【作者】 丁发兴；

【导师】 余志武；

【作者基本信息】 中南大学 ， 结构工程， 2006， 博士

【摘要】 本文对常温和高温(火灾)下圆钢管混凝土结构受力性能进行深入的理论分析和试验研究,提出了常温和高温下混凝土多轴强度准则和本构关系,探讨了常温和高温下圆钢管混凝土轴压短柱的受力机理,开展了常温下钢管混凝土偏压柱受力性能理论分析,进行了常温下钢管混凝土试件受力性能试验研究,建立了常温和高温(火灾)下钢管混凝土结构非线性有限元分析方法,进行了火灾下钢管混凝土结构数值仿真分析。主要研究内容如下:(1)建立常温和高温下混凝土多轴强度准则,提出常温和高温下单轴拉压滞回应力-应变关系和轴对称三轴受压应力-应变关系。将荷载引起的混凝土变形分为弹性应变和非弹性应变,提出损伤泊松比的概念,假定非弹性应变与损伤泊松比有关,应用损伤力学理论和最小耗能原理,建立混凝土在多轴应力状态下强度准则的一般形式并揭示混凝土的破坏机理,根据已有试验结果初步确定损伤泊松比的表达式;对各种强度等级混凝土的单轴力学性能试验研究资料进行分析,建立反映不同强度等级的混凝土各种力学性能指标的统一表达式和单轴应力-应变全曲线的统一计算方法、损伤演变方程、损伤本构模型和滞回应力-应变关系;在Ottosen混凝土三轴应力-应变关系的基础上,提出了混凝土轴对称三轴受压应力-应变关系,其中峰值应力点泊松比的取值反映了损伤泊松比的特性。各种方法计算结果与试验结果符合较好。(2)建立常温和高温下钢管混凝土轴压弹塑性全过程分析理论,揭示钢管混凝土轴压套箍约束作用机理。利用混凝土轴对称三轴受压应力-应变关系,基于连续介质力学,采用钢管混凝土同心圆柱体力学模型,建立常温和高温下钢管混凝土弹塑性全过程分析理论,编制非线性计算程序;通过对常温下的钢管混凝土轴压受力机理分析,指出钢管在纵向初应力作用下将降低钢管对混凝土的套箍约束作用,钢管套箍混凝土将套箍约束作用发挥至最大,但轴压刚度较小。(3)建立常温下钢管混凝土轴压、纯弯和偏压柱承载力和变形实用计算公式;提出常温下钢管混凝土组合截面轴力-应变关系和轴力-弯矩-曲率关系实用计算方法(合称钢管混凝土组合截面实用计算方法)。基于钢管混凝土弹塑性全过程分析理论,确立钢管混凝土拉压数值本构关系,建立组合抗压刚度和轴压极限承载力实用计算公式,提出轴力-应变关系实用计算方法;基于平截面假设,利用分层法对钢管混凝土偏压构件截面轴力-弯矩-曲率关系进行全过程分析,建立组合抗弯刚度、抗弯承载力和轴力-弯矩相关方程等实用计算公式,提出轴力-弯矩-曲率关系实用计算方法;利用基于部分正弦曲线的模型柱法对钢管混凝土轴压中长柱和偏压柱(包括等端弯矩和不等端弯矩)进行全过程分析,建立钢管混凝土偏压柱承载力实用计算公式,各种方法计算结果与试验结果符合较好。(4)进行67个常温下钢管混凝土试件受力性能的试验研究,探讨其受力性能并验证本文计算理论和方法的正确性。开展45根钢管混凝土轴压短柱试件、4个钢管混凝土纯弯试件和8个钢管混凝土偏压柱试件试验研究;探讨了各种试件的承载力、荷载-变形曲线和荷载-横向变形系数曲线的变化规律;结合其他学者的试验结果,验证了弹塑性全过程分析理论、分层法和模型柱法及各实用计算公式和实用计算方法的正确性。(5)建立常温和高温(火灾)下钢管混凝土结构非线性有限元计算理论,编制非线性有限元程序NACFSTLF。提出适合于高温下钢管混凝土柱非线性分析的钢管和混凝土纵向热-力耦合本构模型计算方法;基于连续介质力学,推导出火灾下U.L.列式虚功增量方程,通过调整截面形心应变和曲率,使梁端内外力平衡,完善了火灾下分层梁材料非线性分析理论;编制NACFSTLF程序,并用常温和高温下钢管混凝土构件、结构和钢筋混凝土构件等大量试验结果进行了验证,计算结果与试验结果吻合较好;本程序反映了火灾下钢管混凝土结构的约束套箍作用和温度-荷载历史,具有计算功能强和效率高的优点。(6)采用NACFSTLF有限元程序,进行了火灾下足尺钢管混凝土单柱、钢筋混凝土矩形梁和钢管混凝土柱-钢筋混凝土T梁框架结构抗火性能的数值仿真分析。探讨了火灾下钢管混凝土单柱初始缺陷、轴压比、混凝土强度、钢材强度、含钢率和钢管外径对抗火性能的影响,考察了三面受火钢筋混凝土简支梁的抗火性能,分析了钢管混凝土柱-钢筋混凝土T梁框架结构在各楼层火灾下的抗火性能。分析结果表明:局部楼层发生火灾情况下,钢管混凝土框架结构最薄弱环节是底层的钢管混凝土中柱,表现为中柱承载力降低而导致失稳破坏;由于内力重分布的影响,框架柱的抗火性能要优于相同初始荷载下两端固支单柱的抗火性能,但火灾情况下钢管混凝土框架柱仍需进行防火处理。更多还原

【Abstract】 This paper presents theoretical analyses and experimental studies deeply on the behavior of concrete filled circular steel tubular (CFST) structures both at room tempera -ture and in fire. Strength criterion and constitutive model for concrete under multi-axial stress states both at room temperature and at high temperatures were proposed, the behavior of CFST stub columns under axial compression both at room temperature and at high temperatures were discussed, the theoretical models of CFST columns under eccentric compression at room temperature were developed, the experimental investigations on the behavior of CFST specimens at room temperature were presented, the nonlinear finite element analysis theories of CFST structures subjected to in-plane load both at room tempe -rature and in fire were founded, and the fire performance of a full scale CFST plane frame was analyzed. The main contents are listed as follows:(1) Strength criterion for concrete under multi-axial stress states both at room temperature and at high temperatures was founded, and axial stress-stain relations of laterally confined concrete under axial compression and hysteretic stress-stain relations of concrete under uniaxial stress states both at room temperature and at high temperatures were proposed.The total principal strain of concrete was classified into elastic principal strain and inelastic principal strain, the conception of damage Poisson’s ratio was presented, supposing the inelastic principal strain was related to damage Poisson’s ratio, and then the theory of damage mechanics and the theory of minimum energy dissipation rate were applied. The general formula of strength criterion for concrete under multi-axial stress states was proposed. The failure mechanism of concrete was illustrated. The equation for damage Poisson’s ratio was determined basically based on the existing experimental data. Through analyzing large numbers of test results of uniaxial mechanical properties of various strength of concrete, the unified formulas for mechanical indexes, the unified method of uniaxial stress-strain relationship, the evolvement law of damage, damage constitutive model, and the hysteretic stress-stain relations for concrete both at room temperature and at high temperatures were proposed. Based on triaxial stress-strain relationship for concrete proposed by Ottosen, the axial stress-strain relations for laterally confined concrete under axial compression both at room temperature and at high temperature were developed, in which the expression of peak Poisson’s ratio of concrete reflected the feature of damage Poisson’s ratio. These models give a relatively reasonableestimate of the experimental behavior.(2) The elasto-plastic analysis method of CFST stub columns under axial compression both at room temperature and at high temperatures was proposed, and thus the confinement effect of CFST stub columns under axial compression was illustrated. Utilizing the axial stress-strain relations for laterally confined concrete under axial compression, based on continuum mechanics, the mechanical model of concentric cylinders of circular steel tube with concrete core was determined. The elasto-plastic analysis method of CFST stub columns both at room temperature and at high temperatures was proposed, and a computer program was developed. Through analyzing the behavior of CFST stub columns, it was pointed out that the confinement effect decreased when axial pre-stress in steel tube, and for the concrete confined steel tube, the confinement effect strengthened but the composite elastic modulus diminished.(3) Practical calculation formulas of load bearing capacity for CFST columns under axial compression, pure bending, and eccentric compression were proposed, and practical calculation methods of axial force-strain relations and axial force-moment-curvature relations for the composite section of CFST beam-columns were presented. Based on elasto-plastic analysis method, the numerical constitutive model for the concrete filled steel tubes was determined, the practical calculation formulas of composite axial stiffness and axial ultimate capacity for CFST stub columns were proposed, and the practical calculation methods of axial force-strain relations for the composite section were presented. Based on plane section assumption, layered method was applied to calculate the axial force-moment-curvature relations for the composite section of CFST beam-columns, the practical calculation formulas of composite flexural stiffness, flexural capacity, axial force-moment interaction equation were proposed, and practical calculation methods of axial force-moment-curvature relations for the composite section of CFST beam-columns were presented. Fiber model method based on partial sinusoidal shape was applied to calculate the load-deformation relations of CFST columns under eccentric loading with equal or unequal end-moment, and the practical calculation formulas of load bearing capacity for CFST columns under eccentric loading were presented. Good agreement is obtained between these predicted results and experimental results.(4) Experimental investigations of 67 CFST specimens at room temperature were presented, the behavior was discussed, and the calculation theories and methods by the author were validated.45 CFST stub columns under concentric compression, 4 CSFT members under pure bending, and 8 CFST columns under eccentric compression with equal end-moment wereinvestigated, the behavior of load capacity, load-deformation relations, and load-strain ratio relations of the specimens were discussed. Combined with the test results by other researchers, the reliability of the elasto-plastic analysis method, layered method, fiber model method, the practical calculation formulas and the practical calculation methods was verified.(5) The nonlinear finite element analysis theories of CFST structures subjected to in-plane load both at room temperature and in fire were founded, and finite element progra -m named NACFSTLF was developed.An appropriate numerical thermal-stress coupling constitutive model of both steel tube and concrete core and its calculation method in concrete filled circular steel tubes in fire were proposed. Based on the principles of continuum mechanics, the U.L. formula of element incremental equilibrium under fire condition was deduced. Through adjusting the strain at centroid of cross section and the curvature, the external nodal loads was in equilibrium with the internal stress, and thus the layered finite element method was perfected. A FORTRAN program named NACFSTLF was developed and the reliability of the program was tested by the experimental results of CFST columns and structures, and reinforced concrete columns both at room temperature and in fire, showing that the analysis results are in good agreement with the experiment results from references. The program reflects the confinement effect and the temperature-load path of CFST structures in fire, and holds the virtue of higher calculative function and efficiency.(6) Applying the program of NACFSTLF, the fire performance of full scale single CFST columns with both fixed ends condition, full scale reinforced concrete rectangular beams with both pinned ends condition, and full scale CFST plane frame consisting of circular CFST columns and reinforced concrete T beams was analyzed.The influence of initial defect of the single CFST column, axial force ratio, strengths of concrete, strengths of steel, steel ratio, and the outer diameter of steel tube on the fire performance of CFST columns with four surfaces exposed to fire was discussed. The fire performance of full scale reinforced concrete rectangular beams with three surfaces exposed to fire was investigated. The fire performance of a full scale CFST plane frame of six-storey (6×4.5=27 m) and three-bay (3×9=27 m) under storey fire condition was analyzed. From the result, it is indicated that: the worst condition of the full scale frame was the middle CFST column of ground floor when the fire happened in the floor, and the failure mode was stability failure due to decrease of load capacity; due to the redistribution of internal forces, the fire resistance of the frame would be slightly higher than that of single columns of both fixed end condition in fire, and the CFST columns in the structurealso need protection under fire condition.更多还原