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Showing 62 results for Subject: Structure-Earthquake

A. Arabzadeh, A.r. Rahaie, A. Aghayari,
Volume 7, Issue 3 (9-2009)
Abstract

In this paper a new method based on Strut-and-Tie Model (STM) is proposed to determine the shear capacity of simply supported RC deep beams and an efficiency factor for concrete with considering the effect of web reinforcements. It is assumed that, the total carried shear force by RC deep beam provided by two independent resistance, namely diagonal concrete strut due to strut-and-tie mechanism and the equivalent resisting force resulted by web reinforcements, web reinforcing reduces the concrete compression softening effect with preventing from the diagonal cracks opening or concrete splitting. The unknown function and parameters are determined from 324 experimental results obtained by other researchers. To validate the proposed method, the obtained results are compared with some of the existing methods and codes such as ACI 318-05 and CSA. The results indicate that the proposed method is capable to predict the shear strength of variety of deep beams with acceptable accuracy.
M.a. Goudarzi, S.r. Sabbagh-Yazdi,
Volume 7, Issue 3 (9-2009)
Abstract

The main objective of this article is evaluation of the simplified models which have been developed for analysis and design of liquid storage tanks. The empirical formulas of these models for predicting Maximum Sloshing Wave Height (MSWH) are obtained from Mass Spring Models (MSM). A Finite Element Modeling (FEM) tool is used for investigating the behavior the some selected liquid storage tanks under available earthquake excitations. First, the results of FEM tool are verified by analyzing a liquid storage tank for which theoretical solution and experimental measurements are readily available. Then, numerical investigations are performed on three vertical, cylindrical tanks with different ratios of Height to Radius (H/R=2.6, 1.0 and 0.3). The behaviors of the tanks are initially evaluated using modal under some available earthquake excitations with various vibration frequency characteristics. The FEM results of modal analysis, in terms of natural periods of sloshing and impulsive modes period, are compared with those obtained from the simplified MSM formulas. Using the time history of utilized earthquake excitations, the results of response-history FEM analysis (including base shear force, global overturning moment and maximum wave height) are compared with those calculated using simplified MSM formulations. For most of the cases, the MSWH results computed from the time history FEM analysis demonstrate good agreements with the simplified MSM. However, the simplified MSM doesn’t always provide accurate results for conventionally constructed tanks. In some cases, up to 30%, 35% and 70% average differences between the results of FEM and corresponding MSM are calculated for the base shear force, overturning moment and MSWH, respectively.
A. Allahverdi, E. Najafi Kani,
Volume 7, Issue 3 (9-2009)
Abstract

It has been shown that geopolymerization can transform a wide range of waste aluminosilicate materials into building materials with excellent chemical and physical properties such as fire and acid resistance. In this research work, geopolymerization of construction waste materials with different alkali-activators based on combinations of Na2SiO3 and NaOH has been investigated. A number of systems were designed and prepared with water-to-dry binder ratio, silica modulus, and sodium oxide concentration were adjusted at different levels and setting time and 28-day compressive strength were studied. The results obtained reveal that construction wastes can be activated using a proportioned mixture of Na2SiO3 and NaOH resulting in the formation of a geopolymer cement system exhibiting suitable workability and acceptable setting time and compressive strength. Laboratory techniques of Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) were utilized for studying molecular and microstructure of the materials.
M.h. Sebt, A. Gerei, H. Naghash Toosi,
Volume 7, Issue 3 (9-2009)
Abstract

Risks mean cases of uncertainty of project, the impact of which is realized as a threat (negative aspect) and/or opportunity (positive aspect). The traditional viewpoint on risk is a negative viewpoint that implies damages, loss and harmful consequences. Judgments such as this on risk merely emphasize on risks management and pay less attention to opportunities management. It is clear that some uncertainties might be profitable for the project as in many cases, it could be the source of loss. In a developed attitude, focus is made on a common process that could address the integrated management of both opportunities and risks to aim at maximizing the positive effectsopportunities-, and minimizing negative effects- risks-. Therefore, existence of causal-effect relations between risks, relationship, effects of risks and opportunities on each other and variety of strategies in facing risks gives no alternative for risk management team than taking integrated management of risks and opportunities. In another word, reaction to risks, with respect to risks and/or relevant opportunities, separately, will be never effective. In this paper, for the purpose of integrated management of risks and opportunities, the stages of quality analysis and reactions to risk are combined. The method which is used for reaction towards risk is a procedure based on dynamic system. Dynamic system is highly important among uncertainties due to considering the type and intensity of effects. By using dynamic system and attention to the relationship between uncertainties (risks/ opportunities), reaction to risk and decision making on employing suitable strategies to face risks will be more precise and accurate.
M.h. Baziar, A. Ghorbani, R. Katzenbach,
Volume 7, Issue 3 (9-2009)
Abstract

The pile-raft foundation is a combination of a raft foundation with piles. Pile-raft foundation has been widely designed, assuming all structure loads to be transferred to piles without considering contribution of the load taken by contact surface between raft and soil. Methods of analysis currently used in practice are based upon relatively conservative assumptions of soil behavior or on the less realistic soil-structure interaction. In this study the bearing -settlement behavior of combined pile-raft foundations on medium dense sand was investigated. 1g physical model test was performed on a circular rigid raft underpinned with four model piles. Numerical simulation was also carried out on the model test, using FLAC-3D, to show compatibility of the numerical analysis with the test. The obtained results showed very good accuracy of the numerical method used in this study as long as the applied load does not exceed the working load, while the performance of numerical model was relatively good for the loads beyond working load.
M.h. Vahidnia, A.a. Alesheikh, A. Alimohammadi, F. Hosseinali,
Volume 7, Issue 3 (9-2009)
Abstract

Landslides are major natural hazards which not only result in the loss of human life but also cause economic burden on the society. Therefore, it is essential to develop suitable models to evaluate the susceptibility of slope failures and their zonations. This paper scientifically assesses various methods of landslide susceptibility zonation in GIS environment. A comparative study of Weights of Evidence (WOE), Analytical Hierarchy Process (AHP), Artificial Neural Network (ANN), and Generalized Linear Regression (GLR) procedures for landslide susceptibility zonation is presented. Controlling factors such as lithology, landuse, slope angle, slope aspect, curvature, distance to fault, and distance to drainage were considered as explanatory variables. Data of 151 sample points of observed landslides in Mazandaran Province, Iran, were used to train and test the approaches. Small scale maps (1:1,000,000) were used in this study. The estimated accuracy ranges from 80 to 88 percent. It is then inferred that the application of WOE in rating maps’ categories and ANN to weight effective factors result in the maximum accuracy.
A. Mansour Khaki, Sh. Afandizadeh, R. Moayedfar,
Volume 7, Issue 3 (9-2009)
Abstract

Household trip production is not a constant parameter and vary based on socio-economic characteristics. Even households in each category (households with constant socio-economic characteristics) produce several numbers of trips. Purpose of present study is to model the variation of household trip production rate in urban societies. In order to do this, concept of the Bayesian Inference has been used. The city of Isfahan was selected as case study. First, likelihood distribution function was determined for number of household trips, separating odd and even trips. In order to increase precision of the function, the composed likelihood distribution function was utilized. To insert households’ socio-economic variables in the process, disaggregate 2 calibrated model were used at the likelihood distribution function. Statistical indices and 2 test show that likelihood distribution function of numbers of household trip production follows the Poisson distribution. The final composed likelihood distribution was determined based on Bayesian inference. Related function was created with compilation of mean parameter distribution function (Gamma distribution) and numbers of household trip production (Poisson distribution). Finally, disaggregate model was put at final composed probability function instead of mean parameter. Results show that with Bayesian inference method, it would be possible to model the variation of household trip production rate in urban societies. Also it would be possible to put socio-economic characteristics in the model to predict likelihood of real produced trips (not average produced trips) for each household's category.
H. Shakib, F. Omidinasab, M.t. Ahmadi,
Volume 8, Issue 3 (9-2010)
Abstract

Elevated water tanks as one of the main lifeline elements are the structures of high importance. Since they are extremely vulnerable under lateral forces, their serviceability performance during and after strong earthquakes is a matter of concern. As such, in recent years, the seismic behavior of water tanks has been the focus of a significant amount of studies. In the present work, three reinforced concrete elevated water tanks, with a capacity of 900 cubic meters and height of 25, 32 and 39 m were subjected to an ensemble of earthquake records. The behavior of concrete material was assumed to be nonlinear. Seismic demand of the elevated water tanks for a wide range of structural characteristics was assessed. The obtained results revealed that scattering of responses in the mean minus standard deviation and mean plus standard deviation are approximately 60% to 70 %. Moreover, simultaneous effects of mass increase and stiffness decrease of tank staging led to increase in the base shear, overturning moment, displacement and hydrodynamic pressure equal to 10 - 20 %, 13 - 32 %, 10 - 15 % and 8 - 9 %, respectively.


J. Vafaie, T. Taghikhany, M. Tehranizadeh,
Volume 9, Issue 1 (3-2011)
Abstract

The near field ground motions have a high amplitude pulse like at the beginning of the seismogram which are significantly influenced by the rupture mechanism and direction of rupture propagation. This type of ground motion cause higher demands for engineering structures and its response spectrum is dramatically different than far field spectra.

Tabriz is one of the ancient cities in

Azerbaijan province with many industrial factories, financial centers and historical monuments in North-West of Iran. In this region, North Tabriz Fault which has a well known history of intense seismic activity is passing through in close distance of urban area. In this regard investigation of near field ground motion effect on current practice seismic design spectrum in this region is necessary.

Hence, probabilistic seismic hazard analysis is carried out using appropriate attenuation relationship to consider near field effect. The peak ground acceleration (PGA) and several spectral accelerations (SA) over bedrock are estimated for different return periods and maps of iso acceleration contour lines are provided to indicate the earthquake hazard in different points of

Tabriz city.

Afterward, the generated horizontal equal-hazard spectrums considering near field effect are compared with different spectrums developed base on simple pulses model for near field motion. Both types spectrum used to verify current practice seismic design spectrum of Iranian code (2005) and International Building Code (IBC 2000). The results reveal the long-period structures which are seismically designed based on current practice seismic codes are in high risk to be damaged during near fault ground motion.


M.h. Sebt, A. Yousefzadeh, M. Tehranizadeh,
Volume 9, Issue 1 (3-2011)
Abstract

In this paper, the optimal location and characteristics of TADAS dampers in moment resisting steel structures, considering the application of minimum number of TADAS dampers in a building as an objective function and the restriction for destruction of main members is studied. Genetic algorithm in first generation randomly produces different chromosomes representing unique TADAS dampers distributions in structure and the structure corresponding to each chromosome is time history analyzed. Then the damage index for each member and the average weighted damage index for all members are determined. Genetic algorithm evaluates the fitness of each chromosome then selection and crossover as logical operators and mutation as random operator effect the current generation's chromosomes according to their fitness and new chromosomes are generated. Accordingly, successive generations are reproduced in the same way until the convergence condition is fulfilled in final generation and four distributions are suggested as better options. Since these proposed distributions are selected under the one earthquake, therefore, it is better that the four new structures are cost-benefit analyzed in different earthquakes. Finally, the optimal placement for dampers is compared and selected based on a benefit to cost ratio, drift stories and the number of different TADAS types of such structures. The increase in amount of energy dissipated via dampers located in different floors as well as the status of plastic hinges in main members of the structure strengthened with optimum option are the proof of the optimal placement and suitable characteristics for dampers.


Mr. Mehdi Mahdavi Adeli, Dr. Mehdi Banazadeh, Dr. Ardeshir Deylami,
Volume 9, Issue 3 (9-2011)
Abstract

The objective of this paper is to determine the drift demand hazard curves of steel moment-resisting frames with different number
of stories in territory of Tehran this is done through the combination of the results obtained from probabilistic seismic hazard
analysis and the demand estimated through the best probabilistic seismic demand models. To select the best demand model, in
this paper, a Bayesian regression has been used for the statistical analysis of the results obtained from incremental dynamic
analysis in order to estimate the unknown parameters of model and to select the best Intensity Measure (IM) parameter also the
probability of overall collapse of structures has been computed. Considering the efficiency and sufficiency of the models, the
results indicate that the accuracy of models with one single IM is a function of the number of stories, consequently the current
widely used model with spectral acceleration in first period as IM is not suitable for all structural heights. Furthermore,
regarding the fact that it is difficult to prepare a seismic hazard curve for a combined IM, it seems that the best model can be
found among models with two single IMs. In other words, the best model to cover all structural heights is the one with linear
combination of spectral acceleration of the first and the second period. Furthermore, using different models to calculate the
curves shows that regardless of the number of IMs, estimated demands strongly depend on the standard deviation of model.

 


Kabir Sadeghi,
Volume 9, Issue 3 (9-2011)
Abstract

An energy based damage index based on a new nonlinear Finite element (FE) approach applicable to RC structures subjected to cyclic, earthquake or monotonic loading is proposed. The proposed method is based on the evaluation of nonlinear local degradation of materials and taking into account of the pseudo-plastic hinge produced in the critical sections of the structure. A computer program is developed, considering local behavior of confined and unconfined concretes and steel elements and also global behavior and damage of reinforced concrete structures under cyclic loading. The segments located between the pseudoplastic hinges at critical sections and the inflection points are selected as base-models through simulation by the proposed FE method. The proposed damage index is based on an energy analysis method considering the primary half-cycles energy absorbed by the structure during loading. The total primary half-cycles absorbed energy to failure is used as normalizing factor. By using the proposed nonlinear analytical approach, the structure's force-displacement data are determined. The damage index is then calculated and is compared with the allowable value. This damage index is an efficient means for deciding whether to repair or demolish structures after an earthquake. It is also useful in the design of new structures as a design parameter for an acceptable limit of damage defined by building codes.  The proposed approach and damage index are validated by results of tests carried out on reinforced concrete columns subjected to cyclic biaxial bending with axial force.


A. A. Tasnimi, M. A. Rezazadeh,
Volume 10, Issue 3 (9-2012)
Abstract

The torsional capacity of unreinforced masonry brick buildings is generally inadequate to provide a stable seismic behavior. The

torsional strength is believed to be the most important parameter in earthquake resistance of masonry buildings and the shear

stresses induced in the bed joints of such building’s walls is an important key for design purposes. Brick buildings strengthened

with wire-mesh reinforced concrete overlay are used extensively for building rehabilitation in Iran. Their quick and simple

applications as well as good appearance are the main reasons for the widespread use of such strengthening technique. However,

little attention has been paid to torsional strengthening in terms of both experimental and numerical approach. This paper reports

the response and behavior of two single-story brick masonry buildings having a rigid two-way RC floor diaphragm. Both

specimens were tested under monotonic torsional moment.Numerical work was carried out using non-linear finite element

modeling. Good agreement in terms of torque–twist behavior, and crack patterns was achieved. The unique failure modes of the

specimens were modeled correctly as well. The results demonstrate the effectiveness of reinforced concrete overlay in enhancing

the torsional response of strengthened building. Having evaluated the verification of modeling, an unreinforced brick building

with wall-to-wall vulnerable connections was modeled so that the effect of these connections on torsional performance of brick

building could be studied. Then this building was strengthened with reinforced concrete overlay and the effect of strengthening

on torsional performance of brick buildings with vulnerable connections was predicted numerically.


A. H. Molavi-Tabrizi, F. Khoshnoudian,
Volume 10, Issue 3 (9-2012)
Abstract

The application of fuzzy algorithms in the response control of a base isolated building with MR dampers is investigated in this

paper. Most of the previous researches in this field have been focused on fuzzy algorithms with linear membership function

however in the current study the membership functions are assumed to be Gaussian and their effectiveness is studied. For this

purpose, an eight-story building with regularity in plan and height is considered. The adopted base isolation system includes

linear bearings and control devices for improving the behavior of isolated structure under near field ground motions. MR

dampers are used to reduce base displacements and have the capacity of 1000 kN with the maximum applied voltage of 10 V. In

order to verify the control procedure and analyzing the structure, a simulation procedure is developed. This procedure performs

linear analysis of the structure in presence or in absence of the base isolation system. Moreover, the simulation procedure is able

to appropriately determine the MR damper voltage using fuzzy logic algorithms and then analyzing the whole system too. Finally,

seven near-field earthquake records are chosen in order to study the structure responses under these records and the obtained

results demonstrate the accuracy of proposed control procedure


H. Tavazo, H. E. Estekanchi, P. Kaldi,
Volume 10, Issue 3 (9-2012)
Abstract

Endurance Time (ET) method is a response history based analysis procedure that can be used for estimating the seismic response

of structures at different excitation levels in each response history. This seismic analysis method utilizes specific intensifying

acceleration functions to analyze seismic behaviors. One of the potential applications of the ET method is in the seismic

assessment of shell structures. In this study, a procedure for linear seismic analysis of shell structures is proposed and

applications of this method is investigated for several cases of shell structures. These structures are analyzed under three ET

acceleration functions in one direction and the results are compared to time history analysis considering seven actual earthquake

records. Moreover, the results of the ET method are compared to response spectrum analysis method. The outcomes of the study

reveal that the ET method predicts the linear seismic performance of shell structures with acceptable precision and significant

reduction in analysis time. Furthermore, it is conluded that scattering of results of three ET analysis is very low and one analysis

can be used instead of three. Finally, the comparison between THA and RSM results verify that response spectuarm method is a

conservative method which occasionally encounters problems to evaluate bending stresses of shell structures


F.r. Rofooei, M. R. Mirjalili, N. K. A. Attari,
Volume 10, Issue 4 (12-2012)
Abstract

The nonlinear static procedures (NSPs) proposed by design codes do not lead to reliable results especially for tall buildings.

They generally provide inconsistent estimates of inelastic seismic demands, especially for the top floors due to their inabilities in

considering the higher modes effects. In this paper, a new enhanced pushover procedure is proposed which is based on the

envelope of the structural responses resulting from two separate pushover analyses as a combination rule. Also, the suggested

pushover analyses are performed using a newly proposed modal load pattern, i.e., the Modal Spectra Combination (MSC), and

the ASCE41-06 required first mode load pattern. The MSC load pattern is consisted of a number of mode shapes combined with

appropriate weighting factors that depend on their modal participation factors, modal frequencies and design spectral values. A

number of 2-D steel moment resisting frame models with different number of stories are used to investigate the efficiency of the

proposed method. The inter-story drifts and the maximum plastic beam moment and curvature responses are used as a measure

to compare the results obtained from the nonlinear time-history analyses (NL-THA) and some other NSPs. The results obtained

through rigorous nonlinear dynamic analyses show that the application of the proposed method leads to acceptable results for

steel MRF systems in comparison to other available enhanced NSPs. The OpenSees program is used for numerical analysis.


F. Khoshnoudian, O. Nozadi,
Volume 11, Issue 2 (6-2013)
Abstract

It has been pointed out the static lateral response procedure for a base-isolated structure proposed in International Building Code (IBC) somewhat overestimates the seismic story force. That is why in the current paper, vertical distribution of base shear over the height of isolated structures considering higher mode effects under near field earthquakes is investigated. Nonlinear behavior of isolation systems cause variation of frequencies transmitted to the superstructure and consequently higher modes effects should be considered. In this study base shear distribution obtained from nonlinear dynamic analysis is compared with that achieved from IBC for assessment of the international building code. This investigation has been conducted in two parts, in order to have an appropriate base shear distribution formula for isolated structures under near field earthquakes. In the first part using three first mode shapes of isolated structure and introducing coefficient corresponding to each mode, extracted from nonlinear dynamic analysis under near field earthquakes, a new formula has been derived. In the second part, the mode shape coefficients have been obtained theoretically and consequently a new base shear distribution over the height of isolated structures including the isolation system properties under near field ground motions was proposed.
M. Poursha,
Volume 11, Issue 2 (6-2013)
Abstract

Double- unsymmetric-plan medium-rise buildings subjected to bi-directional seismic excitation are complex structures where higher-mode effects in plan and elevation are important in estimating the seismic responses using nonlinear static or pushover analysis. Considering two horizontal components of the ground motions makes the problem more intricate. This paper presents a method for nonlinear static analysis of double unsymmetric-plan low- and medium-rise buildings subjected to the two horizontal components of ground motions. To consider bi-directional seismic excitation in pushover analyses, the proposed method utilizes an iterative process until displacements at a control node (centre of mass at the roof level) progressively reach the predefined target displacements in both horizontal directions. In the case of medium-rise buildings, continuous implementation of modal pushover analyses is used to take higher-mode effects into account. To illustrate the applicability and to appraise the accuracy of the proposed method, it is applied to the 4- and 10-storey torsionally-stiff and torsionally-flexible buildings as representative of low- and medium-rise buildings, respectively. For the purpose of comparison, modal pushover analysis (MPA) is also implemented considering the two horizontal components of the ground motions. The results indicate that the proposed method and the MPA procedure can compute the seismic demands of double unsymmetric-plan low- and medium-rise buildings with reasonable accuracy however, seismic responses resulting from the proposed method deteriorate at the flexible edge of the torsionally-flexible buildings
M. Mohamamdi Ghazimahalleh, R. M. Ghazimahalleh,
Volume 11, Issue 3 (9-2013)
Abstract

A new type of infilled frame has been recently proposed. It has a frictional sliding fuse, horizontally installed at the mid-height of the infill. It has already shown that such infilled frames have higher ductility, strength and damping ratio as well as more enhanced hysteresis cycles, compared with regular infilled frames. This experimental paper is focused on the influence of gravitational load on the behaviour of the fused infill panel. Furthermore, a repairing method in which damaged specimens are repaired by grout plasters is also studied. The results show that the gravitational load, applied to the surrounding frame of the infill for the dead or live loads, arises the ultimate strength of the fused infill specimens. It is also shown that repairing the failed specimen by grout was so efficient that the repaired specimen had greater strength than the original one. However, top gap, between the infill and the top beam of the enclosing frame should be absolutely avoided, because it decays the ultimate strength.
A. R. Rahai, S. Fallah Nafari,
Volume 11, Issue 4 (12-2013)
Abstract

The seismic behavior of frame bridges is generally evaluated using nonlinear static analysis with different plasticity models hence this paper tends to focus on the effectiveness of the two most common nonlinear modeling approaches comprising of concentrated and distributed plasticity models. A three-span prestressed concrete frame bridge in Tehran, Iran, including a pair of independent parallel bridge structures was selected as the model of the study. The parallel bridges were composed of identical decks with the total length of 215 meters supported on different regular and irregular substructures with non-prismatic piers. To calibrate the analytical modeling, a large-scale experimental and analytical seismic study on a two-span reinforced concrete bridge system carried out at the University of Nevada Reno was used. The comparison of the results shows the accuracy of analytical studies. In addition, close correlation between results obtained from two nonlinear modeling methods depicts that the lumped plasticity approach can be decisively considered as the useful tool for the nonlinear modeling of non-prismatic bridge piers with hollow sections due to its simple modeling assumption and less computational time.

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