Seismic Dead Weight of Structures, discussion requested 2

[IJR]

Pals

Seismic Dead weight usually means

1)Design dead wt of structural and nonstructural components
2)some percent of live load

Seismic energy intake depends on this value so much.

But here is an important point from dynamics:

- Seismic energy intake depends on weight that take part fully in earthquake excitation.


one of my concern is thus, shouldnt this weight consider only floor loads, since it is a floor that accelerates with quake excitation in a typical building?

Why should I include weight of vertical elements?

respects
IJR

 

[SlideRuleEra]

In an earthquake everything is the opposite of what seems normal. Inertia "tends" to keep the building stationary - the earth is moving horizontally underneath the building. Of course the building is tied to the earth thru it's foundation and is forced to move - thus the potential for damage as various components are overloaded.

Likewise, when the building moves, the building's contents (live load) also tend to remain stationary because of inertia. However the contents are usually not tied to the structure, or if they are, not very well. As a result, the contents are free "rattle around" inside without really overstressing anything.

http://www.SlideRuleEra.net

 

[whyun]

Vertical elements in the context of seismic dead load consist of exterior cladding and interior partitions. In a multi-story building, these vertical elements are attached to each floor level. In a seismic event, these elements are expected to span between floor levels and upper and lower reactions transfer to upper and lower floor diaphragms.

 

[IJR]

Slide Rule Era and whyun

What about the weight of columns and shear walls?

respects
IJR

 

[WillisV]

Columns and Shearwalls should be include in the seismic mass as they contribute to the intertia of the building system as SlideRuleEra stated. The code is pretty clear on this - IBC states to use the total dead load plus 25% of storage live loads, 10psf for partitions etc, permanent equipment weight, and 20% of snow load in certain cases. (Ref IBC 2003 1616.4.1)

 

[whyun]

I typically include column weight as a part of my dead load.

For shear walls, I consider the weight of the walls perpendicular to the load direction separately and add them to the floor seismic load. Once the seismic load has been distributed to the seismic force resisting elements, I put the weight of the walls parallel to the load direction at the center of wall in addition to the seismic load applied at the floor level. This is for heavy concrete walls only.

I'm not sure if I am making this clear... writing from home... be back next week.