National Building Code Of Canada Research Articles

Simulating the impact and policy implications of telework on home energy use and emissions in Canada

Statistics indicate that after the COVID-19 pandemic, many individuals have opted to work remotely for at least a few days each week. This study investigates the impact of teleworking on energy consumption and carbon emissions in Canadian homes. Four residential building models, aligned with the 2020 requirements of the National Building Code of Canada (NBC), were investigated across six Canadian climate zones. The findings of this study reveal that the increase in energy consumption and CO2 emissions due to teleworking varies according to the type of building and the number of thermal zones. For the selected single-zone house models, the maximum increase in energy consumption and CO2 emissions were 11% and 10%, respectively occurring in a row house two-story building. For the three-zone house models, the increase was 5%. Also, results indicated that full-time teleworking in a four-storey multi-family building with 12.5%, 50% and 100% teleworking ratios increased the total energy of the building by 1%, 4%, and 10%, respectively. The second phase of this study investigated possible enhancements to building energy codes, focusing on the National Building Code of Canada, to address increasing daytime occupancy resulting from teleworkers, retirees, and other occupants.

Canadian seismic design coefficients for coupled composite plate shear wall/concrete filled (CC-PSW/CF)

Concrete-filled coupled composite plate shear walls (also known as as SpeedCore walls) are gaining acceptance for construction in seismic region throughout North America. Design provisions for this lateral load-resisting system have already been added to ASCE 7-22 and to the American Institute of Steel Construction Seismic Design Provisions. Adequacy of the seismic design parameters used for this structural purpose has been validated in the USA using the FEMA P695 methodology. An interest was expressed by the practicing engineering community to use these walls in Canada, which requires demonstration of satisfactory seismic performance within the Canadian context. As such, new analyses are needed using Canadian-specific sets of ground motions to confirm the adequacy of the seismic design parameters proposed for implementation of these composite walls in the National Building Code of Canada. This paper presents the results of these analyses, showing that the proposed seismic performance factors are appropriate for this structural system in Canada.

Resistance Factor Spectra for the Ultimate Limit State of the National Building Code of Canada

Over the years, structural engineering codes and specifications in Canada and elsewhere have moved from an allowable stress design (ASD) approach to a load and resistance factor design (LRFD) philosophy. LRFD methodology takes better account of the inherent variability in both loading and resistance by providing different factors of safety for loads of distinct natures with regard to their probability of overload, frequency of occurrences and changes in point of application. The method also results in safer structures because it considers the behavior at collapse. While resistance factors for traditional construction materials based on LRFD in the National Building Code (NBC) of Canada are available, they cannot be used for non-conventional ones. This is because the resistance of such materials due to various load effects has unique bias factors (λR) and coefficients of variation (VR), which greatly impact their reliability index (β). In this study, relationships between the resistance factor ϕ and critical load effects from the NBC load combinations at ultimate limit states are developed for a wide range of resistance bias factors and coefficients of variation. The relationships are presented in the form of charts that are useful for researchers and code-writing professionals who have expertise in the various fields of structural engineering but lack proper background in reliability theory. The developed spectra showed that for the same ϕ, β increases with an increase in the live-to-dead load (L/D) ratio until it reaches 1; thereafter, the shape of the relationship will depend on the statistics of the resistance as well as on the magnitude of ϕ. For a small ϕ and VR, β will keep increasing with an increase in the L/D ratio from 1 until 3, albeit at a lesser rate. For L/D > 3, the relationship between the critical β and applied load is just about constant. This finding is also true for load combinations involving snow and wind. Application of the method is illustrated by a practical example involving the shear strength of a corrugated web steel beam.

Seismic performance assessment of post-tensioned CLT shear wall buildings with buckling-restrained axial fuses

Post-tensioned cross-laminated timber (PT-CLT) walls have been demonstrated to be a low-damage seismic force-resisting system (SFRS) due to their self-centering capability. However, there is still a need to examine the seismic performance of such SFRS in high-seismic risk zones. This study evaluates the seismic performance of 6-, 9-, and 12-storey PT-CLT shear wall buildings in Vancouver, Canada, equipped with buckling-restrained axial fuses. The prototype buildings were designed using the displacement-based design method, and the assessment considered the most recent seismic hazard model provided in the 2020 National Building Code of Canada. To conduct nonlinear response history analysis (NLRHA) and incremental dynamic analysis (IDA), numerical models were developed in OpenSeesPy and calibrated based on component- and system-level experimental tests. The NLRHA and IDA results demonstrate that all the studied buildings have adequate collapse margin ratios, with less than a 10% chance of collapsing at the maximum considered earthquakes.

Ductility-related seismic modification factor for CLT shear-wall and glulam moment-resisting frame dual system

The cross-laminated timber (CLT) shear-wall and glulam moment-resisting frame (CLTW–GMRF) dual system is a recently completed research prepared for the British Columbia (BC) Forestry Innovation Investment Ltd. With the introduction of new structural systems, the need to update existing building code becomes evident. Accordingly, this study evaluates the ductility-related force modification factor ( Rd) of the CLTW–GMRF system for the National Building Code of Canada, utilizing the FEMA P-695 procedure. In two performance groups, 16 archetype buildings are designed considering different building storey heights, CLT shear-wall locations, and wall-frame moment proportions. Numerical model of the systems is developed in OpenSees and incremental dynamic analyses are conducted using 30 bi-directional ground motion records that represent the seismicity of Vancouver, BC, Canada. Collapse margin ratios are calculated to assess the adequacy of the trial Rd factors. The research determined that with an over-strength factor of 1.5, an Rd of 3 is found to be acceptable for the system.

Structural performance of balloon mass timber shear walls under in-plane lateral loads

Balloon-type mass timber shear walls are one of the most efficient structural systems to resist lateral loads induced by earthquakes or high winds. They are a viable solution for high-rise buildings, since they endure several key advantages, such as reducing connections and avoiding accumulating compression perpendicular to grain in the floors. This system, however, is not included in the 2020 National Building Code of Canada and has no design guidelines in the 2019 Canadian Standard for Engineering Design in Wood, so it is out of reach of most designers. A multi-year research project has been initiated at FPInnovations to quantify the system performance and develop the necessary technical information to codify balloon-type mass timber shear walls. This paper presents results of an analytical study on the structural performance of balloon-type CLT shear walls. A mechanics-based analytical model was updated to predict the CLT panel resistance, in addition to predicting the deflection and resistance of balloon type CLT shear walls. The influence of specific key parameters such as wall length and thickness, aspect ratio, vertical loads, and vertical joints, on the structural performance of this wall system under lateral loads was investigated using the updated model. The results of this study will give a valuable insight into the seismic performance of balloon type CLT shear walls.

Multi-cultural perception of impact sound -- An international online listening survey about the perceived annoyance due to impact sounds

To support the introduction of requirements for protection from impact noise in the National Building Code of Canada, the National Research Council of Canada implemented pilot subjective evaluations of impact sounds to evaluate the best metric to be used in the Code. As an alternative to the typical laboratory-based listening experiments, online-based listening tests were used. The ability to collect data with an online survey allows to reach the general public much more than with any laboratory-based experiment, and it was especially relevant in the context of the Covid-19 pandemic, which forced researchers to re-evaluate in-person procedures. This online listening survey was published for world-wide access, enabling data collection across a diverse target audience in many parts of the world. The survey and its preliminary results are presented and discussed in this paper. Data collected as part of the online survey, such as the person's country of residence and the type of dwelling they lived in, is used to explore the multicultural effects on the annoyance ratings.

Estimation of historical earthquake-induced liquefaction in Fraser River delta using NBCC 2020 GMPEs in deterministic and probabilistic frameworks

Paleo-liquefaction features of sand dykes and sand blows were identified in the 1990s at multiple host sediments in the Fraser River delta in southern British Columbia all younger than 3500 BP. These paleo-liquefaction sites could be linked to Cascadia subduction earthquakes. Empirical magnitude-bound relationships are often used to estimate paleo-earthquake magnitudes. To determine the lower bound magnitude of Cascadia interface earthquakes that could have generated the paleo-liquefaction features, we use ground motion prediction equations for interface earthquakes from the sixth Canadian seismic hazard model of the 2020 National Building Code of Canada. We estimate the minimum M and its peak ground acceleration ( amax) of an interface earthquake required to initiate paleo-liquefaction in the study region. Starting with three full-rupture deterministic scenarios of varying source-to-site distance, we determine the minimum M required from Cascadia subduction zone interface mega-thrust earthquakes to induce liquefaction in the Fraser River delta spans 8.0–8.9 with a corresponding amax range of 0.09–0.13 g. We also perform a back-calculation paleo-liquefaction analysis in a probabilistic framework to incorporate aleatory uncertainties (cone penetration resistance, groundwater table, and amax) and epistemic uncertainties (liquefaction simplified model) via the Monte Carlo simulation. The developed probabilistic methodology is also applicable to a forward liquefaction assessment and other liquefaction sites globally. The median M from this probabilistic paleo-liquefaction for the four investigated sites lies between 8.8 and 9.0. Our probabilistic results also reveal that Cascadia interface earthquakes with M > 8.9 lead to a 31%–57% probability of liquefaction triggering in the Fraser River delta. In addition, we developed deterministic and probabilistic magnitude-bound curves specific to Cascadia interface earthquakes and representative site class E conditions. These curves provide more accurate magnitude estimations for predicting seismic-induced liquefaction from Cascadia interface earthquakes for sites in the Pacific Northwest than empirical bound curves.

Seismic performance evaluation of self-centering balloon-framed CLT building

Balloon-framed cross-laminated timber (CLT) construction has a number of advantages when compared to platform-type construction; however, many international standards only include provisions for the latter as there is little research reported on the seismic performance of the former. In this paper, a seismic fragility assessment of a 4-storey balloon-framed CLT building in Vancouver, Canada, is presented. This structure is the first in North America that adopts a self-centering friction-based technology for the hold-downs (HDs). The seismic performance of the building was assessed by performing incremental dynamic analysis (IDA) on a three-dimensional finite element model using Cascadia Subduction Zone ground motions, and compared to a second building model with conventional dowel-type HDs. The analyses at the design intensity level showed that the self-centering building had an average maximum inter-story drift ratio of 0.67%, well below the 2.5% drift limit specified in the National Building Code of Canada. Based on the IDA and taking into account uncertainties, the building had a collapse margin ratio of 2.96 and a 5.2% probability of collapse at the design level. Compared to the conventional HDs, the friction-based HDs did not improve the building’s collapse capacity, but reduced the building drift by more than 20% at lower damage states, demonstrating the effectiveness of designing balloon-framed CLT structures with a resilient self-centering HDs in high seismic zones.

Wind pressure on a 45° gabled roof: verifying code provisions with field measurements and wind tunnel data

The wind load provisions for gabled roofs with a slope of 27° < α < 45° in the National Building Code of Canada (NBCC) were derived from wind tunnel studies conducted in the 1970s. The coefficients have remained basically unchanged until this time. The paper presents the results of full-scale measurements and wind tunnel experiments to verify the necessity to update the current NBCC provisions. A full-scale building with a gabled roof of 45° was instrumented with pressure taps, and the wind load was monitored for 15 months. Special attention is given to the roof overhang by considering the simultaneous pressure contribution from both the upper and lower surfaces. The building and surroundings were replicated at a wind tunnel scale and investigated by Concordia University and Western University. Based on these three sources of data, the study concluded that the corner and edge provisions for both cases—a roof with and without overhang—need to be increased. It is suggested to merge the corner and edge into a single “perimeter” load provision. This code simplification would help the roofing industry to reduce misleading interpretations of the code and minimize failure due to installation errors.

Seismic Resilience and Design Factors of Inline Seismic Friction Dampers (ISFDs)

While damping devices can provide supplemental damping to mitigate building vibration due to wind or earthquake effects, integrating them into the design is more complex. For example, the Canadian code does not provide building designs with inline friction dampers. The objective of this present article was to study the overstrength, ductility, and response modification factors of concrete frame buildings with inline friction dampers in the Canadian context. For that purpose, a set of four-, eight-, and fourteen-story ductile concrete frames with inline seismic friction dampers, designed based on the 2015 National Building Code of Canada (NBCC), was considered. The analyses included pushover analysis in determining seismic characteristics and dynamic response history analysis using twenty-five ground motion records to assess the seismic performance of the buildings equipped with inline seismic friction dampers. The methodology considered diagonal braces, including different 6 m and 8 m span lengths. The discussion covers the prescribed design values for overstrength, ductility, and response modification factors, as well as the performance assessment of the buildings. The results revealed that increasing the height of the structure and reducing the span length increases the response modification factors.

Vertical floor spectra in low- and mid-rise elastic RC moment resisting frame buildings

To examine how floor spectral accelerations affect the design force of flexible Non-Structural Components (NSCs), the present study discusses the estimation of floor response spectra resulting from strong vertical seismic motion. 3-, 6-, 9- and 12-storey reinforced concrete buildings with moderately ductile moment-resisting frame systems, designed in accordance with the National Building Code of Canada [25] were selected for this research. 65 sets of historical records relating to 31 severe earthquakes from across the world were used to analyze the linear behavior of these structures. A constant amplification of the Vertical Floor Spectral Acceleration (FSAV) was observed along the building height. This amplification was noticeably elevated for slab nodes, especially at the center of the interior slab and in shorter buildings. Furthermore, the vertical component of the earthquake had a greater impact at shorter periods, since the maximum vertical acceleration occurred at periods lasting less than 0.35 sec. Finally, equations to estimate FSAV corresponding to the input vertical ground acceleration were proposed for typical code-conforming RC frame buildings.

A national seismic risk model for Canada: Methodology and scientific basis

Canada is exposed to rare but potentially destructive earthquakes that threaten densely settled metropolitan centers in many parts of the country. To assess the impacts and consequences of future natural-hazard events and help advance policy goals and objectives of the Sendai Framework for Disaster Risk Reduction, Natural Resources Canada, through a collaborative partnership with the Global Earthquake Model Foundation, produced a national seismic risk model. Developing this model has required the creation of a national exposure inventory, Canadian-specific fragility and vulnerability curves, and significant simplification of the Canadian Seismic Hazard Model which forms the basis for the design seismic hazard values of the National Building Code of Canada. Using the Global Earthquake Model Foundation’s OpenQuake Engine, probabilistic stochastic risk modeling is completed under baseline and simulated retrofit conditions to assess seismic risk at the neighborhood level for all settled areas in Canada. Output risk metrics include the expected immediate physical impacts of earthquake events such as building damage, casualties, and direct economic losses. This article documents the technical details of the modeling approach including a description of novel data sets in use, a summary of the extensive sensitivity testing undertaken, and characterization of quality control implemented in the absence of usable validating earthquake loss data. The results from this model, such as loss exceedance curves and annual average losses, provide an open, accessible and quantitative base of evidence for decision-making at local, regional, and national levels. As a large country with a complex seismic hazard model and dispersed populations, this Canadian study is unique. However, the challenges faced and solutions offered are likely to be of interest to other nations pursuing similar programs.

Review of nonlinear modelling parameters and acceptance criteria in ASCE 41 for seismic evaluation and upgrading of steel structures in Canada

The seismic resilience of structures can be quantified through rigorous seismic assessment. Because no detailed guideline is available for nonlinear modelling parameters and the corresponding acceptance criteria for the seismic evaluation and upgrading of steel structures in Canada, the structural commentary of the National Building Code of Canada suggests using ASCE 41, which has been adopted as a standard for seismic evaluation and retrofit of buildings in the United States (U.S.). However, because the steel design standards in Canada and the U.S. are different, their applicability to steel structures in Canada needs to be investigated. To this end, this paper critically reviews the nonlinear modelling parameters and acceptance criteria, and then recommends whether these values need to be revised or are adopted as is for the seismic evaluation and upgrading of steel structures in Canada. A numerical example of a steel moment-resisting frame is presented to demonstrate the recommended parameters being used for seismic evaluation.

CFD wind tunnel investigation for wind loading on angle members in lattice tower structures

Wind loading on lattice structures is studied locally by considering the applied forces on individual angle members. This work represents a comprehensive Computational Fluid Dynamics (CFD) analysis of wind loading on angle members, which includes a quantitative evaluation of the aerodynamic drag and lift loading and also a qualitative investigation of the wake characteristics behind the angle member. The focus is on the flow around the angle member cross-section which has two equal length sides at a right angle to each other. CFD has been used to investigate the flow around a single angle member characterized by its length D, thickness T, and angle of incidence to the oncoming flow. Both Reynolds-Averaged Navier–Stokes (RANS) and Large-Eddy Simulation (LES) are evaluated for a Reynolds number of 37,700, where the k-ϵ RANS and Wall-Adapting Local Eddy-viscosity (WALE) LES models are respectively used. The results are compared with the wind tunnel experiments reported in the literature (Wardlaw, 1967; Slater, 1969; Prud’homme et al., 2014) and the National Building Code of Canada (Canadian Commission on Building and Fire Codes and National Building Code of Canada, 2005), where the drag and lift coefficients at a range of incidence angles were reported. Quantitatively, the RANS performs well when compared to experiments for the aerodynamic coefficients at a range of incidence angles and less well for angles where a cavity style flow is formed and the separation becomes influential. This is in contrast to other bluff body cases where RANS does not perform so well. The LES is thus run at selected incidence angles for comparison and to better understand the flow where the RANS performs well and less well. Details of the turbulence in the wake are difficult to interpret when using RANS modeling, but this behavior is well illustrated with the LES model and details are reported here.

Assessment of seismic acceleration demands on nonstructural components in moderately ductile RC frame buildings designed according to NBC 2015

This paper presents an extensive investigation of the seismic demands on acceleration-sensitive nonstructural components (NSCs) attached to reinforced concrete moment-resisting frame buildings with limited ductility and designed according to the National Building Code of Canada. A total of four benchmark structures with varying heights are considered in this study. Linear and nonlinear time-history analyses were performed using artificial ground motions compatible with Montreal site Class C uniform hazard spectra having 2% and 10% probabilities of being exceeded in 50 years. Seismic acceleration demands on NSCs were evaluated by assessing the horizontal height factor Ax, the component dynamic amplification factor Ar, and the component force factor Sp compared with various building code provisions. The overall acceleration demands of NSCs are discussed, and a corresponding optimized Sp profile is proposed to improve the estimation of the seismic force demands on NSCs at the rooftops of buildings located in moderate seismic zones.

The Vibration Reduction Index of Typical Canadian Cross-laminated Timber Junctions

In support of the National Building Code of Canada, The National Research Council Canada has published research report RR-335 which describes the results of measurements of the transmission of structure-borne noise through junctions between mass timber elements. The Code only allows for the use of measured data for the vibration reduction index from the NRC's reports or reports from other research institutes. The Code does not currently allow for the use of empirical data for the calculation of the apparent sound transmission class of mass timber buildings. A lack of published data for typical mass timber junctions used in Canada can result in the overdesign of buildings or buildings which don't meet the acoustic requirements of the Code. The NRC has embarked on a program to measure the vibration reduction index of a number of mock junctions of typical junctions used in Canada including junctions between cross-laminated timber floors and lightweight timber framed walls. The new data will aid in the development of empirical models of typical Canadian mass timber constructions.

Methodology for determination of seismic force modification factors in Canada: Performance-based unified procedure

The National Building Code of Canada (NBC) employs seismic force modification factors (i.e. ductility-related factor, Rd, and an overstrength-related factor, Ro) for different Seismic Force Resisting Systems (SFRSs), which, since 2005, are largely based on engineering judgment and qualitative comparisons of seismic response characteristics of different SFRSs. Currently, there is no unified procedure in Canada for systematically quantifying these values, which has potentially led to perceived inconsistent levels of performance between buildings built with different SFRSs. While some research has been carried out in Canada to quantitatively evaluate the seismic response of different SFRSs using the FEMA P695 methodology with some modifications, inconsistencies exist among different research works. Moreover, the number of archetypes developed in these studies was limited, due to the computationally laborious incremental dynamic analysis (IDA) step in FEMA P695. Therefore, there is a need for a consistent and efficient methodology for structural performance assessment of different SFRSs in Canada. The proposed performance-based unified (PBU) procedure is to systematically quantify Rd and Ro factors for different SFRSs in the NBC. The PBU procedure is designed to be a performance-based approach (vs the risk-based approach of FEMA P695). In addition, our procedure is devised to optimize the number of archetypes through a two-level screening procedure using a nonlinear pushover and time history analyses before running the IDA. To validate the PBU procedure, we developed 21 different concrete moment frame archetypes covering various key parameters. The results verify the efficiency of the screening feature of the PBU procedure by a significant reduction in the number of archetypes requiring IDA.

Low-Sloped Rooftop Storm-Water Detention Assembly to Mitigate Urban Flooding

Low-sloped roofs such as commercial and high-rise buildings in a dense urban area provide vast “unused” surfaces that can be used to manage storm-water and mitigate urban flooding. Storm-water Detention Assembly (SDA) known as “blue roof” exerts advanced drainage technologies and operational strategies to store-and-release storm-water during and after heavy rainfall events. SDA can reduce peak flow and decrease storm-water run-off volume. However, the SDA application is limited due to the lack of science-based regulatory requirements. This paper introduces SDA, summarizes the benefits and challenges of this system, reviews the existing code specifications on roofing drain systems, and documents the criteria to design and construct SDA. With this systematic approach, the missing links are identified that shall form code change request for possible inclusion in the National Building Code of Canada (NBCC) and National Plumping Code of Canada (NPC). In addition, a road map is stated to calculate and benchmark the drain requirements on low-sloped roofs for a given design climatic load.

Development of ductility-related modification factor for CLT-coupled wall buildings with replaceable shear link coupling beams

The desire of using sustainable materials has reignited the interest in timber-based construction. Researchers and practitioners are developing novel timber-based structural solutions. Cross-laminated timber (CLT)-coupled wall is a recently proposed system for potential use in mid- and high-rise timber construction. The National Building Code of Canada, however, does not include this system and, consequently, the seismic force modification factors are not available. This study evaluated the ductility-related force modification factor ( Rd) using the FEMA P-695 procedure. Nine archetype buildings were designed considering different design parameters: building storey height, CLT wall configuration, and coupling ratios. Using 30 ground motion records (bi-directional), rigorously selected for seismicity of Vancouver, BC, Canada, incremental dynamic analyses were performed. Collapse margin ratios were calculated to assess the adequacy of the trial Rd factors. Using an over-strength factor of 1.5, Rd = 4 is found to be acceptable for this system.