In-Plane Creep Buckling of Concrete-Filled Steel Tubular Arches

The creep-induced deformation of the arch rib of concrete-filled steel tubular （CFST） arches under a sustained load can increase the bending moment, which may lead to earlier stability failure called creep buckling. To investigate the influences of concrete creep on the buckling strength of arches, a theoretical analysis for the creep buckling of CFST circular arches under distributed radial load is performed. The simplified Arutyunyan-Maslov （AM） creep law is used to model the creep behavior of concrete core, and the creep integral operator is introduced. The analytical solutions of the time-dependent buckling strength under the sustained load are achieved and compared with the existing formula based on the age-adjusted effective modulus method （AEMM）. Then the solutions are used to determine the influences of the steel ratio and the first loading age on the creep buckling of CFST arches. The results show that the analytical solutions are of good accuracy and applicability. For CFST arches, the steel ratio and the first loading age have significant influences on creep buckling. An approximate log-linear relationship between the decreased degrees of the creep buckling strength and the first loading age is found. For the commonly used parameters, the maximum loss of the buckling strength induced bv concrete creen is close to 40%

高地震烈度深山区某钢管混凝土格构超高桥墩的施工控制

为了阐述自爬式多功能提升系统施工方法在超高桥墩的应用,本文以某特大桥钢管混凝土格构空心墩施工工程为例,从C80自密实补偿收缩混凝土制备、高抛试验、钢管格构柱施工、自爬式多功能提升系统施工、管内C80混凝土施工及长悬臂爬模施工等关键环节论述控制要点。最终实践证明:自爬式多功能提升系统的施工方法在超高桥墩应用是成功的。本文结果可为类似钢管混凝土格构空心墩施工提供一定的借鉴及参考。

Expansion performance and self-stressing behavior of CFST columns considering concrete creep and shrinkage effect

Expansive concrete is used in the steel tube of Concrete-filled steel tubular(CFST)columns to solve the problem of steel-to-concrete debonding.Self-stress is generated between concrete and steel plate due to concrete expansion,which can effectively improve the mechanical performance of CFST columns.Deformation tests were conducted on concrete and CFST columns,respectively.The free deformation of concrete and circumferential deformation of steel tubes were measured and analyzed.A calculation method was proposed to evaluate the hoop strain,self-stress and creep deformation of the CFST columns.The test and calculation results indicate that the proper addition of expansion agent in the internal concrete can keep concrete expansive and generate self-stresses for a long time.The expansion and self-stresses prevent the debonding between the steel tube and the internal concrete.Increasing the dosage of expansive agents and reducing the curing age both increase the expansive deformation and self-stress of CFST columns.Increasing the tube thickness reduces the expansive deformation and increases the initial self-stress of CFST columns.

Simplified Algorithm for Out-of-Plane Critical Loads of CFST Solid-Rib Arch

The simplified algorithm for out-of-plane ultimate loadcarrying capacity of concrete-filled steel tubular( CFST) solid-rib arches under uniform vertical load was studied. The experimentally validated finite element model was developed. The out-of-plane equivalent length coefficients of solid-rib arches were obtained using out-of-plane elastic eigenvalue buckling analysis. Then the out-ofplane elastic stability coefficient was plotted against the normalized slenderness ratio,and the out-of-plane eigenvalue buckling load or elastic buckling capability of arches was calculated. Lastly effects of different parameters on the out-of-plane ultimate load-carrying capacity of CFST solid-rib arches were determined using geometric and material nonlinear finite element analysis, and a simplified algorithm was established by fitting the out-of-plane elastic-plastic stability coefficient and normalized slenderness ratio using PerryRobertson formula. Ratio of the elastic stability coefficient to the elastic-plastic counterpart was plotted against the out-of-plane normalized slenderness ratio,from which the out-of-plane elasticplastic ultimate load-carrying capacity was determined according to the corresponding elastic buckling load. Results show that the proposed simplified algorithm can accurately predict the out-of-plane eigenvalue buckling load and the elastic-plastic ultimate loadcarrying capacity of the CFST solid-rib arches.

四肢格构型钢管混凝土截面计算模式研究

四肢格构型截面是大跨度钢管混凝土拱桥常用的截面型式,在具体构造上有缀板式和缀条式2种。着重研究了缀板式格构型截面的计算模式,提出板单元法和空间梁单元法2种计算模式,推导了板单元等效厚度计算公式,并介绍了空间梁单元法的建模要点。最后通过一个工程实例分析,表明2种计算模式都能满足工程计算精度要求,在具体应用上板单元法更为方便。

地震作用下钢管混凝土组合桁梁-格构墩轻型桥梁行车安全性分析

为研究地震作用下钢管混凝土组合桁梁-格构墩轻型桥梁的行车安全性,以干海子特大桥为研究对象,建立考虑地震作用的车桥耦合振动方程,并将计算方法添加到基于梁单元的双重非线性有限元程序NL_Beam3D中,实现地震作用下车桥系统相互作用的耦合计算。考虑车辆倾覆指标和桥梁横向变形的影响,进行行车安全性分析。结果表明:有限元计算得到的基频和不同车速下最大动挠度与实桥荷载试验得到的结果接近;与已有振动台试验结果相比,位移时程曲线形状吻合,位移幅值满足相似比关系,验证了计算模型和方法的有效性。柔性高墩轻型桥梁对地震波有滤波效应,地震波传至桥梁时强度明显减弱;最不利的重型货车的倾覆指标阈值大于E1多遇地震时的桥面最大横向加速度,即不存在车辆侧倾现象;墩顶位移满足设计要求,干海子特大桥行车安全性能良好。部分墩顶横向位移在地面峰值加速度达到1. 6倍E1多遇地震动时,将超过《公路钢管混凝土桥梁设计与施工指南》给出的限值。桥面最大加速度在地面峰值加速度为2倍E1多遇地震动时,倾覆指标阈值小于桥面最大横向加速度,重型货车存在倾覆可能;对应的桥墩墩顶最大横向位移与墩高比例系数达1/198,大于指南限值1/300,说明该指南对桥墩墩顶位移限值规定相对比较保守。

往复荷载作用下钢管混凝土格构式柱地震损伤模型及试验研究

为了解巨型组合结构体系中钢管混凝土格构式柱的地震损伤情况,通过对4根四肢钢管混凝土格构柱低周往复荷载试验,得出了四肢钢管混凝土格构柱在低周往复荷载下的破坏形态和构件损伤特征。在试验分析基础上,对经典的Park-Ang损伤模型进行了修正,提出了适用于四肢钢管混凝土格构柱的损伤指数和耗能因子计算公式;并根据试验现象和各阶段特征,选取了经典的Park-Ang损伤模型、基于能量的损伤模型和改进的Park-Ang模型进行对比研究。结果表明:改进的Park-Ang模型能较好的判断四肢钢管混凝土格构柱的损伤程度,且通过损伤值可将构件损伤划分为是否可修、不可修但未破坏和不可修且将破坏三个阶段,并以损伤值0.4作为划分试件是否可修的界限。

新型格构式高墩连续弯梁桥抗震性能分析

以四川雅泸高速公路干海子特大桥为工程背景,采用Midas Civil有限元软件建立三跨一联钢管混凝土格构式高墩连续弯梁桥结构。进行E1弹性地震响应分析,探讨了该类新型梁桥结构的动力特性、内力分布规律,以及地震波激励角度参数对全桥各个指标的影响规律,研究结果表明:钢管混凝土格构式高墩连续弯梁桥结构刚度较柔、周期长,不可忽视弯扭耦合效应。上部主梁弯矩值控制截面位于固定支座位置处,扭矩峰值出现在梁端位置处;下部格构墩弯矩和轴力控制截面均出现在固底墩墩底,墩顶为桥墩位移控制截面。支座中心连线和与之垂直的方向均为最不利激励角度。

钢管混凝土组合桁梁-格构墩轻型桥梁非线性地震响应分析

以干海子大桥第二联为原型,建立基于纤维单元的三维有限元简化模型,分析该钢管混凝土组合桁梁-格构墩轻型桥梁在地震作用下的响应特性,讨论进入非线性后桥墩屈服顺序和内力重分布效应。通过与精细有限元模型、实桥测试、振动台试验比较验证了该文建立的简化单梁计算模型的正确性。以桥墩柱肢钢管边缘应变为判断标准,确定了水平最不利地震动输入方向为两端支座连线的法线方向,同时需要考虑竖向地震动的影响。通过地震响应分析表明,在设计地震动下桥梁处于弹性状态;进入塑性后,格构墩和复合墩以面内受力为主,轴力增幅小于地震动增幅,墩顶位移增幅大于地震动增幅;复合高墩面内弯矩增幅大于矮墩,有利于全桥的抗震。