STEEL-TIMBER HYBRID STRUCTURES: PROBLEMS AND SOLUTION

23-04-21

For: Dr. StiemerCIVL 510University of British Columbia

By: Johannes Schneider and Carla Dickof

23-04-21

Steel Timber Hybrid Structures: Problems and

Solutions 2 of 20

Hybrid Systems

Typical Hybrid Structures Combine two or more

material types that within a system or an element

Common between concrete, steel, and masonry or timber

Timber-steel hybrids are less common but gaining popularity

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Timber Steel

Anisotropic material•Strong parallel to grain•Weak perp to grain•Stronger in compression than tension

Isotropic material•Same strength in tension and compression

Hygroscopic material•changing moisture causes swelling and shrinkage

High thermal expansion coefficient (ie. sensitive to heat)

Untreated wood can decay under certain environmental influences

Steel needs coating or galvanizing for durability

High resistance to chloride Low resistance to chloride

Low resistance to rolling shear

High ratio Strength/weight High strengths leads to small cross sections which are susceptible to buckling

Steel Timber Hybrid Structures: Problems and

Solutions

Material Properties:Timber and Steel

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Material Yield Strength (MPa)

Density(kg/m3)

Modulus Elasticity

(MPa)

Compresion Strength (MPa)

Tensile Strength (MPa)

Steel 350 7800 200,000 400-1000 400-1000

Concrete N/A 2300 20,000 20-40 2.0-5.0

Structural Timber

N/A 400-600 8,000-11,000 Parallel 30Perp. 8

Parallel 6Perp. 1

Steel Timber Hybrid Structures: Problems and

Solutions

Material Properties:Timber and Steel

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Engineered Wood Products

• CLT (Cross-Laminated-Timber)

Crosswise stacked board layers create a isotropic behavior in 2 directions

• Plywood

Crosswise stacked veneer layers create a isotropic behavior in 2 directions

• OSB (Oriented Strand Board)

layering strands of wood in specific

orientations

Engineering products improve performance by spreading imperfections and locating them in regions of low stress. Some provide similar strength in two axes

Steel Timber Hybrid Structures: Problems and

Solutions

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Micro vs. Macro Component Level Hybridization

Flitch beam:• steel plate sandwiched between timber

beams

• Glued and/or pinned to transfer shear

• Load sharing proportionally to relative stiffness of members

Built-in Steel Columns:• High fire protection

• Wood as lateral support and preventing from buckling

Combine two or more material types within single element. A mechanism to transfer forces between materials is required

Steel Timber Hybrid Structures: Problems and

Solutions

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Glued-in rods:• Used for moment connections

• Improvement of strength perpendicular to grain

• Wood as lateral support and preventing from buckling

Steel Timber Hybrid Structures: Problems and

Solutions

Post-tensioned CLT beam:• Low height of beam

• Simple to fabricate

Micro vs. Macro Component Level Hybridization

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Hybrid Trusses:• Combination according to

their properties• Timber in compression• Steel in tension members

• Less corrosive exposure of the truss

• Careful design of connections is required. Avoiding of water in connections

 

SAP Arena – Mannheim Hybrid Space Truss

Hybrid Bridge – Kössen / Switzerland

Steel Timber Hybrid Structures: Problems and

Solutions

A combination of members of different material types within a system

Micro vs. Macro System Level Hybridization

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Vertical Mixed Systems:• Lower levels in concrete or steel

upper levels in timber

• Code height limitation for timber structures

• Big difference in stiffness is major design challenge

• “flexible” wood storeys• “rigid” ground-storeys

 

9-story concrete-timber Hybrid building – London GB

5-story concrete-timber hybrid building Vancouver BC.

Steel Timber Hybrid Structures: Problems and

Solutions

Micro vs. Macro Component Level Hybridization

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Steel frame and timber floor

diaphragm:• Moment resisting frame with timber

floor or timber joist and plywood diaphragm to transfer lateral loads

• Utilizing of Hybeams

• Reducing overall weight of building

seismic benefits

• high degree of prefabrication and less time for erection

 

14-story hybrid building steel frame with hybeams

Cargolifter Office building - Berlin Steel Timber Hybrid Structures: Problems and

Solutions

Micro vs. Macro Component Level Hybridization

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7-story residencial building with steel frames and laminated board stack slabs - Berlin

EXPO 2000 roof - Hannover

Steel frame, timber shear walls

and timber floor diaphragms:• Using the high strength of steel for

gravity loads

• Timber shear walls in CLT or Midply taking the lateral loads

• Distribution of load carrying between steel and timber elements

• Prefabrication and light structure are advantages

Steel Timber Hybrid Structures: Problems and

Solutions

Micro vs. Macro Component Level Hybridization

ConnectionsCapacity design at member connections

Nails, pins, and bolts All dowel type connections Ductility is introduced by

balancing the max plastic steel deformation while maintaining min wood crushing and no wood fracture

tensioning creates clamping force

Screws higher strength and lower

ductility

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Steel Timber Hybrid Structures: Problems and

Solutions

Connections

Post-tensioned systems Post-tensioned tendons

are not bonded to the timber

Mild steel is bonded or glued to the timber

Steel and cabl;e strength must be balance for ductility and self-centering ability

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Steel Timber Hybrid Structures: Problems and

Solutions

Brackets Steel plate elements

connecting to wood members

Ductility & Energy Dissipation

CLT shear walls:No energy dissipation in

panel. Possible dissipation through

Friction in step joints

Deformation energy in connectors

Difficulty to find right balance to get right failure mode

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Steel Timber Hybrid Structures: Problems and

Solutions

Block-failure

Fracture in bracket

Pull-out failure

System Study:Steel Frame with Wood Infill Shear Walls

5 story moment frame with infill shear walls placed in the central bay

Look at one frame of the building

Model with Vancouver Seismicity

Steel moment frame

Wood shear walls

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Steel Timber Hybrid Structures: Problems and

Solutions

Timber Shear Wall Design

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Steel Timber Hybrid Structures: Problems and

Solutions

Midply Shear Walls: Improved strength (more

than twice that of typical shear walls)

Nails in double shear instead of single

Nail head can no longer pull through sheathing

Increased nail edge distance on studs

Risk of buckling out of plane Energy dissipation through

nail pull-out and deformation

Midply wall buckling

SAP2000 Model:Steel Moment Frame

A base steel frame was modeled in SAP2000 to provide a basis for comparison

Type D Ductility Static pushover analysis

performed using NBCC 2005

Vancouver Seismic Hazard Index Used

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Steel Timber Hybrid Structures: Problems and

Solutions

SAP2000 Model:Steel Frame with Wood Shear Walls

Midply Shear walls were used

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Steel Timber Hybrid Structures: Problems and

Solutions

Connection between the shear wall and the steel frame

Lateral connections at top and bottom with multi-linear links

Vertical connections on sides with multi-linear elastic links

Multi-linear links between plywood and studs

Steel Moment Frame

Frame w/ Shear Wall

Ductility (Rd) 5.0 3.0

Building Period (s)

1.32 s 1.07 s

Total Base Shear

114 kN 197 kN

Ductility (Rd) reduces seismic shear force that the system need resist. Energy is absorbed through permanent deformation

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SAP2000 Model:Comparison between Models

Increase in results in higher loads by lowering the period of the structure which increases the spectral acceleration

Steel Timber Hybrid Structures: Problems and

Solutions

SAP2000 Model Results:Steel Frame with Wood Shear Walls

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Steel Timber Hybrid Structures: Problems and

Solutions

Steel Moment Frame

Frame w/ Shear Wall

Total Defl’n

28.7 mm 21.5 mm

StoreyDefl’n

7.08 mm 5.4 mm

References

Khorasani, Y., (2010). Feasibility Study of Hybrid Wood Steel Structures. Thesis, (M.A.Sc). University of British Columbia

Maloney, T.M., (1996), The Family of Wood Composite Materials, Forest Products Journal. Vol. 46 Issue. 2: pg.19-26

Varoglu, E. et. al. (2006) Midply Wood Shear wall System: Concept and Performance in Static and Cyclic Testing, Journal of Structural Engineering, Vol.132 Issue 9:pg. 1417-1425

Yousuf, M., and Baghchi, A. (2009) Seismic design and performance evaluation of steel-frame buildings designed using the 2005 National building code of Canada, Canadian Journal of Civil Engineering, Vol. 36 Issue 2: pg. 280-294

Clarke, C. (2004). Midply Shear Walls use in Non-Residential Buildings. Thesis, (M.A.Sc). University of the West Indies

Schneider, J. (2009). Connections in Cross-Laminated-Timber Shear Walls Considering the Behaviour under Monotonic and Cyclic Lateral Loading. Thesis, (Diploma). University of Stutgart

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Steel Timber Hybrid Structures: Problems and

Solutions