1829 1 Doctoral Student, University of California at Berkeley, 721 Davis Hall, Berkeley, CA 94720, USA, jliu@ce.berkeley.edu 2 Professor, University of California at Berkeley, 781 Davis Hall, Berkeley, CA, 94720, USA, astaneh@ce.berkeley.edu SEISMIC BEHAVIOR AND DESIGN OF STEEL SHEAR CONNECTIONS WITH FLOOR SLABS Judy LIU 1 And Abolhassan ASTANEH-ASL 2 SUMMARY The 1994 Northridge earthquake raised many questions regarding welded steel moment frame structures. The simple connections are typically ignored as far as lateral resistance of these structures, but may have more lateral capacity than traditionally assumed. This project has, as its main goal, the task of determining whether or not these connections can or should be considered for use in lateral load-resisting systems. Cyclic tests on various connection details have been conducted, both with and without the floor slab. A closer look at just a few of the tests done on bolted, single-plate connections shows much about their basic cyclic behavior. This behavior is characterized primarily by slip, yielding, deformation of the bolt holes, and eventually, fracture at large rotations of drift. Tests with and without the floor slab indicated that the contribution of the slab to the lateral resistance was lost by 0.04 radians of drift, but that while the slab was effective, the capacity was practically doubled. Finally, the addition of a supplemental seat angle was very effective in increasing the moment capacity of the connection. Typical moment capacities ranged from 20% of the plastic moment capacity of the beam (Mp) for the bare-steel shear tab connection, to roughly 50% Mp for the shear tab with slab, and 80% Mp for the shear tab with supplemental seat angle and slab. INTRODUCTION In the Northridge earthquake, January 17, 1994, many welded, steel moment frame structures sustained brittle fractures in their welded moment connections. There has been a large effort since then to determine both the causes for and solutions to the problems with these connections. Many studies focus on the localized problem of the welded moment connections; still others evaluate the global behavior and design of these welded steel moment frame buildings. This project attempts to address the question of the contribution of the simple connections to the lateral resistance of moment frame structures. Simple, or shear, connections typically comprise a large percentage of the connections in a welded steel moment frame building. However, these simple connections are traditionally assumed to be pin connections and are ignored as contributors to the lateral load resistance. However, with the composite action of the floor slab, it is possible that these connections actually act as partially-rigid connections, with more lateral load-resisting capacity than previously recognized. The primary objective of this project is to determine if and when these shear connections, with the contribution of the floor slab, can be used to resist seismic loads. If so, they may provide a cost-effective alternative for repair or retrofit schemes for damaged welded moment-frame buildings. Another objective is to explore the use of the lateral resistance of these composite, partially-rigid connections in new construction. This project will fulfill these objectives through an investigation that includes sixteen full-scale cyclic tests and associated analytical studies. Various connection details were studied in the experimental investigation; this paper presents some of the observations and results related to the cyclic behavior of single plate, or shear tab connections.