Calculation models of stress increment of prestressing tendonsusing the deformation of externally prestressed beams

Based on structural deformation analysis, we developed calculation models of externally prestressing tendon stresses increments for simply supported beams on service loads. The Windows program SICPEM for calculating stress increments, based on energy principle, was programmed using the object oriented method. Six beams results, tested by Tan, and the free length of externally straight tendons were recomputed by the program. The ratio of computed results to test results is 0.895, and the standard deviation is 0.013. Furthermore, the free length of externally straight tendons, for which the second order effect can be ignored safely, is ten times beam depth. This coincides with the reference literature.     

Effects of rolling lubrication on flange lateral spread of H-beam

Although rolling lubrication can decrease rolling forces and energy consumption, it also causes defects such as uneven flange lateral spread and web eccentricity during H-beam rolling process. To solve the problem caused by lubrication, finite element models of H-beam universal rolling were established. The different friction conditions of the contact surface between the rollers and work piece were simulated individually. The mechanism of rolling lubrication impacting on flange spread was studied, and the law of flange lateral spread was gained by analyzing the factors such as friction distribution and metal flow in different situations. Analytical results show that lubrication in rolling process can effectively decrease rolling forces and energy consumption. In the condition that technological parameters except friction are fixed, the flange lateral spread decreases in a linear way as the friction coefficient between flange and roller increases, and the flange lateral spread is more sensitive to the friction of flange's the inner side. Design of lubrication process should take full account of the sensitiveness differences of flange lateral spread to the lubrication conditions of different parts of roller surface.     

Fatigue Maintenance Probabilistic Optimization of Cable-girder Welded Anchorage Zones in Suspension Bridges

it is necessary to balance the failure risk and the maintenance expensive. A methodology for reliability based maintenance optimization of steel bridge welded joints subjected to fatigue is proposed considering linear elastic fracture mechanics (LEFM), the structure reliability, life cycle cost method and maintenance strategies. The maintenance cost is divided into inspection, repair and failure sections according to the whole life cycle cost methodology. And the maintenance strategy is transformed to the minimum expected lifetime costs with a constraint of the minimum acceptable reliability index. An case concerning to a transverse stiffener of bottom flange welded joint of Qingcaobei bridge is studied with a certain number of simplifications. Some sensitivity analysis is provided. Among all the parameters, discount rate is the most remarkable.     

Numeric Analysis of the Dynamic Performance of a Prestressed Concrete Beam

The finite element of a prestressed concrete (PSC) beam is analyzed in a case of diverse prestressing forces. The mechanical model applied is that advanced by Clough for a concrete beam bearing axial force. The results indicate that the beam frequencies decrease with increasing prestressing force. A dynamic experiment of a non bonded PSC beam was carried out to validate the veracity of the finite element analysis. Test beam frequencies increase with increasing prestressing force. The analysis model thus is unfit for frequency analysis of a PSC beam. The determinant factor of frequencies is analyzed, and the dynamic model is modified according to experimental results. The modified model analysis result shows that: the calculated frequencies of mode 1 agree with the test results well; the frequencies of mode 2 posses some errors; and, the modified model can reflect the direction of frequency change along with the change of prestressing force well.     

A new type of prestressed concrete hollow girder design for overcoming the typical diseases

This paper proposes a new type of prestressed concrete hollow girder based on the summaries of the current studies on longitudinal cracks and hinge cracks. The match prefabricated method is used with shear key at interface to solve the problem of hingle cracks, and the two-way prestressing strand techniques are used to assure the longitudinal load-bearing capacity and to prevent the emergence of longitudinal cracks because of pressure existing at the match interface. In order to reduce the temperature difference between the internal and external of the prestressed concrete hollow girder, drilling holes are carried out at the bottom slab of girder every distance. To ensure the adhesive effect between the girder and deck pavement, we designed grooves at the top slab of girders. The finite element analysis results of a design example show that the pressure stress of bottom slab of girder is about 2.58 MPa and 0.16 MPa, which are effective to avoid the appearance of longitudinal cracks and hinge cracks.     

轴心受压钢构件高温下局部稳定设计方法

为了得到钢构件高温下局部稳定设计方法,通过试验对建立的有限元模型进行了验证。采用验证后的有限元模型,分析了温度、板件宽厚比、初始几何缺陷、腹板和翼缘相互作用等因素对H形截面轴心受压钢构件局部屈曲应力的影响,提出了Q235钢和Q460钢H形截面轴心受压构件高温下的局部稳定承载力简化计算公式和高温下防止局部屈曲的翼缘宽厚比和腹板高厚比限值。研究表明：当板件宽厚比较小时,构件的局部屈曲应力随宽厚比的增大迅速减小,宽厚比较大时,构件屈曲应力降低不明显;初始几何缺陷对构件局部屈曲应力影响较小;高温下翼缘对腹板屈曲的约束作用比常温下明显;高温下防止局部屈曲的宽厚比限值与常温下宽厚比限值不同。     

平房仓横向通风技术在玉米储藏上的应用研究

为了研究平房仓横向通风技术在玉米储藏上的应用效果,明确玉米储藏过程横向通风工艺及其参数,利用高大平房仓中设计安装的横向通风设施,以及在储藏玉米粮堆中预埋的插入式毕托管,对高大平房仓横向通风系统进行实仓测试。全面开展了玉米储藏过程中横向通风工艺应用研究,测试了在横向通风系统通风时,风速、风量、系统各部分阻力和粮堆压力分布。研究发现,在储藏玉米的高大平房仓中应用横向通风系统时,粮堆单位粮层阻力较小,在实用单位通风量时,横向通风系统总阻力不大于1200Pa;同时横向通风还具有风量分配均匀、粮堆通风均匀性良好的特点。该研究为玉米在配备横向通风系统的高大平房仓储藏提供了技术支持。     

焊接加固热作用对工形截面压弯钢构件承载性能的影响

为研究焊接加固热作用及不同初始负载对工字形压弯钢柱承载性能的影响,基于考虑热影响的热结构耦合分析方法进行了热源模型热输入改进,并考虑初始几何缺陷、初始残余应力及摩擦等,完成了不同负载下焊接加固的3个工字形压弯钢柱的模拟分析。研究了焊接位移时程、腹板应力应变重分布及荷载位移关系,通过有限元分析与相应试验结果对比验证,进而获得了试验无法获得的焊接温度场、翼缘与加固板间的焊接应力应变重分布以及翼缘边缘屈服承载力等结果,并将承载力结果与规范计算结果对比,考察了现有设计方法。结果表明,焊接顺序决定焊接变形的发展过程,焊接热输入和初始负载共同决定持载焊接的位移变化范围和焊接残余变形的大小;初始负载越大,应力应变重分布往偏心受力方向发展更多,承载力越低,而初始残余应力不影响极限承载力;采用考虑热影响的有限元方法具有一定可行性和总体安全性,规范设计方法仍有可提升空间。     

考虑渗流和地震时的砂土边坡稳定性计算

基于极限平衡理论,以砂土边坡为研究对象,推导了渗流和地震存在时拟静力法和拟动力法边坡安全系数的计算表达式。通过程序求解,与已有算例对比表明,计算结果基本一致,验证了2种方法解析式的合理性。参数分析表明,水位越高,边坡失稳越严重,水力梯度与安全系数基本为线性关系。渗流方向向下时,稳定性随水力梯度的增加而增大;渗流方向向上时,变化规律相反。水平地震加速度系数对稳定性的影响剧烈,竖向地震加速度系数对稳定性影响较小,简化计算可以忽略不计。最终得出拟静力法的解析式,简单、实用,而拟动力法则可以更为全面地考察砂土边坡稳定性随时间变化的特点。     

Measurement and Analysis of Prestressed Concrete Flat Beam- Waffle Slab System During Prestressing

During the pre - stressing of the unbonded prestressed concrete wide flat beam - waffle slab system, the displacements and strains of slab and the prestressed concrete beams were site - measured and the results were analyzed. The prestressing construction was simulated by finite element program. The prestressing efficiency of the unbonded prestressed concrete wide flat beam - waffle slab system was discussed. It indicates that the prestressing efficiency was affected by the in -plane stiffness of slab.     

Biological variance in the colour of Granny Smith apples: Modelling the effect of senescence and chilling injury

The colour of ‘Granny Smith’ apples, harvested from three orchards at two stages of maturity, was measured individually using the CIE L*a*b* system during storage in regular atmosphere at three temperatures: 1, 4 and 10 °C. A model was developed based on a simplified mechanism to describe the development of the apple colour during storage as affected by senescence (aging) and chilling injury. Monitoring of individual apples made it possible to include and to describe the biological variance of colour in batches of apples and to correct the colour of each apple individually for its own biological shift factor (biological age; random effect). The biological shift factor is related to the initial condition and range of colour change. The rate of the colour development was estimated in common (fixed effects) for all batches using non-linear mixed effects regression analysis. The variance accounted for by the developed model, including effects of temperature, harvest maturity and orchard location, was more than 95% on 3211 observations. The overall reaction rate constant of decolouration, combining the effects of senescence and chilling injury, was found to depend on temperature. The temperature that showed the lowest overall reaction rate of decolouration is 8 °C, which is in contrast with the currently recommended storage temperature for ‘Granny Smith’ apples.     

THE FULL LOADING HISTORY ANALYSTS OF PRESTRESSED CONCRETE GRIDS WITH UNBONDED TENDONS

This paper presents a matrix structural analysis of variable stiffness on the complete loading history of prestressed concrete grids with unbonded tendons. A model of torsional rigidity affected by moment is derived by the analogy of space truss, and the effect of torque on flexural rigidity is also studied. In order to calculate the increment of stresses in tendons, a corresponding equation is created. Comparison of calculation shows well agreement with the experimental results.     

Analysis on Longitudinal Cracks and Deflection of the Pre-stressed V-shape Slab Roof Structure

In this paper, the finite element method is used to analyze the behavior of the prestressed V-shape Slab Roof structure, especially the effect of temperature change on the stress of slab. The calculated results indicate that when the temperature changes, the tensile stress at the lower extreme fibers of the flange plate near rib exceeds the tensile strength of concrete subjected to the combined action of triaxial stresses and results in the longitudinal cracks of the flange plate. The deflection analysis is based on the mechanical model of the prestressed V shape slab with the longitudinal cracks. The calculated results are in general agreement with the field observations.     

水稻植株通气系统与稻田CH4排放相关性研究

水稻植株是稻田甲烷(CH₄)排放的重要通道,90%的CH₄气体由水稻植株通气组织排放到大气中。探讨水稻植株通气组织与水稻CH4排放量之间的相关性,可为水稻栽培和育种实践中减排CH₄提供理论和实践依据。2005年早、晚2季大田试验测定了16个水稻品种CH₄排放量和植株地上部各节间组织1     

考虑滑移和剪切变形的单箱双室组合箱梁剪力滞效应

为准确分析单箱双室组合箱梁的剪力滞效应,考虑钢混凝土的界面滑移效应和钢腹板的剪切变形,针对顶底板和翼板定义不同的剪力滞翘曲位移函数,基于能量变分法推导出单箱双室组合箱梁剪滞效应的控制微分方程及其闭合解。以单箱双室组合箱梁算例为基础,利用该方法分析其剪力滞效应的规律,结果表明：在同时考虑滑移和剪切变形时,组合箱梁的挠度比初等梁理论解大,且其挠度随界面滑移刚度的增大而减小;组合箱梁在均布荷载作用下,滑移量与荷载值近似成正比关系;在相同条件下,钢箱梁底板的剪力滞效应较混凝土顶板显著。     

新型肥料在水稻轻简化施肥中的稳产效应评估

为了评估新型肥料品种在水稻轻简化施肥中的应用效果,以树脂包膜缓释肥(RCF)、聚氨酯包膜缓释肥(PCF)和有机缓释肥(LSF)等新型肥料产品为研究材料,通过多点大区对比试验,研究了“一基一追”轻简化施肥方式对‘籼粳杂交稻’和‘晚粳稻’产量和氮肥利用效率的影响。结果表明,籼粳杂交稻试验中氮肥减量12.8%(218 kg N/hm²),RCF、PCF和LSF等新型肥料轻简化施肥处理水稻产量、产量构成因子与常规施肥(FF)处理间都没有显著差异;‘晚粳稻’试验中氮肥减量36.1%(177 kg N/hm²),RCF、PCF和LSF等新型肥料轻简化施肥处理分别比FF处理减产20.4%、12.0%和22.8%。PCF处理水稻有效穗数和成穗率与FF处理间差异不显著,RCF和LSF处理则显著降低了‘晚粳稻’有效穗数和成穗率。轻简化施肥各处理氮肥偏生产力都显著高于FF处理。RCF和PCF处理氮肥农学利用率与FF处理间差异不显著,LSF处理“籼粳杂交稻”试验中氮肥农学利用率显著高于FF处理,‘晚粳稻’试验中则显著低于FF处理。水稻轻简化施肥技术的应用效果同时受到施氮量和肥料品种的影响,聚氨酯包膜缓释肥(PCF)在不同水稻类型和试验点上的减氮稳产效应优于树脂包膜缓释肥(RCF)和有机缓释肥(LSF)。     

Spatial Calculation Methods of Three Main Trusses Continuous Plate truss Composite Bridge

According to the structural features of three main trusses continuous plate truss composite bridge, two composite beam methods are presented by constructing the displacement mode of composite beam elements and deriving the stiffness matrix of composite beam elements. The characteristic of composite beam method one is that the bridge slab is taken as the top flange of the chord of main truss and combined with the chord of main truss to form a steel concrete composite beam; the characteristic of composite beam method two is that the bridge slab is taken as the top flange of longitudinal and traverse beam and form a steel concrete composite beam with longitudinal and traverse beams. And as for the conventional plate beam composite method, the slab is characterized by forming bridge slab system with continuous isotropic sheets and longitudinal and traverse beams to bear load. Also, the comparison between theoretical results and experimental ones verifies the effectiveness of the above three methods.     

高强钢焊接薄腹工形截面双向压弯构件的稳定性

应用ANSYS有限元,分析了Q460高强钢焊接薄腹工形截面双向压弯构件的稳定性能,提出了可供实际应用参考的设计公式。分析中考虑的主要参数有腹板高厚比,构件长细比,翼缘宽厚比及荷载偏心率。结果表明,对受压为主的构件,腹板局部屈曲对构件稳定承载力影响较大,而对受弯为主的构件,这一因素对构件稳定承载力影响较小。有限元分析结果与现行规范方法计算结果比较表明,目前规范方法尚不能较好地计算高强钢焊接薄腹工形截面双向压弯构件的稳定承载力,因而提出了修正直接强度法,该法精度较好且偏于安全。     

The Effect on the Column Moment Considering Compress of Prestressed Concrete Beam

Axial compress is produced by the tension of prestressing beam, which engenders the third moment of column. And the third moment is always ignored in design. The thesis analyses elementarily the third moment of column and finds that the third moment must be taken seriously in some condition, and it is not the same value as the manner of tensions is different . As a result, some helpful conclusion and suggestion are presented.     

Axial Bearing Capacity Design Method of Cold-Formed Steel Quadruple-C Built-up Section Members

The finite element model involving geometric large deformation,materials and contact nonlinearity is established.Specimens of cold-formed steel quadruple-C built-up section members are simulated and the finite element models are proved to be valid.Then,numerical analysis on the behavior of specimens with different slenderness ratio and flange flakiness ratio are carried out,and then the axial bearing capacities of specimens are obtained.Based on effective width method and direct strength method (DSM) in related codes,two design methods of cold-formed steel quadruple-C built-up section members under axial compression are proposed:effective length method and correction factor method.It is shown that:the final failure characteristics of all specimens are local buckling and distortional buckling.In the case of not considering the reduction of effective length,the results calculated by each code are slightly lower than those of test and FEM when the slenderness ratio is less than 50,while the results are too conservative when the slenderness ratio is more than 50.