Stress Transfer between Steel Tubular Column and Infill Concrete at A Connection of H-Beams to Concrete Filled Tubular Columns with Diagonal Braces

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In 2003,we performed a push-out test of concrete-filled tubular stub columns to investigate the bond strength between tubular columns and infill concrete and the mechanical shear connector effect due to the cut-through diaphragm for beam-to-column connections. In 2004,frame models composed of a concrete-filled tubular column, H-shape beam and diagonal brace are tested to ensure the realistic bond strength and the effect of mechanical shear connectors in building frames.From the tests, the following conclusive remarks were introduced :(1)The conventional knowledge about the bond strength of concrete-filled tubes were traced by the stab column test. That is the bond strength is affected by tubular section shapes (circular or rectangular hollow section) strongly, but not so much by the concrete strength.(2)The effect of mechanical shear connector caused by the cut-through diaphragm can be predicted by the lower strength either the bearing strength between infill concrete and diaphragm in … More a tube or the shear yield strength of a diaphragm plate even with a large safety margin. In fact, the bearing strength dominated the strength prediction. In such a case, the concrete confining effect should be considered, so that the large safety margin is introduced by the confining effect.(3)In case of frame models with outside diaphragm stiffened connections, the stress transfers from a steel tube to concrete by the bond action. The bond strength observed in the frame models is almost similar to the one obtained from push-out test of concrete-filled tubular stub columns, where only concrete section is subjected to compressive load at the top and only steel tubular potion is supported at the bottom. The bond strength from another test where both of concrete and steel tube are subjected to compressive load at the top will give too much underestimation for the strength obtained from the frame model.(4)In case of frame models with cut-through diaphragm connections, the mechanical shear connector effect can be expected for stress transfer from steel tube to concrete. Even though all of the frame models were designed to have the diaphragm with very large hole for concrete casting, the exposed concrete portion at the column base crushed by the it own axial compressive stress which must be transferred from the steel tube. Therefore, in general, the mechanical shear connecting effect by cut-through diaphragm connections may be large enough for the practical use. Less