Experimental Testing and Numerical Modeling of Slender Reinforced Concrete Columns under Seismic Conditions : Doctoral Thesis

Abstract

U radu su prikazani rezultati eksperimentalnog ispitivanja armiranobetonskih stupova izloženih dinamičkom opterećenju. Istraženi su utjecaji različitih parametara na granično stanje nosivosti i deformabilnosti stupova uslijed potresa. Ispitano je sedam grupa stupova, kod čega je u svakoj grupi istraživan pojedini utjecajni parametar. Naime istražen je utjecaj različitog tipa pobude, utjecaj temeljnog tla (kao potencijalnog seizmičkog izolatora), utjecaj veličine temelja, utjecaj rubnih uvjeta (način oslanjanja temelja), utjecaj vitkosti (visine) stupa, utjecaj uzdužne armature, utjecaj poprečne armature, utjecaj mase na stupu te utjecaj ekscentriciteta mase. Za svaki od promatranih parametara ispitivano je tri do pet stupova. Eksperimenti su provedeni u Laboratoriju za seizmička ispitivanja (STC) u Žrnovnici pored Splita, pomoću potresne platforme. Svaki stup iz pojedine grupe izložen je setu pobuda, uz sukcesivno maksimalne ordinate akcelerograma. Stupovi su izloženi horizontalnom (jedno-komponentnom) ubrzanju platforme. Pobude su nanošene sukcesivno, pri čemu su ordinate akcelerograma linearno povećavane uz prirast maksimalne ordinate akcelerograma za po 0.05 g, sve do sloma stupa ili gubitka njegove stabilnosti. Korišteni su umjetni akcelerogrami potresa kreirani pomoću računalnog programa SIMQKE, za projektni elastični spektar odgovora prema EN 1998 tip 1 i tip tla A. Osim umjetnih akcelerograma, korišteni su akcelerogrami potresa Ston (1996), potresa Banja Luka (1982), potresa Monte Negro-Petrovac (1979) i harmonijska pobuda. Za svaku dinamičku pobudu (gmax=n×0.05 g; n=1,2,3…8) mjereni su karakteristični pomaci i ubrzanja konstrukcije te deformacije u betonu i deformacije klasične armature u karakterističnim točkama, te je praćeno stanje pukotina u stupu sve do dostizanja njegove granične nosivosti. Osim provedbe eksperimentalnih istraživanja, izvršeno je poboljšanje prethodno razvijenog numeričkog modela za nelinearnu statičku i dinamičku analizu konstrukcija. Valjanost numeričkog modela je testirana na rezultatima provedenih eksperimentalnih ispitivanja.This dissertation presents the results of experimental tests of slender reinforced concrete columns exposed to dynamic loads. The effects of various parameters on the ultimate bearing capacity and deformation of the columns under earthquake have been investigated. Seven groups of columns were tested, whereby certain influentialparameter was considered in each group. Namely, the influence of different types of excitation, the influence of foundation soil types (as potential seismic isolators), the influence of foundation layout size, the influence of boundary conditions (the manner of foundation placement), the influence of slenderness (height) of a column, the influence of longitudinal reinforcement, the influence of transverse reinforcement, the influence of different mass at the top of columns and the influence of mass eccentricity were considered. Three to five columns were tested for each of the considered parameters. A shake table at the Laboratory for seismic testing(STC) in Žrnovnica near Split was used for experimental testing. Each column in a particular group was exposed to a set of excitations, where maximal amplitudes of acceleration were successively increased. The columns were exposed to horizontal (one-component) excitations. The excitations were applied successively, with the increase of the maximum amplitude of 0.05 g until the collapse of the columns or their loss of stability. Artificial accelerograms compatible with the design elastic response spectrum according to EN 1998 Type 1 and soil Type A were used as excitations, generated with the SIMQKE software. Besides the artificial excitations, accelerograms of the earthquake Ston (1996), earthquake Banja Luka (1982), earthquake Monte Negro (earthquake Petrovac) (1979) and harmonic excitation were also used. Characteristic displacements and accelerations of the column, as well as concrete and reinforcement strains at specific points were measured for each applied dynamic excitation (gmax= n×0.05 g; n = 1, 2, 3, ... , 8). Also, states ofcracks (damages) in the column until reaching its critical load were monitored. The dissertation also presents the improvements of a previously developed numerical model for nonlinear static and dynamic analysis of structures. The validity of the numerical model has been verified by the results of experimental tests