International Concrete Abstracts Portal

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 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.

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.

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.

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.