Coastal Construction Manual - National Ready Mixed Concrete ...

3 IDENTIFYING HAZARDS
Sparks et al. (1994) investigated the dollar value
of insured wind losses following Hurricanes
Hugo and Andrew and found the following:
Most wind damage to houses is restricted to
the building envelope
COST CONSIDERATION
Even minor damage to the building envelope
can lead to large economic losses, as the
building interior and contents get wet.
Rainfall entering a building through envelope failures causes the dollar value of direct building damage
to be magnified by a factor of two (at lower wind speeds) to nine (at higher wind speeds)
Lower levels of damage magnification are associated with water seeping through exposed roof sheathing
(e.g., following loss of shingles or roof tiles)
Higher levels of damage magnification are associated with rain pouring through areas of lost roof
sheathing and through broken windows and doors
3.3.1.3 Tornadoes
A tornado is a rapidly rotating vortex or funnel of
air extending groundward from a cumulonimbus
cloud. Tornadoes are spawned by severe
thunderstorms and by hurricanes. Tornadoes
often form in the right forward quadrant of
a hurricane, far from the hurricane eye. The
strength and number of tornadoes are not related
to the strength of the hurricane that generates
them. In fact, the weakest hurricanes often
produce the most tornadoes. Tornadoes can lift
CROSS REFERENCE
The FEMA MAT program has published several
MAT reports and recovery advisories following
tornado disasters in the United States.
These publications offer both insight into the
performance of buildings during tornadoes
and solutions. To obtain copies of these
publications, see the FEMA MAT Web page
(http://www.fema.gov/rebuild/mat).
and move huge objects, move or destroy houses, and siphon large volumes from bodies of water. Tornadoes
also generate large amounts of debris, which then become wind-borne and cause additional damage.
Tornadoes are rated using the Enhanced Fujita (EF) Scale, which correlates tornado wind speeds to categories
EF0 through EF5 based on damage indicators and degrees of damage. Table 3-3 shows the EF Scale. For
more information on how to assess tornado damage based on the EF Scale, refer to A Recommendation for an
Enhanced Fujita Scale by the Texas Tech Wind Science and Engineering Center at http://www.spc.noaa.gov/
faq/tornado/ef-ttu.pdf (TTU 2004).
Table 3‐3. Enhanced Fujita Scale in Use Since 2007
EF Scale
Rating
3-Second Gust
Speed (mph)
Type of Damage
EF0 65–85 Light damage
EF1 86–110 Moderate damage
EF2 111–135 Considerable damage
EF3 136–165 Severe damage
EF4 166–200 Devastating damage
EF5 >200 Incredible damage
3-16 COASTAL CONSTRUCTION MANUAL