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 Title Page
 Abstract
 Introduction
 Narratives
 Conclusions
 Recommendations
 Acknowledgement






Group Title: UFL/COEL (University of Florida. Coastal and Oceanographic Engineering Laboratory) ; 90/002
Title: Water and erosion damage to coastal structures
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Permanent Link: http://ufdc.ufl.edu/UF00076131/00001
 Material Information
Title: Water and erosion damage to coastal structures South Carolina Coast, Hurricane Hugo, 1989
Series Title: UFLCOEL
Physical Description: 25 leaves : ill. ; 28 cm.
Language: English
Creator: Wang, Hsiang
University of Florida -- Coastal and Oceanographic Engineering Dept
Publisher: Coastal & Oceanographic Engineering Dept., University of Florida
Place of Publication: Gainesville Fla
Publication Date: 1990
 Subjects
Subject: Flood damage -- South Carolina   ( lcsh )
Soil erosion -- Atlantic Coast (U.S.)   ( lcsh )
Hurricane Hugo, 1989   ( lcsh )
Structural failures -- South Carolina   ( lcsh )
Coastal and Oceanographic Engineering thesis M.S
Coastal and Oceanographic Engineering -- Dissertations, Academic -- UF
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by Hsiang Wang.
General Note: "March 1990."
Funding: This publication is being made available as part of the report series written by the faculty, staff, and students of the Coastal and Oceanographic Program of the Department of Civil and Coastal Engineering.
 Record Information
Bibliographic ID: UF00076131
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: oclc - 22469124

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Table of Contents
    Title Page
        Title Page
    Abstract
        Page 1
    Introduction
        Page 1
        Page 2
        Page 3
    Narratives
        Page 4
        Page 3
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
    Conclusions
        Page 23
        Page 22
    Recommendations
        Page 23
        Page 24
        Page 25
    Acknowledgement
        Page 25
Full Text




UFL/COEL-90/002


WATER AND EROSION DAMAGE TO COASTAL
STRUCTURES SOUTH CAROLINA COAST,
HURRICANE HUGO, 1989






by


Hsiang Wang


March 1990









WATER AND EROSION DAMAGE TO COASTAL STRUCTURES
-SOUTH CAROLINA COAST, HURRICANE HUGO, 1989



ABSTRACT


Hurricane Hugo hit U.S. Mainland on September 21, 1989
just north of Charleston, South Carolina. It was billed
as the most costly hurricane on record. The loss on the
mainland alone exceeded 7 billion dollars, more than
15,000 homes were destroyed and the loss of lives
exceeded forty.

This article documents one aspect of the multi-
destructions caused by the hurricane the water and
erosion damage on water front or near water front
properties. A general damage survey was given first,
followed by assessment on the performance of various
engineered and non-engineering structures, on the major
factors contributing to failures. Conclusions were then
drawn with recommendations for future improvement.


INTRODUCTION


One of the facets that sets Hugo apart from other
hurricanes in recent years was its severity of inflicting
water damages on coastal constructions. It could easily
be ranked one of the worst, comparable to Hurricane
Camille in 1969 which was the only category 5 hurricane
that hit U.S. mainland (along the low land region of
Louisiana and Mississippi) with full force in this
century. A number of factors contributed to the great
destruction:

1. The extremely high storm surge level, second
only to Hurricane Camille in the history.

2. The high density of old structures constructed
before adequate building code and code enforcement.

3. The high chronicle background erosion along
these barrier islands (approximately 6' per year).

Damage reconnaissance was carried cut at selected
locations from Seabrook Island to North Myrtle Beach, an
arc of about 120 miles coastal belt affected by Hugo.









WATER AND EROSION DAMAGE TO COASTAL STRUCTURES
-SOUTH CAROLINA COAST, HURRICANE HUGO, 1989



ABSTRACT


Hurricane Hugo hit U.S. Mainland on September 21, 1989
just north of Charleston, South Carolina. It was billed
as the most costly hurricane on record. The loss on the
mainland alone exceeded 7 billion dollars, more than
15,000 homes were destroyed and the loss of lives
exceeded forty.

This article documents one aspect of the multi-
destructions caused by the hurricane the water and
erosion damage on water front or near water front
properties. A general damage survey was given first,
followed by assessment on the performance of various
engineered and non-engineering structures, on the major
factors contributing to failures. Conclusions were then
drawn with recommendations for future improvement.


INTRODUCTION


One of the facets that sets Hugo apart from other
hurricanes in recent years was its severity of inflicting
water damages on coastal constructions. It could easily
be ranked one of the worst, comparable to Hurricane
Camille in 1969 which was the only category 5 hurricane
that hit U.S. mainland (along the low land region of
Louisiana and Mississippi) with full force in this
century. A number of factors contributed to the great
destruction:

1. The extremely high storm surge level, second
only to Hurricane Camille in the history.

2. The high density of old structures constructed
before adequate building code and code enforcement.

3. The high chronicle background erosion along
these barrier islands (approximately 6' per year).

Damage reconnaissance was carried cut at selected
locations from Seabrook Island to North Myrtle Beach, an
arc of about 120 miles coastal belt affected by Hugo.










Based upon visual inspection, the severity of water
damages was subjectively determined, shown graphically
in Figure 1.

WATER DAMAGE RESULTS IN SOUTH CAROLINA


FLORENCE


COLUMBIA


SN. MYRTLE BEACH

MYRTLE BEACH
SURFSIDE BEACH
GARDEN CITY '11 FIf !


ORANGEBURG


F1


oC,


17 F
OF PALMS


Figure 1: A General Assessment of Water Damages Along
Coastal Region Under the Influence of Hugo (Surge and
Wind Information From Federal Insurance Administration,
1989).

Table 1 tabulates the percentage of destructed beach
front structures along the barrier coast. The destructed
structure is defined as the structural damage is greater
than 66.67%.


Table 1 Percentage of Destructed Beach Front Structures


Surfside
Garden City
Pawleys Island
Folleys
Others


43%
23%
20%
7%


* Source of Information, South Carolina Coastal Council


LEGEND
m Severe Water Damage
i Considerable Water Damage
Li Ught Water Damage









The descriptions of these damages are given in the
following sections.


NARRATIVES


Seabrook Island

The heavily developed portion of this island is a planned
resort community of town houses and multi-unit
condominiums. The Island is obviously under erosional
stress and portion of it is heavily armored with newly
placed revetment. Both wind and water damages were
light. Structure damages were limited to a few broken
windows, missing roof shingles and up-rooted chimneys.
The revetment structure showed differential settlement
at a few locations with torn filters, thus, exposing the
bank soil.

The damage was light in despite of its exposed location.
This was mainly because the Island is located at the
southern fringe of the Hurricane path. The storm surge
never reached the structures. Wave overtopping was also
minimal.

Folly Beach

Folly Beach is on the barrier island south of Charleston.
It is mainly a residential community. The only
substantial commercial building fronting the beach is the
Holiday Inn at the middle section of the island. The
beach is under very heavy erosional stress for lack of
sand supply from the north. In fact, part of the street
system, West Arctic Avenue, crumbled into the sea within
the last decade. A restaurant built 20 years ago on
Arctic Ave was hanging over water before Hurricane Hugo
and it was subsequently completely demolished by the
Hurricane. Many houses on the west side of the town
still have addresses of West Arctic street that no longer
existed. The beach is narrow and low and is almost
entirely covered with groins and revetment of marginal
quality.

The measured storm surge levels were around 12 feet,
slightly lower towards the two ends. The east and
central sections of the island sustained severe water
damage. Many single family homes fronting the beach were
conmpetely destroyed. First floor flooding was common
in the second tier and to a much less extent in the third
row and beyond. Damages due to dynamic force and static
buoyancy were both evident as some structures were
crushed and the others were simply floated off their
foundation. The most devastated section was between West
3









2nd Street and West 7th Street. This was because many
old structures built 20 years ago were clustered in this
section. -his section was also eroded heavily in the
past years and,as mentioned earlier, had lost roads to
the ocean. Amid this devastation, however, well
constructed dwellings did survive and survived well. The
house shown in Figure 2, for instance, escaped with
hardly any visible damage among a row of completely
destructed houses.


I,;
*- A i


Figure 2: A Concrete Residential Structure on Folly
Island Survived With No Damage Amongst Heavy
Destruction.









The descriptions of these damages are given in the
following sections.


NARRATIVES


Seabrook Island

The heavily developed portion of this island is a planned
resort community of town houses and multi-unit
condominiums. The Island is obviously under erosional
stress and portion of it is heavily armored with newly
placed revetment. Both wind and water damages were
light. Structure damages were limited to a few broken
windows, missing roof shingles and up-rooted chimneys.
The revetment structure showed differential settlement
at a few locations with torn filters, thus, exposing the
bank soil.

The damage was light in despite of its exposed location.
This was mainly because the Island is located at the
southern fringe of the Hurricane path. The storm surge
never reached the structures. Wave overtopping was also
minimal.

Folly Beach

Folly Beach is on the barrier island south of Charleston.
It is mainly a residential community. The only
substantial commercial building fronting the beach is the
Holiday Inn at the middle section of the island. The
beach is under very heavy erosional stress for lack of
sand supply from the north. In fact, part of the street
system, West Arctic Avenue, crumbled into the sea within
the last decade. A restaurant built 20 years ago on
Arctic Ave was hanging over water before Hurricane Hugo
and it was subsequently completely demolished by the
Hurricane. Many houses on the west side of the town
still have addresses of West Arctic street that no longer
existed. The beach is narrow and low and is almost
entirely covered with groins and revetment of marginal
quality.

The measured storm surge levels were around 12 feet,
slightly lower towards the two ends. The east and
central sections of the island sustained severe water
damage. Many single family homes fronting the beach were
conmpetely destroyed. First floor flooding was common
in the second tier and to a much less extent in the third
row and beyond. Damages due to dynamic force and static
buoyancy were both evident as some structures were
crushed and the others were simply floated off their
foundation. The most devastated section was between West
3









It is a frame structure with four concrete columns seated
on four 14" square piles. By discussing with the design
architect and the County building inspector, it is
concluded that this structure fared so well for a number
of reasons:

1. Sufficient elevation (bottom of support beam at
elv.15 feet MWL).

2. Deep and strong pilings (22 feet plus 5 feet
tip).

3. Simple and strong connections.

4. Low profile and low roof line.

5. Very rigid main columns.

Further west of West 7th Street, the water damage became
progressively lighter but noticeable. The structures in
this section were usually newer with higher elevation and
better construction. The west end of Folly Beach is the
County Park where only wind damage was noticeable.

The Holiday Inn is the only substantial commercial
building along the open coast. It is a relatively new
construction, built about 5 years ago. The building is
at an exposed location with receding shorelines on both
sides. The front is protected by a retaining wall and
heavy revetment. The building, nevertheless, sustained
heavy water damage. Practically all the ground floor
facilities were destroyed (Figure 3).

Erosion behind the retaining wall was significant,
causing concrete deck to collapse and undermining the
swimming pool. The seawall cap was partially destroyed
due to wave impact. The water damage was certainly
heavier than one would expect for structures of this type
built in such a recent date. A number of contributing
factors are listed here:

1. The elevations of the structure as well as the
protective seawall are inadequate for the surge level.

2. There is no fronting beach to dissipate wave
energy, causing heavy wave runup and overtopping.

3. The structure protrudes beyond the adjacent
shorelines and there is no return wall to protect its
flanks.





























Figure 3: Photo Shown Water Damages to the Ground Level
Units and Water Front Amenity Facilities at Holiday Inn,
Folly Island, a Typical Damage Mode Among High Rise
Hotels and Condominiums.

Charleston and its Vicinity

City of Charleston and its surrounding areas including
Mt. Pleasant and James Island, water damage to structures
related to flooding was minor compared with wind related
damage(including rain water damage due to broken windows
and open roofs. The battery along the southern tip of
town provided adequate protection of city streets and
river front buildings. Hurricane Hugo was a relatively
dry hurricane; heavy rain fall did not occur until two
days later. Thus, river flooding was not a major factor.
High water level in the creeks, intercoastal water ways
and rivers combined with high wind did cause extensive
boat damages. Numerous boats were thrown off water
landed on shore and streets.

Sullivan's Island and Isle of Palms

Sullivan's Island and Isle of Palms belong to the same
barrier island chain separated by Breach Inlet. They
have a combined length of about 11 miles with the major
axis oriented in the east-west direction. The only
access to the mainland is Highway 703 via Ben Sawyer
Memorial Bridge. This bridge has a rotating section in
the center span for boat traffic. This section was
severely damaged by wind during Hurricane Hugo that the
bridge was closed for more than 10 days.









On Sullivan's Island, the storm surge level was estimated
to be about 13 feet above mean sea level whereas on Isle
of Palms, the level was about two feet higher reaching
15 feet. The all over water damage was extensive on both
islands but the sDacial distribution was rather uneven.
As the dominant wind direction at the height of the
hurricane was northeasterly the damage was less severe
on the western end of Sullivan's Island. This section
was also benefited by the wide beach. The sand overwash
onto the streets was substantial. The damage east of 703
was very extensive and became progressively worse towards
the Breach Inlet. Older houses on Marshall Blvd. were
practically all destructed, some crushed by waves and the
others floated off their foundation. These older houses
were mostly constructed on shallow piles, piers or slabs
with elevation around 12 feet or less. After the
Hurricane, many of the damaged houses were raised to 14
feet or higher. A significant number of houses on the
second row across the Marshal were also have to be
condemned due to water damage. The bridge across the
Breach Inlet sustained erosion at the west end but the
bridge was not threatened. The jetties fared well.

Some of the newer constructions with adequate elevations
and pilings did survive even at very exposed locations
east of 29th Street. The types of damages typical to new
constructions are:

1. Erosion and scouring causing decks, pools and
slabs to collapse.

2. Deck structures with access ladders or ramps to
the beach front. These type of structures would
invariably collapse, slamming onto the main
structure, causing extensive damage.

On Isle of Palms, severe damages were concentrated in two
regions; one was in the commercial strip between 10th
Avenue and 14th Avenue and the other was east of 42nd
Avenue to 57th Avenue. The sections west of 9th and
between 14th and 42nd, the damage was less severe. This
appeared to be directly related to the beach width in
front of the structures.

The Sea Cabin Condominiums at Ocean Blvd. and 14th Avenue
sustained heavy water damage. The entire complex was
prefabricated modular units seated on pile foundation.
The ground units and the end unit were completely
damaged. Inadequate elevation and poor structural member
connections were the main reasons of failure. Two
structures on the exposed Ocean Blvd. (#126 and #912)
stood out with little visible damage, wind or water
(Figure 4 shows the post storm condition of #912).
















Figure 4: A Well -
Constructed Pile Supported r-
(Wooden) Frame Residential _________- _
Structure On Isle of Palm
Fared Very Well Even In An
Exposed Location.





Both structures were built by the same builder and the
constructions appeared to exceed the current building
code requirement. Class "B" piles (12" Dia. from butt
in and 14" Dia. above ground) with 3/4" steel diagonal
bracings were used. Frames were connected throughout
with 1/2" and 3/4" plywood using #16 Galvanized penny
nails at 4" intervals around corners to insure shear
rigidity. Hurricane clips were properly installed at
critical connection points around roof frame and at pile-
beam junctions. Roof tiles were nailed properly to 5/8"
roof plywood. Ridge vent was installed to relief
pressure difference. As a consequence, only a minimal
number of roof tiles were missing, uncharacteristic to
the general extensive roof damages in this region.
Members that are subject to lift force were connected by
galvanized screws instead of nails.

Between 14th Avenue and 41st Avenue, there is no spur
road south of Hwy. 703. Therefore, all the structures
were set way back from the water line with exceptionally
wide beach and dunes. Water damage to houses has been
minimal in this reach. Washover over highway was
evident.

East of 42nd Avenue, roads perpendicular to Hwy. 703
extend to the south close to the beach. Houses at the
end, sometimes to second and third rows were mostly
devastated due to the combined effects of high surge
level and the close distance to the ocen water. Unlike
some of the devastated areas mentioned earlier, most of
the houses here were up-scale newer structures. Damages
were mainly due to the dynamic forces as oppose to
flooding. This section provided a classic example of
diminishing damage as a function of increasing distance
to the shoreline. On the 50th Avenue, there were 5









houses in a row. The first two were completely leveled
to the ground; the third, and fourth houses sustained
progressively less damage, some due to the debris of the
destructed houses, and the fifth house which was the
farthermost from the shore had no evident water damage.

At the eastern tip of Isle of Palms is the Wild Dune
luxurious condominium complex and the only high rise
community on the island. Water damage was limited to
washed away walk ways, local scourings near foundation
and ground level utilities. Since this area bore the
front assault of hurricane winds, tree, roof, window and
chimney damages were extensive.

McClellanville and Vicinity

McClellanville is a fishing village dominated by modest
wood frame houses. Mobile homes are also common in this
region. Since the estimated landfall of the hurricane
center was Bulls Bay just south of the town the storm
surge was the highest reaching 20 feet or higher. Water
damage was very extensive. Unlike on the barrier island,
however, damage was mainly due to flooding.

Northern Coast of South Carolina

The northern coast known as the "Grand Strand" area has
developed rapidly in recent years. Non conformity
structures also flourished. Until the last two years or
so, building code enforcement was rather lax and relied
on individual communities. Now, Horry County which has
the jurisdiction over most of the affected areas has
adopted the Southern Standard Building Code and is
intended to strengthen the enforcement and inspection
procedures.

Pawleys Island is a relatively old residential community.
Houses are very closely spaced. Quality of construction,
in general, was marginal at best. The storm surge level
was about 13 feet. Beach was very narrow during post
hurricane survey. Emergency measure was taken by
trucking sand from the south end near North Inlet to
repair the beach on the north. Water damage was very
severe due to the combined factors stated above.

Garden City is also primarily a residential community
with a few condominiums and a controlled-access planned
community at the south end. The main thoroughfare is the
Waccamaw Ave which is also the first street parallel to
the beach. The road surface is about 8 to 11 feet above
MSL. The measured storm surge was about 13 feet.
However, local residence claimed the water level to be
much higher along the coastal front of over 20 feet.
Salt spray was estimated to reach 200 to 300 feet right









after the passage of the Hurricane. This was the first
observation of this kind and was based on the observation
of Mr. Carlos Fredes who is also a county building
official and lives on the island. He made his estimate
on the mist level on a transmitting tower that has a
string of stroboscopic lights.

The water damage and the sand washover were among the
worst of all the areas inspected. Water damages due to
flooding can be traced as far back as 1500 feet, or four
or five rows deed from the first street; the sand
washover was measured to top 1 foot on the second row of
houses (north of Waccamaw Avenue see Figure 5). Right
after the hurricane, debris were piled 20 feet high at
intersections, made passage to the second row impossible
from either side.




















Figure 5: Sand Washover on Second Row of Houses (North
of Waccamaw Avenue, Garden City).

On the north end of Garden City, south of Atlantic
Avenue, the destruction on the first row were almost
total for a stretch of 4 or 5 blocks. Complete
destruction on second row were also common in this
reach. Two fishing piers, each 1000 feet long also
disappeared completely. Most of the structures here,
commercial or residential, were constructed 10 years ago,
some more than 20 or 30 years old. Most of them were on
shallow pier footings and some were on slabs. Judging
by the total crushing pattern and by the form of pier
breakage, waves might have overtopped the structures.

The water damages were still very heavy south from this
location till the Waccamaw Avenue took a dog-lagged turn









towards the north. In this reach, the constructions were
a mixture of old and new. Some of the old ones were
constructed about 20 years ago and the new ones were from
5 to 1 years old. Like the north reach, the old
structures were practically wiped out completely. The
new ones, particularly those built within the last two
years, appeared to have largely survived with varying
degrees orf damage. However, not all the new
constructions made it. A concrete two story structures
built 5 years ago by an architect collapsed completely
(Figure 6). This structure had heavy reinforced concrete
roof beams and precasted concrete walls. But it was
supported by cinder-block piers and bearing walls on a
poured shallow footing. Waves must have hit the
structure causing the concrete front walls to collapse
and the piers on the back to buckle. This concrete
structure indeed provided a drastic contrast to the
concrete structure on Folly Beach discussed earlier.





















Under Its Own Weiht
Due to Weak Foundation
(Garden City). .









The loss of beach and scouring around foundations were
also among the severest we have witnessed along the
entire coast affected by Hugo. Beach loss up to 6 feet
of sand around structural piles were common. An
additional 1 to 1 1/2 feet of scouring were measured
around some large piles.

Further south on Waccamaw Avenue, water damage became
considerably lighter. South of #336 (the junction of a
dog-legged turn), only three houses were destroyed. The
houses are all newer here. The beach is also wider than
north because of the dog-legged turn towards inland.

Surfside is connected to the Garden City on the north.
Unlike Garden City, it is full of commercial structures
along the beach, mainly condominiums and high rises.
Some older commercial establishment just north of
Atlantic Avenue sustained considerable damage. The 1st
floor of Ocean View Motel, for instance, was a total
loss. Water damage became less severe further north
although a few condos sustained considerable wind damage.
The nature of water damage was also quite different from
other regions discussed. Septic tanks, drain field and
sewer lines were the most common components receiving
damage because of erosion. Swimming pools, spas, decks
and other water front auxiliary structures protected by
seawalls and/or revetment also suffered heavy damage due
to undermining. Seawalls, new or old, were found to be
of insufficient elevation. Most of the return walls were
too short and structurally inadequate.

Myrtle Beach and North Myrtle Beach were on the northern
fringe of Hurricane influence. Surge level was also
established around 13 feet. Water damage, however, was
much lighter compared to Garden City or Surfside.
Exposed septic tanks and sewer lines were visible at a
number of locations, particularly between buildings where
the sand losses were severer than at structural front.
Unlike Surfside, many waterfront swimming pools and spas
survived structurally, although the quality of protective
seawall structures were found to be of similar quality
as those on Surfside. This might be partially attributed
to the recent beach nourishment along the Myrtle Beach.

Performance Assessment

Based upon damage surveys, factors that critically affect
the structural performance against water loads are
discussed here.

Foundation

In assessing water damage to coastal construction, the
main focal point is the foundation, that is, what is the









type of foundation? where is it located? and how the
super-structure is connected to the foundation?

In terms of foundation types, one found a great variety
of them along this coast. Generally, they fall into one
of the three categories slab on grade and poured
footings, piers of various material and construction and
piles.

Slab on grade and poured footings were shown over and
over again unfit for coastal application. Hogo's
experience only strengthens the verdict because of the
high storm surge. Structures on such foundation have
very little chance to escape severe damage if water level
reached above the foundation. Two common modes of
failures were observed, the structure being totally
demolished by the dynamic force as illustrated in Figure
7 or the structure being picked up by the flooding water
and floated away as shown to be the case in Figure 8.
Pier foundation is permitted by FEMA's guidelines for
residential buildings as well as most of the building
codes. Hugo's experience showed that this type of
foundation is very vulnerable in the dynamic water force
zone. Failures were frequent. The inherent problem of
this type of foundations is the shallowness of the
footings as most of them were dug and poured in-place.
As the overburden material began to erode away, the
footings simply toppled as shown in Figure 9. Bulky
shallow footings fared the worst as they often promote
local scouring up to 1 to 1.5 feet (Figure 10).





















Figure 7: Structure With Foundation On Grade Totally
Demolished By Wave Force.











































Figure 8: (a) Structure Built On Slab Floated Away From
Foundation And Deposited 100 Feet Away Across the Street.
(b) The Arrangement Inside the Kitchen Remained
Undisturbed in the House.










i e Io

Fire 9: Shallow er Foo s Up Rted
Figure 9: Shallow ?ier Footins Up Rcted.




























4~-4


Figure 10:
Around It.


Bulky Shallow Footing Promoted Scouring


In the above ground section, masonry pier is inferior to
wood or poured concrete piers. Masonry pier often failed
due to inadequate reinforcement, sloppy job on masonry
fills and weak joints between blocks (Figure 11).


Figure 11: Masonry Pier Made of Concrete Blocks Failed
Due to weak Joint and Inadequate Fill.

Failure of poured concrete piers were often due to
inadequate or improper placement of reinforcing bars
(Figure 12).
















............
-I "I


(a) (b)

Figure 12: (a) Poured Concrete Piers Buckled Under
Lateral Load. (b) Broken Piers Revealed Inadequate
Placement of Reinforcing Bars.

The joint between the pier and the footing was also a
common place of failure (Figure 13). Poor construction
practice was prevalent among older structures.


Figure 13: Bad Joint Between Pier and Footing Was a
Ccrmon Failure Made.

Pile foundation is becoming the standard for modern
constructions. Properly sized and installed piles









performed invariably well. It should be the only type
of foundation allowed in dynamic zone. Failures were
mainly due to rot. Failures attributed to inadequate
penetration and pile size were also found in a few
occasions. Both concrete and wooden piles were found to
be effective. Concrete piles usually showed good
rigidity and require simpler connections. Corrosion of
re-bars and their subsequent expansion was the main
source that weakened the pile and led to eventual
failures. Brittle failure was also evident in a number
of cases while the pile size might be inadequate. Wooden
piles require more lateral bracings and closer attention
to connections as they are more flexible. Steel rod
bracing appeared to perform better than wood board
bracing for two main reasons: wood bracings were
susceptible to break or buckle under wave force and they
tended to separate or rotate from the main members. The
latter was because many of them were secured by nailing
instead of bolts and nuts commonly used in metal
bracings. For wooden pile, round piles appeared to
perform better than square piles although some may prefer
square pile for aesthetic reason. For square piles, the
hardened outer layers were often partially sawed off
exposing the younger inner fibers.

Elevation

Elevation undoubtedly was the dominant factor.
Practically all residential type of structures sustained
major damage if not complete destruction if the elevation
was inadequate. Several modes of failures were observed:
structures collapsed under wave force; structures
floated away from foundations; water went through the
structures and took every thing with it. For multi-story
buildings, damage usually was associated with the third
mode. The first two modes were more or less related to
foundation as discussed earlier.

Set Back

There was a definite correlation between the extent of
water damage and the set back of the structure. Wider
beach clearly provided better protection by dissipating
wave energy and retarding erosion when the storm surge
level was not excessive. When the storm surge level
'significantly exceeded the dune, such beneficial effects
appeared to rapidly diminish.

Appurtenant Structures

A surprising amount of damage was caused by failures of
appurtenant structures. Deck structures with access
ladders or ramps to the beach were a main source of
problem. They were not designed to resist water forces,











yet, most of them were secured to the main structures.
Water forces would most certainly destruct them which in
turn would Dunc:ure or tear apart that portion of the
main structure connected to them (Figure 14). Ground
floor garage doors, air conditioners, water tanks, non-
break-away walls, etc., all contributed to additional
damages to the main structures. Revetment armor units
sometimes behaved like missiles powered by waves as
discussed earlier.








4...


Figure 14:
to Hugo).


(a) House With Access Ramp to Beach (Prior


a R


-r --


Fi-gre 14: (b) The Access Ramp Washed Into the House Due
to Wave Force.


1'- '


---
-I,


r

cc~c ~.4
z
~~;$
1~
~
t
`1 -.,;4, ,:









Cornections


Co-nections play a major role in wind damage but a lesser
one in water damage. Improper connections between floor
beams and foundations caused the structures to float
away, to collapse and to lean or shift. Figure 15
shcws an example of a modular unit cc=pletely separated
from the founda:icn piles. Improper nailing practice and
inadequate sizes of nails were a prevailing practice
causing member separations under minor shift (Figure 16).
Missing and inadequate hurricane clips were also
prevalent. Mobile home tie downs were found to be
common. Very few mobile home units were found near the
coast. One small mobile home park sou:h of Myrtle Beach
did incur heavy damage, but was mainly due to inadequate
elevation as opposed to inadequate tie downs.
















Figure 15: (a) Modular Unit Constructions With Poor
Connections


Figure 15: (b) The End Unit of the Modular Structure
Simply Disconnected From the Piles.


























Figure 16: Inadequate and Improper Nailings Caused the
Floor Joist to Separate From Floor Beams.

Coastal Structures

1. Seawalls: Sea walls are numerous in the affected
region. Most of them are actually just retaining walls
built for the primary purpose of supporting amenity
facilities or lawns. And, most of them are grossly
inadequate in height to protect the upland structures
from water damage. Scouring behind seawalls due to
overtopping was the most prevalent damage mode observed
which then led to failures of decks and pools or
collapsing of seawalls themselves (Figure 17). In
addition, most of the return walls were underdesigned
resulting in numerous failures (Figure 18). Once the
return walls failed, water quickly rushed in from behind
like a breached dam causing rapid losses of material.

















Figure 17: Overtopping Induced Seawall Failure.
20































Figure 18: Underdesigned Return Wall Was Common
Occurrences.

2. Revetment, groins and Jetties: Like seawall,
revetments are everywhere in the affected area. They are
particularly common on Folly Beach, Sullivan's Island and
Pawley Island. Most of them are not engineered work but
constructed by local contractors or even owners
themselves. The quality was evidently poor with
insufficient height and inadequate armor size. Some were
single layer piled on bare soil. Those structures should
not be expected to serve their intended function and they
certainly didn't. The armor units on the revetment slope
owing to insufficient height often became missiles
hitting structures behind, thus causing more harm than
good. Some did perform marginally in retarding erosion
behind the structure.

Along Folly Beach, Sullivan's Island, Isle of Palm,
Pawley Island and Garden City, groins are interspersed
with few field of heavy density. The damage to them was
surprisingly light possibly because the high surge level
simply submerged them. Jetties at a number of inlet
entrances also appeared to fared well possibly for the
same reason.

3. Piers: Practically all the piers along this coast
sustained severe damage, if not totally destroyed. The
few surviving ones had their mid sections across the surf
zcne missing (Figure 19), which seemed to indicate where
the most destructive water force had occurred. These
piers, though, might not have savage value.

















I

















Figure 19: Piers With Mid-Section Missing Revealed the
Location of Maximum Dynamic Force to be in Surf Zone.


CONCLUSIONS


Hurricane Hugo inflicted very severe water damage on
structures near the coast. The general consensus was
that in the zones reached by water force, the overall
damage incurred by water far exceeded that due to wind.
Under such circumstances, attempts to separate wind and
water damages were often superfluous. This was quite
different from some of the recent hurricanes such as
Alicia and Diana where wind was clearly the dominant
destructive force.

Damage reconnaissance was carried out by visual
inspection and personal interviews. The important
findings are summarized here:

1. Water damage was extensive but damage distribution
was very uneven spatially.

2. Most of the well engineered and well constructed
structures survived, some with very li-tle damage. Both
concrete and wood structures demonstrated their
survivability. Wood structures usually require much more










attention in details, that is, there are more components
and joints which could go wrong here than concrete
st rctures.

3. Wide beaches and high dunes are definitely beneficial
provided the surge level is not significantly higher than
the dune elevation. For extremely high surge level, the
beneficial effect, if any, is unclear.

4. Elevation appeared to be a pre-requisite if the
structure were to escape severe water damage.

5. Of the variety of the foundation types only deep
pilings of sufficient sizes (over 9 inches at least)
performed consistently.

6. Appurtenant Structures were a significant factor
contributing to damage.

7. Most of the protective structures were ineffective
for lack of proper engineering.

8. Structures, buildings and protective structures,
appeared to retard local beach erosion.

RECOMMENDATIONS

Structures built on open coast should be designed to
avoid water force rather than resisting it. Deep pile
is the only structural element that could be used, within
reasonable cost, to resist hurricane induced water force.
Other structural elements, if have to be exposed in this
water force zone, should be designed to break away under
loading. Structural set back is important for a number
of reasons; it reduces the cost of construction; it
reduces the vulnerability of being exposed to dynamic
water forces and it reduces damage. Figure
illustrates the importance of elevation and setback.
Clearly, the closer to the water line the higher the
structure, the deeper the foundation and the stronger the
foundation are required. Both the water crest line and
the scouring line shown in Figure 20 should be respected
in coastal construction.

















I

















Figure 19: Piers With Mid-Section Missing Revealed the
Location of Maximum Dynamic Force to be in Surf Zone.


CONCLUSIONS


Hurricane Hugo inflicted very severe water damage on
structures near the coast. The general consensus was
that in the zones reached by water force, the overall
damage incurred by water far exceeded that due to wind.
Under such circumstances, attempts to separate wind and
water damages were often superfluous. This was quite
different from some of the recent hurricanes such as
Alicia and Diana where wind was clearly the dominant
destructive force.

Damage reconnaissance was carried out by visual
inspection and personal interviews. The important
findings are summarized here:

1. Water damage was extensive but damage distribution
was very uneven spatially.

2. Most of the well engineered and well constructed
structures survived, some with very li-tle damage. Both
concrete and wood structures demonstrated their
survivability. Wood structures usually require much more










attention in details, that is, there are more components
and joints which could go wrong here than concrete
st rctures.

3. Wide beaches and high dunes are definitely beneficial
provided the surge level is not significantly higher than
the dune elevation. For extremely high surge level, the
beneficial effect, if any, is unclear.

4. Elevation appeared to be a pre-requisite if the
structure were to escape severe water damage.

5. Of the variety of the foundation types only deep
pilings of sufficient sizes (over 9 inches at least)
performed consistently.

6. Appurtenant Structures were a significant factor
contributing to damage.

7. Most of the protective structures were ineffective
for lack of proper engineering.

8. Structures, buildings and protective structures,
appeared to retard local beach erosion.

RECOMMENDATIONS

Structures built on open coast should be designed to
avoid water force rather than resisting it. Deep pile
is the only structural element that could be used, within
reasonable cost, to resist hurricane induced water force.
Other structural elements, if have to be exposed in this
water force zone, should be designed to break away under
loading. Structural set back is important for a number
of reasons; it reduces the cost of construction; it
reduces the vulnerability of being exposed to dynamic
water forces and it reduces damage. Figure
illustrates the importance of elevation and setback.
Clearly, the closer to the water line the higher the
structure, the deeper the foundation and the stronger the
foundation are required. Both the water crest line and
the scouring line shown in Figure 20 should be respected
in coastal construction.




















------- -Storm Surge
I -J Eroslon
> After Hurricane -
5 Hugo
SScou .
5J \ Line ; >.

S< -100 200 30 400 500 .- 600
2 DISTANCE (feet)

-5


-i-\



Figure 20: Sketch Shows the Beneficial Effect of Setback
on Structural Foundation.

Further research should be conducted to simplify
structural connections. In the meantime, connections
should be designed and constructed exceeding the Standard
Design Code to minimize repair cost.



Protective structures are special structures and should
be engineered by personnel with special expertise. These
structures owing to their important function should be
regulated much the same as buildings in terms of
engineering, code enforcement and inspections. The large
number of inadequate structures found along this coast
was the consequence of rampant unregulated activities.
An inadequate, non-engineered structure not only creates
a false sense of security to the upland owners but could
also have adverse effects on the surrounding.
Furthermore, those home-made structures with no
engineering and environmental considerations only serve
to reinforce the public's perception that coastal
structures are uniformly harmful. As a consequence,
coastal structures with legitimate purposes are becoming
increasingly more difficult to be accepted.










Finally, one must realize that the Standard Building Code
is a minimum standard. Certain acceptable risk and level
of damage are expected. Revision of building code is not
needed. Code enforcement and field inspection are
definitely the weak links from the Hugo experience.

ACKNOWLEDGEMENT

This article grows out from a team report prepared by the
Hugo Disaster Survey Team organized by the Committee on
Natural Disasters, National Academy of Engineering. The
author wishes to acknowledge Dr. Dean, Messrs Sam Houston
and Mill Dowd all from University of Florida for their
participation. The author also wishes to thank Mr.
Carlos R. Fredes and Mr. Karl Simmons, Building Officials
of Horry County and Charleston County, respectively and
Mr. Ken Hancuff of Isle of Palm for their valuable
discussions.










Finally, one must realize that the Standard Building Code
is a minimum standard. Certain acceptable risk and level
of damage are expected. Revision of building code is not
needed. Code enforcement and field inspection are
definitely the weak links from the Hugo experience.

ACKNOWLEDGEMENT

This article grows out from a team report prepared by the
Hugo Disaster Survey Team organized by the Committee on
Natural Disasters, National Academy of Engineering. The
author wishes to acknowledge Dr. Dean, Messrs Sam Houston
and Mill Dowd all from University of Florida for their
participation. The author also wishes to thank Mr.
Carlos R. Fredes and Mr. Karl Simmons, Building Officials
of Horry County and Charleston County, respectively and
Mr. Ken Hancuff of Isle of Palm for their valuable
discussions.




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