| Concrete-filled steel tubular (CFST) structure have been developed rapidly duringrecent years, which have many advantages due to the benign confinement effect betweensteel and concrete. However, the debonding in this structure will have unfavorable effecton the confinement. Actually, the debonding is almost unavoidable in CFST structures,which has been demonstrated by previous research works. In order to find out the influenceof debonding on the structural behaviors of CFST columns and arches with single tube, aexperimental investigations and finite element analysis is carried out in this thesis using thedebonding dimension based on real CFST structures. The main works of this thesis includethe following:(1) The experiment on the influence of debonding on CFST columns, subjected toeccentrically loading, was conducted, taking the debonding arc-length ratio as theexperimental parameter. The experimental results show that the ultimate load-carryingcapacity and the ductility of the specimens are greatly decreased with the increase ofdebonding arc-length ratio.(2) The finite element model of the CFST columns with and without debonding areestablished adopting the general purpose finite element programme ABAQUS, which areverified by test results. It is confirmed that the structural behaviors of debonding CFSTcolumns can be simulated accurately by ABAQUS. The reduction factor accounting for theeffect of debonding on the ultimate load-carrying capacity of CFST columns is proposed inthis thesis, considering different arc-length ratio. This factor is named as debondingreduction factor in brief.Utilizing the finite element method, the effect of different parameters on thedebonding reduction factor is investigated. The parametric analysis reveals that thedebonding reduction factor of CFST short columns subjected to axial load is significantlyinfluenced by confinement factor and debonding arc-length ratio. However, due to the factthat confinement effect has small influence on CFST long columns, the debondingreduction factor of long CFST columns subjected to axial loading is greatly influencedby slenderness ratio and debonding arc-length ratio. With regard to the debondingreduction factor of CFST long columns subjected to eccentrically loading, the debonding arc-length ratio, slenderness ratio and load eccentricity are taken into account as the keyfactors.(3) Based on the parametric analysis, the simplified calculation method is proposed tocalculate the debonding reduction factors of CFST columns, KNand KM, in axial loadingand bending condition respectively. With the previous research, this method can be used toestimate the debonding reduction factor with different debonding arc-length ratio underaxial or eccentric load. By comparing the experiment results with the finite element results,it is confirmed that the debonding reduction factor of CFST columns with differentdebonding arc-length ratio can be depicted well by this simplified calculation method,which can be applied in the practical engineering of CFST structures.(4) The FE model of CFST single tubular arches establised by ABAQUS, consideringdifferent debonding arc-length ratio. Using finite element method, the systematic analyseson debonding are carried out to investigate effect of different parameters on ultimateload-carrying capacity of CFST arches, including debonding poisition, debondingarc-length ratio and debonding length. The result shows that the ultimate load-carryingcapacity of the CFST arches are decreased with the increase of debonding arc-length ratioor debonding length, respectively. In addition, it is noted that the debonding location has agreat effect on ultimate load-carrying capacity of CFST arches. For example, when thearch is subjected to two asymmetrical concentrated loading, the debonding at L/4of archrib will have larger effect on the ultimate load capacity of CFST arches, compared with theother debonding positions. When the debonding happened from L/4to springing of arch ribat the same side of loading point, the ultimate load capacity of CFST arch is decreased a lot,which is close to the ultimate load-carrying capacity of arch rib with the debonding lengthof all rib.(5) Considering of the effect of different debonding arc-length ratio on the ultimateload-carrying capacity of CFST single tube arches, the debonding reduction factors in axialloading and bending for CFST columns are embedded into the existing equivalentbeam-column method, which are verified by the calculation results. It is confirmed that thestructural behaviors of CFST arches with different debonding arc-length ratio can bedepicted well by this modified equivalent beam-column method. |
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