A theory for space frames with warping restraint at nodes

Large-span bar structures are used extensively in different areas of engineering. In civil construction their potential for freedom of form over long spans makes them architecturally attractive. From the engineering point of view, they have such properties as lightness, high rigidity and rapid erection. This makes them highly advantageous for various space applications – complex orbital structures, large-span roofs for missions on the Moon and planets of the Solar system, as well as for building of terrestrial infrastructure. The analysis of single structural members for combined stretching, flexure and torsion shows that warping restraint at nodes can lead to torsional moments exceeding the moments due to uniform torsion. Conventional design of space frames with symmetrical closed sections and flexible nodes does not account for warping restraint at the nodes. It is, however, not evident that warping effects can be ignored in novel space frame designs with unsymmetrical thin-walled sections and stiff nodes. Conventional frame analysis using the displacement and rotation coordinates as nodal variables does not account for warping stiffness. The kinematical coordinate axes of the members, using the shear center as origin and the principal axes for bending, do not pass through the nodes of the frame. This impedes corrections of the computed results to account for warping effects. A space frame theory is presented, which can be used as the basis for the implementation of an analysis platform for the first order linear analysis of space frames with significant warping restraint at their nodes. © 2020, Univelt Inc. All rights reserved.