建筑结构用高强度钢材力学性能研究进展

随着钢材生产工艺的提高,新型高强度、高性能结构钢材出现;由于目前钢结构设计规范和钢材标准对结构钢材的力学性能指标有着严格的限值要求,特别是屈强比,高强度钢材钢结构的发展和应用受到了制约。全面介绍国内外建筑结构用高强度钢材的生产工艺和牌号种类,总结包括欧洲、北美、澳大利亚、日本和中国在内的国内外规范标准对结构钢材力学性能的要求,并对几个重要的力学性能指标,如屈强比、断后伸长率等进行对比分析,整理大量国内外高强度钢材材性试验数据和研究进展,分析并得到其力学性能特点,提出适用于数值计算的材料本构模型。研究结果表明,新型高强度结构钢材在具有高韧性的同时也具有较高的屈强比和较低的断后伸长率,且往往超过大多数规范的限值规定,这大大限制了此类钢材钢结构的工程应用。因此,需要进一步讨论和定量研究钢材力学性能与结构安全性的关系,研究是否可以适当放松规范对结构钢材力学性能的限值规定。该研究有利于更合理全面地认识高强度结构钢材的力学性能特点和相应的规范限值规定,促进高强度钢材钢结构的相关研究工作,也有利于高强度钢材钢结构的工程应用和规范修订。     

PVDF膜材在自然老化和人工加速老化下力学性能变化的相关性研究

对6组自然老化下的PVDF膜材和1组人工加速老化试验下的Ferrari 1202T膜材的主要力学性能数据进行了汇总,包括单轴抗拉强度、断裂延伸率、撕裂强度以及单轴和双轴杨氏模量,在此基础上对经历了自然老化的第6组膜材补充了人工加速老化试验并测得其抗拉强度.通过对比第1,2组自然老化膜材的试验结果,研究了环境因素对PVDF膜材老化性能的影响;研究和对比了PVDF膜材在自然老化与人工加速老化试验下力学性能的变化规律,基于性能保持率的等效时间为表征指标,验证了互易定律的失效性.采用两种经典拟合方法估算PVDF膜材的使用寿命,结果表明PVDF膜材的寿命以等效时间表示为1860h,换算成自然老化时间后,第1,2,3,4,6组膜材的寿命分别为18年、20年、17年、19年和19年,最终为膜结构的理论分析、设计计算和寿命预测模型的建立积累了重要数据.     

钢板桩围堰力学性能验算

以某铁路特大桥梁施工过程中采用的钢板桩围堰为例,对钢板桩围堰的力学性能进行了验算。验算的内容包括:钢板桩的验算、围囹的验算、支撑的验算、支撑稳定性的验算等,验算的结果表明,钢板桩围堰的力学性能满足要求,研究成果对相同类型钢板桩围堰的设计及验算具有一定的参考作用。     

A comparison of the mechanical properties of fire-resistant and S275 structural steels

The mechanical properties of two fire-resistant (FR) structural steels and an S275 steel have been investigated from room temperature up to 700°C, with the aim of assessing the viability of FR steels. The major focus has been on the tensile and creep properties of the steels at high temperature and the effect of these properties on the fire resistance of model steel beams. It has been found that the FR steels performed significantly better than the S275 at high temperature, retaining 50% of their room temperature strength at a temperature of approximately 650°C. The S275 steel retained 50% strength to a temperature of 550°C, this being consistent with literature values. In creep tests carried out at 600°C, the FR steels also exhibited lower maximum strains and strain rates than the S275. The improved strength reduction factors led to a significant increase in fire resistance for a model steel beam with various floor slab configurations, showing that FR steels can become a practical alternative to conventional structural steels.     

Water absorption of wood polypropylene composite sheet piles and its influence on mechanical properties

The water absorption behavior and durability of extruded wood polypropylene composite (WPC) material used in Z-section sheet piles was investigated. An experimental technique to determine percentage water absorption and its effect on mechanical properties was implemented. Water absorption tests were carried out on specimens cut from flanges and webs of the Z-section by immersion in tap water at 21, 45 and 70 °C. Freeze–thaw resistance of saturated composites was studied by cycling temperatures in the range of 21 to ?29 °C. The absorption behavior followed the kinetics of a Fickian diffusion process. This behavior was modeled using an analytical solution based on Fick’s second law of diffusion. Quasi-static bending tests were conducted periodically on specimens immersed in water to assess degradation in flexural properties. A significant decrease in mechanical properties of the water-saturated specimens compared to the dry control was observed. Degradation of flexural modulus was found to be a strong function of water absorption with initial decrement as percentage water absorption increased and finally stabilized as the absorption process approached saturation. However, freeze–thaw cycling did not have any significant effect on mechanical properties of saturated composites. A phenomenological model for moisture intrusion and its effect on mechanical properties was implemented and applied to explain the experimental findings.     

Experimental study of the mechanical properties of light gauge cold-formed steels at elevated temperatures

In recent times, light gauge cold-formed steel sections have been used extensively as primary load-bearing structural members in many applications in the building industry. Fire safety design of structures using such sections has, therefore, become more important. Deterioration of mechanical properties of yield stress and elasticity modulus is considered the most important factor affecting the performance of steel structures in fires. Hence, there is a need to fully understand the mechanical properties of light gauge cold-formed steels at elevated temperatures. A research project based on experimental studies was, therefore, undertaken to investigate the deterioration of mechanical properties of light gauge cold-formed steels. Tensile coupon tests were undertaken to determine the mechanical properties of these steels made of both low- and high-strength steels and thicknesses of 0.60, 0.80 and 0.95 mm at temperatures ranging from 20 to 800 °C. Test results showed that the currently available reduction factors are unsafe to use in the fire safety design of cold-formed steel structures. Therefore, new predictive equations were developed for the mechanical properties of yield strength and elasticity modulus at elevated temperatures. This paper presents the details of the experimental study, and the results including the developed equations. It also includes details of a stress–strain model for light gauge cold-formed steels at elevated temperatures.     

氧化石墨烯对粉煤灰基地质聚合物力学性能的影响

通过改进Hummers法制备了一系列不同尺寸的氧化石墨烯（GO）,研究了GO对粉煤灰地质聚合物流变性能、力学性能和微观结构的影响,结果表明当粉煤灰地聚物净浆流动度随GO的尺寸和掺量增大而降低;此外GO的掺入,会阻碍粉煤灰地聚物早期强度发展,但是会提高后期强度的发展速度。通过扫描电镜观察粉煤灰地质聚合物微观结构,结果表明GO的掺入会导致粉煤灰地质聚物中出现大量的针棒状结晶体。     

碳纤维混凝土(粗骨料)中纤维含量对其力学、压敏性能的影响

目前碳纤维水泥砂浆的研究很多,而对于碳纤维混凝土的研究较为少见。作为结构材料必须加入粗骨料。粗骨料的引入使碳纤维混凝土力学和压敏性能较碳纤维水泥砂浆有较大的不同。本文介绍了碳纤维混凝土的试验室配制工艺及其电阻测量方法,并在此基础上研究了碳纤维混凝土的力学、压敏特性。通过综合比较相同条件下不同纤维掺量的混凝土其力学和压敏性能,确定了较为合理的碳纤维掺量。     

Flowability of fibre-reinforced concrete and its effect on the mechanical properties of the material

Fibre distribution is an important factor, affecting both the fresh- and hardened-state properties of concrete. The paper describes a study in which the fibre distribution and orientation were investigated by means of a suitable technique, by using a translucent fluid model with a yield stress (Carbopol 940). The observation confirmed the ability of the developed method to provide data on the orientation and distribution of steel fibres within concrete. It was showed that orientation and distribution are dependent on the yield stress of the fluid material. Concrete specimens, containing 0.5% of 35 mm long hooked steel fibres, were also cast and tested under four-point loading, in order to study the correlation between rheology, fibre distribution and the mechanical properties of steel fiber-reinforced concrete. The results confirm that the rheology of concrete has an important influence on the orientation of the fibres. The flexural strength depends on the fibre distribution and orientation and is significantly improved when the fibres are oriented in the direction of the tensile stresses fresh (concrete with good workability). On the contrary, for concrete with poor workability, an inadequate orientation of fibres occurred, leading to a poor contribution of the fibres to the flexural behaviour of the tested specimens, despite the relatively higher compression strength of the tested concrete material.     

复合保温砌块力学性能与节能效果试验研究

以城市废泥浆、河道淤泥、建筑废料为主要原料制成空心砌块,并在砌块的孔洞中充填保温材料,降低导热系数和传热系数,制成烧结复合自保温砌块,该砌块具有更好的保温节能效果.通过对砌块的物理力学性能和保温性能的研究和对比,为复合保温砌块的生产和应用提供参考依据.     

粗骨料力学特性对混凝土性能影响的数值试验研究

粗骨料的力学特性对混凝土宏观力学性能有着显著的影响,从细观角度,利用数值试验研究含不同力学特性粗骨料混凝土试件的力学性能和破坏特点,分析了不同类型粗骨料混凝土试件破坏时的力学特性,破裂机理和声发射特征。研究结果表明,粗骨料的力学特性在一定程度上影响混凝土材料的力学性能,粗骨料的强度和弹性模量的增加有助于提高混凝土的抗压强度,但混凝土力学性能的提高受其内部各组分参数的综合影响。粗骨料的弹性模量与混凝土基质间的变形协调是提高混凝土性能需要考虑的因素之一。     

Effect of welding on local mechanical properties of stainless steels for concrete structures using universal hardness tests

This study analyses the effect of welding on mechanical properties of ribbed bars of two cold-deformed austenitic stainless steels (new, low-nickel AISI 204Cu and traditional 304L types) and two duplex stainless steels (SAF 2205 type, cold and hot-worked). Welds have been carried out using shielded metal arc welding. The effect of welding on local mechanical properties has been studied using a universal hardness equipment, measuring universal and Vickers hardness, elastic and plastic energies and Young modulus. Measured values are correlated with the microstructure of base materials and heat-affected zone. Results show that heat during welding promotes recrystallisation of the microstructure, effect that depends on the degree of deformation. These phenomena can be easily studied with universal hardness. Results suggest that hot-worked 2205 duplex stainless steel can be welded in construction without meaningful modification of its properties. Cold-deformed grades will comply ductility requirements of Eurocode 2 after welding, although reductions of yield strength can be found in 2205 and 304.     

玻璃粉对玻璃骨料混凝土力学性能和ASR影响的研究

ASR膨胀是限制废弃玻璃作为细骨料运用到混凝土中的主要因素之一,玻璃粉具有潜在的火山灰活性,当一定细度的玻璃粉替代部分水泥可以有效的抑制ASR同时还可以增强混凝土后期强度;在玻璃细骨料混凝土(细骨料替代率分别为10%、20%、30%)中采用玻璃粉取代20%作为辅助胶凝材料,通过混凝土抗压试验和砂浆棒试验,研究玻璃粉对玻璃细骨料混凝土力学性能及ASR影响;研究表明,玻璃粉掺入可以提升玻璃细骨料混凝土后期强度,特别是90 d后玻璃粉混凝土抗压强度超越普通混凝土;同时,玻璃粉可以有效抑制玻璃细骨料混凝土ASR,掺入20%玻璃粉的玻璃细骨料混凝土14 d砂浆棒膨胀率均小于规范限定值0.1%,而未掺入玻璃粉的试件恰恰相反。所以,玻璃粉可以有效的改良玻璃细骨料混凝土的后期强度和ASR膨胀不足。     

考虑应变速率影响的混凝土动态特性的研究

在地震荷载的作用下,不同的建筑物或者建筑物不同的部位,在不同的瞬时其应变率的变化各不相同,而GB 50010—2002《混凝土设计规范》仅给出了混凝土静态荷载下的强度和本构关系。因此,混凝土本构模型的动力研究是一个十分有意义的课题。结合以往对混凝土动态特性研究,综述了混凝土材料动态力学性能的研究现状,分析了混凝土材料速率敏感性机理,对混凝土在单轴应力状态下的动态强度和本构关系做出进一步深入探讨,指出混凝土本构关系研究中所存在的问题,提出主要的研究方向,为进一步的研究提供参考。     

EPS表面改性及其对保温砂浆力学性能的影响

利用三乙醇胺和聚合物乳液对EPS颗粒表面进行改性预处理,并通过在EPS表面包裹无机胶结料来同时解决保温砂浆搅拌过程中的分层和界面粘结问题.通过正交试验确定了改性剂以及改性后EPS颗粒表面包裹胶结料的适宜掺量.     

Effects of logs steaming,veneer drying and aging on the mechanical properties of laminated veneer lumber (LVL)

In this study the effects of steaming and drying condition on the mechanical properties and durability of laminated veneer lumber (LVL) and solid sawn lumber were investigated in a comparative way. Steamed beech and steamed and non-steamed spruce logs were used and two different veneer drying temperatures (20 and 110 °C) were selected for this aim. Aging test was applied according to EN 321 to determine the durability of LVL and solid wood samples. Steaming decreased considerably all investigated strength properties of LVL panels and the least affected was the compression strength. The compression strength and the static bending strength values of both beech and spruce LVL panels were higher than those of the solid wood groups obtained from the same logs. The impact strength values of LVL panels, unlike the static bending strength and the compression strength, were lower than those of the solid samples, which were not steamed and aged.     

石灰对云南膨胀土力学特性影响的试验研究

选取云南省典型的湖相沉积型膨胀土土样,以石灰为改良剂对其进行化学改良,并对改良的膨胀土进行三轴剪切试验,结果表明,石灰改性土中石灰的最优掺量为5.5%,为工程实践中膨胀土改良提供了一定的依据。     

考虑应变率效应的混凝土损伤特性试验研究

利用损伤力学的观点,用弹性模量损伤和能量损伤相结合的方法定义损伤变量,分析了基体强度为40MPa、钢纤维含量为0和2.0%的混凝土在4种应变速率(10-5、10-4、10-3、5×10-3s-1)下的单轴压缩试验数据,比较了普通混凝土和钢纤维混凝土在4种应变速率下的损伤特性,并对混凝土材料的损伤机理进行了分析。试验分析表明:①混凝土材料在加载初始阶段普通混凝土的损伤比钢纤维混凝土的损伤小,混凝土内部为微观裂纹的发育发展;当加载到一定程度时,普通混凝土的损伤则比钢纤维混凝土的损伤大,混凝土内部为宏观裂纹的发展和贯穿;②混凝土在加载的初始阶段,普通混凝土的损伤比钢纤维混凝土的损伤小,但应变速率越大,两种混凝土之间的损伤差异越小;③试验加载速率越高,普通混凝土损伤大于钢纤维混凝土损伤时材料的应变越小,对应的损伤值也相应越小;④普通混凝土加载速率越高,损伤程度会随应变加载速率的提高而增加;⑤钢纤维混凝土在加载初始阶段,混凝土中仅有微观裂纹,不同加载速率下,损伤发展趋势一致;在峰值应变后应变速率越高,裂纹扩展和贯穿的速度越快,损伤程度也越大。     

生物质秸秆灰活性分析及对混凝土力学特性的影响

为评估生物质秸秆灰作为混凝土掺合料时的活性及适用性,分析了直燃获得的生物质秸秆灰的总成分、活性成分、物相、颗粒粒度及烧失量对混凝土力学性能的影响。试验选取4种直燃后的灰样(小麦秸秆灰(WSA)、高粱秸秆灰(SHSA)、水稻秸秆灰(RSA)和大豆秸秆灰(SBSA))进行试验。采用X射线衍射分析(XRD)进行物相分析,采用X射线荧光光谱法(XRF)检测4种秸秆灰的元素组成及含量,根据相应标准检测混凝土的力学特性。研究表明:高粱秸秆灰含有27.79%的活性SiO_2+Al_2O_3总成分和73.94%的SiO_2+Al_2O_3总成分,满足ASTM对F级火山灰材料的规定,其具有4种生物质灰中最高的活性成分和总成分。当高粱灰作为掺合料时,试样7 d抗压强度较对照组强1.5%,而28 d的强度损失为1.2%,这表明未经预处理的直燃高粱秸秆灰作为是4种生物质灰中最优良的掺合料。研究还发现,活性成分和总成分与抗压强度呈正相关,而烧失量呈负相关。