curve steel box.pdf

Engineering Structures 26 (2004) 721–733 www.elsevier.com/locate/engstruct Behavior of curved steel trapezoidal box-girders during construction Cem Topkaya, Eric B. Willi amson , Karl H. Frank Department of Civil Engineering, The University of Texas at Austin, Austin, TX 78712, USA Received 7 November 2002; received in revised form 12 December 2003; accepted 18 December 2003 Abstract In recent years, steel, trape zoida l box-g irders for curve d highway interc hange s have been used extensiv ely. For these structu ral systems, the majority of the steel girder cross-sectional stresses occur during the concrete pouring sequence. This paper describes a comp rehen sive study on the behavior of curve d girder s durin g const ructi on. Data collec ted for the current research shows signifi- cant differences between the measured and predicted quantities, particularly for later pours. An overview of the steel–concrete interface behavior at early concrete ages and the development of an analytical tool to predict the response of systems with semi- cured concre te are given. Field monitoring of two bridg es durin g constructio n is presented. The measured results were compa red to analytical predictions obtained using software developed specifically under this research to address deficiencies with currently available analytical tools. Accounting for strength and stiffness gained throughout the construction process, the developed software is able to accurately capture girder stresses during construction. # 2004 Elsevier Ltd. All rights reserv ed. Keywords: Bridge; Analysis; Field monitoring; Construction; Pour sequence 1. Introduction Due to advances in fabrication technology, the use of steel, trapezoidal box -gi rde rs for cur ved hig hwa y interchanges has become popular. The rapid erection, long span capability, economics, and aesthetics of these girders make them more favorable than other structural systems. A typical box-girder system consists of one or mor e U-s hap ed ste el gir der s tha t act compos ite ly wi th a cast- in-place conc rete de ck. The compos it e act ion betwe en the ste el gir der and concr ete dec k is achieved through the use of shear studs welded to the top flanges of the girders ( Fig. 1). The maj or structural advantage of the trapez oid al box is its large torsional stiffness. A closed box has a torsional stiffness 100–1000 times greater than a com- parable I-section [1]. Before hardening of the concrete deck, however, the steel box is an open U-section with very low tor sional sti ffne ss and str eng th. To sta bil ize the girders during construction and to increase the torsional stiffness prior to hardening of the deck, internal braces are provid ed. Two diff ere nt typ es of int ernal bracing systems are used. The first type is a permanent, top-late ra l truss sy st em that is used to provide a pseudo-closed section. The second type consists of K or X bra ces tha t control sta bil ity and cross- sec tional distortion (Fig. 1). In addition to internal braces, exter- nal diaphragms, which are typically in the form of tem- porary trusses, are used to minimize distortion between dual or multi-gi rder systems. Ex ternal braces ar e usuall y removed aft er the concre te deck hardens for aesthetics and in order to prevent fatig ue probl ems. Composite box-girde rs with liv e loa din g and the quasi-closed steel box-girders during construction must be evaluated for the design of these bridges. Consider- ing both of these cases, the desi gn for cons tru cti on loa din g is the lea st und erst ood [2] and is the mo st impo rtant. Stresses comin g from const ructio n load ing can reach up to 60–70% of the total stress on a cross- section [3] . In addition, the forces acting on the bracing members dep end almost enti rel y on the constru cti on loads. The des ign for construction loadin g requires the determi nat ion of cor rect cro ss-sectional stresses and member forces. Because curved, trapezoidal box-girder bridges hav e a comple x geomet ry, their ana lys is pre- sent s a gr ea t chal lenge. Several me thods exis t for Correspon ding author. Tel.: +1-512-475 -6175. E-mail address: [email protected] (E.B. Williamson). 0141-0296/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.engstruct.2003.12.012

curve steel box.pdf

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