RC detailing

[Enhineyero]

Hi all, here i go again with my simple questions. Why is it that we detail structures with regards to seismic loads? and also we have certain requirements like the SCWB, panel zone shear, etc. for EQ loadings.

How come we dont have such requirements when considering wind loadings, is there such a thing RC wind detailing? because there is such a thing as RC seismic detailing. like those minimum requirements of stirrups, main bars, etc...i know most of these is because of the behavior of RC under seismic events.

Any reply or insight is much appreciated.

 

[Enhineyero]

also We have SCWB, panel zone shear, etc. for EQ loadings. But how come in wind loading we dont have such requirement. even if both are lateral loads...

 

[IDS]

Structures are designed to take the ultimate wind load without excessive yielding. For maximum earthquake loads that is not economic, and in many cases not possible, so members are detailed to have high ductility so that they can absorb the deformations caused by large earthquakes without collapsing.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[PicoStruc]

As IDS said, the specific seismic detailling is there to assure a an energy dissipation mechanism using ductile behiavor at specific plastic hinge locations. This mean that the structure will be damaged.

A lot of specific detailling support local instability that could occur during severe load reversal of an EQ. Rebar local buckling is an example. In that case, the rebar need to be restrained laterrally by seismic hoops because the exposed concrete can spill out during plastic hinge formation or any other unexpected concrete damaging.

 

[Enhineyero]

Thank you for your replies.

@ IDS - Are we not designing structures for the maximum earthquake loads? so you mean that the formulas of UBC/IBC for EQ load does not constitute the maximum earthquake loads (or statistically 1/50 yr theoretical earthquake load) if not, then how much are we designing it with respect to the maximum theoretical loads?

@PicoStruc - as what you have said, the rebar amount that is required by EQ detailing is to provide the structural members energy dissipation mechanism thru ductile behavior, which is focused on the plastic hinge locations. Why is this not required for wind loads? isnt the maximum wind load also require an energy dissipation mechanism as same with the earthquake? because they are both lateral loads. the only difference is that wind load is produced by wind pushing hitting the structure while EQ load is produced by ground motion which will cause the structure to sway (a sway which will be dependent on its mass and inertia).

thanks again for your professional insight

 

[Walterke]

wind=elastic deformation: there will be no permanent deformation when the wind sets.
EQ=plastic deformation: there will be deformation in the structure but it will still stand.

NX 7.5
Teamcenter 8

 

[Enhineyero]

@ Walterke = Isnt it that elastic deformation and plastic deformation is dependent on the amount of loads and structural characteristics of the structural member? and not on the nature of the loads?

 

[PicoStruc]

@Enhineyero

The return period of design wind is about 50 years
The return period of design EQ is about 2450 years (2% excess in 50 Years)

Because the design wind can occur more often, we design elasticly. Wind is not a "extraordinary event" like Earthquake, the energy level is not as high too!

 

[PicoStruc]

@Enhineyero

The type of deformation is dependant of your design capacity versus the load.

If you load is less that the capacity = elastic behiavor

If you load is higher that the capacity, and the rupture Mechanism is ductile = plastic hinge formation and inelastic energy dissipation

If you load is higher that the capacity, and the rupture Mechanism is fragile = Structure collapse

This is why it is important to design shear adequatly.