122 research outputs found
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Dynamic field test of a model levee founded on peaty organic soil using an eccentric mass shaker
A dynamic field test of a model levee was performed to study the behavior of very soft and compressible peaty organic soils that commonly underlie levees in the Sacramento / San Joaquin Delta in northern California. This first-of-its-kind test applied dynamic loads to the levee/peat system using a large eccentric mass shaker mounted on the levee crest. Loads from the shaker and the inertia of the levee section are transmitted to the peaty organic soils as base shear stresses, and rotational demands that manifest as normal pressures at the embankment/peat interface. We seek to characterize the transmission of seismic energy between the underlying soft peat and the overlying, comparatively stiff levee fills. A crucial step in the evaluation of the test data is calculation of the amplitude and phase of shaker forces. We compute the centrifugal force from discretely sampled proximity transducer data using a cosine sweep interpolation function
Influence of Kinematic SSI on Foundation Input Motions for Pile- Supported Bridges
ABSTRACT The seismic analysis of bridge structures is often performed using the substructure method in which the foundation is replaced by an equivalent "spring" representing foundation impedance. Ground motions from seismic hazard analyses correspond to a free-field condition, and therefore should be modified to account for kinematic soil-structure interaction effects before being used as input to the springs. This paper presents closed-form analytical solutions for the response of an elastic pile subjected to harmonic seismic excitation in uniform elastic soil. We use these solutions to compute transfer functions relating foundation input motion to free-field ground motion and use the results to verify predictions from a beam-on-Winkler-foundation numerical model. The two approaches show good agreement, indicating that the numerical modeling method is appropriate for investigating more complex effects such as soil and pile nonlinearity. Ground motion deamplification due to kinematic SSI is demonstrated to be significant for stiff foundations in soft ground conditions. Numerical simulations using recorded ground motions demonstrates that transfer functions can be computed only from frequency bands for which the motions contain adequate energy
Seismic Damage Accumulation of Highway Bridges in Earthquake Prone Regions
Civil infrastructures, such as highway bridges, located in seismically active
regions are often subjected to multiple earthquakes, such as multiple main shocks
along their service life or main shock-aftershock sequences. Repeated seismic events
result in reduced structural capacity and may lead to bridge collapse causing
disruption in normal functioning of transportation networks. This study proposes a
framework to predict damage accumulation in structures under multiple shock
scenarios after developing damage index prediction models and accounting for the
probabilistic nature of the hazard. The versatility of the proposed framework is
demonstrated on a case study highway bridge located in California for two distinct
hazard scenarios: a) multiple main shocks along the service life, and b) multiple
aftershock earthquake occurrences following a single main shock. Results reveal that
in both cases there is a significant increase in damage index exceedance probabilities
due to repeated shocks within the time window of interest
Evolution of Fields in a Second Order Phase Transition
We analyse the evolution of scalar and gauge fields during a second order
phase transition using a Langevin equation approach. We show that topological
defects formed during the phase transition are stable to thermal fluctuations.
Our method allows the field evolution to be followed throughout the phase
transition, for both expanding and non-expanding Universes. The results verify
the Kibble mechanism for defect formation during phase transitions.Comment: 12 pages of text plus 17 diagrams available on request, DAMTP 94-8
The Effects of Long-Duration Subduction Earthquakes on Inelastic Behavior of Bridge Pile Foundations Subjected to Liquefaction-Induced Lateral Spreading
Effective-stress nonlinear dynamic analyses (NDA) were performed for a large-diameter reinforced concrete (RC) pile in multi-layered liquefiable sloped ground. The objective was to assess the effects of earthquake duration on the combination of inertia and liquefaction-induced lateral spreading. A parametric study was performed using input motions from subduction and crustal earthquakes covering a wide range of motion durations. The NDA results showed that the pile head displacements increased under liquefied conditions, compared to nonliquefied conditions, due to liquefaction-induced lateral spreading. The NDA results were used to develop a displacement-based equivalent static analysis (ESA) method that combines inertial and lateral spreading loads for estimating elastic and inelastic pile demands
Liquefaction and Related Ground Failure from July 2019 Ridgecrest Earthquake Sequence
The 2019 Ridgecrest earthquake sequence produced a 4 July M 6.5 foreshock and a 5 July M 7.1 mainshock, along with 23 events with magnitudes greater than 4.5 in the 24 hr period following the mainshock. The epicenters of the two principal events were located in the Indian Wells Valley, northwest of Searles Valley near the towns of Ridgecrest, Trona, and Argus. We describe observed liquefaction manifestations including sand boils, fissures, and lateral spreading features, as well as proximate nonâground failure zones that resulted from the sequence. Expanding upon results initially presented in a report of the Geotechnical Extreme Events Reconnaissance Association, we synthesize results of field mapping, aerial imagery, and inferences of ground deformations from Synthetic Aperture Radarâbased damage proxy maps (DPMs). We document incidents of liquefaction, settlement, and lateral spreading in the Naval Air Weapons Station China Lake US military base and compare locations of these observations to preâ and postevent mapping of liquefaction hazards. We describe liquefaction and groundâfailure features in Trona and Argus, which produced lateral deformations and impacts on several singleâstory masonry and wood frame buildings. Detailed maps showing zones with and without ground failure are provided for these towns, along with mapped ground deformations along transects. Finally, we describe incidents of massive liquefaction with related ground failures and proximate areas of similar geologic origin without ground failure in the Searles Lakebed. Observations in this region are consistent with surface change predicted by the DPM. In the same region, geospatial liquefaction hazard maps are effective at identifying broad percentages of land with liquefactionârelated damage. We anticipate that data presented in this article will be useful for future liquefaction susceptibility, triggering, and consequence studies being undertaken as part of the Next Generation Liquefaction project
Recommended from our members
Liquefaction and Related Ground Failure from July 2019 Ridgecrest Earthquake Sequence
The 2019 Ridgecrest earthquake sequence produced a 4 July M 6.5 foreshock and a 5 July M 7.1 mainshock, along with 23 events with magnitudes greater than 4.5 in the 24 hr period following the mainshock. The epicenters of the two principal events were located in the Indian Wells Valley, northwest of Searles Valley near the towns of Ridgecrest, Trona, and Argus. We describe observed liquefaction manifestations including sand boils, fissures, and lateral spreading features, as well as proximate nonâground failure zones that resulted from the sequence. Expanding upon results initially presented in a report of the Geotechnical Extreme Events Reconnaissance Association, we synthesize results of field mapping, aerial imagery, and inferences of ground deformations from Synthetic Aperture Radarâbased damage proxy maps (DPMs). We document incidents of liquefaction, settlement, and lateral spreading in the Naval Air Weapons Station China Lake US military base and compare locations of these observations to preâ and postevent mapping of liquefaction hazards. We describe liquefaction and groundâfailure features in Trona and Argus, which produced lateral deformations and impacts on several singleâstory masonry and wood frame buildings. Detailed maps showing zones with and without ground failure are provided for these towns, along with mapped ground deformations along transects. Finally, we describe incidents of massive liquefaction with related ground failures and proximate areas of similar geologic origin without ground failure in the Searles Lakebed. Observations in this region are consistent with surface change predicted by the DPM. In the same region, geospatial liquefaction hazard maps are effective at identifying broad percentages of land with liquefactionârelated damage. We anticipate that data presented in this article will be useful for future liquefaction susceptibility, triggering, and consequence studies being undertaken as part of the Next Generation Liquefaction project
First Observation of the Baryon and a New Measurement of the Mass
Using data recorded with the CLEO II and CLEO II.V detector configurations at
the Cornell Electron Storage Rings, we report the first observation and mass
measurement of the charmed baryon, and an updated measurement
of the mass of the baryon. We find
= 231.0 +- 1.1 +- 2.0 MeV, and
= 166.4 +- 0.2 +- 0.3 MeV, where the errors are
statistical and systematic respectively.Comment: 8 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
Strong Decays of Strange Quarkonia
In this paper we evaluate strong decay amplitudes and partial widths of
strange mesons (strangeonia and kaonia) in the 3P0 decay model. We give
numerical results for all energetically allowed open-flavor two-body decay
modes of all nsbar and ssbar strange mesons in the 1S, 2S, 3S, 1P, 2P, 1D and
1F multiplets, comprising strong decays of a total of 43 resonances into 525
two-body modes, with 891 numerically evaluated amplitudes. This set of
resonances includes all strange qqbar states with allowed strong decays
expected in the quark model up to ca. 2.2 GeV. We use standard nonrelativistic
quark model SHO wavefunctions to evaluate these amplitudes, and quote numerical
results for all amplitudes present in each decay mode. We also discuss the
status of the associated experimental candidates, and note which states and
decay modes would be especially interesting for future experimental study at
hadronic, e+e- and photoproduction facilities. These results should also be
useful in distinguishing conventional quark model mesons from exotica such as
glueballs and hybrids through their strong decays.Comment: 69 pages, 5 figures, 39 table
Silicon location through backscattered electron imaging and X-ray microanalysis in leaves of Cyperus ligularis L. and Rhynchospora aberrans C. B. Clarke (Cyperaceae)
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