Stability and Dynamic Properties of Tall Timber Structures - A parametric study of the structural response due
Typ
Examensarbete för masterexamen
Program
Structural engineering and building technology (MPSEB), MSc
Publicerad
2019
Författare
Alalwan, Ahmad
Larsson, Joakim
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
ABSTRACT
The interest in building taller structures in timber is increasing in the building sector.
However, the high strength-to-weight ratio of timber leads to a relatively light
structure which is often associated with vibrations. The dynamic properties are
essential in the design of tall timber structures, where wind-induced vibrations of the
building in service state is addressed. The dynamic response is influenced by mass,
stiffness and damping. These parameters influence the acceleration of the building
which can be perceived as a discomfort for human occupancy.
The aim is to find a structural concept that makes a taller structure than the usual
today feasible. The objective is to make a parametric study and investigate how a
multi-storey residential building of timber can be optimized with respect to
dynamic wind loading. With a combination of numerical and analytical methods,
accelerations are calculated and evaluated against the criteria for human comfort
according to ISO 10137 and ISO 6897. An analytical calculation sheet is set up
according to SS-EN-1991-1-4 and EKS 10 to define wind-induced acceleration.
Starting from a beam-column structure with a central core, the effect of adding inner
walls and exterior bracing is studied to see what limits the number of storeys for an
open plan building. Analysis of the dynamic response due to wind shows the
fundamental mode shape in torsion before exterior bracing is added. Results have
shown that the structure can reach 5-storeys with inner walls of cross-laminated
timber and 4-storeys with no walls. Moreover, it’s found that diagonal bracing in the
facades improves the torsional stiffness significantly and the fundamental mode
becomes a transversal mode.
An outrigger bracing system has been found to be the most efficient, leading to a
structure of 12-storeys. The parameters mass and stiffness are modified by adding
concrete floors and assigning larger sections to the structure. Results show that the
building can achieve 15-storeys with pure timber and 21-storeys when concrete floors
are added. Secondary parametric action i.e. adding another outrigger generates a gain
of one-storey and modifying the truss-work to steel gives a structure of 23-storeys.
Beskrivning
Ämne/nyckelord
Acceleration , dynamic response, , human occupancy , mode shape , parametric study , tall timber structure , wind-induced vibrations