Compression Behavior of Square Pyramid Substructure of Novel Pultruded FRP-Aluminum Space Truss

To realize lightweight and corrosion resistance, a novel hybrid pultruded fiber-reinforced polymer (PFRP)-aluminum space truss system is proposed, which adopts the pretightened teeth connections (PTTCs) and aluminum-bolt-ball connecting system (ABCS). The diagonal and chord members of the system are joined by the ABCSs to form a free-form space truss. To identify possible failure modes, reveal the bearing mechanism, and investigate suitable design methods, compression experiments were separately conducted on two square pyramid substructures. Two loading scenarios were designed for the compression experiments, with top ball rotation unconstrained and constrained denoted as loading scenarios 1 and 2, respectively. Different failure modes, load-strain, and load-displacement responses were recorded. The joint instability phenomenon occurred in loading scenario 1, resulting in the bending failure of the ABCSs around the top ball. Buckling induced splitting failure of the PFRP tube occurred in loading scenario 2. In addition, the pyramid substructure was numerically modeled by a series of line elements and this model could accurately and directly predict the nonlinear compression behavior of the square pyramid substructure. Finally, a direct second-order analysis was recommended for the design of PFRP space truss structures, which could avoid the difficulty in determining the effective length factor and yield a more accurate and reliable structural design. (C) 2020 American Society of Civil Engineers.