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Plastics Product Design Part 8

Tham khảo tài liệu 'plastics product design part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 260 Plastics Engineered Product Design of the pipe industry for steel conduit and pipe AWWA M-ll ASTM and ASME . Deflection relates to pipe stiffness El pipe radius external loads that will be imposed on the pipe both the dead load of the dirt overburden as well as the live loads such as wheel and rail traffic modulus of soil reaction differential soil stress bedding shape and type of backfill. To meet the designed deflection of no more than 5 the pipe wall structure could be either a straight wall pipe with a thickness of about 1.3 cm 0.50 in. or a rib wall pipe that provides the same stiffness. It has to be determined if the wall structure selected is of sufficient stiffness to resist the buckling pressures of burial or superimposed longitudinal loads. The ASME Standard of a four-to-one safety factor on critical buckling is used based on many years of field experience. To calculate the stiffness or wall thickness capable of meeting that design criterion one must know what anticipated external loads will occur Fig. 4.26 . As reviewed the strength of RTR pipe in its longitudinal and hoop directions are not equal. Before a final wall structure can be selected it is necessary to conduct a combined strain analysis in both the longitudinal and hoop directions of the RTR pipe. This analysis will consider longitudinal direction and the hoop direction material s allowable strain thermal contraction strains internal pressure and pipe s ability to bridge soft spots in the trench s bedding. These values are determinable through standard ASTM tests such as hydrostatic testing parallel plate loading coupon test and accelerated aging tests. Stress-strain S-S analysis of the materials provides important information. The tensile S-S curve for steel-pipe material identifies its yield point that is used as the basis in their design. Beyond this static loaded yield point Chapter 2 the steel will enter into the range of plastic deformation that would lead to a total collapse of the .