International Concrete Abstracts Portal

Following the strong earthquake in Chile on March 3, 1985, an intensive study was conducted to ascertain why the large inventory of moderate rise buildings in the coastal city of Vina del Mar performed so well during the earthquake. The major findings were that the vast majority of the buildings in this coastal city had a high wall area to total floor area ratio and that the reinforcement detailing in the boundaries of these walls were considerably less than required by U. S. codes. Analytical studies indicated that the high percentage of walls led to significantly lower drifts under severe seismic shaking, thus lowering the ductility demands on the walls. At lower levels of ductility demand, experimental results have demonstrated that wall boundaries did not need special detailing of transverse reinforcement. The findings from the series of research studies following the Chilean earthquake have led to modified U. S. design procedures that relate the need for special detailing in wall boundary elements to expected strain levels along the compression edge of the wall. The expected strain levels are determined based on the aspect ratio of the wall and the percentage of wall area to floor area used in the building.

Presents a conceptual model for the behavior of structural walls subjected to lateral load reversals. The primary feature of the model is a reduction in shear strength with increasing levels of deformation. Measured and calculated data from structural walls are evaluated to determine conditions for which the strength and deformation capacity of a wall may be limited by the residual shear strength.

An evaluation of the implications of the structural system selected for reinforced concrete buildings with three different plan layouts and four different heights (5, 10, 15, and 20 stories) was performed as part of the calibration of the update of the Colombian Seismic Code (10). The buildings had varying amounts of structural walls. In total, 72 buildings were studied. Expected performance of the buildings under the code design earthquake was evaluated using elastic and inelastic procedures. Using the amount of concrete and reinforcing steel for all the buildings and prevalent material and labor prices, a cost of the structure per unit area was determined. Conclusions with respect to behavior and cost implications were obtained for the parameters studied for the different buildings.

In the earthquake-resistant design of reinforced concrete (RC) buildings, it is necessary to evaluate inelastic behavior and damage of structures both by maximum displacement and by total energy dissipation. In this study, damage assessment of RC structures is carried out based on energy response. Damaging potential of earthquakes to structures is estimated by total input energy; damage of structures is estimated by the damage index taking account of both maximum response and cumulative damage. From the results of parametric inelastic response analyses using simulated earthquakes, it is considered that total input energy depends primarily on earthquake property. The damage parameter proposed by Fajfar, which relates ductility factor to dissipated hysteretic, seems to be relatively stable in many cases. The damage parameter is found useful to represent earthquake response pattern of structures. Using the damage parameter and the damage index, a procedure is presented to find yield force and corresponding ductility factor for given value of damage index. This study shows a possibility of a design concept of RC buildings considering displacement and energy limits.

Describes a research program to investigate the behavior of ductile connections between precast beam-column elements. Eight beam-column connections were tested to characterize the overall behavior of the connection details. Each connection specimen was designed to incorporate one of three behavioral concepts in the connection elements: tension/compression yielding, substantial energy dissipation, or nonlinear-elastic response. Based on the behavioral information collected during connection tests, analytical models were developed to investigate the behavior of complete precast frame systems. Results of the experimental study and preliminary results of the analytical work are presented. The objective of the program is to provide rational design recommendations for engineers to detail precast frame connections for use in regions of seismic risk.

An experimental program is summarized which is aimed at enhancing the knowledge base regarding seismic behavior, analysis, and design of precast concrete shearwalls. The "emulation design" and "jointed construction" philosophies are described and an idealization of the behavior of precast shearwalls presented. A compendium of connection details for precast concrete shearwalls, seven for vertical joints and four for horizontal joints, is selected for further study; the selection process is described. The connection details are proportioned for a prototype shearwall that is designed as part of a six-story precast concrete office building. A description of all connection details and test procedure is given. Highlights from the cyclic load tests of the vertical joint specimens are documented, including connection resistance, displacement response, initial stiffness, and energy dissipation capacity.

The development of concrete offshore structures is illustrated by briefly describing the background for their functions, the development of structural design, brief examples of concrete research and research results, industry research projects, and international standardization. Figures and main specifications of typical structures are shown.

The design of deepwater bottom-founded towers (300 to 1000 m) requires a good understanding of the nature of the design environment, the structural response, design force levels, and practical member sizing. The novel design tools described in this paper included the "Designer Wave" and the "Quickwave" methods. The "Designer Wave" is a practical short portion of random wave simulation that captures enough of the structural response (and shear and moment envelopes) for design purposes. The "Quickwave" method achieves reasonably accurate design forces and member sizes without using time consuming random wave runs and full 3-D structural models. The Designer Wave is essential for the occasional calibration of the Quickwave results. Many design iterations are relatively easy with the Quickwave, so much so that it was extensively used to derive a new deepwater compliant tower concept. The new tower configuration resulted in breakthrough savings in weight and costs relative to existing solutions.

Research on rehabilitation of nonductile reinforced concrete structures located in zones of high seismic risk has been underway at the University of Texas at Austin since 1981. A sampling of details and results from selected experimental programs investigating repair and strengthening of reinforced concrete nonductile frame buildings is presented. Researchers at the University of Texas have integrated knowledge about the behavior of nonductile elements and systems, retrofitted members, subassemblages, and superassemblages into nonlinear time-history analysis models. These models have been used to investigate the response of buildings, retrofitted with techniques studied in the laboratory, to a variety of strong-motion earthquake records. An overview of some of the analytical modeling is presented; results from two studies investigating the use of different concentric bracing schemes or infill wall systems to retrofit a three-story nonductile frame building are discussed.

The objective of this paper is to present models for the design of confined masonry structures based on the available experimental data. In particular, this study deals with in-plane response of masonry walls subjected to lateral forces, with emphasis on aspects of initial stiffness, strength, and deformation capacity. The experimental information used in this work comprises tests performed at the Structures Laboratory of the Catholic University of Peru. Results indicate that stiffness can be calculated considering a wall cross section inertia using the transformed cross section concept with the appropriate moduli of elasticity for concrete and masonry. Bending strength can be estimated reasonably well, assuming for the cross section (1) a rectangular compressive stress distribution, (2) zero strength under tension, and (3) a linear strain distribution. Unit shear strength could be safely calculated as 0.5 f'm, where f'm is the characteristic compressive strength of masonry. It is observed that confined masonry can develop drift values larger than 0.5 percent of wall height, which is comparable to that of reinforced masonry. Deformation capacity is observed to increase for increasing wall horizontal reinforcement ratio and column horizontal and vertical reinforcement and to be reduced with increasing axial load.