Pre Version 4.0

Previously, Eriksson Wall would use the equations in the PCI Design Handbook 5.9.5, shown below.

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This equation was used to compute the thermal bow at midspan. With this, the software would assume a deflected panel shape which would give the provided maximum at midspan. For a restrained thermal analysis, the supports would then be pulled back to have 0 deflection. The FEM model would be setup with the thermal bow built into the coordinates of the nodes. Then any node where a restraint existed would have a boundary condition such that it would be pulled back to 0”, instead of being allowed to thermally deflect. This worked okay for simple jobs, but struggled handling solid zones in IWPs, panel stacks, and moment releases.

Post Version 4.0

To address the issues with the previous method, thermal bowing is now handled by applying curvature directly to the panel in the FEM analysis. Because this is added as an applied load, it supports variable member thickness, end blocks, moment releases, and panel stacks. For a simple system, both methods give the same results. Following the guidance given in 5.9.5 of the PCI Design Handbook, the applied curvature is increased for insulated panels using the percent composite methodology.

Thermal Restraints

The thermal analysis runs prior to the final analysis and it’s results are treated as initial conditions for the final in-place analysis. The user now has control over what restraints are active for the thermal analysis. At times the engineer may decide a restraint is not able to resist the load applied by the thermal analysis. If this is the case, the engineer can uncheck the box in the restraint grid corresponding to the given restraint.

Thermal Elasticity Multiplier

Eriksson Wall also asks for the thermal elasticity multiplier. These values come from the PCI Design Handbook Design Aid 5.16.2 and are given as 0.75 for daily temperature change and 0.5 for season temperature change. Note that reducing the elastic modulus does not change the amount of thermal bow on the panel, but reduces the amount of energy required to resist the thermal bowing.

Seasonal Effects

It has been observed that for certain panels the thermal gradient can reduce the demand at a given location. For example, for a building that is hotter on the exterior of the building, the moment diagram is the same shape as the suction wind case. For this case, when checking the pressure case it is often conservative to ignore thermal. Because of this, the engineer may want to consider both the winter and summer thermal gradients when determining the controlling case.