World Housing Encyclopedia Report

Country: Canada

Housing Type: Single-family wood frame house

Contributors:Carlos E. VenturaMehdi H. K. Kharrazi

Primary Reviewer:Svetlana Brzev

Created on: 9/26/2002Last Modified: 6/17/2003

This encyclopedia contains information contributed by various earthquake engineering professionalsaround the world. All opinions, findings, conclusions, and recommendations expressed herein are those

of the various participants, and do not necessarily reflect the views of the Earthquake EngineeringResearch Institute, the International Association for Earthquake Engineering, the Engineering Information

Foundation, John A. Martin & Associates, Inc. or the participants' organizations.

Table of Contents

General Information............................................................................................1Architectural Features........................................................................................ 6Socio-Economic Issues...................................................................................... 7Structural Features............................................................................................. 8Evaluation of Seismic Performance and Seismic Vulnerability.......................... 23Earthquake Damage Patterns............................................................................ 33Building Materials and Construction Process..................................................... 35Construction Economics.....................................................................................40Insurance............................................................................................................41Seismic Strengthening Technologies................................................................. 42References......................................................................................................... 44Contributors........................................................................................................ 46Figures................................................................................................................47

1 General Information

1.1 CountryCanada

1.3 Housing TypeSingle-family wood frame house

1.4 SummarySingle-family wood frame construction represents the most common housing constructionpractice found throughout Canada. This construction constitutes over 50% of the dwelling stock inthe Province of British Columbia, located in the western Canada. Majority of dwellings of this typeare single-storey structures (commonly called "bungalows" or "ranchers"), however somedwellings are two-storey high. A typical Canadian style modern wood-frame house consists of aconcrete foundation, whereupon a platform is constructed of joists covered with plywood ororiented strand board (OSB) to form the groundfloor level of the house (also known as platformwood-frame construction). This platform is connected directly to the foundation with anchor bolts;alternatively, the platform is supported by a short wall, so-called "cripple wall", #pony wall# or"stub wall" which should be connected to the foundation with anchor bolts (however, that is nottrue for some older buildings). On this base, the exterior and interior walls are erected. The wallsconsist of a horizontal sill plate with vertical timber studs with board or panel sheathing nailed tothe studs on the outside of the building. Once the first storey walls are complete, the secondstorey floor is constructed, which in turn acts as a platform for erection of the second storey walls.This process is continued for all the stories. The roof structure typically consists of prefabricatedtrusses, which are covered with sheathing and roof tiles (Rainer and Karacabeyli 2000). This isgenerally considered to be nonengineered construction in Canada, as the Canadian NationalBuilding Code generally does not require direct professional architectural or engineeringinvolvement related to this construction. Seismic provisions in terms of specific seismicconstruction requirements and calculation/design requirements for seismic resistance arecurrently not included in Part 9 of the Code that addresses low-rise residential wood frameconstruction as described in this contribution. There is no evidence of substantial damage to thistype of construction in the past earthquakes in Canada, which had occurred away from denselypopulated urban centres. However, recent experimental research studies (Earthquake 99 Projectat the University of British Columbia) focused on seismic performance of wood frame constructionhave revealed vulnerability of this type of construction to seismic effects, depending on the ageand wood construction technology used at the time.

1.5 Typical Period of Practice for Buildings of This Construction TypeHow long has thisconstruction been practiced< 25 years< 50 years< 75 years< 100 years< 200 years X> 200 years

Is this construction still being practiced? Yes NoX

Additional Comments: Based on the historical development of wood frame construction in BritishColumbia, one could define three distinctive age classes of construction: Pre-1940, 1940-1980, andPost-1980. Each of these age classes results in a corresponding change in expected seismicperformance based on the wood product technology in use in the building at the time, since seismic code

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provisions for buildings of this class were, and continue to be, largely non-existent. Pre-1940 buildingswere primarily built from wood boards and full-dimensioned lumber and generally were well connectedwith nails driven by hand and other fasteners. Early examples of wood frame construction in the area(mainly found in Victoria and Vancouver) were built in the second half of the nineteenth century. Some ofthese older houses were of log construction, but the vast majority was wood frame construction made outof lumber. Many of these buildings have since become heritage buildings, and are typical periodexamples of residential construction. Historic devlopment of wood frame construction is documented inVictoria (1978), Ovanin (1984) and Kalman (1979). In the pre-1920 period, housing demand madepopular the purchase and erection of prefabricated home kits on prepared footings on a site. The1940-1980 class reflects a shift in sheathing products from boards to panels such as plywood with aresultant change in wall racking performance. Framing continued to use lumber, however in newerstandardized but slightly smaller cross-sections. Concrete was used almost exclusively as a foundationmaterial, with most foundations being a cast slab-on-grade with strip footings placed in the ground at adepth of two feet. Some of the styles and trends popular at the time were: post and beam homes of the1950#s, hybrid plywood beam/stressed skin homes first exhibited at the Pacific National Exhibition in theearly 1960#s, traditional log homes, the #Vancouver Special# of the late 1950#s to mid 1960#s, #monsterhomes# of the 1980#s, etc. (Kalman, et al.1978, 1993, NorthVan 1993). According to Taylor (1996),balloon framing as a framing style was not that very common in Vancouver. Finally, the Post-1980 classreflects the transition to engineered wood products encompassing a wide range of panel and framingproducts that are continuing to gain widespread use in order to optimize the wood resource. A change topneumatic connection methods such as air gun nailing also occurred during this period, and this effectcontinues to be a matter of concern and industry research.

1.6 Region(s) Where UsedWood frame construction can be found throughout Canada, however this contribution describes theconstruction practice typical for the Canadian West Coast, mainly the Province of British Columbia.According to the Census of Canada, single-family dwellings constitute 56% of the dwelling stock in theProvince of British Columbia.

1.7 Urban vs. Rural ConstructionWhere is this construction commonly found?In urban areasIn rural areasIn suburban areasBoth in rural and urban areas X

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Modern Canadian style single-family woodframe construction with OSB sheathing

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A heritage wood house in Victoria, British Columbia

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A typical 1950's stuccoed house with the basement

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2 Architectural Features

2.1 OpeningsAn estimate for the overall window and door area as a fraction of the overall wall surface area depends onthe age of construction. The total area of openings is on the order of 25-40% in the older constructionwhereas it is in the range of 50-80% for the contemporary construction.

2.2 SitingYes No

Is this type of construction typically found on flat terrain? XIs this type of construction typically found on sloped terrain? (hilly areas) XIs it typical for buildings of this type to have common walls with adjacentbuildings?

X

The typical separation distance between buildings is 3 m meters

2.3 Building ConfigurationBuilding plan in older buildings of this type (pre-1980 construction) is generally regular i.e. rectangualr and"T" or "L"-shaped in some cases. In buildings of more recent construction the shape of the building plan isoften irregular due to the modern architectural design trends

2.4 Building FunctionWhat is the main function for buildings of this type?Single family house XMultiple housing unitsMixed use (commercial ground floor, residential above)Other (explain below)

2.5 Means of EscapeFor single-story buildings, the means of escape from the buildings of this type is the main door and anadditional door (usually in the rear part of the building). In general, there is only one staircase in atwo-storey building.

2.6 Modification of BuildingsIn older houses of this type, the basement ceiling has been raised in some cases to increase the floorheight. Other modifications include moving the interior (partition) walls as a part of the renovation.

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3 Socio-Economic Issues

3.1 Patterns of OccupancyTypically, a single family occupies one house. Less often, there are cases in which a house is sharedamong 4 to 6 individual occupants (case of larger rental houses).

3.2 Number of Housing Units in a Building1 units in each building.

3.3 Average Number of Inhabitants in a BuildingHow many inhabitants reside in a typical building of thisconstruction type?

During the day / businesshours

During the evening / night

< 5 X5 to 10 X10-20> 20Other

3.4 Number of Bathrooms or Latrines per Housing UnitNumber of Bathrooms: 1Number of Latrines: 0

Additional Comments: typically up to 3 bathrooms in a single family house. Number of bathroomsdepends on size of house.

3.5 Economic Level of InhabitantsEconomic Status House Price/Annual Income

(Ratio)Very poor /Poor /Middle Class X 4/1Rich /

3.6 Typical Sources of FinancingWhat is the typical source of financing for buildings of this type?Owner FinancedPersonal SavingsInformal Network: friends and relativesSmall lending institutions/microfinance institutions XCommercial banks / mortages XInvestment poolsCombination (explain)Government-owned housing XOther

3.7 OwnershipType of Ownership/OccupancyRent XOwn outright XOwn with Debt (mortgage or other) XUnits owned individually (condominium)Owned by group or poolLong-term leaseOther

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4 Structural Features

4.1 Lateral Load-Resisting SystemLateral load-resisting system in wood frame construction includes horizontal elements (roof and floors)and vertical elements (walls). A Canadian style modern wood-frame house consists of a concretefoundation or a basement, on top of which a platform is constructed of joists covered with plywood ororiented strand board (OSB) to form the floor of the ground level of the house. This platform is connecteddirectly to the foundation with anchor bolts, or through a short so-called "cripple wall", #pony wall# or"stub wall" (this short wall may or may not be connected to the foundation with anchor bolts). On thisbase, the exterior and interior walls are erected. The walls consist of a horizontal sill plate with 38 x 89mm (2# by 4#) or 38 x 140 mm (2# by 6#) vertical timber studs of one storey height at a spacing oftypically 30 to 60 cm. A double top plate from 38 mm thick dimension lumber provides the base for thenext floor structure. Board or panel sheathing is then nailed to the studs on the outside of the building,while the inside spaces are filled with thermal insulation and then covered with a vapour barrier andgypsum board as the interior finishing. This is the general configuration of a typical woodframe shear wallwhich resists the lateral loads of the system. The nailing amount and the type of sheathing and boardinglargely affect the effectiveness of the lateral load-resisting system (Ventura et al. 2002).

4.2 Gravity Load-Bearing StructureGravity load is caried by the wall system, which consists of a horizontal sill plate with vertical timber studsof one storey height spaced at 30 to 60 cm on centre. Gravity loads are transferred from the walls to thefoundation or the stub walls.

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4.3 Type of Structural SystemMaterial Type of

Load-BearingStructure

# Subtypes

Masonry Stone masonrywalls

1 Rubble stone (field stone) in mud/lime mortar or withoutmortar (usually with timber roof)

2 Massive stone masonry (in lime or cement mortar)Earthen walls 3 Mud walls

4 Mud walls with horizontal wood elements5 Adobe block or brick walls6 Rammed earth/Pise construction

Unreinforced brickmasonry walls

7 Unreinforced brick masonry in mud or lime mortar8 Unreinforced brick masonry in mud or lime mortar with

vertical posts9 Unreinforced brick masonry in cement or lime mortar

(various floor/roof systems)Confined masonry 10 Confined brick/block masonry with concrete posts/tie

columns and beamsConcrete blockmasonry walls

11 Unreinforced in lime or cement mortar (various floor/roofsystems)

12 Reinforced in cement mortar (various floor/roof systems)13 Large concrete block walls with concrete floors and roofs

Concrete Moment resistingframe

14 Designed for gravity loads only (predating seismic codes i.e.no seismic features)

15 Designed with seismic features (various ages)16 Frame with unreinforced masonry infill walls17 Flat slab structure18 Precast frame structure19 Frame with concrete shear walls-dual system20 Precast prestressed frame with shear walls

Shear wall structure 21 Walls cast in-situ22 Precast wall panel structure

Steel Moment resistingframe

23 With brick masonry partitions24 With cast in-situ concrete walls25 With lightweight partitions

Braced frame 26 Concentric27 Eccentric

Timber Load-bearingtimber frame

28 Thatch29 Post and beam frame30 Walls with bamboo/reed mesh and post (wattle and daub)31 Wooden frame (with or without infill)32 Stud wall frame with plywood/gypsum board sheathing X33 Wooden panel or log construction

Various Seismic protectionsystems

34 Building protected with base isolation devices or seismicdampers

Other 35

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4.4 Type of FoundationType Description

Shallow Foundation Wall or column embedded in soil, without footingRubble stone (fieldstone) isolated footingRubble stone (fieldstone) strip footingReinforced concrete isolated footingReinforced concrete strip footing XMat foundation XNo foundation

Deep Foundation Reinforced concrete bearing pilesReinforced concrete skin friction pilesSteel bearing pilesWood pilesSteel skin friction pilesCast in place concrete piersCaissons

Other Concrete block masonry strip footing X

4.5 Type of Floor/Roof SystemMaterial Description of floor/roof system Floor Roof

Masonry VaultedComposite masonry and concrete joist

StructuralConcrete

Solid slabs (cast in place or precast)Cast in place waffle slabsCast in place flat slabsPrecast joist systemPrecast hollow core slabsPrecast beams with concrete toppingPost-tensioned slabs

Steel Composite steel deck with concrete slabTimber Rammed earth with ballast and concrete or plaster finishing

Wood planks or beams with ballast and concrete or plaster finishingThatched roof supported on wood purlinsWood single roofWood planks or beams that support clay tilesWood planks or beams that support slate, metal asbestos-cement or plasticcorrugated sheets or tilesWood plank, plywood or manufactured wood panels on joists supported bybeams or walls

X

Other

Additional Comments: The floor is usually considered to be a flexible diaphragm.

4.6 Typical Plan DimensionsLength: 12 - 18 metersWidth: 12 - 18 metersAdditional Comments: These houses are usually characterized with a total built-up plan area less then600 m.sq.

4.7 Typical Number of Stories1 - 3

4.8 Typical Story Height2.7 meters

4.9 Typical Span3 meters

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Additional Comments: span could be 3 to 4 meters

4.10 Typical Wall DensityWall density is widely variable.

4.11 General Applicability of Answers to Questions in Section 4This building was selected from CMHC's "Residential Guide to Earthquake Resistance" and it representsa typical construction practice.

Key load-bearing elements: wood-frame house (Source: CMHC 2001)

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North elevation showing force paths (Source: CMHC)

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South Elevation showing force paths (Source: CMHC)

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West elevation showing force paths (Source: CMHC)

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East elevation showing force paths (Source: CMHC)

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A sample site plan indicating some exterior hazards (Source: CMHC)

Typical basement floor plan (Source: CMHC)

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Typical main floor plan (Source: CMHC)

Typical second floor plan (Source: CMHC)

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Critical structural details: roof trusses (Source: CMHC 2001)

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Critical structural details : sill plate construction (Source: CMHC 2001)

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Critical structural details: end wall framing (Source: CMHC 2001)

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5 Evaluation of Seismic Performance and Seismic Vulnerability

5.1 Structural and Architectural Features: Seismic ResistanceStructural/ArchitecturalFeature

Statement True False N/A

Lateral load path The structure contains a complete load path for seismic force effects fromany horizontal direction that serves to transfer inertial forces form thebuilding to the foundation.

X

Buildingconfiguration

The building is regular with regards to both the plan and the elevation. X

Roof construction The roof diaphragm is considered to be rigid and it is expected that the roofstructure will maintain its integrity, i.e.. shape and form, during anearthquake of intensity expected in this area.

X

Floor construction The floor diaphragm(s) are considered to be rigid and it is expected that thefloor structure(s) will maintain its integrity, during an earthquake of intensityexpected in this area.

X

Foundationperformance

There is no evidence of excessive foundation movement (e.g. settlement)that would affect the integrity or performance of the structure in anearthquake.

X

Wall and framestructures-redundancy

The number of lines of walls or frames in each principal direction is greaterthan or equal to 2.

X

Wall proportions Height-to-thickness ratio of the shear walls at each floor level is: 1) Lessthan 25 (concrete walls); 2)Less than 30 (reinforced masonry walls); 3)Less than 13 (unreinforced masonry walls).

X

Foundation- wallconnection

Vertical load-bearing elements (columns, walls) are attached to thefoundations; concrete columns and walls are doweled into the foundation.

X

Wall-roofconnections

Exterior walls are anchored for out-of-plane seismic effects at eachdiaphragm level with metal anchors or straps.

X

Wall openings The total width of door and window openings in a wall is: 1) for brickmasonry construction in cement mortar: less than 1/2 of the distancebetween the adjacent cross walls; 2) for adobe masonry, stone masonryand brick masonry in mud mortar: less than 1/3 of the distance between theadjacent cross walls; 3) for precast concrete wall structures: less than 3/4 ofthe length of a perimeter wall.

X

Quality of buildingmaterials

Quality of building materials is considered to be adequate per requirementsof national codes and standards (an estimate).

X

Quality ofworkmanship

Quality of workmanship (based on visual inspection of few typical buildings)is considered to be good (per local construction standards).

X

Maintenance Buildings of this type are generally well maintained and there are no visiblesigns of deterioration of building elements (concrete, steel, timber).

X

Other

Additional Comments: There is a concern that this construction type will experience excessive lateral drift(movement of the building relative to the foundations) because of inadequate wall-foundation anchoragei.e. absence of holdowns.

5.2 Seismic Features

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Structural Element Seismic Deficiency Earthquake-Resilient Features Earthquake Damage PatternsWall - Use of horizontal board sheathing in

the construction of exterior shear walls(low-cost construction); - Lack ofanchorage and/or holddowns tofoundations; - Lack of horizontalblocking in the walls; - Joints overinterior load-bearing walls arecommonly not blocked; the lack ofblocking minimizes any effective loadtransfer from the floor diaphragm to thewall. - Absence of effective shear wallsin nonengineered wood buildings.

- High density of wooden shear wallsand stucco; - Provision of holddowns inengineered wood buildings.

No significant damage reported in thepast earthquakes in Canada - seeAdditional Comments below

Frame (Columns,beams)

- Potential loss of gravity load-cerryingcapacity in walls with finger-jointedstuds, since finger joints were neverdesigned for high flexural stresses thatcan develop in the walls with largelateral deformations.

No significant damage reported in thepast earthquakes in Canada - seeAdditional Comments below

Roof and floors - Absence of blocking in the roof and/orfloors; - Inadequate shear studs in theroof openings.

-Blocking of roof and/or floors; -Designof adequate shear studs for openings;

No significant damage reported in thepast earthquakes in Canada - seeAdditional Comments below

Other

Additional Comments: The expected seismic performance of wood frame housing was recently studied atthe University of British Columbia in Vancouver through the Earthquake 99 Woodframe House Project.The main focus of the project was the study of the expected seismic response of residential wood-frameconstruction in the region. The ultimate goal of this project was to develop procedures for improveddesign and retrofit. The first part of the project was mainly concentrated on current construction inCalifornia and on new proprietary framing systems, while the second part was focused on existingresidential (nonengineered) construction in British Columbia (BC). A total of 31 uni-axial shake table testswere conducted on full-scale one and two storey houses with a footprint of 6.1 m (20 ft) by 7.6 m (25 ft).For the California construction tests, records from the 1994 Northridge Earthquake records were used,while selected crustal and subduction earthquake records, adapted to the local geological setting, wereused for the BC tests. For each shaking test complementary forced vibration and ambient vibration testswere conducted to evaluate the dynamic properties of the house before and after the simulatedearthquake (Kharrazi 2001). The need for this research arose from the current construction practice inBritish Columbia that has resulted in many forms of contemporary residential housing being substantiallymore vulnerable to heavy earthquake damage than housing that was built 100 years ago. The project wascompleted in 2001. The key conclusions of this project were: 1. Non-structural materials such as stuccoand gypsum wallboard play a major role in reducing the earthquake damage, and their contributions needto be recognized in the design. 2. There are several forms of high-risk residential construction practice inBC that need to be addressed immediately. Seismic deficiencies studied in the experimental part of theproject included the use of horizontal board sheathing, absence of wall anchorages and hold downs andthe lack of effective shear walls. The results of the experimental study clearly indicate that measures toaddress these high-risk construction practices will substantially reduce earthquake damage. 3. The use ofan inelastic drift control approach to seismic design is strongly advocated in contrast to the currentempirical quasi-elastic force method. Drift control of actual building deflections under real earthquakes isthe best method for predicting earthquake damage and ensuring the reliable seismic performance. 4.Sophisticated software for the inelastic time history analysis has been developed to predict building driftlevels for an arbitrary earthquake ground motion. The results of the laboratory test program have beenused to refine the modeling methods.

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5.3 Seismic Vulnerability RatingVulnerability

High (Very PoorSeismicPerformance)

Medium Low (ExcellentSeismicPerformace)

A B C D E FSeismic

Vulnerability Class< 0 >

0 - probable value< - lower bound> - upper bound

Key seismic deficiency: no blocking between joists at interior load-bearing wall

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Key seismic deficiency: a typical shear wall without holddown

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Key seismic deficiency: a typical shear wall without horizontal blocking

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Key seismic deficiency: finger joint and discontinuous studs

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Key seismic deficiency: rear wall of a house - use of horizontal boards

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Key earthquake-resistant feature: installation of hold-downs in shear walls

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Full-scale model of a two-storey house with OSB shearwalls (left) and one-storey subsystem withhorizontal board sheathing (Earthquake 99 Project, Source: Kharazzi 2002)

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Damage to the two-storey wood frame building specimens tested on the shaking-table: test #13 - 1995Kobe earthquake, nonengineered building; test 14- 1995 Kobe earthquake, engineered building

(Earthquake 99 Project, Source: Kharazzi 2002)

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6 Earthquake Damage Patterns

6.1 Past Earthquakes Reported To Affect This ConstructionYear Earthquake Epicenter Richter magnitude(M) Maximum Intensity (Indicate

Scale e.g. MMI, MSK)2001 Nisqually, Washington (USA) 6.8 MMI=VI FOR GREATER

VICTORIA (GSC)1949 Queen Charlotte Islands,

British Columbia8.1 MMI=<IV FOR GREATER

VICTORIA (GSC)1946 Vancouver Island Earthquake

(Courtenay), British Columbia7.3 MMI=VI FOR GREATER

VICTORIA (GSC)MMI=VFOR GREATER

VANCOUVER (GSC)1918 Vancouver Island

Earthquake, British Columbia7 MMI=<IV FOR GREATER

VICTORIA (GSC)

Additional Comments: Wood frame construction had generally not been exposed to the effects ofdamaging earthquakes in Canada, however experimental studies were recently conducted to study theexpected seismic response of residential wood-frame construction in the region and to explore practicalalternatives for seismic retrofit. For more details on the studies see Section 5.3. For more information onthe Canadian earthquakes see: http://www.pgc.nrcan.gc.ca/seismo/hist/list.htm

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Typical earthquake damage to a wood frame house in Comox, BC in the 1946 earthquake (Source:Natural Resources Canada www.pgc.nrcan.gc.ca/seismo/hist/list.htm)

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7 Building Materials and Construction Process

7.1 Description of Building MaterialsStructural Element Building Material Characteristic Strength Mix Proportions/ Dimensions CommentsWalls OSB PlywoodBoard Depends to the species and /

or composite wood producttype. Wood Species such asS-P-F and D-Fir (Soft WoodLumber)

Wood Species such as SPFand DF (Soft Wood Lumber)

Foundations Concrete concrete mix 1:2:4(cement:sand:aggregate)

Frame Soft Wood Lumber Wood Species such as S-P-Fand D Fir (Soft WoodLumber)usually f (bending)=5to 16 MPa and f (shear) = 0.5to 1.0 MPa and f(compressionparallel to grain) = 4.0 to 16.0dependent to the species.E(0.05)=3500 to 6000. Formore information see theCanadian Wood Council#sWood Frame ConstructionGuide (CWC, 2001)

horizontal sill plate with 38 x89 mm (2# by 4#) or 38 x 140mm (2# by 6#) vertical timberstuds of one storey height ata spacing of typically 30 to 60cm

For furtherinformation seeCMHC "ResidentialGuide toEarthquakeResistance"

Roof and floors Same as Frame Different type of joist andblocking with many availablesizes

For furtherinformation seeCMHC "ResidentialGuide toEarthquakeResistance"

Notes:1. Tension/compression/shear strength (e.g. concrete compression strength, steel yield strength, masonrycompressive/shear strength)2. Explain mix of different materials used in the construction e.g. masonry mortar mix (1:6 cement/sandmortar or 1:3 lime/sand mortar); concrete mix 1:2:4 (cement:sand:aggregate) ; dimensions of masonryunits e.g. brick size 228mm(9")x 114mm(4.5")x 76 (3")

7.2 Does the builder typically live in this construction type, or is it more typicallybuilt by developers or for speculation?It is typically built by developers.

7.3 Construction ProcessThe platform and baloon method of framing are two ways of constructing wood frame houses in Canada.Baloon framing was the most common method of wood-frame construction in the latter part of the 19thcentury, and early part of the 20th century. Platform framing has dominated since the late 1940s andtoday represents conventional practice in Canada. The chief advantage of platform construction is thatthe floor system, assembled independently from the walls, provides a platform or working surface uponwhich walls and partitions may be assembled and erected. Since the studs are one storey high, walls caneasily be prefabricated off the site or assembled on the subfloor in sections and erected one storey at atime without using heavy lifting equipment. The bottom and top plates, which are an integral part of thewall framing, provide fire stops at the floor and ceiling and also nailing support for wall sheathing andinterior finish. Baloon framing differs from platform framing in that the studs used for exterior and someinterior walls are continuous, passing through the floors and ending at the top plates which support theroof framing. Since the connections between the floor joists and studs in baloon framing do not lend lendthemselves to prefabrication or easy assembly on the site, this method of framing houses is rarely used(CMHC 2001).

7.4 Design/Construction ExpertiseThe level of expertise of all parties involved in the design and construction process are as follows:

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- Licensed and Qualified Contractor for homes of area less than 600 m.sq.;- Licensed (professional) Engineer (and Architects if required) for homes of area greater than 600 m.sq.

7.5 Building Codes and StandardsYes No

Is this construction type addressed by codes/standards? X

Title of the code or standard: National Building Code Canada 1995 and City By-Law / Provincial BuildingCodeYear the first code/standard addressing this type of construction issued: 1941National building code, material codes and seismic codes/standards: National Building Code of Canada1995When was the most recent code/standard addressing this construction type issued? 2001

7.6 Role of Engineers and ArchitectsConstruction of most residential wood frame buildings with less than 600 m.sq. in floor area and fourstories in building height should follow Part 9 of the National Building Code (NBC) - Housing and SmallBuildings, and generally do not require direct professional architectural or engineering involvement.Explicit seismic provisions related to wood frame structures have never been provided in the NBC.General nailing schedules for wall sheathing attachment and framing were provided, however specificseismic construction requirements, or calculation/design requirements for seismic resistance did notappear in Part 9. The Vancouver Code has recently been modified to require seismic design of all woodframe buildings except for one- and two-family dwellings, which are required to be constructed accordingto the simplified requirements of the Canadian Wood Council#s Wood Frame Construction Guide (CWC,2001).

7.7 Building Permits and Development Control RulesYes No

Building permits are required XInformal construction XConstruction authorized per development control rules X

7.8 Phasing of ConstructionYes No

Construction takes place over time (incrementally) XBuilding originally designed for its final constructed size X

7.9 Building MaintenanceWho typically maintains buildings of this type?BuilderOwner(s) XRenter(s)No oneOther

7.10 Process for Building Code EnforcementRequirements for plans, permits and inspections vary across Canada; however, most municipalitiesconform to the basic requirements described in the National Building Code of Canada for plans. Buildingpermit needs to be issued in the pre-construction stage, based on the building plans. Several inspectionsare performed in the construction stage, such as framing inspection that verifies the quality ofconstruction. Once the construction is complete, completion inspection (interior and exterior) needs to beperformed. Finally, a certificate of occupancy is issued. The inspections are performed by the inspectorson behalf of the building department of the municipality the building site belongs to. The chart showingapprovals, permits and inspections process for new houses is included in this contribution.

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7.11 Typical Problems Associated with this Type of ConstructionLack of seismic construction requirements, or calculation/design requirements for seismic resistance inthe National Building Code related to wood frame residential buildings (Part 9).

A contemporary two-story wood house under construction

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A modern wood frame house under construction (photo courtesy of Dr. G. Taylor)

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Process for building code enforcement: approvals, permits and inspection process for new houses(Source: CMHC 2001)

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8 Construction Economics

8.1 Unit Construction Cost (estimate)On the order of CAD 100/ft.sq.

8.2 Labor Requirements (estimate)Normally, about 4 months is required from start to finish of the construction. Average size of awood-frame dwelling in Canada is approximately 1200 ft.sq. (CMHC 2001).

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9 Insurance

9.1 Insurance IssuesYes No

Earthquake insurance for this construction type is typically available XInsurance premium discounts or higher coverages are available for seismicallystrengthened buildings or new buildings built to incorporate seismically resistantfeatures

X

9.2 If earthquake insurance is available, what does this insurance typicallycover/cost?In case of single-family houses, insurance covers the insured contents and the structure. The deductibleis usually 5 to 6% of the insured value (depending on the insurance agency), irrespective of the type ofthe building and the location.

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10 Seismic Strengthening Technologies

10.1 Description of Seismic Strengthening ProvisionsType of intervention Structural Deficiency Description of seismic strengthening provision usedRetrofit(Strengthening)

Absence of wall-foundation anchorage Install holddownsInadequate lateral resistance Installation of Oriented strand board (OSB) or plywood sheathingFlexible diaphragm Installation of blockingInadequate wall stiffness Installation of blocking

New Construction See Additional Comments

Additional Comments: The Vancouver Building Bylaw has recently been modified to require seismicdesign of all new wood frame buildings except for one- and two-family dwellings, which are required to beconstructed according to the simplified requirements of the Canadian Wood Council#s Wood FrameConstruction Guide (CWC, 2001).

10.2 Has seismic strengthening described in the above table been performed indesign practice, and if so, to what extent?Yes. Some retrofit projects of heritage and older woodframe buildings have been performed in theVancouver area.

10.3 Was the work done as a mitigation effort on an undamaged building, or asrepair following earthquake damage?The work was done as a mitigation effort on an undamaged buiding.

10.4 Was the construction inspected in the same manner as new construction?Yes, the construction was inspected in the same manner as new construction.

10.5 Who performed the construction: a contractor, or owner/user? Was anarchitect or engineer involved?Generally, the contractor performed the construction and an architect or engineer were involved.

10.6 What has been the performance of retrofitted buildings of this type insubsequent earthquakes?The performance of retrofitted building has not been tested under severe shaking.

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Seismic strengthening technologies: plan of composite force paths and recommended upgrading

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11 ReferencesBlanquera, A. (2000). Evaluation of Structural Earthquake Damage to Buildings in Southwestern B.C.,Technical Report No. 00-03, Department Of Civil Engineering, University of British Columbia, EarthquakeEngineering Research Facility, Vancouver, Canada.

CSA (1994). Design of Concrete Structures, A23.3-94, Canadian Standards Association, Rexdale,Ontario, Canada.

CWC (2001). Engineering Guide for Wood Frame Construction, First Edition, Canadian Wood Council,Ottawa, Canada.

CMHC (1998). Canadian Wood-Frame House Construction, Canada Mortgage and Housing Corporation(CMHC), Ottawa, Canada.

Delcan (1995). Earthquake Hazard Assessment and Seismic Vulnerability for the City of Vancouver,Delcan Corporation, Vancouver, Canada.

Heidebrecht, Basham and Finn (1995). Overview of Major Issues Involved in Preparing New SeismicLoading Provisions for the 2000 Edition of the National Building Code of Canada, Proceedings, SeventhCanadian Conference on Earthquake Engineering, Montreal, Canada.

Institute for Research in Construction (1989). Assessment of Earthquake Effects on Residential Buildingsand Services in the Greater Vancouver Area, National Research Council of Canada, Ottawa, Canada.

Kalman, H., and J. Roaf (1978). Exploring Vancouver 2- Ten Tours of the City and Its Buildings, UBCPress, Vancouver, Canada.

Kharrazi, M. H. K. (2001). Vibration Behavior of Single-Family Woodframe Buildings, M.A.Sc. Thesis,University of British Columbia, Vancouver, BC, Canada.

Kharrazi, M. H. K. et al., (2002), Experimental Evaluation of Seismic Response of Woodframe ResidentialConstruction, 4th Strutural Specialty Conference of the Canadian Society for Civil Engineering, Montreal,QC, Canada.

North Van (1993). District of North Vancouver Heritage Inventory, The Corporation of North Vancouver,report prepared by Commonwealth Historic Resource Management Limited, October, Vancouver, BC,Canada.

NRC (1992). Manual for Screening of Buildings for Seismic Investigation. Institute for Research inConstruction, National Research Council of Canada, Ottawa, Canada.

NRC (1995). National Building Code of Canada 1995. National Research Council of Canada, Ottawa,Canada.

Onur, T., Ventura, C.E. and W.D.L. Finn (2002) Seismic Damage Estimation in Southwestern BritishColumbia, Proceedings of the 7th US Conference on Earthquake Engineering, Boston, Ma., USA.

Ovanin, T.K. (1984). Island Heritage Buildings - A Selection of Heritage Buildings in the Islands TrustArea, Queen#s Printer for British Columbia, Victoria, BC, Canada.

Pryor, S. E., Taylor, G. W., Ventura, C. E., (2000) Seismic Testing and Analysis Program on High AspectRatio Wood Shear Walls, World Conference on Timber Engineering (WCTE 2000), Whistler, BC, Canada.

Rainer, J.H., and E. Karacabeyli (2000). Wood - Frame Construction in Past Earthquakes, Procs. of the6th World Conference on Timber Engineering, Whistler, BC, Canada.

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Statistics Canada (1996). 1996 Census Profile of British Columbia, InternetURL:http://www.bcstats.gov.bc.ca/data/dd/c96drdat.pdf

Taylor, S. (1996). Senior Lecturer, School of Architecture, University of British Columbia, telephonecorrespondence with Dr. Robert J. Taylor, P.Eng. (Research Associate at UBC), 23 Jan 1996.

Taylor, G. W., and Ventura, C. E. (2001). Earthquake 99 Project, Earthquake Damage Estimation forResidential Woodframe Construction, ICLR/IBC Earthquake Conference, Simon Fraser University,Vancouver, BC, Canada.

Ventura, C.E., Taylor, G.W., Prion, H.L.G., Kharrazi, M.H.K. and S. Pryor (2002). Full-scale ShakingTable Studies of Woodframe Residential Construction, Procs. of the 7th US Conf. on EarthquakeEngineering, Boston.

Ventura, C.E., Robertson J., and Brzev S. (2002). Urban Housing Construction in British Columbia,Canada, Procs. of the 7th US Conf. on Earthquake Engineering, Boston.

Victoria (1978). This Old House - An Inventory of Residential Heritage, City of Victoria Heritage AdvisoryCommittee, Victoria, BC, Canada.

Discovery Channel. Video on Earthquake 99 Project http://www.discovery.ca Search "quake-proof house"Quake-proof house (1) and Quake-proof house (2)

CMHC ( ) Residential Guide to Earthquake Resistance.

Rainer, J.H. and Karacabeyli, E. (1999). Wood-Frame Building Construction in Earthquakes. ForintekCanada Corp., Special Publication SP-40, Vancouver, BC, Canada.

Kalman, H. (1979). The Sensible Rehabilitation of OlderHouses, Canada Mortgage and Housing Corporation,Ottawa, Ontario, Canada.

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12 ContributorsName Carlos E. Ventura Mehdi H. K. KharraziTitle Professor Graduate StudentAffiliation Univ. of British Columbia University of British ColumbiaAddress Dept. of Civil Eng, 2324 Main Mall 2324-Main MallCity Vancouver VancouverZipcode BC V6T 1Z4 V6T 1Z4Country Canada CanadaPhone (604) 822-6946 604-822-6944Fax (604) 263-8296 604-822-6901Email ventura@civil.ubc.ca kharrazi@civil.ubc.caWebpage

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13 Figures

A contemporary two-story wood frame house

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