Summary
A new floor connecting system developed for low‐damage seismic‐resistant building structures is described herein. The system, termed Inertial Force‐Limiting Floor Anchorage System (IFAS), is intended to limit the lateral forces in buildings during an earthquake. This objective is accomplished by providing limited‐strength deformable connections between the floor system and the primary elements of the lateral force‐resisting system. The connections transform the seismic demands from inertial forces into relative displacements between the floors and lateral force‐resisting system. This paper presents the IFAS performance in a shake‐table testing program that provides a direct comparison with an equivalent conventional rigidly anchored‐floor structure. The test structure is a half‐scale, 4‐story reinforced concrete flat‐plate shear wall structure. Precast hybrid rocking walls and special precast columns were used for test repeatability in a 22‐input strong ground‐motion sequence. The structure was purposely designed with an eccentric wall layout to examine the performance of the system in coupled translational‐torsional response. The test results indicated a seismic demand reduction in the lateral force‐resisting system of the IFAS structure relative to the conventional structure, including reduced shear wall base rotation, shear wall and column inter‐story drift, and, in some cases, floor accelerations. These results indicate the potential for the IFAS to minimize damage to the primary structural and non‐structural components during earthquakes.
This paper presents an initial evaluation of the seismic demand for diaphragms during a shake table test of a three-story precast concrete structure. Each level of the test structure contained a different precast concrete floor construction technique: topped double tees on the lower level; topped hollow core on the middle floor; and pretopped double tees on the top floor. The diaphragms were designed and detailed according to a new design methodology developed as part of parallel research. The structure was subjected to a series of 16 strong ground motions with increasing intensity including design-basis and maximum considered earthquakes for which the diaphragms were designed. In the paper, the major diaphragm global and local response is quantified. Conclusions are drawn regarding the observed diaphragm behavior.
Abstract-An innovative floor anchorage system is being developed that reduces inertial forces in building structures during major earthquakes. This goal is accomplished by providing the anchorage a design strength lower than that required to transmit the elastic diaphragm forces. Instead, at a predefined "cut-off" load, the anchorage deforms ductily, transforming the diaphragm seismic demands into relative displacement of the floor system with respect to the primary vertical elements of the lateral force resisting system. The floor anchorage system has the potential to reduce the diaphragm inertial forces, thereby lowering floor accelerations and reducing seismic demands on the lateral force resisting system, resulting in less damage to the structure, non-structural elements and building contents. This paper presents preliminary analytical findings on the performance of the floor anchorage system, focusing on the sensitivity of system properties on structural seismic response. The analytical study shows significant seismic response reduction in the proposed floor anchorage system. Index Terms-Seismic resistance system, floor anchorage system, structural damage, structural seismic response.
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