Can our standard digital tools predict the real performance of wooden buildings ? A systematic comparison with field measurements made in new buildings with a variety of floor construction

摘要

Within the research projects AkuLite, Aku20 and the current AkuTimber at LTU, about 30 newly built wooden buildings have been examined since 2010 by means of detailed field measurements of sound insulations and vibration transmissions. In addition, questionnaire surveys have been made which gives us an opportunity to study new buildings with various types of structural design more in detail, where the residents are disturbed by poor sound insulation to some extent. The main focus of those research projects is to determine a new criterion for impact sound that takes very low frequencies (20-2500 Hz) into account. But the field results may also be used to look into another question: - When acoustic consultants apply the most commonly used calculation softwares as well as some own experience of building acoustics, how close to the real performance is reasonable to assume they will get, on the average? To find out, a selection of building cases examined in the research projects have been studied. The first estimates of D_(nt) and L_(nT) were made from drawings only, the second estimates were supported by measurement results and vibration transmission measurements to refine the models of the junctions. Thus, the second estimate may be considered a tool to analyze the measurement result and which part of a construction could be improved. 23 field measurements of D_(nt) and L_(nT) in buildings with cross laminated timber (CLT) floors taken from the project, 8 measurements on CLT-floors taken from other projects, as well as 17 measurements in concrete buildings have been compared to calculations made according to EN ISO 12354. The results are presented as average (systematic) deviations and standard deviations in the comparisons. These values were also combined to indicate provisional safety margins for CLT and Concrete buildings respectively. Some particular concerns that should be observed, e.g. on the apparent vibration reduction at the junctions between walls and floors, are discussed as well.