Sound insulation of planted noise barriers

Transcription

1 Müller-BBM GmbH Robert-Koch-Str Planegg bei München Telephone +49(89) Telefax +49(89) Dipl.-Ing. Dorothee Sauer Telephone +49(89) Dorothee.Sauer@MuellerBBM.de Sound insulation of planted noise barriers Calculation of the expected sound insulation Report No. M106036/01 \\S-MUC-FS01\ALLEFIRMEN\M\Proj\106\M106036\M106036_01_Ber_2E.DOC : Client: Consultants: Total number of pages: Certified quality management system according to ISO 9001 Accredited testing laboratory according to ISO/IEC Naturawall GmbH Brombeerweg Frasdorf Dipl.-Ing. Dorothee Sauer Dipl.-Ing. (FH) MBA & Eng. Manuel Männel 7 pages. Müller-BBM GmbH HRB Munich VAT Reg. No. DE Managing directors: Horst Christian Gass, Dr. Carl-Christian Hantschk, Stefan Schierer, Dr. Edwin Schorer, Norbert Suritsch

2 Table of contents 1 Situation and task 3 2 Wall construction 4 3 Sound insulation 5 4 Evaluation DIN EN and ZTV-Lsw DB guideline References Page 2

3 1 Situation and task The company Naturawall produces planted noise barriers. These consist of a supporting system made of metal with suspended plates. The construction is then filled with soil and can be planted. By means of Berger s mass law, the sound reduction index of the noise barrier system is to be calculated taking into account the surface-related mass of the filled-in soil and depending on the respective frequency. The calculation results are to be evaluated according to the standards valid for noise barrier walls (DIN EN [4], ZTV Lsw 06 [1] and DB guideline 804 [2]) and the corresponding single number rating and classifications are to be derived Page 3

4 2 Wall construction The wall construction is shown schematically in Figure 1. Wall thickness used for the calculation Figure 1. Schematic construction of the noise barrier (manufacturer s drawing, dimensions in m). The noise barrier system calculated here consists of a V-shaped supporting frame made of hot-dip galvanized steel sheet with suspended metal plates on both sides. It has a height of 3.3 m and a width of 1.4 m. During the installation, the frame and plates are filled with soil. The V-shaped construction entails a surface-related mass depending on the height. A simpler calculation of the sound reduction index can be achieved by taking into account a constant wall thickness. For this purpose, the lowest wall thickness of 0.6 m is used, which is safely observed in each horizontal cross section. According to the manufacturer, the weight of the noise barrier system is 5.9 t per running meter. The composition of the filled-in soil and its mechanical properties are not known and thus are not included in the calculations. The filled-in soil is compressed during installation of the noise barrier system. It can be assumed that from the point of view of acoustics the flow resistance is very large Page 4

5 3 Sound insulation From the dimensions of the noise barrier and the weight of 5.9 t per running meter, an average gross density of 1.78 t/m³ results over the height of the noise barrier. From this value, for an even wall thickness of 0.6 m a surface-related mass of m'' = 1072 kg/m 2 results. The calculation of the sound insulation to be expected for a test stand measurement according to DIN EN ISO [3] is carried out on the basis of Berger s mass law. For the present system, the soil filling can be regarded as a so-called flabby mass with no plate eigenfrequencies or coincidence phenomena. Thus, the calculation of the frequency-dependent sound insulation index is only described by the mass law. According to [5], for common applications this can be simplified to R = 20 lg (fm`) 47 db (1) Taking into account a normal system insulation for a test stand, the frequencydependent sound reduction indices (test stand values) listed in Table 1 can be expected for a wall. Any deductions that might be required to transfer the values to the actual construction situation were not taken into account. Table m Naturawall noise barrier: calculated sound reduction indices R in db. Frequency in Hz Sound reduction index R in db Frequency in Hz Sound reduction index R in db The values starting from a frequency of 2500 Hz were not calculated according to (1), but taken over from the calculated value for the frequency of 2000 Hz as sound reduction indices of more than 80 db cannot be technically realized in the test stand. These sound reduction indices can be expected if there are no joints or air inclusions or if all elements have joints with a maximum width of 20 mm which are sealed completely airtight Page 5

6 4 Evaluation 4.1 DIN EN and ZTV-Lsw 06 In order to evaluate the airborne sound insulating properties of the noise barrier system, the single number rating DL a is determined from the frequency-dependent sound reduction indices according to DIN EN [4], section 5.2, and the corresponding sound insulation class B0 to B3 was derived from that. According to ZTV-Lsw 06 [1], section 2.1, the wall has to correspond at least to group B3. The sound reduction indices to be expected for the noise barrier system Naturawall described in section 1, evaluated according to DIN EN ISO [4] and ZTV Lsw 06 [1], are listed in Table 2. Table 2. Evaluation according to EN [4] and ZTV-Lsw 06 [1]. Construction Naturawall noise barrier Constant wall thickness of 0,6 m Evaluation according to EN DL R Class Evaluation according to ZTV-Lsw db B3 Requirement met 4.2 DB guideline The frequency-dependent requirements on the sound reduction index R according to the DB guideline 804 [2] and the calculated sound reduction indices in octave bandwidth (arithmetic average, rounded to full db) are shown in Table 3. Table 3. Requirements according to DB guideline [2] and calculation results: sound reduction index R in octave bandwidth in db (arithmetic average of the third-octave values, rounded to full db). Frequency in Hz Requirement 12 db 18 db 24 db 30 db 35 db 35 db Calculated value 55 db 61 db 67 db 73 db 79 db 80 db Evaluation Requirement met Dipl.-Ing. Dorothee Sauer Page 6

7 5 References This report is based on the following documents: [1] ZTV-Lsw 06 "Zusätzliche Technische Vorschriften und Richtlinien für die Ausführung von Lärmschutzwänden an Straßen." 2006 [2] DB guideline 804 "Eisenbahnbrücken und sonstige Ingenieurbauwerke planen, bauen und instandhalten," section "Lärmschutzanlagen an Eisenbahnstrecken", valid starting from [3] DIN EN ISO "Akustik: Messung der Schalldämmung in Gebäuden und von Bauteilen; Teil 3: Messung der Luftschalldämmung von Bauteilen in Prüfständen" March 2005 [4] DIN EN : Lärmschutzeinrichtungen an Straßen Prüfverfahren zur Bestimmung der akustischen Eigenschaften. Teil 2: Produktspezifische Merkmale der Luftschalldämmung [5] W. Fasold; E. Veres: Schallschutz + Raumakustik in der Praxis. Huss-Medien GmbH, Verlag Bauwesen, 2 nd edition Page 7