Earthquakes And Their Effect On Your Foundation

The violent shaking of an earthquake can quickly damage homes, buildings and bridges. The most noticeable damage appears in the walls or roofs of buildings, but building foundations are also effected by the Earth’s sudden movement. Building foundations are usually a poured concrete wall, post and pier construction, or a graded concrete slab. With all of these foundations, an earthquake can easily move a house off its foundation if it has not been properly secured. Foundations can also crack or split with the shaking of an earthquake.

How An Earthquake Effects Foundations? When an earthquake begins, the Earth can lurch with sudden jolts or roll with several waves. A sudden lurch does little to the foundation itself; however, the walls of a building can quickly shift off the foundation. The foundation moves with the Earth back and forth, but the walls are slow to follow and literally break apart at the seams. Even after the ground and foundation have stopped moving, the walls will continue to sway. The ground can also roll during an earthquake. If the foundation of a building is a poured slab, it can easily crack like a cracker. Other types of foundations can also shift with the movement, sending homes sliding off their foundations. Major damage to a foundation is often identified and fixed soon after an earthquake, but attention should also be given to small cracks that can develop into larger problems over time. Small cracks can shift with time due to soil conditions or small earthquakes, so cracks should be measured every couple of months. If cracks widen, then seek the help of a home inspector to determine if the foundation is sound.

Cracks can also allow water into the foundation, enlarging cracks and washing away soil. Small cracks can be filled with epoxy to repel water and make the area stronger. Larger cracks should be inspected before filled. Ways To Prevent Damage After analyzing the earthquake damage in California, officials updated building codes in most earthquake prone areas. These codes require walls to be bolted to the foundation, reducing the chance of buildings shifting off their foundations. You can retrofit your foundation and walls by anchoring them together with either mechanical wedge anchor bolts or epoxy anchors. The concrete of the foundation should be strong enough to hold the anchor. If it crumbles or cracks, it is weak and needs to be replaced. For concrete wall foundations, the bolt should go through the sill plate and into the foundation at least 7 inches. Bolts should be placed within 12 inches of the end of each section sill plate. For post and pier or concrete slab foundations, the building should be bolted to the foundation by using steel brackets. If there are gaps between the sill and foundation, shim the gap and then bolt the bracket in place. Manufactured homes and mobile homes should also be bolted to their foundations along the I-beam.

During 1998’s San Francisco quake, over a 100 mobile homes were damaged when they slid off their supports, but five remained unmoved. Their I-beams had been anchored. Earthquakes damage foundations, but the effect can be lessened with preventive measures.