology; it has numerous advantages such as cost-effectiveness and environmental friendliness. FQs, TCs, and SAs were most frequently detected in sediments. Concentrations of antibiotics in sewage sludge are higher than that in sediments. TCs and FQs were the predominant antibiotics in sewage sludge, due to their strong adsorption onto sludge. TCs, together with their metabolites, have been detected in manures. Soil contamination by antibiotics is associated with the application of antibiotic-contaminated manures and wastewater irrigation.3.3.1.Anabaena CPB4337 and Vibrio fischeri), algae , crustaceans , fish   ,72–75. Increased . Additioncreased . Microalncreased . Furtherhobicity .Pimephales promelas) was not affected by FQs exposure ) were biodegradable, whereas sulfanilic acid and 5-methylisoxazol-3-yl-sulfamate mainly exhibited abiotic attenuation [2-SMX by microorganism. It was found that SMZ can be eliminated by plant Tripolium pannonicum and further under anaerobic digestion, which suggested that Tripolium pannonicum has a potential ability for treating wastewater [14C-SMX was 3%. The bioavailable SMX fraction slightly decreased from 98% to 94%, while the non-extractable fraction in the sludge slightly increased from 1% to 3.4% under aerobic heterotrophic conditions. These results indicated that the biotransformation was responsible for the removal of SMX, while mineralization and sorption were less important [By contrast, some SAs are easily biodegradable . For exan sludge . Some barimidine ,172. Thoenuation . Interesenuation ; it was stewater . Additiomportant . With thmportant , CTM [17mportant , and CTCmportant . The remmportant .Compared to other abiotic removal methods, biodegradation has its advantages of cost-effectiveness and environmental friendliness in actual application. Considering the actual application situation, current focuses of research interest gradually pay attention to the identification and structural analysis of effective antibiotic-degrading strains and the biodegradation capability of selected microbial community to antibiotics ,175–180.5.2O, CIP, NOR, TC, SMX, and TMP. The factors affecting antibiotic occurrence include antibiotic consumption, national income, population density, wastewater treatment technology, and seasonal rainfall. Both antibiotics and their TPs have toxicity effects on non-target organisms in the aquatic and terrestrial ecosystems. The occurrence and spread of ARGs/ARB in the environment are of growing interest, owing to their potential risks to human health. Studies of the degradation and removal of antibiotics have shown that β-lactams can be hydrolyzed; FQs and SAs can undergo biodegradation by specific microbes; and FQs, TCs, and SAs are most effectively removed by photolysis and oxidation. With the development of LC-MS/MS methods, research interests have expanded to elucidate TPs of antibiotics, their activity, and their fates in the ecosystem.Antibiotics, as emerging contaminants, were found in various environmental compartments of different regions. The concentrations of antibiotic residues were ranging from low ng/L to a few μg/L in aquatic environments, and from ng/g to μg/g in solid matrices. Among all of antibiotic classes, MAs, FQs, TCs, and SAs were the dominant antibiotic groups in the environment. The frequently detected antibiotics were ERY, ERY-HGiven the extensive use and continuous discharge of antibiotics, there is a need for more researches on the environmental occurrence, toxicity, degradation and removal of antibiotics. To achieve the sustainable development, the future research directions are suggested as follows. (1) The development of analytical methods for the detection of a greater number of antibiotics and their TPs, in order to improve risk assessments and establish quality standards for antibiotics in the environment; (2) further toxicological studies must be performed on potential chronic effects of antibiotic mixtures and their degradation products at environment-related concentration; (3) understand better and deeper the toxicity of antibiotics toward non-target organisms by proteomic responses and gene expression study; (4) human health may be affected by the consumption of agricultural products polluted by antibiotics, more attention should be paid to the indirect effects of antibiotics caused by the drinking water and food chain; (5) further research is needed to evaluate the relationship between antibiotic contamination and the presence of ARGs/ARB in the environment; (6) elucidation of degradation products and their bioactivity needs to be further investigated; (7) develop efficient and low-cost treatment technology for controlling the emission of antibiotic contaminants.Click here for additional data file.


The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)/coronavirus disease 2019 (COVID-19) pandemic has amplified the role of hospitals in infectious disease response and capacity building. In efforts to respond to the growing volume of cases, hospitals have become a microcosm for US pandemic response. The COVID-19 outbreak has highlighted that hospital preparedness for biological events, such as a pandemic, are often inadequate and dependent on leadership investment in biopreparedness. This article discusses the proactive decision, before COVID-19, that a Phoenix-based hospital system made to invest in high-consequence disease (HCD) preparedness. Within these efforts, a gap analysis was performed, which led to creation of an HCD subcommittee and corresponding efforts to address vulnerabilities and opportunities for improvement. From establishing enhanced personal protective equipment (PPE) and infectious disease training for frontline staff, to building an outbreak tracking mechanism for travel alerts within the electronic medical record, the HCD efforts of this hospital system created a stronger foundation to respond to biological events like the COVID-19 pandemic. The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)/coronavirus disease 2019 (COVID-19) pandemic has soared past 145 million cases internationally and been a stark reminder of the serious threat of emerging and novel infectious diseases. In the wake of the pandemic, there will surely be lessons learned regarding issues ranging from supply chain to laboratory testing, and public health resources. For many though, none will be as painfully obvious as that of health-care preparedness and response.1 Biopreparedness efforts are those that seek to identify and address vulnerabilities to a spectrum of biological threats within health-care settings. From natural events such as pandemics to intentional threats such as bioterrorism, biopreparedness efforts focus on enhancing readiness to infectious diseases and an awareness of the serious implications they pose to health-care infrastructure. Making the case for biopreparedness is not easy, but these efforts are built on a foundation of infection prevention and control (IPC) that can have far reaching benefits.2Pandemic preparedness in health care is challenged by many roadblocks. How do we make the case for investing in costly efforts that might never be used? Buying additional personal protective equipment (PPE) and ventures to provide enhanced training for staff are not always a priority for hospital leadership, especially in times of economic strain and soaring health-care costs. A 2018 Office of the Inspector General for the US Department of Health and Human Services report found that, while hospital leaders reported improved preparedness of emerging infectious diseases after the 2014/2016 Ebola outbreak, they reported competing priorities that often limited the ability to invest in continued preparedness.Within this article, we detail the efforts and process of establishing a high-consequence disease (HCD) subcommittee and initiative beginning in 2018 and how this enabled enhanced readiness for the COVID-19 pandemic.3In late 2018, under new leadership within a large medical system in Phoenix, Arizona, the IPC team was able to form a new initiative to address biopreparedness gaps across six hospitals and nearly 100 outpatient facilities. Led by the IPC program director and an infection preventionist with a background in biodefense, efforts were made to identify what biopreparedness would mean for a large hospital system. Once senior administrative support was established, the first phase involved a gap analysis to understand the vulnerabilities and opportunities for improvement. The gap analysis was designed by using Ebola readiness and response requirements from the Centers for Disease Control and Prevention (CDC), as well as the National Emerging Special Pathogens Training and Education Center, as well as personal experiences. The decision was made to use Ebola virus disease as the testing scenario as it was not only the most recent experience staff had with an HCD, but also required the most enhanced measures in terms of response and readiness from PPE to environmental disinfection. All hospitals within this health-care system are classified as frontline facilities within the special pathogens tiered hospital network, meaning that the expectation is that they identify, isolate, and inform potential patients with special pathogens and be prepared to care for them for 12-24 h, and transfer them to an assessment or treatment facility.The gap analysis evaluated readiness from the moment a patient walked into an emergency department and throughout their care to the point of discharge. It included 44 points within several categories: emergency department, laboratory services, impatient processes, transportation and security, environmental services and waste management, materials management, information technology, human resources, and IPC. Data points included components such as patient admission intake inclusion of travel history, designated PPE donning and doffing areas, training competencies for collection of laboratory specimens, etc. The gap analysis included aspects such as availability of enhanced PPE and responsibility for maintaining kits, but also travel alerts within the electronic medical record system. Because IPC was primarily responsible for Ebola readiness during the 2014/2016 outbreak, it was also important to include components such as infection preventionist training in Ebola PPE, tracking of exposed staff, and if the IPC program had been maintaining an annual assessment and plan for HCD response.Upon analysis and review, there was considerable opportunities for improvement. The majority of these centered around tacit knowledge and awareness regarding PPE and processes within the emergency department. Gaps included awareness of where one could find the necessary PPE, logs for those entering the room of a patient under investigation for Ebola, knowledge of the communication plan or how to set up a patient room, ability to document relevant travel history or exposure to an HCD in a manner that would alert staff, etc. The gap analysis revealed a deep need for not only PPE training, but also a revision and re-education on processes within the health-care system to respond to patients with an HCD. Last, it also pointed to a need for continued monitoring within the IPC program, of ongoing outbreaks of emerging infectious diseases or special pathogens that might pose a risk for international transmission.4 Preparing the hospitals and staff for a range of biological scenarios was important to ensuring an all-hazards approach that focused on building foundational knowledge and critical thinking during complex, high-stress biological events. The plan included sections on everything from cohorting patients to waste management to PPE kits and laboratory processes for patients under investigation for an emerging pathogen. Last, the plan included a quick guide that consisted of 4 pages that could easily be accessed and guide staff through initial response, including setting up an anteroom barrier for PPE doffing, donning/doffing steps, necessary labs, and cleaning materials.Following the gap analysis, a subcommittee was established to help address each vulnerability and create a unified response across the health-care system. One of the primary goals of this initiative was to establish a written plan that involved all facets of HCD response and could easily be accessed. The goal of the HCD subcommittee and the written plan was to approach biopreparedness, not just for viral hemorrhagic fevers, but also respiratory pathogens, and unknown pathogens, as the World Health Organization has classified “Disease X” as a priority pathogen for research and development.While the written plan was one aspect of standing up biopreparedness, the next was engaging those critical to enhancing readiness within the hospital system. The HCD subcommittee was established in early 2019 and involved key stakeholders including leadership and representatives from the following departments: laboratory, facilities, environmental services, human resources, occupational health, risk, regulatory, nursing, emergency department medical providers, emergency management, and infection prevention. The HCD subcommittee established a monthly meeting schedule and quarterly goals. Between each meeting, the infection prevention leaders of the HCD team met with key stakeholders from each area involved in the gap analysis to help address vulnerabilities and review their section of the HCD plan. This portion was critical for not only engagement, but also to ensure there was unification between the plan and actual processes.The HCD subcommittee worked to address several immediate issues within the hospital system, including PPE kits for care of patients with viral hemorrhagic fever, designation of specific rooms within each emergency department that would act as an “HCD room” and could support the building of an emergency anteroom, and establishing classes for frontline staff to educate on HCDs and the PPE processes required for safe care. From January to December 2019, the HCD subcommittee worked to create PPE kits with all the necessary materials to care for patients with viral hemorrhagic fever. Sixty kits were available in each emergency department with a reserve in each hospital supply chain department. Classes were created for frontline staff with the expectation that 90% of emergency department health-care workers attend. These classes were held at all hospital campuses and at 2 urgent care locations, with Continuing Education credits available for those who completed the 90-min course. The course involved 30 min of lecture on what HCDs were, hospital efforts to prepare for them, and various aspects of the HCD plan, such as workflow to don PPE, enter the patient room, doff PPE in the anteroom, and safely leave the space. The second portion of the course focused on donning and doffing PPE, as well as performing tasks to understand the challenges of working in enhanced PPE. The committee was also able to create a new travel screening tool within the electronic medical record that created an alert for any patient who indicated travel to a region with an active outbreak of an emerging infectious disease. Last, each hospital successfully completed a test of emergently building the barriers for an anteroom outside the designed HCD room. The test involved building the barriers in coordination with emergency department leadership, IPC, and facilities.All of these efforts, including additional endeavors like establishing a waste management contract for hazardous waste and testing of airborne infection isolation rooms (AIIR), were reported to the committee. Moreover, the infection preventionist at each hospital reported on the creation and status of the HCD efforts at several hospital leadership meetings to ensure dissemination of information and awareness of the health-care system efforts. In the midst of ramping up HCD class availability and training though, an outbreak of a novel coronavirus began gaining traction in early 2020.Due to the biopreparedness efforts within the HCD subcommittee, the IPC team had established continued monitoring of international outbreaks and began reporting on the novel coronavirus outbreak to the subcommittee in early January 2020. During this time, a best practice advisory (BPA) alert within the electronic medical record system was created for patients with recent travel to Wuhan City, China, which would alert health-care providers of an ongoing outbreak and consideration for isolation precautions with links to the CDC website on COVID-19. The subcommittee focused on the novel outbreak during a portion of the January meeting and for the February 2020 meeting, had reporting from each hospital on the status of AIIR efficacy and PPE volumes from supply chain. As the first US cases were identified in late January, efforts were ramped up to convert more HCD subcommittee work to focus on COVID-19 rather than the Ebola outbreak in the Democratic Republic of the Congo.HCD classes continued with a new focus on educating around the COVID-19 outbreak and the isolation requirements for potential patients. Beginning in mid-February 2020, PPE supplies were reported to the HCD subcommittee, and weekly meetings were created to address COVID-19 preparedness. These weekly meetings focused on reporting outbreak status updates and then processes measures for response, which included PPE, surge capacity plans, laboratory needs, and widespread communication and training efforts. Infection preventionists at each campus also presented to hospital leadership on the outbreak, ongoing plans, and the current state of the outbreak. Furthermore, infection preventionists did focused, intensive in-person COVID-19 PPE training for all staff, focusing on those emerging department, intensive care units, designated cohort units, respiratory therapists, environmental services, and lab personnel. This training was provided for day and night shift and included return demonstrations to ensure staff felt comfortable with the PPE requirements. Moreover, infection preventionists worked with staff in the cohort units to ensure rooms were set up accordingly and workflow was optimal for success and avoidance of cross-contamination. A new isolation guidance and signage was created for Enhanced Respiratory Precautions, which included CDC guidance and provided visual cues to ensure the appropriate isolation precautions were not only used but staff entering the room were aware. Last, 24/7 just-in-time N95 respirator fit-testing was provided as PPE supplies fluctuated.As a result of the existing HCD infrastructure, modifications to the electronic medical record alerts were easier and allowed for more rapid modification to match evolving guidance from the CDC. This process would later be built out more to provide alerts with directions for proper isolation, testing, and notification processes to ensure staff had the information immediately when the patient was identified as high risk through either self-reported travel or exposure. Through pre-existing alerts to the IPC team for measles and pertussis tests ordered, the team was able to have text and email alerts for those patients identified to meet patient under investigation (PUI) criteria for COVID-19 and then later, positive SARS-CoV-2 tests. This rapid alert ensured there were not communication failures for the IPC team, but also comforted staff in knowing that they were supported. Moreover, the algorithms for patient movement and isolation were used from the HCD plan’s existing respiratory pathogen section. As the HCD trainings had included sections on respiratory pathogens that would include PPE beyond facemasks, these lessons were used for staff training and process measures.In terms of engineering and environmental control aspects, the HCD committee efforts to ensure functioning AIIR, as well as the designation of cohort units for surges of patients with HCDs, were used for COVID-19 response. Due to a heavy focus on the environmental management of HCDs, disinfection products were rapidly assessed to ensure they met claims for Environmental Protection Agency (EPA) Emerging Viral Pathogens efficacy. Last, the focus on how to prepare a room for a PUI or confirmed case, was used from HCD efforts. This involved removing as much unnecessary equipment or materials from the room and ensuring supplies, including PPE, were on carts outside the room as well as clear signage. Furthermore, the use of ultraviolet-C (UV-C) disinfection robots was incorporated into response. While this process was a strategy for the viral hemorrhagic response portion of the plan, the use of the health-care system UV-C disinfection robot fleet was incorporated into disinfection protocols for all PUI and COVID-19 cohorted areas.Last, the creation and development of the HCD subcommittee and health-care system plan meant that key stakeholders, including hospital leadership, were aware of the various components and aspects of biopreparedness and response. Because both the plan and subcommittee had addressed the wide variety of factors that go into responding to bioevents, less time was spent convincing leadership or stakeholders of their roles. The ability to begin an early response and initiate preparedness and readiness protocols considerably aided in health-care system’s ability to manage the COVID-19 pandemic. Having leadership support for these efforts, especially in the early days of the outbreak, allowed for a more strategic rather than frenzied response. HCD efforts were translated into Hospital Incident Command System initiation as the network and hospitals began to see more cases and an influx of patients.While the established HCD subcommittee and efforts aided in response to COVID-19, there were several challenges that we have faced, both internal and external, that will be incorporated into future efforts.5 While we began review of assessment of PPE, especially N95 respirator, use early in the pandemic, this was still a stress and strain on resources. From PPE to disinfecting wipes, the challenges of maintaining a steady stream of supplies was not anticipated, but required a rapid response in terms of using federal protocols for re-use and extended use.The availability of PPE is one that has been felt globally, but nonetheless stressed efforts.6 Transparency and staff trust in processes has become a key piece in infection prevention efforts during COVID-19 and will need to be incorporated into future HCD efforts.7 This aspect of COVID-19 response reinforces the importance of crisis communication and science communication, especially for infection preventionists. While education and communication are critical aspects of infection prevention duties, more emphasis should be placed on ensuring there are training and resources to ensure they are successful communicators for both crisis and daily events.As a result of these new PPE use strategies, as well as the changing federal guidance on masks and respirator requirements, there were challenges in ensuring staff awareness and trust in the new processes. While staff had felt more confident in their PPE skills following HCD classes, having to do emergent education during a pandemic on extended use of N95 respirators was a novel situation and one that required more time addressing questioned protocols. Change in PPE practices coupled with the “infodemic” surrounding staff through social media and other news outlets, became a daily focus for IPC efforts.Last, the limitations in testing were an unexpected hurdle. While we had learned several key lessons in coordinating testing and sample collection during a real-world drill involving a symptomatic patient returning from the Democratic Republic of Congo, the testing roadblocks for COVID-19 were taxing. Coordination of testing with public health had been a learning lesson from our 2019 rule-out-Ebola patient, but the widespread demands for SARS-CoV-2 testing from patients and physicians alike were difficult to manage in the early days of limited testing. In efforts to avoid inundating the local health department, we established a testing request process in which medical providers would call IPC first and if the patient met public health criteria for testing, we would initiate conversations with the local public health department. This process was imperfect and taxing on the IPC team but ultimately resolved when third-party, and later in-hospital, testing became available.Despite the extensive work in developing the HCD subcommittee, there is still much work to be done. Incorporation of the lessons learned from COVID-19 will be built into an extension of the HCD plan, which will be COVID-19 specific. Because there was a considerable amount of process and document development for this pandemic, we are in the process of compiling these efforts in a COVID-19 plan, which would fall under the larger HCD plan. Within this, there will be a collection of the documents and guidance created during the pandemic, but also a review of scaling up and descaling efforts, such as universal masking, which will have trigger points to ensure future response has a clear approach to initiating enhanced infection control measures.As a result of this pandemic, the HCD training will also be designed to focus less on viral hemorrhagic fevers and more on respiratory pathogens, such as COVID-19. The classes will focus more on the nuances to COVID-19 response that have made it challenging but also reflect the majority of questions and hurdles IPC has faced.8 Investing in pandemic and HCD preparedness requires a proactive and willing hospital leadership. The decision to purchase additional and infrequently used PPE kits and support personnel training efforts is one that not every leadership team will view as worthwhile, but our experiences have shown how valuable they can be. Situational awareness and ability to rapidly scale-up efforts have made a considerable difference at our hospital system. Our COVID-19 response efforts have built on the work of the HCD subcommittee, which allowed for a less frenzied, more uniformed and calm approach to pandemic response. As IPC played a significant role in HCD response, our role was further highlighted during COVID-19, which reinforced the critical role of infection prevention during biological events. Furthermore, these efforts facilitated the health-care system in continuing to provide adequate PPE to staff without having to make dangerous compromises or practices. Establishing biopreparedness efforts, such as an HCD subcommittee, can help prepare health-care facilities for future biological events and potentially avoid adverse outcomes. Biopreparedness builds on foundational infection prevention, which strengthens hospital efforts to reduce infectious disease transmission, whether it be a health-care-associated infection or an emerging infectious disease.While the United States is still battling the COVID-19 pandemic and there will likely be a renewed response for secondary waves, the creation and development of HCD efforts has aided in readiness. As these are not mandated or regulatory required efforts, we hope that our experiences will encourage other hospital and health-care systems to invest in biopreparedness.


Based on the finite element (FE) analysis software Abaqus, an FE model of square-cased square steel tube reinforced concrete (ST-RC) columns under the hybridized action of high-temperature and load is established. The accuracy of the FE model is verified using experimental data from existing studies. This model is used to analyze the temperature change, internal force distribution, and failure characteristics of the square-cased square ST-RC columns under the action of fire, as well as the factors affecting the fire resistance limit of the column. The results of FE analysis show that under the action of fire, the maximum internal temperature of the square-cased square ST-RC columns occurs in the corner of the section. Moreover, the stress and strain reach their maximum values at the concrete corner outside the tube. During the heating process, an internal force redistribution occurs in the square-cased square ST-RC column. At the same time, the proportion of the axial force and the bending moment of the reinforced concrete outside the pipe decreases gradually, while the proportion of the internal force of the core concrete-filled steel tube (CFST) increases gradually. In essence, it is a process of load transfer from the high-temperature to the low-temperature zone. In addition, the section size, load ratio, slenderness ratio, cross-sectional core area ratio, steel content, and external concrete strength are the main parameters affecting the fire resistance limit of the square-cased square ST-RC columns. Among them, the cross-sectional core area ratio, section size, steel ratio, and external concrete strength are positively correlated with the fire resistance limit of the composite column. On the contrary, with the increase in the load ratio and the slenderness ratio, the fire resistance limit of the square-cased square ST-RC columns decreases. On this basis, a simplified formula to calculate the fire resistance limit of square-cased square ST-RC columns is proposed. The research results can be used as a theoretical reference for the fire protection design of this kind of structure in practical engineering. A steel-tube-reinforced concrete (ST-RC) column is a composite member formed by the combined action of core concrete-filled steel tube (CFST) components and peripheral reinforced concrete (RC) components. It combines the advantages of CFST columns and RC columns, and has excellent antiseismic, fire-resistant, explosion-resistant, and impact-resistant properties ,2,3. In To date, many studies on the mechanical properties of ST-RC columns have been conducted. Yao et al.  calculatIn this study, to understand the working mechanism of square-cased square ST-RC columns under the combined action of fire and load, an FE model of this type of composite column was established through numerical simulation. The temperature change, stress, strain development, internal force distribution, and failure pattern of this kind of component in the process of fire heating were analyzed. Based on the parametric study of the factors affecting the fire resistance limit of this kind of column, a simplified calculation formula of the refractory limit of square-cased square ST-RC columns was developed.An FE model of square-cased square ST-RC columns under the combined action of fire and load was established by reasonably selecting the thermal parameters and mechanical model of the steel and concrete materials and adopting the thermo-mechanical sequential coupling method in the FE analysis software Abaqus. Using this model, the temperature distribution and mechanical properties of this kind of component were analyzed in detail.The temperature state of the column in a fire was simulated using the standard temperature rising curve of ISO-834 . In the t is 0.5 . Withoutρc′ and cc′ and are the bulk density and specific heat of water vapor evaporation, respectively; ρc and cc are the bulk density and specific heat without considering the evaporation of water vapor, respectively; ρw and cw are the bulk density and specific heat of water, respectively.The thermal parameters proposed by Lie  were useThrough the thermal-mechanical sequential coupling method, the temperature field calculation results were accurately introduced into the mechanical model to analyze the mechanical properties of the square-cased square ST-RC columns. In this model, the isotropic elastoplastic model is used in the steel constitutive model, which satisfies the von Mises yield criterion. The stress–strain relationship of steel under high temperature was obtained from Lie . The plad Denham . The tend Denham , and theThe interface between the steel pipe and the internal and external parts of the concrete was modeled as a surface contact. Hard contact was used in the normal direction, in which the pressure can be transferred completely but the tension cannot. Coulomb friction was used tangentially, which can transfer shear force and allow the steel pipe and concrete to generate a relative slip, with a friction coefficient of 0.6 . StirrupNt and Nu are the experimental and calculated values of the ultimate bearing capacity, respectively. As shown in the figure, the correlation between the test and calculation results of the bearing capacity is 0.917, which shows that the test and calculation results agree well.In this study, the axial compression and eccentric compression data of CC1-CC10 ST-RC columns from Kang at al.  were useUsing the above modeling method, the experimental results of Xu and Liu  and XianTechnical Regulations for Concrete Stacking Collections CECS188-2019 [Concrete Structural Design Specification GB50010-2010 [B) is 600 mm, CFST outer diameter (D) is 300 mm, steel tube thickness (t) is 10 mm, and column height (H) is 6000 mm. The column is symmetrically equipped with fy = 390 Mpa. C40 self-compacting commercial concrete is used for both inner and outer concrete of the steel tube. λ = L/B = 10, the reinforcement ratio ρs is 0.14%, the core area ratio αsc is 0.25, the steel content αs is 0.15, and the column load ratio n is 0.6 . In addition, the initial eccentricity used to analyze the fire resistance limit of the square-cased square ST-RC columns was L/1000.With reference to the material grade and construction requirements specified in the 188-2019  and Conc010-2010 , a typic(1)Normal temperature loading phase (O–A). In this stage, the axial compression of the upper load causes the initial axial compression deformation of the composite column. The larger the load ratio, the greater the axial compression displacement.(2)Temperature expansion stage (A–B). During the initial temperature increase, with the decrease in the load ratio, the increasing rate of the axial displacement compression at the top of the column decreases gradually. When the load ratio is less than 0.3, the axial displacement is positive; that is, the axial expansion displacement is at the top of the column. The smaller the load ratio, the more obvious the axial displacement reduction and the longer the temperature rise expansion phase (A–B). This is due to the simultaneous expansion and degradation during the initial heating process. When the load is relatively large, the material expansion is the dominant factor affecting axial displacement because the heating time is short and the section temperature is lower than the degradation temperature of concrete (450 °C) and steel (200 °C). Therefore, the axial displacement increase rate reduces. With the increase in the heating time, the expansion reaches its peak at point B. Since the upper load is large, the components have an internal force distribution. However, the resistance of the structure is less than the upper load, which causes the axial displacement to increase gradually. As a result, the duration of heating and the expansion of A–B is short. When the axial pressure is small, stage A–B lasts a long time. The main reason contributing to this phenomenon is that as the heating time increases, the internal temperature of the cross-section gradually increases, and the material properties also begin to deteriorate. However, due to the low axial pressure, the deformation caused by the axial compression is still less than that caused by heating and expansion. Until point B, the material degradation is obvious, showing a rapid decline in the composite column’s carrying capacity. Meanwhile, the axial displacement of the composite column begins to increase.(3)Material softening stage (B–C). As the heating time increases, the internal temperature of the member increases gradually, and the material degradation dominates the axial deformation. When the axial pressure is relatively large, stage B–C lasts longer due to the shorter heating time at point B and the lower degree of material degradation. With the increase in the heating time, the component material gradually degrades until point C, where the failure begins to accelerate. When the axial pressure is relatively low, the duration of phase B–C is shorter. This is because the temperature rise at point B has been occurring for a long time and the internal temperature of the cross-section is high, resulting in obvious material degradation. The resistance of the structure is close to the upper load. When the temperature rise continues to point C, the column cannot support the axial load and begins to enter the accelerated failure stage.(4)Accelerated failure stage (C–D). After point C, due to the existence of initial eccentricity and the degradation of the material properties, the column undergoes bending deformation, and the additional bending moment caused by the second-order effect increases rapidly, which leads to the sharp failure after point C.1, the concrete material outside the pipe degrades with the increase in temperature. Meanwhile, the unloaded load is borne by the steel pipe and the longitudinal bar. However, with the increase in the heating time, the internal temperature of the steel pipe and the longitudinal bar increases gradually, and the material degradation leads to a decrease in the load. At this time, the unloaded load is transferred to the interior, which results in a gradual increase in the pressure on the core concrete. Point B1 is the critical point for the flexural deformation of the composite columns. Before point B1, the flexural deformation of the member is small, and it has little effect on the redistribution of the internal force of the member. However, after point B1, the member produces a large lateral displacement, which has an obvious influence on the redistribution of the internal force in the composite column. At the end of point B1, the axial forces of the external concrete, steel reinforcement cage, steel pipe, and interior concrete account for 30%, 8%, 38%, and 24% of the total axial force, respectively. In stage B1–C, due to the large flexural deformation, the second-order effect produces a large additional moment, but the robust compressive capacity of the concrete leads to an increase in the axial compression percentage of the internal and external concrete. When point C enters the accelerated failure stage, the axial forces of the external concrete, reinforcement cage, steel pipe, and interior concrete account for 35%, 5%, 35%, and 25% of the total axial force, respectively. Finally, the ST-RC column enters the accelerated failure stage C–D and the axial pressure on the internal and external concrete begins to rise rapidly. Meanwhile, the axial force on the steel decreases rapidly.1, the properties of the external reinforced concrete materials gradually deteriorate with the increase in temperature. In addition, the axial pressure borne by the external reinforced concrete begins to decrease, and the percentage of the bending moment also reduces. Meanwhile, the steel pipe and the interior concrete experience increased axial force, and the percentage of the bending moment continuously increases. When the heating time reaches the critical point of flexural deformation at B1, the bending moments of the reinforced concrete, steel pipe, and interior concrete account for 70%, 21%, and 9% of the total bending moment, respectively. With continued heating, after point B1, due to the increasing transverse deflection and the bending of the column, the axial force of the peripheral concrete begins to increase and the additional moment caused by the second-order effect also becomes larger. As a result, the proportion of the affected bending moments also begins to increase. At the end of the B1–C stage, the bending moments of the reinforced concrete, steel pipe, and interior concrete account for 74%, 18%, and 8% of the total bending moment, respectively. In the accelerated failure stage C–D, the buckling deformation of the composite column increases sharply, and the lateral deformation of the surrounding concrete is serious. However, due to the existence of the internal concrete-filled steel tube, the column does not show local buckling and it has good bending resistance. Therefore, the increased bending moment is mainly transferred to the internal CFST. As a result, the proportion of the bending moment borne by the external reinforced concrete decreases, while that of the internal core concrete-filled steel tube increases rapidly.According to the above analysis, from the end of loading at ambient temperature (O–A) to the stage of accelerated failure (C–D), the proportion of the axial force of the external reinforced concrete and the bending moment of the composite columns gradually decreases, while the proportion of the axial force of internal concrete-filled steel tube and the bending moment gradually increases. The results show that in the process of heating, the internal force of the square-cased square ST-RC column is redistributed, which is essentially the process of load transfer from the external high-temperature zone to the internal low-temperature zone.t = 30 min, the strain on the tension side is smaller, close to 1/90 of the compression side. At this moment, the strain isolines of the external concrete corner and the square concrete-filled steel pipe corner of the section are dense. The maximum strain also occurs in the corner area. When the temperature continues to rise, the internal material of the section begins to degrade with a significant increase in the component bending. As a result, the neutral layer moves toward the compression zone and the area of the tension zone increases rapidly. When the fire resistance limit reaches 58 min, the strain on the tension side is about one-half that on the compression side. At this time, the height of the tensile area is close to the height of the compression area, and the component is destroyed, as shown in The strain of the square-cased square ST-RC column increases continuously from the time of ambient temperature loading to the accelerated failure stage. However, the tensile strain increases faster than the compressive strain due to the weak tensile property of concrete. Moreover, in the outer concrete material, the cross-section angle strain is the maximum, which is caused by the higher temperature at the corner of the concrete outside the pipe and the rapid degradation of the material.t = 30 min, the maximum tensile stress is only 1/10 of the compressive stress, and the isometric stress lines at the inner and outer concrete corners and steel tubes are dense. Meanwhile, the maximum stress occurs at the corners. When the temperature continues to rise, the height of the tension region begins to increase. At t = 58 min, the maximum tensile stress is only 1/20 of the compressive stress. At this time, the stress isoline is concentrated at the corner of the steel pipe and the interior and external concrete sections. Meanwhile, the height of the tension side is close to the compression side, and the member is destroyed rapidly, as shown in From the loading at ambient temperature to the accelerated failure stage, the internal stress of the square-cased square ST-RC columns increases continuously with the increase in the heating time. However, the growth rate of the compressive stress is faster than that of the tensile stress because the compressive performance of concrete is better than its tensile performance.C), fire load ratio (n), slenderness ratio (λ), cross-sectional core area ratio αsc , eccentricity e/r0(r0 = B/2), steel ratio (αs), yield strength of the steel tube (fy), yield strength of the steel bar (fyb), strength grade of the concrete (fcu), etc. The parameters of a typical example are given as follows: C = 2400 mm, n = 0.6, λ = 10, αsc = 0.25, αs = 0.15, fy = 390 MPa, fyb = 400 MPa, the strength grade of the concrete inside and outside the pipe is fcu = 40 MPa, and the initial eccentricity is L/1000. Previous studies on concrete-filled steel tube (CFST) members ,30,31,32The load ratio is the main factor affecting the fire resistance of the composite column. When the load ratio is less than 0.4, the fire resistance limit of the member meets the requirement of the Eurocode for 3 h. As the load ratio increases, the fire resistance limit of the composite column begins to decrease significantly. When the load ratio is 0.8, the fire resistance limit of the member is only 15 min. Therefore, the upper load limit of composite columns should be strictly controlled in practical engineering applications.The slenderness ratio has a significant influence on the fire resistance limit of the member. As the slenderness ratio increases, the ultimate bearing capacity and the fire resistance performance of the ST-RC column decrease correspondingly. As shown in The cross-sectional core area ratio has a certain impact on the fire resistance limit of a composite column. As shown in The section perimeter has an obvious effect on the fire resistance limit of the composite column. As the size of the member increases, the temperature absorption of the external concrete increases, which leads to a decrease in the temperature of the interior CFST. Finally, the fire resistance limit of the composite column increases significantly.The impact of the steel content on the fire resistance limit of the composite column shows a linear increase. The higher the steel content and the thicker the steel pipe, the longer the member resists the fire.As the steel tube yield strength increases, the ultimate bearing capacity of the composite columns increases at ambient temperature, but it has little effect on the fire resistance performance of the members.As the load eccentricity increases and keeping the load ratio constant, the upper load decreases correspondingly, but it has little effect on the fire resistance limit of the composite columns.The internal temperature fails to reach the core concrete’s material degradation temperature (450 °C) during the heating process, resulting in a lesser effect on the fire resistance limit of the composite columns.With the increase in the heating time, the properties of the concrete material outside the pipe degrade. As the strength grade of the concrete outside the tube changes from C40 to C80, the fire resistance limit of the member changes from 58 to 68 min and the fire resistance limit increases.tR is the fire resistance limit of the square-cased square ST-RC column, n0 = n/0.6, λ0 = λ/10, αsc0 = αsc/0.25, C0 = C/2400, αs0 = αs/0.14, and fcu0 = fcu/40. The application range of this formula combined with engineering examples is n = 0.3~0.8, λ = 6~16, αsc = 0.05~0.5, αs = 0.04~0.20, C = 1600~6000, fcu.in = 40~80 MPa, fcu.out = 40~80 MPa, and fy = 235~420 MPa.The arrangement and analysis of the parameters of the square-cased square ST-RC columns show that the load ratio, slenderness ratio, core area, section perimeter, steel ratio, and concrete strength outside the tube are the main parameters affecting the fire resistance limit of the composite columns. Based on the analysis of the above parameters, a practical formula for calculating the fire resistance limit of square-cased square ST-RC columns under the action of an ISO-834 standard heating curve was designed, shown in Equation (3).tR is the FE result and tRC is the simplified calculation result of Equation (3). The correlation coefficient is 0.948, and, therefore, both results are in good agreement.(1)Under the action of an ISO-834 standard heating curve, the internal temperature of the square-cased square ST-RC columns increases gradually. In addition, the temperature reaches its maximum in the corner area of the external concrete.(2)The axial displacement–time curve of the square-cased square ST-RC columns under the action of fire can be divided into four characteristic stages. The load ratio has an obvious influence on the curve distribution of each stage.(3)The variation curves of the internal axial force and the bending moment of the composite columns under the action of fire show that an internal force redistribution occurs during the fire process. In essence, it is a process of transferring heat from high-temperature zones to low-temperature zones.(4)The load ratio, slenderness ratio, cross-sectional core area ratio, section perimeter, steel content, and concrete strength are the main parameters affecting the fire resistance limit of square-cased square ST-RC columns.(5)A practical formula for calculating the fire resistance limit of square-cased square ST-RC columns was proposed, which was verified from the results of FE analysis. The good agreements between formula predictions and FE results indicate that the proposed formula can be utilized as a reference for practical engineering design.In this study, an FE model of square-cased square ST-RC columns under the combined action of fire and load was established. In addition, the changes in the temperature field, internal force distribution, stress, and strain during the failure of the composite columns were analyzed based on the results of previous studies. The main parameters affecting the fire resistance performance of the composite columns were investigated. Finally, a practical method to calculate the fire-resistance limit of the square-cased square ST-RC column was presented. The following are the conclusions in detail:


The purpose of the work is an experimental analysis of the behavior of reinforced concrete beams with a new, patented system of truss-shaped reinforcement. Experimental tests of reinforced concrete beams with conventional reinforcement and with truss-shaped, mass equivalent reinforcement, with two different values of longitudinal reinforcement ratio, were carried out. The testing results of the load-carrying capacity and displacements of beams are presented. The cracking and failure mechanism of beams with a new truss-shaped reinforcement system was also analyzed. The test results for conventionally reinforced beams and with truss-shaped reinforcement were compared. The test results show that the use of the truss reinforcement has an influence on increasing the load-carrying capacity of beams. The amount of this increase depends on the total longitudinal reinforcement ratio and reaches as much as 95% for beams with a low reinforcement ratio and 12% for beams with a higher reinforcement ratio. Based on the investigation of the cracking mechanism, it can be concluded that the failure of the beams with transverse truss-shaped reinforcement occurs with a greater number of smaller cracks, which are more evenly distributed along the length of the cracking zone, and have a shorter range over the cross-section depth, which results in their smaller opening widths. The comparative analysis shows the effectiveness of the proposed reinforcement system, justifying the high potential possibilities of its use for the reinforcement of concrete structural elements. Concrete structures reinforced with inserts made of high-strength materials are the most commonly used in the building structures of the world.The development of reinforced concrete began with the commonly known inventions of Joseph-Louis Lambot, Joseph Monier, William Boutland Wilkinson, and Francois Hennebique in the nineteenth century. In turn, the development of concrete prestressing technology in the early twentieth century was initiated by Eugène Freyssinet.In the pioneering invention of Khan , a reinfThe current rules for the use of classic reinforced concrete elements in the form of main bars parallel to the middle plane and auxiliary bars essentially located perpendicular to the main reinforcement are well-established and known thanks to the publications of The International Federation for Structural Concrete (fib), e.g., Walraven et al.  or AmeriThese principles are used and developed in many studies of reinforced concrete elements. These studies concern both different types of reinforced concrete elements as well as experimental and computational research methods.Tests of traditional structural elements reinforced with steel bars of the main reinforcement in tension and with usual stirrups in shear are the subject of many works. However, modern research on reinforced concrete beams focuses on the material modification of concrete and the material diversity of reinforcing bars.An experimental and a numerical study were carried out on the flexural crack behavior of reinforced concrete beam members by Sandeep Das et al. . The expA study on the influence of shape memory alloys (SMA), glass fiber-reinforced polymer (GFRP), and steel longitudinal rebars on flexural and shear behavior of reinforced concrete beams was presented by Karimipour and Edalati . The resAn experimental investigation into the effect of GFRP needles as coarse aggregate partial replacement in concrete on the shear behavior of large-scale reinforced concrete beams was performed by Nie et al. . The GFRThe concrete beams were tested to investigate the flexural performance of concrete beams reinforced with three different reinforcement bar type  and the five different reinforcement ratios by Said et al. . The tesResearch to evaluate the structural performance of two-layer fiber-reinforced concrete beams with glass fiber-reinforced polymer (GFRP) and steel rebars under quasi-static loads was carried out by Nematzadeh and Fallah-Valukolaee . The resAlmost all above mentioned experimental tests were carried out using point-contact measurement devices, i.e., clip strain gauges and linear variable differential transducers.Research is being carried out on elements reinforced with traditional steel reinforcement surrounded by a concrete matrix additionally reinforced with a system of steel fibers or a mixed system of steel, polypropylene, or glass fibers. Smarzewski presented research on slabs, beams, and deep beams with/and without openings made of high-performance concrete and hybrid (steel and polypropylene) fiber reinforced high-performance concrete ,19,20. IIn terms of research methods, the non-contact methods of recording the results and measurements of displacements and deformations are increasingly used. Liu et al. proposed a framework to optimize two-dimensional measurements in concrete structure models with a digital image correlation (DIC) system at different orders of accuracy . A good In the literature, modifications of the transverse shear reinforcement replacing usual stirrups in reinforced concrete beams are not often found.However, there are examples of entwined reinforcement, also known as laced reinforcement. This reinforcement is used in reinforced concrete elements and is specially called laced reinforced concrete (LRC), Anandavalli et al. . In thisEntwined reinforcement is also used in the laced steel–concrete composite (LSCC) system, wherein two outer steel overlays on concrete are joined by steel laced bars and horizontal cross bars without welding, Anandavalli et al. . This paThe use of continuous spiral reinforcement has been examined in RC elements with rectangular cross-sections by Karayannis and Chalioris . Test reAn experimental study on assessing the possibility of obtaining more ductile shear failures using a Ni-Ti alloy spiral reinforcement was presented by Mas et al. . It was The presented literature review shows that (to the best of the authors’ knowledge) geometrical shear reinforcement arrangements based on the permanent connection of crossed transverse bars, which can be an alternative to the conventional reinforcement arrangement, have not been presented in the literature so far.This fact derived the authors’ motivation and strive to design the more homogeneous structural elements as concrete material compositions reinforced with special arrangements of reinforcing steel.Such a goal is met by the innovative truss-shaped reinforcement arrangement of reinforced concrete elements proposed in this paper.The subject of this paper is a new type of concrete reinforcement in the form of plane meshes with a truss arrangement of bars , the solMesh arrangement of steel bars consists of longitudinal bars—chords (1) and repeatedly crossed diagonal transverse bars—cross braces (2).All the truss bars are durably connected at the joints (3) by bonding (welding or resistance welding) in a hyperstatic (over-stiffened) truss system.Transverse bars—cross braces—are arranged in two directions at an angle The innovation of the proposed system of plane meshes for concrete reinforcement with a truss bar arrangement is specific in the following features:The truss-shaped reinforcement is self-supporting even before concreting. Using the self-supporting truss reinforcement, much higher load-carrying capacities are obtained than using the conventional type of reinforcement with the use of the same amount of steel.The truss arrangement of bars increases the homogeneity ratio of the concrete-steel composition and thus strengthens the reinforced concrete elements not only in the places where diagonal cracks occur, but also in the entire element.Due to the homogenization of the concrete-steel composition by the use of a system of flat meshes with the truss arrangement of reinforcing bars, the stresses are more evenly distributed in the element, and the failure mode occurs as a result of the appearance of many cracks with relatively small widths, dispersed at greater distances from the points of load application.The anchoring conditions of the crossed truss bars in concrete improved in the places of the welded joints. However, the required anchorage lengths in accordance with the standard requirements should be used. The spacing of the diagonal transverse bars should be at least 3 times the maximum size of the aggregate used for the concrete.Connections between structural elements should be designed using the principle of reinforcement continuity of each element and taking into account the principle of mutual interpenetration of meshes. In critical joints places, the welded joints of reinforcing bars can also be used in accordance with the standard requirements.As described in The arrangement of the transverse bars (cross braces) of the reinforcement mesh at a different angle also allows for the optimization of the strengthening of the structure in the most stressed places. The application of the same configuration of the slope angle of the transverse bars throughout the structural element enables this element to be adapted to the variable system of external loads. In contrast, it is possible to differ the configuration of the slope angle of the transverse bars along the length of the element in a situation of ensuring a fixed and time-invariant system of external loads.the need to prefabricate the reinforcement meshes,the need for multi-spot welding that is effective only in industrial conditions, andthe need for precise design and realization of connection of various structural elements from prefabricated reinforcing meshes.The application of the proposed reinforcement system may be limited by:These limitations can be significantly minimized in the perspective of the development of automation of the reinforcement mesh arrangement fabrication, even to the level of the “printing” technology of flat and spatial reinforcement. Thus, it would be possible to take advantage of the qualitative advantages of the proposed reinforcement arrangement leading to a reduction in the cost of manufacturing and transportation.The work of Stolarski and Zychowicz  presentsAs the properties of the elements observed on short beams may not fully reflect the actual work of the elements, the aim of this paper is an experimental comparative analysis of the behavior of reinforced concrete beams with a truss-shaped system of transverse reinforcement bars, with a span of 3 m.Experimental tests of reinforced concrete beams with conventional reinforcement and with appropriately mass equivalent truss-shaped reinforcement, each with a different reinforcement ratio of longitudinal reinforcement, were performed. It was assumed that the reinforcement mass balance determines the equivalence of conventional and truss reinforcement.The beams were investigated until failure in a four-point flexural test. The results of testing the load-carrying capacity and displacement of beams are presented. The non-contact digital image correlation method was used to measure the displacements.The cracking and failure mechanism of beams with a new truss-shaped reinforcement system was also analyzed. The images of the crack pattern are presented without measuring the crack width, but with visualization of the cracks’ range at the height of the cross-section.The test results for conventionally reinforced beams and with truss-shaped reinforcement were compared. The effectiveness of the truss-shaped reinforcement system was indicated.Reinforced concrete beams with a support span of 3.0 m were tested. The beams were loaded in a four-point pattern.C) and with truss reinforcement (T). For each type of beam, two series of beams were tested with the use of reinforcement systems with different rates of longitudinal reinforcement.The beams with double, symmetrically reinforced, rectangular cross-sections were tested. Two types of beams were compared: beams reinforced with conventional reinforcement (The descriptions of geometry and the reinforcement layouts of the beams are shown in s1) beams, the longitudinal ribbed bars with a diameter s2) beams—with diameter of s1 is s2—is C-type beams and in the form of two flat trusses in T-type beams were made of ribbed bars with a diameter of In the Series 1  was analyzed in relation to the reference point on the steel base of the beam supports, The load was applied with a constant increase in force over time of 1 kN/s. The tests were performed up to the value of the failure load of the beams.The course of the study was recorded using the Phantom MIRO M310 camera with a recording speed of 3260 frames per second (fps) at a maximum resolution of 1280 × 800 pixels and a maximum speed of 650,000 fps, with a minimum resolution of 64 × 8 pixels.X, Y} coordinate axes of the image. The displacement values read in pixels were then converted to displacement measurement units in millimeters. The pixel size has been converted to displacement measurement units using the standard pixel dimension.The registration of the results at particular time instants made it possible to determine the displacements of the measurement points in relation to the reference point in the {The range of cracks along the height of the cross-section was estimated based on optical analysis of the recorded images at selected time instants. The accuracy of the estimation results from the resolution of the recorded image. This fact affects the possibility of determining the time of the appearance of the first crack defining the cracking force and, to a lesser degree, of determining the range of the cracks, and practically makes it impossible the determination of crack occurrences with a width smaller than the pixel size.Load and deflection in the time function, allowing to determine the dependence of the load as a displacement function.The order of appearance, number, and location of cracks in the load function, allowing to determine cracking and the failure mechanism of the beam.Based on the recording of the beam testing process, the following parameters and phenomena were recorded:As part of the experiment, strength tests of the construction materials were also carried out: compressive strength of concrete and tensile strength of reinforcing steel bars.The beams of Series 1 and Series 2 were made of two lots of concrete mixes of the designed class C50/60. The beams and the material testing were made in accordance with the requirements of standard EN 206:2016  and relaBefore concreting the beams, the consistency of the concrete mixture was tested using the falling cone method. Concrete samples with the declared dimensions of 150 × 150 × 150 mm were made. The samples were stored after demolding in a chamber with humidity above 95% and temperature 20 ± 2 °C.The compressive strength test of the concrete was performed on the CONTROLS I class testing machine.Samples of ribbed steel bars used for reinforcement of the beams were tested. Stress-strain diagrams with a clear yield limit were obtained for all bars. As a yield limit The results of compressive strength tests of concrete samples Based on the compliance criteria for initial production and the test results given in www.epstal.pl accessed on 18 March 2021). Reinforcing steel of grade B500SP with the increased ductility of class C was used For the point c4, under the load in the range of the load-carrying capacity strengthening, a layout of seven “fan-shaped” cracks over the entire area of pure bending  was observed, with second and third order cracks connecting to the original cracks, except for the farthest cracks. The spacing of these cracks corresponded to the stirrups spacing. The cracks had almost the same a range of about For the point c5, with the load corresponding to the load-carrying capacity of the beam, the appearance of a longitudinal crack along the bars in the compressed concrete layer in the central part of the pure bending area was observed, together with a range increase of the second and third order cracks. In the vicinity of the first main crack, four secondary cracks were found, one of which reached a range of For the point c6, at the post-critical load corresponding to the maximum beam displacement and preceding the rapid disintegration of the concrete in the compressed zone, an elongation of the longitudinal crack range along the bars in the compressed concrete layer was observed. An increase in the range of all cracks to about 1—point t1, asymmetrically—on the left, just beyond the boundary of the pure bending area, the first two initiating cracks with a range of For the beam with the truss reinforcement, For the next point t2, under the load in the range of the load-carrying capacity strengthening, the alignment of the first two cracks was observed without changing their width. In addition, the third crack appeared in the center of the pure bending region, with a range of For the point t3, four consecutive cracks were observed in the pure bending region, with a range from For point t4, further cracks were observed in the pure bending region, with a range of For the t5 point, under the load corresponding to the beam load-carrying capacity, a similar to the previously analyzed “comb-shaped” layout of cracks was observed, with the range gradually increasing towards the center of the beam from For the t6 point, at the lowest post-critical load corresponding to the maximum beam displacement and preceding the concrete crushing of the compression zone, the appearance of longitudinal cracks along the reinforcement bars in the compressed concrete layer in the right part of the pure bending region was observed. There were also other transverse cracks beyond the right boundary of the pure bending region with a range of C-s2, T-s2, C-s2 for the point c6, T-s2 for the point t6, In turn, 1 and even a value greater than the calculated load-carrying capacity according to Equation (2)2—point c1, the first, single crack was observed with a range of about For the beam with conventional reinforcement, For the next point c2, at the load exceeding the load causing plasticization of the tensile reinforcement steel, a layout of 4 cracks was observed, among which the range of the first crack extended to For the point c3, at the load close to the beam load-carrying capacity, the first longitudinal crack appeared in the cover of the compressive reinforcement, in the short region of the transfer of the left loading force. A layout of 6 main normal cracks was formed: the first one with a range of For the point c4, with the load corresponding to the beam load-carrying capacity, the length increasing in the longitudinal crack was observed along the reinforcement bars in the compressive concrete layer in the left part of the pure bending region. The layout and the range of the main cracks hardly changed. However, new secondary cracks appeared at the first and the third main cracks.For the point c5, under the load in the post-critical range, a further increase in the longitudinal crack length was observed along the reinforcement bars in the compressive concrete layer towards the right part of the pure bending area. There were also new secondary cracks at the second and the fifth main cracks. An inclined seventh main crack appeared on the left edge of the pure bending region with a range of For the point c6, with the load preceding the ultimate failure load, the occurrence of a longitudinal crack along the reinforcement bars in the compressive concrete layer was observed in the entire pure bending region. The final layout of the first order main normal cracks was formed, with ranges from 1 and a value greater than the calculated load-carrying capacity according to Equation (2)2—point t1, the first single normal crack was observed with a range of about For the beam with truss reinforcement, For the next point t2, at the load exceeding the load causing plasticization of the tensile reinforcement steel, a layout of 4 cracks was observed, among which the range of the first crack extended to For the point t3, the longitudinal crack appeared in the axis of the compressive reinforcement, in the central region of pure bending. Furthermore, the layout of 7 normal cracks occurred with the following ranges: the first crack For the point t4, with the load preceding the reaching of the beam load-carrying capacity, the length increasing of the longitudinal crack was observed along the reinforcement bars in the compressive concrete layer in the left part of the pure bending region. The ranges equalization of the previous crack layout was observed. The range of the first crack shortened to For the t5 point, at the load corresponding to the beam load-carrying capacity, the appearance of a second longitudinal crack along the reinforcement bars in the compressive concrete layer in the left part of the pure bending area was observed. Moreover, a “comb-shaped” layout of single 16 normal cracks was observed, with the range gradually increasing towards the center of the beam from For the t6 point, for the post-critical load preceding the concrete crushing of the compressed zone, the appearance of a third longitudinal crack was observed along the reinforcement bars in the compressive concrete layer in the left part of the pure bending region. Moreover, one new transverse crack was observed beyond the left boundary of the pure bending region with a range of The main goal of study was to compare the load-carrying capacity of beams with possibly the same stiffness over the entire length of the beam. The tests were carried out for a truss reinforcement with a fixed angle between transverse bars. Due to the truss structure of the reinforcement, a higher load-carrying capacity could be expected in the areas where shear forces dominated. Further tests are planned for truss reinforcement with different angles between the transverse bars.The shear resistance of the beam was not investigated in this study because the beams with a very high shear slenderness ratio  and measuring the crack width.The practical implementation of the proposed reinforcement system is planned after a more comprehensive studies of various structural elements. Such structural solutions are presented in detail in the patent description [P1].The similarities in the behavior of the beams of Series 1 and Series 2 relate primarily to the cracking mechanism. The comparative analysis of the cracking mechanisms presented in The range of perpendicular cracks at the height of the cross-section along the pure bending region is smaller in beams with the truss reinforcement system.The region of perpendicular cracks occurrence exceeds the region of pure bending both in the beam with conventional reinforcement and in the beam with the truss reinforcement system.A greater number of perpendicular cracks with a smaller spacing and a shorter range over the cross-section height, are observed in the beams with the truss reinforcement system, than in the beam with a conventional reinforcement system.The “comb-shaped” crack pattern is in beams with a truss reinforcement system, and the “fan-shaped” crack pattern is in beams with a conventional reinforcement system.The comparison of the behavior of the beams of Series 1 with conventional reinforcement and with truss reinforcement shows the following facts.Very significant increase in the load-carrying capacity by 95% in the beam with truss reinforcement compared to that for the beam with conventional reinforcement was stated.The load-carrying capacity was achieved with displacements of 40% less in the beam with truss reinforcement than for the beam with conventional reinforcement.The occurrence of the load-carrying capacity decreasing path after achieving the load-carrying capacity in the beam with truss reinforcement was observed.The cracking appearance in the beam with the truss reinforcement system was recorded at almost three times higher load level than in the beam with the conventional reinforcement system, assuming the available image recording accuracy.At the load corresponding to the load-carrying capacity in the beam with the truss reinforcement system, no horizontal cracking along the reinforcement bars in the compressive concrete layer was observed.The process of post-critical behavior of the beam with the truss reinforcement system is significantly extended and the occurrence of a sudden breakdown of the compressive zone of concrete is not observed even when the maximum displacements of the beam was reached, with a value corresponding to the ratio of the beam span equal to More than 5.5 times lower ductility ratio was observed for the beam with truss reinforcement than for the beam with conventional reinforcement; however, the absolute value of the ductility ratio of the beam with truss reinforcement was large and was of about 15% greater than that for Series 2 beams.The comparison of the behavior of Series 2 beams with conventional reinforcement and with truss reinforcement indicates the following facts.Increase in the load-carrying capacity by 12% in the beam with truss reinforcement compared to that for the beam with conventional reinforcement was stated.The load-carrying capacity was achieved with displacements of 68% greater in the beam with truss reinforcement than for the beam with conventional reinforcement.The appearance of a crack in a beam with the truss reinforcement system was recorded at a load level about 6% greater than in the beam with the conventional reinforcement system, assuming the available image recording accuracy.At the load equal to the load-carrying capacity, both in the beam with the conventional reinforcement and in the beam with the truss reinforcement system, the occurrence of horizontal cracking along the reinforcement bars in the compressive concrete layer was observed.The process of post-critical behavior both in the beam with the conventional reinforcement and in the beam with the truss reinforcement system is elongated, but there is a rapid disintegration of the compressive zone of concrete when the maximum displacement of the beam was reached, with a value corresponding to the ratio of beam span equal to about Almost the same ductility ratio was observed both for the beams with truss reinforcement and with conventional reinforcement.The paper demonstrates experimental verification of the effectiveness of the proposed innovative truss type reinforcement system for reinforced concrete beams.The originality of the proposed reinforcement system consists in the truss shaping of diagonal transverse bars and the permanent connection of the reinforcement bars at all connection points. Its main feature is self-supporting and the ability to carry the initial load even before concreting.The following basic conclusions were derived from our novel experiments on reinforced concrete beams with truss reinforcement.The most important achievement of the research is proof that the use of the truss reinforcement influences increasing the load-carrying capacity of beams.The magnitude of load-carrying capacity increase depended on the total longitudinal reinforcement ratio of beams. For beams with a low value of longitudinal reinforcement ratio, the influence of the transverse truss-type reinforcement on load-carrying capacity of beams was considerable. Thus, for the total longitudinal reinforcement ratio equal to For the beams in Series 1 with a low value of total longitudinal reinforcement ratio, the load-carrying capacity was achieved with displacements of 40% less in the beam with truss reinforcement than for the beam with conventional reinforcement, whereas for the beams in Series 2 with a high value of total longitudinal reinforcement ratio, the load- carrying capacity was achieved with displacements of 68% greater in the beam with truss reinforcement than for the beam with conventional reinforcement. These observations confirm the greater degree of stiffening for the beams with truss reinforcement at a lower longitudinal reinforcement ratio.The non-contact optical method was used in the study to determine with sufficient accuracy for the displacement measurement to build a displacement curve as a load function. However, such accuracy was not sufficient for measuring the crack width. Therefore, only the crack pattern with visualization of the cracks’ range at the cross-section height could be presented.Based on the investigation of the cracking mechanism, one can conclude that the failure of beams with transverse truss reinforcement occurs with a greater number of scattered cracks, more evenly distributed over the length of the cracking zone and with smaller crack ranges over the cross-sectional height.The cracking pattern stated in the research proved once again the stiffening effect of the truss-shaped reinforcement on the effort distribution over a larger part of the beam than in the case of using conventional transverse reinforcement in the form of stirrups perpendicular to the longitudinal axis of the beam.The authors perceive the potential of the non-contact optical method development in the context of deformation analysis of structural elements, based on the recorded displacements in the set of measurement points marked on the element.The authors are fully conscious of the need to further develop research in order to confirm the full effectiveness and high potential application possibilities of the new type of truss reinforcement under various loads and in various structural elements.P1. Stolarski, A.; Zychowicz, J. Flat grids system with the lattice arrangement of bars for concrete reinforcement. Patent description PL 226083 B1, 30.06.2017. Number of patent declaration 398305, 05.03.2012. Polish Patent Office. Patent holder Military University of Technology, Warsaw, Poland.


Debridement, antibiotics, and implant retention (DAIR) is appropriate for select acute postoperative and hematogenous periprosthetic joint infections (PJIs). However, the optimal duration of antimicrobial therapy in patients treated with DAIR has not been defined. Therefore, we aimed to identify the ideal duration of parenteral and oral antibiotics after DAIR. We performed a retrospective study of patients >18 years of age with hip or knee PJI managed with DAIR between January 1, 2008, and December 31, 2018, at Mayo Clinic. PJI was defined using criteria adapted from the International Consensus Meeting on PJI. The outcome was defined as either PJI recurrence or unplanned reoperation due to infection. Joint-stratified Cox proportional hazards regression models with time-dependent covariates were used to assess nonlinear effects of antibiotic duration. Hazard ratios were computed based on prespecified time points for comparison, whereas p-values represented the overall effect across the entire range of durations.There were 247 unique episodes of PJI in 237 patients during the study period. Parenteral antibiotics were given in 99.2% of cases (n=245). This was followed by chronic oral antibiotic suppression in 92.2% (n=226) with a median duration of 2.2 years (1.0-4.1).DAIR failed in 65 cases over a median follow-up of 4.4 years, with a 5-year cumulative incidence of 28.1%. After adjustment for risk factors, there was no significant association between duration of parenteral antibiotics and treatment failure (p=0.203), with no difference between four versus six weeks  . However, both use and longer duration of oral antibiotic therapy was associated with a lower risk of failure (p=0.006). To account for the possibility that this association was driven by results during early follow-up, conditional analyses at one- and two-year follow-up were performed. Both showed a significantly lower risk for a longer duration of antibiotics . Figure 1. Time-Dependent Analysis of Parenteral Antibiotic DurationFigure 2. Time-Dependent Analysis of Oral Antibiotic Suppression DurationAfter DAIR, efficacy from four weeks of parenteral antibiotics was no different from six weeks when followed by chronic oral antibiotic suppression. Our results could not establish an optimal duration but suggested that continuing suppression portends a lower risk of failure of DAIR. Elie Berbari, MD, Uptodate.com  Matthew P. Abdel, MD, Stryker and AAOS Board of Directors  Aaron J. Tande, MD, UpToDate.com