Seismic Microzonation and Damage Assessment of Bam City,Southeastern Iran

This article aims to study the dynamic characteristics of soil in Bam, southeastern Iran. Fundamental frequency and amplification factor of soil sediment were estimated by microtremor measurement. This procedure was performed at 49 sites in the city. Two 120-second data were recorded at each site. Segmental cross spectra were applied to calculate spectrum, Nakamura's method (H/V) was used for analyzing data and fundamental frequency and amplification factor values were derived. Iso-frequency and iso-amplification maps of the city were prepared. Results show that soil type in Bam city is mainly stiff, although amplification factor is relatively large. There is a short period zone in northwest to southeast direction. Sediment depth was estimated using a correlation between fundamental frequency and sediment thickness. Results obtained from microtremors were compared to the geotechnical boreholes and it was shown that microtremors can be used for a rough estimation of sediment thickness. Damage distribution map of Bam due to the Bam earthquake on December 26, 2003 was prepared by both field and aerial investigation. Quality of buildings in Bam was evaluated, as a result a crude zoning map on the building quality was prepared. Finally, it was concluded that several factors have contributed to damage intensity variation; earthquake characteristics, local site effect, and buildings' quality. All mentioned parameters affected the damage variation.     

Predicting Probabilistic-Based Strong Ground Motion Time Series for Citadel of Arg-E-Bam (South-East of Iran)

The main objective of this article is to present a probabilistic-based strong motion compatible with the source-path and site soil condition given the probability of exceedence for citadel of Arg-e-Bam site bed rock (South-East of Iran). A Fourier amplitude spectral attenuation relation for bed rock beneath the site is proposed which permits the estimation of time-histories through a probabilistic seismic hazard analysis procedure. Due to lack of data, the two well-known simulation techniques, point source and finite fault models have been used for generating hundreds of strong motion as input data. Tens of model parameter values such as stress-drop nucleation points were used, in each specified magnitude-distance, to reduce the uncertainty effects inherently existing in seismological/geological parameters. The proposed attenuation relation is validated by comparing the estimated strong motion, in the form of Fourier amplitude spectral, using the proposed attenuation relation with those of recorded ground motion data at three stations far away from the assumed source so that the results would not be influenced by the near source problems such as directivity and fling step. The results of proposed technique is assessed by comparing the estimated response spectra, with 10% probability of exceedence and 5% damping ratio, with those of traditional uniform hazard spectra. The proposed technique is supposed to be used in retrofitting procedure of international historical adobe structures in Arg-e-Bam site, which have been damaged during the destructive Bam earthquake 2003, Iran     

基于概率法的木构古建筑地震破坏综合评价方法

为了研究木构古建筑地震破坏状态评估的准确性,应用概率的方法,以结构损伤指数、最大层间位移角作为评价因子,建立了地震破坏综合评价模型,提出了基于概率法的木构古建筑地震破坏综合评价方法。该方法在综合现状分析与实验数据,在一定烈度下计算各种破坏状态等级中每一种破坏状态出现的概率,古建筑地震破坏状态应为概率最大的地震破坏状态,从而比较准确地判别木构古建筑地震破坏程度。并对经受过汶川地震的两种结构形式的古建筑进行了验证,从而验证了该方法的合理性和有效性。这一方法将提高木构古建筑震害预测的准确性,为古建筑抗震加固提供有效的理论支持。     

GENERATION OF ARTIFICIAL EARTHQUAKE MOTION RECORDS USING WAVELETS AND PRINCIPAL COMPONENT ANALYSIS

In the last century alone two to three million people died in earthquakes; More than 240 000 perish in Tangshan earthquake in China, 20 000 in the Izmit [Ikeya, 2004] 50 000 in India Bhuj earthquake, 100000 in Sumatra and 90000 in Pakistan earthquakes. Earthquake engineering has progressed to the stage where it is now computationally practical and desirable to perform a dynamic analysis of most civil engineering structures. Such an analysis requires the engineer to create an accurate analytical model of the structures as well as prescribe an earthquake input excitation. The design earthquake input excitation for the site under consideration is usually prescribed in the form of response spectra or in the form of an ensemble of artificial earthquake acceleration time histories. There is every need for generating artificial accelerograms since recorded accelerograms are very limited at site. This paper proposes five neural network based models for the generation of artificial earthquake and response spectra using wavelet transforms (WT) and principal component analysis (PCA) where the recorded accelerograms are limited at site of interest. The proposed model is compared with Lee and Han's model. The data for 25 earthquakes are taken for training and 4 for testing. Just like response spectra, this is also a convenient way of obtaining the design solution to a structural dynamics problem and is certainly an important tool.     

Public and Private Lives in Iran: An Introduction to the Archaeology of the 2003 Bam Earthquake

Bam, Iran, was destroyed by a powerful earthquake in December 2003. In what is perhaps Iran’s greatest tragedy in living memory, the majority of the mud brick houses and concrete buildings were completely flattened and more than half of the city’s population was killed. Five years after the disaster, a team of Iranian archaeologists and ethnographers excavated the remains of six houses destroyed in the earthquake. The excavated material culture demonstrates the stark contrasts between the residents’ public lives lived outside of their homes, and their private lives lived inside of their homes.     

The Interaction of Body, Things and the Others in Constituting Feminine Identity in Lower Socio-Economic Ranks of Bam, Iran

Identity is one of the most important matters in social theory, especially in recent decades. Identity is a fluid phenomenon which forms in the process of every day activities. Individuals get practical knowledge of society to do intentional practices. They operate actively in identitizing process. Gender identity is one of important dimensions of individual identities constituting in social relations to others. Different socio-economic classes experience different social relations and engage in different identity processes. This research studies the formation process of feminine identity in the process of marriage (in contrast with the concept of virginity) in lower socio-economic classes of Bam. Body as site of identity and focus of close contact between agency and structure becomes the object of various changes and with creating difference-especially within group differences-distinguishes individuals from one another. Cultural materials is used intentionally in this process. The research is based on finds of “Bam Contemporary Archaeology Project: Excavation in Disastrous Layers”. Six collapsed houses ruined by 2003 earthquake have been excavated. Meshkani House which is represents low socio-economic class is the focus of research. The research take an archaeological approach (reconstructing behavioral patterns of individual and societies base on material culture) investigating gender structure and gender sociability processes in Bam, Iran. The sites being contemporary, has created an extended range of facts. In some cases for better understanding of the context, local people were interviewed .The information from “Disaster Ethno-archaeology Project of Bam” was also used in this study.     

Predicting the Seismic Response of Capacity-Designed Structures by Equivalent Linearization

An equivalent linearization procedure is developed for predicting the inelastic deformations and internal forces of capacity-designed structures under earthquake excitations. The procedure employs response spectrum analysis, and mainly consists of the construction of an equivalent linear system by reducing the stiffness of structural members that are expected to respond in the inelastic range. These members are well defined in structures designed with capacity principles. Maximum modal displacement demands of the equivalent linear system are determined either from the equal displacement rule, or from independent nonlinear response history analysis of SDOF systems representing inelastic modes.

Predictions obtained from the proposed equivalent linearization procedure are evaluated comparatively by using the results of nonlinear response history analysis as benchmark, linear elastic response spectrum analysis and conventional pushover analysis. The deformations and capacity controlled actions of a 12-story symmetrical plan concrete frame and a 6-story unsymmetrical plan concrete frame are obtained by each method under 96 strong ground motions. It is observed that the proposed procedure results in better accuracy in estimating the inelastic seismic displacement response parameters and capacity controlled forces than the other two approximate methods.     

Seismic Load Capacity of Historical Masonry Mosques by Rigid Body Kinetics

ABSTRACT

Kinetic analysis methods based on linear and nonlinear rigid body dynamics are used to evaluate earthquake safety of masonry structures. In this study, the formulas used to calculate the in-plane and out-of-plane load capacities of masonry load-bearing walls were evaluated and a procedure based on rigid body mechanism was proposed to calculate the out-of-plane load capacities of the walls of Ottoman period masonry mosques. New aspects of the method with respect to existing formulations is the inclusion of dynamic axial load and definition of the collapse limit spectral acceleration on the overturning wall. The calculated capacities of the mosque and individual walls were compared with the results of nonlinear pushover analysis and time history analyses performed under 1.0 and 0.5 scaled forms of nine different 3-component ground motion records. It was displayed that the seismic load capacity estimated by the proposed method is very close to the values calculated by pushover and time history analyses. The method was developed on Lala Pasha Mosque, and the reliability and applicability of the proposed methodology is verified on a different historical masonry mosque in comparison to finite element analyses results.     

Estimation of the Displacement of Viscously Damped Pinching Hysteretic Structures Subjected to Near-fault Ground Motions

To fulfill a displacement-based design or response prediction for nonlinear structures, the concept of equivalent linearization is usually applied, and the key issue is to derive the equivalent parameters considering the characteristics of hysteretic model, ductility level, and input ground motions. Pinching hysteretic structures subjected to dynamic loading exhibit hysteresis with degraded stiffness and strength and thus reduced energy dissipation. In case of excitation of near-fault earthquake ground motions, the energy dissipation is further limited due to the short duration of vibration. In order to improve the energy dissipation capability, viscous-type dampers have been advantageously incorporated into these types of structures. Against the viscously damped pinching hysteretic structure under the excitation of near-fault ground motions, this study aims to develop a seismic response estimation method using an equivalent linearization technique. The energy dissipation of various hysteretic cycles, including stationary hysteretic cycle, amplitude expansion cycle, and amplitude reduction cycle, is investigated, and empirical formulas for the equivalent damping ratio is proposed. A damping modification factor that accounts for the near-fault effect is introduced and expanded to ensure its applicability to structures with damping ratios less than 5%. An approach for estimating the maximum displacement of a viscously damped pinching hysteretic structure, in which the pinching hysteretic effect of a structure and the near-fault effect of ground motions are considered, is developed. A time history analysis of an extensive range of structural parameters is performed. The results confirm that the proposed approach can be applied to estimate the maximum displacement of a viscously damped pinching hysteretic structure that is subjected to near-fault ground motions.     

Seismic Retrofitting of Non-Seismically Designed RC Beam-Column Joints using Buckling-Restrained Haunches: Design and Analysis

Many existing reinforced concrete (RC) structures around the world have been designed to sustain gravity and wind loads only. Past earthquake reconnaissance showed that strong earthquakes can lead to substantial damage to non-seismically designed RC buildings, particularly to their beam-column joints. This paper presents a novel retrofit method using buckling-restrained haunches (BRHs) to improve the seismic performance of such joints. A numerical model for RC joints is introduced and validated. Subsequently, a new seismic retrofit strategy using BRHs is proposed, aimed at relocating plastic hinges and increasing energy dissipation. The results indicate the retrofit method can effectively meet the performance objectives.     

Constant Ductility Energy Factors for the Near-Fault Pulse-Like Ground Motions

This study is focused on the constant ductility energy factors for bilinear system under the near-fault pulse-like ground motions. The variation of energy factors is studied in consideration of the earthquake magnitude, rupture distance, damping ratios, and post-yield stiffness ratios. The results indicate that the near-fault pulse-like ground motions would increase the energy dissipation of structures. The energy factors are significantly influenced by the earthquake magnitude. The damping ratios have more obvious influences on the energy factors than the post-yield stiffness ratios. A predictive model is proposed for the application of constant ductility energy factors for near-fault pulse-like ground motions.     

INSTANTANEOUS OPTIMAL CONTROL FOR SEISMIC ANALYSIS OF NON-LINEAR STRUCTURES

In this paper, an effective active control algorithm is developed for the vibration control of non-linear structural systems subjected to earthquake excitation. It is an attempt to include the non-linear characteristics of the structural behaviour throughout the entire analysis (design and validation), accounting for the eventual cumulative structural damage and energy dissipation. This is a very important factor since, in current design practice, structures are assumed to behave nonlinearly when subjected to strong ground motion. The proposed algorithm focusses on the instantaneous optimal control approach for the development of the control algorithm where the nonlinearities are brought into the analysis through a non-linear state vector and a non-linear open loop term. A performance index that is quadratic in the control force and in the non-linear states and is subjected to a non-linear constraint equation, is minimised at every time step. The effectiveness of the proposed non-linear instantaneous optimal control (NIOC) strategy is critically evaluated in comparison with currently available active control techniques. Numerical simulation results indicate that the proposed approach provides a significant reduction of the peak response quantities, such as maximum response deformation, maximum response acceleration, ductility of the system, associated with a reduced maximum control force.     

Preparation of Engineering Geological Maps of Bam City Using Geophysical and Geotechnical Approach

Engineering geological mapping was carried out at a scale of 1:25000 in the city of Bam, located in southeastern Iran, to provide engineering geological information as a base for seismic microzonation of the city. In this study, Seismic Refraction and Vertical Seismic Profiling (VSP) surveys were employed along with boreholes in order to identify the characteristics of subsurface material in Bam city. A number of different kinds of maps of the city were prepared consisting of Iso-depth, Iso-velocity, and Iso-Poisson's Ratio maps. The study also involves trial pitting and continuous core recovery, in-situ, and laboratory tests. Borehole data, index properties of soils, and standard penetration test results were used to assess subsurface conditions. Geophysical and geotechnical data were combined to simulate geotechnical boreholes and prepare engineering geological maps to provide basic data for seismic geotechnical microzonation to facilitate in the reconstruction of the city of Bam.     

NONLINEAR ANALYSIS OF REINFORCED CONCRETE SHEAR WALL UNDER EARTHQUAKE LOADING

A constitutive model for predicting the cyclic response of reinforced concrete structures is proposed. The model adopts the concept of a smeared crack approach with orthogonal fixed cracks and assumes a plane stress condition. Predictions of the model are compared firstly with existing experimental data on shear walls which were tested under monotonic and cyclic loading. The same model is then used in the finite element analysis of a complete shear wall structure which was tested under a large number of cyclic load reversals due to earthquake loading at NUPEC's Tadotsu Engineering Laboratory. Two different finite element approaches were used, namely a two-dimensional and a three-dimensional representation of the test specimen. The ability of the concrete model to -reproduce the most important characteristics of the dynamic behaviour of this type of structural element was evaluated by comparison with available experimental data. The numerical results showed good correlation between the predicted and the actual response, global as well as local response being reasonable close to the experimental one.     

A Simplified Calculation Method for Liquefaction-Induced Settlement of Shallow Foundation

This work was aimed at developing a practical and simple settlement estimation of shallow foundation on liquefiable deposits. The study conducted a centrifuge test, a series of comprehensive numerical analysis, back analysis, equation calibration, and verification with data from not only centrifuge test but also the literature. It finally proposed a quick calculation method based on Meyerhof’s settlement equation (1965). A two-dimensional numerical analysis, named ALID, (Analysis for Liquefaction-induced Deformation), was employed for obtaining settlement of shallow foundations on liquefiable soils with different relative densities under various seismic conditions. Its performance was first verified through a centrifuge test conducted in this study. Then, the developed method based on Meyerhof’s settlement equation was employed, and a new parameter, N_LR, was proposed to present the strength of liquefied soils by replacing N value in the original equation. The N_LR was obtained through back analysis of the numerical results and modified accordingly after comparison with the data from the literature. This paper, finally, demonstrated the practical use of the proposed method involving N_LR by predicting 199 sets of liquefaction-induced settlement of shallow foundation reported in the past, including a latest most liquefaction-induced settlement of a house in 0206 earthquake on February 6, 2016, in Taiwan.     

Non-Iterative Equivalent Linearization Based on Secant Period for Estimating Maximum Deformations of Existing Structures

The capacity spectrum method of ATC-40 uses the secant period as the equivalent period of equivalent linear systems. Therefore, it results in a direct graphical comparison. The maximum inelastic displacement and acceleration demands of structures can be simultaneously obtained from the intersection of the demand and capacity diagrams. However, for evaluation of existing structures, the demands need to be determined through iterations since the equivalent period and damping of the equivalent linear systems currently available are both a function of the (displacement) ductility ratio, which is unknown and is the target of evaluation. In addition, the equivalent damping used in the capacity spectrum method is independent of periods of vibration. It may lead to poor estimations of maximum responses especially for short-period systems. This article proposes two equivalent linear systems based on the secant period to estimate the maximum displacement and acceleration responses of existing structures. Both the recommended equivalent period and damping are defined by the strength ratio (elastic lateral strength/yield lateral strength), rather than the ductility ratio. Because the strength ratio of existing structures is a known parameter, the maximum displacement and acceleration responses of these structures can be determined without iterations. Besides, effects of periods of vibration on the equivalent linear systems are also included in this study. The equivalent damping is derived from statistical analyses for bilinear single-degree-of-freedom (SDOF) systems with different periods of vibration, strength ratios and post-yield stiffness based on 72 earthquake ground motions recorded on firm sites. Procedures and examples for applications of the proposed equivalent linear systems on nonlinear static analysis procedures are also provided.     

Statistical Characterization of Structural Demand under Earthquake Loading. Part 2: Robust Estimation of the Dispersion of the Data

Performance-based earthquake engineering methodologies often require a probabilistic model of structural demand. Since observations masking the probability distribution of the majority of the data are frequently found, robust estimation methods are proposed to estimate the probabilistic model parameters (i.e., central value and dispersion). The performance of thirty-three robust dispersion estimators is evaluated, for different sample sizes, using the chord rotation, curvature, shear force, and inter-story drift demands obtained after analyzing five reinforced concrete structures under real earthquake records scaled to several intensities. Based on the results, combinations involving dispersion and central value (defined in a companion article) estimators are proposed.     

Mine blast vibration response spectrum for structural vulnerability assessment: case study of heritage masonry buildings

Ground-borne vibrations induced by mine blasting are typically of low amplitudes, which are not considered a major concern for modern engineered structures. However, historic structures are often considered more vulnerable due to inadequate knowledge regarding the state of construction materials and structural response. Specifically, the construction materials used might be fragile or have deteriorated to a stage that could be vulnerable to such vibrations. Simplistic rule based on peak ground motion parameter has been adopted worldwide for safety assessment, while the frequency characteristics of vibrations are not taken into account. Further, there is very limited study on response of heritage structures to near-field blasting. This article presents a practical structural vulnerability assessment method for mine blast-induced vibrations. In particular, a design response spectrum model is proposed based on close range measurements of nearby mine blasting, which is compared with an existing design spectrum model for far-field mine blasts and a typical design spectrum model for earthquake actions. The method is illustrated through a case study of heritage masonry buildings in Australia. The unique blast data presented and the generalized methodology would be useful to both structural engineers and blast engineers in considering potential effects of blasting on heritage structures.     

Investigation of the Seismic Behavior of a Historical Masonry Minaret Considering the Interaction with Surrounding Structures

This study examines the seismic behavior of the minaret of the well-known historical structure “Sultan Ahmed Mosque” under strong earthquake motion. Despite their slenderness and height, minarets are towers with well-established earthquake resistance. In general, these structures were constructed adjacent to the main structure and/or its components. Hence, it is expected that the dynamic behavior of the minarets is influenced by the dynamic characteristics of the adjacent structures as well as the contact conditions. In the presented study, the dynamic behavior of the M6 minaret of the Sultan Ahmed Mosque, which is in contact with the portico that surrounds the courtyard of the mosque, is considered. Ambient vibration tests were conducted on site in order to identify the individual and coupled vibration modes of the minaret and the portico. A finite/discrete model was developed and seismic analysis was carried out. The comparative study reveals considerable differences in responses of different models under strong and very strong earthquake motion.