现浇钢筋混凝土楼板裂缝的成因及预防

钢筋混凝土的裂缝控制问题是建筑工程中很重要的问题之一，实际施工中有必要对其进行有效控制，特别是避免有害裂缝的产生。章主要从施工操作方面来剖析裂缝的成因，探讨施工中具体的防治措施。     

基于时频分析的裂纹转子碰摩故障特征研究

为研究转子系统耦合故障特性,采用有限元方法建立了含有横向裂纹、转静碰摩的非线性转子动力学模型。首先研究了不同转速下裂纹、碰摩单一故障下转子系统的振动响应,其次研究了两种故障耦合情况下系统的振动响应特征。采用波形图、FFT谱图、瞬时频率和Hilbert-Huang时频谱(HHS)相结合的方法对故障转子振动信号进行了分析。分析结果表明:运用多种时频分析相结合的方法可以较为全面地了解转子的故障特征,裂纹转子在1/5、1/3临界转速时会发生较为明显的5X、3X谐波,且裂纹的产生会导致响应幅值增大,从而引起更为严重的碰摩。      

房屋建筑中漏缝的成因及控制

房屋建筑的实践表明,住宅产生裂缝的原因和类型很多,本文针对产生裂缝的原因和类型进行了分析,关提出了尽可能地在材料、施工过程、设计初期对裂缝问题进行有效控制的相应对策,相信这次研究会对完善房屋建设工作有着至关重要的作用.     

Illegal drugs and public corruption: Crack based evidence from California

Do illegal drugs foster public corruption? To estimate the causal effect of drugs on public corruption, we adopt the synthetic control method and exploit the fact that crack cocaine markets emerged in California in 1981, before reaching any other U.S. state. Our results show that public corruption more than tripled in California in the first three years following the arrival of crack cocaine. We argue that this resulted from the particular characteristics of illegal drugs: cheap technology and rigid demand, which fosters a convergence of interests between criminals and corrupted public officials resulting in a positive causal impact of illegal drugs on corruption.     

What can we learn from the history of gasoline crack spreads?: Long memory,structural breaks and modeling implications

In this paper, we investigate the long-range auto-correlations of crack spreads using a nonparametric method, named detrended moving average (MF-DMA). We find that the auto-correlations display multiscaling behaviors and are dominated by the anti-persistence (mean-reversion) in the long-term. Moreover, the auto-correlations are multifractal, indicating that various small and large fluctuations display different scaling behaviors. Using a technique of rolling windows, we find that some extreme events can drive the degree of anti-persistence and the multifractality (complexity) to rise up. In other words, these events have negative impacts on market efficiency. However, the effects of these events are not alike. We also detect long-range auto-correlations in crack spread volatilities and find a strong persistent behavior and multifractality. Finally, we discuss the modeling implications of the findings on long-range auto-correlated patterns. Our results indicate that ARFIMA-GARCH models can capture the major dynamics of large fluctuations. For small fluctuations, they are misspecified. Interestingly, we find that the strong long-range auto-correlated behaviors do not imply that ARFIMA model which takes long memory into account can outperform random walk model in the sense of out-of-sample prediction. The major reason may be that market complexity exploited in this paper causes the low predictability of ARFIMA model.     

200m~3液氨球罐裂纹成因分析及修复措施

本文对一台200m3液氨球罐使用过程中产生裂纹的原因进行了分析并提出了相应的返修方案。     

泵送混凝土的裂缝分析与处治

广西一些高速公路、桥梁工程表明，泵送混凝土强度不足、凝结异常时有发生，特别是裂缝普遍存在，在一定程度上影响结构的抗渗性和耐久性，值得引起足够的重视。文章重点分析其产生原因，找出处治裂缝的措施。     

预应力混凝土箱梁桥裂缝成因分析

针对目前大跨度预应力混凝土箱梁桥普遍存在的裂缝问题，详细分析了各种产生裂缝的原因，并提出处理措施，给同类型的桥梁设计施工提供参考。     

大体积混凝土结构裂缝控制与防止措施

本文主要从选择使用外加剂、混凝土水化热温度监测、混凝土养护以及混凝土温差这四个方面对大体积混凝土结构裂缝控制进行分析。     

地下室混凝土墙板裂缝的防治

本文主要介绍了地下室混凝土墙板产生裂缝的原因和一些常用的处理办法和防治措施,以及应注意的 一些问题。