EnhancedFujitaScale

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Slide1:

An Introduction to the Enhanced Fujita Scale Mary Jo Parker March 28, 2007 Aftermath of the Blue Ash Tornado April 9, 1999

Topics to Be Covered:

Topics to Be Covered Limitations of the Fujita Scale Development of the Enhanced Fujita Scale Using the EF-Scale to estimate tornado strength

The Fujita Scale:

The Fujita Scale F0: 45-78 MPH F1: 79-117 MPH F2: 118-161 MPH F3: 162-209 MPH F4: 210-261 MPH F5: 262-317 MPH

Limitations of the Fujita Scale:

Limitations of the Fujita Scale Not enough damage indicators Does not account for construction quality No definitive correlation between damage and wind speed Difficult to apply consistently Overestimates wind speeds greater than F3

Why the EF-Scale was created:

Why the EF-Scale was created More damage indicators Recalibrate winds associated with F-scale ratings Better correlation between wind and rating Less subjective Account for construction variability Flexibility, Extensibility, Expandability The framed house is one of only a few F-scale damage indicators. Evidence indicates a well constructed house can be blown away by winds much less than 260 mph (Phan and Simiu,2003).

EF-Scale Development:

EF-Scale Development Nationally renowned meteorologists and engineers developed the EF scale Texas Tech University Wind Science and Engineering (WISE) Center Developed 28 Damage Indicators (DI) Building type, structure, trees Each DI has several Degrees of Damage (DOD) Range from no damage to total destruction Arranged in order of increasing damage Correlation of F-Scale and EF-Scale wind speeds

Damage Indicators (DI):

Damage Indicators (DI) Residences Commercial and Retail Structures Schools Professional Buildings Metal Buildings and Canopies Towers and Poles Vegetation (Trees)

Degrees of Damage (DOD):

Degrees of Damage (DOD) DOD for a framed house (FR12) – DI #2

Why an upper bound and a lower bound for potential wind speeds?:

Why an upper bound and a lower bound for potential wind speeds? Upper Bound Winds – Design exceeds US building codes for typical home/structure, better than average load path Expected Winds – Design exhibits typical construction Lower Bound Winds – Design fails to meet US building codes, poor maintenance or load path

Construction Load Path:

Construction Load Path Failing Standard Building Code Standard Building Code Exceeding Standard Building Code Photos copyrighted by Tim Marshall The construction quality of the structure(s) will determine whether the wind speeds are shifted towards the upper bound or lower bound values

EF-Scale vs. F-Scale:

EF-Scale vs. F-Scale Wind speeds in mph, 3-second gust

One- and Two-Family Residences (FR12):

One- and Two-Family Residences (FR12) Typical Construction: Asphalt shingles, tile, slate or metal roof covering Flat, gable, hip, mansard or mono-sloped roof or combination thereof Plywood or wood plank roof deck Prefabricated wood trusses or wood joists and rafter construction Brick veneer, wood panels, stucco, vinyl or metal siding Wood or metal stud walls, concrete blocks or insulating concrete panels Attached single or double garage