"Let's simplify the art of Structural Engineering"

Why Bolt and not Weld? Why Weld and not Bolt?

July 31, 2020 Posted by Parishith Jayan , , , 8 comments

As a practicing design engineer, during the initial stage of the career, each and every one of us would be subjected to this particular dilemma.  

"Choosing between bolted and welded connections."

 Where should we adopt bolted connection and at what circumstances we should incorporate welded connection? 

Over experience, we would have figured it out. Let me share my own experience with it so that it would be beneficial for upcoming engineers.

Choosing between a bolted connection and a welded connection is not so difficult. 

Design engineers choose their connection type (bolted or welded) based on one important factor. “FEASIBILITY OF FABRICATION AND ERECTION”.

One important rule to follow.

Designing a structure might involve several design constraints and complexities based on the loads that are about to act on the structure. The solution to these difficulties should be “SIMPLE” & “FEASIBLE”.

Having the above-mentioned rule in concern, the choice of bolted or welded connection should be decided based on the feasibility of production, transportation, and erection process.

To have a clear understanding. Let us say we are designing an industrial building whose cross-section looks similar to this. (clear span gable frame)

The connection between the column and the rafter is usually the bolted connection because providing a welded connection, in this case, is not practically possible. Say the height of the column is around 8 m. In site, one cannot lift all the welding equipment to such height and provide proper weld. If you suggest going for welding at the fabrication shop itself, then, in that case, it is very hard to transport the entire arrangement. So, a practically possible and simple solution to this problem is adopting “bolted connection”.

Now, let us go for a building with a roof truss.

As you see the above picture, the rafter is a truss arrangement that constitutes a top chord member, bottom chord member, diagonal, and vertical truss members. The knee connection (column and truss connection) will be bolted connection similar to the previous case. Whereas, the member connections within the truss will be welded connection.

Because individually bolting each of the truss members is a tedious process and it employs erection difficulties. The simplest solution to this case will be welding the truss members (top chord, bottom chord, vertical and diagonal members) in the fabrication shop itself up to transportable length (say 12 m). Then the truss members can be joined together with bolted connections in the site to form the complete truss.

So, the choice of bolted and welded connection is not only a design consideration. While doing so, the practical feasibility of the connection has to be addressed to come up with a simple solution.

8 comments:

  1. Awesome explanation sir. Well put together.

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  2. Good blog and good topic too. insightful :)

    Hoping for more such blogs on practice considerations in structural Engineering.

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    1. Will definitely write more on practical aspects of design

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  3. Good explanation sir. It helps a lot for graduating engineer's.

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  4. Very simple and clear explanation...expecting to see more on topics regarding the practical design of steel structures..so that it will help many of us...

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  5. Well simplified explanation 👏👏

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