SWITZERLAND: PUBLIC REGISTER FOR HAIL IMPACT
RESISTANT BUILDING MATERIALS CREATED
P.H. Flüeler1/2, O. Lateltin3, M. Jordi3
1 Flüeler Polymer Consulting GmbH, Switzerland
2 EMPA, Swiss Federal Labs for Materials Testing and Research, Switzerland [email protected]
Corresponding author
3 Association of Public Building Insurance Companies, Switzerland, [email protected] and [email protected]
ABSTRACT
In Switzerland, a register for hail impact resistant HIR building materials was newly created. To
be registered, a material/product has to withstand five ice ball impacts of a given size (1 to 5 cm).
Damage is assessed for 5 prime functions of structural elements like water tightness, light
transparency, light screening, mechanics and appearance. The technique of testing, ice quality,
damage assessment and its difficulties, and the HIR-classification are discussed. For several
material groups real HIR-values are presented. In the future, the national standards envision a
HIR class 3 (no damage by 3 cm hailstones) to get full compensation for hail damaged building
materials. The register will enhance research and marketing for higher quality products and
eliminate low profile materials with time.
1. INTRODUCTION
In 2008 as part of a new prevention strategy,
the Swiss Association of Public Building
Insurance Companies (APBIC) established a
general register for classified building
materials and products. Classification and
guidelines were established to realize a
publicly accessible register. The motivation
for such an initiative is based on weather
statistics of central Europe for Austria, France,
Germany, Italy and Switzerland [1]. The past
15 years have shown a marked increase of
severe weather conditions, in which
hailstorms can form. The figures of APBIC
companies show a trend for higher payments
for compensations of hail damaged buildings.
The aforementioned guidelines are based on
an extensive experimental study on 57
different materials from 11 fields of
applications conducted by P. Flüeler in 2005 2007 [2, 3].
Figure 1. Hail storms in central Europe in 5 levels (I=low,
V=high) according to Swiss Re
The intensity pattern show highest hail risks
along zones of middle to high mountains like
the Pyreneans, the Alps and southeastern Alps
(Slovenia). But large hailstones also
devastated flat land and hilly areas in recent
times (Emden, North-Germany, Arnhem,
Netherlands 2008).
Page 1 of 8
2. HIR CLASSIFICATION
2.1 Classification
The HIR classes 1 – 5 describe the ice ball
size in centimeters at which a material will not
be damaged when hit by natural hail stones of
the same size. The class limits are created by
the calculated kinetic energy Ek and the given
properties of laboratory made ice balls [table
1].
Table 1. Ball size, mass, speed, kinetic energy
and HIR-classes
Ice
ball Ø
(cm)
1
2
3
4
5
Daily
object
Mass
(g)
pea
0.5
hazelnut 3.6
walnut
12.3
golf ball 29.2
egg
56.9
Speed
Ek
(m/s)
13.8
19.5
23.9
27.0
30.8
(Joule)
0.04
0.7
3.5
11.1
27.0
HIRClass
1
2
3
4
5
B and E. If a material/product like a sky light
or a solar collector has additional functions it
is classified for A, B, D and E. Specific
guidelines for each application domains
prescribe the mandatory functions to be
classified [table 2].
Table 2. Application fields and mandatory
building functions (edition 2009)
Material
Build. function
A B C D E
Bituminous boards
m
m
Roofing membranes
m
Fiber cement boards
m
f m
Window/door shutters
m m m
Window/door profiles
m
m
Glass, plane
m
f m
Plastic panels
m m
f m
Sky lights
m m
f m
Sun shutters, metallic
m m m
Roller blinds
m m m
Natural stone boards and facades m
m
Ext. insulation & finished system m
m
Tiles and shingles (all materials)
m
f m
Swimming pool covers
m
m m
m: mandatory
f: mandatory if fitted
The speed represents the calculated terminal
velocity of a vertical falling round ice stone.
For the density of ice 0.875 g/cm3, for the air
density 1.226 kg/m3 and for the air drag
coefficient 0.5 were taken [2, 4]. Ice density
and air drag coefficients are set conservatively
because test speed is taken for roofs and
facade materials.
The next APBIC testing guideline release in
2010 covers eight additional application
fields. It covers solar elements, sun awnings,
pneumatic membranes constructions, facade
glasses, sandwich boards, plasters, tent like
constructions and antenna shells.
2.2 Prime Building Functions
2.3 Registration
There are five primary building functions
insurers usually pay compensations for.
They are:
- water tightness (A)
- light transparency (B)
- light screening (C)
- mechanics (performance functions) (D)
- appearance (E)
Companies who can present reports of
materials/components/systems
having
successfully passed the prescribed test
procedures are eligible for a HIR registration
[5]. The register is kept and up-dated by
APBIC. It is publicly accessible and can be
frequented from all interested parties
including building owners, planners and
building authorities.
According to its application, a material will be
classified for more than one function. Roofing
membranes are classified only for A, roofing
tiles for A and E, transparent materials for A,
Page 2 of 8
3. TESTING PROCEDURE
3.1 Equipment
To impact an object at a defined angle and
speed with an icy projectile affords an ice ball
production technique, a freezer, a balance, a
launcher and a heavy tilting frame to bear the
test object. The launcher – mechanically or
pneumatically operated – must be equipped by
a time efficient release mechanism. An aiming
device and precise light gates accurately
measure the speed of each ice ball prior to
impact (figure 2, 3).
Figure 4. Laboratory made ice ball with diameter 2, 3, 4 and
5 cm (~ 2 inches)
The ball sizes of 2, 3, 4 and 5 cm (figure 4)
have to meet the kinetic energy requirements
according to table 1 which represents the
lower limits of a HIR-class. Launching should
be in the time frame of 40 to 60 s after
removal from the storage freezer. Ice balls that
split prior to impact are not valid.
3.3 Procedure and Number of Impacts
Figure 2, 3. Vertical operating test apparatus with steel frame
support (left 2), mobile ice ball launcher for horizontal/tilted
(right 3) impact
3.2 Projectiles
To simulate natural hail impact can be a
highly demanding task. Natural hailstones
show often a shell like structure formed in a
storm cell by several up and down cycles.
Also they consist of accreted conglomerates of
smaller ice stones. For testing purposes
reproducibility is of higher importance than
simulation the natural phenomenon. Balls of
clear ice are produced with de-mineralized
water in a very elaborate freezing process to
achieve the requested properties. They are
stored at a temperature of -20° C and must be
free of cracks, irregularities and have low
porosity content. They can be produced in
rubber molds or be cut and shaped from
blocks of clear ice.
The first critical action is to assess the most
susceptible, weakest position of a test object
by
applying
engineering
evaluation
techniques. Then, a number of exploratory
shots are made by varying ice ball sizes to
produce a defect. Subsequent tests are made
with smaller ice balls until 5 impacts show no
defect. Each target area is impacted only one
time. A safe distance from the former impact
area is to respect (ball size dependent).
3.4 Main Specifications
Main specifications of the test procedure are:
- launcher/gun: vertical or horizontal
- impact angle: 90° (roofs), 45° (facades)
- distance to test object: 30 – 100 cm
- speed accuracy: 0.01 m/s
- ice ball temperature: -20° ± 2° C
- balance, reading: 0.01 g
- time delay to launch: 40 - 60 s
- ice ball speed: 13.8-30.8 m/s (see table 1)
- distance between targets: 10 -15 cm
- mass of mounting frame / projectile: >100
Page 3 of 8
- testing climate: room temperature
- test object conditioning: 3 min. ice scales
exposure (temperature sensitive materials)
or wetting if sensitive to water
- test object pretreatment: cement-like
materials are tested after 28 days, polymers
3 days at 23° C/ 50 % r. h.
4. DAMAGE ASSESSMENT
4.1 General
The classification is based on the idea to
evaluate the greatest ice ball size causing no
damage for the selected building functions.
With respect to insurance payouts, a damaged
material qualifies a building owner to claim
for compensation based on this assessment.
In general, damage has to be assessed in
progress of testing, immediately after each
impact. This requires short-term methods
yielding to instant results. Preferred practices
were taken from per-installation checks and
from performance acceptance procedures.
Also, the methods should apply, at the 5
selected prime building functions, and all
applicable fields.
4.2 Water Tightness
Water tightness represents the first and most
important function for a building envelope. A
leakage if not directly obvious may be the
result of different causes. Checking
procedures should also detect intrinsic damage
or reveal inner defects causing leakage in the
future or effects due to aging. Most common
defects affecting water tightness are:
- deformation (stretching, yielding)
- fracture (cracking, shear-yielding, shear)
- instability (buckling, distortion, folding)
- perforation
- splitting
- out break
- inner defect (delamination, debonding)
- peeling, separation, pull out
- incoherence of elements/components
- dislocation etc.
For each material group the failure criteria and
test methods are given. Most frequently test
methods are:
- eye check at 0.5 m distance
- magnifying glass and light source
- vacuum test
- air pressure test
- penetration of colored liquid
- wetting and drying/evaporation
- knock test (wood pecker, inner defect)
4.3 Light Transparency
Light transparent materials like glass and
polymers may change light transparency when
damaged (plastic sheets). A reduction of the
transparency is assessed by an eye test from 5
m distance. The light source must be in front
of the observer and behind the test object. No
change of the visibility passes the criteria.
4.4 Light Screening
The reduction of the screening capacity in a
blind, shutter or awning is assessed by
measuring a gap, opening or perforation
caused by ice ball impact. To pass the criteria
the opening has to be smaller than 1 mm. It is
measured by a caliper or by an equivalent
device with a reading of 0.1 mm or smaller.
4.5 Mechanics
In this clause functions like opening/closing
mechanism are checked. The general test is to
activate the function 5 times or to measure a
percentile loss of a function electrical (solar
panels), electro (light element), electromagnetic functions (antenna) are measured.
For a system assembly, also disturbance, give
way of the system integrity or damage of the
fastening element to the sub-structure counts
for pass or fail.
Page 4 of 8
4.6 Appearance
Modern architecture of today values the
appearance and shape of a building higher
than functional aspects. Therefore, the
appearance of a structure is often the subject
of insurance claims. Prominent examples are
indentions or surface deformations in roller
blinds, shutters or in metal facades. Every
year, roller blinds and shutters absorb more
than 50% of hail compensation payments of
APBIC.
The observer assesses the object by an eye test
in oblique view and with frontal light source.
He respects a quarter circle of ± 45° angle out
of 5 m distance. View applications respect
diffuse light sources. If a change in
appearance is observed the test has failed.
Unclear results often demand a second
assessment at another day and by additional
observers.
4.7 Further Aspects
The structural integrity of a material as a
separate prime building function was subject
of intense discussions in the technical
committee. With respect to the applicability of
the classification system, also to non material
scientists and to avoid expensive postinvestigations it was abandoned.
5. HIR-CLASSIFICATION RECORDS
Within the full palette of materials used for
building envelops and its behavior against
impact loads one can differentiate materials in
stiffness or moment of inertia versus the hail
impact resistance. Also, materials, structures
and entire systems have to be respected. In the
following context they are treated in 3 groups.
The figures were tested on new materials.
5.1 HIR of Soft, Compliant Materials
Soft or flexible materials like membranes need
a rigid (steel plate), a soft (rigid foam) or an
air cushion support to be tested. Usually the
surface is cooled by ice for 3 minutes before
impact. Ice balls usually split or remain intact
depending on the support (hard/soft).
Scientific and practical experiences over 35
years have yielded to membrane thickness as
listened in table 3.
Table 3. Classified soft materials
Membrane material
PVC-P glass reinforced 1.8 mm
TPO 1.6 mm
SBS sanded, 3.7 mm
SBS slated, 5.2 mm
EPDM 1.5 mm
*ETFE transparent foil 200 µ
*tested with an air pressure of 250 Pa
Build. function
A B C D E
5
5
4
4
4
5 4
3
5.2 HIR of Semi Rigid Materials
This material group includes mainly low and
medium E-modulus products like polymers
and composites of it. Typical examples are
thin faced sandwich and externally plastered
thermal insulation (EIFIS). Ice balls usually
remain intact at impact and do not split.
Examples of HIR classifications are given in
table 4.
Table 4. Classified of semi rigid materials
Membrane material
Build. function
A B C D E
Shutters / roller blinds
1
1 3 1
Skylight PMMA 3 mm (3 shells)
2 2
5 2
Skylight PC 3 mm (2 shells)
5 4
5 4
Multi wall sheet PC 40 mm
5 5
4
Multi wall sheet PC 16 mm
5 4
3
Multi wall sheet PC 10 mm
4 4
3
Multi wall sheet PMMA 16 mm
1 1
1
Multi wall sheet PMMA 16 mm +
4 3
3
Swimming pool protection PVC-U
2
2
EIFIS 3 mm, inorganic finish
2
3
EIFIS 5 mm, inorganic finish
3
3
EIFIS 3 mm, polymer mod. ++
4
5
EIFIS 5 mm, polymer mod. ++
5
5
EIFIS: external insulation and finished system
+ modified PMMA
++ special reinforcements
Page 5 of 8
Typical examples of the appearance of surface
damaged multi wall PC panels (table 4 and
figure 5, 6).
Figure 7. Examples of tested aluminum roller blind (3 cm ice
ball, left) and clay tiles (5 cm ice ball, right)
Figure 5 and 6. Typical damage by 5 cm ice balls on multi
wall PC panels, inside deformations (left 5), surface
indentations (right 6)
HIR of Rigid Materials
The nature of rigid materials varies from
metallic, inorganic, reinforced organic and
mixtures of both. In addition, the structures
vary in a broad range. The failure modes may
be brittle, semi ductile to ductile - tough.
Therefore they performed in all HIR-classes.
Ice balls collapse totally and form a white
cone on the rough surface. Typical examples
are listened in table 5.
Table 5. Classified of high stiffness materials
Membrane material
Build. function
A B C D E
Clay tile (beaver tail)
4
4
Clay tile (flat, large)
4
4
Metal tile aluminium, 0.7 mm
4
2
Float glass 4 mm
5
5
Tempered glass 6 mm
5
5
Laminated glass 8/8 mm
5
5
Wire glass 7 mm
3
3
Fiber cement corrugated 5.5 mm
4
4
Fiber cement board flat 6 mm
5
5
Metal sheet TiZn 0.7 mm, new
5
2
Metal sheet TiZn 0.7 mm, patinated 5
3
Metal sheet TiZn 1 mm, new
5
3
Steel sheet corrugated 0.75 mm
5
2
Steel sheet corrugated 1.0 mm
5
4
Fir wood, saw cut/planed*
3
Larch wood, saw cut/planed*
3
Douglas fir, saw cut/planed*
3
Wood fir, thick coated
2
1
Wood shingle facade
3
3
* natural, water-repellant, thin coated
Remark:
Figures listed in table 3-5 are for new products
and may change with time. The figures should
not be taken as constants. The final class
depends on material configuration, shape and
boundary conditions. Furthermore the
appearance can be greatly influenced by the
surface properties and top finish. Details can
be found in the hail register of APBIC (see
www.hagelregister.ch).
6. OUTLOOK AND DEVELOPMENTS
6.1 2009 Weather Experience
Recent weather patterns in Switzerland show a
dramatic increase in hail damage. On July 23,
2009 a hailstorm, spanning a length of 200 km
from the lake of Geneva to the lake of Zurich,
caused substantial damage to buildings, crops
and automobiles (figure 6).
Figure 6. Hail storm path of July 23 with stone size
distribution (APBIC)
By this single summer storm, insurance
companies paid out 6 times more than the
Page 6 of 8
annual claims combined. In a changing
climate a classification system for determining
HIR resistance to building structures is
paramount.
6.2 Development of Protection Systems
As a consequence, the hail protection register
triggered research and development for hail
protection systems. First tests were conducted
and improvements will finally yield in more
robust buildings. Special testing procedures
have to be worked out. By creating the hail
register, precise requirements can be deduced
and a degree of protection generated.
6.4 Building Recommendations
As an additional step to the hail register [4]
general recommendations for planners,
building owners and agents have been issued
about protection and damage preventions.
Detailed procedures are required for each
application field in collaboration with
industries [5].
7. ACKNOWLEDGEMENTS
The contributions from APBIC and members
from the technical committee FER (listened
below) are greatly acknowledged.
6.3 Research
Meteorology can explain and simulate the
nucleation of hail, can predict and track
storms and post-analyze events. However, hail
impact simulation data of the measured
surface and inside temperature of freshly
fallen hailstones is difficult to determine. The
impact force is directly related to temperature
and structure. This requires acceptance
procedures to evaluate ice ball quality of
different laboratories. Also, national and
European standards (figure 7) have to be reevaluated and up-dated respecting recent hail
weather records. Prognosis for future weather
development needs adjustments to smaller,
local areas.
O. Lateltin
M. Jordi
D. Aller
H. Donzé
J. M. Lance
R. Lösch/C. Stillhard
S. Orecchio
W. Maffioletti
T. Egli
P. Flüeler
VKF
VKF
GVZ
GVL
ECA
GVS
GVB
GS-SIA
EE
FPC
APBIC, president
APBIC, deputy
insurance
insurance
insurance
insurance
insurance
standardization
consultant
consultant
8. REFERENCES
[1] P. Zimmerli, "Hail storms in Europe, a new
view to a known risk". Fokus report of Swiss
Re 2005, Schweizerische RückversicherungsGesellschaft Zürich, 8 pages
[2] Association of Public Building Insurance
Companies APBIC (2007), Elementarschutzregister Hagel, Synthesebericht, Untersuchungen zur Hagelgefahr und zum Widerstand
der Gebäudehülle, VKF Bern, 7/2007, 32
pages
[3] Flüeler. P. et. alt.. (2007) "Hail impact
resistant
building
materials,
testing,
evaluation and classification", Proceedings of
11th DBMC Durability of building materials,
Istanbul Turkey, 27 (4) pp.249 -265.
Figure 7: Hail hazards map with a return period of 50 years
in current Swiss standard SIA 261/1 with frame of hail path of
July 23 (figure 6)
[4] APBIC "Schweizerisches Hagelschutzregister
on-line", public webside of Swiss hail
Page 7 of 8
registry. www.hagelregister.ch, APBIC 2009
Bern, Switzerland
[5] Association of Public Building Insurance
Companies APBIC (2007), "So schützen sie
Gebäude gegen Hagel". Special print of VKF,
Bern 2010, 4 pages
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