Steel Proves Its Mettle Under Earthquake Conditions

Studies Demonstrate Steel Provides Safety and Reliability:
Study teams, organized by the American Iron and Steel Institute, have been sent into eight different disaster areas since the Agadir, Morocco, earthquake of 1960. These studies of post-earthquake structural behavior have shown that steel is the safest and most reliable material under earthquake conditions. As a result of these studies, a number of publications have been prepared detailing the success of steel when both buildings and bridges are subjected to earthquakes.

One publication, "Lessons from Earthquakes," concludes that these lessons are fairly simple, but they all point toward steel as the logical material of choice for earthquake resistance. This theme has been followed within AISI, within some of the member companies and more recently in a publication by the International Iron and Steel Institute. The recent Mexico City earthquake also generated an additional publication based on the findings of that earthquake and the lessons learned and re-learned many times before.

The Richter Scale in Perspective:
On October 17, 1989, San Francisco was hit with the first major earthquake since the San Fernando earthquake of 1971 struck the continental United States. Now called the Loma Prieta earthquake to differentiate it from the San Francisco earthquake of 1906, it had a Richter magnitude of 7.1.

The Richter magnitude is determined by measuring ground motion amplitude for specific seismic waves recorded at several instruments. The scale is logarithmic, so that amplitude measured on one of these instruments during an earthquake of magnitude 8 is ten times the amplitude of magnitude 7 and 100 times the amplitude of magnitude 6. In energy terms, an earthquake of magnitude 8 radiates 30 times the energy of an event of magnitude 7 and 900 times the energy of an event of magnitude 6.

To put the Loma Prieta earthquake in perspective, a 7.0 earthquake is a weekly occurrence in the world, 8.0 is an annual occurrence and 6.0 is a daily occurrence. We have many earthquakes; many of them occur in sparsely populated rural areas of the world and receive little public attention worldwide.

Construction Quality, Building Code Enforcement and Steel Make the Difference:
Obviously, the most serious concern of any earthquake is its ability to cause death and destruction. Comparison by damage is difficult, because no two places on earth are really alike in terms of geology, construction type and economic base. In the Loma Prieta earthquake (Richter 7.1), there were 64 fatalities. In the San Fernando earthquake of 1971 (Richter 6.4), there were 58 fatalities. In the Mexico City earthquake of 1986 (Richter 8.1, but over 300 miles distant) unofficial estimates place the death toll at between 20,000 and 24,000. In the more recent Russian Armenia earthquake of 1988 (Richter 7.0), the Russian government admits to over 25,000 fatalities.

Clearly, something is different between the effects of earthquakes in this country and in other places around the world. The reason is quite simple: We have a substantially higher level of construction quality through the enforcement of well-engineered building codes in some parts of the country--and California is one of those parts. These building codes do not allow the use of unreinforced masonry or lightly reinforced concrete. They do require more steel in all types of construction. The bottom line is more steel is required to make a structure seismically resistant, regardless of the type of construction.

Need To Extend Codes Beyond West Coast:
We know that the codes of California (and many other Western states) seem to be adequate to protect most of the population from the ravages of an earthquake. But what about the rest of the country? Unfortunately, east of the Rocky Mountains most of our building codes are not adequate for earthquake conditions. Nor are we prepared in terms of our design experience, construction expertise, or public perception of an earthquake's potential for catastrophic damage.

There is no question about the likelihood for an earthquake: One will strike, and it is likely to happen near a major metropolitan area. One of the problems that we face in the East is that the seismic track record is based on relatively infrequent occurrences in relatively old rock formations and under relatively heavy soil covers. We don't even know what to be afraid of, when it will occur or its potential magnitude.

The eastern United States is relatively unprepared for the eventuality of a significant earthquake, with many building codes presently containing outdated seismic provisions. Through the efforts of AISI and others, those building codes are now considering much more up-to-date provisions which, if used, should greatly reduce loss of life and structural damage. The key, however, is getting local jurisdictions to adopt these new provisions. New York City is presently upgrading its seismic code, and Boston, Massachusetts, and Charleston, South Carolina, require seismic design; but many others, such as Memphis, Tennessee, downgrade the problem. Owners and developers need to become aware of the advantages of good seismic design and the benefits of steel is providing seismically tough buildings.

Loma Prieta Reinforces Previous Lessons:
AISI sent a team to California to investigate the Loma Prieta earthquake. Although the data are still under study, it is likely that few new lessons will be learned--just a reinforcement of those that had been observed many times before.

From both Loma Prieta and earlier earthquakes is coming a definite common message: Simply but accurately stated, steel is the only construction material that imparts safety and reliability to a structure--any structure. For steel, the product range includes structural shapes, plates for bridges, cold-formed members of metal buildings, straps and ties for timber construction, reinforcing bars and even prestressing strand for concrete construction.

The issue is not one of material competitiveness; it is not even an issue of whether or not steel construction is better than other construction materials. At issue is the basic concept that steel is essential to seismic safety no matter what other medium is used in construction. Steel, and only steel, is the common denominator for seismic resistance and the resulting benefits of life and safety.

Bridge Name	Type of Damage	Status	Construction
Nimitz Freeway I-880	Total Collapse	Closed	Concrete
Bay Bridge	1 Span Collapsed	Opened 11/18	Steel
China Basin I-280	Severe Cracking Several Columns	Closed	Concrete
Embarcardero Freeway I-480	Severe Cracking Several Columns	Closed	Concrete
Struve Slough US-1	Complete Collapse	Closed	Concrete
Distribution Structure I-980	Spalled Column -Deformed Outrigger Bent	Opened 10/23	Steel & Concrete

The California Department of Transportation reported major damage to 25 bridges and tunnels and minor damage to 64 bridges. It is important to note that while there was some damage to steel bridges, the majority of damage was caused by inadequate concrete column detailing. All steel bridges were back in service one month after the earthquake. However, the same cannot be said of concrete bridges.