CTI Engineering Co., Ltd. has developed a rational deck slab update design method for steel bridges in consideration of deck slab compositing effects.

At CTI Engineering, we have developed a rational deck slab update design method in consideration of deck slab compositing effects. This method is the result of verifying the compositing effects between the main girders and deck slabs when updating steel bridge deck slabs and the reinforcement effects of existing main girders with this in mind.

1. Conventional challenges in updating concrete deck slabs
Steel bridges built during periods of rapid growth have become stressed due to larger vehicles, increased traffic volume, and damage over time due to deteriorating factors, making them a prime candidate for urgent concrete deck slab update in the maintenance process. On the other hand, in order to avoid a drop in service standards during construction while updating the deck slabs, it is common to design using non-composite girders without considering the compositing effects of deck slabs, with growing scale of reinforcement work resulting in issues.

2. Overview of the rational deck slab update design method
Through joint research with Osaka City University on compositing effects between the main girders and deck slabs when updating deck slabs, we have performed quantitative evaluation of the issues from both experimental and analytical sides, developing the rational deck slab update design method.

　

(1) Optimized stud dowels for integration with precast deck slabs
To confirm the integration of precast deck slabs with stud dowels and deck slab compositing effects, we clarified the relationship with fracture morphology and loads and deformation in element tests. Based on the results, we can build a three-dimensional FEM model in consideration of deck slab composite action and create a rational structural proposal with optimized stud dowel spacing taking into consideration shift rigidity between precast deck slabs and the main girders.

　

　　

　

Steel girder deck slab update configuration diagram

　

(2) Rationalizing structural reinforcement of existing main girders when updating deck slabs
In general, if reinforcement of existing main girders is necessary when updating deck slabs, additional L-shaped steel pieces are added to increase load bearing capacity, however, the reinforcement effects are not clearly proven in this method.
Thanks to FEM analysis taking into consideration the deck slab composite effect when using the same reinforcement method for existing main girders, it is possible to identify stress generation in existing main girders, optimizing the layout of the reinforcing materials (L-shaped steel) to achieve a rational construction with a high level of reinforcing effectiveness.

　

　

　

Stress distribution before and after reinforcement

　

　

3. Future prospects
Based on the knowledge gained, we plan on continuing research beginning with improving the concrete mortar used in precast deck slabs.