Optimal target performance for cost-effective seismic design of bridges

A systematic approach is proposed for evaluating the cost-effectiveness of existing bridge design codes based on expected lifecycle cost. In the life cycle cost formulation, costs of construction, damage cost, road user cost, as well as discount cost over the design life of the bridge are considered. The optimal performance is selected on the basis of minimum life cycle cost. The performance of a typical two-span bridge designed according to a current code provision for different earthquake ground motion levels is predicted and optimal target performance is selected based on life cycle cost with different assumptions of user cost. It is demonstrated that life cycle cost should be considered in the design phase of new or retrofitted structures and the target performance significantly depends on the expected average daily traffic using the road

Seismic assessment of hollow core concrete bridge piers

Hollow core concrete bridge piers are traditionally believed to be vulnerable to seismic action. However, the seismic vulnerability of such piers has not been investigated fully. In this paper, an analytical model to assess seismic vulnerability of hollow core concrete bridge pier is developed. The model is validated with available experimental results. Code recommendations for hollow core bridge piers are evaluated. It is shown that confinement reinforcement requirements in the codes are sometimes highly conservative and sometimes non-conservative. However, the recently developed confinement reinforcement equations for solid bridge piers at Sherbrooke University can be applied for economic and safe design. It is demonstrated that hollow core bridge piers are not as vulnerable as it is traditionally believed. Such piers can attain expected ductility, if designed properly

Behavior of High-Strength Concrete Columns Reinforced with Galvanized Steel Equal-Angle Sections under Different Loading Conditions

Experimental results are presented for a new method of reinforcing concrete columns with galvanized steel equal-angle (GSEA) sections. For the same cross-sectional area, a GSEA section has a higher second moment of area than a conventional steel bar, which leads to a higher bending stiffness of the GSEA reinforced concrete member. In addition, the area of confined concrete is higher in GSEA reinforced concrete members than in steel bar reinforced members, which results in higher strength and ductility. The experimental program involved testing of 20 square, high-strength concrete (HSC) specimens under concentric axial load, eccentric axial load, and four-point loading. The specimens were reinforced longitudinally with either four N12 (12-mm-diameter deformed steel) bars or four GSEA sections and transversely with R10 (10-mm-diameter plain steel) bars. The specimens were 800 mm high with a 210 x 210 mm square cross section. Fifteen specimens were tested under either a concentric or eccentric axial load. The remaining five specimens were tested under four-point loading. Effects of the type of longitudinal reinforcement, spacing of transverse reinforcement, and loading conditions on the behavior of HSC specimens were investigated and discussed. Experimental results showed that, in general, specimens reinforced with GSEA sections had higher load-carrying capacities than the specimens reinforced with steel bars. In addition, the postpeak load-deformation behavior was observed to be more pronounced in specimens reinforced with GSEA sections than in specimens reinforced with steel bars

Flexural design of GFRP bar reinforced concrete beams: An appraisal of code recommendations

In this paper, two design codes for the flexural design of Fibre Reinforced Polymer (FRP) bar reinforced concrete beams have been reviewed and compared with the results of the experimental investigations of eight GFRP (Glass Fibre-Reinforced Polymer) bar reinforced concrete (GFRP-RC) beams. It has been demonstrated that experimentally determined load carrying capacities, maximum deflections and energy absorbing capacities have been over-predicted by the relevant code recommendations for the under-reinforced and balanced GFRP-RC beams while being under-predicted for the over-reinforced GFRP-RC beams. This paper will provide a better understanding on the design methods in the two codes to the designers and rational suggestions for further improvements to the code design recommendations

Axial Load and Bending Moment Behaviour of Square High Strength Concrete (HSC) Columns Reinforced with Steel Equal Angle (SEA) Sections

This paper presents the behaviour of square high-strength concrete (HSC) specimens reinforced longitudinally with steel equal angle (SEA) sections under different loading conditions. For the same cross-sectional area, a SEA section has a higher second moment of area than a steel bar, which results in a greater bending stiffness of the concrete member reinforced with SEA sections. Also, the area of confined concrete is greater in concrete members reinforced with SEA sections compared to members reinforced with steel bars, which results in higher strength and ductility. A total of 8 specimens of 210 mm square cross-section and 800 mm height were constructed and tested. The specimens were divided into two groups with four specimens in each group. Group R-S50 specimens serve as the reference group and were reinforced longitudinally with four N12 (12 mm diameter) deformed steel bars. Group A30-S50 specimens were reinforced longitudinally with four A30 (29.1 mm x 29.1 mm x 2.25 mm) SEA sections. All specimens were reinforced laterally with R10 (10 mm diameter) plain steel bars and spaced at 50 mm centres. The main variables considered in the study included the type of longitudinal reinforcement and the magnitude of load eccentricity. It was obtained from the experimental results that specimens reinforced longitudinally with SEA sections showed greater ductility compared to specimens reinforced longitudinally with steel bars under different loading conditions

Investigation of engineering properties of normal and high strength fly ash based geopolymer and alkali-activated slag concrete compared to ordinary Portland cement concrete

Fly ash-based geopolymer (FAGP) and alkali-activated slag (AAS) concrete are produced by mixing alkaline solutions with aluminosilicate materials. As the FAGP and AAS concrete are free of Portland cement, they have a low carbon footprint and consume low energy during the production process. This paper compares the engineering properties of normal strength and high strength FAGP and AAS concrete with OPC concrete. The engineering properties considered in this study included workability, dry density, ultrasonic pulse velocity (UPV), compressive strength, indirect tensile strength, flexural strength, direct tensile strength, and stress-strain behaviour in compression and direct tension. Microstructural observations using scanning electronic microscopy (SEM) are also presented. It was found that the dry density and UPV of FAGP and AAS concrete were lower than those of OPC concrete of similar compressive strength. The tensile strength of FAGP and AAS concrete was comparable to the tensile strength of OPC concrete when the compressive strength of the concrete was about 35 MPa (normal strength concrete). However, the tensile strength of FAGP and AAS concrete was higher than the tensile strength of OPC concrete when the compressive strength of concrete was about 65 MPa (high strength concrete). The modulus of elasticity of FAGP and AAS concrete in compression and direct tension was lower than the modulus of elasticity of OPC concrete of similar compressive strength. The SEM results indicated that the microstructures of FAGP and AAS concrete were more compact and homogeneous than the microstructures of OPC concrete at 7 days, but less compact and homogeneous than the microstructures of OPC concrete at 28 days for the concrete of similar compressive strength

Axial load-axial deformation behaviour of circular concrete columns reinforced with GFRP bars and helices

Fibre Reinforced Polymer (FRP) bars has attracted a significant amount of research attention in the last three decades to overcome the problems associated with the corrosion of steel reinforcing bars in reinforced concrete members. A limited number of studies, however, have investigated the behaviour of concrete columns reinforced with FRP bars. Also, available design standards either ignore the contribution of or do not recommend the use of GFRP bars in compression members. This study reports the results of experimental investigations of concrete specimens reinforced with GFRP bars and GFRP helices as longitudinal and transverse reinforcement, respectively. A total of five circular concrete columns of 205 mm in diameter and 800 mm in height were cast and tested under axial compression. The experimental results showed that reducing the spacing of the GFRP helices or confining the specimens with CFRP sheet led to improvements in the strength and ductility of the specimens. Also, an analytical model has been developed for the axial load-axial deformation behaviour of the circular concrete columns reinforced with GFRP bars and helices. The model has been validated with the experimental results

Axial compressive behaviour of circular CFFT: Experimental database and design-oriented model

Concrete Filled Fibre Reinforced Polymer Tube (CFFT) for new columns construction has attracted significant research attention in recent years. The CFFT acts as a formwork for new columns and a barrier to corrosion accelerating agents. It significantly increases both the strength capacity (Strength enhancement ratio) and the ductility (Strain enhancement ratio) of reinforced concrete columns. In this study, based on predefined selection criteria, experimental investigation results of 134 circular CFFT columns under axial compression have been compiled and analysed from 599 CFFT specimens available in the literature. It has been observed that actual confinement ratio (expressed as a function of material properties of fibres, diameter of CFFT and compressive strength of concrete) has significant influence on the strength and ductility of circular CFFT columns. Design oriented models have been proposed to compute the strength and strain enhancement ratios of circular CFFT columns. The proposed strength and strain enhancement ratio models have significantly reduced Average Absolute Error (AAE), Mean Square Error (MSE), Relative Standard Error of Estimate (RSEE) and Standard Deviation (SD) as compared to other available strength and strain enhancement ratios of circular CFFT column models. The predictions of the proposed strength and strain enhancement ratio models match well with the experimental strength and strain enhancement ratios investigation results in the compiled database

Experimental Investigation of Circular High-Strength Concrete Columns Reinforced with Glass Fiber-Reinforced Polymer Bars and Helices under Different Loading Conditions

Existing design codes and guidelines do not adequately address the design of concrete columns reinforced with fiber-reinforced polymer (FRP) bars. Accordingly, a number of research studies investigated the behavior of FRP bar-reinforced concrete columns. However, the previous studies were limited to FRP bar-reinforced normal-strength concrete (NSC) columns. In this study, the behavior of glass fiber-reinforced polymer (GFRP) bar-reinforced high-strength concrete (HSC) specimens under different loading conditions was investigated in terms of axial load-carrying capacity, confinement efficiency of the GFRP helices, as well as the ductility and post-peak axial load-axial deformation response. The effects of the key parameters such as the type of the reinforcement (steel and GFRP), the pitch of the transverse helices, and the loading condition (concentric, eccentric, and four-point loading) on the performance of the specimens were investigated. It was observed that the GFRP bar-reinforced HSC specimen sustained similar axial load under concentric axial compression compared to its steel counterpart, but the efficiency of GFRP bar-reinforced HSC specimens in sustaining axial loads decreased with an increase in the axial load eccentricity. Direct replacement of steel reinforcement by the same amount of GFRP reinforcement in HSC specimens resulted in about 30% less ductility under concentric axial load. However, it was found that the ductility and post-peak axial load-axial deformation behavior of the GFRP bar-reinforced HSC specimens can be significantly improved by providing closely spaced helices

Maximum axial load carrying capacity of Fibre Reinforced-Polymer (FRP) bar reinforced concrete columns under axial compression

In this study, a new equation is proposed to compute the maximum axial load carrying capacity of FRP bar reinforced concrete columns under axial compression. The equation proposed in this study was critically compared with the equations proposed in the previous research studies using a wide range of experimental data taken from the available literature. In general, it was found that computing the contribution of the FRP longitudinal bars in concrete columns based on the modulus of elasticity (stiffness) of the FRP bars provides more rational predictions than computing the contribution of the FRP longitudinal bars based on the ultimate tensile strength of the FRP bars. It was also found that using a concrete compressive strength-based empirical equation in estimating the axial strain in the FRP longitudinal bars in concrete columns provides more accurate predictions of the contribution of the longitudinal FRP bars in the axial load sustained by the FRP bar reinforced concrete columns