Comparison of EC2 and BS8110

[Agent Coconut]

Hi everyone,

I was assigned as designer engineer for a new project recently and this is my first time to lead on a project.
While the analysis of building frame is not a trouble for me, I have several questions on the detailing part.

As for the background, in my region most of the structural consultant including my seniors are still adopting the old BS8110:1997 but while local authority has requested us to use EN1992, but they have not enforce this yet and even accepted and approved our engineering design submission including calculation that was still adopting BS8110. Even worse, our clients are aware of this phenomenon. The issue is, I am intend to adopt EN1992 for the new and future project but I was questioned by many engineer of my field including my seniors therefore I am looking for clarification from everyone here who is not from my region and was hoping that I can some new insight.

My clients and my seniors is in opinion that BS8110 will give a cheaper structural solution and better flexibility as compared to EN1992 despite EC2 allow a lower load factor based on the following argument.

1) Anchorage and lapping length of reinforced concrete element.
We all know that the lbd and l0 length for Eurocode 2 is much longer than BS8110 and even was acknowledged from concretecenter

https://www.concretecentre.com/TCC/media/TCCMediaLibrary/PDF%20attachments/Lecture-9-Detailing-PHG-A1-Rev-12-16-Nov-17.pdf

The client and my senior are in opinion that since most of our project is adopting lower concrete grade (C20/25 or C25/30), the will incur a lot of additional cost if we adopt EN1992.
For example: a H12 bar will need to lap for a total of 56d at poor zone but 87d for EC2

2) Additional tensile reinforcement due to shear
These tensile force due to shear is not presented/required when using B8110, thus, with this new detailing rules, the bottom reinforcement at support are more than what is required when it is based on BS8110, especially when we are analyzing a high rise where lateral load is significant and beams are now acting as tie beam, thus no longer behave as normal moment and shear force diagram that we always know in some critical load case.

3) Deflection of band beam/conceal beam
In BS8110, the deflection using l/d is straightforward but in EC2 and if we adopt UK NA (we foresee our regions will follow the recommendation from UK NA based on past experience) it is limited to 40K, this has made conceal beam concept most likely cannot be adopted due to deflection by mean of l/d is not being satisfied, which on paper, BS8110 can made this beam happened, and become a preference for our clients.

Anyone can enlighten me on the technical background that lead to these changes and more importantly, any technical explanation to explain and to clarify all these so that I can explain to my client, who obviously prefer a cheap solution rather a robust and modern design practice?
Apologize for the long post and thank you everyone for your time.

 

[Greyhill]

Can't say I know the answers to those questions off the top of my head but both the British standards and eurocode committee did create background documents to explain the reasoning behind the values chosen in the UK national annex and EC2 respectively ,

1 . PD 6687-2:2008 Recommendations for the design of structures to BS EN 1992-2:2005​

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Provides background information relating to decisions for the Nationally Determined Parameters (NDPs) in the National Annex of BS EN 1992-2, commentary on some subclauses and commentary on those subclauses of BS EN 1992-1-1 that are also applicable to bridge structures in BS EN 1992-2.

2. Eurocode 2 Background documents​

The Background Documents Database is a source of information on the theoretical justification of the Eurocodes technical rules, on the recommendations for the NDPs and on the National decisions about the choice of the NDPs.



Between the two sets of commentary documents you should be able to better understand the reasons for the rules and they might even provide some information on the differences between bs8110 and ec2.
There might be additional commentary documents for bs8110 but I don't know for sure.

Edit
Don't have EC2 to have at the moment but I think there should be a references section, maybe near the beginning which points towards other background information and sources for the rules

 

[rapt]

1 EC2 development lengths are not overly conservative. I would use them rather than the old BS8110 values.

2, BS8110 3.12.9 is the equivalent requiring reinforcement to extend D past where it is required.

3 I would never use L/D ratios for deflection. They give sa good starting point. Calculate the deflections.