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8 CHAPTER 3 Published Literature Review A large body of published literature is related to curved Article 4.7.4.3, "Multispan Bridges," specifies the minimum concrete box-girder bridges. Some of the documents most requirements for the seismic analysis of multispan bridges. important to this project are discussed below. Analysis requirements are based on the classification of a bridge as "regular" or "irregular." The classification of a curved bridge includes the maximum subtended angle Codes and Design Standards and whether the spans are continuous or are multiple Currently, there is no U.S. code specifically developed for the simple-spans. design of curved concrete box-girder bridges. AASHTO LRFD Article 5.4.6, "Ducts," specifies the requirements for duct Bridge Design Specifications provide comprehensive specifica- material and curvature. tions with commentary for the design of highway bridges. Our Article 5.8, "Shear and Torsion," specifies comprehensive review of Codes and Design Standards is summarized below. design procedures for flexural shear and torsion. The mod- ified compression field theory is specified for flexural re- AASHTO, 2004, AASHTO LRFD Bridge Design Speci- gions. Strut-and-tie models are specified for regions near fications, 3rd Edition with Interims, AASHTO, Washing- discontinuities. Alternative design procedures are permit- ton, D.C. ted for segmental bridges. Article 5.9.1.6, "Tendons with Angle Points or Curves," A number of sections apply to the design issues associated cross references Articles 5.4.6 and 5.10.4 for duct curvature with curved concrete box-girders. Selected specifications and stress concentration considerations, respectively. articles are as follows: Article 5.9.5.2.2.2, "Friction," specifies the friction loss due to curvature and includes specific requirements for deter- Article 4.6.1.2.2, "Single-Girder Torsionally Stiff Super- mining the total 3-D angle change as typically found in structures," allows for the analysis of horizontally curved, curved girders with draped tendons. torsionally stiff single-girder superstructures for global Article 5.10.3.3.3, "Curved Post-Tensioning Ducts," spec- force effects as a curved spine beam. ifies the clear distance between curved ducts as required for Article 4.6.1.2.3, "Multicell Concrete Box-Girders," allows tendon confinement as specified in Article 5.10.4.3 but not for the design of horizontally curved cast-in-place multicell less than that required for straight ducts. box-girders as single-spine beams with straight segments, Article 5.10.4.3, "Effects of Curved Tendons," specifies that, for central angles up to 34within one span, unless concerns where tendons are placed in curved webs, additional cover about force effects dictate otherwise. and/or confinement reinforcement shall be provided. Article 4.6.3.4, "Cellular and Box Bridges," allows for the Article 5.10.4.3.1, "In-Plane Force Effects," defines the in- refined analysis of cellular bridges by any of the methods plane deviation force effects due to the change in direction specified in Article 4.4, "Acceptable Methods of Structural of the tendon as Fu-in = Pu/R where Pu is the factored tendon Analysis," except the yield line method, which accounts for force and R is the radius of curvature of the tendon. Specific the two dimensions seen in plan view and for the model- requirements for local lateral shear on the unreinforced ing of boundary conditions. Models intending to quantify concrete cover are given and neglect any increase in lateral torsional warping and/or transverse frame action should shear capacity for widely spaced tendons. Where the factored be fully three-dimensional. in-plane deviation force exceeds the lateral shear resistance