Thomas D. O’Rourke

Northridge Earthquake Effects on Pipelines and Residential Buildings

This article is focused on the spatial variability of earthquake strong motion and its relationship with the performance of water-distribution pipelines provided by Los Angeles Department of Water and Power (ladwp) and residential buildings. Analyses of strong-motion characteristics and their correlations with pipeline and building damage were conducted with an immense geographical information system (gis) database for the 1994 Northridge earthquake, which was collected, digitized, and organized by researchers at Cornell. There are statistically significant correlations among pipeline repair rate (repairs/km) and peak ground velocity (pgv) for cast iron, ductile iron, asbestos cement, and steel pipe. Statistically significant regressions have been developed between damage ratio, dr (percent of existing structures with damage equal to or exceeding a particular damage factor, df [percent of building replacement cost]) and the magnitudes of seismic parameters, such as pgv and spectrum intensity (si). Regressions developed between dr and scaled seismic parameters (seismic parameters normalized with respect to df) resulted in predictive equations having a very high degree of statistical significance. Algorithms to visualize damage patterns for buildings were developed and validated to choose optimal gis mesh dimensions and contour intervals. Ordinary kriging was used to develop regressions of pipeline repair rate and residential building dr associated with 90% confidence pgv and spectrum intensity (weighted average pseudovelocity). Such regressions provide an explicit means of characterizing the uncertainty embodied in the strong-motion data.

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.

The 1906 San Francisco Earthquake and Fire—Enduring Lessons for Fire Protection and Water Supply

Prior to 18 April 1906 the San Francisco Fire Department and knowledgeable persons in the insurance industry regarded a conflagration in San Francisco as inevitable. The 1906 San Francisco earthquake and ensuing fire is the greatest single fire loss in U.S. history, with 492 city blocks destroyed and life loss now estimated at more than 3,000. This paper describes fire protection practices in the United States prior to 1906; the conditions in San Francisco on the eve of the disaster; ignitions, spread, and convergence of fires that generated the 1906 conflagration; and damage to the water supply system in 1906 that gave impetus to construction of the largest high-pressure water distribution network ever built—San Franciscos Auxiliary Water Supply System (AWSS). In the 1980s hydraulic network and fire simulation modeling identified weaknesses in the fire protection of San Francisco—problems mitigated by an innovative Portable Water Supply System (PWSS), which transports water long distances and helped extinguish the Marina fire during the 1989 Loma Prieta earthquake. The AWSS and PWSS concepts have been extended to other communities and provide many lessons, paramount of which is that communities need to develop an integrated disaster preparedness and response capability and be constantly vigilant in maintaining that capability. This lesson is especially relevant to highly seismic regions with large wood building inventories such as the western United States and Japan, which are at great risk of conflagration following an earthquake.

Lateral Soil-Pipe Interaction in Dry and Partially Saturated Sand

AbstractThis paper describes finite-element (FE) modeling, validated by large-scale tests, to simulate the lateral force versus displacement relationship of pipelines under plane-strain conditions in both dry and partially saturated sand. The FE model is based on an elastoplastic characterization of the soil, with Mohr-Coulomb strength parameters to determine the soil yield surface. Direct shear test data and strain softening models are used to represent peak and postpeak strength behavior. A methodology for defining a strain-compatible secant modulus is also presented. The analytical results are compared with numerous large-scale experimental test results, showing excellent agreement in terms of prepeak, peak, and postpeak performance. The modeling process is used to show the relationship between the maximum lateral force and pipe depth and to explain decreased dimensionless maximum lateral forces mobilized by large diameter pipes at low depth to diameter ratios in dense sand.

Direct Tension Performance of Steel Pipelines with Welded Slip Joints

Full-scale direct tension test results are presented in this paper for two steel pipelines with welded slip joints, using high quality external welds, and an outer diameter and wall thickness of 320 and 6.4 mm, (12.5 and 0.25 in.) respectively. The test pipes were loaded to complete circumferential tensile failure. The results of numerical simulations with a two-dimensional axisymmetric solid finite-element (FE) models using the program ABAQUS compare favorably with the experimental measurements. The FE results show that pipelines in the field with high quality welds can sustain maximum tensile strain of about 0.03 even with internal pressure. Assuming good welds, an allowable tensile strain level of 0.01 to 0.015 is recommended. The test results are discussed with respect to welding and inspection practices, as well as their application in the design and risk assessment of pipelines subject to large ground deformation caused by earthquakes, landslides, and subsidence.

Pipelines Subjected to Fault Movement in Dry and Unsaturated Soils

Because pipelines traverse large geographical areas, they frequently must cross active faults when constructed in locations vulnerable to earthquakes. In this study, the authors performed three-dimensional (3D) finite-element analyses to investigate the behavior of buried pipe subject to strike-slip fault movement in dry sand and, more realistically, in partially saturated sand. The performance of the finite-element model was first validated by comparing the computed results with the data from the full-scale experiments at Cornell University. The analysis was then extended by varying the initial conditions of the sand (e.g., sand type, density, moisture content), pipe material, pipe burial depth, and pipeline–fault-rupture inclination to assess the effect of these parameters on the soil loads applied to the pipe and the corresponding deformations. On the basis of the simulation results, the authors propose a soil–structure interaction mechanism for pipelines crossing active faults. The authors also propose design recommendations for the mitigation of ground-deformation effects at buried pipeline crossings of strike-slip faults.

Compression Performance of Steel Pipelines with Welded Slip Joints

The results of full-scale compression tests are presented for the welded slip joints (WSJs) of steel pipelines of nominal 300, 810, and 910 mm (12, 32, and 36 in.) diameter (D) , representing diameter-to-thickness (t) ratios ( D/t ) ranging from 48 to 255. Also, the results of numerical simulations with a 2D axisymmetric solid finite-element model using the program ABAQUS are presented and shown to compare favorably with the experimental measurements. On the basis of finite-element simulations, dimensionless charts are developed that show the ratio of the maximum axial compressive load to yield load of the pipe versus D/t for various wall thicknesses. The charts also apply for internal, external, and for combined internal and external fillet welds. Conclusions are drawn with respect to WSJ ductility, pipeline performance, axial compressive capacity of the joints, fatigue cyclic response, and capacity of WSJ due to earthquake loading. In general, the WSJ capacity is shown to decline from approximately 85% ...

Liquefaction and Ground Failures in San Francisco

This paper examines the liquefaction and ground failures observed in San Francisco after the 1906 earthquake. It summarizes soil conditions, land development, and local seismic intensities within the city. Earthquake damage of the San Francisco water distribution system is discussed, and an account is provided of how city planners used the water supply damage to map locations of “infirm ground,” which are used today in the design and operation of the city fire protection system. Maps are presented that show subsurface conditions, current street system, permanent ground deformation, and infrastructure damage in 1906. With the use of approximately 500 soil borings and soundings compiled in a geographical information system (GIS), liquefaction hazard maps are generated for the Mission Creek and South of Market areas of the city.

ShakeOut Scenario: Water System Impacts from a Mw 7.8 San Andreas Earthquake

Seismic response simulations of the Los Angeles water supply to a Mw 7.8 San Andreas Fault earthquake scenario are used to assess the regional aqueduct and water distribution system performance in Southern California. Aqueducts sustain significant damage, and restoration of water flow is estimated to take between 4 and 18 months. Local emergency water supplies are insufficient to match the duration of aqueduct repairs, requiring severe water rationing. System serviceability declines rapidly due to numerous pipe leaks, causing serious difficulties for firefighting. Water service restoration to all customers is projected to take several months, with restoration of pre-earthquake water demand requiring more than a year. Business interruptions from long-term water rationing affect the regional economy greater than previously anticipated. Results from this scenario show how critical it is for all water agencies to prepare for a large-magnitude San Andreas earthquake.