2006 IBC seismic design 4

[fasboater]

I am trying to wrap my arms around this. I am just trying to get a broad over view of the design method. For example this is how I believe it works.

1) SDS SD1
2) Building period
3) Seismic base shear
4) Later force @each story
5) ?
6) ?

I am just trying to make sure I have the procedure correct. Could someone give me a boot in the correct direction?


Thanks for the help..

 

[JAE]

Brief Summary of Seismic Design Steps

1. Determine location of project and find S1 and Ss.
2. Determine site classification (A-F) and get Fa and Fv
factors
3. Determine SDS and SD1
4. Determine Seismic Design Category from S_DS
and S_D1
5. If SDC = A, then use the 0.01w load for E in load
combinations
6. If SDC = B or above, then determine whether
the “simplified method” or standard method is
applicable (simplified is usually for light framed
construction or lower buildings with flexible
diaphragms throughout).
7. Develop the type and layout of the bracing system
8. Determine the R, [Ω]_o, and
C_d factors for the system chosen
9. Calculate a [ρ] factor (reliability factor) based
on number and features of the bracing system.
10. Determine the period of the building
11. Determine the base shear V either from the simplified
or standard methods.
12. Determine the vertical distribution of the base shear
at each level (formula given for each F_x)
13. Analyze the building for deflections and member forces.
using the definition of
E = [ρ]Q_E +/- 0.2S_DSD
in the code load combinations.
14. Determine if P[Δ] effects are required to be
included in the design.
15. Design members
16. Some members such as braces, brace connections,
collectors, diaphragms, moment frames, etc. require
special detailing to ensure ductile behavior – make
sure to work through each individual material
specification such as AISC’s Seismic criteria or ACI
Chapter 21.
17. Check for maximum building drift limits.
18. Design using Fp values for structural components,
architectural, mechanical, and electrical components –
using Fp for E in load combinations as directed in the
code and using [ρ] = 1.0.

Also need to check for torsional application of the seismic demand if applicable.

 

[fasboater]

Thanks JAE that helps.

I guess it would be your number 15, 16 and Torsion that confuses me. I will start with 16.

#16 detailing procedures. I want to make sure I understand this correctly. After I get my design done I go into the applicable code pull out the design info for the connections. (this is not specified in the ASCE)

#15 the vertical design, how do you apply this to a horizontal member?

I understand that you get movement and on a moment connection you will then have to add additional moment to this connection based on that movement. Although for a shear connection will this only add additional shear upward which would essentially counteract the dead load? I am unsure how to apply the load to get maximum loading.

Torsion- This part is driving me crazy. The code calls for accidental torsion, but how do you apply the accidental torsion? What I am thinking is you find the mass center VS the placement for the mass center for accidental torsion and then you increase you vertical loads based on a percentage of the distance between the two centers divided by total length (or width).

Thanks again.

 

[JAE]

Detailing - for steel design, the AISC Seismic Specification pretty well outlines what is required. The theory behind this is that you design all the brittle, non-ductile connections for higher loads (times the omega factor) to ensure ductile failure mechanisms. Same for concrete - more attention paid to beam/column interfaces to ensure a ductile and non-brittle failure. To go into all the details here is impossible. You just need to understand all the specified requirements - again - for steel look through AISC if that is your applicable spec.

#15 - not sure what you mean by "vertical design" in light of what #15 is saying.

Torsion: I think you are close in your understanding. Basically the building codes have specific instances when the application of the story shear is required to be applied at a slight horizontal distance off from the actual center of mass - separately in each direction. This produces either a further, or closer, eccentricity between your center of mass and center of rigidity, which produces horizontal torsion in the floor/roof diaphragm. This then induces higher and lower lateral forces in the braces on each side of the floor system.

 

[fasboater]

# 15, I was asking how your vertival loads are applied in reference to you member design. (I can figure this out though)

thanks, for all of your help.

 

[JAE]

Vertical loads are in the IBC load combination in the form of 0.2(S_DSD.

Vertical distribution of the horizontal base shear is per the IBC - where there is an equation for F at each level of the building.

which are you referring to?

 

[OldPaperMaker]

fasboater,

There is a good article on the Internet, in the April 08 edition of gostructural.com, titled "2006 IBC Section 1605.2.1".
The article outlines, with some examples, what JAE has been describing for you.
Hope that this helps.

 

[prsconsultant]

Follow the link below for very detailed analysis and design examples for seismic design.

http://www.bssconline.org/Design Examples/451chapters.htm