whats the different between straight bar and hooked bar in terms of slab anchorage? 3

[rebarfixer.hk]

hi there, i am new to this industry and this forum, but i encountered some problem and it seems eng-tip is the only forum that can answer my question.
So, in the general notes of the site that i am working with, there is a typical anchorage detail of slab says that the top bar of slab can be straight as long as it has a full anchorage length to beam.

but unfortunately, there are hooks in every single slab drawing, especially to beam that is located at the edge of building.

The length of hooks were not specified, and it seems to me that it is just merely illustration but not a construction requirement. However some people disagreed...
So, is it a must to have slab top bar hooked down？
whats the different between straight bar and hooked bar given that they both have sufficient length to fulfill the anchorage requirement?

sorry for my poor english and thank you very much for your time

 

[le99]

I would send an RFI or RFC to the designer to clear up the inconsistency between the drawings and the note, though a fully developed straight bar is as good as a standard hook.

 

[DaveAtkins]

And maybe you already know this, but a hooked bar will require a much shorter embedment than a straight bar.

DaveAtkins

 

[phamENG]

There's no discrepancy. Typical detail (standard detail of a common condition that is used and reused to save production time and budget) says that you can use a straight bar IF there's sufficient development length. Rebar shop drawings (or structural drawings? Looks like rebar shops to me) show hooks everywhere...because the rebar detailer determined there was inadequate length for straight bar development.

Now I don't know where you are or what code you use, but most codes (I'm familiar with ACI) have standard geometry definitions for these hooks including the radius or diameter of the bend, straight bar extension after the bend, and how far into the base concrete the hook must be embedded to achieve full development of the bar.

 

[KootK]

I have some familiarity with concrete design practice in southeast asia and this is one aspect of how things seem to be done there that has always bothered me. I've often seen hooks EOR detailed on flat slab interior steel where there is no ostensible reason for those hooks. No spatial constraints etc.

Sure, hooks develop faster than straight bars but, out in the open field of a flat slab, who cares? At those locations, surely the fabrication and installation hassles associated with the hook would outweigh the any, tiny benefit associated with "faster" rebar development.

I've not yet gotten a straight answer on why it's done this way in some parts of the world. My suspicion is that there is simply a perception out there that a hook is mechanically better than no hook so let's just default to providing hooks everywhere. Hopefully I'm wrong about that someone can offer up a more logical justification for the hooks.

 

[Lomarandil]

No, KootK, you're right (at least for SE Asia). There's an understanding by contractors that hooks are needed (generally) at slab edges, there isn't a lot of communication between the engineer and the contractor (and even less inspection/verification in the field once construction actually starts)... so it's common to have an overly conservative (and overly difficult) detail applied.



----
just call me Lo.

 

[rebarfixer.hk]

Thank you everyone, but unfortunately I am from Hong Kong and most engineers in here share the same understanding that having a hook is a common practice and there is nothing to argue.
Well, I also do not want to argue with the inspector in the field.
So...I guess this "common practice" sticks around southeast asia for a reason, no one want to argue and no one want to change. It is our culture...

btw,I asked the inspector once and the response was "follow the drawing, drawing have hook, you need hook".

 

[rebarfixer.hk]

And by the way, one of my friend mentioned something about hook inside confined area with concrete can prevent "kick off", but I can't find any material about slab "kick off". The closest thing that I know of is about stirrup/links "kick off", but is it true that this logic for stirrup can apply to slab? thus justify the requirement of hooked down for slab top bar?

 

[le99]

With greater edge distance, the tail of the hook is fully confined, that prevents the tail from breaking the concrete cover and kick-off.

 

[ukengineer58]

quite interested if I am reading this right and practice in other parts of the world. Here (UK), we would design and produce RC drawings and a bending schedule. The contractor (normally) would send off the schedule to a bar benders who would make the bars as per the schedule, send them to site where they would be installed by the contractor according to the drawing. There would be no optional notes of different details that the contractor can decide work or not - how would they know? And not ambiguous notes that allowed the contractor without RFI to change the detail on their own. Does it work differently with you guys? interested if there are different ways in other parts of the world.

 

[rebarfixer.hk]

Here in Hong Kong, the rebar schedule is actually produced by the rebar fixing contractor(which usually doesnt have an engineer), and the contractor can either bend bars on site or send the bending schedule to other company for off-site cut and bend -- this is optional. And there are no engineer or designer intervent this process, they has the power to step in but in reality they never check. They only provide drawings and details to contractor, and answer questions from contractor. So if the rebar fixer decided to follow a debatable detail that is ambiguous, no one would know until it is fabricated and installed on site, and then inspector would have to decide on site.

 

[ukengineer58]

interesting - seems like a high risk of delays and pauses when someone figures out if its correct or queries are answered. I assume the rebar schedule is produced off a rebar 'intent' drawing by the designer? but it seems odd the designer then doesn't have to approve it at least. I've reviewed rebar drawings that don't meet the design intent when the same company has done the design and detailing. So I do wonder how the quality of the detailing is maintained. Especially as it will be in the interest of the rebar fixers to reduce materials and costs for their benefit.

 

[phamENG]

uk - in the US it's a mixed bag (like everything else). Some regions are just as you describe it in the UK. Here in the mid-Atlantic, DOT and bridge projects tend to go as you describe, but building projects are a hybrid of the UK and Hong Kong models (if I can call them that). I don't do much concrete, but the way it typically works is that I'll do a slab plan, identify rebar size and spacing, and identify anchorage and bar termination in critical areas. But I don't do a bend schedule - that's the detailer's job. There may be a typical detail that gives some leeway, but I also include limits (minimum develop/lap lengths, hook geometry, etc.). Before construction begins, I get rebar shop drawings with bend schedules, quantities, layouts, etc. which I review and ensure they meet the intent of my design. After they're approved, the contractor orders the bars and puts them in and inspect placement.

I asked the inspector once and the response was "follow the drawing, drawing have hook, you need hook".

I tend to agree with that sentiment. It doesn't address whether or not the engineer was correct, but if that's how the engineer designed it then that's how it should be built unless there's a really compelling reason to revisit it...like excessive congestion, hook doesn't fit, etc.

 

[ukengineer58]

interesting. I am aware of projects where the detail has been commissioned by the contractor to an intent drawing. Which in the situation you describe, where you get to review them, seems fine. I suppose its swings and roundabouts whether that's the most efficient. We've had issues in the past where outsourcing the detail in a similar manner has led to several iterations of a drawing. Here in UK steel is done in a similar manner you describe mostly. We would do a GA drawing and note connection forces. A fabricator will do their fab drawings and design the connections themselves. We would then review it all to ensure it matches the intent.