Project contact is Chris Pantelides at the University of Utah
A mass timber buckling-restrained braced frame is proposed to enhance the seismic resilience of mass timber buildings. Constructed using wood generated from the national forest system, the mass timber buckling-restrained brace will be integrated with a mass timber frame for structural energy dissipation under seismic or wind loads. The team will improve and optimize the design of structural components based on feedback from a real-time health monitoring system. Outcomes include guidelines for a lateral force resisting system of mass timber buildings in high seismic or wind regions.
Recent interests in adopting sustainable materials and developments in construction technology have created a trend of aiming for greater heights with timber buildings. With the increased height these buildings are subjected to higher level of lateral load demand. A common and efficient way to increase capacity is to use shearwalls, which can resist significant part of the load on the structures. Prefabricated mass timber panels such as those made of Cross-Laminated Timber (CLT) can be used to form the shearwalls. But due to relatively low stiffness value of timber it is often difficult to keep the maximum drifts within acceptable limit prescribed by building codes. It becomes necessary to either increase wall sizes to beyond available panel dimensions or use multiple or groups of walls spread over different locations over the floor plan. Both of the options are problematic from the economic and functional point of view. One possible alternative is to adopt a Hybrid system, using Steel Plate Shear Walls (SPSW) with timber moment frames. The SPSW has much higher stiffness and combined with timber frames it can reduce overall building drifts significantly. Frames with prefabricated timber members have considerable lateral load capacity. For structures located in seismic regions the system possesses excellent energy dissipation ability with combination of ductile SPSW and yielding elements within the frames. This paper investigates combination of SPSW with timber frames for seismic applications. Numerical model of the system has been developed to examine the interaction between the frames and shear walls under extreme lateral load conditions. Arrangements of different geometries of frames and shear walls are evaluated to determine their compatibility and efficiency in sharing lateral loads. Recommendations are presented for optimum solutions as well as practical limits of applications.
Buckling Restrained Brace Frames (BRBF) are a proven and reliable method to provide an efficient lateral force resisting system for new and existing structures in earthquake prone regions. The fuse-type elements in this system facilitate stable energy dissipation at large load deformation levels. Currently, the new trend towards mass timber vertical...
This study investigated the vibration serviceability of timber structures with dowel-type connections. It addressed the use of such connections in cutting-edge timber structures such as multi-storey buildings and long-span bridges, in which the light weight and flexibility of the structure make it possible that vibration induced by dynamic forces such as wind or footfall may cause discomfort to occupants or users of the structure, or otherwise impair its intended use. The nature of the oscillating force imposed on connections by this form of vibration was defined based on literature review and the use of established mathematical models. This allowed the appropriate cyclic load to be applied in experimental work on the most basic component of a dowel-type connection: a steel dowel embedding into a block of timber. A model for the stiffness of the timber in embedment under this cyclic load was developed based on an elastic stress function, which could then be used as the basis of a model for a complete connector. Nonlinear and time-dependent behaviour was also observed in embedment, and a simple rheological model incorporating elastic, viscoelastic and plastic elements was fitted to the measured response to cyclic load. Observations of the embedment response of the timber were then used to explain features of the behaviour of complete single- and multiple-dowel connections under cyclic load representative of in-service vibration. Complete portal frames and cantilever beams were tested under cyclic load, and a design method was derived for predicting the stiffness of such structures, using analytical equations based on the model for embedment behaviour. In each cyclic load test the energy dissipation in the specimen, which contributes to the damping in a complete structure, was measured. The analytical model was used to predict frictional energy dissipation in embedment, which was shown to make a significant contribution to damping in single-dowel connections. Based on the experimental results and analysis, several defining aspects of the dynamic response of the complete structures, such as a reduction of natural frequency with increased amplitude of applied load, were related to the observed and modelled embedment behaviour of the connections.
The research is directed to explore the possible applications of the space frames system in the field of wooden construction, the proposed construction technology can provide ample opportunity even for timber engineering. The aim of the thesis is to prove the possible application of the timber material considering that the design of wood structures is very complex and requires detailed theoretical knowledge accompanied by the intuition and the ability which comes from an understanding of the critical points of the structures. The work is organized into several parts that try to consider all the thematic relating to the design of the specific construction technology and the material particularities.
Project contact is Asif Iqbal at the University of British Columbia
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.
Recently, an innovative hybrid structure has been developed as an alternative lateral-load resisting system at The University of British Columbia. The hybrid structure incorporates Cross Laminated Timber (CLT) shear panels as an infill in steel moment resisting frames (SMRFs). In order to increase the applicability of the proposed system, in this thesis, a direct displacement based design methodology has been developed and analytically validated.
Initially, a nonlinear time history analysis (NLTHA) was carried out to study the lateral behaviour of the proposed hybrid structure. For this purpose, a total of 162 different hybrid buildings were modeled and analyzed in OpenSees by using twenty earthquake ground motions (2% probability exceedance in 50 years). Post-earthquake performance indicators (Maximum Interstory Drift (MISD) and Residual Interstory Drift (RISD)) were obtained from the analyses. To assist the post-seismic safety assessment of the hybrid buildings, surrogate models for MISD and RISD were developed using Response Surface Methodology and Artificial Neural Network (ANN). By using the ANN surrogate models as fitness functions for the Genetic Algorithm, optimal modeling parameters of the hybrid system were obtained.
Secondly, to represent the energy dissipative capacity of the hybrid system, an equivalent viscous damping (EVD) equation was developed. To formulate the EVD equation, 243 single-storey single-bay CLT infilled SMRF models were developed and subjected to monotonic static and semi-static cyclic analysis. The EVD of each model was calculated from the hysteretic responses based on Jacobsen’s area based approach and later calibrated using NLTHA.
Finally, an iterative direct displacement based design method was developed for the proposed hybrid structure. A detailed description of the proposed methodology is presented with a numerical example. In order to verify the proposed method, hybrid buildings with 3-, 6-, and 9- storey heights were designed. A calibrated EVD-ductility relationship was used to obtain the energy dissipation of the equivalent SDOF system for all case study buildings. Nonlinear time history analysis using twenty ground motion records was used to validate the performance of the proposed design methodology. The results indicate that the proposed design method effectively controls the displacements resulting from the seismic excitation of the hybrid structure.
Glulam members which are manufactured with Japanese cedar plantation timber are constructed into a box type of portal frames to investigate the moment-resisting performance when subjected to a lateral load. The joints of the frame are connected using aluminium connectors and self-tapping screw fasteners, and the placement of fasteners on the connection are arranged into three patterns. The loading protocol is applied laterally in seven cyclic stages for the racking test. The maximum lateral load of 51.4 kN is attained for the portal frame fastened using self-tapping screws arranged in square pattern, followed by single circular pattern and double circular pattern. Resulted dissipated energy obtained from the portal frame with square pattern placement is 1224.2 kNmm during the cyclic loading stages, higher than the other fastener arrangement by 20%. The allowable shear strength of the box-type portal frame is decided by the load corresponding to the shear deformation of 1/120 radian.