钢纤维混凝土抗压阻裂性能研究

为增强混凝土的抗压阻裂韧性,减少裂缝的产生,对短钢纤维及超短钢纤维混凝土进行机理分析及实验研究。研究表明钢纤维能有效增强混凝土抗压强度,增加混凝土的整体性能;超短钢纤维抗压抗裂性能好于短钢纤维,能有效阻止裂缝的产生及开展,达到增强阻裂效果。通过煤炭工程一实例分析易裂部位,采用超短钢纤维混凝土,有效阻止了工程裂缝的产生。

木材横纹抗压的影响因素及加固增强技术研究进展

木材作为一种弹塑性材料,具有优异的强重比,被广泛应用于木结构建筑。由于其各向异性,木材不同方向的力学性能差异较大,在横纹受压荷载下存在屈服强度低、变形大等受力特征。木材横纹受压破坏现象在工程实际应用中普遍存在且难以避免,若不能及时妥善处理,会严重影响木结构的安全稳定性。由于各地保护政策以及修复技术的限制,对古建筑残损木构件进行增强与加固历来为学者们极力攻克的难题,因此对木材在横纹受压下的性能及加固增强进行研究具有重要意义。文中介绍中国、美国、日本等国家的木材横纹抗压测试标准,并梳理木材横纹受压影响因素的研究现状;概述木材横纹抗压强度的增强方法,尝试提出木材横纹受压及加固增强的发展趋势,以期为今后开展相关研究提供思路。

Square concrete columns strengthened with carbon fiber reinforced plastics sheets at low temperatures

Twenty-one square concrete columns were constructed and tested. The testing results indicate that bonded carbon fiber reinforced plastics(CFRP) sheets can be used to increase the strength and improve the serviceability of damaged concrete columns at low temperatures. The failure of the specimens,in most cases,takes place within the middle half of the columns. And the failure of strengthened columns is sudden and explosive. The CFRP sheets increase both the axial load capacity and the ultimate concrete compressive strain of the columns. The ultimate loads of strengthened columns at-10,0 and 10 ℃ increase averagely by 9.09%,6.63% and 17.83%,respectively,as compared with those of the control specimens. The axial compressive strength of strengthened columns is related to the curing temperatures. The improvement of axial compressive strength decreases with reducing temperature,and when the temperature drops to a certain value,the improvement increases with falling temperature.

Microstructure,mechanical and wear properties of aluminum borate whisker reinforced aluminum matrix composites

The microstructural features and the consequent mechanical properties were characterized in aluminium borate whisker(ABOw)(5, 10 and 15 wt.%) reinforced commercially-pure aluminium composites fabricated by conventional powder metallurgy technique. The aluminium powder and the whisker were effectively blended by a semi-powder metallurgy method. The blended powder mixtures were cold compacted and sintered at 600 ℃. The sintered composites were characterized for microstructural features by optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), transmission electron microscopy(TEM) and X-ray diffraction(XRD) analysis. Porosity in the composites with variation in ABOw contents was determined. The effect of variation in content of ABOw on mechanical properties, viz. hardness, bending strength and compressive strength of the composites was evaluated. The dry sliding wear behaviour was evaluated at varying sliding distance at constant loads. Maximum flexural strength of 172 MPa and compressive strength of 324 MPa with improved hardness around HV 40.2 are obtained in composite with 10 wt.% ABOw. Further increase in ABOw content deteriorates the properties. A substantial increase in wear resistance is also observed with 10 wt.% ABOw. The excellent combination of mechanical properties of Al-10 wt.%ABOw composites is attributed to good interfacial bonds, less porosity and uniformity in the microstructure.

Compressive Behaviours of Concrete Cylinders Wrapped with 2-D Glass Fabrics

Concrete cylindess wrapped with glass fabrics of various constructions were fabricated. Compressive behaviours of cylinders with and without fabric wrapping were investigated. Comparisons of the compressive characters while using different fabrication parameters were made. It was demonstrated that the effect of the fabric reinforcent was obvious. The tensile strength of the filament used in the fabric played an important role as far as the anti-compression behaviour of the reinforced cylinders is concened.

Theoretical study on constitutive relationship of fiber reinforced polymer confined concrete

We proposed a bilinearity constitutive curve model of fiber reinforced polymer(FRP) confined concrete which includes a parabola in the first stage and a straight line in the second stage. The FRP-confined concrete has powerful confinement status and weak confinement status leading to different equations of parabola. We analyzed the impacts of factors such as confinement ratio and restrain stiffness on confined concrete compressive strength,ultimate strain and other control parameters through finite element analysis. The results show that the confinement ratio determines the confinement status,and the increase of the confinement ratio has a limited capacity to increase the compressive strength. The deformation of confined concrete is influenced by restrain stiffness. The stronger the restrain stiffness is,the less the lateral deformation is and the greater ultimate axial strain will be. The consideration of equivalent section coefficient kse is needed in the non-circular section confined concrete. We analyzed the results and proposed boundary values of strong and weak confinement styles,a peak/inflection point stress and strain model,and a compressive strength and ultimate strain model.