Podrobna analiza geometrijskih nepopolnosti na nosilnost vzdolžno ojačanih pločevin

diplomska naloga

Gašper Lužar (Author), Darko Beg (Mentor), Janko Logar (Thesis defence commission member), Marijan Žura (Thesis defence commission member), Klemen Rejec (Co-mentor)

Abstract

Keywords

gradbeništvo;diplomska dela;UNI;jeklene konstrukcije;izbočenje pločevn;geometrijske nepopolnosti pločevin;vzdolžne ojačitve;

Data

Language:	Slovenian
Year of publishing:	2013
Source:	Ljubljana
Typology:	2.11 - Undergraduate Thesis
Organization:	UL FGG - Faculty of Civil and Geodetic Engineering
Publisher:	[G. Rigler]
UDC:	624.014.2(043.2)
COBISS:	6292577
Views:	1932
Downloads:	479
Average score:	0 (0 votes)
Metadata:

Other data

Secondary language:	English
Secondary title:	Detailed analysis of the effects of initial geometric imperfections on longitudinally stiffened plates
Secondary abstract:	The graduate thesis addresses slender longitudinally stiffened steel plates subjected to pure shear and uniform compression respectively. After buckling such plates develop significant post-critical resistance, which is not the case for column buckling. The resistance of slender plates is highly dependent on the amplitude and shape of the initial imperfections. Therefore reliable imperfections should be taken in account when evaluating the resistance of slender plates. The theoretical background and procedures for the design of plated structures are given in SIST EN 1993-1-5 design code. The code recommends the initial imperfection shape and the limit of imperfect plate maximal amplitude, which should be considered in numerical analyses. It is known that such imperfection shapes are not necessarily the worst possible. The present thesis contains an extended study, which deals with seeking the most unfavourable initial imperfection shape for representative stiffened slender plates. The tolerance and technical constraints for slender plates were considered. For this purpose, an advanced optimization method for direct determination of the most unfavourable imperfection of structures developed at the Chair of Steel Structures was utilized. The constraints of the optimization process were represented by maximal allowable imperfection amplitude obtained from SIST EN 1993-1-5 and maximal curvature of the imperfect geometry. The boundaries for the maximal allowable curvature have been developed specifically in the context of the thesis. Pure shear and uniform compression load cases were considered. The influence of the plate aspect ratio, slenderness ratio, number of longitudinal stiffeners and its geometric parameters on the shape of worst initial imperfection was investigated. In the case of plates subjected to uniform compression, the resistances considering the most unfavourable imperfection are up to 10% lower than those obtained by considering the imperfections suggested in the code. In the case of pure shear, the resistances are up to 5% lower. It was also found out, that the worst initial imperfection shape is very similar to the deformation shape of the plate at the limit state.
Secondary keywords:	graduation thesis;civil engineering;steel structures;plate buckling;worst initial imperfections;longitudinal stiffeners;
File type:	application/pdf
Type (COBISS):	Undergraduate thesis
Thesis comment:	Univ. v Ljubljani, Fak. za gradbeništvo in geodezijo
Pages:	XV, 119 str., 2 pril.
Type (ePrints):	thesis
Title (ePrints):	Detailed analysis of the effects of initial geometric imperfections on longitudinally stiffened plates
Keywords (ePrints):	jeklene konstrukcije;izbočenje pločevin;geometrijske nepopolnosti pločevin;vzdolžne ojačitve
Keywords (ePrints, secondary language):	steel structures;plate buckling;worst initial imperfections;longitudinal stiffeners
Abstract (ePrints):	V diplomski nalogi obravnavamo strižno in tlačno obremenjene vitke pločevine, ojačene z vzdolžnimi ojačitvami. Posebnost vitkih pločevin je, da po izbočenju ne izgubijo nosilnosti, ampak izkazujejo veliko post-kritično nosilnost. Vitke pločevine so občutljive na velikost in obliko začetnih nepopolnosti, zato je v računskih analizah pravilna izbira nepopolnosti zelo pomembna. Pravila za dimenzioniranje ojačenih in neojačenih pločevin so zajeta v standardu SIST EN 1993-1-5, ki podaja predlog oblike začetne nepopolnosti in omejitev največje dovoljene amplitude nepopolnosti. Oblike nepolnosti, ki jih priporoča standard, niso nujno najbolj neugodne. Zato je bila v okviru diplomske naloge opravljena obširna študija s katero smo določili najbolj neugodne začetne nepopolnosti ob upoštevanju toleranc in tehnoloških omejitev za tankostenske ojačene pločevine. Pri tem smo uporabili napredno optimizacijsko metodo, ki je bila razvita na Katedri za metalne konstrukcije. Obravnavali smo vitke ojačene pločevine z reprezentativno geometrijo. Upoštevali smo obtežna primera, kjer smo pločevine obremenili v čistem strigu oz. enakomernem tlaku. Pogoja optimizacijskega problema sta bila največja dovoljena amplituda nepopolnosti in ukrivljenost nepopolne geometrije. Vrednost največje amplitude smo povzeli po SIST EN 1993-1-5. Meje za največjo ukrivljenost pa smo opredelili sami. Opazovali smo vpliv razmerja dolžin stranic pločevine, vitkosti pločevin ter števila in togosti vzdolžnih ojačitev na obliko najbolj neugodne začetne nepopolnosti. V primerjavi z oblikami nepopolnosti, ki so predlagane v SIST EN 1993-1-5, dobljene najbolj neugodne oblike nepopolnosti izkazujejo do 10% nižjo nosilnost v primeru obremenitve s čistim strigom oz. do 5% v primeru enakomerne tlačne obremenitve. Ugotovili smo tudi, da so najbolj neugodne oblike nepopolnosti zelo podobne deformacijskim oblikam pri doseženem mejnem stanju nosilnosti.
Abstract (ePrints, secondary language):	The graduate thesis addresses slender longitudinally stiffened steel plates subjected to pure shear and uniform compression respectively. After buckling such plates develop significant post-critical resistance, which is not the case for column buckling. The resistance of slender plates is highly dependent on the amplitude and shape of the initial imperfections. Therefore reliable imperfections should be taken in account when evaluating the resistance of slender plates. The theoretical background and procedures for the design of plated structures are given in SIST EN 1993-1-5 design code. The code recommends the initial imperfection shape and the limit of imperfect plate maximal amplitude, which should be considered in numerical analyses. It is known that such imperfection shapes are not necessarily the worst possible. The present thesis contains an extended study, which deals with seeking the most unfavourable initial imperfection shape for representative stiffened slender plates. The tolerance and technical constraints for slender plates were considered. For this purpose, an advanced optimization method for direct determination of the most unfavourable imperfection of structures developed at the Chair of Steel Structures was utilized. The constraints of the optimization process were represented by maximal allowable imperfection amplitude obtained from SIST EN 1993-1-5 and maximal curvature of the imperfect geometry. The boundaries for the maximal allowable curvature have been developed specifically in the context of the thesis. Pure shear and uniform compression load cases were considered. The influence of the plate aspect ratio, slenderness ratio, number of longitudinal stiffeners and its geometric parameters on the shape of worst initial imperfection was investigated. In the case of plates subjected to uniform compression, the resistances considering the most unfavourable imperfection are up to 10% lower than those obtained by considering the imperfections suggested in the code. In the case of pure shear, the resistances are up to 5% lower. It was also found out, that the worst initial imperfection shape is very similar to the deformation shape of the plate at the limit state.
Keywords (ePrints, secondary language):	steel structures;plate buckling;worst initial imperfections;longitudinal stiffeners
ID:	8312830