Quality assurance of timber structures

The combination of modern architecture with the
renewable raw material wood leads to impressive
and demanding timber structures with high requirements
for planning, production, logistics,
commissioning and use. The demands placed on
modern wooden structures are constantly increasing
in terms of design, appearance, slender
cross sections and large spans. Meanwhile, quality
assurance during the construction and operational
phase is crucial. The realistic estimation of
the risks for the timber structure during the construction
and operation phase as well as the distribution
of wood moisture content in the timber
load bearing elements, the risk of cracking and
the shape stability of the cross sections are important.
The research project focuses on impacts of the
local climate, the resulting wood moisture distribution,
dimensional stability, moisture induced
stresses and possible cracks in the cross-sections.
The aim is to provide recommendations
for the erection of wooden structures with new
research results. The focus lies on the transfer of
results from the developed numerical models
and methods to secure recommendations for design
and planning in practice.

The used and developed basics of the project are
the climate data of Switzerland, measurements
of climate and moisture content in load bearing
cross-sections obtained from long-term monitoring
campaigns, and the developed numerical
model to calculate the moisture diffusion, the dimensional
change and the resulting moisture induced
stresses. In addition, required material parameters
were determined in small laboratory
series that improve and support measurements
made during the monitoring campaigns.
The climatic data and wood moisture content values
obtained within the long-term measurement
were classified according to the building type
and visualized accordingly for the practicing engineers.
Published data from other research institutes
were also included into the analyses
where possible. In addition to the general information
on moisture content as listed in the
SIA 265:2012, useable climate profiles are now
available for a variety of building types and for
bridges, too. Specific questions concerning
bridges that still led to discussion and unanswered
questions were considered and evaluated.
The application of a quality assurance monitoring
method and system is described.
The created numerical model was validated and
used in parameter studies to assess the effects
of cross-section size or the impact of the construction
period. realistic climate profiles found
in ice rinks, riding halls and bridges were used
to calculate dimensional changes and moisture
induced stresses.

Recommendations are given on the seasonal
fluctuations of humidity and its effects on the
timber structures. This could support engineers
during the planning and building phase. In addition
to the expected fluctuations listed in the SIA
265:2012, obtained results give the planning engineer
and authorities new benchmarks for the
estimation of the expected wood moisture content
within a supporting structure. Of interest
could be the distribution across the section
width during erection and operation.