introduCtion Live Loads Live load distribution refers to the traffic loading of a structure. This force is considered temporary and has an associated impact and safety factor depending on the standards followed. Live loading has the greatest influence on structures when directly exposed to the ground surface. The most common live loading conditions encountered in the design of precast concrete drainage materials include: • • • • • Highway Loading Aircraft Loading Railway Pedestrian Other (Heavy Equipment) Highways ConCrete pipe Pavements designed for heavy truck traffic substantially reduce the pressure transmitted through a wheel to the subgrade, and consequently to underlying concrete pipe. The pressure reduction is so great that generally the live load can be neglected. For heavy duty asphalt or flexible pavements, the reduction in intensity will be comparable to that for concrete pavements. The economies that can be realized by the reduction of pipe strength requirements can be substantial and should not be overlooked. For intermediate thicknesses of asphalt or flexible pavements, there is no generally accepted theory for estimating load distribution effects. The layered system theory, first advanced by Burmister in 1943, has been extended and solved for conditions that could apply to concrete pipe. However, this theory is not in common use. Local engineering practices control the basis for estimating the live load. Relatively thin pavements do not reduce the pressure transmitted from the wheel to the subgrade to any significant degree. Such pavements are generally considered as unsurfaced roadways for determination of the effect of live loads on buried concrete pipe. stormwater treatment teChnologies box seCtions manhole and CatCh basin material LAFARGE PIPE eMANUAL PAGE 31