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{{Test Problem

name = Staged construction for precast concrete girder bridge

description = Analysis, modeling and design of precast concrete girder bridge.

keyword = staged construction; bridge; bridge modeler

program = SAP2000

version = V12.0.2

status = in progress

id = ok/brim - precast concrete girder bridge}}

This test problem shows how construction stage analysis can be done for bridges that are simply supported for dead load and continuous for live load.

Model Screenshot

Image Removed

Approach 1 - Using Section Modifiers (Model B)

Key modeling steps

...

 On this page:

Table of Contents

Overview

The purpose of this model is to illustrate how to set up staged construction for a two-span precast girder bridge that is simply supported for dead loads and continuous for live loads. Since the main focus is on setting up the staged construction load case, no tendons have been added to the model for simplicity.

Image Added

Figure 1: Deflection of the structure under self-weight

Model description

Key steps for setting up the model

  • Use the Quick Bridge template to create a 2-span precast-girder bridge. Designate double bearings at the interior pier.

  • Manually define 15 continuity links

    connecting

    at the interior pier to connect the girders and deck

    of

    between span 1

    with girders

    and

    deck of

    span 2

    at the interior pier.
  • Create 3 groups to be used for the construction stage analysis for continuity links, deck and all other remaining objects.
  • Use "

    . Note the the continuity links have zero length, because they are drawn between two joints that share the same location. These joint are however not connected, because they have different merge numbers.

  • Use the "Bridge Tab > Bridge Objects > Groups"  menu command to create two bridge groups, one for the deck and the other for the rest of the structure.

  • Select the continuity link elements and use "Advanced Tab > Define > Groups" menu command to create group for the continuity link elements.

  • Use the "Advanced Tab > Define > Named Property Sets > Area Modifiers" command to define two sets of property modifiers for the deck shell elements to simulate

    the hardening of concrete.Set

    wet concrete with zero stiffness and full weight and hardened concrete with full stiffness and weight.

  • Use "Analysis Tab > Load Cases > New" to set up construction stage analysis with separate stages to:

    (1) add and load

    1. Add the girders

    (2) add

    1. and apply their self-weight

    2. Add deck shell elements

    (3) reduce

    1. Reduce the stiffness of

    the

    1. deck shell elements to simulate

    fresh

    1. wet concrete

    (4) apply

    1. Apply the deck

    dead load(5) reset

    1. self-weight

    2. Reset the stiffness of the deck shell elements to full stiffness to simulate

    hardened

    1. the hardening of concrete

    (6) add the

    1. Add continuity links to the model

    .

    1. to model continuous superstructure for subsequent loading, such as moving loads

  • Save the results at the end of each stage.

  • Define moving-load analysis, starting from the end of staged-construction analysis.

...

Modeling

...

comments

  • The bridge has fixed bearings

    (

    at the bent which restrain vertical, longitudinal, and transverse

    translations fixed) at the bent and sliding bearings (only

    translation. Sliding bearings at the abutments restrain vertical and transverse

    translations fixed) at the abutments. However

    translation. For all other bearing DOF, it is

    required

    necessary to add small stiffness

    for other bearing DOFs

    to stabilize the girder before the deck is erected

    . Otherwise

    , otherwise stability problems may occur.

...

Discussion of results

...

  • Check bridge forces

    /

    and stresses for each step of the staged construction analysis

    →

    to ensure that moments are as expected for a simply-supported

    bridge

    condition, see Figure 2.

  • Check moments for the results of moving-load analysis

    →

    to ensure that moments are as expected for a continuous-girder

    .

Additional Screenshots

  • system, see Figure 3.

  • Since the deck self-weight is applied when the deck has negligible stiffness (to model wet concrete), the deflections of the deck itself in the staged construction are exaggerated and do not represent the true deck deflections. In the actual structure, the wet concrete would be supported by forms that will provide sufficient stiffness. However, the stiffness of the forms has not been modeled in this model.

Image Added

Figure 2: Moment diagram at the end of staged construction (

...

simply supported

...

superstructure)

...

Image RemovedImage Added

Figure 3: Live load

...

moment diagram (continuous superstructure)

Show if
groupeditors

Important Comments:

As of SAP2000 V14.1.0., forces for each stage are reported to the centroid of the full bridge deck section. You may need to transform the forces to the centroid of the section that is active when the forces are applied. See bridge modeler forces and stresses diagrams for additional information.

Approach 2 - Change Section Properties (Model C)

Key modeling steps

  • Create 2-span precast girder concrete bridge from BrIM template, with double bearings at the interior pier.
  • Manually define 15 continuity links connecting girders and deck of span 1 with girders and deck of span 2 at the interior pier.
  • Create 3 groups to be used for the construction stage analysis for continuity links, deck and all other remaining objects.
  • Set up construction stage analysis with separate stages to:
    • (1) add and load the girders
    • (2) add deck shell elements
    • (3) reduce the stiffness of the deck shell elements to simulate fresh concrete
    • (4) apply the deck dead load
    • (5) reset the stiffness of the deck shell elements to simulate hardened concrete
    • (6) add the continuity links to the model.

See Also

Attachments

  • File | filename = Staged construction of precast concrete girder bridge model B SAP2000 V12.0.2 sapfile.zip | title = Model B V12.0.2 Sapfile (Zipped SDB File)

{{To Do

comment = Show powerpoint presentation with screenshots for model B.

who = ok}}

</html>

TODO: to be reviewed in the latest version.

Attachments

Metadata

  • Name: Staged-construction analysis of two-span precast-girder bridge

  • Description: Modeling and construction stage analysis of precast-girder bridge which is simply supported for dead load and continuous for live load.

  • Program: CSiBridge

  • Program Version: 18.1.1

  • Model ID: 1407