Non-uniform temperature gradient loading applied to bridge superstructure or other structure may cause that certain regions of the model will expand or contract more that the surrounding regions. The surrounding regions will then effectively provide a restraint and this will generate internal temperature-induced stresses.
When temperature gradient loading is specified as a temperature bridge load for a bridge object, the program creates equivalent temperature distribution (constant uniform temperature and linear temperature gradient) that gets applied through the depth of the bridge deck section. This approach will capture the global response of the model, but not internal stresses resulting from the original non-uniform temperature gradient loading.
If you need to capture the internal stresses, you can manual assign temperature loading base on joint pattern that will represent the true non-uniform temperature gradient. The response will then correctly capture the internal temperature-induced stresses. This approach is illustrated in the attached model and report.