Gravity Load Capacity of Earthquake Damaged Slab-Column Connections

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PI: James Jirsa, UT-Austin.The objective of this project is the determination of critical shear, moment, and deformation interactions for reinforced concrete slab-column buildings. Flat plate and flat slab floor systems are widely used in residential and commercial buildings with low gravity loads. Two-way or punching shear capacity of flat plate and flat slab floors is quite low. Shear strength calculations for such connections are complex and involve interaction between moment and shear transfer. Shear capacity is adversely affected by inelastic action that occurs at the connection. Deformation or drift must be controlled to limit damage. The poor performance of buildings in the 1985 Mexico City and other earthquakes since then has demonstrated the weaknesses in these structures. Little is known about the effect of inelastic deformations due to lateral displacements of the structure on subsequent shear transfer capacity under gravity loadings. The keystone of the research program is experimental testing to determine the relationship between punching shear capacity of the slab-column connection under gravity loads and the level of previous damage to the slab by earthquake (or other severe loading such as blast, wind, or settlement) actions on the structure. The information will be valuable for the following uses: 1. Determining the conditions under which punching shear failures due to gravity loads will occur after the structure has suffered earthquake damage by determining the degree of damage through visual observations, measured local or global deformations, or with non-destructive techniques. 2. Developing response characteristics for slab-column connections for use in pushover or other seismic analyses of new or existing structures. 3. Establishing reasonable deformation limits for evaluation and design of rehabilitation schemes for existing slab-column structures. 4. Evaluating the feasibility of strengthening slab-column connections. The project will create knowledge in an area that is new to the profession and essential to understanding the performance of structures during and after an earthquake. There is very little experimental evidence available to guide the research and design community in evaluating and rehabilitating systems where damage during an earthquake (or other severe loadings such as blast, wind, or settlement) can have deleterious impact on the subsequent behavior of the structure under different load combinations. The PI will make data available to the NEES network. Results will be disseminated through reports made available to the earthquake engineering community, articles in technical journals, and presentations at technical conferences. Practicing engineers will be involved in the development of the project details. Special efforts will be made to secure students from the graduate and undergraduate student bodies in the UT, CE program that has large fractions of women and Hispanic students. The findings from the research will be utilized immediately in a graduate course on evaluation and rehabilitation of existing reinforced concrete structures. The PI will use existing University programs, and direct contacts with local high school science teachers, to encourage a high-school student to choose engineering as a career.