Strengthening steel bridge sections using CFRP laminates

This paper presents results from an experimental investigation to determine the feasibility of using carbon fiber reinforced polymer (CFRP) epoxy laminates to repair steel composite bridge members. Six specimens, each consisting of a 6.1 m long W8×24 wide flange A36 steel beam acting compositely with a 0.114 m thick by 0.71 m wide reinforced concrete slab, were first loaded past yield of the tension flange to simulate severe service distress. The damaged specimens were then repaired using 3.65 m lengths of 2 or 5 mm thick CFRP laminates bonded to the tension flange and tested to failure. The results indicated significant ultimate strength gains but more modest improvement in the elastic response. Non-linear finite element analyses were in good agreement with the experimental results. The study suggests that it is feasible to strengthen steel composite members using CFRP laminates.     

Strengthening of a bridge pier capbeam using bonded FRP composite plates

Application of fiber reinforced polymer (FRP) composite plates to strengthen the capbeam of Pier 3 of East Church Street Bridge in Chemung County, New York, is discussed in this paper. Addition of a concrete wearing surface and a median barrier to the bridge superstructure increased dead load, contributing to deficiencies in moment and shear capacities of the capbeam structure. As a result, the concrete capbeam suffered flexural and shear cracking, and was considered for strengthening using bonded FRP composite plates. Service load tests were performed before and after the plates were installed, to investigate effectiveness of the strengthening system. Installation of the plates and results from the performed load tests related to flexural behavior of the beam are discussed in the paper.     

Reliability-based failure cause assessment of collapsed bridge during construction

Until now, in many forensic reports, the failure cause assessments are usually carried out by a deterministic approach so far. However, it may be possible for the forensic investigation to lead to unreasonable results far from the real collapse scenario, because the deterministic approach does not systematically take into account any information on the uncertainties involved in the failures of structures.Reliability-based failure cause assessment (reliability-based forensic engineering) methodology is developed which can incorporate the uncertainties involved in structural failures and structures, and to apply them to the collapsed bridge in order to identify the most critical failure scenario and find the cause that triggered the bridge collapse. Moreover, to save the time and cost of evaluation, an algorithm of automated event tree analysis (ETA) is proposed and possible to automatically calculate the failure probabilities of the failure events and the occurrence probabilities of failure scenarios. Also, for reliability analysis, uncertainties are estimated more reasonably by using the Bayesian approach based on the experimental laboratory testing data in the forensic report. For the applicability, the proposed approach is applied to the Hang-ju Grand Bridge, which collapsed during construction, and compared with deterministic approach.     

循环荷载作用下钢桥面铺装疲劳损伤失效行为研究

针对钢桥面铺装工程中普遍采用的改性沥青(Stone Matrix Asphalt,SMA)、浇筑式沥青(Guss asphalt,GA)、环氧沥青(Epoxy asphalt,EP)混合料双层铺装结构,进行了循环车载作用下钢桥面与沥青混凝土铺装疲劳损伤特性理论分析与试验研究。基于疲劳损伤度,研究了钢桥面铺装疲劳损伤失效行为和疲劳开裂过程中损伤场、应力和应变场动态演变机制,推导出疲劳失效时的损伤场、应力和应变场计算表达式,并给出钢桥面铺装疲劳寿命理论公式。以三座钢箱梁桥桥面铺装(润扬长江大桥2005,南京长江三桥2005,苏通大桥2008)为例,对不同铺装结构组合方案下的复合梁进行疲劳试验分析和使用寿命理论预测。实例研究结果表明,钢桥面铺装疲劳损伤失效行为预估模型合理可行;相较于改性沥青、浇筑式沥青,环氧沥青混合料具有较强高的强度低变形能力,更适合于大跨径钢桥面铺装抗疲劳的设计要求;由环氧沥青混合料组合而成的“双层环氧沥青混凝土”和“浇注式沥青混凝土(下层)+环氧沥青混凝土(上层)”的抗疲劳性能优于其它沥青混合料铺装结构组合方案,同等厚度组合情况下疲劳使用寿命可延长1倍~2倍以上;“双层环氧沥青混凝土”已应用于润扬长江大桥、南京长江三桥和苏通长江大桥钢桥面工程,并已成功运行10年以上,其跟踪观测结果良好。     

A comparative study of different fatigue failure assessments of welded bridge details

Five different welded joints frequently used in steel bridges have been selected to investigate the accuracy and applicability of three fatigue assessment methods. The first method, also categorised as the global method, is the nominal stress method, while the more advanced methods are the hot spot and the effective notch stress methods. Solid element based finite element models for welded bridge details were created by following the modelling requirements of each fatigue assessment method. A statistical evaluation based on the results of the finite element analyses and the fatigue test data collected from the literature was performed to determine the mean and characteristic fatigue strength. In addition, the standard deviation for each data series was also determined to conclude how well each method describes the fatigue strength of each welded detail. A method with a lower standard deviation is regarded as more accurate. Moreover, the evaluated results from each method were compared with the recommended fatigue strength values in the Eurocode 3 (EN 1993-1-9:2005) and IIW codes. In the light of the test results in this study, it appears that the codes are in reasonable agreement with the test data, even though a few examples of the opposite occurred. The conclusion based on the revised results in this article indicates that the nominal stress method yields satisfactory results, despite its simplicity. When considering the effort involved in creating FE models for numerical analysis, it seems clear that the choice of the nominal method is fairly acceptable.     

Strengthening of a reinforced concrete bridge with externally bonded steel reinforced polymer (SRP)

This paper introduces steel reinforced polymer (SRP) as a way to strengthen civil structures. This technique consists of cords formed by interwoven high-strength steel wires embedded within a polymeric resin. A comprehensive study addressing analysis, design, installation, load rating and monitoring of a bridge strengthened with this technology is reported. The SRP system was easily installed, demonstrating its similarity to more traditional fiber reinforced polymer (FRP) strengthening techniques. Load tests were performed to evaluate the bridge structural behavior prior and after the strengthening in accordance with AASHTO specifications, showing that the rehabilitation performed as predicted and therefore created the possibility to remove the bridge load posting.     

Reliability-based fatigue failure analysis for causes assessment of a collapsed steel truss bridge

This paper is intended to demonstrate conventional and reliability-based approaches to the collapse cause assessment in order to identify the effects of mis-installed bracket and H-beam members on the collapse of a steel truss bridge over the Han river in Korea only 15 years after opening to traffic. Based on extensive numerical investigations with parametric studies on various possible failure causes in terms of failure probability and expected fatigue life, it has been found that the mis-installation of bracket and H-beam members accelerated the fatigue failure of the vertical pin-connected hanger. Moreover, it may be observed that both the conventional and reliability-based S-N and linear elastic fracture mechanisms (LEFM) approaches in terms of the expected fatigue life and the fatigue failure probability provide about similar and compatible results. This indicates that any of the reliability approaches could be used as effective and rational techniques for the quantitative investigation of the complex collapse causes, together with the aids of conventional S-N/LEFM fatigue analysis.     

Optimised design of mandrels after fatigue failure

The drive shaft of a steel mandrel used in the production of glass-fibre-reinforced composite cylinders had failed in service. A fractographic analysis revealed that the shaft had failed by rotation-bending fatigue in the welded region where the shaft was attached to the flange. Subsequent non-destructive testing (NDT) of the remaining mandrels still in service showed that approximately half of these were cracked in the same region. It was only a question of time before these mandrels failed too, posing a severe safety hazard and resulting in production down-time.Fatigue life calculations showed that even with material properties within specification and flawlessly executed welds, the stresses in the welds were above the fatigue limit and failure during operation was to be expected. Thus, the design of the shafts had to be modified to reduce the operational stresses below the fatigue limit.The operational loads were measured by means of strain gauges during a full production cycle, including the loading and unloading of the mandrel, and the revolutions about its own axis during winding. The data showed that peak stresses due to dynamic shock loads of up to 1.3 times the quasi-static stress needed to be taken into account.Optimisation of the design was complicated by the highly constrained space within the machine. However, by moving the weld out of the most highly stressed region and increasing the fillet radius, the local stresses could be sufficiently reduced, as was verified by FEM and analytical stress assessment.The new weld was not trivial to produce and several iterations of weld trials were required to achieve a sound weld. Since some imperfections are permitted in a standard quality weld and must be expected for this type of weld, it had be shown by fracture mechanics that the new design remains crack-free throughout its service life and that inspections are not necessary to guarantee safety.     

A nonlinear CDM model for ductile failure analysis of steel bridge columns under cyclic loading

A nonlinear cyclic plasticity damage model for ductile metals, which is able to take large deformation effects into consideration, has been developed using a new damage dissipation potential formulation in order to predict the cyclic inelastic behavior of steel bridge piers. The cyclic constitutive equations that employ the combined isotropic–kinematic hardening rule for plastic deformation is incorporated into the damage mechanics in conjunction with the large strain formulation. The damage growth law is based on the experimental observations that the evolution of microvoids results in nonlinear damage accumulation with plastic deformation. The damage model parameters and the procedure for their identification are presented. The proposed model has been validated and successfully applied to thin-walled steel bridge tubular columns subjected to alternating lateral displacements to evaluate the seismic performance.     

High-cycle fatigue failure of low-carbon steel after long-term aging

The characteristics of nucleation and development of fatigue cracks under high-cycle loading of plane samples of low-carbon steel are studied after its natural aging for 15 years. Cumulative distributions of the number of microcracks with respect to their length are constructed and the fracture microrelief is studied. It is found that the fatigue strength of the steel decreases considerably in the high-cycle region (>10⁷ cycles) at a stress less than the fatigue strength.     

Nonlinear static cyclic pushover analysis for flexural failure of reinforced concrete bridge columns with combined damage mechanisms

In a fixed connection of a reinforced concrete bridge column, experiments have shown that the longitudinal reinforcing bars slip at the interface of the connection under cyclic seismic loading. The bond-slip (or strain penetration) of the longitudinal reinforcing bars causes a pinching effect in the column’s hysteresis curve. The bond-slip (or strain penetration) reduces the column’s stiffness and increases its deformations during an earthquake event, significantly affecting the performance of the column. Significant strength degradation has also been observed after the column reaches its ultimate strength. This study is to model a reinforced concrete column’s performance under cyclic pushover analysis with combined damage mechanisms including concrete cracking, concrete strength degradation due to concrete spalling, longitudinal reinforcing bars buckling, and bond-slip between longitudinal reinforcing bars and concrete. Two multi-scale nonlinear finite element models with and without the bond-slip (or strain penetration) of a reinforced concrete bridge column are proposed. The simulated column’s hysteresis curves under nonlinear cyclic pushover are compared with available experimental data. The results show that the proposed models with bond-slip together with combined damage mechanisms can effectively predict the seismically induced flexural failure behavior of the reinforced concrete bridge columns.     

空分设备全线停电后的应对措施

针对近期因电网故障造成两套40000 m3/h空分设备和两套20000 m3/h空分设备区域先后发生全线停电事故,采取一系列切实可靠的处理措施,从空分系统关键操作项、设备防冻等方面着手,保证设备的安全。详细介绍在空分系统、空气净化系统、空气压缩系统和产品压缩系统,以及电气、仪表等方面所采取的应对措施。     

考虑桥面随机不平顺的桥梁动态响应研究

基于随机振动理论研究了桥面不平顺影响下,车桥耦合振动作用时的中小桥梁动态响应曲线。通过建立车桥耦合振动方程,基于虚拟激励法对重力引起的确定性激励和桥面不平顺引起的随机激励求解,得到了桥梁跨中挠度和应力响应的均值和标准差。运用 法则定义随机激励的确定值值域,分析了桥梁跨中位移和应力响应在不同车速和桥面不平顺等级作用下的特性,并讨论了动态响应曲线与准静态影响线的差异。结果表明：桥梁跨中挠度和应力标准差受车速和桥面不平顺等级变化的影响很大;桥梁动态响应值域范围很大,具有较强的随机性;相比准静态影响线,动态响应曲线更能体现车桥之间激励的耦合随机作用。     

Numerical life estimation after fatigue failure of a complex component

Failure of a large ethylene‐reciprocating compressor was found to be due to fatigue growth of cracks in the crosshead of one of the cylinders, initiated at material defects near stress raisers. Total fatigue crack growth time was required in order to identify the cause of the failure. The applied stress field near the initiation sites and along fatigue path was estimated using FEM. The stresses were found to vary steeply and become partly compressive along a large part of the fatigue crack path. A weight function based on numerical method was developed, which was able to predict exactly the shape of the crack front during propagation. Fatigue crack initiation was traced to a disassembly 6 months before final failure. This failure was found to be jointly the result of non‐conformities in manufacture and maintenance.     

Performance of a fiber reinforced polymer web core skew bridge superstructure. Part II: failure modes and parametric study

A finite element model, validated using field test data, has been developed to study the structural behavior of a fiber reinforced polymer (FRP) web core skew bridge superstructure. The failure modes are considered in this second part of a two-part paper. The multi-step finite element analysis is performed to study the structural strength failure based on the Tsai-Hill theory. Moreover, the shear transfer capacity and the local buckling behavior of the bridge superstructure are investigated. Using the finite element model, a parametric study is considered to assess the contributions of the individual structural components to the structural behavior. Parameters including the integral parapet, web thickness, and configuration are considered. This parametric study revealed several possible design improvements to this kind of FRP bridge construction.     

Importance of early dialysis for acute renal failure after an open-heart surgery

Coronary artery disease is a major cause of death in patients with a renal dysfunction. Among the patients who undergo coronary artery bypass grafting, renal dysfunction is known to be a major predictor of in-hospital and out-of-hospital mortality. From 2004 to 2007, we performed elective open-heart surgeries on 2380 patients in whom there was no primary renal failure. Of those patients, only 185 in whom acute renal failure (ARF) was developed were included in the study. The patients were divided into 2 groups: a late dialysis group (n=90) and an early dialysis group (n=95). The mean age of the patients was 62.3±6.4 in the late dialysis group and 64.5±5.2 in the early dialysis group. There were 32 female and 58 male patients in the late dialysis group and 36 female and 59 male patients in the early dialysis group. Acute renal failure developed only in 185 patients out of 2380 open-heart surgery patients. The overall mortality in the 2380 open-heart surgery patients was 1.97%. Mortality among the ARF patients was 5.9%. However, there was no significant difference in hospital mortality between the 2 groups. Major complications, such as postoperative pneumonia, prolonged ventilation time, arrhythmia, the number of times postoperative hemodialysis was performed, development of chronic renal failure, time spent in the intensive care unit and the period of hospitalization, sepsis, and low cardiac output, were significantly higher in the late dialysis group. There was no difference in mortality between the 2 groups. Early dialysis for open-heart surgery patients who develop ARF postoperatively does not decrease mortality. However, it decreases morbidity, the amount of time spent in intensive care, and the period of hospitalization and thus reduces patient costs.     

Strengthening of cement foams

Lightweight cellular concretes are attractive building materials for a number of reasons: they offer a unique combination of moderate thermal insulation and stiffness, low cost and incombustibility. They have relatively low strength, however, and are brittle. In this paper we describe the behaviour of composite cement/polystyrene foams with improved strength and ductility.     

桥头引道沉降对简支梁冲击效应的影响分析

摘 要：针对旧桥中经常出现的桥头引道及伸缩缝破损情况,考虑接缝处沉降差引起的桥头跳车对桥梁振动的影响,提出与错台高度相关的桥头衔接状况五个等级划分标准。以我国常见的中小跨径简支梁为对象,基于五参数车辆模型的车桥耦合系统运动方程,用Newmark法进行数值求解,分析桥头引道沉降差对桥梁振动的影响。研究表明随着沉降差增加,汽车对桥梁的冲击效应明显变大,且随着车速的增大,冲击效应变大。沉降差在桥梁中产生的动力放大系数随着跨径增大而减小。另外,桥头沉降差使车辆竖向加速度瞬时变大,其绝对值随着错台高度的增加而迅速增大,该加速度变化与桥梁跨径无关。