International Concrete Abstracts Portal

Expansion joints in bridge slabs are designed to absorb horizontal displacement due to the temperature fluctuation and moving vehicular load. The expansion joints, however, are very often damaged due to a repeated loading of the moving vehicles. The joints in the existing simple span structures can be eliminated by converting the structural types into continuous spans. When existing simple span bridges are converted into continuous spans, rigid (pin and roller) support conditions have to be changed to elastic supports in order to absorb and distribute the energy of horizontal motion due to an earthquake loading. However, development of additional reaction forces and stresses on the concrete slab due to the unequal displacement of the elastic supports have been overlooked. In this study, two-span continuous specimen, which is converted from two simple span structures is tested and analyzed to investigate the stress distributions of the concrete slab. Durability of the concrete slab under the service load is also discussed. The results of this study show that the change of strain in the longitudinal direction can be reduced by using the elastic supports and the vertical shear stress increases, directly affecting the fatigue life of the concrete slab.

The purpose of this study is to determine the characteristics of the mechanical anchorage of reinforcing bars with screw-type coupler and perforated plate, so called MAB-COP (Mechanical Anchorage of Bars with screw-type Coupler and Perforated plate) in precast concrete beam-column joint. The newly proposed mechanical anchorage; MAB-COP is a kind of headed reinforcement, but not screw-threaded on the reinforcement. The bottom bars of the precast beam are anchored by MAB-COP in beam-column joint. A series of test specimens was prepared to consider the effects of the variables, such as the anchorage length of the reinforcing bar (14db, 12db, 9db), and anchoring method. Pullout tests conforming to the ASTM were carried out to assess the effects of several variables on anchoring strength of bars. Based on the test results, it is concluded that the behavior of the specimen anchored by MAB-COP with the anchorage length of 12db, was as good as, or better than that of the specimen anchored with 90-degree standard hook.

The losses in the structural performance of reinforced concrete members with corroded rebars are caused by the loss in the effective cross-sectional area of concrete due to cracking in the cover concrete, loss in the mechanical performance of rebars due to the loss in their cross-sectional area, and loss in the bond performance of concrete with rebars. Accordingly, the mechanism of the reduction in the performance of concrete structural members with corroded rebars may be elucidated using the finite element method (FEM), if the constitutive law for each material factor can be derived using the degree of rebar corrosion as a parameter. The purpose of this study is to investigate the relationship between the degree of rebar corrosion and the structural performance of RC beams damaged by rebar corrosion with the FEM. As a result, the structural performance of RC beams damaged by rebar corrosion can be analyzed with the FEM using experimentally determined material models representing the bond properties between concrete and the corroded rebars and the mechanical properties of corroded rebars. So, it is needed to investigate the bond properties and the mechanical properties of the corroded rebar considering degree of rebar corrosion to evaluate the strength of RC beams damaged by rebar corrosion with cross section analysis method which has been used conventionally.

Current codes of reinforced concrete design, mainly concerned with ductile steel reinforcements, do not yet address the use of brittle FRP (Fiber Reinforced Plastic) tendons. In order to use them more frequently in structural applications in industry, reliable design methods and code coefficients should be established, taking into account the material properties. This paper discusses the flexural design of concrete beams prestressed with FRP tendons with emphasis on the strength reduction factors in the USD (Ultimate Strength Design Method). According to the code requirements, the reduction factor should consider the degree of ductility. New reduction factors for the flexural design are recommended based on a reliability analysis, in which the target reliability indices have been set in due consideration of the ductility. The recommended factors range from 0.7 to 0.9 depending upon the degree of ductility. The factors are lower than that (=0.9) of beams with steel reinforcements, allowing for the possible lack of ductility in beams with FRP tendons.

To deepen the understanding of shear behaviour in beams without transverse reinforcement, the relative importance of two major contributing elements to concrete shear resistance(V), such as the friction at crack faces and the residual tensile stresses between cracks, was explained by comparing two analytical methods based on the truss model concept. One is called the Modified Compression Field Theory(MCFT) " considering the two elements explicitly, and the other the Crack Friction Truss Model(CFTM) more dominantly the former element in determining the concrete shear resistance. To evaluate their validity in considering such complex behaviour, the predictions were also made for twenty KAIST beam tests, designed more likely to the development of the size effect law based on the fracture mechanics concept. Experimental findings with varying of shear span-to-depth and longitudinal reinforcement (pt) ratios, and beam depths were well captured by the two methods, and the complete analysis results obtained from the MCFT enabled additional explanations that were difficult to measure in tests. In addition, the simplified Vc+ Vs approach, but including the empirical factor to reflect the size effect, predicted test results with reasonable accuracy.