Wind-induced vibration is an important design consideration in tall buildings in any structural material. The two main forms of wind-induced vibration - across-wind vibration due to vortex shedding and along-wind vibration due to turbulence - were taken into consideration when undertaking this study. Both types are addressed in Eurocode 1.
This research summary discusses a study which, following a sensitivity study into the effect of stiffness and damping on wind-induced vibration, addresses a shortfall in current knowledge of stiffness in dowel-type connections. This type of connection is found in the glulam frame and CLT structures currently at the forefront of tall timber construction, and its behaviour was investigated by measuring and analysing stiffness and damping under oscillating loads representative of wind-induced vibration.
This research summary covers a number of factors relating to wind-induced vibration which must be considered when constructing a tall timber building, such as how to assess connection stiffness under in-service vibration. The various conditions were then applied to a case study - the proposed Barentshaus building.
Folkhem is a Swedish company exclusively building timber residential buildings in the Stockholm area. The company is currently in the planning stages of what would be the world’s tallest timber building, a 22-storey timber residential buiding in Hallonbergen, Sundbyberg. In this master thesis, this proposed building has been analyzed with regards to its wind-induced dynamic response. The work includes studies of stabilization of tall structures, case studies of existing buildings and developed systems for tall timber construction and analyzed options for structural design of the Hallonbergen project. Eleven different structural systems have been investigated with regards to their displacement at the top and their peak acceleration when subject to wind loading. The peak acceleration has been calculated using both Eurocode and ISO 4354. The values have been assessed against ISO 6897 and ISO 10137. The results indicate that it is possible to construct the Hallonbergen project without risk of unacceptable dynamic response, using any of the following options:
The Martinson’s system with 259 mm CLT plates
The Kauffmann system
The structural system presented in “The Case for Tall Wood Buildings”
The structural system presented in “The Timber Tower Research Project”
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.
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.
This document outlines the basis of design for the performance-based design and nonlinear response history analysis of the Framework Project in Portland, OR. It is intended to be a living document that will be modified and revised as the project develops and in response to peer review comments.
Performance-based design is pursued for this project because the proposed lateral force-resisting system, consisting of post-tensioned rocking cross-laminated timber (CLT) walls is not included in ASCE/SEI 7-10 Table 12.2-1. Lateral force-resisting systems included in ASCE/SEI 7-10 Table 12.2-1 may be designed for earthquake effects using the prescriptive provisions in ASCE/SEI 7- 10. Lateral force-resisting systems not included are still permitted but must be demonstrated to have performance not less than that expected for included systems. This option is available via the performance-based procedures of ASCE/SEI 7-10 Section 1.3.1.3. Note that lateral forceresisting systems for wind effects are not restricted in ASCE/SEI 7-10. Therefore, design for wind effects will still be approached within the performance-based design framework but in a more state-of-the-practice manner.
This paper describes the design of a 12-story apartment building on a single story basement, which has wood floor diaphragms, and structural steel gravity and lateral load resisting systems. The design objective was to develop the most cost-effective structural system while meeting building functionality goals and adhering to code requirements. The main structural and non-structural design issues considered in this all-wood floor building are reviewed: gravity loads, lateral loads imposed by wind and earthquake, floor vibration, acoustics, and changes in wood moisture content. The lightweight structural form proved to be a practical system to lower construction material cost and enable alternative construction techniques to be employed. A comparison with a concrete floor option is briefly made.
The Canadian Society for Civil Engineers Annual Conference
Research Status
Complete
Summary
The rapid growth of urban population and the associated environmental concerns are partly influencing city planners and construction stakeholders to consider “Sustainable Urbanization” alternatives. In this regard, recent urban design strategies are entertaining the use of “tall timber buildings.” Generally, tall mass-timber buildings (MTBs) utilize pre-engineered wood panels to form their main gravity and lateral load resisting systems, which makes them lighter and more flexible than buildings made from concrete, masonry or steel. As a result, frequent exposure to excessive wind-induced vibrations can cause occupant discomfort and possible inhabitability of the buildings. This paper attempts to apply a risk-based procedure to design a 102-meter tall MTB by adapting and extending the Alan G. Davenport Wind Loading Chain as a probabilistic performance-based wind engineering framework. The structural systems of the study building are composed of Cross Laminated Timber (CLT) shear walls, CLT floors, glulam columns, and reinforced-concrete link beams. Initially, aerodynamic wind tunnel tests were carried out at the Boundary Layer Wind Tunnel Laboratory of Western University on the 1:200 scale MTB model to obtain transient wind loads. Subsequently, using the wind tunnel data, the study MTB was structurally designed. In the riskbased performance assessment, uncertainties were incorporated at each step of the Wind Loading Chain, i.e., local wind, exposure, aerodynamics, dynamic effects, and criteria. These uncertainties were explicitly modeled as random variables. Dynamic structural analyses were carried out in the frequency domain to include the amplification due to the resonance component of the excitation. Structural reliability analysis through Monte Carlo sampling was used to propagate the uncertainties through the Wind Loading Chain to quantify the risk of inhabitability and excessive deflection. The results of reliability analysis were used to develop fragility curves for wind vulnerability estimations. Based on the results, the effects of various uncertainties are discussed, and risk-based design decisions are forwarded.
In this paper, we examined the effects of extreme tornadic wind loads on mass-timber buildings. In general, mass-timber buildings utilize pre-engineered wood panels to form their main gravity and lateral load resisting systems. The lightweight nature of timber makes these types of emerging buildings lighter and more flexible than buildings made from concrete, masonry or steel. In general, global lateral instability of buildings can occur when the overturning forces due to wind loads exceed the dead load of the structures. In the present study, wind loads were obtained from laboratory simulations of tornado-like wind field and atmospheric boundary layer flow at Western University, Canada. Tornado wind loads from the laboratory tests were scaled to five Enhanced Fujita wind speeds representing various levels of damage. Dynamic structural analyses were carried out to assess floor level demands. It is shown that extreme tornado wind loads may pose significant damage to mass-timber buildings designed for 1-in-50 wind speed using a load factor of 1.4. Based on the obtained results, design strategies are suggested for mass-timber buildings in tornado-prone areas.
Modern building tend to strive towards more slender and lightweight constructions. That is to be more provident with space and materials as well as for aesthetic reasons. The effect of these lightweight slender buildings is an increased sensitivity to lateral loads with regard to the dynamic behaviour of the structure. Since the european union changed to more function based standards, the development of timber and timber products have increased during the past 20 years. It is now both in the interest of and feasible to build taller and larger buildings with the primary load bearing system made of timber. Timber have a relatively low mass compared to other construction materials which can result in larger deformations and discomfort if the dynamic response in the structure is too large. The purpose of this report is to make a parametric study on how mass, stiffness and damping affect the feasible building height of a tall timber structure with regard to dynamic effects caused by wind. This is performed via simulations and analyses of a planned timber structure above 10 floors. The general design parameters are modified in order to fulfill the acceleration requirements for a structure with an increasing number of floors. The initial structure is composed of load bearing Cross Laminated Timber (CLT) walls and floors that acts in diaphragm action. A FE-model is used to determine the eigenfrequencies of the structure and the swedish Annex, EKS 10, is used to calculate the peak acceleration. The determined eigenfrequency and acceleration curve is compared with the requirements of horizontal acceleration according to ISO 10137. If the structure fulfills the requirements, the structure is successively increased with 2 storeys at the time. If the structure does not fulfill the demands, it is improved with mass, stiffness and/or damping in an iteration process until it fulfills the requirements. The result of this study is divided into a "general behaviour" and a "structural behaviour" chapter, to make it possible to understand the impact of each individual parameter separately and the combined impact on the structure. The improvements of adding mass and stiffness separately did not result in dramatic improvements of the acceleration. But by combining mass, damping and stiffness, considerable improvements with respect to the dynamic response is achieved and a building height of 26 storeys was feasible. Improvements of mass and damping combined made it possible to fulfill the demands on a 22 storey timber structure. This study conclude that the most feasible solution is to add mass and damping in forms of a concrete top storey (floor and walls) together with a TMD (Tuned Mass Damper) on the top floor.
Advancement in engineered wood products altered the existing building height limitations and enhanced wooden structural members that are available on the market. These coupled with the need for a sustainable and green solution to address the ever-growing urbanization demand, avails wood as possible candidate for primary structural material in the construction industry. To this end, several researches carried out in the past decade to come up with sound structural solutions using a timber based structural system. Green and Karsh (2012) introduced the FFTT system; Tesfamariam et al. (2015) developed force-based design guideline for steel infilled with CLT shear walls, and SOM (2013) introduced the concrete jointed mass timber hybrid structural concepts. In this research, the basic structural concepts proposed by SOM (2013) is adopted. The objective of this research is to develop a wind and earthquake design guideline for concrete jointed tall mass timber buildings in scope from 10- to 40-storey office or residential buildings. The specific objective of this research is as follow:
1. Wind serviceability design guideline for hybrid mass-timber structures.
2. Calibration of design wind load factors for the serviceability wind design of hybrid tall mass timber structures.
3. Guidelines to perform probabilistic modeling, reliability assessment, and wind load factor calibration.
4. Overstrength related modification factor Ro and ductility related modification factor Rd for future implementation in the NBCC.
5. Force-based design guideline following the capacity based design principles.
