DYNAMIC INTERACTION BETWEEN RETAINING WALLS AND RETAINED STRUCTURES

ABSTRACT The seismic response of retaining walls that support soil layers has been examined by various researchers in the past. However, in engineering practice retaining walls are very frequently used to support, apart from soil layers, structures founded on the retained soil layers. Therefore, during a seismic event it is evident that the dynamic response of each component of this complex system (wall, soil, and structure) may affect substantially the response of the rest, and vice versa. This phenomenon, which could be adequately described as "dynamic wall-soil-structure interaction" (DWSSI), is a rather complicated issue that combines: (a) the dynamic interaction between the wall and the retained soil layers, and (b) the "standard" one-dimensional dynamic interaction of a structure with its underlying soil layers. In the present study, using numerical simulations, the influence of the wall flexibility on the free-field ground shaking behind the wall is investigated. Subsequently, a simple structure founded on the retained soil is included in the numerical models. A parametric study is being performed in order to examine at what extend the presence of the wall may affect the inertial accelerations imposed on the structure (with respect to its position and its fundamental eigen-period). In addition, it is investigated how the location and/or the characteristics of the structure may affect the dynamic earth pressures induced on the retaining wall. Numerical results provide a clear indication of the direct dynamic interaction between a retaining wall and its retained structures

Vulnerability assessment of structures and infrastructures

Μη διαθέσιμη περίληψηNot available summarizationΠαρουσιάστηκε στο: Structure and Infrastructure Engineerin

Seismic Vulnerability Assessment of Liquid Storage Tanks Isolated by Sliding-Based Systems

Liquid-filled tanks are effective storage infrastructure for water, oil, and liquefied natural gas (LNG). Many such large-scale tanks are located in regions with high seismicity. Therefore, very frequently base isolation technology has to be adopted to reduce the dynamic distress of storage tanks, preventing the structure from typical modes of failure, such as elephant-foot buckling, diamond-shaped buckling, and roof damage caused by liquid sloshing. The cost-effective seismic design of base-isolated liquid storage tanks can be achieved by adopting performance-based design (PBD) principles. In this work, the focus is given on sliding-based systems, namely, single friction pendulum bearings (SFPBs), triple friction pendulum bearings (TFPBs), and mainly on the recently developed quintuple friction pendulum bearings (QFPBs). More specifically, the study is focused on the fragility analysis of tanks isolated by sliding-bearings, emphasizing on isolators’ displacements due to near-fault earthquakes. In addition, a surrogate model has been developed for simulating the dynamic response of the superstructure (tank and liquid content) to achieve an optimal balance between computational efficiency and accuracy

Multi-Objective Optimization of Base-Isolated Tanks with Supplemental Linear Viscous Dampers

Base isolation of liquid storage tanks has proven to be an efficient seismic protection measure, leading to a drastic reduction of a superstructure’s distress. However, many such tanks are located near seismic tectonic faults, which generate strong pulse-like ground motions that can impose excessive displacement demands on the isolators. For this reason, viscous dampers are incorporated into the isolation system to avoid overconservative isolators design. To optimize the seismic performance of hybrid isolation systems consisting of single friction pendulum bearings and linear viscous dampers, two novel multi-objective optimization approaches are proposed in the current study. Furthermore, suitable constraint functions and design variables are selected, considering the most critical parameters of the hybrid isolation system. The multi-objective genetic algorithm optimizer is used for the solution of both problems. The results are presented in the typical form of Pareto and certain optimal design solutions are carefully chosen and compared in terms of isolators fragility curves and tank accelerations. The main aim is to optimize the critical design parameters by achieving a reasonable balance among contradicting objectives. The tank industry can substantially benefit from this study, as a more cost-efficient design of hybrid base-isolation can be attained for large-scale tanks

Large-scale reliability-based structural optimization

Summarization: A robust and efficient methodology is presented for treating large-scale reliability-based structural optimization problems. The optimization is performed with evolution strategies, while the reliability analysis is carried out with the Monte Carlo simulation method incorporating the importance sampling technique to reduce the sample size. Efficient hybrid methods are implemented to solve the reanalysis-type problems that arise in the optimization phase with evolution strategies and in the reliability analysis with Monte Carlo simulations. These hybrid solution methods are based on the preconditioned conjugate gradient algorithm using efficient preconditioning schemes. The numerical tests presented demonstrate the computational advantages of the proposed methods, which become more pronounced for large-scale optimization problems.Παρουσιάστηκε στο: Structural and Multidisciplinary Optimizatio

Multi-Objective Optimization of Base-Isolated Tanks with Supplemental Linear Viscous Dampers

Base isolation of liquid storage tanks has proven to be an efficient seismic protection measure, leading to a drastic reduction of a superstructure’s distress. However, many such tanks are located near seismic tectonic faults, which generate strong pulse-like ground motions that can impose excessive displacement demands on the isolators. For this reason, viscous dampers are incorporated into the isolation system to avoid overconservative isolators design. To optimize the seismic performance of hybrid isolation systems consisting of single friction pendulum bearings and linear viscous dampers, two novel multi-objective optimization approaches are proposed in the current study. Furthermore, suitable constraint functions and design variables are selected, considering the most critical parameters of the hybrid isolation system. The multi-objective genetic algorithm optimizer is used for the solution of both problems. The results are presented in the typical form of Pareto and certain optimal design solutions are carefully chosen and compared in terms of isolators fragility curves and tank accelerations. The main aim is to optimize the critical design parameters by achieving a reasonable balance among contradicting objectives. The tank industry can substantially benefit from this study, as a more cost-efficient design of hybrid base-isolation can be attained for large-scale tanks

Application of dynamic programming to evaluate the slope stability of a vertical extension to a balefill.

Summarization: The slope-stability of a proposed vertical extension of a balefill was investigated in the present study, in an attempt to determine a geotechnically conservative design, compliant with New Jersey Department of Environmental Protection regulations, to maximize the utilization of unclaimed disposal capacity. Conventional geotechnical analytical methods are generally limited to well-defined failure modes, which may not occur in landfills or balefills due to the presence of preferential slip surfaces. In addition, these models assume an a priori stress distribution to solve essentially indeterminate problems. In this work, a different approach has been applied, which avoids several of the drawbacks of conventional methods. Specifically, the analysis was performed in a two-stage process: (a) calculation of stress distribution, and (b) application of an optimization technique to identify the most probable failure surface. The stress analysis was performed using a finite element formulation and the location of the failure surface was located by dynamic programming optimization method. A sensitivity analysis was performed to evaluate the effect of the various waste strength parameters of the underlying mathematical model on the results, namely the factor of safety of the landfill. Although this study focuses on the stability investigation of an expanded balefill, the methodology presented can easily be applied to general geotechnical investigations.Παρουσιάστηκε στο: International Solid Wastes and Public Cleansing Associatio

Impact of Soil Saturation Level on the Dynamic Response of Masonry Buildings

The present study investigates the impact of the soil saturation level on the performance of unreinforced masonry (URM) buildings when subjected to seismic excitations. More specifically, this paper examines the dynamic response of an ordinary stone-built URM building, firstly in its initial state and subsequently when it is slightly retrofitted with reinforced concrete beams at the perimeter in both storeys and also reinforced concrete instead of wooden lintels above the openings. The assessment of the behavior of this typical URM building, taking into account the soil-structure interaction (SSI) along with the nonlinear behavior both of the soil and the structure is examined through incremental dynamic analyses. For this purpose, a compatible in terms of soil conditions, set of 20 ground motions was selected, each scaled to several levels of seismic intensity. Subsequently, multiple nonlinear dynamic analyses of the coupled model of soil and structure were performed. In addition, these calculations were repeated for eight different saturation levels covering a wide range of soil conditions to elaborately investigate the problem at hand