Experimental Study On Mechanical Properties Of High Strength Q690 Steel At Elevated Temperatures

Steel structure has been widely used in large span structures and high-rise buildings because of its light weight, high strength and convenient construction.The use of high strength steel HSS in build construction can promote to reduce the dimension of cross-section of memebers and the structure weight.As we all know,steel is non-combustible material but not fire-resisitant material. Most of rigidity and strength of steel loses at 600℃.The fire resistance study on steel structure is significant.The mechanical properties at elevated temperatures are the foundation of fire resistance study on steel structure. Research shows that the creep of steel has a great impact on structure at elevated temperatures. Design of structures in fire is unsafe when not considering the impact of creep at elevated temperatures.Local fire does not generally cause fundamental damage to structure.Demolitin and reconstruction will result in a serious waste of resources. The post-fire mechanical properties are the foundation of security assessment on steel structure. This article studied the mechanical properties at elevated temperautres, creep properties at elevated tempretures and the post-fire mechanical properties of high strength Q690 steel,and the fire resistance analysis of Q690 steel clomun considering creep effect at elevated temperatures was completed. The main contents are as follows:(1)Tensile tests at elevated temperatures: Tensile tests at elevated temperatures range of 300℃-900℃ were completed.The elastic modulus, yield strength, ultimate strength and stress-strain curves at elevated temperatures were obtained.The mechanical properties at elevated temperatures of HSS Q690 was compared with other kinds of hig strength steels and Euro code EC3.The stress-strain curves at elevated temperatures were fitted based on Young model.Then parameter m was fitted out.(2)The creep tests at elevated temperatures: Experimental investigations were carried out to clarify the creep of HSS Q690 at elevated temperatures. The creep-time curves of HSS Q690 at elevated temperatures were obtained and were compared with those of Q460 and Q345. The creep-time curves at elevated temperatures were fittet based on Field&Field creep model, and the parameters were fitted as the function of temperatures.(3)Post-fire tensile tests:After reaching every pre-selceted evlated temperature, two cooling methods were considered, which is natural air cooling and cooling by water.3 groups of tests were tested for every temperature and every cooling method. The post-fire mechanical properties, namely elastic modulus, yield strength, ulitimate strength and the elongation, were obtained and were compared with that of other kinds of steels. Predictive equations were proposed for the post-fire mechanical properties reduction factors of high strength Q690 steel.(4) Finite element analysis:The fire-resistanse analysis of Q690 steel column considering influence of creep at elevated temperatures was completed by finite element software ABAQUS.The test results of mechanical properties and fitted creep model of HHS Q690 at elevated temperatures were used in the analysis.The finite element model was validated by steel column tests.The impact of slendness,heating rate,load ratio and reduction factor at elevated temperatures on the fire-resisitance of Q690 column was analyzedInnovation:(1)Comprehensive study on the mechanical properties of high strength Q690 steel was carried out.(2) The elastic modulus at elevated temperatures was calculated by stress-strain curve.(3) The influence of creep on fire-resistance of strcucture was analyzed by finite element.