Steel structures - Book suggestions on load path? 1

[Eagleee]

Hi all

I am looking for suggestions from you guys...I am interested in getting a good book which would deal with load path in steel structures, both at a member level (i.e. deck -> beams -> columns, etc.) and at a connection level (e.g. web-> weld -> end-plate -> bolts -> flanges) so to say. For connections, I am tired of the simple examples found throughout the literature where everything lines up with everything else. My intention is not specifically to use the book practically for design (low chances that a I come across an uncommon situation which I can find in the book) but to overall improve structural understanding and what to look out for. I am a relatively 'fresh' engineer, in a way I want to compensate a bit for that. I can elaborate on what I am after course if needed.

 

[dhengr]

Eagleee:
I don’t really know of (can’t think of) a textbook which specifically covers ‘load paths, in steel’ structures. You should have been learning, thinking, feeling that during every structures course you’ve taken. A good background in Engineering Mechanics, Strength of Materials, Theory of Elasticity, material properties and behavior, etc. really helps. How does that load get from the bolt, or several bolts (all acting in perfect unison?, or not), through the shear pl. to the weld, and then down the column to the ground? Look at every structure you work on and ask how does it move under load, deflection, elongation, lateral deflection or movement, P-delta, etc. etc. Larger deformations almost always point to high stresses and load paths. How does that gusset pl. deform under the loads from the members framing into it? What is the most direct path from one member to the other, is it logical, can buckling be a problem? You should always have this thought process in the back of your mind while designing. The structure is sometimes smarter than we are, it knows how it must act, given the way we detailed it. You don’t often need to know these answers to +/- 1 psi, but you do need to have the correct (a very good) gut feeling for how the detail will perform. You don’t often see failures cause by a 5-10% stress change (or calc. error, sliderule vs. FEA), but you see lots of failures and problems caused by the designer not having the right feel for the structure, or out-n-out bad detailing and construction. And, you learn this by doing lots of design and by asking lots of question, that is experience.

 

[Eagleee]

dhengr, it is precisely that gut feeling / right feel I want to improve. Indeed this is strengthened in time through experience and asking the right questions. I fully agree with what you say about failures and that is why I should mention that I am interested in principles, not necessarily detailed calculations. I have had of course the courses you mention, but there is a general problem in our field I think because the information which bridges the gap between theory and practice is less than or less apparently available than compared to other fields. Maybe it's just the nature of our field, I don't know. Anyway, you say 'Look at every structure you work on and ask how does it move under load, deflection, elongation, lateral deflection or movement, P-delta, etc. etc. Larger deformations almost always point to high stresses and load paths. How does that gusset pl. deform under the loads from the members framing into it? What is the most direct path from one member to the other, is it logical, can buckling be a problem? You should always have this thought process in the back of your mind while designing'...I am basically asking if you know of a book in which this statement is expanded upon. Maybe with examples. thanks for the reply.

 

[WARose]

I always thought the SEAOC seismic design manuals were pretty good. Others that come to mind:

-'246 Solved Structural Engineering Problems', by C. Dale Buckner. (A little dated by this point (as far as code goes) but a great reference.)

-'Metal Building Systems: Design and Specifications', by Alexander Newman. (I've got the first edition. It's more for PEMB than normal steel structures.....but I thought it had good concepts.)

 

[skeletron]

"Transfer Forces in Steel Structures" by Bo Dowswell is an informative article to read regarding the load path for forces into and through connections. And Carol Drucker also has some good AISC presentations about connection design.

 

[Ron247]

I have never heard of a book or course that directly addresses this, but I think you have all the "tools" in your head already to figure these out. The more you work, the more will become intuitive. But, the first thing to nail down is the fact there is an extremely limited number of ways a component can respond to a force and there is a very limited number of force "profiles" that can act on a component. How forces move through structures is directly related to how the component responds to forces and how it is connected.

What all can you do to a "stick-like" component and what all can you do to a "sheet-like" component. That answer is the same regardless of buckling, wood vs steel and other factors. Example-stick-like component can be axially compressed, axially stretched, torqued, sheared, bent in any of the 360 degree directions but you cannot easily "rack" a stick-like component. You can also do more than 1 of these at a time.

Next thing to nail down is the fact that all structural designs have 3 areas to review but are not necessarily related to each other.

1. Design loads-comes from the building code; somewhat independent of the structure you are designing.

2. Frame some type of structural system to support those required loads. The system, regardless of how complex, consists of the stick-like and sheet-like (flat or curved) components. Because you fastened them together in a pinned or fixed connection did not change the limited things you can do to them. You then analyze it based on Area, Ix, E and some other properties. You do not analyze based on wood, steel, unbraced length etc. Other than E and G, you use very little material properties such as Fb, Fv etc. This step is the ONLY step that involves Load Path. Nothing fails at this stage. Buckling does not occur, things never break in the analysis stage. And, the structure never knows it is a seismic force versus wind. It just knows 1,000 lbs pushing this direction at this point. This stage is where connectivity matters. The pinned connection act this way whereas the fixed connection act different. So you have to visualize the component and how it is connected.

3. Once you do the analysis, you do a check of the material used for the components for the forces you now know exist in them. Now you use unbraced length, Fb, etc to check and see if the wood stud can withstand 600 lbs of compression while being subjected to 1300 in-lbs of bending. This step is where you 'calculate" failure. If it fails, you modify the components in step 2 and go again. The change in A, Ix etc can now change the forces in the structure.

So, in short, frame yourself a structure. Then picture different loads placed in different places and directions and visualize, "If i push here with a point load, which of these limited things it can do happens. And then based on what it attaches to, where does the force go from there. That is load path. If you can do an easy structure, make a harder one. You will see real quick, bigger structures just take longer because there are more pieces to picture. You will not be able to visualize magnitude, but you probably will be able to say "more goes here than there".

 

[txeng91]

I’ll say something that helped me when I was just starting out was getting my hands on structural plans done by other firms. I would look through all the plan sheets and details and ask myself “why did they do this here” and try to figure it out. Then when I came across a similar situation I could apply the same concepts. I think by aggregating other engineers designs and reverse engineering them until I had an underetanding of their design concepts and methods, it helped me grow a lot. Especially in terms of schematic design, which is very important part of running successful and efficient projects.

In regards to some of the other things you mentioned, you have to understand that in many cases, analysis is often simplified in that your not necessarily checking exact deformations and stresses on every single component like it’s a finite element model. But you do want to develop an intuition that allows you to identify scenarios where a more detailed analysis may be warranted. In this day and age there is so much information on the internet you can bring up endless standards, research papers, and technical reports on almost any topic with a simple google search. The key is to identify any items in your design project that may fall outside of simple analysis and do your research on how to address those items.

 

[klaus.]

'Load Path' is more a issue of basic mechanics ...regardless of material ....

 

[Guest262653]

Although not exclusive to steel structures I'd recommend the following guides for understanding load paths and building stability:

- Stability of buildings (IStructE guides), parts 1, 2, 3 and 4
Parts 1 and 2: General philosophy and framed bracing
Part3 - Shear walls
Part 4: Moment frames

- Concrete Buildings Scheme Design Manual
Concrete bookshop

- Tall Building Structures - Analysis and Design, Smith
Amazon

- Structural Analysis of Regular Multi-Storey Buildings, Zalka
CRC Press

- Global Structural Analysis of Buildings, Zalka
CRC Press

 

[SlideRuleEra]

Eaglee - In the 1980's I found that a good way to study load paths is to read about the ones that did not work. One book that I purchased, and still have, is "Construction Disasters: Design Failures, Causes and Prevention", published by Engineering News-Record. I'm sure there are other, more recent books on similar failures.

At Engineering Tips, read the links, details, and discussions in Engineering Failures & Disasters Forum.

http://www.SlideRuleEra.net

 

[KootK]

I would start here: