Wind Load Methods
Steel Structures the devastating and destructive power of wind action has been evidenced by recent hurricanes along the Gulf Coast, most especially Hurricane Katrina (2005). When a photo of powerful tornado and hurricane devastation is televised, the demand to ensure that all-steel buildings are as impervious to extreme wind as engineering can provide is never so stark.
The correct structural design for pre-fabricated, pre-engineered steel structures to be resistant to the wind involves bolstering the principle structural elements. As new causations in the results of wind forces in regards to pre-engineered steel structures are revealed, additional structural regulation adjustments are adopted.
There normally is a “design wind speed” that is given in miles per hour for any given area of the country. A precise location will be chosen wherein the resultants are gleaned from the indicator of a maximum “three second wind gust”. The applicable measurement that involves velocity pressure expressed through pounds per square feet required for the steel building is realized by a credited calculation that converts the calculated velocity of the wind. The necessary design wind pressure determinants that will act on a specific structure can then be decided by a method associating the exposure and height of any steel building to the job site ground surface readings.
Severe wind impact investigation evidences that the collapse of wall support and rooftops in a steel building are generally at the rooftop lower edge and corners of the specific steel building system. A larger amount of layout consideration, then, needs to be paid to these areas of the steel structure so that severe wind complications are not a factor. These areas of extreme wind building loading concentrate on a salient corner approach that gives larger strengthening and engineering thought to the 4 corners of any steel structure.
There are several ways that extreme wind forces can weaken a pre-engineered steel building. Sliding is one circumstance. This event commences provided a pre-fabricated, pre-engineered building actually slips off of its base as a whole unit because of the lack of linkage to the foundation caused by wind. Total destruction of the pre-engineered steel building is the most devastating of these failure patterns. This is the total breakdown of the entire structure due to an extreme wind episode that cause the structure to totally fall in upon itself, not unlike a house of cards. A given severe wind episode can produce only a section of the steel building to collapse or fail, ending in damage to building elements. Segments of the wall torn out, garage doors buckled, and also limited roof failure are all representative of what can come about. Rolling over of the pre-engineered steel structure can also result from severe wind destruction. The entire building will turn over as one assemblage due to inadequacies of base connection to the structure and not enough weight load that permits the acute winds to compromise the structure.
For a number of years, it was thought, that when figuring impact on a metal building, that extreme wind should only be articulated as a horizontal quantity. Non-horizontal wind forcing, though, is now required in any estimates.
Pre-engineered steel building forcing of the wind industry technology continues to evolve.