No abstract is provided for this article.
The large number of deteriorating bridges and the goal of sustainable development mean that maintenance actions should not only effectively improve the current condition of bridges but also enhance post-maintenance durability. In this paper, a probabilistic life-cycle optimization method is proposed for the planning of this type of maintenance actions. A physics-based deterioration model is directly employed in the optimization process. The computational efficiency of the proposed method is ensured by efficient sampling algorithms, multi-objective particle swarm optimization, and a bookkeeping technique. The proposed method can provide bridge maintenance schedules that account for two conflicting objectives, i.e. the maximization of life-cycle performance and the minimization of maintenance cost. A deteriorating RC bridge superstructure under chloride-induced corrosion is used to illustrate the proposed method. Point-in-time and cumulative-time failure probabilities are compared as life-cycle performance indicators. As an example of maintenance actions that enhance durability, FRP strengthening implementations for different structural components of the superstructure are scheduled during the service life of the deteriorating superstructure.
No abstract is provided for this article.
An important application of fiber-reinforced polymer (FRP) composites is to provide confinement to reinforced concrete (RC) columns to enhance their load-carrying capacity. However, this application is generally restricted to short columns as existing design guidelines do not contain provisions for the design of FRP jackets for slender columns. This situation has been due to both the scarcity of test data and the lack of rigorous theoretical studies into the behavior of slender FRP-confined RC columns. This paper presents a theoretical model for slender FRP-confined circular RC columns based on the numerical integration method; Lam and Teng’s stress–strain model is employed to describe the behavior of FRP-confined concrete in the column. Predictions from the theoretical column model are compared with existing test results, which demonstrates that the theoretical model is reasonably accurate in reproducing the experimental results of FRP-confined circular RC columns. These comparisons also demonstrate the need to conduct careful tests on large-scale columns to eliminate some uncertainties associated with the existing test data to enable a more conclusive verification of the proposed theoretical column model.
No abstract is provided for this article.
Recent research at the University of Queensland (UQ) has led to the development of a new type of structures called “hybrid fibre reinforced polymer (FRP)-timber (HFT) structures”. In HFT structures, FRP is combined with timber veneers to create high-performance, lightweight, easy-to-construct structural members. These HFT members utilize the orthotropic properties of both timber and FRP in a complementary combination to produce much improved composite properties and to maximise the load-carrying capacity of members for a given amount of material. While preliminary experimental work has demonstrated the potential of HFT sections as high-performance sustainable structural components, much more work is needed to better understand the behaviour of HFT structures. This paper presents the results of an experimental study into the local buckling behaviour of HFT thin-walled Cee section short columns. The experimental programme consisted of fifteen HFT column specimens, including all-timber columns and three different types of HFT columns. The test results are presented and discussed. HFT Cee section short columns carried significantly higher axial loads than the corresponding all-timber columns. The ultimate load-to-weight ratio of the HFT sections is shown to be comparable to or significantly higher than that of cold-formed thin-walled steel Cee sections.
Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) are an attractive form of hybrid compression members incorporating FRP. CFFTs have several advantages over traditional column forms, including their excellent corrosion resistance and ductility. Much research has been conducted on CFFTs over recent years, but no systematic experimental study has been concerned with the cyclic axial compressive behavior of CFFTs with a filament-wound FRP tube; such studies are needed for the development of a cyclic stress-strain model for the concrete in CFFTs. This paper therefore presents an experimental study on the behavior of circular CFFTs under cyclic axial compression. The experimental program included the strength of concrete as a key variable so that it also provides a much needed supplement to the very limited existing research on the cyclic compressive behavior of FRP-confined high-strength concrete (HSC). The test results are compared with a monotonic stress-strain model and a cyclic stress-strain model for FRP-confined concrete, both of which have been based on test databases that are limited to concrete confined with an FRP wrap and include only a small number of tests for HSC. The test results show that the cyclic axial stress-strain behavior of concrete in CFFTs is generally similar to that of concrete confined by an FRP wrap. The test results also show that the monotonic stress-strain model perform reasonably well for HSC in CFFTs, but revisions to the cyclic stress-strain model are needed before it can provide accurate predictions for HSC in cyclically loaded CFFTs.
Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) are an attractive form of hybrid members, in which the FRP tube is typically manufactured by filament-winding with fibers suitably oriented for desired mechanical properties. A significant number of studies have been conducted on the behavior of CFFTs under axial compression, in which the FRP tube is commonly assumed to have linear-elastic behavior, and is often taken to be under a uniaxial stress state (i.e., hoop tension), especially when the fibers are oriented close to the hoop direction. However, in reality, FRP tubes in CFFTs are subjected to biaxial stresses (hoop tension in combination with axial compression) and may exhibit significant nonlinear behavior. This paper presents an improved model for the axial compressive behavior of CFFTs with the nonlinear biaxial behavior of the FRP tube duly taken into account. To verify the proposed model, seven circular CFFTs were tested under axial compression. Ancillary tests on bare FRP tubes were also conducted to determine the material properties of the FRP tubes. Comparison between predictions and test results indicates that the proposed model leads to more accurate predictions of the CFFT behavior than the existing ones in which the biaxial nonlinearity of the FRP tube is ignored.
No abstract is provided for this article.
No abstract is provided for this article.
The compressive behavior of fiber-reinforced polymer (FRP)-confined concrete columns with a noncircular cross section has been investigated through extensive experimental, analytical, and numerical research, but a unified theoretical/numerical approach that can accurately predict both their section-average behavior and local concrete behavior is not yet available. In noncircular columns under axial compression, the concrete is typically under a nonuniform stress state of three-dimensional (3D) compression, with the lateral compressive stresses being the reactive stresses from the confining device (i.e., passive confinement). The authors of the present paper recently developed a plasticity constitutive model for concrete under general 3D compressive stresses, which possesses a potential surface with an evolutionary deviatoric trace that can accurately capture the results of existing compression tests of concrete cubes under nonuniform, passive confinement. This paper explores the application and capability of this evolutionary potential-surface trace (EPT) plasticity constitutive model in finite-element (FE) analysis of FRP-confined square, rectangular, and elliptical plain-concrete columns under concentric compression. The section-average behavior of all the selected noncircular columns predicted by these FE analyses was close to the existing experimental data. The numerical results obtained with the EPT plasticity constitutive model were then examined in detail to achieve an improved understanding of local concrete behavior in FRP-confined noncircular columns.
No abstract is provided for this article.
No abstract is provided for this article.
Fiber-reinforced polymer (FRP) jacketing has become an attractive technique for strengthening/retrofitting reinforced concrete (RC) columns. Extensive research has been conducted on FRP-confined rectangular columns under axial compression, leading to a significant number of stress-strain models for FRP-confined concrete in these columns. However, most of these models have been developed based on test results of small-scale columns, so their applicability to large FRP-confined rectangular RC columns has yet to be properly validated. To this end, the present paper first presents the test results of an experimental study consisting of nine large-scale rectangular RC columns, including eight FRP-confined RC columns and one RC column without FRP jacketing as the control specimen, tested under axial compression. The experimental program examined the sectional corner radius and the FRP jacket thickness as the key test variables. Five representative design-oriented stress-strain models for FRP-confined concrete in rectangular columns, identified from critical reviews of the existing literature, are then assessed using the test results to examine their validity for these large-scale columns.
Over the past decade, fiber-reinforced polymer (FRP) composites have gained wide acceptance as a new generation of structural materials for civil engineering applications due to their unique advantages including their high strength to weight ratio and excellent corrosion resistance. In particular,many possibilities of using FRP in concrete construction have been explored, including the strengthening of existing concrete structures with bonded FRP reinforcement, the use of FRP reinforcing/pre-stressing bars in new concrete structures, and the combination of FRP shapes with concrete to arrive at hybrid FRP-concrete members such as concrete-filled FRP tubular columns. More recently, the use of FRP in steel structures has received much attention. Because both FRP and steel are capable of resisting high tensile stresses, they do not complement each other as well as do FRP and concrete. As a result, the potential for the beneficial use of FRP in steel structures is less than that in concrete structures. This paper first presents a critical discussion of applications where the use of FRP with steel presents significant advantages and then provides a summary of recent research at The Hong Kong Polytechnic University exploring the use of FRP to enhance the performance of steel structures.
A novel method to recycle concrete is to crush demolition concrete into large pieces and then to directly mix the resulting recycled concrete lumps (RCLs) with fresh concrete to produce a new kind of recycled concrete referred to as “compound concrete”. This method avoids the complexity of recycling concrete into aggregates and enables the achievement of a higher recycling ratio and a lower recycling cost. However, due to the large sizes of RCLs and the weak interfaces between fresh concrete and RCLs, compound concrete is much more heterogeneous than normal concrete. A new technique has recently been explored to improve the properties of such compound concrete, in which the compound concrete is provided with a substantial amount of confinement from an external fiber-reinforced polymer (FRP) confining tube. This paper presents the results of an experimental program of axial compression tests on compound concrete-filled FRP tubular columns in which the FRP tubes were prefabricated using the wet lay-up method with fibers only in the hoop direction. The tubes had a negligible axial stiffness, which allows the stress-strain behavior of FRP-confined compound concrete to be clearly revealed. The test results show that, when a significant level of FRP confinement is provided, the behavior of FRP-confined compound concrete is similar to that of FRP-confined normal concrete with a strength equal to that of the fresh concrete. An existing stress-strain model previously developed for FRP-confined normal concrete is evaluated in the paper using the test results of FRP-confined compound concrete.
