Experimental study on exposed steel column bases connected to riser foundation concrete

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It is known that the ultimate strength of an exposed type column base greatly depends on the bearing strength of concrete under the base plate. Experimental studies on concrete bearing strengh have been carried out for many years, but they mostly deal with reduced size models which have no reinforcement, and rarely use full scale models.This study, however, achieved a life-size under -stress representation of the bottom surface of the exposed type column base plate, and evaluated its bearing strengh.From this experiment, the following facts were clarified.If the edge distance remains the same, as the bearing width decreases, the bearing strength ratio increases. If the bearing width remains the same, as the edge distance increases, the bearing strengh ratio increases. The bearing strength is generally given in the following formula. sigmab/sigmac=alpha(Ab/Ae)^<beta>,sigmab : Bearing stress, sigmac : Cylinder compressive stress of concrete, Ab : Bearing area, Ab=b*x, Ae : Effective supporting area, Ae=(b+2e)*(x+2e), alpha, beta : Coefficients determined by experiment.The mean values of coefficients (alpha and beta)in this experiment were as thus calculated to be alpha=0.86 and beta=-0.441, respectively.On the other hand, compressive stress distribution under the bass plate bottom surface is assumed to be rectangular, the above relationship was then used to obtain a relation between the axial compression on the bearing area and the bending moment due to eccentricity of the gravity of them. Then, a new method to evaluate the ultimate strength of the exposed type column base, based on the experimental result is proposed. Values obtained using this method closely match the experimental values.