Study on bond behavior of cold-formed thin-walled C-section steel partially encased concrete composite columns

Cold-formed thin-walled C-section steel partially encased concrete composite columns prevent steel buckling, enhancing the specimen bearing capacity. To investigate the bond-slip mechanism of concrete-filled cold-formed lipped channel PEC stub columns (CLC-PEC), this study conducted push-out tests on 12 CLC-PEC. The results indicate that before peak load, specimens are mainly influenced by chemical bonding and partial mechanical interlock forces. With the same slenderness ratio, the slip region size remains consistent. After peak load, the interaction between concrete and steel transitions from mechanical interlock to frictional forces. Initial bond stress depends solely on the contact concrete properties. For specimens of equal length, peak bond stress rises by over 15 % as the slenderness ratio decreases. Among specimens with the same slenderness ratio, altering connector type or reducing connector spacing by 25 mm most significantly boosts peak bond stress by over 24 %. The test and numerical simulation show that the bond-slip performance of the CLC-3 specimen is better. The calculation formula of peak bond stress is obtained by considering the key parameters such as slenderness ratio, specimen length, connector spacing, and connector type. The calculation results are in good agreement with the experimental results.