International Concrete Abstracts Portal

Results of an experimental investigation to determine inelastic load-deformation character istics of reinforced concrete structural walls are reported. Sixteen large structural walls have been tested. These tests show that structural walls possess signif icant rotational ductility when subjected to reversing loads. In addition, it was found that shear distortions within the hinging region of a wall are coupled to flexural rotations. Therefore, inelastic shear distortions should be considered in structures designed to utilize the inelastic capacity of struc-tural walls for earthquake resistant construction.

Two three-story, two-bay l/10 scale reinforced concrete model frame structures were subjected to combined gravity and lateral loads. One frame was subjected to unidirectional lateral loading, and the second was loaded with gradually increasing reversing lateral loads; loads were increased to failure in both cases. Distribution of lateral loads was in accordance with the SEAOC requirements for seismic design; steel reinforcement was also designed to conform to these requirements. A nonlinear, incremental stiffness analysis approach was developed for uni-directional loading and was applied to the experimental frame and to a single bay portal frame reported in the literature. Stiffness reduction of the frame subjected to reversing lateral loads was not more severe than that for the unidirectionally loaded frame at loads less than about 80% of the ultimate lateral load capacity of the frame. There was minor reduction in strength and stiffness caused by cycling at higher load levels. Ductility requirements were met by the frames, and no adverse shear-induced effects were observed in the joint regions of the frames. The analytical method gave excellent predictions of frame deformations.

This paper presents the results of tests on three four-storey coupled shear wall specimens tested under an equivalent of monotonically increasing static upper triangular loading. Specimens No. 1 and No. 2 failed due to rupture of reinforcing steel in both walls after hinges had been formed at both ends of all coupling beams. An overall ductility factor of 14.2 was attained for both specimens while the ductility factors for rotation in the coupling beams and the shear walls were considerably higher. Specimen No. 3 also failed due to rupture of tension steel in the shear walls, however no hinges were formed in the coupling beams and the overall ductility ratio was only 5.7. Experimental results for Specimens No. 1 and No.2 were analysed using Paulay's elastoplastic analysis. The calculated ultimate strengths showed good agreement, however the calculated deflections were smaller than the experimental values. More research is needed in this area. The results of this investigation show that small-scale models can be used effectively in behavior studies of structural subsystems such as coupled shear walls, shear wall-frame structures, etc.

In developing a design procedure for earthquake-resistant structures, information on demand as well as capacity has to be obtained. Data on demand are most conveniently obtained through dynamic inelastic analysis. Capacity values are generally deter-mined by tests of large-size specimens subjected to slowly reversed loads. In correlating demand with capacity, an important consideration is the degree to which the laboratory loading represents earthquake response conditions. A valid correlation is possible only if it can be shown, among other considerations, that the loading program used in tests is comparable to, or more severe than, conditions that can be expected under earthquake excitation. This paper presents the results of an investigation to determine appropriate loading programs for use in quasi-static tests to simulate response to earthquakes. The study is part of a combined analytical and experimental project to develop design procedures for earthquake-resistant structural walls and wall systems. In the first phase of the project, the structure considered is an isolated wall. Frame-wall systems are considered in later phases of the project.

The concepts of capacity design philosophy, which aims to ensure a desirable sequence in the plastification of ductile frames during severe seismic excitation, are introduced, In the establishment of desirable strength hierarchies the relationship between beam load inputs and ideal column strengths are examined in detail. Simple procedures, that recognise relative strength values and general characteristics of dynamic behavior, are proposed for the evaluation of moments, axial and shear forces for columns of frames. The proposals intend to ensure a high degree of protection against premature damage to columns, and to eliminate the possibility of concentrated energy dissipation in storey mechanisms in frarnes that may be subjected to unidirectional earthquake attack or to concurrent orthogonal seismic excitations. Because hinging is not expected in upper storey columns, the re-quirements for confining reinforcement in the end regions of these columns can be greatly relaxed.