The new edition, released as ASME BTH — Design of Below-the-Hook Lifting Devices , updates and supersedes the version of the standard, continuing to serve as a guide for designers, manufacturers, purchasers, and users of below-the-hook lifting devices. Below-the-hook lifting devices, or devices used for attaching a load to a hoist, can contain components such as slings, hooks, and rigging hardware. They can be in the form of structural and mechanical lifting devices, vacuum lifting devices, operated close proximity lifting magnets, remotely operated lifting magnets, or scrap and material handling grapples. It covers provisions for specified rated loads, load geometry, Design Category, and Service Class, which users are to adhere to during the design of any below-the-hook device.
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RE: Design of lifting lugs dhengr Structural 27 May 10 You are looking at several different cookbooks and debating whether we should use a pinch of salt or a pinch and a half, however much that is and whatever kind of salt you are using. An acceptable bearing stress, when looked at from the Theory of Elasticity standpoint, is considerably higher than the bending or tension stress that we would allow, it just works differently.
The AISC code is a fine guide to understanding steel design in general, and in most any field, if we really understand the basis of what they are doing, and where their equations came from.
But, more and more that basic understanding is lost in the manipulation of the many factors included in the recipe. No need to understand, just follow the recipe. The design of lifting lugs involves a Hertz stress problem as relates to the bearing btwn. And, they involve a combined stress problem with the max. You should also have an understanding of the mating lifting equip.
Those are some of the design considerations. That leads to a vague understanding of how the lifting lug works and is loaded. Then we can argue about load factors and resistance factors, etc.
Oil fields and rigs, pressure vessels, OEM equip. It just keeps acting the same old way. I found the BTH publication, commentary sections very usefull. I did not find the David T. Ricker article usefull. I think you are only taking one part of the ASME code section. BTH, The commentary is a great document. It is well written and taken in context with ASD makes good sense. It takes care of the impact factors by assigning design categories. The logic is straightforward and well defined.
The only additional check I sometimes perform is to make sure lug does not yield if pulled in the perpendicular to the face of the lug. Whereas, a lot of lifting lugs are used to initially set the item, and then seldom if ever again. Note that the equations for bearing strength generally assume yielding at the pin hole. RE: Design of lifting lugs boo1 Mechanical 28 May 10 I have designed one time use fixtures, that are now 20 years old that our riggers still use.
This is not to say that Chapter D cannot be modified for use with lifting lugs. The first thing that would have to change is the factor of safety omega in the 13th Edition Manual. There can be a lot of uncertainty surrounding the loads and impact factors for lifting lugs. The factors of safety in the AISC Specification are not set to account for this level of uncertainty.
Ricker in his paper suggests a factor of safety of 5. The AISC bearing checks serve the same purpose. Again, the checks in J7 assume a close fit, so this is not an appropriate check.
A better option might be the checks in J3. As was stated by some of the other contributors, the ASME checks depend on the number of cycles. Since this check is based on empirical data, it is not surprising these kinds of differences exist. If we adjust the 1. For the AISC requirement, assuming a bearing check where significant deformation is tolerable, we get 1. If significant deformation at the hole cannot be allowed, we get 1. From this we can see that the two requirements are not all that different.
Ricker recommends 0. The Commentary to ASME BTH-1 states that there all 4 strength limit states that must be considered: net tension perpendicular to the load, single plane shear rupture parallel to the load, double plane shear rupture parallel to the load, and out-of-plane buckling dishing of the plate. The net tension check is essentially the same. It should be noted that Duerr and Pincus sound that the clearance effect was less pronounced when the strength was governed by net tension, so it makes sense that the two standards take essentially the same approach.
Buckling in both standards is prevented by limiting the effective width of the plate. This is done somewhat differently, but the intent is the same. Since the approaches involve different variables, it cannot be determined whether one approach is always more conservative. The most significant difference is in the checking of shear. The AISC equation assumes a tight fitting pin, and since Duerr and Pincus found a significant clearance effect on this limit state, the AISC values must be adjusted to account for this effect.
The two approaches also differ in that AISC limits the dimension "a" relative to "b". I believe the intent is to prevent the single plane shear failure.
Again since the two approaches use different variables, it is not easy to compare the two. However, the intent of each is the same. Some comments should also be made relative to the Ricker paper, which is often used as a reference by the structural steel community. The Ricker paper does limit the "b" dimension he calls this "a" , so does address the dishing problem. He also makes some recommendations relative to a lower bound thickness relative to the hole size, which he states are intended to prevent dishing.
He does not seem to address the net tension limit state. I agree that the basics have largely been overlooked in this thread, but the "cookbooks", though they take somewhat different approaches, are all trying to address the same problem and all are based on the same sources. Finally, I do not believe OSHA cites a standard in their regulations though I may have missed something , so the design decisions seem to be left to the discretion of the engineer, which is probably a good thing.
Asme Bth-1-2008 Design of Below-The-hook Lifting Devices
Tojatilar The Eng-Tips staff will check this out and take appropriate action. WillisV, Agreed, this makes sense to me despite being a mechie. We just recently designed some lifting lugs where the dimensions were pretty much set by the client. Provides minimum structural and mechanical design and electrical component selection criteria for ASME B I also need to determine this for a flexion analysis in the weak axis. Any help would be appreciated.
ASME BTH 1 2008 - ASME Standard Compliance