International Concrete Abstracts Portal

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.

Considerable research has been done to study the fatigue behavior of concrete structures. Plain concrete and reinforced concrete, when subjected to repeated loads, may exhibit excessive cracking and may eventually fail after a certain number of load repetitions. A quantitative analysis of cyclic behavior of reinforced concrete beams is important to understand safety and serviceability problems under repeated shear critical loading conditions. In this study, a quantitative analysis method for the damage process of reinforced concrete beams under repeated shear loading is proposed. It is based on the progressively increasing strain and stiffness reduction. The analysis technique is mainly based on the modified compression field theory and scalar damage concept, which describes the strain and stress configuration in the shear zone by considering the 2-dimensional effect. It expresses the degradation of principal compressive strut by cyclic strain increment, secant modulus decrement, and modifying the parabolic stress strain relationship. The analysis f the response of reinforced concrete beams under repeated shear-flexure loading has been carried out and compared with the experimental results. The present theory may efficiently be used to evaluate the deflection and strain accumulation under repeated loads.

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.