Introduction
The structural deficiencies inherent in hillside homes have caused the deaths of many people in addition to catastrophic losses of property. These photos are pictures of what happened to hillside homes in the Northridge Earthquake in an area that was some distance from the fault. Many homes in the Bay Area, including homes that are brand new, will suffer a similar fate. The Hayward Fault is centered under many hillside homes.
The City of Los Angeles has a special retrofit building code for hillside homes and is the basis of the methods we use in our retrofit of hillside homes.
 Photo 1- the view is why people love hillside homes.
Photo 1 (right) shows why people love hillside homes; the views can be spectacular. Notice the police tape going across the photo. As you can tell by the shadows, this picture was taken late in the day…the next photo (photo 2, below) shows the same location, taken earlier in the day….
Photo 2 - This is what lies down the hill,
past the police tape and beyond the cement
slab that once was a driveway.
Photo 2 (left) is what lies down the hill, past the police tape and beyond the cement slab that once was a driveway. Why is it that this home was completely destroyed in the Northridge earthquake while other homes around it withstood the earthquake forces? The answer to that question was the focus of an extensive engineering study conducted by The Los Angeles Department of Building and Safety and the Structural Engineers Association of Southern California Task Force on Hillside Homes. Their findings were unexpected.
 Photo 3-
Photo 3 (right) - These are the remains of the house that disconnected from the uphill ledger and fell down the hill. Notice the line of trees just beyond the rubble and the debris past the trees.
Photo 4 -
Photo 4 (left) shows the debris beyond the trees….the next door neighbor's house. Notice that the floor diaphragm and roof are intact. All supporting structures are totally destroyed.
 Photo 5-
Photo 5 (right) shows where a concrete slab ripped away from its uphill attachment….possibly the house in the picture shown at the beginning of this presentation.
Illustration 6 -
Illustration 6 (left) illustrates a typical hillside home with hillside hazards. See how the foundation that goes from the top of the hill towards the bottom of the hill is stepped?
These stepped foundations are the reason hillside homes collapse. Normal plywood shear walls do not work on stepped foundations.
 Photo 7-
Photo 7 (right) shows an example of a stepped foundation.
Illustration 8 -
Illustration 8 (left) represents the main floor level for a typical downhill hillside home and the downstairs walls that support it. The vertical lines represent the studs of the downstairs walls sitting on the foundation that secures the house to the hillside. The studs and walls may be those of a living area below the main floor or they may be the studs and shear walls of the cripple wall that supports the main floor.
 Illustration 9-
Illustration 9 (right) This drawing demonstrates the effect of cross-slope forces on a hillside home. The main floor remains secure at an uphill corner then rotates around that point, moving the house away from the hill.
In reality, earthquake forces are generated in all directions; the combined effect is a circular motion that all people living in earthquake country are familiar with.
Illustration 10
Illustration 10 (left) What the researchers found was that in hillside homes, the plywood on the shortest, stiffest shear panel (Panel A in our illustration) absorbed the earthquake forces until it failed. Then the plywood on the next shortest and stiffest panel (Panel B) absorbed the forces until it failed. Then the plywood on the next shortest shear wall (Panel C) absorbed the forces until it failed, and so on, until the house collapsed. The research concluded that in steep hillside homes, shear panels do not work together as one unit but rather work sequentially, one after another, failing one after another until the house collapses.
 Photo 11-
Photo 11 (right) - A photo of a primary anchor bolted built from the previous detail.
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