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RE: Calculations of Base Shear

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Dear Bobby,
Since the weight of structure (or mass, to be precise) generates inertia forces, when accelerated by an earthquake (or any other dynamic load), the whole mass on a certain level has to be considered (that includes all non-structural elements and sometimes part of the live load).
I hope this do help you.
Tarik R. Berair, PE
-----Original Message-----
From: Jenkins Engineering, Inc. [mailto:jei(--nospam--at)]
Sent: Monday, February 24, 2003 11:55 AM
To: seaint
Subject: Calculations of Base Shear

Greetings and Salutations:
I have managed to get myself confused as I attempt to determine the weight of the structure for base shear calculations.
When determining the weight of a structure for base shear, I understand that the weight for the floor or roof system along with the tributary weight of the walls is "lumped" at each level.
When making this calculation, is the direction of the earthquake force considered?  That is, do I include the weight of vertical elements parallel to the direction of the earthquake force considered?  I have seen discussion elsewhere that indicated wall weight parallel to the EQ force was not included in the base shear calculation and I have seen examples where the total values were determined without regard to force direction - that is - the earthquake force was the same in each direction of the structural system.
What is correct? 

Thanks in advance!
Bobby Jenkins, PE
Jenkins Engineering, Inc.
PO Box 2101
218 S Thomas St  Suite 209
Tupelo, MS  38803
(662) 840.1233 vocal
(662) 840.1103 fax