Figure 6
A two-story house blown away in Zone 9 and located in the vortex (rated as
"total destruction") |
Figure 7
A house blown away in Zone 5 and located in the vortex (rated as "total
destruction") |
Figure 8
A house blown away located in Zone 5 in the vortex (rated as "total
destruction") |
Figure 9
Parts of a house entangled in a tree located in the vortex in Zone 4 (rated as
"total destruction") |
Figure 10
Damage to buildings in a commercial district of La Plata (just west of Zone 4
in the path of the vortex) |
Figure 11
Damage to trees at the east end of Zone 4 (note that the electric pole was just
replaced) |
Figure 12
Survival of a small brick veneer home in Zone 4 in the path of the vortex |
Figure 13
Survival of an old two-story home in Zone 4 located in the path of the vortex
(rated as "finish damage only") |
Figure 14
Survival of an older one-story duplex home in Zone 4 located in the path of the
vortex (note that the diagonal board sheathing attaches to the roof framing) |
Figure 15
Survival of this town house building in the near-to-vortex inflow winds of Zone
4 was marginal in that the roof attachment was severely stressed and some roof
sheathing was lost (the walls were sheathed with foam sheathing and braced at
corners, but party walls located between each dwelling unit for property
separation and fire protection purposes probably contributed substantially to
the resistance of this building) |
Figure 16
Wood members are rarely broken as an initial failure in extreme winds |
Figure 17
Failure of connections to foundation due, in part, to missing or improperly
installed strap anchors (note that a piece of one anchor has sliced deep into
the heel of the boot) |
Figure 18
Foundation block attached to the strap anchor is dislodged and, in other cases,
straps were snapped in two |
Figure 19
Foundation straps not tied to wall bottom plate and spaced too widely |
Figure 20
Failure of proper wall-to-floor connection in two-story home rated as "totally
destroyed" located in the path of the vortex in Zone 3 |
Figure 21
A one-story house rated as "totally destroyed" with properly installed
toe-nails for truss-to-wall connection (Zone 3 in the vortex) |
Figure 22
Proper toe-nail connection of rafter-to-wall (house was "totally destroyed") |
Figure 23
Damage to roof with properly installed tie straps on home in Zone 8 in the
near-to-vortex inflow wind (building rated as "partial collapse") |
Figure 24
Damage to correctly fastened rafter-to-ridge board connection (Zone 3, in the
vortex) |
Figure 25
Staples properly installed in a blown-off piece of plywood roof sheathing
(overall house damage was rated as "partial roof loss") |
Figure 26
Roof uplifted from walls and walls collapsed outward on a home in Zone 10
located in the path of the vortex (note the broken chimney and the mattress
still in the bedroom) |
Figure 27
Upper story walls and roof uplifted from 2nd story floor deck. Engineered rim
board on end of engineered I-joists is also torn off due, at least in part, to
connection issues associated with the use of these materials |
Figure 28
Complete roof loss in Zone 9 on one-story home in the path of the vortex (note
the absence of damage to walls except a blunt impact between the double
windows) |
Figure 29
Front elevation of case study house with damage rated as "partially collapsed"
(see rear elevation). This house was just completed and not sold. It was
located in Zone 8 in the inflow winds within 150 feet of the vortex |
Figure 30
Rear elevation of case study house |
Figure 31
Wind indexed by 90-pound bag of cement rolled along ground for a distance of
about 30 feet as the tornado passed near by |
Figure 32
Gable end wall blow-out which might have been mitigated by lapping of the
interior wall top plate with the exterior wall top plate (hidden from view) |
Figure 33
This home, while similar to the case study home, was in the vortex in Zone 2
and suffered a greater degree of damage (especially racking) though it is still
essentially standing (perhaps due in part to the contributing strength of the
brick veneer which was also severely damaged though still in place) |
Figure 34
Debris damage from tree limb penetrating the wall (7/16" OSB panel bracing at
corner under siding) |
Figure 35
Debris damage to wall from a blunt impact (foam insulation board under aluminum
siding) |
Figure 36
Severe debris damage from a multitude of small projectiles which broke all
windows but where not observed to penetrate walls. Debris source was crushed
rock from a nearby railroad track (Zone 4, in vortex) |
Figure 37
Section of wall (center foreground) thrown a few hundred feet from source
building (center background) in Zone 4 located in the path of the vortex |
Figure 38
Damage to block wall with sill plate still attached but the rest of the
building blown away. (The eccentric load path created by sill strap is evident
and may have contributed to wall detachment from the foundation) |
Figure 39
Concrete foundation wall torn apart and building blown away |
Figure 40
House shifted about 6 feet off block foundation in Zone 4, but house is intact.
The house was fully sheathed with board sheathing that laps to roof framing
(opposite side of home experienced greater damage primarily from debris
impacts) |
Figure 41
Demonstration of structural redundancy of wood frame house - floor is still
supported though main bearing wall is gone. This degree of redundancy in
gravity load resistance, however, is not necessarily present in resistance to
wind uplift. (Note the large oak tree heaved up and strewn several feet across
the yard) |