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Laboratory and Field Investigations for Causes of Unwanted Deformations in Existing Steel Girder Bridges Rehabilitated with Concrete Decks

Belcher, Kendall Ke'Vonn
Many older steel girder bridges are rehabilitated by placing a new concrete deck upon the existing steel superstructure. In recent years, the Oklahoma Department of Transportation has reported issues of ride performance on some newly rehabilitated concrete and steel composite bridges. Shrinkage, creep, temperature, and other sources of time-dependent volume change can affect the ride quality, deck cracking, deflection, and long-term performance of steel girder bridges made composite with concrete decks. These time-dependent effects are sometimes considered minimal and ignored. After the initial set, concrete will experience volumetric changes caused primarily by shrinkage. Other time dependent changes, specifically temperature and creep, will have some effects, but these are likely small compared to shrinkage. Some researchers recommend waiting for concrete to develop its strength and full composite action to counter the effects of shrinkage before applying load (Chaudhary et al. 2009). Time-dependent volume changes do not impact the load carrying capacity of a simply supported bridge, but instead affect the composite response to service loads and deflections in supporting steel beams and the whole system. Some research has theorized that volumetric changes in concrete are the cause of unpleasant driving surfaces and unexpected deflections. My research develops new knowledge on volumetric effects in rehabilitated composite bridges through: 1) experimental research and 2) forensic investigation. Research included laboratory analysis and forensic investigation. Companion laboratory concrete specimens and prototype bridge specimens were built. Various concrete mixtures were batched and standard ASTM tests were performed to measure compressive strength, splitting cylinder tensile strength, elastic modulus, and shrinkage over time. On the prototype bridges, temperature, deflections, and strains were measured daily. Forensic investigations were performed on three bridges in Oklahoma to determine the causes of serviceability problems. Serviceability issues refer to unsatisfactory performance of a bridge under service loads for its intended purpose; i.e. excessive deflections and adverse riding surfaces. The laboratory data show that concrete shrinkage is one possible contributor to poor ride quality and unanticipated deflections in rehabilitated bridges. However, the field investigations provide evidence that construction errors are likely the main cause of poor elevation control of finished bridge deck surfaces.