Simple Seismic R-Value Question

[Enhineyero]

For a single storey house with an RC column and steel truss, since the Trusses is pinned at supports, what R-Value is appropriate to use when computing for the seismic loads using UBC'97? if we use R=2.2 (cantilever column)the base shear value will be about 50% of the total Weight. Which I think is very large, considering that a small structure is very stiff.

Also when designing say a small booth or a guard house (2m x 2m) do you still needed to consider seismic design? In my opinion i don't think it is need because it is very small, but code requires us to design it with seismic loads, is it ok to neglect this?

 

[msquared48]

There are no shear walls to use in this "house"?

Mike McCann
MMC Engineering

 

[Enhineyero]

Thanks for replying msquared48, the House or the small structure will just use Brickwall or Masonry wall, we assume the wall (interior and exterior) to be a non-structural component so they act only as loads. The only structural members are RC column, RC beam, and Steel Truss

 

[msquared48]

Depending on how large the "house" is, I would look to a lot more than that.

Is this "house" all steel, concrete and masonry, with no wood? I would add wood shear walls... or reinforced CMU walls where possible.

Also, where I live, a structure under 150 square feet does not need a permit, so you might check your local codes to see if a similar limitation exists. You may not need to provide any calcs for the guard house, particularly if you classify and construct it as a "temporary" structure.

Mike McCann
MMC Engineering

 

[Enhineyero]

We don't usually use wood here because wood is not used here anymore due to environmental issues and its lack of availability in the local market. So we just use RC beam, RC col, and steel truss. The houses are usually around 50-400 sq.meters in plan.

Also for masonry we don't usually design masonry framed structures because of 1st the quality of workmanship during implementation, 2nd The strength quality and lack thereof of masonry materials and its availability in the market, 3rd (and its the lamest) structural engineers were not trained during college to design Reinforced masonry structures (there is not even a subject about masonry).

Going back to the question is really the R = 2.2 really to be used? I don't think it is logical to use 50% of the weight to be use as a base shear value for such a small structure. Thanks again mike

 

[MJB315]

Enhineyero,

Where is your structure being built?

MJB

"We shape our buildings, thereafter they shape us." -WSC

 

[Enhineyero]

Some where in south east asia (highly earthquake active zone), I am a PE there. We follow UBC for earthquake loads, ASCE for wind loads, ACI for concrete design, AISC for steel design. A lot of "structural" engineers here are not well informed on how to compute the correct earthquake loads, there are times that i checked some calaculations where in the use R=8.5 even if their structure is not detailed as with an SMRF.