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 />
For <strong>the</strong>se conditions, S = 1.0 <strong>and</strong> <strong>the</strong> reference periods TB, TC, <strong>and</strong> TD are<br />
respectively equal to 0.05 s, 0.25 s, <strong>and</strong> 1.2 s. The period T1 for <strong>the</strong> structure was<br />
calculated with <strong>the</strong> formula: T1 = 0.05·H 0.75 , with H = 7.5 m (total structure height),<br />
giving T1 = 0.22 s. The value <strong>of</strong> Sd (0.22 s) = 0.167.<br />
The <strong>seismic</strong> weight at each level includes <strong>the</strong> total gravity loads <strong>and</strong> <strong>the</strong> following<br />
fraction <strong>of</strong> <strong>the</strong> imposed live load: 48% at <strong>the</strong> first level (φ= 0.8, ψ2i = 0.6) <strong>and</strong> 60%<br />
at <strong>the</strong> second level ((φ= 1.0, ψ2i = 0.6). The resulting total <strong>seismic</strong> weight, W,<br />
including <strong>the</strong> weight <strong>of</strong> <strong>the</strong> structural members is given in Table 4.1. In this<br />
calculation, <strong>the</strong> weight <strong>of</strong> a 3.5 m <strong>and</strong> a 1.75 m long column segments were<br />
applied respectively at <strong>the</strong> first <strong>and</strong> second levels. Assuming rigid diaphragm<br />
response, <strong>the</strong> <strong>seismic</strong> weight was divided equally between <strong>the</strong> 5 moment resisting<br />
frames, resulting in W = 552 kN/frame. The parameter in Eq. (4.2) is equal to<br />
0.85 because T1 < 2 TC. Substituting <strong>the</strong>se values, <strong>the</strong> base shear, Fb, is equal to<br />
78.2 kN per frame. In Table 4.1, <strong>the</strong> base shear force was distributed at each level<br />
using Eq. (4.1) <strong>and</strong> assuming mi = Wi/g.<br />
Level<br />
z<br />
(m)<br />
wd<br />
(kPa)<br />
ψewL<br />
(kPa)<br />
TOTAL W<br />
(KN)<br />
W / Frame<br />
(kN)<br />
F / Frame<br />
(kN)<br />
2 7.0 3.94 3.00 1398 280 52.6<br />
1 3.5 3.94 2.40 1361 272 25.6<br />
2759 552 78.2<br />
Table 4.1. Calculation <strong>of</strong> <strong>the</strong> <strong>seismic</strong> weights <strong>and</strong> <strong>seismic</strong> loads (torsion excluded)<br />
The design was performed only for one <strong>of</strong> <strong>the</strong> interior moment resisting frames.<br />
Accidental torsion was included in <strong>the</strong> design <strong>and</strong> <strong>the</strong> most critical frames are<br />
those located at 3.0 m from <strong>the</strong> center <strong>of</strong> <strong>the</strong> structure. For <strong>the</strong>se frames, an<br />
amplification factor, , equal to 1.15 (= 1.0 + 0.6·3.0/12.0) was used. Therefore, <strong>the</strong><br />
final <strong>seismic</strong> loads were: 60.5 kN <strong>and</strong> 29.4 kN at levels 1 <strong>and</strong> 2 with a total base<br />
shear <strong>of</strong> 89.9 kN. In <strong>the</strong> design <strong>of</strong> <strong>the</strong> frames, <strong>the</strong>se loads were combined with <strong>the</strong><br />
total gravity dead load <strong>and</strong> 60% <strong>of</strong> <strong>the</strong> imposed live loads.<br />
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