International Concrete Abstracts Portal

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.

This paper presents an analysis of reinforced concrete deep beams tested to failure. A nonlinear strut-tie model approach implemented with an interactive computer graphics program was utilized to evaluate the behavior and strength of the beams. Different types of strut-tie models for the beams were developed based on the compressive principal stress trajectories, actual specimen detailing, and loading and support conditions. It was shown that the proposed nonlinear strut-tie model approach in the present study could provide simple and effective solutions for a large number of analysis situations by describing the essential aspects of structural behavior and predicting the strength of structural concrete. It also allows for the conceptual representation of the complex interactions of concrete and reinforcing steel, and permits the study of localized effects through the nodal zone concept. The framework provided by this nonlinear strut-tie model approach for handling combined actions across the entire range of structural concrete is a strong endorsement for its use with structural concrete deep beams.

shear and When structural concrete members are subjected to a combination of flexure, the behavior under lateral loading becomes complex and difficult to predict, even with sophisticated nonlinear finite element methods of analysis. As a way of resolving the situation, this paper introduces CIST (Cyclic Inelastic Strut-Tie) modeling and demonstrates the implementation of the technique with a general-purpose inelastic computer program. However, the proposed CIST technique requires the proper selection of element models and their dimensioning. For this, a numerical integration scheme is employed. In application of CIST modeling technique to shear-critical concrete members, the post-cracked state is considered. Element models for longitudinal and transverse reinforcing steel and concrete in compression and tension are grouped as per the lateral loading direction to represent the shear and flexural components, connected together through the idealized nodes. The proposed CIST technique was validated against the experimentally observed behavior of shear-critical reinforced concrete members subjected to reversed cyclic lateral loading. It is demonstrated that the CIST modeling technique is able to capture the combined response of shear and flexure quite well.