Of all of the Earth’s natural hazards, earthquakes are the rarest. They occur without warning and are impossible to predict. If that was not enough, earthquakes also present the biggest challenges when it comes to translating advances in impact mitigation from the science lab into enforced building codes – even at the highest risk locations.
Modern earthquake engineering really began to move forward with the 1906 San Francisco earthquake. The episode subjected some of the first modern tall building construction to a strong seismic event and drew experts from all over the world to learn. Interestingly Japan almost immediately incorporated these lessons into their building code while the City of San Francisco did not do so until 1948.
In 2011, as a guest of Japanese earthquake experts, I had the valuable experience of participating in a technical survey of the large area of Japan subjected to the Tōkoku M 9.0 earthquake. At the same time I had the historic opportunity of observing U.S. experts learning lessons from this rare event that will influence the introduction of the first tsunami provisions into the next U.S. model building code.
Thus I witnessed first-hand the truth of a universal expression of wisdom with my Japanese colleagues in learning from the rare:
Loosely translated it means I must learn from the lessons of others, because I don’t have enough time to experience them myself.
This post is the first in a series in which I’ll share my firsthand experiences with building codes and try to answer the question, “do they work?” Each post will focus on an aspect of basic earthquake protection and its affect on the intended outcome. Collectively, I hope my posts will simplify for you the overall construction cycle from design to installation.
Before we start, let’s get some ground rules in place. First, for the purpose of establishing performance objectives, earthquakes are lumped into two general categories: The Maximum (rare) and the Design event (most likely). The building code basis of how these ground shaking demands are defined vary somewhat for different regions of the world. The intent underlying the performance objectives are universal and have been carefully selected to establish economically feasible basis of design. These performance objectives are collapse prevention (ultimate) for ordinary buildings and post event operable (serviceable).
Second, we need to dispel the common myth that equates the phrase “meeting code” with “earthquake proof.” This is far from reality (with the possible exception of Japan). The reader may be shocked to realize that earthquake building code performance objectives are based on “death, downtime and dollars.” For a design earthquake, the ultimate, or “life safe”, performance objective is deemed to have been met if no more than 10% of code-compliant buildings collapse. Put another way “meeting code” is not a guarantee that the building will not collapse when subjected to an earthquake that equals or exceeds the basis of code compliance.
The fact is that to keep construction costs manageable, the structural design provisions to meet “life safe” actually create a very low bar. When this is coupled with the uphill challenge of the public policy process required in order to establish a legal basis for enforceable codes, you find we still have a long way to go.
Another common misperception is to assume the prescriptive rules in a model code are actually observed in practice. The reality is that it is challenging to meet these objectives during actual construction. Unless codes are fully adopted into law by the local or national legislative and independently enforced, there’s no guarantee they will be. Especially in competitive markets and in the absence of either public demand or the fear of adverse economic impact.
As Schneider Electric’s Edison Expert for earthquake codes and standards for almost two decades, I’ve had the privilege of working with and learning from some of the world’s top experts in fields of earthquake research, engineering and public policy-making. This exceptional experience has given me the opportunity to witness how state-of-the-art, science-based engineering can bring dramatic and affordable improvements in earthquake survivability.
I hope you will enjoy the series and find it informative. Please feel free to add your thoughts below and I’ll respond to keep the dialog going.