We model the dynamic behavior of laminated curved beams on the assumption that the different layers of such structures are perfectly bonded at the interface and can show different flexural rotations from one another. We formulate a mechanical theory and a finite element model accounting for bending, shear, warping and extensional deformation modes, as well as radial, tangential and rotary inertias. The main novelty of the proposed theory consists of a generalization of layer-wise displacement approaches available in literature to the dynamics of beams with finite curvature. The work includes some numerical results related to the free vibration of laminated arches and showing different support conditions and aspect ratios to establish comparisons with different theories in the literature. We observe that an accurate mechanical modeling of curved laminated beams is crucial for correct estimation of the eigenfrequencies and eigenmodes of such structures within a 1D framework.
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.
Project contact is Christian Dagenais at Université Laval
The National Building Code of Canada (NBCC, NRC 2015) proposes equations to limit acceleration at the top of a tall building. These equations were developed and validated on several buildings designed between 1975 and 2000. The buildings built during these years are made of concrete or steel. It is therefore not certain that the NBCC equations can be applied for tall wooden buildings; wood being a lighter material than concrete and steel. In this project, the PhD candidate will study the impact of lateral load resistance systems and fastening systems used in timber framing on natural frequency and damping as well as its response due to wind loads. The influence of non-structural elements will also be studied. Two high-rise wooden buildings (Origine, 13 floors in Quebec City and Arbora, 8 floors in Montreal) are currently being instrumented to obtain information on the dynamic behavior of the structure. The measurements taken on these two buildings will be used, among other things, to validate theoretical models developed in the context of the doctorate.
This research focuses on the dynamic behaviour of long span LCC flooring systems. Experimental testing and finite element modelling was used to determine the dynamic behaviour, with particular regard to the natural frequency, fn and mode shape of an LCC floor.
Both the experimental results and the finite element analyses agreed and showed that increased stiffness increased the natural frequency of the floor, and the boundary conditions influenced the dynamic behaviour of the LCC floor. Providing more restraint increased the stiffness of the floor system. The connectors' stiffness did not influence the dynamic performance of the floor.
The research showed that a 8 m LCC long span floor can be constructed using LVL joists of between 300 mm to 400 mm depth with a concrete thickness of 65 mm for the longer spans, and joists of between 150 mm to 240 mm depth in conjunction with a concrete topping thickness of 100 mm for the shorter spans.
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.
In this thesis, the technical feasibility of a super tall hybrid wood-concrete building was evaluated and its wind-induced dynamic behaviour was optimized. To this end a 300m tall building of timber and concrete was designed for construction in the city-centre of Rotterdam, The Netherlands. Due to the absence of seismic activity in the area, wind loading was identified as the governing parameter for lateral stability design. The structural design was therefore optimized to satisfy serviceability criteria for lateral drift and occupant comfort. Based on these requirements, the structure was designed as a reinforced concrete core surrounded by a glued-laminated timber (GLT) frame and floor slabs consisting of a cross-laminated timber (CLT) panel with a thin concrete top layer. Lateral stability was ensured by an outrigger/belt-truss system at three levels, resulting in a significant increase of the global stiffness in the structure, and in a reduction of the maximum lateral inter-storey drift by a factor two.
Pres-Lam timber structures are being adopted throughout New Zealand and around the world. This innovative method of timber construction combines the use of large engineered timber members with posttensioning cables/bars. The hybrid version of the Pres-Lam system improves seismic performance through the addition of external or internal steel reinforcing. While the post-tensioning provides re-centering properties, the steel increases energy dissipation from the system as well as increasing moment resistance. The design of these structures is performed to withstand high levels of seismic loading without damage to the structural system. Over time, the post-tensioning force being applied to the structural timber members causes them to reduce in length that has a subsequent impact on the quantity of force being applied. This paper looks at the dynamic characteristics of fundamental period and elastic damping of three recently constructed Pres-Lam buildings, investigating the influence of these losses on the dynamic characteristics. Following this a study of the performance under strong motion is performed. The paper concludes that although the losses in post-tensioning are clear they do not impact on the dynamic characteristics and have only a minor impact on strong motion response.
The following paper describes the numerical modelling used to predict the dynamic behaviour of a posttensioned timber building with the addition of a hysteretic energy dissipation system. This modelling is in support of a shaking table test programme performed on a 2/3rd scale, 3-dimensional, 3-storey structure made from post-tensioned timber frames in both directions. Testing was carried out in the structural laboratory of the University of Basilicata in Potenza, Italy as part of a collaborative project between the University and the University of Canterbury in Christchurch, New Zealand. Modelling used two non-linear finite element codes, SAP2000 and RUAUMOKO. This paper compares numerical results obtained from the model with and without additional dissipative elements in order to better understand the dynamic behaviour of post-tensioned timber structures. Comparison is made with the results of the experimental campaign and amongst the finite element programs themselves.
Timber buildings are characterized by a thermal inertia lower than other technological solutions in construction. For this reason, some configurations may lead to higher cooling demand and poorer energy performance in hot climates, such as the Mediterranean ones. Possible improvement interventions often regard additional thermal mass but, if not accurately designed, they can worse significantly structural and seismic perfo rmance of timber buildings - which is of primary importance in many Italian regions. In this framework, the TimBEESt project studied some technological solutions for timber buildings in Light Timber Frame and Cross-Laminated Timber, able to improve the dynamic behaviour of the opaque components without worsening their seismic performance. First, the Italian territory was analysed in order to find classes of climate and seismic solicitations and energy and structural performances of reference LTF and CLT building models were simulated. Then, for each Italian province, specific interventions and improvements were defined and evaluated.
In this paper, dynamic analyses of two untypical, modern footbridges made of glued-laminated timber are presented. One of them is among the longest cable-stayed bridges for pedestrians in the world, made of such a structural material. Both structures are qualified as having low sensitivity to vibrations. The results of numerical modal analysis using FEM and non-destructive experimental dynamic tests of investigated footbridges are compared. Important differences in obtained results are captured, which are identified as the positive effect in relation to design aspects. Moreover, the same in situ measurements confirm the high level of damping in footbridges made of glued-laminated wood, which is a very significant and distinguishing feature not commonly recognized. The study also calls attention to the choice of timber as an advisable material for footbridges. This is not only because of environmentally friendly and aesthetic reasons, but also due to providing highly satisfying vibration comfort for pedestrians.