Constrained layer damping concept used on isolated gym floors. Bet- ter than Concrete? Marina Rodrigues 1 CDM Stravitec nv Reutenbeek 9-11 3090 Overijse Belgium Paulo Pinto 2 CDM Stravitec, Unipessoal, Lda Azinhaga da Torre do Fato, 33B Esc. A 1600-297 Lisboa Portugal

ABSTRACT

As the global fitness trends continues in a post-pandemic world, intra-building disruptions from high- energy fitness create serious acoustical isolation challenges. Solutions from simple roll-out mats and rubber tiles to concrete floating floors supported by spring jack-up isolators are used to achieve acoustical separation for fitness spaces. Understanding the sources of sound and vibration produced in fitness environments and finding ef- fective solutions was a journey that CDM Stravitec began in the 1970s and this area of the acoustics industry has been most intensively researched as part of the development of our range of lightweight floating floors. As part of this research, we extensively investigated how the concept of constrained layer damping (CLD) could be employed to mitigate vibration radiation through structures. In the application of fitness flooring, the CLD functions to restrict the physical movement between the rigid board layers, decreases the area of influence from the impact, reduces the energy radiation through the composite panel system to its support and subsequently reduces the energy transfer into the structure. Our research has also shown that elastomeric supports balance low-resonant frequency performance to prevent energy build-up at the driving frequencies and can achieve high levels of transmission loss which are comparable to concrete based solutions.

1. INTRODUCTION

As the global fitness trend towards at-home and accessible fitness continues, the disturbance caused inside buildings by high-energy fitness activities such as spinning, HIIT group workouts and cross- fit creates serious acoustic insulation challenges for both architects and acoustic consultants designing

1 m.rodrigues@cdm-stravitec.com

2 p.pinto@cdm-stravitec.com

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new residential and mixed-use buildings or refurbishing existing commercial and industrial buildings with acoustically sensitive and high-energy spaces. In attempts to attenuate the high impact and acoustic energy of commercial and residential gyms, a wide range of mitigation measures are still being prescribed. Solutions ranging from easy roll-out mats and rubber fitness tiles to thick concrete floating floors supported by spring isolators are used to achieve acoustic isolation of fitness areas. The results of these solutions are sometimes surprising, and additional challenges need to be ad- dressed. Since the 1970s, CDM Stravitec has been identifying and studying the various sources of noise and vibration produced in gyms and searching for effective and consistent solutions to reduce them. This area of acoustics has been most intensively researched during the past 5 years during the development of the Stravigym range of lightweight fitness floating floors and has been the topic of several industry white papers. The high-performance floating floors developed as part of this research make use of the "constrained layer damping" (CLD) concept, which has been extensively researched and documented by Ross, Kerwin, and Ungar (RKU) as a method to reduce continuous vibrations within structures and which has also been thoroughly examined by us regarding transient vibration and impacts, as explained in this paper. 2. CONSTRAINED LAYER DAMPING TECHNOLOGY

2.1. Story What began as an experiment in the 1930s to reduce noise and vibration in metals and plastics, has become a common treatment in a wide variety of applications. Constrained-layer damping (CLD) is a specific treatment method commonly used in the nautical, aerospace, and military industries. The foundation laid for constrained-layer damping in the 1950s has led to some significant advances and diverse applications of CLD treatments, starting with the rather obvious application in naval ships and aircraft to reduce both the radiation efficiency and transmission coefficient for inward and out- ward propagating sound waves and mechanical vibration. Vibrating computer hardware components can be a source of annoyance and stress in modern work environments. CLD has been used to reduce the vibration of various parts of the computer without adding much weight and thickness to the computer casing. The automotive industry has also benefited from CLD research. For example, there is a known case in which the vibrations of an engine and an engine compartment were dissipated using a viscoelastic interlayer applied between two moulded engine covers. One unlikely application of CLD has recently been developed for the construction industry. CLD drywall panels are used to reduce the transmission of sound through wall and ceiling partitions. The CLD technique enables builders to achieve an ade- quate transmission loss through partitions, often without having to drastically increase the thickness and the mass of the partition or the assembly. Active CLD, which often involves the use of piezoelectric materials, has been modelled and used to reduce vibrations in rotating beams and other sandwich beams and panels. Applications such as these may yet be discovered as the technological world advances and brilliant scientists and researchers apply the right theory to the application.

2.2. CDM Stravitec’s first steps with CLD techniques CDM Stravitec CLD solutions (pka ISO-CORE) were developed in the early 1990s as lightweight alternatives to the industry’s gold standard of “heavy mass layers”. The technological drive to develop lightweight viscoelastic materials came from the transportation industry (buses, boats, trains, airplanes) where weight limitations are an economic driver for innova- tion.

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Overall Thickness

Surface

Thermal Conductivity

Core Material

Rw (dB)

Panel Composition

Weight (kg/m²)

K (W/m²K)

(mm)

Plywood 15 8.4 13.3 CDM-29 15 9.4 7.4 CDM-15 15 8.3 10.7 CDM-17 15 9.5 12.7

18 29

Plywood (15mm) Plywood (6mm) + CDM-29 (3mm) + Plywood (6mm)

30 31

Plywood (6mm) + CDM-15 (3mm) + Plywood (6mm)

Plywood (6mm) + CDM-17 (3mm) + Plywood (6mm)

Measurements in dB (*)

40.0

Air Borne Noise Transmission Loss

f in Hz Plywood CDM-29 CDM-15 CDM-17

100 10.5 20.2 21.3 17.5

35.0

125 12.5 19.2 15.2 16.8

160 9.0 19.9 19.2 22.4

30.0

200 15.0 23.9 20.3 21.7

250 14.8 23.0 22.6 24.0

25.0

315 16.0 25.1 24.5 25.4

R in DB

400 17.0 25.1 26.4 25.9

500 18.0 27.6 28.5 28.0

20.0

630 17.5 28.4 29.4 30.0

800 18.5 30.6 30.1 30.3

15.0

1000 19.0 30.8 30.6 30.4

1250 18.0 31.9 31.5 32.6

10.0

1600 17.5 32.3 31.8 33.9

2000 15.5 30.7 30.5 33.9

5.0

2500 16.0 28.2 29.1 32.9

3150

4000

5000

1000

1250

1600

2000

2500

125

160

200

100

250

315

400

500

630

800

3150 18.5 28.5 28.9 30.5

f in Hz

4000 23.0 31.4 31.5 30.8

CDM-15 CDM-17 CDM-29 Plywood

5000 24.0 34.0 34.4 33.0

Figure 1: Influence of different lightweight viscoelastic materials (CDM-29, CDM-15 and CDM-

17) used as a (CLD) interlayer in plywood.

Overal Thickness

Surface

Thermal Conductivity

Core Material

Rw (dB)

Panel Composition

Weight (kg/m²)

K (W/m²K)

(mm)

Plywood (13mm) + Heavy Mass (6mm) + Plywood (13mm)

Heavy Mass 32 31 38 6.3 CDM-17 32 24 40 5.9

Plywood (12mm) + CDM-17 (8mm) + Plywood (12mm)

Measurements in dB (*)

50.0

f in Hz Heavy Mass CDM-17

Air Borne Noise Transmission Loss

100 28.8 26.8

45.0

125 30.8 26.2

160 32.2 30.0

40.0

200 30.9 31.8

250 34.2 34.5

R in DB

315 34.4 33.9

35.0

400 34.8 34.0

500 35.7 34.7

30.0

630 37.4 37.4

800 37.1 39.0

25.0

1000 36.7 40.2

1250 36.2 40.8

1600 35.9 42.3

20.0

2500

1000

1250

1600

2000

3150

4000

5000

100

500

125

160

200

250

315

400

630

800

2000 37.8 43.1

2500 40.0 43.4

f in Hz

3150 42.2 44.1

4000 45.0 44.2

CDM-17 Heavy Mass

5000 47.2 45.2

Figure 2: Influence of CDM Stravitec lightweight viscoelastic material, aka CDM-17, vs heavy

mass layer used as a (CLD) interlayer in plywood assembly.

2.2.1. CLD as part of lightweight acoustic floor systems Ever lighter and longer floor spans and large partition-free office layouts have brought the issue of floor vibration to the attention of designers and owners. In composite construction, footfall-induced floor vibration is now an essential consideration in the design of floors and has even become the governing factor in some circumstances. Increasing the damping can be an effective means of reduc- ing floor vibration. A constrained layer damping system may be incorporated into a composite floor, potentially improving the floor’s dynamic performance by a factor of two or more. The improved damping can be achieved without significant increases to the structure’s mass or depth and thus offers

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considerable cost savings over alternative methods for reducing footfall vibration (such as increasing the mass and/or stiffness).

2.2.1. CLD as part of lightweight acoustic fitness floor systems CDM Stravitec has a long-term experience since the 1970s in gym and sport floor isolation, mainly with high-performance floating floor systems for gym and multi-disciplinary sport halls installed in the imme- diate vicinity of spaces with specific high-performance acoustic requirements, such as classrooms below or above sport facilities in schools (e.g. PHI College – Borgerhout BE (1977), RITO College – Diksmuide BE (1979), Holy Trinity College – Leuven BE (1980)) and has been many times called in to troubleshoot said noise complaint cases with success. By combining (1) wet floating floor solutions for gym & sport floors, (2) dry floating floor solutions for the building renovation (timber, masonry, and concrete struc- tures) and (3) an extensive research program started in 2014 to better understand the main driving param- eters behind structure-borne noise isolation for dry solutions, innovative high-performance “dry solu- tions” using CLD-technology were successfully introduced. Today, high-performance dry floor solutions based upon a combination of load-distributing lightweight panels and added damping and resilience are becoming more common and set a higher standard capable of meeting the evolved acoustic comfort criteria more and more defined by the lower part of the frequency spectrum and in function of energy impact levels. CLD may be described as a type of shear-related energy dissipation achieved by interconnecting two or more structural materials using a relatively thin viscoelastic interlayer, as it is contemporarily termed in the book Structure-Borne Sound and in Kerwin’s 1959 paper as “damping tape”. The advantage of a CLD treatment is, for many applications, the ability to obtain an exceptionally high amount of dissipation in a beam or plate without significantly changing the stiffness or mass of the composite system. The advantages of using CLD as a damping treatment include the possibility of obtaining high loss factors with relatively thin configurations and the fact that the stiffness of the composite system is not significantly increased. When designing acoustic floor systems in general and acoustic floor sys- tems for fitness in particular, total build-up height and weight are critical parameters because most of them are installed within existing buildings with limited load capacity and available space between ceiling and floor. Concrete is not an option in these particular cases, not only because of the extra weight, but because concrete-based systems aren’t quick to install and the gym operator never wants to close the club during the time of intervention, and because these types of floors can’t be dismantled and operators do not want a permanent solution, as the majority of gyms are located in rented prem- ises. As part of acoustic lightweight floor systems, load distribution towards the supporting structural floor is guaranteed by lightweight paneling, giving bending stiffness to the floor system. To reduce noise and vibration radiation under impact loads, a combination of panels with an as low as possible radi- ation efficiency should be used. Panels with the best ductility/strength ratio are wood-based panels such as plywood and OSB/3 [Load bearing/structural board for use in humid conditions (e.g. conden- sation, cleaning water, etc.)]. These panels have low damping and show dips in the coincidence and resonance-controlled regions of transmission loss. These dips in the resonance and coincidence-controlled region are mitigated by well-known CLD techniques with high damping viscoelastic acoustic membranes – damping layer. The system’s performance below the resonance-controlled range (i.e., stiffness-controlled range) is primarily controlled by the overall structure’s stiffness. This will always limit the performance that can be achieved from new impact isolation systems introduced to a space.

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Figure 3: Damping effect on transmission loss resonance & coincidence-controlled regions.

The added damping layer works as “impedance mismatch” (more effect from damping). The impact on the panels results in shear stress of the damping layer that controls the panel displace- ment and converts the mechanical energy (vibration) into heat.

Figure 4: CLD mechanism on converting impact energy into heat by shear stress.

‘Tansmis J Frequency (Ha) igh Damping Medum Damping © Low damping

The combination of wood-based panels with damping membranes offers the best mix of bending strength, high ductility, high damping and low radiation efficiency. And due to its simplicity, it is a valid solution for a high quantity of jobs. Many people think of damping as being an intrinsically heavy viscoelastic material (e.g., MLV, Accu- Seal, or DAUBERT 932). However, for constrained layer damping, internal friction characteristics are more important than mass for maximizing performance. Lightweight damping membranes have similar effects as heavy mass layers bringing less extra weight to the floor solution.

Figure 5: Acoustical isolation considering a weight drop with energy of 235N.m (55 lbs 36’’) in the

same lightweight floor system using 5 mm (3/16’’) lightweight damping layer – yellow – and 2

heavy damping layers, Acuseal – grey.

Acelaration Levels 4B] 8s 80 75 70 65 55 50 45 40 35 30 Frequency [Hz]

2.3. Case study The French decree no. 2006-1099 defines specs in which the occurring noise levels are compared with the background noise level and in which an acceptable noise level is defined as equal to the background noise plus 5 dBA during the day and plus 3 dBA at night. In addition to defining global values (above background noise), limits are also set per frequency range. Table 1: Maximum emergence levels (day-time) by frequency range according French decree no 2006-1099.

Octave Band 31.5 Hz (1) 63 Hz (1) 125 Hz 250 Hz 500 Hz 1k Hz 2k Hz 4k Hz

Maximum emer-

+9 dB +9 dB +7 dB +7 dB + 5 dB + 5 dB + 5 dB + 5 dB

gence level

(1) Addition from some acousticians side to complete the regulation which does not specify emergence at 63 and 31.5 Hz. In a club in Vélizy, France, located on the ground floor with residential flats on the first floor, the difference between the noise level generated at the neighbours - by weights of 24 kg (53 lbs) falling from 1.2 m (3 ft 11-1/4'') and weights of 80 kg (176 lbs) being dropped from 0.6 m (1 ft 11-5/8'') height - and the background noise was higher than the values defined by the local standard. Table 2: Measurements of configuration 1: 24 kg (53 lbs) dropped from 1.2 m (3 ft 11-1/4’’).

E

E max

L eq

L eq

day Comments

(L eq config.1 – L eq

Background noise

Config .1

background)

Global 23.6 44.8 21.2 5 NC

16 34.6 39.1 4.5 -

31.5 35.2 48.8 13.6 -

63 37.6 58.8 21.2 -

125 36.5 58.6 22.1 7 NC

250 22 48.2 26.2 7 NC

500 18 30.8 12.8 5 NC

1000 14.8 19.2 4.4 5 C

2000 13.2 17.6 4.4 5 C

4000 13.2 15.4 2.2 5 C

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Table 3: Measurements of configuration 2: 80 kg (176 lbs) dropped from 0.6 m (1 ft 11-5/8’’).

E

E max

L eq

L eq

day Comments

(L eq config.2 – L eq

Background noise

Config .2

background)

Global 23.6 38.5 14.9 5 NC

16 34.6 39.8 5.2 -

31.5 35.2 54.4 19.2 -

63 37.6 61.4 23.8 -

125 36.5 50.6 14.1 7 NC

250 22 35.5 13.5 7 NC

500 18 23.1 5.1 5 NC

1000 14.8 16.5 1.7 5 C

2000 13.2 13.8 0.6 5 C

4000 13.2 13.5 0.3 5 C

For many acoustic consultants, in-situ tests using mock-ups are common practice to understand how a resilient surface treatment or a floating floor system will perform. Therefore, two different mock- ups were installed and tested, one wet and one dry system, as described below. We used this experi- ence and the support we gave to the acoustic consultant involved to reconfirm the theory that a light- weight system using CLD can be an alternative to concrete-based acoustic floor systems. Table 4: Description of the systems tested on site.

Stravigym XP with Gympact- Layer-45 & dBooster ® technol-

Stravifloor Channel with

Layer

GympactLayer-45

ogy

Floor covering Existing rubber tiles, 23 mm (1’’) Existing rubber tiles, 23 mm (1’’)

Impact absorption layer GympactLayer-45 (1) GympactLayer-45 (1)

Load distribution layer 3 x OSB/3 with 18 mm (3/4’’) + 2

lightweight Damping Layer 100 mm (4’’) concrete slab

dBooster ® technology Yes No

Resilient support (2) Channel-M HR 50 (3) Channel-H HR 50 (3)

(1) Atop the floating floor system, resilient surface treatment has an important function: to increase the time of contact, which in turn helps to protect the floating floor system and reduces airborne noise generated within the fitness space.

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(2) 40 mm (1-9/16’’) insulation material installed between pads. (3) Spacing between channels and bearings defined according to the expected loads. Different pads have been considered since the self-weight of a concrete floating slab is different than that of a panel- ized system.

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Figure 6: Systems tested on-site (wet system not showing impact absorption layer that was used

during the drop weight tests).

From the in-situ tests and taking into account the two previously described configurations in terms of impact energy, it appeared that both systems complied with the local regulations, as shown in the graphs below.

Acoustical isolation - 24Kg from 1,2m (283N.m) Acoustical isolation - 80Kg from 0,8m (628N.m) 45 45 40 0 38 sgeev es segs sgeese seg? Frequency (ih) Frequency [Hz]

Figure 7: Acoustical isolation of both systems (red: dry & dark blue: wet) and E eq max (day) (yellow).

In the same club, an alternative panelized solution was tested side-by-side CDM Stravitec’s Stravi- gym XP system.

Table 5: Description of the two panelized systems tested side-by-side.

Layer Stravigym XP with Gympact- Layer-45 & dBooster ® technology

Competitor panelized floor sys-

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tem

Floor covering Existing rubber tiles, 23 mm (1’’) Existing rubber tiles, 23 mm (1’’)

Impact absorption layer GympactLayer-45 [45 mm (1-

[25 mm (1’’) + 25 mm (1’’)] 50

3/4’’)]

mm (2’’) polyurethane mats

Load distribution layer 3 x OSB/3 with 18 mm (3/4’’) + 2

2 x OSB/3 with 22 mm (7/8’’)

lightweight Damping Layer

No Damping

dBooster ® technology Yes -

Resilient support (1) Channel-M HR 50 [50 mm (2’’)] 50 mm (2’’) polyurethane pads

(1) 40 mm (1-9/16’’) insulation material installed between pads.

Figure 8: Competitor panelized system (left) and CDM Stravitec’s Stravigym XP system (right).

Figure 9: Acoustical isolation of different systems tested considering 30 kg (66 lbs) weights dropped from a 0.4 m (1ft 3-3/4’’) height. Red: 23 mm (1’’) existing rubber tiles; dark grey: 50 mm

(2’’) rubber tiles; orange: competitor panelized system; blue: CDM Stravitec’s Stravigym XP.

3. CONCLUSION

Lightweight systems, if well-designed in terms of stiffness, damping and the combination of layers, can have an equal or even better performance than concrete floating floor systems (wet solutions). Panels with the best ductility/strength ratio are wood-based panels, but if these are used as a load distribution layer of an acoustic floor system without viscoelastic materials, the system will show acoustic weakness at specific frequencies, as these panels have low damping and exhibit dips in the coincidence and resonance-controlled regions of transmission loss. The combination of wood-based panels (e.g. OSB/3, plywood) with damping layers offers the best mix of bending strength, high ductility, high damping and low radiation efficiency. For constrained layer damping, internal friction characteristics are more important than mass for max- imizing acoustic performance. Lightweight damping membranes have similar effects as heavy mass layers bringing less extra weight to the floor solution. When used on fitness floors, CLD limits the physical movement between the rigid board layers, re- duces the area of impact, reduces the energy radiated by the composite panel system to the support, and subsequently reduces the energy transfer to the structure, thus reducing the vibration radiated through structures. It should be noted that the building structure which supports the floating floor is the foundation upon which a high-performance isolation system is built. If there are vibration issues prior to the introduction of a high-performance floating floor, e.g. the structure is very flexible or very lightweight, it will be very difficult or even impossible to achieve high levels of separation by introducing a floating floor system, without corrective measures to the building structure. 4. REFERENCES

1. B. Shafer and B. Tinianov “Use of damped drywall in architectural acoustics”, Journal of the

Acoustical Society of America 130, 2388 (2011) 2. D. Ross, E. E. Ungar, and E. M. Kerwin, Jr., “Damping of plate flexural vibrations by means of vis-

coelastic laminae,” Structural Damping, ASME Publication, pp. 49–88, New York (1959). 3. L. Garibaldi and H.N. Onah “Viscoelastic Material Damping Technology” – Becchis Osiride – To-

rino (1996) 4. N.B. Roozen , H. Muellner , L. Labelle , M. Rychtarikova, C. Glorieux “Influence of panel fas-

tening on the acoustic performance of light-weight building elements: study by sound transmission and laser scanning vibrometry” – Journal of Sound and Vibration 346 (1)- (2015)

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