Analysis and modelling of the seismic behaviour of high ... - Ingegneria
Analysis and modelling of the seismic behaviour of high ... - Ingegneria
Analysis and modelling of the seismic behaviour of high ... - Ingegneria
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4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS<br />
116<br />
• Joint panel zones <strong>of</strong>ten develop a maximum strength that is significantly<br />
greater than <strong>the</strong> strength at first yield. This additional strength has been<br />
attributed to strain hardening <strong>and</strong> to contributions <strong>of</strong> <strong>the</strong> column flanges in<br />
resisting panel zone shear forces. Large inelastic panel zone deformations<br />
are typically required in order to develop <strong>the</strong> maximum panel zone<br />
strength.<br />
• Panel zone deformations can add significantly to <strong>the</strong> overall deformation <strong>of</strong><br />
a moment resisting frame, for both elastic <strong>and</strong> inelastic ranges <strong>of</strong><br />
<strong>behaviour</strong>.<br />
• Panel zone stiffness <strong>and</strong> strength can be increased by <strong>the</strong> attachment <strong>of</strong><br />
web doubler plates to <strong>the</strong> column within <strong>the</strong> joint region. The effectiveness<br />
<strong>of</strong> doubler plates is affected by <strong>the</strong> method used to connect <strong>the</strong>m to <strong>the</strong><br />
column.<br />
• In <strong>the</strong> inelastic range, panel zones can exhibit very ductile <strong>behaviour</strong>, both<br />
for monotonic <strong>and</strong> cyclic loading. Experimentally observed hysteresis loops<br />
are typically very stable, even at large inelastic deformations.<br />
Current US building code provisions (AISC, 1997; FEMA 350, 2000) permit <strong>the</strong><br />
formation <strong>of</strong> plastic hinges in <strong>the</strong> panel zones <strong>of</strong> steel moment frames under<br />
earthquake loading. Thus, ra<strong>the</strong>r than forming plastic flexural hinges only in <strong>the</strong><br />
beams or columns, a primary source <strong>of</strong> energy dissipation in a steel moment frame<br />
can be <strong>the</strong> formation <strong>of</strong> plastic shear hinges in <strong>the</strong> panel zones. Consequently, an<br />
accurate analytical model is needed to predict <strong>the</strong> response <strong>of</strong> <strong>the</strong> panel zone in<br />
order to predict accurately <strong>the</strong> response <strong>of</strong> a steel moment frame under earthquake<br />
loading,. The traditional center-to-center line representation <strong>of</strong> <strong>the</strong> frame must be<br />
modified to include panel zone deformation in frame analysis.<br />
Several researchers, including Krawinkler et al. (1971) <strong>and</strong> Wang (1988) proposed<br />
relationships between panel zone shear force V <strong>and</strong> panel zone deformation γ for<br />
monotonic loading. These relationships have been used as <strong>the</strong> basis <strong>of</strong><br />
ma<strong>the</strong>matical models for non-linear rotational springs representing <strong>the</strong> panel zone.<br />
Krawinkler’s V–γ relations have been adopted in several building codes (ICBO,<br />
1997; AISC, 1997) as a basis for computing <strong>the</strong> shear strength <strong>of</strong> panel zones.<br />
However, it was pointed out by Krawinkler that a new model might be needed for<br />
joints with thick column flanges since his V–γ relations were derived from<br />
experimental <strong>and</strong> analytical results for panel zones with relatively thin column<br />
flanges. Wang also showed that Krawinkler’s V–γ relations may overestimate panel<br />
zone shear strength for panel zones with thick column flanges.<br />
The ma<strong>the</strong>matical model for strength <strong>and</strong> stiffness calculations is shown in Figure<br />
4.12. It consists <strong>of</strong> an elastic-perfect plastic shear panel surrounded by rigid