In bridge widening projects, the stitching method involves a phased approach to ensure structural integrity and minimize disruptions. Initially, the widening section is constructed independently and left undisturbed for several months. This allows the new structure to settle and carry its own dead load, preventing any unintended stress transfer to the existing bridge.
A primary concern in this process is the shrinkage-induced stress from the new section. To mitigate this, a strategic waiting period of 6-9 months is implemented before stitching. This allows the majority of shrinkage to occur within the new structure, minimizing its impact on the existing bridge.
To address the challenges of traffic vibration on freshly placed stitches, rapid hardening cement is employed, accelerating the setting time. Additionally, stitching work is often scheduled during low-traffic periods, such as Saturday nights, and the existing bridge may even be temporarily closed to ensure undisturbed curing.
While longitudinal joints can be used as an alternative connection method, they pose safety risks due to varying frictional coefficients when vehicles change lanes. These joints are also challenging to maintain, further complicating their use.
Overall, the stitching method offers a robust solution for bridge widening, ensuring a secure connection between new and existing structures while minimizing potential risks and disruptions. The strategic timing of construction and careful material selection are crucial factors in the successful implementation of this method.