CMMehanicalWorks:
What seems like a pretty simple and straight forward question, is really pretty complicated if you are going to do it right. And, you better do it right or you could drop a pump on someone’s head. You should develop a relationship with an engineer who can help you with these sorts of problems. And, don’t assume he is just there as an insurer of last resort, or someone you can sue if things go wrong. They don’t like working for people who think that way. He is not clairvoyant, doesn’t have x-ray vision, etc., there is still plenty of leg work for you to do to get him the info. he needs to give you an answer; or you can pay him to dig it out. Actually, designing the lifting lug and its weld is the easy part.
Desertfox’s link gives some good info. on general weld design, and there are other ref. texts on weld design if you are really interested. But, there are also a number of questions that you must answer, dig the info. out and then guarantee for your work to be successful. Are your welders qualified, do you trust their welding, are they qualified to do overhead welding? What is the embedded plate, is it actually weldable, by what processes and welding rods, etc., how is it fixed to the structure above to take your load? These are actually questions you should be taking up with the building owner during the initial bidding process, so you can plan and price your work. When you go to an outside engineer with these questions, you are asking him to trust that that plate didn’t just fall into the bottom of the form before the conc. was poured. All he can see is the width of the bottom flange of a beam, he has no other info. on the strength of that beam, or the conc. or the ceiling system/floor system above. Your engineer has to work with the bldg. owner, and have access to the original bldg. plans to start to solve this problem. On some bigger jobs these lifting points are designed and certified, and left in place, so your question doesn’t come up. They know that heavy equipment is going to have to be installed and serviced so some of these lifting points are designed into the structure and should show up on the plans for the benefit of future users.
