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The lateral strength and stiffness requirements due to wind loads usually govern the design of tall buildings. The current building codes in the US, Canada, and Europe recognize the first s...

Part I of the two companion papers postulated and proved the capability of self-centering systems in controlling the wind-induced damage accumulations due to long-duration along-wind loads....

In this work, a 10-story uncoupled (10S-U) hybrid seismic force resisting system, consisting of cross-laminated timber (CLT) walls and reinforced concrete (RC) beams, is considered. Require...

Tall mass-timber buildings utilize 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 even steel. In general, drift sensitive components of tall mass-timber buildings could be susceptible to damages due to increased deflection when subjected to extreme wind storms like violent tornadoes. This paper assessed the structural performance of a multi-story mass-timber building, which was designed using the customary 1-in-50 years design wind speed of the 2010 National Building Code of Canada with a load factor of 1.4, under experimentally simulated tornado-like wind fields. In the study, wind loads were obtained from laboratory simulations of tornado-like wind field and atmospheric boundary layer flow at Western University, Canada. Tornadic 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 in time-domain to include the possible amplification due to the dynamic component of the excitation and assess floor level inter-story drift and shear force demands for various parameters. The varied parameters were tornado intensity level, the orientation of the building (aerodynamic direction), and critical damping ratio. Based on the obtained results, the vulnerability of drift sensitive components of the study building under tornado-like wind field was estimated. It is shown that strong tornadoes may pose significant damage to drift sensitive non-structural components of multi-story mass-timber buildings. Finally, roadmaps to improve the design of mass-timber buildings in tornado-prone areas are forwarded.

In this paper, the second of two companion papers, the serviceability-performance of a tall mass-timber building is evaluated probabilistically. For the assessment, the Alan G. Davenport Wind Loading Chain is adapted to a probabilistic Performance-Based Wind Engineering (PBWE) framework. The framework allows incorporation of uncertainties at each step of the wind loading chain, i.e., local wind climate and exposure, aerodynamics, dynamic effects, and criteria. As a case study, the framework is applied to quantify the serviceability-performance of a 102-m tall mass-timber building. Initially, parametric analyses are carried out to study the influence of critical damping ratio, wind direction, and local turbulence intensity on the response of the case study tall mass-timber building. Results showed the dependence of story level structural responses on the studied parameters and hence the need to consider the role of uncertainties. Therefore, uncertainties in various parts of the Wind Load Chain are explicitly modeled using fifteen random variables. Structural reliability analysis using Monte Carlo sampling is performed to propagate the uncertainties through the Wind Loading Chain. The results from reliability analysis are used to develop fragility curves for wind vulnerability estimations. Based on the results, design recommendations based on building functionality are forwarded.

Tall mass-timber buildings utilize engineered wood panels to form their main gravity and lateral load resisting systems, which makes them lighter and very flexible. As a result, frequent exposure to excessive wind-induced vibrations can cause occupant discomfort and unserviceability due to horizontal floor acceleration and excessive deflection. Therefore, the objective of this and the companion paper is to assess the serviceability performance of tall mass-timber buildings probabilistically. For this purpose, the Alan G. Davenport Wind Loading Chain is adapted as a probabilistic Performance-Based Wind Engineering framework. The framework is applied to quantify the serviceability performance of a 102-m tall mass-timber building. In this paper, a complete tall-mass timber building structural design process is outlined. Wind loads are obtained from aerodynamic wind tunnel tests conducted at the Boundary Layer Wind Tunnel Laboratory at Western University. The design process involves preliminary strength design using the provisions of building codes, design revisions using wind load from wind tunnel tests, and serviceability checks. The structural design of the case study tall mass-timber building considers the axial compression, in-plane-shear, and in-plane and out-of-plane bending moment demands, along with their interactions due to gravity and wind loads. Dynamic analysis is carried out to assess the drift performance of the case study mass-timber building. The results show that the building satisfies the drift requirements prescribed by the building codes with a small safety margin. For the designed tall mass-timber building, an in-depth probabilistic serviceability-performance assessment and vulnerability estimations are presented in the companion paper.

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 three-, six-, and nine-story hybrid buildings, each with three bays and a CLT-infilled middle bay. Nonlinear time history analysis, using 20 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.

The current performance-based building design considers maximum interstorey drift (MISD) ratio as the main structural performance indicator. Observations from past earthquake and reported studies, however, have highlighted that residual interstory drift (RISD) ratio has become an important factor in assessing post-earthquake safety of buildings, and decision in economic feasibility of repair and reconstruction. Improving post-earthquake performance evaluation of buildings enables decision-makers prioritise repair and tag high-risk buildings. The MISD and RISD are subject to uncertainties and have non-linear relation with the input parameters. Thus, in this paper, analytical surrogate model of MISD and RISD ratios are developed using Gaussian process (GP). To show utility of the GP model, a new hybrid building system, cross laminated timber (CLT)–steel moment resisting frame hybrid system, was considered. The hybrid building was design for the seismicity of Vancouver, BC, and meets the current steel design...

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 article, seismic vulnerability assessment is carried-out on a novel hybrid structure (steel moment resisting frame (SMRF) and cross laminated timber (CLT) infill panels). For the seismicity of Vancouver, Canada, a three-bay, 3-, 6-, and 9-story height SMRFs are designed for two ductility levels (ductile and limited ductility). To study the seismic vulnerability CLT infilled building, parametric analysis was performed by varying infill configuration (bare frame, one-bay infilled, two-bay infilled, and fully infilled). The structure is modeled in OpenSees and nonlinear dynamic analysis is performed. Peak inter-story drift demand and corresponding FEMA performance limits (capacity) values are used to compute the corresponding fragility curves. From the analyses, it can be seen that as more bays are infilled, the fundamental period and seismic vulnerability is reduced significantly. The results highlight that, within the performance-based earthquake engineering, different objectives can be met with va...

In the direct displacement-based design method, energy dissipative capacity of structures can be represented by an equivalent viscous damping (EVD). A number of studies have been reported in the formulation of EVD for different structural systems and hysteretic models. In this paper, an EVD model is developed and calibrated for steel-timber hybrid structures, where cross-laminated timber (CLT) shear panels are used as an infill in steel moment-resisting frames (SMRFs). To develop the EVD model, 243 single-story, single-bay CLT-infilled SMRFs analytical models are subject to semi-static cyclic analysis. Different model parameters of the hybrid structure are varied: gap between CLT panel and steel frame, bracket (connection) spacing, CLT panel thickness and strength, and postyield stiffness ratio of steel members. The EVD of each model was computed from the hysteretic responses based on an area-based approach. The design of computer experiments and response surface methodology were utilized to formu...

A timber-steel hybrid system, where cross-laminated timber (CLT) shear panels are used as infill in steel moment resisting frames, is analytically investigated. The proposed hybrid system combines ductile behavior of steel moment frame with lighter and stiffer CLT panels. Initial parametric study is carried out with a single-bay-single-story model using pushover analysis to investigate effect of CLT panel thickness, crushing strength, and confinement gap. Results showed that the parameters studied have a significant influence on system’s ultimate strength, ultimate drift capacity, and post-peak behavior. Subsequently, parametric studies are carried out for three-bay hybrid buildings with three-, six-, and nine-story hybrid buildings for varying panel configuration (a given gap, panel thickness, and crushing strength) values. The parameters varied and are design ductility level (limited ductility and ductile) and infill pattern. A monotonic pushover analysis was performed to develop a preliminary d...