Application of diaphragm stiffness and strength equations to bridge metal deck forms

Abstract

The building and bridge industries commonly use light gage metal sheeting for concrete formwork. The building industry has long relied on the in-plane strength and stiffness of metal forms to prevent lateral torsional buckling of the beams. The flexibility in the current connection details between the forms and girders in the bridge industry often limit the amount of bracing provided by these forms. In a recent research study, modified connection details were developed that substantially improve the bracing behavior of bridge metal deck forms. However, there is currently not a design aid that a bridge engineer can utilize to predict the stiffness and strength of bridge metal deck forms. Hence, specifying the right PMDF system for bracing purposes becomes troublesome. For applications in the building industry, the Steel Deck Institute (SDI) Diaphragm Design Manual provides numerical expressions to determine the stiffness and strength of various types of metal sheeting and their corresponding connection details. The expressions in the SDI Design Manual are not directly applicable to bridge metal deck forms since PMDF used in the bridge industry differ from those utilized in the building industry by both shape and connection detail. In this paper results from shear diaphragm tests on bridge metal deck forms with modified connection details are compared with SDI expressions. Results indicate that slightly modified SDI expressions can be used to predict the stiffness and strength of bridge metal deck forms with modified connection details.