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Hurricane Resistant Buildings – Design and Materials
Posted on October 11th, 2016 by Dr. Sina Ebnesajjad in Chemical Manufacturing Excellence
In October of 2016 Hurricane Matthew made its arrival felt on the East Coast of America, hitting the states of Florida, Georgia and South and North Carolina. Several deaths and many billions dollars of damages occurred as a result of Matthew. The loss of life and property among the millions of people affected could have been even higher. A multitude of factors are credited for the relatively limited loss of life and material damages (one life lost is too many). One of those factors is the laws passed by coastal states, over decades, requiring enhancement of housing construction codes. The construction codes have altered the way new residential buildings are constructed so that they would withstand the high winds and forces of hurricanes.
American Society of Civil Engineers publishes the standard ASC-7, titled Minimum Design Loads for Buildings and Other Structures. ASC-7 provides requirements for general structural designs, which are suitable for inclusion in building codes and other documents. It also reflects improvements made over the years in the design of buildings to withstand hurricanes.
There are three main issues affecting a house during a hurricane. Strong winds, battering rains and ocean water swells. Wind speed reached up to 193 km/hr (120 miles/hr) during the category 3 Hurricane Matthew. Hurricane Katrina, Category 5, blasted the US Gulf Coast with winds approaching an astounding speed of 280 km/hr (174 miles/hr) in August 2005. Nearly, 2000 people perished, many as a result of slow and insufficient assistance by the US Government. The total cost of damages to the states of Louisiana and Mississippi exceeded $150 billion.
Driving rain can easily enter a structure, if special measures have not been taken to render the building waterproof. The water leak due to rain is a minor problem compared to the ocean water driven ashore into inhabited lands. Basements start to flood followed by the first floor and even higher stories. That was a particular problem in New Orleans during Hurricane Katrina because the city is built on land below sea level. It is protected with levees that continuously channel water out of the city. Those levees broke because they were only designed to withstand category 3 hurricanes.
One strategy for building hurricane resistant houses in coastal areas that are above sea level, albeit a few feet, is to put the house on steel and concrete pillars (Figure 1). The pillars supporting the house are 46 cm (18 in) in diameter and driven 3 meters (10 feet) into the ground. A 10 cm thick concrete slab and 60 cm concrete beams link the underground columns supporting the house. Reinforced concrete columns, each with a cross-sectional surface area of 930 cm2, lift the house 7.6 meters above ground. The house may be built from wood as long as each piece is secured using metal straps. The entire wooden structure must be bolted to the concrete columns. Finally, the roof is secured to the house fame with metals straps and the shingles attached to the substructure using 15 cm (6 in) nails.
Reinforced windows and doors are installed to withstand the raindrops battering the house. It is usually a requirement to install 240 km/hr (150 miles) tested windows in hurricane prone areas. These windows should have plastic panes, shatterproof glass or glass with protective membranes (impact glass). The windowpanes must be more firmly attached than normal windowpanes, possibly even using screws or bolts through the edges of larger panes. Hurricane shutters are installed on windows and doors to provide effective protection, generally windows, doors, and other openings are usually the weakest points in a building and are susceptible to collapse by high wind pressure and gusting debris (Sources: Builder’s Guide, www.buildgrenada.com/built-to-withstand-hurricanes.html).
All opinions shared in this post are the author’s own.
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Dr. Sina Ebnesajjad
President at FluoroConsultants Group, LLC