This report documents two studies that were conducted to review, assess, and provide recommendations regarding the seismic design of bridge foundations. Specifically, the report addresses modeling approaches and parameters that affect the seismic design and response of pile groups and drilled shafts. The report attempts to bridge the interface between the structural and geotechnical design process by describing a two-step design and analysis procedure for these bridge foundation components. Recent research results on pile group effects and the design of pile foundations to resist lateral spreading of liquefiable soils are also reviewed. Recommendations are provided concerning: modifications to p-y curves to account for cyclic loading conditions, pile group effects and soil-pile interaction behavior, and development of p-y curves for the design of drilled shafts.
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GEOTECHNICAL ENGINEERING CIRCULAR NO. 4: GROUND ANCHORS AND ANCHORED SYSTEMS
Author: Sabatini, P J Pass, D G Bachus, R C | Size: 4.51 MB | Format:PDF | Quality:Original preprint | Publisher: GeoSyntec Consultants | Year: 1999 | pages: 312
This document presents state-of-the-practice information on the design and installation of cement-grouted ground anchors and anchored systems for highway applications. The anchored systems discussed include flexible anchored walls, slopes supported using ground anchors, landslide stabilization systems, and structures that incorporate tiedown anchors. This document draws extensively from the FHWA-DP-68-IR (1988) design manual in describing issues such as subsurface investigation and laboratory testing, basic anchoring principles, ground anchor load testing, and inspection of construction materials and methods used for anchored systems. This document provides detailed information on design analyses for ground anchored systems. Topics discussed include selection of design earth pressures, ground anchor design, design of corrosion protection system for ground anchors, design of wall components to resist lateral and vertical loads, evaluation of overall anchored system stability, and seismic design of anchored systems. Also included in the document are two detailed design examples and technical specifications for ground anchors and for anchored walls.
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USING GEOLOGIC MAPS AND SEISMIC REFRACTION IN PAVEMENT-DEFLECTION ANALYSIS
Author: Paine, J G | Size: 6.95 MB | Format:PDF | Quality:Original preprint | Publisher: University of Texas, Austin | Year: 1999 | pages: 128
The researchers examined the relationship between three data types - geologic maps, pavement deflection, and seismic refraction data - from diverse geologic settings to determine whether geologic maps and seismic data might be used to interpret deflections and assess pavement condition. Deflections measured with the Falling-Weight Deflectometer (FWD) are correlated to bedrock type as depicted on geologic maps, particularly at distant sensors. Comparisons of FWD data with mapped geologic units along six roadway segments revealed differences in FWD response that are likely to be related to differences in either bedrock type or depth. From FWD data alone, it is difficult to determine whether the relationship between rock type and deflections is caused by differences in bedrock type or depth. To resolve this ambiguity, the researchers employed the FWD and a soil-probe hammer as impulsive sources for seismic-refraction experiments at three test sites. The refraction experiments suggest that combined FWD-refraction systems could be used on pavement to aid deflection analysis by estimating bedrock depth and assist in rock-type identification by measuring compressional velocities for bedrock and overburden. The success of the refraction experiments led to the design and construction of a refraction system optimized for on-pavement use.
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UNDRAINED LATERAL PILE AND PILE GROUP RESPONSE IN SATURATED SAND
Author: Ashour, Mohamed Norris, G M | Size: 5.16 MB | Format:PDF | Quality:Original preprint | Publisher: University of Nevada, Reno | Year: 2000 | pages: 160
This report examines the use of strain wedge (SW) model formulation to evaluate the response of single piles or groups of piles in layered soils under lateral static loading. Application of the model provides behavior prediction under a wide range of strain or deflection. In this study, the capability of the SW model is extended to predict the response of a single pile or pile group under lateral loading in liquefied soil. The results from the tests suggest that the behavior of laterally loaded piles is both a function of soil and pile properties and is influenced by the level of porewater pressure that is built up in the soil surrounding the pile. Under these conditions the capacity of a loaded pile or pile group might drop significantly under such conditions.
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Author: Patty, Jill Seible, F University of California, San Diego Uang, Chia-Ming University of California, San Diego | Size: 18.66 MB | Format:PDF | Quality:Original preprint | Publisher: University of California, San Diego | Year: 2001 | pages: 146
This report describes a research program that involved experimental testing and force transfer modeling in order to characterize the behavior of a bridge design detail that integrates a steel superstructure with a concrete substructure using a concrete bent cap. During a seismic event, it is essential that the bent cap remain elastic. Focus of the research was therefore to establish a behavior profile of the bent cap connection to define limit states. The effect of two design parameters on the bent cap torsional behavior and moment capacity was examined through a series of four component tests. The two parameters examined included: bent cap reinforcement, and girder web configuration inside the bent cap. Results from the tests indicate a recommended design of stiffened steel girders integrated with a post-tensioned bent cap. Design guidelines for an integral bridge were developed, based on the experimental finds and force transfer models. The methodology for determining the bent cap torsional strength for a given earthquake, as well as recommended limits, is indicated in a design example.
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METALLIC DAMPERS FOR SEISMIC DESIGN AND RETROFIT OF BRIDGES
Author: Chen, G Mu, H Bothe, E R | Size: 6.34 MB | Format:PDF | Quality:Original preprint | Publisher: University of Missouri, Rolla | Year: 2001 | pages: 146
A practical bearing scheme is proposed in this study, consisting of expansion rocker bearings and steel rods (metallic dampers). It can accommodate seismic effects while it allows for free thermal expansion. Tests of metallic dampers have shown that dampers of straight rods can contribute over 10% damping at the small-to-medium displacement range. Extensive tests on a 1/10-scale bridge model indicated that metallic dampers can also significantly reduce the dynamic responses of the bridge by isolating vibration propagating from the substructure to the superstructure. High rocker bearings provided considerable damping to the bridge-damper system by dissipating energy along the friction surface between pin and web of the bearings. They remain stable even at the peak ground acceleration of 0.54g at resonance. To account for pounding effect at the expansion joints of bridges, design equations for determining the equivalent viscous damping corresponding to various sizes of bridge joints were developed. Integrating the equivalent damping into the response spectrum analysis procedure allows engineers to analyze the bridges with pounding effect in a linear fashion.
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Author: Bobet, A Purdue University Salgado, R Loukidis, D | Size: 5.92 MB | Format:PDF | Quality:Original preprint | Publisher: Purdue University/Indiana Department of Transportation JHRP | Year: 2001 | pages: 109
Detailed investigations of pile foundations affected by earthquakes around the world since the 1960s indicate that pile foundations are susceptible to damage to such a degree that the serviceability and integrity of the superstructure may be affected. Although numerous cases of seismically damaged piles are reported, the detailed mechanisms causing the damage are not yet fully understood. As a consequence, an effective seismic design of pile foundations has not been yet established in practice. Many road bridge structures supported on piles exist in southern Indiana. This is a region where the risk of occurrence of a dangerous earthquake is high due to its proximity to two major seismic sources, the New Madrid Seismic Zone (NMSZ) and the Wabash Valley Fault System (WVFS). The present study is a first step towards the assessment of potential earthquake induced damage to pile foundations in southern Indiana. Credible earthquake magnitudes for each of the two potential seismic sources are assessed for a return period of 1000 years. SHAKE analyses are performed at nine selected sites in southwestern Indiana to estimate the potential of ground shaking and liquefaction susceptibility. The soil profile and soil properties at each site are obtained from the archives of the Indiana Department of Transportation. The amplitude of the rock outcrop motion is estimated using attenuation relationships appropriate to the region, and estimated values are compared with predictions from the USGS. SHAKE analyses are performed for two earthquake scenarios: a NMSZ earthquake and a WVFS earthquake. Two sets of input motions are considered for each scenario. The liquefaction potential at those nine sites is assessed based on the Seed et al. (1975) method. Data from a total of 59 real cases of earthquake-induced damage to piles have been gathered through an extensive literature survey. The collected and compiled data have been used to identify the causes and types of pile damage, and the severity of damage. Based on the survey, damage is usually located near the pile head, at the interfaces between soft and stiff layers, and between liquefiable and non-liquefiable layers. Large inertial loads from the superstructure can cause crushing of the head of concrete piles. Imposed deformations due to the response of the surrounding soil can produce small to large cracks on concrete piles depending on the soil profile. In contrast, large inertial loads, liquefaction and lateral spreading can cause wide cracks. Few cases of steel piles are found in the literature. Steel casing seems to improve the performance of concrete piles. Numerical simulations of a concrete pile at a selected road bridge site with and without steel casing are used to investigate the effect of steel casing on the performance of concrete piles. Results from this work suggest that major credible seismic events can generate accelerations high enough to produce damage to concrete piles in southern Indiana. The potential of liquefaction and lateral spreading increase the likelihood of damage.
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INFLUENCE OF SOIL SOFTENING AND LIQUEFACTION ON RESPONSE SPECTRA FOR BRIDGE DESIGN
Author: Youd, T L Carter, B | Size: 18.50 MB | Format:PDF | Quality:Original preprint | Publisher: Brigham Young University | Year: 2003 | pages: 159
The purpose of this investigation is to assess the adequacy of seismic bridge design criteria and to suggest modifications to account for the influence of soil softening and liquefaction. To define the influence of soil softening on response spectra and assess the adequacy of LRFD seismic criteria, records are analyzed from five sites underlain by soils that liquefied. Findings are: (1) Where pore water pressures rose early during ground shaking, soil softening reduced short period (<0.7 sec) spectral accelerations. (2) Where soil softening did not occur early, softening has little influence on short period (<0.7 sec) ground motions. (3) Soil softening usually causes enhanced long-period (>0.7 to 1.0 sec) spectral values due to the onset of ground oscillation that persisted after strong ground shaking ceases. (4) For short fundamental periods (< 0.7 sec), LRFD acceleration coefficients, A, of either 0.60 g or 0.30 g and Code Soil Profile Types (CSPT) III or IV, elastic seismic design coefficients, Csm, conservatively envelope calculated spectra, indicating that criteria in the LRFD code are adequate for liquefiable sites. (5) For structures with fundamental periods >0.7 sec, an A of 0.60 g and a CSPT IV generates Csm, that conservatively envelope the calculated actual response spectra. (6) For design at liquefiable sites, increased ground deformation within the liquefied zone must be considered.
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1. Response of a tank under blast loading -- part I: experimental characterisation of blast loading arising from a gas explosion
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2. Response of a tank under blast loading – part II: experimental structural response and simplified analytical approach
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Seismic Analysis of Retaining Walls, Buried Structures, Embankments, and Integral Abutments
Author: Burnell, Kelly P Megally, Sami Hanna Restrepo, Jose I University of California, San Diego Seible, Frieder University of California, San Diego | Size: 7.28 MB | Format:PDF | Quality:Original preprint | Publisher: University of California, San Diego | Year: 2005 | pages: 112
This report presents the primary findings of a test that examined the seismic behavior of a precast, post-tensioned, segmental bridge superstructure with a cast-in-place, hollow, rectangular column. The test was completed in two stages. In the first stage, the prestressing level was designed to avoid any joint openings. The second stage involved removing some of the tendons in order to enable inelastic deformations of the joints in the superstructure and to impose a more severe loading condition on the joints nearest the column. This second stage of the test was conducted to serve as an introductory examination of the performance of a bridge when damage is not limited to the column and inelastic motion is allowed in the superstructure. The primary objectives of the test were to investigate the response of the opening of the superstructure joints, column-superstructure interaction, plastic hinge formation in the column, and the anticipated system failure mechanism. Detailed instrumentation was used in both the column as well as the joints of the superstructure in order to record the damage and performance of the bridge components.
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