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Cherry
Architect
| تاريخ الالتحاق: | الاربعا مارس 23rd, 2005 |
| الموقع: | Boston, MA |
| عدد المواضيع: | 359 |
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كتب: الخميس مارس 24th, 2005 04:42 pm |
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Which one?
Ballast uses V=CvIW/RT
or
ALS uses V=ZICW/Rw.
Thanks!
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Marc Mitalski w/ PREPA.R.E., Inc.
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كتب: الخميس مارس 24th, 2005 09:25 pm |
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Dear Cherry,
The equation offered by the Ballast book is from the 1997 UBC and the equation you have listed from the ALS is from the 1994 UBC. As you are aware some municipalities have adopted the 2000 or 2003 IBC and again the equations and variables for the Seismic Static Force Procedure have changed.
Though the variable symbols have changed over time, what goes into determining the seismic force on your building is still basicallly the same. Each equation can simply break down into Force = Mass x Acceleration or F = ma.
It is important to understand the variables within each of the formulas you presented and then you will see the overlap between them.
For instance the variable W is constant. This is the mass part of the equation within the formular F=ma. So the greater the W (or dead load weight and other weight that needs to be considered per the code) the greater seismic demand forces you will be designing for.
All of the other variables are part of the acceleration part of the formula F=ma......
What about Cv, well this coefficient relates the seismic zone / geographic risk and ground velocities to the site soil conditions (A,B,C,D,E & F).
I, is the Importance Factor. i.e., is you building and essential facility.
T, is the fundamental period of vibration of the building. Depending on the site response spectra, the period of the building will effect the design accelerations.
R, is the response modification factor. This is based on the system you select. In earthquake engineering (as well as other aspects of engineering) we are concerned about ductility, or the ability of a system to dissipate energy beyond the elastic limit. The more ductile the system, the better it should perform (if properly detailed) during a marjor earthquake event. If you compare the 'R' values for various systmes, the greater the R, the better the system is at dissipating energy beyond the elastic limit. In the equations that you presented, you can see that 'R' is in the denominator, thus the greater the response modification factor, the less your design force level will be.
The lower the 'R' value, means that you are working with a system that can not dissipate much energy beyond the elastic limit.
Be sure to compare a concrete shear wall system to a special steel moment resisting frame (SMRF) and see it for yourself. Which one is more ductile?
Sincerely,
Marc
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Cherry
Architect
| تاريخ الالتحاق: | الاربعا مارس 23rd, 2005 |
| الموقع: | Boston, MA |
| عدد المواضيع: | 359 |
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كتب: الخميس مارس 24th, 2005 10:28 pm |
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Thanks, Marc!
I am just curious which formula the exam uses because read ALS first. Their formula is has the first mover advantage. I kept thinking of the UBC 1994 formula, then convert Cv = ZC and R = Rw/1.4, which is definitely not an efficient and rational way to remember things. I do try to relate that bigger R is smaller V, smaller W is smaller V and how the numerator and denominator related. Somehow, somewhere along the line, I kept forgetting to add the T onto the denominator!
Any idea if I have to memorize other formulas like the Vmax and Vmin or Fx formula? Thanks!
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Marc Mitalski w/ PREPA.R.E., Inc.
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كتب: السبت مارس 26th, 2005 07:17 am |
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Dear Cherry,
As noted on Page 31 of the NCARB ARE Guidelines Version 3.0, dated February 2004: '....Candidates should be familiar with the latest edition of one of the following model code series....".
With this in mind, if the UBC is the model code that you are familiar with and the basis of your studying you should probably spend your time with the 1997 UBC equations.
Marc
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architect-to-be
Member
| تاريخ الالتحاق: | الاحد مارس 27th, 2005 |
| الموقع: | Oakland, California USA |
| عدد المواضيع: | 11 |
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كتب: الاربعا مارس 30th, 2005 12:55 am |
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Cherry,
From my experience in the test, I don't think I need to use the base shear equation. All of them are just simple math. There's a question with equation provided. You just need to look up the numbers from a table and apply them in the equation. When is your test? Good luck! 
architect-to-be
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Cherry
Architect
| تاريخ الالتحاق: | الاربعا مارس 23rd, 2005 |
| الموقع: | Boston, MA |
| عدد المواضيع: | 359 |
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كتب: الاربعا مارس 30th, 2005 01:45 am |
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Thanks everyone,
My exam will be this Thursday (less than 2 weeks after my GS exam). It makes me nervous to think that my performance on ALS mock exam wasn't so great. I've got an image of the formulas burnt in my head already even though that's not my intent. I think it helped to paint a picture as I read the question.
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skyhook
Member
| تاريخ الالتحاق: | السبت مارس 15th, 2008 |
| الموقع: | BT Or Bust |
| عدد المواضيع: | 1021 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP | | Describes Me: | support where beam or wall not available |
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كتب: الجمعة أوكتوبر 24th, 2008 11:44 am |
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good stuff
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الوقت الحالي هو 09:19 pm | |
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