3.pdf Homework#3 1. A one-lane bridge consists of a 9-inch thick, 16-ft wide rei

Question

3.pdf Homework#3 1. A one-lane bridge consists of a 9-inch thick, 16-ft wide reinforced concrete deck supported on two steel girders spaced 10-ft. apart. The girders are 65-ft. long (centerline-to-centerline of bearings) and weigh 425 lb/ft. The bridge is to be designed for a uniform live load of 700 lb/ft acting over the entire length of the bridge. Determine the maximum reaction applied to an end support of a girder due to dead, live, and impact loads. The live load may be assumed to act along the centerline of the deck slab and divide equally between the two girders. Each concrete curb weighs 250 lb/ft and each rail 120 lb/ft. Reinforced concrete has a unit weight of 150 Ib/ft3 Assume an impact factor of 0.29, which is applied as an increase to live load. 65-0 3'-0" 10'-0 3'-0"

Explanation / Answer

weight of concrete per ft== volume x density = (16x9/12x1)*150=1800 lb/ft

span is 65 ft total weight of concrete = 1800 x 65/1000= 117 kips

weight of griders = 2*65*425/1000=55.25 kips

weight of concrete carb + rail = 2x(250+120)*65/100=48.1 kips

total dead load = sum of all three = 117+55.25+48.1= 220.35 kips

total live load = 700*65/1000= 45.4 kips

impact load = 0.29 of live load =13.195 kips

hence total load associated to structure = 220.35+45.4+13.195= 278.945 kips

there are four supports to bear this load

hence max load per support = 278.945/4=69.7363 kips

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