Autoclaved aerated concrete (AAC) masonry infills in upper stories can be beneficial for improving the seismic response of open-ground-story (OGS), reinforced concrete (RC)–frame buildings. Two reduced 1:2.5-scale models of single-story, single-bay RC frames with and without AAC infill masonry were tested for resistance properties and hysteretic behavior. Low strength and stiffness of AAC masonry, about half of the conventional brick masonry, led to improved load sharing between the infill and the frame, which helped an early development of frame yield mechanism for enhanced energy dissipation. Test results were used to evaluate the reliability of using existing strength and stiffness relations of conventional masonry infilled RC frames for AAC infilled frames. Analytical models were developed to predict the observed hysteretic behavior of tested specimens. Nonlinear analyses of a five-story, four-bay OGS-RC frame were performed for conventional brick masonry infills and relatively softer and weaker AAC infills in upper stories. The results indicated that the undesirable effect of weak/soft ground story mechanism of OGS-RC frames can be reduced to an acceptable level by using AAC infills in upper stories.

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