Splicing of Vertical Bars

The lower wall steel reinforcement should project 50xdiameter beyond the top of the wall/slab joint to allow the secondary fix to be spliced at 40 x diameter with space to spare.

For example, if the thickest rebar is 20mm dia then the splice needs to be 800mm long and the first fix steel should project 1000mm above the slab. This will mean the splice starts at least 200mm above the finished floor slab.

You are correct in your assumption that putting the splice in a critical joint is not best practice.

That may be acceptable under the British Standard (BS), but we don't know where the OP is from and what concrete specification/code he/she must adhere to....

Also, your approach & description regarding lap splices is somewhat limited and doesn't necessarily take into account different types of applied stresses withing the composite section, whether they are compressive or tensile in nature. A compressive stress in the steel will have a lesser lap splice than one that is experiencing tensile forces due to applied bending moments. All I am trying to convey is that it is not entirely wise to use a simplistic approach because the actual conditions may not dictate it's acceptability, and may in fact be more complicated than you realize.

I do realize that this is a simplistic approach being applied here, and I'm trying to help out the OT, but properly (and I stress safe) structural design of reinforced concrete members is an extensive undertaking and cannot be discussed herein in any great detail. There's just not enough space or time to go into great detail in this forum............

Fair point. My experience is predominantly site based where steel is actually placed, cut and bent to suit. The designers' drawings are generally taken as a guide rather than a perfect outline of what must be adhered to. I understand the factors of safety built into any design and realise that many designers never actually set foot on a real site more than once or twice a year. I am a setting out engineer/surveyor and am probably in the minority in that I can actually read a steel drawing as well as any steel fixer. The benefits of grey hair!

Steel on site is marked out with half inch thick crayons making rough marks on the layer below or blinding layer and tied as near as possible to those marks. The accuracy is surprising given the methods employed but it is nowhere near perfect. Steel is also cut, bent moved and otherwise abused when detailers have put stupid amounts of steel into a junction and then expect a set of holding down bolts with casting cones to miraculously fit into a gap that exists only in their minds. This where they draw thin lines on paper and don't realise just how much metal is involved.

My point is, I have met precious few steel designers/detailers who have more than a few hours (unrealistic) site experience per year or less. They tend to turn up in pristine jackets, wander around for twenty minutes getting the "tour" before retiring to the offices for tea and a meeting about progress. I know this is true as I have given the tours and sat in on hundreds of these meetings. My guess is 35% of designers don't have a clue. About anything.

Steel fixers on site will and do revert to standard details time and time again because they know them and don't have time to ask questions every five minutes. Designers need to be aware of this, spend some time on site and really understand what they are designing by seeing it in the flesh and getting to grips with practicalities. I wish.

Rant over. Thank you.

I'm most likely the exception to the rule (at least here in the USA) when it comes to being a SE. You're right, a lot of engineers don't have a clue about what the field guys have to go through to correct mistakes.

I was very lucky to have spent a huge amount of time on jobsites in my early engineering years, and later while serving in the US Army Corps of Engineers.

Have a great week and thanks for the post!

You're most welcome! I love it when a designer with site knowledge comes on site - it's like a breath of fresh air, we would probably get on famously. I was 10 years in the Royal Engineers as well as 25 years in Civil Engineering post military so I've got a few grey bits here and there. I once got a rollicking for asking a particularly arrogant (and inept) designer if he had come to site to apologise. Complete sense of humour bypass!

I am actually involved in the design & planning stages myself now, so I am dragging youngsters out into the mire and making them wade through mud and see the job up close. I even get the Planners out on site at least an hour or two every week. Wonderful to see eyes opening wide to what can and can't be done in the real world - and realising that their designs will change as a result of my 'unreasonable' demands on their time. I don't do the twenty minute tours, I get in holes, ask questions and wait for the 'design team' to work it out. Better than any college.

My role has taken an odd twist as I have become involved in Polymer Engineering for waterproofing of water structures and that is where I will be going next, into chemistry. Funny old world, isn't it? I won't miss the mud too much.

A great day to you too. Laugh a lot, it worries people.

Hey doggibag, it looks like we have a bunch of experience in common! Kewl beans!

Next time Mrs. Moosie and I are in the UK, I'll look you up! Possibly will happen sometime next year at the earliest. She has a handful on Aunts, Uncles, and Cousins there and in Ireland that she wants to visit.....one crazy cousin lives in Birmingham BTW.

We could go visit a local pub and raise our pints of Bitters mate!

I agree with passington on this one. It is always advantageous to place any rebar lap splice above the slab for a number of reasons.

Placing them at the juncture of the slab and a column or bearing wall is a big no no, as there are high stresses located there + the resultant rebar installation would be too crowded and hence you may not be able to place the concrete fully around the individual rebar. Also, high stresses due to loading will undoubtedly occur at such a juncture....shear loads, axial loads, and bending moments due to both floor loadings and in the columns due to wind loads and/or seismic loadings.

Are we talking about where a suspended concrete floor slab meets a concrete column, or is it at a bearing wall?

We don't know where you are located. What country? If in the USA, then you must follow the provisions of ACI 318 in regard to proper reinforcement installation as well as lap splices. It is not as simple as providing a minimum of 40 bar diameter laps as one gentleman has stated herein. Consideration must be taken in regard to the type of loading in a concrete column: usually, if there are bending moments applied to the column, then tensile stresses will be present in the rebar, and thus the required development length of the rebar lap is much different than a column subjected to only compressive axial loadings.

Do you have any formal education and experience regarding the design of concrete structures?

BTW, ACI = American Concrete Institute.

The column beam/slab junction will be always critical in nature because the moment reaction shall be more on the node point.

Also the column splices have to be placed between the h/3 at bottom or top zone between the unsupported length of the column as per the detailing.