Abstract
Free-form grid spatial structures and facades that follow the envelope surface of a complex-shaped skin, such as the DZ-Bank in Berlin (Frank 0. Gehry), the British Museum in London (Norman Foster), the My Zeil in Frankfurt (Massimiliano Fuksas), have become a very interesting issue in modern architecture. There are several important factors in such single layer lattice dome and complex-shaped spatial structures, for instance, optimal form finding and strong material strength and so forth, but the optimal design and analysis of connection are significant points in free-form spatial structures, because such extraordinary geometries and its continuously changing curvature can be defined by the angles of the connections' geometries, and the stiffness of connection can determine the stability of the whole free-form structure. Therefore, it is very important to recognize that the appropriate analysis and connection design have to be performed, in order to design the reasonable global single layer spatial structure and free-form spatial structures.
General procedures
For the FEA of four connection systems, bending stiffness (My and Mz) and axial force (F) tests were performed. These analyses include the modeling of the bolt assembly, the contact stiffness and the influence of bolt clearances, which were considered using two parameters, such that D..V=0.1 mm and 2.0mm. Due to a specific function of COMBIN39 in ANSYS, the moment-rotation behaviors and load-displacement curves could be transferred to nonlinear spring elements in global grid shells with 25 m and 50 m span that have three different rise-span ratios (0.1, 0.2 and 0.3), to realize the non linear characteristics of the connection systems.
Results
Connection system having two shear planes showed higher stiffness than those with one shear plane. On the other hand, node connectors with one shear plane were not as influenced by differing bolt-holes as those with two shear planes due to shape-of-joint behaviour. Secondly, the low connection stiffness with initial geometrical imperfection easily leads membrane stress to bending stress, so that the critical point of the grid shell occurred with low load failure factor. The influence of bolt clearance depends mainly on the node stiffness and rise-span ratio. The overall structural behavior of an imperfect high-rise grid shell can be very sensitive, displaying a large deviation of bending stiffness due to bolt clearances.
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