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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.

The New Zealand Standard for design loadings for buildings (NZS4203) was revised in 1992 superseding the earlier standard NZS4203 (1984). Some of the most significant changes in the new code are a considerable increase in the allowable interstory drifts and a marked reduction in the seismic lateral forces for structures with longer natural periods. Designers may now be encouraged to design buildings to the maximum allowable drifts as the resulting buildings will attract smaller lateral loads. Reinforced concrete buildings designed with the new loadings code may be constrained by the minimum reinforcement requirements rather than strength requirement of the loadings code; as a result, they may have a different distribution of strength capacity from that assumed in the code design. Because of this, buildings designed using the capacity design principles may not have the strength distribution that the designer intended. The reasons for this problem are discussed in this paper and the effects of the irregular distribution of strength capacity are investigated using inelastic response analysis. It was found that the large reduction of the design lateral forces resulting from the large allowable interstory drifts may lead to the problem. The design lateral forces or the deflection limits defined in the new code, NZS4203 (1992), may need to be reconsidered.

Reviews the aspects considered to be major limitations, from a conceptual point of view if not always from a practical one, in the view of a codified approach to design and, more generally, in the ability to describe seismic response of structures. The state of progress and current research efforts on three interrelated subjects are first discussed, including capacity design criteria and procedures, definition of the state of collapse and damage of a structure, and viable techniques for a probabilistic calibration of safety factors. It should be noted that a fuller rationalization of these aspects is more acutely needed in Europe due to the larger variety of structural typologies, which calls for more refined differentiations and, in turn, for more rational and visible justifications In the second part of the paper, the specific problem of shear-bending interaction is considered; this behavior is qualitatively known, but is neither quantitatively well defined nor commonly implemented in computer programs. A simple proposal for an analytical model is presented and discussed. The results of some preliminary numerical simulations show interesting results, their main merit consisting in an indication of the relevance of the problems. Similar elements could be easily integrated into nonlinear dynamic programs and used for probabilistic calibrations. The paper is concluded by a brief presentation of a broad experimental and analytical research program just started in Europe to support the final preparation of a unified seismic code.

A new conceptual code format has been developed for earthquake- resistant design (EQ-RD) of buildings. It consists of guidelines for conceptual overall design of entire building systems and a conceptual methodology for numerical EQ-RD of building systems in compliance with the worldwide accepted EQ-RD philosophy and based on energy concepts, fundamental principles of structural dynamics, mechanical behavior of entire building facilities, and comprehensive design. The numerical EQ-RD methodology considers the desired seismic performance of the entire building system explicitly from the beginning of the EQ-RD process and concludes by evaluating whether such performance would be achieved. A discussion of the main aspects and problems involved in the preliminary numerical EQ-RD procedure is presented in this paper. Main results from its application to at 30-story reinforced concrete space-frame building are discussed and compared to results from analysis of the performance of the same building designed according to 1991 UBC, showing the weakness of present UBC seismic regulations when applied to tall buildings, particularly regarding performance under service level EQ ground motions. The main advantage of the proposed conceptual methodology is that uncertain quantifications of its concepts can evolve without changing the format of the codified methodology as new and more reliable data are acquired.