The latest developments in seismic design philosophy have been geared towards developing of so called "resilient" or "low damage" innovative structural systems that can reduce damage to the structure while offering the same or higher levels of safety to occupants. One such innovative structural system is the Pres-Lam system that is a wood-hybrid system that utilizes post-tensioned (PT) mass timber components in both rigid-frame and wall-based buildings along with various types of energy disspators. To help implement the Pres-Lam system in Canada and the US, information about the system performance made with North American engineered wood products is needed. That information can later be used to develop design guidelines for the designers for wider acceptance of the system by the design community.Several components influence the performance of the Pres-Lam systems: the load-deformation properties of the engineered wood products under compression, load-deformation and energy dissipation properties of the dissipators used, placement of the dissipators in the system, and the level of post-tensioning force. The influence of all these components on the performance of Pres-Lam wall systems under gravity and lateral loads was investigated in this research project. The research project consisted of two main parts: material tests and system tests.
This paper presents an experimental investigation of the structural behaviour and dynamic characteristics of an innovative, double-span, point-supported Cross Laminated Timber (CLT) floor system for an 18-stroey woodhybrid student residence building at the University of British Columbia Campus in Vancouver, Canada. Eighteen CLT floor specimens with or without service openings were fabricated by three manufacturers and tested. The fundamental natural frequency, stiffness and deformability, load-carrying capacity, two-way action, compression perpendicular to grain at the supports, and the failure mechanism of the floor systems were investigated. In addition, the effect of openings in the floors was investigated along with the manufacturer-related properties of the CLT floors were examined. The tests gave an insight into the structural behaviour of this innovative floor system, provided test data that was used for calibration of the Finite Element Models of the building, and helped choose the right product for the floors.
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
This paper presents the seismic design and analysis of a 20-storey demonstration wood building, which was conducted as a part of the NEWBuildS tall wood building design project. A hybrid lateral load resisting system was chosen for the building. The system consisted of shear walls and a shear core, both made of structural composite lumber, connected with dowel-type connections and heavy-duty HSK (wood-steel-composite) system. The core and the shear walls were linked with horizontal steel beams at each floor. The wood-based panel-to-panel interface was designed to be the main energy dissipating mechanism of the system. A detailed finite element model of this building was developed and non-linear time history analyses were performed using 10 earthquake motions. The results showed that the seismic response of the 20-storey demonstration building met the various design criteria and the design details are appropriate.
The following topics in the field of seismic analysis and design of mid-rise (5- and 6-storey) wood-frame buildings are included in this paper: Determination of the building period, linear dynamic analysis of wood-frame structures, deflections of stacked multi-storey shearwalls, diaphragm classification, capacity-based design for woodframe...
Wood-concrete composite slab floors provide a promising solution for achieving long spans and shallow wood-based floor systems for large and tall wood buildings. In comparison with conventional wood floor systems, such long span and heavy floors have a lower fundamental natural frequency, which challenges the floor vibration controlled design. A laboratory study, including subjective evaluation and measurement of the natural frequencies and one-kN static deflections, was conducted on wood-concrete composite floors. Method of calculation of the composite bending stiffness of the wood-concrete composite floor is proposed. The design criterion for human comfort was derived from the subjective evaluation results using the calculated fundamental natural frequency and 1 kN static deflection of one meter wide strip of the composite floor. The equation to directly determine the vibration controlled spans from the stiffness and mass was derived. Limited verification was performed. Further verification is needed when more field wood-concrete composite floors become available.
In this paper, a performance-based seismic design (PBSD) of a CLT building was conducted and the seismic response of the CLT building was compared to that of a wood-frame structure tested during the NEESWood project. The results from the quasi-static tests on CLT walls performed at FPInnovations were used as input information for modelling of the CLT walls, the main lateral load resisting elements of the structure. Once the satisfactory design of the CLT mid-rise structure was established through PBSD, a force-based design was developed with varying R-factors and that design was compared to the PBSD result. In this way, suitable R-factors were calibrated so that they can yield equivalent seismic performance of the CLT building when designed using the traditional force-based design methods.
Based on the results of this study it is recommended that a value of Rd=2.5 and Ro=1.5 can be assigned for structures with symmetrical floor plans in the National Building Code of Canada (NBCC). In the US an R=4.3 can be used for symmetrical CLT structures designed according to ASCE 7. These values can be assigned provided that the design values for CLT walls considered (and implemented in the material design standards) are similar to the values determined in this study using the kinematics model developed that includes the influence of the hold-downs in the CLT wall resistance. Design of the CLT building with those R-factors using the equivalent static procedures in the US and Canada will result in the CLT building having similar seismic performance to that of the tested wood-frame NEESWood building, which had only minor non-structural damage during a rare earthquake event.
Second European Conference on Earthquake Engineering and Seismology
August 25-29, 2014, Istanbul, Turkey
Cross-laminated timber (CLT) as a structural system has not been fully introduced in European or North American building codes. One of the most important issues for designers of CLT structures in earthquake prone regions when equivalent static design procedure is used, are the values for the force modification factors (R-factors) for this structural system. Consequently, the objective of this study was to derive suitable ductility-based force modification factors (Rd-factors) for seismic design of CLT buildings for the National Building Code of Canada (NBCC). For that purpose, the six-storey NEESWood Capstone wood-frame building was redesigned as a CLT structure and was used as a reference symmetrical structure for the analyses. The same floor plan was used to develop models for ten and fifteen storey buildings. Non-linear analytical models of the buildings designed with different Rd-factors were developed using the SAPWood computer program. CLT walls were modelled using the output from mechanics models developed in Matlab that were verified against CLT wall tests conducted at FPInnovations. Two design methodologies for determining the CLT wall design resistance (to include and exclude the influence of the hold-downs), were used. To study the effects of fastener behaviour on the R-factors, three different fasteners (16d nails, 4x70mm and 5x90mm screws) used to connect the CLT walls, were used in the analyses. Each of the 3-D building models was subjected to a series of 22 bi-axial input earthquake motions suggested in the FEMA P-695 procedure. Based on the results, the fragility curves were developed for the analysed buildings. Results showed that an Rd-factor of 2.0 is appropriate conservative estimate for the symmetrical CLT buildings studied, for the chosen level of seismic performance.