Firstly, a plastic-damage constitutive model for concrete complying with the laws of thermodynamics is proposed based on continuum damage mechanics theory. The damage constitutive equations, damage evolution equations and plastic deformation of concrete are derived. Secondly, Fiber damage analysis model(FDAM) for RC beam-column member is established by analyzing section of fiber beam column element, which was developed with VUEL subroutine based on ABAQUS/Explicit platform, with the uniaxial damage constitutive relations of concrete proposed in present paper being used. The member damage index is defined, which can describe the nonlinear damage behavior of RC members under any loadings. Accuracy of the model is identified preliminarily by comparing with the analysis results of solid element. Finally, a numerical analysis model based on finite element program ABAQUS combined with the proposed damage model is built to analyze the seismic damage of a high-rise structure, and the structure analysis results are compared to the data from shaking table test.
Structurally deficient civil engineering infrastructure: Concrete, metallic, masonry and timber structures Fibre-reinforced polymer composites used in rehabilitation Surface preparation of component materials Flexural strengthening of reinforced concrete beams with fibre-reinforced polymer composites Shear strengthening of reinforced concrete beams with fibre-reinforced polymer composites Strengthening of reinforced concrete columns with fibre-reinforced polymer composites Design guidelines for fibre-reinforced polymer strengthened reinforced concrete structures Strengthening of metallic structures with fibre-reinforced polymer composites Strengthening of masonry structures with fibre-reinforced polymer composites Flexural strengthening application of fibre-reinforced polymer plates Durability of externally bonded fibre-reinforced polymer composite systems Quality assurance/quality control, maintenance and repair Case studies.
One important application of fibre reinforced polymer (FRP) composites in the retrofit of reinforced concrete (RC) structures is to provide confinement to columns for enhanced strength and ductility. As a result, many theoretical and experimental studies have been carried out on the compressive behaviour of FRP-confined concrete. This paper provides a critical review of existing studies on this subject, with the emphasis being on the revelation of the fundamental behaviour of FRP-confined concrete and the modelling of this behaviour. Although the paper is explicitly limited to concrete confined with FRP jackets in which the fibres are oriented only or predominantly in the hoop direction, many of the observations made in this paper are also applicable or relevant to concrete confined with FRP jackets with a significant axial stiffness, as found in concrete-filled FRP tubes as new columns.
7th International Conference on FRP Composites in Civil Engineering, CICE 2014, Vancouver, 20-22 August 2014
Extensive research has been conducted on the replacement of steel rebars with fibre-reinforced polymer rebars to eliminate the steel corrosion problem in conventional steel bar–reinforced concrete ...
Ultra-high-performance concrete is typically defined as an advanced cementitious material that has a compressive strength of over 150 MPa and superior durability. This article presents the development of a new type of ultra-high-performance concrete, namely, ultra-high-performance seawater sea-sand concrete. The development of ultra-high-performance seawater sea-sand concrete addresses the challenges associated with the shortage of freshwater, river-sand and coarse aggregate in producing concrete for a marine construction project. When used together with corrosion-resistant fibre-reinforced polymer composites, the durability of the resulting structures (i.e. hybrid fibre-reinforced polymer–ultra-high-performance seawater sea-sand concrete structures) in a harsh environment can be expected to be outstanding. The ultra-high strength of ultra-high-performance seawater sea-sand concrete and the unique characteristics of fibre-reinforced polymer composites also offer tremendous opportunities for optimization towards new forms of high-performance structures. An experimental study is presented in this article to demonstrate the concept and feasibility of ultra-high-performance seawater sea-sand concrete: ultra-high-performance seawater sea-sand concrete samples with a 28-day cube compressive strength of over 180 MPa were successfully produced; the samples were made of seawater and sea-sand, but without steel fibres, and were cured at room temperature. The experimental programme also examined the effects of a number of relevant variables, including the types of sand, mixing water and curing water, among other parameters. The mini-slump spread, compressive strength and stress–strain curve of the specimens were measured to clarify the effects of experimental variables. The test results show that the use of seawater and sea-sand leads to a slight decrease in workability, density and modulus of elasticity; it is also likely to slightly increase the early strength but to slightly decrease the strengths at 7 days and above. Compared with freshwater curing, the seawater curing method results in a slight decrease in elastic modulus and compressive strength.
Circular concrete columns confined with a fiber reinforced polymer (FRP) jacket fail because of the rupture of the FRP jacket due to hoop tension at an average hoop strain considerably lower than the FRP tensile strain at failure obtained from tensile tests of flat coupons. This well-established phenomenon, referred to as premature rupture, is governed by the interaction between a heterogeneous material (i.e., concrete) and a brittle material (i.e., FRP) and has been difficult to explain. The present study adopts a meso-scale model, the so-called Lattice Discrete Particle Model (LDPM), for the simulation of concrete, in conjunction with the Spectral Stiffness Microplane Model (SSMM) for simulating the fracturing behavior of the FRP jacket. The numerical predictions, experimentally validated, demonstrate clearly that due to the heterogeneity of concrete, the circumferential strain is highly non-uniform around the circumference of the column right from the beginning of the loading process rather than uniform as conventionally assumed or expected. This strain non-uniformity is the main reason for the premature rupture of the FRP jacket. In addition, stress concentrations at the finishing end of the FRP jacket are also shown to have a significant effect on the premature rupture of the FRP jacket.
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.
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.
No abstract is provided for this article.
No abstract is provided for this article.
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.
For the passage of utility ducts and/or pipes, openings often need to be created in the web of a reinforced concrete (RC) beam. Such a web opening can lead to a significant decrease in the ultimate load (i.e., strength) of the beam due to the reduced cross-sectional area and/or the severing of some of the existing steel reinforcement (particularly stirrups). In such cases, an externally-bonded fibre-reinforced polymer (FRP) strengthening system may be installed around the web opening to ensure the safety of the weakened beam. While existing experimental and numerical studies have provided useful information on the structural behaviour of RC beams with an FRP-strengthened web opening, this paper presents a theoretical study on the strength of such beams. First, a relatively simple, iterative numerical procedure (referred to as the iterative method) based on the static method of plastic limit analysis for predicting the plastic limit load (i.e., strength) of RC beams with an FRP-strengthened web opening is proposed, and then a closed-form, algebraic strength equation (referred to as the strength model) for such beams is established as a simplified approach of the iterative method. The accuracy of the proposed iterative method and strength model is verified with test results.
Due to their various advantages including excellent corrosion resistance and high strength-to-weight ratios, fibre-reinforced polymer (FRP) composites have been widely used as bonded external reinforcement to enhance the performance of concrete, masonry, metallic and timber structures. In addition, FRP composites have attracted increasing attention for use in the construction of highperformance new structures. In particular, the combined use of FRP composites with one or more traditional materials to create hybrid structural systems is a promising direction for new structures in coastal/marine and other severe environments. This presentation will provide a summary of recent research advances in both areas at The Hong Kong Polytechnic University (PolyU). In the area of strengthening and retrofit of reinforced concrete (RC) structures with externally bonded FRP reinforcement, the following topics will first be covered: (1) suppression of debonding failures; (2) fire resistance and reliability-based design; (3) computational models for FRP-confined concrete and FRP-confined RC columns; (6) Seismic retrofit. Some fundamental issues in the strengthening of steel members with externally-bonded carbon FRP plates/sheets are then discussed. Finally, strengthening of RC beams with near-surface mounted carbon FRP (CFRP) strips, a more recent alternative technique to externally boned FRP reinforcement, is examined. In the area of new construction, this presentation will be focused on structural members based on concrete-filled FRP confining tubes manufactured using the filament winding process. These FRP tubes have fibres oriented close to the hoop direction, so their main functions are to confine the concrete, enhance the shear resonance, protect the column against corrosion, and serve as the stay-inplace formwork. Particular attention will be paid to hybrid FRP-concrete-steel double-skin tubular columns (DSTCs) which consist of a layer of concrete sandwiched between an outer FRP tube and an inner steel tube. The presentation will conclude with an outline of some future opportunities and challenges in the structural use of FRP composites in construction. For example, the use of FRP reinforcement in new structures made of sea-sand seawater concrete should be an interesting area to explore.
No abstract is provided for this article.
Structural members with confined concrete are becoming increasingly popular in civil engineering applications because of their superior strength and ductility. In these structural members, the concrete is subjected to dilation-induced (passive) lateral compressive stresses from the confining device (e.g., a steel tube). Existing research has led to theoretical models that predict closely the stress–strain behavior of concrete under uniform confinement (e.g., concrete in circular steel tubes under concentric axial compression), but theoretical models with a similar capability have not been achieved for the more common situation of concrete under non-uniform confinement (e.g., concrete in rectangular steel tubes). This paper presents a three-dimensional (3D) plasticity constitutive model that is accurate in predicting the stress–strain behavior of concrete in various scenarios of confinement. In the proposed model, a well-established open strength surface with associated open yield surfaces is combined with a hardening/softening rule compatible with both plastic volumetric compaction and dilation. In addition, a novel potential surface with a triangle-like deviatoric trace is proposed and calibrated with available experimental data of non-uniformly confined concrete. The implementation of the constitutive model in finite element analysis with an enhanced stress-return algorithm suitable for the novel potential surface is explained. While the focus of the present work is on monotonic compression-dominated loading, the model can be combined with fracture and damage theories to depict the behavior of concrete under tension-dominated and cyclic loading conditions. The performance of the proposed model is evaluated by comparing its predictions with a wide range of experimental data covering uniform active, uniform passive, and non-uniform passive confinement conditions, which demonstrates the capability and high accuracy of the proposed model.
