Please help 1

[Kevin9679]

Hello all,

I am a geotechnical engineer. I just asked my structural engineer friend from back in college about a basic structural-load-calculations question and he chewed me out like I was illiterate. So here's the issue. I want to pass the California Seismic exam. I don't know how to calculate structural loads outside of influence area as taught by Hibbler. I am a relatively experienced geotech engineer, and at my rate there is NOBODY that will tolerate the level of inexperience I have with regards to calculating structural building dead and live loads. I am also not interested in switching disciplines to become a full-time structural engineer.

What are some text books with tons of examples that I can study to get myself up-to-par with regards to calculating building dead and live loads? Obviously I know ASCE 7-16 exists. I'm afraid I might not use it properly. The only chance in undergrad for students to do this type of thing was Senior Design, and I was in charge of several tasks that did not involve this. So please, somebody recommend a text book or a big book of solved problems that is dedicated to calculating structural loads.

Thanks,
Kevin

 

[dauwerda]

I would recommend you take the aei review class found here:

https://www.aei-california.com/courses?field_course_category_tid=29

This course comes with a binder that had all the material you would need for the exam and has multiple examples.
I took their review class for the SE exam and can't recommend them enough.

 

[Kevin9679]

Does it give you many examples of calculating structural dead and live loads? I need to get those basics down first before I move over to seismic.

 

[dauwerda]

You really don't need to be able to calculate dead and live loads for the exam. But what is there to calculate for those? You use actual material weights for dead loads (many common construction assemblies are available in table) and find the required live load in tables based on use of area.

 

[Tomfh]

Yeah, what’s the specific difficulty in calculating dead and live loads?

 

[Ron247]

I think you are confused about what influence lines are. To my knowledge, they are not methods to calculate dead and live loads. Dead and live loads are in the building code. You don't "calculate" them like you would the magnitude of shear or the magnitude of moment in a beam.

Also "tons of examples" won't help as much as just a good explanation of the theories or processes. I do not know of any text that is mostly examples.

 

[Kevin9679]

For example. In The Seismic Design Handbook example 4-2, a structure looks like the sketch I drew and attached.

The weight determination went exactly like this, but I don't understand where these numbers came from. I especially don't understand why after calculating these weights in PSF, the wall weight is multiplied by 6 instead of 12.

Roof level:
Composition roof 9psf
Lights, ceiling, mechanical 6psf
Trusses 2.6 psf
Roof purlins, struts 2psf
Bottom chord bracing 2.1 psf
Columns (10ft, 9in) 0.5psf
Total = 22.2psf
Walls:
Framing, girts, windows 4psf
Metal lath and plaster 6psf
Total 10psf

Total weight and mass:
W = 22.2*100*75 + 10*6*(200+150)

When I say "tons of examples" it's because even if people explain this example to me it might not help me with other examples. If there are books that can explain all this that would be great as well.

See, when I ask structural engineers how about these things they look at me like I'm a dock-builder. Then they tell me to go back to school or I should have learned it in undergrad. But I'm just trying close the gap in terms of my structural engineering fundamentals.

Thanks!
Kevin

 

[STrctPono]

Kevin9679,

The 6 comes from the standard practice of taking half the wall height. When you are calculating your lumped mass per floor, you use the tributary floor height. Since the lumped mass is on the roof for this example, the tributary floor height would be the upper half of the wall. The lower half of the wall goes to the floor below (or foundation).

 

[dauwerda]

That sort of thing is definitely covered in the class I mentioned above. It is put together for someone in your shoes (no structural background). You will find it money very well spent and will learn a lot in the process.

 

[Aesur]

@Kevin9679,

Here is a link to a previous post where I provided a breakdown of many loads: Link

Hopefully this helps.

 

[rb1957]

Sorry, I see no short cuts. I think we all appreciate you're trying to advance yourself, and I think we're all trying to help (in our own way).

I fear there are fundamental gaps in your learning, and these need to be filled first. You can't build a good house on a bad foundation.

I'd suggest going back to 2nd year texts ... seeing what you remember, what makes sense and what doesn't.

Good luck, and success in your endeavours.

another day in paradise, or is paradise one day closer ?

 

[r13]

You have a good friend. Stick with him.

 

[BadgerPE]

To expand on what STrctPono said, the 6 represents 1/2 of the wall height which is the seismic weight assigned to the level in question. This is important in determining how much load the diaphragm delivers to the LFRS.

 

[ATSE]

r13 is right. You have a good friend that gives you the truth - harshly.
You can't stuff years of base knowledge into a weekend bag.
Adjust your expectations. You can do this, with time. You would probably benefit from a structured class on structural fundamentals (no pun intended), with a focus on code application.
Either the class mentioned by dauwerda, or an equivalent. Steve Hiner (in California) has a 30-hour course which is geared for engineers like you.
And in the end, you will be a better GE.

 

[Givemeamoment]

Kevin9679, it sounds like you may be looking for examples relating to tributary areas. For example, if you wanted to find loads onto a column, you'd take the dead and live psf and multiply by the trib area. ASCE 7-10 Commentary on page 343 shows different trib areas for different elements such as columns and beams. Also, Design of Wood Structures by Breyer has a good explanation of dead loads starting in Chapter 2.2. I have the 7th edition but I'm sure any edition will suffice. Then there are practice problems at the end of the chapter, where solutions can be found online. If you can't find the solutions, let me know and I can email you what I found. Best of luck!

 

[Kevin9679]

Hi guys. Don't want to start a new thread but for the same exact sample problem I gave above, I couldn't understand why the stiffness was calculated the way it was.

The N-S direction is the strong axis of the column, and it is an unbraced moment frame. The author took the stiffness as 12EI/L^3, and multiplied it by 24. I assume it's because there are 24 columns.

But in the E-W direction. What I showed above does not accurately depict this but:
the first, third and fifth bay have X-bracing of 1" diameter.
The author does not specify that only one line of frame is braced like this, so I'm assuming all 4 lines are braced (pardon the horrible Structuralese, it had given professors tons of grief in the past). The author takes the stiffness of one brace, AE/L * cos[sup]2[/sup]Θ, and multiplies it by SIX. At first I thought, "Ok, there are three bays with cross bracing, so it makes sense. And because it's the weak axis of the column stiffness is ignored."

But now looking at it again. I might be completely off which is why I need structural engineers to tell me if I'm wrong. But if there were four lines of braced frame, wouldn't they all be counted toward the stiffness? Also, since all six braces are in line with each other, wouldn't the stiffness be calculated differently, and not just added arithmetically together?

Thank you all for your patience.

Kevin

 

[dauwerda]

You have tension only bracing in 3 bays of one line and you have two lines of bracing (outside walls) (this would be much more clearly depicted on an exam and would not be something you have to assume). So, the author found the stiffness of one tension brace then multiplied by 3 for three braces per line and again by 2 for two lines of bracing.

 

[Ron247]

I see what you are looking for. You want the source that says columns are 0.5 psf and "framing, girts and windows" are 4 psf. In the example, the author is probably just creating those numbers themselves. The purpose of the exercise is to apply the loads properly. So what you appear to need is "a source for Dead Loads". Live loads are in the building code.

The following are sources:
[ul]
[li]Back of the AISC steel manual[/li]
[li]"typical dead load values" as an internet search[/li]
[li]other[/li]
[/ul]

Columns are not 0.5 psf in all cases. Real world you would choose a column size, calculate its weight and then divide by the trib area. In other words, you come up with the dead load. Using a 12' tall w10x68 column on a 25'x30' grid would be (68x12)/(25x30) = (816)/750 = 1.088 psf The author created a lot of the values given in the problem.

I created a spreadsheet years ago with different stud sizes/spacing, different drywall thickness etc to calculate wall weights. For example 2x6 pine @ 16" oc with one layer of 5/8" drywall and one layer of 1/8" paneling. The sheet had base values for the materials. The sheet just added them for me because there is no source i know of that is that detailed.

 

[Kevin9679]

I bought the Breyer 8th edition. Amazing that it costs less than the 7th edition. Probably because the professors are still currently using the 7th edition.

 

[moments]

I want to pass the California Seismic exam...
...Obviously I know ASCE 7-16 exists. I'm afraid I might not use it properly.

The CA Civil Seismic Principles Exam, for better or worse, is largely a test of ASCE 7 seismic chapters.

It is not much else than that.

I recommend majorly refocusing your preparation for this test.