Concrete is among the most frequently used building materials for bridges as a readily available local option. Precast concrete decks have an expedited construction schedule and are both cost- and time-effective.
How Precast Bridge Decks Are Designed
Two layers of steel bars that are normally coated with epoxy to prevent corrosion serve as reinforcement for the concrete slab. Concrete is a norm for many settings, such as structures over salt water, due to its inherent durability and long lifespan. Concrete can sustain high temps and resist deterioration due to its durability.
The length and width of a full-depth precast deck are set by the specific bridge geometry and consist of a number of precast concrete panels that are full-depth in thickness, as needed by the structural design. The panel's length along the road is between 8 and 12 feet. Usually, the width of the panels is the same as the entire width of the bridge. Based on handling and transportation, both the length and width are chosen. In general, the goal is to use the fewest number of panels to accomplish a project with speed and economy.
Designers can find answers to some of the most commonly asked questions about precast deck panels here.
Precast Bridge Deck Connections to Bridge Girders
Precast concrete panel decking is a relatively affordable and expedient bridge-building solution. In the best cases, these are made to be put in place in a single day and be ready for activity by the close of the next day.
Light excavation equipment can easily raise the slabs and install them to the superstructure. The headed studs and grout pockets generated in the precast concrete planks serve as anchors for the planks to the superstructure. On-site batch mixing and pouring of grout with a quick setting time is also possible.
Deck panels and supporting girders can be joined together utilizing composite or non-composite connections. Shear connectors should be able to withstand movement in both the vertical and horizontal directions between the precast and the supporting structure.
Because of their structural effectiveness and decreased total depth and cost of the superstructure, composite full-depth precast concrete deck systems are frequently used. To allow the shear connectors of the supporting girders, existing full-depth, full-width composite deck systems either employ continuous open channels along each girder line (trough) or sparsely spaced discrete openings (pockets). The deck surface needs to be covered by an overlay similar to that used on CIP concrete decks before the troughs or pockets are field grouted. Additionally, transverse joints between neighboring deck panels are either longitudinally post-tensioned utilizing integrated ducts or conventionally reinforced.
Benefits of Precast Deck Panels
Compared to cast-in-place (CIP) concrete decks, precast concrete deck systems provide a number of advantages. Examples include increased quality and safety, shorter building times, and lower maintenance expenses.
Precast concrete decks have better quality than CIP concrete decks because production takes place in a controlled environment, which eliminates variations in the weather, the casting crews, and the curing processes. Additionally, there is a comparatively smaller panel size, two-way prestressing, and delayed composite action with supporting girders to reduce shrinkage cracking in bridge decks in precast systems.
Using precast to rehabilitate existing or steel concrete girder bridges on roadways with major traffic shortens the time for construction and reduces the overall time for bridge closures.