Cyclic behaviour of interior post-tensioned flat plate connections S. W. Han*, S.-H. Kee*, T. H.-K. Kang†, S.-S. Ha*, J. W. Wallace† and L-H. Lee* Hanyang University; University of California In high seismic regions, post-tensioned (PT) slab – column frames are commonly used to support gravity loads in conjunction with a lateral-force resisting system (LFRS) such as a core wall. The LFRS is designed to resist 100% of the design lateral forces as well as to limit lateral displacements to an acceptable level, whereas the slab – column frame must sustain the gravity loads under the expected (design) displacements. Given the relatively sparse data on the seismic performance of PT flat plate slab – column frames, cyclic tests of four interior PT slab – column connections were conducted. Primary test variables were the level of gravity shear at the slab – column connection and the slab tendon arrangement. Test results indicate that both the test variables strongly influence the cyclic behaviour of the PT connections, and that the use of slab bottom reinforcement at the slab – column connection was effective in resisting positive moment developed under lateral loading as well as improving the hysteretic energy dissipation capacity. Notation A ps area of tendons A sm area of continuous bottom bonded reinforcement b 0 perimeter of critical section b 1 width of critical section parallel to loading direction b 2 width of critical section perpendicular to b 1 c distance from the centroid of critical section to the perimeter of critical section c 2 column dimension perpendicular to the loading direction d effective slab depth d b bar diameter d p effective slab depth of tendons f 9 c peak concrete compressive stress f pc average compressive stress in concrete owing to effective post-tensioning force only f ps nominal stress in an unbonded tendon (limited to lesser of f py and f se + 210) f py tendon yield stress f se effective tendon stress f y yield stress of slab bottom reinforcement h slab thickness J c polar moment of inertia of critical section l 1 centre-to-centre spans parallel to the loading direction l 2 centre-to-centre spans perpendicular to the loading direction M n, c þ 3 h nominal moment for a slab width of c 2 + 3h M n,fs nominal moment for a full slab width M u,ub peak unbalanced moment V c nominal concrete shear strength V g gravity force to be transferred from a slab to a column V p vertical component of effective post- tensioning force at section V u factored shear force to be transferred from a slab to a column â c ratio of long side to short side of a column ª f factor used to determine the unbalanced moment transferred by flexure at slab– column connections ª v fraction of unbalanced moment transferred by eccentric shear í c nominal shear strength provided by concrete í u maximum shear stress Ł u drift ratio at punching Ł y drift ratio at yielding * Division of Architectural Engineering, Hanyang University, Seoul 133–791, Korea. † Department of Civil and Environmental Engineering, University of California, Los Angeles (UCLA), California 90095, USA. (MCR 51489) Paper received 29 November 2005; accepted 7 August 2006 Magazine of Concrete Research, 2006, 58, No. 10, December, 699–711 699 www.concrete-research.com 1751-763X (Online) 0024-9831 (Print) # 2006 Thomas Telford Ltd