Determining the effective area of a fillet or groove weld is easy.

Now ask your boss what type, grade, and how many threads per inch 3/4" bolt?

Chuck,
The AISC Manual of Steel Construction has the information you are looking for. HOWEVER, as you are aware, you need a lot more information (and engineering training) in order to consult the book and make that call. You need to know how the connection is loaded, what type of bolts are being used. Is that a shear-bearing connection or slip critical? Where would the weld be located in relation to the primary stress? And many other concerns.

You already know what the questions are and you already know the answer to your own question. I see your post as an opportunity to blow off a little steam and get a consensus.

Your supervisor, or someone, needs to consult the customer's engineer to make the determination. I have run into inspectors that like to play engineer but they are not and they don't realize how big a risk they are taking.

I think it is unreasonable to expect you to make the decisions.

Chet Guilford

I've done the calculations for this / with bolts and welds.... and it is far from a magical number.

Although there is a standard for plug welds, in AWS D1.1 - stating the minimum diameter is to be the thickness of the plate + 5/16 in. This is nothing remotely close to the calculations needed for strength though.

An overview of the calculations involved with bolts are based on:
1. The force on the bolt. (based on plate thickness)
2. The surface area involved on the bolt / plate.
3. The number of bolts / length and ksi strength of mat'l.

An overview of the calculations involving welds are based on:
1. Weld type, strength, area, and location.
2. Strength based on the ksi given in the first 2 digs of the electrode.
3. Type will give you the formula needed to calculate how much weld area there is.
4. Location - especially important on welds which go around bends in plate. These type of welds have their own formula.

If you would like, I can get you the formulas you need (or your engineer should be using) to calculate this. After the calculation is done, you should also add a safety factor to it.

Depending on the application, safety factors usually are 2 for objects with minimal stress changes, up to 4 for objects which are under alot of stress changes.

When considering your safety factors, you should also look over the whole design, and figure out where you want the weakest link to be. This will make your maintainers happy - as I am sure we all have experienced fixing something that has broken in a place that couldn't be accessed easily. Grrr!! As you can see... these calculations are definitely based on design.

As for my opinion, it is not the CWI's roll to figure this out. As the CWI, you should insure welds are to standard - which does not seem to touch on the design of, or revisions of designs to be made.

Maybe your "stupidvisor" should take a course on understanding professional roles and responsibilities!

Vicki

Hello all!
As a trained welder and engineer in training, I have came across some really good information regarding this, but most of it has been in texts(e.g "Mechanical Engineering Design"). The applicable info in these types of sources, though, should be very common. All that is necessary is the physical strength of the bolt, the strength of the base steel, and, as stated before, a little common sense, and this should give you a fairly good approximation. You see, a bolt's tensile strength and threaded area (a little less than 3/4" for a 3/4" bolt) determine the strenth of that joint. Assuming the weld to be round(as if you were simply replacing the bolt with a plug weld) the factor of increase of diameter will just be the dividend of bolt tensile and base metal tensile strengths(most engineering calculations do not take into account that the weld will be stronger than the base because they assume that since the two are fusing, it is safer to take the lower strength and gives a hidden safety factor).
As for removing a drilled hole and replacing with a fillet somewhere else on the piece (e.g. bolt in corner of plate to weld around edge of plate) there is no magic number, and this does require a little bit of number crunching to get similar safety factors. However, in my own opinion, safety factors should always be as high as possible whenever possible(intentional fail points, aircraft design, ect. being the exception), and, again, this simply comes back around to common sense.
Hope that helps and that this, my first post, didn't sound too dumb. And thanks to all for all the great info and posts I find on here!
G. L.