逐时温度变化对混凝土夹心板温度作用的影响

混凝土结构构件通常体积较大,一般不需要考虑日气温变化和太阳辐射引起的逐时温度变化,但混凝土夹心板的外叶往往较薄,逐时温度变化对其结构构件设计的影响变得不容忽视。本文通过傅里叶级数将逐时温度作用简化为谐波热(日温度),建立了保温层厚度为无穷大的两层平壁模型,用解析法推导得出了谐波热作用时混凝土夹心板的温度场及平均温度理论公式,并分析了混凝土夹心板外叶厚度对其平均温度的影响,提出了夹心板外叶平均温度的简化计算公式。     

航站楼使用阶段钢结构温度取值研究

为了准确确定大跨度钢结构在使用阶段的温度作用和方便钢结构温度变化模拟分析,对厦门高崎机场T4航站楼屋盖钢结构夏季的温度进行了全面测试,提出太阳辐射与室外气象温度的日变化计算模型。根据气象条件、室内分层温度控制方法以及屋面构造做法,通过CFD模拟技术研究高大空间温度场沿高度方向的变化规律,并在天窗部位考虑了太阳辐射的影响。结果表明:金属屋面具有良好的保温隔热性能,室内与室外钢结构的最高温度均与最高气温非常接近,钢结构昼夜温差主要受室外气温变化的影响;受到太阳辐射的影响,天窗部位钢结构的温度明显高于最高气温;CFD模拟计算得到高大空间空气温度沿竖向分布的结果与实测值的变化趋势相一致,顶部热滞留区的温度明显高于等温空调区,计算温度与实测温度相对误差为5%~10%;通过实测与模拟分析,可以较为合理地确定在使用阶段大跨度钢结构的温度,该方法可供类似大型公共建筑设计时参考。     

大直径圆钢管混凝土截面温度场分布的试验研究

为了研究温变对大直径圆钢管混凝土构件截面温度场分布的影响,分别在室外环境和人工气候模拟试验箱内进行了温变试验,测得不同温变条件下钢管混凝土试件和素混凝土对照试件的温度场。试验结果表明:钢管混凝土试件和素混凝土对照试件温度场变化规律基本一致,无日照作用时截面温度场呈均匀分布,日照作用下截面温度场呈非均匀分布。两种环境下,试件截面温度场均呈现出从外往内越靠近圆心,温度变化越滞后的现象,而且试件截面最大温差主要取决于太阳辐射和气温变化幅度。     

混凝土小型空心砌块建筑温度场的数值模拟

裂缝问题严重影响了混凝土小型空心砌块建筑的推广应用。综合分析影响建筑物温度场的各种因素：包括太阳辐射、空气对流、各种长波辐射等，结合传热学理论，借助有限元计算软件ANSYS，对试点建筑屋面和墙体外表面进行了典型日逐时温度的数值模拟，与实测结果吻合较好，说明采用有限元方法，综合考虑多种影响因素进行温度场计算是可行的，模拟结果可为温度应力计算提供温度参数。     

基于气象参数的混凝土结构日照温度作用分析

气象参数是分析日照环境下混凝土结构温度作用的关键参数之一。影响日照环境下混凝土结构温度场的气象参数主要有太阳辐射、气温和风速。本文分析了这些气象参数变化的一般规律,提出其时程分析模型,并从概率统计的角度分析了这些参数的分布规律,确定了具有一定重现期的气象参数代表值。最后以一个混凝土箱梁为例,利用这些气象参数代表值计算分析了其日照温度场,并根据计算温度场拟合得到竖向温差分布曲线。计算表明,分析日照环境下混凝土结构温度场时应考虑气象参数的随机分布。     

考虑太阳辐射影响的双向张弦梁结构温度效应研究

对于采用透光性材料或直接曝露于室外的大跨度钢结构,在太阳辐射作用下结构温度远高于环境温度且极不均匀,可能成为结构的控制荷载,而现有规范和文献并未给出明确科学的温度作用取值依据。结合双向张弦梁实际工程,通过建立太阳辐射作用下钢结构温度场数值模拟方法,分析温度场分布规律以及结构的温度响应,给出考虑太阳辐射影响的结构温度作用的取值原则。     

混凝土圆筒仓日照温度分布有限元分析

为研究日照作用对大直径钢筋混凝土筒仓的影响,本文以热传导理论为依据结合有限元方法,考虑太阳辐射、气温变化、地理位置和几何尺寸等对温度分布的影响,以大型有限元软件ANSYS为平台,利用其参数化设计语言(APDL)建立混凝土圆筒仓日照分布的参数化有限元计算程序,对钢筋混凝土筒仓空仓时的温度场进行瞬态分析。分析得出日照作用下温度分布规律,结果表明不同截面的日照非线性温差以及同一截面的日照非线性内外温差都较大,应对钢筋混凝土圆筒仓的日照温度效应予以重视。     

膜下索穹顶太阳辐射非均匀温度效应研究

索穹顶结构常采用膜屋面,高透光膜屋面可使太阳辐射透过膜材作用在下部结构上,且降低了结构周围的对流换热作用,可能形成"温箱效应",使膜下索穹顶结构产生显著的非均匀温度效应。基于内蒙古伊旗全民健身中心索穹顶,分别考虑ETFE、PTFE两种膜材,对其进行膜下索穹顶结构太阳辐射非均匀温度场和温度效应分析。结果表明:膜下索穹顶结构存在显著的太阳辐射非均匀温度场和温度效应,膜材的太阳辐射透射系数是主要影响因素之一。升温导致索穹顶结构预应力损失严重,考虑太阳辐射非均匀升温工况比考虑极端气温均匀升温工况的膜下索穹顶预应力损失更为明显,在设计中应予以考虑。     

严寒地区矩形钢管混凝土截面温度分布试验

为研究严寒地区钢 混凝土组合结构的温度荷载,以西宁市作为严寒地区的代表,在现场进行了水平放置带加劲肋的矩形钢管混凝土构件截面温度场测试试验,对日照作用下钢管混凝土构件截面温度分布进行了研究。同时还将矩形钢管混凝土构件的三维温度场简化为二维温度场,建立了ABAQUS有限元热力学分析模型,在考虑太阳辐射、风速以及环境温度等参数的作用下提出了构件截面温度场有限元计算方法。结果表明:钢管混凝土构件钢管测点及管内混凝土测点温度的实测值均与有限元计算值吻合良好;考虑日照作用的矩形钢管混凝土截面温度场为非均匀温度场,构件截面存在着明显的温度梯度;钢管温度受到环境温度的直接影响,其温度变化略微滞后于环境温度变化,温度极值明显大于环境温度极值;管内混凝土的温度则受到环境温度的间接影响,其温度变化明显滞后于环境温度变化,温度极值则小于钢管温度极值;矩形钢管混凝土截面温度分布还会受到管内纵向加劲肋的影响,该加劲肋增大了其与混凝土的接触面积,减少了管内混凝土温度变化的滞后程度,降低了构件截面的梯度温差。     

建筑围护结构的温度场数值模拟

本文综合分析了影响建筑围护结构温度场的各种因素:太阳辐射、空气对流以及天空辐射、地表环境辐射、自身辐射等,采用有限元数值模拟方法,结合某混凝土小型空心砌块建筑温度场实测资料,对屋面和墙体进行了典型日变化温度场的数值模拟,与实测结果吻合较好;同时与室外综合温度法的计算结果进行对比,证明综合考虑多种影响因素进行温度场计算更加合理。     

Structural behaviour of eccentrically loaded precast sandwich panels

Results of an experimental investigation to study the ultimate strength behaviour of precast concrete sandwich panels (PCSP) with steel truss shear connectors are reported. Six full-scale sandwich panels with variable slenderness ratio were cast and tested under eccentric loads. Deflection characteristics, variations of strains across the insulation layer, strains in shear connectors, crack appearance and propagation under increasing load were recorded and analysed. The role of the shear truss connectors in transferring load from the outer wythe (layer) to the inner and ensuring composite behaviour was also observed. Results obtained showed that all panels behaved in a fully composite manner under eccentric load till failure. The ultimate strength of the PCSPs was found to decrease non-linearly with the increase in the slenderness ratio. Because of the complex behaviour of PCSP due to its material non-linearity and the interaction between its various components, finite element analysis (FEA) was conducted. Comparison with test results indicated that the FEA closely estimate the wall strength and formulae based on reinforced concrete principles underestimate the wall strength.     

路基温度场长期模拟中的地表热边界条件研究

在路基温度场模拟中,地表热边界常基于"附面层原理"确定,即假设一定深度(附面层厚度)的土体温度函数等于大气日平均温度函数加上一个温度增量。目前,附面层厚度和温度增量一般通过实际观测值回归分析得到,尚未建立起相应的理论和参数确定方法,无法定量分析路面材质、路面结构、太阳辐射、路面辐射对附面层厚度和温度增量的影响。首先通过理论分析,建立了附面层厚度的确定方法;然后建立了一维路面路基结构温度场模拟模型,并通过路基温度场反演分析,验证了数值模型的正确性;进而通过数值分析,研究了太阳辐射、路面辐射、对流换热和路面结构等因素对附面层底部温度增量的影响,给出了温度增量的确定方法和相应的设计图表和计算公式。     

Thermal performance evaluation of precast concrete three-wythe sandwich wall panels

Precast concrete sandwich wall panels are commonly constructed of two wythes of concrete separated by a layer of thermal insulation. In these two-wythe panels, solid concrete regions are often provided for embedded hardware for lifting, handling, and connections, or to provide composite action. These solid concrete regions can have a significant adverse impact on the thermal performance of the panels. This research was directed towards the development of precast concrete three-wythe sandwich wall panels with potential improved thermal and structural performance. A three-wythe panel has three concrete wythes and two insulation layers, and all three concrete wythes are connected by solid concrete regions. However, the connections between successive concrete wythes are staggered in location so that the total thermal path length through the concrete is extended.Practical panel configurations of the three-wythe panels were developed to reduce thermal bridge effects caused by regions of solid concrete. The thermal performance of the three-wythe panel was evaluated by estimating its thermal resistance (R-value) using the finite element method. It was found that, in general, the thermal performance of three-wythe panels is better than that of two-wythe panels due to the increased thermal path length through the panel.     

两种手段提升太阳能新风热利用效率的研究

严寒地区居住建筑面临较为严重的冬季新风不足问题,太阳能新风系统是改善室内空气品质的一种重要手段。研究目的:了解空气流道厚度降低和使用双层玻璃盖板对于提升基础型太阳能新风集热器效率的实际效果。方法:通过搭建太阳能新风集热器实验平台,自制单层、双层玻璃盖板太阳能新风集热器,对比研究空气流道厚度(10mm和30mm)以及不同玻璃盖板层数对集热器效率的影响,并对不同工况下的出口温度和逐时效率进行监测和分析。结果表明:改小集热器空气流道厚度之后平均集热效率上升了10.8%,使用双层玻璃盖板之后平均集热效率上升了7.5%。双层玻璃盖板在低温下能够进一步发挥保温优势,减少了玻璃盖板表面的热损失。结论:减小空气流道厚度,采用双层玻璃盖板具有明显的实际效果,太阳能新风系统具有很好的推广应用潜力。     

Newspaper sandwiched aerated lightweight concrete wall panels—Thermal inertia, transient thermal behavior and surface temperature prediction

Experimental investigation on aerated lightweight concrete (ALC) wall panels in terms of thermal inertia, transient thermal behavior and surface temperature prediction using finite difference method (FDM) are the main focus of this study. ALC wall panels of different density and different aerial intensity of newspaper sandwiched were produced and installed on a prototype house. The ALC wall panels were facing east direction and subjected to Malaysia natural environment condition. The inner and outer surface temperatures of the wall panels were recorded at 3 min interval, 24 h a day for a period of one year. Time lag and decrement factor were computed from the surface temperatures recorded. The results showed that thermal diffusivity has a positive relationship to the thermal inertia of ALC wall panels. FDM was used to predict the surfaces temperature and the predicted temperature was close to the observed temperature. The average differences between the observed and the predicted outer wall surface temperature lied between 1.4 and 2.4% whereas for the inner wall surface, the range was 1.3-2.2%. Greater deviations were detected on the predicted outer surface temperature could be due to some unaccounted factors such as wind direction and relative humidity in the present FDM.     

Real climate experimental study of two double window systems with preheating of ventilation air

This paper aims to characterize the thermal performance of a window system that consists in doubling an existing window, converting it into a ventilated double window. The air coming from the outside circulates upwards through the channel between windows and enters the building through a vent on the top of the window's case. A series of experimental measurements was conducted in a test cell exposed to real outdoor weather conditions located in a mountain region at Centre of Portugal, during heating season in order to determine how this window system can act as a heat exchanger. It was found that such window system act as an efficient heat exchanger using transmission heat losses and solar radiation to preheat ventilation air, thus reducing the building's operational energy costs. An average of about 19 m³/h of air flow rate was found with an air temperature increment within the air gap of about 6 °C, during night-time, for an indoor/outdoor temperature difference of about 16 °C. Air temperature increment reached up to 12 °C using a plastic shutter. With solar radiation, the average of that increment was about 10 °C. This is a simple and cheap building technology which can be implemented both in new and existing buildings.     

Prediction of the optimum slope and surface azimuth angles using the Genetic Algorithm

In this paper, the Genetic Algorithm is applied to calculate the optimum slope and surface azimuth angles for solar collectors to receive maximum solar radiation. An area of Iran is selected to verify the results of this algorithm. The optimum angles and the collector input solar energies for these angles are calculated in hourly, daily, monthly, seasonally and yearly bases respectively. Then, the influence of different combinations of solar radiation components on the optimum slope angle and the energy gain is investigated. The results show that the Genetic Algorithm is a useful technique to find the optimum angles specifically when the number of independent parameters is large. The results show that the daily, monthly and yearly optimum surface azimuth angles for receiving the maximum solar energy are zero. Adjusting the collector at the daily optimum slope angle slightly increases the collector input energy compared with the case of monthly optimum slope angle so that the gain of solar energy is almost the same. The results also show that the hourly optimum surface azimuth angle is not zero and mounting the solar collector at the hourly optimum slope and azimuth angles increases the input energy significantly compared with the case of daily optimum angles. It is shown that the optimum slope angles are mostly dependent on the beam solar radiation. Furthermore, the results indicate that the optimum slope angles of solar collector and Photovoltaic panels are almost the same.     

混凝土箱形输水桥日照温度场及温度应力研究

分析了箱形输水桥产生日照温差及温度应力的原因,借助有限元软件ANSYS对某输水桥日照温差及温度应力进行有效的仿真模拟,计算结果表明：箱形输水桥的日照温差分布比较复杂,从箱形桥身的温度分布来看,顶板温度变化最剧烈,腹板次之,底板最小,温差近似为二次曲线分布。日照温差作用下混凝土箱形输水桥桥身内无论沿纵向和横向都将产生可观的温度应力,其值已超过混凝土的抗拉设计强度。所以,在箱形输水桥身结构设计中对日照温差作用下的温度应力必须予以重视,在设计中应配置适当的温度钢筋。     

Thermal performance of a solarium with removable insulation

A thermal model for a solarium with removable insulation has been developed; the air inside the house is assumed to be at constant temperature corresponding to air conditioning). The model enables the evaluation of the temperature of the air in the sunspace and the thermal flux through the south wall into the house as a function of time, from the hourly variation of solar insolation and atmospheric temperature. The effect of various parameters, like the thickness of the thermal wall, its area and the presence of an isothermal mass, on the temperature of zone 1 and the heat flux through the thermal wall into zone 2 has been investigated.