Disaster Mitigation

in Health Facilities:
Wind Effects
Structural Issues
Hurricane paths in the Caribbean Region
during 1998

2
Hurricane Georges’ path - 1998

3
Hurricane Mitch’s path - 1998

4
Floods are a very important
consequence of hurricanes

5
 Natural hazards impact in
health facilities (1981 - 2001)

According to the Pan American Health Organization, between

1981 and 2001 more than 100 hospitals and 650 health
centers suffered serious damages as a result of natural
disasters. The Economic Commission for Latin America and
the Caribbean (ECLAC) reported direct economic losses of
US$ 3,120 million.

This could be compared to an extreme situation in which 20

countries in the region had each suffered the loss of 6 major
hospitals and 25 health centers.

6
 Hospitals are specially
vulnerable to natural hazards

 The occupancy rate is constant, 24 hours a day, year-round.

It is almost impossible to evacuate a hospital in the event of an
emergency.

 The survival of some patients depends on the proper operation of

the equipment and the continuity of basic services.

 Hospitals are highly dependent on public utilities (water, electricity,

communications, etc.) which are often interrupted by the effects of
a disaster.

 In emergencies and disasters, health facilities are essential and

must continue to function after the event has taken place.

7
 The ingredients
a hurricane
needs

•Warm water – above 80ºF

•Converging winds
•Unstable air
•Humid air being pulled into
the storm(up to about
18,000 ft)
•Pre-existing winds coming
from nearly the same
direction
•An upper atmosphere
high-pressure area helps
pump away air rising in the
storm
 Hurricane stages during its path
towards the Caribbean Region

Hurricane
Tropical
Tropical
Storm Depression

Tropical
Disturbance

9
9
Anemogram of Hurricane
Georges - 1998

10
 Saffir-Simpson scale
for hurricane categories

Category Velocity Pressure Damages

1 minute (mb)
(km/hr)

1 120 - 150 > 980 Minimum

2 150 – 175 965 – 980 Moderate

3 175 – 210 945 - 965 Extensive

4 210 – 250 920 - 945 Extreme

5 > 250 < 920 Catastrophic

11
Hurricanes categories in the
North Atlantic and the
Caribbean Region 1944-2001

12
Turbulent flow of wind on
longitudinal and transverse
sides of high-rise buildings

13
Turbulent flow on high-rise
buildings due to upwind
obstructions

14
Wind velocity increase due to
large openings at lower floors

15
Wind flow on gabled roof
buildings showing turbulence
on leeward roof and walls

16
 Wind’s basic pressure

Dynamic part of
Bernoulli’s basic
equation

q 1 V 2
2

17
 Different international
design standards

Standard Identification
ISO International Standard Organization

CUBiC Caribbean Uniform Building Code

ENV Eurocode

DRBC Dominican Republic Building Code

AIJ Japan Standard

AS Australian Standard

BNSCP Barbados Standard

18
 Different calculations for design
wind speeds and dynamic
pressures

Standard Speed Pressure Building

Pressure/Force
ISO 4354 q ref  1 V2 W  qref Cexp Cfig Cdyn 
V 2
CUBiC V q ref  1
2
V2   
W  q ref Cexp Cfig Cdyn

ENV 1991-2-4 Vref  Cdir C tem Calt Cref ,0 q ref  1

2
 Vref  2
We  q ref Cexp Ze Cpe

DRBC-03 V3s  gust  q z  12 K z K zt K d IV 2  

p  q z GCp  q h GCpi  
AIJ U H  Ug Ef Eg R qh  1 U H
2 Wf  q h Cf G f A
2
AS1170.2-89 Vz  Vz,cat M s M t M i q h 1 Vz2 Pe  Cp,e K a K l K pq z
2
BNSCP28 V q 1
2
VS1S2S3 2
P  qC pe

19
 Building types in seven
international wind
standards

Building ISO CUBiC ENV DRBC AIJ AS1170 BNS

Shape/Type 4354 1991 2003 .2 CP28
Stepped Roofs no no no yes no no yes

Free-standing walls yes yes yes yes no yes no

Multispan canopies no no yes yes no no no

Arched roofs yes yes yes yes yes yes yes
Domes no no yes no yes no no
Silos and tanks yes yes yes yes no yes no
Circular sections yes yes yes yes yes yes yes
Polygonal sections no no yes no no yes yes
Lattice towers yes yes yes yes no yes yes
Spheres no yes yes no no no yes
Signs yes yes yes yes yes yes yes

20
The trend for international
standards is to adopt and
adapt the ASCE-7 approach
for primary systems.

21
 Meaning of factors in
ASCE-7

Notation Factor What does it mean?

Takes into account the probability that the
Directionality maximum wind has the same direction as
Kd that of the maximum pressure
Converts a 50-year return period into a
Importance I 100-year return period recommended for
hospitals
Represents the wind velocity at a ‘z’ height
Exposure Kz above the ground
Takes into account the fact that the
K zt structure may be located on top of a hill or
Topography
on an escarpment, increasing the wind
velocity

22
 Meaning of factors in
ASCE-7

Notation Factor What does it mean?

Represents the turbulence-structure
3-sec gust G interaction and the dynamic
amplification of the wind
External pressure Estimates the wind pressure on the
coefficient
Cp building, external walls
Internal pressure C pi Reflects the internal pressure due to
coefficient wall opening quantity and sizes
Design pressure p Represents the design pressure
Represents the net force on open
Design force F
structures

23
 500
Zg = Height wind gradient

400

1/7

V Z 1/9.6
Zg Z
V
300
Zg
Effects of terrain
roughness and 100

height on wind
speeds 50
10

EXPOSURE B - EXPOSURE C -
FOREST, SUBURB OPEN SOIL

24
 Effects of exposure and
altitude

Exposure B Exposure C
400 400

300 300

200 200

100 100
0 0
0 10 20 30 40 50 0 10 20 30 40 50

25
 Exposure Coefficients Kz Kh

Exposure type B C
Exposure Exposure
Height Z (m) B C Height Z (m) B C
Case 1 Case 1
Case 1 Case 2 Case 1 Case 2
and 2 and 2
NOTE:
≤5 .70 .57 .85 32 1.03 1.03 1.30
1. Case 1 shall be
used for all primary 6 .70 .62 .90 34 1.07 1.07 1.34
systems in 8 .70 .67 .96 36 1.10 1.10 1.37
buildings with
10 .72 .72 1.00 38 1.14 1.14 1.4
height ‘h’ less than
18 m and for 12 .76 .76 1.04 40 1.17 1.17 1.43
secondary systems
14 .79 .79 1.07 42 1.20 1.20 1.46
of any type of
structure 16 .82 .82 1.11 44 1.23 1.23 1.48

2. Case 2 shall be 18 .85 ..85 1.13 46 1.25 1.25 1.51

used for all primary 20 .88 .88 1.16 48 1.28 1.28 1.53
systems of any
other structure not 22 .90 .90 1.18 50 1.30 1.30 1.55
indicated in case 1 24 .92 .92 1.20 52 1.32 1.32 1.57
3. For values of Z 26 .93 .93 1.21 54 1.35 1.35 1.59
not shown, linear
interpolation shall 28 .96 .96 1.24 56 1.37 1.37 1.61
be permitted 30 .98 .98 1.26 58 1.39 1.39 1.63
 Topographic effect showing
wind velocity increase

z z

z V(z) z V(z)
speed up
speed up
x x x
(windward) x (windward) (leeward)
(leeward) V(z)
V(z)
H/2 H/2
H H
L H/2 L H/2
m m

Hill Escarpment

27
 Sketch showing effects of
topography on wind velocity on
a hilly island

Vg 100

Speed up
120
Vs

Vg 100 100 100

Vg Vg

80 60
Vs Vs 40
10 m

Open sea Wind ward Speed up over Sheltered leeward

Coast hill crest coast

28
 Different ways of
measuring wind velocity

Average time Wind velocity

1 Hour 120 113 91 79

10 minutes 127 120 96 84

Fastest mile 158 149 120 105

3 second gust 181 171 137 120

29
 Wind velocities in the
Caribbean for a return period
of 100 years

23 N
89.5 W

59 W
N

9N

Storm Category 0 1 2 3 4 5
knots 25 50 75 100 125
mph 25 50 75 100 125 150
kph 50 100 150 200 250
m/s 10 20 30 40 50 60 70

30
 Modified basic pressure in
ASCE-7 to accommodate local
parameters

Modified basic pressure-

ASCE-7

q 1 K K K IV2
2 z zt d

31
A high percentage of wall
openings are dangerous for a
health facility

32
Different types of forces
acting on structural
elements

33
Wind can induce torsional
effects on structural steel

34
 Design pressure on primary
systems (structural)

Rigid primary systems

p = q GCp - qh (GCpi)
Flexible primary systems

p = qGf Cp - qh (GCpi)

35
 Pressure coefficients on
high- rise buildings

Pressure
keeps constant
- 0.6 with height
- 0.5 - 0.6
(Leeward)
- 0.6 - 0.6
- 0.6
ROOF
0.9
0.8
- 0.5
0.7 WIND
- 0.6

- 0.6
0.6 Pressure varies
- 0.5 with
- 0.5 height
0.5 (Wind ward)

- 0.6
0.4
- 0.7

0.3

0.30.3
0.4 0.4
SIDE FRONT BACK

36
 Design pressure diagram
on gabled roof building

q hGCp q hGCp


q zGCp

Wind h
direction
z q hGCp

L
37
Total destruction of Princess
Margaret Hospital in Jamaica

38
Absence of an appropriate
anchorage led to the overturning
of a clinic

39
Failure of steel beams support

40
Timber roof split due to
strong hurricane winds

41
In health facilities, a connection
between structural elements
and the roof must be adequate

42
Construction close to the sea
shore might result in great
losses

43
When there is a lack of symmetry
among resisting elements, wind will
induce torsional effects

44
 Hipped roofs with slope from
20 to 30 degrees interact better
with the wind forces

Hatched area indicates

where more frequent
fixings are required

PLAN ISOMETRIC

Hipped roof

45
 Pressure increase due to
wind on overhanging roofs

Wind ward Roof

Leeward
SECTION

46
 Protection effect of
hospital building

A favorable location of
adjacent buildings can
decrease the hurricane
effects by reducing the
wind loads

47
 Unfavorable location of
buildings adjacent to a hospital

A bad location of
nearby buildings might
induce increase of wind
loads

48
Bridge base erosion as a
consequence of river flow
increase

49
Landslide obstructing
highway access

50
 Pressure sketch for wind
perpendicular to the ridge on a
pitched-roof industrial building

-246.68

-180.22

11.64 Internal pressure (+)

-226.90
3.88

Net pressure Perpendicular to ridge

51
 Pressure sketch for wind
parallel to the ridge on a
pitched-roof industrial building

-306.03 -226.90 -187.34

44.21

38.01
-203.16
Internal pressure (+)
20.94
11.64
3.88

Net pressure Parallel to ridge

52
Flat-slab systems without capitals present
little resistance against lateral forces.
Their use on hospitals should be avoided

53
Wind load path on
pitched-roof buildings

54
Structural steel frame collapsed
due to strong winds

55
 Hurricane design philosophy
for hospitals

The hospital structure must be designed and

built in such a way that it:

withstands, without any damage, the design

hurricane event;

withstands, with minorand easily repaired

damage, hurricanes greater than the design
event.

56
 Vulnerability assessment
objectives

Objective Available
methodologies
To evaluate the
likelihood of a
structure suffering  Qualitative
damage due to the methods
effects of a
hurricane, and to  Quantitative
characterize the methods
possible damage

57
 Qualitative methods for
vulnerability assessments

Qualitative methods

They assess quickly and simply the structural safety

conditions of the building, taking into account the
following parameters:

• The age of the building

• The state of conservation and maintenance
• The characteristics of the materials used
• The number of stories
• The architectural plan

58
 Quantitative methods for
vulnerability assessments

Quantitative methods

The goal is to determine the levels of resistance of

the structure by means of an analysis similar to
that used in new buildings and incorporating
nonstructural elements.

59
 Structural retrofitting

 The goal is to ensure that the health care facility

will continue to function after a hurricane, by
reinforcing existing components or incorporating
additional structural components to improve the
levels of strength and stiffness.

 The retrofitting measures should not interfere with

the operation of the hospital during the process.

60
 Detail of stud to concrete
footing connection

Galvanized strap Stud

Double base plate

Ground
surface

Concrete pier
3'-0"

Concrete base

Stud to concrete connection

61
 Stud and top plate connection

Double top plate

Galvanized plate

Stud

Stud & top plate connection

62
 Rafters and top plates should be
anchored with galvanized straps

Rafter

Double top plate

Galvanized hurricane
strap

Rafter & top plate connection

63
 Anchorage of timber
beams to concrete beams

Rafter

Galvanized hurricane
straps either side
of rafter

Use of galvanized Beam

hurricane straps is
recommended

Timber rafter connection to concrete

64
 Anchorage details between
steel joist and masonry walls

Open web Steel joist

steel joist

Lap as
required
Weldable steel rod
welded to joist
bearing plate

Anchor welded to lintel

As required
for
hold-down Tension rod in
concrete filled core
at each joist

65
Interaction between structural
and nonstructural elements

66
 Considerations for infilling
masonry partitions

If the infilling
masonry wall acts as
part of the
structural system, it
will undergo great
deformations and
failures

67
Reinforcement
method: addition of
(interior or exterior)
walls

68
 2

Tie beam

Blocks

Tie beam

Blocks

Tie
column
Retrofitted wall in
children’s hospital
1 1

in Santo Domingo
Tie beam

69
 Tie
beam 0.20 Tie beam

0.20 0.40

0.20
Tie beam

0.20

Details of retrofitted
wall sections Tie beam

0.20

0.20

70
 INSIDE
0.30 OF BEAM

Formwork Formwork

Construction method
details of retrofitted
wall
INSIDE
0.30
OF BEAM

71
 0.30
INSIDE
OF BEAM

1.50
0.30 0.25 0.40 0.25 0.30

0.20

Front view of 1 1 (ALL END WALLS)

retrofitted wall
Ø 3/8 @ .10

0.30
INSIDE
OF WALL

72
 INSIDE OF BEAM

0.30

1 1

0.30

Lateral view of INSIDE OF WALL

retrofitted wall 0.30

3.60
3.10 0.20

0.20 0.40

(ALL END WALLS)

Ø 3/8 @ 0.10

73
 Pan American Health Organization • 2005
These slides have been made possible through the financial
support of the Disaster Preparedness Program of the
European Commission Humanitarian Aid Department
(DIPECHO III).

Grupo de Estabilidad Estructural (Ge2) / INTEC Ph: (809) 567-9271

Ave Los Próceres, Galá Fax: (809) 566-3200
Apdo 349-2 danielc@intec.edu.do
Santo Domingo, Dominican Republic www.intec.edu.do