Pushover Analysis Of Beam Retrofitted Multi Storey RCC .

KEC Conference 2021ISBN 978-9937-0-9019-3Pushover Analysis of Beam Retrofitted MultiStorey RCC Building using CFRPNamaraj KafleDepartment of EarthquakeEngineering,Thapathali campusKathmandu, NepalNamaraj.kafle@gmail.comAbstract— In this study seismic response of two storeyreinforced concrete building is analysed by pushoveranalysis. Building frame is structurally analysed by usingsoftware SAP 2000 (version 14). Nonlinear pushoveranalysis is perform to check the performance point. Effectof external wrapping of carbon fiber reinforcement polymer(CFRP) on fail beam investigate the improvement onperformance of beam. CFRP is used as retrofittingtechnique. It has been concluded that after the use of CFRPfor retrofitting of beam, the structure were found to bewithin the targeted performance level.Keywords— CFRP, Capacity Curve, Performance Point,Seismic retrofitting, Pushover analysisI. INTRODUCTIONNatural disaster are originated from natural event,causes loss of life and property. The most commonnatural disasters are earthquake, flood, storm, tsunamietc. Nepal is the one of most seismic regions of theworld. Seismic retrofitting is considered one of mosteffective technique for earthquake risk reduction [1].Retrofit refers to strengthening of existing structure.The retrofit process is general term that may consistof variety of treatment, including preservation,rehabilitation, restoration and reconstruction.According to the United Nations, Nepal is the 11thmost earthquake prone country [2]. Therefore,earthquake vulnerability in Nepal is great concern.Generally, used retrofitting technique for reinforcedconcrete structure are base isolation, seismic damper,reinforced concrete jacketing, steel caging, fiberreinforcement polymer. For masonry structure areplaster stitching, cement grouting, shotcreting, splintand bandage.In the recent decades, the availability of fiberreinforcement polymer (FRP) with its favorableproperty such as ease of application, high stiffness,strength, light in weight, advanced fatigue andcorrosion resistances, etc., providing significantfunctional and economic benefits, ranging fromstrength enhancement and weight reduction todurability features [3]. However, the FRPstrengthening technique has a few drawbacks, whichare mainly associated with the use of epoxy resins—namely, high cost, poor performance in hightemperatures, inability to apply on wet surfaces, andKEC Conference 2021, April 18, 2021“3rd International Conference On Engineering And Technology”Kantipur Engineering College, Dhapakhel, Lalitpur, Nepalincompatibility with substrate materials (concrete ormasonry). In an attempt to alleviate the problemsarising from the use of epoxies, researchers havesuggested the replacement of organic (epoxy resins)with inorganic (mortar) matrix repairing of structural beam columnjoints has confirmed in many studies worldwide.Researchers have also investigated the relatedproblems such as FRP-concrete interface interactionand creep behavior in FRP strengthened structuralmembers [5]. However, very few studies havescrutinized the overall behavior of FRP rehabilitatedRC structures. Seismic performance of a full-scaleRC structure repaired with carbon FRP (CFRP)laminates and wraps. Their experimental resultsproved the existence of a large displacement capacityin the repaired structure without any reduction ofstrength after the application of FRP at the beamcolumn joints and walls. In addition, the energydissipation remains almost identical to the originalstructure. On the contrary, a reduction in thedeformability of shear walls observed during theexperiments due to the presence of CFRP laminatesover the entire height. In another experimental study,Di Ludovico et al. [6] Investigated seismic retrofittingof an under-designed, full-scale RC structure withFRP wrapping. In their study, a bi-directional testwith peak ground acceleration (PGA) equal to 0.2gapplied to the original structure prior to retrofittingunder which the structure found inadequate. Thestructure was then retrofitted in order to withstand a50% higher PGA of 0.3g. The successful outcome ofthe tests proved the effectiveness of FRP inimproving the global performance of the structure interms of ductility and energy dissipating capacity.Improving the seismic behavior of deficient RCstructures with FRP composites has also confirmedby Garcia et al. [7] Who through experimental testsand numerical modelling found that FRP retrofitresults in substantial improvement of seismicperformance of damaged RC frames. Following themain trend of the argument, the current studyconducted to investigate to the seismic behavior ofFRP retrofitted RC buildings. To pursue thisobjective, FRP sheets applied at the beams andcolumns regions that are prone to the development of198

KEC Conference 2021plastic hinges in such a way that increases theflexural strength. As a result, FRP sheets applied atthe top and bottom flanges of members with fibersoriented parallel to the longitudinal steelreinforcements. Of particular interest was to comparethe effects of GFRP and CFRP application. As thecase study, a 2-storey moment resisting RC buildingselected representing the buildings. The seismicbehavior of the structure evaluated using thenonlinear pushover method. In addition, the conceptof lumped plasticity with flexural hinges at both endsof beams and columns implemented in thecharacterization of nonlinear properties of thestructural members. The analyses carried out in SAP2000, a commonly used finite element program bythe structural engineering profession. SAP2000 canperform static or dynamic, linear or nonlinearanalysis of structural systems.Two storey residential building is located inseismic zone v. 3-d model of two storey buildingstructure model as shown in fig 1. there are twonumber of bay in x and y direction. 27 fit in xdirection and 24 fit in y direction in plan. Theanalyses carried out in SAP 2000. To performpushover analyses in SAP2000, users can create andapply hinge properties. In SAP2000, a frame elementis modelled as a line element having linearly elasticproperties and nonlinear force displacementcharacteristics of individual frame elements aremodelled as hinges represented by a series of straightline segments. There are three types of hingeproperties in SAP2000. They are default hingeproperties, user-defined hinge properties andgenerated hinge properties. Studies show that userdefined hinge model gives better results than defaulthinge model [8]. Moment-curvature relationship isused to model plastic hinge behaviour in non-linearanalysis. The seismic performance of a structure canbe evaluated in terms of pushover curve, plastic hingeformation etc. The maximum base shear capacity ofstructure can obtained from base shear versus roofdisplacement curve.Equivalent compressive strength of the sectionconfined by CFRP was calculated using the equationformulated by (Riad Benzaid, 2013).Non-linear staticpushover analysis was done by using the equivalentcompressive strength and the behavior of thestructure at maximum roof displacement of 300 mmwas studied. The design base shear of the buildingwas calculated using the IS 1893:2016 and iscompared with the performance base shear obtainedfrom analysis.1Materials PropertiesMaterials/sectionGrade/sizeConcretegrade M2034567891011II. METHODOLOGYS.N.2UnitKEC Conference 2021, April 18, 2021“3rd International Conference On Engineering And Technology”Kantipur Engineering College, Dhapakhel, Lalitpur, teel city E (steel)Column sizeBeam sizeSlab thicknessFloor heightWall thicknessDensityofconcreteDensity of brickThickness of CFRPModulusofelasticity (E) ofCFRPTensile strengthofCFRPStrain (CFRP)Number of layer ofCFRPISBN 978-9937-0-9019-3M15Fe50019364.92for m1522360.68for nth level3 for IVALENTCOMPRESSIVE STRENGTHThe maximum value of the confinement pressure thatthe FRP can exert is attained when thecircumferential strain in the FRP reaches its ultimatestrain and the fibers rupture leading to brittle failureof the cylinder. This confining pressure f1 is given by:F1 Where,E Modulus of elasticity of CFRPƐ Ultimate CFRP tensile strainT Thickness of CFRPn number of wrap of CFRPb Dimension of sectionThe effective CFRP strain coefficient (𝞰 0.68)represents the degree of participation of the CFRPjacket, and the friction between concrete and CFRPlaminate. Type bond, geometry, CFRP jacketthickness, and type of resin affect the effective CFRPstrain coefficientF1 1.74The Equivalent confined compressive strength isgiven byFCC FUC 3.3 f1FUC Unconfined Compressive Strength of Concrete199

KEC Conference 2021FCC 20 3.3*1.74 25.74 N/MM22. CALCULATION OF DESIGN BASE SHEARThe design base shear of the building is calculatedfrom IS1893 (Part 1):2016Vb AH*WAh Where,Vb Design Base ShearW Seismic Weight of the Building 3852.31KNDeadload and 1.5KN/m live load is used.AH Design horizontal Acceleration CoefficientZ Seismic Zone Factor 0.36I Importance Factor 1R Response Reduction Factor 5Sa/g Design Acceleration coefficient 2.5 for soft soilsite with time period 0.27 secTherefore equation (3) becomesVb 346.71KNISBN 978-9937-0-9019-3III. RESULT AND DISCUSSIONPushover analysis is iterative analysis and designprocess continues until the design satisfies a preestablished performance criteria. The performancecriteria for pushover analysis is generally establishedas the desired state of the building given a rooftop orspectral displacement amplitude.Pushover analysis is carried out by vertical loading(gravity load) followed by a gradually increasingdisplacement con-trolled lateral load in both x and ydirection. The design base shear calculated as per ISspecifications is compared with the overall capacity ofthe structure obtained from the pushover curve.Moment-curvature parameters are used as the inputfor modeling the hinge properties and it can beidealized asshown in Fig. AB represents the linear elastic rangefrom unloaded state A to its effective yield B,followed by an inelastic but linear response ofreduced (ductile) stiffness from B to C. CD shows asudden reduction in load resistance, followed by areduced resistance from D to E, and finally a totalloss of resistance from E to F.Figure 2 Idealized moment-curvature relationshipFigure 1 plan and elevation of modelKEC Conference 2021, April 18, 2021“3rd International Conference On Engineering And Technology”Kantipur Engineering College, Dhapakhel, Lalitpur, NepalTable indicate the ordinary buildings are designed asfrequently in fully operational, occasionally lifeoperational, rarely in safe and very rarely in nearcollapse zone. Essential buildings are designed asoccasionally fully operation, rarely life operational200