Masonry Magazine June 2009 Page. 36
At a Glance The Seismic Progress of Masonry
Since 1900, there have been 54 recorded earthquakes in California with a magnitude of 6.0 or greater. Sixteen of the 54 have had a magnitude of 7.0 or greater, with the 1906 San Francisco Earthquake topping the list at a magnitude of 7.8. In the first three months of 2009, 29 earthquakes measuring greater than a magnitude of 3.0 are documented. Are we ready for the Big One?
The big transition came after the 1933 Long Beach Earthquake, which made unreinforced masonry in high seismic areas obsolete. Since then, we have refined code requirements based on masonry performance in subsequent earthquakes.
The 1971 Sylmar-San Fernando earthquake showed that wall-to-roof connections were inadequate, causing a number of roof collapses. Fortunately, this event occurred at 6 a.m., outside of normal work hours, keeping the death and injury toll low. Stringent connection requirements were implemented in the code and tested in the 1994 Northridge earthquake.
The Northridge event measured unanticipated ground accelerations. Instrumentation at the Cedar Hill Nursery in Tarzana measured an east-west ground acceleration of 1.78g, far in excess of anticipated accelerations. Northridge also revealed a vertical component, or upward thrust, to earthquakes. When comparing the measured ground movements to engineering design criteria, one would expect an inordinate amount of catastrophic damage. That did not happen, since masonry has a high factor of safety and redundancies within the system.
plastic snap-on pieces, but height was a problem in the joint, and it added an extra step for the mason by having to install an extra part. With spacing at 16 inches on center horizontally and vertically, costs of the system increased significantly in labor and parts with the plastic piece. Wire-Bond also tried welding continuous straight and cut wire
While damage was widespread in the Northridge earthquake, it is significant to note that of the 57 fatalities, not one was attributed to masonry. Was that good planning, or luck? Perhaps it was a little of both.
One must understand that the primary purpose of the Building Code (IBC Section 101.3) is life safety. That means that during any catastrophe, including earthquakes, hurricanes or tornados (to name a few), the occupants should be able to exit or find a safe haven within the building to avoid death and injury. When this happens, the code has successfully served its purpose.
Today's building codes and reference documents offer a balanced approach of cost versus performance. The West Coast is seismically active and must take that reality into consideration. The marriage of deformed reinforcement into a grouted masonry system is an accepted code reality. Designers are aware of the requirement and prepare project documents accordingly.
The quality of masonry installation can vary widely. While most contractors are quality conscious, occasionally, a poor representation of installed masonry may exist. That is, someone has taken unacceptable shortcuts in building the project.
Chapter 17 of the International Building Code and the reference standard, Building Code Requirements for Masonry Structures (ACI 530-05/ASCE 5-05/TMS 402-06) and Specification for Masonry Structures (ACI 530.1-05/ASCE 6-05/TMS 602-05) address this issue with inspection requirements. Essential facilities, such as hospitals and police stations, located in high-seismic areas, must be inspected by an independent observer to
to the hook, but the welding accuracy could not be achieved to meet the ACI 530 specification.
A welded metal clip that provided a continuous channel was the answer. The Wire-Bond welded clip consists of a 14-gauge, flat steel part with a lip that is tack welded to the back of the 3/16-inch adjustable hook (Figure 2). The curled lip
SUSTAINABLE MASONRY
THE TOTAL SYSTEM APPROACH
21st century masonry walls have become more complex with stricter code requirements, demands for increased energy efficiency and more creative designs. The need has developed for systems or groupings of products that will function together and that have been tested to assure their compatibility and effectiveness.
Hohmann & Barnard is leading the way with complete systems for various wall types that include all of the required accessories for your project. Our extensive field experience along with testing at our R&D lab allows us to offer complete systems of complementary and compatible products to give designers, contractors and building owners peace of mind. To find out more, or to determine a system specific to your project needs, please go to www.h-b.com/MM609
Hohmann & Barnard manufactures HB-200-X from 50% recycled material. Steel wire products are a minimum of 95% recycled material.
1. H&B HB-200-X ANCHOR & PINTLE
2. H&B TEXTROFLASH LIQUID AIR & VAPOR BARRIER
3. MORTAR NET
4. H&B TEXTROFLASH GREEN (SHOWN SURFACE-MOUNTED)
5. H&B TERMINATION BAR
6. H&B QUADRO-VENT
7. H&B FLEX-FLASH DRIP EDGE
B. H&B TRANSITION MEMBRANE
"EASILY ADAPT HB-200-X FOR SEISMIC ZONES BY ADDING AN
H&B SEISMIC HOOK & CONTINUOUS WIRE