High modulus carbon fiber materials for retrofit of steel structures and bridges
This paper summarizes the research work dealing with the use of high modulus carbon fiber reinforced polymer (HM CFRP) materials for the retrofit of steel structures and bridges. The research work included selection of an appropriate adhesive for bonding HM CFRP materials to steel and the performance of Large-scale steel-concrete composite beams tested to examine the behavior of different strengthening schemes. The research findings demonstrate the effectiveness of the proposed HM CFRP strengthening system.
FUNDAMENTAL CHARACTERISTICS OF HIGH MODULUS CFRP MATERIALS FOR STRENGTHENING OF STEEL-CONCRETE COMPOSITE BEAMS
This paper presents the findings of a research program which was conducted to investigate the fundamental behavior of steel-concrete composite beams strengthened with high modulus (HM) carbon fiber reinforced polymer (CFRP) materials. The first part of this paper presents a brief description of the HM CFRP materials and the adhesive selection. The second part of the paper focuses primarily on the flexural behavior of steel-concrete composite beams strengthened with CFRP laminates. The behavior of steel-concrete composite beams strengthened with different configurations of CFRP materials and loaded under monotonic, overloading and fatigue loading conditions is presented. Based on the findings of the experimental program flexural design guidelines are proposed to facilitate the design of the CFRP strengthening for steel bridges and structures. The final section of the paper discusses in detail the bond behavior of the CFRP laminates. The bond behavior is investigated using both double-lap shear coupon tests and large-scale flexural tests. The effectiveness of implementing a reverse taper at the end of the CFRP plates is investigated as a means of enhancing the bond characteristics. The proposed analytical tools and finite element analysis, used to predict the bond behavior of the CFRP bonded joints, are in good correlation with the experimental results. This paper demonstrates that high modulus CFRP materials can be effectively implemented for strengthening and repair of steel bridges and structures. INTRODUCTION Recently, considerable research has been conducted on the use of carbon fiber reinforced polymer (CFRP) materials for rehabilitation and strengthening of steel bridges and structures (Mertz & Gillespie, 1996; Sen et al., 2001; Liu et al., 2001, Tavakkolizadeh and Saadatmanesh, 2003; Al-Saidy et al., 2005; Lenwari et al., 2005). The previous research indicates that externally bonded CFRP laminates can be used to increase the ultimate strength of steel girders and to restore the lost capacity and stiffness of damaged or deteriorated girders. However, due to the relatively low modulus of elasticity of conventional CFRP materials as compared to steel, large amounts of strengthening materials are required to achieve a significant increase of the elastic stiffness. The use of high modulus CFRP (HM CFRP) materials has been demonstrated to be a more effective technique to increase the stiffness of steel beams (Rizkalla and Dawood, 2006). HIGH MODULUS CFRP MATERIALS High modulus carbon fiber materials are commonly produced as dry fiber tow sheets. The sheets can be impregnated with a saturating resin on-site using a wet lay-up technique and are well suited for application on curved or highly irregular surfaces. For applications requiring a higher degree of strengthening, the carbon fibers can also be pultruded into a precured laminate which can be subsequently bonded to the surface of the structure using a structural adhesive. The typical material properties of the dry fibers and pultruded laminate HM CFRP materials are given in Table 1 . Table 1: HM carbon fiber material properties Fiber Properties (Mitsubishi, 2004) Laminate Properties Tensile modulus of elasticity, E 640 GPa 460 GPa Tensile ultimate strength, fu 2600 MPa 1540 MPa Tensile rupture strain, εu 0.004 0.0033 Fiber volume fraction, FVF 70% ADHESIVE SELECTION The first phase of the research program focused on the selection of a suitable adhesive to bond carbon fiber laminates to steel surfaces (Schnerch, 2005). A total of six different adhesives were evaluated using small scale flexural tests. The test specimens consisted of an 813 mm long steel I-beam with a steel plate welded to the compression flange to simulate the presence of a composite concrete deck slab. The beams were strengthened by bonding 36 mm wide x 1.4 mm thick CFRP laminates of varying lengths to the bottom of the tension flange. The beams were subsequently loaded to failure in a four point bending configuration. Of the six adhesives tested, the SP Spabond 345 two part epoxy adhesive was capable of developing the full rupture strength of the 1.4 mm thick HM CFRP strips within a development length of 102 mm. Due to its relatively short development length and its workability and suitability for overhead application, this adhesive was selected for the remaining study of the behavior of the CFRP strengthening system. FLEXURAL BEHAVIOR Once a suitable adhesive was identified, the fundamental behavior of steel-concrete composite beams strengthened with CFRP materials was investigated. Three 6400 mm long steel-concrete composite beams were tested to investigate the effectiveness of using different configurations of CFRP laminates to increase the strength and stiffness of typical steel highway bridge girders. The configurations studied included externally bonded high modulus (HM) CFRP laminates, externally bonded intermediate modulus (IM) CFRP laminates and prestressed high modulus CFRP laminates. A detailed description of the study is presented by Schnerch (2005). The load-deflection behavior of the three tested beams is presented in Figure 1(a). The ultimate capacity of the beams was governed by rupture of the CFRP as shown in Figure 1. Failure occurred due to crushing of the concrete in all three cases. A typical beam after failure is shown in Figure 1(b). Installation of both the intermediate modulus and the high modulus CFRP materials effectively increased the elastic stiffness and the ultimate capacity of the strengthened beams. Alternatively, the prestressed CFRP system was designed primarily to increase the stiffness of the beam without increasing the ultimate capacity of the member. This may be advantageous in cases where it is desired to improve the serviceability of a member while maintaining the full ductility of the unstrengthened section. (a) Load-deflection behavior (b) Typical beam failure Figure 1 Flexural behavior of large-scale beams strengthened with CFRP laminates FATIGUE LOADING AND OVERLOADING BEHAVIOR An additional six scaled steel-concrete composite beams were tested to study the behavior of the strengthening system under fatigue loading and overloading conditions as presented in detail in Dawood (2005). The typical test beams were tested in four-point bending with a span of 3050 mm and a 610 mm long constant moment region. Two of the test beams were strengthened with different reinforcement ratios of high modulus CFRP materials and subjected to several loading and unloading cycles to simulate severe overloading conditions. A third unstrengthened beam was tested as a control beam for comparison purposes. The typical load-deflection behavior of an unstrengthened beam and a strengthened beam are shown in Figure 2(a). In addition to increasing the ultimate capacity and elastic stiffness of the beams, installation of the high modulus CFRP materials also helped to increase the yield load of the beams as shown in the figure. Figure 2(a) also indicates that the presence of the CFRP materials significantly reduced the residual deflection of the strengthened beam due to the simulated overloading conditions as compared to the unstrengthened control beam. This suggests that in the event of overloading conditions, an unstrengthened beam would likely exhibit a significant residual deflection which may necessitate replacement of the member while a similar strengthened beam would remain in excellent serviceable condition. The remaining three test beams were tested under fatigue loading conditions. Two of the beams were strengthened using the same reinforcement ratio of CFRP materials however, using different bonding techniques to investigate the effect of the bond on the fatigue performance of the system. The third beam remained unstrengthened to serve as a control beam for the fatigue study. All three of the test beams were subjected to three million fatigue loading cycles. The minimum applied load used for the cyclic loading for all three beams was selected to be equivalent to 30 percent of the calculated yield load of the unstrengthened beams to simulate the effect of the sustained dead-load for a typical bridge structure. For the unstrengthened beam, the maximum load in the loading cycle was selected to be equivalent to 60 percent of the calculated yield load to simulate the combined effect of dead-load and live-load. The maximum load for the two strengthened beams was selected to be equivalent to 60 percent of the calculated increased yield load of the strengthened beams. The maximum load simulated an increase of 20 percent of the allowable live-load level in comparison to the unstrengthened x x x – CFRP rupture o – concrete crushing Bonded HM CFRP
Impacts of climate and land use changes on flood risk management for the Schijn River, Belgium
Abstract Flooding is the most common natural disaster in Europe. Modern flood risk management relies not only infrastructure development but also on governmental and non-governmental actors applying legal, economic and communicative water management instruments. Within the European Union (EU), flood management closely relies on policy set at the EU and national levels. It is now recognized that a sound understanding of climate change is required in addition to current management by taking into account land use change and socio-political context, as climate and land use changes have major impacts on hydrological responses. This paper investigates the hydrological behavior due to urbanization under current and future climate scenarios of high summer and high winter rainfall for 20 sub-catchments of the Schijn River, located in the Flanders region near Antwerp, Belgium. As urbanization increases and existing rainfall-runoff models neglecting the specific behavior of urban runoff, a hydrological model was developed based on a basic reservoir concept and applied to the existing rainfall-runoff model (PDM) flow to examine the specific urban contribution. Results revealed that peak flow for urban runoff and the total peak flow (i.e. rural and urban runoff) were significantly higher (i.e. ranges from 200% to 500%) than the existing rainfall-runoff model (PDM) flows, because of faster and more peaked urban runoff response. The impact of climate change on current and future conditions was also assessed by estimating peak flows with respect to return periods from the flood frequency curve. The predicted peak flow of high summer future climate scenario was significantly higher (i.e. ranges from 200% to 250%) than that of the current climatic condition for this region. Furthermore, hourly peak flow and daily volume ratios of 100-year return period for the highest, lowest and average impervious area were projected for the time horizon of the year 2100. It is concluded that climate change impacts contribute the most in producing peak flow in coming years, while increased urbanization takes the second place for both hourly and daily values. Results on urbanization effect and climate change impact assessment are useful to the water managers for spatial planning, emergency planning and insurance industry.