The following paper describes the first stage of dynamic testing of a post-tensioned timber building to be performed in the structural laboratory of the University of Basilicata in Potenza, Italy as part of a series of experimental tests in collaboration with the University of Canterbury in Christchurch, New Zealand. During this stage of testing a 3-dimensional, 3-storey post-tensioned timber structure will be tested. The specimen is 2/3rd scale and made up of frames in both directions composed of post-tensioned timber. The specimen will be tested both with and without the addition of dissipative steel angles which are designed to yield at a certain level drift. These steel angles release energy through hysteresis during movement thus increasing damping. The following paper discusses the testing set-up and preliminary numerical predictions of the system performance. Focus will be placed on damping ratios, displacements and accelerations.
The objective of this project was to quantify and compare the environmental impacts associated with alternative designs for a typical North American mid-rise office building. Two scenarios were considered; a traditional cast-in-place, reinforced concrete frame and a laminated timber hybrid design, which utilized engineered wood products (cross-laminated timber (CLT) and glulam). The boundary of the quantitative analysis was cradle-to-construction site gate and encompassed the structural support system and the building enclosure. Floor plans, elevations, material quantities, and structural loads associated with a five-storey concrete-framed building design were obtained from issued-for-construction drawings. A functionally equivalent, laminated timber hybrid design was conceived, based on Canadian Building Code requirements. Design values for locally produced CLT panels were established from in-house material testing. Primary data collected from a pilot-scale manufacturing facility was used to develop the life cycle inventory for CLT, whereas secondary sources were referenced for other construction materials. The TRACI characterization methodology was employed to translate inventory flows into impact indicators. The results indicated that the laminated timber building design offered a lower environmental impact in 10 of 11 assessment categories. The cradle-to-gate process energy was found to be nearly identical in both design scenarios (3.5 GJ/m2), whereas the cumulative embodied energy (feedstock plus process) of construction materials was estimated to be 8.2 and 4.6 GJ/m2 for the timber and concrete designs, respectively; which indicated an increased availability of readily accessible potential energy stored within the building materials of the timber alternative.
This paper describes numerical modelling to predict the fire resistance of engineered timber floor systems. The floor systems under investigation are timber composite floors (various timber joist and box floor cross sections), and timber-concrete composite floors. The paper describes 3D numerical modelling of the floor systems using finite element software, carried out as a sequential thermo-mechanical analysis. Experimental testing of these floor assemblies is also being undertaken to calibrate and validate the models, with a number of full scale tests to determine the failure mechanisms for each floor type and assess fire damage to the respective system components. The final outcome of this research will be simplified design methods for calculating the fire resistance of a wide range of engineered timber floor systems.
In this study, glulam beams were strengthened by inserting compressed wood (CW) blocks into the precut rectangular holes with one-thirds of the beam depth from the top of the beams. This practice was to make use of moisture-dependent swelling nature of the compressed wood which was conditioned with the moisture content significantly lower than the ambient one. The test results showed that a pre-camber was produced in the mid-span of the beam reinforced due to expansion of the compressed wood blocks on the top part of the beam. As a result, significant initial tensile and compressive stresses were generated on both the top and the bottom extreme fibres of the beam, respectively. Subsequent bending tests revealed that the initial stiffness and load carrying capacity of the pre-stressed beams were increased significantly in comparison to the beam without pre-stressing.
New Zealand Society for Earthquake Engineering Conference
April 13-15, 2012, Christchurch, New Zealand
The Nelson Marlborough Institute of Technology Arts and Media building was completed in 2011 and consists of three seismically separate complexes. This research focussed on the Arts building as it showcases the use of coupled post-tensioned timber shear walls. These are part of the innovative Expan system. Full-scale, in-situ dynamic testing of the novel building was combined with finite element modelling and updating to obtain an understanding of the structural dynamic performance within the linear range. Ambient testing was performed at three stages during construction and was combined with forced vibration testing for the final stage. This forms part of a larger instrumentation program developed to investigate the wind and seismic response and long term deformations of the building. A finite element model of the building was formulated and updated using experimental modal characteristics. It was shown that the addition of non-structural elements, such as cladding and the staircase, increased the natural frequency of the first mode and the second mode by 19% and 24%, respectively. The addition of the concrete floor topping as a structural diaphragm significantly increased the natural frequency of the first mode but not the second mode, with an increase of 123% and 18%, respectively. The elastic damping of the NMIT building at low-level vibrations was identified as being between 1.6% and 2.4%
The world tallest timber building with height of 45 meters, is planned for Bergen, Norway. In this master thesis the dynamic properties of the case building, as proposed by Sweco and Artec, are investigated. The proposed structural concept with a glulam frame and power-storeys, have never previously been built, and it is desirable to develop and understanding of the dynamic problems concerning this building. Previous work have shown problems with acceleration levels for tall timber building, mostly due to the material properties of timber. Timber has high flexibility and strength combined with low weight. The main aim of the work have been to build a 3D-model of the case building in a finite element program, where numerical methods can be used to find the dynamic properties of the building. The wind load and acceleration levels are investigated, and found to be reasonable compared to various criterions presented. The effect of the stiffness in the connections, as well as the use of apartment modules are investigated. In addition a dynamic analysis is run, and stochastic subspace state space system identification is used to verify the model. This can later be used for verification of the actual building when finished, and will be an important method to determine the actual damping and stiffness. Based on the findings in this work, the concept is assumed feasible, possible with some changes an even better concept is achieved. It will be exciting to see how Sweco will develop the concept further in the next planning phase.
Report of Testing Cross Laminated Timber Panels for Compliance with CAN/ULC-S101 Standard Methods of Fire Endurance Tests of Building Construction and Materials: Loadbearing 3-Ply CLT Wall with Attached Wood Frame Partition
Intertek Testing Services NA, Inc. (Intertek) has conducted testing for the Canadian Wood Council, on Cross-Laminated Timber Panels, to evaluate their fire resistance. Testing was conducted in accordance with the applicable requirements, and following the standard methods, of CAN/ULC-S101 Standard Methods of Fire Endurance Tests of Building Construction and Materials, fourth edition, July 2007. This evaluation took place on December 30, 2011.
At the institute of structural engineering at the ETH Zurich multiple of investigations are conducted to analyse the material properties of Norway spruce timber boards. The investigations are part of the research project “Influence of varying material properties on the load bearing capacity of glued laminated timber (glulam)”. The majority of the investigations are non-destructively.
The investigations are taking place on 400 timber boards. On all specimens the moisture content, the density, the Eigenfrequency and the longitudinal ultrasonic runtime was investigated. Further all knots with a diameter larger then 10mm are measured. Thereby the position and the size of all the knots are documented. Subsequently on 200 selected boards non-destructive tensile test are performed to analyse the local young modulus. Herewith it was particularly focused on the investigation of the stiffness of areas having knots or knot clusters and areas without knots. The strains are measured with an optical coordinatemeasurement device. In the last part of the experimental investigation the deformation and failure behaviour of significant knot clusters is analysed. The strains are measured with digital image correlation.
Focus of the entire experimental analysis was the investigation of the young modulus and the quantifications of its variability within timber members and between timber members. Within this study a database was produced to evaluate existing test methods for the estimation of the young modulus. Further, the results can be used as a basis for further investigations on the variability of structural timber.
Key point to development of environmentally friendly timber structures, appropriate to urban ways of living, is the development of high-rise timber buildings. Comfort properties are nowadays one of the main limitations to tall timber buildings, and an enhanced knowledge on damping phenomena is therefore required, as well as improved prediction models for damping.
The aim of this work has consequently been to estimate various damping quantities in timber structures. In particular, models have been derived for predicting material damping in timber members, beams or panels, or in more complex timber structures, such as floors. Material damping is defined as damping due to intrinsic material properties, and used to be referred to as internal friction. In addition, structural damping, defined as damping due to connections and friction in-between members, has been estimated for timber floors.
Twenty real dimensions beams from the glued laminated timber were tested in our previously works. Twenty advanced FE models were created precisely according to tested beams. Input files for FE models are lengths of segments and local moduli of elasticity. The segment is part of lamella between two finger joints. Each local modulus of elasticity was obtained via non-destructive penetration test. The output for comparison between real beam and FE model is displacement in half span. The quality of input data file from experiments is very important for the good agreement between real tested beams and FE models. In advanced FE models is described distribution of local moduli of elasticity via distribution function. The solution is based on the LHS. Accuracy of each distribution function is dependent on the number of measured local moduli of elasticity. In presented work was used probabilistic approach for determination of corresponding number of penetration tests as function of segments lengths. Results of this analysis will be used in the latter series of bending tests of new real dimensions beams and corresponding advanced FE models.