building w-shapes from plate

huangyhg

building w-shapes from plate
i have a situation to which i have lack experience and kindly request some discussion.
we have a structure that uses approximately 10,000 feet of 175mm deep i beam (h175x175x7.5 鈥?a chinese shape).  the chinese fabricator is asking to build up all of the sections from plate material (apparently a sourcing problem for hot-rolled shapes).  the welding of the flanges to the webs will be done with continuous fillet welds, however, a penetration weld is not to be performed through the web (fabricator is worried about warping).  i have my doubts regarding the quality control and nde that will be performed on the welds.  i have been told that building beam profiles is common in this region.  as the structure was designed using hot rolled shapes, i have some obvious concern over whether built-up beams from plate will be sufficient or not.  without significant experience with this sort of situation, i thought i would post.
the structure could be re-designed using plate girder techniques, but am hoping to minimize re-work.  i have concern over the level of residual stress introduced into the structural shapes due to their small profiles.  additionally, manufacturing the exact geometry of the hot rolled profiles would be very difficult when considering the radius between the web and the flanges.
surely, this subject has come up before but my searching on the forum has not yielded much success.  thank you in advance for any discussion you may be able to offer.
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you say, "the structure could be re-designed using plate girder techniques, but am hoping to minimize re-work."  i'm confused.  if what they're proposing is not to replace the rolled sections with built-up plate girders, then what are they proposing?  you don't have to redesign, just take their proposed design and analyze it.
if the fabricator is asking for a substitution, you are in a position to dicate nde requirements, which will probably come down to what percentage of the length of the weld you want them to mt.
this is a very small section.  how thick is the web?  what welding process are they going to be using?  are they going to be welding both sides of the web simultaneously?  with a thin web, they may very well wind up with full penetration regardless unless they're using a very low-heat process.
hg
this happened to me once on a project.  what i disliked the most was how the flanges were butt welded together at random locations (to use up smaller pieces i guess) where i had no idea what the splice detail was.  i think are correct to be concerned.
regards,
-mike
you can't just substitute a built-up shape for a hot-rolled shape.  you have some differences in design requirements that you'll have to check.  the other concern is exactly what you stated: they cannot manufacturer the exact dimensions of a rolled shape from plate.  you will have some changes in geometry to take into account.   
you're other option is to require them to hire their own engineer for the work they want to change, that you will then review and accept and reject.
mike has a point about the splices, you need to specify that no splices are to be permitted unless you first approve them, make them do shop drawings of all the beams, you would get shops anyway, right, quality control is important.
thanks for the responses so far.  i am happy to see similar concerns.  
i realize i can dictate the nde requirements, but that does not constitute there will be 100% joint efficiency between the web and flange unless perhaps i spec 100%rt... however, that would be ridiculous on this much steel.  the members are stress to capacity under maximum loading conditions.
i realize that i can take their proposed design and analyze it, but that would constitute re-work that we are trying to avoid.  
not sure about the welding process (none yet proposed) but the steel is thin (web will be 6mm).  the heat process will be high i am sure due to the amount of welding that will be required.  they may get penetration due to high heat, but that could also result in higher residual stress.  if all of the members are built up, there will be over 25,000 lineal feet.  that would be over 50,000 ft of welding!!!!
it has dawned on me to have the fabricator prove their proposal to me (via engineer) for our review and of course is an option.
welcome any additional comments and look forward to reading them.
has this fabricator done jobs like this in the past, can they provide you a list of successful jobs? once they propose their weld procedure, (likely a stitch weld), would they do a load test to failure on the beam.
is this similar to a bar joist, where you specify a size and joist manufacturer certifies it?, maybe you should just specify your izz and sxx and let them and their engineer design the shapes and have their engineer seal the drawings and calcs.
there is no way to allow this without analyzing the proposed fillet welds to see if they can carry the required shear between web and flange.  you could save yourself a little bit of work by requiring them to submit calculations and checking those, but it has to be done one way or another.  they also need to demonstrate that they have the required cross-sectional area, moment of intertia, torsional properties, or whatever else you feel is relevant.
you need to watch out for the full penetration, actually.  if what they wind up with is something longer from one side of the web to another than it is deep, you can get a crack that separates the web from the flange.  see p. 9 of
i like the idea of specifying the critical profile properties (such as izz, sxx... etc) and having the fabricator's engineer design shapes that meet the criteria.
regarding hgtx comment regarding a high-heat process.  i am making an assumption that due to the lineal feet of welding that they will try to lay as much weld down as they can in one pass, and therefore intorducing more heat into the weld than desirable.
appreciate the comments.
i'd also specify dimensional tolerances - ie flatness, camber, etc.  depending on their process and qc, they may not wind up with straight beams within the tolerance for rolled shaeps.
you're within your rights to require them to submit a welding procedure.  if it looks hinky to you, you might get away with making them run a qualification test.
but with such a small section (it's 175 mm, not 175 cm, right?), your fillet weld size will probably be governed by the minimum size required for heat purposes.  what code are you operating under?  for aisc and aws d1.1, the minimum weld size is 6 mm for plate thickness 20 mm and under, and 8 mm for thicker plate.  an 8 mm weld is typically done in one pass regardless, so i don't see them doing anything untoward to "lay as much weld down as they can in one pass".
given that this is probably inherently a one-pass weld, i still think your worry may rather be insufficient heat because they're trying to run too fast.
hg