| As the vertical load-bearing and lateral-resisting component of light-gauge cold-formed steel(CFS)building structures,the fire resistance of light-gauge CFS framed composite walls is crucial to the fire safety of whole structures.Meanwhile,with the increasingly complete scientific research theory of single disaster,related technologies are becoming more and more mature.However,the potential hazards of various disasters are intertwined and superimposed,and the muti-disaster investigation is gradually becoming a research hot spot in the field of civil engineering.Fire following earthquake is one of the most frequent coupling disasters,and the corresponding damage are serious.Previous studies have shown that the post-earthquake fire safety of CFS framed composite walls is particularly prominent.This paper carried out fire resistance and post-earthquake fire resistance research on CFS framed composite walls from the perspective of convenient construction,seismic and fire resistance improvement.The main contents are as follows:Non-bearing fire test studies of seven mid-scale CFS framed composite walls are carried out,and the adverse effects of the overlapped board joints on the fire resistance of such walls are investigated.The results show that: a.The unexposed surface corresponding to the stud is the weak area of the temperature rise of the CFS framed composite walls during the fire tests,leading to the insulation failure of the wall.Hence,it is recommended that the unexposed surface corresponding to the stud be monitored emphatically in the fire tests;b.For the present CFS walls(specimens S3 and S4)lined with gypsum plasterboards(GP)and calcium-silicate boards(CS),the overlapped board joints could accelerate the temperature rise of stud and the unexposed surface,reducing the fire resistance time(FRT)for the insulation failure and structural failure(under a load ratio of 0.27)by 16 min and 30 min,respectively;c.In the case of similar thickness of rock wool cavity insulation,the configuration of additional board strips on the stud flange was not able to weaken the adverse effects of overlapped board joints on the stud temperature,and could not extend the FRT for the structural failure of the CFS framed composite walls;d.When the staggered board joint can not be guaranteed,which means the existing of overlapped board joints is inevitable,the configuration of using steel sheet between face and base layer sheathing on one side of the wall and adding steel strips at the joints on the other side of the wall is recommended.The fire resistance and post-earthquake fire resistance experimental studies of five full-scale light-gauge CFS framed composite walls were carried out.The results show that: a.The steel sheet improves the mechanical properties of the self-tapping screw connection between the steel stud and CS board,resulting the shear capacity of the CFS walls sheathed with autoclaved lightweight concrete board,steel sheet and CS board(ALC-SS-CS)becomes approximately 20.1% higher than that of the GP-CS sheathed CFS walls;b.Under low cyclic loading up to the drift ratio of 3.0%(corresponding to specimen S10 sheathed with ALC-SS-CS on the fire side),obvious in-plane residual deformation is observed and local buckling at the bottom of stud is identified,which resulted in the change of the fire failure mode of the stud and the decreasing of the FRT by 35 min compared with the specimen S8 without earthquake damage;c.the specimens S8 and S10 sheathed with ALC-SS-CS on the fire side show excellent fire resistance and post-earthquake fire resistance performance,and the corresponding FRT are more than 120 min higher than those of the GP-CS sheathed CFS framed composite walls.In particular,the present sheathing construction effectively reduces the earthquake damage to the sheathing boards,so that the earthquake has insignificant effect on the temperature rise of the composite wall under post-earthquake fire condition;d.Both steel sheet and steel strips have good fire protective effects on the board joint of the base layer sheathing to achieve almost the same thermal insulation effect as the wall boards without joint.The thermal-mechanical coupling numerical simulation research of post-earthquake light-gauge CFS framed composite walls was carried out,and the influence of different load levels on the fire resistance of the wall was investigated.The results show that: a.When the load ratio reaches 0.7 and above,the fire-induced failure modes of the three types of light-gauge CFS framed composite walls are transformed into the local crushing near the top of the stud;b.With large load ratio,the FRT of the three types of CFS walls decreases significantly under the axial expansion constraint of the floor.For example,under the load ratio of 0.9,the FRT of the GP-GP sheathed CFS walls(specimen W2～W5)with complete axial expansion constraint of the floor is reduced by 52.8% on average compared with that without the axial expansion constraint of the floor;c.The three-dimensional relationship surface chart of drift ratio-load ratio-FRT of the three types of CFS framed composite walls is given,which can provide reference for the post-earthquake fire resistance design of light-gauge CFS building structures.The innovations of this paper are as follows:1 The adverse effect of overlapped board joint on the fire resistance of light-gauge CFS framed composite wall was quantified,and the convenient fire-prevention structural measures of board joints were proposed for the fire resistance design of such structure.2 The post-earthquake in-situ load-bearing fire resistance experiments of CFS framed composite walls with the FRT exceeding 120 min was firstly carried out.The corresponding investigation reveals the fire-induced failure mechanism and provides the design suggestions for the fire resistance design of such walls. |
