Final Report Summary - BEST (Building with environmentally sustainable structural timber)
According to the PIRSES programme and the activities information described in two mid-term reports, the objectives and technical goals have been achieved, despite the less research exchanges predicted for the entire four-year project duration.
As reported from the researcher group of Stuttgart, the work performed by them may be summarised as follow: the scientific researcher Dipl. Ing. Katrin Stephan (KE) spent two months in New Zealand at UoC in 2011. The main objective of this exchange was the transfer of knowledge regarding design methods, technologies and testing methods for Timber-concrete composite (TCC) structures according to New Zealand standards and Eurocodes. Advantages and disadvantages of glued laminated timber (glulam) and Laminated veneer lumber (LVL), material properties in general, different connection types, design procedures and the long term behaviour were discussed and a parameter analysis was done. Furthermore the KE researcher had the chance to look at long term tests on TCC beams with LVL which were performed at UoC and she visited the prototype of a multi-storey timber building with post-tensioned frames. She also reported about push-out and beam tests on notched connections in TCC beams performed at KE.
New objectives established during the course of work and new lines of research: The field of application has been extended to TCC road bridges, which is an innovative, economical and sustainable construction method. This new system allows for prefabrication and rapid construction, for example the formworks for concrete casting can be placed at the timber beams off-site in advance and these modules are transported to the construction site. Generally speaking, TCC road bridges are definitely a competitive solution compared to conventional steel and concrete bridges for lower lorry weights and traffic categories. The feasibility of TCC bridges in New Zealand was looked at and common interests were identified.
In addition floor system and construction have regarded: analytical design procedures: Strut-and-tie model can be used for the design. The internally statically indeterminate system of a composite beam with a semi-rigid connection can be modelled as framework. The concrete and timber members are implemented as top and bottom chords. For the connection of these chords one possibility of modelling is the combination of rigid struts and cantilevers with hinges at the joint. The effective bending stiffness of the cantilevers depends on the connections slip modulus and the stiffness of the timber and concrete member. Whereas the rigid struts ensure equal deformation of timber and concrete members, the cantilevers with hinges represent discrete connectors. Shear forces and bending moments needed for the calculations are obtained directly from the model. Point loads and temperature effects can be considered.
Furthermore a first Finite element model (FEM) for a TCC bridge has been developed.
With particular reference to structural performance, following points are of new interest: connection types: A notched connection is most suitable for floors and bridges to connect timber beams and concrete slab. It has high strength and stiffness values and it is easy to construct. Prefabrication and rapid site erection is possible. In 2009, KE performed 3 static and 9 cyclic push-out tests as well as 3 static and 6 cyclic tests on beams with notched connections and the same number with X-connectors (glued-in inclined rebars). The structural behaviour (static and fatigue strength and stiffness) of both connection types has been characterised.
A parameter analysis on TCC bridges with different span lengths and materials has been performed in order to identify the best system regarding strength and stiffness.
Similarly, the group of Sassary University, in collaboration with Stuttgart group, has produce research in the field of timber floors for multi-story timber buildings. In particular they carried out tests on prestressed floor systems, shear connections, and strips of TCC floors at UoC, under serviceability and ultimate vertical loads. Tests on floor systems under in-plane load were also carried out at UoC in collaboration with UNISS. Design methods for both floor solutions were developed and validated to the experimental results. Tests to failure, numerical modelling, and simplified design methods were carried out on timber joisted floors with penetrations.
In addition full-scale tests to failure under fire conditions were carried out at Building Research Association of New Zealand (BRANZ) on timber-concrete floors with different connection systems in collaboration with UoC and UNISS. FEM was implemented in ABAQUS for prediction of the fire resistance of different types of floors at UNISS in collaboration with UoC.
Has well vibration tests have been carried out at UoC within the collaboration of UNISS on simply supported and continuous strips of floors, and on an entire composite floor.
The third research group, i.e. POLIMI group, strictly work with Canterbury University by developing analytical and testing procedure for either multi-story pre-stressed timber walls and frames, either in the field of maximisation the sustainability wooden buildings, with particular reference to seismic zone.
In the first case of pre-stressed timber frames identification of structural arrangements suitable for 10-20 m spans has been done through an extensive literature review, detailing of pre-stressing anchorage, support and connection details has been studied, even in collaboration UNISS.
The long-term performance of this kind of pre-stressed timbers frames have been also completed at UoC, with collaboration of POLIMI and UNISS, monitoring of two real buildings. With regard to seismic behaviour of seismic resisting wood elements and structures, the work performed the key aspects of the design and modelling of external mild steel dissipator for wooden structural wall.
In particular the features of a new external 'Plug and Play' device, developed at University of Canterbury have been analytically and experimentally studied and tested.
As a matter of fact, important aspect of sustainable building are related not only to the acceptable safety level avoiding catastrophic failures, but even two higher performance level requested for some important buildings, like hospital, school, police-station, communication centres.
As reported from the researcher group of Stuttgart, the work performed by them may be summarised as follow: the scientific researcher Dipl. Ing. Katrin Stephan (KE) spent two months in New Zealand at UoC in 2011. The main objective of this exchange was the transfer of knowledge regarding design methods, technologies and testing methods for Timber-concrete composite (TCC) structures according to New Zealand standards and Eurocodes. Advantages and disadvantages of glued laminated timber (glulam) and Laminated veneer lumber (LVL), material properties in general, different connection types, design procedures and the long term behaviour were discussed and a parameter analysis was done. Furthermore the KE researcher had the chance to look at long term tests on TCC beams with LVL which were performed at UoC and she visited the prototype of a multi-storey timber building with post-tensioned frames. She also reported about push-out and beam tests on notched connections in TCC beams performed at KE.
New objectives established during the course of work and new lines of research: The field of application has been extended to TCC road bridges, which is an innovative, economical and sustainable construction method. This new system allows for prefabrication and rapid construction, for example the formworks for concrete casting can be placed at the timber beams off-site in advance and these modules are transported to the construction site. Generally speaking, TCC road bridges are definitely a competitive solution compared to conventional steel and concrete bridges for lower lorry weights and traffic categories. The feasibility of TCC bridges in New Zealand was looked at and common interests were identified.
In addition floor system and construction have regarded: analytical design procedures: Strut-and-tie model can be used for the design. The internally statically indeterminate system of a composite beam with a semi-rigid connection can be modelled as framework. The concrete and timber members are implemented as top and bottom chords. For the connection of these chords one possibility of modelling is the combination of rigid struts and cantilevers with hinges at the joint. The effective bending stiffness of the cantilevers depends on the connections slip modulus and the stiffness of the timber and concrete member. Whereas the rigid struts ensure equal deformation of timber and concrete members, the cantilevers with hinges represent discrete connectors. Shear forces and bending moments needed for the calculations are obtained directly from the model. Point loads and temperature effects can be considered.
Furthermore a first Finite element model (FEM) for a TCC bridge has been developed.
With particular reference to structural performance, following points are of new interest: connection types: A notched connection is most suitable for floors and bridges to connect timber beams and concrete slab. It has high strength and stiffness values and it is easy to construct. Prefabrication and rapid site erection is possible. In 2009, KE performed 3 static and 9 cyclic push-out tests as well as 3 static and 6 cyclic tests on beams with notched connections and the same number with X-connectors (glued-in inclined rebars). The structural behaviour (static and fatigue strength and stiffness) of both connection types has been characterised.
A parameter analysis on TCC bridges with different span lengths and materials has been performed in order to identify the best system regarding strength and stiffness.
Similarly, the group of Sassary University, in collaboration with Stuttgart group, has produce research in the field of timber floors for multi-story timber buildings. In particular they carried out tests on prestressed floor systems, shear connections, and strips of TCC floors at UoC, under serviceability and ultimate vertical loads. Tests on floor systems under in-plane load were also carried out at UoC in collaboration with UNISS. Design methods for both floor solutions were developed and validated to the experimental results. Tests to failure, numerical modelling, and simplified design methods were carried out on timber joisted floors with penetrations.
In addition full-scale tests to failure under fire conditions were carried out at Building Research Association of New Zealand (BRANZ) on timber-concrete floors with different connection systems in collaboration with UoC and UNISS. FEM was implemented in ABAQUS for prediction of the fire resistance of different types of floors at UNISS in collaboration with UoC.
Has well vibration tests have been carried out at UoC within the collaboration of UNISS on simply supported and continuous strips of floors, and on an entire composite floor.
The third research group, i.e. POLIMI group, strictly work with Canterbury University by developing analytical and testing procedure for either multi-story pre-stressed timber walls and frames, either in the field of maximisation the sustainability wooden buildings, with particular reference to seismic zone.
In the first case of pre-stressed timber frames identification of structural arrangements suitable for 10-20 m spans has been done through an extensive literature review, detailing of pre-stressing anchorage, support and connection details has been studied, even in collaboration UNISS.
The long-term performance of this kind of pre-stressed timbers frames have been also completed at UoC, with collaboration of POLIMI and UNISS, monitoring of two real buildings. With regard to seismic behaviour of seismic resisting wood elements and structures, the work performed the key aspects of the design and modelling of external mild steel dissipator for wooden structural wall.
In particular the features of a new external 'Plug and Play' device, developed at University of Canterbury have been analytically and experimentally studied and tested.
As a matter of fact, important aspect of sustainable building are related not only to the acceptable safety level avoiding catastrophic failures, but even two higher performance level requested for some important buildings, like hospital, school, police-station, communication centres.