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
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
5. SEISMIC BEHAVIOUR OF RC COLUMNS EMBEDDING STEEL PROFILES<br />
Elastic <strong>and</strong> inelastic convergence studies have been conducted to evaluate <strong>and</strong><br />
arrive at <strong>the</strong> final mesh for <strong>the</strong> finite element models. The finite element model was<br />
verified by comparing <strong>the</strong> measured cyclic response <strong>of</strong> specimen with <strong>the</strong> predicted<br />
monotonic (see Figure 5.40). As far as concerns <strong>the</strong> cyclic test, <strong>the</strong> envelope curve<br />
<strong>of</strong> <strong>the</strong> experimental tests was found <strong>and</strong> compared to <strong>the</strong> curve found using <strong>the</strong><br />
finite element model. Even if <strong>the</strong> model is not able to capture <strong>the</strong> loss <strong>of</strong> resistance<br />
<strong>and</strong> stiffness due to <strong>the</strong> crushing <strong>of</strong> <strong>the</strong> concrete after a certain level <strong>of</strong> <strong>the</strong><br />
imposed displacement, <strong>the</strong> experimental data are in good agreement with <strong>the</strong><br />
numerical simulation. The elaboration <strong>of</strong> <strong>the</strong> numerical evidences has led to <strong>the</strong><br />
modification <strong>of</strong> some geometrical <strong>and</strong> mechanical parameters related to <strong>the</strong><br />
formulae <strong>and</strong> it has permitted to better figure out <strong>the</strong> experimental response <strong>of</strong> <strong>the</strong><br />
joint subjected to shear loading. Also <strong>the</strong> measurements obtained from <strong>the</strong> local<br />
instrumentation by means <strong>of</strong> strain gauges helped in <strong>the</strong> underst<strong>and</strong>ing <strong>of</strong> <strong>the</strong><br />
activation <strong>and</strong> evolution <strong>of</strong> <strong>the</strong> resistance mechanisms, proposed in Section 5.4,<br />
while testing.<br />
5.7.2 Steel web panel shear mechanism verification<br />
By means <strong>of</strong> a set <strong>of</strong> elements extracted in <strong>the</strong> web panel zone <strong>of</strong> <strong>the</strong> steel pr<strong>of</strong>ile,<br />
it was possible to monitor <strong>the</strong> evolution <strong>of</strong> <strong>the</strong> shear stress σ13 at <strong>the</strong> increasing <strong>of</strong><br />
<strong>the</strong> imposed top displacement. As depicted in <strong>the</strong> following Table 5.16, <strong>and</strong> as<br />
expected, <strong>the</strong> stress state <strong>of</strong> web panel increases during <strong>the</strong> test until it yields<br />
uniformly for a top displacement equal to 6ey. From this point <strong>the</strong> concentration <strong>of</strong><br />
<strong>the</strong> stresses moves in <strong>the</strong> four corners <strong>of</strong> <strong>the</strong> steel web panel, where <strong>the</strong> stiffeners<br />
are welded. In this moment <strong>the</strong> resistance <strong>of</strong> <strong>the</strong> panel zone in <strong>the</strong> steel pr<strong>of</strong>ile is<br />
given to <strong>the</strong> contribution <strong>of</strong> four plastic hinges that have been formed.<br />
This hypo<strong>the</strong>sis results confirmed analysing <strong>the</strong> experimental results obtained from<br />
<strong>the</strong> strain gauges positioned in <strong>the</strong> web <strong>and</strong> in <strong>the</strong> flange <strong>of</strong> <strong>the</strong> steel pr<strong>of</strong>ile in<br />
correspondence <strong>of</strong> <strong>the</strong> stiffeners. The graphs below, deduced from <strong>the</strong><br />
experimental data (strain gauges), give explanation <strong>of</strong> <strong>the</strong> shear mechanisms<br />
activated in <strong>the</strong> steel web, steel flanges <strong>and</strong> stiffeners. To obtain <strong>the</strong> shear strain<br />
by <strong>the</strong> measurement <strong>the</strong> hypo<strong>the</strong>sis that <strong>the</strong> principal stress σ1 <strong>and</strong> σ3 are aligned<br />
with <strong>the</strong> axes <strong>of</strong> <strong>the</strong> steel column is made. As depicted in Figure 5.41, <strong>the</strong><br />
measured web strain increases uniformly up to a displacement equal to 4ey÷6ey<br />
when it exceeds <strong>the</strong> steel yield strain. It is <strong>the</strong> central zone <strong>of</strong> <strong>the</strong> panel that<br />
deforms most. It can be imagined <strong>the</strong> web stresses increasing during <strong>the</strong> test until<br />
<strong>the</strong> panel zone yields uniformly for a top displacement equal to 6ey. From this point<br />
on, concentration <strong>of</strong> stresses shifts to <strong>the</strong> four corners <strong>of</strong> <strong>the</strong> steel web panel in<br />
correspondence <strong>of</strong> <strong>the</strong> stiffeners, <strong>and</strong> <strong>the</strong> resistance <strong>of</strong> <strong>the</strong> panel zone is given by<br />
<strong>the</strong> contribution <strong>of</strong> <strong>the</strong>se four local plastic hinges.<br />
232