Michael O’Rourke

Buried high-density polyethylene pipelines subjected to normal and strike-slip faulting — a centrifuge investigation

Permanent ground deformation is arguably the most severe hazard for continuous buried pipelines. This paper presents results from two pairs of centrifuge tests designed to investigate the differences in behavior of buried high-density polyethylene pipelines subjected to normal and strike-slip faulting. The tests results show that, as expected, the pipeline behavior is asymmetric under normal faulting and symmetric under strike-slip faulting. In the case of strike-slip faulting, the soil–pipe interaction pressure distribution is symmetric with respect to the fault. However, in the case of normal faulting, there is a pressure concentration close to the fault trace on the up-thrown side, with much lower soil–pipe interaction pressures at other locations on the pipe. The soil–pipe interaction force versus deformation relationship (i.e., the p–y relationship) was obtained based on the experimental data. The p–y relationships for both the strike-slip and normal faulting cases were also compared with the relatio...

Tactile Pressure Sensors for Soil-Structure Interaction Assessment

This paper provides an assessment of tactile pressure sensors for geotechnical applications. A tactile pressure sensor is an array of small sensing units, called sensels, embedded in a polymeric sheet or pad that measures the magnitude and distribution of stresses normal to the sheet surface. Methods for minimizing the effects of shear on sensor measurements are discussed and the efficacy of these methods are demonstrated by laboratory experiments. The time-dependent characteristics of the sensors are evaluated and recommendations are provided for measurements that account for time-dependent effects. Tactile pressure sensor measurements in response to vertical loading and unloading and to lateral loads on full-scale pipelines affected by large horizontal ground movements are compared with independent measurements of the loads. Sensor measurements are used to show the distribution of normal stress on pipelines subject to large lateral soil movement.

Model for Snow Loading on Gable Roofs

AbstractA particularly large database containing simultaneous measurements of roof and ground snow loads were analyzed for the purpose of establishing a simple empirical model for gable roof snow loads. Due to the nature of the database, the model was developed specifically for unheated structures with nonslippery roof surfaces. As such, it is expected to provide conservative load estimates for heated structures and structures with slippery roof surfaces. The model results are compared to corresponding provisions for balanced and unbalanced snow loads in various United States and European codes and load standards.

Performance-Based Design of Buried Steel Pipes at Fault Crossings

Buried steel pipes are commonly used in oil and gas industry for transmitting hydrocarbon products. Fault crossing is considered as one of the most important extreme events. Buried steel pipes are more vulnerable to compressive strains as compared to tensile strains. Therefore, the orientation angle of the pipe with respect to the fault should be arranged in such a way so as to promote net tension in the pipe.In this study, a numerical study is carried out on a simplified numerical model to determine the seismic demand on steel pipes at fault crossings. The proposed model permits plastic hinge formation in the pipe due to incrementally applied fault movements, allow determining the critical length of the pipeline and measure strains developed on the tension and compression sides in the pipe. Based on the analyses carried out on the simple model and previous studies, two performance levels are defined for pipelines; namely, fully functional and partially functional.Copyright

Local Buckling of Buried HDPE Pipelines Subjected to Earthquake Faulting: Case Study Via Numerical Simulations and Experimental Testing

ABSTRACT This paper presents an integrated experimental and numerical study of high-density polyethylene pipeline behavior under earthquake faulting that induces both bending and compression. The experimental studies were conducted utilizing equipment for large-scale soil-structure interaction and centrifuge-scale split-box testing. The numerical results support the experimental observation that local buckling initiation in the plastic hinge region of the pipeline is due to high plastic strains controlled by local buckling of the cross-section. In addition to evaluating the effectiveness of finite element models for simulating the response of pipelines subjected to faulting, parametric analyses were performed to further investigate the buckling phenomenon.

Seismic Behavior of Buried PE Pipelines Subject to Fault Offsets

The paper presents the results of a series of centrifuge tests on the behavior of buried PE pipe subject to the fault offset hazard. The tests simulated both Strike-Slip (SS) and Normal offsets. Besides fault type, the three main parameters that were varied include the pipe burial depth, the intersection angle between the pipe axis and the fault (SS faults) and the direction of faulting (SS with right lateral or left lateral offset). Instrumentation allowed acquisition of pipe strain data which was decomposed into axial strain and flexural (bending) strain components. The paper will describe the rates at which strain decreases with distance from the fault, and the strong influence of burial depth and intersection angle on the magnitude of axial and flexural strain. New instrumentation allowed acquisition of the normal pressure between the buried PE pipe and the surrounding soil. As one might expect the normal pressure varied in the circumferential direction, as well as with distance from the fault. These pressures were used to estimate force-deformation characteristics of the equivalent ‘soil-springs’. Unlike the 2-D behavior assumed for soil-spring models currently used in practice, the centrifuge results show that the behavior is actually 3-D in nature. Fortunately, as will be shown in the paper, 2-D soil-spring models yield conservative results in terms of pipe strains.Copyright

Wave Propagation Effects on Buried Pipe at Treatment Plants

Closed form analytical relations are developed for wave propagation effects on buried pipelines which interconnect tanks and/or buildings. The relations cover the axial strain induced in a pipe with various end conditions, the induced axial force at the pipe/tank interface, and the relative displacement at the tank for a pipe with a free end condition. The relations utilize the concept of a pipe development length, defined as the distance over which soil friction forces must act to induce a pipe strain equal to a given level of ground strain. If the available length is less than this development length, the pipe strain is less than the ground strain. Finally an example illustrates the application of the relations and presents simplified upper bound values for pipe strain, axial force, and relative displacement.