Reduction of fire spalling in high-performance concrete by means of superabsorbent polymers and polypropylene fibers: Small scale fire tests of carbon fiber reinforced plastic-prestressed self-compacting concrete

High-performance concrete (HPC) is prone to explosive spalling when exposed to fire, which may lead to failure of the concrete elements. Polypropylene fibers (PP) are often added to HPC, as upon their melting they create channels through which water vapor is evacuated, preventing the build-up of high vapor pressures. In self-compacting HPC (HPSCC), the amount of PP fibers needs to be limited in order to keep the self-compacting properties, which may reduce the fire resistance.In this paper, a novel strategy to reduce fire spalling in HPSCC is illustrated, based on adding small particles of superabsorbent polymers (SAP) during mixing. The SAP end up as empty macropores, similar to air voids, in the HPSCC matrix. The PP fibers-SAP voids system percolates at a lower fiber loading than the fibers alone, allowing maintenance of the self-compacting properties while reducing substantially the fire spalling. In particular, in this paper it is shown how addition of SAP is able to reduce fire spalling in thin-walled HPSCC slabs prestressed with carbon fibre reinforced plastic reinforcement.     

An empirical model for confined concrete after exposure to high temperature

In this study, constitutive relationships have been developed for confined concrete subjected to elevated temperature to specify the fire‐performance criteria for concrete structures after exposé to fire. This study extends over a total of 63 circular hoop confined concrete specimens that were casted and tested under concentric compression loading after exposure to high temperature. The test variables studied are the yield strength of transverse reinforcement, spacing of the hoop, and exposure to temperatures from ambient to 800°C. It is shown that all of these variables have significant influence on concrete behavior at different temperatures and further an improvement in the thermal resistance of concrete when confined using transverse steel reinforcement. On the basis of experimental results, a model for confined concrete after exposed to high temperature is proposed to predict the results of residual behavior after thermal cycles. The proposed empirical stress‐strain equations are suitable to predict the postfire behavior of confined normal strength concrete in compression. The predictions were found to be in good agreement and well fit with experimental results.     

断层影响区工作面支架稳定性及围岩控制措施

为了解决工作面过断层期间煤层倾角变化及围岩破碎导致支架易出现倾倒、煤壁片帮及顶板冒顶的问题,结合义城煤业18201工作面情况,分析了煤层倾角增大时支架防倾倒技术措施和过断层方法及煤壁片帮控制技术措施。采取相应措施后,保证了支架稳定,工作面的煤壁片帮次数、范围、深度等都明显降低,确保工作面安全回采。     

大模板施工中飘窗板浇筑方法改造探讨

由于现阶段大模板工程施工中对不同标高结构施工采取二次浇筑的方法,既不经济,又存在质量隐患。本文以飘窗板施工为例,通过模板改造从而改变施工方法的角度,从技术质量、经济、施工进度等方面对新旧方法进行了对比讨论。     

一种提高汽车板件刚度的工艺设计

针对汽车板件拉深成形后刚度不足的问题,在修边工序中利用压料芯在刚度不足区域成形加强筋,然后经整形复原其设计形状,提高了板件的塑性变形量,从而达到提高板件刚度的目的,为类似板件的工艺设计提供了一种思路。     

大采高综采工作面煤壁片帮的研究与防治

通过对大采高综采工作面煤壁片帮机理、特征及其影响因素的了解,结合西山煤电斜沟煤矿18102工作面的实际情况,分析防治片帮的技术途径与措施,为类似工作面煤壁片帮防控提供参考。     

加劲肋对吊车梁用钢量的影响

在吊车梁设计中通过合理设置加劲、减小腹板厚度,达到节约钢材、优化设计的目的。通过具体设计实例,深入理解规范,对比设置加劲对吊车梁用钢量的影响,得出合理的设计方案。     

InP/InGaAsP脊波导的单模特性与偏振特性研究

以InP/InGaAsP脊形波导结构为研究对象,采用有限元算法(FEM),系统地仿真分析了在固定芯层厚度的情况下,不同脊高和脊宽条件下脊形波导的单模特性和偏振特性.在芯层厚度一定的情况下,脊宽越窄,刻蚀深度越浅,波导的传输模式越接近单模.在深刻蚀情况下,脊波导模双折射系数受到脊宽的影响较大,波导的偏振不敏感性较差;在浅刻蚀情况下,模双折射系数(△n=nTE-nTM)受到脊宽和脊高的影响较为微弱,稳定在1.2×10-3.相关仿真和分析为基于InP/InGaAsP脊波导的光电子器件的结构设计提供了一定的理论支持.     

Failure modes of ceramic elements with ring-crack defects

A hybrid ceramic/steel angular contact ball bearing is experimentally modelled using a modified four-ball machine. Ceramic ball surfaces are artificially damaged with ring pre-cracks. Rolling contact fatigue failure modes are studied after testing with high contact stresses and speeds. The ceramic ball surface and subsurface are analysed in detail using electron microscopy and a dye-penetration technique.     

圆锥滚子轴承内圈挡边磨床研制

介绍了圆锥滚子轴承内圈直线形挡边磨床的磨削原理、结构特点、主要技术参数、砂轮直径的选择、机床磨削精度和实际使用情况。