Questions and discussion for this lecture live here. Fire away by hitting Reply below 
Hello Sean,
I have a question regarding the limit of x/d of 0.45.
Is this a code limit mentioned in the UK national annex to Eurocode? or is it considered a good practice by UK engineers? I tried to search for this specific limitation in the Eurocodes but I couldn’t find it.
Your course is brilliant, and I enjoyed it, I am actually an engineer who has a couple of years in the industry, however in my country, I used the American codes, and after I moved to Italy I needed to familiarize myself with the Eurocodes, and your course was just what I needed.
Thank you for your efforts and this awesome platform.
Best Regards.
Ahmed.
Hi Ahmed,
Great to hear that you enjoyed the course! Perhaps you would consider leaving a review here?
In terms of the limit on neutral axis depth, I believe this is specifically mentioned in the UKNA. But as far as I’m aware it is broadly adopted as good practice - certainly within UK and Irish design practice (the only territories I have first hand experience with).
You’ll also see this in any text book that deals with Eurocode-based design.
Seán
Hi Ahmed,
I too wondered about this. After going through NSEN (Norway) and my textbooks, all I could find was on this limit was in EN 5.6.3.
Regards Simen
Correct. It is a the 0,45 limit for statically indeterminate members relating to the rotation capacity of plastic hinges.
x/d = 0,45 for < C50/60 and even less (0,35) for > C55/67 RC. I consider 0,35 more academic, since you would not pour concrete on site more than C50/60 anyway.
my source: DIN EN 1992-1-1:2011, 5.6.3 (2)
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Hi Sean,
@18:25, you’ve mentioned that the we have an upper limit material behaviour. Can you elaborate more on this.
Sure - this simply means that there is an upper limit on the strains that the materials can withstand. Once these strains have been reached, the materials will fail (concrete will crush and steel with yield) - as such the capacity of the structure is limited by these material strength limits - they are the upper limits of the material.
Seán
Hi Sean, I wanted to confirm, are the strain values you have given (0.0035 for concrete and 0.00217 for steel) assuming 30MPa concrete and 500MPa steel? So if we were to use different concrete and steel strengths, say 20MPa concrete and 450MPa steel, would these strain values change? Im relatively certain the steel would change, but I am not as certain for concrete
Hey @Grant - great question.
For concrete, the ultimate strain of 0.0035 is relatively stable for concrete grades C50/60.
For reinforcing steel, the yield strain is obtained as follows:
epsilon_y = (fyk/gamma_m) / E_s
where,
fyk = yield stress (taken as 500N/mm^2)
gamma_m = the partial factor for steel (taken as 1.15)
E_s = Young’s modulus (200kN/mm^2).
So you can see the impact changing any of those variables will have.
For example, in the BS8110 days, when yield stress was taken as 460N/mm^2 and gamma_m was 1.05 for steel, the ultimate yield strain was taken as 0.00219.
Seán