Steel pipes are widely used in offshore structures and buried seafloor pipelines. Buried single-wall pipelines or piles of fixed offshore platforms crossing the earthquake fault can experience very large displacement, which could cause considerable damages or failures to the pipes. The elevated strains induced in pipelines from welding connection between the pipes also can drastically reduce the pipe’s performance. Therefore, to prevent these types of damages and failures, this research used an enhanced strain-based design method along with finite element analysis, developed bonded and unbonded double-wall composite pipes, which were in replacement of the single-wall ones, and studied the effects of welding on the double-wall composite pipeline in terms of wrinkles, ovalization, stresses, and strain. Here, the double-wall annulus of the pipelines was grouted with polymer. Extensive experiments were performed with displacement loads being applied to the pipelines in clay and in air and the results were analyzed. It was found that using an enhanced strain-based design method, failures in the pipelines could be significantly reduced or possibly even eliminated. This work would also potentially lead to a new area of research in the oil and gas industries since the elevated strains induced in pipelines due to weld could lead to several modes of failure. In addition, this research found some significant impacts in terms of safety due to the bond between steel and polymer and weld imperfection in the pipelines.
Drafts of the AISC guide for hotspot stress contained several radical technical proposals that could benefit from exposure and peer review before publication in the design guide. These are:
– S‐N slope of –1/3.6 with no transition knee,
– notch stress size effect based on mesh density, and
– thickness‐dependent strain limits for TxT meshing.
These proposals are presented here along with their supporting data.
As follow-up to recent papers by Marshall et al. (2010, 2012), research on steel-concrete-steel (SCS) sandwich shells for Arctic offshore structures continues at two universities. National University of Singapore is testing heavy transverse reinforcement which ties the outer steel plates together. Lamar University in Texas originally studied the composite ice wall concept in the late 1980s, and is now testing surface treatment with a size-tiered gradation of mini-studs, macro fibers (steel) and micro fibers (synthetic), intended to develop the full bulk properties of the Fiber Reinforced Concrete (FRC) core in radial tension and punching shear. Using ISO’s design non-hydrostatic partial span loading on the Singapore Cone, radial bond stress at the inner steel plate is low and deemed attainable for both the stud enhanced bonding surface and the bulk concrete core. The steel shell serves as prefabricated permanent formwork, and the arched vaults resist external ice loading mainly by compression, provided the sandwich does not disintegrate in an unstable fashion.
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