混杂PVA-ECC配合比优化设计及力学性能试验研究

为了降低工程用水泥基复合材料(ECC, Engineered Cementitious Composites)制造成本,使ECC能够在实际工程中大规模应用,将中国产PVA纤维和日本产PVA纤维以一定的比例混合,配制混杂PVA-ECC。基于ECC的材料设计理论,兼顾抗压强度和受拉能力,对掺有硅粉的混杂PVA-ECC中的纤维体积含量进行了优化设计。通过四点弯曲试验和轴心抗压试验,研究了混杂PVA-ECC在不同龄期下的弯曲性能和抗压性能。试验结果表明,混杂PVA-ECC试件均表现出明显的应变硬化和多缝开裂的特征,此外,其抗压强度后期增长明显。基于UM法,提出一种改进的反分析方法,可利用四点弯曲试验结果推导ECC的极限拉伸应变,并与试验结果进行了比较,结果表明,通过建议的反分析方法得到的预测值与试验值吻合较好。     

Composite Steel- concrete Frame Beam with Reinforced Negative Bending Regions

Considering the large negative bending moment at the end of frame beam and low tensile strength of concrete,a new composite steel-concrete frame beam(CSCFB),reinforced by a T shape steel beam at the negative bending regions,was brought forward.Through two full-scale of single-layer CSCFB frame models experiment,the load-displacement curves of CSCFB and strain distribution at cross section were obtained.Compared with the ordinary composite beam,the T shape reinforcing section can enhance the beam stiffness effectively,and make it distribute reasonably.The segment flexural rigidity method is presented and validated.     

Calculation Method of Shear Behavior of Hybrid Fiber Reinforced High Performance Concrete Deep Beams

The static tests on hybrid fiber (steel fiber and polypropylene fiber) reinforced high performance concrete deep beams according to the orthogonal experimental design were conducted. The shear capacity and calculation method of deep beams were discussed as well. The contributory factors such as the characteristic parameters of steel fiber (types, volume fraction, aspect ratio), the volume fraction of polypropylene fiber, the ratio of web horizontal reinforcement and the ratio of web vertical reinforcement were analyzed. Results show that the shear failure mode of deep beams is changed with adding a reasonable volume of hybrid fibers, and hybrid fiber can greatly increase the diagonal cracking strength and shear strength of HPC deep beams. The diagonal cracking strength is increased by 45.2% averagely while the shear strength is increased by 25.6% averagely. A satisfied result is obtained when the plasticity theory is used to analyze shear behavior of hybrid fiber reinforced HPC deep beams. The contribution of web horizontal reinforcement and web vertical reinforcement to shear strength of deep beams is not obvious but the former plays a major role. After analyzing the strengthening mechanism of hybrid fiber, a formula to calculate the shear capacity of hybrid fiber reinforced HPC deep beams is presented based on spatial strut-and-tie mode and splitting failure.     

Experimental Analysis on the Mechanical Properties of Concrete Composite Slabs with Precast Prestressed Rectangular Rib Panels

For the convenience of industrialized production and site operation,specification design of PPCRP (precast prestressed concrete ribbed panels) is discussed. In order to obtain ultimate bearing capacity,bending rigidity and crack resistance,four PPCRP with two types of spans are studied,and the results show that PPCRP can satisfy the requirements of bearing capacity in construction phase and can serve as stay-in place formwork. To verify the mechanical property,shear behavior on contact interface of composite member and moment redistribution factor of continuous composite member,two single-span composite members and one two-span continuous composite member are studied. It is indicated that computational method for bearing capacity of composite member can be the same as cast-in-situ concrete slab. Besides,section strain analysis for composite member in two-loading is conducted,which suggests that thickness of bottom board can be used as calculated height with the consideration of two-loading.     

TENTATIVE INVESTIGATION OF THE BEHAVIOR OF REINFORCED CONCRETE FRAME CORNER JOINTS UNDER LOW CYCLE LOADING

In this pager, four full-scale corner joint assemblies of reinforced concrete frame beam and column with different detail structure are tested under low cycle loading, The process of damage development and the characteristics of break of the assemblies in the course of alternately increasing positive and negative bending deformation are learned Strength, stiffness and ductility of assemblies and the various regulations of energy consumption are also studied. Compared with these properties, the anti-seismic behavior is tentatively commented. Besides, the test results of the strain distribution of beam and column longitudinal bars and stress state of joint stirrups are analyzed.     

Contrast Analysis of Mechanical Behavior of Confined Concrete with Stirrups and CFRP Under Axial Compression

Aiming at confined concrete with stirrups and carbon fiber reinforced plastic(CFRP) respectively, the major influence factors of mechanical behavior of confined concrete under axial compression were studied based on reported experimental data. The equations for calculating the peak stress, peak strain and ultimate strain were proposed respectively for confined concrete with stirrups and CFRP. Contrastive analysis shows that the behavior of confined concrete with stirrups is better than confined concrete with CFRP in low characteristic value, whereas the conclusion is contrary in high characteristic value.     

Experimental Study on Flexural Toughness and Fatigue Property of Polypropylene (PP) Fiber Reinforced Cement-stabilized Macadam

By four-point bending test and fatigue test,the authors studied the flexural toughness and fatigue property of semi-rigid base course of cement-stabilized macadam with and without polypropylene(PP) fiber.Some significant data about these two kinds of material have been obtained,such as the load-deflection curves,toughness index according to the standard methods of JCI and ASTM C1018-97,the fatigue lifetime under different stress levels and the fatigue lifetime regression equation.The results show that the reinforcing effect of the PP fiber is remarkable;the bending strength,ultimate deformability,JCI toughness index,ASTM C1018-97 toughness index and fatigue life of cement-stabilized macadam with PP fiber are increased by about 10%,150%,67.7%,36.1%~79.8%,and 126%~352%,respectively,when the volume fraction of PP fiber is only 0.077%.At the same time,the authors revealed the toughness improving mechanism and the anti-fatigue mechanism of the fiber in such material based on the fracture mechanics theory.     

Strain rate effects on dynamic behavior of reinforcement concrete columns with various reinforcement ratio

The mechnical characteristics of concrete is sensitive to the strain rate and it is crucial to consider the effect of load rates on the behavior of reinforced concrete (RC) structures subjected to dynamic loads such as severe earthquakes. In this study, numerical simulations on the dynamic behavior of typical RC column specimens under dynamic loadings with different load rates were performed. Concrete constitutive model considering the strain rate effects proposed by the CEB code was employed with a fiber model to characterize the nonlinear strain rate dependent behavior of RC columns. The developed dynamic fiber element model was validated by comparing the simulated results of four RC column specimens with the fast loading test results. Results show that the developed fiber element model can predict the behavior of RC columns with acceptable accuracy. After valiating the proposed fiber elemen model considering the strain rate effect, the load carrying capacity of different RC columns with various longitudinal reinforcement ratios and volumetric stirrup ratios were simulated. Results show that the trends of the influences of longitudinal reinforcement ratios and volumetric stirrup ratios on the load carrying capacity of the RC columns under dynamic loadings are different.     

塑性铰区采用FRC柱试验研究及正截面承载力分析

采用简化的纤维增强混凝土应力应变关系,根据截面变形的平截面假定和截面力的平衡方程,推导出塑性铰区采用纤维增强混凝土柱在不同极限状态时的曲率。根据各极限状态点曲率,求得截面上各分布力,对截面形心轴取距,到塑性铰区采用FRC柱的开裂、屈服、峰值和极限点的弯矩表达式。与试验结果对比表明,计算值与试验值吻合较好。     

氯氧镁水泥混凝土中钢筋的腐蚀与防护试验研究

结合氯氧镁水泥混凝土耐水性,研究氯氧镁水泥混凝土中钢筋的腐蚀与防护,试验变量包括钢筋种类、混凝土保护层厚度和腐蚀龄期等。钢筋种类包括裸露钢筋和美加力涂层钢筋;混凝土保护层厚度包括25、50 mm;腐蚀龄期包括60、120、180、240、300、360 d。试验采用自来水长期浸泡至试块2/3处,并采用扫描电子显微镜（SEM）和能谱仪（EDS）对腐蚀后的钢筋微观结构和化学元素组成进行分析,研究钢筋的腐蚀机理。结果表明,通过软化系数分析,氯氧镁水泥混凝土的软化系数处于0.78～0.87,说明试验设计的氯氧镁水泥混凝土可用于干燥地区、受潮较轻地区或次要建筑结构。通过极化曲线及其电化学参数分析,裸露钢筋腐蚀速率为美加力涂层钢筋腐蚀速率的40～80倍,说明涂层防腐效果明显。     

Deformation Analysis of Thermo Elastic Plastic on ReinforcedConcrete Structure Subjected to Fire

To investigate the mechanical behavior of reinforced concrete structure subjected to fire, the incremental thermo elastic plastic creep constitutive equations of steel and concrete in consideration of temperature and creep deformation were obtained based on different yield rules and the elastic plastic theories. The nonlinear analysis for reinforced concrete simply supported slab was carried out with consideration the variation of the mechanical properties of steel and concrete with temperature. The effectiveness and applicability of the constitutive equations were verified with the test results from relevant literature. The nonlinear analysis was employed for one bay one storey reinforced concrete frame under fire and the variation of displacement at partial nodes was analysed. It was found that the reinforced concrete structure at a high temperature would have a significant deformation. And the displacement change curves of beam column joints of reinforced concrete frame were not monotonous trend and there were inflexion points. The vertical displacement values of beam column joints were less than those at midspan of cross beam.     

Experimental Investigation of "Column with Weaker Beam" Frame and "Column with Equally Strong Beam" Frame

By the way of experiment and analysis of two "one story and one bay" reinforced concrete frames, namely a "beam with weaker column" frame and a "column with equally strong beam" frame, the features of internal force redistribution are investigated and an elementary comparison about bending moment redistribution of three kinds of frames namely the "column with weaker beam", "beam with weaker column" and "column with equally strong beam" is given. Through this comparison, the objective existence of such "three kinds of frame" is proven, the moment redistribution is different for each frame and for the moment modulation, the elastic moment diagram and the difference of the internal force redistribution in different frames should be considered together.     

多点锚固体外无粘结CFRP预应力加固RC梁的抗弯性能

在梁侧或梁底用波形齿横向张拉CFRP片材并锚固的体外预应力加固混凝土结构技术,对3根完全相同的7 m跨T形截面梁进行加固：其中2根梁侧面加固;1根梁底部加固。试验表明：多点锚固体外无粘结CFRP预应力可以依据构件的弯矩来调整各段的加固量从而更有效的利用CFRP材料的高强性能;梁底与梁侧加固对提高构件的抗弯刚度差别不大;波形齿能彻底解决预应力CFRP片材的锚固问题。以该3根加固梁的试验结果为基础,提出了梁体极限状态下塑性绞区长度的体外无粘结预应力碳纤维加固受弯构件的抗弯承载力公式,以及考虑二次效应的有效惯性矩法的挠曲变形的计算公式,通过与试验值的对比分析可知,所提出的方法可供设计参考使用。     

Experimental analysis of strengthening effect of corroded reinforced concrete beams strengthened with bolted steel plates

In order to study the mechanical behavior of corroded reinforced concrete beams strengthened with bolted steel plates, this paper designed 12 reinforced concrete beams. These beams were corroded by using accelerated electrochemical corrosion method with a designed corrosion ratio of 10%. The pre-compression experiments were performed for all RC beams before strengthening and the maximum crack width was controlled as 0.2 mm. According to the thickness of concrete cover, the beams were divided into 3 groups. Each group was composed of one comparative beam and three tested beams strengthened by steel plates bolted with study according to the thickness of steel plates which were 3 mm, 4 mm and 5 mm, respectively. It was shown that the strain distributions along the height of the strengthened beams at middle-span were in good agreement with the plain section assumption basically. The serviceability performances of corroded RC beams were significantly improved and these ultimate bearing capacities increased obviously. The steel plate bolted with stud effectively reduced the crack width and the extension height of reinforced concrete beams. It was indicated that an increase of steel plates with 35 mm resulted in a decrease of deflection by 13%51% when beams had the same thickness of concrete cover and corrosion ratio. Influence of the thickness of concrete cover on the ultimate bearing capacity was not obvious.     

油菜秸秆灰分混凝土与钢筋之间粘结性能研究

为了探究油菜秸秆灰分的掺入对钢筋-混凝土之间粘结性能的影响。对3种不同油菜秸秆灰分掺量的钢筋-油菜秸秆灰分混凝土试件进行中心拉拔试验,并与钢筋-普通混凝土粘结性能作对比试验。结果表明:钢筋-油菜秸秆灰分混凝土粘结强度与混凝土抗压强度呈正相关。当水胶比一定时,随着油菜秸秆灰分掺量的增加,钢筋-油菜秸秆灰分混凝土的粘结强度降低。水胶比为0.47时的钢筋-油菜秸秆灰分粘结性能与普通混凝土最为接近,为最优配合比。由试验结果可知,在承重要求较低的普通钢筋混凝土结构中,采用适量油菜秸秆灰分等量替代水泥,对于节省水泥生产能源和科学合理利用农业废弃物两方面均具有重要意义。     

Non-nodal Connection Method for Plane Beam Elements

In reasonably modeling reinforced concrete structures with plane beam elements, the reinforcement and the concrete are regarded as different elements respectively, which would be joined together with the non-nodal connection method put forward under the principle of virtual work based on the displacement analysis at an arbitrary point in a plane beam element and according to the consistent condition of displacements. Then with that method, more problems of complex combination and connection can be conveniently and precisely simulated, such as reinforced members or members with changing sections in different construction phases. In the numeric crete beam and the strengthening effects on another reinforced concrete is verified and its convenience is demonstrated. examples, the displacement of a reinforced con- beam are analyzed, the feasibility of the method is verified and its convenience is demonstrated.     

Experimental Analysis on the Frost Resistance of Steel Fiber Reinforced Concrete

The frost resistance of steel fiber reinforced concrete (SFRC) was studied based on the fast freeze thaw tests in water and in a 3.5% sodium chloride solution, with different mass fraction of steel fiber in concrete at 0%, 0.5%, 1.0%, 1.5% and 2.0%, respectively. The effects of the number of freeze thaw cycles and the volume fraction of steel fiber on the mass lose rate, the splitting strength loss rate and the dynamic modulus of elasticity of SFRC were analyzed. The reinforcement mechanism of the steel fiber under the action of freeze and thaw was also discussed. Moreover, mercury intrusion method and SEM analysis were carried out to study the pore size distribution features and the performance of microstructure on the impact of frost resistance of SFRC. The results show that adding an appropriate amount of steel fiber into concrete can reduce the pore porosity and improve the compactness of concrete. Furthermore, the presence of steel fiber proves to shrink the porosity and improve evidently the frost resistance of concrete. It is also shown that the steel fiber content has a great influence on the frost resisting property of SFRC. The best performance of SFRC can be achieved when the volume fraction of steel fiber is 1.5%.     

A Model Analysis to Beam Bar Slippage of Seismic Structure Joints

Many experimental results indicates, beam bar slippage within joints is a frequent local nonlinear response of reinforced concrete structures under the rare earthquakes. For the sake of modeling and evaluating seismic behaviors of reinforced concrete structures entirely and rational, the model way of the quantity and hysteresis order of beam bar slippage within joints, which was found in the elasto plastic earthquake response of structures, is discussed thoroughly. And the personal characteristics of several structure analysis ways to model the beam bar slippage within joints are evaluated respectively. Based on the results already gotten, a hysteresis model of beam bar slippage within frame joints is advanced, and the relative issues are also discussed. The beam bar slippage model suggested is convenience to the elasto plastic dynamic response analysis of whole reinforced concrete structures.     

Analysis of Fiber Renforced Concrete Beam-Column Joints Model

Due to the large stirrup ratio and reinforcement congest in beam-column joints, the ordinary reinforced concrete beam-column joints take inconvenience to construction. Cracked fiber renforced concrete (FRC) has strong bridge ability and better tensile performance so that it can replace part or all of the stirrups. Based on previous researches on resistance mechanism of reinforced concrete joints, a new model using FRC materials in the core zone of beam-column joints is presented. It is a kind of model in which horizontal shear supported by the diagonal strut mechanism and softening truss mechanism with a certain percentage. The calculation results of the model is compared with the existing test results. It is a bit conservative to specimens with low axial load ratio. However, the results are in line with the specimens with high axial load ratio. Therefore, the results totally demonstrate the rationality of the proposed model in this paper. Meanwhile, according to the proposed model, the shear capacity of beam-column joints can be not only calculated, it also check whether FRC compressive strength in core zone of joints and horizontal stirrup ratio meets design requirements, which has a higher practicability.     

Parameters design of powertrain system of electric vehicle with two-speed gearbox

The Brilliouin optical time domain analysis (BOTDA) is a newly developed technique adopted to measure and monitor the strain and temperature generated along optical fibers. The BOTDA has the characteristics of distributed measurement, long distance, high precision and durability, so it is suitable to structural health monitoring. Then a new optical fiber sensor embedded method based on air-blowing and vacuum grouting is introduced. It can lay the long distance distributed optical fiber into the concrete easily in short time. An experiment has been set up to study the validity of the new method, which shows that the embedded optical fiber can measure the concrete strain accurately, and it can realize the comprehensive, long-term, stable and real-time health monitoring to the civil structure.