鋼筋混凝土梁之最大剪力強度研究

A Study on Maximum Shear Strength of Reinforced Concrete Beams

楊于暄(Yu-Hsuan Yang)

指導教授 ： 黃世建

國立臺灣大學/工學院/土木工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202002088

摘要

鋼筋混凝土梁的剪力強度，來自混凝土與剪力鋼筋的剪力強度貢獻。若欲提升鋼筋混凝土梁的剪力強度，可增加斷面之剪力鋼筋量。剪力破壞可分為剪拉破壞及剪壓破壞模式，當鋼筋混凝土梁配置之剪力鋼筋量提升至一定上限時，梁會由剪拉破壞轉變成剪壓破壞，此會造成剪力強度無法再隨著剪力鋼筋量的增加而持續上升。上述兩者皆屬於脆性剪力破壞，但剪拉破壞之破壞程序較剪壓破壞和緩。為了排除剪壓破壞發生的可能，需要對梁之最大剪力強度予以規定。目前 ACI 318-19規範在規定了最大剪力強度設計上限。但規範對於梁在何種情形下會轉換破壞模式，以及對於此設計上限之物理意義，尚未提出剪力傳遞模型來解釋此一現象發生之原因。
本論文以剪力跨深比(a/h)為分界，a/h>2 歸類為一般梁，a/h<=2 歸類為深梁。對一般梁及深梁均提出剪力傳遞模型，並建立鋼筋混凝土梁之資料庫，以驗證剪力傳遞模型於強度預測及破壞模式預測之準確性。在一般梁方面，此解析模型可清楚解釋破壞模式由剪拉破壞轉變至剪壓破壞之情形。藉由具備力學依據的剪力傳遞模型，能夠釐清對剪力強度有重要影響的參數。希望本研究建議之鋼筋混凝土梁最大剪力強度計算公式，能夠在工程設計上，對最大剪力強度提供清晰且有效率之設計依循。

關鍵字

鋼筋混凝土梁 ； 剪力強度 ； 最大剪力強度

並列摘要

Shear strength of reinforced concrete beams is derived from shear strength contribution of concrete and shear reinforcement. In order to increase the shear strength of reinforced concrete beams, we can increase the amount of shear reinforcement in the beam section. The proposed model recognizes two failure modes, which are shear tension failure and shear compression failure. When the amount of shear reinforcement is raised to the upper limit, the failure modes of a beam will be transformed from shear tension failure into shear compression failure. At this moment, the shear strength cannot continue to rise as the amount of shear reinforcement increases. Both failure modes belong to brittle shear failure, however the destruction process of shear compression failure is more dramatic than shear tension failure. In order to eliminate the possibility of shear compression failure, it is necessary to specify the maximum shear strength. The current ACI 318-19 specification specifies the upper limit for shear strength. However, the specification does not propose a shear transfer model to explain the reason why this phenomenon occurs and does not provide the physical meanings of the upper limit.
This paper devides beams into two categories based on their shear span-depth ratio(a/h), which we have typical beams with a/h>2 and deep beams with a/h<=2 . After that, this paper will propose a shear transfer model and build a reinforced concrete beam database to verify the accuracy of the shear transfer model in prediction of strength and failure mode. Then, this paper will use the proposed model to explain the transformation of the shear failure modes and comprehend how the shear force is transmitted. Based on physical meanings, several important parameters can be found. It is hoped that the proposed calculation formula for the maximum shear strength will be able to provide a design method with efficiency for engineering design.

並列關鍵字

Reinforced Concrete Beams ； Shear Strength ； Maximum Shear Strength

參考文獻

AASHTO (2014), “LRFD Bridge Design Specifications and Commentary,” seventh edition, American Association of State Highway Transportation Officials, Washington, DC, 2160 pp.

ACI Committee 318 (2008), “Building Code Requirements for Structural Concrete (ACI 318-14) and Commentary (ACI 318M-14),” American Concrete Institute, Farmington Hills, Michigan, 520 pp.

ACI Committee 318 (2014), “Building Code Requirements for Structural Concrete (ACI 318-08) and Commentary (ACI 318R-14),” American Concrete Institute, Farmington Hills, Michigan, 473 pp.

ACI Committee 318 (2019), “Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary (ACI 318R-19),” American Concrete Institute, Farmington Hills, Michigan, 623 pp.

Angelakos, D., Bentz, E. C., and Collins, M. P. (2001), “Effect of Concrete Strength and Minimum Stirrups on Shear Strength of Large Members,” ACI Structural Journal, Vol. 98, No. 3, pp. 291-300.