Experimental measurements and numerical modelling of a green roof

Green roof utilisation has been known since ancient times both in hot and cold climates. Nowadays, it has been reconsidered at issue of energy saving and pollution reduction. In this paper, some measurement sessions on a green roof installed by the Vicenza Hospital are described. A data logging system with temperature, humidity, rainfall, radiation, etc. sensors surveyed both the parameters related to the green roof and to the rooms underneath. The aim is to evaluate the passive cooling, stressing the evapotranspiration role in summer time. Furthermore, the enhanced insulating properties have been tested during winter time. A predictive numerical model has been developed in a building simulation software (TRNSYS) to calculate thermal and energy performances of a building with a green roof, varying the meteorological dataset for a specific geographic zone.     

某大桥动力分析

以某大桥为工程背景,采用结构分析软件ANSYS建立了三维有限元模型,进行了模态分析,算出了前10阶自振频率和振型,并且选取1940年美国El-Centro地震记录进行了全桥动力分析,得到了一些具有价值的结论。     

CFRP加固钢筋混凝土桥梁柱节点的试验研究

对5个碳纤维加固钢筋混凝土斜腿钢架桥节点试件和1个对比试件进行了试验研究,试验分析表明,在加固以后,与裂缝斜交的碳纤维起着与箍筋类似的抗剪作用,节点的强度和变形能力有了明显的提高,同时在节点受弯部位粘贴的碳纤维与其相对应处的受弯钢筋相比,承受了较大的应力和应变。     

Damaged RC beams repaired by bonding of CFRP laminates

This paper summarizes the results of experimental studies on damaged reinforced concrete beams repaired by external bonding of carbon fiber reinforced polymer (CFRP) composite laminates to the tensile face of the beam. Two sets of beams were tested in this study: control beams (without CFRP laminates) and damaged and then repaired beams with different amounts of CFRP laminates by varying different parameters (damage degree, CFRP laminate width, concrete strength class). All beams were tested in four-point bending over a span of 1800 mm. The tests were carried out under displacement control. The most investigated parameter in this experimental study is damage degree (ratio between pre-cracked load and load capacity of control beam). Repairing damaged RC beams with externally bonded CFRP laminates were successful for different degrees of damage. The observed failure modes were peeling off and interfacial debonding. These failure modes depend only on the laminate width.The results indicate that the load capacity and the rigidity of repaired beams were significantly higher then those of control beam for all tested damage degrees. The authors remarked that for a load capacity improvement, reinforcement with a CFRP having about a half width of the beam is satisfactory. Finally, the contribution of CFRP laminates on the load capacity and rigidity of repaired RC beams is significant for any concrete strength class.     

Experimental and numerical investigations of bond between CFRP and concrete

It is known that the bonding failure between concrete and externally bonded CFRP-strips sets in where high shear forces and high bending moments occur. Despite this knowledge, experimental and theoretical studies had been exclusively focused on the situation at the end of the CFRP-strip until 2000–2001. Since then theoretical work on the bonding between concrete and externally bonded laminate at a section between two cracks has been done. But neither experimental nor numerical studies on a section between two cracks have been carried out. For experimental studies a test set-up has been developed, in order to simulate geometrical and mechanical conditions between two cracks of a post-strengthened concrete slab. Nine test series with 67 tests at a section between two cracks have been carried out. Thirty-seven tests were bonding tests without a relative displacement at crack-surface and 30 tests were bonding tests with a relative displacement. A three-dimensional finite element model with solid and shell elements has been used for numerical calculations. This paper undertakes to describe the results of these test series, the results of the finite element calculations and a mathematical algorithm to considerate an incline of the laminate at the calculation of the maximum stress difference at a section between two cracks.     

CFRP筋夹片式锚具数值分析

采用ANSYS有限元软件建立CFRP筋夹片式锚具数值有限元模型,通过分析计算结果,得出Tsai-Wu失效准则能够较好地模拟CFRP筋在复杂应力作用下的失效、荷载滑移的理论计算曲线基本能反映实际情况,锚杯外表面轴向应力和环向应力的计算值与实测值基本一致。     

钢筋混凝土修补梁的试验研究及数值分析

对钢筋混凝土修补梁的受荷性能,进行了系统的试验研究和数值计算分析,以揭示界面粘结质量对修补梁工作性能的影响,及在长期荷载作用下修补梁的受荷特征。     

CFRP锚杆黏结性能试验及数值模拟分析

通过对锚固长度分别为240、300、350mm的碳纤维CFRP锚杆进行黏结性能试验,研究其破坏形式、弹性模量、平均黏结强度等基本力学性能及黏结滑移性能。基于以上拉伸试验滑移曲线,采用非线性弹簧单元COMBIN39模拟CFRP筋和黏结介质环氧砂浆之间的黏结滑移,研究锚固段受力随锚固深度变化情况,并对不同锚固长度锚固段受力情况进行分析,对于研究锚固段受力演变具有重要意义。     

CFRP加固筒-柱支承式筒仓结构动力特性分析

以都江堰某筒-柱支承式钢筋混凝土圆形筒仓结构震后CFRP加固为背景,研究CFRP加固后的筒-柱支承式混凝土筒仓动力特性。根据结构形式及加固措施建立结构加固前后的动力特性分析模型;对结构加固前及加固后的自振频率和周期进行分析;结合汶川地震八角波拟加速度反应谱,对结构加固前后的频率、周期及振型进行了比较与评价。研究表明：①CFRP加固筒仓薄弱部位后,其前10阶频率及周期与加固前相比无明显变化,即CFRP加固未明显改变筒仓的动力特性;②加固后,其第一周期仍然刚好位于拟加速度反应谱的峰值附近,仍属于刚度较大的短周期结构,受地震的影响较大;③加固后,从第3振型开始出现扭转,即扭转振型提前。     

CFRP吊索钢管混凝土系杆拱桥模型试验研究

碳纤维筋(CFRP)具有优良的物理力学性能,可作为钢管混凝土系杆拱桥中的吊索。一种CFRP筋的树脂封装型锚具也已开发,它可调整CFRP吊索索力大小,并有可能应用于CFRP吊索钢管混凝土系杆拱桥。本文的试验研究对钢管拱桥模型及钢管混凝土拱桥模型的受力与变形性能分别进行了测试与对比分析。在系梁施加预应力过程中,对CFRP吊索拉力、系梁与钢管拱的竖向挠曲变形及应力的变化进行了测试。与钢管混凝土拱桥相比,相近荷载作用下钢管拱桥吊索拉力较大,系梁的竖向变形较大,钢拱相应截面的压应力较大,系梁裂缝宽度较大。试验结果表明CFRP吊索钢管混凝土系杆拱桥的受力与变形性能较好,为CFRP吊索在系杆拱桥中的推广应用提供了一系列试验依据。     

Two-dimensional modelling of laminated piezoelectric composites: analysis and numerical results

We propose a new approach to laminated piezoelectric plates based on a refinement of the electric potential as function of the thickness coordinate of the laminate and accounting for shear effects. Moreover, the variation of the electric potential as function of the thickness coordinate is modelled for each layer of the laminate. The equation for the laminated piezoelectric plate are then obtained by using a variational formulation involving mechanical surface loads or prescribed electric potential on the top and bottom faces of the plate. In addition to the equations for the generalized stress resultants (due to the shear effects), the equation of the electric charge conservation is also deduced for the 2D model.Particular attention is devoted to the single piezoelectric plate and bimorph structure and the through-thickness distribution of the displacements, electric potential as well as stresses are given for different kinds of electromechanical loads. The results thus obtained are compared to those provided by a finite element method performed for the full 3D model. A good agreement is observed for plates made of layers of PZT-4 piezoelectric material. The comparison ascertains the effectiveness of the present 2D approach to piezoelectric laminates.     

Model test and numerical analysis of a special joint for a truss bridge

This paper presents a study on the mechanical behaviours of a special joint between a rigid suspension cable and a truss girder in a rigid suspension stiffened steel truss bridge. Both a model test and a numerical finite element analysis (FEA) have been conducted, and relevant information about the models used, loading procedure and test scheme is presented. The model test shows that the maximum stress in the joint is less than the material allowable stress and the maximal stress induced from the secondary moment accounts for about 30% of the total stress. A three-dimensional finite element model is used in the numerical analysis and the results are in very good agreement with those of the model test. This study shows that the design of the special joint is reasonable and the structure safe. It is also expected that the results presented in this paper would be useful as references for future research and design of rigid suspension stiffened steel truss bridges and joints.     

Post-rehabilitation assessment of a centenary steel bridge through numerical and experimental analysis

This paper presents an experimental and numerical analysis regarding the structural assessment of an existing steel bridge – the Eiffel Bridge – after a recent rehabilitation. The Eiffel Bridge, a centenary road–rail truss bridge, comprising two superimposed decks, was subjected to major rehabilitation works involving the replacement of the top concrete deck, the strengthening of the upper chords of the main truss girders and the replacement of the support bearings. In this context a load test and an environmental test were carried out aiming at the assessment of the new structural condition and the evaluation of the effectiveness of the elements' strengthening. A structural analysis was carried out in order to characterize the most relevant aspects of the structural behavior and to support the discussion of the field results. Particular aspects concerning the main girders' bending, the nature of nodes' rotations, and the response under temperature changes are highlighted. The effectiveness of the strengthening of the top chords is verified based on the strains' measurements. Finally, it is shown that the thorough characterization of the structural behavior enabled the establishment of a reference condition for future assessments of the structure.     

An experimental and numerical study of the effect of thickness and length of CFRP on performance of repaired reinforced concrete beams

Experimental and numerical analyses are performed to predict the loading carrying capacity of reinforced concrete beams strengthened with carbon fibre reinforced plastics (CFRP) composites. The effect of CFRP thickness and length on the failure load and ductility is studied and curves of initial cracking load, ultimate load, stiffness, ductility and fibre stresses are presented. The results of tests and simulations show a good agreement and indicate that, in contrast with a control beam, initial cracking loads of strengthened beams increase slightly, whilst stiffness and ductility increase more and the ultimate loads increase considerably. Stresses in the carbon fibre decrease with the increase of fibre sheet thickness. Cracking patterns of strengthened beams are improved. Crack propagation varies with the change of fibre length and results in the variation of failure mode of beams. Variation of the length of CFRP sheet is the main reason of variation of the stress of interface. Therefore, debonding failure, unless adequately considered in the design process, may significantly decrease the effectiveness of the strengthening.     

Dynamic analysis of a cable-stayed deck steel arch bridge

A theoretical and experimental research work in relation to the cable-stayed Barqueta bridge is described in this paper. Barqueta bridge, across Guadalquivir river, links the city of Seville with Scientific Park Cartuja 93. During rush hour cars may cover one half of the bridge lanes for more than one hour. Full-scale tests were carried out to measure the bridge dynamic response. The experimental program included the dynamic study for two different live load conditions: the bridge with one half of its lanes full of cars, and the bridge empty of cars. Modal parameter estimations were made based on the acquired data. Ten vibration modes were identified in the frequency range of 0-6 Hz by different techniques, two of these modes being very close to each other. The traffic-structure interaction is also studied. Experimental results were compared with those obtained from a three-dimensional finite element model developed in this work. Both sets of results show very good agreement. Finally, a damage identification technique has been applied to determine the integrity of the structure. Results obtained from a test developed in July 2005 have been correlated with experimental results obtained in October 2006 using the damage index method.     

Experimental study and numerical analysis on mechanical behavior of T-shape stiffened orthotropic steel-concrete composite bridge decks

A new-type of orthotropic steel-concrete composite bridge deck system was developed, by casting the concrete overlay on the top of the orthotropic steel deck ribbed with T-shape steel members. To study its mechanical behavior (in terms of failure mode, load-deflection relationship, concrete crack initiation and propagation, strength, stiffness and so on), two new-type orthotropic steel-concrete composite bridge decks with different section dimensions were experimentally investigated and two reference decks (reinforced concrete deck and orthotropic steel deck) were also involved in the research for comparison. For the two new-type orthotropic steel-concrete composite decks, the average value of ultimate loads per width is 885.7kN, which is 2.35 and 1.61 times of that of the concrete and steel reference decks with almost the same section height. Experimental results proved that the composite deck can effectively control the crack initiation and propagation in the concrete and postpone the yielding of the steel bars and steel plates, due to the composite action between the concrete overlay and the underlying steel plate. Furthermore, the Finite Element (FE) model of the orthotropic steel-concrete composite deck was developed and validated by test results. A parametric study is conducted regarding to the stiffness of shear studs. With the validated FE model, stress distribution in the underlying steel plate and T-shape stiffeners and development of concrete cracking in the concrete overlay were characterized at different load levels.     

Compressive strength of concrete cylinders with variable widths CFRP wraps: Experimental study and numerical modeling

There is an urgent need for models that can accurately predict performance of fiber-wrapped concrete columns. Axial compression tests on a total of 30 carbon-wrapped concrete cylinders of normal concrete and different number of wraps and height of confinement were used to verify the finite model. A nonlinear finite element model with a non-associative Drucker–Prager plasticity was used. The model compared favorably with test results. It was concluded that the adhesive bond between concrete and the wrap would not significantly affect the confinement behavior. From tests results, one can conclude that the wider the wrap, the higher the strength, also the thicker the wrap the higher the strength. However, it was impossible to reach a clear conclusion on the effect of the combination of variation of number of CFRP wraps and height of confinement. In a couple of cases, the same amount of material resulted in the same increase in the strength of the cylinders.     

单跨悬索桥的动力分析

以重庆鱼嘴长江特大桥为研究对象，建立了空间有限元模型，进行了成桥阶段的特征值分析、动力荷载时程分析及地震反应分析，研究了车速对桥梁动力反应的影响。     

碳纤维布补强压力管道试验研究及有限元分析

在粘贴不同厚度的碳纤维布(CFRP)的工况下来测定管道的环向应变与内水压力之间的变化规律,以此试验数据与ANSYS数值模拟值进行比较,可知模拟值和试验结果吻合得较好。通过建立有限元模型分析纤维复合材料的弹性模量、管道壁厚、管道直径对管道屈服时承压能力的影响,结果表明:高模量碳纤维加固的管道达到屈服强度时管内可施加的压力最大;管道外径的增大对粘贴了碳纤维布的管道屈服时内水压力值提高比例并无影响,而随着管道壁厚的增加,提高比例却依次降低。为碳纤维布修复补强大型输送管道的设计与施工提供试验基础依据。     

Dynamic monitoring and numerical modelling of communication towers with FBG based accelerometers

This study presents the dynamic monitoring of two telecommunication tall slender steel towers with an optical FBG accelerometer. Numerical simulation for both towers was used recurring to finite elements modelling in order to demonstrate the feasibility of using optical technology in this type of structural monitoring. The results show a good agreement between experimental and simulated data, demonstrating that the optical accelerometer can be a very useful tool in the monitoring of tall slender structures.