Il-Sang AhnMethee ChiewanichakornAaron F. NottisJeffrey A. Carpenter...
p.3-12页
查看更多>>摘要：This paper presents experimental results of the ultimate behavior of the negative moment region of a quarter-scale full model and a half-scale subassemblage model of a two-span continuous composite bridge of concrete deck slab on steel girder. The two specimens are based on a prototype bridge that has a large girder spacing [3,800 mm (13 ft)]. At the ultimate state, it is shown that a larger portion of the deck is activated to resist tensile stress compared with the effective width specified in the AASHTO load and resistance factor design bridge specifications. Also, a plastic hinge that forms at the internal support has enough rotational capacity (ductility) to enable development of a second plastic hinge within the span. Experimental results show a reasonably good match with accompanying finite element method analyses.
Methee ChiewanichakornAmjad J. ArefStuart S. ChenIl-Sang Ahn...
p.13-26页
查看更多>>摘要：A composite section is made up of a steel girder and concrete slab connected by shear connectors. The shear lag phenomenon usually takes place in such a section and results in underestimation of stresses and strains at the web-to-flange intersections of the girder. With the introduction of the concept of effective slab width, the actual width can be replaced by an appropriate reduced slab width. The classical effective slab width definition does not take into account the strain variation through the slab thickness. More sophisticated definitions are introduced and used with finite element analyses. The method of finite element modeling is discussed, and the model is successfully verified with experimental results. Parametric study is conducted to investigate the effective slab width for both positive and negative moment sections. The effective slab width is computed and compared with the current AASHTO load and resistance factor design (LRFD) specifications. The results demonstrate that full width can be used as the effective slab width in the design and analysis in most cases for the design and analysis of both positive and negative moment sections. The current AASHTO LRFD specifications are found to be conservative for configurations with widely spaced girders, especially in negative moment sections.
Timothy E. BradberryJeffery C. CothamRonald D. Medlock
p.27-38页
查看更多>>摘要：Traditionally, bridge bearings supporting steel trapezoidal box girders (tub girders) consist of fabricator-designed mechanical devices, such as pot or disc bearings, that may be guided or unguided and are expensive to fabricate and place. Performance of these bearings has been mixed: some are maintenance-free and others require significant maintenance, repair, or replacement. In Texas, bridge bearings supporting concrete and steel superstructure types are typically steel-laminated elastomeric bearings that are tapered or have a constant thickness. Recently, the Texas Department of Transportation has used these structurally engineered elastomeric bearings for tub girders in place of mechanically engineered pot or disc bearings. This paper describes the rationale for the application of elastomeric bearings to tub girders and outlines design recommendations that are based on the use of elastomeric bearings for the tub girder direct connectors of the interchange of US-290 and I-35 built in Austin in the late 1990s and placed in service in 2001.
查看更多>>摘要：The AASHTO 2001 Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals include revised wind load provisions and new criteria for fatigue design. These provisions and criteria differ considerably from those in previous editions of the specifications, and their impact on the design of cantilevered overhead sign supports has not been fully studied. This study assesses the effect of these provisions and criteria on the design of cantilevered overhead sign support structures with the horizontal support composed of a four-chord truss. Wind and fatigue load design calculations of typical structures, located at sites across the United States, were performed with the design provisions of the 2001 supports specifications and compared with design in accordance with the previous edition of the specifications. The induced forces in the primary members of the cantilevered sign support structure were calculated, and corresponding member sizes and weights were estimated. The results of the study demonstrated the effect of the wind and fatigue load provisions on the design of cantilevered overhead sign support structures.
查看更多>>摘要：The new 17th Street Bridge provides a vital link between midtown Atlanta, Georgia, and the proposed Atlantic Station development. The project was presented to the community as an opportunity to create a signature structure for Atlanta—a gateway into the city. The community was extensively involved in the development of the bridge. Through a series of community workshops, focus groups, and architectural task groups, the bridge was defined and detailed, and pedestrian mobility and safety were the focus of the final product. The resulting bridge, though significantly different from the original vision, has met with approval from the community.
查看更多>>摘要：In light of the adoption of the load and resistance factor design (LRFD) philosophy by the AASHTO Subcommittee on Bridges and Structures, research efforts are under way to facilitate the transition from load factor rating (LFR) to load and resistance factor rating (LRFR) in New Mexico. Five prestressed concrete girder bridges, courtesy of the New Mexico bridge inventory, were rated with the BRASS-GIRDER and BRASS-GIRDER (LRFD) structural software. The objectives for this study were to evaluate and verify the BRASS (bridge rating and analysis of structural systems) software, to identify the source of dissension between LFR and LRFR rating factors, and to examine any trends in the rating factors as affected by bridge geometry. The comparison of LFR and LRFR focused on both flexure and shear for the strength limit state. The LRFR method generally yielded lower rating factors for flexure, with the longer-span bridges demonstrating a larger deviation between LFR and LRFR. The live load effects were identified as the major factor contributing to the difference in flexure ratings; the dead load effects and flexural resistance had little effect. The LRFR rating factors for shear also were generally lower than those produced by LFR. The discrepancy in the shear ratings was caused by both the live load effects and shear resistance. The dead load effects contributed little to the variation in LFR and LRFR rating factors for shear. Overall, the shear ratings controlled over those based on flexure.
查看更多>>摘要：Double-mast arm cantilevered sign structures are widely used in Indiana and in many other states. Because of the large sign area and relatively high flexibility, wind loading on these sign structures occasionally produces significant stress cycles. Cracking caused by fatigue damage may occur at several critical spots on the sign structures. An analytical investigation of the fatigue lives of the critical details in double-mast arm sign structures is discussed in this paper. An analytical procedure is introduced, and wind load selection and simulation are explained. Finite element models based on a prototype double-mast arm sign structure are described, and dynamic analyses and fatigue life results are presented. It was found that the post-to-base plate socket weld connection was the most critical detail and that variations in the fatigue life occurred because of differences in the wind environment at various sites.
查看更多>>摘要：This paper presents findings of NCHRP Synthesis Project 35-08 that gathered available information on bridges with fracture-critical members (FCM) from the literature, from a survey of bridge owners and consultant inspectors, and from targeted interviews. In the 1970s, material, design, fabrication, shop inspection, and in-service inspection requirements were improved for steel bridges in general. Special provisions for FCM were then implemented, mainly in reaction to bridge collapses. These requirements transformed the industry and the design of modern bridges so that fatigue and fracture are rare in bridges built in the past 20 years. There is a hidden initial cost in some cases because more expensive superstructure designs are being used than necessary to maintain an acceptable reliability level because of restrictions or more subtle prejudice against bridges with FCM. The major impact on life-cycle costs is the additional mandate for hands-on in-service inspection of FCM. There are also varying definitions of "fracture critical," and consequently there is wide disagreement in classifying different types of superstructures as fracture critical. Numerous bridges have had a full-depth fracture of a fracture-critical girder and did not collapse, usually because of the alternative load-carrying mechanism of catenary action of the deck under large rotations at the fracture. The capacity of damaged superstructures (with FCM removed from the analysis) may be predicted with refined three-dimensional analysis. However, there is a strong need to clarify the assumptions, load cases and factors, and dynamic effects in these analyses. This paper reports on results of this study.
查看更多>>摘要：Bridge 207 is a two-span horizontally curved steel plate girder bridge near Port Matilda, Pennsylvania. Although the curvature is not severe, the curvature combined with the unequal span balance caused an unusual distribution of foree effects in the girders. A global twisting of the superstructure was caused by the unequal vertical deflections in the two spans. The computer program BSDI-3D was used to analyze the curved superstructure. To account for the ont-of-plumb condition of the girders in their final condition, additional lateral flange bending moments were calculated. The magnitude of the additional lateral moments was a function of the vertical bending moments and the degree of twist in the girder. Field monitoring of the structure is focusing on the effects of curvature during construction. This is being accomplished by developing a detailed time line of superstructure erection and deck placement and through monitoring of the bridge by using vibrating wire strain gauges and tiltmeters positioned at critical locations on the girders and cross-frames. Field data were recorded before and after critical construction events, such as girder erection, cross-frame and formwork placement, and the deck pour. This information is being used to determine the effects of curvature on the cross-frames during construction by using axial stresses and strains and on the girders by using warping stresses and strains.
John W. van de LindtTheresa M. AhlbornSridhar Kethu
p.92-100页
查看更多>>摘要：Corrosion of steel beams caused by deicing media is a common problem in northern and mountainous regions of the United States. A common problem is deterioration of steel beam ends in the web and flange near or directly above the bearing area. This results in decreased shear capacity, web-crippling, and web-buckling capacity. This paper presents the results of a study sponsored by the Michigan Department of Transportation (MDOT) to provide the structural analyst with a simplified, accurate, rapid, and slightly conservative approach for computing the reduced capacity of a rolled steel section. The approach is based on the results of several hundred three-dimensional finite element analyses for a suite of 16 typical steel bridges. The most common shapes and locations for steel beam end deterioration were identified by reviewing detailed inspection reports. Finite element analyses for the steel beam ends with simulated damage of various sizes and shapes was performed with the finite element software ABAQUS. A small experimental program focused on a selected beam to check the validity and accuracy of the finite element approach. Design charts were developed for an array of damage cases, which enable the analyst to simply apply a factor to the undamaged buckling capacity of the beam. The approach is compared to MDOT's current technique to demonstrate its efficiency and potential cost savings.
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