International Concrete Abstracts Portal

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.

objective of this study is to investigate the seismic performance of repaired structural walls. The structural walls under consideration have specific details that have been widely used in Korea. In this study three isolated large-scale wall specimens were made. After testing, all specimens were repaired. The aspect ratio under consideration is 1 to 3. Because of the space limitation of the laboratory the dimensions of all walls are the same. The aspect ratio was controlled by the combination of axial and lateral forces using the special test setting. The walls were tested using the incremental pseudo static cyclic loads until failure occurs. After that, only the damaged regions are repaired using a concrete with the same properties of the original concrete. The sectional area was unchanged after repairing. The severely yielded reinforcements were replaced by new reinforcement having the same sectional area and properties. Also, epoxy resins were used to fill the cracks in the damaged walls. From this study the capacities of repaired structural walls with specific details after severely damaged is evaluated and compared with those of the corresponding original specimens.

This study proposes a new design formula for the development of positive moment reinforcement in tension. A review of current design code provisions for the end anchorage at simply supported beams shows unsatisfactory requirement for flexural bond strength and that an additional length beyond simple supports is needed. The code provisions neglect a tensile force increase due to shear force and hence, the formulas assume zero tensile force at simple support locations. This paper shows that the treatment for both the flexural bond strength and anchorage requirements is necessary for the safe detailing of reinforcement at beam end regions. Investigation of bond-related failures in these regions shows that it is necessary to differentiate between the anchorage force and flexural bond strength along the bar. Comparison between bond strengths required by current design concept and the proposed formula shows a need for modification of current code provisions for end anchorage.

Production of high performance concrete (HPC) depends on several factors including the use of low water-to-cementitious material ratio, proper dosage of high-range water-reducer (superplasticizer), and a careful selection and dosage of a mineral pozzolanic admixture such as silica fume. Most of the improvement in the strength and durability characteristics of the hardened concrete is attributed to the filler effect and pozzolanic action of the fine size silica fume. Results of tests conducted at the American University of Beirut (AUB) on tension lap splices in full-scale beam specimens and on reinforcing bars anchored in eccentric pullout specimens, indicate that the replacement of part of the cement by an equal weight of silica fume resulted in reduction in bond strength. The reduction was independent of specimen type, bar size, super-plasticizer dosage, and casting position. The mode of failure of the high strength concrete beam specimens was a very brittle bond splitting failure. Tests were conducted to check the effect of transverse reinforcement in the splice region on the bond strength and mode of failure. This paper will provide an overview of the research performed at AUB.