Influence of buckling of longitudinal reinforcement in columns on seismic response of existing reinforced concrete bridges : doctoral thesis

Anžlin, Andrej (author), Isaković, Tatjana (mentor)

Experimental and analytical studies of the influence of buckling in longitudinal reinforcement on the seismic response of existing reinforced-concrete bridge columns were performed. Based on the results of previous tests of typical I-shaped bridge piers, new cyclic tests of rectangular columns were performed. The impact of inappropriate seismic detailing and of the concrete cover on the achieved drifts and load-carrying capacity, as well as on the buckling of bars, were analysed. After the literature review data about 63 experimental tests of RC columns were assembled, in which the collapse of the element was mainly controlled by the buckling of bars. All these tests were included in a newly established ‘buckling’ database. Using the latter, new empirical equation for the estimation of the post-capping stiffness of rectangular columns was introduced. All columns from the ‘buckling’ database were analysed with the existing macro models which are typically used in seismic engineering. It was concluded that, in the case of rectangular RC columns with inadequate seismic detailing, the principal assumptions regarding their behaviour are often not fulfilled. A new procedure for the evaluation of the effect of inappropriate hook angles of the lateral reinforcement and of bar buckling on confinement effectiveness was derived. It is based on the results of numerous detailed FE analyses of concrete columns with different reinforcement detailing configurations. Experimental tests of strengthened RC columns were also performed. At first, the efficiency of the strengthening of a typical I-shaped bridge pier with substandard reinforcement was investigated using CFRP wrap. It was concluded that, due to the unfavourable aspect ratio of the section flanges, conventional strengthening methods are rather ineffective. Improved strengthening of substandard rectangular column was therefore investigated, the column being jacketed with pre-stressed CFRP fibres. In this way the deformation capacity of the columns was increased by more than 70%. The behaviour of the strengthened columns was analysed with similar numerical models as the previously described columns. For RC members of this type some modifications of the existing numerical models were also proposed.

• Language: English
• Keywords: building environment, civil engineering, thesis, buckling of the longitudinal reinforcement, effective confinement, bridge columns, substandard transverse reinforcement, I- shaped columns, rectangular columns, seismic strengthening
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FGG - Faculty of Civil and Geodetic Engineering
• Place of publishing: Ljubljana
• Publisher: [IA. Anžlin]
• Year: 2017
• Number of pages: LXIV, 329 str., [7] pril.
• PID: 20.500.12556/RUL-92515
• UDC: 624.012.45:624.042.7:624.075.2:624.21(043)
• COBISS.SI-ID: 8079713
• Publication date in RUL: 07.06.2017

Secondary language

• Language: Slovenian
• Title: Vpliv uklona vzdolžne armature stebrov na potresni odziv obstoječih armiranobetonskih mostov : doktorska disertacija

Abstract

V okviru disertacije so bile opravljene eksperimentalne in analitične raziskave vpliva uklona vzdolžne armature na potresni odziv armiranobetonskih mostnih stebrov. Na osnovi obstoječih testov tipičnih mostnih stebrov I oblike so bili zasnovani ciklični preizkusi pravokotnih pasnic mostnih stebrov oz. pravokotnih stebrov. Analiziran je bil vpliv neustreznih konstrukcijskih detajlov, vpliv krovne plasti na nosilnost in duktilnost elementov ter na uklon vzdolžne armature. Po pregledu literature so bili zbrani podatki o 63 eksperimentih, v katerih je bil dokumentiran globalni ali lokalni uklon vzdolžne armature. Vsi so bili uvrščeni v novo zgrajeno t.i. `uklonsko' bazo podatkov, s pomočjo katere je bil predlagan tudi analitičen izraz za ocenitev postkritične togosti armirano betonskih stebrov. Vsi stebri iz `uklonske' baze so bili analizirani z obstoječimi inženirskimi modeli, ki se običajno uporabljajo za potresno analizo konstrukcij. Ugotovljeno je bilo, da v stebrih s pomanjkljivimi konstrukcijskimi detajli dostikrat niso izpolnjene temeljne predpostavke teh modelov, zato so bile za primer pravokotnih stebrov predlagane njihove izboljšave. Izpeljan je bil nov postopek za določitev vpliva uklona vzdolžne armature in stremen z neustreznimi konstrukcijskimi detajli na efektivnost objetja jedra betona. V ta namen so bile narejene analize z bolj podrobnimi modeli končnih elementov. Izvedene so bile tudi eksperimentalne raziskave utrjenih stebrov. Najprej je bil ciklično testiran tipičen I mostni steber, ki je bil utrjen s karbonskimi vlakni. Ugotovljeno je bilo, da je zaradi neugodnega razmerja višine in širine prečnega prereza pasnic običajna pasivna utrditev neučinkovita. Zaščitna plast betona se sorazmerno hitro zdrobi in objetje iz karbonskih vlaken postane nefikasno. Na osnovi teh zaključkov je bila zasnovana bolj učinkovita potresna utrditev pravokotnih stebrov. Steber je bil objet s prednapetimi karbonskimi vlakni, odstranjena je bila krovna plast betona, izravnana s slojem epoksidne smole in v največji možni meri so bili zaokroženi robovi prereza. Na ta način je bila povečana deformacijska kapaciteta stebra za več kot 70%. Utrjeni stebri s pomanjkljivimi detajli so bili analizirani s podobnimi numeričnimi modeli kot predhodni stebri.Tudi za primer takih stebrov so bile predlagane primerne spremembe obstoječih numeričnih modelov.

• Keywords: grajeno okolje, gradbeništvo, disertacije, uklon vzdolžne armature, efektivno objetje, mostni stebri, neustrezni konstrukcijski detajli, I stebri, pravokotni stebri, potresna utrditev