Glass Fibre Reinforced Polymer (GFRP) bars have been developed as an alternative to steel reinforcement for various structural concrete applications. Due to their non-corrossive nature, they are particularly suited for harsh environments where steel reinforcement is prone to corrosion. The purpose of this research is to determine the feasibility of GFRP reinforcing bars as concrete bridge deck reinforcement for locations, such as coastal New Zealand, where the non-corrosive benefits of GFRP may offer an alternative to traditional mild steel reinforcement. GFRP use as structural reinforcement may offer life-cycle cost benefits for certain structures as maintenance to repair corroded reinforcement is not necessary. The use of GFRP reinforcement in a New Zealand design context was investigated to directly compare the structural performance of this alternative reinforcing product. Mateen-bar, manufactured by Pultron Composites Ltd, is the GFRP reinforcing bar used in the experimental tests. Experimental investigation of tensile properties of GFRP bar samples was carried out to understand the mechanical behaviour of GFRP reinforcement and validate the manufacturer’s specifications. This series of tests highlighted the complexities of carrying out tensile testing of FRP products, due to the inability to grip the GFRP directly in a testing machine without crushing the specimen. Two phases of full-scale tests were carried out to compare the performance of bridge deck slabs reinforced with typical mild steel and GFRP reinforcing bar. This experimental testing was different to most existing research on GFRP reinforced slab performance as it did not compare the performance of a GFRP reinforcing bar area equivalent to steel, but was designed in such a way as to dependably give the same moment capacity of the steel reinforced slab design. This incorporated the recommended limit of 20% of design stress given by the manufacturer which led to an apparent over-reinforced section for the GFRP slab design. The aim of the experiments was to investigate the comparative performance of a typical New Zealand bridge deck design and a GFRP reinforced equivalent designed in such a way as is currently recommended by the manufacturer. The over-reinforcement lead to differences in conclusions drawn by other authors who have studied GFRP reinforced slab behaviour. Both flexural and concentrated loading (simulating vehicle loading) tests were carried out on both the steel and GFRP reinforced slab designs. Due to over-reinforcement the GFRP slab was considerably stiffer and stronger than the steel design, indicating that serviceability issues are unlikely to be as much of a design issue as existing literature would suggest. Deflection prediction models generally underestimate the strength of over-reinforced sections. All slabs failed in punching shear under concentrated loads, indicating that punching shear may be a critical failure mechanism for GFRP reinforced slabs Based on the findings from the extensive experimental phases, a set of design recommendations were made to further improve the potential for GFRP to be used for bridge deck design in a New Zealand context.

This thesis discusses the development of a new type of fibre-reinforced polymer (FRP) beam for use in civil engineering systems. After a detailed evaluation of the advantages and disadvantages of current FRP beam technology, a different approach is proposed which combines traditional laminates with a novel casting technique. To pre-dimension the beam, the classical beam theory is adapted to allow for FRP materials. The resulting formulae were used to determine critical parameters, such as laminate thickness and location in the cross-section, and core dimensions, and to identify failure modes. Based on the results of this analytical study, a detailed testing program was developed. In addition to classical tests, such as bending, shear, and lateral torsion, the performance of the beam was also examined under particular loading regimes specifically designed to induce local failure modes, such as buckling of the web and bearing failure of the section under concentrated loads. The experimental results revealed very good agreement with the analytical predictions. These results were corroborated by a detailed non-linear finite-element analysis, including core cracking and laminate damage. This analysis, in particular, highlighted the synergy between bending and shear behaviour of the beam. This study has revealed that this new type of FRP beam behaves in a predictable manner. Furthermore, the experimental results verified that the cross-section, which combines traditional laminates with cast polymer concrete, did not suffer from many of the disadvantages identified in current FRP beams. The cracking of the polymer concrete under shear, however, does cause the beam to fail prior to the laminates reaching their ultimate shear stress.

Structural elements in buildings and civil engineering infrastructure can often be vulnerable to various kinds of impact actions during their service life. These actions could result from various sources e.g. collision of vehicles, ships and vessels or falling masses in industrial buildings. Since, for various reasons, such accidental actions have not always been considered in the existing engineering design of buildings and civil engineering structures such as bridges etc., investigation of effective structural strengthening techniques is justified. As fibre reinforced polymer (FRP) composites have commonly been employed efficiently to strengthen steel members against static and fatigue loads, examining the FRP strengthening technique to enhance structural steelwork in impact situations is the main focus of this study. The research aims to experimentally investigate the dynamic behavioural response of axially loaded steel columns and steel beams strengthened with various carbon fibre reinforced polymer (CFRP) configurations. To achieve this goal, a series of experimental tests was implemented including testing a number of CFRP strengthened and unstrengthened steel beams and columns under static and impact loads. The experimental results show that CFRP can improve the global and local behaviour of steel members subjected to impact loads. This improvement varied depending on the CFRP configuration, the amount of CFRP and the pre-existing axial load value in the member. In order to examine all the parameters that can affect the dynamic behaviour of CFRP strengthened steel members in addition to those not included in the experimental programme, a comprehensive numerical simulation of the experimental work was carried out using a validated finite element model. Afterwards, an extensive parametric study was conducted to provide a comprehensive understanding of the behaviour of CFRP strengthened steel members subjected to impact load. The simulation results illustrate that the effectiveness of CFRP increases with high impact energies. The parametric study results have also revealed that the configurations and distributions of CFRP have a major influence on the effectiveness of the reinforcement. A detailed numerical assessment has also been performed to find the CFRP effectiveness when applied to full-scale steel columns. It has been found that strengthening with CFRP in practical quantities and configurations could prevent steel columns from failure under transverse impact loading. The strengthening effectiveness was found to be dependent on boundary conditions, impact velocity, impact mass, impact location, preloading level, impact direction, CFRP configuration, and the length and thickness of the CFRP. Based on the results obtained from the full-scale simulation, it has been found that the CFRP strengthening technique can be used efficiently and effectively at the scale of elements common in everyday building and infrastructure. This study also provides a useful database for different kinds of strengthening configurations, impact velocities and masses, boundary conditions, etc.

Applying lateral confinement to concrete columns using fibre-reinforced polymer (FRP) composites is a very promising technique. FRP rupture is the typical failure mode of FRP wrapped columns under axial compression. numerous experiments have shown that the FRP rupture strain in an FRP wrapped circular column is significantly lower than the FRP ultimate rupture strain determined from flat coupon test of FRP. Despite a large number of studies on the application of FRP confined columns, the mechanisms and level of lower-than-apparent FRP rupture strain still remain unclear. This thesis presents theoretical, Numerical and experimental studies aiming at developing a deeper understanding of the fundamental mechanisms of this phenomenon. A comprehensive literature review was presented providing the background on FRP confined columns, material properties of FRP composites as well as some factors which may lead to premature FRP rupture. A FE analysis was conducted to investigate the FRP hoop strains in the split-disk test, explaining for the first time that the fundamental mechanism of the lower FRP rupture strain in the split-disk test than in the flat coupon test is because strain localisation due to geometric discontinuities at the ends of the FRP and bending of the FRP ring at the gap due to change of curvature caused by the relative moment of the two half disks, as the FRP (as a brittle material) ruptures once the maximum strain at one of these locations reaches the FRP rupture strain. A list of contributory factors affecting the apparent FRP rupture strain in FRP wrapped columns were next identified and classified. An analytical solution was developed to investigate the influence of the triaxial stress state on the FRP strain efficiency, this factor has been shown to have a potentially significant effect on the failure of the FRP wrap but considerable discrepancies exist between predictions using different failure criteria so further research has been identified in this area. FE models were developed to examine the effect of the geometrical discontinuities on the strain efficiency of FRP jackets in FRP wrapped concrete-filled circular steel tubes and FRP wrapped concrete columns. It is demonstrated that severe FRP hoop strain concentrations occur in very small zones near the ends of the FRP wrap in both types of FRP wrapped columns, leading to premature FRP rupture and thus lower strain efficiency. The combined effects of end constraint and FRP overlap on the behaviour of FRP wrapped concrete columns was investigated using a three dimensional FE model considering one half of the length of an FRP-wrapped concrete cylinder. The results have shown that the frication between both ends of a column and the loading platens provides constraints to the ends of the column, but this constraint has little effect on the strain concentration caused by the geometrical discontinuities of the FRP overlap, though the ultimate axial strain of the FRP wrapped columns can be significantly overestimated if the end constraints are not considered.

Steel silos are widely used as long-term or short-term containers for the storage of granular solids, of which a huge range are stored, from flour to iron ore pellets, coals, cement, crushed rocks, plastic pellets, chemical materials, sand, and concrete aggregates. The radius to thickness ratio for silos is in the range of 200 to 3000, so they fall into the category of thin shells, for which failure by buckling is the main concern and requires special attention in design. The primary aim of this thesis is to investigate the possible application of Fibre Reinforced Polymer (FRP) as a new repair and strengthening technique to increase the buckling capacity of thin metallic cylindrical shells. Extensive research has been conducted on the use of fibre reinforced polymer (FRP) composites to strengthen concrete, masonry and timber structures as well as metallic beams. However, all these studies were concerned with failure of the structure by material breakdown, rather than stability. As a result, this thesis marks a major departure in the potential exploitation of FRP in civil engineering structures. Many analyses of cylindrical shells are presented in the thesis. These are all focussed on strengthening the shell against different failure modes. Two loading conditions were explored: uniform internal pressure accompanied by axial load near a base boundary, and axial loads with geometric imperfections. For the latter, local imperfections are usually critical, and two categories of imperfection were studied in detail: an inward axisymmetric imperfection and a local dent imperfection. For the first loading condition, which leads to elephant’s foot buckling, an analytical method was used to derive general equations governing the linear elastic behaviour of a cylindrical shell that has been strengthened with FRP subject to internal pressure and axial compression. It was used to identify optimal application of the FRP. All the later studies were conducted using nonlinear finite element analysis (using the ABAQUS program) to obtain extensive predictions of many conditions causing shell buckling and the strengthening effect of well-placed FRP. In all the cases studied in this thesis, it was shown that a small quantity of FRP composite, applied within a small zone, can provide a significant enhancement of the resistance to buckling failure of a thin metal cylinder. These calculations demonstrate that this new technique is of considerable practical value. However, it is clear that not all the relevant questions have been fully answered, so the author poses appropriate questions and makes suggestions for future work.

An extensive amount of research has been reported in previous literature on the behaviour of FRP-confined concrete subjected to concentric axial compression. However, data on the behaviour of high strength concrete confined with various types and configurations of FRP systems is still lacking and no consensus exists on the complete response of FRP-confined concrete. In addition, no appropriate design guidelines are currently available. This thesis reports results from an experimental program involving 112 cylindrical concrete specimens, 88 of which were FRP-wrapped and the remaining 24 were control specimens. All the specimens were 152 mm in diameter and 305 mm in length. Test variables included: amount of FRP materials used, strength and stiffness of FRP materials, concrete strength, and the health of concrete at the time of strengthening. Experimental results indicated that a pre-repair load of up to 77% of the unconfined concrete strength had no appreciable effect on the stress-strain response of FRP-confined concrete. With an increase of the unconfined concrete strength, the strength enhancement, energy absorption capacity, ductility factor and work (energy) index at rupture of FRP jackets all decreased remarkably. A positive correlation was found between confined concrete ductility and FRP rupture strain. In addition, a gradual post-peak failure of the specimens, observed previously from FRP-confined concrete columns tested at the University of Toronto, was also observed in some of the current tests -- owing to the high speed data acquisition system. That ductile failure can be attributed to the gradual unzipping failure of FRP jacket, which in turn is related to specimen size. A new constitutive model was developed based on material properties, force equilibrium and strain compatibility. The size effect was taken into account in the model, which is able to accommodate concrete with a wide range of strength (25 MPa to 110 MPa) confined with various types and configurations FRP systems. Design equations from CSA S806-02 and CSA S6-06 provide reasonable and conservative estimates for the FRP-confined concrete strength. To calculate the peak strain for FRP-confined concrete, an equation based on the work by Berthet et al. (2006) is proposed.

An extensive amount of research has been reported in previous literature on the behaviour of FRP-confined concrete subjected to concentric axial compression. However, data on the behaviour of high strength concrete confined with various types and configurations of FRP systems is still lacking and no consensus exists on the complete response of FRP-confined concrete. In addition, no appropriate design guidelines are currently available. This thesis reports results from an experimental program involving 112 cylindrical concrete specimens, 88 of which were FRP-wrapped and the remaining 24 were control specimens. All the specimens were 152 mm in diameter and 305 mm in length. Test variables included: amount of FRP materials used, strength and stiffness of FRP materials, concrete strength, and the health of concrete at the time of strengthening. Experimental results indicated that a pre-repair load of up to 77% of the unconfined concrete strength had no appreciable effect on the stress-strain response of FRP-confined concrete. With an increase of the unconfined concrete strength, the strength enhancement, energy absorption capacity, ductility factor and work (energy) index at rupture of FRP jackets all decreased remarkably. A positive correlation was found between confined concrete ductility and FRP rupture strain. In addition, a gradual post-peak failure of the specimens, observed previously from FRP-confined concrete columns tested at the University of Toronto, was also observed in some of the current tests -- owing to the high speed data acquisition system. That ductile failure can be attributed to the gradual unzipping failure of FRP jacket, which in turn is related to specimen size. A new constitutive model was developed based on material properties, force equilibrium and strain compatibility. The size effect was taken into account in the model, which is able to accommodate concrete with a wide range of strength (25 MPa to 110 MPa) confined with various types and configurations FRP systems. Design equations from CSA S806-02 and CSA S6-06 provide reasonable and conservative estimates for the FRP-confined concrete strength. To calculate the peak strain for FRP-confined concrete, an equation based on the work by Berthet et al. (2006) is proposed.

This study addresses the flexural performance of sandwich panels composed of a polyurethane foam core and glass fibre-reinforced polymer (GFRP) skins. Panels with and without GFRP ribs connecting the skins have been studied. While the motivation of the study was to develop new insulated cladding panels for buildings, most of the work and findings are also applicable to other potential applications such as flooring, roofing and light-weight decking. The study comprises experimental, numerical, and analytical investigations. The experimental program included three phases. Phase I is a comprehensive material testing program of the polyurethane core and GFRP skins and ribs. In Phase II, six medium size (2500x660x78 mm) panels with different rib configurations were tested in one-way bending. It was shown that flexural strength and stiffness have increased by 50 to 150%, depending on the rib configuration, compared to a panel without ribs. In Phase III, two large-scale (9150x2440x78 mm) panels, representing a cladding system envisioned to be used in the field, were tested under a realistic air pressure and discrete loads, respectively. The deflection under service wind load did not exceed span/360, while the ultimate pressure was about 2.6 times the maximum factored wind pressure in Canada. A numerical study using finite element analysis (FEA) was carried out. The FEA model accounted for the significant material nonlinearities, especially for the polyurethane soft core, and the geometric nonlinearity, which is mainly a reduction in thickness due to core softness. Another independent analytical model was developed based on equilibrium and strain compatibility, accounting for the core excessive shear deformation. The model also captures the localized deformations of the loaded skin, using the principals of beam-on-elastic foundation. Both models were successfully validated using experimental results. Possible failure modes, namely core shear failure, and compression skin crushing or wrinkling were successfully predicted. A parametric study was carried out to explore further the core density, skin thickness, and rib spacing effects. As the core density increased, flexural strength and stiffness increased and shear deformations reduced. Also, increasing skin thickness became more effective as the core density increased. The optimal density was 95-130 kg/m3. Reducing the spacing of ribs enhanced the strength up to a certain level; It then stabilized at a spacing of 2.9 times the panel thickness. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2010-09-21 16:29:00.315

Masonry arch bridges have played a significant role in the road and rail transportation network in the world for centuries. They are exposed to damage due to overloading and deterioration caused by environmental actions. In order to reestablish their performance and to prevent their collapse in various hazardous conditions, many of them require strengthening. Fibre reinforced polymer (FRP) systems are increasingly used for repair and strengthening of structures, with particularly widespread application to concrete structures. However, the application of FRP composites to masonry structures is less well established due to the complexity of masonry caused by the material discontinuity. FRP strengthening masonry arch bridges has been even less studied due to the additional complexity arising from the co-existence of the normal interfacial stress and the shear interfacial stress at the curved FRP-to-masonry bondline. This thesis presents an extensive study investigating the behaviour of FRP strengthened masonry bridges. The study started with a laboratory test of a two span masonry arch bridge with sand backfill. A single ring arch bridge was first tested to near failure, and then repaired by bonding FRP into their intrados and tested to failure. It was found that the FRP strengthening not only improved the loading capacity and stiffness of bridge, but also significantly restrained the opening of cracks in the masonry. Shear and peeling debonding of FRP was observed. There have been two common strategies in finite element (FE) modelling of FRP strengthened structures in meso-scale: direct model and interface model. The former is necessary when investigating the detailed bond behaviour but challenges remain due to the difficulties in concrete modelling. A new concrete damage model based on the plastic degradation theory has been developed in this study to study the bond behaviour of FRP strengthened concrete structure. This robust model can successfully capture this bond behaviour and simulate the entire debonding process. A numerical study of masonry arch bridges including the backfill was conducted to study the behaviour of masonry arch bridge. A total of four modelling strategies were examined and compared. Although they all can successfully predict the behaviour of arch, a detailed solid model newly developed in this study is more suitable for modelling both plain masonry and FRP strengthened structures. Finally, a numerical study of bond behaviour and structural response of FRP strengthened masonry arch structures with sand backfill was conducted. In addition to the masonry and backfill, the mixed mode interfacial behaviour was modelled by the aforementioned interface model strategy and investigated in detail to achieve a deeper understanding of the behaviour of FRP strengthened masonry arch structures. The results are in close agreement with test results, and highlight the influence of the key parameters in the structural response to failure and revealed the mechanisms on how the load is transmitted through this complex multi-component structural system.

Tests results of three flanged and two rectangular cross-section concrete beams reinforced with carbon fibre reinforced polymer (CFRP) bars are reported. In addition, a companion concrete flanged beam reinforced with steel bars is tested for comparison purposes. The amount of CFRP reinforcement used and flange thickness were the main parameters investigated in the test specimens. One CFRP reinforced concrete rectangular beam exhibited concrete crushing failure mode, whereas the other four CFRP reinforced concrete beams failed owing to tensile rupture of CFRP bars. The ACI 440 design guide for FRP reinforced concrete members underestimated the moment capacity of beams failed owing to CFRP tensile rupture and reasonably predicted deflections of the beams tested. A simplified theoretical analysis for estimating the moment capacity of concrete flanged beams reinforced with FRP bars was developed. The experimental moment capacity of the CFRP reinforced concrete beams tested compared favourably with that predicted by the theoretical analysis developed.