Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
1 Horizontally curved and/or skewed bridges generally exhibit significant torsional dis- placements. Twisting of the girders, and of the overall bridge as a structural system, is unavoidable in these structures. Steel I-girder and tub-girder bridges have performed well in a vast majority of the cases involving horizontal curvature and skew in highway bridge engineering. Indeed, they are arguably the premier design option for handling of curved and skewed roadway alignments. However, in situations where problems have occurred, they often have been during, or related to, the construction. Furthermore, these problems often have involved issues in addressing the torsional response. Within the structural design profession, little has been published in the way of guide- lines or recommendations on the level of structural analysis sufficient for the construction engineering of curved and skewed steel I- and tub-girder bridges. The key construction engineering considerations for these types of structures include the following: 1. The prediction of the deflected geometry at the intermediate and final stages of the construction, 2. Determination and assessment of cases where the stability of a structure or unit needs to be addressed, 3. Identification and alleviation of situations where fit-up may be difficult during the erection of the structural steel, and 4. Estimation of component internal stresses during the construction and in the final constructed configuration. Bridges with significant span lengths, curvature, and/or skew generally require detailed planning of the erection procedures and sequences such that lifting and assembly of their spatially deformed components is achievable. Conversely, shorter bridges with minor curvature and skew can be built with less attention to the construction engineering. With respect to all of the above considerations, it is important that an appropriate level of analysis is applied for the task at hand. This research has systematically evaluated the accuracy of various 1D (line-girder analysis based) as well as 2D-grid structural analysis procedures to assess when the simplified 1D and 2D methods are sufficient and when 3D methods may be more appropriate for prediction of the constructability and of the constructed geometry of curved and/or skewed steel girder bridges. Both steel I-girder and tub-girder bridges are addressed. A method of estimating the accuracy of conventional 1D line-girder and 2D-grid procedures as a function of the bridge geometry is provided. In addition, a number of improvements to conventional line-girder and 2D-grid methods of analysis are developed, which provide substantial benefits at little S U M M A R Y Guidelines for Analysis Methods and Construction Engineering of Curved and Skewed Steel Girder Bridges
2 Guidelines for Analysis Methods and Construction Engineering of Curved and Skewed Steel Girder Bridges additional computational cost. Furthermore, cases where locked-in forces from steel dead load fit (SDLF) or total dead load fit (TDLF) detailing of cross-frames should be considered using an accurate 2D-grid or 3D finite element analysis are explained, and procedures for incorporating the corresponding initial lack-of-fit displacements in these analysis meth- ods are provided. Finally, the project has developed guidelines on the level of construction analysis, plan detail, and submittals for curved and skewed steel girder bridges. These guide- lines are suitable for direct incorporation into specifications or other guideline documents.
