International Concrete Abstracts Portal

The paper investigates the shear strength and the failure modes of high strength concrete beams with and without steel fibers ( fC = 110 MPa). Sixteen reinforced high strength concrete beams (3600x350~200 mm) were tested under different combinations of shear force and bending moment. The beams were singly reinforced and without shear (web) reinforcement. The test results indicated that the addition of steel fibers to high strength concrete increases the ultimate shear strength, improves the brittle characteristic and transforms the failure mode into a more ductile one. The average gain of the ultimate shear strength due to the addition of steel fibers varied from about 14% to 14 1% depending on the shear span to depth ratio and the longitudinal steel ratio. Four modes of failure of reinforced high strength concrete are clearly distinguished as; diagonal tension, shear compression, shear flexure, and flexural failure. In general, cracks in fiber reinforced concrete beams are closer, narrower, and more than those in beams without fibers. This reflects the effect of steel fibers in redistributing the stresses beyond cracking.

In the aftermath of the Great Hanshin-Awaji Earthquake of 1995, the seismic retrofitting of existing structures has been implemented on a nation-wide basis throughout Japan, and it is in this context that new methods for seismic retrofitting utilizing aramid fiber reinforced plastic rod have been developed. Aramid fiber rod is not only lightweight and flexible, but has superior strength and corrosion resistance characteristics, which make it an ideal material for use in the seismic retrofitting of reinforced concrete structures. AWS method involves the use of aramid fiber rods to introduce prestress into wall-type piers, again improving the ductility and shear strength of the existing wall. Testing of scale models gave results showing this method to provide sufficient strength. The guidelines available for retrofitting of highway bridge piers in Japan are presented. The design equations for ultimate shear strength and ductility of retrofitted RC structures are introduced. AWS method is now used in the seismic retrofitting wall-type piers of highway bridges.

This paper describes a nondestructive method to evaluate two-dimensional size and depth of interfacial flaws between concrete members and the enclosing steel plate by the infrared thermographic technique. In this procedure, in order to investigate the influence of a defect in a thermography, liquid nitrogen was used to cool the surface of the steel plate. Its thermal distribution was measured. From these measurements, it was possible to estimate the diameter of circular defects from the calculated inflection points in the thermal distribution curve. The process to evaluate the depth of the flaws by using the relation betweenthe volume tof the flaws and proposed thermal parameters is also presented.

Gypsum is widely used for the manufacture of various building materials because of its advantages such as rapid setting, good thermal insulating property and fire resistance, but their use is limited to interior finishings because of its poor water resistance. This paper deals with an improvement in the water resistance of gypsum composite by the polymer modification and partial replacement of sum with ground granulated blast-furnace slag (Blaine fineness=1 0,000 cm /g , silica fume and ordinary portland cement. Polymer-modified gypsum-based composites are prepared with various polymer-binder (a mixture of gypsum and mineral admixtures) ratios, and tested for water absorption, flexural and compressive strengths before and after water immersion. The water resistance of the gypsum composite is markedly improved by the polymer modification and partial replacement of gypsum with ground granulated blast-furnace slag, silica fume and ordinary portland cement. In addition, the effects of curing conditions on the strength properties of the polymer-modified gypsum-based composites are investigated. As a result, an SBK-modified gypsum-based composite with an optimum mix proportion is proposed from the viewpoints of water resistance, strength development and hair crack disappearance.

This study evaluates the nonlinear response characteristics of precast concrete frame buildings where plastic hinging occurs in the connection between the precast elements. Buildings of 5, 10, and 15 stories were designed for moderate seismic risk regions of the U.S. Analysis were carried out using DRAIN-2DX (1992) and following the nonlinear static analysis procedure of ATC 19 (1997). The main variables of the analysis were the strength and stiffness of the connection. The tri-linear response model, developed by Shan Shi and D. Foutch (1997) was used for the analysis. It was shown that the strengths of the buildings, as well as their displacement capacities, decrease with as either the strength or stiffness in the connection decreases. This requires for reduction in the response modification factors for such buildings. However, if plastic hinging occurs in a connection of the precast concrete frame, that exhibit a more ductile behavior than the monolithic concrete frame, then no reduction in the response modification factor would be necessary. The rotational ductility required of the connection to achieve that condition can be determined from a nonlinear static analysis.