Ev factor in seismic design. (1997 UBC)

[PJD]

There has been a lot of discussion in our office about the Ev factor in earthquake design (1997 UBC). Is this factor a horizontal component due to vertical seismic load or is this a vertical load that should be added in a vertical (y direction) manner? Should this component be added horizontally or as some type of vertical impact load?

 

[MarkRPflow]

A good referenece would be the SEAOC ( Structural Engineerins Association of California - Seismology Committee

 

[PJD]

Been there, done that. I just wanted to know if anybody had some common sense explinations.

 

[JAE]

Just came across Eng-Tips and saw your question on Ev factor used in Section 1630 of the 1997 UBC. Initially, we puzzled over it, but soon realized that the E in the load combinations of Section 1612 is not a load in a particular direction, but a load effect, which can include either or both vertical and horizontal loads. Thus, part of E is rhoEh, which is your horizontal seismic demand on your structure. The other part, Ev, is a vertical load and is equal to a fraction (0.5CaID) of the vertical dead load. When you combine your various load cases into a load combination, rhoEh and Ev are included together (as dictated by Section 1612) under E. The difficulty arises in visualizing this from the fact that load cases D, L, Lr, W, etc. are typically either ALL vertical or ALL horizontal. For the 97 UBC, E is a load effect that includes both vertical and horizontal forces.

 

[PJD]

Thanks JAE,<br>
<br>
I hope the 2000 code has more insight into earthquake load E. I have seen engineers place Ev horizontally in combination with Eh and vertically with the DL. Thanks for comments again.<br>
<br>
The most helpful reference I've found is the PCA publication &quot;Design of Concrete Buildings for Earthquake and Wind Loads&quot;. Ghosh explained in a recent seminar, with this manual, that Ev is a vertical component that acts vertically with gravity loads.