Masonry Magazine December 1994 Page. 26
1.0
Across the street from Cal State Northridge Parking Structure brick chimney stands tall.
Another common failure was the brick chimney. According to the City of Los Angeles, approximately 15,000 chimney failures were recorded within their jurisdiction. Conservatively, this represents about 2% of the masonry chimneys that were exposed to this earthquake. Field observations showed that over 90% of the observed failures were due to non-compliance with the current Code.
These shortcomings included lack of reinforcement, inadequate grouting of the reinforcement and deficient connections of the chimney to the structure. Failures of nonreinforced old chimneys as expected were abundant.
Many connection failures of metal chimneys were reported after the earthquake. Not visible from the exterior, these failures will allow dangerous, hot gasses to escape inside the chimney chase if not corrected.
One of the most visible failures was the Cal State Northridge Parking Structure, a ductile concrete frame system that collapsed at the East and West ends. Opposite the East end of this parking structure, across Zelzah Avenue, are five houses in a row, all with brick chimneys that suffered no damage due to the earthquake.
We must not lose sight of the fact that hundreds of thousands of masonry chimneys withstood the Northridge Earthquake without damage.
A large portion of the old unreinforced masonry buildings within the City of Los Angeles fell within the jurisdiction of Division 88. Division 88 is an attempt to secure the masonry of the old pre-1933 buildings to the roof and floor diaphragms to keep the building from total collapse in the event of a major earthquake. It was never intended to prevent damage to the structure.
Most of these old pre-1933 buildings are economically marginal, therefore, the Division 88 fix had to be cost effective. More elaborate recommendations could have been made in the Division 88 ordinance, at an economic hardship to the public.
Since the retrofitted buildings performed better than those that were not retrofitted, it is reasonable to say that Division 88 was effective.
Reinforced masonry constructed over the past 30 years performed very well in this very significant earthquake. According to the current Uniform Building Code, most buildings are designed to withstand a lateral seismic force of 30% (0.3 g) of the weight of the building and there is no direct design criteria for vertical uplift.
Unreinforced, retrofitted building in Los Angeles heavily damaged without collapse.
2.0
3.0
Below 3.0 felt by very few people.
3.0-3.9 Felt indoors. Vibrations feel like passing light trucks. May not be recognized as an earthquake.
4.0
4.0-4.9 Felt outdoor. Sleepers awakened. Pictures Move. Some