Author: Hung-Jung Hung

Publisher:

Published: 2012

Total Pages:

ISBN-13: 9781267657008

Current practice in California requires up to 60 days waiting period for closure pour after the release of falsework for both staged construction and widening of existing bridges. The relatively long waiting time is intended to reduce the stress build-up and mitigate the damage in the bridge deck due to the potential differential displacement between the newly constructed deck and previously constructed deck. The current waiting period does not take into account the displacement capacity of the closure slab, which varies depending on the dimensions and reinforcement details, and the time-dependent differential displacement that will be imposed on the closure slab. In this research, closure pour waiting time is evaluated in three steps. In step 1, a predictive model based on an age-adjusted effective modulus with traditional elastic analysis is used to predict the time-dependent displacement of the bridge. The predictive model is shown to correlate well with field-measured deflections for two concrete box-girder bridges. In step 2, four full-size closure slabs were tested to determine the displacement capacity of typical California closure slabs. Closure slabs with current California details exhibit rather brittle shear failure with limited displacement capacity. In step 3, a procedure based on the predictive model of differential displacements and laboratory-determined displacement capacity is proposed to determine the closure pour waiting time. Preliminary numerical examples in this research indicate that the current waiting time is conservative, especially in staged construction or bridges with small instantaneous deflections, and shortening of closure pour waiting time is warranted.