Beam Splice Model
Beam Splice Model
(OP)
Please see attach sketch. One splice in one span works fine. But when I placed two splices, left most span, both sap and staad show instability. But it is a real life situation and a evry senior engineer is doing it manually. I just wanted to cross check and learn using s/w. Any tips ?






RE: Beam Splice Model
Also, it appears on the far right spans that you have double pins (two small circles side by side). A joint must have at least one non-pinned member framing into it.
RE: Beam Splice Model
RE: Beam Splice Model
What is s/w? If senior engineers are doing this, they ought not to be senior engineers.
BA
RE: Beam Splice Model
Joel Berg
RE: Beam Splice Model
If all supports are truly hinged, then the structure is stable, but I seriously doubt that every senior engineer is "doing it".
My tip to you is "don't do it".
BA
RE: Beam Splice Model
If you draw a FBD of each individual member you will see that the two left-most members are like a simple span beam with a hinge along the span - again, it's a mechanism.
RE: Beam Splice Model
RE: Beam Splice Model
RE: Beam Splice Model
Mike McCann
MMC Engineering
RE: Beam Splice Model
I agree with what the previous posts have said.
Only one of those thre spans is truly stable.
In real life, a system of members with higes at each end is called a 'chain' great for tension but not much good as a beam. Three of your spans contain a chain link.
It is a worry that neither you or your senior engineer picked this up.
RE: Beam Splice Model
Assume his beam was a W12.
Each approved splice (what we see as a single "pair" of bolt holes in the software) could be actually a pair of 10x6x3/8 thick plates with 6 bolts through each web, making a sandwhich joining the two beams.
RE: Beam Splice Model
If all but one of the supports is changed to a roller, more of a real world situation, then I agree that the structure is unstable.
BA
RE: Beam Splice Model
Mike McCann
MMC Engineering
RE: Beam Splice Model
Question 1. I think both beams meeting at splice release the moment therefore I showed two circles of moment release at splice location?
Question 2. When there is two splices in one span than S/w always shows instability? any way to overcome it
RE: Beam Splice Model
2. There can be two splices in one span provided the adjacent spans continue through to the next support. That is called a drop-in span.
You cannot have two splices in an end span, so remove the splice near the leftmost support.
If you wish, you can move the next splice to the right of the second support. You will have two splices in the second span and the structure will be stable.
BA
RE: Beam Splice Model
RE: Beam Splice Model
So, back to the orignal question. Draw - not in your modelling siftware, but on a piece of paper - then scan it - exactly HOW the splice is constructed. Not how it is modelled. How it is built.
RE: Beam Splice Model
Mike McCann
MMC Engineering
RE: Beam Splice Model
RE: Beam Splice Model
AhA! OK...
Mike McCann
MMC Engineering
RE: Beam Splice Model
More "analysis" of a WRONG connection definition inside a problem will only waste your time, your company's time, and give you additional WRONG answers.
RE: Beam Splice Model
It is probably easier and faster to check this beam by hand than to use S/W (software). The original designer would likely have considered each splice to be a point of zero moment.
BA
RE: Beam Splice Model
Dik
RE: Beam Splice Model
The beam to the left of Splice #1 continues left beyond the column to another support.
dgkhan,
As stated earlier, it should be easy to perform all calculations using hand methods because each span is statically determinate.
If you want to model only four spans of a multi-span structure, move your left support to Splice #1. The leftmost span is a simple span, sometimes called a drop-in span because it rests on the ends of a cantilevered beam at each end.
What is the purpose of this exercise? Are you simply checking an old design or are you proposing changes to it?
I don't know which code you are using, but be sure to check for patterned loading in accordance with the code. When the cantilever portion of a beam is fully loaded and the span is unloaded or partially loaded, the bottom flange has a large unsupported length and probably requires lateral bracing.
BA
RE: Beam Splice Model
RE: Beam Splice Model
"Ignoring splice, beams start to fail in moment if treated as simple supported." do you mean analyzing each span indiviaully, rather than as a continuous span beam with several supports ?
"So by looking closely at vague drawings, I figured out splices. In my understanding, purpose of this mechanism is to reduce moment and make this beams work." A splice cannot reduce moment; now it is possible i guess that if the spilices intentionally don't react moment, that the design thought was to create a structure that reacted the applied loads as axial load in the members, which would mean that the supports react transverse load (assuming vertical loads). this would probably cause very large deflections ... not sure why you'd have two hinges close together.
"It is a large frame.400 x 400 feet." ... is the structure a frame or a beam ?
RE: Beam Splice Model
RE: Beam Splice Model
While not as common, some engineers do (or did) it that way. Some prefer it, as erection can be from end to end, reducing the amount of temporary support required.
RE: Beam Splice Model
No problems to date but one erector one time pointed out that if the first beam gets damaged or looses support, the whole beam run becomes unstable - sort of a progressive collapse mechanism.
RE: Beam Splice Model
That would be true, while doing it the other way, the collapse mechanism would be confined to at most 3 spans.