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EXAMPLEII <br />Given: A 30-inch diameter, B wall, concrete pipe is to <br />be installed as a storm drain under a flexible <br />pavement and subjected to AASHTO highway <br />loadings. The pipe will be installed in a trench <br />with a minimum of 2 feet of cover over the top of <br />the pipe. The AASHTO LRFD Criteria will be <br />used with Select Granular Soil. <br />Find: The maximum live load on the pipe in pounds <br />per linear foot. <br />Solution: <br />1. Review project data. <br />A 30-inch diameter, B wall, circular concrete pipe <br />has a wall thickness of 3.5 inches, therefore B, is <br />3.08 feet and Ro is 3.08 feet. Height of earth cover <br />is 2 feet. Use AASHTO LRFD Criteria with Select <br />Granular Soil Fill. <br />2. Calculate average pressure intensity of the live load <br />on the plane at the outside top of the pipe. <br />From Table 3, the critical load, P, is 16,000 pounds <br />from an HS 20 single dual wheel, and the Spread <br />Area is: <br />A = (Spread a)(Spread b) <br />A = (1.67 + 1.15x2)(0.83 + 1.15x2) <br />A = (3.97)(3.13) <br />A = 12.4 square feet <br />I.M. <br />= 33(1.0 - 0.125H)/100 <br />I.M. <br />_ .2475 (24.75%) <br />w <br />= P(1 + IM)/A <br />w <br />= 16000(1 +.2475)/12.4 <br />w <br />= 1.610lb/ft2 <br />3. Calculate total live load acting on the pipe. <br />WT = (w + LL)LSL <br />Assuming truck travel transverse to pipe centerline <br />LL <br />= 64 <br />L <br />= Spread a = 3.97 feet <br />Spread b = 3.13 feet <br />8, <br />= 3.08 feet, which is less than Spread b, <br />therefore <br />SL <br />= 3.08 feet <br />WT = (1610 + 64)r.3.97x3.08 = 20,500 pounds <br />Assuming truck travel parallel to pipe centerline. <br />Lt. = 64 <br />Spread a = 3.97 feet <br />L = Spread to = 3.13 feet <br />8, = 3.08 feet, which is less than Spread a, <br />therefore <br />SL = 3.08 feet <br />WT = (1610 + 64) 3.08 x 3.13 = 16,100 pounds <br />WT Maximum = 20,500 pounds; and truck travel is <br />transverse to pipe centerline <br />4. Calculate live load on pipe in pounds per linear foot. <br />Ro = 3.08 feet <br />Le = L + 1.75(3/419a) <br />L� = 3.97 + 1.75(.75x3.08) = 8.01 feet <br />WL = WL/Le <br />WL = 20,500/8.01 = 2,559 pounds per linear foot <br />EXAMPLE 2 <br />Given: Same as Example 1,except use AASHTO LRFD <br />Criteria with Other Solis Fill. <br />Find: The maximum live load on the pipe in pounds <br />per linear foot. <br />Solution: <br />1. Review project data. <br />Awall B 30-inch diameter circular concrete pine has <br />a wall thickness of 3.5 inches, therefore B. is 3.08 <br />feet and Ro is 3.08 feet. Height of earth cover is 2 <br />feet. Use AASHTO LRFD Criteria with Other Soils <br />Fill. <br />2. Calculate average pressure intensity on the plane <br />at the top of the pipe. <br />From Table 4, the critical load, P, is 16,000 pounds <br />from an HS 20 single dual wheel, and the Spread <br />Area is: <br />_ (Spread a)(Spread b) <br />_ (1.67+1.00x2)(0.83+1.00x2) <br />_ (3.67)(2.83) <br />= 10.4 square feet <br />I.M.= 33(1.0.0125H)/100 <br />I.M.= .2475 <br />w = P(I+IM)/A <br />w = 16,000(1 +.2475)/10.4 <br />w = 1,920lb/fl7 <br />i06.7682 7 <br />