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Buildings 2024, 14, 767. https://doi.org/10.3390/buildings14030767 www.mdpi.com/journal/buildings
Article
Mitigating Blast Hazards: Experimental Evaluation of
Anti-Shaer Films and Catcher-Cable Systems on
Conventional Windows
Mahias Andrae
1,
*, Jan Dirk van der Woerd
1,2
, Mahias Wagner
2
, Achim Piesch
2
and Norbert Gebbeken
1
1
University of the Bundeswehr Munich, Research Center RISK, Research Group Bauprotect, Institute of
Engineering Mechanics and Structural Analysis, Werner-Heisenberg-Weg 39, 85579 Neubiberg, Germany;
jan.vanderwoerd@unibw.de (J.D.v.d.W.); norbert.gebbeken@unibw.de (N.G.)
2
MJG Ingenieur-GmbH, Gofried-Keller-Str. 12, 81245 Munich, Germany; m.wagner@mjg-ing.com (M.W.);
a.piesch@mjg-ing.com (A.P.)
* Correspondence: mahias.andrae@unibw.de; Tel.: +49-89-6004-2897
Abstract: In light of terrorist aacks and accidents, the need for structural protection against explo-
sive events has increased significantly in recent decades. Conventional unprotected windows pose
a particularly high risk of injury to building occupants due to glass fragments and window frames
being propelled into the interior and exterior of a building. This article addresses new experimental
research on the protection of conventional single casement windows with insulating glass units
(double-paned) and window frames made of un-plasticized polyvinyl chloride (uPVC) against blast
loads. Entire window systems were tested in ten shock-tube tests using different retrofit-configura-
tions. The retrofied protective measures include anti-shaer films and catcher-cable systems. Fur-
thermore, the influence of steel profiles inserted in the window frames is investigated. The applied
blast loads met the requirements for ER1-certification according to EN 13541:2012 (tested at a re-
flected peak overpressure of 66.7 kPa and a reflected maximum impulse of 417.7 kPa·ms). In the test
series, various measurement methods were used to capture the velocity of the window fragments,
the dynamic cable forces, and the hazard. The data provide valuable information for the design and
implementation of catcher-cable systems for existing buildings, which can improve the occupant
safety in the event of an explosion.
Keywords: explosion; blast protection; retrofiing; windows; anti-shaer film; glazing;
catcher-cable system; witness panel; digital image correlation; shock-tube testing
1. Introduction
Current security challenges require rethinking of the need for structural protection
against explosive events. On the one hand, major bomb aacks, such as those in Oslo
(2011) or in Brussels (2016), highlight the vulnerability of public spaces. On the other
hand, accidental explosions, such as in the ports of Tianjin (2015) and Beirut (2020), lead
to discussions about the necessary security in exposed areas. The protection of critical
facilities has become even more prominent due to the ongoing war in Ukraine since the
beginning of 2022.
Conventional windows made with frames of flexible materials, such as un-plasti-
cized polyvinyl chloride (uPVC) or wood, are known to be particularly vulnerable to blast
loads. If a glazing unit breaks, glass fragments are propelled by the blast wave at high
velocity into the interior and exterior of the building. Annealed glass, commonly used in
conventional windows, can shaer into sharp shards, which poses a high risk of cut inju-
ries for personnel [1]. Additionally, the blast may also tear off the window frame from its
Citation: Andrae, M.; van der
Woerd, J.D.; Wagner, M.; Piesch,
A.; Gebbeken, N. Mitigating Blast
Hazards: Experimental Evaluation of
Anti-Shaer Films and Catcher-
Cable Systems on Conventional
Window s. Buildings 2024, 14, 767.
hps://doi.org/10.3390/
buildings14030767
Academic Editor: Duc-Kien Thai
Received: 10 January 2024
Revised: 1 March 2024
Accepted: 8 March 2024
Published: 12 March 2024
Copyright: © 2024 by the authors.
Licensee MDPI, Basel, Swierland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Aribution (CC BY) license
(hps://creativecommons.org/license
s/by/4.0/).
Buildings 2024, 14, 767 2 of 23
anchorage. Such heavy fragments can cause blunt trauma if they collide with individuals
[2,3].
This article focuses on retrofiing existing windows. The aim is to minimize the risk
of injury in the event of an explosion while preserving the existing building structure.
Using retrofied protective measures represents a compromise. On the one hand, retrofit-
ting can be performed relatively uncomplicated and quickly compared to replacing exist-
ing windows with blast-resistant security windows. A sustainable solution may be possi-
ble as the existing windows will be preserved. On the other hand, retrofied windows do
not currently offer the same level of protection as blast-resistant security windows. More-
over, retrofit measures are typically tested on a stand-alone basis, rather than on an entire
window system with the complex interaction of its components. This encourages further
research into retrofit measures and testing them in realistic situations on full-scale win-
dow systems. Examples of the most common retrofit measures are anti-shaer films and
catcher systems.
1.1. Anti-Shaer Films (ASF)
In engineering practice, so-called anti-shaer films (ASFs) are often used to reduce
risks during explosive events associated with shaered glass panes [4]. Similar to lami-
nated safety glass, glass fragments adhere to the ASF after the glass pane breaks, reducing
the risk of cut injuries. The thin transparent polymer films can be installed directly onto
an existing glazing unit. The required thickness of ASFs depends on the desired level of
protection and the dimensions of the glazing unit. Typical thicknesses range from approx-
imately 0.1 mm to 0.5 mm [5,6]. Further information on the characteristics of ASFs for blast
protection can be found in [7,8]. It should be noted that the durability of ASFs has not yet
been conclusively assessed [9]. Often a warranty of about 10 years is given.
In Europe, ASF certification testing typically follows the EN 13541:2012 [10] test
method. The respective shock-tube test is performed on an ASF-retrofied glazing unit
with well-defined dimensions in a controlled seing. Tested ASF-retrofied glazing units
currently achieve the resistance class ER1 according to EN 13541:2012, which corresponds
to a blast load with a reflected peak overpressure 𝑝 of 50 kPa and a reflected maximum
impulse 𝑖 of 370 kPa·ms.
It is important to stress that the described certification tests of EN 13541:2012 solely
determine the blast-resistance of glazing units, without considering the overall perfor-
mance of the entire window system. For example, the test method specifies that the glaz-
ing unit is clamped in a rigid steel frame. Conventional window frames are somehow
rather flexible, and it is often not possible to clamp the glazing in the glazing rebate. In the
experimental study presented throughout this article, we will focus on the blast-resistance
of full-scale window systems that are equipped with ASF-retrofied glazing units. The
presented approach corresponds more closely with practical applications [11], since it con-
siders the entire window assembly rather than just the glazing unit itself.
1.2. Catcher Systems
Catcher systems are used if parts of the window need to be stopped from being pro-
pelled into the protected area. Commonly applied are catcher-cable systems, catcher-bar-
systems, or blast curtains:
1. Catcher-cable systems (CCS) are installed together with ASF-retrofied glazing units.
Larger fragments can be caught by several cables placed in the interior of the room
at close proximity to the window.
2. Catcher-bar systems are installed together with ASF-retrofied glazing units and
consist of several steel bars placed at close proximity to the window at the inside of
the room. The protective principle is similar to that of a catcher-cable system; how-
ever, the bars are stiff obstacles, while the cables show a more flexible response.
Buildings 2024, 14, 767 3 of 23
3. Blast curtains are typically made from heavy-duty fabrics and are placed in front of
windows at the inside of the room. Fragments are caught by the fine mesh of the
curtain. Note that daylight and comfort in the building may be affected as the cur-
tains must be kept always closed.
1.3. Objective and State of the Art
The primary objective of this study is to evaluate the effectiveness of catcher-cable
systems (CCSs). Experimental and numerical studies in this particular application field
are relatively sparse, especially including full-scale window systems.
One of the few studies on CCSs for retrofiing full-scale window systems was pre-
sented by Dogruel and Field [12]. In this study, free-field blast tests were performed on
historic wood-framed windows. The windows were subjected to blast loads that are
slightly less intense than those required for ER1-certification (27.5 kPa reflected overpres-
sure and 193 kPa·ms reflected maximum impulse). Laminated glass was used to replace
the conventional glass panes of the historical windows. Note that replacing the glazing of
existing windows can be relatively costly compared to retrofiing the window with anti-
shaer films. In the study, a CCS is installed to stop window fragments from being pro-
pelled into the protected area. It consists of 2.6 mm diameter steel wire ropes included in
so-called blast-blinds. Hiding the protection in the blinds can be an architecturally appeal-
ing solution.
In summary, the tests of Dogruel and Field [12] achieved GSA Condition 3b [13],
which is associated with high protection and a low hazard level [11]. The experimental
study concluded that for large-paned windows at least two cables are required to effec-
tively prevent glass fragments from being propelled into the protected area.
The efficiency of a CCS is generally driven by the performance of the cables, the cable
anchorage, and the response of the impacting fragments [14]. A rather simplified ap-
proach would be to design catcher-cables and cable anchorage directly on the distributed
blast loads. In fact, the tensile forces in the cables are a result of the impact of the window
fragments and are characterized by the impact velocity and the mass of the fragments.
Depending on the shape of the window fragments, the CCS may be subjected to local
punctual loads or extended areal loads. Moreover, the flexibility of the cables influences
the reaction forces.
Even though the failure-mechanism of catcher-cables essentially corresponds to the
cable tensile forces, measurements during experiments with entire retrofied windows
are rather rare. Remennikov and Brodie [15] have published an experimental study on
cable forces and how their flexibility affects the response of a CCS. In this study, the
catcher-cables were subjected to local impacts, which may represent a single impacting
frame fragment. In this case a 600 kg hammer was utilized to be dropped with velocities
of 1.1 m/s to 1.29 m/s onto the center span of the steel cables. The following can be con-
cluded from the study [15]:
• By using energy-absorbing plates for anchoring the cables, the tensile forces can be
reduced by approximately one-third compared to rigid anchorage.
• Since greater cable deflections can be achieved, the energy-absorbing anchorage re-
sulted in an increase in the deceleration duration of the impacting hammer compared
to the rigid anchorage.
• Conversely, the extended deceleration time results in lower forces on the fragments.
This concept shall prevent fragments from being “cut” during the impact.
Similar measures for controlling energy dissipation at the cable anchorage are well
known for cable-net façades, e.g., in [16,17] and curtain walls, e.g., in [18]. Specific viscoe-
lastic and frictional devices can be applied to control the tensile forces at the connection
between glass and cables, as well as at the anchorage of the cables. A numerical approach
to study the cable forces in a CCS was presented by Lan and Crawford [19]. However, the
Buildings 2024, 14, 767 4 of 23
response of the CCS was evaluated solely for the impact of an ASF-retrofied glass pane,
without considering possible fragments of window frames.
This article presents new experimental research on the effectiveness of catcher-cable
systems (CCSs) in combination of anti-shaer films (ASFs) to retrofit windows. The blast
tests are performed using entire window systems, i.e., conventional single-casement win-
dows with insulating glass units (double-paned) and window frames made of un-plasti-
cized polyvinyl chloride (uPVC). In addition to these retrofit measures (CCS and ASF),
the influence of the steel profiles installed in the window frames on the response of the
windows is examined. Note that based on the available literature, it can be concluded that
such conventional single casement windows have generally not been tested against blast
loads yet. Therefore, the study also includes a discussion on the failure mechanism of such
windows.
In the blast tests, the windows are subjected to blast loads that meet the requirements
for ER1-certification according to EN 13541:2012 with a reflected peak overpressure of
66.7 kPa and a reflected maximum impulse of 417.6 kPa·ms. The CCS is exposed to win-
dow fragments with a realistic mass, stiffness, and velocity in the event of a window fail-
ure because the blast tests are performed on entire window systems. Various measure-
ment methods were used to capture the velocity of the window fragments, the dynamic
cable forces, and the hazard. The captured data provide valuable information for the de-
sign and implementation of catcher-cable systems for existing buildings, which can im-
prove the occupant safety in the event of an explosion.
2. Test Setup
The blast tests are carried out in the gas-driven shock-tube Blast−STAR (Blast Security
Test and Research Facility) located at the Fraunhofer Ernst Mach Institute (EMI). The basic
layout of the shock-tube facility can be found in Millon and Haberacker [20].
2.1. Overview
Table 1 summarizes the 10 configurations examined in the shock-tube tests. All test
specimens are conventional single-casement windows with insulating glass units (double-
paned) and window frames made of un-plasticized polyvinyl chloride (uPVC). Various
retrofit-configurations, including anti-shaer films (ASFs) and catcher-cable systems
(CCSs), are applied to the conventional windows. In addition, the influence of steel pro-
files installed in the window frames is examined.
Table 1. Overview of test configurations of the tested windows.
Tes t Configuration ASF Steel Profiles CCS
U1 Basic unprotected - - -
ASF01
ASF-retrofied
yes - -
ASF02 yes - -
ASF03 yes yes -
CC01
ASF-retrofied
including CCS
yes - yes (soft)
CC02 yes - yes (soft)
CC03 yes yes yes (soft)
CC04 yes yes yes (soft)
CC05 yes - yes (hard)
CC06 yes - yes (hard)
The test program is structured as follows.
• The first test U1 is carried out with a specimen referred to as “basic unprotected”.
The tested conventional window has no blast protective measures and serves as a
benchmark for all other tests.
Buildings 2024, 14, 767 5 of 23
• Subsequently, the effectiveness of an ASF applied to the glazing of such a basic un-
protected window is evaluated in tests ASF01 to ASF03. In practice, window frames
are often fied with steel profiles to meet the increased structural requirements. For
this reason, the specimen in test ASF03 is additionally equipped with steel profiles to
determine the contribution of the increased frame stiffness to the overall blast re-
sistance of the window.
• Finally, six shock-tube tests (CC01 to CC06) are performed on specimens equipped
with CCSs and ASFs. The test series examines two different stiffnesses of the CCS
(soft and hard) to determine their effect on protection. In addition, the window
frames in tests CC03 and CC04 have steel profiles installed, while the rest of the tests
are conducted without steel profiles.
The below sections detail the respective configurations and the retrofit measures.
2.2. Basic Unprotected Configuration of the Tested Windows
In test U1 (Table 1), a basic unprotected configuration is tested. Figure 1 shows tech-
nical details on the components of the window. The conventional window consists of
three main parts: the frame, the sash frame, and the insulating glazing unit (IGU).
The IGU consists of an outer 4 mm-thick float glass pane, a 16 mm-wide inter-pane
cavity filled with an argon gas mixture, and an inner 4 mm-thick float glass pane. The
dimensions of the IGU are 883 mm in width and 1133 mm in height (Figure 1a), which is
consistent with the glazing dimensions of 900 mm × 1100 mm, as outlined in the EN
13541:2012 test method [10]. Therefore, the test results of these full-scale studies can be
compared to the results of the ASF certification tests on single glazing units. But remark-
able discrepancies at the glazing support conditions are valued in this test series.
Figure 1. Tested conventional single-sash window with an insulating glazing unit; (a) front view
and (b) cross section of the window.
Figure 1b shows a cross section of the window. The frames consist of multiple thin-
walled hollow chambers that improve thermal efficiency. Optional in the test series are
steel profiles that are fied into the hollow chambers of the window frames during pro-
duction. These steel profiles are typically used in uPVC-window frames to add strength
and stability to the window system. However, they usually end several centimeters from
the corner joints of the frames, thus adding no additional strength to the frame corners.
The unprotected window in test U1 was designed without steel profiles, representing a
window configuration with low frame strength.
Fiing systems are required to open and lock sashes of casement windows. With the
window locked, the fiings provide the mechanical load-bearing connection between the
sash (the moveable part of the window) and the frame (the stationary part of the window).
The tested windows are equipped with a conventional fiing system, which provides low
Buildings 2024, 14, 767 6 of 23
resistance against burglary (resistance class RC1 N according to EN 1627:2021 [21]). Here,
five conventional strikers, one security tilt striker, and two corner bearings are installed.
The arrangement is illustrated in Figure 2. The counterpart of the strikers are mushroom
head pins that can slide into the recesses of the strikers.
Figure 2. Arrangement of the fiing system.
Figure 3 shows the window installed in the shock-tube. It is fixed with 8 anchor pins
to a steel adapter frame that was firmly bolted to the mounting frame of the shock-tube
(Figure 3a). The adapter frame also provides the bearings for the catcher-cable system
(Figure 3b), which will be discussed in Section 2.3.
Figure 3. Tested window mounted to the adapter frame at the shock-tube; (a) front view on the
shock-tube and (b) anchors of the window and bearings for the CCS.
All window configurations explained in the following are retrofied upgrades of the
basic unprotected configuration U1.
2.3. Tested ASF-Retrofied Configuration
Three tests are performed with ASF-retrofied configurations without a catcher-cable
system (ASF01, ASF02, and ASF03, Table 1). The applied anti-shaer films (ASFs) were
selected because they are a certified product in accordance with the EN 13541:2012 test
method. They have the following characteristics:
• The applied ASFs achieved ER1-certification according to the EN 13541:2012 test
method. They were tested on a monolithic float glass pane. In the new series of tests
presented here, the windows are also subjected to blast loading at an ER1 intensity.
Buildings 2024, 14, 767 7 of 23
• The applied ASFs have a thickness of 0.5 mm (19 mil) and are installed in a “daylight”
application. This means the films are placed underneath the glazing beads with no
gaps between the edges of the films and the outer edges of the glass panes [22]. The
films are not fixed to the sash frame.
• As recommended by the manufacturer, the ASF is aached only to panes of the insu-
lating glazing units (IGUs), which are facing the protected side (here: inside of the
building, Figure 1b). The exterior pane of the IGU facing the aacked side (here: out-
side of the building, Figure 1b) was not retrofied with an ASF.
The three conducted tests, ASF01, ASF02, and ASF03 (Table 1), also examine varia-
tions in the frame’s stiffness. Tests ASF01 and ASF02 are carried out without steel profiles
strengthening the frame (Figure 1b). Test ASF03 is performed using such steel profiles.
2.4. Tested ASF-Retrofied Configuration with Catcher-Cable System
Six tests, designated as CC01 through CC06 (Table 1), are performed using a combi-
nation of an ASF-retrofied glazing unit and a catcher-cable system. The catcher-cable
system (CCS) comprises two stainless steel (type 1.4401) wire ropes. These are positioned
155 mm from the window frame on the protected side. The spacing between the two steel
cables is 400 mm. The cable length between each bearing is 1640 mm. The bearings are
located at the top and boom of the adapter frame (Figure 3). In practical applications, the
cables would be anchored in the floor and ceiling of the room. Alternatively, horizontal
anchorage to adjacent structural components is also possible.
Figure 4 illustrates details of the CCS. At bearing A, located at the top, the steel cables
are flexibly anchored by elastic compression springs (spring-supported). If tensile forces
are applied to the cables, the springs are compressed. Lateral deflections of the springs are
avoided by using welded-on sleeves. At bearing B, located at the boom, the steel cables
are rigidly anchored to the adapter frame (Figure 4). Here, the tensile forces are measured
using cylindrical load transducers.
Figure 4. (a) Installed catcher-cables; anchoring (b) at bearing A and (c) at bearing B.
The test series examines two different stiffnesses of the CCS. System properties are
summarized in Table 2. The “soft” configuration comprises an 8 mm-thick steel cable and
an elastic compression spring with a stiffness of 71 N/mm. The “hard” system is composed
of a 10 mm-thick steel cable and an elastic compression spring with a stiffness of
186 N/mm. The static ultimate tensile strength of the soft system is 21.84 kN, while that of
the hard system is 32.19 kN. Both systems can achieve a maximum spring deflection of
about 15 mm in compression.
Buildings 2024, 14, 767 8 of 23
Table 2. Mechanical properties of the tested catcher-cable systems.
Configuration Test Cable Diameter
[mm]
Static Ultimate
Tensile Strength
[kN]
Spring Stiffness
[N/mm]
Soft CC01, CC02,
CC03, CC04 8 21.84 71
Hard CC05, CC06 10 32.19 186
The window frames in the tests CC03 and CC04 have steel profiles installed (Table 1).
In the remaining six tests, the window frames are assembled without steel profiles.
2.5. Instrumentation and Documentation
The tests use several methods of documentation, which are described below.
2.5.1. Blast Load and Pressure Measurements
The blast loads are measured by two pressure gauges (D1 and D2) installed next to
the tested windows. The gauges used are model 8510C-15, manufactured by Endevco (Ir-
vine, CA, USA). They can accurately measure peak overpressures of up to 103.42 kPa (15
Psi), with a maximum possible error of 0.5% in the measured values [23]. All measured
peak overpressures are below this given limit (Table 3). Figure 5 depicts the measured
reflected overpressure–time histories from test ASF01 and the respective reflected im-
pulse–time histories. The overpressure–time histories at the two pressure gauges D1 and
D2 are almost identical. Slight deviation in the blast loads can be observed after reaching
the maximum reflected impulse at around 22 ms. The deviations are likely due to the
asymmetric displacement of the torn-off window parts.
Figure 5. Measured reflected overpressure−time history in test ASF01.
The initial seings of the shock-tube were established to meet the blast intensity for
ER1-certification according to EN 13541:2012. Table 3 summarizes the average measured
reflected blast loads at the two pressure gauges. The actual blast loads deviate slightly
from the ER1 target values. The mean value of the reflected peak overpressures from all
10 tests is 66.7 kPa (Table 3), which is approximately 1/3 higher than the target value of
50 kPa. The mean value of the reflected impulses is 417.7 kPa·ms, which is also slightly
higher than the target value of 400 kPa·ms. Nevertheless, these two blast characteristics
correspond well to the load required for ER1-certification. The measured average duration
of the positive pressure phase is 1.7 ms shorter than the target value of 20 ms. This minor
discrepancy is accepted.
Buildings 2024, 14, 767 9 of 23
Table 3. Mean intensity of the measured blast loads from the 10 shock-tube tests.
Reflected Peak
Overpressure [kPa]
Reflected Maximum
Impulse [kPa·ms]
Duration of the
Positive Pressure Phase
[ms]
Mean value 66.7 417.7 18.3
Coefficient of
variation 3.2% 4.6% 3.8%
By evaluating the statistical data, a maximum coefficient of variation of 4.6% at the
maximum impulse can be found (Table 3). This indicates a relatively low statistical scaer
compared to a free-field blast [24]. Consequently, during the test series, the 10 windows
were consistently exposed to similar blast loads.
Typical for shock-tube tests is the multiple exposures of the test specimen to blast
loads. This rather undesirable effect occurs because the blast wave is re-reflected in the
partially confined shock-tube [25]. In the presented test series, the arrival of the secondary
shock is observed with the secondary increase in overpressure starting at about 70 ms
(Figure 5). At this instant, all tested windows were already shaered. Thus, it can be con-
cluded that the secondary shock does not have influence on the structural behavior.
2.5.2. Displacement and Velocity
The displacement of the tested windows are determined by digital image correlation
(DIC) following the method described by Schneider et al. [26]. Each test is recorded at a
frame rate of 4000 frames per second, with an image resolution of 1024 × 1024 pixels. The
velocity is computed based on numerical differentiation of the displacement-time histo-
ries.
Alternatively, in test U1 (unprotected window), the displacement of the window is
measured using laser rangefinders. The laser rangefinders are aached to a wooden sup-
port beam, which is arranged at the protected side of the window. This method has the
disadvantage of partially obstructing the flight trajectory of the window fragments. There-
fore, the DIC method proved to be more suitable for this test series.
2.5.3. Cable Tension
The dynamic cable tensile forces in the CCS are measured using cylindrical force
transducers located at the bearings B (boom, Figure 4a) of the steel cables. From the
measured strain in the cylinders, the force–time histories in the cables are computed.
2.5.4. Hazard Capture
The method described in ISO 16934:2007 [27] is used to evaluate the hazard from
fragments propelled into the protected area. The protected area (Figure 6) is subdivided
into 6 hazard zones, A to F, respectively. More details on the procedure can be found in
[11].
Figure 6. According to ISO 16934:2007 [27], (a) hazard zones and (b) hazard rating.
Buildings 2024, 14, 767 10 of 23
To assess the hazard posed to individuals, a witness wall is placed at a distance of
3.0 m to the specimen (Figure 6a). The witness wall consists of 15 individual witness pan-
els made of extruded polystyrene foam (XPS). The material of the panels has an elastic
modulus of 3.0 MPa and a mass density of 33.0 kg/m
3
. These properties comply with the
recommendations of ISO 16934:2007 [27]. The total dimensions of the wall are 3.75 m × 3.0
m (width × height).
2.5.5. Optical Analysis for Hazard Assessment
A novel approach was used to assess the impact of the window fragments on the
witness wall. This includes taking high-resolution digital photographs (5570 × 3710 pixels)
of the damaged panels after the tests (Figure 7a). The photographs are later digitally
aligned and cropped to precisely correspond with the outer boundaries of the designated
witness panels. The marks left by the fragments are clearly visible on the panel’s surface,
since the initially white witness panels were painted black prior to the test.
A method proposed by Dorafshan et al. [28] is implemented to determine the damage
on the panels by analyzing the high-resolution photographs. This method is widely ac-
cepted for detecting defects on surfaces with a monochrome texture, such as cracks in
concrete structures. It incorporates subroutines, such as filtering, thresholding, and mor-
phological operations. The following procedure is employed during the analysis:
1. Reading the raw RGB image;
2. Converting the image to grayscale;
3. Applying a bilateral filter [29] to the grayscale image to remove image noise while
preserving object edges;
4. Applying the Canny algorithm [30] to detect object edges; and
5. Applying morphological operations, specifically dilation and erosion [31].
To ensure an accurate analysis, all traces of fasteners and labels on the panels (as seen
in Figure 7a) were manually removed from the images. In addition, the captured damage
is carefully compared visually with each photo of the witness panel. Figure 7b shows the
result of the analysis.
Figure 7. (a) Digitally aligned and cropped image of a witness panel, and (b) binary representation
of a witness panel.
By employing the image-analysis method, a binary representation of the panel is pro-
duced (Figure 7b). Black pixels represent undamaged regions, while white pixels indicate
damaged regions. T proposed method not only locates damaged areas, but also helps
quantify the hazard. This is performed by analyzing each row and column of pixels in the
image and calculating the percentage of the damaged area.
Buildings 2024, 14, 767 11 of 23
3. Test Results
3.1. Basic Unprotected Configuration
In test U1, the basic unprotected window was tested. Figure 8 shows the global fail-
ure mode of the window taken from the high-speed video recordings. The window sash
was torn off from the frame by the blast load and propelled into the protected area. After
about 39 ms, the torn-off window sash collided with the wooden support beam that was
used to aach the laser rangefinders. While the sash frame was stopped by the wooden
support beam, the glass fragments proceed unhindered into the protected area.
Figure 8. High-speed video recordings of the unprotected configuration in test U1.
3.1.1. Failure Mechanisms of the Window
The high-speed video recordings in Figure 8 suggest a combined failure of the frame
corners and the fiing system of the window, which caused the window sash to be torn
off. To detail the failure at the frame corners, Figure 9a depicts the lower right corner at
15 ms, during the overpressure phase of the blast. Along the connecting surfaces of the
uPVC frames, significant separation cracks appeared almost simultaneously within a pe-
riod of 6.0 ms to 6.7 ms. In comparison, as can be seen in Figure 8, the failure of the glazing
occurs much later at approximately 20 ms. In conclusion, the frame corners can be identi-
fied as one of the vulnerable parts of the window that are currently not strengthened.
Figure 9. Failure mode at the frame corner; (a) high-speed video at 15 ms, (b) original unloaded
condition, and (c) deformed window under the blast load.
To elaborate on the observed failure mode at the corners of the frame, Figure 9b,c
shows cross-sections of the window, (b) in the original unloaded condition, and (c) de-
formed under the blast load. The deformation of the sash and frame profiles was primarily
due to torsion caused by an eccentric load transmied by the glazing unit. After exceeding
Buildings 2024, 14, 767 12 of 23
the strength of the uPVC at the frame corners, smooth separation cracks appeared along
the joint surfaces.
The following failure mechanisms of the fiing system, or a combination of them, are
possible. Schematic representations are given in Figure 10.
• Failure mechanism A: The centrally arranged screw and the interlocking connection
to the frame cannot sufficiently prevent the striker from twisting.
• Failure mechanism B: The pull-out resistance of the screw is exceeded, resulting in
the striker to be torn-off from the frame.
• Failure mechanism C: The mechanism unlocked due to the large rotational move-
ment of the sash frame. In this case, the mushroom head pin disengages from its an-
chorage within the striker.
Figure 10. Possible failure mechanism of the fiing system.
In all failure mechanisms of the fiing system described above, forces between the
frame and the sash can no longer be transferred. The window sash tears off from the
frame. In the test series conducted, it was observed that almost all conventional strike
plates were torn from the frame, i.e., failure mechanisms A and B did most likely occur.
3.1.2. Displacements and Velocities of the Fragments
In the test U1 with an unprotected window, the displacements of the window were
measured using two laser rangefinders, targeting the sash frame and the center of the
glazing. Figure 11 shows the obtained displacement– and velocity–time histories at those
two locations.
Figure 11. Measured displacements and velocities in the test with an unprotected window (U1).
Buildings 2024, 14, 767 13 of 23
Since the glazing and the sash frame were torn off simultaneously from the window
frame (Figure 8), the measured displacements and velocities increase equally, as expected.
The maximum velocity reached is about 15 m/s. The measurements stop abruptly due to
the impact of the fragments on the laser rangefinders mounted on the wooden beam.
3.1.3. Hazard Level
Figure 12 shows the witness wall, which was analyzed using the optical method de-
scribed in Section 2.5.4. For orientation, the original position of the unprotected window
and a person with a height of 175 cm are indicated. A very large number of glass fragments
impacted the witness wall. Some of the glass fragments bounced off the panel-surface and
left cut marks, and others penetrated directly into the witness panel. The penetrated glass
fragments had a maximum length of up to 16.5 cm and a maximum mass of about 100 g.
Figure 12. Analyzed witness wall with impact damages after test U1.
About 0.99% of the total area of the witness wall was damaged in the test U1, which
corresponds to a total area of about 1114 cm
2
. The most severe damage can be seen in the
center of the witness wall at a height of about 1.5 m above the ground.
In summary, the evaluation of the witness panel concludes hazard level F according
to ISO 16934:2007 [27]. It must be noted that the impact of the sash frame on the witness
wall was prevented in this test by the wooden support beam for the laser rangefinders
(see Figure 8). However, from the initial velocity of the sash frame of about 15 m/s (see
Figure 11), it can be concluded that the sash frame would also hit the witness wall in haz-
ard zone F.
3.2. Windows Retrofied with ASFs
Three tests were performed on windows with ASF-retrofied glazing units (ASF01,
ASF02, and ASF03). Figure 13 shows the corresponding high-speed video recordings at
60 ms. In each test, the sash was torn off from the window frame. Again, the loss of struc-
tural integrity is aributed to separation cracks at the frame corners, as well as the failure
of the fiing system.
Buildings 2024, 14, 767 14 of 23
Figure 13. High-speed video recordings of the protected ASF-retrofied configurations.
Variation in the strength of the window frames was studied by using steel profiles.
In the tests ASF01 and ASF02, the window frames were fabricated without steel profiles
fied into the window frames (Table 1). In test ASF03, the window frames were reinforced
by additional steel profiles. When analyzing the high-speed video footage in Figure 13, it
appears that the sash with steel profiles (tests ASF03) was propelled more compactly into
the protected area than the sash without steel profiles (tests ASF01 and ASF02). In addi-
tion, the lower window frames without steel profiles were broken in the middle.
In summary, using ASFs as retrofit measures had no influence on the failure mecha-
nism of the window. Moreover, steel profiles in frames do not prevent the sash from being
torn off. Regardless, the sash equipped with steel profiles appeared to fly more compactly
into the protected area.
3.2.1. Displacements and Velocities of the Fragments
The displacements and velocities of the fragments were captured using the DIC
method. The tracking was performed at several marker points located at the center of the
glazing and at the sash frame. Figure 14 shows the measured displacement–time histories
of test ASF01 and the corresponding velocity–time histories.
Figure 14. Measured displacement and velocity of the sash in test ASF01.
As expected, almost similar displacements and velocities are obtained at the sash
frame and at the center of the glazing. The sash was accelerated up to a velocity of about
6 m/s to 8 m/s during the first 10 ms. Subsequently, the velocity–time history appears to
Buildings 2024, 14, 767 15 of 23
reach a kind of plateau. With the onset of the negative-pressure phase starting at about
20 ms (Figure 5), the fragments of the window were decelerated. An average velocity of
about 4 m/s was reached at about 40 ms. In test ASF02, the fragments reached a similar
maximum velocity as in test ASF01. In test ASF03, no window displacements were deter-
mined since one of the two high-speed video cameras showed technical dysfunctionality.
In summary, the windows were about 60% slower than in the test U1 without an ASF-
retrofied glazing unit. A possible reason is the influence of the negative-pressure phase,
which causes suction into the direction of the origin of the explosion. Because the ASF
provides more surface area for the blast load than the glass fragments alone, the suction
may cause more deceleration.
3.2.2. Hazard Level
All three conducted tests clearly demonstrated that retrofiing the glazing unit with
an ASF does not contribute to the load-bearing capacity of the remaining components of
the window, such as the window frames and window fiings. However, by retrofiing a
glazing unit with an ASF, the uncontrolled propagation of glass fragments into the pro-
tected area was partly prevented, since they still adhere to the film.
Note that in this test series, the ASF was only applied to the glass pane facing the
protected area. The glass pane on the aacked side was not retrofied by an ASF. Thus,
hazards emanate from the torn-off sash frame, the ASF with adhering glass fragments,
and the glass fragments from the non-retrofied glass pane. Figure 15 shows the analyzed
witness wall with traces of the impacting window fragments in test ASF01.
Figure 15. Analyzed witness wall with impact damages after test ASF01.
About 1.05% of the total witness wall area was damaged in the test (about 1181 cm
2
).
Cuing marks of the impacting glass fragments were documented up to a height of about
290 cm. The impact of the sash frame is clearly visible by an ~20 cm × 20 cm punched area
in the witness wall at a height of about 1.8 m above ground. The remaining relatively low
density of impacts at the center of the wall indicates the impact of the ASF.
Buildings 2024, 14, 767 16 of 23
In summary, the tests on the windows with ASF-retrofied glazing units showed that
despite the presence of a retrofit measure, a high number of glass fragments impacted
hazard zone F. In addition, the tests demonstrated the potential hazards posed by the torn-
off window frame. If the frame impacts a person, blunt trauma or bone fractures are pos-
sible. It can be assumed that there is a high risk to individuals due to the combination of
sharp glass fragments and heavy hard frame fragments.
3.3. Windows Retrofied with ASFs and Caught by a CCS
In the tests CC01 to CC06, the windows were equipped with ASFs, and the fragments
are caught by various catcher-cable systems (CCSs). Tests CC01 to CC04 were conducted
with a soft CCS configuration (Table 2) and CC05 and CC06 with a hard CCS configura-
tion. In addition, the window frames in tests CC03 and CC04 were equipped with steel
profiles, while in the remaining test, no steel profiles were installed (Table 1). During test
CC01, the ASF was cut along the bare steel cables. Hence, for all remaining five tests, the
cables were sheathed with flexible pPVC tubes. This has proven to be effective in prevent-
ing cuing.
Figure 16 shows the high-speed video recordings of test CC02 over a period of 10 ms
to 60 ms. As in the previous tests, the sash was torn off from the frame. However, the
trajectory of the torn-off window sash was abruptly stopped by the CCS at about 16 ms.
During the impact, the ASF was fully detached from the sash frame and wrapped around
the two cables (at about 40 ms). On the one hand, the sash frame and the ASF are retained
by the CCS. On the other hand, the glass fragments of the non-retrofied pane are not
retained by the cables, as can be seen at about 50 ms. They are propelled further towards
the protected area (Figure 16, 60 ms). Similar mechanisms to those described above were
observed in the other five tests with CCSs.
Figure 16. High-speed video recordings of test CC02 with a soft CCS configuration.
In summary, the CCS can effectively stop the heavy window frames and the ASF.
Regardless, hazardous glass fragments can still fly into the protected area.
3.3.1. Displacements and Velocities of the Fragments, and Cable Forces
Figure 17a shows the measured displacement–time and velocity–time histories in test
CC02 at the center of the glazing and at the sash frame. In test CC02, a soft CCS configu-
ration was used. Impact velocities in the six tests ranged from 6 m/s to 15 m/s. The result-
ing force–time histories in the cables S1 and S2 are shown in Figure 17b.
Buildings 2024, 14, 767 17 of 23
Figure 17. (a) Measured displacement and velocity of the sash in test CC02; (b) measured tensile
forces in test CC01 and CC02 conducted with a soft CCS−configuration.
The impact time 𝑡 at about 16 ms (Figure 17a) can be correlated with the initial in-
crease in tensile forces in the cables, at about 16 ms (Figure 17b). At the same time, it marks
the onset of the velocity decay of the sash frame (Figure 17a). The velocity at the center of
the glazing was abruptly reduced shortly after reaching the maximum cable force F
max
(at
about 26 ms), correlating with the unloading of the CCS. This verifies the measurements
since cable tensile force and the deflection are directly related. Similar effects were ob-
served in the remaining five CCS tests.
Figure 18 depicts the measured maximum cable forces F in each test. Cable S1 is
located at the outer left side of the window (Figure 16). It tends to be generally subjected
to slightly higher forces than the cable S2. This effect might be due to a slightly asymmetric
impact of the sash on the CCS.
Figure 18. Maximum tensile forces measured in the catcher-cable systems.
No significant differences can be observed between the response of the tested soft
and hard CCS systems. Most importantly, the cables did not fail in any of the six tests.
3.3.2. Hazard Level
In all six tests, the sash frame was retained by the CCS. Similarly, the ASFs were re-
tained, except for test CC01, where the ASF experienced a cut-through failure. However,
in all tests, the glass fragments from the non-retrofied glass pane on the aacked side of
the window were not stopped and were propelled into the protected area. Consequently,
the used retrofit measures were not able to reduce the hazard to personnel sufficiently. All
six CCS tests resulted in hazard rating F according to ISO 16934:2007 [27]. About 0.06% to
0.35% of the witness wall area was damaged in the tests.
Buildings 2024, 14, 767 18 of 23
3.4. Effectivness of the Blast Protection Measures
In summary, all 10 conducted tests resulted in hazard level F according to ISO
16934:2007 [27]. Since hazard level F is associated with a high hazard, the retrofit measures
applied did not sufficiently reduce the hazard to people in the protected area.
Nevertheless, when comparing the different sets of protective measures, a significant
improvement in protection can be observed. As a benchmark for this improvement, the
damaged area of the witness wall evaluated through the optical analysis can be used. Fig-
ure 19 shows the percentage of the total witness wall area damaged in each test.
Figure 19. Total damaged area of the witness wall.
The following results are obtained:
• Unprotected window: About 0.99% of the total witness wall area sustained damage
solely by impacting glass fragments. It is important to note that in this test, the torn-
off sash frame was retained by a wooden support beam deployed for the laser range-
finders. If the sash frame had also impacted the witness wall, the damaged area
would likely have been much greater.
• Window retrofied with ASF: About 1.05% of the total witness wall area sustained
damage in the test with no steel profiles fied in the window frames. The impact of
the sash frames punched a hole into the witness walls. This displays the severe haz-
ard posed by propelled parts of the window frame.
• Window frame with steel profiles, retrofied with ASF: In the test using steel pro-
files fied into the window frames, the damaged area was reduced by about 41%
compared to the test without steel profiles. The frame and the glass fragments still
impacted the witness wall.
• Window retrofied with ASF and CCS: Generally, the CCS was able to catch the
window frame and the ASF; however, some glass fragments were still propelled into
the protected area, they mostly originated from the un-retrofied pane. In the test,
0.35% of the area of the witness wall was damaged using an ASF and a soft CCS.
Compared to the test configuration without a CCS, a reduction of about 66% of the
damaged area was achieved.
• Window frame with steel profiles, retrofied with ASF and CCS: The tests incorpo-
rating an ASF, a soft CCS, and steel profiles fied into the window frames yielded
the lowest percentage of damaged area (0.06%). This marks a remarkable reduction
in the damaged area, approximately 94%, compared to an unprotected window.
4. Practical Considerations Using Catcher-Cable Systems
The test series generally demonstrated that retrofiing conventional uPVC windows
with a combination of anti-shaer films (ASFs) and catcher-cable systems (CCSs) offers
Buildings 2024, 14, 767 19 of 23
only limited protection against ER1 blast loads. This suggests that such protective
measures should only be employed with careful risk considerations, e.g., as a temporary
solution. In certain situations, it might be more practical to additionally strengthen the
window frame and to implement advanced anchorage for the ASF, such as mechanical
anchorage [22]. For new buildings, more efficient protective measures, such as blast-re-
sistant security windows, should be implemented.
When considering catcher-cable systems (CCSs) as a protective measure, it is crucial
to take into account several aspects:
• The CCS will only be efficient if it is used in combination with an anti-shaer film
(ASF) aached to the glazing of the window.
• In cases where an insulating glazing unit is retrofied, the ASF should be applied on
both panes, at the aacked and protected side, to prevent the uncontrolled flight of
glass fragments.
• To prevent the window sash from sliding past them, a minimum of two cables should
be utilized. This recommendation is also outlined in [32].
• The cables should be distributed evenly, considering the mass distribution and the
expected trajectory of the fragments.
• To prevent cuing of the ASF, it is important to coat or sheath the bare steel cable
with soft polymers and to ensure a minimum diameter.
Note that during the conducted test CC01, the impact on the bare steel cables resulted
in the cuing of the ASF. Subsequently, for all remaining tests, the cables were sheathed
with flexible pPVC tubes. This has proven to be effective in preventing cuing.
4.1. Calculating Cable Forces
The conducted test series showed that the catcher-cables were subjected to an impact
load, rather than to a blast load. This statement becomes clear when comparing the aver-
age duration of the overpressure phase, which was 18.3 ms (Figure 5), with the onset of
the cable tensile forces at around 16.5 ms (Figure 17b). In our case, the scenario might
therefore be simplified as a pure impact scenario, without considering air blast effects. It
should be noted that this consideration is only valid for the tested configuration. However,
in other blast scenarios, with significantly longer overpressure phases (e.g., gas explo-
sions), the blast loads may additionally affect the cable forces.
The impact scenario is defined by the mass, velocity, and rigidity of the impacting
window sash. The following sequence of the impact was observed from the high-speed
videos:
(a) The relatively rigid sash frame acts on the CCS in the immediate vicinity of the an-
chorages (Figure 20a). The cable deflects particularly at these impact locations.
(b) The soft anti-shaer film with adhering glass fragments acts on larger areas of the
catcher-cable system (Figure 20b). The film adapts to the cable accordingly.
Figure 20. Impact on the catcher-cable system: (a) window sash; (b) glazing with ASF.
Numerous analytical solutions of a cable system under static loading can be found in
the literature, e.g., in Petersen [33]. However, the impact of the window sash represents a
dynamic loading, incorporating effects, such as mass inertia. Analytical calculations might
be conducted by utilizing a single degree of freedom system (e.g., [34]). Here, non-linear
approaches become essential to consider cable and spring deformations. Furthermore, it
Buildings 2024, 14, 767 20 of 23
is crucial to determine a suitable force–time history that accurately represents the impact
of the window sash. This force–time history varies depending on the rigidity of both the
impacting window sash and the catcher-cable system.
Given these complexities, an analytical approach proves cumbersome. Numerical
simulations utilizing a detailed finite element model of the window may provide a more
effective solution to overcome these challenges [35].
4.2. Anchoring of the Cables to Supporting Structures
Securely anchoring the CCS in the supporting structure can be challenging. In the
conducted tests series, the maximum tensile force within the cables was around 21.5 kN.
If the supporting structure cannot withstand these anchoring forces, the CCS is at risk of
failure, potentially posing a hazard itself. It should be stressed that in this test series, a
CCS anchored with a spring-supported bearing was used. Without such spring elements,
cable tension forces are expected to be even higher since fewer deformations are possible.
Vertical anchoring of the cables can be achieved in both the floor and ceiling, while
horizontal anchoring is possible between the window reveals. Optimal anchoring condi-
tions can be found in reinforced concrete, as masonry proves to be a comparatively weak
support. Due to the significant forces involved, anchoring in wooden support structures
is often inappropriate. For masonry and wood, the most effective solution for anchoring
cables is probably to use counter plates on the opposite side of the structure along with
threaded rods. If the maximum allowable forces are exceeded, another possible solution
may be to increase the number of cables.
Note that using bending-resistant steel pipe structures (i.e., catcher-bar systems)
might reduce the issues with anchoring and avoid the cuing effects of the ASF at the
same time. Regardless, this was not within the scope of the study presented here.
4.3. Limitations for the Use of Anti-Shaer Films and Cable-Catcher Systems
In the test series presented here, the retrofied protective measures were examined
at specific blast loads, with a specific window size, window type, type of anti-shaer film,
type of cable, type of cable anchorage, etc. Below, potential limitations and scalability of
the tested protective measures are discussed.
Most importantly, it is crucial to know how the selected anti-shaer film has been
certified. For instance, the ASFs applied in this test series were certified according to the
EN 13541:2012 [10] test method against an ER1 blast load. This certification test method
requires the dimensions of the glazing to be 1100 mm × 900 mm. Consequently, this also
considerably limits the possible window size. Moreover, in the EN 13541:2012 [10] test
method, the edges of the glazing are clamped into a stiff test frame. This type of clamping
is nearly impossible to implement in a standard window frame. Consequently, the possi-
ble protective effectiveness achieved in certification tests of glazing units and real window
glazing can significantly differ.
One significant limitation of cable-catcher systems is the anchoring of cable forces to
adjacent structural components. As the cable span increases, the forces quickly reach lev-
els that can no longer be secured, unless a large number of cables are used, which is also
not favorable.
Generally, due to the highly nonlinear behavior of the tested window type and ret-
rofied protective measures, the test results can only be transferred to a very limited ex-
tent to other dimensions. To expand this scope, numerical simulations can be used.
It is expected that the measures are more suitable for rather small window dimen-
sions and moderate blast loads (below ER1). For blast loads with a higher intensity and
larger window dimensions, replacement with blast-resistant windows is advisable. How-
ever, the protective design needs to be assessed individually.
Buildings 2024, 14, 767 21 of 23
5. Summary and Conclusions
In the event of an explosion, conventional unprotected windows can pose a particu-
larly high risk of injury to occupants as glass fragments and window frames are propelled
both inside and outside a building. This article explored the effectiveness of various pro-
tective measures for conventional single casement windows against blast. The results of
10 shock-tube tests were presented, analyzed, and discussed. Subjected to an ER1-blast
load, the retrofit measures for the windows include anti-shaer films (ASFs) and catcher-
cable systems (CCSs). A range of measurement methods, including digital image correla-
tion and force transducers, was utilized to capture the velocity of window fragments and
measure the cable forces. Additionally, an optical method for hazard evaluation was sug-
gested and implemented to assess the impact of fragments on a witness wall.
In all 10 tests, the windows experienced failure, and the window sashes were pro-
pelled towards the protected area. Here, the effectiveness of the CCS was demonstrated,
as they successfully caught the sash frame and the anti-shaer film along with adhering
glass fragments. Note that even though the CCS caught the heavy frame parts of the win-
dow, several glass fragments were still thrown into the protected area. More severely,
without a CCS, the frames were propelled 3 m into the protected area, where they im-
pacted against a witness wall. The measured average velocity of the fragments was about
10 m/s. Caught by the CCS, the maximum measured tensile force within the cables was
around 21.5 kN.
When analyzing the witness wall, it can be concluded that despite the presence of
retrofit measures, an unacceptable hazard rating of F (high hazard) according to ISO
16934:2007 [27] was consistently reached. Nevertheless, when comparing the different sets
of protective measures, a significant improvement in protection can be observed. Com-
pared to the results with an unprotected window, a window with a combination of ASF,
CCS, and steel profiles fied into the frame profiles remarkably lowered the hazard. With
this combination, the damaged witness wall area was reduced by approximately 94%. It
should be stressed that the CCS was particularly effective in mitigating the flight of the
heavy frame fragments, which can cause blunt trauma and bone fractures.
Despite the lack of acceptable hazard reduction, the results of the experiments pro-
vided important information for the design of catcher-cable systems. To underline this,
the results presented in this article are supplemented by practical considerations using
catcher-cable systems. Finally, it should be noted that retrofit measures need to be tested
on full window systems. This approach will provide detailed information on blast-re-
sistance in practical applications. Retrofiing only one component of a window, such as
glazing, is often not sufficient because the weakest link in the chain determines perfor-
mance.
For future studies, the following research and development potential for anti-shaer
films (ASFs) and catcher-cable systems (CCSs) can be recognized:
• Improving the aachment of the protective films to the window frames: In the tests
conducted, the ASF was installed in a “daylight” application, meaning that the films
are simply placed under the glazing beads without any aachment to the window
sash. However, in the event of glass breakage, the films must be aached to the sash
in order to create a membrane effect. In the tests conducted, this was not the case,
resulting in the film being torn off from the sash, especially after the impact on the
CCS. In future tests, the ASF could be bonded or mechanically aached to the sash.
• Tes ting flexible cables: In the tests conducted, relatively stiff steel cables were an-
chored using simple elastic springs. This technique allowed for greater cable deflec-
tions than a fixed anchorage. Future tests may include catcher-cables made of more
stretchable synthetic materials (nylon or polyamide) or a combination of natural and
synthetic fibers.
• Testing energy-absorbing anchoring techniques: Energy-absorbing effects, e.g.,
from plastic deformation, played a minor role in the tested CCS. However, it is well
known from impact tests [15] that an energy-absorbing anchorage of the cable can
Buildings 2024, 14, 767 22 of 23
also significantly reduce the cable forces. In future tests, such techniques can be
tested, e.g., by simply anchoring the cables to deformable steel plates.
Author Contributions: Conceptualization, M.A., J.D.v.d.W., M.W., A.P. and N.G.; methodology,
M.A., J.D.v.d.W. and N.G.; investigation, M.A. and J.D.v.d.W.; formal analysis, M.A., J.D.v.d.W.,
M.W. and A.P.; writing—original draft preparation, M.A. and J.D.v.d.W.; writing—review and ed-
iting, M.W., A.P. and N.G.; visualization, M.A.; supervision, N.G.; project administration, M.A.;
funding acquisition, M.A. and N.G. All authors have read and agreed to the published version of
the manuscript.
Funding: This research was funded by the Federal Office of Civil Protection and Disaster Assistance
(BBK), Department II.5, in Germany (grant number BA2533). The support is gratefully acknowl-
edged.
Data Availability Statement: The raw data supporting the conclusions of this article will be made
available by the authors on request.
Conflicts of Interest: The authors declare no conflicts of interest. The funders had no role in the
design of the study; in the collection, analyses, or interpretation of data; in the writing of the manu-
script; or in the decision to publish the results.
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