青岛火车站预应力混凝土框架结构裂缝预防与控制

混凝土结构不可避免地会出现裂缝,当结构出现裂缝时,工程结构的耐久性和力学性能都会受影响.针对混凝土结构裂缝产生的各种原因,结合青岛火车站大型预应力框架结构的实践,提出从材料、施工和维护等方面控制裂缝的技术措施,应用于工程实践,获得了预期效果.     

倾斜疲劳裂纹在混合型应力下张开及滑移特性

对于存在裂纹的机械零件或者构件,它很有可能会受到来自不同方向的作用力, 因此有必要研究裂纹在混合型应力条件下的传播特性. 该文使用具有不同倾斜角度的裂纹--这些裂纹是在应力比R=0的Ⅰ型循环应力下制作的,通过测量裂纹的开口方向和滑移方向的位移量,计算了裂纹端部Ⅰ型应力强度因子(KⅠ)mes和Ⅱ型应力强度因子(KⅡ)mes.裂纹的倾斜角度是指载荷方向与裂纹间的夹角.结果表明,对于存在压缩残余应力的疲劳裂纹,当倾斜角度较大,即β=60°时,应力强度因子的实验值(KⅠ)mes小于理论计算值(KⅠ),但此时实验值(KⅡ)mes与理论值(KⅡ)基本一致.另一方面,对于倾斜角度较小β=45°的疲劳裂纹,其(KⅠ)mes减少的同时,由于裂纹上下表面相互接触,从而导致(KⅡ)mes同时下降.     

Theoretical analysis on bending behavior of functionally graded composite beam crack-controlled by ultrahigh toughness cementitious composites

Ultrahigh toughness cementitious composites (UHTCC) obviously show strain hardening property under tensile or bending loading. The failure pattern of the UHTCC components exhibits multiple fine cracks under uniaxial tensile loading with prominent tensile strain capacity in excess of 3%, with merely 60 μm average crack width even corresponding to the ultimate tensile strain state. The approach adopted is based on the concept of functionally-graded concrete, where part of the concrete, which surrounds the main longitudinal reinforcement in a RC (reinforced concrete) member, is strategically replaced with UHTCC with excellent crack-controlling ability. Investigations on bending behavior of functionally-graded composite beam crack controlled by UHTCC has been carried out, including theo- retical analysis, experimental research on long composite beams without web reinforcement, validation and comparison between experimental and theoretical results, and analysis on crack control. In addition to improving bearing capacity, the results indicate that functionally-graded composite beams using UHTCC has been found to be very effective in preventing corrosion-induced damage compared with RC beams. Therefore, durability and service life of the structure could be enhanced. This paper discusses the development of internal force and crack propagation during loading process, and presents analysis of the internal force in different stages, moment-curvature relationship from loading to damage and calculation of mid-span deflection and ductility index. In the end, the theoretical formulae have been validated by experimental results.     

应力吸收层沥青混合料的低温抗裂性能

通过对自主研发的Sampave等3种改性沥青结合料和不同级配的应力吸收层沥青混合料进行低温弯曲和低温蠕变试验,分析沥青结合料和矿料级配对应力吸收层沥青混合料低温抗裂性能的影响.结果表明:自主研发的Sampave特种改性沥青混合料具有优良的低温抗裂性能,但单一改性剂SBR改性沥青并不能达到应力吸收层沥青结合料的性能要求;矿料4.75 mm、0.075 mm筛孔通过率对其低温抗裂性能影响较敏感.     

煤仓漏斗的焊接工艺

针对Q235-B钢板制成的原煤仓漏斗锈蚀、磨损严重的问题,更换采用了内层为4Cr13马氏体不锈钢,外层为Q235-B钢板的双层结构漏斗,并通过焊接工艺试验为煤仓漏斗的制造工艺确定了正确的焊材和焊接方法,取得了良好的效果。     

天然橡胶/顺丁橡胶并用硫化胶的力学破坏机理

用扫描电子显微镜对天然橡胶／顺丁橡胶并用硫化胶的力学破坏机理进行了研究，结果表明试验样拉伸疲劳破坏断面具有拉伸断裂和屈挠龟裂的双重特征。白炭黑和Ｓｉ６９的加入使硫化胶的屈挠疲劳初始裂口形式发生变化。热氧老化使试样的拉伸断裂由韧性向脆性转化。     

Pavement crack detection using hessian structure propagation

Pavement images are widely used in transportation agencies to detect cracks accurately so that the best proper plans of maintenance and rehabilitation could be made. Although crack in a pavement image is perceived because the intensity of crack pixels contrasts with that of the pavement background, there are still challenges in distinguishing cracks from complex textures, heavy noise, and interference. Unlike the intensity or the first-order edge feature of crack, this paper proposes the second-order directional derivative to characterize the directional valley-like structure of crack. The multi-scale Hessian structure is first proposed to analytically adapt to the direction and valley of cracking in the Gaussian scale space. The crack structure field is then proposed to mimic the curvilinear propagation of crack in the local area, which is iteratively applied at every point of the crack curve to infer the crack structure at the gaps and intersections. Finally, the most salient centerline of the crack within its curvilinear buffer is exactly located with non-maximum suppression along the perpendicular direction of crack. The experiments on large numbers of images of various crack types and with diverse conditions of noise, illumination and interference demonstrate the proposed method can detect pavement cracks well with an average Precision, Recall and F-measure of 92.4%, 88.4%, and 90.4% respectively. Also, the proposed method achieves the best performance of crack detection on the benchmark datasets among methods that also require no training and publicly offer the detection results for every image.     

UHPC的轴拉性能与裂缝宽度控制能力研究

为研究3种类型超高性能混凝土(ultra-high performance concrete,简称UHPC)的轴拉应力-应变曲线及其裂缝宽度控制能力,包括高应变强化UHPC、低应变强化UHPC和应变软化UHPC.采用轴拉试验方法测试狗骨头形试件,得到UHPC的轴拉应力-应变曲线和缝宽-应变曲线.试验结果表明:高应变强化UHPC和低应变强化UHPC的轴拉应力-应变曲线均包括弹性段、应变强化段和应变软化段,应变软化UHPC只有弹性段和应变软化段;UHPC应变强化段和应变软化段的转折点是裂缝缓慢扩展和迅速扩展的临界点;提高UHPC的极限拉伸应变,即延长其应变强化段,有助于提高其裂缝宽度控制能力;高应变强化UHPC拉伸应变在0.42%之前,其裂缝宽度均小于0.05 mm.对比C50混凝土(极限应变、极限强度分别为0.012%、2.3 MPa),高应变强化UHPC优异的裂缝宽度控制能力避免了结构设计中受正常使用状态裂缝宽度验算限制的影响,同时可在钢筋屈服前与其全程协同工作,这使得钢筋增强高应变强化UHPC在某些需要对裂缝宽度进行严格控制的结构类型中具有很高的应用价值.     

考虑多因素作用下的RC梁抗力时空退化模型

为研究钢筋混凝土结构锈蚀后的力学性能和抗力退化规律,基于RC梁加速锈蚀试验结果,首先综合考虑均匀锈蚀和点蚀同时发生的影响,对钢筋截面面积的时变模型进行分析,其次探讨裂缝宽度与氯离子扩散系数及RC梁抗力的关系,随后考虑受拉主筋锈蚀不均衡的影响,对结构抗力计算模型进行讨论,最后基于材料性能和结构尺寸的空间变异性,建立RC梁抗力时空退化模型,并对桥梁服役100 a后的抗力进行预测.研究发现:当考虑各参数的空间变异性时,不考虑裂缝影响得到的抗力值比考虑裂缝影响得到的抗力值高了9.91%;考虑各参数空间变异性时的抗力值比不考虑时下降了14.68%;适当的选取波动系数和单元尺寸对考虑结构各参数的空间变异性十分重要;潮汐区和浪溅区环境下结构的剩余抗力分别为初始抗力的43.23%和36.45%,较海岸线大气区环境下的抗力值分别下降了6.73%和21.35%,因此在结构服役期间,应尽量做好防腐措施,减少氯离子侵蚀对结构耐久性的破坏.     

Fractal characterization for the mining crack evolution process of overlying strata based on microseismic monitoring technology

In order to study the evolution laws during the development process of the coal face overburden rock mining-induced fissure,we studied the process of evolution of overburden rock mining-induced fissures and dynamically quantitatively described its fractal laws,based on the high-precision microseismic monitoring method and the nonlinear Fractal Geometry Theory.The results show that:the overburden rock mining-induced fissure fractal dimension experiences two periodic change processes with the coal face advance,namely a Small→ Big→ Small process,which tends to be stable;the functional relationship between the extraction step distance and the overburden rock mining-induced fissure fractal dimension is a cubic curve.The results suggest that the fractal dimension reflects the evolution characteristics of the overburden rock mining-induced fissure,which can be used as an evaluation index of the stability of the overburden rock strata,and it provides theoretical guidance for stability analysis of the overburden rock strata,goaf roof control and the support movements in the mining face.