Braced Frame Connections With Square CFT Columns Penetrated By Gusset Plates

Braced frames with square concrete-filled tube columns are stiff,strong and economical structural systems because concrete-filled tube columns provides large axial stiffness and bracing system provides substantial lateral strength and stiffness.Gusset plates penetrating through the column have been usd in current design practices for these brace-beam-column connections for its great mechanical ability.The behavior of braced frame connections with square concrete-filled tube columns,comprised of a penetrating gusset plate,was studied in this paper.Some useful conclusions are proposed afteword,which could give some advice to the design of brace-beam-colun connections.Major contents are as follows.(1)The eight connections with four different details of the gusset plates were loaded in axial compression.The final failure mode of the gusset plate,the distribution of the internal force and the relative slip results were analyzed.The results showed that the maximum transfer forces between steel and concrete with penetrating brace frame connections was delivered through the edge of the gusset plate into the concrete or through bearing ribs or holes added to the plate.Some load transfer occured because of friction between the steel and concrete.(2)Numerical simulations were carried out using the finite-element package ABAQUS and compared with the experimental results.The force transferring path and stress distribution in the steel and concrete were analyzed.Large bearing stresses occur in the concrete immediately below the gusset plate at the corner intersection of the plate and tube.Stress concentrations also occur in the steel tube and the gusset plate at the juncture of them.(3)The composite action of the specimen was calculated using the theory of concrete filled steel tube.The connection details including with ribs and holes can improve the efficiency of internal force transmission and the level of the composite actin of concrete-filled steel tube.The braced frame connections with square concrete-filled tube columns assure that the square concrete-filled tube column and the composite connection is adequate to develop the required resistance for a wide range of braced frame systems.