Structures are commonly designed to withstand an earthquake of certain magnitude, say, the 50-yr earthquake, i.e., that of magnitude recurring once every 50 years. In 1967, I attended a one-week short course taught by the Late Prof. Alfonso Rico Rodriguez, a professional of great stature and experience. Professor Rico had headed a large government agency responsible for a large number of highway bridges in Mexico.

Professor Rico told his listeners that his agency had experienced a 100-yr earthquake during his tenure, and three bridges, out of more than 1000 total, had sustained structural damage. After the earthquake, he gathered his staff for a fact-finding meeting. The staff was prepared to answer questions about the failed bridges. Instead, Prof. Rico reminded his staff that since the earthquake was a 100-yr earthquake, and the design was for a 50-yr earthquake, theoretically, ALL the bridges should have failed. Thus, he wanted to find out why only three bridges had failed.


Old bridge on Pirai river, Santa Cruz, Bolivia

Old bridge on Pirai river, Santa Cruz, Bolivia.