负筋截断时纵筋率对有腹筋约束梁受剪性能影响的研究
|
摘要
以往对钢筋混凝土梁抗剪性能的实验研究中,为保证最终发生剪切破坏,常有意将梁的单侧纵筋配筋率设置得很大,通常大于2.8%,这与实际工程中单侧纵筋配筋率一般在1.0～1.5左右的实际情况差距较大。所以,建立在这种单侧纵筋配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。
张川教授的硕士研究生陈臣同学已就集中荷载作用下剪跨比为1.5不同单侧纵筋配筋率的有腹筋约束梁进行了抗剪性能研究,这些试件采用上下对称的纵筋通长布置; 而实际工程中上部纵筋一般要截断。因此本课题提出在试验构件各种参数与陈臣试验均相同的情况下按现行规范把梁上部纵筋截断,探索在这种情况下约束梁的抗剪性能与陈臣试验结果是否存在差异,以找出更接近工程实际的单侧纵筋配筋率对有腹筋约束梁的抗剪性能的影响规律。
本文通过集中荷载作用下五根不同单侧纵筋配筋率的有腹筋约束梁在负筋截断时的试验,深入研究了在纵筋截断下有腹筋约束梁的受剪破坏全过程及纵筋配筋率对抗剪强度的影响。
首先,通过单调静力加载试验,对梁的裂缝的产生和发展、纵筋应变、箍筋应变、梁的挠度等指标进行了记录和数据采集,试图追踪试件中纵筋应变状态的变化和裂缝发展程度的相关性,进而总结出有腹筋约束梁裂缝开展及钢筋应力分布的一般规律。其次,通过对比研究不同单侧纵筋配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,初步总结了纵筋配筋率的影响规律,并与陈臣试验结果进行对比。
研究结果表明,钢筋混凝土有腹筋约束梁的裂缝开展过程大致可分为裂缝扇形区的逐步形成、劈裂裂缝出现和发展、临界斜裂缝加速发展至破坏等阶段;纵筋率的变化对裂缝的发展有显著的影响;抗剪承载力实测值高于我国规范计算值平均61%;随着单侧纵筋配筋率的提高,约束梁的抗剪承载力有规律的增长;与陈臣试验的结果相比,没有发现二者之间明显的规律,说明考虑上部纵筋截断的有腹筋约束梁的抗剪承载力没有因上部纵筋截断而降低。
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 circumstance the longitudinal reinforcement ratio is among 1.0~1.5%. The codified design equations based on such testing data may be unconservative.
ChenChen ,the master of zhangchuan professor,has studied the effect of longitudinal reinforcement ratio on shear behavior of restrained beams with web reinforcement when shear-span ratio is 1.5,and the longitudinal reinforcement of his tries was disposed through the whole beam;But the top longitudinal reinforcement of beam is usually truncated in practice. Therefore,it is put forward that studies that the effect of longitudinal reinforcement ratio on shear behavior of restrained beams with web reinforcement when the top longitudinal reinforcement of beam is truncated according to the China Design Code,and comparing the results of different tests,and then wishing that that find some disciplinarian approaching the civil practice.
In this paper,five restrained beams with web and different longitudinal reinforcement ,and above longitudinal reinforcement is truncated,were tested under static point loads . 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 cracking 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,and the tests results were compared with ChenChen tests results.
The experiments showed that the cracking process of such restrained beams in this paper can be divided into three phases,that is,formation of the fanning zones,initialization and development of splitting cracks along longitudinal reinforcement,and
accelerating development of the critical cracks. Different amount of longitudinal reinforcement has a significant impact on formation of different cracks. As for ultimate shear capacity,the difference between the predicted results obtained from the China Design Code and the tested results is 61%. Ultimate shear capacity of restrained beams is increasing disciplinarian with the increasing longitudinal reinforcement ratio. It was not founded of evident disciplinarian between the results of this test and the results of ChenChen test,and it shows that shear behavior of restrained beams with web reinforcement is not receded when the top longitudinal reinforcement of beam is truncated.
张川教授的硕士研究生陈臣同学已就集中荷载作用下剪跨比为1.5不同单侧纵筋配筋率的有腹筋约束梁进行了抗剪性能研究,这些试件采用上下对称的纵筋通长布置; 而实际工程中上部纵筋一般要截断。因此本课题提出在试验构件各种参数与陈臣试验均相同的情况下按现行规范把梁上部纵筋截断,探索在这种情况下约束梁的抗剪性能与陈臣试验结果是否存在差异,以找出更接近工程实际的单侧纵筋配筋率对有腹筋约束梁的抗剪性能的影响规律。
本文通过集中荷载作用下五根不同单侧纵筋配筋率的有腹筋约束梁在负筋截断时的试验,深入研究了在纵筋截断下有腹筋约束梁的受剪破坏全过程及纵筋配筋率对抗剪强度的影响。
首先,通过单调静力加载试验,对梁的裂缝的产生和发展、纵筋应变、箍筋应变、梁的挠度等指标进行了记录和数据采集,试图追踪试件中纵筋应变状态的变化和裂缝发展程度的相关性,进而总结出有腹筋约束梁裂缝开展及钢筋应力分布的一般规律。其次,通过对比研究不同单侧纵筋配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,初步总结了纵筋配筋率的影响规律,并与陈臣试验结果进行对比。
研究结果表明,钢筋混凝土有腹筋约束梁的裂缝开展过程大致可分为裂缝扇形区的逐步形成、劈裂裂缝出现和发展、临界斜裂缝加速发展至破坏等阶段;纵筋率的变化对裂缝的发展有显著的影响;抗剪承载力实测值高于我国规范计算值平均61%;随着单侧纵筋配筋率的提高,约束梁的抗剪承载力有规律的增长;与陈臣试验的结果相比,没有发现二者之间明显的规律,说明考虑上部纵筋截断的有腹筋约束梁的抗剪承载力没有因上部纵筋截断而降低。
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 circumstance the longitudinal reinforcement ratio is among 1.0~1.5%. The codified design equations based on such testing data may be unconservative.
ChenChen ,the master of zhangchuan professor,has studied the effect of longitudinal reinforcement ratio on shear behavior of restrained beams with web reinforcement when shear-span ratio is 1.5,and the longitudinal reinforcement of his tries was disposed through the whole beam;But the top longitudinal reinforcement of beam is usually truncated in practice. Therefore,it is put forward that studies that the effect of longitudinal reinforcement ratio on shear behavior of restrained beams with web reinforcement when the top longitudinal reinforcement of beam is truncated according to the China Design Code,and comparing the results of different tests,and then wishing that that find some disciplinarian approaching the civil practice.
In this paper,five restrained beams with web and different longitudinal reinforcement ,and above longitudinal reinforcement is truncated,were tested under static point loads . 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 cracking 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,and the tests results were compared with ChenChen tests results.
The experiments showed that the cracking process of such restrained beams in this paper can be divided into three phases,that is,formation of the fanning zones,initialization and development of splitting cracks along longitudinal reinforcement,and
accelerating development of the critical cracks. Different amount of longitudinal reinforcement has a significant impact on formation of different cracks. As for ultimate shear capacity,the difference between the predicted results obtained from the China Design Code and the tested results is 61%. Ultimate shear capacity of restrained beams is increasing disciplinarian with the increasing longitudinal reinforcement ratio. It was not founded of evident disciplinarian between the results of this test and the results of ChenChen test,and it shows that shear behavior of restrained beams with web reinforcement is not receded when the top longitudinal reinforcement of beam is truncated.
引文
[1] K.G.Moody,I.M.Viest,R.C.Elstner,E.Hognestad. Shear strength of Reinforced Concrete Beams,Part2-Test of Restrained Beams Without Web Reinforcement.ACI Structrural Journal.1955.52(5)
[2] John E.Bower and Ivan M.Viest.Shear Strength of Restrained Concrete Beams Without Web Reinforcement.ACI Structrural Journal. 1960.57(4)
[3] 陈文钦、牛绍仁等. 集中荷载下钢筋混凝土约束梁的抗剪强度. 同济大学学报.1979.1
[4] R.C.Elstner,K.G.Moody,I.M.Viest,E.Hognestad.Shear Strength of Reinforced Concrete Beams,Part 3-Test of Restrained Beams With Web Reinforcement.ACI Structrural Journal 1955.52(6)
[5] 卫纪德. 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. 哈尔滨建筑工程学院学报. 1985.3.
[6] 卫纪德. 连续构件抗剪性能研究之二:集中荷载作用下有腹筋连续梁的抗剪强度. 哈尔滨建筑工程学院学报. 1985.4.
[7] 卫纪德等. 集中荷载作用下钢筋混凝土伸臂梁、连续梁的抗剪强度. 建筑结构学报. 1989.
[8] ACI-ASCE Committee 326. Shear and Diagonal Tension.ACI Structrural Journal. 1962.59(2).277-333 .
[9] 龚绍熙、王春光. 钢筋混凝土约束深梁的试验研究. 郑州工学院土建系. 1983.11.
[10] 刘立新、谢丽丽、陈荫. 钢筋混凝土深受弯构件受剪性能的研究. 建筑结构.2000.10.
[11] Gerardo Aguiliar,Adolfo B.Matamoros,Gustavo J.Parra-Montesinos,Julio A.Ramfrez and James K.Wight,Experimental Evaluation of Design Procedures for Shear Strength of Deep Reinforced Concrete Beams,ACI Structural Journal,July-August 2002.
[12] ACI-ASCE Committee 326. Shear and Diagonal Tension.ACI Structural Journal. 1962.59(1),pp1-30.
[13] K.G.Moody,I.M.Viest,R.C.Elstner,E.Hognestad. Shear strength of Reinforced Concrete Beams,Part2-Test of Simple Beams ACI Structrural Journal.1954.51(12).317-332.
[14] G.N.J.Kani,Basic Facts Concerning Shear Failure,ACI Structrural Journal 1966.6.
[15] Barrington deV,Bathelor and Bankit,Kwun, Shear in RC Beams Without Web Reinforcement,ASCE,Journal of Structrural Journal. 1966.4.
[16] William J.Krefeld and Charles W.Thurston, Contribution of Longitudinal Steel to Shear Resistance of Reinforced Concrete Beams, ACI Structural Journal, 1996.4.
[17] 施岚青、徐有邻. 钢筋混凝土受弯构件的剪切强度控制区及其下包线. 建筑结构学报.1983.
[18] P.S.Chana, Investigation of the Mechanism of Shear Failure of Reinforced Concrete Beams, Magazine of Concrete Research, Vol.39,December 1987,pp.196-204.
[19] 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.
[20] 白生翔等. 钢筋混凝土结构设计与构造-85年设计规范背景资料汇编. 北京. 中国建筑科学研究院.1985.
[21] 中华人民共和国国家标准,《混凝土结构设计规范》GB50010-2002. 中国建筑工业出版社.2002.
[22] 陈臣. 不同纵筋率对剪跨比为1.5的有腹筋约束梁受剪性能的影响. 重庆大学硕士学位论文.2003.
[2] John E.Bower and Ivan M.Viest.Shear Strength of Restrained Concrete Beams Without Web Reinforcement.ACI Structrural Journal. 1960.57(4)
[3] 陈文钦、牛绍仁等. 集中荷载下钢筋混凝土约束梁的抗剪强度. 同济大学学报.1979.1
[4] R.C.Elstner,K.G.Moody,I.M.Viest,E.Hognestad.Shear Strength of Reinforced Concrete Beams,Part 3-Test of Restrained Beams With Web Reinforcement.ACI Structrural Journal 1955.52(6)
[5] 卫纪德. 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. 哈尔滨建筑工程学院学报. 1985.3.
[6] 卫纪德. 连续构件抗剪性能研究之二:集中荷载作用下有腹筋连续梁的抗剪强度. 哈尔滨建筑工程学院学报. 1985.4.
[7] 卫纪德等. 集中荷载作用下钢筋混凝土伸臂梁、连续梁的抗剪强度. 建筑结构学报. 1989.
[8] ACI-ASCE Committee 326. Shear and Diagonal Tension.ACI Structrural Journal. 1962.59(2).277-333 .
[9] 龚绍熙、王春光. 钢筋混凝土约束深梁的试验研究. 郑州工学院土建系. 1983.11.
[10] 刘立新、谢丽丽、陈荫. 钢筋混凝土深受弯构件受剪性能的研究. 建筑结构.2000.10.
[11] Gerardo Aguiliar,Adolfo B.Matamoros,Gustavo J.Parra-Montesinos,Julio A.Ramfrez and James K.Wight,Experimental Evaluation of Design Procedures for Shear Strength of Deep Reinforced Concrete Beams,ACI Structural Journal,July-August 2002.
[12] ACI-ASCE Committee 326. Shear and Diagonal Tension.ACI Structural Journal. 1962.59(1),pp1-30.
[13] K.G.Moody,I.M.Viest,R.C.Elstner,E.Hognestad. Shear strength of Reinforced Concrete Beams,Part2-Test of Simple Beams ACI Structrural Journal.1954.51(12).317-332.
[14] G.N.J.Kani,Basic Facts Concerning Shear Failure,ACI Structrural Journal 1966.6.
[15] Barrington deV,Bathelor and Bankit,Kwun, Shear in RC Beams Without Web Reinforcement,ASCE,Journal of Structrural Journal. 1966.4.
[16] William J.Krefeld and Charles W.Thurston, Contribution of Longitudinal Steel to Shear Resistance of Reinforced Concrete Beams, ACI Structural Journal, 1996.4.
[17] 施岚青、徐有邻. 钢筋混凝土受弯构件的剪切强度控制区及其下包线. 建筑结构学报.1983.
[18] P.S.Chana, Investigation of the Mechanism of Shear Failure of Reinforced Concrete Beams, Magazine of Concrete Research, Vol.39,December 1987,pp.196-204.
[19] 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.
[20] 白生翔等. 钢筋混凝土结构设计与构造-85年设计规范背景资料汇编. 北京. 中国建筑科学研究院.1985.
[21] 中华人民共和国国家标准,《混凝土结构设计规范》GB50010-2002. 中国建筑工业出版社.2002.
[22] 陈臣. 不同纵筋率对剪跨比为1.5的有腹筋约束梁受剪性能的影响. 重庆大学硕士学位论文.2003.