Unified Shear Strength Model for Reinforced Concrete Beams-Part I: Development. Paper by Kyoung-Kyu Choi, Hong-Gun Park, and James K. Wight/AUTHORS' CLOSURE

Discussion by Himat Solanki

ACI member, Professional Engineer, Building Dept., Sarasota County Government, Sarasota, FL

The authors have presented an interesting concept on the unified shear strength model of reinforced concrete beams. Based on the outline in the paper, it appears that the concept in this paper is an extension of the authors' previous paper,35 although they have included beams having shear reinforcement and reinforced concrete deep beams.

The discusser would like to offer the following:

1. It is unclear in the paper how the authors have accounted for the inclined shear reinforcement bars (such as 45 or 67.5 degrees or any other angle), and/or spiral stirrups reinforcement, and/or U-shaped stirrup reinforcement, and/or staggered pin (single/multiple pin[s]) shear reinforcement in calculating the NA to resist the shearing force.

2. It is also unclear from the paper how the equivalent scc (Fig. 11) was calculated. Was it based on an equivalent rectangular block? Was it based on the shear compression strength based on an octahedral plane stress relationship? Or was it based on a relationship (some factor [less than 1.0]) between the shearing strength in concrete to the compressive strength in concrete?

3. It appears that the authors are unaware of the research published by Tanaka and Suenaga,36 Tsuboi et al.,37 and Tominaga.38

ACKNOWLEDGMENT

The discusser gratefully appreciates S. Unjoh, Leader, Earthquake Engineering Team, Public Works Research Institute, Tokyo, Japan, for providing the Japanese publications.

REFERENCES

35. Park, G.-H.; Choi, K.-K.; and Wight, J. K., "Strain-Based Shear Strength Model for Slender Beams without Web Reinforcement," ACI Structural Journal, V. 103, No. 6, Nov.-Dec. 2006, pp. 783-793.

36. Tanaka, Y., and Suenaga, Y., "Theoretical Studies on Ultimate Shearing Strength of Reinforced Concrete Beams," Transaction of the Architectural Institute of Japan, No. 60, 1958, pp. 605-608. (in Japanese)

37. Tsuboi, Y.; Tanaka, H,; and Suenaga, Y., "A Study of Failure of Reinforced Members Under Combine Stresses (Part 4): Especially on Beams under Bending Moment and Shearing Force," Transaction of the Architectural Institute of Japan, No. 67, 1961, pp. 1-9.

38. Tominaga, M., "Ultimate Strength Evaluation of Reinforced Concrete Simple Beams Failing in Shear Compression," Summaries of Technical Papers, Annual Meeting of Architectural Institute of Japan, Transaction of the Architectural Institute of Japan, No. 89, Sept. 1963, 153 pp. (in Japanese)

AUTHORS' CLOSURE

The authors thank the discusser for providing an opportunity to clarify the concept of the proposed model further. Each item of the question and comment presented by the discusser is discussed separately, as follows.

1. The proposed strength model was developed for its application to the concrete beams with/without conventional longitudinal and transverse web reinforcement, as presented in Fig. 12. Thus, in this paper, the proposed method was not verified for the beams with other shear reinforcement methods including inclined shear reinforcing bars and spiral stirrups. The authors believe, however, that the proposed method is readily applicable to the beams with such various shear reinforcement methods.

In the proposed method, the shear contribution of concrete depends on the depth of the compression zone, which is not significantly affected by the types of shear reinforcement method except the longitudinal web reinforcement. Therefore, if the shear contribution of the shear reinforcement is appropriately addressed, the proposed method is expected to be applicable to the beams with various shear reinforcement methods.

2. The value of scc does not indicate the material strength of concrete, but indicates the average compressive normal stress developing at the failure surface (HJ in Fig. 11). Therefore, scc is calculated by sectional analysis for flexural action of the beam, considering the equivalent rectangular block as given in Eq. (27). In the proposed model, the shear capacity of the compression zone is expressed by a function of the current normal compression stresses scc and sct (Eq. (21)), based on the material failure criteria in Eq. (1).

3. As the discusser indicates, the authors were not aware of the papers by Tanaka and Suenaga,36 Tsuboi et al.,37 and Tominaga38 because they are written in Japanese. The references are expected to provide useful information on our research.

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