بررسي امكان افزايش شكل پذيري و بازتوزيع لنگر در تيرهاي سراسري قاب هاي بتن مسطح تقويت شده با ورق هاي كامپوزيت CFRP

چكيده انگليسي :

Abstract Strengthening of continuous beams in reinforced concrete RC frames is seriously underattention of civil engineers in repair and rehabilitation of RC structures In the meantime redistribution of the moments is recognized as an important phenomenon in continuous flexuralmembers that leads to the formation of plastic hinges at the points that the ultimate flexuralcapacities are reached In fact if the flexural member is ductile enough redistribution of thestresses and moments occurs mainly simultaneous to formation of the first plastic hinges leading tobetter utilization of the material strength in the other points of the member and higher load carryingcapacity The current thesis is dedicated to investigation of the possible increase of ductility andmoment redistribution in RC frames strengthened with CFRP laminates Eleven two span RCbeams connected to the top and bottom columns at the middle support were cast and tested including two control specimens and nine strengthened specimens with CFRP laminates The framespecimens were categorized in two groups A and B The beams in group A specimens had 0 4 btensile reinforcement and 0 4 b compressive reinforcement at mid spans and at middle supportadjacent to the columns b is the tensile balanced reinforcement ratio Furthermore the beams ingroup B specimens had 0 4 b tensile reinforcement and 0 2 b compressive reinforcement at mid spans and 0 2 b tensile reinforcement and 0 4 b compressive reinforcement around the columnsat middle support Small chamfers were provided at the junction of the columns to beams and L shape FRP strengthening was performed at this region To prevent debonding of the FRP laminatesat the end region and at the beam to column junction U shaped FRP anchorages were provided onFRP laminates for all of the frame specimens at appropriate locations Furthermore mechanicalanchorages of steel plate strips and bolts were added to the laminates for one specimen in eachgroup Test results showed that the load carrying capacity of the strengthened frames in groups A andB compared to that of control frames had an increase of 16 to 33 and 22 to 38 respectively Furthermore the flexural capacity of the strengthened frames compared to that ofcontrol frames increased up to 20 and 58 at the faces of the columns and at the mid spans respectively therefore the flexural strengthening at the mid span regions was more effective thanthat at the face of column regions The curvature ductility factor in the strengthened frames withoutplates and bolts decreased 1 5 to 2 2 times compared to that in the control frames Furthermore thecurvature ductility factor of the strengthened frames with plates and bolts had 1 5 times morereduction compared to the strengthened frames without plates and bolts The moment redistributionof 20 to 56 was observed in all of the strengthened frames The amount of momentredistribution in the frames with strengthening FRP laminates only at the positive moment regionswas more than that of the frame specimens with laminates at both positive and negative momentregions Furthermore the frames with four strengthening layers showed more momentredistribution than the frames with two layers of FRP The experimental results compared with the analytical results using Ansys software Furthermore 77 frame specimens were selected with variable properties of FRP laminates yieldstrength of steel and compressive strength of concrete and were analyzed using Ansys The resultsshowed that FRPs with stronger fibers increased the curvature ductility factor up to 70 andincreased the amount of moment redistribution up to 30 Furthermore higher yield strength of thereinforcement decreased the ductility factor and the amount of moment redistribution up to 80 and up to 25 respectively Higher compressive strength of concrete also decreased both theductility factor and the amount of the moment redistribution in the strengthened frames As a part of this study the flexural rigidity method was devel

فرحبد، فرهنگ

بررسي امكان افزايش شكل پذيري و بازتوزيع لنگر در تيرهاي سراسري قاب هاي بتن مسطح تقويت شده با ورق هاي كامپوزيت CFRP

الياف كربن، شيشه،آراميد , رزين ها , ورقFRP , صليب خمشي