Calculation - Advanced
- Question
Answer
Yes. First, make sure the junctions are correct for the elements you want to apply. Then, d-click in the right column and de-select the Adopt SR-element button to the top-left of the table in the Construction Chooser. You are then free to select any element that matches the selected type of junction, e.g. where there is a mix of heavy and light weight elements.
- Question
The results table shows 50.8 dB for L'nw, but the Xw box under the Results diagram shows 50 dB, which seems to be an unsafe way of rounding. Why so?
Changed 2009-02-06: In the Xw box, acccessed from the Resulting Diagram window, all combinations of Xw and C-terms are displayed for convenience, as rounded integers with 1 dB shifts of the reference curve according to the ISO 717 standards. In the table however, decimal Rw and Lnw are calculated to allow for small changes to be studied. Of course, this may cause the wrong impression. The tabulated rounded Xw-values are the correct. Always remember that the Worksheet table values should be rounded downwards (conservatively).
- Question
Measured airborne sound insulation between very large rooms is sometimes less than calculated, but the impact sound agrees. Why so?
Answer
There are at least three reasons for this: 1) junctions/flanking and structural
losses must be modelled correctly, see next question. 2) The data for
concrete elements were calculated for ordinary sized rooms. In large
rooms (>200 m3), modal coupling may decrease R at low frequency
somewhat. Look at the German data for concrete, these indicate what may
happen although these data may appear somewhat exaggerated for many practical situations. 3) Air leakage reduce R at medium
and high frequency, this must be prevented at ALL junctions. Prescribe
silicone sealing compound to be filled between all dry elements. Concrete fillers must be specially adapted to make up a tight air sealant.
- Question
Light-weight concrete walls, are there any particular pre-cautions to take ?
Answer
YES - BEWARE !!! Flanking transmission through thin light-weight monolithic structures may cause severe deterioration of sound insulation if they are connected firmly to the slabs in both ends. Walls, also inner walls, made by l-w concrete, aerated concrete and similar materials with fc in the mid frequency region must NOT be attached firmly to the upper slab. See ph.d. thesis by Kihlman (Chalmers 1960), available at www.isac.cc. This may now be illustrated in BASTIAN with new element data (no 202 and 203 b-e). In the preference settings, Option tab, activate limits for alpha by the default button (0,050,5). In practice, always use a soft joint to the upper slab, e.g. with mineral wool and a plastic seal to prevent problems. Also avoid firm connections between building service equipment and such walls. To hide pipes in these walls used to be considered a very practical solution, BEWARE... The flanking problem was explained by Tor Kihlman, where the poor R around fc caused both excitation of the wall in the S-room, as well as radiation in the R-room. The bending waves in the wall may cause in-plane waves in the slab concrete floor, which would reduces the junction attenuation compared to the EN 12354-1 value (~high mass ratios). Another transmission may be caused by longitudinal wave resonances in the l-w wall, causing excessive transmission through several joints/floors. The soft joint blocks all of these transmissions, also from various impact sounds (doors, kitchen lockers, WC), but the l-w walls must be completely separated by the soft joints. Take care to insulate any stability reinforcements with rubber pads and prevent any pipes to run through the joints.
- Question
How can I model junctions between plasterboard walls, according to the manufacturers?
Answer
The predefined junctions in BASTIAN refer to solid junctions between
solid elements, which is hardly applicable to common junctions between these double walls, at least not in higher sound classes. Until EN 12354-1 has
been updated (work in progress, gently, contribute), the user has to choose a
junction without attenuation (#15), and then add their own flanking
transmission element where the correct junction attenuation is included.
Please contribute examples to the SAU database. However, frequently it turns out this path is not so important, using one of the standard junctions is on the safe side with one exception, timber joist floors on light weight walls.
- Question
The calculated sound insulation sometimes appears to be too HIGH. Why ?
Answer
The structural loss factor may in some cases be OVERESTIMATED by the
default setting "Maximum coupling".
A recent example: A corner room with light weight facade elements on
three sides. The default setting will assume a continous slab,
although the border of the slab may be considered reflective. Change to
User
defined SRT and define the types of junction of all connecting elements
(4 borders
face each element). In practice, this means that second order
transmission paths are taken into account with respect to structural
loss factor, but they are not used to estimate second order flanking
transmission (as follows from the theoretical model in
EN12354). Use the Worksheet menu, Export option to view all details in
Excel.
Typically, the structural rev. time correction (the "diagram button") is in the range (-2, -4 dB) when several of the borders of the slab do not transmit energy to the surrounding structures. Tell us if you have another experience on this matter. See question "area factor".
- Question
How can I model the S & R rooms, when the new rules for V/S=3,1 (m) and V=31 (m3) are applicable according to SS 25267(v3 2004)?
Answer
Change the parameters from R'w/L'nw to DnT,w/L'nT,w in the Extra menu, Preferences choice, Performance tab. Bastian now restricts the influence of the V/S and V according to SS 25267, but the room and element border absorption factors are still calculated from the actual dimensions. How the R-to-DnT awa Ln-LnT relate is explained in EN 12354, section 7.
- Question
How can I model a) staggered rooms or b) a partition, where only a minor part is common to both rooms (e.g. when a bathroom module blocks part of the common partition) using junctions between light weight constructions ?
Answer
EN 12354 does not include staggered junctions between l-w constructions because the transmission loss is not defined. Alt. a: Make a room model that encloses the relevant transmission paths. Turn off walls that do not contribute to the sound transmission (d-click the X-mark to the left in the table). Alt b: Make the model and then assign the actual areas of the direct path and the flanking paths using the geometry control (menu Extra/Geometry). Click and write the actual values in the geometry table. You may make several models to get an idea of the sensitivity of the model. Note: If SS 25267(2004) is applicable, see previous Q. Also note the guidelines about determination of area and volumein the new ISO 140-14.
- Question
Row houses, detached by a common thin (10 cm) concrete slab casted on EPS or min-wool heat insulation: The calculated sound insulation appears to be too low, compared to experience. Why ?
Answer
A) Up to version 2.2, there was a bug in B. that returns to high L'nw.
Upgrade to v2.3.98!
B) Measurements suggest that the loss factor of the plate is much higher than expected just from border absorption of the plates. We suggest that you either a) use a +20% thicker slab or b) force one border absorption factor to 0,5 to coop with this. In v 2.3 choose the Extra menu, Struct. Rev. Menu, change fc of each of the borders to 500 Hz. You may also change border absorption in Extras menu. Typically, a 3-4 dB higher insulation should be the result. If more knowledge is gathered on this point, tell us.
- Question
Which type of junction is appropriate to describe precast heavy slabs (eg HD/F) on massive wall elements ?
Answer
A. Use junction type 9 or 10 to calculate a case with a flexible
connection at the junction. Then change to
type 1 or 2 to calculate a case with a rigid connection. The most
plausible estimate is somewhere inbetween
these two cases, as supported by some measurement results. One reason
for this is suggested: the precast slabs
(e.g. hollow core concrete elements) do not transmit moment (tension
fores) since there is no reinforcement in the upper part.
There will always be small cracks in the element or the in situ casting.
However, shear forces do transmit vibrational power to the other side,
causing about 3 dB less flanking transmission than estimated with the
junction type 1 or 2, but certainly more than with
junction type 9 or 10. There has been one case, where the junction
between the slabs (and the holes to some extent) was filled with
concrete. The idea was to reduce flanking, but this should rather
increase flanking since the mass ratio is then less favourable and the
moment is transferred. The measurements indicated indeed, after
comparison with another partition cast in the trad. way, that sound
insulation was reduced a few dB. In case more knowledge is gathered on
this matter, please tell us.
B. HD elements parallel to a massive wall may cause flanking transmission and air leakage. Make sure the junction is properly reinforced and cast with the wall!
C. Details about HDF slabs and walls, look at the manual ByggaMedPrefab
- Question
How do I account for the direction of holes in precast heavy hollow slabs in a junction with massive wall elements (perpendicular/parallell to the junction)?
Answer
The holes themselves do not influence the sound insulation but of course they relieve the weight of the slab. The important thing is the joint. If the elements are parallell to a wall AND the joints between the elements are made in the ordinary way (i.e. they do not transfer moments at high frequencies), flanking sound transmission may be decreased, i.e. the real sound insulation will be higher than calculated. This effect is not taken into account in the database (i.e., a safe approximation). Select junction type according to the above advise. See next question as well. In case more knowledge is gathered on this matter, please tell us.
- Question
How do I account for the influence of holes and joints in precast heavy hollow core slabs without topping or with thin toppings without reinforcement?
Answer
The data in the database is already corrected for the influence of joints, cast in an ordinary way. Do not apply forced or restriced border absorption according to the question below, just apply the normal BASTIAN calculation procedure. The results are still within the 3 dB uncertainty interval, this has been tested on a limited number of field measurements. For example, HDF20 330 kg/m2 would be on the limit to pass R'w+C50-3150 52+/-1 dB (class C in SS 25267). Thanks to Spenncon, Aprobo, Strängbetong, Skanska Norge, Bo Gärdhagen and others for their kind support of this investigation. If the HD-elements are parallell to the wall AND the joints between elements are open, i.e. they do not transfer moment, flanking sound insulation may be reduced. This effect is not taken into account in the database (safe approx.). Select junction types as usual. In case the elements are not bonded to each other at the element joints and these are oriented in parallell to the junction, the sound insulation may be greater than calculated. A reason for this is suggested: the hollow core concrete elements do not transmit moment (tension fores) across the joints since there is no reinforcement in the upper part. There will always be small cracks in the element or the topping. However, shear forces do transmit vibrational power to the neighboroughing elements, causing about 3 dB less transmission across joints than estimated. In principle, this applies also to massive precast elements that are jointed without reinforcement. In case more knowledge is gathered on this matter, please tell us.
- Question
How can I calculate heavy double walls as separating walls?
Answer
Heavy double walls are only handled in version 2.1 or higher. There is
no support on this type of junction in EN 12354-1, annex E. A model has
been added
to include effects of two sheet, see paper by Metzen and Pedersen at
Forum Acusticum 2002.
At present
time there is little practical experience with the algorithm, but it is
well known that the apparent sound reduction of the double wall does not
yield in situ because of flanking transmission by the supporting slabs
(common to both wall leafs). Double wall elements that rest on resilient
material around the perimeter do not interact with the slab and they
may be handled as monotlithic walls. Junctions 5 and 6 may be then be
applicable, or even 15-16, this depends on the momentum of intertia of
the junction between the wall and the slab. These solutions require a
high sound insulation of the slabs since there is virtually no junction
attenuation. Also see question
"area factor".
- Question
Can I use only light weight walls and floors?
Answer
Yes, BUT with great care. Radiation from light weight load bearing walls is not included in the model. CEN/TC 126/WG 3 works on this item now to find Kij:s between light-weight junctions. Look at the Vinnova report (SP 2008:16, order at www.sp.se) . At InterNoise 2004 (Prague) and Forum Acusticum 2005 (Budapest), some results were presented by Warnock, Quirt and Nightinggale from NRC Canada. Get a new report from http://irc.nrc-cnrc.gc.ca/fulltext/rr/rr168/ (Flanking transmission at the wall/floor junction in multifamily dwellings - quantification and methods of suppression. Research Report 168). This is a complicated matter. At present time there is little practical experience with the algorithm, but the values obtained in BASTIAN with separated sheets in the junctions seem realistic, even slightly conservative. Check the sigma_free/sigma_forced correction box (ON) for light-weight constructions, in the Preferences section. The input data of the separating element typically refer to a case where flanking transmission does not contribute significantly. Floors resting directly on the studs of light weight walls in the recieving room may cause 5-7 dB less sound insulation than the laboratory result of the slab alone, i.e. BASTIAN would return 2-4 dB better insulation than achieved. The advise in SS 25267 annex F is to keep at least 4 dB margin between calculation results (incl. flanking paths) and requirements. Additional structual bridges may increase this difference. If this is expected to resemble the field situation, adjust the floor element data accordingly. Open the database, high-light the floor, righ-click and choose NewAsCopy. Change the title and input data. Always contact the manufacturer of the floor system to get additional information on the influence of flanking transmission in typical building constructions, as determined by measurements. The SBUF data (project 11254) on light-weight floors were taken as lab-data, then reduced by 3 dB for these reasons.
- Question
Is the "area factor" according to EN 12354 taken into account, i.e. does BASTIAN correct properly for the increased loss factor due to flanking transmission through connected large heavy structures when only light-weight walls define the rooms ?
Answer
Yes & No. BASTIAN does increase the loss factor, but unfortunately not enough if the slab is continous and very large (homogenous concrete) (v 2.3). In case of large heavy walls or slabs with only light weight walls that encloses a much smaller area, e.g. in an office or in a hospital, the vibrational power flow may direct away from the recieving room. The sound insulation horisontally will be underestimated (-1.5,-3 dB) by BASTIAN v 2.3 in extreme cases. For hollow core concrete slabs with a thin topping, the following advice is not applicable unless the joints are bonded in a special way or there is a thick reinforced topping, see question above.
We suggest the use of a practical compromise, as supported by measurement results from the field (*). The loss factor of continous concrete slabs or walls may be increased by the user to get more accurate results. More measurement results would be needed to confirm this way of handling the "area effect" (please contribute!). In the Extras/Structure Reverberation time, first choose Max Coupling. Then choose UserDefined Coupling. Then change fc of each of the connected slabs to 500 Hz along one of its borders, preferably the one at the common junction. This will add 1.5-3 dB horisontally and 0.5-1.0 dB vertically. Use this correction with when YOUR experience tells that the losses at the borders are high, e.g. when the heavy partition wall or slab is much larger (as limited by supporting heavy structures) than the sending or recieving room. Typically, the structural rev. time correction (look at the Diagram) will be in the range (-5, -7 dB) when 3 or 4 of the borders of the slab do transmit energy efficiently to the surrounding structures. (*) Comparison with 7 measured cases in Norway and Sweden (*) have been used to define this procedure. Thanks to contributions from Delta Akustik&Vibration, Brekke&Strand, Sinus, Ingemanssons, WSP and others! NOTE: This does not apply to light weight floorings and sub-floors that are continous under the walls. See paper by Quirt (NRC Canada) at InterNoise 2004.
- Question
How can I calculate flanking transmission through heavy sandwich walls (as facades) with BASTIAN?
Answer
Use a massive element that is similar to the inner sheet of the sandwich wall, possibly with half the mass of the outer wall added, if the following condition is fulfilled: If the heating insulation is elastic and the outer sheet is comparably weak or is interrupted at the partition/junction. If not, you must ask the manufacturer of the element for the flanking transmission data. Use the appropriate junction type to define the coupling to the inner wall or slab. Assure that the coupling between the elements is properly done at the building site if you depend on this to meet a certain requirement - excess flanking transmission may occur if the blocking effect of the partition fails.
- Question
The sending room and the recieving room are shifted or of different size, all heavy constructions. How do I model this ?
Answer
We suggest that you make several models, that resembles as close as possible the assumed power flow between the rooms. You may use the staggered junctions, but the experience with these are much less than the simple "cross-shaped" junctions. Apply both, and judge from experience what looks reasonable. It may be necessary to apply a more advanced kind of theory. It may be worthwile to contact us to get a second opinion about the results.
- Question
Can I include a room inbetween the sending and the receiving room?
Answer
No. EN 12354 include only 1st order transmission paths. Do not add sound insulation values obtained by consecutive calculations - this will certainly overestimate the sound insulation in situ. You may make a rough estimate (probably safe) by choosing a high insulation element or adding an extremely efficient lining, to simulate the blocking effect of the room to the direct sound transmission path.
- Question
How can a select an insulated lightweight roof as the exterior element for outdoor sound transmission?
Answer
Choose the sloped roof type of calculation sheet. Change the number of exterior elements at the worksheet menu. Change the junction type at all four junctions. Then select the roof and the flanking elements via the CONSTRUCTION CHOOSER dialog box.
- Question
Answer
Yes. First of all, you may enter several windows of the same type by right-hand click and Insert a new element row. You may repeat this procedure to add more elements. Or, you may copy and modify the data of a window in the database. N.B. Changing the area from the actual area used in the tests may add an error, typically in the order of 3 dB according to EN ISO 140-3. Larger panes tend to decrease the sound insulation. Finding data for a window with a changed area as compared to the actual test calls for a theoretical approach. We can assist you finding such data based on calculations and measurement results. See also EN 14351.
- Question
Answer
There is certainly no general answer to this question that covers all aspects. But before going into long discussions, we recommend all users to keep a margin of at least 3 dB to a required value in an individual case. If some averaging of several cases is allowed, or there is some practical experience with the calculation model for the element used, it may be appropriate to reduce the margin to (say) 1-2 dB. When the main transmission occurs through light weight constructions, such as a timber joist floor, 4 dB seem more appropriate. Some reasons for discrepancies between calculated and measured results are discussed in the body text of the standard (EN 12354). In the NORDTEST tech report 603 (NORDTEST reports.), a comparison between about 40 field results and calculations support this recommendations. Also look at dissertation by Simmons at www.dissertations.se. The data for light-weight floors labelled SBUF xxx have already been reduced by 3 dB, so the 3 dB margin on the overall result should be on the safe side (no guarantees though!).See our paper for a more details.
