Date of this Version
Al-Kady, K., Wittich, C. E., Wood, R. L., Morcous, G. (2022). Phased Construction Bridges: Monitoring and Analysis for Traffic-Induced Vibration. NDOT Research Report SPR-P1(20) M102.
Phased construction is a common technique utilized to allow bridges to remain partially open to traffic throughout the construction process. The segment of the bridge deck that is constructed second cures under the effect of traffic-induced vibration transmitted from the adjacent bridge-deck segment, which is open to traffic. However, subjecting bridge decks to traffic-induced vibration during early-age curing raises concerns about the durability of the decks. The primary goal of this study is to generate a fundamental understanding of the transmission of traffic-induced vibration, the extent of degradation on phased construction bridge decks, and the impact of potential mitigation measures. In this study, the response of two phased-construction bridges in Nebraska were monitored before, during, and after the second stage of phased construction. Within 6-7 hours of the second-phase pour, the two phases of the bridges converged dynamically and began to behave as a single structure. To further understand this behavior, an experimental program was executed incorporating two phased-construction specimens and one which was constructed in a non-phased manner. The phased-constructed specimens were subjected to simulated traffic-induced vibration protocols for 0 – 12 and 7 – 12 hours from the start of the pour. Within hours of the pour, significant cracks were observed in the specimen subjected to traffic for 0 –12 hours. While cracks were similarly noted for the other phased specimen, the cracks were much less extensive and did not exceed hairline widths. No cracks were observed for the non-phased specimen. Upon further evaluation, it was concluded that the critical time window of 6-7 hours during which traffic-induced vibration has the most significant impact on deck cracking corresponds to the concrete setting time. Therefore, it is recommended that phased construction bridges close for the duration of the concrete setting time to reduce premature deterioration.