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

众所周知，外露式柱脚的极限强度在很大程度上取决于底板下混凝土的承载强度。混凝土承载强度的试验研究已经进行了多年，但大多是没有配筋的缩尺模型，很少使用足尺模型。然而，本研究实现了裸柱底板底面真人大小的应力表示，并对其承载强度进行了评估。通过试验，澄清了以下事实：如果边缘距离保持不变，随着承载宽度的减小，承载强度比增加。如果支座宽度保持不变，则随着边缘距离的增加，支座强度比增加。承载强度一般按下列公式给出。Sigmab/Sigmac=α(Ab/Ae)^&lt；β&gt；，Sigmab：承重应力，Sigmac：混凝土圆筒压应力，AB：承重面积，AB=b*x，Ae：有效支承面积，Ae=(b+2e)*(x+2e)，α，β：试验确定的系数。本试验中系数(α，β)的平均值分别为α=0.86，β=-0.441。在此基础上，提出了一种基于试验结果的裸露柱脚极限强度评估方法。用这种方法得到的值与实验值非常接近。

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.