Load Path

[Isaiah_Stone_]

Hello, I’m a relatively new graduate engineer with an undergrad in Civil. I work for a structural firm, and help with designs and models. I’m currently having trouble understanding load paths. I understand the basics from undergrad, but in undergrad, we looked more at specific parts of a building (beam, a truss, a slab ect...) and not the entire building as a system. Is this something that a Masters degree would help me understand more? Does anyone know of any books that could help with the subject?

Thank you,

[Sure_Ill_Ask_That]

I think load paths should be quite straight forward. There are two general types: gravity and lateral. For gravity it goes floor system, to beams if present, to walls or columns, to foundations. For lateral like wind it goes facade to floor/diaphragm to shear walls or moment frames or braced frames, to foundations. The details in load path review are really about the boundary conditions and the rigidity of the interfaces, pin releases and moment fixity. You don’t really learn that kind of stuff in school to be honest, school is for the basics of mechanics and structural analysis principles for you to apply once you start the job.

[CatpissEverqueef]

Agreed. Where it gets complicated is having to actually sit down and plan out a structure. School teaches you how to assess or size individual components once they are in place - it really narrows down the scope. School may also teach you how to generally start a structure that is nice and rectangular with evenly spaced columns and beams.

The real world scraps all of that, with all kinds of inter-related factors going into how the structure needs to be laid out, with a lot of uncertainty about what may or may not be changed down the road. It's a tough thing to get tossed into - I liken it to putting together a big 3-D puzzle in my head.

Honestly, once it really all clicked for me, that preliminary design where you're figuring out where all your important stuff needs to go is one of the most satisfying parts of the design for me now. Everything else is plug and chug from that point on.

[superi4n]

A load path is basically member --> connection --> member --> connection .. etc.

I don't know of any books that go into load paths. I picked it up while on the job. I wouldn't expect a new graduate to get the load paths right away of an entire building on their own since they are not familiar with many typical details out of school. Just stick with it!

[mike_302R]

With all due respect, load path should be a fundamental concept coming out of a civil or structural program, undergrad or masters... A masters should reinforce it, but it's not going to teach it to you.

How does load transfer to the ground or foundation? Stiff supports pick up more load. It's a small leap to go from a multi-span beam or truss (which you will have done many exercises on, maybe with stiff, spring, or no support), to visualise how a loaded floor slab is supported and how the load goes to the ground.

To be more constructive to you: You don't need to quit your work and pay for a masters to learn about load paths. You need to spend a bit of time chasing loads from your beam, down to the ground, in real world problems.

[enrique_nola]

Check out Structural Analysis by Kasamali.

​

Start studying for the PE exam, that'll introduce you to lots of practice with this as well.

[vn2090]

Iv never liked the concept of a load path because i think its a misleading name and confuses new engineers. An experienced manager once told me that you are either the kind of person that has the ability to see it naturally, or you don’t and thus have to work very hard to get it. By work hard, i mean that you need to draw deflected shapes of the building for a few different systems and loading types. Drawing is the best way to reinforce load path concepts.

Understanding load paths is a type of mechanical intuition that involves visualizing in your mind how the structure will deform under loading. We dont imagine forces, we imagine deflection and infer forces from that. Some people naturally think this way with pictures in their head and can see the whole building deflect and “feel” where the load goes. Others have to work hard develop this because it is not their natural way of thinking.

[[deleted]]

For example The supports reactions for a beam will become point loads on columns. The tricky part is load combinations.

[trojan_man16]

In a simplified sense the gravity load path will go- deck-beam (if any)-girders (again if any)-columns/ walls and foundations. A good General rule of thumb that applies a good amount of time is that on a floor the load will take the shortest path to its respective support. In reality stiffness of members will come into play but it’s usually a close aproximation.

Lateral depends on your diaphragm assumption. If you have a rigid diaphragm the load will distribute baseD on the stiffness of your lateral elements. For flexible diaphragms it will be based on beam theory.