DRAWING ON EXPERIENCE … BUILDING ON STRENGTH Six Storey Wood-Framed Buildings Unique Structural Opportunities & Challenges Kurt Ruhland, P.Eng. Director, Building Structures MTE Consultants

Overview OBC changes came into effect Jan. 1, 2015 permitting wood-framed building up to six storeys Adopted previously in other provinces: British Columbia (2009), Quebec (2014) and Calgary (2014) Code changes are “Made in Ontario” They do not exactly match the code provisions in other provinces

Opportunity Opportunities for Cost Savings Use of renewable resources Structural Design Factors of Safety as high or higher than comparable structures New options for Builders and Developers

Structural Engineering Design Considerations Increased loads Gravity Lateral Wood shrinkage Cladding Mechanical Shafts Fire and life safety Sprinklers Shafts Exits Roof Anchors Possible system constraints Shear wall layouts

Increased Gravity Loads Increase Loads are Simply Due to Added Floors to Building; Two Extra Floors Since Floors are typically heavier than roofs: 50% more floor area Results in about 60% more weight in the building Requires Engineered Design using same design codes and factors of safety as previously used

Increased Gravity Loads Design loads can be resisted by conventional wood framing Alternatively, Engineered Lumber or Concrete Block could be used on lower levels Due to “heavy” wood in walls consideration should be given to plumbing, electrical, etc. in bearing walls. Also need to consider sound transmission and insulation Recommend use of shop fabricated panelized walls

Increased Lateral Loads Increased lateral loads (seismic) Seismic loads are proportional to weight of the building, so 60% increase due to increase in building mass OBC (4): In higher seismic regions there are added requirements for vertical alignment of shearwalls through the building (shearwalls must stack full height) OBC (11): Provides additional restrictions on use of a dynamic analysis

Wood Shrinkage Actual Code Change: OBC A Sealing and Drainage. As a consequence of increased building height, wood construction buildings exceeding 4 storeys may experience increased loadings on environmental separators and may require different design considerations than common approaches used by industry for buildings of 4 storeys or less. These considerations include but are not limited to, the following:  air barrier assemblies,  fenestration selection,  protection from precipitation,  differential movement due to wood shrinkage,  roofing selection and design, and  risk of deterioration due to longer exposure of materials to the elements during construction.

Wood Shrinkage Proposed Code Change: A Design Basis for Wood The design criteria for wood, CAN/CSA 086 “Engineering Design in Wood”, makes assumptions that the wood products being used are in a condition as intended by their grading. This includes the limits of moisture content as specified by the grade. However, conditions such as transportation, site storage, and construction conditions can impact the original design assumptions. Design considerations should include, and be specific to, shrinkage that may occur due to changes in moisture content of the wood. This is of particular concern where the building height can be up to 6 storeys, including those built under Articles , , and The potential building movement due to shrinkage should be indicated to other design professionals for their considerations such as cladding systems and mechanical systems, hold-down devices for structural walls and connections to non-shrinking elements including firewalls and elevator shafts. Municipalities may require, as part of the building permit process, that the designer provide analysis satisfactory to the building official to demonstrate that shrinkage of the wood framing will not have adverse effects on the structure or any building services installations due to excessive shrinkage or differential movements caused by shrinkage. Computations to determine the required size of wood members should be based on the actual net dimensions and not nominal size.

Wood Shrinkage Nevertheless: Current OBC (1) In proportioning structural members to limit serviceability problems resulting from deflections, consideration shall be given to (d) creep, shrinkage, temperature changes and prestress. The existing language of the code requires the engineer to deal with potential problems caused by shrinkage.

Wood Shrinkage

Wood will shrink on the order of ¾” per floor for stick- framed structures to ¼” per floor for structures with precast floors. Effect is cumulative over height of the building Regardless of how it is regulated in the Code designers must consider the interaction of wood with other elements of the building that will not shrink 1.Brick Cladding 2.HVAC Ducts 3.Plumbing Stacks 4.Non-Combustible Shafts 5.Shear wall hold-downs

Wood Shrinkage Shrinkage Compensating Tie-Down Rods

Challenges Combining block or concrete wall in a wood structure Magnitude of seismic loads depend on the lateral force resisting system Max. V=2/3 x S 0.2 x I E x W/(R d R o ) Wood Shearwalls: R d R o =3.0x1.7=5.1 Concrete Shearwalls: R d R o =1.5x1.3=1.95 Masonry Shearwalls: R d R o =1.5x1.5=2.25 OBC : When combining lateral force resisting systems the lowest R d R o shall be used

Challenges Combining block or concrete wall in a wood structure For instance: S 0.2 =0.16 I E =1.0 W=50,000 kN The seismic load V is equal to 1050 kN for wood shear walls (resisted by several long walls) 2750 kN for concrete shear walls (resisted by only the shafts) 2350 kN for concrete block shear walls (resisted by only the shafts) Using non-wood shear walls negates some of the savings of wood

Challenges Stair Non-Combustible Shafts Exiting on the Ground Floor

Other Considerations Brick support Requirement for non- combustible cladding Roof Anchors OBC NFPA13R vs. NFPA13 Limitations on Roof Construction