Structural analysis of pipe-framed greenhouses using interface elements for cross-over connections

Abstract

Cross-over connections using clamps are commonly employed to join structural members, such as steel pipes, which cross each other. In finite element analyses reported previously, such cross-over joints were usually treated as monolithic nodal points, ignoring the relative displacements between the connected members. This paper presents a new type of interface element to model the semi-rigid behavior of cross-over connections, and discusses its application to the structural analyses of steel pipe-framed greenhouses.The semi-rigid behavior of a joint was captured by six deformation modes of the interface element. The stiffness matrix of the element was formulated by modifying that of a 3-dimensional (3-D) frame element in terms of the stiffness coefficients of the deformation modes. The new element was implemented in the computer program GHModeler which performs finite element modeling of greenhouses constructed with steel pipe frames. The program solves the structural model through a nonlinear plastic hinge analysis, after taking into account the semi-rigid behavior of the cross-over connections. The results of numerical case studies show that using the interface elements changes the collapse mechanism of the structure, causing significant differences in the results of the structural analysis.The structural attributes of an interface element are defined by its stiffness coefficients and yielding limits related to the six deformation modes. They can be evaluated experimentally through load tests. The sensitivity analyses indicate that considering the semi-rigid behavior has a considerable effect on the structural analysis results. Therefore, the use of interface elements is justified even when their attributes are estimated only approximately.