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Showing 65 results for Static

Bakhtiari Nejad F., Rahai A., Esfandiari A.,
Volume 2, Issue 2 (6-2004)
Abstract

In this paper a structural damage detection algorithm using static test data is presented. Damage is considered as a reduction in the structural stiffness (Axial and/or Flexural) parameters. Change in the static displacement of a structure is characterized as a set of non-linear undetermined simultaneous equations that relates the changes in static response of the structure to the location and severity of damage. An optimality criterion is introduced to solve these equations by minimizing the difference between the load vector of damaged and undamaged structures. The overall formulation leads to a non-linear optimization problem with non-linear equality and linear inequality constraints. A method based on stored strain energy in elements is presented to select the loading location. Measurement locations are selected based on Fisher Information Matrix. Numerical and experimental results of a 2D frame represent good ability of this method in detecting damages in a given structure with presence of noise in measurements.
Ghodrati Amiri G., Sedighi S.,
Volume 2, Issue 4 (12-2004)
Abstract

In the past decade design procedure changed to �performance-based design� from�force-based design�, by this mean many researchers focused on nonlinear static analysis (NSA)and the procedure named �PUSHOVER�. Advantages of this method are defining the inelasticbehavior of structure without nonlinear dynamic analysis (NDA) effort and also defining plastichinges formation in critical elements, and the order of formed plastic hinges. In spite of these goodadvantages NSA is limited to short and planar structures and application of that in tall andtorsionaly asymmetric structures may yield unreliable results.In this study reliability of NSA is investigated by performing both nonlinear static and dynamicanalysis on six 2D moment resisting concrete frames. Non linear dynamic analysis has been doneby the suggested method in FEMA356 guideline called �Target Displacement Method�. A groupof 4 different lateral increasing loads were used in pushover analysis and 3 different groundmotions were applied in NDA. Results indicate that same responses can be obtained by performingNSA, but errors will be increased by frames height increment.
H. Moharrami, S.a. Alavinasab,
Volume 4, Issue 2 (6-2006)
Abstract

In this paper a general procedure for automated minimum weight design of twodimensional steel frames under seismic loading is proposed. The proposal comprises two parts: a) Formulation of automated design of frames under seismic loading and b) introduction of an optimization engine and the improvement made on it for the solution of optimal design. Seismic loading, that depends on dynamic characteristics of structure, is determined using "Equivalent static loading" scheme. The design automation is sought via formulation of the design problem in the form of a standard optimization problem in which the design requirements is treated as optimization constraints. The Optimality Criteria (OC) method has been modified/improved and used for solution of the optimization problem. The improvement in (OC) algorithm relates to simultaneous identification of active set of constraints and calculation of corresponding Lagrange multipliers. The modification has resulted in rapid convergence of the algorithm, which is promising for highly nonlinear optimal design problems. Two examples have been provided to show the procedure of automated design and optimization of seismic-resistant frames and the performance and capability of the proposed algorithm.
F. R. Rofooei, N. K. Attari, A. Rasekh, A.h. Shodja,
Volume 4, Issue 3 (9-2006)
Abstract

Pushover analysis is a simplified nonlinear analysis technique that can be used to estimate the dynamic demands imposed on a structure under earthquake excitations. One of the first steps taken in this approximate solution is to assess the maximum roof displacement, known as target displacement, using the base shear versus roof displacement diagram. That could be done by the so-called dynamic pushover analysis, i.e. a dynamic time history analysis of an equivalent single degree of freedom model of the original system, as well as other available approximate static methods. In this paper, a number of load patterns, including a new approach, are considered to construct the related pushover curves. In a so-called dynamic pushover analysis, the bi-linear and tri-linear approximations of these pushover curves were used to assess the target displacements by performing dynamic nonlinear time history analyses. The results obtained for five different special moment resisting steel frames, using five earthquake records were compared with those resulted from the time history analysis of the original system. It is shown that the dynamic pushover analysis approach, specially, with the tri-linear approximation of the pushover curves, proves to have a better accuracy in assessing the target displacements. On the other hand, when nonlinear static procedure seems adequate, no specific preference is observed in using more complicated static procedures (proposed by codes) compared to the simple first mode target displacement assessment.
S.a. Sadrnejad, M. Labibzadeh,
Volume 4, Issue 4 (12-2006)
Abstract

Analysis and prediction of structural response to static or dynamic loading requires prediction of concrete response tovariable load histories. The constitutive equations for the mechanical behavior of concrete capable of seeing damage effects or crack growth procedure under loading/unloading/reloading was developed upon micro-plane framework. The proposed damage formulation has been built on the basis of five fundamental types of stress/strain combinations, which essentially may occur on any of micro-planes. Model verification under different loading/unloading/reloading stress/strain paths has been examined. The proposed model is capable of presenting pre-failure history of stress/strain progress on different predefined sampling planes through material. Many of mechanical behavior aspects happen during plasticity such as induced anisotropy, rotation of principal stress/strain axes, localization of stress/strain, and even failure mechanism are predicted upon a simple rational way and can be presented.
M. Heidarzadeh, A.a. Mirghasemi, S. Etemadzadeh,
Volume 5, Issue 1 (3-2007)
Abstract

A new chemical grouting method has been developed for conglomerate formations based on the experimental studies. Due to the lack of chemical grouting experience of conglomerate formations, the testing programs were performed to evaluate the performance of chemical grouting in the water sealing of part of conglomerate foundation of Karkheh earth dam using a combination of field and laboratory tests. First, the chemical grouts alone were examined with regard to viscosity-time behavior, gelation time, temperature-influence, stability, and deformability. These laboratory tests, led to the selection of the final chemical grout which was a solution of sodium silicate, water, and ethyl acetate as reactant. The second step tested grout-soil interaction: The injectability and permeability reduction of the selected chemical grout was examined in field injection tests. In this step two field tests were performed including shallow test holes without hydrostatic pressure and full scale tests under dam real hydrostatic pressure head. Based on these two field injection tests, performed in the conglomerate foundation of Karkheh dam, a new chemical grouting method for conglomerate formations is proposed and satisfactory results led to the recommendation of this method for eventually successful application.
Mehdi Poursha, Faramarz Khoshnoudian, Abdoreza S. Moghadam,
Volume 6, Issue 2 (6-2008)
Abstract

The nonlinear static pushover analysis technique is mostly used in the performance-based design of structures and it is favored over nonlinear response history analysis. However, the pushover analysis with FEMA load distributions losses its accuracy in estimating seismic responses of long period structures when higher mode effects are important. Some procedures have been offered to consider this effect. FEMA and Modal pushover analysis (MPA) are addressed in the current study and compared with inelastic response history analysis. These procedures are applied to medium high-rise (10 and 15 storey) and high-rise (20 and 30 storey) frames efficiency and limitations of them are elaborated. MPA procedure present significant advantage over FEMA load distributions in predicting storey drifts, but the both are thoroughly unsuccessful to predict hinge plastic rotations with acceptable accuracy. It is demonstrated that the seismic demands determined with MPA procedure will be unsatisfactory in nonlinear systems subjected to individual ground motions which inelastic SDF systems related to significant modes of the buildings respond beyond the elastic limit. Therefore, it’s inevitable to avoid evaluating seismic demands of the buildings based on individual ground motion with MPA procedure.
Shahram Feizee Masouleh, Kazem Fakharian,
Volume 6, Issue 3 (9-2008)
Abstract

A finite-difference based continuum numerical model is developed for the pile-soil dynamic response during pile driving. The model is capable of simulating the wave propagation analysis along the pile shaft and through the soil media. The pile-soil media, loading and boundary conditions are such that axisymmetric assumption seems to be an optimized choice to substantially reduce the analysis time and effort. The hydrostatic effect of water is also considered on the effective stresses throughout the soil media and at the pilesoil interface. The developed model is used for signal matching analysis of a well-documented driven pile. The results showed very good agreement with field measurements. It is found that the effect of radiation damping significantly changes the pile-soil stiffness due to the hammer blow. The pile tip response shows substantial increase in soil stiffness below and around the pile tip due to driving efforts.
A. Ghanbari, M. Ahmadabadi,
Volume 8, Issue 2 (6-2010)
Abstract

Inclined retaining walls with slopes less than perpendicular are appropriate candidates in several

engineering problems. Yet, to the knowledge of authors, only a few analytical solution for calculation of active earth

pressure on such walls, which will be usually smaller than the same pressure on vertical ones, has been presented

neither in research papers nor in design codes. Considering limit equilibrium concept in current research, a new

formulation is proposed for determination of active earth pressure, angle of failure wedge and application point of

resultant force for inclined walls. Necessary parameters are extracted assuming the pseudo-static seismic coefficient

to be valid in earthquake conditions. Moreover, based on Horizontal Slices Method (HSM) a new formulation is

obtained for determining the characteristics of inclined walls in granular and or frictional cohesive soils. Findings of

present analysis are then compared with results from other available methods in similar conditions and this way, the

validity of proposed methods has been proved. Finally according to the results of this research, a simplified relation

for considering the effect of slope in reduction of active earth pressure and change in failure wedge in inclined

retaining walls has been proposed.


A.r. Khaloo, I. Eshghi, P. Piran Aghl,
Volume 8, Issue 3 (9-2010)
Abstract

In this paper the response of cantilevered reinforced concrete (RC) beams with smart rebars under static lateral loading has been numerically studied, using Finite Element Method. The material used in this study is SuperelasticShape Memory Alloys (SE SMAs) which contains nickel and titanium elements. The SE SMA is a unique alloy that has the ability to undergo large deformations and return to their undeformed shape by removal of stresses. In this study, different quantities of steel and smart rebars have been used for reinforcement andthe behavior of these models under lateral loading, including their load-displacement curves, residual displacements, and stiffness, were discussed. During lateral loading, rebars yield or concrete crushes in compression zone in some parts of the beams and also residual deflections are created in the structure. It is found that by using SMA rebars in RC beams, these materials tend to return to the previous state (zero strain), so they reduce the permanent deformations and also in turn create forces known as recovery forces in the structure which lead into closing of concrete cracks in tensile zone. This ability makes special structures to maintain their serviceability even after a strong earthquake


M. Mahmoudi, M. Zaree,
Volume 9, Issue 1 (3-2011)
Abstract

Inelastic deformation of structural components is generally acceptable in seismic design. In such behavior, the strength of structures increases while plastic hinges are formed in members frequently. The strength revealed during the formation of plastic hinges is called "overstrength". Overstrength is one of the important parameters in the seismic design of structures. The present study tries to evaluate the overstrength of the concentrically steel braced frames (CBFs), considering reserved strength, because of members post-buckling. As such, a static nonlinear (pushover) analysis has been performed on the model buildings with single and double bracing bays, different stories and brace configurations (chevron V, invert Vand X-bracing). It has been realized that the number of bracing bays and the height of buildings have a low effect on reserve strength due to brace post-buckling. However, these parameters have a profound effect on the overstrength factor. These results indicate that the overstrength values for CBFs, proposed in seismic design codes, need to be modified.


A. Asakereh, S.n. Moghaddas Tafreshi, M. Ghazavi,
Volume 10, Issue 2 (6-2012)
Abstract

This paper describes a series of laboratory model tests on strip footings supported on unreinforced and geogrid-reinforced sand
with an inside void. The footing is subjected to a combination of static and cyclic loading. The influence of various parameters
including the embedment depth of the void, the number of reinforcement layers, and the amplitude of cyclic load were studied.
The results show that the footing settlement due to repeated loading increased when the void existed in the failure zone of the
footing and decreased with increasing the void vertical distance from the footing bottom and with increasing the reinforcement
layers beneath the footing. For a specified amplitude of repeated load, the footing settlement is comparable for reinforced sand,
thicker soil layer over the void and much improved the settlement of unreinforced sand without void. In general, the results
indicate that, the reinforced soil-footing system with sufficient geogride-reinforcement and void embedment depth behaves much
stiffer and thus carries greater loading with lower settlement compared with unreinforced soil in the absent of void and can
eliminate the adverse effect of the void on the footing behavior. The final footing settlement under repeated cyclic loading becomes
about 4 times with respect to the footing settlement under static loading at the same magnitude of load applied.


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.


A. Kaveh, M. Farahani, N. Shojaei,
Volume 10, Issue 4 (12-2012)
Abstract

Barrel vaults are attractive space structures that cover large area without intermediate supports. In this paper, the charged

search system (CSS) optimization algorithm is employed for optimal design of barrel vaults. This method utilizes the governing

laws of Coulomb and Gauss from electrostatics and the Newtonian law of mechanics. The results demonstrate the efficiency of

the discrete CSS algorithm compared to other meta-heuristic algorithms.


R. Prasanna Kumar, G. Dhinakaran,
Volume 11, Issue 1 (3-2013)
Abstract

Delay is one of the principal measures of performance used to determine the Level of Service (LOS) at signalized intersections and several methods have been widely used to estimate vehicular delay. Very few studies only have been carried out to estimate delay at signalized intersections under mixed traffic conditions prevailing in developing countries like India. In the present study, various problems associated with delay estimation under mixed traffic conditions in a developing country (India) and the methods to over come them were discussed and an attempt was made to improve the accuracy estimating the same. Five isolated signalized intersections from a fast developing industrial city located in TamilNadu, India were chosen for the study. Site specific PCU values were developed considering the static and dynamic characteristics of vehicles. Saturation flow was also directly measured in the field for the prevailing roadway, traffic and signalized conditions and expressed in PCU/h. Control delay was also measured following HCM 2000 guidelines. Later, this was compared with that estimated from the theoretical delay model. Even after taking several measures, good correlation between observed and predicted delay could not be obtained. Therefore, in the present scenario field measured control delay was taken into account to define LOS. A new criteria for Indian cities recently published in the literature was used to assign LOS grades of study intersections and found to be better reflecting the field conditions.
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
R. Kamyab Moghadas, E. Salajegheh,
Volume 11, Issue 2 (6-2013)
Abstract

The present paper focuses on size optimization of scallop domes subjected to static loading. As this type of space structures includes a large number of the structural elements, optimum design of such structures results in efficient structural configurations. In this paper, an efficient optimization algorithm is proposed by hybridizing particle swarm optimization (PSO) algorithm and cellular automata (CA) computational strategy, denoted as enhanced particle swarm optimization (EPSO) algorithm. In the EPSO, the particles are distributed on a small dimensioned grid and the artificial evolution is evolved by a new velocity updating equation. In the new equation, the difference between the design variable vector of each site and an average vector of its neighboring sites is added to the basic velocity updating equation. This new term decreases the probability of premature convergence and therefore increases the chance of finding the global optimum or near global optima. The optimization task is achieved by taking into account linear and nonlinear responses of the structure. In the optimization process considering nonlinear behaviour, the geometrical and material nonlinearity effects are included. The numerical results demonstrate that the optimization process considering nonlinear behaviour results in more efficient structures compared with the optimization process considering linear behaviour. .
F. Askari, M. R. Arvin, O. Farzaneh,
Volume 11, Issue 2 (11-2013)
Abstract

Seismic stability of slopes is typically evaluated by conventional methods under the assumption that the slope is subjected to an

earthquake just for one time. In general, time histories of loadings on slopes are unknown and loads are of variable repeated

nature. Shakedown phenomenon can be considered as a safe state for slopes subjected to variable repeated loadings. In this study,

lower bound dynamic shakedown theorem is employed for the seismic stability of slopes as a comprehensive verification. A

numerical method applied previously to evaluate roads under the traffic loads was modified to make it appropriate for dynamic

shakedown analysis in the present study. The numerical method is based on the combination of finite element and linear

programming methods. Critical PGA is employed as a comparative parameter to compare shakedown and pseudostatic methods.

Results show that, unlike pseudostaic method, shakedown approach is able to consider dynamic properties of load and slope.

Also, it is indicated that contrary to pseudostaic approach, shakedown solutions are different for slopes and embankments.

Shakedown and pseudostaic critical PGA versus dynamic properties of load and slope creates four distinct zones. It is shown that

the forgoing zones can be used as appropriate tools for seismic zonation of slopes based on their short term and long term safety


I. Hosseinzadeh Attar, K. Fakharian,
Volume 11, Issue 2 (11-2013)
Abstract

Pile foundations are frequently used in industrial projects in southwest lowlands of Iran. Although high setup of shaft resistance

is usually reported in the area, no reliable formulation or guidelines are available for considering the increased capacity in design

applications. Therefore, the pile design practices are usually not optimized. The main objective of this paper is presenting a site

specific formulation for setup effects of a utility plant in southwest Iran in which a good database of prestressed concrete driven

piles is available. Fajr-II Petrochemical site in PetZone of Mahshahr accommodating a utility plant is selected as the database of

the current study. The setup factor (A) and the reference time (t0) are evaluated through processing of a relatively large database

of this well-supervised piling project. As the main portion of variations of driven piles capacity with time is related to shaft, only

shaft resistance variations are considered in this research. The shaft capacity variations are derived from signal matching analysis

on PDA tests. Reliability of PDA tests has been confirmed through comparing with the static load test results. Influence of driving

the surrounding piles on setup factor is also investigated. The results show that the average setup factor (A) and the reference time

(t0) of 0.30 and 0.01 day, respectively, are proper values for estimating the long term capacity in this region. Evaluation of the

results indicates that driving 8 piles around the test pile has increased the “A” factor average of 40% resultingin increase of the

shaft capacity about 19% in one month and 22% in one year, in comparison with the tested piles with no surrounding piles driven.



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