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Project Title: Behaviour of Continuously Supported Self-Compacting Concrete Deep Beams

  • PhD Student: Mahmoud Khatab
  • Supervisors: Dr Ashraf Ashour, Professor Dennis Lam and Dr Therese Sheehan

Introduction

Self-compacting concrete (SCC), also known as self-consolidating concrete, is a relatively new type of concrete that was introduced to the civil engineering industry in the late 1980s in Japan in order to overcome the common durability problems associated with the use of normal concrete. SCC can be defined as a type of concrete that can flow and easily be placed in moulds and formwork under its own self-weight with no need for external vibration. It has the ability to completely fill the formwork and flow through the spaces within heavy reinforcement without mechanical vibration. It is considered to be a revolution in the concrete industry and has become one of the most important concrete developments in recent decades. It can be employed in various civil engineering applications, especially when it is difficult to place and vibrate normal concrete, in structures such as pile caps, bridge girders and offshore structures.

Reinforced concrete deep beams have become very popular structural elements, especially when construction requires space that is free of columns. They are used in different civil engineering applications such as stores, hotels,offshore structures, theatres, tanks, pile caps and others. They differ from shallow beams in terms of their small thickness when compared to their high depth and short span. In practice, continuously supported deep beams are mostly used in construction rather than simply supported ones. In the case of deep beams made with SCC, all of the existing research has been conducted on simply supported beams. In contrast, there is almost no information about research on continuous deep beams made with SCC. 

Research Significance

To date, there have been no research investigations on reinforced SCC continuous deep beams. This area of research is of special interest due to the high depth and steel reinforcement congestion of deep beams, making it difficult for normal concrete (NC) to be properly placed and vibrated. SCC offers unique characteristics in quality and economy. It improves productivity and achieves engineering properties similar to those of NC with more durable structures. As stated previously, all of the previous research in this area has been carried out on simply supported deep beams, despite the fact that continuously supported deep beams are more commonly used in construction.

Aims

The main aim of this research is to evaluate the behaviour of continuous deep beams made with SCC. This can be achieved as follows:

  • Testing of different full-scale SCC continuously supported deep beams to study the influence of various parameters such as compressive strength, shear span-to-depth ratio and reinforcement ratios on the behaviour of SCC continuous deep beams including cracking load, load carrying capacity, deflection and shear strength
  • Developing a nonlinear finite element model using ABAQUS to analyse the effect of the different parameters considered in this research on the behaviour of SCC continuous deep beams
  • Developing a mechanism analysis technique based on the upper bound theory to analyse the failure mechanism and predict the failure load of continuously supported deep beams made of SCC.  

Methodology

SCC will be produced in the laboratory using readily available raw materials. Trial mixes will be conducted to achieve the aimed compressive strength. The fresh properties will be assessed using some tests provided in the literature. The flow ability will be tested by the slump flow, the filling ability will be assessed by V-funnel tests, the passing ability will be examined depending on the J-ring test and the segregation resistance will be assessed using the sieve stability test. On the other hand, the hardened properties of SCC will be examined depending on EC2 (BS EN 1992-1-1:2004). The compressive strength will be evaluated by testing cube specimens under direct compression whereas the tensile strength will be evaluated by the splitting tensile test.

With regard to the test specimens, 8 different two-span SCC deep beams will be tested. All of the specimens will have the same compressive strength of 30 MPa. The main parameters investigated in the current research are the shear span-to-depth (a/d) ratio, the longitudinal reinforcement ratio and the web reinforcement ratio. Two different a/d ratios will be used; 1.0 and 2.0. All the tested beams will be demoulded 24 hours after casting and kept wet until the day of testing. The beams will be subjected to a concentrated load at the middle of each span using a 50 tonne capacity PACT testing machine.

Comparison between the current ABAQUS model and Birtel and Mark, (2006)

Figure 1. Comparison between the current ABAQUS model and Birtel and Mark, (2006)

Average stress distribution for a beam tested by the proposed ABAQUS model

Figure 2. Average stress distribution for a beam tested by the proposed ABAQUS model

References

Ashour, A. F. 1997. Tests of reinforced concrete continuous deep beams. ACI Structural Journal, 94.

Ashour, A. F. & Morley, C. T. 1996. Effectiveness factor of concrete in continuous deep beams. Journal of structural engineering New York, N.Y., 122, 169-178.

Yang, K. H. & Ashour, A. F. 2008. Load capacity of reinforced concrete continuous deep beams. Journal of Structural Engineering, 134, 919-929.

Yang, K. H., Chung, H. S. & Ashour, A. F. 2007b. Influence of section depth on the structural behaviour of reinforced concrete continuous deep beams. Magazine of Concrete Research, 59, 575-586.

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