Hybrid intelligent inference model for enhancing prediction accuracy of scour depth around bridge piers

Bridge-pier scouring is a main cause of bridge failures. Thus, accurately predicting the scour depth around bridge piers is critical, both to specify adequate depths for new bridge foundations and to assess/monitor the safety of existing bridges. This study proposes a novel artificial intelligence (AI) model, the intelligent fuzzy radial basis function neural network inference model (IFRIM), to estimate future scour depth around bridge piers. IFRIM is a hybrid of the radial basis function neural network (RBFNN), fuzzy logic (FL), and the artificial bee Cclony (ABC) algorithm. In the IFRIM, FL is used to handle the uncertainties in input information, RBFNN is used to handle the fuzzy input–output mapping relationships, and the ABC search engine employs optimisation to identify the most suitable tuning parameters for RBFNN and FL based on minimal error estimation. A 10-fold cross-validation method finds that the IFRIM model achieves at least 21% and 14.5% reductions in root mean square error and mean absolute error values, respectively, compared with other AI techniques. Study results support the IFRIM as a promising new tool for civil engineers to predict future scour depth around bridge piers.     

Particle swarm optimization model to predict scour depth around a bridge pier

Scour depth around bridge piers plays a vital role in the safety and stability of the bridges. The former approaches used in the prediction of scour depth are based on regression models or black box models in which the first one lacks enough accuracy while the later one does not provide a clear mathematical expression to easily employ it for other situations or cases. Therefore, this paper aims to develop new equations using particle swarm optimization as a metaheuristic approach to predict scour depth around bridge piers. To improve the efficiency of the proposed model, individual equations are derived for laboratory and field data. Moreover, sensitivity analysis is conducted to achieve the most effective parameters in the estimation of scour depth for both experimental and filed data sets. Comparing the results of the proposed model with those of existing regression-based equations reveal the superiority of the proposed method in terms of accuracy and uncertainty. Moreover, the ratio of pier width to flow depth and ratio of d50 (mean particle diameter) to flow depth for the laboratory and field data were recognized as the most effective parameters, respectively. The derived equations can be used as a suitable proxy to estimate scour depth in both experimental and prototype scales.     

Significance of non-uniform scour on the seismic performance of bridges

Multiple hazards such as flood-induced scour followed by earthquakes can adversely impact the performance of bridges spanning over waterways. Scour is the erosion of soil around the foundation of bridges, which can result in loss of the structure’s lateral support and possible failure. The impact is specifically amplified when a flood event resulting in the development of a scour hole is followed by an earthquake event. Recent inspections have shown a non-uniformity in the scour depths at bridge foundations with multiple piers. More specifically, the upstream and downstream pier foundations are exposed to notably different scour depths. However, the practice falls short in capturing this effect as commonly, a uniform scour depth is assumed at all bridge foundations in the water stream when evaluating the lateral stability of the structure. A comparative case is used to identify the unintended consequences of uniform local scour depth assumption for bridges with multiple columns in the direction of flow. This analysis considers bridges with both uniform and non-uniform scour depth at the support foundations. The effects of variable scour depths on the behaviour of bridge components are evaluated by tracking the demand redistribution as the scour depth changes. The results help to understand the performance of bridges crossing waterways when they are subjected to multi-hazard effects from flood-induced scour and earthquakes.     

规则型隔震桥梁结构的简化分析方法

由于桥墩的质量与上部结构的质量相比通常是比较小的,各桥墩高度和截面大致相同的连续桥梁可以简化为单自由度体系进行抗震设计.当在桥面大梁与桥墩之间设置隔震橡胶支座时,上述规则型桥梁可以看作串连型双自由度体系.文中根据桥墩的水平刚度远大于橡胶支座的水平刚度和上部结构的质量甚大于桥墩的特点推导了此双自由度体系的自振特性(包括自振周期、振型、地震作用的振型参与系数和振型阻尼比)的简化计算公式.这些公式可以方便地应用于隔震桥梁的抗震设计.此外,文中还分析了这些简化公式的计算精度与双自由度体系质量比和刚度比的关系.精度分析和数字实例的计算结果表明,文中提供的公式具有足够的精度.     

古交矿区某公路桥冲刷计算

对古交矿区汽车队一座跨屯兰河公路桥的冲刷进行了比较计算 ,阐述了设计水位和冲刷深度的计算过程 ,为桥墩台基础的安全埋深提供了可靠的依据     

Alluvial channel hydrodynamics around tandem piers with downward seepage

In this paper, we report the turbulent flow structures and the scour geometry around two piers with different diameters. An experiment was conducted on a non-uniform sand bed with two types of tandem arrangements, namely, pier (T1) with a 75 mm front and 90 mm rear, and pier (T2) with a 90 mm front and 75 mm rear, with and without-seepage flows, respectively. A strong wake region was observed behind the piers, but the vortex strength diminished with downward seepage. Streamwise velocity was found to be maximum near the bed downstream of the piers and at the edge of the scour hole upstream of the piers. Quadrant analysis was used to recognize the susceptible region for sediment entrainment and deposition. Upstream of the piers near the bed, the moments, turbulent kinetic energy (TKE), and TKE fluxes were found to decrease with downward seepage, in contrast to those in a plane mobile bed without piers. The reduction percentages of scour depth at the rear pier compared with the front one were approximately 40% for T1 and 60% for T2. Downward seepage also resulted in restrained growth of scouring with time.     

Image‐based crack assessment of bridge piers using unmanned aerial vehicles and three‐dimensional scene reconstruction

Crack assessment of bridge piers using unmanned aerial vehicles (UAVs) eliminates unsafe factors of manual inspection and provides a potential way for the maintenance of transportation infrastructures. However, the implementation of UAV‐based crack assessment for real bridge piers is hindered by several key issues, including the following: (a) both perspective distortion and the geometry distortion by nonflat structural surfaces usually appear on crack images taken by the UAV system from the pier surface; however, these two kinds of distortions are difficult to correct at the same time; and (b) the crack image taken by a close‐range inspection flight UAV system is partially imaged, containing only a small part of the entire surface of the pier, and thereby hinders crack localization. In this paper, a new image‐based crack assessment methodology for bridge piers using UAV and three‐dimensional (3D) scene reconstruction is proposed. First, the data acquisition of UAV‐based crack assessment is discussed, and the UAV flight path and photography strategy for bridge pier assessment are proposed. Second, image‐based crack detection and 3D reconstruction are conducted to obtain crack width feature pair sequences and 3D surface models, respectively. Third, a new method of projecting cracks onto a meshed 3D surface triangular model is proposed, which can correct both the perspective distortion and geometry distortion by nonflat structural surfaces, and realize the crack localization. Field test investigations of crack assessment of a real bridge pier using a UAV are carried out for illustration, validation, and error analysis of the proposed methodology.     

桥墩自振频率的能量公式

采用瑞利法,导出了计算浅平基桥墩、桩基桥墩及沉井基础桥墩基频的近似公式。在形函数中,将桥墩的总变形分解为墩身的弹性变形与基础平、转动所产生的刚体位移之和。墩身的形函数采用简单的三次多项式。由地基变形所引起的刚体位移用线性函数表示。地基变形由平动、转动及平转动耦合弹簧表示。本文所导出的计算公式具有物理意义明确、计算简单、精度高等优点,除适用于各种基础类型桥墩外,也适用于烟囱及水塔等构筑物。     

An investigation of water-flow pressure distribution on bridge piers under flood loading

This study simulates the flood effect on piers using a finite volume method in the ANSYS-FLUENT package. The pier is modelled as a non-structural column with a rectangular and a circular cross-section. To simplify the methodology, the pier, as well as the bed and side walls, is assumed to have non-slip boundaries for the fluid domain. A crucial feature of this investigation is the consideration of the effect of water while it is flowing around an object like a bridge pier and the distribution of pressure along the pier height. A numerical model is proposed to explore the influence of variation of velocity on the hydrodynamic force and pressure distribution exerted on piers. A significant finding is that the shape of the pier cross-section has a significant effect on the fluid pressure exerted on bridge piers under flood loading. It is noted that the AS5100 method is appropriate for a conservative estimation of the pressure on rectangular piers, whereas the technique will have a risky safety margin for bridge piers with a circular cross-section and need to be used with caution.     

内侧钢筋不连接的预制空心桥墩设计

采用空心的预制桥墩能够减轻预制结构重量。以某示范工程为例,提出不制作实体连接段、且内侧钢筋不连接的预制空心桥墩方案。制作7组试验模型,开展试验分析。结果表明,空心墩柱破坏承载能力和开裂弯矩与现浇实心墩较为接近,并且现有规范公式可用于墩柱的设计。以试验结果为依据,提出设计思路,开展示范工程预制空心桥墩方案设计。     

界限为随机过程的工程结构时变动力可靠度

基于结构时变抗力的统计特性 ,提出了考虑时变抗力瞬变衰减的一个随机过程界限 ,并推导了基于这种随机过程界限的时变动力可靠性计算基本公式 ;给出了非平稳过程线性组合的首次超越动力可靠度的一个有效数值计算方法。算例的结果表明 ,考虑时变抗力瞬变衰减时 ,动力可靠性随动荷载的持续时间迅速下降     

弹性约束高墩的稳定性分析

实际工程中桥梁上部结构的约束对桥墩的稳定计算具有不可忽略的作用,从能量原理出发,推导出了考虑墩顶受桥梁弹性约束的高墩失稳临界力的计算公式,并建立有限元模型验证了公式的正确性,同时分析了墩顶约束刚度、墩高和桥墩直径对高墩稳定性的影响。该公式计算简单,精确度高,能满足工程需要,可为设计人员提供参考。     

考虑冲刷深度变化的桩基小型振动台试验研究

岷江3号桥遭遇2008年“5.12”8级强烈地震,又面临令人震撼的严重冲刷。为了弄清楚该桥实际工况,按照实际桥梁墩桩的1:20模型,采用小型振动台试验的方法,分析在不同冲刷深度、不同地震波作用下桥梁墩桩的抗震性能。试验结果表明:模型桩基冲刷深度在15 cm(相当于桩长1/8)左右时,桩顶弯矩、轴力达到最大值;随着冲刷深度的加大桩身弯矩也随之增大,桩身最大弯矩位置(即最不利位置)随之下移,墩顶弯矩不变而墩底弯矩逐渐减小。岷江3号桥存在继续加剧冲刷的趋势,桩基承载力将继续下降,抗震性能将逐渐降低,需要进行墩桩加固。研究可为强震区受严重冲刷桥梁的抗震设计与加固提供参考依据,对类似工程有较强的借鉴意义。     

Seismic performance of new-type box steel bridge piers with embedded energy-dissipating shell plates under tri-directional seismic coupling action

Accurate numerical models are necessary to evaluate the seismic performance and load-bearing mechanism of new-type box steel bridge piers with embedded energy-dissipating shell plates under tri-directional seismic coupling action. Numerical simulations of seismic performance under six types of tri-directional seismic coupling action was conducted. The effects of this stress on the seismic performance of the new-type steel bridge piers was evaluated through analysis of damage mode, hysteresis curve, skeleton curve, stiffness and strength degradation characteristic, and energy-dissipating capacity. This study also compared the numerical analysis with experimental results in order to validate the accuracy of the proposed finite element model. Based on this model, the range of relevant parameters expanded and 88 numerical specimens were analysed for seismic performance, producing further information about the influence of thickness and curvature of the embedded shell plate, spacing of transverse stiffening ribs of the shell, axial compression ratio, and slenderness ratio. Results showed that tri-directional seismic coupling action significantly affects the specimen’s deformation capacity; the embedded shell plate effectively improves the piers’ load-carrying and deformation capacity; and the thickness of the embedded shell plate, width-to-thickness ratio of the wall plate, axial compression ratio, and slenderness ratio significantly affect the seismic performance of the new-type steel bridge piers. To promote the ease of seismic design of new-type box steel bridge piers, this study used theoretical analysis and numerical simulation to calculate equations for the minimum height of the energy-dissipating zone of the bottom embedded shell plate. Finally, formulas were also established to calculate the relevant stability bearing capacity and displacement ductility factor of the new-type steel bridge piers under tri-directional seismic coupling action in order to improve their seismic design.     

大跨度斜拉桥边墩新型横向钢阻尼器减震体系及设计方法

针对大跨度斜拉桥边墩的横向抗震问题,提出桥梁新型横向钢阻尼器与滑动支座组合的一种边墩横向减震体系,以及基于桥梁实际抗震需求的减震 体系设计方法。之后,以一座主跨620m的大跨度斜拉桥为工程背景,验证该方法的可行性。并从关键位置的地震反应、阻尼器对横向基本控制振型的影响、 减震体系的耗能能力和地震动输入的影响等方面对边墩新型横向减震体系的减震效果进行全面分析。结果表明,大跨度斜拉桥边墩新型减震体系具有显著的 减震效果;与常规体系相比,对地震动输入较不敏感。     

基底摇摆隔震桥墩振动台试验与数值模拟研究

为了研究不同构造形式的基底摇摆隔震桥墩在不同水准地震作用下的响应规律和抗震性能，提出了设置高阻尼橡胶垫块和线性弹簧的两种基底摇摆隔震桥墩模型。通过振动台试验和数值模拟，对两种摇摆隔震桥墩的地震响应规律和抗震性能进行了对比研究。结果表明：两种基底摇摆隔震桥墩在不同水准地震作用后，桥墩均没有出现严重的破坏，其破坏特征主要表现为限位钢板的弯曲变形和提离约束部件的移位，桥墩呈现出良好的抗震性能；两种基底摇摆隔震桥墩相对于传统桥墩能够显著降低墩顶加速度和墩底应变响应，但墩顶水平位移响应也会相应增加，在摇摆隔震桥墩的设计上，应将墩顶水平位移作为主要设计参数；提出了两种基底摇摆隔震桥墩改进的Winkler两弹簧数值计算模型，通过与振动台试验结果对比，证明了该模型能够较好地模拟两种基底摇摆隔震桥墩的摇摆行为及其地震响应规律。     

Impact protection of bridge piers against rockfall

The Dujiangyan-Wenchuan highway serves as a vital passage to and from the region severely damaged by the 5.12 Wenchuan Earthquake in China. Chediguan Bridge is located on the highway and spans the Minjiang River. During the earthquake, the bridge was severely destroyed by rockfalls. Although the bridge was subsequently rebuilt and opened to traffic on May 12, 2009, it was destroyed again on July 25, 2009 by rock avalanches that had been located perilously high on the right bank of the Minjiang River, and caused deaths, casualties, and roads being cut off. A subsequent investigation revealed multiple perilous rocky areas on the massif along the Minjiang river bank, indicating an extremely high risk of another rockfall hazard, which could, again, lead to damage to the bridge and a further disastrous outcome. To mitigate the rockfall hazard to the bridge, a new flexible, energy-dissipating crashworthy device for bridge piers is developed to withstand the impact of rockfall. Numerical simulations using nonlinear finite element analysis was carried out to simulate the rockfall impact process on bridge piers. The following influencing factors during the impact process were taken into account: material nonlinearity, geometric nonlinearity, as well as contact nonlinearity. The results show that the new protective structure of bridge piers can effectively buffer rockfall impacts and significantly improve the anti-impact capability of the bridge piers.

     

结合施工图审查对桥梁墩柱与桩连接构造的讨论

本文首先综合陈述了桥梁墩柱与钻孔桩连接构造的几种型式,包括:现浇混凝土墩柱和桩主筋焊接;现浇混凝土墩柱与桩主筋搭接、钢管混凝土墩柱与桩连接,以及预制墩柱与桩杯口连接等。其中指出了每一种连接构造中的要点及设计中应该注意的问题。然后,由于桥梁规范对墩柱和桩杯口连接型式的设计构造论述很少,故着重介绍了这种连接型式并较详细地叙述了其受力原理。在此基础上,提出了杯口配筋计算公式及柱子插入杯口深度计算公式等等。为了方便理解"定量"的概念,对每一种连接方式都列举了一个计算例题。     

预制拼装桥墩地震易损性分析

为研究灌浆波纹管连接和带榫头的灌浆波纹管连接两种预制拼装桥墩的抗震性能并对其在地震作用下的易损性进行评估,根据预制拼装桥墩墩底接缝的特点,通过拟静力试验研究,以墩顶漂移率为损伤指标,对其不同的损伤破坏状态进行描述,并确定了对应不同破坏等级的损伤量化指标限值Dcr、Dcy、Dcm和Dcu。采用有限元软件对现浇及预制拼装桥墩进行不同地震作用下的时程分析并建立概率地震需求模型,对其易损性进行评估,并通过改变轴压比、纵筋配筋率,来进一步研究这些参数对预制拼装桥墩易损性的影响。结果表明：虽然预制拼装桥墩与现浇桥墩大部分的破坏形式都为弯曲破坏,但是损伤状态因为接缝而存在差异;采用波纹管连接的预制拼装桥墩与现浇桥墩的地震易损性差别不大,抗震性能基本一致;有榫头构造的预制拼装桥墩在各级地震作用下发生四种损伤破坏的概率最低,这种构造形式的抗震性能优于平面接缝的预制拼装桥墩;轴压比、纵筋配筋率这两种参数对桥墩的易损性影响较大,随着轴压比的增大或配筋率的减小,桥墩的损伤概率增大。