Deck (Construction) [STG]

Composite deck pouring is a method of constructing a bridge deck where the deck and the girders act together as a single structural unit, which can significantly increase the load-carrying capacity of the bridge. In steel tub girder bridges, composite deck pouring is achieved by using a concrete deck that is poured onto the top flanges of the steel girders, which are typically designed with shear connectors such as studs or shear tabs.

The composite deck pouring sequence typically involves the following steps:

1. Preparing the steel girders: The steel girders are fabricated and erected, and the top flanges are prepared with shear connectors such as studs or shear tabs.

2. Placing the formwork: Formwork is placed on top of the girders to create a mold for the concrete deck.

3. Placing the reinforcement: Reinforcement, such as steel bars or mesh, is placed within the formwork to provide additional strength to the deck.

4. Pouring the concrete: Concrete is poured into the formwork and leveled to create a flat surface for the deck.

5. Finishing the surface: The surface of the concrete is finished with a trowel to create a smooth, even surface.

6. Curing the concrete: The concrete is left to cure, typically for several days, to gain strength and durability.

7. Applying the wearing surface: A final layer of asphalt or other wearing surface is applied to protect the concrete deck and provide a skid-resistant surface for vehicles.

During composite deck pouring, the girders and the concrete deck are designed to work together to carry the load of the bridge. The shear connectors on the top flanges of the girders transfer the load between the girders and the deck, creating a composite structure that is stronger than either component alone. The result is a bridge that can carry heavier loads and has a longer lifespan than a non-composite deck.

Prior to the deck pouring stages, it is important to confirm that the substructure elements such as foundations, piers, pier caps, abutments, and superstructure elements girders, and bracings have been constructed. In some models, substructure elements may not exist and fixed supports may be present at the bearing locations. For such models, it is necessary to ensure that girders and bracings have been constructed in the previous stages. It is also crucial to apply the formwork load in the previous stages.

For typically sized bridges, the most common placement sequence involves pouring the positive bending moment regions first, followed by the negative moment zones. The positive moment zone pour is typically defined as being between points of dead load contraflexure. After the positive moment zones have sufficiently cured (usually several days), the concrete for the deck in the negative moment regions is poured. This technique of using separate pours aims to minimize deck cracking over the piers. Most of the girder rotations at the bearings occur when the concrete in the positive zones is placed.

Deck Casting

Pouring Stage [Weight Only]: At this stage, the deck load and haunch load are calculated and applied on the top of non-composite girder. It is crucial to differentiate between the deck hardening stage (composite) and the non-composite state load applications.

During finite element analysis, the self-weight of shell elements is computed and distributed to the nearest girders. Consequently, it is not possible to visualize the applied loads graphically due to the self-weight of deck shell elements since this occurs during the load vector generation process of finite element analysis. Nonetheless, the haunch load is calculated in the library object and can be observed graphically in the FEA loading view.

Hardening Stage [Gains Stiffness]: During this stage, the deck(shell elements of deck) gains stiffness, and no load is applied. If no further loads are added during this stage, the results of the finite element analysis will remain unchanged because the sole modification is in the stiffness matrix.

Deck: Choose the deck to define the pouring sequence of the deck.

Start Skew: It specifies the boundary of the deck pouring area, in addition to the start station under longitudinal tab. A skew value of 0 implies that the line defined is perpendicular to the alignment. A positive value rotates the perpendicular line clockwise, while a negative value rotates the perpendicular line counterclockwise.

End Skew: It specifies the boundary of the deck pouring area, in addition to the end station under longitudinal tab. A skew value of 0 implies that the line defined is perpendicular to the alignment. A positive value rotates the perpendicular line clockwise, while a negative value rotates the perpendicular line counterclockwise.

Haunch Load[Include/ignore]: If the "include" option is selected, the haunch load is automatically computed and applied to the girder in the selected pouring stage. The calculation of the haunch load is based on the unit weight of the deck material, the selected taper parameter for the overhang region, and the haunch thickness.

Self Weight Factor: It's possible to define a self-weight factor that accounts for the cases where loading needs to be increased according to sacrificial thickness. To illustrate, if the deck thickness needs to be 8” for composite section properties and 8.5” for the calculation of the weight (0.5” sacrificial thickness), the user would input the Self-Weight Factor as 1.0625 (8.5”/8).

Longitudinal

Start Station: It defines the boundary of the deck pouring area along the PGL with a specified start station.

End Station: It defines the boundary of the deck pouring area along the PGL with a specified end station.

Transverse

Transverse Const. Type[Complete/Partial]: Typically, the deck pouring sequence does not require separating the pour in the transverse direction, and users can achieve this by selecting the "complete" option. However, in some cases, such as rehabilitation projects, it may be necessary to separate the pour in this direction. In such cases, the "partial" option can be selected.

Left Offset Start [PGL]: When looking up station along the alignment, the left transverse offset value from PGL is utilized to define the region at the start station.

Right Offset Start [PGL]: When looking up station along the alignment, the right transverse offset value from PGL is utilized to define the region at the start station.

Left Offset End [PGL]: When looking up station along the alignment, the left transverse offset value from PGL is utilized to define the region at the end station.

Right Offset End [PGL]: When looking up station along the alignment, the right transverse offset value from PGL is utilized to define the region at the end station.