Seismic Design of Composite Steel Deck and Concrete-filled Diaphragms

Building structures are typically composed of horizontal spanning elements, such as beams and floor and roof decks; vertical elements, such as columns and walls; and foundation elements. Together these elements comprise an integral system that resists both vertical and lateral loads. Seismic design of building systems entails controlling the building displacements, typically by providing resistance to the inertial forces generated by the acceleration of the building mass. Often the great majority of the load is derived from the mass of the roof and floor systems themselves, and resistance is composed of a continuous lateral load path from these spanning elements to vertical elements that have lateral resistance (e.g., walls, braced frames, moment frames), which in turn deliver the forces to the foundation.

The first segment of this load path is composed of the diaphragm system. This system is typically conceived of as spanning horizontally between the vertical elements of the lateral load-resisting system. Without this element of the load path there would be no resistance to the movement of the distributed building mass, and thus large movements, and
perhaps collapse, would result. Thus, diaphragms are a critical component of seismic design and must be properly designed to ensure adequate performance. Additionally, diaphragms serve a number of other functions in providing structural stability and resistance to lateral loads, as discussed in Section 2.

This Guide addresses the design of diaphragms composed of steel beams and steel deck with concrete fill. In passing, the Guide addresses some issues related to the design of diaphragms with non-composite (bare) steel deck, but a future Technical Brief devoted entirely to bare steel-deck diaphragms is anticipated.