After each construction stage, the finite element analysis produces results that can be utilized to ensure structural compliance with codes. To create the stages correctly, users must understand the underlying logic. At the start of the stage construction analysis, all structural elements are in an unconstructed state.
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.
Stage
Prior Stage: The continuity of stages is maintained using the prior stage parameter, which instructs the software on which stage to analyze next. For the first stage, the prior stage will be none. If users wish to apply temporary loads like wind or live load, they can select the final permanent load stage as the prior stage for all transient loads. (screenshot for the transient load example)
Construction Method[none/equal/match]: Usually, node coordinates are utilized as user inputs without any modification. However, certain scenarios require adjustments to the node locations based on prior stage deflections. For example, during the construction of girders and the application of deck load, girder nodes experience displacement while deck nodes do not. In construction site scenarios, the deck formwork also undergoes deflection due to girder displacement. To address this, the node coordinates of the deck must be adjusted based on girder displacements. The "equal" parameter modifies the initial node coordinates of the deck shell elements by applying the top node displacements of the girder to the closest nodes. For a typical steel I-girder bridge, pier construction, steel I-girder construction, load application on deck, and transient load stages will typically be defined with the "none" parameter. However, the stage that represents the deck construction (the deck hardens stage) should be defined with the "equal" parameter. The match cast technique is typically not used in the construction of steel I-girder bridges and is generally applicable to segmental bridges.(need screenshot)
Load Type: Selecting the appropriate load types, such as dead load, wearing surface load, and wind load, for each stage is crucial, and different load types should not be combined in a single stage. In the following steps, users must combine the results of each stage based on their load type using AASHTO load factors before code checks. Combining results becomes more challenging if more than one load type is applied in one stage or if load types are not selected correctly. In summary, load type allows users to filter results according to its load type, providing a way to organize and analyze results more effectively.
Active[Yes/No]: Users can deactivate specific stages to expedite the model's runtime, especially if they are interested in something from the earlier stages. However, if the deactivated stages negatively affect the continuity of stages, the staged construction analysis will fail to run successfully. Therefore, when users deactivate certain stages, they must ensure that all active stages' prior stages are still active.
Time Dependent
Typically, in a steel I-girder design project, time-dependent staged construction analysis is not necessary. However, if the bridge owner requests CEB-FIP 1990 creep/shrinkage computations for the substructure, or if post-tensioned tendons are employed for the pier cap or pier columns, time-dependent analysis can be conducted. In such cases, the following parameters can be used:
Construction Day:
Code[CEB-FIP 1990]: At present, only the CEB-FIP 1990 code is supported. If any other code is required, please contact the support team, and it can be added to the OpenBrIM Library.
Temperature [F]:
Humidity [%]:
Time Dependent Elastic Modulus[Include/Ignore]:
Concrete Creep Effect[Include/Ignore]:
Concrete Shrinkage Effect[Include/Ignore]:
Steel Relaxation Effect[Include/Ignore]:
PT Losses from Structure[Include/Ignore]:
AASHTO N-3N
Material: Choose the deck material to override for short-term and long-term properties
Composite Section[NA/Short Term/Long Term]: If the short-term option is selected, this parameter will override the modulus of elasticity values of the selected material. The short-term modulus of elasticity is computed by dividing the selected deck material's modulus of elasticity by 3. As per AAHSTO standards, the deck's modulus of elasticity and section modulus must be adjusted for design purposes when calculating stresses. OpenBrIM already computes stresses during the design phase based on long-term/short-term section properties. However, if an analysis beyond the design phase is required with modified E for short-term and long-term loads, this parameter can be used.
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