| Abstract: |
5.1 CONCLUSIONSFrom the experimental results of the tested beams in this study, the following conclusions can be made:1- Strengthening of IPE 160 steel beam by CFRP plate (1.2 mm x 70 mm) bonded to the tension face had a marginal effect on the elastic stiffness and the load carrying capacity. On the other hand, the presence of 3 mm thick welded steel plate in compression side enhanced the yield load and the load carrying capacity by about 32% and 11%, respectively. Also, it caused enhancement in the elastic stiffness by about 20% over the control beam.2- Strengthening by two layers of CFRP sheets wrapping around the tension flange of the I-beam enhanced the yield load and the load carrying capacity of the beam by about 35% and 32%, respectively. Also, this technique enhanced the plastic stiffness significantly. While the increase in the elastic stiffness was only by about 9%.3- Strengthening by CFRP sheets showed more efficient than generic CFRP plate (one strip) due to the high resistance of CFRP sheet to debonding.4- Two extra different techniques of bonded CFRP plate were examined, namely, two 3 cm wide strips bonded either to the lower face of the tension flange, or to the upper face of the tension flange. Among the three techniques used of bonded CFRP plate, two 3 cm wide strips bonded to the lower face of the tension flange (no bonded plate beneath the web) was the most efficient technique. This technique enhanced the yield, the debonding and the ultimate loads compared to the other techniques.5- In beams strengthened by CFRP plate in tension, increasing the thickness of the welded steel plate in compression from 3 mm to 6 mm caused increase in the yield, debonding and ultimate loads by about 14%, 12% and 12%, respectively. Also it caused enhancement in both the elastic and the plastic stiffness. However, the ductility decreased by increasing the thickness of the plate.6- (Bonded/welded) hybrid joint technique for attachment of the steel plate in tension side was the most efficient technique. It enhanced the yield and the ultimate loads compared to welded and end welded techniques.7- In beams strengthened by welded steel plate (3mm thickness) in compression, strengthening by welded steel plate in tension was more effective than strengthening by end welded steel plate in enhancement of the elastic stiffness. However, after yield the two techniques gave almost the same behavior.8- Strengthened beams by two layers of 3 mm thick steel plates (long & short) in tension and by 6 mm thick welded steel plate in compression showed no difference in the elastic stiffness. However, the welded technique for attachment of these plates to the I-beam and to each other was the most efficient technique.9- Strengthened beam by welded steel plate (6 mm thickness) in compression and by hybrid joint steel plate (6 mm thickness) in tension was the most efficient beam in enhancement of the yield load by about 83% over the control beam.10- Plate end anchorage has a great benefit to improve the efficiency of strengthened steel beams by bonded plates.11- All strengthened beams and control beam failed due to distortional buckling after the yield occurrence. The exceptions between strengthened beams and control beam are the values of yielding and buckling loads in addition to debonding of the bonded plates which occurred before the strengthened beams reached their ultimate loads.5.2 RECOMMENDATIONSBased on the results of this study, strengthened steel beams in flexure by the application of steel plates and CFRP plates/sheets need future investigation. The following points are required to be studied.1- The use of different method for surface preparation to improve the bond strength.2- Durability of the new strengthening techniques by CFRP plates/sheets needs to be investigated under different environmental conditions and possible damaging actions.3- An extensive comparison between the efficiency of three techniques for bonded CFRP plates, i.e., two separate CFRP strips bonded to the upper face of the tension flange, two separate CFRP strips bonded to the lower face of the tension flange and one CFRP strip bonded to the lower face of the tension flange for different size of I-beams, different spans, different thickness of the plate and different type of adhesive.4- An extensive comparison between the efficiency of the different methods of attachment of the steel plate to the I-beam, i.e., hybrid, welded and end welded for different size of I-beams, different spans, different thickness of the plate and different type of adhesive.
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