1960's era 116' diameter x 90' bulk storage bin 1

[smb4050]

I have an interesting problem to solve, and thought I ask if there are any suggestions or standards and design manuals available that may help. The problem is in a late 1960's era 116' diameter x 90' bulk storage bin. At the interior, the rotating bridge is supported by a 11'-6 diameter central tower made from 5/16" plate steel. The existing bearings of a rotating loading and unloading conveyor and support bridge are no longer operational, so I've been tasked to design a new bridge support with casters below the failed bearing system. I have drawings for the bin and central tower, but nothing on rotating bridge manufactured he Nils Weilbull AB or Weilbull Silo of Sweden. Does anyone know what became of this firm? I am using Tubular Steel Structures by Troisky and published The James R Lincoln Arc Welding Foundation, but would like more information. I am specifically concerned about fastening to the 5/16" plate steel of 11'-6 x 90' tall central tower. Any comment will be appreciated. Thanks

 

[dhengr]

Smb4050:
Based on what you’ve indicated so far, I would study the existing rotating bridge bearing systems, and work to just replace the bearings with new working bearings. Get some good pictures of the existing bearings and the structure immediately around them, including the circular bearing track. What are the bearing numbers, the load roller/wheel numbers, and manufacturers, etc. Then, the design question is what new bearings can be made to work with min. changes to the existing structures. You don’t claim there is anything wrong with the rotating bridge or with its “11'-6 diameter central tower made from 5/16" plate steel.” Apparently, the rotating bridge and its support tower have performed well, and I wouldn’t change them without good reason.

 

[JStephen]

I would suggest working very closely with whoever is actually to do the work. Access, scaffolding, hoisting, crane access are likely to be major parts of the cost and need to be included in the design of any repairs.

 

[smb4050]

I agree with your thoughts, but I've been told that isn't possible. The bearings have been replaced once with an oversized bearings, but now reportedly the replaced bearings are worn out and the bottom race is also ruined. As you will see on the attached bearing section drawing, everything is enclosed, so getting access to the actual bearings pictures is difficult. I have seen the exterior and have pictures of it.

 

[robyengIT]

Sweden is the main seat of SKF bearings manufacturer. Another solution could be the bearings used for similar structures and made by DeFontaine (or ROLLIX)

 

[SlideRuleEra]

Here is the U.S. patent, from the correct time period, for a Nils Weibull Silo Unloading Device. The information is of general nature, but may give insight into it's operation.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[smb4050]

Thanks robyengIT and SlideRuleEra on sharing the information. Both are helpful. I am looking at the bearing manufacturer's website for information. On the attached drawing's material list for the bearing, Kullager is written in. I'm checking if that could be the bearing manufacturer's name and part number. The patent is dated 1967 and the drawing shows the same layout as what is installed. The bin drawings are dated 1968, so maybe due to patent concerns Weibull never gave the owner drawings for the rotating bridge and conveyor. Thanks again to everyone who responded to my post.

 

[dhengr]

Smb4050:
Let’s see the photos you’ve taken, you probably need many more, of various details. Let’s see some overall photos of the system, if you don’t have any manuf’ers. drawings. Is the patent that SRE found fairly representative of what you have on your silo system? It is pretty difficult to read that drawing and make sense out of exactly how the rotating bridge and the center tower really interact. How is the rotating bridge generally arranged over/around the central tower? Without much more info. and investigation on various components it’s pretty difficult to know exactly what to do or say. You will have to do much more inspection to understand how the various components really interact and work. So, I’m just throwing out ideas and food for thought at the moment.

It is not real difficult to imagine that ball bearings wouldn’t work very well in that application. How many ball bearing are there in the entire bearing race, and what’s their size, (my guess is 1.5 - 1.75" dia.)? I suspect that a few of the ball bearings at any one time, and in only several locations, would actually be carrying most of the loads. So, some of the bearing stresses are very high. That two part bearing race would be a real bitch to align perfectly (or well enough). It will take vert. loads and horiz. (lateral) loads, [but there appears to be no provision for uplift or overturning moments from the bridge. So does that mean the bridge is pretty well balanced both empty and loaded? This latter, appears to be answered by the patent.] It would appear that you can’t mess around with the slip rings, without completely redoing them. But, it would be nice to know how much clearance and vert. and lateral (horiz.) movement they can tolerate. Given how light that channel is and how it is welded to the center tower shell, and the fact that it hangs out there off the flg. tips, the vert. loads from the bridge can’t be too great. I suppose they assumed that the vert. load was distributed to the whole tower circumference. And, that is probably not completely true, or a real good assumption, thus the bearing failures. This is a critical redesign consideration.

I assume that the large I-beam on the left is a long straight framing member on the rotating bridge, one on each side of the central tower, maybe also like beams as cross framing btwn. the main I-beams and also near the tower; and that the box sections above it are all some sort of ring shaped beams, and are part of the support framing structure on the rotating bridge. Which of these are ring shaped and how do they transmit the bridge loads to the existing bearing race? Similarly, the ball bearing race halves and the channel, toes into the center tower, are ring beams attached to the center tower shell, and they take the rotating bridge load into the center tower structure. The center tower shell and structure has not buckled yet so they must have done/designed that part right. But, this might partly be predicated on a fairly uniform loading from the bearing race, as long as all the ball bearings last. Is there stiffening structure inside the central tower at this load transfer elevation or just the 8mm shell pl?

I think I would try to do away with the ball roller bearings and that two part bearing race. Although, 46yrs. in a dusty environment, and only two sets of ball bearings may not be bad in that arrangement. Those flat pls. on top of the channel are about .75 - 1" and 1 - 1.25" thk. The bot., 1" thk., pl. is welded to the channel and a bunch of stiffeners, and each stiff. will cause a hard spot; while the top, 1.25" thk., pl. is bolted to the bot. half of the bearing race. Then, there is about a 1.75 - 2" thk. pl. with a 45̊ chamfer (down and inward), which is the bot. flg. of the narrow box section above. The vert. space btwn. the 1" pl. and the underside of the 2" pl. is about 7" for some new bearing system. I’m in St. Paul, MN at rwhaiatcomcastdotnet, let’s talk. Maybe you should use some sort of rail/ring and a double flanged roller similar to what they do at the outer end of the rotating bridge. There should be self adjusting rail scrappers fore and aft of all these wheels on rails. You should make some calcs. to estimate the loads/reaction on the bridge at the center tower, do they make sense? Then, locate the inner wheels to try to equalize the wheel loads. Then, what do these 4 or 6 point loads do to the central tower structure? With good sound engineering judgement and design, you should try to give your client something better than what they have now, which is causing some problems. You should sell your client on the need for your further investigation and understanding of the whole system and for design and detailing time to try to improve the system. Your design should also provide them with a clean, nifty way to accomplish this conversion, and to provide clean ways of maintenance of the system. You will likely have to work along side of the contractor during this rebuild, because you just can’t see all the details at the moment. This is as much a mechanical problem as it is a structural problem, probably not as simple as replacing the ball bearings, in kind. You might find that these kinds of problems are more fun and interesting than plane everyday structural design.