Masonry Chimneys & Earthquakes

Masonry Chimneys & Earthquakes
From an article about reinforced masonry buildings published in Earthquake Spectra Magazine in 1999
submitted by John Chrysler, Director of the Masonry Institute of America.

Referrence: Klingner, Richard E. 1994. Performance of Masonry Structures in the Northridge, California Earthquake of January 17,1994. Ed. Richard E. Klingner. Technical Report 301-94. The Masonry Society, Boulder, Colorado, June.

PERFORMANCE OF REINFORCED MASONRY BUILDINGS
As a whole, modern reinforced masonry structures, whether single- or multistory, apparently performed well. They showed little or no structural damage, and usually resumed normal functioning soon after the earthquake even in areas of greatest shaking.
PERFORMANCE OF MASONRY CHIMNEYS
The Uniform Building Code and the One and Two Family Dwelling Code give prescriptive requirements for fireplaces and chimneys. These requirements include both minimum reinforcement and bracing requirements. Unfortunately, experience in past earthquakes, such as the 1992 Landers-Big Bear earthquakes, showed that poor construction procedures and lack of adherence to those prescriptive requirements result in considerable damage from ground motion. The Northridge earthquake offered similar lessons.
Reinforcement Requirements
Numerous apparent violations of prescriptive reinforcement requirements for chimneys were observed. Even if these requirements are followed, they may be inadequate because chimney weights and dimensions vary widely from house to house.
In view of the generally satisfactory performance of chimneys that presumably were reinforced in accordance with the current code, which requires a minimum of four No. 4 bars, the current code appears adequate. However, without proper grouting to ensure bonding of the reinforcement to the surrounding masonry, chimneys are susceptible to collapse (Figure 7-12).
For chimneys in high seismic zones, the requirement for rational determination of the amount of reinforcement should also be followed.
Strap Tie Requirements
Examples of leaning and collapsed chimneys were common. In some cases, the strap ties were apparently placed in the chimney but not connected to the house.
No failures were observed for chimneys anchored to houses in accordance with current code requirements. This suggests that unless chimney foundations and reinforcement are designed for cantilever action, strap tie requirements for chimneys should be retained.

The Nisqually Quake And Masonry chimneys a report prepared for FEMA
See especially the "conclusions and recommendations"