Dynamic experimental study on anti-progressive collapse of polyline-shaped large-span double-layer grid space structure

This study investigates the dynamic response and failure mechanism of the polyline-shaped large-span double-layer grid space structures subjected to progressive collapse. A grid model was designed and fabricated to represent a typical area of a large-span double-layer grid space structure from a specific engineering project. Three representative locations were selected to simulate failure of the test model, and dynamic collapse tests were conducted. In the tests, four conditions were considered: D1 (120 kg, failure at A), D2 (120 kg, failure at B), D3 (120 kg, failure at C), and D4 (200 kg, failure at C). The dynamic response of the structure under various conditions was studied by comparing strain, displacement, and failure patterns derived from the test analysis. Furthermore, the collapse process and mechanism of the structure were analyzed. The results indicate that the upper chord rods are key components in collapse resistance design. Under test conditions D4, significant vertical displacement occurred, and out-of-plane deformation increased markedly after the lateral constraints were removed, causing the structure to tilt towards the side without a failure device. The strain and displacement changes were most significant under test conditions D3 and D4, especially near the failure locations. Under condition D3, the strain change is 1109 microstrain larger than that before the failure, with the maximum vertical displacement increase being 59.109 mm. Under condition D4, the strain change is -1126 microstrain larger than that before the failure, with the maximum vertical displacement increase being 74.795 mm. Through multi-condition testing, the collapse mechanisms at different failure locations in the structure were clarified. The failure of web members and lower chord rods led to a redistribution of internal forces, but the effect on the double-layer grid structure was minimal. After the failure of the upper chord rods, significant displacements occurred near the failure location, and buckling of surrounding members was observed.