【作者】 丁勇；

【导师】 王卫永；

【作者基本信息】 重庆大学 ， 土木工程， 2022， 硕士

【摘要】 高强钢相对于普通结构钢而言,强度更高,在建筑结构中使用可以节约材料、降低成本和提升抗震性能。随着我国炼钢技术的进步,和“碳达峰、碳中和”双碳战略的推进,高强钢在建筑结构中的应用逐步增多,尤其是Q460高强钢,已经被大量应用到大跨或高层等结构中。但Q460高强钢在高温下弹性模量和屈服强度会迅速下降,使得高强钢结构在火灾下容易丧失稳定性和承载力。当前钢结构抗火设计方法是针对普通结构钢提出的,而Q460高强钢在高温下的力学性能与普通钢有较大区别,所以现行的抗火设计理论不能直接应用于高强Q460钢梁。本文为了获得约束Q460钢梁在火灾下的力学响应,采用试验方法、有限元分析方法和理论分析方法,对约束Q460钢梁的耐火性能进行了系统研究。主要的研究工作如下:1、完成了3个瞬态试验,分别对比研究了荷载比和梁端约束刚度对约束Q460钢梁耐火性能的影响。研究发现,荷载比对钢梁临界温度影响较大,梁端约束刚度对钢梁临界温度影响不明显;荷载比和梁端约束刚度对梁端附加轴力影响均较大。2、完成1个钢梁抗弯承载力试验和1个740℃下钢梁的稳态试验,对比分析了740℃时约束Q460钢梁极限承载力和跨中变形刚度相对于常温时的下降幅度。研究发现,740℃时约束Q460钢梁极限承载力下降幅度低于740℃时Q460钢材屈服强度下降幅度;740℃时约束Q460钢梁跨中变形刚度下降幅度与740℃时Q460钢材弹性模量下降幅度接近。3、对比研究了瞬态试验和稳态试验两种试验模式对约束Q460钢梁耐火性能的影响。研究发现,在稳态试验选取的温度与瞬态试验临界温度接近的情况下,稳态试验的附加轴力峰值比瞬态试验约高40%,稳态试验的极限荷载值比瞬态试验荷载值低8%。同时,约束Q460钢梁在横向荷载和高温热膨胀引起的附加轴力联合作用下,更容易发生整体弯扭失稳破坏。4、考虑Q460钢梁几何初始缺陷、Q460钢高温蠕变和高温材料属性退化等因素,建立了约束Q460钢梁热力耦合分析模型,同时将有限元模型计算得到的位移-温度曲线、轴力-温度曲线、试件表面温度升温曲线和试件破坏模式与试验实测数据进行对比验证,证明有限元模型的可靠性。5、完成约束Q460钢梁耐火性能参数分析,研究钢梁荷载比、钢梁截面高宽比、钢梁高跨比、梁端轴向约束刚度、梁端转动约束刚度、温度分布模式对约束Q460钢梁耐火性能的影响。研究发现钢梁荷载比和梁端转动约束刚度为钢梁临界温度的显著影响因素,影响程度在20%以上;钢梁高跨比、高宽比和梁端轴向约束刚度为钢梁临界温度的重要影响因素,影响程度在10%左右;温度分布模式为钢梁耐火极限的显著影响因素,三面受火钢梁对比于全截面受火钢梁,其耐火极限提高约50%。6、完成约束Q460钢梁在升温阶段的火灾响应理论分析,并用试验数据证明了理论分析的正确性。将强度破坏控制条件和稳定破坏控制条件分别设置为理论分析停止条件,得到钢梁的强度破坏和稳定破坏临界温度,且将钢梁的强度破坏和稳定破坏临界温度与有限元分析得到的钢梁临界温度进行对比,发现稳定破坏临界温度与钢梁临界温度接近。7、根据约束Q460钢梁稳定破坏条件,推理得到适用于约束Q460钢梁的临界温度简化计算方法,并且分析证明该方法计算得到的临界温度与有限元分析临界温度之间相差控制在5%以内,此临界温度简化计算方法能够一定程度指导约束Q460钢梁临界温度计算。更多还原

【Abstract】 High-strength steel has higher strength than normal steel,which can save materials,reduce costs and improve seismic performance in building structures.With the progress of steel smelting technology and the promotion of the‘carbon peaking,carbon neutralization’dual-carbon strategy,the application of high-strength steel in building structures has gradually increased.In particular,Q460 high-strength steel has been widely used in long-span and high-rise structures.But the elastic modulus and yield strength of Q460 high-strength steel decrease rapidly at high temperature,which makes high-strength steel structure lose stability and bearing capacity easily under fire.The current fire resistance design method of steel structure is proposed for normal steel,but the mechanical properties of Q460 high-strength steel at high temperature are quite different from those of normal steel,so the current fire resistance design method cannot be directly applied to Q460 high-strength steel beams.In order to obtain the mechanical response of constrained Q460 steel beam under fire,the fire resistance of constrained Q460 steel beam was systematically studied by using experimental method,finite element analysis method and theoretical method.The main research work includes:(1)Three transient tests were carried out to study the influence of load ratio and constraint stiffness of beam end on the fire resistance of constrained Q460 steel beam.The research shows that the load ratio has a great influence on the critical temperature of the steel beam,while the constraint stiffness of beam end has no obvious influence on the critical temperature of the steel beam.Both the load ratio and the constraint stiffness of beam end have great influence on the additional axial force of beam end.(2)The bending bearing capacity test of steel beam and the steady-state test of steel beam under 740℃ were completed,and the decline of ultimate bearing capacity and mid-span deformation stiffness of Q460 steel beam under 740℃ compared with that under normal temperature were analyzed.The research shows that the decrease of ultimate bearing capacity of restrained Q460 steel beam at 740℃ is lower than that of yield strength of Q460 steel at 740℃.The decrease of mid-span deformation stiffness of restrained Q460 steel beam at 740 ℃ is close to that of elastic modulus of Q460 steel at740℃.(3)The effects of two test modes,transient test and steady-state test,on the fire resistance of constrained Q460 steel beam were compared.The study shows that when the temperature selected by the steady-state test is close to the critical temperature of the transient test,the maximum additional axial force of the steady-state test is about 40%higher than that of the transient test.The ultimate load of steady state test is about 8%lower than that of transient test.At the same time,under the combined action of lateral load and additional axial force caused by thermal expansion at high temperature,the restrained Q460 steel beam is prone to flexural-torsional buckling failure.(4)The thermal-mechanical coupling analysis model of Q460 steel beam with constraints was established considering the initial geometric defects,thermal creep and material property degradation of Q460 steel.At the same time,the displacement-temperature curve,axial force-temperature curve,specimen surface temperature curve and specimen failure mode calculated by the finite element model are compared with the experimental data to verify the reliability of the finite element model.(5)The fire resistance performance parameters of constrained Q460 steel beam were analyzed.The effects of load ratio,aspect ratio,height-span ratio,axial constraint stiffness,rotational constraint stiffness and temperature distribution mode on fire resistance performance of constrained Q460 steel beam were studied.The research shows that the load ratio and the rotational constraint stiffness are the significant influencing factors of the critical temperature of the steel beam,and the influence degree is more than 20%.The height-span ratio,aspect ratio and axial constraint stiffness are important factors affecting the critical temperature of the steel beam,and the influence degree is about 10%.The temperature distribution mode is obvious factor affecting the fire resistance limit of steel beams.The fire resistance limit of 3-side heating steel beams is increased by about 50%compared with that of full-section heating steel beams.(6)Theoretical analysis of fire response of restrained Q460 steel beam in heating stage was completed,and the correctness of theoretical analysis was proved by experimental data.The strength failure control condition and stability failure control condition were set as the theoretical analysis stop condition respectively to obtain the strength failure and stability failure critical temperature of steel beam.The critical temperature of strength failure and stability failure of steel beam was compared with the critical temperature of steel beam obtained by finite element analysis,and it was found that the critical temperature of stability failure is close to the critical temperature of steel beam.(7)According to the stability failure condition of Q460 steel beam,a simplified calculation method for the critical temperature of Q460 steel beam was deduced.The analysis shows that the difference between the critical temperature calculated by this method and the critical temperature of finite element analysis is controlled within 5%.And this simplified calculation method of critical temperature can guide the calculation of critical temperature of Q460 steel beam to a certain extent.更多还原