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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Seismic Analysis of Retaining Walls, Buried Structures, Embankments, and Integral Abutments
Author: McLean, David I | Size: 2.11 MB | Format:PDF | Quality:Unspecified | Publisher: Washington State Transportation Center | Year: 2005 | pages: 82
Experimental tests were conducted on seven 1/3-scale specimens to define the vulnerabilities of existing outrigger bents under in-plane and out-of-plane seismic loading and to develop appropriate retrofit measures that address the identified vulnerabilities. The specimens represented bents with short and long outrigger beams in the SR-99 Spokane Street Overcrossing in western Washington State. The as-built specimens failed at low ductility levels due to shear distress, low torsional strength of the beam, and reinforcement bond failures within the joint. Circular and D-shaped steel jackets were used to retrofit the regular and split as-built specimens, respectively. The retrofitted specimens developed plastic hinging in the column, with enhanced strength, energy and ductility capacities. Threshold principal tension stress values describing the expected condition of the joints were established and compared to values obtained by other researchers. Design and detailing guidelines for retrofitting outrigger bents were proposed. The guidelines include equations for the jacket thickness required to form a stable force transfer mechanism between the beam and the column reinforcement as well as to prevent joint failure.
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This study evaluates the impact of the newly recommended seismic design guidelines from NCHRP 12-49 on seismic design of bridges in New Jersey. It also provides seismic design criteria and guidelines for integral abutments, retaining walls, embankments, and buried structures. The study provides an overall review of the recommended guidelines and compares them to the current AASHTO LRFD specifications. It provides recommendations on seismic hazard and performance objectives and soil site factors for New Jersey that incorporate design criteria from NCHRP 12-49 guidelines, AASHTO LRFD specifications, South Carolina seismic design criteria, and NYCDOT seismic design guidelines. The study also includes two design examples based on the NCHRP 12-49 guidelines and current AASHTO LRFD specifications. Research results showed that: (1) the MCE ground motion level adopted by NCHRP 12-49 which has a 2500-year return is acceptable for safety evaluation of 'critical bridges' in New Jersey, (2) a reduced (2/3 MCE) ground motion is acceptable for safety evaluation of 'non-critical' bridges; (3) soil-site factors have increased dramatically for soft soils subjected to small ground motions which will have an impact on seismic design in Southern Jersey, (4) the USGS National Seismic Hazard Maps adopted by NCHRP 12-49 for ground motion accelerations may not necessarily reflect the actual geological soil conditions and realistic hazard levels in New Jersey, (5) NCHRP 12-49 SDAP E (pushover analysis) is preferable for the seismic analysis and design of bridges in New Jersey, and (6) NCHRP 12-49 SDAP C is a relatively simplified design procedure for many bridges and should be used when applicable. Recommendations from this study include adoption of NCHRP 12-49 subject to the above conclusions. However, there is a need to: (1) predict extreme earthquake events for New Jersey and the Northeast United States, (2) prepare Seismic Hazard Maps for bridge design in New Jersey and re-evaluate NCHRP 12-49 soil-site factors proposed for New Jersey, and (3) quantify damage level by using structural capacity and demand.
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Condition Indexing and Hazards Analysis for Communications Towers
Author: Likos, William J Salim, Hani | Size: 5.23 MB | Format:PDF | Quality:Unspecified | Publisher: University of Missouri, Columbia | Year: 2005 | pages: 118
Design and construction of the Missouri Department of Transportation (MoDOT) two-way radio network was initiated in the 1950’s and 60’s and was motivated primarily by the need to provide a statewide communication system for civil defense related issues. Today, the system is one of the largest networks in the state for providing voice and data communications associated with daily field operations as well as during times of emergency. Increasing reliance on the network is envisioned in the future to support wireless interoperability (e.g., with police and fire) and to support an increasing load of data communications for intelligent transportations system (ITS) infrastructure. Growing concern regarding the network’s performance during natural hazard events, most notably the possibility for significant earthquakes originating from the New Madrid Seismological Zone, has stimulated the desire for a comprehensive analysis of the network and the development of systematic asset management tools. A recent statewide emergency preparedness exercise involving a mock 6.7 magnitude earthquake revealed that the chief obstacle encountered as field crews attempted to communicate with each other was failure of the radio towers. Many of the towers are over 40 years old and in relatively poor physical condition. The primary objectives of this project were (1) to develop a rational condition indexing (CI) system as an asset management tool that may be used to systematically quantify the physical condition of towers in the network; (2) to conduct detailed dynamic and static structural analyses of key towers under seismic, wind and ice loading; (3) to evaluate the general effects of physical deterioration (e.g., corrosion related to aging) on tower dynamic response and stability; and (4) to develop a centralized electronic database. A CI system has been developed to quantify the physical condition of guyed communications towers. Use of the proposed system is demonstrated for two towers (Taum Sauk and Ashland) selected to represent towers in relatively poor and relatively good condition, respectively. Results from structural analysis indicate that the Taum Sauk tower (as built condition) is not loaded to near its capacity under simulated seismic loading. The Taum Sauk tower is shown to pass TIA-222-F code specifications with respect to wind and ice loading. Deterioration to the Taum Sauk tower was simulated by reducing the cross sectional areas of the guy cables, diagonal braces, and axial leg members. A free standing tower in Kansas City was also analyzed and is shown to be loaded to 2% over capacity according to TIA-222-C but meets the more recent 222-F code requirements. An electronic web-based database was developed for implementation into management of the tower network. General recommendations for implementing the results of these efforts are provided, which includes a recommendation to consider the proposed CI approach for a wide range of infrastructure managed by MoDOT.
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