Field Load Test Based SHM System Safety Standard Determination for Rigid Frame Bridge

The deteriorated continuous rigid frame bridge is strengthened by external prestressing. Static loading tests wereconducted before and after the bridge rehabilitation to verify the effectiveness of the rehabilitation process. Thestiffness of the repaired bridge is improved, and the maximum deflection of the load test is reduced from 37.9 to27.6 mm. A bridge health monitoring system is installed after the bridge is reinforced. To achieve an easy assessmentof the bridge’s safety status by directly using transferred data, a real-time safety warning system is createdbased on a five-level safety standard. The threshold for each safety level will be determined by theoretical calculationsand the outcomes of static loading tests. The highest risk threshold will be set at the ultimate limit statevalue. The remaining levels, namely middle risk, low risk, and very low risk, will be determined usingreduction coefficients of 0.95, 0.9, and 0.8, respectively.

Fatigue Safety Assessment of Concrete Continuous Rigid Frame Bridge Based on Rain Flow Counting Method and Health Monitoring Data

The fatigue of concrete structures will gradually appear after being subjected to alternating loads for a long time,and the accidents caused by fatigue failure of bridge structures also appear from time to time.Aiming at the problem of degradation of long-span continuous rigid frame bridges due to fatigue and environmental effects,this paper suggests a method to analyze the fatigue degradation mechanism of this type of bridge,which combines long-term in-site monitoring data collected by the health monitoring system(HMS)and fatigue theory.In the paper,the authors mainly carry out the research work in the following aspects:First of all,a long-span continuous rigid frame bridge installed with HMS is used as an example,and a large amount of health monitoring data have been acquired,which can provide efficient information for fatigue in terms of equivalent stress range and cumulative number of stress cycles;next,for calculating the cumulative fatigue damage of the bridge structure,fatigue stress spectrum got by rain flow counting method,S-N curves and damage criteria are used for fatigue damage analysis.Moreover,it was considered a linear accumulation damage through the Palmgren-Miner rule for the counting of stress cycles.The health monitoring data are adopted to obtain fatigue stress data and the rain flow counting method is used to count the amplitude varying fatigue stress.The proposed fatigue reliability approach in the paper can estimate the fatigue damage degree and its evolution law of bridge structures well,and also can help bridge engineers do the assessment of future service duration.

Load Test Analysis and Research on Long-Span Concrete Continuous Rigid Frame Bridge

Based on the as-built load test of a large bridge,this paper introduces the procedure of the prestressed concrete continuous rigid frame bridge load test.Numerical analysis of the bridge was carried out by simulating and establishing a finite element model,and comparative analysis was carried out with the measured values.The results show that the calculated values were basically consistent with the measured values,which showed that the establishment method of the model was reasonable,and the mechanical performance of the bridge met the service requirements of the designed live load.

Experimental investigation on seismic performance of rigid frame tied-arch bridge with split-piers

A novel seismic design method, namely split-pier seismic design, is proposed. A vertical gap and connect elements are set in split-piers. The lateral stiffness of piers is reduced by cracking of the connect elements under severe earthquake, and the seismic response of bridges is reduced by avoiding the site predominant periods. A model of tied-arch rigid frame bridge with split-piers was designed. Seismic performance was investigated by pseudo-static experimentation on the scale model, The failure process of split-piers, the hysteresis characteristic and the effect of split-piers on the superstructure are presented. Results show that the split-pier has better seismic performance than common ductile piers do.

Vibration analysis of maglev three-span rigid frame bridge considering magnetic force

The dynamic interaction between the maglev vehicle and the three-span rigid frame bridge is discussed. With the consideration of magnetic force, the interaction model is developed. Numerical simulations are performed to study the dynamic characteristics of the bridge during vehicle movement along the bridge. The results show that a reasonable value of the linear stiffness ratio of columns to beams is between 2. 0 and 3.0. The dynamic responses of the bridge are aggravated with the decrease in bending rigidity and the increase in vehicle speed and the span ratio of the bridge. It is suggested that a definite way is to control impact coefficients and acceleration in the dynamic design of the bridge. It is unsuitable to adopt the moving load model and the moving mass model in the design. The proposed results can serve in the design of high-speed maglev three-span rigid frame bridges.

Seismic response analysis of continuous rigid frame bridge considering canyon topography effects under incident SV waves

To evaluate the importance of the canyon topography effects on large structures, based on a rigid frame bridge across a 137-m-deep and 600-m-wide canyon, the seismic response of the canyon site is analyzed using a two-dimensional finite element model under different seismic SV waves with the assumptions of vertical incidence and oblique incidence to obtain the ground motions, which are used as the excitation input on the pier foundations of the bridge with improved large mass method. The results indicate that canyon topography has significant influences on the ground motions in terms of inci- dent angle. The peak ground acceleration values vary greatly from the bottom of the canyon to the upper comers. Under ver- tical incident SV waves, at the upper comers of canyon the peak ground accelerations greatly increase; whereas the peak ground accelerations diminish at the bottom comers of canyon. Under oblique incident SV waves, the shaking of the canyon slope perpendicular to the incidence direction is much more severe than that of the opposite side of canyon. And the ground surface has been characterized by larger deformations in the case of oblique incident waves. It is also concluded that the low piers and frame of the continuous rigid frame bridge ape more sensitive to the multi-support seismic excitations than the flexible high piers. The canyon topography as well as the oblique incidence of the waves brings the continuous rigid frame bridge severe responses, which should be taken into account in bridge design.

EARTHQUAKE RESPONSE OF SEMI RIGID FRAME WITH ROTATIONAL DAMPER

The seismic behavior of frames with semi rigid connections and rotational dampers is examined.The ground acceleration due to earthquake is regarded as a stochastic process,and a pseudo excitation algorithm in frequency domain is implemented in a computer program to handle non orthogonal damping properties of the system.The computer program which incorporates detailed connection models and rotational damping models is used to investigate the effect of the connection of the semi rigid frame.It is shown from analytical studies that semi rigid frames with rotational dampers improve the seismic response of the building and may provide an effective and reliable earthquake resistant design solution.

Nonlinear Stability Analysis of Long Span Continuous Rigid Frame Bridge with Thin Wall High Piers

By utilizing the current finite element program ANSYS, two types of finite element models (FEM), the beam model (BM) and shell model (SM), are established for the nonlinear stability analysis of a practical rigid frame bridge—Longtanhe Great Bridge. In these analyses, geometrical and material nonlinearities are simultaneously taken into account. For geometrical nonlinearity, updated Lagrangian formulations are adopted to derive the tangent stiffness matrix. In order to simulate the nonlinear behavior of the plastic hinge of the piers, the multi lines spring element COMBIN39 is used in the SM while the bilinear rotational spring element COMBIN40 is employed in the BM. Numerical calculations show that satisfying results can be obtained in the stability analysis of the bridge when the double coupling nonlinearity effects are considered. In addition, the conclusion is significant for practical engineering.

Stability Analysis of Long-Span Continuous Rigid Frame Bridge with Thin-Wall Pier

During cantilever cast in construction of high-pier and large-span continuous rigid frame bridges, structural stability in the longest cantilevered stage is very important. Based on a practical design case of a large-span continuous rigid frame bridge in Wuhan, the longest span stability coefficient is calculated with linear-buckling and nonlinear-buckling methods, respectively. The influences of both geometrical nonlinearity and the dual nonlinearity of material and geometry are considered. Numerical results indicate that the nonlinear solution is necessary to stability analysis because linear buckling loads are much higher than those of nonlinear buckling. Thus, the edge fiber yield criterion is more convenient and faster than ultimate loading criterion when estimating nonlinear stability of structure, and can be used easily in the initial engineering design.

Time-varying Reliability Analysis of Long-span Continuous Rigid Frame bridge under Cantilever Construction Stage based on the Monitored Strain Data

In general,the material properties,loads,resistance of the prestressed concrete continuous rigid frame bridge in different construction stages are time-varying.So,it is essential to monitor the internal force state when the bridge is in construction.Among them,how to assess the safety is one of the challenges.As the continuous monitoring over a long-term period can increase the reliability of the assessment,so,based on a large number of monitored strain data collected from the structural health monitoring system(SHMS)during construction,a calculation method of the punctiform time-varying reliability is proposed in this paper to evaluate the stress state of this type bridge in cantilever construction stage by using the basic reliability theory.At the same time,the optimal stress distribution function in the bridge mid-span base plate is determined when the bridge is closed.This method can provide basis and direction for the internal force control of this type bridge in construction process.So,it can reduce the bridge safety and quality accidents in construction stages.

Seismic analysis of long-span continuous rigid frame bridges in cold regions:a case study of Bridge 1 in north of international tourism resort in Changbai Mountain

It is helpful to improve the seismic design theory of long-span continuous bridges for studying the seismic performance of each cantilever construction state.Taking the Bridge 1 in the north of Changbai-Mountain international tourism resort as an example,the authors studied it in shutdown phase and the cantilever construction process,established the simulation model by using Midas / civil,and analyzed time-history of each construction stage for the bridge.The study shows that long-span bridge cantilever construction in northeastern China can be divided into two-year tasks for construction(suspending in winter).It is needed to think about seismic stability of the cantilever position in shut-down phase of winter.The effect of longitudinal vibration is the most disadvantageous influence to bridge,and its calculation results can provide reference for seismic design of similar bridges in the future.

Maintenance Management Research of a Large-span Continuous Rigid Frame Bridge Based on Reliability Assessment by Using Strain Monitored Data

When the bridge components needing maintenance are the world problem at present,and the health monitoring system is considered to be a very help­ful tool for solving this problem.In this paper,a large number of strain data acquired from the structural health monitoring system(SHMS)installed on a continuous rigid frame bridge are adopted to do reliability assessment.Firstly,a calculation method of punctiform time-dependent reliability is proposed based on the basic reliability theory,and introduced how to cal­culate reliability of the bridge by using the stress data transformed from the strain data.Secondly,combined with“Three Sigma”principle and the basic pressure safety reserve requirement,the critical load effects distribu­tion function of the bridge is defined,and then the maintenance reliability threshold for controlling the unfavorable load state which appears in the early operation stage of this type bridge is suggested,and then the combi­nation of bridge maintenance management and health monitoring system is realized.Finally,the transformed stress distribution certifies that the load effects of concrete bridges practically have a normal distribution;as for the concrete continuous rigid frame bridge with C50 strength grade concrete,the retrofit reliability threshold should be valued at 6.13.The methodology suggested in this article can help bridge engineers do effective maintenance of bridges,which can effectively extend the service life of the bridge and bring better economic and social benefits.

大跨铁路混凝土梁矮塔斜拉桥结构体系研究

为研究不同结构体系对大跨铁路混凝土梁矮塔斜拉桥力学性能的影响,并寻求最优的结构体系,以崇凭铁路上金左江双线特大桥为背景,采用MIDAS Civil和ANSYS软件建立主桥有限元模型及车-轨-桥耦合动力学模型,对半飘浮体系、刚构体系、塔梁固结体系和塔梁固结-刚构组合(高墩塔墩梁固结、矮墩纵向设置双排活动支座)体系方案进行比选,分析典型工况下主桥的静、动力特性。结果表明:在列车活载和温度作用下,采用塔梁固结-刚构组合体系的桥梁受力性能良好,采用较小的梁高即可满足桥梁结构的刚度要求;CRH2列车编组通过时不同结构体系的桥梁结构和列车编组的动力响应值均满足要求,考虑温度变形影响时不同结构体系对列车运行的安全性和舒适性的影响较小。基于力学性能计算结果,上金左江双线特大桥主桥最终采用塔梁固结-刚构组合体系。

考虑墩-梁碰撞效应的连续刚构桥系统易损性与概率地震风险性分析

为研究连续刚构桥主梁与过渡墩碰撞效应对其地震系统易损性和概率地震风险性的影响,以一座主桥跨径为(120+220+120)m的连续刚构桥为研究背景,通过模拟实际施工过程以获得真实成桥内力状态,基于等效荷载法建立考虑该内力状态的动力弹塑性分析模型,采用Hertz-damp接触模型考虑包括主梁与过渡墩碰撞在内的伸缩缝处碰撞效应。选取90条具有速度脉冲的脉冲型近断层地震动沿纵桥向输入,通过时程分析解释了墩梁碰撞过程和破坏机理;采用增量动力分析法,建立考虑桥墩和支座权重系数的全桥复合系统易损性曲线,并与一阶界限法串联模型下限和并联模型上限系统易损性曲线进行对比,将场地危险性函数与易损性函数卷积,建立概率地震风险曲线,考察桥梁系统易损性、概率地震风险性及墩梁碰撞效应的影响。结果表明,若忽略过渡墩与主桥梁体的碰撞效应,将会低估过渡墩的位移反应3~5倍,低估其地震风险性概率120%;当地震动强度为0.2g~0.6g时,轻微破坏和中等破坏的损伤概率被低估了35%~80%;地震动强度为0.6g~1.5g时,严重破坏和完全破坏分别被低估13%~68%和15%~59%。

海洋复杂气候多塔公铁同层斜拉桥主梁施工控制关键技术

珠海西江公铁大桥为(58.5+116+3×340+116+58.5)m公铁同层斜拉桥,两中塔塔梁墩固结,两边塔塔梁固结、塔墩分离。主梁采用单箱三室截面钢箱梁,总宽49.6 m,梁高4.676 m;全桥钢梁共划分为47个节段,标准节段长24 m;钢梁节段接头除顶板为焊接外,底板、腹板均为高强度螺栓连接。考虑既有施工机具和桥址环境特点,钢梁节段均为超大、超重、超高结构。边跨、次边跨钢梁节段最长80.25 m、最大吊重2600 t,利用大型浮吊吊装,通过“分段顶升(下降)、逐端合龙”的施工控制方法,3个大节段钢梁无折角拼接;中塔两侧主梁采用一侧钢梁节段吊装时另一侧配水袋压重的“小步快走,多轮次平衡”异步悬拼施工,将结构抗倾覆稳定系数控制在1.5以上;利用在中中跨合龙口施加主动顶推力结合改变合龙口结构构造的保障措施,实现大桥在高温条件下的高精度合龙。成桥结构内力、线形状态均达到设计理想状态。

预制节段拼装城市高架桥梁结构体系分析

为研究预制节段拼装城市高架桥梁适宜的结构体系,以江西省南昌市洪都大道3×35m预制节段拼装桥梁为背景,通过建立空间杆系有限元模型,分别研究中墩固结、边墩固结的全固结体系和中墩固结、边墩设支座的半固结体系下结构的受力性能。然后在全固结体系下,研究桥墩刚度、预制节段梁龄期对结构受力的影响。研究结果表明:预制节段拼装城市高架桥梁采用中墩固结、边墩设支座的半固结体系具有更好的综合性能;减小桥墩抗推刚度、增加预制节段存梁时间可显著改善结构的受力性能。

智能传输系统在渡槽连续刚构张拉中的应用

探讨了智能传输系统在亭子口水利工程渡槽连续刚构张拉应用中具有的潜力和优势。阐述了渡槽连续刚构的背景以及传统渡槽连续刚构张拉方法存在的操作效率低、安全风险高以及监测数据不稳定的缺陷,详细介绍了智能传输系统的概念、工作原理和特点,强调了其在渡槽连续刚构中的应用;探讨了智能传输系统中采用的关键技术,包括传感器技术、控制算法和通信技术以及如何优化其系统性能,分析了其与传统方法相比具有的优势,包括实时监测、远程控制和自动化操作;最后进行了性能评估,强调了智能传输系统在提高工程效率、减少人力成本和提高施工安全性方面具有的潜力;总结了所取得的主要研究成果以及智能传输系统在渡槽连续刚构领域应用的前景。

华南大桥墩柱加固设计与施工

华南大桥为110 m+190 m+110 m三跨连续刚构桥,经检测墩柱存在开裂现象并持续恶化,主要原因是墩身刚度相对主梁刚度较大,需尽快对主墩进行加固处置。主墩防撞设施采用混凝土墙结构,墩与墙之间空间狭小。墩柱加固常采用增大截面法,涉水加固施工常采用钢围堰形成干环境。为避免墩柱加固后过大增加墩柱截面刚度,提出了型钢骨架外包UHPC增大截面法进行墩柱加固,计算分析表明加固设计方案对桥梁其他构件受力较小。墩柱加固施工原设计方案为先拆除混凝土防撞墙再采用钢围堰,后期再重建混凝土防撞墙,针对原设计方案存在环境影响大、经济性差和水下作业难的问题,提出改造混凝土防撞墙并形成干环境在狭小空间内进行墩柱加固施工的方案。工程顺利实施为类似工程设计与施工提供借鉴。

V型墩刚构桥自平衡组合支护体系设计与施工

宁波舟山港六横公路大桥梅山水道跨堤桥为(60+100+60)m V型墩刚构桥,主梁采用预应力混凝土箱梁,主墩为V型墩。针对该桥施工重难点,提出一种自平衡组合支护体系进行V型墩和0号块施工。该体系由临时支架系统和拉杆系统组成,临时支架系统包括V型墩外侧支架和0号块中部支架两部分,在墩身竖直方向设置3层拉杆,每层布置5根拉杆。有限元计算结果表明:V型墩和0号块施工时支护体系受力满足要求,待主梁合龙后方可拆除V型墩外侧支架和墩身拉杆,4号梁段预应力施工完后方可拆除0号块中部支架。承台施工完成后,安装V型墩外侧支架及拉杆系统,墩身采用滑槽一次浇筑成型,拉杆分3个阶段张拉;V型墩施工完后安装0号块中部支架,0号块混凝土采用汽车泵分2次浇筑完成,拉杆分4个阶段张拉;0号块施工完成后进行主梁挂篮悬浇施工,支护体系按计算确定的拆除时机拆除。主梁施工完成后,墩身线形良好,墩底内、外侧及0号块箱梁内、外均无裂缝产生。

非对称刚构-连续组合体系梁桥受力特性研究

为给非对称刚构-连续组合体系梁桥的设计与应用提供理论基础,以渝湘复线高速长头河特大桥主桥为背景,引入非对称比例系数研究不对称程度对非对称刚构-连续组合梁桥力学特性的影响,提出采用在连续墩处设置组合阻尼支承体系改善该体系梁桥连续墩处主梁在横向风荷载作用下受力不利的问题。保持该桥主跨跨径180 m不变,调整刚构侧和连续侧单侧主梁长度在主跨范围内的占比,采用MIDAS Civil软件建立10个不同非对称比例系数的刚构-连续组合体系梁桥有限元模型,分析不同模型在恒载、汽车荷载、温度荷载、收缩徐变等作用下的主梁内力和支座反力,以及组合阻尼支座不同水平等效刚度对主梁受力的影响。结果表明:非对称刚构-连续组合体系梁桥不对称程度对结构内力影响最大的荷载为收缩徐变;非对称比例系数m>0.2时需适当加大连续墩处主梁梁高、延长小边跨长度以减小非对称性的不利影响,m最大限值建议采用0.3;在连续墩处设置组合阻尼支承体系,利用阻尼位移使主梁协调变形,能有效降低横向风荷载引起的主梁弯矩和应力幅。