Click for next page ( 13

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement

Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 12
12 bv effective web width (in.) (Article Where de effective depth from extreme compression fiber to the centroid of the tensile force in the tensile reinforcement Vc = 0.0632K fc bvdv (Equation (in.) (Article Vs = Avfydv/s (Equation dv effective shear depth (in.) (Article Av/s = Vs/(fydv) The amount of transverse reinforcement required for tor- Step 3 Check if Torsion Must be Considered sion is found from Check if torsion must be considered: Tu Tn Tu > 1/3Tcr (Equation Where Tcr = 0.0632K fc 2Aobe (Equation Tn = 2AoAvfy/s (Equation C5.8.6.4-2) f pc Av/s = Tn/(2Aofy) K= 1+ 2.0 (Equation 0.0632 fc For the exterior web of a box section, the combined area of fpc = Unfactored compressive stress in concrete after prestress both stirrup legs in the web, Astirrups, contributes to the trans- losses have occurred either at the centroid of the cross verse hoop reinforcement for flexural shear and torsion, there- section resisting transient loads or at the junction of fore, the maximum spacing of the stirrups, Smax, is given by the web and flange when the centroid lies in the flange. (Article Smax = Astirrups/[(Av/s)flexural shear + (Av/s)torsion] When vertical tendons are provided in the web, the design Step 4 Check the Web Width yield strength for flexural shear and torsion design shall be Verify the effective web width is adequate to prevent web taken in accordance with Article crushing: Step 6 Check the Longitudinal Vu Vn Reinforcement Vn 0.379fc 0.5bvdv (Equation The minimum additional longitudinal reinforcement re- Vu/(bvdv) + Tu/(2Aobe) 0.474 fc 0.5 (Equation quired for torsion (in addition to that required for other con- current actions), shall satisfy (Comment It appears that Vu and Tu should be replaced by Vn and Tn, respectively, in this equation to be consistent with Al = Tuph/(2Aofy) (Equation Article 12.3.1b of the Segmental Guide Specification.) Comment: The distribution of Al within the cross section Increase web width if either Equation or Equa- needs to be clarified. Article 5.3, "Notation," and Article, tion is not satisfied. "Torsional Reinforcement," define it as the area of longitudinal Check the allowable principal tensile stress for Service torsion reinforcement in the exterior web of the box-girder, Limit State III and during construction in accordance with which appears to be incorrect. Article contains a con- Article 5.8.5. Consider the compressive stress due to vertical flicting statement that Al shall be distributed around the perim- tendons in the webs. Increase the web width or the vertical eter of the closed stirrups in accordance with Article prestressing force in the web if the allowable principal stresses which appears to be correct. LRFD Equation is are exceeded. essentially identical to the equation in Article 12.3.8 of the Seg- mental Guide Specification which specifies that Al shall be dis- tributed around the perimeter of the closed stirrups. Step 5 Determine Required Spacing of Stirrups In determining the required amount of longitudinal rein- forcement, the beneficial effect of longitudinal prestressing is The amount of transverse reinforcement required for shear taken into account by considering it equivalent to an area of is found from reinforcing steel with a yield force equal to the prestressing force. (Commentary Article C5.8.6.4) Vu Vn Subject to the minimum reinforcement requirements of Vn = Vc + Vs (Equation Article, the area of additional torsion reinforcement in