Storediaphragm

Storediaphragm is a term used in structural engineering to describe the floor or roof assembly at a given storey that acts as a diaphragm to transfer lateral loads, such as wind or seismic forces, to the building’s vertical resisting elements (shear walls, frames, or braced systems). The term is often written as storey diaphragm or story diaphragm, with American usage typically using the spelling story.

The diaphragm serves as a rigid or semi-rigid horizontal force-transmission path. Its primary function is to distribute lateral loads evenly across the building plan and transfer them to the vertical elements that resist movement. The behavior of a storediaphragm depends on its stiffness, geometry, and the connections to surrounding structural elements. In high-rise or irregular buildings, the diaphragm’s performance can influence torsional effects and the overall stability of the structure.

Common diaphragm types include concrete floor slabs, timber or light-frame decks with sheathing, and steel decking with concrete topping. Design considerations cover material properties, diaphragm thickness or depth, presence of openings, and how partitions or mechanical penetrations affect stiffness. Connections to shear walls or frames must be detailed to ensure adequate load transfer and to avoid localized failures around openings or penetrations.

In practice, engineers may model a storediaphragm as an equivalent rigid or semi-rigid plane and verify its behavior under anticipated loads using codes and standards such as the IBC or Eurocode. The diaphragm is a key element in achieving a coherent lateral-load-resisting system.