论桥梁钢索的安全评定与索力检测

基于疲劳断裂理、材料失效分析(材料诊断学)及结构完整性科学的安全评定理论和准则,桥梁钢索的服役安全性评定,为实际广义应力(复合应力)小于实际广义抗力(剩余强度)。论述准则参量的理论含义及索力检测,考查钢索的破断与实验。认为随机活载作用下,服役桥梁钢索的索力为随机系列;通常的检测索力,仅为索力系列的一个(或有限个)样本,不可能评定钢索的安全。比较钢索设计与安全评定,指出二者为理论体系各异、性质不同的两类问题,不能混淆、不能替代。

大型桥梁钢索塔制作关键技术探析

首先对国内外桥梁钢索塔建造现状及应用前景进行了介绍,然后对典型桥梁钢索塔的结构特点进行了分析。结合桥梁钢索塔结构特点,重点对制作方案策划、焊接变形及几何精度控制技术、曲线形钢索塔节段制作技术、钢索塔预拼装技术及自动化制作等方面进行了阐述,解决了钢索塔制作的难题,取得了良好的效果。

剩余强度广义应力与桥梁钢索的破断--论检测索力不能评定钢索的服役安全性

由于载荷及环境介质作用的随机性、共同性或耦合性以及协合效应等,桥梁钢索的服役破断是不确定的。导致钢索断裂的是损伤热点的广义应力;控制钢索断裂的是剩余强度。基于疲劳断裂理论、材料失效分析(所谓材料诊断学)、结构完整性科学建立的服役安全性评定准则:为实际的广义应力小于剩余强度。以检测索力计算的名义应力,与桥梁钢索的破断无直接关系;检测索力、设计准则,不能评定钢索的服役安全性。

桥梁钢索服役破断的安全评定与索力检测

钢索的安全为索结构桥梁正常服役的重要控制因素;基于索力检测、寿命预测的钢索安全评定,当下颇为流行;研究和断索实例表明,其理论正确性及技术可靠性,值得商榷。由于桥梁载荷及环境介质作用的随机性、共同性或耦合性,以及反映作用效果权重的协合效应,桥梁钢索的破断强度、破断寿命以及破断形态,均是不确定的:随时、随处不相同,不可预测。疲劳断裂理论、材料失效分析(所谓材料诊断学)及结构完整性科学认为:钢索的服役,为其剩余强度的消耗过程;损伤热点的广义应力随时增长。服役结构的安全性评定准则,为实际的广义应力(复合应力)小于剰余强度;而不是基于检测索力计算的名义应力与设计标准强度的比较。检测索力及其均匀分布的名义应力,与桥梁钢索不确定的、随机损伤断裂,无直接关系;不能评定钢索的服役安全性。

Dynamic Characteristics of Long -Span Steel -Concrete CompositeBeam Bridge Based on Vehicle -Bridge Coupling Effect

In order to investigate the effect of vehicle-bridge coupling on the dynamic characteristics of the bridge,a steel-concrete composite beam suspension bridge is taken as the research object,and a three-dimensional spatial model of the bridge and a biaxial vehicle model of the vehicle are established,and then a vehicle-bridge coupling vibration system is constructed on the basis of the Nemak-βmethod,and the impact coefficients of each part of the bridge are obtained under different bridge deck unevenness and vehicle speed.The simulation results show that the bridge deck unevenness has the greatest influence on the vibration response of the bridge,and the bridge impact coefficient increases along with the increase in the level of bridge deck unevenness,and the impact coefficient of the main longitudinal girder and the secondary longitudinal girder achieves the maximum value when the level 4 unevenness is 0.328 and 0.314,respectively;when the vehicle speed is increased,the vibration response of the bridge increases and then decreases,and the impact coefficient of the bridge in the middle of the bridge at a speed of 60 km/h achieves the maximum value of 0.192.

功能型环氧粉末涂料有望被大面积推广

功能型粉末涂料主要被应用于关系到建筑物安全的钢筋及桥梁斜拉桥钢索保护、油气管道防腐及特种电机绝缘保护等领域。

Dynamic analysis and modal test of long-span cable-stayed bridge based on ambient excitation

To study the stiffness distribution of girder and the method to identify modal parameters of cable-stayed bridge, a simplified dynamical finite element method model named three beams model was established for the girder with double ribs. Based on the simplified model four stiffness formulae were deduced according to Hamilton principle. These formulae reflect well the contribution of the flexural, shearing, free torsion and restricted torsion deformation, respectively. An identification method about modal parameters was put forward by combining method of peak value and power spectral density according to modal test under ambient excitation. The dynamic finite element method analysis and modal test were carried out in a long-span concrete cable-stayed bridge. The results show that the errors of frequencies between theoretical analysis and test results are less than 10% mostly, and the most important modal parameters for cable-stayed bridge are determined to be the longitudinal floating mode, the first vertical flexural mode and the first torsional mode, which demonstrate that the method of stiffness distribution for three beams model is accurate and method to identify modal parameters is effective under ambient excitation modal test.

Controlling deflection of long steel I-shaped girder bridge using two V-shaped pre-tensioning cables

Despite appropriate design of girder under bending and shear,the deflection of long steel girders usually exceeds the allowable range,and therefore the structural designers encounter challenges in this regard.Considering significant features of the cables,namely,low weight,small cross section,and high tensile strength,they are used in this research so as to control the deflection of long girder bridges,rather than increasing their heights.In this study,theoretical relations are developed to calculate the increase in pre-tensioning force of V-shaped steel cables under external loading as well as the deflection of steel girder bridges with V-shaped cables and different support conditions.To verify the theoretical relations,the steel girder bridge is modeled in the finite element ABAQUS software with different support conditions without cable and with V-shaped cables.The obtained results show that the theoretical relations can appropriately predict the deflection of girder bridge with V-shaped cables and different support conditions.In this study,the effects of the distance from support on the deflection of mid span are studied in both simply supported and fixed supported girder bridge so as to obtain the appropriate distance from support causing the minimum deflection.

Research of 1770 MPa galvanized steel wire for stay cable of domestic bridges

This paper focuses on introducing the manufacture technology of 1 770 MPa galvanized steel wires for stay cables applied to domestic bridges.During the development practices of high strength galvanized wire for stay cables used in Sutong Bridge,Baosteel has established three key technologies based on research of manufacture technology and technical innovation.The three key technologies are:"Double Tensioning + limiter die" process,"dominant process + fine adjustment" in integrated optimization technology and "three-level control" in hot dip galvanization.With these key technologies,Baosteel has produced 1 770 MPa galvanized wires for stay cable,which has high tensile strength,low relaxation and good torsion performances.

Mechanical Analysis and Numerical Simulation for New Type of Dynamic Control Devices

The conventional dynamic control devices,such as fluid viscous damper(VFD)and isolating bearings,are unsuitable for the double-deck cable-stayed bridge due to a lack of sustainability,so it is necessary to introduce some high-tech dynamic control devices to reduce dynamic response for double-deck cable-stayed bridges under earthquakes.A(90+128)m-span double-deck cable-stayed bridge with a steel truss beam is taken as the prototype bridge.A 3D finite element model is built to conduct the nonlinear time-history analysis of different site categories in fortification intensityⅨ(0.40 g)degree area.Two new types of dynamic control devices-cable sliding friction aseismic bearings(CSFABs)and elasticity fluid viscous dampers composite devices(EVFDs)are introduced to reduce the dynamic responses of double-deck cable-stayed bridges with steel truss beam.The parametric optimization design for the damping coefficient C and the elastic stiffness of spring K of EVFDs is conducted.The following conclusions are drawn:(1)The hybrid support system by EVFDs and CSFABs play a good function under both seismic and regular work,especially in eliminating the expansion joints damage;(2)The hybrid support system can reduce the beam-end displacement by 75%and the tower-bottom bending moment by 60%under the longitudinal seismic excitation.In addition,it can reduce the pier-bottom bending moment by at least 45%under transverse seismic and control the relative displacement between the pier and beam within 0.3 m.(3)Assuming the velocity indexα=0.3,the parametric optimization suggests the damping coefficient C as 2000 kN·s·m-1in siteⅠ0,4000kN·s·m-1in siteⅡ,6000 kN·s·m-1in siteⅣ,and the elastic stiffness of spring K as 10000 kN/m in siteⅠ0,50000 kN/m in siteⅡ,and 100000 kN/m in siteⅣ.

Temperature gradient and its effect on flat steel box girder of long-span suspension bridge

The temperature field variation law and distribution characteristics of an orthotropic flat steel box girder under sunny conditions were analyzed through a field temperature test on the steel box girder of the operational Runyang Yangtze River Bridge(the suspension bridge part).Function optimization fitting and error analysis of the test data were conducted.A temperature gradient distribution curve applicable to a hexagonal flat steel box girder was proposed.Based on the measurement results,the temperature effect of an orthotropic flat steel box girder was analyzed using finite element method and the effects of different temperature gradient modes on the mechanical characteristics and stress distribution of the steel box girder were compared.Under sunny conditions,heat conduction in the flat steel box girder structure shows distinct "box-room effect" characteristics,and the actual temperature gradient distribution is inconsistent with the one suggested by the existing standards.The thermal stress of a steel box girder calculated from the measured temperature gradient mode exceeds that calculated from the standard,and the intensity approximates that under the action of designed vehicle loads.The temperature-induced stress is distributed centrally near the manufacturing welds of the orthotropic steel box girder,which should be considered in design,construction and research.Results from this study could supplement the existing bridge and culvert design standards.