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PT design to EC2

PT design to EC2

PT design to EC2

(OP)
Hi all,

My boss asked me to prepare PT design to EC2. I don't have senior engineer. I only have 2 years experience and 24. I know I shouldn't be doing this but...
Enclosed is my 1st draft. Reference was made to EC2 and TR-43 second edition. Your comments and suggestions are welcome.

If you guys have any sample detailing drawings to EC2 or anything that I can refer to, please share that will be greatly helpful for me.

Thanks

RE: PT design to EC2

Sorry to read of your predicament with respect to lack of mentor/senior engineer.

I have no experience with PT design to EC2, but since you have received no reply to your inquiry I would like to see if I can help you out some.

Your draft list it quite comprehensive and suggests that you have given this task some considerable thought, of which you are to be commended.

From your previous posts at Eng-Tips I seem to recall that you are based in Singapore and possibly work for/with a local Sing PT contractor or PT consultant. If so, then you probably have some relevant experience with designing PT floor systems to your local building code, and I therefore would suggest that the theory will be the same regardless of code. You just need to 'match' and review similar clauses between the code you are familiar and EC2 - e.g. load factors, capacity reduction factors, stress limits, deflection, etc...essentially the list that you have draft.

The PT design to EC2 you are tasked with, shall it be using commercial software that you are familiar, or is it some hand-calcs for a preliminary design?

Hopefully, RAPT will see this post and make comment...he has much experience with various international PT codes, including EC.

RE: PT design to EC2

(OP)
Hi Ingenuity,

Thanks

Some people including you in this forum are like mentor to me. Luckily I don't have to do hand calculation. My company is using commercial software so I hope there isn't much to worry about :D.

RE: PT design to EC2

Don't forget to look for stiff elements that will provide restraint to shortening in the floor system and introduce slip-joints or pour strips as needed.

RE: PT design to EC2

Struggle,

Your comment about commercial software is worrying. The developers of the software do not take responsibility for your design, you do. It is up to you as the designer to ensure that the results of the software reflect what you think they should. So you should be doing hand checks and controlling the design options both of which require you to know the code and good design practice.

TR43 actually gives 2 tiers of design for serviceability, one based on average moments and one based on logical design strips (column and middle for simple flat slabs and strips that reflect the stress distributions for more complex slab layouts and/or load patterns). You need to differentiate between these methods in using your software.

eg in table 4 of TR43 which is based on average moments, you cannot improve crack control by adding extra un-tensioned reinforcement. That only applies for use of table 5 and the strip method. In the table 4 method, the stress limits are final.

RE: PT design to EC2

The Concrete Center has published a design guide for prestressed concrete bridges to Eurocode 2 (albeit to the UK NA) which should be helpful to you. I believe its freely available. Concise Eurocode 2 for bridges is also a handy book to refer to which takes a lot of the unnecessary tedium out of the Eurocodes.

Even if you're using software I strongly recommend being able to calculate net tensile and compressive stresses and losses before relying on it. "Simple Bridge Design using Prestressed Beams" by PCA is a handy text, which gets to the point showing calculations very quickly, but obviously without the depth of a proper book on the subject.

RE: PT design to EC2

(OP)
RAPT,

THANKS!

My comment about commercial software is just joking. Using the software without understanding the code, principles and design practice makes me feel stupid.

In Singapore, almost all PT specialists have been using average moment method. So I am thinking to stick to that method that have been long familiar with us.

Adding extra un-tension reinforcement

I understand that I can't apply that to Table 4 but I will apply it to Table 3 and 5.

Crack control

In TR 43 second addition, for one way design, it is allowed to control the crack width by controlling the design hypothetical tensile stress Table 3. Can I apply it to apply it to average moment flat slab design which is allowed to apply in BS 8110 or just follow the section 7 of EC2?

Min As
In EC2 the contribution of tendon to crack control is within a distance 150 mm from the centre of the tendon so count tendon as min As and comply spacing requirement. Is it?

It is great to have your reply.smile

Hi Lion06,

Thanks

RE: PT design to EC2

Struggle,

Yes most in Singapore use average moments and they use it with drop panels and non uniform loads. That is wrong as I have pointed out many times. It should not even be used with uniform loads with very random column layouts in my opinion.

Yes, it can be used for table 3 and table 5, but table 5 does not apply for average moment design.

EC2 does not condone average moment design. Only TR43 makes that mistake. So no you cannot do it in accordance with EC2. You cannot use table 3 or Section 7 of EC2 to justify it. Only TR43.

You will have to expand on the last question. Yes, in EC2 crack control calculations, tendons (or reinforcement) are only considered if their pacing is <= 300mm. I do not know what you mean by the rest of the question.

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