钢纤维混凝土高温后SHPB试验研究

为了研究钢纤维混凝土(SFRC)常温以及经历400和800℃高温后的动态压缩性能,采用改进的分离式Hopkinson压杆装置,结合应变直测技术对其进行了单轴冲击压缩试验.结果表明:经历400和800℃高温后,未掺钢纤维混凝土的峰值应力分别只有常温时的79.2%和38.9%,弹性模量分别降为常温时的82.8%和56.2%,同时,试件的能量吸收能力大幅度下降;钢纤维混凝土400,800℃对应的峰值应力分别降为常温时的76.8%和39.0%,弹性模量稍有降低,分别为常温的91.8%和82.7%,较基准混凝土有了较大的提高.钢纤维的加入可以增加混凝土的极限应力对应应变,曲线的下降段较为平缓,同时增强了混凝土的能量吸收能力,在20,400和800℃时,分别提高了38.5%,27.5%和25%.     

Dynamic mechanical property of hybrid fiber reinforced concrete(HFRC)

The uniaxial compressive response of steel-polypropylene hybrid fiber reinforced concrete(HFRC) and steel fiber-reinforced concrete(SFRC) was analyzed under high strain rate loading with a 74 mm diameter split Hopkinson pressure bar(SHPB).The experimental investigation focused on recorded data and resulted in distinguishing the strain rate that mobilized different ductility of steel-polypropylene hybrid fiber reinforced concrete(HFRC) and steel fiber-reinforced concrete(SFRC).64 specimens of HFRC and SFRC with higher static compressive strength were tested at the strain rates changing from 20 to 120 s-1.The static compressive strength and dynamic stress-strain curves of the two materials were obtained at 4 different strain rates and the failure stress,and peak strain and peak toughness were also analyzed.The results show that HFRC has quite good dynamic mechanical property and clear strain-rate effect,and the failure mechanism of HFRC and SFRC was also compared based on the specimens’ failure modes in static and dynamic compressive tests.     

钢纤维砼的动态本构关系

在对钢纤维砼冲击动态力学实验研究的基础上,分析了砼材料动态力学行为的应变率敏感的非线性粘弹性和计及损伤的动态本构关系的力学模型和本构特性,从而给出了钢纤维砼的计及损伤演化的率型本构方程,理论预示与实验结果吻合良好。     

Experiences in Barcelona with the use of fibres in segmental linings

This paper presents the most outstanding experiences regarding the use of fibres as the main reinforcement in precast segmental linings in the metropolitan area of Barcelona. It is known that the addition of structural fibres improves, on the one hand, the mechanical behaviour of the structure during its construction, especially in cases such as the thrust of the jacks, and on the other hand it leads to a reduction of the global costs by reducing the conventional passive reinforcement. The aim of this paper consists in presenting three real experiences that are representative of the application of FRC in urban tunnels and a design methodology to take into account the structural contribution of the fibres. Two particular cases of the application of this design method are presented. In the first case, the use of 25 kg/m³ of fibres has led to a reduction of 70% of the conventional reinforcement initially proposed in the project. In the second one, which was planned to employ fibres but without considering its structural contribution, the parametric study reflected the possibility of reducing up to a 38% of the rebars adding 25 kg/m³ of steel fibres in the concrete mixture. In light of good results, construction companies in Spain have become aware of the advantages of using fibres in these structures and have carried out experimental stretches. This attitude has also been influenced by the approval of the new Spanish Code, which includes the FRC as a construction material with design purposes.     

密筋梁钢纤维混凝土施工技术

钢纤维砼在隧道壁、边坡支护以及机场、港口、仓库等重要工程应用较为广泛,但对于大型结构转换梁,特别是在密筋梁的施工,应该怎样去控制,该文结合实际施工实践,介绍其施工控制技术,经实践证明其施工技术可供同行参考。     

疲劳裂纹扩展理论及其在混凝土疲劳性能研究中的应用

指出了研究疲劳裂纹扩展阶段对于工程材料疲劳性能研究所具有的重要性。对工程材料疲劳裂纹扩展理论的发展进行了回顾,并且对该理论在混凝土材料中的应用及研究现状进行了介绍;对传统Ｐａｒｉｓ公式和Ｆｏｒｍａｎ公式在高密度钢纤维混凝土等复合材料中应用所面临的问题进行了探讨,提出按照分形理论,以表面裂纹的分维值Ｄ来建立材料断裂准则。     

Strength and ductility of stiffened thin-walled hollow steel structural stub columns filled with concrete

It is generally expected that inner-welded longitudinal stiffeners can be used to improve the structural performance of thin-walled hollow steel structural stub columns filled with concrete. Thirty-six specimens, including 30 stiffened stub columns and six unstiffened ones, were tested to investigate the improvement of ductile behaviour of such stiffened composite stub columns with various methods. The involved methods include increasing stiffener height, increasing stiffener number on each tube face, using saw-shaped stiffeners, welding binding or anchor bars on stiffeners, and adding steel fibres to concrete. It has been found that adding steel fibres to concrete is the most effective method in enhancing the ductility capacity, while the construction cost and difficulty will not be increased significantly.     

Experimental and analytical study of the structural response of segmental tunnel linings based on an in situ loading test.: Part 1: Test configuration and execution

During the last years the use of segmental linings in tunnels bored with tunnel boring machines (TBMs) have increased considerably. Despite this, uncertainties remain on the structural behavior of segmental tunnel linings. To overcome them, a new methodology for an in situ real scale test on this kind of tunnels was developed and applied on an experimental section placed at the new Line 9 (L9) of the metro of Barcelona. The main particularity of this test falls on its performance in the definitive placement of the rings and, therefore, in the real work conditions of the tunnel. The main advantage to previous real scale test experiences was the consideration of the real ground–structure interaction. The experimental section was composed by 15 rings built using steel fibers as a unique reinforcement. Significant loads were applied to the tunnel crown (max 3000 kN) by means of three hydraulic flat jacks embedded at the extrados of the loaded ring. A complete set of internal and external instrumentation was placed on the experimental section to obtain the necessary measurements to characterize the lining behavior. Such measurements were intensively treated and its main results are presented and analyzed in detail in this paper. This in situ test provides significant evidences of the structural response of SFRC segmental tunnel linings in hard ground conditions.     

围压条件下钢纤维混凝土动态压缩试验研究

研究了钢纤维含量分别为0、1.0%、1.5%、2.0%、2.5%、3.0%等6种混凝土在围压条件下的动态压缩试验,围压分别为0、8、16、24 MPa等4个量级;基于试验数据建立了不同围压和不同体积率钢纤维混凝土三向受力状态的模型.分析结果表明:在不同围压条件下,发挥钢纤维混凝土最佳性能的纤维含量是不同的,围压越高相应的钢纤维含量则越小.该模型可以描述围压条件下钢纤维混凝土的动态力学性能.     

钢纤维混凝土抗拉性能试验研究

研究了钢纤维体积率、钢纤维长径比、钢纤维类型对钢纤维混凝土劈裂抗拉强度、轴心抗拉强度及轴心受拉应力-应变全曲线的影响规律。试验采用两端埋设钢筋的变截面轴心受拉试件并在普通万能试验机上加辅助刚性架,进行钢纤维混凝土轴心受拉应力-应变全曲线测试。研究表明,随着钢纤维体积率、长径比的增大,钢纤维混凝土劈裂抗拉强度、轴心抗拉强度呈线性增大规律。采用设计的试验装置可测得钢纤维混凝土轴心受拉应力-应变全曲线,分析了纤维掺量和基体混凝土强度对轴心受拉应力-应变全曲线的影响规律。根据试验数据分析,提出了钢纤维混凝土轴心抗拉强度与劈裂抗拉强度间的关系式,提出了钢纤维混凝土轴心受拉应力-应变全曲线的解析表达式。