Experimental Research on the Flexural Behavior of Thin Protective Concrete-Encased Narrow Rectangular Concrete-Filled Steel Tube Columns

To promote high-performance steel structure residential systems suitable for industrial production， this paper presents a thin protective concrete-encased narrow rectangular concrete-filled steel tube （CFST） column. This component offers several advantages， including industrialized production， prefabricated construction， reduced plastering procedures， and lower maintenance costs throughout its service life. To investigate the overall mechanical properties of this system under static loading， as well as the load transfer and failure modes of the thin concrete cladding， axial and eccentric compression tests were designed and conducted on three thin protective concrete-encased rectangular CFST column specimens. The tests utilized eccentricity as the primary variable， focusing on the analysis of bearing capacity， failure characteristics， and the load-displacement， load-deflection， and load-strain curves of the specimens under varying eccentricity conditions. Additionally， this study examined the cracking and failure of the thin concrete cladding. The test results indicated that： 1）Implementing structural measures to prevent the thin concrete cladding from directly bearing loads at the column end， while ensuring compatibility with the inner steel tube， significantly enhanced the overall compressive stability of the steel tube column. 2）When the eccentricity in the long-side direction of the component was minimal， the relatively small cross-sectional area of the steel tube resulted in the failure mode being governed by the compressive bearing capacity associated with the out-of-plane bending moment. 3）In a fully compressed cross-section state， the thin concrete cladding， when equipped with appropriate anti-cracking measures， did not exhibit cracks or peeling failure under normal service loads. The ultimate failure modes of the specimens consistently manifested as local bulging in the long-side direction of the end steel tube. Consequently， appropriate reinforcing measures should be incorporated into the design.