Proceedings of the Institute of Acoustics

 

 

Effect of concrete topping on floor impact sound insulation performance of CLT floor

 

Atsuo Hiramitsu¹, Building Research Institute, Tsukuba, Japan

Susumu Hirakawa², National Institute for Land and Infrastructure Management, Tsukuba, Japan

 

ABSTRACT

 

The use of wood is being promoted to achieve the goals of the SDGs around the world. In Japan,” the Act on Promotion of Utilization of Wood in Buildings and Other Structures to Contribute to the Realization of a Decarbonized Society” promotes the use of wood in buildings in general. In addition, CLT is being promoted to make effective use of domestic timber. There have been many requests to show wooden structural materials when CLT is adopted in the building. This paper examined the approach to increase the floor impact sound insulation performance of the CLT floor without ceiling. First, the measurements of the driving-point impedance of test specimens were carried out. Then, the measurements of the floor impact sound insulation performance were carried out in the model building using concrete floating floor or composite floor on the CLT floor panel with and without floor finishing. As a result, the performance of the concrete floating floor or composite on the CLT floor showed that the performance was almost the same as the concrete floor itself. Moreover, the effect of the floor finishing on the floor impact sound insulation performance was investigated.

 

1. INTRODUCTION

 

The promotion of the utilization of wood contributes to the reduction of CO2 and achieving the goals of the SDGs (Sustainable Development Goals). In Japan, “the Act on Promotion of Utilization of Wood in Buildings and Other Structures to Contribute to the Realization of a Decarbonized Society” was enforced, and a low-rise building is to be positively constructed of wood. CLT (Cross Laminated Timber) is being promoted to make effective use of domestic timber, and CLT has been standardized as a building material by JAS (Japanese Agricultural Standard). The acoustics environment performance of CLT buildings is lower than that of concrete construction buildings. Hence, it is important to study the acoustics environment performance of wooden CLT buildings^1-8. This is especially because the floor impact sound insulation performance is affected by the area density and stiffness of the floor structural frame. The floor impact sound insulation performance becomes many problems and troubles in timber construction buildings.

 

There have been many requests to show wooden structural materials when CLT is adopted to the building (i.e., without ceiling and CLT panel itself is exposed). However, when the ceiling structure is not constructed, there is no sound insulation effect by the ceiling structure. This paper examined the approach to increase the floor impact sound insulation performance of the CLT floor without ceilings.

 

2. FLOOR IMPACT SOUND REDUCTION IN TIMBER CONSTRUCTION BUILDING

 

The basics of floor impact sound insulation measures for timber construction buildings are summarized in Table 1. The change in floor impact sound insulation performance can be estimated by the driving-point impedance change in the floor structure shown in Equations 1 and 2. This study focused on "3) Reduction by floor structure" in Table 1. Here, a method of placing concrete on the CLT floor was investigated as a way to increase the weight and stiffness of the floor structure.

 

 

where,

Z_b : Driving point impedance (kg/s)

B : Bending rigidity of floor section (N/m²)

m : area density of floor structure (kg/m²)

E : Young's modulus of floor structure (N/m²)

I : Secondary moment of the cross-section of floor structure (m⁴)

 

Table 1: Basics of floor impact noise measures for timber construction building.

 

 

3. DRIVING-POINT IMPEDANCE OF CLT WITH CONCRETE TOPPING MEASURE MENTS

 

The driving-point impedances were measured for two types of specimens; a floating floor and a composite floor with concrete on the CLT panel.

 

3.1. Floating Floor

 

The driving-point impedance measurements were carried out on 210 mm thick CLT panels (7 layers, 2,000 mm x 2,000 mm) for the specimens shown in Table 2. Specimen A0 is a bare CLT panel, specimens A1 and A2 are concrete placed directly on the CLT panel and specimens A3 - A6 are floating floors with a 96K glass wool for vibration isolation layer and the thicknesses of the glass wool and concrete were changed. For the floating floors, polyethylene film was installed under the concrete. The measurements were taken at two positions; near the position of excitation (top surface) and directly below the position of excitation (bottom surface). Table 2 shows the results of the driving-point impedance level. As a result, the response impedance during impact time at the measurement position of bottom surface (radiating surface of floor impact sound), the value of specimen A6 is larger. These results indicate that 50 mm thick glass wool and 100 mm thick concrete are effective.

 

Table 2: Outline of section specifications of specimen and measurement results of driving-point impedance level in a floating floor.

 

 

Although the results of 3.1 showed that the floating floor is effective in increase floor impact sound insulation, a composite floor consisting of CLT panel and concrete was investigated to ensure the holding ultimate lateral strength. The composite floor was made of CLT and concrete using connectors made of steel plates and reinforcing bars. The driving-point impedance measurements were car ried out on two types of 150 mm thick CLT panels (5 layers, 1,000 mm x 3,000 mm); specimen B1 without any connecters and specimen B2 with connecters installed at four diagonal quarter positions, excluding the center of the specimen. The top surface of the specimen was excitated with an impact hammer at the center of the specimen and the diagonal quarter position (1/4 position) and measurements were taken at two positions: near the point of shaking (top surface) and directly below it (bottom surface). Table 3 shows the results of the driving-point impedance level. When the connector was impacted (1/4 position), there was an increase of only approximately 1 dB.

 

Table 3: Outline of section specifications of specimen and measurement results of driving-point impedance level in the composite floor.

 

 

4. FLOOR IMPACT SOUND INSULATION PERFORMANCE MEASUREMENTS

 

4.1. Six-story Wood-frame Model Building

 

The measurements of the floor impact sound insulation performance were carried out in the six-story wood-frame model building⁹. In this model building, earthquake protection, fire resistance, workability, durability, and sound insulation performance, etc. are verified. It is 7,280 mm wide, 5,005 mm deep and 17,309 mm in height. Each of the five floors (1st floor to 5th floor) has almost the same arrangement of living space, and there were two living areas (dwelling units, 3,640 mm wide and 2,502.5 mm deep) on each floor except for the 6th floor. The 6th floor has one living area. The five different separating floors exist on each floor, The 2nd floor is made of 210 mm thick CLT (7 layers), and the floor impact sound insulation performance was measured in one of the rooms on the 2nd floor.

 

4.2. Measurement Method

 

The floor impact sound insulation performances were measured in conformity with the requirements of JIS A 1418-2: 2019¹⁰ for the heavy-weight floor impact sound insulation and JIS A 1418-1: 2000¹¹ for the light-weight floor impact sound insulation. The impact sources for measurement of the heavy weight floor impact sound were a car-tire source (a bang machine) and a rubber ball source, and of the light-weight floor impact sound source was a tapping machine. The impact positions were five positions, and the sound receiving positions were five positions. The floor impact sound insulations were evaluated with JIS A 1419-2: 2000¹². A-weighted floor impact sound pressure levels by synthesis were also calculated; heavy-weight floor impact sound: 31.5 to 500 Hz octave band, light-weight floor impact sound: 125 to 2000 Hz octave band.

 

4.2. Floor Section Specification

 

Table 4 shows the outline of section specifications of the specimen. Specimen No. 1 was originally constructed with triple-layer 21 mm thick fire-resistant gypsum boards on and bottom surfaces of the CLT floor panel, assuming a 2-hour fireproof construction. Specimens No. 2 and No. 3 were constructed with a floating floor (the fireproofing layer of the bottom surface was removed for specimen No. 3), specimen No. 4 had the floating floor layer removed, specimen No. 5 had the bare CLT floor, and specimen No. 6 had the composite floor installed. For the composite floor, connectors were installed at six locations. The concrete and the walls were separated by buffer material. Moreover, specimen No. 7 had a dry-type double floor structure on specimen No. 6. The cross-sectional specifications of the dry-type double floor structure (finished floor height: approximately 155 mm) consist of wooden flooring (t=12), asphalt vibration-damping sheets (t=8) and particleboard (t=20) from the finished surface.

 

Table 4: Outline of section specifications of the specimen.

 

 

4.3. Results and Discussions

 

Figure 1 shows the measurement results of floor impact sound pressure level and Figure 2 shows the calculation results of floor impact sound pressure level difference from No. 5 (CLT bare floor). The performance of specimens No. 1, No. 4 and No. 5, which had not concreted, was low; performances were Lr-70 to 75 of heavy-weight floor impact sound (car-tire source) and Lr-90 to 95 of light weight floor impact sound. The performances of specimens No. 2 and No. 3 with floating floors were high; performances were Lr-60 of heavy-weight floor impact sound (car-tire source) and Lr-70 light weight floor impact sound. The amount of effect of the floating floor layer was similar to that of the concrete slab. The 21 mm thick fire-resistant gypsum boards installed on the bottom surface had little effect due to the small change in driving-point impedance, and specimen No. 2 showed dips in the 125 Hz and 500 Hz octave bands that appeared to be a resonance of the fire-resistant gypsum board. The performance of specimen No. 6, a composite floor, was lower than that of the floating floor, Lr 65 of heavy-weight floor impact sound (car-tire source) and Lr-95 of light-weight floor impact sound, indicating that the performance was generally that of the cast concrete.

 

After the construction of the dry-type double floor structure, the performances were Lr-70 for heavy weight floor impact sound (car-tire source) and Lr-60 for light-weight floor impact sound, indicating that the light-weight floor impact sound insulation performance was improved, but the heavy-weight floor impact sound insulation performance was decreased. In the evaluation of Architectural Institute of Japan grades of the floor impact sound insulation for apartment house¹³, the heavy-weight floor impact sound insulation was outside the grade range of applicable grade and the light-weight floor impact sound insulation was Third Grade. The countermeasures are considered necessary to improve the floor impact sound insulation.

 

 

Figure 1: Measurement results of floor impact sound pressure level. (left: car-tire source, middle: rubber ball source, right: tapping machine)

 

 

Figure 2: Calculation results of floor impact sound pressure level difference from No. 5 (CLT bare floor). (left: car-tire source, middle: rubber ball source, right: tapping machine)

 

Figure 3 shows the results of the reduction of transmitted floor impact sound pressure level of results of dry-type double floor structure to investigate the effect of the dry-type double floor structure on the floor impact sound insulation performance of a composite CLT floor. The positive values in Figure 3 indicate that the construction of the dry-type double floor structure e improved the performance. Although the dry-type double floor structure on the CLT floor contributed to the improvement of heavy-weight floor impact sound insulation performance in the previous reports^3-7, the performance of heavy-weight floor impact sound insulation performance decreased in this study. The values of the two standard heavy-weight impact sources in the 31.5 Hz and 63 Hz octave bands in Figure 3 were almost the same, while the rubber ball source tended to be larger above the 125 Hz octave band. These results are similar to those for concrete floors such as homogeneous concrete slabs. The performance of the light-weight floor impact sound insulation performance was improved by the installation of the dry-type double floor structure.

 

 

Figure 3: Reduction of transmitted floor impact sound pressure level of the dry-type double floor structure. (left: car-tire source, middle: rubber ball source, right: tapping machine)

 

5. CONCLUSIONS

 

This paper presents the driving-point impedance and the floor impact sound insulation performance of concrete poured CLT floor without a ceiling structure. As a result, the performance of the concrete floating floor or composite on the CLT floor showed that the performance was almost the same as the concrete floor itself. Moreover, it was shown that the heavy-weight floor impact sound insulation performance of composite CLT floor tends to be reduced by the construction of a dry-type double floor structure.

 

6. ACKNOWLEDGEMENTS

 

This CLT model building was constructed under the fund by Ministry of Land, Infrastructure and Transport. This research was conducted as a part of the joint research of the Building Research Institute (BRI) and the Japan CLT Association.

 

7. REFERENCES

 

1. Zeitler, B., Schoenwald, S., Sabourin, I. Direct impact sound insulation of cross laminate timber floors with and without topping. Proceedings of INTER-NOISE 14, Melbourne, Australia, November 2014.

2. Hiramitsu, A., Harada, K., Noji, K. Improvement of Sound Insulation Performance of Cross Laminated Timber Separation Wall. Proceedings of International Western Pacific Acoustics Conference 2015, Singapore, Singapore, December2015.

3. Hiramitsu, A., Harada, K., Noji, K. Effect of difference in specification on sound insulation in cross laminated timber separation wall. Proceedings of International Congress on Acoustics 2016, Buenos Aires, Argentine, September2016.

4. Hiramitsu, A., Otsuru, T., Tomiku, R., Harada, K. Improvement of floor impact sound insulation in cross laminated timber model building for experiment. Proceedings of INTER-NOISE 16, Ham burg, Germany, August2016.

5. Hiramitsu, A., Hirota, T., Miyauchi, J., Uematsu, T., Nabeta, Y. Experimental study on floor impact sound insulation and vibration characteristics in cross laminated timber building. Proceedings of INTER-NOISE 17, Hong Kong, Hong Kong, August2017.

6. Hiramitsu, A., Tsuchimoto, T., Kurumada, S. Floor impact sound insulation and airborne sound insulation on CLT model building. Proceedings of INTER-NOISE 18; Chicago, USA, Aug sut2018.

7. Hiramitsu, A., Tsuchimoto, T., Kurumada, S. Influence of floor finish structure on floor impact sound insulation in CLT model building. Proceedings of INTER-NOISE 19; Madrid, Spain, June2019.

8. Hiramitsu, A., Hirakawa, S., Tsuchimoto, T., Yamauchi, T. Effect of different types of ceilings on floor impact sound insulation performance in CLT model building. Proceedings of INTER NOISE 21; Washington, America, August2021.

9. Hiramitsu, A., Tomita, R., Hirakawa, S., Sato, M. K. Floor impact sound insulation of the six story wood-frame model building. Proceedings of International Congress on Acoustics 2019, Aachen, Germany, September2019.

10. Acoustics – Measurement of floor impact sound insulation of buildings – Part 2: Method using standard heavy impact sources, Japanese Industrial Standard JIS A 1418-2: 2019, Japanese Industrial Standards Committee, 2019.

11. Acoustics – Measurement of floor impact sound insulation of buildings – Part 1: Method using standard light impact source, Japanese Industrial Standard JIS A 1418-1: 2000, Japanese Indus trial Standards Committee, 2000.

12. Acoustics – Rating of sound insulation in buildings and of building elements – Part 2: Floor impact sound insulation, Japanese Industrial Standard JIS A 1419-2: 2000, Japanese Industrial Standards Committee, 2000.

13. Architectural Institute of Japan, Floor Impact Prevention Design of Building, Tokyo, Gihodo Shuppan, 2009.

 

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¹ hiramitu@kenken.go.jp

² hirakawa-s92ta@mlit.go.jp