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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-5 of 15 Abstracts search results
October 1, 1991
The analysis of the response of building structures to dynamic loads is a difficult task, especially if the response is nonlinear, as in the case of concrete buildings subjected to strong seismic ground shaking. This is one of the most difficult tasks facing the structural engineer. The methods available for linear elastic analysis are summarized briefly, together with comments on the development of proper mathematical models for such analysis. A discussion of the main techniques suitable for the inelastic analysis of concrete buildings follows, again accompanied by practical guidelines for mathematical modeling for such analyses. The last section provides a list of several computer programs for engineers contemplating inelastic analyses of concrete buildings.
Deformation capacity of reinforced concrete columns is investigated by examining the available test data. Tests of square columns, conducted under constant axial load and lateral displacement reversals, as well as those conducted under concentric compression, are considered. The test data are evaluated in terms of ductility and drift ratios. The results indicate that high axial compression, and high shear stress reversals, as well as high rates of loading, reduce column deformability. Confinement of core concrete improves column deformability significantly. This is achieved through the use of closely spaced transverse and longitudinal reinforcement, where the longitudinal reinforcement is laterally supported by closed hoops and crossties. The confinement action also improves with the volumetric ratio and yield strength of transverse reinforcement. The ACI 318-89 requirements for the amount of confinement reinforcement appear to be adequate for the columns evaluated in this paper.
Characteristic features of reinforced concrete response relevant to hysteretic modeling are discussed. The relationships between hysteretic features, and design and detailing parameters are illustrated. Experimentally obtained hysteretic force-deformation relationships are used to demonstrate the significance of each hysteretic feature on modeling. A brief review of selected hysteretic models is presented, Strength, as defined by primary curve, stiffness degradation, strength decay, and pinching of hysteresis loops are discussed as basic features of hysteretic response. The mechanisms behind these features and related design and detailing parameters are presented. The significance of each of these parameters in terms of deformation components resulting from flexure, shear, and reinforcement extension/slip is discussed. The dominant response shows stable hysteretic loops with little or no strength decay within the realistic range of deformations. Therefore, a simple hysteretic model may be appropriate for modeling flexural response. Shear response as well as hysteresis loops resulting from reinforcement slippage show pinching action, and hence should be modeled accordingly. Axial compression, lack of shear/confinement reinforcement, and poor anchorage of members may lead to early and rapid strength decay. Strength decay may have to be considered in such members. Stiffness degradation during unloading and reloading is a characteristic feature of reinforced concrete response, and should be considered in modeling all deformation components.
James Robert Harris and Gene R. Stevens
Current building standards contain complex sets of rules for detailing reinforced concrete structures to resist earthquakes. The rules are intended to deliver reliable post-elastic energy dissipation. This is necessary because structures are designed to yield at levels of motion that are only a fraction of the real motions in a strong earthquake. The detailing rules are intended to prevent brittle modes of failure, such as shear and unconfined compression of concrete, while encouraging widespread flexural yielding. The rules also take into account two other distinctive characteristics of earthquake loading reversal of direction and repetitive cycles. This paper attempts to set forth the rationale for these detailing rules that will allow the designer to see the overall design philosophy and to relate a particular design to the intended performance.
Catherine Wolfgram French and Arturo E/ Schultz
In an effort to provide the structural design profession with an indication of the deformation capacity of reinforced concrete beams subjected to cyclic loading, results of 69 isolated reinforced concrete beam tests were assembled and interpreted. The influence of several parameters, including longitudinal reinforcement ratio, web reinforcement ratio, shear stress, shear span-to-depth ratio, axial load, floor slabs, loading rate, and loading history on deformation capacity were investigated. It was found that ductility factors in the range of two to nine reasonably may be expected from reinforced concrete beams. Of the parameters investigated, shear was identified as the single most important factor affecting deformation capacity. It was further determined that the effects of shear can be controlled most directly by limiting the demand placed on web reinforcement. To insure that beams exhibit ductility factors of at least five, it is recommended that the maximum shear force demand on web reinforcement be limited to 60 percent of its nominal capacity.
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