A new proposal of lateral load pattern for nonlinearstatic analysis of structures by ISERP ISERP

S.Etedali et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 5, Issue No. 2,201 -208

A new proposal of lateral load pattern for nonlinear static analysis of structures M.A.Irandegani

Department of Civil Engineering, Faculty of Engineering University of Sistan and Baluchestan Zahedan, Iran s_etedali@mail.usb.ac.ir sadeghetedali@gmail.com

structure; however, because of the practical complexities and problems, the use of this method is faced with some restrictions. For that reason, in the recent years, extensive efforts have been made for development and evaluation of the applied and simplified methods of nonlinear analysis while having appropriate accuracy. The introduction of the structure design issue based on the performance levels has caused many efforts to be made in the recent years with respect to the methods of design and evaluation of buildings based on the displacement and the use of the nonlinear analyses for more realistic evaluation of the structures behavior against the different levels of earthquake. The resultant of these efforts is the nonlinear static analysis known as pushover analysis which has increasingly been developed in the earthquake engineering as an appropriate applied tool and can provide with useful information about nonlinear behavior of the structures, the location of plastic joints formation and the way of redistribution of the loads, etc which cannot be obtained by linear static analysis methods. The nonlinear static analysis called pushover analysis is an alternative simple method from the most complete and precise structural seismic analysis, i.e. the nonlinear dynamic analysis. In this method, firstly a load pattern is assumed to be exerted on the structure, then, this load pattern is increasingly applied to the structure until the displacement of a certain point of the structure reaches a certain value known as target value, while the nonlinear behaviors of structural elements have been considered. Then, the values of internal displacements and the forces are determined. The sequence of happening of fractures, plastic joints and the failures of structural elements can easily be shown during the process. This process continues until either the structure displacement exceeds the target displacement or the structure collapses. In these methods, it is intended to the target displacement to be equal to the maximum probable displacement under expected earthquake. In fact, in the pushover analysis method, the capacity spectrum of the structure is compared to the seismic demand spectrum (SDS) in order to evaluate the structure performance.

Abstractâ&#x20AC;&#x201D; The capacity curve is a valuable tool for study of global behavior of structures. The quality of lateral load distribution in the process of nonlinear static analysis has a dramatic effect on estimation of the need to the force and the displacement of systems and structural elements. In this paper, two lateral load patterns existing in the FEMA-365 code (the uniform and triangular lateral load patterns) have been evaluated. Moreover, a new lateral load pattern has been offered for nonlinear static analysis of structural models. For evaluation of its accuracy and performance in estimation of seismic behavior of structures, the capacity curves obtained from the results of nonlinear static analysis of structural models have been depicted and compared to the capacity curve obtained from incremental dynamic analysis. The studied structures include three regular symmetric frames with 4, 12 and 20-storey. Two lateral resisting system, steel moment-resisting frames and concrete special moment resisting frames assumed for structural models. The results show that in the low-period steel moment-resisting frames, the triangular load pattern and with the increase of the period, the uniform lateral load patterns are appropriate for lateral load distribution. In these structures, the offered pattern also enjoys appropriate accuracy and performance for determining the lateral load of the structure. In low-period concrete special moment resisting frames, the uniform load pattern offered by FEMA is an appropriate pattern for performing pushover analysis in these structures, but with increase of the period in these structures, the lateral load patterns offered by FEMA will no longer be appropriate patterns for seismic behavior evaluation of these structures. In these structures, the offered load pattern indicates more precise estimation of seismic behavior of the structure and hence, the use of it is suggested for evaluation of structural nonlinear behavior and estimation of the need to the force and displacement of system and the elements of these structures.

Islamic Azad University, Zahedan Branch Department of Civil Engineering Zahedan, Iran m.a.irandegani@iauzah.ac.ir m.a.irandegani@gmail.com

S.Etedali

Keywords- capacity curve; lateral load patterns; pushover analysis; incremental dynamic analysis

INTRODUCTION

Regarding the exiting imperfections in the linear static method and the nonlinear nature of structural elements, the nonlinear dynamic analysis of the structures is considered as the most precise method for determining seismic demand of the

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The pushover analysis is accompanied by some estimations and simplifications that cause some uncertainties in the results. The quality of the lateral load distribution in the

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S.Etedali et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 5, Issue No. 2,201 -208

process of nonlinear static analysis has a considerable effect on determining nonlinear behavior of the structure and estimation of the need to the force and displacement of the system and structural elements. The lateral load pattern is in fact representative of the distribution of the lateral inertia forces exerted on the structure under effect movements of earth in earthquake. From a design standpoint, the lateral load distribution must be selected in such a way that the most critical conditions to be created. If the structure is linear in the range of elastic behavior, the lateral load distribution will be a function of many parameters such as frequency content and the earthquake vibration range, the frequencies and the mode shapes of the structure. If the structure has nonlinear behavior, the lateral load distribution will be a function of the local or global yield of the elements in addition to the abovementioned parameters and hence, it will be more complicated. Although this method has found an extensive use as one of the best methods of structure design, but investigations on the accuracy and validity of the results of this method and attempts to simplify it and make it practical are still ongoing.

mutual effect of the flexural moment and the axial force in the columns wouldn't have considerable effect on the capacity curve of the structure.

Pu et al. [1] have suggested a lateral load pattern as an estimation of the inertia forces distribution obtained from the results of the dynamic analysis of the MDOF systems.

Where Ai is amplification of lateral load, i is the storey's number and n is the number of stories. In a 17-storey structure, the capacity curve resulted from the pushover analysis with the suggested load pattern and the value of P=0.3 and in a 22storey with p=0.5 will coincide with the capacity curve resulted from the nonlinear incremental dynamic analysis.

Weixing [10] has suggested a load pattern known as Parabola pattern through comparison of the results of incremental dynamic analysis (IDA) and the pushover analysis in the 17 and 22-storey concrete structures with shear wall. Equation (1) expresses Parabola pattern. +1â&#x2C6;&#x2019;

(1)

Hosseini and Yaghoobi [2] verified the available designs based on linear dynamic and pushover analysis in the 3D structures. Their studies focused on asymmetric 8-storey steel structure. In this study, the coefficient 1.7 was suggested for multiplying the lateral forces resulted from the earthquake. This suggestion has agreement with the suggestions of many worlds' famous codes in this field.

Abhilash et al. [9] have compared the capacity curves resulted from pushover analysis of a 4-storey concrete structure with SMF system by four load patterns: uniform load adopted from FEMA-273, the equivalent lateral load adopted from FEMA -257, the load pattern suggested by the Indian standard (IS 1893_2002) and the upper band pushover analysis (UBPA) suggested by Janetal in 2004. They concluded that for the investigated structure, the capacity curves obtained from four abovementioned load patterns are almost close to each other.

Chopra and Goel [3]-[5] have developed a pushover analysis process based on the structure dynamic theory known as modal pushover analysis (MPA). Comparison of the maximum nonlinear response of a 9-storey structure and the offered method indicates that this process shows good estimations of roof displacement, inter-story drifts and determination of plastic joints locations. Moreover, in another study, they developed the modal pushover analysis (MPA) for asymmetric structures.

Kalkan and Kunnath [6] performed nonlinear static analyses on the 8 and 12-storey steel structures with SMF system and concluded that the modal combination method shows more appropriate estimations of inter-story drifts and the roof displacement in comparison to the load patterns suggested by FEMA. Matsumori et al. [7] studied the inter-story drift distributions and the need to members' plasticity in the floors of the structures through comparison of the nonlinear dynamic analysis and the pushover analysis. They show that if the pushover analysis is performed by considering sum of tow first modes of the structure, then a logical estimation of distribution of members displacement demand during the earthquake will be obtained. Colina et al. [8] have deployed the pushover analysis for reaching the mutual effect of the flexural moment and the axial force in the columns of low-story concrete structures with consideration of twist and they concluded that consideration of

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In the current paper, a new and simple lateral load pattern has been presented for performing the nonlinear static analysis of the structures precisely which presents a precise estimation of nonlinear and seismic behavior of the structures in the form of capacity curve. For evaluation of the accuracy and performance of the uniform lateral load pattern, the triangular pattern and the load pattern suggested in the estimation of seismic behavior of the structures, the capacity curve obtained from the results of nonlinear static analysis of structural models has been depicted and compared to that of incremental dynamic analysis. II.

SPECIFICATION OF THE STRUCTURAL MODELS

The studied structures include three regular symmetric frames with 4, 12 and 20-storey.two lateral resisting system, steel moment-resisting frames and concrete special moment resisting frames assumed for structural models. Structural models with span ratios in the range of H/B<1.5, 1.5<H/B<3 and H/B>3 have been optioned. H is the height of the structure and B is the width of the structure plan. The 4, 12 and 20storey frame are sample of common structures with low, intermediate and high period respectively. In table I, the specifications of the structural models and the nomenclature used for each of them have been shown. TABLE I. THE SPECIFICATIONS OF THE STRUCTURAL MODELS Ratio H/B

Number of Stories

Concrete Special Moment Resisting Frame

Moment Resisting Frame Steel

H/B<1.5

SMRF-4

MRF-4

1.5<H/B<3

SMRF-12

MRF-12

H/B>3

SMRF-20

MRF-20

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Also, A the moddels used to perform p the annalyses have been show wn in the Fig. 1.

speccification of these accelerrometers. In the accelerom meter selecction, some factors f like th he magnitude of the earthqquake, distaance from thee fault, soil tyype, the effecttive time of quake q and the fracture mechanism m of the t fault have been considerred. TABLEE III. SPECIFICATIION OF ACCELERO OMETERS USING IN I INCREMENT TAL DYNAMIC AN NALYSIS

Earthquake Name

3 Figure1. Struuctural models 4

The T propertiees of the maaterials used in the strucctural elem ments (includinng steel and co oncrete) have been shown in the tablee . TABLLE II. PROPERTIESS OF THE MATERIA ALS USED IN THE

Concrrete

E=22e+10

Fy=3.6e+07

Fu=2.4ee+7

(Modulus of Elasticity)

(Yield Stress)

(Ultimate Stress) S

E=2.334e+09 (Modulus of Elasticity)

=2.4e+05

(Compressive C Strenggth)

The T initial dessign of the struucture has beenn performed based b on the t UBC 97 code [11]. For F this purppose, it has been assu umed that the structures are entirely locatted in the regiion 4 of th he earthquake and the soil under u the strucctures is of SD type (the average sheaar wave speed d of subsoil iss between 3755 and 750 m/s). The noonlinear dynaamic and statiic analyses of the strucctures have beeen performed d by the Zeus--NL software [12]. The P-Δ effects haave been conssidered in the seismic s analyssis of the structures s andd the moment--curvature nonnlinear equatio on of the columns c and thhe beams baseed on FEMA [13] [ code has been used d for assigninng the nonlinnear behaviorr to the strucctural elem ments. III.

ANALYSIS OF STRUCTURAL MODELS

A. Incremental I dyynamic analyssis (IDA) In I the incremeental dynamicc analysis (IDA A), one or several earth hquake recordds are scaled until u reaching a certain inteensity of the t earthquakke and are exerted e on thhe structure. The dynaamic pushoveer diagram is i obtained by depictingg the maximum valuess of the basee shear versus the maxim mum d displlacement of tthe structure (the target displacement) after everry implementaation of the annalysis. This method m show ws the capaacity of the strructures in adddition to seism mic behavior of o the strucctures. Althouugh the nonlinear dynamic analysis a is thee best meth hod in estimattion of the seiismic behavior of the structtures, but this t analyticall method is very costly, tim me-consumingg and non--economical and a on the otther hand it has h direct relation with h the records of selected earthquakes. e IIn the increm mental dynaamic analyssis of the structural models, seven s acceelerometers hhave been used. Table III shows the

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1940

1117 El Centro Arraay #9

0.3133

1971

135 LA - Hollywoodd Stor Lot

0.21

1984

57382 Gilroy arrayy #4

0.2244

1987

90084 Lakewoood

0.2777

1989

57382 Gilroy arrayy #4

0.4177

cape Mendocino

1992

89156 Petroliaa

0.59

Northridge

1994

Can noga park-Topanga can

0.3566

B. P Pushover anallysis A expressedd previously, the nonlinearr static methood is As accoompanied by some estimaations and siimplificationss that causse some uncerrtainties in the results. Thee advantage of this methhod with respeect to the increemental dynam mic analysis (IDA) ( is thhe lesser time of the analyssis which resuults in reductio on of the analysis costss. The load paattern applied to the structu ure is p anaalysis. one of the most important isssues in the pushover Therre are many methods m for determining d thhe load patternn that eachh of them has led to acceptaable results in some cases and a in som me cases, the go ood results haave not been obtained, o hence, the FEM MA code sugggests that at least two typpes of load paattern musst be applied to o the structuree to reach morre confidence level. l Thiss method hass been describbed in differeent codes succh as Euroocode8, SEAO OC (1995) and a ATC40. In I this paper,, two patteerns of laterall load (the uniiform and triaangular laterall load patteerns) availablle in the FEM MA-365 codee [14] and also a a sugggested lateral load l pattern has h been used for nonlinear static anallysis of the struuctural modells.

Steeel

Material Property M Unit: kg/m2

PGA(g g)

STRUC CTURAL ELEMENT TS

Typee of Material

Station Location

Imperial Valley (El Centro) San Fernando Morgan Hill Whiter Narrows Loma Prieta

Event Year

1 Triangular lateral 1) l load paattern I this pattern, distribution of In o lateral load is given by: =

∑

(2)

K = 0.5T + 0.75 0

(3)

W Where wi is the portion of o the total sttructure weigh ht W assiggned to i-th floor, hi is the height h from thhe base to floo or i-th leveel, V is the pseudo lateral load and T is i the fundam mental periood of the struccture in the dirrection under consideration. 2 Uniform latteral load pattern 2) I this patternn, the lateral loads In l have been considered d as a ratioo of total struccture mass in each floor according (4), which w mi is the mass of i-th floor and V is the pseuddo lateral loadd.

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F =∑

. V (4)

3) 3 The suggestted lateral loadd pattern The T suggestedd lateral load pattern is prresented accorrding (5): .V

(5)

V. IV

Figure 2. Capaacity curves of MR RF-4 from IDA

Where, W h is the height between the base and a the ith floo or, H is th he total heighht of the struccture; p is a constant whicch is deterrmined depennding on the laateral force reesistance systeem of the structure and its height. The T suggestedd load pattern is a good d representattive of the two describbed uniform and trian ngular lateral load l patterns and every forrm of load paattern betw ween them. B By selection of o an approprriate value forr the consstant P, one caan determine the suitable lateral l load paattern for each e structuree. For this purrpose, the cappacity curve of o the struccture is depicted using thhe results off the increm mental dynaamic analysis and then the capacity curvves of the struucture resullted from thee pushover annalysis are depicted d usingg the preseented lateral load pattern and a with diffferent values of o P. Amo ongst the curvves resulted froom pushover analysis, the curve c whicch has more aggreement withh the structuraal capacity curvve of the results r of incrremental dynaamic analysis is determinedd and its corresponding c g P value is used for nexxt analyses off the similar structures (in terms of height and the type t of the defined laterral force resistance system m) for evaluuation of seiismic perfo ormance andd performancee level of existing e and new strucctures in ordder to select appropriate rehabilitation and retro ofit strategies.

F =

RESULTS OF THE ANALY YSIS

Figure 3. Capaccity curves of MRF F-12 from IDA

The T capacityy curve (cuurve of basse shear - roof displlacement) is considered ass a valuable tool for studdy of glob bal behaviors of structurees. The incrremental dynnamic analyysis of structuural models haas been comppared to the reesults obtaained from the nonlinear stattic analyses reesulted from laateral load d patterns and the capabilityy of each of thhem in estim mation The of the structuraal behavior has been investigated. i increemental dynam mic analysis (IDA) ( of structural modelss was perfo ormed underr seven acceelerometers dderived from m the earth hquakes indiccated in the table and thhe capacity curve c resullted from thesse analyses forr structural moodels was deppicted and then the avverage valuee obtained fr from these seven s acceelerometers haas been used too depict the fiinal capacity curve c of the structure. In order to investigate the accuracy and perfo ormance of thhe uniform, trriangular and the offered laateral load d patterns in estimation of the seismicc behavior off the strucctures, the cappacity curve obtained o from m the results of o the nonllinear static analysis a of thhe structural models has been depicted and com mpared to the capacity c curvee resulted from m the mic analysis. increemental dynam

A. Steel momentt resisting fram me (MRF) Capacity C curvves of 4, 12 an nd 20-storey frames with MRF M systeem obtained ffrom the resuults of the inccremental dynnamic analyysis of sevenn selected acccelerometers and the aveerage curv ve of them haave been deppicted in the Figs. 2, 3 and a 4 respeectively.

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Figure 4. Capaccity curves of MRF F-20 from IDA

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In I order to evvaluate the acccuracy and thhe performancce of the uniform, u trianngular and thee offered laterral load pattern rns in estim mation of thee seismic beehavior of thhe structures,, the capaacity curve obbtained from the results of o nonlinear static s analyysis of structuural models has h been depiccted and comppared to th he average caapacity curve resulted from m the increm mental dynaamic analysiss of the strucctures under records of seven s seleccted accelerom meters. The reesults of this comparison for f 4, 12 and a 20-storey fframes have been b depicted in Figs. 5, 6 and a 7 respeectively.

Figure 7. Capaciity Curves of MRF F-20 for three differrent Load Patterns and ID DA-average

F Fig.5 shows that t in 4-storeey structure, thhe capacity cu urves obtaained from thee pushover an nalysis with thhe triangular laateral loadd pattern and th he offered loaad pattern (witth considering p=1) havee a good coinccidence with the t capacity ccurve resulted from the incremental dynamic annalysis and inn the linear and nonllinear regionss show the same results. The uniform load patteern isn't an appropriate pattern forr abovementiioned struccture and esppecially in thhe nonlinear regions has been diveerged from thhe average currve of IDA analysis a and shows struccture energy depreciation d m more than its real r value whiich is obtaained from the t IDA anaalysis. Hence, in the low w-rise strucctures with loow period, thee depiction of the capacity curve c withh considering the triangulaar and the offfered lateral load patteerns (with co onsidering p= =1) will resullt in more prrecise resuults.

Figure 5. Capaciity Curves of MRF F-4 for three differeent Load Patterns and IDA A-average

Figure 6. Capacitty Curves of MRF-12 for three differrent Load Patterns and IDA A-average

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F 6 shows that in 12-sto Fig. orey structure, the offered laateral loadd pattern with p=0.1 and thee uniform loadd pattern sugggested by FEMA F are co oincided with the results off capacity curvve of IDA A analysis. Heence, with coonsidering two abovementiioned laterral load patterrns, the pushoover analysis will lead to more preccise results in middle-periood structures. Evaluation off this probblem for high-period structuures (20-storeey structure) in i the fig. 7 shows thhat using th his offered load l pattern with conssidering p= -00.1 will lead to t more preciise results. Allso in these structures, the t use of the uniform loadd pattern sugggested by FEMA F is suitaable for estim mation of the seismic behaviior of these structures and a determin nation of theirr capacity cuurves.Â Figss. 6 and 7 shhow that in pushover anaalysis of the steel mom ment resisting frame with thhe intermediatte and high peeriod, by using u triangullar load patteern, the seism mic capacity of o the struccture is conssidered to be low and the lower en nergy absoorption is conssidered for thee structure thann its real valuee. B. C Concrete speccial moment reesisting framees (SMRF) C Capacity curvves of 4, 12 annd 20-storey fframes with SMRF systeem obtained from the ressults of IDA analysis of seven s seleccted acceleroometers and their t average curve have been depiicted in Figs. 8, 8 9 and 10 resspectively.

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In order to ev valuate the acccuracy and performance p o the of o lateral load patternns in unifform, triangullar and the offered estim mation of thhe seismic beehavior of thhe structures, the capaacity curve obtained from the results oof nonlinear static anallysis of structu ural models has h been depiccted and comppared to average a capacity curve resu ulted from ID DA analysis of o the strucctures under records r of sevven selected acccelerometers. The resuults of this com mparison for 4, 4 12 and 20-sstorey frames have beenn shown in Figgs. 11,12and 13 1 respectivelyy.

Figure 8. 8 Capacity curves of SMRF-4 from IDA I

Figure 11. Capaccity Curves of SMR RF-4 for three diffeerent Load Patternss and IDA A-average

Figure 9. 9 Capacity curves of SMRF-12 from m IDA

Figure 12. Capaciity Curves of SMR RF-12 for three diffferent Load Pattern ns and IDA A-average

Figure 10. 1 Capacity curvess of SMRF-20 from m IDA

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Fig. F 11 shows that in 4-storeey structure, the t capacity cu urves obtaained from thhe suggested load patternn (with p=0.22) is locatted in the reegion between the pushovver analyses with unifo orm and trianngular distribuution and has coincided c with h the capaacity curve reesulted from the t IDA analyysis. The uniiform load d pattern is a m more appropriiate pattern foor abovementiioned struccture than thee triangular pattern p and shhows the ultiimate capaacity of the strructure for esttimation of thee seismic behavior moree precisely, esspecially in thee nonlinear reggions.

Figure 13. Capacitty Curves of SMRF F-20 for three diffe ferent Load Patternns and IDA A-average

curvve obtained fro om the resultss of the nonlinnear static anaalysis of thhe given strucctural models was depictedd and comparred to that of IDA anaalysis. The offfered lateral load pattern is a simpple load patterrn that the value of its unknnown parameteer (p) is deetermined dep pending on the lateral forcee resistance sy ystem of the t structure and its heigh ht. It should be noted thaat the obtaained results are reliable only for obttaining the global g capaacity curve off the structuree. In order too evaluate thee real perfformance of thhe structure, it's necessaryy to investigatte the dispplacement of other o levels annd the perform mance points of o the struccture, too. Thhe obtained results show that in the steel mom ment-resisting frames, usingg the load pattterns suggesteed by FEM MA estimates the ultimatee capacity off the structure for evalluation of its seismic behavvior more acccuracy. In the lowperiood structures, the use of thee triangular loaad pattern andd with increease of the strructure's perio od, the use of the uniform laateral loadd pattern is suuggested. In these t structurees, by selectioon of suitaable values off P (shown in the t table4), thee suggested paattern for load distributtion enjoys good g accuracyy and perform mance and can be used d to determiine the capaccity curve off the struccture. In the low-period SMRF frames,, the uniform load patteern suggestedd by FEMA is an approopriate pattern n for perfforming the puushover analyssis in these strructures. How wever, withh increase of period of thhese structures, the lateral load patteerns suggesteed by FEMA will no longger be suitablle for inveestigation of th he seismic behhavior. Becauuse, it considerrs the seism mic capacity of o the structurre at minimum m value and shows the quantity of ennergy absorpttion smaller than t its real value. v Hennce, in the SM MRF structuress, using the offered load paattern withh considering the P values shown s in the table t 4 will leead to morre precise resuults and the reesulted capacitty curve will show morre precise esstimation of the seismic behavior off the struccture. Summaary of the resullts has been shhown in table IV. I

TABLE IV. SUMMARY U OF THE STRUCTURAL S ANA ALYSIS RESULTS

Structural system

Fig. F 12 shows that in 12-sto orey structure, the triangularr and unifo orm patterns suggested byy FEMA arenn't appropriatee for laterral load and have been diveerged from thee average cappacity curv ve of the IDA A analysis especially in the nonlinear reg gions and shows the sttructure energ gy depreciation smaller thaan its real value resuulted from IDA analyysis. While for abov vementioned structure, s the capacity c curvee resulted from m the push hover analysiss with the offfered lateral load pattern with p= -0.9 has coinciided with the capacity curvve of IDA anallysis. Hencce, the pushoover analysis in the middlee-period strucctures will lead to more precise resultts using the ooffered lateral load patteern which shhows the accuuracy and peerformance off the offerred lateral looad pattern in estimationn of the seiismic behaavior of the m middle-height (middle-periood) structures with SMR RF system.

Concrete Special Moment Resisting Frame

Evaluation E of this problem for high-periiod structures (20storeey structure) inn Fig. 13 show ws that in the pushover anaalysis of th he high SMRF F structure, with the use off triangular and the unifo orm patterns,, the seismicc capacity off the structurre is conssidered to be minimum an nd smaller eneergy absorptioon is conssidered for thhe structure than the reaal value. In these t strucctures, the usee of the offereed load patternn with P= -1.1 1 will lead to more precise results and a the resultted capacity curve c gives more precisee seismic behaavior. V.

CONCLUSIONS O

In I the current paper, the accuracy and peerformance off two laterral load patternns available inn the FEMA-3365 code (uniiform and triangular lateeral load patterns) and also a suggested laateral load d pattern for estimation of the seismicc behavior off the strucctures were investigated. i F this purppose, the cappacity For

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Steel Moment Resisting Frame

Number of Storiess N Ratio H/B Nomenclature

4 H/B<1.5 MRF-4 12 1.5<H/B<3 MRF-12 20 H/B>3 MRF-20 4 H/B<1.5 SMRF-4 12 1.5<H/B<3 SMRF-12 20 H/B>3 SMRF-20

Suitable load patterrn suggested by b FEMA

Triangulaar

Proposedd load patterrn

Uniform

Not Suitable Not Suitabble

. .

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Y. Pu; L. Yingm min; W. Yayong; L. Ming, “A Stuudy on Improvem ment of pushover Analyssis’’, Journal of building b structurees; 2000-01.

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S.Etedali et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 5, Issue No. 2,201 -208

ISSN: 2230-7818

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