مجله مهندسی عمران شریف
سال سی و چهارم شماره 4 (زمستان 1397)

A rehabilitation technique that utilizes a thin steel plateas a supplemental shear wall system for steel momentframes is described. In the proposed system, the plateand surrounding boundary elements are installed in themiddle of the bay, separate from existing columns (SW-TB =Steel Plate Shear Wall with Tension-Bracing). Thisgeometry intends to reduce the forces transferred to theexisting columns. In this paper, the behavior of steel mo-ment frames using the proposed system is investigated.Among the methods of retro tting of the steel frames,application of steel bracing system has been studied bysome researchers. The results of these studies show thatretro tting of steel frames by adding braces has dis-advantages such as increasing axial forces in adjacentcolumns, brittle behavior in the frame joints, bucklingthe bracing member, and creating a permanent deforma-tion on the frame. In order to remove these disadvan-tage researches such as the use of non-compression brace,buckling-restrained braces, dissipative bracing systems, displacement-restraint bracing and thin in ll panels areexamined. Steel plate shear wall systems have attractedmore attention in the past few years as one of the majorlateral-load resisting system in steel buildings. In thiscontext, many investigations have been conducted in dif-ferent countries. In this study, to eliminate the above-mentioned disadvantages, a SW-TB system is used toretro tting of a steel frame. Recent researches indicatethat this type of shear walls has a very good perfor-mance in comparison to its traditional form (i.e., SSW=Steel Plate Shear Wall). For this purpose, the Finite-Element Model (FE) of steel frame retro tted with steelshear walls and tension-bracing has been made. Theobtained results of this model are compared with Lab-oratory data. The comparison shows that the nite-element model produces similar results to those of theproposed method in the laboratory. After the experi-mental validation, this method is compared with threeother methods. The FE analysis results show that usingthis method causes the lateral resistance of the structureto increase as much as 50 percent with good ductility,and the need to enhance the lateral columns and foun-dations will be limited.

Shallow foundations are among the most common typesof foundations used to support mid-rise buildings in ar-eas with high seismic hazard. Recent studies have indi-cated that dynamic interaction of soil-foundation andbuilding can a ect the seismic response of structuresduring an earthquake. Therefore, the foundation fea-tures can also change the dynamic characteristics, suchas natural frequency and damping of the soil-foundation-structure system. In this research, a 14 story momentresistant frame building built on shallow foundationswith various dimensions has been considered and thethree dimensional prototype of all three components ofsoil-foundation-structure system has been modeled byABAQUS nite element software. Also modal analysiswas performed to calculate the natural frequencies ofeach model. In the present study, in nite boundarieswere applied in order to simulate free eld conditionand appropriate contact elements were used to modelthe slip and separation phenomena between foundationand soil elements. To do so, nite element direct modelswere developed. Cone model, as one of the approximatemethods that considers SFSI with practical engineeringprecision was veri ed and then applied in the series ofsimulations. An assessment procedure was applied tocheck the accuracy of Cone model as an approximatemethod in comparison with direct method. Structuralresponses including lateral deformation, drift, rotationand shear force distribution were studied for all cases in-cluding xed-base, cone model and SFSI direct models.Modal analysis implies that SFSI can reduce the natu-ral frequencies of the building. The results show thatshallow foundation size, due to the interaction betweensoil, foundation and structure, in uences the dynamiccharacteristics and seismic response of building. As aresult, engineers should carefully consider these param-eters to ensure the safety and economic seismic design.Cone Model with an appropriate engineering precision,functionality and high analysis speed is capable of assess-ing dynamic sti ness of soil due to the soil-foundation-structure interaction phenomena.

Impact damper is considered as a passive control sys-tem. Experimental and analytical studies have shownthat this group of non-linear dampers has a better per-formance than linear vibratory neutralizers in terms ofreducing structural vibrations. The main factor in u-encing this type of damper in controlling vibrations isthat the small forces, created by moving masses of im-pact dampers reduce sharp vibrations by creating dis-ruption in the oscillation range of the structure.So far, modeling of the impact damper has been con-ducted solely through MATLAB software. Naturally,the functional aspects of this software are limited in re-search and development aspects compared to the com-mon programs such as SAP2000 and ETABS. In thisstudy, using SAP2000 software in modeling impactdampers, relatively tall building models are used to com-pare the performances of impact damper in high-risebuildings, and the seismic performance of such build-ings with impact damper is investigated. The purposeof this study is to evaluate the performance of impactdamper in tall buildings and to determine the best place-ment of damper in reducing the amplitude response ofthe system under vibration.In order to achieve favorable results for tall buildingsunder seismic vibration, both near- and far- eld earth-quakes are selected and applied to 10- and 25-story steelbuildings. The analysis used in this study is of non-linear time-history kind, and the design of structuralelements is performed considering AISC360-10 Code re-quirements. One of the main results of this study is thedecreased amplitude response of 10 and 25-story steelbuildings under vibration due to the placement of impactdamper on the roof up to 14% and 16% under far- andnear- eld earthquakes, respectively. It is also observedthat if the height and number of openings increase, thee ect of the placement of impact damper in the middle oors will become closer to the placement of damper onthe roof due to the combination of vibration modes.

High-performance ber cementitious composites are newmaterials in construction industry. Investigation intotheir behavioral characteristics needs experiments dueto the lack of data. In this study, tensile, compressiveand bending behavior of this material is examined us-ing experimental tests"High-performance ber rein-forced cementitious composites (HPFRCC) have strainhardening response under straight tension after cracking.Numerous cracks are formed before the crack widen-ing occurrence when these composites show hardeningbehavior. HPFRCC are basically integrated with twomain components including ber and mortar. Thesetwo ingredients are interactively a ected due to inter-facial bonding which develop a strong composite. Theadvantages of HPFRCC in comparison with normal and ber reinforced concrete (FRC) are ductility, durabil-ity, and high-energy absorption capacity. In this paper,evaluation of strain hardening behavior in HPFRCC isconducted using straight tension and tensile strain-stresscurve. Moreover, bending behavior, load-displacementcurve, and toughness factor of this material are evalu-ated using four-point bending test, and the performanceis compared with bending behavior of normal concrete.In these tests, three ber types, including hooped steel ber, corrugated steel ber, and poly propylene ber, areused in the mortar separately and in combination witheach other by volume percentage of 1.5%. To achievea proper strain hardening behavior, di erent mix ra-tios are investigated and the best mix design is deter-mined. The results showed that all specimens mixedwith bers have strain hardening behavior accompanied by more cracks; consequently, the strength and strainof the HPFRCC specimens are increased signi cantlycompared to those of normal concrete. The strengthof HPFRCC specimens is between 5 to 8 times greaterthan that of normal concrete. In addition, the ultimatestrains of the specimens are 70 to 100 times higher thanthat of normal concrete. Furthermore, toughness fac-tor of HPFRCC specimens is 5 to 9 times higher thanthat of normal concrete. It is revealed that the mechan-ical properties of HPFRCCs have been considerably en-hanced compared to normal concretes. HPFRCCs canbe applied as an appropriate technique to restrain the re-inforcement congestion, decrease the high value of trans-verse reinforcements at beam-column joints, and alsoimprove the shear capacity and ductility of the mem-bers.

The presence of oil in the soil media, by changing theinteraction between soil particles, reduces the shearstrength of the soil compared with clean soil. Finally,oil pollution, reduces permeability, internal friction an-gle and bearing capacity and increases volumetric strainand the resulting settlement of the structure. On theother hand, most of the foundation analysis methodsrequire the use of subgrade reaction modules as a ba-sic parameter to assess elastic situation of the subgradeand determination of the sti ness and load-deformationbehavior of the soil. It should be noted that, subgradereaction modulus is obtained mainly through eld plateloading testing. In this study, using physical modelingwith plate loading, deformation behavior and sti ness ofoil-contaminated sand and reaction modulus for the dif-ferent percentages of oil contamination will be reviewed.The results can present a more appropriate estimate ofthe amount of elastic settlement of the structures restedon the contaminated soils, also re ne the amount of foot-ing's exibility on this group of soils. The most e ectiveparameters on the soils sti ness in this eld include thesoil classi cation, relative density, type of contamina-tion and the amount of contamination in the soil. Thesevariables can be e ective in the process of the possiblechanges of sti ness and soil reaction modulus. Gas oil,crude oil and kerosene have been used as contaminationmaterials. These liquids have been added into the sandin three di erent percent rates, 2, 4 and 6. The sandhas been compacted in three di erent situations; loose,medium and dense. Based on this research, oil contam-ination causes substantial decrease in soil sti ness andmore greasy oil contamination is even more e ective inreducing the soil subgrade reaction. In addition, densesoils sti ness is less sensitive to oil contamination e ects.These results can be used for investigating the sites inwhich there is a possibility of oil leakage to layers ofthe land. Results have been presented in the form ofempirical equations.

Nonlinear time history analysis is the most accuratemethod for seismic response analysis of structures, andperforming it for designing and evaluating purposes isinevitable in some cases. The most important issue innonlinear time history analysis is the scaling method ofground motion records in order to have an accurate es-timation of structural responses. In this paper, a newmethod for scaling of ground motion records is proposed,in which the nonlinear behavior of structures is consid-ered. In the proposed method named SNSP (Scalingbased on Nonlinear Structural Properties), the scalingfactor of each record is determined in a way that the peakdisplacement of the equivalent single degree of freedom(SDOF) system subjected to the scaled record matchesthe target displacement. The target displacement is de-termined by averaging the values of the peak displace-ment of the equivalent SDOF system subjected to a largenumber of unscaled ground motion records. The charac-teristic parameters of the equivalent SDOF system aredetermined based on the modal pushover analysis, inwhich the load pattern is derived from the modal storyshear pro le of the structure. Thus, in the equivalentSDOF system, the e ect of higher modes and the in-teraction between them in the inelastic phase are con-sidered. Furthermore, the characteristics of the selectedground motion records are also considered using their re-sponse spectra in the proposed scaling procedure. Theaccuracy and eciency of the proposed method were ver-i ed through four 4-, 8-, 14- and 20-story buildings under21 near-fault records and was compared with the scalingmethod of the Iranian code of practice for the seismicresistant design of buildings, Standard No. 2800. Re-sults show that the structural responses obtained fromthe proposed scaling method are close to the averageresponses considering site-speci c records and the dis-persion of responses is low.

Modern methods of reinforcing walls were used in the 60sby Henry Vidal. Reinforced soil wall is an alternative toretaining walls and traditional embankments. The useof geosynthetics as reinforcement in reinforced soil wallshas been signi cant in recent years. Reinforced soil wallshave been used in Iran since 70s. Accordingly,in someareas, due to the lack of access to suitable materialsand high cost of material supply from far zones, ne-grained soils may be used for wall back ll. Reinforcedslopes and walls come with various applications, includ-ing its use in bridge abutment. In this study, the e ectof ne-grained soils, strip surcharge, and wall angle onbehavior of geosynthetic reinforced soil walls using cen-trifuge modeling has been studied. In this study, a set of8 centrifuge testes on saturated ne-grained walls rein-forced with geotextile was performed using the geotech-nical research center of Iran University of Science andTechnology centrifuge, and behavior of physical modelsusing digital image processing technique was studied.The comparison between place of rupture on geotextileand slid surface obtained from digital image processingwas a good matched. Therefore, combination of cen-trifuge modeling with digital image processing is a goodway to study the behavior of geosynthetic reinforced soilwalls.The results showed that with increasing load of stripfooting, the amount settlements of top of wall increased,and this e ect on vertical walls is more than the batteredwalls. Moreover, stains of reinforced layers and defor-mation of facing wall also increase when nes in back llincreased from %10 to %20. It was observed that slidesurfaces were entry from behind of strip footing and de-veloped to the toe of the walls. With increasing percentof ne-grained in back ll from %10 to %20, sliding sur-faces were deeper. In addition, with the decreasing ofangle of face, the models were stable. In addition, exis-tence of %10 nes in sand back ll improves performanceof geosynthetic reinforced soil wall (GRSW). If nes inthe back ll increased to %20, GRSW would have poorperformance.

Lifelines are essential for human life and economic de-velopment. Buried steel pipelines are the sort of life-lines that their strength under extreme events, suchas earthquakes, is very essential. One of the causesof failure of buried pipelines is seismic wave propaga-tion. Buried steel pipelines are vulnerable in extremeevents such as earthquakes. In this study vulnerability ofburied steel pipelines was evaluated using the results ofincremental dynamic analysis (IDA). Several IDA anal-yses of three buried steel pipe models with a di erentdiameter to thickness and burial depth to diameter ra-tios and di erent soil properties, were performed usingfar- eld earthquake ground motion records. The mod-els were designed based on American Lifeline Alliance(ALA) guidelines. The nite-element method was usedin the analyses. The buried pipeline and the surroundingsoil were modeled using beam, spring, and damper ele-ments. The peak axial compression strain at the criticalsection of pipe was used as an engineering demand pa-rameter of buried pipe and peak ground velocity (PGV)was considered as a ground motion intensity measure.Then, limit states for buried pipelines were proposedand fragility curves of pipes were developed based onIDA results for the limit states. In addition, a rela-tion for damage ratio of buried pipelines in term of axialcompression strain of pipe was proposed. The resultsof this study show that the maximum axial compressivestrain of pipeline, due to seismic wave propagation, be-comes 5.7 times with doubling the PGV. It was foundthat the predicted number of repairs increases by a fac-tor of about 1.87 when PGV is double. The seismicdamage probability of pipeline increases with increasingnatural frequency of vibration of the pipe-soil system.It seems that the ALA guidelines are not enough forseismic design of some steel buried pipelines especiallythe soil-pipe systems with high natural frequency. Thisrequires a more comprehensive study.

Finite-element method is a famous and robust numericalmethod like other numerical methods. Due to the use ofpre-de ned and standard form of shape functions, thismethod will face a dicult situation and without anyaccuracy for exact modeling of the areas. The processof the nite-element network generation, with the appro-priate number and type of elements, is one of the futurechallenges to this approach; its aim is to reduce the com-putational costs in order to discretize and solve the pre-dominant equations of the problem. The derivatives ofanswer usually need the re nement operations to achieveacceptable accuracy in network-based methods. For thispurpose, the methods of the enrichment-displacementre nement, re nement of enhancing element order andre nement of increasing the number of elements, andthe combination methods can be used. The re nementin numerical methods is an ecient tool to reduce thecomputational costs and increase the accuracy of the re-sults obtained. If the parts of the area of solving problem that needs more accuracy be clear, it can greatly reducethe computational complexity with an appropriate pro-cess. In this paper, energy norm of error method andre nement of enrichment-displacement, using the opti-mization algorithm of charged system search, are pre-sented to improve the accuracy of the two-dimensionallinear elasticity. Problems simultaneously use two meth-ods of enrichment and displacement techniques. At rst,replacing the points would reduce the predominant er-ror of the problem. Moreover, in the event of failure toreach an allowable error, in the next step, elements thathave a higher error than permissible one using enrich-ment method of new nodes enter the domain of problem,and new meshing is o ered. Enrichment-displacementmethod continues to obtain the desired accuracy. Theproposed method with achieving a suitable layout for nite-element network, in addition to solving the prob-lem of some nodes occurring in conventional enrichmentmethods, improves the accuracy of answers as well. Fur-thermore, the approximate answers will be provided withthe lower number of degrees of freedom than the com-pared methods. A comparison of result for the presentmethod by other researchers show the eciency and ac-ceptable accuracy of the method.

The numerous collapse of reinforced concrete (RC) build-ings reported during destructive earthquakes, happeningaround the world, are pertaining to short column fail-ure. Shear collapse mode is the most devastating causesof failure in short RC columns due to intensive seismiccyclic loads. Since the code-based design equation forestimating the strength of these structural elements isbasically based on pragmatic models, they cannot ap-propriately estimate the resistance over a wide rangeof involved variables. Evaluating collapse capacity ofthese structural elements has been an attractive topicof research for the last few decades. The major goal ofthis paper is to propose a model for shear strength ofbeam-column with shear span-to- depth ratio less than2.5. To complete few available experimental samples,the purposed ABAQUS general nite-element methodsoftware is used to model 52 numerical samples to covera wide range of various parameters involved in shearresistance. According to the performed experimentalworks, the e ective shear strength parameters are axialforce, transverse and longitudinal reinforcement, columnaspect ratio, concrete compressive strength, and ductil-ity. The nite-element models are validated against ex-perimental data. To develop a closed form solution forevaluating shear strength, Genetic Programing (GP) isused. GP is an automated method for creating a workingcomputer program from a high-level problem statementof a problem. GP starts from a high-level statementand automatically creates a computer program to solvethe problem. This method is successfully used in vari-ous elds, including symbolic regression, image process-ing, network protocol design, patching buggy codes androbot control.The proposed GP model is compared against shearstrength provided by the existing relations of two majorcodes, e.g., ACI and EC2. Compared with experimentalresults, the average errors from the application of GP,ACI and EC2 are %15, %45, and %43, respectively. Thisshows that the proposed equation using GP is a preciserelationship for the prediction of the shear capacity ofrectangular short RC columns.

The phenomenon of negative skin friction (NSF) is afriction force downward on the pile surface which oc-curs as a result of the settlement of the surroundingsoil and causes extra load on the pile. Hence, bearingcapacity of pile decreases and its settlement increases.Therefore, NSF is considered one of the problems in thedesign of piled foundations in soft soils. On the otherhand, by the advancement of geotechnical engineeringscience, a new type of piles was introduced called ta-pered piles.In this type of piles, by the increase of the depth, theirsection area decreases, and nally, the bottom of thepile will have a smaller cross-section compared to itstop side. Hence, in this research, by using ABAQUS nite-element software, a single pile with a uniform sec-tion is modeled in a clayey layer under the e ect ofNSF phenomenon. Afterward, by tapering the pile un-der various tapering angles and comparing the obtainedresults, the e ect of pile tapering on the NSF phenom-ena and also neutral plane location have been examined.In addition, in order to validate the numerical model-ing, an in-situ pile load test with the measured nega-tive skin friction value on a uniform pile in Bangkokwas simulated. Besides, in order to investigate the in u-ence of the pile cross-section shapes on the NSF, mod-eling of three type piles with a constant volume hasbeen conducted using di erent shapes including circu-lar, triangular and square cross-sections. The obtainedresults indicated that using tapered piles is economi-cally bene cial, unlike the granular soils; in cohesivesoils, the NSF values and neutral plane location are in-creased which can noticeably reduce the bearing capac-ity of piles. In addition, using the tapered piles with tri-angular cross-section causes a decrease in soil settlementaround tapered piles compared to other cross-sectionsand consequently the NSF could also be decreased. In-deed, using piles with a triangular cross-section whichhas more contact surface with soil, because of more cre-ation of friction between soil and pile compared to otherpiles, soil settlement in the vicinity of tapered pile isdecreased; following that, the negative skin friction alsodecreases.

Knowledge of allowable di erential settlement is neces-sary for foundation design. Di erential settlements maycause additional stresses and strains in structural mem-bers. The stresses induced by di erential settlements arenot conventionally considered in designing superstruc-ture. The di erential settlements are generally deter-mined from separate analysis of foundation slab overlaidon soil by applying the structural loads onto it. Then,the calculated settlements are limited to the allowablevalues. The allowable di erential settlements in con-struction codes are not strongly hooked on the type, de-sign method, and application of structures. The currentapplied criteria are mainly based on the observations onactual problematic buildings. It is necessary to numeri-cally determine the limiting values of di erential settle-ments which endanger the performance of structures. Inthis research the allowable settlements of steel momentresisting frames are determined based on seismic perfor-mance level. Four moment-resisting steel structures wereanalyzed and designed according to conventional meth-ods without applying any di erential settlements. Then,di erent patterns of di erential settlements (point, axial,and block patterns) were applied to the structures andthe structures were analyzed by nonlinear nite-elementmethod. Based on the analysis results, the limiting val-ues of di erential settlements at life safety performancelevel were calculated according to FEMA-356 code. Theresults of this research revealed that the height of struc-ture considerably a ects the allowable di erential settle- ments such that increasing structure height can reducethe allowable di erential settlements up to 50%. The re-sults of this research also revealed that the geometricalshape and properties of building plan a ect the amountof allowable di erential settlements, such that moment-resisting structures with rectangular plan tolerate higherdi erential settlement values compared with the struc-tures with square plan shape. According to the resultsof the present study the allowable angular distortion atlife safety performance level of moment-resisting steelframe structures is suggested to be limited to 1/94 inthe buildings with maximum ve stories, and 1/200 in ve to ten-story buildings. The results indicate that theheight of structure should be taken into consideration inthe allowable di erential settlement criteria.

In recent years, the need for consistency between thepractical implementation steps of construction processand the design stage of high-rise concrete structurethrough the use of nonlinear sequential construction anal-ysis has been strongly recommended by researchers. Be-sides, it is known by research and experiment that con-crete structures are subjected to larger displacementsand stresses because of the long-term behavior andthe time-dependent parameters of concrete such as creepand shrinkage. This brings about the increase in beamde ections, expansion of tensile cracks in members, ex-cessive column shortenings, di erential displacements ofhorizontal structural members, such as beams, causedby unequal and increasing axial displacements in ad-jacent frame members and considerable redistributionof stress in structure. All these outcomes, which a ectstructure's response directly or indirectly, must be con-sidered in the nonlinear and time-dependent sequentialanalysis of multi-story buildings. In this paper, the mostimportant methods of predicting the long-term behaviorof concrete, stating the advantages and disadvantages ofeach, has been introduced, and the proposed equationsto describe the manner of applying certain features ofthe aforementioned methods in the updated version ofthe common analysis and design software for structuresare presented. In addition, for getting familiar withthe manual method of calculation of creep and shrink-age e ects, the exact implementation of the Fintel andKhan's model is expressed by establishing the tables ofbefore and after the casting of concrete and consideringthe changes that illuminate the obscure aspects of thecorresponding method. Proper compliance of the ob-tained results with the corresponding values of the sim-ilar method, named PCA, which has the nite-elementmodeling functionality, indicates the possibility of pro-viding a reliable sample for error calibration and valida-tion process. For vivid understanding of the e ects oftime-dependent parameters of the concrete on the axialdeformation of the vertical elements of the structures,the invoked example of Fintel and khan has been ap-plied similarly to all the studied methods under conven-tional one-step and nonlinear staged analyses. More-over, the column shortening results have been comparedafter 1,000 days of construction time.

An accurate material quantity take-o and estimationare vital issues in various construction projects. Suchan accurate estimating and material quantity take-o isrequired prior to initiating a project for tendering andbidding purposes, and during the construction phasefor procurement and project control purposes. Thus,a number of Building Information Modeling (BIM) ap-plications have been utilized recently not only for ef- cient material quantity take-o and estimating pur-poses, but also for other construction engineering andmanagement commitments (e.g., visualization, clash de-tection, 4D 5D planning, and virtual reality). The mostcommon BIM applications can be named as \AutodeskRevit" and \Tekla Structures" for integrated modeling(e.g., structure, architectural, and MEP modeling) and\Autodesk Navisworks Manage" for site managementand 4D Planning purposes. In this research, the ac-curacy of automatic quantity take-o , using aforemen-tioned BIM applications, has been investigated. First,such an exercise is performed on simple steel and re-inforced concrete elements modeled using Revit struc-tural extension. Furthermore, this exercise is extendedto steel and reinforced concrete 3D structures, modeledin both TEKLA and Revit structures. By recognizingthe points of weakness of such BIM applications, somepractical recommendations are provided to enhance theaccuracy of automatic quantity take-o and estimation.Another side product of knowing the accuracy of auto-mated material quantity take-o is providing a realisticestimate based on the utilized estimating approach andemploying BIM software to avoid unplanned mistakes inestimating and quantity take-off.