In an earthquake, the ground rocks, twists and heaves violently like a bucking bronco, and regular buildings are torn apart. Special building codes are implemented in earthquake-prone regions to minimize the damage from seismic activity. Old buildings may be retrofitted to conform. Homeowners should also ensure that heavy items such as water heaters, furnaces, washers, dryers and refrigerators are strapped down and an automatic safety valve is installed at the gas meter.
Wood Frame Buildings
A frame building is made of wood and is the optimum type of construction to resist damage in earthquake prone areas. Planks are secured to the floor with anchor bolts and the framework of the home is built upwards with wooden planks. Wood and siding panels are attached to the framework with nails and screws, followed by the roof joists and the roof. When an earthquake occurs, the entire structure moves from side to side. Steel framing anchors should be installed throughout the framing to reinforce every joint.
Both homes and high-rise concrete buildings benefit from the construction of shear walls. Shear is the lateral force which causes most of the damage in an earthquake. A shear wall is basically a reinforced or braced wall that should be engineered by a professional. Wood frame shear walls incorporate four main elements: framing members, sheathing, nails and hold-downs. The way these are attached makes it resistant to earthquakes.
Most homes are attached to the footings with anchor bolts. The sill plates or foundation plates should be anchored to the building with 1/2-inch anchor bolts spaced no more than 6 feet apart, according to the Universal Building Codes. One bolt should be 12 inches from each end of each section. The concrete foundation must be solid. Crumbly or weak concrete will not hold the anchor bolts. Mechanical wedge anchor bolts are recommended for areas where seismic movement is prevalent.
Pier Posts and Shear Wall Hold-Down Anchors
After the sill plate of the home has been bolted to the foundation, shear wall hold-down anchors should be installed in each corner. These are attached to the walls with machine bolts through a steel bracket and to the floor with anchor bolts. Shear wall hold-down anchors help to stop the house from overturning. Pier foundations for a raised floor must be reinforced with steel T-straps and sheet metal connectors.
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