Strengthening Steel I-Beams By Welding Steel Plates

International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 4 Issue 07, July-2015Strengthening Steel I-Beams by Welding SteelPlates before or While LoadingDr. N. M. YossefStructural Engineering Department,Faculty of Engineering, Tanta University,Tanta, Egypt.Abstract— In this paper, the behavior of strengthening steel beams isinvestigated experimentally. Full scale tests on six specimens strengthenedwith steel cover plates are present. All tested beams have IPE sections.They were tested under four point loads with one end hinged and theother end roller. Four specimens were strengthened before loading.Nevertheless, two specimens were strengthened while under load using anew welding technique. The new welding technique is based on reducingdeflection before welding of cover plate. Test parameters includechanging the length of strengthening cover plate, two strengtheningpatterns, and three levels of preloading. The experimental results showedthat the cover plate length affects the ultimate carrying capacity of thetested specimens. In addition; the ultimate carrying capacity was affectedby the area of the welded plate. The proposed welding technique (used toweld cover plate while under load) was found to be effective in increasingthe load capacity by up to 5.7% and reducing the maximum deflection by30.7%.Keywords— Strengthening; Steel Beams; Cover Plate;Experimental; Reducing of Deflection, WeldingI.INTRODUCTIONStrengthening the existing structures is a common way toavoid failure due to change in function or construction error[1]. Two different techniques are currently used to increase orrestore the load capacity of steel structures: 1) Bonding FRPsheets [2]; and 2) welding steel plates. Using of FRP sheetsovercome several difficulties such as corrosion resistance andbigger value of the resistance / weight ratio [3] & [4]. Thereare many factors affecting the capacity of strengthenedstructure, like type of FRP, number of layers, type of adhesiveand special considerations must be applied at the place ofbonding [5, 6].The use of fiber reinforced polymer FRP is wellestablished [2, 7, 8], many research on the application of FRPcomposites to steel structures have been published [2, 9-13].Even the use of FRP material for strengthening andrehabilitation of steel members hold numerous benefits, butapplications involving wide flange beams have been limiteddue to the negligible increases in elastic stiffness [14].Strengthening by steel plate is a popular method due to itsavailability, cheapness, uniform materials properties(isotropic), easy to work, high ductility and high fatigueIJERTV4IS070454strength. However, several disadvantages of steel plateincluding the transportation, handling and installation ofheavy plates, corrosion of the plates, and limited deliverylengths of plates which necessitates the work and difficulty offorming joints, the need for massive and expensive false workto hold plates in position during adhesive cure, and the need toprepare for steel surface for bonding are very apparent [15].Strengthening of existing structures may be carried outwhile under load or with the load temporarily relieved. Forbeams carrying loads, strengthening is possible and safe [16].Few researches have been focused on the behavior of the steelstructures strengthened while loaded by welding steel plates.Early research of Tall [17], studied the strengthening ofloaded steel columns. He stated that columns can bestrengthened by welding of steel cover plates, or by changingthe residual stress distribution with laying of a weld. Tallchanged the orientation of welded cover plates with discussionof residual stresses magnitudes and distributions. He proposedthat the strengthening of steel columns by cover plates weldedto the flanges improves column strength than laying the weldalone.Wu et al. analyzed 317 finite element models to verify thebehavior of strengthening wide flange steel columns withwelded cover plates [18]. The study showed that columnslenderness and initial out of straightness remain the importantfactors for reinforced columns. The interactions of theorientation of the cover plates and the buckling direction wereobserved to affect the strength of strengthened columns.Liu et al. [16] conducted an experimental study on Wshaped beams strengthened while under load. The W-shapedbeams were tested under four point loads. The results statedthat the effect of preload level, at the time of strengthening, onthe ultimate loads of the beams associated with the beamsfailure modes. In a follow-up study, Liu et al. [16, 19]extended their research to investigate several influentialparameters. Deflection charts of tested specimens [16] showedan increment of deflections during the welding process, whilethe load was held.www.ijert.org(This work is licensed under a Creative Commons Attribution 4.0 International License.)545

International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 4 Issue 07, July-2015Applied loadP/210 cmIntermediatestiffener(6 mm)60 cm60 cm10cm60 cmHinged support0.56 cm0.85 cmBearingstiffener(6 mm)10 cm20 cmP/2Roller supportStiffener(6 mm)IPE200200 cmFig. 1 Test setup for Beam BCThe increment of deflection during welding isunacceptable action, since structural elements must bedesigned to satisfy requirements that prevent excessivemovement or deflection. Due to that fact, the author producesthe reduction of deflection before the beam is strengthened.This is achieved through experimental study described herein.This study was therefore carried out to investigate thebehavior and ultimate load carrying capacity of beamstrengthened with steel cover plates. It is on an experimentalstudy of the behavior of six strengthened IPE beams. Twospecimens were strengthened while loaded after reducing thebeam deflection, and their performance was compared withthat of testing specimens strengthened before loading. Theadopted strengthening patterns use the welded cover platewhose area is less than that of the flange area.Where:X describes strengthening patterns such that (C) for thecontrol beam, (L) for plate welded to lower flange and (U) forplate welded to upper flange. Y indicates the length of coverplate in cm. Z is the ratio of preload (load applied while thebeam was strengthened Pstr/ ultimate load capacity Pu).Four tensile coupons were obtained to determine themechanical properties of steel. The average value of the yieldstress (Fy) for beams and plates are 284 MPa and 279 MParespectively.TABLE 1 TESTED BEAMS DESCRIPTIONBC-Cover platelength 0-50A9050Tested beams Strengthening patternII.EXPERIMENTAL PROGRAMA. The ScopeAn experimental program was conducted to investigate thebehavior and ultimate capacity of flexural I-beams reinforcedwith welded plates. The following subtitles provide a detaileddescription of the tested beams, experimental procedure andinstrumentation.B. Description of the Tested BeamsDetails of test specimens are listed in table 1. All sixbeams used in the experimental study are IPE 200 with totallength Lt 200 cm such that the length between supports is L 180 cm. Four vertical stiffeners at four point load (two bearing& two intermediate) were welded to the tested beams beforeloading. The dimensions of tested beams and the test setup areshown in Fig. 1. The tested beams were strengthened by acover steel plate (8 x0. 6 cm) with weld size 6mm, the twostrengthen patterns (labeled as A and B) are shown in Fig. 2.Pattern A was to weld the cover plate to lower flange of thetest specimen, where pattern B was to weld the plate to theupper and lower flanges.Preload ratio*%-* Preload ratio is calculated as ratio between load during welding of cover plate / ultimate Load ofcontrol beam BC.Stiffener(6 mm)LowercoverPlate(80 x 6 mm)80 mmUpper and lowercoverPlate(80 x 6 mm)Weld6 mm(a) Pattern A80 mm(b) Pattern BFig. 2 Strengthening patternThe tested beam is referred, throughout the paper, as:BX-Y-ZIJERTV4IS070454www.ijert.org(This work is licensed under a Creative Commons Attribution 4.0 International License.)546

International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 4 Issue 07, July-2015P/2P/2Mid spansectionLVDT3Spacing betweenstiffener 60 cmLVDT2Strain gaugeS110 cmWelded cover platefor lower flange 90 cm20 cmLVDT3Straingauge S1LVDT2Straingauge S2Strain gauge S210 cm90 cm45 cm10cm45 cmLVDT1LVDT1200 cmFig. 3 Instrument locations for tested beam BL-90C. The Test Instruments and SetupThree LVDTs (linear variable differential transformer)were installed to monitor the behavior of test specimens at themid-span section, as shown in Fig. 3, which is an illustratedfigure of test specimen BL-90. LVDTs were used to recorddeflection and lateral displacements of the test specimens. Inaddition, two strain gauges were used to measure the strain oflower flange.The test specimens were loaded on steel loading frameunder four point loads with hinge-roller supports. The loadcell capacity is 900 kN. Load distributed beam and 20 mmbearing plates were used to distribute load at two points asshown in photo1.The specimens are placed and centered on the loadingframe. The test procedure begins by Appling a load ofapproximately 10% of experimental ultimate load (Pu) andthen removed. For beam strengthened before loading, themain load is applied and increased till failure. While, loadingprocedure and welded technique used for beam strengthenedwhile loaded is as follows: 1) The load is applied to certainload value Pstr then the loading process is paused, 2) part ofthe beam deflection is reduced manually and measured, 3) thestrengthening cover plate is welded. 4) After that the load wascontinued until failure happened as shown in Fig. 4 and photo2. Fig. 5 shows the welding sequences for strengtheningpatterns. Similar sequences have been used by Lui et al. [16].Photo2 Welding process during loading of specimen BL-90-50Test specimenbefore loadingDeflected shapeat preload ratioStep 1: loading till preload ratioAn automatic testing technique is used to allowcomputerized control of the displacement of the testingmachine head. The reading data for all instruments is recordedwith a personal computer using a data logger system.Deflected shapeat preload ratio wTest specimenbefore loadingStep 2: reducing deflection beforweldingDeflected shapeat preload ratioWelding plateStep 3: welding platePhoto1 Test setup for tested beam BL-65Fig. 4 Strengthening technique during loadingIJERTV4IS070454www.ijert.org(This work is licensed under a Creative Commons Attribution 4.0 International License.)547