H-Beam Slotted Through Joint Capacity 2

[NimChimpsky]

Hello All,

Has anyone come across slotted H-beam through joints as a means of simplifying skid frames and base frames manufacture for steel structures?

https://www.youtube.com/watch?v=5Kv2xAsP8YI

I am thinking of a skid base frame with two full length H beams (203x203x52) requiring equally sized cross member beams passing through the main beams. The current design is to break the cross member into three sections, profiling out each end to match the profile of the main H-beam and welding each end. I would like to see a slotted transverse beam used as highlighted in the video and on the attached image but with an additional fillet weld running round the joint on all four sides.

My concern is with introducing notches to the flange and web of both beams and the effect this has on the beams capacity for bending moment and for localised stresses at the notches. Does anyone have any experience with this?

Many Thanks for your help,


R.

 

[KootK]

The video didn't show how the beam flanges would be reconstituted across the notches. Groove welds? Fillet welded flange plates? I would expect all of those connections, and switching from parallel to transverse grain flange flexural stresses to negatively affect fatigue performance. I'm not sure if that's a concern here however.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dhengr]

Richward5:
The trick is that you have to determine which members, which orientation or direction of stresses and bending is most important and should be continuous from the stress flow, stress path, stress magnitude standpoint and fatigue standpoint. In particular, you want to keep these tension flanges continuous and intact. This may mean that you assemble the frame upside down, or in several steps. And, you must pay attention to the welding details at critical stress or fatigue locations. My guess would be that the cross members are primarily load distribution and stiffening members and that they can have broken flanges which get rewelded. You said two longitudinal beams and some cross members, so the cross members just get cut, coped, trimmed to fit the primary longit. members, and that’s that. If you have three or four longit. members, they are still the primary bending members, keep them intact at the tension flanges, and then you have something akin to what the video shows. If you have cutting equipment with the accuracy to do it, cut the cross members as shown in the video. The advantage is that you are handling fewer pieces during the cutting and during the assembly. The welding details must be worked out in either case, but they will end up being about the same details, either way. In the case of the flange/web radius, don’t try to fit that or weld into it, rather cut a chamfer greater than the radius on the secondary member web so that you can’t weld into that radius.

 

[NimChimpsky]

Two fantastic responses already, thanks guys. I have attached a very quick cad sketch of the joint in question. The gold cross members are those I'm investigating.

KootK - Yes groove weld where the two beam flanges meet as the two beams are required to finish flush with each other. The structure will be a topside skid frame and will experience high cyclic loads due to dynamic vessel motions.

dhengr - This is where it gets interesting... the gold cross members are used as lifting points and therefore the joint in question is subject to large bending moments through the longitudinal and the transverse members. The upper flange will be in compression and the lower flange in tension as the beam deflects (This is true of both longitudinal and cross members). In my head... having a profiled cross member provides a more continuous path for the stress along the upper flange of the cross beam and the negative impact of notching the longitudinal beam will be countered by having increased bending resistance (second moment of area - due to benefit of cross bracing) at the notched region.

Many thanks for your help guys.

 

[dhengr]

Richward5:
Please attach your sketches as PDF’s they are easier for most of us to deal with, in terms of printing and viewing, etc. You haven’t bothered to show your lifting points, final reaction points, load points, load magnitudes, member sizes, etc., all very important items. Your lifting points are used a couple times in the life of the structure, so while they are not unimportant, they are secondary. The rest of the structure sees thousands of loadings and vibration cycles per month, so they are the primary consideration. In your sketch, I see two primary longit. beams, four cross beams/braces, maybe bringing some loads to the primary beam members, and four outriggers or lifting points. The lifting points are just applied to the outside of the longit. beams as lifting lugs or brackets. Otherwise, the cross beams are just cut and fitted to the longit. beams and welded to them.