International Concrete Abstracts Portal

The objective of the paper is to evaluate the dynamic prop-erties of model materials. Dynamic tests were conducted on micro-concrete with no. 4 maximum aggregate size, and gypsum concrete with no. 4 maximum aggregate size. The effects of strain rate (up to 2.5 in. /in. /sec) on ultimate compressive strength were obtained. The results are compared with results of dynamic tests conducted on proto-type concrete by others. Microconcrete with a no. 4 maximum aggre-gate gives good correlation with prototype values of dynamic strength increase. The ratio of dynamic to static modulus of elasticity with increasing strain rate and dynamic strength increase factor also gives good correlation. Microconcrete experiences higher strains at ultimate load than the prototype. Gypsum concrete experiences dynamic strength increase factors of approximately half those of the prototype. It may be significant that the increase in modulus of elasticity with increasing strain rate for gypsum concrete is not similar to that of prototype concrete. Strains in gypsum concrete at ultimate load are slightly higher than those for prototype concrete.

Two identical small scale six storey three dimensional reinforced concrete framed structures were constructed consisting of columns, beams and floor slabs. Each structure had a single bay in each direction and was approximately one fifth of full size. All members were designed for ductility according to the seismic design requirements of ACI 318-71, One structure was subjected primarily to static lateral loading and the other structure was subjected primarily to dynamic loading on a shaking table. The lateral load strength of the statically loaded structure was accurately predicted when the actual properties of the structure were taken into account. Severe stiffness degradation occurred during cyclic loading in the inelastic range. The displacement response of the dynamically loaded structure was compared with the displacement response predicted by a dynamic frame analysis computer program and the accuracy of the predicted response was found to be extraordinarily dependent on the stiffness and-damping. The tests revealed that under lateral loading significant torsion is induced into the beams at right angles to the direction of loading and this may lead to severe torsional cracking of those beams and a consequent decrease in stiffness and strength of the framed structure.

Modeling techniques used in an experimental study of frame-wall interaction in multistory buildings subjected to strong earthquake motions are described. Considerations involved with the selection of materials, structural configuration, amounts of mass, and frequency contents and intensities of base motions are discussed with respect to limitations of small-scale modeling of reinforced concrete structures behaving in the nonlinear range of response. Samples of response observations are presented to demonstrate the applicability of using small-scale models for earthquake-engineering research.

The basic purpose of this research was to investigate the feasibility of studying the nonlinear earthquake response behavior of concrete arch dams on a 20 ft. square shaking table. Assuming a length scale of l/150, the essential similitude requirements for the model material are derived. The development of suitable plaster, celite, sand and lead powder mixtures is described, and the proportions and properties of adopted materials are listed. Shaking table tests are described of a segmented arch rib model designed of this material to simulate the monolith joint opening behavior of an arch dam, and preliminary results are presented. Also, the test of a model of Koyna Dam is mentioned, where the model behavior simulated the observed cracking of the prototype. The principal conclusion of the investigation is that shaking table research is a practical means of studying the nonlinear earthquake response of concrete arch dams, including their actual failure mechanisms.

This paper discusses shaking table tests conducted on models of two long-span curved highway bridges to study seismic response. The first is a microconcrete model study of a multi-span highway overcrossing of the type that failed in the 1971 San Fernando earthquake. This shows the predominant influence of the expansion joints in the system on gross dynamic behavior and on the failure load. The second is an elastic model study of a proposed single-span cable-stayed curved box girder bridge designed without expansion joints and cast integrally with the abutments. This shows the small damping in such a system, the influence of cable vibrations on the overall dynamic behavior, the degree to which linear dynamic analysis is applicable in determining seismic response and the efficiency of such a design in resistin horizontal ground motions.