Tension hook anchorage design in concrete 2

[boobathims]

Dear All
Can anyone suggest preferably there is sample design for the design of hook and anchorage in
concrete? This hook will be used for liting 40 kN(9 kips)

Regards
M.S.Boobathi

 

[r13]

Reinforcing steel shall not be utilized for lifting purpose, there are numerous failure reports. You shall use smooth steel rod made of suitable materials, and design the hook with adequate safety factor, then design the embedment using ACI App. D. The most important thing is to find design standard and follow through.

 

[Lomarandil]

Have to disagree with you on this one retired13... Rebar (or prestressing strand) lifting loops are commonly used for construction applications. I wouldn't use it for a repeated use condition, but if you're moving deadmen around site, or lifting precast components, it's fine.

However, you are correct to point toward ACI App D. Depending on what exactly is being lifted, anchorage calculations per ACI App D (now chapter 17) are usually more relevant than simple development length.

If you do use rebar, make sure to consider that the loop won't deform under load and "pinch" (reduce the bend radius) at the shackle point load. This is one reason prestressing strand is used -- the flexible strand can handle that more easily.




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just call me Lo.

 

[BAretired]

The detail shown in the OP is not safe for a 40kN (9000#) load. Deformed reinforcing bars should not be used for lifting loops as the deformations result in stress concentrations from the shackle pin. Prestressing strand and wire rope could be used if they can be adequately anchored in the slab, but the strength of cable when bent around the short radius bend is significantly less than the straight tensile capacity. It may be better to use an insert bolt with a swivel plate to allow the angular pull.

BA

 

[r13]

FYI. I remember, maybe incorrectly, the use of rebars as lifting device was barred in the early 90s by OSHA after several incidents involving snagging and slashing the rebar ring, due similar to the effects BA pointed out. But I couldn't find the reference to support my claim.

Thomas writes:

Under what conditions can concrete reinforcing steel be used safely as lifting devices?

NPCA Technical Services engineers answered:

Use of rebar as lifting devices is not recommended. Lifting inserts used in precast concrete products must be verified for capacity and must have an adequate factor of safety for lifting and handling products. Safety factors include the various forces acting on the device, including form release suction, impact and the various positions of the product during handling. The capacity of commercial lifting devices must be marked on the devices or posted in production areas.

Lifting inserts, which are embedded or otherwise attached to precast concrete members, must be capable of supporting at least four times the maximum intended load applied or transmitted through them, as required in OSHA 29 CFR 1926.704 (c).

Lifting hardware such as slings, lift bars, chains, hooks, etc., must be verified for capacity and must have an adequate factor of safety for lifting and handling products. Lifting hardware must be capable of supporting at least five times the maximum intended load applied or transmitted to it, as required in OSHA 29 CFR 1926.704 (d).

Non-commercial lifting inserts and hardware must be proof-tested by a certified testing lab for the rated working load limit. OSHA requirements for lifting devices and apparatuses are documented in Title 29 of the Code of Federal Regulations.

 

[Lomarandil]

Good point about the shackle point loading against a deformation. I would include a short sling between the shackle and lifting loop.

I believe the other concerns raised are concerns about badly designed lifting loops, not directly about the use of rebar. Is that correct?

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just call me Lo.

 

[r13]

Lo,

I think you are right, the practice is not recommended, but apparently not "prohibited" by any code or regulations. I don't think the precasters would follow the call to use a hoop that is to be discard after a limited uses. However, the "ban" I mentioned had caused a rush to change our standard details for lifting device, instead of lifting ring, use metal insert and forged eye bolt with threaded end.

 

[KootK]

While this merely reiterates what has already been discussed, we all love an official-ish, published reference to point to. The clip below is taken from

http://www.precast.org

and can be found at: Link