Welding beam to girder/aditional stiffening

[bureqq]

hi to all

I'm analyzing the certain deck of certain module which will be installed onshore,
that deck is consisting of joints made of plates, girders and mostly the beams like heb700, hea400 and hea180

my issue here is welding beams like heb700 and hea400 to girder that has height of 1800 mm, width 670 mm, flange thk 35 and web thk 25 mmm. Also the possible stiffening, difference in height is big and i'm not sure how to design those stiffener plates, should they be so big or just partially installed?

in attachment there is a detail 1 from similar project how those beams were welded to girder, there is a cut on bottom flange and i don't know why..apparently because beam to be welded have thicker flange than the web of a girder so to avoid possible deformation of the girder's web? heb700 has thicker flange but hea400 don't have so i don't if that is the only "rule"..so i don't understand that cut on the bottom flange?

after some calculations were made it seems that certain heb700 beams are stressed maybe more that they should be, so i was considering to add some stiffeners to detail 1 (see detail 2) keeping that cut on bottom flange for now because i'm not sure about it's purpose..hea 400 beams aren't stressed significantly but i would also like to add some stiffeners maybe just for precaution in certain areas and i don't know should i apply the same stiffening process like in detail 2 and keeping that cut on bottom flange?

Also i was advised to weld some stiffening plates (detail 3) to heb700/hea400 web because of shear stress in that zone, should i then also strech stiffener n2 to "fit" stiffener n3, would that make some positive impact also?

is there any AISC standard which has some rules about joints like beam to beam/girder and something regarding stiffening those joints, what if the difference in height is so big like in mine case, are there any similar details?



Basically i'm wondering, what would be the correct way to join beams like heb700 and hea400 to such a big girder, what is the point of cutting that bottom flange and what is the best way for stiffening those connections to minimize stress/deformations and is there any standard, preferably AISC where i can see some rules about welding those joints, adding stiffeners..?




thanks in advance

 

[bureqq]

Anyone please?

 

[dhengr]

Bureqq:
I have no idea what heb700 or hea400 and hea180 means, please explain. Also, put some dimensions on the sketches, although you have given some sizes for the girder, what are the smaller beam sizes and dimesnions? What are the loads, reactions, end moments on the smaller beams? These are all important parts of the total design problem. The cope in the bot. flg. is most likely as you think, to prevent a concentrated punching/buckling force into the girder web. But, those smaller beams will still rotate at their ends, under load. And, all that flg. cope detail does is concentrate that rotation or punching action even more severely at the termination of the web to web weld on the girder web, the small beam will still rotate. It seems to me that you have to determine what kind of a connection you really want/need at the smaller beams to the girder. If you could transmit the shear at the end of the smaller beams, and almost no end moment, would that be o.k.? Then a couple clip angles or a shear pl. to the web of the smaller beams would be enough, and you would cope the top flg. on the smaller beam (no full pen. weld of that flg.) and use a weld or a few bolts to the clip angles or shear pl. These do not all have to be totally fixed connections. And, welding that top flg. properly requires run-out tabs and radius grinding, a bevel and welding from above, gouging and welding from below, to do it properly, so its not inexpensive either. You assume some slip in the connection or rotation and flexing in the clip angles to accommodate the end rotation of the side beams. The stiffeners will provide more weld length, to get a reaction into the girder web, which is what you really want to do. They will stiffen the web if you force the side beam end rotation into the girder web. Otherwise, web stiffeners on that deep a pl. girder will be based on overall web crippling or buckling more likely than some small beams framing in from the either side.

 

[bureqq]

thanks for your response,

heb700, hea400, hea180 are wide flange h beams
the dimensions are


hea400

http://www.staticstools.eu/profil_HEA.php?profil=HE400A&act=zobraz&lang=EN&je=0

heb700

http://www.staticstools.eu/profil_HEB.php?profil=HE700B&act=zobraz&lang=EN&je=0

hea180

http://www.staticstools.eu/profil_HEA.php?profil=HE180A&act=zobraz&lang=EN&je=0

in the attachment is a plan view of that main deck,

green color represents girder
light blue are heb700 beams
blue are hea400 beams (some of them are considered as primary and some as secondary)
yellow ones are hea180 beams (joists, not so important)

for the moment i only possess (see other attachment), some values from sap2000 analysis which indicate that the most stressed beams are located in areas where control cabin and battery room are located.

apparently every beam joint in sap was considered as fully constrained (i'm not performing analysis)

my problem is that i don't know should i only focus at those areas which are "critical" or should i also provide some stiffening even on other connections because that's a lot of material to use in the end..especially when using those big stiffeners.
for all other area "non critical" i can understand putting smaller stiffeners into beams from each side,right at the point where the equipment will land but is it really neccessary also to put those big stiffeners in girder and below beams which are to be connected to girder?


Is it ok for me to perform stiffening for that heb700 to girder connection like in detail from my first post, having the bottom flange cut-out?...having back stiffener in girder, one below heb700 and one from each side installed into web of heb700?

except from those heb700 profiles from the picture, there are also some hea400 beams which are "critical", should i apply the same process of stiffening like for heb700, also cope the bottom flange and put some stiffeners? the big difference in height kind of worries me, is it normal to use that big of stiffeners, not used to it..

how would you join those beams to girders, would you only apply stiffening for the beams which are "critical" or even for not significantly stressed beams? is coping the flange only required when you have a significantly stressed beam with thicker flange than girder's web?

 

[bureqq]

i'm trying to avoid coping the top flange, adding shear plate or clip angles/bolting them etc.

i forgot to add in previous post..

in attachment is a plan view of main deck where some important hea400 primary beams are marked, they aren't really stressed and i'm wondering if i can welded them to girder without coping the flange, do i need to put there some stiffeners even if they aren't really stressed? is it enough to weld bottom flange with fillet if that's the case?

 

[bureqq]

also, all connections should be fully restrained moment connections..i was trying to find out some examples from aisc standards but basically most of those connections are beam to column made to end plate, also with some clip angles..bolted or welded, even when beam enters other beam similar stuff, what i need i beam entering other beam which flange is welded by full penetration and web welded by i suppose fillet weld, no end plates or clip angles, or some bolting options..

if there is some big moment at beam-girder joint, is it wise to cut down bottom flange although it will be put some stiffener under the beam and also one in the girder?

 

[Duwe6]

"all connections should be fully restrained moment connections . . ."

You appear to be overthinking it. A Moment Conn requires full-penetration welding, so effectively, there are no cuts in the flanges. Everything that was cut off has been replaced, and it is one solid and continious weldment. Only thing I would do is to specify a radius of at least 20mm on the ends of the flange-teeing-into-flange welds, to eliminate that square corner.

Mother Nature never made a square corner, and she had a good reason not to.

Lastly, check the stress on your Det. 2. Just glancing at it, the web on the side opposite the beam may need reinforcement - gusset plates.

 

[bureqq]

hi, thanks for your response

yea, i was told that if flanges and webs are welded that it should be considered as fully restrained moment connection but is it "the same" thing (regarding fully restrained moment conenction) if two beams have equal height when welded and when two beams don't have equal height when welded like in my case?
also if i am forced to cut bottom flange of a beam that needs to be welded to girder will it still be considered as fully restrained connection if webs and top flange are welded and not bottom flange? do i need to add gusset plate below to make it a "fully restrained"? also i'm worried about size of gusset plate in that case which would be installed below conencting beam..beacause it should have height from 1100-1400, can it be partially installed and not all the way to the bottom?

also, when you are mentioning det 2..are you reffering to my 1st post 4th post? because both have gusset plates below and back

 

[Duwe6]

Det. 2 of 1st post.

 

[racookpe1978]

Off shore platform -> New steel being welded with full-penetration welds.

OK, but that means it must be welded in place above water out in space (on scaffolding!) also above water before adjacent platforms or steel goes up.

A fully-welded full-penetration joint can't be pre-fabricated at its final connection joints, and can't be pre-fabricated at all if it can't be stored, lifted into place, suspended and final-positioned into final position before welding, and then accessed to do that final welding. Can it be moved to sea and lifted up as an assembly at all?

Yes, full-penetration welds are easier to calculated than bolted joints of flanges and gussets and holes. But, there are reasons for bolts in erecting steel!

This will be very, very expensive (total assembly and in-place welding) price at the sizes you propose.

 

[dhengr]

Bureqq:
I really think you should be talking with the guy who did the original design and analysis. What do they want and need, what kinds of details did they intend? Are the details with all the stiffener pls. their details, or what you think might have to be done? Look at the details on existing structures like this for guidance. What code is this structure designed to, and what does that code say about these connections? What kind of a structure is this? Did the guy who did the SAP2000 analysis fix all of those secondary beam ends because he needed them to be fixed? Or, did that happen because he didn’t know any better in using the software and in modeling the structure? I’m not trying to be a smart ass here, you would be surprised how often these kinds of things happen when using that black-box software. I would also want to talk with an experienced detailer on these types of structures and with the fabricator. They will have some good, preferred details. The details you have shown are very difficult to do, and very expensive, what with all the fit-up needed and all of the out of position welding, etc. I would not use them unless they were absolutely needed. That pl. girder is pretty husky, but you can’t just put fixed end moments into the sides of it, at random locations, without having some significant torsional affects on the girder. You may be “trying to avoid coping the top flange, adding shear plate or clip angles/bolting them etc.” But, they are most often the more economical beam to beam connection when you can use them, and you should find that out. These types of connections tolerate some small end rotation of the secondary/smaller beams rather than imparting large fixed end moments into the girders. Note that you have to clip the corners of the webs on the small beams and on the stiffener pls. in the region of the flg. to web weld on the pl. girder, and you should not weld into those corners.

 

[bureqq]

yea, i know that all those details are not easy to to and are expensive but that they (client) wants for all beam connections to be welded..question is only, how to weld all those connections and where/how to use stiffeners if needed. we are also trying to follow some very similar project regarding details etc. but are not sure why some things were designed as they are.


that main deck is made of those large girders, special joints (made out of plates), hea180 tertiary beams (not that important), hea300, hea400 (some primary, some secondary beams) and heb700 primary beams.


connection of girders to "special joints" is let's say solved and also those tertiary beams..we need to decide how to weld all other beams and to add some stiffeners if needed.

hea180 to girder/other beams will not require stiffener and it will be joined in way that top flange will be welded by full penetration and web along with bottom flange by fillet weld. (when welding to girder, web of hea180 will be cliped like you already mentioned to avoid weld crossing)

now we are left to beams like hea300, hea400 and heb700..their joint to girder and between them

plan should be the same like for those smaller hea180 beams, to weld top flange by full penetration and web & bottom flange by fillet weld and if the beams of equal height are to be welded, bottom flange will also obviously be welded by full penetration.

BUT..

we have noticed that they were coping bottom flange for beams like hea400 and heb700 (they also had hea400 and beams like heb600, heb450)..we didn't know why but apparently they performed the cutting after some calculations were made and we don't know which ones..is it possible that flanges of those beams had some "negative" impact on the web of the GIRDER? btw, they hadn't any stiffeners for those connections.


now coping or not coping the bottom flange, i still have problems where to install the stiffeners for those connections..should i follow only the results of some calculations, to see which areas are more stressed or there are some other "rules" when joining those beams and applying the stiffeners?
right now i have these connections (see attachment1) i don't know where to add stiffeners or do i need cut the bottom flange of some beams because the girder's web could be significantly stressed?


for example, in offshore for some certain project..you have a platform deck which is made of primary beams, secondary beams, tertiary beams, joints..if the beams with same and certain height are to be joined, use back stiffener, if the beams have same height and are below certain height do not use back stiffener, if there is difference in height use below stiffener and back stiffener, do the slope on bottom flange..etc..(see attachment2)

also, attachment 3..am i reading these symbols right (according to iso), overall when full penetration welding/back gouging is performed, is it better that preparation of top and bottom flange is made in a way that groove weld can be deposited on the top?

 

[bureqq]

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