Seismic Category / Hazard / Groups / 1,2,3 / A,B,C

[feral9er]

Could someone please delineate clearly in a list format with a small caption above each (if explanation or use or when to use, etc) would be beneficial the following:

Differences in...

1) Seismic Design Categories A - F

2) Seismic Hazard Exposure Groups

3) Site Class

4) Categories of Soil (A - E for good measure)

5) Some other category or class with regard to seismic I'm forgetting


I feel like there is a lot of information dependent on these divisions but that I haven't been able to find a good listing of them nor how to know best when one should apply them, etc. Any thoughts or help here?

[dmentzer]

Could someone please delineate clearly in a list format with a small caption above each (if explanation or use or when to use, etc) would be beneficial the following:

Differences in...

1) Seismic Design Categories A - F See attachment. These are based on the occupancy and the sort period and 1 sec response accelerations from the maps provided in the code. The chart gives you A-D, but for E & F you need to read section 1613.5.6

2) Seismic Hazard Exposure Groups I don't know what a "hazard exposure group" is, but there is a difference between the 2003 IBC, referenced in Ballast, the 2006 IBC occupancy chart. I don't know what happened to the importance factor - perhaps this is now built in to the occupancy categories

3) Site Class Site class is based on soil type. See attachment. Once you have the Site Class, you can determine two site coefficients Fa and Fv

4) Categories of Soil (A - E for good measure). See above.

5) Some other category or class with regard to seismic I'm forgetting


I feel like there is a lot of information dependent on these divisions but that I haven't been able to find a good listing of them nor how to know best when one should apply them, etc. Any thoughts or help here?

It looks like much has been stripped out of the 2006 IBC vs. the 2003 version (used in Ballast) in deference to design in accordance with ASCE 7. With reference to seismic design, 2006 IBC chapter 16 spends most of the time discussing classification of the site, but offers no real "design" methodology. There is no equation like V=Cs * W for base shear in the sections related to seismic design.

A structural engineer could perhaps weigh in? PM? Maybe a Structural Systems veteran could weigh in on how much this may impact the exam content?

[babak-LA]

Could someone please delineate clearly in a list format with a small caption above each (if explanation or use or when to use, etc) would be beneficial the following:

Differences in...

1) Seismic Design Categories A - F

2) Seismic Hazard Exposure Groups

3) Site Class

4) Categories of Soil (A - E for good measure)

5) Some other category or class with regard to seismic I'm forgetting


I feel like there is a lot of information dependent on these divisions but that I haven't been able to find a good listing of them nor how to know best when one should apply them, etc. Any thoughts or help here?

Consider the followings:
first, A to F are general site class definitions
Based on short period (lower height buildings) or taller (high rise buildings) for 1 second period, we choose from table 1613.5.3 for the value of site class coefficient
Then based on the site classifications and according to the proposed type of occupancy from I to IV from table 1604.5, we determine the seismic design category based on 2 factors of occupancy category and the soils classifications for short term or 1 second category calculations.(table 1613.5.6) IBC 2006

[maryj]

dmentzer - that is a thorough explanation (and also an excellent question - I have been feeling the same way).

but to be honest, even when outlined clearly it is difficult to take away concise, useful rules of thumb or 'conclusions' from this series of categories, tables and abbreviations.

[MikePM]

IBC 2006 refers back to ASCE 7-05 for almost all formulas. The formulas are the same as the IBC 2003 version.
Seismic Design Categories:
A - There are not earthquakes here
B - There are only minor tremors here
C - You will feel earthquakes here and there may be minor damage
D - Time to get serious, there will be serious damage from a quake
E & F - You are basically on top of a fault line and only special systems are allowed for construction

Site categories
A & B - Building is sitting on rock
C - good material, most soils in the midwest meet this
D - Default if you don't know what the composition of the soil
E - Strong play-doh, soft clay Houston
F - weak play-doh that turns to mush in an earthquake - Mexico City
Site categories DO NOT relate to proximity to a fault line. Only the amount of movement of the soil due to an earthquake.

Seismic Hazard Group is not longer used. Occupancy category is use to determine the importance factor:
Occupancy category I - who cares if it falls down
Occupancy category II - normal buildings
Occupancy category III - schools, hospitals, water and sewer plants, power generation stations. Stuff that would make life very difficult if we did not have them after an quake
Occupancy category IV - Essential for life safety immediately after an earthquake. Designed to take the impact from a quake and keep going, like the energizer rabbit. Hospitals with ER and surgery suites, police and fire station.

Good luck

[feral9er]

IBC 2006 refers back to ASCE 7-05 for almost all formulas. The formulas are the same as the IBC 2003 version.
Seismic Design Categories:
A - There are not earthquakes here
B - There are only minor tremors here
C - You will feel earthquakes here and there may be minor damage
D - Time to get serious, there will be serious damage from a quake
E & F - You are basically on top of a fault line and only special systems are allowed for construction

Site categories
A & B - Building is sitting on rock
C - good material, most soils in the midwest meet this
D - Default if you don't know what the composition of the soil
E - Strong play-doh, soft clay Houston
F - weak play-doh that turns to mush in an earthquake - Mexico City
Site categories DO NOT relate to proximity to a fault line. Only the amount of movement of the soil due to an earthquake.

Seismic Hazard Group is not longer used. Occupancy category is use to determine the importance factor:
Occupancy category I - who cares if it falls down
Occupancy category II - normal buildings
Occupancy category III - schools, hospitals, water and sewer plants, power generation stations. Stuff that would make life very difficult if we did not have them after an quake
Occupancy category IV - Essential for life safety immediately after an earthquake. Designed to take the impact from a quake and keep going, like the energizer rabbit. Hospitals with ER and surgery suites, police and fire station.

Good luck

Excellent. Thank you all... keep it coming if you have any additional thoughts.

[feral9er]

Occupancy category III - schools, hospitals, water and sewer plants, power generation stations. Stuff that would make life very difficult if we did not have them after an quake
Occupancy category IV - Essential for life safety immediately after an earthquake. Designed to take the impact from a quake and keep going, like the energizer rabbit. Hospitals with ER and surgery suites, police and fire station. NCARB 3.1 practice exam in Lateral forces sample questions says Police Stations are category III. Question #19.

Good luck

Any thoughts or clarification. Technically calls it "Seismic Hazard Exposure Group III". This is the reason I asked this question. Is that the same thing as Occupancy category or a whole new set of "titles". Yuck.

[cberreau]

Looking at both IBC 2003 and 2006, police stations are category IV.
http://publicecodes.citation.com/ico...-P-2006-000019

However, looking at IBC 2000, police stations are category III


This test should be based upon IBC 2006.

[MikePM]

Glad you re-asked the question. There was a change in the code (hard to believe?). In the old code there were "seismic use group", group 3 was called "high hazard exposure structure". building is occupancy category IV were assigned to seismic use group 3.
The 2006 IBC and ASCE 7-05 dropped the "seismic use group". Now the codes use the occupancy category directly for importance factor and seismic design category.
Don't use the 3.1 guide to study seismic to much stuff has changed (My title is an attempt to get others to read this.)

[feral9er]

Glad you re-asked the question. There was a change in the code (hard to believe?). In the old code there were "seismic use group", group 3 was called "high hazard exposure structure". building is occupancy category IV were assigned to seismic use group 3.
The 2006 IBC and ASCE 7-05 dropped the "seismic use group". Now the codes use the occupancy category directly for importance factor and seismic design category.
Don't use the 3.1 guide to study seismic to much stuff has changed (My title is an attempt to get others to read this.)

Yeah... ok - got it. Scary to keep going back and forth.