The Influence of the Shape of Slab on Heavyweight Impact Sound Reduction for an Apartment Building

Transcription

1 The Influence of the Shape of Slab on Heavyweight Impact Sound Reduction for an Apartment Building Young-Soo Chun 1 ; Bum-Sik Lee 2 ; Seong-Bok Lee Land and Housing Institute, Korea Land and Housing Corporation, Daejeon, South Korea, ABSTRACT In this study, vibration and acoustic analyses were carried out for the development of a spatially-customized efficient slab structure that can be applied to diverse apartment sizes and floor plans for reduction of heavyweight impact sound. As a result of these analyses, the plan to use ribbed slab was shown to reduce the heavyweight impact sound most significantly among the three slab structures presented for reduction of the heavyweight impact sound. Though there were some deviations in the amount of impact sound reduced and in the frequency bands, the results of a single number rating showed that a heavyweight impact sound reduction from as little as 1 db up to a maximum of 4 db could be expected compared to a bare slab. Further studies need to determine the actual heavyweight impact sound reduction of the ribbed slab structure through a mockup, and the detailed location, size and interval of joist need to be taken into account as well as the influence of mechanical equipment and construction interference. Keywords: Ribbed slab, Heavy weight, Floor impact noise I-INCE Classification of Subjects Number(s): INTRODUCTION Wall-slab structure, a widely used structural type for apartments in Asian countries, including Korea, comprises a structure in which the residents are readily exposed to noises through the walls and floor, as these are shared with adjacent apartments as well as the apartments above and below. As problems caused by inter-floor noises are commonly raised issues, studies to determine a solution to these problems have been widely carried out. Existing methods to reduce impact sounds include increasing the thickness of the slab and applying buffering materials on the slab. However, these methods are currently applied only as a method to solve the problem of lightweight floor impact sound. However, in the case of heavyweight impact sounds, a desirable performance in reducing the impact sound has not been achieved (Bang et al., 2013). Though an increase in the thickness of the slab has a definite effect on reducing heavyweight impact sound, increasing the thickness uniformly over the entire slab has the disadvantage that it increases the cost of slabs as they become excessively thick from a structural design point of view. In the case of applying buffering materials on the slab, recent studies have found that, although this has an effect on reducing lightweight impact sound to some degree, it has limitations when it comes to reducing heavyweight impact sound (Chun et al., 2015). Other factors that have an effect on reducing floor impact sound include site condition, structural type, size and type of floor, and boundary conditions, in addition to floor rigidity and thickness. Accordingly, simply increase the thickness of the floor uniformly is not considered the most suitable method to solve the problem of inter-floor noise. From such a viewpoint, in this study, vibration and acoustic analyses were performed to develop a spatially customized efficient slab structure that could be applied to different apartment sizes and floor plans in order to reduce heavyweight impact sound. Reduction in the heavyweight impact sound can be expected by reinforcing the wide beam and joist on the existing apartment-type bare slab to increase the rigidity of the slab. This is also expected to be advantageous in that it is cost-effective when compared to the existing method of simply increasing the thickness of a slab. 1 hr2864@ lh.or.kr 2 cysoo@ lh.or.kr 3 bslee417@lh.or.kr 132

2 2. STUDY METHOD 2.1 Floor Plans to be Analyzed and Slab Structures for Reduction of Heavyweight Impact Sound Analysis was carried out for four small/medium standard floor plans (29 m 2, 36 m 2, 49 m 2, and 59 m 2 ) of a wall-slab structure widely utilized in apartments in Asian countries. Figure 1 shows the four different floor plans of the wall-slab structures that were analyzed. The slab structures (refer to Fig. 2), having a floor thickness of 210 mm and designed to reduce heavyweight impact sound, were first applied to the floor plan with an exclusive area of 59 m 2. a. 29 m 2 b. 36 m 2 c. 49 m 2 d. 59 m 2 Figure 1 The four different floor plans analyzed The slab structure found to have the largest heavyweight impact sound reduction effect was then applied to all the four floor plans (each with a floor thickness of 180 mm and 210 mm), based on the result of a single number rating as per the inverse A weighting reference curve. The results for all the four different floor plans were compared and analyzed. The different slab structures that were applied are shown in Fig. 2. a. The one wide beam slab had a beam having a width of 1,000 mm and a depth of 360 mm located at the center of the living room. b. The two wide beams slab was designed with two beams placed at an interval of 1,500 mm; the beams had a width of 500 mm and a depth of 360 mm. considering that the slab would be installed on a Void Ceiling (hereafter referred to as V-Ceiling) in the center part of the living room. c. The ribbed slab was designed with joist intervals of 600 mm and depths of 360 mm. The modeling was carried out by converting the joist, with an upper width of 250 mm, a lower width of 150 mm, and a depth of 360 mm, into a shell element with a rectangular cross section of depth 360 mm and width 250 mm, and with the same moment of inertia (I) for convenience of analysis. a. One wide beam b. Two wide beams c. Ribbed slab Figure 2 Sectional views of the slab structures for reduction of heavyweight impact sound 133

3 2.2 Analysis Method Finite Element Method (FEM) analysis was performed to analyze the floor structure. The analysis was performed using Virtual-lab, a FEM-based commercial program for analysis of vibration and noise. As this method performs modeling to analyze the air in the solid element, which is the transfer medium of the sound generated indoors, a sound pressure can be obtained at all indoor positions, and the acoustic mode for diverse types of rooms can be easily calculated. Next, the sequence of analysis is detailed below. First, modal analysis was carried out by modeling the structure as shell elements. Second, vibration analysis was conducted using the results of the modal analysis by inputting the impact load for a heavyweight impact source. Finally, the sound pressure at an arbitrary indoor position was calculated based on the results of the vibration analysis. The input properties are shown in Table 1. In order to evaluate the results, Korean Industrial Standards (KS F and KS F ) were applied. Five positions were considered for the input source and receiver point, including the center point of the living room and points 0.75 m away from the edges of the walls. The height of the receiver point was set to 1.2 m. The results were compared using the single number rating as per the inverse A weighting reference curve. Table 1 Input properties Classification Input Property Concrete Density 2,400 kg/m 3 Concrete Elasticity N/m 2 Concrete Poisson s Ratio Air Density kg/m 3 Air Elasticity N/m 2 Air Velocity Mesh Size 340 m/s 0.2 m Damping Ratio 1% Acoustic Impedance 80,000 kg/m 2 s 3. RESULTS 3.1 Results of Analysis of the Heavyweight Impact Sound for the Four Different Slab Structures, for the Specific Conditions of a Floor Plan Area of 59 m 2 and a Floor Thickness of 210 mm Table 2 and Fig. 3 show the results of analysis of the heavyweight impact sound reduction for the four different slab structures, for the specific conditions of a floor plan area of 59 m 2 and a floor thickness of 210 mm. Table 2 Single number rating result (Floor Plan Area: 59 m 2, Floor Thickness: 210 mm) 63 Hz 125 Hz 250 Hz 500 Hz L'i,Fmax,AW Bare slab One Wide beam (+1) Two Wide beams (0) Ribbed slab (-2) 134

4 Figure 3 Analysis results (floor plan area: 59 m 2, floor thickness: 210 mm) The results of the analysis of the bare slab applied to a floor plan area of 59 m 2 and with a floor thickness of 210 mm showed a sound pressure level of 50 db by the method of single number rating, as per the inverse A weighting reference curve. The results of the analysis of the one wide beam showed a single number rating result of 51 db, an increase of 1 db compared to the bare slab. The analysis further showed that, at a frequency of 63 Hz, while the impact sound was reduced by approximately 1 db during the excitation at the center point, the impact sound increased from approximately 1 db to 3 db during the excitation at an edge. This is considered to be due to an increase in the natural vibration mode to a value closer to 63 Hz, as the slab is divided by the wide beam passing through the center part of living room. At a frequency of 125 Hz or higher, the sound was reduced by approximately 1 2 db. The results of the analysis of the two wide beams showed a single number rating of 50 db, the same as that of the bare slab. The reason for this is thought to be the same as for the one wide beam. The results of the analysis of the ribbed slab showed a single number rating of 48 db, a decrease of 2 db compared to the bare slab. This is considered to be because, contrary to the wide beams, all five excitation points, including the center point, had an evenly reduced impact sound. In the next step, additional analyses were carried out on the ribbed slab structure, shown to have the most significant effect on the reduction of heavyweight impact sound compared to the other slab structures, for the other small/medium standard floor plans. In this procedure, two floor thicknesses of 210 mm and 180 mm were analyzed. Furthermore, the ribbed slab V-ceiling slab structure, with a length and width of 1,500 mm located at the center of ceiling, was also analyzed. 3.2 Results of Analysis of the Heavyweight Impact Sound for a Ribbed Slab Structure (1) Analysis Results for the Floor Plan Area of 29 m 2 Table 3 and Fig. 4 show the results of analysis of the heavyweight impact sound for a ribbed slab applied to the floor plan area of 29 m mm 180 mm Table 3 Analysis results for a ribbed slab of area 29 m 2 63 Hz 125 Hz 250 Hz 500 Hz L' i,fmax,aw Bare slab Ribbed slab (-2) Ribbed slab V-Ceiling (-2) Bare slab Ribbed slab (-3) Ribbed slab V-Ceiling (-2) 135

5 a. 210 mm b. 180 mm Figure 4 Analysis results of heavyweight impact sound for the ribbed slab applied to the floor plan area of 29 m 2. (a) Floor thickness of 210 mm The results of the analysis for the bare slab applied to the floor plan area of 29 m 2 and with a floor thickness of 210 mm showed a sound pressure level of 47 db by the single number rating method as per the inverse A weighting reference curve. The results of the analysis for the ribbed slab showed a single number rating of 45 db, a reduction of 2 db compared to the bare slab. The reduction from 2 db to 4 db in the frequency bands, excluding 125 Hz frequency band, is considered to have greatly contributed to the single number rating. The sound showed an increase of approximately 1 db in the 125 Hz frequency band. For the ribbed slab V-Ceiling, the sound was also evaluated to be 45 db. Though the sound increased at 63 Hz by approximately 1 db compared to the floor without V-Ceiling, the single number ratings were shown to be the same. (b) Floor thickness of 180 mm In the case of a floor thickness of 180 mm, the results of analysis of the bare slab showed a single number rating of 50 db. The results of analysis of the ribbed slab showed a single number rating of 47 db, a reduction of 3 db compared to the bare slab. The results also showed that the sound was evenly reduced by approximately 3 4 db across the whole frequency band, contrary to the results for the floor thickness of 210 mm. This is thought to be due to the fact that the increase in rigidity due to the joist was larger for the floor thickness of 180 mm than for the floor thickness of 210 mm. For the ribbed slab V-Ceiling, the sound was evaluated to be 48 db, an increase of 1 db compared to the structure without V-Ceiling. (2) Analysis Results for the Floor Plan Area of 36 m 2 Table 4 and Fig. 5 show the results of analysis of the heavyweight impact sound for a ribbed slab applied to the floor plan area of 36 m mm 180 mm Table 4 Analysis results for a ribbed slab of area 36 m 2 63 Hz 125 Hz 250 Hz 500 Hz L' i,fmax,aw Bare slab Ribbed slab (-4) Ribbed-slab V-Ceiling (-1) Bare slab Ribbed slab (-4) Ribbed-slab V-Ceiling (-2) 136

6 a. 210 mm b. 180 mm Figure 5 Analysis results of heavyweight impact sound for ribbed slab applied to the floor plan area of 36 m 2. (a) Floor thickness of 210 mm The results of analysis of the bare slab applied to a floor plan area of 36 m 2 and with a floor thickness of 210 mm showed a sound pressure level of 48 db based on the single number rating method as per the inverse A weighting reference curve. The results of analysis for the ribbed slab showed a single number rating of 44 db, a reduction of 4 db compared to the bare slab. The reduction from 1 db to 6 db in the frequency bands excluding 250 Hz is thought to have greatly contributed to the single number rating. For the ribbed-slab V-Ceiling, the sound was evaluated to be 47 db, a reduction of 1 db compared to the bare slab. As a large difference appeared at 63 Hz, compared to the results for the ribbed slab without V-Ceiling, a floor plan with a V-Ceiling is thought to have a negative impact on reducing heavyweight impact sound. (b) Floor thickness of 180 mm In the case of a floor thickness of 180 mm, the results of analysis for the bare slab showed a single number rating of 49 db. The results of analysis of the ribbed slab showed a single number rating of 45 db, a reduction of 4 db compared to the bare slab. The sound was shown to have been evenly reduced by approximately 2 5 db across the entire frequency band same, as was the case for the 29 m 2 floor plan. In the case of the ribbed slab V-Ceiling, the sound was evaluated to be 47 db, a reduction of 2 db. It is assumed that the heavyweight impact sound in the frequencies of the 63 Hz band increased greatly as the reinforcement of the center part was weaker due to the V-Ceiling, as was shown for the 210 mm slab. (3) Analysis Results for the Floor Plan Area of 49 m 2 Table 5 and Fig. 6 show the results of the analysis of the heavyweight impact sound for a ribbed slab applied to the floor plan area of 49 m mm 180 mm Table 5 Analysis results for a ribbed slab of area 49 m Hz 125 Hz 250 Hz 500 Hz L' i,fmax,aw Bare slab Ribbed slab (-4) Ribbed slab V-Ceiling (-3) Bare slab Ribbed slab (-4) Ribbed slab V-Ceiling (-2) 137

7 a. 210 mm b. 180 mm Figure 6 Analysis results of heavyweight impact sound for ribbed slab applied to floor plan area of 49 m 2. (a) Floor thickness of 210 mm The results of analysis of the bare slab applied to the floor area of 49 m2 and with a floor thickness of 210 mm showed a sound pressure level of 52 db by the single number rating method as per the inverse A weighting reference curve. The results of analysis for the ribbed slab showed a single number rating of 48 db, a reduction of 4 db compared to the bare slab. The large reduction at 63 Hz and 125 Hz is thought to have contributed to the single number rating. In the case of the ribbed slab V-Ceiling, the sound was evaluated to be 49 db, an increase of approximately 1 db compared to the ribbed slab without V-Ceiling. (b) Floor thickness of 180 mm In the case of a floor thickness of 180 mm, the results of analysis of the bare slab showed a single number rating of 53 db. The results of analysis of the ribbed slab showed a single number rating of 49 db, a reduction of 4 db compared to the bare slab. In the case of the ribbed slab V-Ceiling, the sound was evaluated to be 51 db, an increase of approximately 2 db compared to the ribbed slab without V-Ceiling. The reason for the increase in the impact sound is assumed to be the same as for the other slabs. (3) Analysis Results for the Floor Plan Area of 59 m 2 Table 6 and Fig. 7 show the results of analysis of the heavyweight impact sound for a ribbed slab applied to the floor plan area of 59 m mm 180 mm Table 6 Analysis results for a ribbed slab of area 59 m Hz 125 Hz 250 Hz 500 Hz L' i,fmax,aw Bare slab Ribbed slab (-2) Ribbed slab V-Ceiling (0) Bare slab Ribbed slab (-3) Ribbed slab V-Ceiling (-1) 138

8 a. 210 mm b. 180 mm Figure 7 Analysis results of heavyweight impact sound for a ribbed slab applied to the floor plan area of 59 m 2. (a) Floor thickness of 210 mm The results of analysis of the bare slab applied to an area of 59 m 2 and with a floor thickness of 210 mm showed a sound pressure level of 50 db based on the single number rating method as per the inverse A weighting reference curve. The results of analysis of the ribbed slab showed a single number rating of 48 db, a reduction of 2 db compared to the bare slab. The significant reduction of approximately 5 db at 63 Hz is thought to have contributed to the single number rating. In the case of the ribbed slab V-ceiling, the sound was evaluated to be 50 db, the same as that of the bare slab. The reason for this is considered to be due to the fact that, although the heavyweight impact sound was slightly reduced in the band above 250 Hz, no significant reduction occurred in the 63 Hz band. (b) Floor thickness of 180 mm In the case of the floor thickness of 180 mm, the results of analysis of the bare slab showed a single number rating of 51 db. The results of analysis of the ribbed slab showed the single number to be 48 db, a reduction of 3 db compared to the bare slab. In the case of the ribbed slab V-ceiling, the sound was evaluated to be 50 db, an increase of approximately 2 db compared to the ribbed slab without V-ceiling. 4. DISCUSSION AND CONCLUSIONS Among the three different slab structure designs studied for reduction of heavyweight impact sound, the ribbed slab structure was shown to reduce the heavyweight impact sound most significantly. Though there were differences in the frequency bands in which reduction was achieved and in the amount of impact sound reduction achieved for each floor plan, the results of the single number ratings showed that a heavyweight impact sound reduction from as little as 1 db and up to a maximum of 4 db can be achieved compared to a bare slab. Further studies need to validate the actual heavyweight impact sound reduction for the different slab structure designs through a mock-up. Furthermore, the detailed location, size, and interval of the joists need to be taken into account, as well as the interferences of mechanical equipment and work execution. ACKNOWLEDGEMENTS This research was supported by a grant (16RERP-B ) from Residential Environment Research Program funded by Ministry of Land, Infrastructure and Transport of Korean government. 139

9 REFERENCES 1. J.D. Bang, B.S. Lee, S.Y. Kim, Y.S. Chun, H.J. Kim, W.J. Cho, S.Y. Yoo and O.H. Kim, "A study of technical development for reduction of heavyweight impact sound in apartments", Report of Land & Housing Institute, (2013) 2. Y.S. Chun, H.S. Yang, B.S. Lee and S.B. Lee, "Review on the characteristics of resilient materials used for floating floors", Proceedings of the KSNVE Annual Spring Conference, pp. 807~808, (2015) 3. D.H. Mun, H.G. Park, J.S. Hwang and G.H. Hong, "An Analysis of Characteristics of Floor Dynamic Properties and Bang-machine Impact Force on Floating Floor Using System Analysis", Transactions of the KSNVE, 24(5), (2014) 4. D.H. Mun, H.G. Park and J.S. Hwang, "Prediction of Concrete Slab Acceleration and Floor Impact Noise Using Frequency Response Function", Transactions of the KSNVE, 24(6), (2014) 140