Can someone please explain the differences, and similarities, between a steel deck concrete roof/floor, and a composite slab/roof? I googled each of those examples, and they look very similar, only that the composite slab/roof (composite decking?) has steel stud that lock the steel deck to the...
Thank you so much for all your replies.
It is a form deck, and not a composite slab. The building is old enough that the original specifications for the form deck is not available anymore, although the profile is clearly visible from below (at about 20 feet high), and the concrete on top of the...
...that you can take the thickness of concrete, multiply by the concreteweight, and then by the numner "3". In my example above, it would be 5"/12*150 pcf * 3 = 187.5 psf. So, the load bearing capacity would be somewhere in the region of 187.5 psf. Does anybody know where this formula came...
...Design Considerations, Page 5-181) provides guides for the depth of fully stressed beams and girders in floors (not less than Fy/800 * Span) and for fully stressed roof purlins (Not less than Fy/1000 * Span).
Also, an article in the Engineer's Notebok section of Civil Engineering (December...
I have got a question about the analysis and design of tapered-section columns, either in a pre-engineered building, or in a steel structure. What is the best way to approach this? What is the theory behind it?
Now, I have done some design for columns for purely axial loads, and for...
I've got a question about when to design torsion in structural members, say steel, but maybe reinforced concrete as well. A colleague of mine was designing structural steel members for bending and axial loads, but not for torsion and was put on the "hot seat" when his calcs were checked by the...
...shear reinforcement , Av min, shall be provided in all reinforced concrete flexural members (prestressed and nonprestressed) where Vu exceeds 0.5 * phi * Vc, except:
(a) slabs and footings;
(b) Concrete joist construction defined by 8.11;
(c) Beams with h not greater than the largest of 10...
...bracing member with an axial load of T. Allowable stress is 0.6Fy. Now the area required for the bracing member will be:
A = T/(Allowable Stress * 0.85)
What is the 0.85 factor in the denominator of the above equation?
Another question is that since my bracing members are all tension-only...
Thanks for the quick responses, JAE and SHBH. Now, if I may expand my question a little bit. There is also the case of compression-only bracing, or struts. These are apparently very common in steel structures. Under what conditions do we specify these compression-only bracing, and is it...
I've got a question about the theory of bracing for steel structures, primarily vertical bracing but it applies to horizontal bracing also. Bracing primarily provides a load path for the lateral loads to be transferred to the foundation by being able to take tension and compression, right?
It...
...to 2.5 might not actually be when when using LFRD. On page 31 of the Design Guide, the required base plate area, a1 req'd. for LFRD is Pu/(phi * 0.85 * f'c). When using ASD, A1 req'd. is OMEGA * Pa/(0.85 * f'c). The note that follows states that: "Throughout these examples, a resistance...
...Method) for axial loads only without any substantial moments. The AISC Manual 9th Ed on Pg. 3-106 provides that t be the larger of or {2m or 2n} * SQRT(fp/Fy). My CERM 8th Ed also states that this is also equal to {m or n} * SQRT (3fP/Fb), where Fb, tensile bending stress, = 0.75 Fy. I am...
Thanks for helping out, people. The discussion and feedback was very useful and I hope, useful, to others, as well. My oversight, as I see it, is to use A, instead of Af, in my calcs. The other parts of the formulas were ok, but discussing and going to and fro about it reinforces the...
...book" as Page 2-30. The formulas on that page for Lu are exactly the same ones that I put in my original question, i.e. Lu as the larger of 20000*Cb/((d/Af)Fy) or rT*(102000*Cb/Fy)^1/2. I got mine from the Civil Enginereing Reference Manul, 8th Ed. though.
Here's my thing, though. I think...
Thanks for the prompt response, 3doorsdwn. No, I am looking for the formula for Lu, which is the maximum unbraced length of compression flange for which Fb=0.60Fy.
Lc is the maximum lengthn of compression flange for which Fb=0.66Fy.
Does anyone know of an accurate formula for Lu, please? I...
...allowable bending stress may be taken as 0.60 Fy.
My Civil Engineering Reference Manual, 8th Ed. on Page 59-3 provides Lu as the larger of 20000*Cb/((d/Af)Fy) or rT*(102000*Cb/Fy)^1/2. However, I think there is a typo in the first equation as I can't seem to get the right Lu.
For instance...
Thanks for all the responses, people. YoungTurk, were you talking more about radius of gyration in general?
For JAE, when you said to include the 1/3 of the portion of the web that is above the neutral axis of the member, did you mean only 1/3 of the top half of the web. The N/A is gnerally...
I am trying to find out how to calculate the term "r subscript T". rT is used in the determination of Lu, which is the maximum unbraced length of compression flange for which Fb=0.60 Fy. In PPI's Civil Engineering Reference Manual 8th Ed on Page 59-3, rT is defined as the radius of gyration of...
jike and shin25, thank you very much for your quick responses. You basically confirmed what I had in mind, but you provided verification of what had been done before and the numbers certainly helped and gave me a feel of what I need to do.
csd72, you brought up a very interesting and important...
I am designing shear lugs for my base plates on my mat foundation. The base plate is sitting on top of the mat foundation and the shear lug and shear lug pocket where they do occur (around vertical bracing areas, primarily) will interfere with the top reinforcement of my mat.
To get a feel of...
