Advanced sustainable lateral load resisting systems that combine ductile and recyclable materials offer a viable solution to resist seismic load effects in environmentally responsible ways. This paper presents the seismic response of a post-tensioned timber-steel hybrid braced frame. This hybrid system combines glulam frame with steel braces to improve lateral stiffness while providing self-centreing capability under seismic loads. The proposed system is first presented. A detailed numerical model of the proposed system is then developed with emphasis on the connections and inelastic response of bracing members. Various types of braced frames including diagonal, cross and chevron configurations are numerically examined to assess the viability of the proposed concept and to confirm the efficiency of the system. A summary of initial findings is presented to demonstrate usefulness of the hybrid system. The results demonstrate that the proposed system increases overall lateral stiffness and ductility while still being able to achieve self-centring. Some additional information on connection details are provided for implementation in practical structures. The braced-frame solution is expected to widen options for lateral load resisting systems for mid-to-high-rise buildings.
To support the associated Sir Matthew Begbie Elementary School and Bayview Elementary School projects in pushing the boundaries forward for long-span floor and roof construction, this testing project aims to compare different connection approaches for composite connections between glulam and cross-laminated timber (CLT) – for vibration, stiffness, and strength. Working with the University of Northern British Columbia (UNBC), Fast + Epp aimed to complete a series of vibration and monotonic load tests on 30’ long full-scale double-T ribbed panels. The tests consisted of screws in withdrawal, screws in shear, and nominal screws clamping with glue. Both the strength and stiffness are of interest, including slip stiffness of each connection type. This physical testing was completed in January and February 2020, where the full composite strength of each system was reached. Initial data analysis has provided information for comparison with existing models for shear connection stiffness. Publications will follow in 2021.
Project contact is Thomas Tannert at the University of Northern British Columbia
Summary
The project will validate an innovative hold-down system for tall mass-timber structures that will satisfy the seismic performance demands of the revised CSA-O86 design provisions for such components. Subsequent to a numerical optimization of the hold-downs, full-scale CLT shear walls equipped with the hold-downs will be coupled with different energy-dissipative shear connectors (U-shaped dissipaters and self-tapping screws) and tested under monotonic push-over and reversed-cyclic loads. The project will facilitate the development of reliable design guidance for CLT systems that constitute a promising solution for many applications including tall structures where reduced weight is advantageous for seismic design.
Project contact is Thomas Tannert at the University of Northern British Columbia
Summary
The project will validate the viability of Glued-in Rods (GiR) as high-performance connections in CLT. Small- and full-scale tests will be conducted to evaluate the performance of GiR, considering different connection parameters. The project will facilitate the development of reliable design guidance for GiR connections in CLT systems that constitute a promising solution for many applications, including tall structures where the design is governed by wind loading.
Project contact is Asif Iqbal at the University of British Columbia
Summary
Braced frames are a solution to provide stiffness to buildings to address seismic and wind loads. There is a demand for compact arrangement and efficient lateral load resisting systems. The project examines the applicability of the braced-frame structural system, with respect to seismic forces. Design recommendations will be developed for buildings located in seismic regions such as Vancouver and Victoria.
Sound insulation performance is critical to the broader market acceptance of mass timber buildings in both residential and non-residential building markets. The project aims to develop dry floating floor solutions for mass timber floors with improved sound insulation performance. The specific objectives are:
1. To design floating floor assemblies using wood-based panels such as medium density fiberboard (MDF), gypsum board, and structural concrete panels for mass timber floors with considerations for fire requirements;
2. To evaluate the impact sound insulation performance of developed floor assemblies with a focus in the low-frequency range.
Cross-laminated timber (CLT) constitutes a promising solution for numerous structural applications, including for large and tall residential and commercial buildings. The prospect of building larger timber structures creates some structural challenges, amongst them being that lateral forces created by high winds and strong earthquakes are higher and create higher demands of “holddowns”. The Canadian Standard for Engineering Design in Wood CSA-O86 does not (yet) provide any specific procedures to estimate the resistance of mass-timber Lateral Load Resisting Systems (LLRS) nor how to facilitate the targeted kinematic mode, especially for multi-panel walls where the LLRS behaviour is a function of connection behaviour.
The project investigated the viability of internal-perforated-steel-plates (ISP) with self-drilling dowels as high-performance connections for CLT LLRS. The project objective was to contribute towards the development of reliable design guidance for ISP connections. To achieve this objective, first at the material level, the properties of the used steel-plates and dowels were verified. Then, at the component level, the performance of shear connections and hold-downs were investigated by performing quasi-static monotonic and reversed cyclic tests.
The most significant finding of the component level tests was the proof that it is possible to control the strength, stiffness, and ductility only through the IPSP and avoid bending of the SDD or crushing of the wood. Furthermore, the length of the steel perforations had a large impact on the performance with the steel-plates with the long slots (Type-D and Type-E) exhibiting lower strength and stiffness. For the hold-down tests, the same perforation geometry as for the shear-connection tests was chosen. As already determined in the shear-connection tests, the hold-down specimens with the short perforation slots resulted in the strongest and stiffest connection.
The results from this project will be used to design and test CLT shear walls with ISP connections.
Project contact is Jianhui Zhou at the University of Northern British Columbia
Summary
The impact sound perceived in the lower volume in a building is radiated by the vibration of the ceiling transmitted from the vibration of the floor generated by an impact source in the upper volume. Thus, the dynamic behaviour of a floor is one crucial intermediate step to understand the impact sound insulation performance of such a floor. A key to reducing the impact sound is to isolate the structural floor from the subfloor. Floating floor construction is a common way of improving the impact sound insulation, which is to float a concrete topping on the mass timber floor with an elastic layer in between. There are two types of floating floor solutions, a) with a continuous elastic layer and b) with point bearing elastic mounts as shown in Figure 1. This study will investigate both solutions and will provide guidance on how to adopt both solutions for mass timber floors with an exposed ceiling.
The objectives of this project are:
1. To measure the sound insulation performance of mass timber floors with full-scale concrete topping on various continuous elastic interlayer materials
2. To measure the sound insulation performance of mass timber floors with full-scale concrete topping on discrete elastic load mounts
Project contact is Jianhui Zhou at the University of Northern British Columbia
Summary
Floor vibration performance could govern the allowable span of mass timber floors. The objectives of this project are:
1. to develop a mobile app to collect data from lab and field mass timber floors for acceleration-based performance criteria;
2. to investigate the dynamic properties of mass timber floors under different boundary conditions;
3. to adopt frequency equations to predict the fundamental frequencies of mass timber floors under different boundary conditions;
4. to develop numerical modeling strategies for predicting vibration response of mass timber floors under footfall excitations.
Project contact is Guido Wimmers at University of Northern British Columbia
Summary
The WIRL has a footprint of 30m x 30m on a raft slab foundation and consists of shop space equipped with a concrete strong wall and floor and a crane bay, as well as a portion of the building that will consist of a two-storey office space. The structural system will be predominantly wood with glulam post and beam with a set of trusses for the middle span. The building envelope and mechanical systems is high performance in order to achieve Passive House certification. This phase 2 is for the data acquisition and analysis from the building sensors and energy meters. A data acquisition (DAQ) system will be created to monitor the performance of the building over the next few years and store the data in an accessible, organized fashion. The building temperature, relative humidity and metering data will be used to evaluate if all the models and calculations created for the WIRL during the design phase are reasonably close to reality and if the high performance wood structure is as energy efficient as predicted.
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