professor ben schafer's thin-walled structures research group - johns hopkins university
Thin-walled thermoplastic pipe
Thin-walled thermoplastic pipe typically fail due to local buckling limit states. Recent work simulating the performance of these pipe in the parallel plate test and in the buried condition has shed new light on their behavior. Two recent TRB presentations (January 2003) are abstracted and given below. What if we had a way to design almost any pipe profile and quickly understand the local buckling behavior of that profile? Maybe we can! Extensions of the Direct Strength Method for thin-walled pipe profiles is a real possibility and ideas along this line were presented to the TRB Committee on Culverts and Hydraulic Structures at the 2004 TRB meetings as excerpted below.
Local buckling design without effective width: new developments in the building industry (slides)
(Note this talk was presented at the 2004 TRB Committee meeting on Culverts and Hydraulic Structures)
The objective of this brief talk is to introduce the Direct Strength Method, recently adopted as an alternative design procedure in the cold-formed steel building industry and demonstrate the potential of this method for profile-wall pipe. For more information on the Direct Strength Method please go here, and for more information on CUFSM the engine that runs the method please go here.
(Note this paper has been accepter for publication in the Transportation Research Record)
Schafer, B.W., McGrath, T.J.
The objective of this paper is to demonstrate a computational method for assessing the allowable depth of fill over a buried thermoplastic profile wall (corrugated) plastic pipe and compare the results to the recently adopted AASHTO design method. The computational method is demonstrated for a 1500 mm (60 in.) diameter HDPE profile wall pipe, but is applicable to all profile wall thermoplastic pipe that exhibit local buckling limit states. The computational model compares strain demands predicted from a two-dimensional plane strain finite element model of buried pipe in the embankment condition with strain capacity predicted from a three-dimensional finite element model of a pipe-soil segment undergoing thrust and/or positive and negative bending. The strain demands indicate the dominance of thrust strains, as opposed to bending strains, in the overall behavior, particularly for intermediate to larger fill depths. In the examined profile the ultimate strain capacity is limited by local buckling for thrust strains and/or positive bending (crest in compression), and inward radial movement of the crest for negative bending (liner in compression). Depth of fill predictions between the new AASHTO design method for thermoplastic pipe and the computational method agree within 10% of one another when uniform soil distribution is considered, and within 20% of one another when a soft haunch and other soft soils are considered in the pipe-soil envelope.
Parallel Plate Testing and Simulation of Corrugated Plastic Pipe (TRB paper)
McGrath, T.J., Schafer, B.W.
This work presents the results of a series of parallel plate tests and finite element simulations of those tests, conducted on corrugated HDPE plastic pipe, to investigate the role of material and geometry on the behavior of the pipe during the test. Specifically, the work considers parallel plate tests on 1500 mm (60 in.) diameter pipe, and finite element simulation of 450 mm, 750 mm, and 1500 mm (18 in., 30 in. and 60 in.) diameter pipe. It is demonstrated that the applied strain demands in a parallel plate test are largely independent of the loading rate in the test, although the stiffness at 5% deflection and the peak load are strongly rate dependent. The tests and analyses show that the deflection at peak load in the parallel plate test is imperfection sensitive. Further, investigation of strain demands around the profile indicates that the pipe material must carry local strains in excess of those typically assumed to occur in the parallel plate test.
Schafer, B.W., McGrath, T.J. (2003). "Buried Corrugated Thermoplastic Pipe: Simulation and Design." Annual Meeting of the Transportation Research Board, Washington, D.C. (Accepted for Publication in the Transportation Research Record, currently In Press)
McGrath, T.J., Schafer, B.W. (2003). "Parallel Plate Testing and Simulation of Corrugated Thermoplastic Pipe." Annual Meeting of the Transportation Research Board, Washington, D.C.
last edited on 07/19/05
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