ABSTRACT
Abstract In this paper the experimental behaviour of top-and-seat angle connections under cyclic reversal loading is examined in order to improve the state of knowledge related both to the main parameters affecting the cyclic response and to the dissipation capabilities of the energy associated to cyclic loads. In particular, the effect of bolt slippage, which increases to a large extent the joint flexibility, is quantitatively evaluated. On the basis of standard codes for steel design some practical indications are also given to reduce such effect. Finally, a numerical model, based on a pure mechanical approach, is used for simulating the joint behaviour. Keywords: Semirigid Connections, Cyclic Response, Bolt Slippage, Mechanical Model
1 Introduction
The behaviour of semirigid connections represents a subject of extensive discussion within the fields of research in constructional steel design. It is now agreed that any connection has to be considered as semirigid and therefore the appropriate values of stiffness, ultimate moment capacity and ultimate rotation have to be assumed within the analysis of a semicontinuous frame. The studies are now being more and more specialized since each form of connection (header plates, flush-end-plate, extended-end-plate, top-and-seat angle, web angle, etc.) deserves specific studies devoted both to the experimental behaviour and to the analytical simulation. During past years, numerous tests have been conducted to study the monotonic flexural response of semirigid connections (Nethercot 1985; Goverdan 1983), whereas only few cyclic tests have been performed in order to achieve better understanding of their behaviour under earthquake type loadings. Among the latter test programs, it is worth mentioning a series of cyclic tests conducted by Ballio et al. (1987) on flange plates connections, flange and web cleated connections, extended-end-plate connections and welded connections. This study evidenced the influence of column web stiffeners on the connection behaviour and the large bolt slippage phenomena, which affect to a large extent the shape of the experimental loops. Azizinamini et al. (1989) investigated the response of top-and-seat connections with double web angle. Different types of loading sequences were applied: low-to-high amplitude, high-to-low amplitude and constant amplitude loading histories were considered. Furthermore, geometry of angles and bolts was varied to identify how joint properties and behaviour were affected. Astaneh et al. (1989) examined hysteresis moment-rotation behaviour of double angle connections subjected to earthquake type loadings, focusing on performances in terms of ductility and capacity for energy dissipation.
558 Bernuzzi, de Stefano, d 'Amore, de Luca and Zandonini Bernuzzi et al. (1991) have tested top-and-seat angle (TSC) and flush-end-plate (FPC) connections under cyclic loadings, evidencing the influence of the loading history (Bernuzzi 1992) and of the connection details (Bernuzzi et al. 1992). In this paper the response of TSC connections (Figure 1) is analyzed with respect to their experimental behaviour and to the possibility of implementing a mechanical model capable to simulate the cyclic response. Test behaviour has been examined in order to improve the state of knowledge related both to the main physical phenomena affecting the cyclic response and to the dissipation capabilities of the energy associated to cyclic loads. In particular, a special attention has been paid to evaluate effects of bolt slippage, that appears to increase to a large extent the joint flexibility. On the basis of the experimental response, some guide-lines are provided for reducing slip through a 'slip capacity design'.
