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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5. SEISMIC BEHAVIOUR OF RC COLUMNS EMBEDDING STEEL PROFILES<br />
5.6 Results <strong>of</strong> <strong>the</strong> tests<br />
As said before, <strong>the</strong> specimens belonging to <strong>the</strong> Static category have been<br />
designed only with regard to <strong>the</strong> gravity loads, whereas <strong>the</strong> specimens belonging<br />
to <strong>the</strong> Low Ductility <strong>and</strong> Medium Ductility categories have been designed both<br />
considering <strong>the</strong> gravity loads <strong>and</strong> <strong>the</strong> equivalent horizontal <strong>seismic</strong> loads. The Low<br />
Ductility <strong>and</strong> <strong>the</strong> Medium Ductility categories differ one from <strong>the</strong> o<strong>the</strong>r mainly for <strong>the</strong><br />
magnitude <strong>of</strong> <strong>the</strong> <strong>seismic</strong> forces applied to <strong>the</strong> original RC structure, depending on<br />
<strong>the</strong> grade <strong>of</strong> ductility <strong>the</strong> designers are to attribute to it at <strong>the</strong> design stage.<br />
Consequently, <strong>the</strong> specimens differ on <strong>the</strong> amount <strong>of</strong> longitudinal reinforcement, on<br />
<strong>the</strong> spacing <strong>of</strong> stirrups placed in <strong>the</strong> critical zones <strong>of</strong> <strong>the</strong> main elements <strong>and</strong> on <strong>the</strong><br />
dimensions <strong>of</strong> <strong>the</strong> embedded steel pr<strong>of</strong>iles. For this reason, only an abridgement <strong>of</strong><br />
<strong>the</strong> results obtained from testing is hereafter illustrated along with some<br />
commentaries. The comments can be extended to <strong>the</strong> o<strong>the</strong>r study cases.<br />
The F-∆ curves <strong>of</strong> five specimens belonging to <strong>the</strong> same study case are<br />
represented. In detail, <strong>the</strong> specimens RCT5, COT9-COT10, <strong>and</strong> COT11-COT12 for<br />
<strong>the</strong> medium ductility design case, according to <strong>the</strong> test programme illustrated in<br />
Subsection 5.5.2, have been presented. The test conducted on <strong>the</strong> specimen RC-T<br />
(sample without steel pr<strong>of</strong>ile) is used as test control <strong>and</strong> reference for <strong>the</strong> o<strong>the</strong>r<br />
tests <strong>of</strong> <strong>the</strong> same category. In fact, <strong>the</strong> <strong>behaviour</strong> <strong>of</strong> this specimen relies only on<br />
<strong>the</strong> resistance <strong>and</strong> ductility <strong>of</strong> a reinforced concrete section. The previsions<br />
obtained in <strong>the</strong> design <strong>of</strong> <strong>the</strong> specimens have been confirmed, as <strong>the</strong> tests have<br />
shown that <strong>the</strong> specimen collapse has been caused by failure in <strong>the</strong> joint. The<br />
global <strong>behaviour</strong> for each test will be shown below with some pictures that illustrate<br />
clearly <strong>the</strong> problems occurred in <strong>the</strong> joints during <strong>the</strong> tests.<br />
5.6.1 RCT5 Specimen<br />
The test conducted on specimen RCT5 is used as test control <strong>and</strong> reference for<br />
<strong>the</strong> o<strong>the</strong>r tests <strong>of</strong> <strong>the</strong> same category. As illustrated in Figure 5.30, <strong>the</strong> <strong>behaviour</strong> <strong>of</strong><br />
this specimen relies only on <strong>the</strong> resistance <strong>and</strong> ductility <strong>of</strong> a reinforced concrete<br />
section. Once again, <strong>the</strong> curves above show <strong>the</strong> classical aspects <strong>of</strong> a RC column:<br />
regular stiffness <strong>and</strong> resistance up to a 100÷110mm = 6ey displacement from<br />
which <strong>the</strong> column loses very fast its mechanical properties (from <strong>the</strong> <strong>high</strong>er value<br />
<strong>of</strong> ≈110kN to <strong>the</strong> lower <strong>of</strong> ≈70kN) anticipating <strong>the</strong> final failure at <strong>the</strong> beginning <strong>of</strong><br />
<strong>the</strong> first 8ey cycle. The column collapsed in a brittle way in <strong>the</strong> closeness <strong>of</strong> <strong>the</strong><br />
connection with some cracks <strong>and</strong> spalling <strong>of</strong> <strong>the</strong> concrete at <strong>the</strong> joint panel. The<br />
joint region was ra<strong>the</strong>r deteriorated, as showed in <strong>the</strong> following Figure 5.31.<br />
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