Do we need to increase the code-required minimum design wind speed now after Yolanda?

The answer to this question is NO, there is no need to provide NEW wind load code requirements for higher wind speeds.


In the NSCP since its 2001 version, 250 kph is already defined as the 50-year return period gust wind speed in Zone I, which includes Bicol, Quezon, and Samar (not Leyte and other areas severely affected by Typhoon Yolanda). For Leyte and the other affected areas except Palawan, it is 200 kph.

This 50-year return period gust wind speed is used for Allowable Stress Design, or Service Limit State Design. In short, under these wind speeds, no damage is expected for properly designed and constructed structures.

Under LRFD, Strength Design, or Ultimate Limit State Design, a 700-year return period gust is equivalently used. This corresponds to approximately 315 kph gust speed in Zone I, and 250 kph in Zone II. At these wind speeds, yielding and some minor damage is expected to occur.

If the gust wind speeds experienced in Leyte during the passage of Yolanda were 315 kph, that makes it a rather rare event. Which doesn't mean it won't happen again. But it might be a little too uneconomical to design structures to withstand such rare events. This maximum gust wind speed experienced in Leyte during Typhoon Yolanda, per my estimation, is a 7,500-year return period one.

There is also no need to increase the wind load code requirements as the code only prescribes the minimum. Individual owners can choose to design for much higher wind speeds, but note that for every increase in wind speeds, there is approximately a twofold increase in wind loads. In some cases, engineers design for 10,000-year return period winds, but that is their choice.

Lastly, note also that most of the devastation is due to storm surges. If it were just blown-off roofs, it would have been a different story.

The answer to the question is NO, we just need to inform people that we have minimum standards for buildings that we only need to follow. A competent engineer will know how to use and how to meet these standards.