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
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摘要
以往对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是偏不安全的。在纵筋率对梁受剪性能的影响方面,已有一些学者进行了试验研究,但这些研究较为偏重于纵筋率对承载力的影响,而较少关注纵筋率对裂缝开展特征和最终破坏形态的影响。尤其在相同纵筋率的情况下,上部纵筋的部分截断对抗剪承载力的影响方面,研究甚少。
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1.5、不同纵筋率的无腹筋约束梁(其中5根上下纵筋通长配置、3根上部纵筋截断一半)的试验,深入研究了无腹筋约束梁的受剪破坏全过程及纵筋率对其的影响。
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。文中还将试验实测承载力与我国现行混凝土结构设计规范抗剪设计公式的预测值和基于修正斜压场理论的抗剪分析程序Response2000的分析结果进行了对比。
研究结果表明,纵筋率的变化对裂缝的发展有显著的影响;纵筋率的变化将引起破坏形态的变化;纵筋率对钢筋应变分布有显著的影响;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。在承载力方面,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高51%,比按修正斜压场理论的抗剪分析程序Response2000的分析结果高86%。
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 bahavior of reinforced concrete baeams. It is very different from that in practice as under such circumstances the longitudinal reinforcement ratio is among 1.0~1.5%. The codified design equations based on such testing data may be unconservative. Systematic investigation for effect of longitudinal reinforcement ratio on shear behavior of RC beams is particularly rare. A majority of previous studies on the effect of longitudinal reinforcement ratio on shear behavior of reinforced concrete members concerned about beams without web reinforcements and ultimate capacity; few gave detailed recording of development of cracking and failure process of RC beams without web reinforcements.
This paper is a part of series of experimental study. Eight restrained beams without web reinforcements and different longitudinal reinforcement were tested under static point loads, with the shear-span ratio being kept around 1.5. On this basis, the overall process of cracking development under shear and the effect of longitudinal reinforcement ratio on it was investigated.
At first, development of various cracks carefully recorded and strains on both the rebars and the stirrups were measured in detail, together with the deflections of the beam. In such a way, correlation between the measured strain profiles of the reinforcement and the observed cracking development of each specimen was pursued. Principal factors contributing to the crcking pattern and failure mode were figured out as a result. Secondly, comparison of the tested results unveiled effect of various longitudinal reinforcement ratios on development of cracks, final failure mode, and ultimate capacity. Primary conclusions were thus drawn. Moreover, the measured ultimate shear from the tests were compared with that predicted from China Design Code of Reinforced Concrete structures, GB50010—2002, and that from the Response2000, which is based on modified compression field theory by Michael Collins, both were undertaken before the experiments.
The experiments showed that different amount of longitudinal reinforcement had a significant impact on formation of different cracks. To some degree, the distribution of strains in reinforcements reflects development of cracks. As for ultimate shear capacity,
the difference between the predicted results obtained from the China Design Code, GB50010—2002, and the tested results is 51%, the predicted results from the Response2000, and the tested results is 86%.
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1.5、不同纵筋率的无腹筋约束梁(其中5根上下纵筋通长配置、3根上部纵筋截断一半)的试验,深入研究了无腹筋约束梁的受剪破坏全过程及纵筋率对其的影响。
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。文中还将试验实测承载力与我国现行混凝土结构设计规范抗剪设计公式的预测值和基于修正斜压场理论的抗剪分析程序Response2000的分析结果进行了对比。
研究结果表明,纵筋率的变化对裂缝的发展有显著的影响;纵筋率的变化将引起破坏形态的变化;纵筋率对钢筋应变分布有显著的影响;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。在承载力方面,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高51%,比按修正斜压场理论的抗剪分析程序Response2000的分析结果高86%。
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 bahavior of reinforced concrete baeams. It is very different from that in practice as under such circumstances the longitudinal reinforcement ratio is among 1.0~1.5%. The codified design equations based on such testing data may be unconservative. Systematic investigation for effect of longitudinal reinforcement ratio on shear behavior of RC beams is particularly rare. A majority of previous studies on the effect of longitudinal reinforcement ratio on shear behavior of reinforced concrete members concerned about beams without web reinforcements and ultimate capacity; few gave detailed recording of development of cracking and failure process of RC beams without web reinforcements.
This paper is a part of series of experimental study. Eight restrained beams without web reinforcements and different longitudinal reinforcement were tested under static point loads, with the shear-span ratio being kept around 1.5. On this basis, the overall process of cracking development under shear and the effect of longitudinal reinforcement ratio on it was investigated.
At first, development of various cracks carefully recorded and strains on both the rebars and the stirrups were measured in detail, together with the deflections of the beam. In such a way, correlation between the measured strain profiles of the reinforcement and the observed cracking development of each specimen was pursued. Principal factors contributing to the crcking pattern and failure mode were figured out as a result. Secondly, comparison of the tested results unveiled effect of various longitudinal reinforcement ratios on development of cracks, final failure mode, and ultimate capacity. Primary conclusions were thus drawn. Moreover, the measured ultimate shear from the tests were compared with that predicted from China Design Code of Reinforced Concrete structures, GB50010—2002, and that from the Response2000, which is based on modified compression field theory by Michael Collins, both were undertaken before the experiments.
The experiments showed that different amount of longitudinal reinforcement had a significant impact on formation of different cracks. To some degree, the distribution of strains in reinforcements reflects development of cracks. As for ultimate shear capacity,
the difference between the predicted results obtained from the China Design Code, GB50010—2002, and the tested results is 51%, the predicted results from the Response2000, and the tested results is 86%.
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抗剪强度. 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抗剪强度的试验研究. 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抗剪强度,1984
[6]卫纪德,钢筋混凝土伸臂梁、连续梁的抗剪强度,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抗剪性能的试验研究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,连续构件抗剪性能研究之一:集中荷载作用下有腹筋约束梁的抗剪强度,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).
[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抗剪强度. 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抗剪强度的试验研究. 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抗剪强度,1984
[6]卫纪德,钢筋混凝土伸臂梁、连续梁的抗剪强度,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抗剪性能的试验研究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,连续构件抗剪性能研究之一:集中荷载作用下有腹筋约束梁的抗剪强度,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).