Thermal Effect of the Cable-Stayed Bridge Tower

This paper studies the thermal effect of the cable-stayed bridge tower based on full time accurate measurement and finite element analysis on Xiantao Hanjiang River Highway Bridge. The measured results and the displacement variation of top tower show that the tower rotates periodically when it is exposed in sunshine. But the tower column will not decline when there is no sunshine. In spite of in winter or in summer, the period when the tower column changed smallest is from 0∶00 am to 5∶00 am. The time period when the tower column has maximum deviation lags behind the time when the tower column has maximum temperature difference, and this phenomenon is obvious in winter. The conclusions also have directive value in predicting the tower deformations and their directions in construction control of cable-stayed bridge, and in verifying the finite element program.

Numerical investigation of temperature gradient-induced thermal stress for steel–concrete composite bridge deck in suspension bridges

A3D finite element model(FEM)with realistic field measurements of temperature distributions is proposed to investigate the thermal stress variation in the steel–concrete composite bridge deck system.First,a brief literaturereview indicates that traditional thermal stress calculation in suspension bridges is based on the2D plane structure with simplified temperature profiles on bridges.Thus,a3D FEM is proposed for accurate stress analysis.The focus is on the incorporation of full field arbitrary temperature profile for the stress analysis.Following this,the effect of realistic temperature distribution on the structure is investigated in detail and an example using field measurements of Aizhai Bridge is integrated with the proposed3D FEM model.Parametric studies are used to illustrate the effect of different parameters on the thermal stress distribution in the bridge structure.Next,the discussion and comparison of the proposed methodology and simplified calculation method in the standard is given.The calculation difference and their potential impact on the structure are shown in detail.Finally,some conclusions and recommendations for future bridge analysis and design are given based on the proposed study.

Investigation the Correlation between Thermal Bridging and Geometries in Concrete Buildings

This article focuses on the investigation of the correlation between thermal bridging and various geometric configurations. The article employs QuickField software for conducting three-dimensional steady-state heat transfer simulations to investigate the thermal behaviors of diverse geometric shapes. Significantly, this study involves the simulation of four distinct geometries including concrete circular, square, rectangular, and triangular column through an insulated concrete layer while all geometries maintain the consistent surface areas. The simulations yield findings indicating that circular thermal bridging has the best thermal performance, while rectangular thermal bridging displays comparatively the lowest thermal efficiency. Furthermore, the results indicate that alterations in the perimeter of thermal bridge interfaces, while maintaining a constant area, exert a more pronounced influence on the thermal performance of the geometries compared to proportional changes in area while preserving the perimeter. The study’s findings aid building designers and architects in creating more energy-efficient structural and architectural elements by incorporating thermally efficient geometries and forms. .

Analysis of Thermal Bridge Impact in a Hotel Building for the Eight Brazilian Bioclimatic Zones

This article aims to present an analysis of the influence of thermal bridges on reinforced concrete structural systems regarding energy performance of the envelope of a commercial building located in the bioclimatic zones 1 to 8 in Brazil, using computer simulation. The method used to achieve this goal includes the following steps： （1） definition and configuration of the base case; （2） definition and configuration of the reference model; （3） optimization of energy modeling; （4） energy modeling and comparison of consumption between the base case and the reference model. Main results showed that thermal bridges in reinforced concrete interfere on the building＇s energy performance and that the impact is related to the WWR （window-to-wall ratio） on the building. For hotel buildings with WWR from 30% to 45%, thermal bridges imply a decrease in estimated consumption, which can reach 10%, depending on the bioclimatic zone. For 60% WWR, the non-consideration of thermal bridges can represent up to 5% of increase in estimated consumption, depending on the Brazilian bioclimatic zone.

Thermal Bridges Impact on Energy Consumption in Residential Buildings Considering the Brazilian Bioclimatic Zoning

With the considerable increase in electric power consumption, searching for buildings with lower energy impact has become a crucial factor on controlling energy consumption, as well as designing buildings with high thermal comfort. Thermal bridges are weak points in buildings where the thermal resistance varies considerably between two distinct points. Depending on the situation, the existence of thermal bridges in a building can be favorable to the achievement of the expected thermal comfort and lower energy consumption. The aim of this paper is to analyze the impact of thermal bridges of reinforced concrete structure regarding to energy consumption for residential buildings in the Brazilian bioclimatic zones. The used method is characterized by computer simulations of distinct cases configured with and without thermal bridges. The results show that in most bioclimatic zones, the presence of thermal bridges in the wall composition contributes to the reduction of energy consumption for both heating and cooling, and independent of the wall＇s insulation level, solar absorptance is a major factor in the energy consumption levels, walls with smaller absorptance consume less and this consumption increases gradually with increasing absorptance.

An integrated computational method for calculating dynamic thermal bridges of building facades in tropical countries

Identifying thermal bridges on building façades has been a great challenge for architects,especially during the conceptual design stage.This is not only due to the complexity of parameters when calculating thermal bridges,but also lack of feature integration between building energy simulation(BES)tools and the actual building conditions.For example,existing BES tools predominantly calculate thermal bridges only in steady state without considering the temperature dynamic behaviour of building outdoors.Consequently,relevant features such as thermal delay,decrement factor,and operative temperature are often neglected,and this can lead to miscalculation of energy consumption.This study then proposes an integrated method to calculate dynamic thermal bridges under transient conditions by incorporating field observations and computational simulations of thermal bridges.More specifically,the proposed method employs several measurement tools such as HOBO data logger to record the actual conditions of indoor and outdoor room temperature and thermal cameras to identify the surface temperature of selected building junctions.The actual datasets are then integrated with the simulation workflow developed in BES tools.This study ultimately enables architects not only to identify potential thermal bridges on existing building façades but also to support material and geometric exploration in early design phase.

Formation Process of Intermittent Molten Bridge Between Au-Plated Contacts at Super Low Breaking Velocity

This paper presents the molten bridge behaviors of Au-plated material at super low breaking velocity conditions by introducing our new designed test rig. The typical waveforms of the contact voltage and contact force during breaking are investigated under the load of 5- 25 V/0.2-1 A and velocity of 25-150 nm/s. It is shown that the intermittent molten bridge is formed from the competition of multitude contact a-spots for current distribution and the solid- liquid mixing characteristics of a molten bridge. Also, it is proved that the bridge is not composed by the completed melted metal by using FEM thermal simulation and the voltage-temperature relation. The observed surface morphology reveals that the scattered and stacked melted regions are attributed to the intermittent bridge. Finally, the effects of breaking velocity and electrical load on bridge length and duration are also analyzed.

Numerical calculation on solar temperature field of a cable-stayed bridge with U-shaped section on high-speed railway

Based on transient temperature field theory of heat conduction, the solar temperature field calculation model of U-shape sectioned high-speed railway cable-stayed bridge under actions of concrete beams and ballast was established. Using parametric programming language, finite element calculation modules considering climate conditions, bridge site, structure dimension and material thermophysical properties were compiled. Six standard day cycles with the strongest yearly radiation among the bridge sites were selected for sectional solar temperature field calculation and temperature distributions under different temperature-sensitive parameters were compared. The results show that under the influence of sunshine, U-shape section of the beam shows obvious nonlinear distribution characteristics and the maximum cross-section temperature difference is more than 21℃; the ballast significantly reduces sunshine temperature difference of the beam and temperature peak of the bottom margin lags with the increase of ballast thickness; the maximum cross-section vertical temperature gradient appears in summer while large transverse temperature difference appears in winter.

Study on the Temperature of the Bridge Wire in the Initiator Used in Nuclear Explosion Valve

This paper established the mathematical model of bridge wire temperature rise under direct current condition and gave the solution. It computed bridge wire temperature by using the thermal-electric coupling method provided by ANSYS-Workbench finite element analysis software. In the end, the temperature bridge wire applied to different electric current was measured by the infrared thermal imaging temperature measurement method. The result shows that the ANSYS simulation results are in agreement with the theoretical calculation and the experimental results. It is feasible to compute bridge wire temperature of initiator by using ANSYS-Workbench software, and it is an important method to analyze complex structure of pyrotechnics.

Simulation of Temperature Field in Original Segment of Concrete Box-Girder Bridge

Temperature field and its variation with time are necessary for analyzing the thermo-mechanical performance of mass concrete structures at their early ages. This paper carries out a temperature field simulation analysis for an original segment of a real box girder bridge with the finite element software ANSYS. Two representative exothermic rate models are used to describe the heat- releasing process caused by the cement hydration in concrete. The exothermic rate model that conforms to reality more closely is recognized by comparing the simulation results with the data gathered from the optical fiber temperature sensors pre-embedded in the original segment. The air temperature and wind velocity that constitute thermal boundary conditions are determined in the light of the local meteorological department and correlative research achievements of recent years. Moreover, the consideration for the steel formwork acting as a barrier to heat loss is also proved to be beneficial to improve the simulation effect.

Eliminating Fastener Thermal Bridging in Low Slope Roofs: Energy Efficiency Savings versus Installation Costs

Low-slope roofing assemblies include a wide range of insulation and single ply membrane attachment methods. Previous studies have shown that mechanical attachment using metal fasteners leads to significant thermal bridging and consequent loss of insulation value and reduction of long term thermal efficiency. This study calculates the costs associated with mechanical attachment in terms of lost insulation value, increased long-term energy costs, and the material and labor costs associated with installation of these common systems. Energy efficiency reductions using metal fasteners were modeled for eight US cities in a range of climate zones. From the data, it was possible to calculate target costs (labor plus materials) that would make adhered systems cost effective. There are many options available to adhere single ply roof system components, such as solvent-based adhesives and low-rise urethane foams, together with different application approaches such as broom, spray, and ribbon methods. The cost targets derived in this study can help optimize the use of such materials and application methods such that the thermal bridging due to fasteners could be substantially reduced or eliminated.

SFCC现场导热系数与温度场实测及预测方法研究

为确定钢纤维页岩陶粒混凝土(SFCC)现场实际的导热系数,与桥面板施工同步制作了不同钢纤维体积分数的SFCC试件,采用热板法进行测定,校核并扩展了导热系数预测公式,并且对高温沥青摊铺时SFCC桥面板的温度场进行了实测和数值模拟.结果表明:环境湿度为67%时,SFCC的实测导热系数为0.915~1.409 W/(m·K),增加钢纤维体积分数可提高SFCC导热系数;考虑湿度和钢纤维影响后的扩展Maxwell公式预测值与实测值吻合良好;高温沥青摊铺时桥面板SFCC混凝土内的温度梯度可达20.5℃,超过规范日温差,采用数值模拟可有效计算桥面板温度场.

预制内外复合保温模壳拼装墙体热工性能研究

为探究预制内外复合保温模壳拼装墙体结构中的卡板连接件对墙体热工性能的影响,通过热工理论计算、试验研究、ANSYS有限元热分析模拟软件3种方法,对比分析了无连接件、不同数量连接件以及双面抹灰不同条件下墙体的传热系数。结果表明:在无连接件条件下,实际墙体热工试验测试值与热工理论计算值的误差较小;连接件数量越多,热桥效应越明显,墙体的热工性能越差;采用有限元模拟软件对墙体进行热工设计结果较精确,可作为设计依据;研究结果可为模壳拼装墙体在超低能耗建筑的应用及能耗分析提供借鉴。

常泰长江大桥主航道桥纵向约束索CFRP筋材及成品索试制试验研究

常泰长江大桥主航道桥为主跨1208 m的公铁两用双塔钢桁梁斜拉桥,采用温度自适应塔梁约束体系实现对温度的完全自适应,该体系采用CFRP索作为纵向约束索。CFRP索采用127-∅7 mm扭绞型热挤聚乙烯平行CFRP筋材成品索。为保证CFRP索的质量,首先在工业化生产线上进行CFRP筋材试制及静载拉伸试验,然后在CFRP筋材试制基础上,进行CFRP成品索的试制及静载拉伸试验研究。结果表明:CFRP筋材试拉伸的强度为3099~3886 MPa,拉伸弹性模量为181~201 GPa;CFRP成品索加载至大于100%公称破断索力时,索体内的CFRP筋材未出现开裂、损伤、断丝等现象,锚固体(锚具及铸体)未见异常,拉伸弹性模量大于160 GPa,试验结果均满足相关要求。

基于BP神经网络的混凝土箱梁最大温度梯度预测

混凝土箱梁受到太阳辐射、大气温度波动等多种气象因素的综合作用,结构内部会产生显著的非均匀温度分布。截面内温度梯度可能会导致桥梁结构产生过大的温度应力与温度变形,影响桥梁结构的安全性和耐久性。本文旨在探究气象因素对混凝土箱梁温度场的影响机理,并提出一种能精确预测中国多区域混凝土箱梁截面最大温度梯度的方法。首先建立了日照条件下混凝土箱梁温度场计算模型,将2 a以上气象资料作为输入条件,对多个地区混凝土箱梁温度场长期变化进行了仿真模拟,并对混凝土箱梁截面温度梯度的长期变化趋势进行了分析。然后利用主成分分析(PCA)确定了混凝土箱梁截面最大温度梯度预测模型所需的输入参数。最后利用遗传算法优化的BP神经网络建立预测混凝土箱梁竖向、横向温度梯度的网络模型,并与混凝土箱梁截面温度梯度进行比较。结果分析表明BP神经网络模型可以精确地预测混凝土箱梁最大温度梯度,预测值平均绝对误差(AAE)均小于0.9℃,均方根误差(RMSE)均小于1.2℃,决定系数(R^(2))均大于0.9。基于当地气象条件,本文利用经典的BP神经网络模型所建立的预测模型对中国不同地区的混凝土箱梁截面最大温度梯度均能给出准确的预测,为混凝土箱梁设计和施工阶段的最大温度梯度的计算提供一种高效的方法。

混凝土小箱梁早龄期开裂风险与防控

预制混凝土小箱梁在浇注期间水化热作用下产生显著里表温差,存在早龄期开裂风险,影响其安全性及耐久性。为明晰预制混凝土小箱梁早龄期开裂风险,以陕西省安康地区某混凝土小箱梁桥为依托,研究其早龄期温度作用、温度效应及开裂风险,并通过正交试验分析得到了影响预制混凝土小箱梁早龄期开裂风险的主要因素。结果表明:预制混凝土小箱梁在浇注后水化反应迅速,12~16 h后,混凝土温度达到峰值54.9℃,温度最高位置集中于顶部梗腋处及底板,而底板位置受环境作用影响水化放热时间最长,在浇注后72 h内混凝土小箱梁整体温度基本呈对称分布;水化反应期间小箱梁各位置抗力水平增长基本一致,但翼缘、梗腋及腹板中部应力水平较高,开裂风险较大,最大拉应力达到2.71 MPa,最大开裂因子达到1.2;材料属性、结构参数、环境作用对混凝土小箱梁预制期间水化热温度作用均有影响,其中材料属性影响最为显著,主要包括水泥放热量和水泥掺量,调整材料参属性及入模温度可有效降低预制混凝土小箱梁开裂风险。研究结果可以指导预制混凝土小箱梁设计及施工,降低其早龄期开裂风险,提高其安全性及耐久性。

基于瞬态热桥法的固体材料导热系数测量及其不确定度的评定

在Hammerschmidt建立瞬态热桥(THB)法理论的基础上,改进了恒定输入电流模式下导热系数解析模型和修正模型,对THB测量传感器进行了结构设计和仿真验证。搭建了测量范围为0.01~150 W/(m·K)的实验装置,并对修正模型进行了测量验证。对聚苯乙烯、有机玻璃和45号钢等7种固体材料进行了实验测量,对测量结果进行了不确定度的评定,并与不同仪器的测量结果进行了比较。结果表明,实验装置的测量重复性优于1.7%,与参考值的相对偏差在±5%以内,经评定测量结果的相对扩展不确定度为U_(rel)=2.94%(k=2)。

超低能耗建筑悬挑构件热桥隔断措施研究

相较于常规建筑,超低能耗建筑对围护系统的保温性能有着更严格的要求,其中,围护系统热桥控制是实现超低能耗建筑的关键措施。在围护系统保温构造设计时,由于悬挑构件隔断了保温层,成为热桥集中的部位,为削弱或消除此部位热桥,通常采用保温材料包覆悬挑构件的方式进行处理,但此方式存在工期影响严重及成本增量大的弊端,随着超低能耗建筑的推广,更多形式的热桥隔断措施在实际工程中得到了应用。结合常见的超低能耗建筑悬挑构件热桥隔断措施,从施工角度及隔热性能方面进行研究分析,以供同类工程借鉴。

寒冷A区超低能耗建筑围护结构热桥部位的节能设计策略——以烟台飞龙集团有限公司创新研发中心为例

为响应“双碳”背景下实现节能减排降碳绿色转型的需求,结合烟台飞龙集团有限公司创新研发中心项目的实践,探讨并提出了适合寒冷A区超低能耗建筑发展的围护结构热桥部位的节点优化策略,有利于解决普通节能建筑的典型通用节点设计与超低能耗建筑节点设计之间的不适配问题。

基于升降轨SAR数据的连续箱梁桥精细变形

针对桥梁精细变形监测问题,提出一种考虑由温度引起的桥梁变形(简称温度变形)的升降轨合成孔径雷达(synthetic aperture radar,SAR)数据融合方法.首先,以连续箱梁桥为研究对象,分别使用升降轨SAR数据集,基于小基线子集干涉测量法(small baseline subsets interferometric SAR,SBAS-InSAR)提取视线向(line-of-sight,LOS)变形;然后,利用最小二乘法构建温度变形模型,分离周期性温度变形与长期性趋势变形;最后,结合桥梁结构特征,基于时空插值和奇异值分解方法实现升降轨数据融合,提取温度变形、纵桥向(即桥梁延伸方向)及垂直向趋势变形,分析桥梁变形机制及变形成因.结果表明,该方法可提取精确的桥梁温度变形及三维变形,为桥梁健康监测提供可靠的方法支撑.