SPECIFYING EXPANSION JOINT WIDTH IN SUPPORTED CONCRETE SLABS

This paper presents a procedure for specifying expansion joint width in supported concrete slabs taking into account creep, shrinkage, instantaneous elastic shortening and temperature variation. For a desired joint width at a specific point in time, the procedure can be used to specify the joint width to be constructed when the slabs are formed, the expected joint width at the time the expansion joint is installed, and the maximum and minimum expected joint width during the life of the slabs. The procedure can be summarized in three basic steps. In the first step, the designer identifies the desired expansion joint width at a certain time and at a certain concrete temperature. Second, from the targeted joint width, the joint width at any earlier time of interest can be calculated using empirical data adapted from previous research to approximate the creep and shrinkage of the slab. In the final step, joint width at the targeted temperature at casting, at the time when the joint hardware is installed, and long term can be extrapolated using the coefficient of thermal expansion of concrete to represent the joint width at other concrete temperatures. A numerical example illustrates the specification procedure.