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1.
利用拉氏分析研究冲击载荷下混凝土应力——应变关系   总被引:1,自引:0,他引:1  
张磊  胡时胜  梁宗宪 《工程力学》2005,22(4):163-166
混凝土材料的动态本构关系对冲击载荷作用下的混凝土结构分析很重要。Lagrange分析方法是一种研究材料的动态力学性能特别是本构关系方面的常用方法。利用改进的φ74的直锥变截面Hopkinson压杆作为加载设备,测量在不同位置的应变波形,通过Lagrange分析得到了混凝土材料在冲击加载条件的应力—应变关系,并讨论了混凝土材料的应变率效应和重复加载对材料性能的影响,拓宽了Lagrange分析方法的应用。另外文中还指出利用拉氏方法分析混凝土材料时应该注意的问题。  相似文献   

2.
混凝土材料具有明显的应变率效应,对其力学性质增强机理的认识还不统一。在细观随机骨料模型基础上,采用特征单元尺度划分试件网格,推导了考虑材料拉/压强度应变率效应的细观单元等效本构关系,建立了非均质混凝土材料的细观单元等效化数值模型。基于二维模型对Dilger等混凝土动态压缩试验进行了数值模拟,获得的数值结果与试验数据及随机骨料模型结果吻合良好,证明了细观单元等效化方法的准确性;进而对三维混凝土试件动态单轴拉伸和压缩破坏模式及宏观力学性质的加载速率效应进行了研究。数值结果表明:随着加载速率的增加,混凝土裂纹(损伤)数量增大,混凝土破坏将耗散更多的能量,是混凝土动态强度提高的主要原因。  相似文献   

3.
混凝土类材料SHPB实验若干问题探讨   总被引:1,自引:0,他引:1  
方秦  洪建  张锦华  陈力  阮征 《工程力学》2014,(5):1-14,26
分离式霍普金森压杆(SHPB)实验是研究混凝土类材料动态力学性能的主要方法。该文简要回顾了当前混凝土类材料SHPB实验中存在的若干问题(如端面摩擦、骨料大小、惯性效应、温度效应等)的研究进展;通过对混凝土SHPB实验的精细化数值模拟,进一步分析了惯性效应产生机理,提出了材料的塑性流动引起的横向加速度是产生围压的关键原因,围压波在试件中心的反射和边缘的卸载形成试件中围压从中心向四周逐渐减小的抛物线型分布;利用该文所提的SHPB实验惯性效应产生机理,较好地解释了SHPB实验的尺寸和主动围压的影响规律;基于自主研制的可进行围压和温度共同加载的SHPB实验装置TSCPT-SHPB,对在5MPa~25MPa围压作用下以及在40℃~80℃温度下盐岩动态力学性能进行实验研究,结果表明,高围压下应变率效应不如低围压下显著,温度越高,强度越低;基于考虑粗骨料大小、形状及空间随机分布的三维混凝土细观模型,对混凝土各细观组分对动态效应影响进行了研究,结果表明:各组分材料静态强度越高,混凝土动态强度也越高;在相同骨料粒径条件下,骨料体积率越高,混凝土动态强度也越高;而相同骨料体积含量条件下,骨料尺寸越大,混凝土动态强度越低。  相似文献   

4.
数值模拟是研究混凝土类材料在动载下响应的有效方法,准确输入材料真实的应变率效应曲线对预测结构在动载下的响应有重要作用。收集了1990年以来针对混凝土类材料的动态抗压实验数据,并将惯性效应对材料动态强度的影响进行剥离,得到真实的材料应变率效应引起的抗压动态强度放大因子(DIF?(5))与应变率对数的关系曲线。分析数据发现:实验得到的抗压动态强度放大因子(DIFs)和惯性效应引起的抗压动态强度放大因子(DIFi)都随试件尺寸的增大而增大;随着材料准静态强度增大,混凝土类材料DIFi随应变率增长的增长幅度减小。对比拟合曲线与其他曲线可知,在高应变率下,新的应变率效应拟合曲线比已有半经验公式能更好地反映实验数据的DIF?(5);模拟时分别输入新的应变率效应曲线和CEB推荐公式,将输出结果与DIFs对比,验证了新的应变率效应曲线的优越性。  相似文献   

5.
混凝土杆系结构滞回全过程分析   总被引:4,自引:0,他引:4  
本文基于非线性有限元原理,采取由材料本构关系直接形成单元M—N—φ关系的方法,推导了混凝土杆系结构的单元刚度矩阵,该矩阵考虑了材料非线性、几何非线性、轴力二次矩、混凝土的裂面效应、预应力的特点、钢筋的粘结滑移以及材料的双切线模量等的影响;编制了相应的分析程序,并对两榀混凝土门架的滞回性能进行了模拟计算,计算值与试验结果吻合较好。本文程序实现了混凝土杆系结构包括下降段在内的滞回全过程分析,从而为该类结构的抗震研究提供了一个准确、实用的工具。  相似文献   

6.
介绍了混凝土的疲劳、徐变、收缩和温度等时变效应,深入阐述了各种时变效应对混凝土材料和结构产生损伤的机理与研究进展。介绍了国内外广泛使用的混凝土强度破坏准则,提出混凝土强度破坏准则中应充分考虑时变效应的影响。对混凝土的损伤机理和强度破坏准则的研究具有一定的借鉴意义。  相似文献   

7.
基于线弹性和一维应力波假定,采用Φ75mmSHPB对钢纤维体积率Vf分别为0、0.75%和1.50%的三种混凝土材料进行了一维杆层裂实验,考虑了应力波在混凝土材料内传播时的波形弥散效应和应力幅值衰减,通过计算应变片记录的应力信号确定了材料的动态抗拉强度。结果表明,钢纤维混凝土的动态抗拉强度受应变率和钢纤维体积率的影响,本文为测试脆性材料的动态抗拉强度提供了一种有效方法。基于微观扫描技术,对钢纤维增强机理进行了分析。  相似文献   

8.
混凝土材料是典型的率敏感材料,不同动态应变率下混凝土柱的抗压性能有明显的变化。本文通过混凝土柱的轴心动态抗压试验,在10-5/s10-2/s应变率范围内研究了混凝土材料本构关系的应变率效应,系统研究了应变率效应对混凝土抗压强度、弹性模量、峰值应变、吸能能力以及破坏机理的影响,并讨论了试验机刚度、惯性效应对试验结果的影响。试验结果表明:随着应变率的增加,混凝土材料的抗压强度也随之增加,当应变率为10-4/s、10-3/s、10-2/s时混凝土的抗压强度相对准静态抗压强度(应变率为10-5/s)分别增加了7.45%、19.51%和29.23%,弹性模量相对于准静态弹性模量变化不大,峰值应变具有一定的离散性,但是基本趋势也是增加的,混凝土的吸能能力也随着应变率的增加而显著增加。另外,刚性元件的使用有效的改善了试件应变率的稳定性,惯性效应对本次试验结果的影响可以忽略  相似文献   

9.
借助DSC-TG、扫描电镜和压汞实验,并结合混凝土宏观性能实验,研究了建筑垃圾复合粉体材料对C30混凝土力学强度及抗冻性能的影响机理。结果表明:建筑垃圾复合粉体材料掺量为30%时,C30混凝土强度及抗冻性能最优;中低盐溶液浓度时,试件更容易发生盐冻腐蚀破坏。建筑垃圾复合粉体材料由于其填充效应及火山灰效应减少了取向性较强的Ca(OH)_2含量,生成性能较优、微观结构较为致密的低碱度水化硅酸钙凝胶,使得混凝土内部较为致密,孔结构和孔级配趋向合理,宏观上表现为混凝土强度及抗冻性能的提高。  相似文献   

10.
基于φ74 mmSHPB实验平台进行了混凝土及轴向钢筋增强混凝土(UDRC)杆的一维应力层裂实验,采用超高速相机拍摄实验中杆表面的实时变形情况,使用数字图像相关法(DIC)分析杆表面的位移场及应变场演化过程,探讨混凝土及增强混凝土在应力波加载过程中发生拉伸断裂(层裂)的规律,并进一步结合有限元分析了钢筋在层裂过程中的作用。结果表明:UDRC杆中应力波的传播满足一维应力假设;钢筋对UDRC发生拉伸层裂的影响可以忽略,而在混凝土基体断裂后将使结构保持完整;断裂试件中的裂纹在拉压应力波交替作用下反复张开闭合,随着应力波在杆中的衰减而趋于稳定;UDRC与混凝土的层裂强度基本相同,且具有相似的应变率增强效应;在实验加载范围内,光圆钢筋和螺纹钢筋的结构增强效果没有区别。  相似文献   

11.
Transporting fresh concrete constitutes a significant part of the production process. Transferring ready-mixed concrete on-site is done using concrete pumps. Recent developments in concrete technology, and in mineral and chemical additives, have resulted in new developments in pumping techniques and the use of different concrete mixtures and equipment. These developments required further knowledge of the behavior of fresh concrete under pressure. Two criteria were determined for the pumpability of concrete: the power required to move the concrete or of the repulsive force; and the cohesion of the fresh concrete. It would be insufficient to relate pumpability to these two criteria; the values of segregation pressure, diffusion ability, water retention capacity, and side friction of the mixture are significant parameters in ensuring that concrete is pumped freely along the pipe. To solve the pumpability problem, friction stresses should be determined as a function of the linear pressure gradient, the pressure leading to segregation of the fresh concrete should be determined, and tests for the bleeding of concrete under pressure should be examined. The scope of the research is the examination of the behavior of fresh concrete under pressure. To determine the segregation pressures, a test apparatus was designed for the bleeding of concrete under pressure. The main purpose of the study is to determine whether the concrete can be pumped easily and whether it will lose its cohesion during the pumping, based on tests of concrete workability and bleeding of concrete under pressure.  相似文献   

12.
刘巍  荣辉 《材料导报》2011,25(19):134-142
对国内结构混凝土疲劳性能的研究动态进行了较为全面详细的阐述。着重阐述了应用较多的钢筋预应力混凝土、高强混凝土、高性能混凝土、纤维混凝土的疲劳研究,同时简单介绍了活性粉末混凝土和多孔混凝土疲劳性能的研究。通过对国内各类结构混凝土疲劳性能研究现状分析,以期对国内研究者以后研究混凝土疲劳性能有所帮助。最后提出研究结构混凝土在多重环境因素耦合作用下疲劳性能的必要性。  相似文献   

13.
Two layers of aluminum foils are inserted between the concrete column and the filament wound glass/epoxy composite jacket to form a non-adhesive wrapping for concrete columns. Different compressive fatigue stress amplitudes are applied on the concrete specimens to investigate their compressive strength after fatigue. Experimental results show that the compression after fatigue (CAF) strength of the non-adhesive filament wound composite/concrete columns is better than that of a pure concrete column under the same fatigue cycle and stress amplitude. The CAF strength of both concrete columns and composite/concrete columns is dominated by the pre-applied fatigue stress amplitude when it is greater than 1/3 of the compression strength of the plain concrete column. For stress amplitude less than this threshold value, the CAF strength reduction is less than 5%. The hysteretic loops during the fatigue cycle are recorded to evaluate the energy dissipation of both concrete and composite/concrete systems. The stress–strain curve of the CAF coupons is measured to locate the influence of stress amplitude on the lateral compliance of the composite/concrete system. Statistical prediction models of CAF strength for concrete and composite/concrete systems correlate well with the experimental data.  相似文献   

14.
Fly ash concrete is finding increasing applications in construction; however there is lack of data on fire performance of fly ash concrete structural members. This paper presents results from fire resistance tests on fly ash concrete columns. Data generated from tests on high strength fly ash concrete columns is compared with those of conventional high strength concrete (HSC) columns. The effect of concrete type, fire exposure scenario, fly ash, and fibers in concrete mix on fire performance of fly ash concrete columns is discussed. Results from fire resistance tests show that fly ash concrete columns exhibit almost similar fire resistance to that of conventional HSC columns. Further, the addition of polypropylene fibers mitigates fire induced spalling in high strength fly ash concrete columns.  相似文献   

15.
This paper offers an innovative practical technique for applications in which high workability concrete is needed. In this technique, concrete is produced by compressing the fresh concrete through a fabricated pressure apparatus without incorporating additives and no need for external vibration and workability control. Applying this technique, excess water is completely expelled out from the fresh concrete and porosity is remarkably decreased. In this study, several mixes having different excess water contents with the same cement and aggregates were prepared to attain different workability levels. To evaluate the effect of excess water content on properties of hardened concrete, the physical and mechanical properties of both compressed and uncompressed concrete were determined, including compressive strength, modulus of elasticity, strain at peak stress, stress–strain curve, failure mode, water absorption, density and ultrasonic pulse velocity. The results obtained from this study showed that the excess water content added to the fresh concrete does not influence the physical–mechanical properties of the compressed concrete while those of the uncompressed concrete are significantly degraded. Moreover, compressing the fresh concrete dramatically improves the properties of the compressed concrete, as compared to the corresponding uncompressed concrete.  相似文献   

16.
为探究自密实轻骨料混凝土压-剪复合受力力学性能,应用液压伺服机和材料压-剪试验机,对自密实轻骨料混凝土进行单轴受压、单轴劈裂抗拉和压-剪复合受力试验研究,通过试验得到不同加载工况下自密实轻骨料混凝土破坏形态和力-变形曲线,引用文献对普通混凝土和轻骨料混凝土压-剪复合受力研究数据,对比分析自密实轻骨料混凝土压-剪复合受力性能。研究结果表明:自密实轻骨料混凝土压-剪复合受力破坏形态与普通混凝土和轻骨料混凝土相类似,随着轴压比的提高,剪切破坏断面摩擦痕迹逐步明显,混凝土碎渣也逐步提高,自密实轻骨料混凝土剪切破坏强度、残余荷载和剪切破坏位移也随之提高;剪切破坏强度提高幅度高于普通混凝土和轻骨料混凝土,残余荷载受轴压比影响提高幅度高于普通混凝土,但略低于轻骨料混凝土。基于主应力空间结合普通混凝土和轻骨料混凝土压-剪试验数据,提出混凝土压-剪复合受力统一破坏准则,同时基于八面体应力空间,提出自密实轻骨料混凝土破坏准则,所提出的破坏准则具有良好的适用性。  相似文献   

17.
预拌混凝土生产企业共同面临的一个问题是混凝土生产中“废水”的回收利用,而回收“废水”的质量对混凝土的强度性能、工作性能、耐久性能影响较大。通过对“废水”的磁化混凝土强度都能达到强度设计要求,磁化“废水”配制的混凝土对凝结时间的影响不大。  相似文献   

18.
The surface protection can improve the waterproofness of concrete, thus reducing the saturation inside and improving the freeze-thaw resistance (FT). Polyvinyl alcohol (PVA) membranes with different thicknesses and silane with varying impregnation depths are selected to improve the FT resistance of concrete as surface protection. The damage morphology, mass variation, ultrasonic pulse velocity, and mechanical characteristics of concrete after 125 FT times are analyzed according to the slow freezing method, and the damage mechanism is studied by scanning electron microscope in different depths of concrete. The results show that PVA membrane can improve the FT resistance of concrete and do better than silane because the silane can only keep dry inside the concrete but the surface still spalls off. And, the protection effect of PVA is a negative correlation with membrane thickness because the thicker the PVA membrane the better the air tightness and the membrane is easier damaged. On a microscopic level, the damage of PVA-protected concrete is gradually weakened from the surface of concrete to inside, and there is an obvious boundary between the damaged and undamaged zone of silane-protected concrete. This article provides a new idea for FT protection of concrete.  相似文献   

19.
In this paper, the electrodeposition method for repair of reinforced concrete with cracks, based on the electrochemical technique, is presented. The aim of electrodeposition in a concrete repair method is to fill the cracks in concrete and to coat the concrete surface by electrodeposits of chemical compounds. Investigations on concrete specimens with drying-shrinkage cracks were conducted in this study. The results indicate that electrodeposits formed on the concrete surface are able to close concrete cracks and to coat the concrete surface. In addition, the investigations show that the presence of electrodeposits led to improvement of the concrete watertightness and protection against detrimental materials.  相似文献   

20.
Investigation on mechanical properties of young concrete   总被引:3,自引:0,他引:3  
Young concrete usually refers to the concrete with an age less than 7 days. Due to the progress of hydration, the mechanical properties of young concrete are quite different from those of mature concrete. This investigation is aimed at understanding the mechanical properties of young concrete under both uniaxial compression and tension. The uniaxial compression and uniaxial tension tests have been conducted on the concrete specimens at ages of 12 hours, 18 hours, 24 hours, 48 hours, 72 hours, and 168 hours. By utilizing the circumferential control and adaptive control, the complete stress-strain (deformation) curves have been obtained for young concrete under either uniaxial compression or unixial tension. The experimental results show that the behavior of young concrete is quite ductile until about 3 days. The effect of incorporating metakaolin into concrete mix has also been studied in this research. It is found that the metakaolin can significantly enhance the mechanical properties of young concrete.  相似文献   

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