SECTION 12: BURIED STRUCTURES AND TUNNEL LINERS 12-65 12.10.4.3.2b—Earth Load Bedding Factor for Arch and Elliptical Pipe The bedding factor for installation of arch and elliptical pipe shall be taken as: BFE = CA CN (12.10.4.3.2b-1) xq where: CA = CN = = = constant corresponding to the shape of the pipe, as specified in Table 12.10.4.3.2b-1 parameter that is a function of the distribution of the vertical load and vertical reaction, as specified in Table 12.10.4.3.2b-1 parameter that is a function of the area of the vertical projection of the pipe over which lateral pressure is effective, as specified in Table 12.10.4.3.2b-1 ratio of the total lateral pressure to the total vertical fill load specified herein Design values for CA, CN, and x are listed in Table 12.10.4.3.2b-1 Table 12.10.4.3.2b-1—Design Values of Parameters in Bedding Factor Equation Pipe Shape Horizontal Elliptical and Arch Vertical Elliptical CA Installation Type CN 0.630 0.763 0.516 0.615 1.337 1.021 Projection Ratio, p 0.9 0.7 0.5 0.3 0.9 0.7 0.5 0.3 The value of the parameter q is taken as: • For arch and horizontal elliptical pipe: q = 0.23 TeraPaper.com • B p 0.35 p c Fe H (12.10.4.3.2b-2) For vertical elliptical pipe: q = 0.48 B p 0.73 p c Fe H (12.10.4.3.2b-3) where: p TeraPaper.com = projection ratio, ratio of the vertical distance between the outside top of the pipe, and the ground of bedding surface to the outside vertical height of the pipe © 2014 by the American Association of State Highway and Transportation Officials All rights reserved Duplication is a violation of applicable law x 0.421 0.369 0.268 0.148 0.718 0.639 0.457 0.238 12-66 AASHTO LRFD BRIDE DESIGN SPECIFICATIONS, SEVENTH EDITION, 2014 12.10.4.3.2c—Live Load Bedding Factors C12.10.4.3.2c The bedding factor BFLL for live load, WL, for both circular pipe and arch and for elliptical pipe shall be taken as specified in Table 12.10.4.3.2c-1 For pipe diameters not listed in Table 12.10.4.3.2c-1, the bedding factor may be determined by interpolation Table 12.10.4.3.2c-1—Bedding Factors, BFLL The relatively large bending stiffness in the longitudinal direction of concrete pipe results in the distribution of the live load force along the length of the pipe This ratio of distribution length to pipe diameter is higher in small diameter pipes designed by the Indirect Design Method The bedding factor has been adjusted in Table 12.10.4.3.2c-1 to account for this higher distribution length Fill Height, ft Pipe diameter, in < 2.0 ft ≥ 2.0 ft 12 3.2 2.4 18 3.2 2.4 24 3.2 2.4 30 and larger 2.2 2.2 TeraPaper.com 12.10.4.4—Development of Quadrant Mat Reinforcement 12.10.4.4.1—Minimum Cage Reinforcement In lieu of a detailed analysis, when quadrant mat reinforcement is used, the area of the main cage shall be no less than 25 percent of the area required at the point of maximum moment 12.10.4.4.2—Development Length of Welded Wire Fabric Unless modified herein, Article 5.11.2.5 shall apply the provisions of 12.10.4.4.3—Development of Quadrant Mat Reinforcement Consisting of Welded Plain Wire Fabric The embedment of the outermost longitudinals on each end of the circumferentials shall not be less than: • The greater of 12 circumferential bar diameters or three-quarters of the wall thickness of the pipe beyond the point where the quadrant reinforcement is no longer required by the orientation angle, and • A distance beyond the point of maximum flexural stress by the orientation angle plus the development length, d, where d is specified in Article 5.11.2.5.2 The mat shall contain no less than two longitudinals at a distance 1.0 in greater than that determined by the orientation angle from either side of the point requiring the maximum flexural reinforcement The point of embedment of the outermost longitudinals of the mat shall be at least a distance determined by the orientation angle past the point where TeraPaper.com © 2014 by the American Association of State Highway and Transportation Officials All rights reserved Duplication is a violation of applicable law SECTION 12: BURIED STRUCTURES AND TUNNEL LINERS 12-67 the continuing reinforcement is no less than double the area required for flexure 12.10.4.4.4—Development of Quadrant Mat Reinforcement Consisting of Deformed Bars, Deformed Wire, or Deformed Wire Fabric When deformed bars, deformed wire, or deformed wire fabric is used, the circumferential bars in quadrant mat reinforcement shall satisfy the following requirements: • Circumferentials shall extend past the point where they are no longer required by the orientation angle plus the greater of 12 wire or bar diameters or threequarters of the wall thickness of the pipe, • Circumferentials shall extend on either side of the point of maximum flexural stress not less than the orientation angle plus the development length, hd, as required by Article 5.11.2.5.1 and modified by the applicable modification factor or factors, and • Circumferentials shall extend at least a distance determined by the orientation angle past the point where the continuing reinforcement is no less than double the area required for flexure 12.10.5—Construction and Installation The contract documents shall require that the construction and installation conform to Section 27, “Concrete Culverts,” AASHTO LRFD Bridge Construction Specifications 12.11—REINFORCED CONCRETE CAST-INPLACE AND PRECAST BOX CULVERTS AND REINFORCED CAST-IN-PLACE ARCHES 12.11.1—General C12.11.1 The provisions herein shall apply to the structural design of cast-in-place and precast reinforced concrete box culverts and cast-in-place reinforced concrete arches with the arch barrel monolithic with each footing Designs shall conform to applicable Articles of these Specifications, except as provided otherwise herein These structures become part of a composite system comprised of the box or arch culvert structure and the soil envelope Precast reinforced concrete box culverts may be manufactured using conventional structural concrete and forms, or they may be machine made with dry concrete and vibrating form pipe making methods Standard dimensions for precast reinforced concrete box culverts are shown in AASHTO M 259 (ASTM C789) and M 273 (ASTM C850) TeraPaper.com TeraPaper.com © 2014 by the American Association of State Highway and Transportation Officials All rights reserved Duplication is a violation of applicable law 12-68 AASHTO LRFD BRIDE DESIGN SPECIFICATIONS, SEVENTH EDITION, 2014 12.11.2—Loads and Live Load Distribution 12.11.2.1—General C12.11.2.1 Loads and load combinations specified in Table 3.4.1-1 shall apply Live load shall be considered as specified in Article 3.6.1.3 Distribution of wheel loads and concentrated loads for culverts with less than 2.0 ft of fill shall be taken as specified in Article 4.6.2.10 For traffic traveling parallel to the span, box culverts shall be designed for a single loaded lane with the single lane multiple presence factor applied to the load Requirements for bottom distribution reinforcement in top slabs of such culverts shall be as specified in Article 9.7.3.2 for mild steel reinforcement and Article 5.14.4.1 for prestressed reinforcement Distribution of wheel loads to culverts with 2.0 ft or more of cover shall be as specified in Article 3.6.1.2.6 The dynamic load allowance for buried structures shall conform to Article 3.6.2.2 For cast-in-place box culverts, and for precast box culverts with top slabs having span to thickness ratios (s/t) >18 or segment lengths