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.     

Fire Resistance Analysis of High Strength Q460 Steel Beams-Part II：Theory Validation

In the previous companion paper, the fire resistance of high strength steel beams made from Q460 was theoretically studied. The methods to obtain temperature distribution, critical moment, critical temperature and stability coefficient were presented. The temperature distribution and load bearing capacity was analyzed by finite element method, and the validation was evaluated by comparison of results between theoretical computation and finite element analysis as well as experimental results. The comparison was made between Q460 steel beam and mild Q235 steel beam and the difference on fire resistance was obtained. A simplified approach for fire resistance of high strength Q460 steel beams was proposed and an example was given to show the application and reference of the approach.     

Fire Resistance Analysis of High Strength Q460 Steel Beams-Part I：Theoretical Analysis

In order to investigate the fire resistance of high strength steel beams made from Q460, the method to compute temperature distribution of high strength Q460 steel beams was derived and the temperature distribution was calculated by using finite difference method. The modified equations of temperature for components of steel beam were proposed. According to critical moment at room temperature and mechanical properties of high strength Q460 steel at elevated temperature, the critical moment and stability checking coefficient were obtained by analysis. The load bearing capacity and critical temperature as well as stability factor were studied by using equivalent stiffness method through considering the effect of temperature gradient on stiffness.     

Numerical Method for Load Bearing Capacity of High Strength Steel Columns at Elevated Temperature

In order to make fire resistance design of high strength steel columns in building structures, the numerical calculation method on load bearing capacity of high strength steel columns at elevated temperature was investigated. By taking the mechanical property of high strength steel at elevated temperature into consideration, extension was made on the inverse calculation segment length method and the program to compute the load bearing capacity of high strength steel columns at elevated temperature was performed. The program was adopted to compute the load bearing capacity. The results obtained by the program and the finite element analysis were compared and good agreement had been found. The influence of magnitude, distribution mode of residual stress and initial geometry imperfection on ultimate load bearing capacity was analyzed by employing the program. It is shown that the extended method can be is shown used to calculate the load bearing capacity of high strength steel columns at elevated temperature; the magnitude and distribution mode of residual stress had little influence but the geometry imperfection have significant influence on ultimate load bearing capacity.     

STUDY ON THE CHIP BREAKING LIMITING AND DISCRIMINANT OF TWO-DIMENTION CHIP BREAKING GROOVE

Tool bits with two-dimention chip breaking groove for turning stainless steel 1Cr18Ni9Ti are investigated, the formulas of limiting feed and depth of cut are obtained, the effects of tool cutting edge angle, chip breaking groove width, corner radius and cutting speed on chip breaking region are analyzed, and the chip breaking discriminant is established. This discriminant may be used to forecast the possiblity of the breaking of chips of tool bits with two-dimention groove or to select the suitable tool bit in turning stainless steels according to a given regime of machining.     

Breaking incompatibility of Brassica oleracea L. by steel-brush pollination

Summary A method is described of breaking self-incompatibility in Brussels sprouts by mutilating the stigmata during pollination with a brush of which the hair had been replaced by steel wire. The results are similar to those obtained with bud pollination and the method opens up prospects for practical use.     

Finite Tension Element Analysis of Post TensioningPrestressed Concrete Hollow Slab

The prestressed tension is an important part of the prestressed concrete component construction.In order to find out the influence on the concrete hollow slab of different tension sequence,in this paper,the 30 m assembled post tensioning concrete hollow slab is simulated by the means of finite element analysis software ANSYS. The variation of the hollow slab's stress and strain are discussed according to the result of the different tensioning sequence, then, the reasonable sequence of tensioning prestressed steel wires is put forward.     

不同熟期“川油”系列甘蓝型油菜品种主要性状与产量的相关分析

探讨在成都地区气候条件下不同熟期甘蓝型油菜产量的主要影响因素,以期为油菜抗性育种提供理论基础。采用相关分析、通径分析和主成分分析等方法,分析不同熟期甘蓝型油菜主要农艺性状、茎秆抗折力和菌核病发病率等与产量的关系。相关分析结果表明,早熟品种产量与单株有效角果数、每果粒数和茎秆中上部抗折力均呈显著或极显著正相关,中熟品种产量与株高、一次分枝高度、单株有效角果数、茎秆下部和茎秆中下部抗折力均呈极显著正相关。通径分析结果表明,早熟和中熟品种主要性状中,单株有效角果数对产量的直接作用最大。主要性状中,每果粒数对早熟品种产量的间接综合效应最大,中熟品种间接综合效应最大的是茎秆下部抗折力。主成分分析结果表明,早熟品种主要性状分为抗倒性状、株型性状、产量构成性状和抗病性状等4类性状。中熟品种为产量构成性状、株型性状和抗倒性性状等3类性状。研究表明,在四川省自然气候条件下,无论是早熟品种还是中熟品种选育,应在保证产量性状的同时,加强植株株型、抗倒性和抗病性的选择。     

方形高强钢管混凝土叠合柱轴压极限承载力分析

对于新提出的方形高强钢管混凝土叠合柱的极限承载力,基于统一强度理论,考虑中间主应力和材料拉压比的影响,引入有效约束系数和非有效约束系数并考虑箍筋对钢管外混凝土约束作用的不同,把钢管外箍筋约束混凝土划分为有效约束区和非有效约束区,将方形截面等效为圆形截面以考虑钢管核心混凝土受到的钢管和外围钢筋混凝土的双重约束效应,提出了方形高强钢管混凝土叠合柱的一种新的轴压极限承载力计算方法。将所得理论计算结果与文献试验结果进行对比,吻合良好,证明了公式的正确性。对各参数的影响规律分析表明,方形高强钢管混凝土叠合柱的承载力随着侧压系数、中间主应力影响系数、材料拉压比和纵向配筋率的增大而增大,随着钢管径厚比的增大而减小。     

ECC/钢筋混凝土叠合梁正截面受弯承载力试验与理论研究

为了探究ECC/高强钢筋混凝土叠合梁的正截面受弯特征,以及ECC层厚度对叠合梁整体受弯性能的影响,做了两组共5根梁试件的正截面受弯试验。发现与高强钢筋混凝土梁相比,叠合梁的承载力更高,相同荷载下的挠度值和最大裂缝宽度较小。在受弯全过程中其截面应变仍符合平截面假定,钢筋与ECC也可以实现协调变形,说明受拉区使用ECC可以使得高强钢筋的应力得到充分发挥。但ECC层厚度过大可能会使叠合梁发生脆性破坏。进一步地,在此研究的基础上,对已有ECC的本构模型进行简化,忽略其应力强化贡献,并运用叠加原理,提出一种用于计算ECC/钢筋混凝土叠合梁正截面受弯承载力的方法,将计算结果与试验结果及诸多文献结果进行比较,发现吻合度较高。     

Static Behavior of Rigid Connections of H-beams with Corrugated Webs

Steel H-beams with corrugated webs can provide high shear-buckling resistance with very thin webs, which results in saving of steel. Common beam-to-column rigid connections are not suitable for H-beams with corrugated webs, so 2 types of rigid connections are proposed .In this paper,2 static tests of beam-to-column rigid connections of H-beams with corrugated webs were conducted. And the test results were compared with the results from finite element analysis and the results calculated from the practical design formulas to verify the validity of the results from ABAQUS FEA and reliability from the practical design formulas. Parametric studies were carried out to investigate the bearing capacity of the pinned connection with variations in the thickness of the endplate, the connecting plate and the corrugation at the breaking point.     

Finite Element Method of 3D Stable Heat Conduction of Steel Fluid in Continuous Casting Moulds

The heat transfer of steel fluid in continuous casting mould is a stable process and can be depicted with three-dimensional stable heat conduction equation depending on tension speed. The corresponding finite element equation, including the first, second and third boundary conditions, is deduced out with Galerkin residual method. The coded FEM program is used to analyze the temperature distribution of Q235 steel in continuous billet casting mould. The method proposed is a foundation of thermo-mechanical coupled analysis for the formation of solidified shells and stress in the shells in continuous casting.     

基于内聚力模型的锈蚀砼梁抗弯刚度

粘结性能退化是导致锈蚀钢筋混凝土构件力学性能下降的主要因素之一,基于锈蚀构件粘结性能实验研究成果与内聚力模型,建立了有厚度的双线性内聚力单元与分离式钢筋混凝土梁分析模型,引入粘结界面层,研究了粘结性能退化对锈蚀钢筋混凝土梁抗弯刚度的影响。结果表明,双线性内聚力单元可以有效模拟钢筋与混凝土之间的粘结机制,而根据锈蚀深度确定的有厚度的粘结单元能合理描述锈蚀程度对粘结性能的影响。数值分析结果与实验及经验公式对比,表明了文中方法的有效性和合理性。     

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%.     

再生混凝土与锈蚀钢筋间的粘结性能试验研究

为了探究再生混凝土结构的耐久性能,对5组不同钢筋锈蚀率(0~9%)的再生混凝土梁式试件进行加载试验。分析不同钢筋锈蚀率对再生混凝土梁式试件的钢筋应变、局部粘结应力、粘结滑移和极限粘结应力的影响。结果表明：钢筋锈蚀率大于3%时试件底部开始有细微锈胀裂缝出现;锈蚀率越大,荷载作用下钢筋应变沿锚固位置的变化曲线越平缓;局部粘结应力沿锚固段呈现出双峰分布,峰值主要集中在加载端和自由端附近;加载端附近位置滑移现象最先发生,远离加载端滑移现象延后;随着钢筋锈蚀率的增大,极限粘结强度先增加后降低,极限荷载下的滑移值增大。     

3D Meso scale Failure Simulation of Four phase Composite Concrete

Taking into account the influence of the internal micro cracks on the strength and deformation of concrete, a four phase composite material model was proposed, in which it included mortar, aggregate, interface and random defects. Meso scale unit in concrete was subjected to elastic plastic damage constitutive of increments form in strain space. With the simulation of mesh concrete crack growth by damage elimination, the damage processes of concrete under 3 D uniaxial compression and the elasto plastic damage process of concrete under uniaxial tension with heterogeneous specimen were obtained. It was shown that the proposed four phase model added the simulation of random defects, with which it was more appropriate to the actual situation in concrete forming. The percentage of random defects in volume was the key to determine the weakening degree of macro strength of concrete. The cracks occlusion was obvious for the lower homogeneous uniaxial tension specimen and the fracture was clearer for higher homogeneous specimen. The simulation results was in good agreement with test results.     

Computational Model and Influencing Factor Analysis of Reinforced Concrete Walls under Fire

The finite element software ABAQUS is used to calculate the deformation of reinforced concrete walls under fire. The calculated results agree well with previous experimental results. Based on the finite element model, the influences of such parameters as axial load level, lateral load level, height-to-thickness ratio, wall thickness, concrete compressive strength, steel reinforcement yield strength, steel reinforcement ratio and concrete protection thickness on deformation and fire resistance of walls are analyzed systematically. It is found that, under the conditions of big axial load level or wall thickness without lateral load and small height-to-thickness ratio, the reverse deflection of reinforced concrete walls in fire is apt to occur. Within the work range of parameters in common use, the fire resistance of walls decreases with the increase of axial load level, lateral load level, height-to-thickness ratio, steel reinforcement yield strength or steel reinforcement ratio, and increases with the increase of wall thickness or concrete compressive strength.     

Critical Temperature of Axially Restrained Steel Columns withPartial Fire Retardant Coating Damage

In order to investigate the fire resistance of steel columns with partial fire retardant coating damage in fire, based on the differential equation of equilibrium on each portion of steel column, the deflection of steel column after the fire retardant coating damage was derived, with the pined ends and rigid ends of the columns at elevated temperatures. The critical temperature calculation method was proposed for partial fire protection damage and axial restrained steel columns by taking the edge yielding criteria. The deflection and axial displacement were verified by finite element method at elevated temperature. With a case study, the critical temperature and relationship of axial force and temperature were obtained for pined column with axial restraint. It was shown that the axial force of the steel column at elevated temperatures was increased and the critical temperature was decreased by the axial restraint. The longer the fire retardant coating damage was and the higher the axial restraint was, the lower the critical temperature was.     

蠕变模型对约束钢梁抗火性能分析的影响

钢材在高温和荷载作用下产生明显蠕变变形,影响火灾中结构的变形和受力性能。现有的蠕变模型较多,但没有一个广泛适用的蠕变模型。不同的蠕变模型对钢结构抗火分析结果有很大影响。为了量化蠕变模型对约束钢梁抗火性能分析的影响,对5种常用的蠕变模型进行了对比分析。采用编写的约束钢梁计算程序,分别计算5种蠕变模型下约束钢梁的抗火性能并与试验数据进行对比。结果表明,采用Norton蠕变模型的计算结果与试验数据吻合最好。最后对影响约束钢梁抗火性能参数进行了研究,研究发现,Harmathy蠕变模型对约束梁抗火性能分析结果影响最大;不同蠕变模型对不同荷载比、约束刚度下的约束钢梁抗火性能影响程度均不同。     

重穗型水稻植株抗倒伏能力的研究

以18个不同穗重型水稻品种为材料，研究了重穗型水稻植株的抗倒伏能力及其与茎秆的物理性状、机械组织特性的关系。结果表明：重穗型品种单穗重大、产量高与其株高的适当增加密切相关。重穗型品种由于单穗重和株高的增加，弯曲力矩加大，但抗折力也明显提高，故而其茎秆抗倒伏能力并未降低。重穗型品种茎秆抗折力强的主要原因