| 2011 |
Seku Catacoli, Carlos E. Ventura, Steve McDonald |
Directionality in the Transverse Response of Skewed Multi-Span Bridges with Integral Abutments |
Structural Engineering |
This paper presents the results of the system identification for the transverse direction of skewed bridges and how these have been used to illustrate that the predominant direction of transverse response occurs in the azimuth of the skewed bents. Ambient vibration tests were conducted at two skewed bridges with integral abutments located in British Columbia, Canada. For the case of integral abutment bridges, this paper provides experimental support for the recommendations to define the directions of maximum displacement response contained in AASHTO-2009. |
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| 2011 |
Miguel Fraino, Carlos E. Ventura |
Analysis of Seismic Records to Evaluate Soil-Structure Interaction Effects on Bridges |
Structural Engineering |
Includes results of several analyses conducted with seismic records obtained from two instrumented bridges in California -Via California and Lake Crowley- in order to determine how SSI affects their dynamic properties. The records correspond instruments located on free field, foundation piles, substructure and superstructure. The results include fundamental mode properties identified for each bridge, comparison of spectral response quantities, determination of directionality effects and evaluation of signals using frequency domain techniques. |
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| 2012 |
Amin Rahmani, Mahdi Taiebat, W.D. Liam Finn, and Carlos E. Ventura |
Evaluation of p–y Curves Used in Practice for Seismic Analysis of Soil–Pile Interaction |
Geotechnical Engineering |
In this paper the efficiency of API p-y curves for seismic analysis of soil–pile interaction is investigated. For this purpose, recorded results of four centrifuge tests conducted on single pile foundations are compared with the computed results based on the BNWF approach employing the API p–y curves. The prediction of the seismic response based on the API p–y curves was found to be poor in the studied cases. |
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| 2012 |
Miguel Fraino, Carlos E. Ventura, W.D. Liam Finn, Mahdi Taiebat |
Seismic Soil-Structure Interaction Effects in Instrumented Bridges |
Structural Engineering |
Presents preliminary results from a major study of the seismic response of bridges, based on acceleration records from instrumented bridges. The first objective is to investigate soil structure interaction (SSI) and how it has affected the responses of the bridges and especially the input motions to the bridges. The effects of SSI are demonstrated by comparing the acceleration spectra of the free field motions with the spectra of the bridge motions recorded at the foundation level. The results show that the free field motions are not always deamplified, which is not due only to differences in bridge structure or site conditions. The paper provides a detailed exposition of SSI effects on the instrumented bridges and clarify mechanisms leading to the observed phenomena. |
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| 2012 |
M.S. Fayyazi, M. Taiebat, W.D.L. Finn and C.E. Ventura |
Evaluation of Group Factor Method for Analysis of Pile Groups |
Geotechnical Engineering |
It is common practice to use a p-multiplier for modifying the single pile p–y curve to account for group reduction effects. Use of the p-multiplier technique in pile group design relies on the ratio of the pile spacing in the loading direction to the pile diameter and it is defined row by row. The direction of loading changes during the seismic and cyclic loading event. Therefore rather than defining p-multipliers row by row, an average p-multiplier for all piles in the group is used. This average p-multiplier is called group factor. The group factor is obtained through static tests. Group factor is a function of different parameters like pile spacing, soil type, and pile group size. In this study group factors for pile groups with different pile spacings are calculated and the effect of spacing on the group factor is investigated. |
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| 2012 |
B.H. Pandey, C.E. Ventura and W.D.L. Finn |
Modification of Free-Field Motions by Soil-Foundation-Structure Interaction for Shallow Foundations |
Earthquake Engineering |
This paper describes the effects of soil-foundation-structure interaction (SFSI) on 22 instrumented buildings in California. A total of 99 earthquake records obtained from these building sites have been analysed. Comparisons of response spectra from the free-field with the corresponding spectra from the foundations clearly show the effect of SFSI. 66 records showed significant reductions in spectral values at the foundation level for periods less than about 0.5- 0.6s and 33 records showed amplification in spectral values. ASCE41-06 recognizes that foundations with interconnected grade beams or concrete slab will always reduce the free-field motions except for buildings sitting on soft clay sites and having flexible roof and floor diaphragms. These methods and ASCE41-06 provisions were applied to the free-field data of those 66 records that showed reduction in spectral values to estimate the corresponding foundation motions. From the comparisons it was observed that, in general, the agreement was poor. A preliminary study of the foundations, buildings and site conditions of 33 records showing spectral amplification found that these buildings had rigid floors diaphragms and were not on soft clay soils. Therefore according to ASCE41-06 the spectral response of the foundation should have been reduced instead of amplified. This discrepancy needs to be explored. |
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| 2012 |
S. Molnar, C. E. Ventura, W. D. L. Finn, M. Taiebat, S. E. Dosso, and J. F. Cassidy |
Probabilistic site characterization based on Bayesian inversion of ambient vibration array recordings in SW British Columbia, Canada |
Site Response |
Probability distributions for common predictors of site amplification are computed based on a sample of VS profiles drawn from the posterior probability density (PPD) of the microtremor inversion. Sites of contrasting site amplification behaviour in SW British Columbia, Canada, were chosen, collocated with invasive VS measurement sites, to apply and evaluate the microtremor array method for site response characterization. |
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| 2012 |
S. Molnar, C. E. Ventura, W. D. L. Finn, M. Taiebat, S. E. Dosso, and J. F. Cassidy |
Evaluation of shear-wave velocity profiles from ambient vibration array recordings in SW British Columbia, Canada |
Site Response |
This paper presents the process of determining and evaluating acceptable VS models at a site. A best-fit VS profile is determined from inversion of ambient vibration array recordings, for a given model parameterization, using a hybrid optimization scheme. The most appropriate model parameterization is determined using the Bayesian information criterion, which provides the simplest model consistent with the resolving power of the data. The best-fit VS profiles are assessed for reliability by direct comparison with collocated invasive VS measurements. |
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| 2012 |
M.S. Fayyazi, M. Taiebat, W.D.L. Finn and C.E. Ventura |
Evaluation of p-multiplier method for performance-based design of pile groups |
Geotechnical Engineering |
The analysis method for soil–pile interaction significantly affects the predicted response of pile-supported structures; therefore, the method in which soil–pile interaction is simulated is very important for PBD. p-multiplier method is the most widely used in practice. In the proposed p-multipliers in practice, the influence of pile spacing in the same row, which is normal to the loading direction, is usually ignored. In this paper, first the influence of row by row spacing and influence of spacing in a row on the response of a pile group are evaluated separately and compared with each other. Then for observing the influence of spacing in a row in a real pile group, response of a 3×3 pile group is analyzed using a continuum model. The analytical results are compared with data from a full scale pile group test to investigate the reliability of the continuum model. Then, using continuum model, the effect of changing the spacing in a row is evaluated to see the difference. |
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