Collapse Resistance Modeling of Encased Pipes

Abstract

Two different collapse models are developed for predicting the collapse resistance of encased pipes for pipe rehabilitation applications. One model corresponds to an unsymmetrical collapse mode and the other one corresponds to a symmetrical collapse mode. Attention is focused here on modeling the effect of the small radial gap between the encased pipe and the host pipe on encased pipe collapse resistance. This small radial gap is assumed to have developed when installing the encased pipe into the host pipe. It increases in size when subjected to temperature change, swelling, and application of external hydrostatic pressure. The predictions by the models correlate well with some collapse test results on encased pipes.

Elastic stability analysis of loosely fitted thin liners – A proposed simplified procedure and evaluation of existing solutions

“…Most of the available solutions have used simplifying assumptions that may or may not provide a good approximation for the liner buckling pressure. The following sections review and evaluate five of such solutions namely; Jacobsen (1974), Lo and Zhang (1994), Boot (1998), Thépot (2000), and Madryas and Szot (2003). Then, both Jacobsen and Boot solutions are extended to allow for the evaluation of the thrust and bending moment induced in the liner, which are required to check the validity of the elastic buckling assumption.…”

“…Therefore, these formulae are derived herein for comparison purposes. The thrust, N o , and bending moment, M o , at the most heavily stressed point in the liner (mid-point of the detached segment) can be expressed as: (9) and (10) Lo and Zhang (1994) studied the effect of the lack of fit of the liner on the critical pressure for cured-in-place polymer liners. Fig.…”

“…It is experimentally evident that the encased liner subject to external pressure may buckle at a critical pressure level that is significantly higher than the one for the unsupported (free) liner (Kyriakides and Babcock, 1983;Aggarwal and Cooper, 1984;Lo and Zhang, 1994;Guice et al, 1994;Boot and Welch, 1996;Bakeer et al, 1999). For slender liners commonly used in practice it is assumed, and confirmed experimentally, that geometrical instability (i.e., elastic buckling) always precedes any material failure.…”

“…In particular, the solutions provided by Jacobsen (1974), Lo and Zhang (1994), Boot (1998), Thépot (2000), and Madryas and Szot (2003) are discussed. Modification to Jacobsen's solution is proposed to allow for the calculation of the elastic buckling pressure.…”

New Approach to Design of Circular Liner Pipe to Resist External Hydrostatic Pressure

“…Reduction factors on two-lobe buckling pressure due to symmetrical gap imperfection expressed as a function of gap/thickness ratio Boot & Javadi (1998) Lo & Zhang (1994) Test data Aggarwal (1984) Seeman et al (2001) Although considered by Boot to be near enough straight, the lines for non-zero gap in fact curve downwards slightly, implying some variation of m with D/t. As previously pointed out by the writer (Gumbel, 1993) this apparent increase in sensitivity to relative gap w 02 /R (or in the case of one-lobe buckling w 01 /D) as dimension ratio D/t increases can be attributed almost entirely to the relationship of gap size to liner thickness 2 .…”