【作者】 田明革；

【导师】 易伟建；

【作者基本信息】 湖南大学 ， 结构工程， 2008， 博士

【摘要】 钢筋混凝土框架结构施工期性能是结构施工期安全和使用期安全以及耐久性能的研究前提和基础。国内外在早龄期混凝土性能、施工期混凝土框架结构特性和可靠性方面取得了一些研究成果。借鉴这些成果,本文对早龄期受载混凝土性能、施工期混凝土框架结构性能和动力特性等开展试验研究和理论分析。本文主要研究内容包括:对标准养护条件下早龄期混凝土力学性能和本构关系随养护龄期变化的时变规律进行了试验研究。建立了早龄期混凝土抗压强度和弹性模量与养护龄期之间的函数关系并且采用非线性最小二乘法计算给出拟合方程系数。根据试验数据,对无量纲化的早龄期混凝土棱柱体单轴受压应力应变全过程曲线与混凝土设计规范中的过镇海曲线进行比较分析,并给出了公式中参数a和α的取值范围。对早龄期施加荷载并且持续至28天的混凝土力学性能和本构关系随养护龄期变化的时变规律进行了试验研究。混凝土早龄期持续受载将降低28天的混凝土抗压强度值和减小混凝土的塑性变形能力。加载龄期越低、施加的应力越高、混凝土强度等级越低,降低程度越大。通过试验数据分析研究界定了混凝土持续加载的龄期和持续应力的大小对降低程度的影响范围,建立了无量纲化的混凝土棱柱体单轴受压应力应变全过程曲线与混凝土设计规范中的过镇海经验公式曲线进行比较分析,并给出公式参数的取值范围。对以粉煤灰作为掺合料的高性能混凝土,在不同水胶质量比,不同掺入量,从成型到180天龄期内的抗压强度、弹性模量以及收缩的混凝土时效性能进行了试验研究。建立了以粉煤灰为掺合料混凝土的自收缩应变与抗压强度之间非线性关系的拟合公式。对施工期混凝土框架与模板支撑相互作用机理进行了试验研究。试验表明:施加小于按照加载龄期混凝土力学指标计算得到的开裂荷载值的荷载,混凝土框架与模板支撑作用系统为线性系统,混凝土收缩徐变效应引起系统非线性程度较小。钢管支撑承担的荷载随着混凝土龄期的增加而减小。共同作用系统的内力和变形协调在15天龄期基本达到稳定。采用数值模拟方法对混凝土框架结构施工过程的时效特性进行了研究。基于混凝土徐变的应力—应变—时间耦合本构关系,应用梯形积分公式导出混凝土时效性能的数值迭代模型及其算法,并基于有限元法建立了非线性增量型数值迭代模型及其算法。采用该方法对混凝土偏心受压柱和简支粱进行数值计算,计算结果与试验值吻合较好。应用逐层叠加分析方法,建立了考虑施工次序和混凝土收缩徐变影响的施工期混凝土框架结构计算模型。应用该法研究了不同施工周期、不同钢管支撑间距和收缩徐变效应对混凝土框架柱的累积竖向变形的影响。施工周期越长对框架柱累积竖向变形的影响越小;支撑刚度增大,框架结构顶部楼层的累积竖向变形减小,底部楼层增大;收缩徐变效应对混凝土框架内柱累积竖向变形的影响比外柱的大。提出以混凝土开裂为失效模式,引入施工期混凝土结构极限状态方程。考虑施工期的混凝土结构抗力的时效性不能忽视,建立了结构抗力的随机过程模型,及荷载效应的概率模型。利用模拟重要性抽样的蒙特卡洛随机算法,推导了施工期混凝土动态结构的可靠度计算方法。对一栋施工期混凝土框架结构开裂可靠度进行计算分析,提出施工期混凝土结构的施工建议。对随时间变化的力学参数、混凝土浇筑、临时模板支撑系统和施工机械对施工期混凝土框架结构的结构动力特性的影响进行了试验分析研究。应用环境激励法对一栋8层混凝土框架的第6层和屋顶施工阶段的动力特性进行检测。试验获得各施工阶段的结构响应传递函数,及其模态频率、振型和阻尼比,分析了施工阶段结构响应传递函数,及其模态频率、振型和阻尼比的变化。更多还原

【Abstract】 Studies about performances of reinforced concrete framed structures during construction provide research foundation for security during construction, and safety and durability during usage. Performances of concrete at early age, structural characteristics and reliability have played important roles in domestic and foreign studies about structures during construction. In this paper, performances of loaded concrete at early age, characteristics and dynamics of reinforced concrete framed structures during construction were experimentally and theoretically studied. The following research contents were mainly obtained:Time-variant rules about mechanical properties and constitutive relationship of concrete conserved with standard condition at early age versus conserved time were experimentally studied. Relationship functions between both compressive strength and elastic modulus of early-aged concrete and conserved time were established, whose fitting coefficients were gained by non-linear least squares fitting to experimental data. Dimensionless experimental relationship curves about uniaxial compression stress versus strain of early-aged concrete prism specimens were researched, and were compared with Z. H. GUO’s empirical curves supplied in national concrete design code, whose parameters: a andαwere recommended.Time-variant rules about mechanical properties and constitutive relationship of concrete loaded from early age to 28 D versus conserved time were experimentally studied. At earlier age loading higher stress to concrete specimens of lower strength grade, compressive strength and plastic deformation ability of concrete loaded were decreasing more distinctly. Through analysis of test data, their affected range on loading time and stress continuously loading were gained. Dimensionless experimental relationship curves about uniaxial compression stress versus strain of concrete prism specimens loaded at early age were given, which were compared with Z. H. GUO’s empirical curves and parameters of empirical formulas were recommended.Experimental studies were carried out, and focus on the effects of fly ash replacement content and water-to-cementations mass ratio on time-dependent compressive strength, elastic modulus and shrinkages of concretes cured for a period from curing to 180 day after curing. Fitting formulas about relationship of shrinkage versus compressive strength were given based on test data. Interactional mechanism about reinforced concrete framed structure during construction and temporary shoring frameworks were researched by experiments. Experimental results show that interactional systems of reinforced concrete framed structure and temporary shoring frameworks loaded less than cracked loading calculated by concrete properties at loading age was linear system, and to less extent, concrete’s shrinkage and creep effected systems on the non-linear. Internal force on steel pipe supports had been decreasing with concretes’increasing age. It was at basic age of 15 d when internal forces and deformation of the system achieved stabilization.With numerical simulation, time-dependent characteristics about construction procedure of concrete framed structures were studied. Numerical computational formulas about concrete’s time-dependent stress-strain coupled mechanism were deduced, in which the creep deformation of concrete was described in accordance with a trapezoid integral algorithm based on the expansion of a degenerated kernel of the compliance function. In addition, the finite element method submitted to the increment algorithm was established to analyze both non-mechanical deformations induced by the time-dependent deformations of concrete and mechanical deformations induced by external loads after long-term loads. They were illustrated with a reinforced concrete beam and a column, which of time-dependent behaviors by being loaded in early period had been tested. The numerical analysis results were in agreement with experimental data. Based on floor-by-floor superposition method and considering impacts of construction procedures, concrete shrinkage and creep, calculating models about concrete framed structures during construction were established, using which effects of constructional cycle, supporting stiffness, and concrete shrinkage and creep on cumulated vertical deforms of columns were calculated. The results show that 1) longer constructional cycle versus less cumulated vertical deforms of columns, 2) more supporting stiffness versus less deforms at the top of structures, and more deforms at the bottom, 3) concrete shrinkage and creep affects more on cumulated vertical deforms of inside columns than outsider ones.It was based on failure model of concrete cracks that limit-stated equations of reinforced concrete structures during construction were presented. Based on concrete time-dependent characteristics, both random model of time-variant resistance and probability model of loading effect were established. Monte-Carlo method in which essentially sampling procedures were numerically simulated was deduced, with which reliability analysis of dynamic structural model during construction was carried out. It was illustrated that crack reliability about reinforced concrete framed structure during construction was calculated,and some recommendation about construction were presented.The effects of concrete’s time-variant elastic modulus, casting structural components, assembling temporary shoring framework system, and shock by operating construction equipments on dynamic characteristics of reinforced concrete frame structure during construction were experimentally investigated. Dynamic tests of an eight-storey reinforced concrete framed structure during full-scaled stages of the sixth storey and the housetop construction cycle were carried out by ambient vibration. Transfer functions of Structures were gained processing the testing signal data in frequency domain, with which natural frequencies, corresponding mode shapes and damping ratio were determined, and their rules at different construction stages were given.更多还原