April 3-5, 2014, Boston, Massachusetts, United States
Cross-laminated timber (CLT) is widely perceived as the most promising option for building high-rise wood structures due to its structural robustness and good fire resistance. While gravity load design of a tall CLT building is relatively easy to address because all CLT walls can be utilized as bearing walls, design for significant lateral loads (earthquake and wind) can be challenging due to the lack of ductility in current CLT construction methods that utilize wall panels with low aspect ratios (height to length). Keeping the wall panels at high aspect ratios can provide a more ductile response, but it will inevitably increase the material and labor costs associated with the structure. In this study, a solution to this dilemma is proposed by introducing damping and elastic restoring devices in a multi-story CLT building to achieve ductile response, while keeping the integrity of low aspect ratio walls to reduce the cost of construction and improve fire resistance. The design methodology for incorporating the response modification devices is proposed and the performance of the as-designed structure under seismic is evaluated.
The high performance in-plane of cross laminated timber (CLT) panels has created a potential for the use of CLT members act as diaphragms in steel structures. The behaviour of this diaphragm system depends strongly on the connections involved in linking the panels together and to the steel members. A study of the connections at both locations was made using experimental testing of two connection designs for the panel-to-panel case, and the development of a staggered lag screw connection for the panel-to-steel beam case. The results showed good performance for the double spline and fully-threaded inclined screws panel-to-panel connections. The lag screw connection showed high strength, stiffness, and ductility. The CSA Standard O86-09 was found to best predict the strength of both types of connections. Characteristic design stiffness values were presented for the stiffness at low levels of displacement and the initial, elastic stiffness.
In Phase I (2018-19) of this project on Prefabricated Heavy Timber Modular Construction, three major types of connections used in a stackable modular building were studied: intramodule connection, inter-module vertical connection, and inter-module horizontal connection. The load requirement and major design criteria were identified...
The structural use of wood in North America is dominated by light wood-frame construction used in low-rise and – more recently – mid-rise residential buildings. Mass timber engineered wood products such as laminatedveneer-lumber and cross-laminated timber (CLT) panels enable to use the material in tall and large wood and woodbased hybrid buildings. The prospect of constructing taller buildings creates challenges, one of them being the increasein lateral forces created by winds and earthquakes, thus requiring stronger hold-down devices. This paper summarises the experimental investigation on the performance a high-capacity hold-down for resisting seismic loads in tall timberbased structural systems. The connection consists of the Holz-Stahl-Komposit-System (HSK)™ glued into CLT with the modification that ductile steel yielding was allowed to occur inside the CLT panel. The strength, stiffness, ductility and failure mechanisms of this connection were evaluated under quasi-static monotonic and reversed cyclic loading. The results demonstrate that the modified hold-down-assembly provides a possible solution for use in tall timber-based structures in high seismic zones
Provincial code changes have been made to allow construction of light wood-frame buildings up to 6 storeys in order to satisfy the urban housing demand in western Canadian cities. It started in 2009 when the BC Building Code was amended to increase the height limit for wood-frame structures from four to six. Recently, provinces of Quebec, Ontario and Alberta followed suit. While wood-frame construction is limited to six storeys, some innovative wood-hybrid systems can go to greater heights. In this report, a feasibility study of timber-based hybrid buildings is described as carried out by The University of British Columbia (UBC) in collaboration with FPInnovations. This project, funded through BC Forestry Innovation Investment's (FII) Wood First Program, had an objective to develop design guidelines for a new steel-timber hybrid structural system that can be used as part of the next generation "steel-timber hybrid structures" that is limited in scope to 20 storey office or residential buildings. ...
The increasing interest in cross-laminated timber (CLT) construction has resulted in multiple international research projects and publications covering the manufacturing and performance of CLT. Multiple regions and countries have adopted provisions for CLT into their engineering design standards and building regulations. Designing and building CLT structures, also in earthquake-prone regions is no longer a domain for early adopters, but is becoming a part of regular timber engineering practice...
Timber-steel hybrid systems utilize timber as main construction material, but also take advantage of the ductility and stiffness that steel provides. For a novel hybrid system to gain recognition, experimental data must be supported by numerical analysis to predict its structural performance. “Finding the Forest Through the Trees” (FFTT) is one proposal for a timber-steel hybrid system using mass-timber panels as shear walls and floor slabs connected with steel header beams. This thesis presents research to evaluate the seismic performance of the FFTT hybrid system using experimental methods, numerical modeling, and reliability analysis. The FFTT system was investigated on two levels: i) component design, and ii) system design. On the component level, the strength, stiffness, ductility, and failure mechanisms of the two key connections were evaluated experimentally. CLT (Cross Laminated Timber) wall to steel beam connection tests results demonstrated that appropriate connection layouts can lead to the desired failure mechanism while avoiding crushing of the mass-timber panels. For the hold-down connection, a modified HSK (Holz-Stahl-Komposit) assembly with high force and stiffness capacity together with ductile behaviour was proposed. On the system level, the seismic response of the FFTT system with different ductility values was investigated using nonlinear 2D and 3D models subjected to a number of ground motion acceleration records. The seismic reliability with various uncertainties was analysed in order to investigate the FFTT system from a performance based approach. Based on the results, an appropriate seismic force reduction factor specific to the FFTT system was proposed. Finally, a feasibility study confirmed the possibility of the practical application of this system. This thesis can serve as a precursor for developing design guidelines for tall wood-hybrid building systems in seismic regions.
Project contact is Erica Fischer at Oregon State University
This Faculty Early Career Development (CAREER) award will create innovative building technology that will enable mass timber modular construction as a building solution to many of the issues the nation's major cities face today. The architecture, engineering, and construction (AEC) sector is on the cusp of a significant disruption that will change the way buildings are manufactured, assembled, and designed, the catalyst of which is the integration of building information models (BIM) and automated construction and manufacturing. This disruption will significantly impact structural engineers. With the streamlining of building manufacturing, assembling, and design, engineers will need to take advantage of three opportunities: (1) design for constructability, (2) design for manufacturing, and (3) design for the whole life of the building (considering future modifications, maintenance, and easily replacing parts of the building). Modular construction, as one method to take advantage of these three opportunities, can address labor and housing shortages that exist in almost every U.S. city today and also can provide rapid construction methods for post-disaster reconstruction and additional patient care facilities. This research will contribute to the state of Oregon’s economy, which has made significant investments in mass timber production, manufacturing, and research. This research will be complemented through the development of best practices for using interdisciplinary, collaborative classroom environments to enhance engineering identities of underrepresented minorities and women at the graduate level. This award will support the National Science Foundation (NSF) role in the National Earthquake Hazards Reduction Program and the National Windstorm Impact Reduction Program.
The specific goal of this research is to develop a novel framework for robust and ductile mass timber modular construction that can be applied to buildings with varying lateral force resisting systems. Through this framework, the relationship between the rigidity of modular interconnections and overall structural behavior will be investigated. The research objectives of this project are to: (1) quantify the demands in interconnections that provide ductility when the building framing is subjected to combined gravity and lateral forces (seismic and wind); (2) quantify the impact of interconnection configuration and design on the ability of interconnections to meet the strength and serviceability performance criteria for mass timber high-rise modular buildings; (3) quantify ductility and overstrength for mass timber modular construction and explore applicability of conventional seismic performance factors and how these factors influence the adjusted collapse margin ratio for archetype buildings; (4) explore the influence of interconnection stiffness on the behavior of high-rise modular mass timber buildings subjected to wind demands; and (5) explore the relationship between team-focused and interdisciplinary educational practices with engineering identity and knowledge retention. New connection technology will be created and its contribution to the overall building behavior will be investigated through a rigorous testing plan and complex physics-based numerical simulations of archetype buildings subjected to combined gravity and lateral loads (seismic and wind). This research is a critical first step to develop innovative technology that will change how buildings are designed, manufactured, and assembled. This project will enable the Principal Investigator to establish interdisciplinary research, teaching, and mentorship in the area of mass timber and hybrid construction. This research will use the NSF-supported Natural Hazards Engineering Research Infrastructure (NHERI) Boundary Layer Wind Tunnel facility at the University of Florida. Experimental datasets will be archived in the NHERI Data Depot (https://www.DesignSafe-ci.org) and made publicly available.
The seismic behaviour of timber buildings is strongly related to the energy dissipation capacity of connections. According to Standard, since timber is characterized by a brittle failure when subjected to tensile or bending actions, the dissipative zones shall be located in joints and connections, whereas timber members themselves shall be regarded as behaving elastically. In order to ensure the global structural ductility, connections and joints shall be able to deform plastically at the associated ductility level without a significant reduction of their resistance under cyclic loads. The paper deals with an experimental campaign for the mechanical characterization of timber connection systems, commonly adopted in Europe, in the seismic design of timber buildings. The main objective was to find out the capacity, the stiffness and the ductility of the tested connections and to investigate their loss of capacity under cyclic loads. The obtained results were analysed in order to understand if the current provisions, reported in Standard for the different typology of traditional connectors, can be adopted in case of connection systems used for seismic purposes, such as hold-down or angle brackets. Their interaction with other structural parts was then investigated testing six fullscale timber walls, subjected to monotonic and cyclic loads. The tests were carried out at the Laboratory of Materials and Structural Testing of the Trento University (Italy).