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《深圳大学学报理工版》[ISSN:1000-2618/CN:44-1401/N]

卷:

第23卷

期数:

2006年3期

页码:

189-194

栏目:

土木建筑工程

出版日期:

2006-07-30

文章信息/Info

Title:

Experimental study on shear failure modes for ultrahigh strength concrete RC beams without stirrups

文章编号:

1000-2618(2006)03-0189-06

作者:

王卫仑; 邢锋; 曹征良

深圳大学建筑与土木工程学院

Author(s):

WANG Wei-Iun; XING Feng; and CAO Zheng-liang

College of Architecture and Civil engineering Shenzhen University

关键词:

超高强度混凝土; 无腹筋梁; 剪压破坏; 斜拉破坏; 剪切计算公式

Keywords:

ultrahigh strength concrete;  RC beams without stirrups;  shear compression failure;  diagonal tension failure;  shear strength design equations

文献标志码:

A

摘要:

通过3组10根超高强度混凝土梁剪切试验，考察混凝土强度、有效高度及剪跨比等变动因子，对梁剪切破坏性状进行研究，试验结果表明，即使在超高强度区域，混凝土强度及梁有效高度对梁剪切破坏模式的影响也无明确界限，剪跨比范围2.5～3.0是斜拉破坏和剪压破坏的过渡区，指出区分不同的破坏模式计算超高强度RC梁斜截面极限承载力极为重要。在超高强度领域，目前GB50010对斜拉破坏梁的评估尚欠安全，且随着混凝土强度的进一步提高，评估结果的安全性也会递减。

Abstract:

The study on the shear failure modes of RC beams without stirrups was carried out by 3 sets of ultrahigh strength specimens, The variable factors are the concrete compressive strength (fe ’) ，the effective depth(d) and ratio of shear span to effective depth(a/d) respectively. The experimental results show that the behavior of the shear compression failure mode is quite different from the diagonal tension failure mode although both shear failure modes are sudden and brittle. For the experimental beams failed in the mode of shear compression failure despite the appearance of diagonal crack, the specimen exhibited much load-carrying capacity by compressive strut. And another mode of shear failure is diagonal tension failure，in which a single diagonal crack developed suddenly and persisted in opening up with increasing load until the failure occurred rapidly. The effect of fc’ on the shear strength is quite different between the shear compression failure and diagonal tension failure For the ultrahigh strength concrete beams without web reinforcements failed in shear compression, the ultimate shear strength increases significantly with increase of the concrete compressive strength. However , it varies insignificantly with increase of the concrete compressive strength, for the ultrahigh strength concrete beams failed in diagonal tension failure mode. It is also apparent from varying the effective depth in this test that the apparent shear strength decreases as the size of the specimen increases. When the specimens failed in diagonal tension mode，the shear strength could be reduced 40% with increasing d from 0. 35 m to 0. 60 m. In other words，the influence of primary parameters fc’ or d on shear strength of the ultrahigh strength beams without stirrups should be calculated on the basis of various shear failure modes，but the two failure modes are difficult to be divided by the parameter of fc’ or d. Actually，the investigation shows that a/d is one of the most important factors to distinguish between the diagonal tension failure and shear compression failure. Accordingly, the failure under shear compression and diagonal tension，divided in accordance with a/d of 2.5 for ultrahigh strength beams，should be governed by dissimilar design equations. In addition, the applicability of conventional bearing capacity equations from current codes was also examined sufficiently for ultrahigh strength members in comparison with the test results. Shear strength of the ultrahigh strength RC beams with diagonal tension failure is overestimated by the current design provisions，and the evaluation becomes more unsafe in higher strength zone with increasing concrete strength. On the other hand, for the ultrahigh strength concrete beams failed by shear compression mode, a safe evaluation could be given by the design equation which should be inaccurate to evaluate the effect of every factor.

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