Strength and Stability of Structures with Nodes Flexible in Terms of Shift

Abstract

Abstract Distribution of internal forces in bar structures in relation to rotational flexibility of their nodes is widely discussed in the literature. However, the investigations concerning such structures with nodes flexible in terms of shift are less frequent. This paper presents examples of structures, in which the shift flexibility of lap joints determined their load-bearing capacity and stability, as well as the serviceability limit states. A low-rise dome, a covering of the exhibition hall in Chorzów, which collapsed in 2006, and a mobile telephony tower were depicted. Mechanical models describing rotational stiffness and shift flexibility of various lap joints by means of component method were used. Mathematical model by Kishi and Chen was applied to model the susceptibility of lap joints under alternating loads. In case of the low-rise dome, the results indicated that the failure was determined by joint clearances. In case of covering of the exhibition hall in Chorzów, flexibility of joints resulted in excessive utilization of resistance in certain lattice purlins, which could have initiated the disaster. In turn, flexibility of connections rarely considered in the design of mobile phone towers may result in an excessive sway of the tower legs on which the antennas of the radio link are suspended and thus interfere transmitted signals. The study showed that there is a need to take into account the influence of flexible nodes, not only in the structures sensible to deformations like low-rise domes, but also in the other structures, like mobile phone towers, in which their serviceability limit state is decisive.