Site Effects Estimation in Tehran City by Using Empirical Methods

In this paper, site effects assessment in Tehran city, the capital of Iran, were estimated by using empirical methods. Both spectral ratio of the horizontal components of sedimentary site to rocky site (Hs/Hr) or site/reference, and Horizontal to Vertical Spectral Ratio (HVSR) methods have been used for estimation the site effects parameters. For this purpose, the recorded motions in BHRC (Building and Housing Research Center) acceleration stations were analyzed. These motions were recorded from Changureh-Avaj (2002), Tehran (2003), Firozabad-Kojour (2004) and Kahak-Qom (2007) earthquakes, which have been occurred near to the Tehran city. Some of these motions recorded in rocky stations and were used for site/reference (Hs/Hr) analysis. Site predominant frequency and soil amplification factor in various frequency ranges were estimated in each station by using calculated amplification functions by two empirical techniques. The results reveal a large contribution of site effects on ground motion at the majority of the studied sites. The value of predominant frequency in southern part of city is less than northern part. Therefore, the level of damage in southern part might be increased and short frequency structures, such as high-rise buildings and long span bridges might be strongly affected by the site effects in this part of the city

Recorded Bedrock Motions and Site Effects Evaluation in Tehran City

In this paper, the results of theoretical analyses related to the evaluation of site effects in Tehran city, the capital of Iran, are presented. To evaluate the response of site, recorded bedrock motions in BHRC (Building and Housing Research Center) acceleration stations at Tehran city were used as bedrock input motion. These motions were recorded during Firozabad-Kojour (2004) earthquake (Ms=6.4), which occurred near Tehran city. Equivalent linear analysis was performed to evaluate the seismic response of each selected geotechnical and geophysical profile subjected to the scaled 475-year bedrock input motion. The results are presented in terms of site response spectrum and site amplification factor, computed in the period ranges 0.1- 0.5 and 0.1- 2.5 s. The estimated site response spectra were compared with the suggested one in Iranian Code (Standard No. 2800). This comparison reveals that there are acceptable trend between the estimated response spectra and Iranian Code. The values of amplification factor in ranges of period 0.1–0.5s and 0.1–2.5 s can also be considered in designing typical and generic buildings of the area

Sustainable seismic retrofitting of a RC building using performance based design approach

In the past twenty years, sustainable development has become a challenging subject across many scientific fields. With the built environment as the major component of societies, sustainable construction has been the main player in the whole sustainability mentality. To emphasize on the importance of incorporating sustainability in to seismic retrofitting, three different retrofitting methods (base isolation, concrete jacketing, and steel jacketing) are evaluated for a typical 4-story RC school building under the 1994 Northridge earthquake’s ground motion. Using Performance Based Design approach, the objective of retrofitting is to make the building perform in the Immediate Occupancy performance level according to FEMA guidelines so that it can be used as a shelter after disasters. Results show that although retrofitting by concrete or steel jacketing can control story drifts to satisfy maximum allowable values, the performance of the building and consequent damages do not meet the desired performance objective. In addition, accounting for economic and human losses, these retrofitting options will not provide a sustainable structure if a strong earthquake happens in the future. On the other hand, not only base isolation meets the desired performance objective, but also it will provide a sustainable retrofitted structure by drastically reducing economic and human losses

Revisiting element removal for density-based structural topology optimization with reintroduction by Heaviside projection

We present a strategy grounded in the element removal idea of Bruns and Tortorelli [1] and aimed at reducing computational cost and circumventing potential numerical instabilities of density-based topology optimization. The design variables and the relative densities are both represented on a fixed, uniform finite element grid, and linked through filtering and Heaviside projection. The regions in the analysis domain where the relative density is below a specified threshold are removed from the forward analysis and replaced by fictitious nodal boundary conditions. This brings a progressive cut of the computational cost as the optimization proceeds and helps to mitigate numerical instabilities associated with low-density regions. Removed regions can be readily reintroduced since all the design variables remain active and are modeled in the formal sensitivity analysis. A key feature of the proposed approach is that the Heaviside functions promote material reintroduction along the structural boundaries by amplifying the magnitude of the sensitivities inside the filter reach. Several 2D and 3D structural topology optimization examples are presented, including linear and nonlinear compliance minimization, the design of a force inverter, and frequency and buckling load maximization. The approach is shown to be effective at producing optimized designs equivalent or nearly equivalent to those obtained without the element removal, while providing remarkable computational savings

Topology optimization of nonlinear periodically microstructured materials for tailored homogenized constitutive properties

A topology optimization method is presented for the design of periodic microstructured materials with prescribed homogenized nonlinear constitutive properties over finite strain ranges. The mechanical model assumes linear elastic isotropic materials, geometric nonlinearity at finite strain, and a quasi-static response. The optimization problem is solved by a nonlinear programming method and the sensitivities computed via the adjoint method. Two-dimensional structures identified using this optimization method are additively manufactured and their uniaxial tensile strain response compared with the numerically predicted behavior. The optimization approach herein enables the design and development of lattice-like materials with prescribed nonlinear effective properties, for use in myriad potential applications, ranging from stress wave and vibration mitigation to soft robotics

Numerical Modeling of Electrochemical and Mechanical Intercalations in All Solid-State Lithium-Ion Batteries

The rapid development of new technologies in recent decades has caused an ever increasing demand for energy storage devices that are lightweight, durable, and maintain high life-cycle expectancies. Lithium-ion batteries have emerged as a universal solution due to their exceptional energy storage and high power delivery. Lithium-ion batteries based on organic electrolytes suffer from safety concerns; specifically flammability, low temperature thresholds, and coupled electrochemical-mechanical degradation. From a design perspective, introducing a new type of lithium-ion battery with enhanced storage capacity, safe and reliable performance is the most ongoing challenge in battery research communities. This research focuses on the numerical modeling of electrochemical and mechanical interactions in all solid-state lithium-ion batteries. In particular, we present physical and numerical modeling frameworks to model and understand the electrochemical and mechanical performance of all solid-state lithium-ion batteries under the influence of some electrochemical and mechanical degradation phenomena. To this end, we developed finite element modeling frameworks based on multi-scale and full resolution modeling methods. These models facilitate detailed understandings and comprehensive studies of the behavior of lithium-ion batteries under the evolution of degradation phenomena. While our model is not limited to any particular battery system and failure mechanism, we focus on the evaluation of the electrochemical performance of both thin and bulk solid-state lithium-ion batteries, stress-diffusion-damage coupling effects in the electrode active materials and interfacial debonding effects in the battery cell. The involved coupled physical phenomena includes mechanical deformation, diffusion-migration processes, stress-diffusion-damage coupling, electrochemical surface reactions, and cohesive zone model. To provide a predictive numerical tool for optimizing the performance of battery cell, our finite element model is augmented with a parameter identification method. The parameter identification method provides unique opportunities for parametric study and identifying key design parameters in the life-time performance of all solid-state lithium-ion batteries. The characteristics of the research are explored by presenting comprehensive numerical examples. The presented numerical examples illustrate the performance of the battery cell under the influence of different physical phenomena. We verified and calibrated the accuracy and stability of the developed framework by numerical and experimental examples. The parameter identification method is applied for parametric study and error minimization in the battery. The results revealed the great influence of material properties and geometric configuration on the electrochemical performance of the battery cell. The influence of damage evolution on the mechanical and electrochemical performance of the battery is explored by numerical examples. The results showed that diffusion-damage coupling has significant influences on the life-time performance of the battery cell. The results of cohesive zone modeling revealed the main contribution of the interface properties on the separation and the debonding phenomena at the interface of multi-phase material