As an alternative to transverse spiral or hoop steel reinforcement, fiber reinforced polymers (FRPs) were introduced to the construction industry in the 1980's. The concept of concrete-filled FRP tube (CFFT) has raised great interest amongst researchers in the last decade. FRP tube can act as a pour form, protective jacket, and shear and flexural reinforcement for concrete. However, seismic performance of CFFT bridge substructure has not yet been fully investigated. Experimental work in this study included four two-column bent tests, several component tests and coupon tests. Four 1/6-scale bridge pier frames, consisting of a control reinforced concrete frame (RCF), glass FRP-concrete frame (GFF), carbon FRP-concrete frame (CFF), and hybrid glass/carbon FRP-concrete frame (HFF) were tested under reverse cyclic lateral loading with constant axial loads. Specimen GFF did not show any sign of cracking at a drift ratio as high as 15% with considerable loading capacity, whereas Specimen CFF showed that lowest ductility with similar load capacity as in Specimen GFF. FRP-concrete columns and pier cap beams were then cut from the pier frame specimens, and were tested again in three point flexure under monotonic loading with no axial load. The tests indicated that bonding between FRP and concrete and yielding of steel both affect the flexural strength and ductility of the components. The coupon tests were carried out to establish the tensile strength and elastic modulus of each FRP tube and the FRP mold for the pier cap beam in the two principle directions of loading. A nonlinear analytical model was developed to predict the load-deflection responses of the pier frames. The model was validated against test results. Subsequently, a parametric study was conducted with variables such as frame height to span ratio, steel reinforcement ratio, FRP tube thickness, axial force, and compressive strength of concrete. A typical bridge was also simulated under three different ground acceleration records and damping ratios. Based on the analytical damage index, the RCF bridge was most severely damaged, whereas the GFF bridge only suffered minor repairable damages. Damping ratio was shown to have a pronounced effect on FRP-concrete bridges, just the same as in conventional bridges. This research was part of a multi-university project, which is founded by the National Science Foundation (NSF) Network for Earthquake Engineering Simulation Research (NEESR) program.

Sign and signal structures involved in vehicular accidents are often partially damaged, and it is possible to repair them instead of replacing them, even when the extent and severity of the damage are substantial. The replacement of these poles is costly and involves interruption for pedestrians and traffic. Therefore, some trials were performed to retrofit these poles in-situ with low cost and short time. Previous research has substantiated that the damage can decrease the strength of the these structures with increasing the dent depth and the use of externally-bonded fiber-reinforced polymer (FRP) composites are beneficial to repair them. The composite systems were comprised of glass or basalt fibers paired with epoxy or polyurethane matrices. The effectiveness of FRP in repairing the damaged poles was demonstrated in previous tests on dented poles using 3-point, 4-point, and cantilever bending tests. The repair systems were able to develop the load carrying capacity of the damaged poles, and their behaviors were controlled by various types of failure modes like yielding of the metallic substrate, FRP tensile rupture, FRP compressive buckling, and debonding of FRP from the substrate. This thesis investigates the resistance of repaired full-scale metallic poles retrieved from the field for monotonic, cyclic, and impact loading. These poles, which have rounded and multi-sided cross sections with and without access ports, were dented in the field or dented mechanically in the laboratory and repaired with the same repair systems mentioned previously. Six of these poles were mounted horizontally in a cantilever configuration to test them monotonically, while three of them were tested cyclically. In both tests, the load was applied as a point load at 9 ft from the base plate. Additionally, two poles were mounted vertically using a cantilever configuration to test them for impact. This test was performed by hitting the poles using an impact pendulum with a 1100 kg mass.The results of static tests show that the repair systems failed because of the aforementioned failure modes. However, most of the failure was located outside the dented region, which indicates the effectiveness of these repair systems in restoring the capacity of the damaged area. During the fatigue tests, the repair experienced no damage before weld rupture in the original steel tube-base plate connection. Moreover, the repair systems proved their effectiveness in resisting the impact load, because they were ruptured at the contact region between the pole and the impactor at the time the poles were deformed at the free side of the poles, as well as the impact side, during the test. In all these tests, the access ports affected the behavior of the repaired poles. Depending on the geometry of the pole, metal substrate, and dent depth and location, FRP repair system recommendations will be presented.

Aramid fiber reinforced polymer (AFRP) composite materials show promise for prestressed concrete bridge applications. However, there are still some knowledge gaps due to lack of sufficient data to assess the long-term performance and therefore sustainability of beams prestressed with AFRP composite materials. The objective of this research is to effectively characterize the material properties based on the short-term and long-term characteristics of AFRP bars. Tensile, creep-rupture, and relaxation tests are experimentally conducted using AFRP bars to validate testing procedures and expand an existing limited database. Previous results from tensile tests show that the stress-strain behavior of Arapree® AFRP bars is linear until failure with tensile strength of approximately 210 ksi (1448 MPa) and strain of 2.1%. For the creep-rupture tests, three specimens are tested and monitored at four different load levels (50, 60, 75 and 85% of maximum tensile strength) throughout a period of 14 days (short-term evaluation) and 42 days (long-term evaluation). From these tests, it is expected that for a 100-year life span, 55% of the ultimate load, Fu, must be applied as an initial stress to obtain a long-term residual strength of 0.80 Fu. For the relaxation tests, six specimens at four different strain levels (50, 60, 75 and 85% of maximum tensile strain) are tested and monitored throughout a period of 14 days and 42 days. Relaxation loss profiles of the AFRP bars are developed based on the experimental data collected from prestressed AFRP bars, which have been less well understood given lack of sufficient experimental data. Overall, the results of this study provide more insight as to the reliability and potential long-term performance of AFRP bars embedded within prestressed bridge structures.

<div>Research has shown that many adjacent box beam bridges in Indiana experience premature deterioration. Primarily caused by leaking joints between beams, this deterioration leads to corrosion and/or fracturing of prestressing strands, ultimately resulting in flexural deficiency of the bridge. A testing program was designed to simulate this observed deterioration by constructing test specimens and implementing various strengthening techniques using fiber reinforced polymer (FRP) systems. The objective of this testing program is to investigate the effectiveness of FRP strengthening systems to increase or even regain the full capacity of beams that have effectively lost tension reinforcing steel due to corrosion. The FRP-strengthened beam specimens incorporate the use of near-surface-mounted and externally bonded systems. Reinforcing bars in the beams are excluded or cut to simulate deterioration. Furthermore, two different methods of end anchorage for the externally bonded sheets, FRP fan anchorage and U-wrap anchorage, are investigated. Results and conclusions from the testing program are described in order to help advise best practices in implementing the aforementioned strengthening systems. </div>

The use of fibre reinforced polymer (FRP) composites for strengthening reinforced concrete structures has become increasingly popular in recent years. However, before FRPs can be implemented in interior building applications their performance during fire must be assessed and understood. There currently remains a paucity of information in this area for most currently available FRP strengthening systems. This thesis presents a study of the mechanical and bond properties of selected currently available FRP strengthening systems for concrete structures at elevated temperatures such as might be experienced during a fire. Testing has been performed and is reported to study the continuous unidirectional coupon tensile strength, lap-splice FRP-to- FRP shear bond strength and tensile elastic modulus at elevated temperatures. Results of thermal characterization tests are also completed in an attempt to relate properties of the polymer matrix, such as the glass transition temperature, and thermal decomposition temperature to the losses of strength and stiffness observed for FRP coupons during steady-state and transient exposure to elevated temperatures up to 200oC. A simple analytical model is presented, for which the input parameters can be determined using dynamic mechanical thermal analysis and thermogravimetric analysis, to describe the reduction in mechanical and bond properties of the FRP systems at elevated temperatures. Based on this testing and subsequent analysis it is recommended that a conservative limit on the allowable temperature exposure for FRP systems during fire be set as the glass transition temperature measured using dynamic mechanical thermal analysis. Furthermore it is suggested that differential scanning calorimetry may not be an appropriate method of determining the glass transition temperature for available FRP systems used in concrete strengthening applications. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-04-30 19:06:24.31

The Near Surface Mounted (NSM) strengthening is an emerging retrofitting technique, which involves bonding Fibre Reinforced Polymer (FRP) reinforcement into grooves cut along the surface of a concrete member to be strengthened. This technique offers many advantages over external bonding of FRP reinforcement, for example, an increased bond capacity, protection from external damage and the possibility of anchoring into adjacent concrete members. To date, significant research has been conducted into the NSM FRP strengthening technique. However, there are still some areas which need further research in order to fully characterise bond and anchorage of NSM FRP bars. Lack of experimental data, design tools and analytical models addressing these areas create obstacles for the efficient use of these advanced polymer materials. The particular objectives of the research are; to investigate bond behaviour between NSM FRP bars and concrete, to understand the critical failure modes involved and their mechanics, and to develop a rational analytical model to predict bond strength and anchorage length requirements for NSM FRP bars. Several significant variables affecting bond, such as bond length, size, shape and type of bar, resin type, groove dimensions and concrete strength, have been considered. In particular, attention has been focussed on the effect of bar shape on bond behaviour. A comprehensive set of laboratory testing and their results, including the effect of the investigated parameters are presented. Various modes of anchorage failure of NSM FRP bars are identified and the underlying mechanics are investigated. Analytical models are developed to predict bond capacity and anchorage length requirements of NSM FRP bars, and are verified with experimental results.

Blasts and impacts are two of the severest loads a structure can experience. Blast experimenters, however, have observed that the load imparted to a circular member was lower than the predicted design load. Additionally, numerous investigations have established the superiority of concrete filled FRP tubes (CFFTs) over conventional reinforced concrete members. These observations indicated CFFTs’ potential to resist dynamic blast and impact loads. The experimental and numerical investigations presented in this thesis aimed to demonstrate the suitability of CFFTs to resist blast and impact loads, to determine the parameters that influence their behaviour under such loads, and to develop a design procedure for resisting these loads. The initial numerical investigation determined the reflected blast loading parameters experienced by a circular cross section. The experimental phase consisted of testing twelve full scale specimens, two monotonically, four under impact loading, and six under close-in blast loading. The monotonically tested specimens acted as controls for the entire program. The results of the impact testing investigation were used to develop and validate a non-linear single degree of freedom (SDOF) model. This impact phase also led to the development of relatively simple procedures for designing CFFTs under impact loading using either SDOF modeling or the conservation of energy. Analysis of the blast testing results led to the development of numerical procedures for obtaining an equivalent close-in blast loading for SDOF analysis of CFFTs and Pressure-Impulse diagrams. The use of SDOF modeling and conservation of energy in blast design were also discussed. Finally, a non-linear explicit dynamic model of CFFTs was developed using the commercial software ANSYS Autodyn. This model was verified using the experimental impact and blast test results and used to conduct a parametric study. The results of these investigations indicated that CFFTs were particularly suitable for blast and impact resistant applications, as their geometry diffracted blast waves and the addition of the tube increased their energy absorbing capacity significantly giving them additional strength and ductility. The tube also confined and protected the concrete core and simplified construction. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2014-01-27 15:57:52.768

The use of fibre-reinforced polymer (FRP) as an internal reinforcement for concrete has many advantages over steel, most notably lack of corrosion which is considered to be a major problem for structures incorporating steel. In Europe alone, it is estimated that the annual repairing and maintenance costs associated with steel corrosion in infrastructure are around £20 billion (Nadjai et al., 2005). Despite of its corrosion resistance, the widespread use of FRP as an internal reinforcement for concrete was hindered due to its relatively weak performance at elevated temperatures, such as in the event of fire. Under heating, the polymer matrix in FRP softens, which causes bond degrading between reinforcement and concrete. The softening of polymer matrices occurs around their glass transition temperatures, which is typically in the range of 65– 150 °C. The sensitivity of FRP bond to temperature is recognised in design guidelines, therefore many advise against utilising FRP as an internal reinforcement for concrete in structures where fire performance is critical. On the other hand, fibres, the other component of FRP, can tolerate temperatures much higher than polymer matrices. This research investigates a new design for FRP internal reinforcement, which exploits the fact that the FRP fibres in general and carbon fibres in particular are capable of sustaining a large proportion of their original strength at high temperatures. Instead of the traditional way of using separate bars, FRP reinforcement was made as closed loops produced through the continuous winding of carbon fibre tows. When the surface bond degrades at elevated temperatures, interaction with concrete can still be provided through bearing at loop ends. The concept of FRP loops was investigated through a series of experimental work. Firstly, the performance of carbon FRP (CFRP) loops was evaluated through a series of push-off tests in which specimens consisting of CFRP loops bridging two concrete cubes were tested in pull-out using hydraulic jacks. Specimens with straight and hooked reinforcement were produced as well for comparison. A total number of 18 specimens were tested at ambient temperature, glass transition temperature (Tg), and above Tg. Results showed that while at ambient temperature there was no distinction in performance. At elevated temperatures, CFRP loops developed strength about three times higher than specimens with straight or hooked bars. Also, while failure mode occurred due to de-bond in the case of straight and hooked reinforcement, rupture failure occurred with CFRP loops. For better demonstration of the concept in more realistic conditions, four-point bending tests were conducted upon 28 beam specimens reinforced either with CFRP loops or straight bars as flexural reinforcement. Beams were tested under monotonic loading at ambient temperature, or under sustained loads with localised heating over the midspan region that contained the reinforcement overlaps. The benefit of CFRP loops became evident in the elevated temperature tests. Beam specimens with spliced straight bars failed due to debonding after a short period (up to 15 minutes) of fire exposure. Conversely, the fire endurance increased four to five times when CFRP loop reinforcement was used. Unlike straight bars, debonding failure was avoided as failure occurred due to reinforcement rupture. The overlap length of the CFRP loops was found to be important in the order for the loop to develop full capacity. Premature failure can occur with short overlap length due to shear off concrete within the overlap zone. The presence of transverse reinforcement increases confinement levels for reinforcement, so the bond failure of straight bars at ambient temperature testing was eliminated when stirrups were provided. However, at elevated temperatures straight bars failed by pull-out even in presence of transverse reinforcement. To facilitate design with CFRP loops, a numerical analysis tool was developed to calculate the bond stress-slip response of reinforcement at ambient and elevated temperatures. A Matlab programme was designed based on a one-dimensional analytical model for steel. The bond law was modified to be used for CFRP reinforcement. Other analytical models from the literature to account for bond degradation with temperature and tensile strength of curved FRP were also utilised. The developed Matlab code has the capability of producing slip, axial stress, and bond stress distribution along reinforcement. The novel FRP loop reinforcement was demonstrated to be a promising solution for enhancing the fire performance of CFRP internal reinforcement at elevated temperatures. It contributes to removing a major obstacle preventing widespread use of FRP-reinforced concrete, and paves the way for CFRP reinforcement to be used in situations where fire performance is critical.

No description available.

Lateral forces generated by wind, earthquakes, and other horizontal loads are trans-mitted from the floor diaphragms to the columns and walls that comprise the vertical lateral force resisting system in a building. Strengthening of the diaphragms in older reinforced concrete buildings may be necessary for several reasons, including to enhance seismic performance, address inadequate strength or stiffness, provide missing or incomplete load paths, improve inadequate shear transfer/connection capacity, and to accommodate changes in the use and occupancy of the structure. Engineers are currently using externally bonded fiber reinforced polymer (FRP) composites to retrofit deficient diaphragms. However, this application is beyond the scope of current FRP-related design documents, including ACI PRC-440.2R-17 "Guide for the Design and Construction of Externally bonded FRP Systems for Strengthening Concrete Structures". The lack of consensus around design recommendations for FRP strengthening of diaphragms is problematic and creates uncertainty about which approaches are proven and what are best practice. This thesis summarizes the results from an experimental research program designed to investigate the shear behavior of reinforced concrete diaphragms strengthened using external-ly bonded FRP. Six one-half scale reinforced concrete cantilever diaphragms were tested in shear to evaluate the influence of FRP material, density, spacing, orientation, and intermediate anchorage configuration on the performance of diaphragm strengthening. The specimens were designed to represent the diaphragm shear zone adjacent to a shear wall in a concrete building. The tests were performed using a reverse cyclic displacement protocol representative of earthquake actions. The tests included a baseline unretrofitted concrete specimen, followed by five retrofitted specimens with different configurations of externally bonded FRP. Each retrofitted specimen was designed to maintain a similar FRP axial stiffness while varying the FRP retrofit parameters. The results demonstrated that externally bonded FRP retrofitting improved both the shear strength and stiffness of the strengthened test specimens. All the retrofitted specimens experienced an FRP debonding failure initiated by intermediate shear cracks with the field of the diaphragm, occurring after yielding of the internal steel rebar. The results highlighted that the overall behavior of the specimens was influenced by the way the retrofit schemes were proportioned and detailed. For example, the application of FRP parallel to the direction of applied shear was found to be most effective at increasing the diaphragm strength. Conversely, the application of FRP perpendicular to the applied shear was found to increase the diaphragm ductility. In addition, the shear strength contribution of externally bonded FRP was significantly influenced by the retrofit surface coverage. Compared with narrow strips of high-density fabric, retrofits detailed with less dense fabric spread uniformly over the surface exhibited superior performance due to better control of the shear cracks. Furthermore, no meaningful difference in performance was observed between diaphragms strengthened with glass and carbon FRP composites, provided the retrofits were proportioned to achieve com-parable levels of stiffness. This finding suggests that either type of fabric may be suitable for diaphragm strengthening. Finally, the use of overstrength intermediate FRP anchors did not noticeably affect the FRP shear strength contribution. However, the presence of intermediate anchors led to localized failures that concentrated inelastic diaphragm response between anchor locations, resulting in a significant reduction in diaphragm deformation capacity. The test results were used to develop design recommendations for shear strengthening existing concrete diaphragms using externally bonded FRP. The recommendations included guidance on how to establish the effective FRP design strain and the nominal shear strength contribution of the FRP, both of which tended to be conservative and underestimated the actual behavior observed during the experiments. The recommendations also address the use of intermediate and end FRP anchors, limitations on the clear spacing between sheets, and other factors pertinent to retrofit design. / Master of Science / The floor diaphragm in a reinforced concrete building transmits lateral forces generated by wind, earthquakes, and other horizontal loads to the building's vertical lateral force resisting system. Diaphragms in older reinforced concrete buildings are often retrofitted to meet seismic demands. Retrofitting deficient diaphragms increases infrastructure sustainability by promoting reuse and reconfiguration of existing buildings while mitigating structural deficiencies. Using externally bonded fiber reinforced polymer (FRP) composites is a com-mon strengthening technique often used without supporting guidance or test data. An industry need for diaphragm retrofit provisions, coupled with a substantial lack of data clearly indicates a need for experimental testing of diaphragm elements strengthened with externally bonded FRP. This thesis summarizes the results from an experimental research program designed to investigate the shear behavior of reinforced concrete diaphragms strengthened using externally bonded FRP. Six reinforced concrete diaphragm specimens were tested to study how variations in FRP material, density, spacing, orientation, and anchorage configuration impacted the performance of the retrofit. One specimen served as a control while the five other specimens were retrofitted with various configurations of FRP. The control specimen experienced a diagonal tension shear failure while each FRP strengthened specimen exhibited an FRP debonding failure, which was initiated by intermediate shear cracks occurring within the field of the diaphragm. The experimental results were analyzed to understand how the FRP retro-fits affected the strength, stiffness, ductility, and energy dissipation of each specimen. It was concluded that externally bonded FRP improves the seismic performance of a building by increasing the in-plane shear strength of the diaphragm. Existing design provisions were evaluated and compared to the experimental findings. Design recommendations were formed based on the observed affect of the test variables.