Keywords: nonlinear analysis, single-layer structures, reticulated shells, joint-rigidity, rise-span ratio, wind loads.

The interest in single-layer reticulated shells has grown significantly in recent decades as a result of the development of new joint system designs [1]. This paper is focused on the improvements achieved by the use of semi-rigid joints, and includes an analysis of the different behaviour of single-layer structures when some parameters are changed. A total of 36 structures were numerically analyzed. They were divided into three groups according to their different mesh density. In each mesh density group, structures of four different rise-span ratios were analyzed: 1/10, 1/5, 3/10 and 2/5. The shape of the structures was derived from the hanging-net method. Finally, for each geometric configuration, three different joint rigidities were investigated: a pinned joint and two semi-rigid joints with different values of joint rigidity. Those values were taken from previous experimental tests conducted by the authors and were such that the joints would be classified as nominally-pinned using Eurocode 3 [2].

The results of the analyses for the pinned structures demonstrated that, although the percentage of the supported load was important for the highest structures, they were not able to support 100% of the design loads. On the contrary, the behaviour of the semi-rigidly jointed structures was quite the opposite: there was hardly any difference between the results of the linear and nonlinear analyses and the influence of the value of joint rigidity was almost insignificant. Some exceptions to these statements were some of the shallowest structures. Therefore, it can be concluded that the fact that the joints have some rigidity, even though the value of it is small, produces an important improvement in the capacity of the structure.

Some conclusions may be drawn regarding the influence of mesh-density. For the mesh with the largest number of members, poor performance was found, as expected, due to the decrease in the angle sustained between members. However, the influence of the lack of symmetry in the load cases decreases when comparing the denser structures to the ones with fewer members. The fact that the surface is divided into more facets is possibly followed by a more homogeneous distribution of internal forces. This partition is likely to be of particular relevance when considering the wind loads and in all probability explains the distinct behaviour of the structure with larger members under asymmetric load cases.

1

Z.S. Makowski, "Development of Jointing Systems for Modular Prefabricated Steel Space Structures", Lightweight Structures in Civil Engineering, Proceedings of the IASS International Symposium, Warsaw, Poland, 17-41, 2002.

2

EN 1993-1-8, "Eurocode 3: Design of steel structures. Part 1-8: Design of joints", 2005.

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