HRB500级钢筋混凝土框架结构静载试验研究
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摘要
本文主要研究了HRB500级钢筋混凝土构件剪弯段的裂缝性能。HRB500级钢筋是一种新型高强热轧带肋钢筋,采用此高强钢筋能够显著提高混凝土构件的承载力,降低用钢量。但是,作为主要受力钢筋,由于其处于高应力工作状态,正常使用状态下的裂缝宽度可能会超过规范限值。因此,在设计中正常使用状态下裂缝宽度的计算就有可能取代承载力强度的计算而成为控制设计的主要因素,使其高强度难以发挥。我国规范公式是根据纯弯段的试验结果及粘结滑移理论来计算平均裂缝间距和平均裂缝宽度的,而对于变弯矩区段的弯剪裂缝宽度计算并没有相应的规定。而在连续梁、框架梁的支座端,其剪力和弯矩同时达到最大,这与简支梁纯弯段受力性能有所不同,必须考虑剪力对裂缝宽度的影响。
本文对三榀一层两跨的框架结构进行静力试验研究,其中两榀框架梁采用HRB500级钢筋作为受力主筋,一榀框架梁作为对比采用HRB400级钢筋作为受力主筋。试验在初始阶段采用框架梁跨中集中对称加载方案,而在破坏阶段则采用跨中位移控制的加载方案。试验过程中记录了每级荷载下框架梁框架柱各关键截面的混凝土和钢筋应变、梁端柱顶转角以及梁跨中挠度,确定框架梁的开裂荷载和极限荷载,观测裂缝的开展情况以及测定裂缝宽度等。使用所测柱底截面混凝土及钢筋应变,计算柱底反力,从而推算出框架梁任意截面的弯矩和剪力,并通过框架梁各关键截面所测的应变数据进行计算校核。
试验过程中通过记录框架梁的挠度、梁端柱顶转角以及各关键截面的应变等数据,深入研究了框架结构的非线性受力、变形性能、内力重分布规律以及塑性铰的转动能力。框架的受力性能试验研究表明,由于HRB500级钢筋具有较好的延性,在超静定结构中可形成破坏机构,实现较大的塑性内力重分布,可用于按考虑塑性内力重分布设计的结构。
通过柱底反力可计算出框架梁控制裂缝截面所对应的弯矩和剪力,通过将控制裂缝宽度实测值与按现行规范计算的裂缝宽度对比分析可得:框架梁跨中截面的最大裂缝宽度仍可按现行规范公式计算,而支座端裂缝宽度的计算需考虑剪力的影响,采用剪力影响系数k v对计算的最大裂缝宽度公式进行修正。
The crack behavior of concrete members reinforced with HRB500 steel in varying moment region is experimental studied in this paper. HRB500 bar is a new hot-rolled ribbed bar with yield strength of 500MPa, which can enhance the bearing capacity of concrete member and reduce the amount of steel. But it always reaches high stress and the crack width may exceed the limit of the code, as a result the crack width may become primary instead of the bearing capacity in the design, which makes the high strength of HRB500 bar cannot exert. The calculation formula of crack width in Chinese code is based on the experimental results of constant moment region and the theory of bond stress and bond slip, but the corresponding formula in varying moment region is not suggested. Especially on the support of the frame beam, the moment and the shear both reach the largest, so the influence of the shear on the crack width must be considered.
The static test of two HRB500 reinforced concrete frames and one HRB400 reinforced frame is studied. In the initial stage the concentrated symmetric loads are applied and in the failure stage the deflection of the frame beam is controlled. During the experimental process, the strain in the key sections, the rotation angle in the beam-column end and the deflection are recorded, meanwhile the crack width and distribution are also recorded. By use of the strain in the section of column base, the reaction force can be calculated, so the shear force and the bending moment on the arbitrary section of the frame beam can also be computed, which can be checked by the strain of the key sections of the frame beam.
Using the measured data, the nonlinearity, the deformation performance, the internal force redistribution and the rotation capacity of the plastic hinge are further studied. The test shows, owing to good ductility of HRB500 bar and enough rotation capacity of the plastic hinge, the frame can implement the plastic internal force redistribution, so this can be taken into account in the design.
By use of the reaction force, the shear force and the bending moment on the dominating crack section of the frame beam can be calculated. By comparing the measured crack width with that computed according to the code, the coefficient of the shear is given on the formula of the crack width.
本文对三榀一层两跨的框架结构进行静力试验研究,其中两榀框架梁采用HRB500级钢筋作为受力主筋,一榀框架梁作为对比采用HRB400级钢筋作为受力主筋。试验在初始阶段采用框架梁跨中集中对称加载方案,而在破坏阶段则采用跨中位移控制的加载方案。试验过程中记录了每级荷载下框架梁框架柱各关键截面的混凝土和钢筋应变、梁端柱顶转角以及梁跨中挠度,确定框架梁的开裂荷载和极限荷载,观测裂缝的开展情况以及测定裂缝宽度等。使用所测柱底截面混凝土及钢筋应变,计算柱底反力,从而推算出框架梁任意截面的弯矩和剪力,并通过框架梁各关键截面所测的应变数据进行计算校核。
试验过程中通过记录框架梁的挠度、梁端柱顶转角以及各关键截面的应变等数据,深入研究了框架结构的非线性受力、变形性能、内力重分布规律以及塑性铰的转动能力。框架的受力性能试验研究表明,由于HRB500级钢筋具有较好的延性,在超静定结构中可形成破坏机构,实现较大的塑性内力重分布,可用于按考虑塑性内力重分布设计的结构。
通过柱底反力可计算出框架梁控制裂缝截面所对应的弯矩和剪力,通过将控制裂缝宽度实测值与按现行规范计算的裂缝宽度对比分析可得:框架梁跨中截面的最大裂缝宽度仍可按现行规范公式计算,而支座端裂缝宽度的计算需考虑剪力的影响,采用剪力影响系数k v对计算的最大裂缝宽度公式进行修正。
The crack behavior of concrete members reinforced with HRB500 steel in varying moment region is experimental studied in this paper. HRB500 bar is a new hot-rolled ribbed bar with yield strength of 500MPa, which can enhance the bearing capacity of concrete member and reduce the amount of steel. But it always reaches high stress and the crack width may exceed the limit of the code, as a result the crack width may become primary instead of the bearing capacity in the design, which makes the high strength of HRB500 bar cannot exert. The calculation formula of crack width in Chinese code is based on the experimental results of constant moment region and the theory of bond stress and bond slip, but the corresponding formula in varying moment region is not suggested. Especially on the support of the frame beam, the moment and the shear both reach the largest, so the influence of the shear on the crack width must be considered.
The static test of two HRB500 reinforced concrete frames and one HRB400 reinforced frame is studied. In the initial stage the concentrated symmetric loads are applied and in the failure stage the deflection of the frame beam is controlled. During the experimental process, the strain in the key sections, the rotation angle in the beam-column end and the deflection are recorded, meanwhile the crack width and distribution are also recorded. By use of the strain in the section of column base, the reaction force can be calculated, so the shear force and the bending moment on the arbitrary section of the frame beam can also be computed, which can be checked by the strain of the key sections of the frame beam.
Using the measured data, the nonlinearity, the deformation performance, the internal force redistribution and the rotation capacity of the plastic hinge are further studied. The test shows, owing to good ductility of HRB500 bar and enough rotation capacity of the plastic hinge, the frame can implement the plastic internal force redistribution, so this can be taken into account in the design.
By use of the reaction force, the shear force and the bending moment on the dominating crack section of the frame beam can be calculated. By comparing the measured crack width with that computed according to the code, the coefficient of the shear is given on the formula of the crack width.
引文
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[3]裴智,王友权,王学忠等.HRB500钢筋的研究开发与应用,建筑结构学报, 2003, 33(8): 28-29
[4]钢筋混凝土用钢第2部分:热轧带肋钢筋(GB1499.2-2007).北京:中国标准出版社, 2007, 11
[5]崔培耀,俞敏,徐军. HRB500钢筋的试制开发.中国冶金, 2003, 79(11): 31-32
[6]孟宪珩,白宗奇.承钢HRB500钢筋的研制及市场开发.冶金标准化与质量, 2005, 43(3): 32-33
[7]胡伦坚,刘立新,阎红兵. HRB500级钢筋连接性能研究.施工技术, 2005, 34(7): 46-48
[8]毛达岭,刘立新,范丽. HRB500钢筋粘结锚固性能及设计建议.郑州大学学报, 2004, 25(2): 54-58
[9]李娟. HRB500级箍筋混凝土梁斜截面受力性能试验研究: [湖南大学硕士学位论文].湖南:湖南大学, 2007, 52-63
[10]徐有邻.我国混凝土结构用钢筋的现状及发展,土木工程学报, 1999, 32(5): 4-9
[11] Borges.J.F, Lima, J.A. Formation of cracks in Reinforced concrete Beams, ACI Journal, 1958,55(4):1122~1124
[12] Saligar.R. High grade steel in Reinforced Concrete, Preliminary Publication, Second Congress of the IABSE, Berlin-Munich, 1936: 20-26
[13] Watstein D, Mathey R, Widths of Cracks in Concrete at the Surface of Reinforcing Steel Evaluated by Means of Tensile Bond Specimens. ACI Journal, 1959, 56(7): 45~57
[14] Borms B.B, Lutz L.A. Effects of Arrangements of Reinforcement on Crack width and spacing of Reinforced Concrete Members. ACI Journal, 1965, 62(11): 1395~1410
[15]过镇海,时旭东.钢筋混凝土原理和分析.北京:清华大学出版社, 2003,246-249
[16] G. C. Frantz, J. E. Breen, Design Proposal for Side Face Crack Control Reinforcement for Large Reinforced Concrete Beams. Concrete International, 1980, 22(10): 23~26
[17] G. C. Frantz, J. E. Breen, Control of Cracking in Concrete Structures, Concrete International, 1980, 22(10): 122~127
[18]丁大钧.试论钢筋构件裂缝力学机理.土木工程, 1983, (5): 41~47
[19]祝明桥.冷轧带肋钢筋混凝土受弯构件裂缝和变形性能的试验研究: [湖南大学硕士学位论文].湖南:湖南大学, 1999, 16-20
[20]钱伟. 500MPa螺旋肋钢筋混凝土构件受力性能的试验研究: [郑州工业大学硕士学位论文].郑州:郑州大学, 2000, 28-32
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