184 / 2022-04-30 21:18:46

Fire resistance performance of concrete-filled steel tubular column protected by FRCR-ECC

concrete filled steel tubular, engineered cementitious composites, fireproof and anti-corrosion integrated protective performance, high ductility.

Subjected to environmental impact, or seismic load even service load, the traditional fire insulation material will be easy to cracking or even drop off from protected substrate, due to low tensile strength, limited ductility and poor bonding with anti-corrosion primers. Deteriorated protection is supposed to an impair or even totally loss of fire insulation capacity.



In this paper, a lightweight, high ductility (Fig. 1)  fire-resistive and corrosion-resistive engineered cementitious composites (FRCR-ECC) suitable for spraying (Fig. 2) was developed for the protection of concrete filled steel tubular (CFST) columns. Lightweight fly ash cenosphere (FAC) was added to the matrix as artificial defect. FAC reduces the matrix density and thermal conductivity (Fig. 3), and also activates the development of fine multi-cracks in the ECC and makes the cracks width less than 50 μm (Figure 4). These help to prevent the transfer of high external temperature to the interior of the structure and effectively resists the ingress of corrosive media. According to the requirements of the GB14907-2018 Fireproof Coatings for Steel Structures, the bond strength of FRCR-ECC to steel substrate was tested. The results show that FRCR-ECC has good bonding performance with steel (Fig. 5).



In this paper, the finite element software ABAQUS was used to analyse and simulate the fire test of CFST columns without fire coating and with FRCR-ECC protection. The temperature field distribution of CFST columns with the protection of different thickness FRCR-ECC subjected to four-side fire (Fig. 6) and vertical deformation-time curve (Fig. 7) were obtained. When the CFST column with axial compression ratio of 0.51 suffered  fire for 240 minutes, temperature of steel tube wall without fire coating is 1142℃, temperature of steel tube wall with 30 mm thick FRCR-ECC protection is 607℃, and the case of  40 mm thick FRCR-ECC protection  is 512℃. With a certain axial compression ratio, the section temperature of CFST column decreases significantly with the increase of  FRCR-ECC layer thickness. Fire resistance of CFST column without fire coating is only 29 minutes, that of the column with 30 mm thick FRCR-ECC protection is 246 minutes, and that of the column with 40 mm thick FRCR-ECC protection is more than 250 minutes. The fire resistance of CFST columns with FRCR-ECC protection is significantly improved, which is more than 240 min, and fully meets the 1-Class fire resistance requirement.



The fire test of CFST column with FRCR-ECC protection under constant load heating condition would be carried out to investigate the effect of protective coating thickness and load ratio on fire resistance of the column, and the results would be compared with those of finite element analysis.