International Concrete Abstracts Portal

Summarized in this paper are the background state of the art in reinforced concrete beam-column joint design leading to the U. S.-N. Z.-Japan trilateral cooperative research, outline of the trilateral research, and its conclusions affecting the design practice in each country. Particular emphasis is placed on the transition of structural engineering research from empirical approach to rational approach which became apparent in the course of trilateral research and discussion.

Problems associated with design of beam-column joints for shear have been studied extensively in many countries. Work in New Zealand on the performance of joints in reinforced concrete moment resisting frames in seismic zones served to alert designers all over the world to consider these problems. Fundamental studies conducted by Paulay and his colleagues and students contributed immeasurably to our understanding of the behavior of joints. However, the approaches used in design codes have not always been the same as those used in New Zealand. The reasons for these differences have much to do with design philosophies, research objectives, and code development procedures. Shear problems at locations other than joints and in elements where rehabilitation (repair and strengthening) is needed to improve performance of structures under earthquake generated deformations still lack definition sufficient for developing code provisions.

Presents the findings of an experimental study to evaluate a method of retrofit which addresses a particular weakness that is often found in reinforced concrete structures, especially older structures, namely the lack of sufficient reinforcement in and around beam-to-column joints. Many of these structures lack the required confining reinforcement within the joints and in adjoining beams and columns. The result is a reinforced concrete frame that is weak in the joint areas and lacks sufficient ductility during a seismic event. The proposed retrofit method consists of encasing the reinforced concrete joint with a grouted steel jacket that provides confinement to the joint area and imparts ductility to the frame. In this study, two styles of retrofit jacket were tested: a circular steel tube and a rectangular casing. The circular steel jacket provided direct confinement as well as a ductile force transfer mechanism through the jacket itself, but it was more difficult and expensive to fabricate than the rectangular casing. Although the rectangular jacket did not provide the same amount of concrete core confinement, it seemed to be sufficient to prevent damage in the joint area. The load transfer mechanism of the rectangular jacket was found to be adequate in withstanding the loads and deflections typical for seismic events. In the paper, the two jacket styles are evaluated for strength, stiffness, and ductility and their relative merits are discussed.

Waffle-flat plate buildings are very popular in different countries. Their seismic performance has been very poor. Several research projects on the seismic response of these buildings have been performed at the Instituto de Ingenieria, UNAM; their results and findings are summarized in this paper. First, the main features of the structural system and of its resistance to lateral loads are presented. The most common mechanisms of collapse are described and the observed performance during the 1985 Mexico earthquake is discussed. A case study of building performance during the earthquake is briefly presented. Results of an experimental research on a two-story model of a waffle-slab building are described. The specimen was first tested in a haking table and later subjected to cycles of static lateral loads. The specimen showed a rather poor behavior with very small lateral stiffness and limited energy dissipation capacity. The failure mechanism was mainly governed by the shear and flexural strengths of the columns and by flexural cracking in waffle slabs. Recommendations for the proper use of the system are given, emphasizing the need to combine it with structural walls, bracings, or stiff frames to achieve the necessary lateral stiffness and strength in a building.

The difficulties in assessing the probable deformation and force states of structural wall buildings under lateral earthquake forces were evaluated by means of laboratory test results from a five-story full-scale reinforced masonry structural wall research building tested to failure at the University of California, San Diego, under simulated seismic loads. The individual structural components and actions which contribute predominantly to the seismic response characteristics of a structural wall building, such as axial loads on walls, coupling between structural walls, lintel beam force, and deformation capacities, as well as floor and wall-flange participation were evaluated based on individual component tests, the full-scale prototype test, and parallel diagnostic analyses. The importance of a realistic assessment of these parameters in a capacity design approach for structural wall buildings was evaluated. The outline for rational design models which allow a prediction of the complex behavior characteristics of structural wall buildings for all design limit states is presented in this paper.