Wind-induced dynamic excitation is becoming a governing design action determining size and shape of modern Tall Timber Buildings (TTBs). The wind actions generate dynamic loading, causing discomfort or annoyance for occupants due to the perceived horizontal sway – i.e. vibration serviceability failure. Although some TTBs have been instrumented and measured to estimate their key dynamic properties (natural frequencies and damping), no systematic evaluation of dynamic performance pertinent to wind loading has been performed for the new and evolving construction technology used in TTBs. The DynaTTB project, funded by the Forest Value research program, mixes on site measurements on existing buildings excited by heavy shakers, for identification of the structural system, with laboratory identification of building elements mechanical features coupled with numerical modelling of timber structures. The goal is to identify and quantify the causes of vibration energy dissipation in modern TTBs and provide key elements to FE modelers. The first building, from a list of 8, was modelled and tested at full scale in December 2019. Some results are presented in this paper. Four other buildings will be modelled and tested in spring 2021.
The majority of research on high strain-rate effects in timber structures has been limited to the study of the load-bearing members in isolation. Limited work has been conducted on timber connections and full-scale timber assemblies under blast loading, and these have generally been constrained to qualitative observations. In North America, the increasing prevalence of mid- and high-rise timber structures makes them susceptible to blast effects. In addition, questions remain on how to design and optimize these timber assemblies, including the connections, against blast loads, due in part to the limitations on comprehensive design provisions.
The effects of far-field blast explosions were simulated using the University of Ottawa shock tube. A total of fifty-eight dynamic tests were conducted on connection-level and full-scale specimens. The research program aimed to investigate the behaviour of heavy-timber connections when subjected to simulated blast loads. The experimental results showed that connections with a main failure mechanism consisting of wood crushing experienced significant increases in dynamic peak load when compared to the static peak load. In contrast, connections where steel yielding and rupturing occurred experienced no statistically significant increase in dynamic peak load. Full-scale glulam specimens with bolted connections designed to yield via wood crushing and bolt bending performed better than those with overdesigned connections. Bolted connections which failed in splitting led to premature failure of the glulam assembly. Reinforcement with self-tapping screws allowed these bolted joints to fail in a combination of bolt yielding and wood crushing, and provided more ductility when compared to unreinforced specimens. Specially designed energy-absorbing connections significantly increased the energy dissipation capabilities of the timber assemblies. The basis of these connections was to allow for connection yielding while delaying failure of the wood member. This was achieved via elastoplastic connection behaviour, which effectively limited the load imparted onto the wood member.
Based on the experimental results, limitations in the current Canadian blast provisions were highlighted and discussed. A two-degree-of-freedom blast analysis software was developed and validated using full-scale and connection-level experimental results and was found to adequately capture the system response with reasonable accuracy. Sensitivity analyses regarding the applicability of using single-degree-of-freedom analysis were presented and discussed.
Cross Laminated Timber (CLT) is increasingly used as a structural material for tall buildings, due to its structural properties and low carbon footprint. CLT is a mass timber product, which is made by crosswise gluing layers of timber lamellae. Recent architectural trends include having visible CLT surfaces, which, in the event of a fire, can become involved in the fire and act as fuel to the fire. A study by the Fire Protection Research Foundation (FPRF; USA), National Fire Protection Agency (NFPA; USA), National Research Council Canada (NRC-CNRC; Canada), Research Institutes of Sweden (RISE; Sweden) and National Institute of Standards and Technology (NIST; USA) has focused on the contribution of exposed CLT to compartment fires. The study included a review of previous compartment fire tests, full-scale fire tests of compartments with and without exposed CLT structures, the development of design methods for engineers and intermediate scale fire tests to identify high-temperature resistant adhesives for CLT. The full-scale compartment tests showed the undesirable consequences of CLT delamination during a fire (i.e. fall-off of exposed lamellas), which occurred due to weakening of the CLT adhesive. These consequences included fire regrowth after a period of decay or a continuation of a fully developed fire. This can make self-extinction of a compartment fire not possible, implicating that the fire will lead to collapse if the fire is not manually extinguished or extinguished by sprinklers. In order to achieve self-extinction of flaming combustion in compartments with exposed CLT it is important to avoid fire-induced delamination. It was shown that fire-induced-delamination can be avoided using high-temperature-resistant adhesives. A test method was developed to identify adhesives that are not prone to fire-induced-delamination under relevant fire conditions. A summary of the test methodology, evaluation and results is discussed in this article.
Through collaboration with the NHERI TallWood Project funded by the National Science Foundation,an alternative non-prestressed cross-laminated timber rocking wall system with replaceable fuse components was developed by Katerra engineers and tested at the outdoor shake table at the University of California San Diego. The objective of this specific design and testing is to prove a concept for a new high performance seismic lateral system that is easy to modularize and install, and can be rapidly repaired after major earthquakes. This paper presents the results from a total of thirteen tests conducted on the proposed system, including several repairs after major shaking. The test results showed that the structural system was damage-free under service level ground motions, and experienced repairable damage at designated connection locations for design basis earthquakes and maximum considered earthquakes. Overall the system was able to limit residual drift to an acceptable level and provide a high load displacement capacity for the building system.
With the rising popularity of mass timber building in the United States, there is a need to develop efficient wood-based lateral systems to enable design of mass timber buildings in regions with high seismicity. This thesis summarizes the construction and testing details of a full scale shake table testing program for a two-story mass-timber structure with a resilient post-tensioned rocking wall lateral system made from cross laminated timber (CLT) product. The post-tensioned rocking walls helped to dissipate seismic forces while allowing the other parts of the structure to remain damage-free through multiple seismic events. The utilization of a balloon framing style rocking wall system and heavy timber gravity frame enabled an open floor plan (compared to compartmentalized CLT construction) that has better potential for modern commercial and office use, which can help improve market competitiveness of mass timber construction. Since the work conducted in this thesis is only part of a large multi-university collaborative research project aiming at designing tall wood buildings for high seismic regions, only the construction, testing process, and resulted data related to building resiliency are discussed. The details and data that are in part presented in this thesis are to serve as a benchmark dataset for dynamic performance of this new building type that can be referenced by the wood design community. The first part of the thesis discusses design considerations, construction methods, and instrumentation setup employed in the test program. Practical issues encountered during construction and testing were also discussed together with suggestions for improvement in the future. The second part of the thesis presents the data collected from the shake table tests, with comparison to initial design assumptions. The final section of the thesis contains some conclusions that can be drawn from direct observations of the test results.
There is a current trend towards mid- and high-rise mass timber buildings. With this trend, there is a research need to develop a comparison between mass timber compartment fires and non-combustible compartment fires. In an effort to address the knowledge gaps in the fire performance of cross-laminated timber compartments, a full-scale fire test series was developed. The fire test series included five tests with varying levels of exposed cross-laminated timber on a two story cross-laminated timber structure. Here we present a detailed summary of the fire test series, instrumentation plan, and an overview of the results.
There is a current trend towards mid- and high-rise mass timber buildings. With this trend, there is a research need to develop a comparison between mass timber compartment fires and non-combustible compartment fires. In an effort to address the knowledge gaps in the fire performance of cross-laminated timber compartments, a full-scale fire test series was developed. The fire test series included five tests with varying levels of exposed cross-laminated timber on a two story cross-laminated timber structure. Here we present a detailed summary of the fire test series, instrumentation plan, and an overview of the results.
Timber-concrete systems (TCC) present one of the most effective bearing systems and have been extensively used in recent years. They can be used in construction of new buildings and bridges, as well as for rehabilitation and restoration of existing structures, where unsound material, damaged for various reasons, is replaced by a new composite system. While a lot is known about their behaviour at ambient conditions, knowledge about the fire resistance of TCC systems is less known and further research is needed. Aim of this document is to provide guidelines for numerical modelling of timber-concrete composite systems in various numerical software’s and thus, to enable further development and knowledge of behaviour of TCC systems in fire.
An experimental study of four full-scale cruciform sub-assemblages of beam-to-column steel-timber composite joints with extended end plates was conducted to simulate the behaviour of an internal joint in a semi-rigid steel-timber frame. In this system, the Cross-Laminated Timber (CLT) panels were attached compositely to the steel beam using coach screws to achieve the shear connection and the steel-CLT composite beams were connected to the steel columns by bolted extended end plates. In addition, one specimen without a CLT slab was constructed and tested as a control with which to assess the influence of the CLT panels on the performance of the joint. The structural behaviour of this type of joint which requires the connection of the two juxtaposed CLT panels subjected to tension near the column was explored. The test results show that these novel composite joints have credible rotation and moment capacities and provide a viable alternative to their steel-concrete counterparts within a paradigm of reduced carbonemissions in the construction sector.
International Association for Bridge and Structural Engineering Symposium
Research Status
Complete
Notes
September 19-21, 2018, Nantes, France
Summary
Contemporary structures are required to be earthquake-resistant, sustainable and flexible to changing occupancy needs over time. Hybrid wood-based construction systems are promising solutions for modern buildings and research for cost-efficient systems is underway to compete with more traditional and widely spread non-wood building systems. This paper presents an innovative modular and prefabricated wood-based hybrid construction technology. It is a dry solution obtained by fastening on-site steel frames and composite CLT-steel members using only bolts and screws. The main results obtained from a comprehensive experimental programme with focus on the in-plane and out-of-plane behaviour of floors are reviewed. The influence of connections on the response of floors is discussed. The findings are of practical relevance with direct impacts on other applications.
