The top space frame can be assumed to have infinite stiffness in its own plane, functioning like rigid floor slabs that connect columns into a whole. However, it doesn’t provide lateral stiffness for the structure. The space frame’s role is to link the columns, collectively providing lateral stiffness, which is the sum of each column’s lateral stiffness.
The impact of the space frame on cantilevered columns includes axial forces, shear forces, and bending moments at the column tops. Normally, the space frame’s supports don’t consider bending moments, and axial forces are not within this discussion’s scope. So, let’s focus on shear forces. Stiffness issues are transformed into displacements, and the support’s shear forces at the column top are borne by the reaction generated by column top displacements (except for sliding hinge supports). With shear forces, one can determine the column’s drift displacement, eliminating the need to address equivalent stiffness issues, simplifying the overall modeling.
Due to its efficiency, low steel usage, light foundation loads, and aesthetic appearance, space frame steel structures are typically made using regular pipes, stainless steel pipes, plastic-coated pipes, and other materials. These structures come in various shapes, sizes, and formats, making them a popular choice in large sports arenas, office buildings, transportation hubs, shopping centers, and other applications.
The cross-sectional dimensions of space frame steel structure members should be determined based on strength and stability calculations. To increase the stability of compression members and reduce the calculation length, measures like intermediate struts and bracing struts can be added. Joints for plate-type space frame and double-layer shell space frame made of steel typically take three forms: cross-plate joints, welded hollow sphere joints, and bolted sphere joints.
Simplified calculation methods, such as cross-beam differential analysis and pseudoplate methods, can be used for internal force and displacement calculations in space frames. Single-layer shell space frame joints are generally assumed to be fully fixed and calculated using the finite element method for fully fixed bar systems. Double-layer shell space frames can be calculated using the finite element method for hinged bar systems. Both single and double-layer shell space frames can also utilize the pseudoshell method for simplified calculations.