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Model overview

Internal shrinkage forces are evaluated for one-span and continuous two-span bridge structures. These bridges have the following properties:

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• Deck-section type: T-beam section with a 0.5m-deep, 3m-wide deck and two 0.5m-wide, 1.5m-deep beams

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A 3D view of the one and two-span bridge models is shown in Figure 1:

Figure 1 - Bridge model

The cross-sectional geometry of the bridge deck is shown in Figure 2: 

Figure 2 - Bridge deck section

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Key modeling steps

• Define shrinkage characteristics for the default, 4000psi concrete material. Create a copy of this material and label it '4000psi no shrinkage'. Concrete girders will use this new material, and shrinkage will not be considered. Next, add shrinkage properties to the 4000psi concrete material as follows:
  
  
  • Use "Components Tab > Properties > Materials > select 4000psi material > click the Modify button" to ope the "Material Property Data" form
  • Check the "Switch to Advanced Property Display" checkbox
  • Click the "Modify/Show Material Properties..." button to open "Material Property Data" form
  • Click the "Time Dependent Properties..." button to open "Time Dependent Properties for Concrete" form
  • Under "Time Dependence Considered For" heading, check Shrinkage.

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For both the one-span and the two-span bridge objects, the deformed shape indicates that deck shrinkage causes shortening of deck fibers, and it causes the entire bridge to bow downwards, as expected. This behavior is shown in Figure 3: 

Figure 3 - Shrinkage deflection

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For the one-span bridge, since the structure is statically determinate, no internal forces are generated. However, the two-span bridge is statically indeterminate, and redundant reactions do cause internal moments. At the interior pier, tension is generated in the top fibers, as shown in Figure 4: 

Figure 4 - Shrinkage moment

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