19-58072 - Phase II - a Design Example for a 12-storey CLT Shearwall Prototype Building (19-58072)

1.1 Introduction

The National Research Council‘s Canadian Construction Materials Centre, has been charged to produce a Technical Guide for the procedure for the evaluation of Timber Seismic Force Resisting System (SFRS) in Tall Mass Timber buildings, and to provide a design example for a 12-storey CLT shearwall prototype building as a “demo” project.

1.2 Background

Engineering community around the world has been exploring taller wood construction options since the early 2000s. It should be noted that most of those tall wood projects are not in high seismic zones; and of those that are, most use a non-wood seismic force resisting system. Where projects used a mix of structural systems and materials, detailing interfaces between differing materials have been identified as a major effort and challenge. And therefore work needs to be done to move towards complete timber seismic systems.

1.3 Technical Issues

Currently, only light frame wood-based shearwall, and braced or moment-resisting frames are given in the NBC 2015 as acceptable solutions, with the height for these SFRSs in high seismic zones being limited to 20 m (6 storeys). There is no acceptable solution for using Timber SFRS in buildings more than 20 m high in high seismic zones. The Tall Wood building projects in Canada have been following the “Alternative Solution” path with supporting test data and analysis that could demonstrate equivalent or better performance than conventional building meeting local code requirements. These are approved on a case-by-case basis by the Authority Having Jurisdiction (AHJ) based on the structural engineer’s design submission. The Tall Wood projects have been and will be faced with increasing level of difficulties and structural design challenges depending on the familiarity of the designer and AHJ with tall wood construction. Furthermore, there are no consistent procedures and performance criteria to analyze and evaluate the Timber SFRS in tall mass timber buildings that could be referenced by a designer or AHJ as part of their due diligence for code compliance.

1.4 Scope of work

A Technical Guide has been developed in Phase I of the project, and a design example for a 12-storey CLT shearwall prototype building is to be developed in this Phase II of the project in order to illustrate and validate the procedure in the CCMC Technical Guide. Since there are currently: (i) no provisions (RdRo) for CLT shear walls in the Part 4 of the National Building Code (NBC), (ii) limited information on tested connections, and (iii) no established CSA O86 design procedures for tall balloon-type CLT shear walls, the design of balloon type CLT shear walls is to be addressed through a worked and detailed example. This 12-storey design example will also illustrate the use of the Phase I Technical Guideline in establishing RdRo based on components that have been tested and can be used in practice.

The design example shall account for the effects of seismic hazard (Vancouver and Montreal) and gravity loads (lightly and heavily gravity loaded walls) and other parameters deemed important to affect the seismic performance of the chosen system. The design shall clearly define the energy-dissipative elements and/or energy-dissipating mechanisms. Choosing and scaling earthquake ground motions shall be performed following the procedure specified in the CCMC Technical Guide. The determination of RdRo factors shall be clearly explained in the design example and non-linear time history analysis shall be performed to demonstrate the acceptable performance in accordance with the CCMC Technical Guide.