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<br />Section 3. STRUCTURAL CHARACTERISTICS OF CULVERTS <br /> <br />3-3.1 Loads on Culverts. <br /> <br />In addition to their hydraulic functions, culverts must also support the <br />weight of the embankment or fill covering the culvert and any load on the <br />embankment. There are two general types of loads that must be carried by <br />culverts: dead loads and live loads. <br /> <br />a. Dead Loads--Dead loads include the earth load or weight of the soil over <br />the culvert and any added surcharge loads such as buildings or additional <br />earth fill placed over an existing culvert. If the actual weight of earth is <br />not known, 120 pounds per cubic foot is generally assumed. <br /> <br />b. Live Loads--The live loads on a culvert include the loads and forces <br />which act upon the culvert due to vehicular or pedestrian traffic plus an <br />impact factor. The highway wheel loads generally used for analysis are shown <br />in exhibit lB. The effect of live loads decreases as the height of cover over <br />the culvert increases. When the cover is more than two feet, concentrated <br />loads may be considered as being spread uniformly over a square with sides <br />1.75 times the depth of cover. This concept is illustrated in exhibits 19 <br />and 20. <br /> <br /> <br />14ft. <br />to <br />114ft. ,30ft. <br />= = <br />4000lb I I=\ 16000lb <br />4000lb ;.; 16000lb <br />= = <br />= <br /> <br />I <br />= <br />=116OO01b <br />16000lb <br />= <br />= <br /> <br />AASHTO <br />HS20 LOAD <br /> <br />AASHTO <br />ALTERNATE LOAD <br />12oo0lb 12000lb <br />00-00-"- <br />I I <br />00-00. <br />120001b 12000 Ib- 4ft. <br /> <br />H20. HS20 and <br />ALTERNATE LOADS <br /> <br />b:J <br /> <br />T 611. ,411.1" 6ft. '-I' <br /> <br />AASHTO <br />H20 LOAD <br />4000 Ib 4000 Ib <br />0-0. <br /> <br />Hi"' <br /> <br />00-001- <br />15000 lb 16000 Ib <br /> <br />Exhibit lB. AASHTO live load spacing for highway structures. <br /> <br />30 <br />