After each construction stage, the finite element analysis produces results that can be utilized to ensure structural compliance with codes. At the start of the stage construction analysis, all structural elements are in an unconstructed state.
Required Stages
Constructing a typical steel bridge requires defining at least four stages: pier/foundation construction, girder and bracing construction, application of deck loads on non-composite girders, and deck stiffness gain
Introducing deck pouring stages will require additional stages for non-composite and composite stages. For example, if the deck is poured in three stages, six stages will be necessary (three for deck load application on girders and three for deck stiffness gain stages)
For permanent loads, such as wearing surface loads and barriers, two extra stages may be required
Additional stages will be necessary for each transient load, such as wind loads, braking loads, live loads, and temperature loads
Steps
Step 1: Navigate to Construction Stage
Navigate to Loading > Construction Stage in the tree view.
Construction Stage navigation
Construction Stage tree
Construction Stage table
Step 2: Define First Construction Stage
Begin by defining the first construction stage.
Ensure that the Prior Stage cell is Null as the first stage does not have a preceding stage.
Step 3: Assign Construction Method and Load Type
Click the three-dot icon on the Construction Method and Filter by Load Type cells and select the appropriate options.
Step 4: Enter First Stage Data
Enter the following data for the 1st Stage:
Parameter
Value
Name
SubstrConstStage
Prior Stage
NULL
Construction Method
None
Filter by Load Type
Dead
Active
Yes
Step 5: Define Remaining Stages
Repeat steps 2 through 4 to define all construction stages in the project.
All construction stages
Step 6: Configure Time Dependent Properties
Navigate to the Time Dependent tab to configure creep and shrinkage parameters if needed.
Time Dependent tab
Step 7: Configure AASHTO N-3N Properties
Navigate to the AASHTO N-3N tab.
Set the Material parameter to the deck material to modify the modulus of elasticity for each stage.
Enter the Composite Section parameter as:
Long-Term (3n) for permanent loads
Short-Term (n) for transient loads
AASHTO N-3N configuration
Composite section settings
Quick Tip: Construction Method Options
In Staged Construction Analysis, when joints are activated they normally enter at the location that was initially given to them. Joints sometimes need to become active in a location relative to the deformed structure of the model, rather than in an exact position known ahead of time.
The construction method option specifies how to place a joint relative to the deformed location of other joints.
In Steel Tub Bridges, deck formwork deforms and follows girder displacements. Therefore deck nodes should be constructed by shifting the node down to match the translational displacement of the girder nodes. This can be achieved with Construction Method = Equal for deck stiffness gain stages.
Construction method diagram
Quick Tip: Composite Section Modular Ratio
For the Composite Section parameter refer to AASHTO (2020) 6.10.1.1.1 - Stresses.
The modular ratio should be taken as n = E/Ec, where Ec = modulus of elasticity of the concrete.
Modular ratio diagram
Short term and long term applications depend on the sequence of loading which results in the stress at the section.
Per AASHTO (2020) 6.10.1.1.1b - Stresses for Sections in Positive Flexure:
For transient loads assumed to be applied to the short-term composite section, the concrete deck area shall be transformed by using the short-term modular ratio, n. For permanent loads assumed applied to the long-term composite section, the concrete deck area shall be transformed by using the long-term modular ratio, 3n. Where moments due to the transient and permanent loads are of opposite sign at the strength limit state, the associated composite section may be used with each of these moments if the resulting net stress in the concrete deck due to the sum of the unfactored moments is compressive. Otherwise, the provisions of Article 6.10.1.1.1c shall be used to determine the stresses in the steel section. Stresses in the concrete deck shall be determined as specified in Article 6.10.1.1.1d.
Verification
All construction stages should be defined with appropriate prior stages, construction methods, and load types.
