Shrinkage Induced Deformations in Steel Bridges Made Composite with Concrete Deck Slabs

Abstract

Concrete bridge deck cast upon steel girders form a composite steel-concrete bridge. Volume changes in the concrete caused by shrinkage, temperature or other effects can alter the finished elevations of the bridge decks. Some of the state’s newly constructed bridges have experienced downward deflecting decks, causing uneven riding surfaces. It has been suggested by some that the excessive deflections are caused by drying shrinkage of concrete. The research investigated the shrinkage characteristics of concrete, examined analytically the likely effects of concrete shrinkage on composite steel and concrete girder bridges, examined experimentally the system of concrete and steel bridge beams, and performed forensic field investigations of existing bridges. In various phases, material properties of concrete were studied, and a full-scale prototype bridge was constructed in the laboratory. That bridge was used to examine bridge deformations during deck casting and curing. The bridge was tested with heat loads and results are reported. Causes for excessive deflections are examined. It is concluded that the construction means and methods are largely responsible for unwanted bridge deformations and poor ride quality in some new bridges. Recommendations are made to the ODOT to help mitigate adverse effects.