This study proposes an iterative direct displacement based design method for a novel steel-timber hybrid structure. The hybrid structure incorporates Cross Laminated Timber (CLT) shear panels as an infill in steel moment resisting frames. The proposed design method is applied to design 3-, 6-, and 9-story hybrid buildings with three bays and CLT infilled middle bay. Nonlinear time history analysis, using twenty earthquake ground motion records, is carried out to validate the performance of the design method. The results indicate that the proposed method effectively controls the displacements due to seismic excitation of the hybrid structure.
Provincial code changes have been made to allow construction of light wood-frame buildings up to 6 storeys in order to satisfy the urban housing demand in western Canadian cities. It started in 2009 when the BC Building Code was amended to increase the height limit for wood-frame structures from four to six. Recently, provinces of Quebec, Ontario and Alberta followed suit. While wood-frame construction is limited to six storeys, some innovative wood-hybrid systems can go to greater heights. In this report, a feasibility study of timber-based hybrid buildings is described as carried out by The University of British Columbia (UBC) in collaboration with FPInnovations. This project, funded through BC Forestry Innovation Investment's (FII) Wood First Program, had an objective to develop design guidelines for a new steel-timber hybrid structural system that can be used as part of the next generation "steel-timber hybrid structures" that is limited in scope to 20 storey office or residential buildings. ...
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.
In this paper, we examined the effects of extreme tornadic wind loads on mass-timber buildings. In general, mass-timber buildings utilize pre-engineered wood panels to form their main gravity and lateral load resisting systems. The lightweight nature of timber makes these types of emerging buildings lighter and more flexible than buildings made from concrete, masonry or steel. In general, global lateral instability of buildings can occur when the overturning forces due to wind loads exceed the dead load of the structures. In the present study, wind loads were obtained from laboratory simulations of tornado-like wind field and atmospheric boundary layer flow at Western University, Canada. Tornado wind loads from the laboratory tests were scaled to five Enhanced Fujita wind speeds representing various levels of damage. Dynamic structural analyses were carried out to assess floor level demands. It is shown that extreme tornado wind loads may pose significant damage to mass-timber buildings designed for 1-in-50 wind speed using a load factor of 1.4. Based on the obtained results, design strategies are suggested for mass-timber buildings in tornado-prone areas.
The Canadian Society for Civil Engineers Annual Conference
The rapid growth of urban population and the associated environmental concerns are partly influencing city planners and construction stakeholders to consider “Sustainable Urbanization” alternatives. In this regard, recent urban design strategies are entertaining the use of “tall timber buildings.” Generally, tall mass-timber buildings (MTBs) utilize pre-engineered wood panels to form their main gravity and lateral load resisting systems, which makes them lighter and more flexible than buildings made from concrete, masonry or steel. As a result, frequent exposure to excessive wind-induced vibrations can cause occupant discomfort and possible inhabitability of the buildings. This paper attempts to apply a risk-based procedure to design a 102-meter tall MTB by adapting and extending the Alan G. Davenport Wind Loading Chain as a probabilistic performance-based wind engineering framework. The structural systems of the study building are composed of Cross Laminated Timber (CLT) shear walls, CLT floors, glulam columns, and reinforced-concrete link beams. Initially, aerodynamic wind tunnel tests were carried out at the Boundary Layer Wind Tunnel Laboratory of Western University on the 1:200 scale MTB model to obtain transient wind loads. Subsequently, using the wind tunnel data, the study MTB was structurally designed. In the riskbased performance assessment, uncertainties were incorporated at each step of the Wind Loading Chain, i.e., local wind, exposure, aerodynamics, dynamic effects, and criteria. These uncertainties were explicitly modeled as random variables. Dynamic structural analyses were carried out in the frequency domain to include the amplification due to the resonance component of the excitation. Structural reliability analysis through Monte Carlo sampling was used to propagate the uncertainties through the Wind Loading Chain to quantify the risk of inhabitability and excessive deflection. The results of reliability analysis were used to develop fragility curves for wind vulnerability estimations. Based on the results, the effects of various uncertainties are discussed, and risk-based design decisions are forwarded.
In this paper, to supplement the Canadian building code for a timber-steel hybrid structure, over-strength, and ductility-related force modification factors are developed and validated using a collapse risk assessment approach. The hybrid structure incorporates cross-laminated timber (CLT) infill walls within steel moment resisting frames. Following the FEMA P695 procedure, archetype buildings of 3-story, 6-story, and 9-story height with middle bay infilled with CLT were developed. Subsequently, a nonlinear static pushover analysis was performed to quantify the actual over-strength factors of the hybrid archetype buildings. To check the FEMA P695 acceptable collapse probabilities and adjusted collapse margin ratios (ACMRs), incremental dynamic analysis was carried out using 60 ground motion records that were selected to regional seismic hazard characteristics in southwestern British Columbia, Canada. Considering the total system uncertainty, comparison of the calculated ACMRs with the FEMA P695 requirement indicates the acceptability of the proposed over-strength and ductility factors
In this paper, over-strength and ductility-related force modification factors are developed and validated using a collapse risk assessment approach for a timber-steel hybrid structure. The hybrid structure incorporates Cross Laminated Timber (CLT) infill walls within steel moment resisting frames. Following the FEMA P695 procedure, initially, archetype buildings of 3-, 6-, and 9-storey height with middle bay infilled with CLT were developed. Subsequently, a nonlinear static pushover analysis is performed to quantify the actual over-strength factors of the hybrid archetype buildings. To check the FEMA P695 acceptable collapse probabilities and Adjusted Collapse Margin Ratios (ACMRs), Incremental Dynamic Analysis is carried out using 60 ground motion records that are selected to regional seismic hazard characteristics in southwestern British Columbia, Canada. Considering the total system uncertainty, comparison of the calculated ACMRs with the FEMA P695 requirement indicates the acceptability of the proposed overstrength and ductility factors.
Advancement in engineered wood products altered the existing building height limitations and enhanced wooden structural members that are available on the market. These coupled with the need for a sustainable and green solution to address the ever-growing urbanization demand, avails wood as possible candidate for primary structural material in the construction industry. To this end, several researches carried out in the past decade to come up with sound structural solutions using a timber based structural system. Green and Karsh (2012) introduced the FFTT system; Tesfamariam et al. (2015) developed force-based design guideline for steel infilled with CLT shear walls, and SOM (2013) introduced the concrete jointed mass timber hybrid structural concepts. In this research, the basic structural concepts proposed by SOM (2013) is adopted. The objective of this research is to develop a wind and earthquake design guideline for concrete jointed tall mass timber buildings in scope from 10- to 40-storey office or residential buildings. The specific objective of this research is as follow:
Wind serviceability design guideline for hybrid mass-timber structures.
Calibration of design wind load factors for the serviceability wind design of hybrid tall mass timber structures.
Guidelines to perform probabilistic modeling, reliability assessment, and wind load factor calibration.
Overstrength related modification factor Ro and ductility related modification factor Rd for future implementation in the NBCC.
Force-based design guideline following the capacity based design principles.