22 Sep 2022

Development and optimization of a wood-concrete composite ceiling using beech

WHFF Project 2017.08

Project management: Prof. Dr. Christoph Geyer

 

The most important facts in brief

– The parameters necessary for the design – summer thermal insulation, room acoustics and sound insulation – were determined for HBV-Beech ceilings.

– The dynamic heat capacity was determined for the beech HBV-ceiling as well as for a solid concrete ceiling and a solid concrete ceiling with acoustic elements for comparative purposes.

– Optimization measures for improved properties were investigated and their influence on the input parameters was measured

– Essential structural-physical parameters of the wood-concrete composite ceiling with beech were determined and optimized

 

Project description

In order to make good use of the growing proportion of hardwood, especially beech, in Swiss forests, the use of beech in new market segments has been researched and developed for years. The use of beech wood as construction timber allows the ecological potential (in particular its property as a CO2 reservoir) to be fully exploited. In order to simplify the use of beechwood-concrete composite ceilings in future buildings, the structural-physical properties of the ceiling system were determined and, among other things, the sound absorption of the underside of the ceiling was optimized. Thus, the input parameters for the design of summer thermal insulation, sound insulation and room acoustics are available.

The dynamic heat capacity was calculated as the first building physics parameter of the wood-concrete composite ceiling with beech. To compare the performance of this ceiling system with others, the heat capacity of two other ceiling systems was also determined – a solid concrete ceiling and a solid concrete ceiling with acoustic elements. The acoustic parameters were determined by measurements in test rigs, and prototypes were fabricated for the building acoustic test rig measurements. The building acoustic parameters of the floor slab were measured in a direct run in the ceiling test rig of the Swiss Federal Laboratories for Materials Testing and Research (EMPA) in Dübendorf. Through the research project, the main structural-physical parameters of the wood-concrete composite floor with beech were determined and optimized. In addition, it was investigated how different profiles of the underside of the ceiling affect the dynamic heat capacity as well as the sound insulation of the ceiling system.

 

Conclusions

The underside of the wood-concrete composite ceiling affects the heat storage capacity of a room. Based on the dynamic heat capacities of the different profiling of the underside of the wood-concrete composite ceiling, it can be seen that the profiling could increase the dynamic heat capacity of the underside of the ceiling up to 72kJ/(m2K).

To improve the room acoustic properties of the underside of the ceiling, recesses were created on the underside of the ceiling, which are filled with sound-absorbing materials. The dynamic thermal capacities of the different profiles with sound-absorbing material of the wood-concrete composite ceiling with beech were analyzed. The results showed that these variants increased the dynamic heat capacity of the underside of the ceiling with sound absorption by up to 51%.

For the sound absorption levels, two ceiling undersides were studied:

1) ceiling underside with linear profiling.

2) ceiling underside with linear profiling and recesses filled with sound absorbing material.

The results show that the sound absorption coefficients of the ceiling underside with profiling are comparatively low. However, by placing the sound-absorbing material on a quarter of the area of the underside of the ceiling, the sound absorption coefficient could be significantly increased in almost all frequencies.

In order to test the airborne and impact sound insulation of the ceiling, a prototype of a wood-concrete composite ceiling with beech was built and metrologically verified. Comparing the obtained values of room-to-room sound insulation with the requirement values from SIA 181, it can be seen that the measured values are below the requirement values for multi-family buildings with sufficient reserve.

 

The project was supported by the Swiss Forest and Wood Research Promotion WHFF-CH of the Federal Office for the Environment BAFU.

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