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Stiffness Requirement for Flat-Bar Longitudinal Stiffener of Box-Girder Compression Flanges
Do Dai Thang,구민세,정영도,Asif Hameed 한국강구조학회 2009 International Journal of Steel Structures Vol.9 No.2
In this paper, the moment of inertia requirement of flat-bar longitudinal stiffener of bottom flange in steel box girder is investigated through finite element modeling. The required minimum stiffness for longitudinal stiffeners of box girder flange is given in the AASHTO LRFD Bridge Design Specification and is modified by Yoo. However, this requirement is adopted for T-shape stiffeners. Here, the effect of important parameters on the minimum required moment of inertia of flat-bar stiffener is numerically investigated by examining the anti-symmetric mode of buckling. This study presents the results that are based on 3D finite-element analysis of four hundred hypothetical compression flange models stiffened by varying numbers of flatbar longitudinal stiffeners with realistic dimensions such as the height of stiffener, the thickness of the compression flange, the number of longitudinal stiffeners and the aspect ratio of plate panel. A new proposed equation for required minimum stiffness of the flat-bar longitudinal stiffeners is derived from nonlinear regression analyses. Beside that the study has taken into account the effect of boundary conditions and the effect of inelastic transition on the critical buckling stress of compression flange. Through the evaluation of a design example, the validity and reliability of the new proposed equation is demonstrated. In this paper, the moment of inertia requirement of flat-bar longitudinal stiffener of bottom flange in steel box girder is investigated through finite element modeling. The required minimum stiffness for longitudinal stiffeners of box girder flange is given in the AASHTO LRFD Bridge Design Specification and is modified by Yoo. However, this requirement is adopted for T-shape stiffeners. Here, the effect of important parameters on the minimum required moment of inertia of flat-bar stiffener is numerically investigated by examining the anti-symmetric mode of buckling. This study presents the results that are based on 3D finite-element analysis of four hundred hypothetical compression flange models stiffened by varying numbers of flatbar longitudinal stiffeners with realistic dimensions such as the height of stiffener, the thickness of the compression flange, the number of longitudinal stiffeners and the aspect ratio of plate panel. A new proposed equation for required minimum stiffness of the flat-bar longitudinal stiffeners is derived from nonlinear regression analyses. Beside that the study has taken into account the effect of boundary conditions and the effect of inelastic transition on the critical buckling stress of compression flange. Through the evaluation of a design example, the validity and reliability of the new proposed equation is demonstrated.
Optimum Cost Design of Steel Box-Girder by Varying Plate Thickness
Do-Dai Thang,구민세,Asif Hameed 대한토목학회 2009 KSCE JOURNAL OF CIVIL ENGINEERING Vol.13 No.1
In recent years, steel box-girders have been used extensively and especially for long span due to its high torsional rigidity and rapid erection. In order to decrease the amount of costly steel material, the variations in thickness of web, top flange and bottom flange are always considered in cross sectional design. This design depends on the notable changing of the moment distribution along the length. Variation in plate thicknesses may represent a girder with the least weight; however, this may not be the most economical girder due to the increase in fabrication costs, which are associated with excessive variations in plate thicknesses. A parametric study is carried out to determine the optimum cost design of changing thickness of continuous beam over equal span. The objective function includes material and welding fabrication cost. The parameters varied are the length of span, the loading and the number of segments in each span. Both closed rectangular and open trapezoidal sections are considered. Finally, the relationship between cross-section dimensions of steel box girders is defined. The recommended design guidelines can be useful to the designer in the first stage of the designing procedure when he faces the problem of defining basic structure dimensions that would be close to the optimum ones.
Effect of Lead Rubber Bearing Characteristics on the Response of Seismic-isolated Bridges
Asif Hameed,구민세,Thang Dai Do,정진훈 대한토목학회 2008 KSCE JOURNAL OF CIVIL ENGINEERING Vol.12 No.3
A parametric study is conducted to investigate the effect of lead rubber bearing (LRB) isolator and ground motion characteristics on the response of seismic isolated bridges. The purpose was to investigate the most favorable parameters of the LRB for minimum earthquake response of the isolated bridge system for different ground motions. The important parameters included are: ground motion characteristic by considering peak ground acceleration to peak ground velocity, PGA/PGV ratio as damage index; characteristic strength, Qd of the LRB isolator normalized by the weight acting on the isolator; flexibility of isolator by varying post yield time period, Td; and yield stiffness to post yield stiffness, Ku/Kd ratio. The performance of seismic isolated bridge is measured by the variation of maximum isolator displacement (MID), maximum isolator force (MIF), deck acceleration and pier base shear. For a specified ground motion, smaller MID and MIF are regarded as indicator of better seismic performance. It is found that there exists a particular value of Qd/W, Td and Ku/Kd for which the MID, MIF, deck acceleration and pier base shear attain the minimum values. Finally the recommendations are made which are useful for the design engineers at the preliminary seismic isolation design of the bridges with LRB isolator for the ground motion having different characteristics.