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 ambient movement of three modern multi-storey timber buildings has been measured and used to determine modal properties. This information, obtained by a simple, unobtrusive series of tests, can give insights into the structural performance of these forms of building, as well as providing information for the design of future, taller timber buildings for dynamic loads. For two of the buildings, the natural frequency has been related to the lateral stiffness of the structure, and compared with that given by a simple calculation. In future tall timber buildings, a new design criterion is expected to become important: deflection and vibration serviceability under wind load. For multi-storey timber buildings there is currently no empirical basis to estimate damping for calculation of wind-induced vibration, and there is little information for stiffness under wind load. This study therefore presents a method to address those gaps in knowledge.
During the last years the interest in multi-storey timber buildings has increased and several medium-to-high-rise buildings with light-weight timber structure have been designed and built. Examples of such are the 8-storey building Limnologen in Växjö, Sweden, the 9- storey Stadthaus in London, UK and being constructed at the moment, the 14-storey building Treet in Bergen, Norway. These are all light-weight and flexible structures which raise questions regarding the wind induced vibrations. For the building in Norway, the calculated vibration properties of the top floor are on the limit of being acceptable according to the ISO 101371 vibration criteria for human comfort. This paper will give a review of building systems for medium-to-high-rise timber buildings. Measured vibration properties for some medium-to-high-rise timber buildings will also be presented. These data have been used for calculating the peak acceleration values for two example buildings for comparison with the ISO standards. An analysis of the acceleration levels for a building with double the height has also been performed showing that designing for wind induced vibrations in higher timber buildings is going to be very important and that more research into this area is needed.
The paper presents the design and modelling of Cathedral Hill 2, a 15-storey timber building, planned for construction in Canada. The building is a 59-metre tall office-use construction with an all-timber structure where the lateral-load-resisting system consists of segmented Pres-Lam walls. The paper firstly presents the design philosophy, and the motivations for the use of the Pres-Lam system, which was mainly driven by serviceability limit-state wind loading. The final part of the paper shows the verification of the building’s dynamic behaviour using non-linear time-history analysis, showing that, although the lateral-load design is governed by serviceability limit-state wind deflections, earthquake demand must not be overlooked due to higher-mode amplifications.
The low carbon footprint and high structural efficiency of engineered wood materials make tall-timber buildings an attractive option for high-rise construction. However, due to the relatively low mass and stiffness characteristics of timber structures, some concerns have been raised regarding their dynamic response. This paper examines the dynamic behaviour of tall timber buildings under tornado and downburst wind loads. It summarizes the results of extensive response history analyses over a suite of FE structural models subjected to different wind actions and compares them with the ISO10137 comfort criteria. In general, large levels of floor accelerations are observed in particular for stiffer medium-rise structures with significant density of walls. It is shown that downburst loading governs the peak acceleration response of medium-rise buildings whilst tornado loading becomes more critical for taller buildings. The effectiveness of TMDs in reducing peak acceleration values is explored. This study emphasizes the need for further studies on the dynamic behaviour of tall timber buildings.
Cross laminated timber (CLT) has been rapidly developed and utilized for multi-rise constructions in recent years, even high-rise CLT buildings with 40 stories have been proposed and designed. A use of unbonded post-tensioning (PT) steel bars through over CLT walls of the high-rise CLT buildings to take up the tensile forces produced by wind load has been considered, following the regulations of unbonded post-tensioned (UPT) concrete walls. This paper introduces a finite element model to simulate the nonlinear lateral load behavior of the UPT high-rise CLT buildings with elastic connections between the CLT elements. The analysis results indicate that the unbonded PT bars can effectively reduce the lateral displacement of the high-rise CLT building. While compared with a theoretical full rigid CLT model, the advanced model is found to be more accurate for estimating the response of UPT high-rise CLT building under horizontal load.
During the last years the interest in multi-storey timber buildings has increased and several medium-to high-rise buildings with light-weight timber structures have been designed and built. Examples of such are the 8-storey building “Limnologen” in Växjö, Sweden, the 9-storey “Stadthouse” in London, UK and the 14-storey building “Treet” in Bergen, Norway. The structures are all light-weight and flexible timber structures which raise questions regarding wind induced vibrations.
This paper will present a finite element-model of a 22 storey building with a glulam-CLT structure. The model will be used to study the effect of different structural properties such as damping, mass and stiffness on the peak acceleration and will be compared to the ISO 10137 vibration criteria for human comfort. The results show that it is crucial to take wind-induced vibrations into account in the design of tall timber buildings.