Larry,
That's a great question, and you have no reason to be embarrassed. Static loads exhibit very little movement and have little or no change due to the balance and the equal action of the opposing forces in the structure. On the other hand, cyclic loaded structures have movement due to impact, waves, wind gusts and strong earthquakes. I can usually look at the types of connections, welding, etc. and can determine whether a structure is static or cyclic, however, that is not 100% reliable because I'm not an engineer. I've just been around it for so long. As Hogan stated, it should always be noted in the contract documents, and to take it a step further, with any applicable notes being added to the shop and field drawings, but I've never seen any of it done. With that being said, a simple phone call to the EOR would clear it up. Without that clarification, the fabrication shop tends to go to the extreme "just to be safe", and proceed to follow the D1.1 criteria for cyclic structures, which will add additional fabrication time that most likely was not picked up during the estimating phase. I'd like to know if other fabricators address this in some way other than a phone call to the EOR.
I agree with swnorris. If it isn't stated on the drawings, then by all means, contact the EOR for clarification. There are certain types of structures that are always considered to be cyclically loaded, such as crane beams, bridges, or other structures that have moving loads. Still, it is best to ask the engineer to be certain.
I don't believe any engineer would see it as a character weakness or a difficiency in training to be asked that question by a CWI. It is one of the first questions I ask if it isn't stated on the drawings. It not only affects the welding, but the bolting requirements as well.
Best regards - Al
Thank you very much all of you...hogan,swnorris and Al.I respect your oppinions and that information really helps. I worry about making mistakes.I like the comments on writing reports so much I had to print those.Its a very great service the more experienced guys here do,shareing their knowledge with all.
thanks again
Alot of people think buildings are static and bridges are cyclic. That would be incorrect. There are alot of ways that a building, even though it just sits there, may have sections that could fall under the cyclic catagory. Maybe there's a portion that is cantelevered out over a sidewalk, and the opposite end of the building would be pulled up, to counter effect this action.
Basically, what everyone else said earlier is correct, that it's in the contract documents. If it's not in there or you don't have access to it, go with the stricter cyclic condition until someone can show you different.
Chris
Almost every component in a building is under some type of cyclic loading. How so? Snow, rain water, wind etc create different loads on the roof or sides of the building. Simply put if a member is subject to a variable load it is cyclic in nature. If the member is subject to steady load it is static.
An example would be a simple cart designed to support, let's say 1000 lbs. if the cart is sitting in one place without the load all members are under static load, if the same cart has the load placed on it and then removed the members underwent cyclic loading. If the load is placed on the cart and left there, the cart is under static loading but if the cart is then moved from place to place cyclic loading occurs as the forces normal to the vertical sections of the cart act upon it cyclically.
There are many things to consider when cyclic loading is present such as the cycles, the strain, displacment and more.
It is not the CWI's job to detrmine the load, stress, strain, etc. this falls to the engineer. It can be assumed that when the part was designed the nature of loading was taken into account and the welds were sized and placed accordingly. I suggest, as others have, that the engineer of record be consulted whenever the CWI has a concern. Remember D1.1 was not written just for the CWI but also for the desinger.
When in doubt ...ask. Seriously, the designer should spell all of this out in the contract docs/specs. See below:
AWS D1.1:2006, paragraph 2.12.3 Engineer's Responsibilty.
The engineer shall provide either complete details, including weld sizes, or shall specify the planned cycle life and maximum range of moments, shears, and reactions for the connections in contract documents.
Every single reply has helped me understand more.[started out clueless]I had wondered about it for a year.At the seminar before the exam I asked the instructor this question,he said something like its obvious...look at the drawing!,and he said a cyclically loaded object has waves of energy that pass to and fro from end to end.And then he moved on while some of us were still lost.So thank you all have made it much more clear.
If you look at D1.1, Section 2 Design, there is a couple of SN charts. If you look at the bottom left side you will see that the chart start with 10 000 cycles. The would be the minimum number of cycles required to be considered cyclic loading.
Assuming there is 365 days per year over a ten year span, the structure could under go 2.75 cycles per day before you would have to take fatigue into consideration. That would be 2.75 wind storms per day or 2.75 heavy snow falls, or what ever. Also note the magnitude of the stress, it is very high, starting with about 30ksi and higher depending on the category. A typical allowable stress for steel would be in the range of 21 to 27 ksi.
Many structural engineers don't design for fatigue unless there is a moving load involved that involves sufficient mass and cycles to place you above one of the lines on the chart Even live loads, i.e., people moving around in an office or school is designed as static loads. There is a phenomenon known as low cycle fatigue, but the loads are very high. and in general the component is over stressed because of an unforeseen condition.
The conditions of loading has to consider the total change in the magnitude of the loads imposed on the structure. So it is possible for a structure that is subjected to complete load reversals to experience higher unit stresses at lower loads than a structure that only see a positive load with no reversals.
As stated by several responses, the engineer is in the best position to understand the nature and conditions of the loads the structure has to resist.
Best regards - Al
Thank you Al, I meant to include that chart in my reply and I was called away from my desk to UT some weird connections in our shop and I hurried my reply before I had finished my thought......
Hello John;
How's the world treating you?
In my case, "It's a dog eat dog world, and my butt feels like a Milkbone dog biscuit!" That is a quote stolen from Norm on the old television show "Cheers", but it does seem appropriate at times.
I finally settled on the KB 35X UT machine. I like it and I feel very comfortable with it. It's paid for itself in a matter of a couple of weeks. It's 1/10th the weight of my old Sperry unit. The lead acid battery in the old unit alone weighed more than the new machine!
Best regards - Al
10/day 7/week...kind of busy...LOL plus small inspection jobs at night at some nearby fabricators.....
Refer to AWS D1.1/D1.1M 2006, as 2008 has not been released yet, Section 6 Inspection, 6.1.5 / 6.1.6 and 6.1.7. The information you are looking for will be in the documentation that you, as stated "shall" not "should" be provided. If this info is not in the documents that "shall" be provided then you need to contact the EOR.
As a structural engineer, we consider the type of loading in the design and specify eveything to suit that type of loading. If fatigue is an issue, it is our responsibility to detail the weld to provide for that, and the welder should be able to just follow the welds specified without having to judge what kind of loads they will see. A new exception to this is the welds (and bolts) in the seismic force resisting systems. These welds have to be identified on the drawings, now, so all the new seismic requirements for these welds are not missed.
On a final note, also as structural engineer, I apologize for those engineers out there who are sloppy in identifying proper welds and details. Sadly there are a bunch.
Bob G.
No need to apologize for someone else.
I deal with an engineering firm that employs fresh out of school kids, and they tell us we know what would hold, so weld accordingly.
not the way anyone should design anything.
OUTSTANDING! My response as a welder and/or inspector would be and HAS in the past been, " I am not an engineer, I build, weld and inspect to what is on the drawing provided to me by you, the engineer. If the information is not there, I can not do my job correctly." You are right that that is not the way to design anythin. Sounds to me like that engineering firm is actualy a reverse engineering firm. LOL
They spend alot of time down at the shop thats how i know they are kids. they started just recently putting notes on their drawings about all welds are half the size of the thinest plate unless there's a bevel, in which case the bevel is filled flush!
I will say it again, OUTSTANDING!!
I just pointed out to some designers last week that specs and drawings are like programming a computer. If you don't specifically say to do it, you can't assume it will happen.
Now to get designers to rethink their use of "weld all around" symbols.
Hg
Topic American Welding Society Services / Technical Standards & Publications / How to determine load is Statically or Cyclically loaded?
