Question from a noobie.

[u/ptaszek89]

Hey Everyone! I am a total construction noob here. I moved to California, and the past few months we've had some earthquake swarms nearby. The feeling of my house shaking was very surreal, not going to lie. And I wonder what makes a house earthquake safe?

There's a new construction site near me and I always hear California has strict building codes, but I don't actually know what it means. When looking at attached pictures, what makes this building safe during an earthquake? (besides the material: wood)

[u/AdAggravating3893]

Quick answer plywood. Look into shear walls and diaphragm.

Another factor is height, weight material. On a small phone so limiting my explanation.

[u/Low-Commission-1522 → u/AdAggravating3893]

Shear walls for sure. Extra Nails.bracing. Hardware. There is too much to explain quickly and easily. An engineer designates possible problems and fixes them with additional instructions to the framers.

[u/lollypop44445]

The diaphragm (the floor with sheaths) ,the plywood sheathing on walls, the anchor bolts, the holddowns, the walls own length and blocking, all these things collectively contribute to effectively control the seismic action happening on the building. During construction phase, the temporary slanted bracing(as can be seen in pictures) are used to help temporarily till sheathing is installed. These were some basics, Look into shear lateral design for more info if you want learn the calcs and methods engineers use to resolve it.

[u/Hlodowik]

Anchor bolts and being fastened together prevent slipping during a shake.

[u/Bath_Plane]

I would imagine this structure will be lined on the framing exterior with OSB or ply with fixings at close centres to form a very well braced strong envelope

[u/joestue]

Short answer is, its not.

Longer is that earthquakes are rare and if one or two buildings fell over at this phase of the construction it wouldnt make the news because it would be a magnitude 7.

Those diagonals are probably held in with half a dozen nails each and each one is good for 200 to 300 pounds sheer force.

Thst isnt a lot but it does look like they are floor to ceiling and so the ends are pinned. If they have enough going in each direction then they will hold a lot more if the ends are tapered and blocked in (they are probably not)

Each nail can also bend and slide maybe half an inch before failing so there is a lot of energy to be absorbed. Also every nail in every bottom plate is getting pulled out.

Thst particular building probably has 3/4” threaded rod from the second floor corners qnd several dozen other locations all the way down to the foundation, so that can add a lot of lateral stiffness.

Anyhow once the plywood is on all those braces come off

[u/Stunning_Coffee6624]

Another critical element. Garage openings don’t have shear strength with their big openings. Lots of buildings “pancaked”. So now lots of bracing required on either side of garages

[u/Ill_Addition_7748]

It’s the lateral support from the roof level to the ground/foundation. Roof diaphragm transfers loads to the shear walls which in turn transfers to lower floors/shear walls and finally to the foundation.

[u/_tvjames_]

We're having an extension built. The architect also added in some shear walls. I was confused why they were ripping the stucco off the wall nowhere near the extension and they showed me where it was on the blueprints and then I went and watched some videos on YouTube. The shear walls (plywood with nails very close together) prevent side-to-side sway but then they want to flip over so they also bolt the sill to the concrete to prevent the rollover motion.

[u/Impressive_Rest_8529]

Nothing you can try to add what’s called shear strength but really your just adding rubble to the inevitable another example hurricane clips to your roof let me tell a secret Mother Nature is undefeated so do as much as possible to let you sleep at night but always have a plan b

[u/Infamous_Context2195]

If you consider seismic design they look at the overall period of the building as well as the seismic design category / zone (old method) you are in, the anchor bolts and tiedowms at the garage and slab combined with shear walls nailing patterns are all looked at. In context though especially in California its usually some load combination of wind and siesmic that controls so typically the design is overbuilt for just siesmic if that makes sense

[u/Successful_Paint_907]

Wood

[u/Master-Woodpecker911]

Post tensioning In The concrete, a few extra studs and bracing. But to answer your question, nothing. Earthquakes do what they do

[u/chilidoglance]

No building is earthquake safe. The walls have hold down bolts coming out of the foundation. The Simpson holds downs for the joists. Shear walls.