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This test problem explains and demonstrates the application of temperature gradient to bridge objects. To summarize the process, temperature gradient is specified and applied to the transformed section, axial force (P) and moment (M3) are calculated, then an equivalent temperature distribution (constant + linear) is applied over the depth.
This process enables the correct calculation of overall crosssectional force and moment. Nodal application of actual temperatures induced by the temperature distribution specified would yield incorrect net fore force and moment without the cross section being finely discretized.
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Procedure
The stress distribution of a temperature gradient is calculated as E α T. Users may analytically solve for axial force (P) by integrating this expression over the section, accounting for the web and flange areas. To solve for M3, integrate the moment of stresses about the neutral axis.
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A singlespan concretebox bridge, fixed at both abutments, is created using the bridge modeler. The linked bridge object is updated as a solid model. Loading from temperature gradient is defined as shown in Figure 1:
As mentioned earlier, an equivalent constant + linear temperature gradient generates the temperature load for a solid model. This procedure correlates precisely with the attached hand calculations , as shown in Figure 2:
For bridge response, loading from the temperature gradient induces a moment of 2568 kipft, which closely correlates with the hand calculated moment of 2669 kipft. Software output is shown in Figure 3:
Example 2: Single frameelement model
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For example 2, a single, beam frame element is fixed at both ends and manually loaded with the constant + linear temperature gradient. Element cross section is defined to match those properties of the entire bridge deck section from example 1. The temperaturegradient loading creates a moment of 2668 kipft, nearly identical to the handcalculated moment of 2669 kipft. Software output is shown in Figure 4:
Attachments
 SAP2000 V14.0.0 models (zipped .SDB files) – Example 1: Bridgemodeler model, Example 2: Single frameelement model
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