Experimental Research On Reinforcing Bearing Capacity Of Single Foundation Under Column Reinforced By Increasing The Thickness

With the development of the construction field, the reinforcement andtransformation of the existing buildings has become an important part in the currentconstruction business. The reinforcement of the concrete structure has accounted formore than50%. Reinforcement on the existing buildings may cause the problem ofinsufficient bearing capacity of the foundation under column. As for the reinforcementdesign of concrete foundation under column, our country has not yet given the specificregulations and requirements. This paper studies the collaborative performance of newand old concrete of single foundation under column after reinforcement and the failurephenomenon of the foundation, and achieves good results, which have importanttheoretical and practical value.Based on the analysis of sixty-six new and old concrete shear tests and related datafinished in Chongqing University, this paper finished axial compression tests of sevensingle foundations under column. The tests got the crack’s development mode, concreteand steel strain, the specimen cracking load, as well as the ultimate load and drew thefollowing conclusions:1) Reinforced by increasing the thickness of single foundation under column, if theoriginal concrete surface is artificial chiseled, the new concrete which has certain heightand width can work collaboratively with the old concrete. In this paper, the variousreinforcement methods, interface bars or horizontal bars in ring beam used to limitcolumn’s horizontal deformation, are effective in strengthening the cooperative work ofnew and old concrete.2) When the lateral restraint is very small under the bottom of single foundation,the first crack takes place in the middle of each side under axial compression, extendingfrom the bottom of the slab. Cracking load is about25%~50%of ultimate load. Thispaper advise the proposal increase anti-crack construction measures for singlefoundation on rigid footings.3) After50%of the ultimate load, new expansion cracks appear in both side of themiddle crack, from the bottom center to edge of the foundation extending obliquelyabout45~60degrees. During the whole testing, the middle crack is always the widestcrack.4) Experiments show that, direct shear failure in single foundation under column exist, the shear strength is approximately equal to1.5times the tensile strength, on basisof the experimental results and analysis, this paper puts forward direct shear strengthcalculation formula in single foundation.5) In the new ring beam, the annular horizontal steel bars in the bottom of the ringbeam can play an effective role in reinforcement; the ones on the top can not.6）Using the method of augmented section of reinforced concrete column, increasecross section should satisfy certain width requirements, otherwise, it’s difficult for newand old concrete to work together effectively.