Inelastic response of steel roof deck diaphragms with nailed and welded connections

A series of in-plane shear tests were carried out on twenty-one steel roof deck diaphragms. This test program was initiated and designed to evaluate the seismic inelastic response of steel roof decks with different thicknesses and different types of deck-to-frame connections: nails and arc spot welds. Self-drilled screws were used for sheet side lap fasteners in all specimens. The tests included monotonic, quasi-static reversed cyclic inelastic deformation, and seismic motions. Shear performance and failure mode of the steel decks for both types of deck-to-frame connections were investigated. Lateral resistance and elastic stiffness of steel decks with different panel thicknesses and connector types were determined and compared with those available in the Diaphragm Design Manual. Testing of all specimens confirmed that the inelastic deformation of a deck is mainly concentrated on the edge of the diaphragms parallel to the lateral loading. The cyclic tests showed a pinched hysteretic behavior for all the specimens. Nail specimens sustained large inelastic deformation cycles with progressive strength degradation. In contrast, weld specimens showed very significant deterioration and very rapid strength reduction after the peak load was reached. These tests confirm that the response modification factor for structural systems built with steel decks with nail-screw connectors should be greater than the current value in the building codes.