استحکام پانچ نمونه های ورقه-ستون معمولی
Abstract
1- Introduction
2- Punching failure
3- Summary of current major Code methods [11,12], the fib Model Code (2010) method and background to proposed method
4- Proposed modifications to Rankin & Long’s (1987) method [16]
5- Summary of proposed prediction method
6- Correlation of prediction methods with test results
7- Conclusions
8- Funding
References
Abstract
This paper presents an improved rational method for predicting the punching strength of conventional reinforced concrete slab-column specimens extending to the nominal line of contraflexure in a flat slab structure. The proposed method of analysis is for square and circular, isotropically reinforced, conventional slab-column specimens, concentrically loaded using square or circular columns. The method is based on an earlier two-phase approach, in which the punching strength was predicted as the lesser of the flexural punching strength and the shear punching strength. The earlier approach had previously been shown to be more reliable than other methods, including the major building code methods, and the proposed method represents a further significant improvement. The improvement in the proposed method is due to the incorporation of slab depth factors for both the flexural and shear modes of punching failure and refinements to the effects of concrete strength, reinforcement percentage and reinforcement yield strength, for the shear mode of punching failure. Comprehensive test data is presented for 217 tests on conventional slab-column specimens reported in the literature in the sixty year period 1956–2016. Analysis of these results by the proposed method resulted in significantly improved correlation over that of the authors’ previous two-phase approach. The method is also shown to be significantly more accurate and consistent than the current Eurocode 2 (2004) method, the ACI 318-14 (2014) method and the fib Model Code (2010) method for predicting the punching strength of conventional reinforced concrete slab-column specimens.
Introduction
Reinforced concrete flat slab structures were introduced in both North America and Europe at the beginning of the twentieth century. Technical and commercial development was primarily instigated by Turner [1] in the USA and Maillart [2] in Switzerland. In the early years, theoretical methods of analysis had not been developed and load capacity was generally proven by full scale load testing, as demonstrated by Lord [3]. The historical development of flat slab construction has been well documented by authors such as Sozen and Seiss [4], Faulkes [5] and Gasparini [6]. Over the years, there have been justifiable concerns amongst structural engineering designers over the potential for punching failure at interior slab-column connections (Fig. 1). Thus, the development of a reliable rational method for predicting the punching strength of reinforced concrete slab-column connections has been the subject of a considerable amount of research. As a result of flat slab development, the first punching tests on conventional slab-column specimens extending to the nominal line of contraflexure, taken to be at 0.22 L from the column centre (Fig. 2), were carried out by Elstner & Hognestad [7]. Subsequent work by Base [8], Kinnunen and Nylander [9], Moe [10] and many others, through the decades to the present day, has provided a wide range of punching test results on conventional slab-column specimens. Contemporaneously, with the provision of test results, there have also been many efforts to develop more reliable methods for predicting the punching strength of conventional slab-column specimens. However, to date, there is no widely accepted rational approach to predicting punching strength, as demonstrated by the widely different approaches currently adopted in the major building codes [11,12] and the more recent fib Model Code (2010) [13,14] approach, proposed for use in the forthcoming revised Eurocode.