Project contact is Cristiano Loss at the University of British Columbia
This research aims at developing novel multi-material deconstructable hybrid connections for mass timber prefabricated buildings. Connections will be conceived in order to (i) meet multi-objective structural performance, (ii) favour modular construction, (iii) favour quick erection of buildings, (iv) quick disassemble and possible reuse of the timber members, and (v) provide seismic-resistant structural assemblies.
Many of the woodframe buildings in United States, particularly along the pacific coast, have more than one story with the first floor used either for parking or commercial space which require large openings and few partition walls at that level. This open space condition
results in the earthquake resistance of the first story being significantly lower than the upper stories thus creating first stories that are both “weak” (low strength) and “soft” (low stiffness) in nature. This feature has the potential to allow formation of the soft first story mechanism during earthquakes. The United States National Science Foundation (NSF) – funded NEES-Soft project has been undertaken to develop and validate economical retrofit concepts for these types of buildings. Shake table tests on a four-story full scale model building were performed with different retrofit schemes as part of the experimental investigation. One of the retrofit measures investigated was addition of cross laminated timber rocking walls at the first floor level for increased seismic resistance. This paper focuses on the experimental performance of soft-story buildings retrofitted with cross laminated timber rocking walls. Moderate damage was observed at the first story level of the building while theupper three stories exhibited very little signs of distress. The focus of this paper is to establish correlation between the observed damage and drift. The Cross laminated timber (CLT) rocking walls were designed as per FEMA P-807 guidelines to satisfy the San Francisco mandatory softstory retrofit ordinance requirements. The tests confirmed the efficiency of CLT retrofit with expected levels of drifts throughout the structure.
European experience shows that besides single family housing, Cross-Laminated Timber (CLT) can be competitive in mid-rise and high-rise buildings. Although this system has not been used to the same extent so far in North America, it can be viable wood structural solution for the shift towards sustainable densification of urban and suburban centres. FPInnovations has undertaken a multidisciplinary project on determining the structural properties of a typical CLT construction, including quantifying the seismic resistance and force modification factors of CLT buildings. In this paper, some of the results from a series of quasi-static tests on CLT wall panels are presented as well as preliminary estimates for the force modification factors (R-factors) for seismic design of CLT structures. CLT wall panels with various configurations and connection details were tested. Wall configurations included single panels without openings with three different aspect ratios, panels with openings, as well as multi-panel walls with step joints and fasteners between them. Connections for securing the walls to the foundation included off-the-shelf steel brackets with annular ring nails, spiral nails, and screws; a combination of steel brackets and hold-downs; and custom made brackets with timber rivets. Results from two storey configurations that include two walls and a CLT slab in between are presented and discussed. Finally preliminary estimates and recommendations for the force modification factors (R-factors) for seismic design of CLT structures according to National Building Code of Canada (NBCC) are also made.