The Deck Placement Sequence command allows previously defined slab segments (from the Deck Slab command) to be placed into the construction stages, which define the order in which the segments will be placed on the bare steel for the constructibility analysis.

By default there is always an Initial and Final stage. The Initial stage consists of the weight of the steel girders, cross frames and any other dead loads entered by the user that act on the non-composite steel section only. The Final Stage is treated separately from the construction stages and represents the fully assembled bridge, assuming the deck has been placed all at once on the steel.

During the staged construction analysis process, the analytical model is created and analysis performed as follows:

• The Initial stage consists of the weight of the girders, cross-frames, stiffeners and any additional ad-hoc dead loads defined by the user for this stage that act on the non-composite section. The analytical model is non-composite and all loads are applied as DC1 loads. All stresses on the non-composite girders (including flange lateral bending stresses) are computed and stored, along with the girder shears. At all POIs, the factored steel girder stresses are used in the Article 6.10.3.2 constructibility code checks for local and lateral torsional buckling of the compression flange and for web bend-buckling, and the accumulated factored shears are used in the Article 6.10.3.3 constructibility code check for shear. The design checks are output in the Constructibility Design Report.

  

• Stage 1 includes the weight of the initial slab segment(s) to be placed on the non-composite steel girders, as specified by the user. The load from the stage is applied over the defined length of the stage to the non-composite structure as a DC1 load. All factored stresses on the non-composite girders (including flange lateral bending stresses) due to this stage at each POI are computed and stored. Factored stresses on the steel girders are accumulated with the factored stresses from the Initial stage. At all POIs, the accumulated factored steel girder stresses are used in the Article 6.10.3.2 constructibility code checks for local and lateral torsional buckling of the compression flange and for web bend-buckling, and the accumulated factored shears are used in the Article 6.10.3.3 constructibility code check for shear. The design checks are output in the Constructibility Design Report.

  

• All subsequent stages apply the slab segment(s) acting over the defined length of the stage under consideration to the non-composite structure, again as a DC1 load. The analytical model is non-composite everywhere, but at the locations where the slab has been placed in previous stages; at these locations, the girder is assumed fully composite with the steel. At POIs where the girders are still non-composite, the factored steel girder stresses are computed using the non-composite section properties. At POIs where the member is composite, the factored steel girder stresses are computed using the short-term composite section properties at sections subject to either positive or negative bending. At all POIs where the girders are non-composite, the accumulated factored steel girder stresses are used in the Article 6.10.3.2 constructibility code checks for local and lateral torsional buckling of the compression flange and for web bend-buckling, and the factored shears are used in the Article 6.10.3.3 constructibility code check for shear.

  The factored slab stresses are also accumulated and stored at all POIs where the girder is assumed composite. At these POIs, if the accumulated factored stress in the slab is compressive, only the accumulated factored girder shears are checked (Article 6.10.3.3). If the accumulated factored stress in the slab is tensile, in addition to the check of the factored shears, the provisions of Article 6.10.3.2.4 are also checked. That is, the factored tensile stress in the slab is checked against a limiting value of 0.9f_r, where f_r is the modulus of rupture of the concrete as defined in Article 6.10.1.7. If this limit is exceeded, the minimum one-percent longitudinal reinforcement is required in the slab at the POI under consideration. The design checks are output in the Constructibility Design Report.

Example:

In the following example for a three-span continuous bridge illustrated in Figure 2, there are four construction stages. The progression at Point of Intersection 1 (POI 1) is described.

• Initial Stage, steel only

  • An analytical model of the steel only (non-composite) structure is automatically created.
  • Analysis takes place for the self-weight of the steel.
  • Factored steel girder stresses are computed and stored.
  • Constructibility design checks are made as outlined above for the Initial stage and are output in the Constructibility Design Report.
  
• Stage1, Placement of Slab 1

  • An analytical model of the non-composite structure is automatically created.
  • Analysis takes place for the weight of the wet concrete applied to the non-composite structure over the length of Slab 1.
  • Factored steel girder stresses are computed and accumulated with the stresses from the Initial stage at all POIs.
  • Constructibility design checks are made as outlined above for Stage 1 and are output in the Constructibility Design Report.
  
• Stage2, Placement of Slab 2

  • An analytical model of the structure is created with short-term composite section properties over the length of Slab 1 and non-composite section properties elsewhere.
  • Analysis takes place for the weight of the wet concrete applied to the non-composite structure over the length of Slab 2.
  • Factored steel girder stresses are computed and are accumulated with the stresses from Stage 1 at all POIs.
  • Factored deck slab stresses are computed and stored at all POIs where the girders are composite (including POI 1 in this case).
  • Constructibility design checks are made as outlined above for all subsequent stages and are output in the Constructibility Design Report.
  
• Stage3, Placement of Slab 3

  • An analytical model of the structure is created with short-term composite section properties over the length of Slab 1 and Slab 2 and non-composite section properties elsewhere.
  • Analysis takes place for the weight of the wet concrete applied to the non-composite structure over the length of Slab 3.
  • Factored steel girder stresses are computed and accumulated with the stresses from Stage 2 at all POIs.
  • Factored deck slab stresses are computed and are accumulated with the deck stresses from Stage 2 and stored at all POIs where the girders are composite (including POI 1 in this case). Constructibility design checks are made as outlined above for all subsequent stages and are output in the Constructibility Design Report.