File Name: advanced geotechnical engineering soil-structure interaction using computer and material models .zip
Advanced Geotechnical Engineering Civil and Environmental Geotechnical engineering geotechnical engineering has evolved into a highly specialized engineering practice as technology has advanced and analytical methods have improved.
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Refworks Account Login. Open Collections. UBC Theses and Dissertations. Featured Collection. Upul Atukorala, Golder Associates Ltd. Despite its major effects, SSI is not sufficiently addressed in current design code and practice.
In this study, the effect of SSI on the seismic response of Reinforced Concrete RC bridges is studied within the framework of performance-based earthquake engineering. This thesis is organized in three phases that investigate three different aspects of SSI in relation to analysis, assessment and design. Phase one is focused on investigating the kinematic effect and variation of foundation motion from the free-field motion. To achieve this, detailed 3D continuum models are developed.
Response time history analyses are performed on the models using ten unscaled ground motions to investigate variation of bridge foundation motions from free-field motions.
The finite element simulation results show that an amplification of the free-field motions takes place in the low frequency regime that covers the first few natural frequencies of the system.
The tau-averaging method and Elsabee and Morray Transfer function are unable to predict the amplification regime observed in the simulations. In phase two, a discrete simulation approach is adopted to carry out performance assessment of RC bridges considering soil-structure interaction.
Four archetype models with various levels of SSI representation are developed. Incremental Dynamic Analysis IDA is performed using a set of 22 ground motions to derive collapse fragility curves for each archetype model. The role of SSI in the calculated collapse fragility curves and corresponding failure modes is investigated.
In phase three, a comprehensive nonlinear continuum model of the MRO is developed. Seismic response of the continuum model in terms of drift, base shears, and spectral acceleration is compared to the discrete model developed in previous phase. It is shown that the responses predicted using the discrete and continuum approaches are significantly different mainly due to their differences in material constitutive models or representation of SSI effects, specifically the kinematic effect.
This research aims to investigate SSI effects on the seismic response of bridges in three phases. Phase one focuses on the variation of bridge foundation motion from the free-field motion. Investigation shows an amplification of the bridge foundation motion in the low frequency regime. In phase two, the role of SSI in the probability of collapse of RC bridges and change of failure mode is investigated using the discrete method, and a collapse assessment procedure is proposed for evaluation of seismic performance of RC bridges.
In the third phase, seismic response of a nonlinear continuum model of the MRO bridge in California is compared with the response obtained from the discrete model. This comparison showed a significant difference in predicted responses from two models. Some parts of this thesis, listed below, have been published in conference proceedings by the same authors. I was the principal author of the paper and conducted all the numerical analyses and writing of the paper.
Professors Ventura and Finn supervised this research and aided in revising this manuscript. Calculated plastic hinge length and hinge to total length ratio for the pier column. Image reproduced from Kramer, Abutment embankment is not shown for clarity Compression strength is considered a negative value. Red color is an indicator of yielding state around the piles and the observed time in the calculated acceleration time histories.
Predicted spectral acceleration- Bridge foundation S1 Horizontal response spectral acceleration coefficient at 1. Geological Survey xliv Acknowledgements I would like to express my deepest gratitude to my academic supervisor, Professor Carlos Ventura, for his outstanding guidance in research and generous advice in teaching and many other aspects offered by him.
I feel truly honoured to have the opportunity of being his student. The completion of this thesis would have not been possible without his insightful comments and valuable feedback.
His penetrating questions taught me to question more deeply. I thank him for enlarging my vision of science and providing coherent answers to my endless questions.
I offer my enduring gratitude to my supervisory committee, Dr. Farzad Naeim, Dr. Upul Atukorala, Dr. Anoosh Shamsabadi, and Professor Ahmed Elgamal.
Their feedback was essential to the success of this research. I offer my enduring gratitude to the faculty of the department of Civil Engineering, especially, Professors Reza Vaziri and Ricardo Foschi, who have inspired me to continue my work in this field. I owe particular thanks to Dr. Alireza Forghani, who was a true mentor to me. He guided me to move forward in my research while keeping my ideas and efforts focused on the main theme of the thesis.
His comments and feedback inspired me to excel my work every step of the way. I am deeply thankful to my wife, Maryam, and my son, Mohammad, for their continual support, inspiration, and being there for me at hard times and sharing the happy moments throughout the years of studying and living in Vancouver.
Words cannot express my appreciation to them. I am eternally grateful to my parents who always listened to me and shared a piece of advice on the different challenges I faced. This degree and all my achievements would not be possible without their encouragements and continuous support.
Lack of understanding and consideration of the effect of Soil-Structure Interaction SSI is among the major reasons behind these devastating collapses Mylonakis et al. One of the famous examples where SSI had a major contribution to bridge failure is the collapse of the Cypress Structure in Oakland California during the Loma Prieta earthquake in The loose sand that the structure was built on, contributed to a more severe response of the structure which ultimately resulted in structural collapse of many sections of this bridge Ohuchi et al.
During the Northridge earthquake in , several bridge piers were damaged due to soil-pile-bridge seismic interaction Mitchell et al. Figure shows a bridge column failure due to the Northridge Earthquake in An analytical study of the Hanshin Expressway Bridge showed that soil characteristics had a significant effect on the behavior of this structure.
Figure shows the catastrophic failure of the two bridge structures due to the Loma Prieta and Kobe earthquakes. Since then many studies have been conducted that showed the potentially detrimental role of soft soil in intensifying the structural response.
Furthermore, soft soil can result in amplification of the ground motion causing a more severe response of a structure Rayhani and El Naggar, These examples show the importance of consideration of SSI effects in the analysis and design of bridges. This would include consideration of SSI in calculation of deflections, ductility demand, and forces induced in the structure.
In such systems, response of structure and soil are inter-dependent Tuladhar et al. The possibility of severe damage to bridges that are subjected to rare earthquakes leads to the necessity of collapse potential evaluation of bridges, particularly those which have been or will be designed as lifeline or major route bridges in the high seismic zones.
When it comes to performance assessment, there is a lack of guidelines and pre-defined workflows to properly address the SSI effects and site hazards on performance of bridges.
There is a crucial need for developing a practical methodology for quantitatively determining global seismic performance for use in seismic design and retrofit. Some codes provide simplified approaches such as application of factors to account for SSI effects.
The issue is that such approach is only applicable to the case that was tested and cannot offer a general solution to variety of soil types and layers.
The code provides guidelines to include SSI effects in simplified discrete models in an approximate manner such as springs and spring-dashpot systems. These guidelines, however, may not be able to capture all 4 aspects of SSI such as slab averaging and wave scattering effects.
In addition, the code does not provide specific guidelines on collapse assessment CSA-S, To minimize seismic risk and avoid catastrophic failure of bridges, changes in the structural response due to soil-structure interaction need to be effectively addressed in the next generation of bridge design codes. This is especially important for bridges in regions with soft soil and high earthquake risks. Presence of soil alters the dynamic characteristics of the system by elongating its natural periods and introducing additional damping.
Inertia developed in the structure due to its vibrations creates base shear and moment, which in turn leads to displacements of the foundation relative to the free-field Stewart et. The extent of this effect is dependent on the stiffness and geometry of the foundation and soil. Large and stiff foundations can significantly alter the effective motion of the foundation compared to free-field motion.
The kinematic SSI effect can be captured through base-slab averaging, embedment effect and wave scattering Stewart et. There are two possible approaches to consider the effect of Soil Structure Interaction SSI ; namely empirical and analytical. In the empirical approach, results of several test measurements are distilled into models that can be used in analysis and design to estimate the seismic response of a structure. One of the best examples of the experimental measurements of bridge abutment behavior is full-scale testing of monolithic abutments.
This class of tests was carried out on cohesive backfill by Romstad et al. Although empirical models offer a valuable insight into the effect of soil on structural response, their application is limited to the cases studied in tests.
Constraints in scale, material, and geometric configuration limits the applicability of test observations to real situations experienced by the structure.
In the long-term, accurate evaluation of the effects of soil-structure interaction SSI on the seismic response of structures using the empirical method will be possible when a significant body of strong motion data becomes available in future from sites with instrumented structures and free-field accelerographs.
Prior to availability of data from sites with instrumented structures, study of the Inertial and Kinematic interaction phenomena in a general sense can be only done by analytical methods Stewart et al. In analytical SSI methods, soil-structure models are constructed, and the seismic response of this combined system is predicted using computational methods such as nonlinear dynamic analysis.
To appropriately estimate geotechnical and structural demands, detailed numerical models that consider geotechnical and structural components are required in analyses. Accurate representation of behavior of soil as well as structural components going through a nonlinear regime is a key factor in analytical SSI models. In practice most bridge engineers use simplified discrete models to analyze SSI effects. These models include a limited set of SSI aspects.
As discussed earlier, there is a lack of clear and unified guidelines for engineers to follow in developing the SSI models. Within the analytical framework, there are two approaches to simulate soil-structure interaction effect; namely, discrete and continuum approaches. In the discrete approach, the effect of soil is represented by sets of springs and dashpots attached to piles, abutment backwalls and abutment buried foundations.
Properties of these discrete elements are determined based on soil characteristics. Although the discrete approach offers a computationally effective solution, as discussed by Finn , this approach is inherently incapable to accurately capture the inertial and kinematic SSI effects.
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Chapter 4 Three-Dimensional Applications. Chapter 5 Flow through Porous Media Seepage. Soil—structure interaction is a topic of significant importance in the solution of problems in geotechnical engineering.
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It discusses factors such as in-situ conditions, elastic, plastic and creep deformations, stress path, volume change, existence of fluids water , non-homogeneities, inherent and induced discontinuities leading to softening and failure, healing or strengthening, and type of loading" A Look Inside Summaries. Main Description. This book provides readers with a comprehensive treatment of computer methods so that they can use them for teaching, research, and solution of a wide range of practical problems in geotechnical engineering.
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