砖混住宅顶层墙体裂缝的受力分析与防治

文章对砖混结构墙体裂缝向题进行了温度应力、地基不均匀沉降、砌体温度、变形等若干项分析,并针对墙体裂缝提出有效的防治措施。     

Repair of 130-Year Old Masonry Bridge using High-Performance Cement Grout

The restoration of a masonry bridge pier built in 1887 was carried out using cement-based grout. Erosion of the pointing mortar of the pier core outer surface and cracks and voids in the pier core were encountered. This paper presents the methodology used to develop high-performance cement grouts for injection of deteriorated joints and cracks in the stone pier and describes the repair and monitoring operations. Portland and microfine cement-based grouts were optimized in the laboratory. An epoxy resin grout was used as a benchmark to compare the performance of the cement-based grouts. The effectiveness of the grout injection was assessed with core samples testing and nondestructive testing using the sonic tomography method to compare the quality of the medium before and after grouting. High penetrability of the grout was achieved for the high-performance mixtures. The use of high-early-strength cement with some silica fume replacement resulted in a relatively economical mixture exhibiting high performance. The results of this pilot study were later recommended for the rehabilitation of similar masonry piers.     

Temperature and thermal stresses in work rolls during the hot rolling of strip

In this paper the solution of the unsteady, three-dimensional heat transfer in work rolls was derived by using Bessel functions and the δ-function and expressed by an infinite series. In this manner other problems of heat transfer in solid cylinders and hollow cylinders can also be calculated. The temperature profile of the work roll due to the distribution of the temperature in the axial direction can cause unregular pressure distribution between work roll and backup roll and can influence the quality of strip. Therefore, the thermal crowns must be considered at various moments during rolling. The thermal crown can be determined by using the FE-Method or others. The reason for the fire-cracking in the roll surface can be determined as the thermal shock load in the contact zone, in which the sharp compressive stresses lead to local plastic deformation. The local plastic deformations are followed by residual deformations. Therefore, residual tensile stresses occur in the cooling zone. On each revolution, the surface undergoes plastic strain in compression and in tension. The result is thermal fatigue. The fine network of cracks in the roll surface can result in a sharp stress concentration which is dangerous for the rolls loaded with a bending moment. The maximum tensile stresses due to the temperature distribution occur in the roll core, which usually do not lead to damages of the rolls.     

冷变形对0Cr25Ni35AlTi组织与力学行为的影响

采用室温拉伸和硬度测试研究了不同冷变形量对0Cr25Ni35AlTi室温力学性能和硬度的影响。通过OM、TEM对冷变形后的组织进行观察,分析不同冷变形后力学性能的变化机制。结果表明,随着变形量的增加,合金的抗拉强度、屈服强度和硬度增加。当变形量为20%时,合金的屈服强度提高了1.5倍,抗拉强度提高了1.2倍,分别达到了679和762 MPa。合金加工硬化指数随着冷变形量的增加而减小。在10%和15%形变量之间存在一个临界值,小于临界值时,位错运动主要是单滑移,真应力-真应变曲线可用Ludwigson模型描述;大于临界变形量,位错运动出现了多滑移和交滑移,真应力-真应变曲线可以用Hollomon方程描述。     

TC16钛合金板材冷轧工艺及组织性能研究

进行了TC16钛合金板材多道次冷轧试制,利用光学显微镜、 扫描电镜和X射线衍射等手段研究了变形量对冷轧板材微观组织与力学性能的影响.结果表明:α+β两相TC16钛合金板材冷轧加工是可行的,其极限冷变形量达到79％,冷轧板材表面无裂纹.大幅度冷轧变形后,TC16钛合金组织为分布均匀的纤维状结构,且存在极少量未充分变形的α...     

Load Rating of Masonry Arch Bridges: Refinements

In a paper previously published by the first writer, a procedure for load-rating masonry arch bridges was introduced. The procedure uses the Load Factor Method of the 1994 American Association of State Highway and Transportation Officials Manual for the Condition Evaluation of Bridges, applied to a frame analysis model of a masonry arch spanning from abutment to abutment. The procedure is based on the assumption of the arch barrel having no tensile strength. The objective of this technical note is to complement the initial procedure by enabling the assessing engineer to exercise discretion in deciding whether or not a small value of tensile strength should be allowable in determining a suitable rating for masonry arch bridges. In addition the initially proposed strength values, which are considered overly conservative, are increased. The introduction of these refinements will allow a more accurate assessment of the nation’s stock of stone masonry bridges.     

古砖塔子结构压剪复合受力性能分析

为研究古塔子结构的受力性能,设计制作了3件不同楼层的子结构缩尺模型试件,进行低周反复加载试验,观察试件的开裂、变形及破坏现象;建立数值模型进行计算,得到了试验荷载作用下各试件的等效塑性应变、荷载?位移曲线,将计算结果与试验结果进行对比,分析竖向压应力对古塔砌体抗震性能的影响。结果表明,特征荷载的计算值相对试验值的误差均小于21%,等效塑性应变的分布与试件开裂破坏区域一致;当竖向压力保持恒定时,随着水平荷载的增大,塔体沿砌筑缝逐渐开裂破坏,裂缝宽度亦随之增大,在塔体洞口周围的破坏更为明显,且试件残余变形增大;随着压剪比的增大,古塔砌体开裂破坏的范围减小,抗剪承载力、刚度以及耗能能力均有所提高,但延性和变形能力略有降低。研究结果为砖石古塔建筑结构损伤及抗震能力评定提供参考。      

浅析砖混结构裂缝的成因和防治

在分析由于地基、基础和砌体设计、砌体施工、温度变化等因素产生的砖砌体裂缝,以及混凝土硬化和在较高温度下失水收缩、支座处负筋下沉造成混凝土现浇板裂缝的基础上,提出了针对性的防治措施。     

某主厂房天面裂缝原因及防治措施

由变形变化引起的裂缝即主要由温度收缩变化产生应力引起的裂缝,在结构设计中,为防止这样收缩引起的破裂,可以采取“放”的办法,给结构留有自由变形的余地,或者采取“抗”的方法,限制变形,以强度抵抗最大应力．根据经验,宜采取“抗放兼施,以放为主”的作法较为经济可靠。     

冷拉拔变形对纯铜组织及性能的影响

通过工业拉丝机对纯铜棒材进行多道次冷拉拔得到不同变形量的线材.对不同变形量的线材试样进行退火实验(400℃,1 h),研究组织形貌变化对其力学性能和电学性能的影响.试样的变形量由0增加至60％时,在拉拔方向上晶粒尺寸由101.3μm下降至17.6μm,截面方向上晶粒尺寸由103.4μm下降至16.4μm,晶粒呈现等轴状...     

砌体结构房屋常见裂缝原因及控制

文章从温度收缩变形、干缩变形、地基不均匀沉降、荷载作用等方面分析了砌体结构房屋常见裂缝的原因,在剖析砌体裂缝根源的基础上,结合相关规范的防裂措施,总结裂缝控制的方法.     

Radon penetration of concrete slab cracks, joints, pipe penetrations, and sealants

Radon movement through 12 test slabs with different cracks, pipe penetrations, cold joints, masonry blocks, sealants, and tensile stresses characterized the importance of these anomalous structural domains. Diffusive and advective radon transport were measured with steady-state air pressure differences controlled throughout the deltaP = 0 to 60 Pa range. Diffusion coefficients (deltaP = 0) initially averaged 6.5 x 10(-8) m2 s(-1) among nine slabs with only 8% standard deviation, but increased due to drying by 0.16% per day over a 2-y period to an average of 2.0 x 10(-7) m2 s(-1). An asphalt coating reduced diffusion sixfold but an acrylic surface sealant had no effect. Diffusion was 42 times higher in solid masonry blocks than in concrete and was not affected by small cracks. Advective transport (deltaP < or = 60 Pa) was negligible for the slabs (10(-16) m2 permeability), pipe penetrations, and caulked gaps, but was significant for cracks, disturbed pipe penetrations, cold joints, masonry blocks, and concrete under tensile stress. Crack areas calculated to be as small as 10(-7) m2 significantly increased radon advection. Algebraic expressions predict air velocity and effective crack width from enhanced radon transport and air pressures. Masonry blocks, open cracks, and slab cold joints enhance radon penetration but stressed slabs, undisturbed pipe penetrations, and sealed cracks may not.     

Identification of rolling-sliding damage mechanisms in porous alloys

Lubricated rolling-sliding damage in a relatively soft Fe-0.6 pct C alloy and a relatively hard carbonitrided iron, both produced by powder metallurgy, has been investigated. Damage mechanisms were controlled by large-scale as well as small-scale plastic deformations. A large-scale, bulk plastic deformation process produced surface densification in the Fe-0.6 pct C alloy. Formation of surface cracks by asperity-scale plastic shearing was also observed in both materials. Small-scale plastic deformation processes, restricted to the pore edges, gave rise to the formation of fatigue microcracks at the boundary between the densified and undensified region in the Fe-0.6 pct C alloy. A similar effect was found at a depth of between 550 and 1000 μm in the carbonitrided material. Moreover, in the Fe-0.6 pct C alloy, these plastic deformations also triggered the formation and propagation of macrocracks, which produced macroscopic damage by spalling. The damage mechanisms due to small-scale plastic deformations were explained on the basis of a local approach model, able to account for the influence of pores on the mechanical behavior of the materials. However, this approach could not explain the microcracks, which were found at the surface pores in the carbonitrided material. Their formation was ascribed to the interplay between the surface tensile (friction) stresses and the low matrix toughness of the material near the surface.     

Effects of combined high and low temperature deformation processing of β III titanium

The structure and properties of β III titanium alloy (nominal composition: 11.5 pct Mo, 6 pct Zr, 4.5 pct Sn, bal Ti) were studied as a function of combined high and low temperature ther-momechanical processing. A water quenched extrusion was deformed various amounts by swaging at room temperature prior to the aging treatment. No re-solution heat treatment was employed. The swaging introduced mechanical twinning and a small amount of stress induced orthorhombic martensite. Following a 900°F, 8 hr aging treatment, substantial increases in yield and tensile strength were observed, combined with a severe decrease in tensile ductility in samples with small amounts of swaging. The orientation and morphology of the deformation products have a critical influence on tensile ductility. A decrease in the plane strain fracture toughness accompanied the large increase in tensile strength.     

Theoretical and practical implications of creep curve shape analyses for 8090

For tensile stresses applied parallel to the elongated grain structure of the aluminum alloy, 8090, the creep and creep fracture properties are discussed in relation to the changes in precipitate dispersion and transgranular failure mode observed over stress ranges giving creep lives up to 6000 hours at 373 to 463 K. Specifically, a transition from growth of cracks nucleating on the short transverse boundaries to neck formation occurs when the deformation resistance is reduced progressively by precipitate coarsening as the test duration increases at 427 K and above. All features of the recorded behavior patterns are then explained in terms of the processes governing strain accumulation and damage development by using the ϑ methodology to quantify the systematic variations in creep curve shape with changing stress and temperature.     

Deformation Characteristics of Steel Billets with Liquid Core

To investigate the deformation characteristics of billets with liquid core during soft reduction and to clarify the correlation between internal cracks and deformation of the billet in the mushy zone, a fully coupled thermo‐mechanical Finite Element Model was developed in ABAQUS, furthermore, casting and soft reduction tests were carried out in a laboratory strand casting machine. During soft reduction the temperature distribution, the stress and strain states in the billet were calculated, the deformation characteristics of the billet during soft reduction were determined and the relation between internal cracks and equivalent plastic strain as well as maximal principal stress was analysed. The results show that tensile stresses can develop in the mushy zone during soft reduction and the equivalent strain nearby the Zero Ductility Temperature (ZDT) increases with a decreasing solid fraction. Internal cracks can be initiated when the accumulated strain exceeds the critical strain and /or the applied tensile stress exceeds the critical fracture stress during solidification. In addition, the factors (reduction efficiency and internal cracks) that should be considered to determine the optimal parameter for the soft reduction were established.     

Thermo-elasto-visco-plastic finite element analysis on formation and propagation of off-corner subsurface cracks in bloom continuous casting

The formation and propagation of the popular off-corner subsurface cracks in bloom continuous casting were investigated through thermo-mechanical analysis using three coupled thermo-mechanical models.A two-dimensional thermo-elasto-visco-plastic finite element model was developed to predict the mould gap evolution,temperature profiles and deformation behavior of the solidified shell in the mould region.Then,a three-dimensional model was adopted to calculate the shell growth,temperature history and the development of stresses and strains of the shell in the following secondary cooling zones.Finally,another three-dimensional model was used to analyze the stress distributions in the straightening region.The results showed that the off-corner cracks in the shell originated from the mould owing to the tensile strain developed in the crack sensitive regions of the solidification front,and they could be driven deeper by the possible severe surface temperature rebound and the extensive tensile stress in the secondary cooling zone,especially upon the straightening operation of the bloom casting.It is revealed that more homogenous shell temperature and thickness can be obtained through optimization of mould corner radius,casting speed and secondary cooling scheme,which help to decrease stress and strain concentration and therefore prevent the initiation of the cracks.     

热镀锌合金化镀层裂纹产生及扩展的原位观察

用装配3点弯曲试验装置的扫描电镜原位分析了GA钢板变形情况下镀层中裂纹的产生、扩展、镀层断裂及GA钢板在塑性变形过程中镀层与钢基体界面交互作用的情况。试验及分析结果表明：镀层承受拉应力的一侧,裂纹在Г／δ,相界面处产生,在δ1相中沿着垂直于镀层平面的方向扩展,并沿着Г相／钢基体界面延伸,镀层塑性变形的迹象不明显;镀层承...     

Structural Analyses and Assessment of Historical Kamanl? Mosque in Izmir, Turkey

Historical structures are one of the most precious pieces of cultural accumulation. In this study, an interdisciplinary work was conducted to assess the structural condition of a historical masonry structure, Urla Kamanl? Mosque in ?zmir, Turkey. The structure is a member of group of structures, Yah?i Bey Complex, which includes a Turkish bath, a tomb, two fountains, and a primary school. The structure dates back to early 14th century to mid-15th century. History investigation, measurement survey, long-term settlement, and moisture observations were conducted. Nondestructive and destructive material tests were performed on stone, brick, and mortar. 3D finite-element model of the structure was used to investigate the critical locations of the structure under its self-weight, seismic load, and settlement load. Linear elastic and nonlinear settlement analyses were conducted to investigate the reason for massive cracks challenging the structural integrity.     

Microstructure effects on tensile properties of tungsten-Nickel-Iron composites

Controlled processing of heavy alloys containing 88 to 97 pct W resulted in high sintered densities and excellent bonding between the tungsten grains and matrix. For these alloys, deformation and fracture behavior were studiedvia slow strain rate tensile testing at room temperature. The flow stress increased and the fracture strain decreased with increasing tungsten content. The tradeoff between strength and ductility resulted in a maximum in the ultimate tensile strength at 93 pct W. Microstructure variations, notably grain size, explain sintering temperature and time effects on the properties. During tensile testing, cracks formed on the surface of the specimens at tungsten-tungsten grain boundaries. The crack density increased with plastic strain and tungsten content. The surface cracks, though initially blunted by the matrix, eventually increased in density until catastrophic failure occurred. An empirical failure criterion was developed relating fracture to a critical value of the surface crack tip separation distance. Application of the model explains the effects of microstructural variables on tensile properties. Formerly Graduate Research Assistant at Rensselaer Polytechnic Institute.