Comparison of performance based design and forced based design PDF
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Added on 2021-08-30
Comparison of performance based design and forced based design PDF
Added on 2021-08-30
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COMPARISONOFPERFORMANCEBASEDDESIGNANDFORCEDBASEDDESIGN APPROACHFORHIGHRISECONCRETEBUILDING ABSTRACT: The main objective of this report is the understanding of the impact of multihazard loading, brought by wind and earthquakes, on the behavior of high-rise buildings, in order to apply such knowledge to design. The main contributions of the current study are summarized as follows: (i)For dynamics and response under wind loads, general agreements between the results of the pressure integration technique and the aeroelastic experiment exist. However, the effect of the aerodynamic damping on the worst responses of a multi story building/highrise in the two lateral directions is shown to be positive, which resulted in partial response reduction. (ii)The study that will be discussed in this project report will show that it is advantageous to predict the responses of tall buildings in their preliminary design stages as this can provide an opportunity to rotate the building to an optimal orientation that can lead to significant reduction in the responses. The results will show that the worst peak acceleration is reduced by 38.5%, by rotating the building (multi story building/highrise) to a suggested orientation. This reduction is achieved without adding any structural elements/components to the primary building (no additional cost). (iii)The results that will be done for load calculations in this project will show that wind and earthquake loads are different from each other and are also different from static loads. This comes from the spectral comparison of the response of a high-rise building under the two types of excitation. The results indicate that earthquake loads excite higher modes that produce less interstory drift but higher acceleration which occurs for a relatively short time (compared to wind loads).. (iv)Although the acceleration under wind loads is lower than that under earthquake loads, it occurs for longer periods that become a comfort issue. (v)It seems that tall buildings designed for wind are safe under moderate earthquake loads. Nevertheless, it is important to mention that, even if the interstory drift ratios in tall buildings may be relatively small with no significant apparent issues for the main force resisting system of the structure, nonstructural systems may represent a high percentage of loss exposure of buildings to earthquakes due to high floor acceleration. Accordingly, appropriate damping techniques are recommended for response reduction under wind and earthquake loads. Seismic design of structures is commonly based on strength or force considerations rather than displacement as the seismic design codes generally use lateral inertia forces to account for seismic ground motion effects. The distribution of these static forces (and therefore, stiffness and strength) is based implicitly on the elastic vibration modes [1, 2]. Therefore, as structures exceed their elastic limits in severe earthquakes, the use of inertia forces corresponding to elastic modes may not lead to the optimum distribution of structural properties [2, 3]. The need for finding cost-efficient and optimum structural designs has led to the development of different structural optimization methodologies. Optimum design of structures for seismic loads has been studied by many researchers over the past decades [4-8]. The conventional methods used in these studies are usually gradient-based solution strategies that require the satisfaction of some specific mathematical conditions. Due to the difficulty in calculating appropriate
expressions for optimisation constraints, these methods cannot be practically applied for optimum design of nonlinear structures subjected to seismic excitations. INTRODUCTION: In today‟s era the aim of limiting excessive damage and to maintain functionality of the building after an earthquake is becoming more desirable. In order to predict damage to a structure in an earthquake, performance based design method is a new method which is rapidly gaining popularity. It is well known that structures designed by current codes undergo large inelastic deformations during high earthquakes. However, current seismic design approach is generally based on elastic analysis. The seismic design of structures is continuously evolving. Conventional design procedures have the objective of achieving life safety in a structure by providing sufficient strength and ductility to resist whole or partial collapse of the structure. Structures designed according to current seismic design provisions or design code should, in general, satisfy the following rules. First, to resist minor level of earthquake ground motions without damage; second, to resist moderate earthquakes without structural damage, but may experience some non- structural damage; and finally, to resist major earthquakes without collapse, but possibly with some structural and/or non-structural damage. The unexpectedly high financial losses related to functional downtime and non-structural damage from recent large earthquakes near prime locations emphasizes the limitations behind the current ductile designs using FBD method. In the current Indian design practice, it is common to calculate design base shear from code specified spectral acceleration, with the assumption that structure to behave elastic. It is also reduced by response reduction factor R. the design forces is also influenced by importance factor I, based on occupancy. By the use of these parameters lateral forces are found, member size will be selected from design results and then analysis regarding drift and deflection of the structure is done, which must be within an acceptable limit. Sometime the structures experienced high earthquake forces however, the structures designed by such procedures have been found to undergo inelastic deformations in a somewhat „uncontrolled‟ manner. This may results undesirable and unpredictable behavior, sometimes total collapse, or difficult and costly repair works. So the societal requirements are pushing the practice to achieving higher levels of performance, safety and economy, including life-cycle costs. Performance Based Plastic Design is a recent designing concept of seismic resistant structure, in which the design criteria are expressed in terms of achieving stated performance objectives when the structure is subjected to higher level of seismic hazards. Since 1994 Northbridge earthquake and other earthquakes in the world during the end of 20th century led the structural engineer to use the concept of Performance based design. DESIGN OF A STRUCTURE OF HIGHRISE BUILDING AND ITS CALCULATIONS: Structures tare ta tgroup tsuch tas tbeams, tcolumns, tslabs, tfoundations, tgirders, tand ttrusses, tthat twork tas ta tunit tto tfulfill ta tpurpose. tAn tengineer's tduty tis tto tdesign tstructures tin ta tprofessional, tsafe, tand teconomical tmanner tin torder tto tfulfill tthe tpurpose tfor twhich tit twas tdesigned tin tthe tfirst tplace. tStructures tas tclassified tinto teither tbeing tstatically tdeterminate tor tstatically tindeterminate. Statically tdeterminate tstructures tare tstructures tthat tcan tbe tanalyzed tusing tstatics tequations tonly, t(i.e., tequilibrium tin tall tdirections). tOn tthe tother thand, tstatically tindeterminate tstructures tcan't tbe tanalyzed tusing tstatics tequations tonly; tthey trequire tother tmaterial tproperties, tsuch tas
tdeformations, tin torder tto tanalyze tthem.When tengineers tconduct tstructural tanalysis, tthey tcalculate tthe treaction tforces tdue tto tthe texternal tforces tapplied tto tthe tstructure tas twell tas tinternal tforces, tsuch tas tthe tbending tmoment, tshear tforce, tand tnormal tforce. tStructural tanalysis tis tnecessary tfor tstructural tdesign tin torder tfor tthe tstructural tengineer tto tchoose tthe tproper tsizes tand tmaterials tso tthe tstructure tcan teconomically tand teffectively tresist tthe teffects tof tthe tpossible texternal tloads tapplied tto tit. METHADOLOGYOFSTRUCTUREDESIGN This tproject tcompare tbraced tand tunbraced tframes tapplied tto teuro tcode tEC tand tBritish tstandard tBS5950. Method tused tto tcompare tare thand tcalculation, tand tsoftware tsuch tas tstrand7 tand trobot tanalysis. tAs tan tengineer twe tknow tthat tone tonly ttrial twouldn’t tbe tsatisfactory tto tmake ta tpoint, tso tit thas tbeen tcreated tbuilding tfor teach tprocedure tand teach tprocedure tcontain tdesigning tof tEUROCODE tand tBRITISH tSTANDARD twith ttwo tdifferent tdimensions tas tdimensions tcan taffect tthe tbuckling tand tbending tof tthe tmember, tand tP-delta tfactor thas tbeen tanalysed. Drawing tare tbeen tmade ton tAUTOCADt(figure1) tthen ttransferred tto trobot tfor tthe tanalysis. After teach tmember tdesign, ta ttype tof tcross tsectional tarea tis tbeen tchosen tfrom tthe tBlue tbook tbased ton ttheir tresistance tformulated ton tthe tcalculation. LOADTYPEDead tLoad Dead tload tas twell tas tknown tas tthe tpermanent tload. tAll tthe tmembers ttaking tpart ton tthe tstructure tand tkeeping ttogether tthe tstructure tare tcalled tdead tLoads, tas teach thas tits town tweight tand teffects tthe tstiffens tof tthe tnext tpermanent tmember. tGood texamples tare: tslab, tbeam tcolumn, troof, tcladding tetc. In torder tto thave ta tsecure tand tdurable tmember ta tsafety tfactor tis tused. tAs tof tthe tEuro-code timply ta tfactor tof t1.35, tand tBS tstandard timply t1.4.
FIG 1: BASEMENT PLAN OF A HIGHRISE BUILDING SHOWING GRID STRUCTURE.
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