Research and Development Needs

nisee


	*National Information Service for Earthquake Engineering* *University of California, Berkeley*


	Research alone is not enough; analytical and experimental studies must be augmented by development work [27]. Specific educational and integrated analytical and experimental research and development needs have been discussed in detail in several publications [12, 13, 28, 29].

RESEARCH CONDUCTED IN THE LAST TWO DECADES


	Despite many unresolved problems in predicting the behavior of buildings and civil engineering structures in general, under the combined effects of normal environments and extreme earthquake ground motions, our understanding has advanced significantly in the last two decades. There is a significant body of knowledge regarding the problems caused by extreme earthquake shaking that has been gained through integrated experimental and analytical research conducted in different research institutions in the world. A few example of the experimental research conducted in the Structural Laboratories of the University of California at Berkeley are illustrated in Slides J109-J113.


	J109. Test set-up for studying the seismic behavior of short column-spandrel deep girder subassemblages.


	A series of integrated analytical and experimental studies has been conducted to investigate the behavior of this type of main assemblage that has been used frequently in buildings located in regions of high seismic risk. Methods to improve the hysteretic behavior of the short columns have been developed. By using the correct amount and detailing of longitudinal and particularly lateral reinforcement it has been possible to attain tough short columns capable of dissipating a significant amount of energy before resistance is lost [30].


	J110. Two-story column-deep girder assemblage after being subjected to severe hysteretic behavior, simulating the expected behavior of this assemblage in tall buildings subjected to severe ground shaking. Note the excellent behavior of the properly confined concrete [30]. The need for improving the behavior of short columns has been emphasized by the numerous failures of this type of column in recent earthquakes.


	J111. Strong column-weak girder assemblage of a ductile moment-resistant reinforced concrete frame. In the experiments conducted on subassemblages of ductile reinforced concrete moment-resistant frames it has been observed that there was significant degradation in stiffness and strength of frames with repeated cycles of deformation reversal. The main sources of this problem have been identified as high shear and/or high bond stress through the joint.


	The design can avoid or minimize this problem by avoiding the formation of the critical regions (plastic hinges) at the faces of the columns. Experiments conducted at Berkeley on subassemblages in which the plastic hinges have been moved away from the columns as illustrated in this slide, and therefore keeping the joint elastic, have shown that it is possible to achieve good stable hysteretic behavior [31, 32]. Note in this slide that all the inelastic deformations occurred in the beams in regions away from the face of the column.


	J112. Weak column-strong girder assemblage of a steel moment-resistant frame. Slide showing the local buckling of a column of the subassemblage that has been subjected to high axial forces and shear reversals simulating the effect of seismic excitations. From this study and similar integrated experimental and analytical research, a series of recommendations has been made regarding the compactness of steel structural shapes as well as the design of beam-column joints in steel moment-resistant frames subject to severe seismic shaking and requiring significant dissipation of energy through inelastic behavior (ductility).




	J113. A 1/5 scale model of the US-Japan 2-story reinforced concrete test structure on the shaking table of the earthquake simulator facility at the University of California, Berkeley. This is the 1/5 scale model of the prototype studied experimentally using a pseudo-dynamic technique at the large testing facility of the BRI at Tsukuka, the Science City of Japan. These studies have been conducted as part of a comprehensive US-Japan Cooperative Research Program, planned to improve the seismic-resistant design and construction of buildings [34].


	The results of the tests conducted have indicated the importance of the three-dimensional interacting behavior of walls and surrounding frames and of the significance of rocking and growth of the wall at the base, and the consequential outriggering action that the surrounding frames will exert on the walls. The results obtained have also indicated the need for considering the contribution of slab reinforcement to the negative moment capacity of the girders cast monolithically with the floor slabs. Important recommendations for improving the states of the practice and of the art in seismic-resistant design and construction of reinforced concrete frame-wall systems have been made, based on the results offered in this cooperative research program.


	The University of California, Berkeley Copyright 1997, The Regents of the University of California. Structural Engineering Slide Library, W. G. Godden, Editor Set J: Earthquake Engineering, V. V. Bertero


	Site Design: Vivian Isaradharm, Oct. 97. Mail to: eerclibrary@berkeley.edu