Square pyramid spacial truss models exposed to non-uniform fire temperature fields were improved on the basis of existing research.147 improved models have been built in this paper.With the help of finite element software ANSYS

we calcutated the thermo-mechanical coupling effects.We have simulated the square pyramid spacial trusses mechanical characteristic database at high temperature.We describe the bars constraint action under local fire by studying the relation of change of members’ length and members’ stress process.This paper summarizes the effects of non-uniform fire temperature fields

loading ratio and mesh size on the bars constraint action.The results show that webs at oblique axis of symmetry and nearby are restricted much more than others.For webs at parallel oblique axis of symmetry

added temperature stress is produced.For webs at vertical oblique axis of symmetry

added temperature tensile stress is produced.More non-uniform fire temperature fields and less mesh size produce greater restraint action

but it is nothing to do with load ratio.And under high load ratio

non-uniform fire temperature fields and mesh size have more effect on restraint action.