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.

Explosion resistance performance of reinforced concrete box girder coated with polyurea:Model test and numerical simulation

To study the anti-explosion protection effect of polyurea coating on reinforced concrete box girder,two segmental girder specimens were made at a scale of 1:3,numbered as G(without polyurea coating)and PCG(with polyurea coating).The failure characteristics and dynamic responses of the specimens were compared through conducting explosion tests.The reliability of the numerical simulation using LS-DYNA software was verified by the test results.The effects of different scaled distances,reinforcement ratios,concrete strengths,coating thicknesses and ranges of polyurea were studied.The results show that the polyurea coating can effectively enhance the anti-explosion performance of the girder.The top plate of middle chamber in specimen G forms an elliptical penetrating hole,while that in specimen PCG only shows a very slight local dent.The peak vertical displacement and residual displacement of PCG decrease by 74.8% and 73.7%,respectively,compared with those of specimen G.For the TNT explosion with small equivalent,the polyurea coating has a more significant protective effect on reducing the size of fracture.With the increase of TNT equivalent,the protective effect of polyurea on reducing girder displacement becomes more significant.The optimal reinforcement ratio,concrete strength,thickness and range of polyurea coating were also drawn.

Fatigue Crack Propagation Law of Corroded Steel Box Girders in Long Span Bridges

In order to investigate the fatigue performance of orthotropic anisotropic steel bridge decks,this study realizes the simulation of the welding process through elastic-plastic finite element theory,thermal-structural sequential coupling,and the birth-death element method.The simulated welding residual stresses are introduced into the multiscale finite element model of the bridge as the initial stress.Furthermore,the study explores the impact of residual stress on crack propagation in the fatigue-vulnerable components of the corroded steel box girder.The results indicate that fatigue cracks at the weld toe of the top deck,the weld root of the top deck,and the opening of the transverse diaphragm will not propagate under the action of a standard vehicle load.However,the inclusion of residual stress leads to the propagation of these cracks.When considering residual stress,the fatigue crack propagation paths at the weld toe of the transverse diaphragm and the U-rib weld toe align with those observed in actual bridges.In the absence of residual stress,the cracks at the toe of the transverse diaphragm with a 15%mass loss rate are categorized as type I cracks.Conversely,when residual stress is considered,these cracks become I-II composite cracks.Residual stress significantly alters the cumulative energy release rate of the three fracturemodes.Therefore,incorporating the influence of residual stress is essential when assessing the fatigue performance of corroded steel box girders in long-span bridges.

基于α-shape与SSA-XGBoost算法的无人机点云孔洞修补

针对极限梯度提升树算法在进行无人机点云孔洞修补时核心超参数难以选取、点云孔洞修补范围识别困难以及孔洞修补精度较低等问题,提出基于麻雀搜索算法优化极限梯度提升树的点云孔洞修补方法。首先利用α-shape算法进行点云的孔洞识别,在此基础上,获取点云孔洞和周围点云的位置信息并将其作为模型的输入样本。再利用麻雀搜索算法优化极限梯度提升树算法中的核心超参数,构建SSA-XGBoost点云孔洞修补模型,并将该模型应用于无人机点云孔洞的修补中。最后将SSA-XGBoost与XGBoost、BP神经网络两组算法进行预测精度的对比。实验结果表明:SSA-XGBoost模型的预测结果相较于其它两组对比算法预测精度更高,在点云孔洞修补方面具有一定的意义。

Discussion on Detection and Evaluation of Simply Supported Prestressed Concrete Small Box Girder Bridge After a Fire

The article takes a simply supported prestressed concrete small box girder bridge project as an example for inspection and evaluation after a fire incident.This includes appearance detection,concrete color hardness detection,concrete strength detection,concrete surface damage layer detection,reinforcement protective layer detection,and concrete carbonation detection.It is hoped that this analysis can be used as a reference for the detection and evaluation of future bridge projects with fire incidents to smoothen its subsequent repair and maintenance.

Evaluation of “J”-shaped Uterine Incision during Caesarean Section in Patients with Placenta Previa:A Retrospective Study

This study evaluated the efficacy and safety of ＂J＂-shaped uterine incision for caesarean section for patients diagnosed with placenta previa. A total of 55 consecutive cases of placenta previa treated in Union Hospital were retrospectively analyzed over a period of two years and 10 months. The subjects were divided into two groups with respect to the uterine incision. Twenty-four pregnant women with placenta previa who were indicated for caesarean section underwent the procedure using a new ＂J＂-shaped uterine incision and 31 pregnant women with placenta previa received caesarean section that used the traditional transverse incision. The two groups were compared in terms of operation time, estimated blood loss, infant expulsion time, exhaust time and postoperative recovery. Meanwhile, comparison was also made in neonatal clinical data between the two groups. Compared with the ＂J＂-shaped incision group, the traditional incision group had a lower Apgar scores （P〈0.05）. However, there existed no statistically significant differences in the overall time of operation and postoperative period of breaking wind （P〉0.05）. It is concluded that, with caesarean section for placenta previa patients, the ＂J＂-shaped uterine incision significantly decreases intraoperative blood loss and facilitates the fetal delivery.

Shortening turn-on delay of SiC light triggered thyristor by7-shaped thin n-base doping profile

A new 4 H–SiC light triggered thyristor（LTT） with 7-shaped thin n-base doping profile is proposed and simulated using a two-dimensional numerical method. In this new structure, the bottom region of the thin n-base has a graded doping profile to induce an accelerating electric field and compensate for the shortcoming of the double-layer thin n-base structure in transmitting injected holes. In addition, the accelerating electric field can also speed up the transmission of photongenerated carriers during light triggering. As a result, the current gain of the top pnp transistor of the SiC LTT is further increased. According to the TCAD simulations, the turn-on delay time of the SiC LTT decreases by about 91.5% compared with that of previous double-layer thin n-base SiC LTT. The minimum turn-on delay time of the SiC LTT is only 828 ns,when triggered by 100 mW/cm^2 ultraviolet light. Meanwhile, there is only a slight degradation in the forward blocking characteristic.

Sagging damage characteristics of hull girder with trapezoidal cross-section subjected to near-field underwater explosion

To investigate the overall damage characteristics and failure modes of a warship subjected to an underwater non-contact near-field explosion,a hull girder with a trapezoidal cross-section was designed,manufactured,and tested.The design criteria and parameters were determined according to the similarity criterion.Dynamic responses of the girder freely floating on water were obtained under varying conditions,including stand-off distance,charge mass,and position of attack.Damage morphologies of the girder model were obtained.Based on our analysis,basic conditions for sagging damage of the hull girder are proposed.The aim of this study was to determine an efficient method of attack resulting in the most severe damage to the ship hull.The experimental results show that the girder mainly exhibits a first-order response when the first wet frequency of the girder is close to the frequency of the explosion bubble pulsation.The largest deformation was observed when the underwater explosion occurred directly below the midspan of the girder compared to other explosions of the same intensity at different attack positions.When the ratio of stand-off to maximum bubble radius(λ)satisfies 0.7≤λ<2,the bubble mainly causes sagging damage instead of hogging.Asλdecreases(1≤λ<2),the sagging damage increases under the same charge mass.However,asλdecreases further(0.7≤λ<1),the sagging deformation decreases.This is likely due to the impact of the liquid jet formed by the collapsing bubble,which causes the girder deformation to shift from sagging back to hogging deformation.The initial shock wave excites the high-frequency response of the girder structure but contributes very little to the overall velocity and displacement.However,bubble pulsation typically causes a low-frequency response,which will affect the velocity and displacement of the girder.The low-pressure region of the flow field formed by bubble pulsation and resonant coupling between the girder and the bubble are the predominant causes of damage to the overall girder structure.

Learning curve for a surgeon in robotic pancreaticoduodenectomy through a“G”-shaped approach:A cumulative sum analysis

BACKGROUND Robotic pancreaticoduodenectomy(RPD)can achieve similar surgical results to open and PD;however,RPD has a long learning curve and operation time(OT).To address this issue,we have summarized a surgical path to shorten the surgical learning curve and OT.AIM To investigate the effective learning curve of a“G”-shaped surgical approach in RPD for patients.METHODS A total of 60 patients,who received“G”-shaped RPD(GRPD)by a single surgeon in the First Hospital of Shanxi Medical University from May 2017 to April 2020,were included in this study.The OT,demographic data,intraoperative blood loss,complications,hospitalization time,and pathological results were recorded,and the cumulative sum(CUSUM)analysis was performed to evaluate the learning curve for GRPD.RESULTS According to the CUSUM analysis,the learning curve for GRPD was grouped into two phases:The early and late phases.The OT was 480±81.65 min vs 331±76.54 min,hospitalization time was 22±4.53 d vs 17±6.08 d,and blood loss was 308±54.78 mL vs 169.2±35.33 mL in the respective groups.Complications,including pancreatic fistula,bile leakage,reoperation rate,postoperative death,and delayed gastric emptying,were significantly decreased after this surgical technique.CONCLUSION GRPD can improve the learning curve and operative time,providing a new method for shortening the RPD learning curve.

A Novel Open C-shaped Molar Band for Orthodontic Applications： Mechanical Characterizations and Clinical Trials

To evaluate the retention properties of the novel ‘C＇-shaped molar bands at a laboratory level. Resin-modified glass ionomer cement（RMGIC） was used as a luting agent for the novel C-shaped molar band. The mechanical properties of the band were examined and the retention performance was characterized in the mesial, distal and vertical directions. A clinical trial was conducted using a spilt-mouth design on 50 patients. The novel C-shaped molar bands fit most molars without a repeated try-in process.The use of both nanoHA coating and RMGIC enhanced the tensile（8.00 ± 1.8 MPa） and shear strengths（27.17 ± 8.6 MPa） of the molar bands, leading to high retention in vertical, mesial and distal directions（ p 〈 0.001）. In clinical trials, the C-shaped molar bands had a failure rate（15%） comparable to that of traditional bands, and 93% of the failed bands demonstrated an adhesive remnant index score of 0, corroborating the observation that no luting agent residue remained on the tooth surface in most cases. The novel C-shaped molar bands appear to be a promising appliance that requires further clinical investigations, and may be used effectively in orthodontics.

预应力UHPC槽形节段与整体式混凝土板组合梁受剪性能

将预制的UHPC槽形节段通过干缝连接和预应力张拉形成槽形梁,再与整体现浇的混凝土板组合成的组合梁,称为预应力UHPC槽形节段与整体式混凝土板组合梁(PUCS-MCS组合梁)。它是一种能充分发挥不同材料的性能、施工方便且整体性能好的新型桥梁结构。为探究其抗剪性能,开展了9根模型梁的试验。分析了接缝数、接缝处剪力键数、剪跨比、UHPC钢纤维体积率、配箍率和纵筋率等参数对试件变形、破坏模式、抗剪承载力的影响;基于试验研究结果,提出了PUCS-MCS组合梁抗剪承载力计算方法。结果表明:PUCS-MCS组合梁均为剪压破坏,所有梁在开裂前的荷载-挠度曲线差异不大,在开裂后刚度不断下降;PUCS-MCS组合梁的抗剪承载力随接缝处剪力键数、UHPC钢纤维掺量、配箍率和纵筋率的增大而增大,随干接缝数量增加和剪跨比的增大而减小,其中影响最显著的是干接缝和剪力键,影响最小的是钢纤维掺量和配箍率,因此PUCS-MCS组合梁可不配箍筋,并可采用较低钢纤维掺量的UHPC。

Overview of Design and Construction Points Analysis for the Rotating Continuous Girder Bridge

With the advancement of the economy,the construction of roads and bridges has assumed a crucial role in the development of China’s highway transportation system.The interplay between the design and construction technologies of road bridges is pivotal,as it directly impacts the subsequent operation and maintenance phases.Although the design and construction techniques for continuous girder transitions have been progressively improving,challenges still persist.This paper takes the example of the continuous girder design for the T-structure(75 m+75 m)of the Xintai Highway Crossing Yanzhou-Shijiusuo Railway Separation Interchange Project and delves into an analysis of the structural design calculations for the bridge transition,the transition structure’s design,and critical considerations during construction.The findings presented here can serve as a valuable reference for similar project designs.

Key Technology and Complete-set Equipment for Intelligent Construction of HSR Simply-supported Girder Reinforcement Framework

In view of the problems such as backward production mode,poor quality stability,high safety risk and incomplete control system during erection of the reinforcement framework of simply-supported box girders for high-speed railway(HSR),and in combination with the key points and main challenges in the reinforcement framework construction of Guangzhou-Zhanjiang HSR,the overall technical route for the intelligent manufacturing of reinforcement framework of simply-supported box girders is put forward.The component design of reinforcement framework of simply supported box girder is carried out based on BIM,and the feasibility of the scheme is verified through segment assembly test.The assembly techniques are studied in combination with the mesh design scheme to achieve rapid forming of the reinforcement framework.R&D of automatic processing equipment for components,material transshipment equipment,automatic hoisting equipment and technological equipment for assembly clamping fixture are carried out to realize the overall design of equipment production line.An intelligent control system is developed for the whole-process intelligent construction of reinforcement framework to realize the full life-cycle applications for the workshop production and visual management including intelligent layout and quality traceability.The research results systematically optimize and innovate the assembly and forming technologies of reinforcement framework in the prefabrication beam yard of high-speed railway,realize the component processing,automatic assembly and information technology management,improve the construction quality,efficiency and information technology level of intelligent manufacturing of reinforcement framework of railway prefabricated beam as a whole,and reduce the construction cost of the project.The research has realized a major breakthrough in the construction technology of railway prefabricated box girders,which has the extensive technical and market promotion values.

古金赤水河大桥主桥总体设计

古金赤水河大桥主桥为(83.5+173.5+575+173.5+83.5)m半飘浮体系双塔双索面斜拉桥。主梁采用双边主梁断面钢-混组合梁,由工字钢主梁和混凝土桥面板组成,全宽43.8 m,设置裙板抑制主梁涡振。桥塔为下塔柱内收的A形塔,南、北塔塔高分别为217 m和261 m。由于山区超高桥塔塔墩景观效果欠佳,采用超高塔柱无塔墩方案,桥塔采用嵌岩群桩基础;针对山区桥梁养护不便的情况,索塔锚固采用耐候钢钢锚梁;针对剪力钉在拉拔力作用下承载能力降低问题,采用以开孔板连接件为主的钢-混结合构造实现锚梁牛腿壁板与塔壁连接。斜拉索采用公称直径15.20 mm、标准抗拉强度1860 MPa的钢绞线拉索,全桥共4×23对(184根),空间双索面扇形布置。由于斜拉索锚拉板+外置减振阻尼器景观效果不佳,选用全内置减振阻尼器方案。

基于联合静动力修正的混凝土斜拉桥主梁挠度变化规律研究

针对混凝土斜拉桥服役期间主梁不断下挠的问题,该文基于修正模型分析大跨度混凝土斜拉桥服役期间主梁挠度变化规律。采用联合静动力的有限元模型修正方法,构造双目标优化问题,基于非支配排序遗传算法(NSGA-Ⅱ)求解,得到Pareto最优解集,从Pareto最优解集中找到协调最优解,从而实现有限元模型修正。模型修正后的静力位移和自振频率计算值与实测值吻合较好,能更好地反映结构的实际工作状态。在此基础上,结合主梁线形历年监测数据,分析不同徐变模式及拉索松弛效应等时变因素对主梁线形的影响,分析结果表明:采用CEB-FIP 2010徐变模式计算的挠度与实测挠度更加接近。中跨跨中下挠量最大,服役20年下挠量约为270 mm;主梁跨中挠度前5年平均增长率达33 mm/年,前5年挠度约占前40年的50%,后期主梁下挠趋于平缓。

新型空心管状翼缘钢板组合梁设计理念与力学性能

工字钢组合梁桥正朝着少主梁、精简横向联系的方向发展。与传统多主梁复杂横向联系组合梁桥相比,双主梁桥由于采用了开口截面的结构形式,极大地削弱了其抗扭能力,在偏载作用下会产生较大的变形及翘曲应力,使钢主梁处于弯扭耦合的受力状态。空心管状翼缘钢板组合梁采用空心钢管取代传统的平板上翼缘,提升了稳定性,改善了结构性能。本文通过理论分析和实体有限元法的计算,研究了单梁在自重与横向风荷载作用下的稳定性;对非组合截面的组合体系下的稳定性能进行了分析与比较,并分离出扭转翘曲应力和纵向正应力,研究了不同跨径下扭转效应的影响。最后,对横向联系、加劲肋的影响进行了分析。研究结果表明,空心管状翼缘钢板组合梁桥扭转刚度大于传统工字形截面组合梁扭转刚度,自身横向稳定性好,并且需要较少的横向联系与加劲肋,可实现单梁吊装,避免采用过多临时加固及支撑措施,提高施工效率。

寒区环境温度对板式橡胶支座连续梁桥地震易损性影响研究

针对现行规范对寒区桥梁减隔震设计中仅考虑橡胶支座力学特性受环境温度作用影响,而忽略桥墩混凝土材料特性受温度影响的不足,以高寒地区一座两联3×30 m混凝土连续梁桥为背景,开展不同环境温度下桥墩混凝土材料抗压性能试验,确定温度对其力学参数的影响,基于试验结果对不同环境温度下的桥墩混凝土力学参数进行修正,从而建立不同环境温度下的全桥精细化非线性有限元模型,并基于增量动力分析(IDA)法探究不同环境温度下该桥的地震易损性。结果表明:极端温度引起桥墩混凝土材料参数和支座刚度的改变,使得该桥自振频率随着温度的升高而降低;地震作用下,极端低温时桥墩墩顶位移较常温增大了26.8%,而极端高温时支座位移增大了19.4%;根据现行规范计算的极端低温时支座和桥梁系统的损伤概率偏小,极端高温时结构和构件的损伤概率偏大,在设计中应予以重视;极端低温下桥墩、支座及桥梁系统的损伤概率,较常温分别增大45.0%、35.2%和27.5%,对于高寒地区该类桥梁设计时需考虑低温对其抗震性能的影响。

基于实测数据的高海拔大日温差地区拱上组合梁桥-无砟轨道体系温度场研究

温度作用是影响桥梁-轨道结构服役性能的重要因素之一。为探究高海拔大日温差地区拱上组合梁桥-无砟轨道体系的温度场变化规律,基于某拟建铁路上承式大跨拱桥桥址处的环境温度持续监测数据与卫星反演得到的太阳辐射数据,建立了考虑太阳辐射阴影遮挡效应的拱上组合梁桥-无砟轨道体系温度场模型,重点分析日温度变化规律和竖向温差分布规律,获得了考虑实测气温和太阳辐射逐时变化的全年日温度场;采用广义帕累托分布对竖向温差样本进行了极值分布估计,确定不同超越概率的竖向温差代表值,提出多折线形式的竖向温度梯度模式。研究结果表明,梯度相较于平原地区更为显著,无砟轨道的遮挡效应使得温度梯度分布上移,钢梁外侧腹板在冬季产生局部梯度作用;基于实测数据的温差极值估计方法考虑了环境温度和太阳辐射对结构温度场的随机影响,可为特殊地区桥梁设计阶段温度作用的计算提供参考。

基于贝叶斯优化支持向量回归的流线型箱梁颤振气动外形优化方法

为解决风洞试验耗时费力和计算流体动力学(CFD)计算量大的问题,提出了一套新型流线型箱梁断面颤振性能气动外形优化方法.以风嘴参数为设计变量,利用CFD获取断面三分力系数,以准定常理论估算的颤振临界风速为优化目标.根据贝叶斯优化支持向量回归构建代理模型,利用混合加点法更新模型,通过寻优算法确定最优断面.以虎门大桥为例,得到桥梁在可行域内颤振性能最佳的断面方案.结果表明,风嘴升高,颤振临界风速先增后减,相对高度为0.6时整体性能较优,相对高度为0.7时可获得最优断面.底板宽增加,颤振性能显著降低,下斜腹板倾角为14°~16°时颤振性能最优.断面优化后桥梁颤振临界风速相比原始断面提升约31%.

基于CFD与风洞试验的边主梁涡振气动措施

为能够快捷且经济地完成开口类钝体桥梁断面涡振制振气动措施的选型,以一座边主梁叠合梁斜拉桥为背景,采用“CFD(computation fluid dynamics)数值模拟选型+风洞试验验证”的思路对其涡振制振气动措施选型进行研究.该桥原设计主梁断面在常遇风速下存在显著涡激振动,为完成气动措施的初步选型,采用CFD数值计算对原设计断面的流场进行模拟,通过研究原设计断面的旋涡脱落状态确定主要旋涡抑制对象,进而有针对性地模拟了3种气动措施(下中央稳定板、导流板与风嘴)对主要脱落旋涡的抑制作用,通过将各断面旋涡脱落状态与三分力系数进行对比分析,得到各断面涡振性能的相对优劣关系,并最终选取风嘴与下中央稳定板结合而成的组合气动措施进行风洞验证试验.试验结果表明:该组合气动措施能够有效抑制梁体在各风攻角下的涡激振动,且在+5°风攻角下,通过风洞试验得到的导流板、下中央稳定板、风嘴组合气动3种措施对原设计断面涡振振幅的减小作用依此递增,分别为2.7%、27.7%与87.4%,制振能力高低关系与数值模拟结果相一致;本次数值模拟结果符合预期要求,未来可针对不同类型桥梁断面进一步扩展数值模拟与风洞试验结果对比的数据集,以期更为准确、快捷地完成气动措施的选型.