不同纵筋率对剪跨比为2.5的无腹 筋约束梁受剪性能影响的研究
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摘要
钢筋混凝土受弯构件斜截面抗剪强度,由于影响因素多,破坏机理复杂,从而成为钢筋混凝土结构中尚未圆满解决的问题之一。各国规范都是根据以往的试验与研究,采用统计方法,提出不同的公式,而在钢筋混凝土梁受剪性能的试验研究中,为了保证最终发生剪切破坏,常有意将梁的纵筋率设置得很大(常常大于2.8%)。这与工程实践中梁纵筋率一般在1.0～1.5%左右的实际情况差距较大。因此,建立在这种纵筋率较高的梁的受剪性能试验数据基础上的规范抗剪设计方法可能偏差较大。
本文属于系列研究的一部分。通过对集中荷载作用下8 根剪跨比为2.5、不同纵筋率的无腹筋约束梁(其中5 根试件上下纵筋通长配置、3 根试件上部纵筋截断一半)的试验,深入研究无腹筋约束梁的受剪破坏全过程及纵筋率对其的影响。
李立仁副教授的硕士研究生冯宏[28]已就不同纵筋率对剪跨比为1.5 的无腹筋约束梁受剪性能影响进行了研究,这些试件除剪跨比和这次试验不同外,其余参数均同本次试验。本文将通过对两次试验结果进行的对比分析,以找出剪跨比不同对无腹筋约束梁抗剪性能的影响。
在本次试验中,首先通过单调静力加载试验研究,对梁的裂缝延伸和开展、纵筋应变、腰筋应变、梁的挠度等指标进行了细致的量测,试图追踪每一试件在裂缝发展及破坏过程中纵筋应变状态的变化和裂缝发展程度的相关性,进而总结出无腹筋约束梁裂缝开展及钢筋应力分布的一般规律。其次,通过对比研究不同纵筋率试件的裂缝开展和延伸规律、破坏形态特征以及承载力等,初步总结了纵筋率的影响规律。
研究结果表明,纵筋率的变化对裂缝的发展有显著的影响,纵筋率较大的构件裂缝发展明显比纵筋率小的构件发展充分;纵筋率的变化将引起破坏形态的变化,纵筋率较小时构件发生剪压破坏,纵筋率较大时试件发生撕裂斜拉破坏;纵筋率对钢筋应变分布有显著的影响,纵筋率大的构件应力重分布比较充分,钢筋应变分布也在一定程度上真实地反映了试件的裂缝开展情况;不同的剪跨比对破坏形态,纵筋应变,裂缝开展情况均有明显的影响。在承载力方面,本次试验实测抗剪承载力平均比按我国规范GB 50010-2002 抗剪设计公式计算的抗剪承载力仅高22%左右,而最小纵筋率的试件抗剪承载力小于规范计算值20%左右。
For the reinforced concrete bend members, many factors can influence the shear strength of oblique section, furthermore the destroy mechanism is complicated, so the shear strength of oblique section is one of the unfathomed problems of reinforced concrete structure. The design codes of many countries exert statistical method, advance different formula, based on previous experiment results and research. Many countries base their design codes on the previous experiment results and researches, and establish different formulas using statistical method. But in general, to ensure the final shear failure, a very large longitudinal reinforcement ratio, usually larger than 2.8%, was chosen as a prerequisite in previous studies on shear behavior of reinforced concrete beams. It is very different from that in practice under such circumstances the longitudinal reinforcement ratio is among 1.0~1.5%. The codified design equations based on such testing data may be produce an error.
This paper is a part of series of experimental study. Eight restrained beams without web reinforcements and different longitudinal reinforcement ratio were tested under static point loads, with the shear-span ratio being kept around 2.5. On this basis, the overall process of cracking development under shear and the effect of longitudinal reinforcement ratio on it was investigated.
FengHong, the master of Liliren professor, has studied the effect of different longitudinal reinforcement ratio on shear behavior of restrained beams without web reinforcement when shear-span ratio is 1.5, so in this test, except the shear-span is 2.5, other parameters are the same as Fenghong’s test. In this paper, on the basis of the two tests results, through comparing and analyzing, find some disciplinarian of effect of different shear-span ratio on shear behavior of restrained beams without reinforcement. In this paper, on the basis of the two tests results and through comparing and analyzing, we hope to find some disciplinarian of effect of different shear-span ratio on shear behavior of restrained beams without web reinforcement.
In this experiment, the monotonic static load experiment was studied, and the extending and development of cracks、strains of the longitudinal reinforcements and deflection of the beams are carefully recorded, the correlation between the change of the strain of the reinforcements and the development of cracks of each experimented member was tried to keep track of, and by this way we hope to find out the general law of the crack development and the reinforcement stress distribution. Another, by comparison of the extending and development of cracks、final failure mode and ultimate capacity of members of different longitudinal reinforcement ratios we unveiled the law of effect of various longitudinal reinforcement ratios.
The experiments showed that the change of longitudinal reinforcement has a significant impact on the development of cracks, the development of cracks of large longitudinal reinforcement ratio member is more sufficient than that the small longitudinal reinforcement ratio member. The change of the longitudinal reinforcement ratio will produce the change the failure mode, shear compressive failure will happen when the longitudinal reinforcement ratio is small and tear tensile failure will happen when the longitudinal reinforcement ratio is large; the longitudinal reinforcement ratio has a significant impact on the distribution of the reinforcement stress, members of large longitudinal reinforcement ratio will have a sufficient stress redistribution)and to some degree, the distribution of strains in reinforcements reflects the development of cracks. Different shear-span ratio obviously influence the failure mode, the strain of longitudinal reinforcement and the development of cracks. As for the ultimate shear capacity, the averaged experiment result is 22% more than the predicted results obtained from the China Design Code, GB50010—2002, and that of member of the least longitudinal reinforcement ratio is about 20% less than the predicted results obtained from the China Design Code.
本文属于系列研究的一部分。通过对集中荷载作用下8 根剪跨比为2.5、不同纵筋率的无腹筋约束梁(其中5 根试件上下纵筋通长配置、3 根试件上部纵筋截断一半)的试验,深入研究无腹筋约束梁的受剪破坏全过程及纵筋率对其的影响。
李立仁副教授的硕士研究生冯宏[28]已就不同纵筋率对剪跨比为1.5 的无腹筋约束梁受剪性能影响进行了研究,这些试件除剪跨比和这次试验不同外,其余参数均同本次试验。本文将通过对两次试验结果进行的对比分析,以找出剪跨比不同对无腹筋约束梁抗剪性能的影响。
在本次试验中,首先通过单调静力加载试验研究,对梁的裂缝延伸和开展、纵筋应变、腰筋应变、梁的挠度等指标进行了细致的量测,试图追踪每一试件在裂缝发展及破坏过程中纵筋应变状态的变化和裂缝发展程度的相关性,进而总结出无腹筋约束梁裂缝开展及钢筋应力分布的一般规律。其次,通过对比研究不同纵筋率试件的裂缝开展和延伸规律、破坏形态特征以及承载力等,初步总结了纵筋率的影响规律。
研究结果表明,纵筋率的变化对裂缝的发展有显著的影响,纵筋率较大的构件裂缝发展明显比纵筋率小的构件发展充分;纵筋率的变化将引起破坏形态的变化,纵筋率较小时构件发生剪压破坏,纵筋率较大时试件发生撕裂斜拉破坏;纵筋率对钢筋应变分布有显著的影响,纵筋率大的构件应力重分布比较充分,钢筋应变分布也在一定程度上真实地反映了试件的裂缝开展情况;不同的剪跨比对破坏形态,纵筋应变,裂缝开展情况均有明显的影响。在承载力方面,本次试验实测抗剪承载力平均比按我国规范GB 50010-2002 抗剪设计公式计算的抗剪承载力仅高22%左右,而最小纵筋率的试件抗剪承载力小于规范计算值20%左右。
For the reinforced concrete bend members, many factors can influence the shear strength of oblique section, furthermore the destroy mechanism is complicated, so the shear strength of oblique section is one of the unfathomed problems of reinforced concrete structure. The design codes of many countries exert statistical method, advance different formula, based on previous experiment results and research. Many countries base their design codes on the previous experiment results and researches, and establish different formulas using statistical method. But in general, to ensure the final shear failure, a very large longitudinal reinforcement ratio, usually larger than 2.8%, was chosen as a prerequisite in previous studies on shear behavior of reinforced concrete beams. It is very different from that in practice under such circumstances the longitudinal reinforcement ratio is among 1.0~1.5%. The codified design equations based on such testing data may be produce an error.
This paper is a part of series of experimental study. Eight restrained beams without web reinforcements and different longitudinal reinforcement ratio were tested under static point loads, with the shear-span ratio being kept around 2.5. On this basis, the overall process of cracking development under shear and the effect of longitudinal reinforcement ratio on it was investigated.
FengHong, the master of Liliren professor, has studied the effect of different longitudinal reinforcement ratio on shear behavior of restrained beams without web reinforcement when shear-span ratio is 1.5, so in this test, except the shear-span is 2.5, other parameters are the same as Fenghong’s test. In this paper, on the basis of the two tests results, through comparing and analyzing, find some disciplinarian of effect of different shear-span ratio on shear behavior of restrained beams without reinforcement. In this paper, on the basis of the two tests results and through comparing and analyzing, we hope to find some disciplinarian of effect of different shear-span ratio on shear behavior of restrained beams without web reinforcement.
In this experiment, the monotonic static load experiment was studied, and the extending and development of cracks、strains of the longitudinal reinforcements and deflection of the beams are carefully recorded, the correlation between the change of the strain of the reinforcements and the development of cracks of each experimented member was tried to keep track of, and by this way we hope to find out the general law of the crack development and the reinforcement stress distribution. Another, by comparison of the extending and development of cracks、final failure mode and ultimate capacity of members of different longitudinal reinforcement ratios we unveiled the law of effect of various longitudinal reinforcement ratios.
The experiments showed that the change of longitudinal reinforcement has a significant impact on the development of cracks, the development of cracks of large longitudinal reinforcement ratio member is more sufficient than that the small longitudinal reinforcement ratio member. The change of the longitudinal reinforcement ratio will produce the change the failure mode, shear compressive failure will happen when the longitudinal reinforcement ratio is small and tear tensile failure will happen when the longitudinal reinforcement ratio is large; the longitudinal reinforcement ratio has a significant impact on the distribution of the reinforcement stress, members of large longitudinal reinforcement ratio will have a sufficient stress redistribution)and to some degree, the distribution of strains in reinforcements reflects the development of cracks. Different shear-span ratio obviously influence the failure mode, the strain of longitudinal reinforcement and the development of cracks. As for the ultimate shear capacity, the averaged experiment result is 22% more than the predicted results obtained from the China Design Code, GB50010—2002, and that of member of the least longitudinal reinforcement ratio is about 20% less than the predicted results obtained from the China Design Code.
引文
[1]K. G. Moody, I. M. Viest, R. C. Elstner, E. Hognestad, Shear Strength of Reinforced Concrete Beams, Part 2—Test of Restrained Beams Without Web Reinforcement, ACI Structural Journal, 1955, 52 (5) .
[2]John E. Bower and Ivan M. Viest. Shear Stength of Restrained Concrete Beams Without Web Reinforcement. ACI Structrural Journal. 1960. 57 (4) .
[3]谢育良、李寿康等. 集中荷载下无腹筋钢筋混凝土约束梁的受剪强度. 同济大学学报. 1979. 1.
[4]陈文钦、牛绍仁、秦文钺,集中荷载下钢筋混凝土约束梁受剪强度的试验研究. 重庆建筑工程学院学报, 1984.
[5]付有仓、朱聘儒、卫纪德,集中荷载作用下钢筋混凝土无腹筋连续梁的受剪强度,1984
[6]卫纪德,钢筋混凝土伸臂梁、连续梁的受剪强度,1985
[7]钱国梁、何英明,集中荷载作用下钢筋混凝土钢筋混凝土连续深梁受剪性能的试验研究1987.6
[8]ACI—ASCE Committee 326,Shear and Diagonal Tension,ACI Structural Journal,January 1962.59(1),pp.1-30.
[9]K. G. Moody, I. M. Viest, R. C. Elstner, E. Hognestad, Shear Strength of Reinforced Concrete Beams, Part 1—Test of Simple Beams, ACI Structural Journal, 1954, pp317-332.
[10]G. N .J. Kani, Basic Facts Concerning Shear Failure, ACI Structural Journal, June 1966, pp.675-690
[11]K. S. Rajagopalan, M. Ferguson, Exploratory Shear Tests Emphasizing Percentage of Longitudinal Steel, ACI Structural Journal, August 1968, pp634-638.
[12]Barrington dev. Batchelor, Bankit. Kwun. Shear in RC Beams Without Wed Reinforcement. ASCE, Journal of Structural Engineering. 1981. 107(5), pp907-921.
[13]卫纪德、朱聘儒,连续构件受剪性能研究之一:集中荷载作用下有腹筋约束梁的受剪强度,1984.9.20
[14]刘立新、谢丽丽、陈萌,钢筋混凝土深受弯构件受剪性能的研究,建筑结构,2000.10
[15]William J.Krefeld and Charles W.Thurston, Contribution of Longitudinal Steel to Shear Resistance of Reinforced Concrete Beams, ACI Structural Journal,1966.4.
[16]ACI-ASCE Committee 426. Shear Strength of Reinforced Concrete Members. ASCE, Journal of Structural Engineering. 1973.99 (6) . 1091-1187.
[17]James G.Macgregor. Reinforced Concrete Mechanics and Design. 1988.
[18]A. H. Nilson 著,过镇海等译,混凝土结构设计,北京.中国建筑工业出版社.1994.
[19]王传志、藤智明,钢筋混凝土结构理论,北京.中国建筑工业出版社.1985.
[20]ACI—ASCE Committee 326,Shear and Diagonal Tension,ACI Structural Journal,January 1962.59(1),pp.1-30.
[21]Eric J. Tompos and Robert J. Frosch. Influce of Beam Size, Longitudinal Reinfocement, and Stirrup Effectiveness on Concrete Shear Strenth. ACI Structrural Journal. 2002. 99 (5) . pp.559-567.
[22]白生翔等.钢筋混凝土构件试验数据集—85 年设计规范背景资料续编.北京.中国建筑科学研究院.1985.
[23]张川、陈臣、张百胜.集中荷载作用下纵筋率对钢筋混凝土无腹筋简支梁受剪性能的影响.重庆建筑大学学报.2003.
[24]白绍良、牛绍仁,钢筋混凝土及砖石结构,中央电大出版社
[25]中华人民共和国建设部,混凝土结构设计规范GB50010-2002,中国建筑出版社.2002.
[26]Frank J. Vecchio and Michael P.Collins. The Modified Compression-Field Theory for Reinforced Concrete Elements Subjected to Shear. ACI Structural Journal. 1986. 83 (2).
[27]Frank J. Vecchio and Michael P.Collins. Predicting the Response of Reinforced Concrete Beams Subject to Shear Using Modified Compression Field Theory.ACI Structural Journal. 1988. 85 (3).
[28]冯宏.不同纵筋率对剪跨比为1.5 的无腹筋约束梁受剪性能影响的研究.重庆大学硕士学位论文.2004.
[29]李凤兰、李芳、杨杰兰.集中荷载钢筋混凝土无腹筋梁的受剪承载力.华北水利水电学院学报.1997.
[30]狄谨.无腹筋钢筋混凝土梁的受剪承载力.长安大学学报.2004.
[31]李广慧、陈捷、刘立新.无腹筋RC 梁受剪承载力统一分析.郑州工业大学学报.1998.
[2]John E. Bower and Ivan M. Viest. Shear Stength of Restrained Concrete Beams Without Web Reinforcement. ACI Structrural Journal. 1960. 57 (4) .
[3]谢育良、李寿康等. 集中荷载下无腹筋钢筋混凝土约束梁的受剪强度. 同济大学学报. 1979. 1.
[4]陈文钦、牛绍仁、秦文钺,集中荷载下钢筋混凝土约束梁受剪强度的试验研究. 重庆建筑工程学院学报, 1984.
[5]付有仓、朱聘儒、卫纪德,集中荷载作用下钢筋混凝土无腹筋连续梁的受剪强度,1984
[6]卫纪德,钢筋混凝土伸臂梁、连续梁的受剪强度,1985
[7]钱国梁、何英明,集中荷载作用下钢筋混凝土钢筋混凝土连续深梁受剪性能的试验研究1987.6
[8]ACI—ASCE Committee 326,Shear and Diagonal Tension,ACI Structural Journal,January 1962.59(1),pp.1-30.
[9]K. G. Moody, I. M. Viest, R. C. Elstner, E. Hognestad, Shear Strength of Reinforced Concrete Beams, Part 1—Test of Simple Beams, ACI Structural Journal, 1954, pp317-332.
[10]G. N .J. Kani, Basic Facts Concerning Shear Failure, ACI Structural Journal, June 1966, pp.675-690
[11]K. S. Rajagopalan, M. Ferguson, Exploratory Shear Tests Emphasizing Percentage of Longitudinal Steel, ACI Structural Journal, August 1968, pp634-638.
[12]Barrington dev. Batchelor, Bankit. Kwun. Shear in RC Beams Without Wed Reinforcement. ASCE, Journal of Structural Engineering. 1981. 107(5), pp907-921.
[13]卫纪德、朱聘儒,连续构件受剪性能研究之一:集中荷载作用下有腹筋约束梁的受剪强度,1984.9.20
[14]刘立新、谢丽丽、陈萌,钢筋混凝土深受弯构件受剪性能的研究,建筑结构,2000.10
[15]William J.Krefeld and Charles W.Thurston, Contribution of Longitudinal Steel to Shear Resistance of Reinforced Concrete Beams, ACI Structural Journal,1966.4.
[16]ACI-ASCE Committee 426. Shear Strength of Reinforced Concrete Members. ASCE, Journal of Structural Engineering. 1973.99 (6) . 1091-1187.
[17]James G.Macgregor. Reinforced Concrete Mechanics and Design. 1988.
[18]A. H. Nilson 著,过镇海等译,混凝土结构设计,北京.中国建筑工业出版社.1994.
[19]王传志、藤智明,钢筋混凝土结构理论,北京.中国建筑工业出版社.1985.
[20]ACI—ASCE Committee 326,Shear and Diagonal Tension,ACI Structural Journal,January 1962.59(1),pp.1-30.
[21]Eric J. Tompos and Robert J. Frosch. Influce of Beam Size, Longitudinal Reinfocement, and Stirrup Effectiveness on Concrete Shear Strenth. ACI Structrural Journal. 2002. 99 (5) . pp.559-567.
[22]白生翔等.钢筋混凝土构件试验数据集—85 年设计规范背景资料续编.北京.中国建筑科学研究院.1985.
[23]张川、陈臣、张百胜.集中荷载作用下纵筋率对钢筋混凝土无腹筋简支梁受剪性能的影响.重庆建筑大学学报.2003.
[24]白绍良、牛绍仁,钢筋混凝土及砖石结构,中央电大出版社
[25]中华人民共和国建设部,混凝土结构设计规范GB50010-2002,中国建筑出版社.2002.
[26]Frank J. Vecchio and Michael P.Collins. The Modified Compression-Field Theory for Reinforced Concrete Elements Subjected to Shear. ACI Structural Journal. 1986. 83 (2).
[27]Frank J. Vecchio and Michael P.Collins. Predicting the Response of Reinforced Concrete Beams Subject to Shear Using Modified Compression Field Theory.ACI Structural Journal. 1988. 85 (3).
[28]冯宏.不同纵筋率对剪跨比为1.5 的无腹筋约束梁受剪性能影响的研究.重庆大学硕士学位论文.2004.
[29]李凤兰、李芳、杨杰兰.集中荷载钢筋混凝土无腹筋梁的受剪承载力.华北水利水电学院学报.1997.
[30]狄谨.无腹筋钢筋混凝土梁的受剪承载力.长安大学学报.2004.
[31]李广慧、陈捷、刘立新.无腹筋RC 梁受剪承载力统一分析.郑州工业大学学报.1998.