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Simplification of curtailment rules as per EC2.

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Hello people,

Do any one of you know how to come up with a simplified curtailment figure for beams and slabs for EC 2 as the one in bs 8110. Like which assumptions are made in taking the curtailment length and rebar percentages? What is the theory involved in it and so on. I need some help for my thesis work regarding it. Please share your thoughts. Any help will be very much appreciated. Thanks. :)

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I will try to explain the theory behind curtailment as good as I can...

Theoretically speaking, curtailment of reinforcing bars is the stopping of some of them (in tension or compression), where they are no longer required because the bending moment is reduced. This is the theoretical curtailment point/length.

However, the bars must be anchored by further extension (lbd) beyond the point which is required for flexural strength. Moreover, inclined cracks due to shear, especially at supports, may increase the forces subjected to the tensile reinforcement. According to the attached image, because of the shear crack, the force of the tensile reinforcement at position 1 is depended on the bending moment at position 2. In order to take this into account, the bending moment diagram is shifted in the direction of reducing moment by an amount al (=d in case of slabs). Therefore, the bars should be anchored for a distance lbd+al. This is the practical curtailment point/length!

It’s very important to mention that curtailment is applied mainly to multi-span slabs and beams because it is more economic compared to simply supported.

As for the simplified rules about curtailment according to Concrete Centre, British Standards etc is concerned, these are just simple tips based on the above theoretical background, experiments and everyday experience. I don’t think that these lengths and reinforcement percentages are derived only from mathematical expressions...


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Thanks for the reply ion.. :)

Well suppose the simplified detailing diagrams were to be derived mathematically, can you please give a break down of working steps which can lead me to the simplified diagrams. I saw the simplified diagram posted on slabs based on EC2.. but i am quiet not sure how the lengths and percentages are derived.. :confused:

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No problem aciyath!

Curtailment lengths depend on the bending moment diagram and the geometry of the slabs (number of spans and supports) therefore the simplified rules are not based on one mathematical model. Practically you can not have only one theoretical model that simulates all the slabs you can have...

A very good approach would be to calculate the curtailment lengths for some characteristic slabs (simply supported, continuous with two spans, three spans etc) and then to check if these curtailment lengths are in accordance with the Concrete Centre's approach.

As for the procedure that you have to follow for the calculation of the curtailment lengths, check the following bibliography:

Worked Examples to Eurocode 2: Volume 1 (page 40)

How to Design Concrete Structures Using Eurocode 2 (page 84)

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Do any one of you know how to come up with a simplified curtailment figure for beams and slabs for EC 2 as the one in bs 8110

In EC2 there is no simplified curtailment figure like the 3.24&3.25/BS8110. In fact 3.25 for slabs is quite ok but for beams, analysis of moment diagrams is necessary.

Don't forget that in general, eurocodes are not a simplified code framework whatever that thing means.

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Yes indeed! In the UK, we say that the Eurocodes are "less prescriptive" than the former British Standards. This means the engineer is bit more 'on his/her own'.

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