Coupled Soil-Structure Interaction Effects of Symmetric and Asymmetric Buildings In Urban Regions

<p>This thesis deals with the response of idealized building clusters during earthquakes, their effect on the ground motion, and how individual buildings interact with the soil and with each other. We simulate the ground motion during the 1994 Northridge earthquake and focus on the coupled response of multiple simplified symmetric and asymmetric building models located within the San Fernando Valley and the Simi Valley. We use the Domain Reduction Method (DRM) in order to perform these simulations efficiently while recurrently modifying the models without having to redo the entire simulation every time. Numerical results show that the soil-structure interaction (SSI) effects vary with the number and dynamic properties of the buildings, their separation, and the impedance with respect to the soil. These effects appear as: (i) an increased spatial variability of the ground motion; and (ii) significant reductions in the buildings’ base motion at high frequencies, changes in the higher natural frequencies of the building-foundation systems and variations in the roof displacement, with respect to those of the corresponding rigid-base and single SSI models. Torsional coupling of the asymmetric structures combined with SSI effects are also investigated, and results, in comparison with the symmetric structures, are given.</p

The Influence of Building Clusters on the Variability of the Ground Motion During Earthquakes

Spatial variability and ground motion uncertainty during earthquakes can significantly influ-ence both our interpretation of seismic data and the behavior of structures and infrastructure systems, especially those susceptible to differential motions, or those that benefit from more diffuse wave-fields. Spatial variations typically observed in ground motions are mostly the consequence of wave interferences, refraction, scattering and other phenomena resulting from the three-dimensional nature of the crust, the surface topography, site conditions, and heterogeneities in the transmitting media. Also influential but regularly ignored is the presence of the built environment, especially in the case of densely urbanized regions. We are interest-ed in investigating the extent to which the presence of building-foundation systems can modify earthquake ground motions and contribute to their variability. We present preliminary results from a series of three-dimensional simulations using a finite element software for seis-mic wave propagation problems, with and without the presence of simplified building (block) models. We explore the level of influence exerted by the built environment on the ground motion through comparisons between the simulations with building models and equivalent simulations without them. This is the initial step of a project in which we seek to identify param-eters that can serve as proxies to characterize site-city interaction effects

Coupled Soil-Structure Interaction Effects of Building Clusters during Earthquakes

This study addresses the responses of idealized building clusters during earthquakes, their effects on ground motion, and the ways individual buildings interact with the soil and with each other. We simulate the ground motion during the 1994 Northridge earthquake and focus on the coupled responses of multiple simplified building models located within the San Fernando Valley. Numerical results show that the soil-structure interaction (SSI) effects vary with the number and dynamic properties of the buildings, their separation, and their impedance with respect to the soil. These effects appear as: (i) an increased spatial variability of the ground motion; and (ii) significant reductions in the buildings’ base motion at high frequencies, changes in the higher natural frequencies of the building-foundation systems, and variations in the roof displacement, with respect to those of the corresponding rigid-base and single SSI models.</jats:p

Effects of High Frequency Hydrodynamic Loads on Structural Integrity and Mechanical Operability of Valves

In-line valves are qualified for static as well as dynamic loads from seismic and hydrodynamic (HD) events. Seismic loads are generally characterized by frequency content less than about 33 Hz whereas HD loads may exhibit a broad range of frequencies greater than 33 Hz. HD loads may also result in spectral accelerations significantly in excess of those due to the design basis seismic events. Current regulatory guidelines do not specifically address the evaluation of equipment response to high frequency loading. This paper investigates the response of skid and line mounted valves of piping systems under HD loads by using several independent rigorous finite element analysis solutions for various piping system segments. It presents a hybrid approach for the evaluation of the response of valves to HD and seismic loads. The proposed approach significantly reduces the amount of individual analysis and testing needed to qualify the valves. First, valve responses are evaluated on the basis of displacements since HD loads are generally characterized by high frequencies and small durations. Second, the damage potential of the loads on the valve actuators is represented by the energy imparted to the actuator quantified in terms of Arias intensity. The rationale for using the energy content is based on the fact that damage due to dynamic loading is related not only to the amplitude of the acceleration response but also to the duration and the number of cycles over which this acceleration is imposed.</jats:p