Study On Punching And Shear Issues Of Reinforced Concrete Shallow Foundation

There are some unclear points about the Reinforced concrete shallow foundation of punchingand shearing calculation in the present code of foundation. This paper mainly found andanalyzed the differences that about independent foundation under column in punching andshearing calculation between GB50007-2002Code for design of building foundation and GB50007-2011Code for design of building foundation and compared with Europe and theUnited States codes. The factors affecting the independent under-post foundations ofpunching and shearing calculation were discussed and the influence rules of the factors wereproved up. The paper put forward related suggestions.To get the boundary between one-way slabs and two-way slabs of slab-and-beam raftfoundations, by using finite-element simulation, this paper discussed and summarized thepunching and shear mechanics regularities of slab-and-beam raft foundations. The slabdeformation and stress characteristics of slab-and-beam raft foundations under uniform loadwere studied. Finally the boundary between one-way slabs and two-way slabs ofslab-and-beam raft foundations was worked out. This paper provides references for theinnovation of foundation code improvement.For the problems of independent foundation punching and shear failures, the followingwork has been done.(1) Using example analysis to analyze the punching and shear formula of new and oldcodes of independent foundation. When the dimension of foundation-slab shorter edge is lessthan or equal to the value that the width of column plus twice effective height of foundation,the calculated thickness of foundation-slab by new-code method will be much larger thanold-code. This is unreasonable and will cause inconvenience for structure designers.(2) For punching and shear checking calculation of spread footing, the influence rules ofthe foundation width, length and the effective thickness for the new and old codes wereachieved.Through data analysis, that the ratio of length to thickness of the foundation-slab can bea good response relationship between the old and the new codes of shear force. When the ratiois greater than4.0, the ratio of shear force to punching force is close to2.0, the new-code is recommended to adopt. When the length to thickness ratio is less than4.0, the differencebetween the old and new norms is larger. Further research should be carried on.(3) According to lots of example analysis of the shear checking calculation, the affectingfactors of shear capacity and shear effects were identified. The influence rules, to the shearcapacity and shear effects of the United States, Europe and China codes, of the foundationlength, width, effective thickness, reinforcement ratio, checking cross-sectional positionwere identified. And corresponding suggestions were raised for China code.For the problems of the punching and shear mechanics regularities and the boundarybetween one-way and two-way slabs of slab-and-beam raft foundations, the following workhas been done.In order to get a more reasonable demarcation, the paper used ABAQUS to model theslab-and-beam rafts. Based on simulation of the actual state of internal force distribution anddeformation of slab-and-beam raft, through analysis and discussion of data, the reaction forceand internal force distribution of slab-and-beam raft were obtained and the demarcation of oneway and two way slabs was proposed.(1) The reaction force of the cross section near the corner tends to0, with close tomid-span, the reaction force increases. Reaching from the corners of plate at1.6m, thereaction force reaches a peak and becomes stable. There is an angle between the direction ofthe reaction force and the cross section and the angle close to45°with close to mid-span.(2) Through a large amount of data analysis and discussions, this paper suggested that toselect the ratio ly/lx=3.0as the demarcation between one way and two way slabs ofslab-and-beam rafts. When ly/lx <3.0, the slab should be designed according to two-way-slabtheories. When ly/lx≥3.0, the slab can be designed according to one-way-slab theories butshould arrange structural steels on perpendicular to the direction of force and reinforcementratio should not less than15%of the direction of force.