Earthquake testing and response analysis of concentrically-braced sub-frames

Abstract

The results of shake table tests on three concentrically-braced sub-frames are compared with a series of correlative inelastic analyses. Both transient time-history and nonlinear static (pushover) analyses are considered. The lateral resistance of the test frames is provided by a pair of coldformed tubular steel members. The brace cross-section is varied between tests to investigate the influence of brace slenderness on the stiffness, resistance and ductility displayed by the frame under strong earthquake loading. Response simulations using a two-dimensional analytical model of the test frame are compared with the experimental results. Brace strengths and elastic test frame properties established in complementary static tensile tests and low-level shake table tests, respectively, are used to determine model input data. The transient acceleration and displacement response of the frames calculated in nonlinear time-history analyses are compared with corresponding experimental measurements. The base shear-frame drift relationship is calculated using pushover analyses that consider either the resistance of both frame braces or the tension brace alone. These are compared with the experimental hysteretic response of the test frame. On the whole, the analytical results are observed to agree well with the experimental results, especially with respect to brace tension forces and frame base shear. Cases where the experimental and analytical responses deviate are identified and the implications for earthquake response assessment and design are discussed.

Assessment of European seismic design procedures for steel framed structures

“…The discrepancy between the actual and characteristic material strength coupled with strain hardening and strain rate effects have a direct influence on the actual tensile strength of bracing members, as observed in recent cyclic and shake table tests Goggins et al 2006;Elghazouli et al 2005;Broderick et al 2008). These effects are largely covered by the material over-strength parameters incorporated in EC8 (i.e.…”

“…Maison and Popov 1980;Popov and Black 1981;Ikeda and Mahin 1986;Goel and El-Tayem 1986) focusing mainly on the response under idealised cyclic loading conditions. A recent collaborative European project (Elghazouli 2003;Broderick et al 2005;Goggins et al 2006;Elghazouli et al 2005;Broderick et al 2008) also examined the performance of bracing members through analytical studies which were supported by monotonic and cyclic quasi-static axial tests as well as dynamic shake table tests. These investigations have provided an insight into the actual performance characteristics of bracing members and their influence on the overall structural behaviour.…”

Rigid‐plastic models for the seismic design and assessment of steel framed structures

“…Several models have been proposed to estimate the cyclic response of bracing members [11,12,13,14]. Nevertheless such models require detailed input (e.g.…”

“…Furthermore, the model assumes that the system is not able to sustain any load reversal until the load carrying capacity is recovered by tension action in the alternate brace, hence introducing effectively a slip-like behaviour. The adopted idealisation ignores the contribution of the braces in compression which in principle is acceptable for slender braces noting that the brace will buckle at a relatively early stage in the response history [11,15]. Where necessary, for bracing members with relatively low slenderness, an alternative model proposed in the next section can be used in order to take into account the contribution of the compression resistance of the bracing members.…”

Performance-based plastic design method for steel concentric braced frames

“…According to some researches in the last two decades or so, current seismic codes (AISC 2005) include provisions to design ductile concentrically braced frames which are known as special concentrically braced frames (SCBFs). Many researchers have shown that SCBFs designed by conventional elastic design method suffered severe damage or even collapse under design level ground motion (MacRae et al 2004;Broderick et al 2008;Richards 2009;Roeder et al 2011). It is well recognized that current codes are based on elastic structural behavior and account for the inelastic behavior indirectly.…”