wooden bridge construction
DESCRIPTION
Wooden Bridge Construction. Strength & Joinery. Wood is very strong parallel to the grain ONLY Wood glues very well on the face grain and edge grain (sides) but poorly on end grain Bond is often stronger than wood itself - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Wooden Bridge Construction](https://reader035.vdocuments.site/reader035/viewer/2022062411/56816945550346895de0ceca/html5/thumbnails/1.jpg)
Wooden Bridge Construction
![Page 2: Wooden Bridge Construction](https://reader035.vdocuments.site/reader035/viewer/2022062411/56816945550346895de0ceca/html5/thumbnails/2.jpg)
Strength & JoineryWood is very strong parallel to the grain
ONLYWood glues very well on the face grain
and edge grain (sides) but poorly on end grain◦Bond is often stronger than wood itself
Wood has high strength in tension and compression but only moderate in shear
![Page 3: Wooden Bridge Construction](https://reader035.vdocuments.site/reader035/viewer/2022062411/56816945550346895de0ceca/html5/thumbnails/3.jpg)
Gluing 2 pieces side by side will double its strength
Gluing 2 pieces o top of each other will quadruple its strength
Pieces that are too short can be over lapped
![Page 4: Wooden Bridge Construction](https://reader035.vdocuments.site/reader035/viewer/2022062411/56816945550346895de0ceca/html5/thumbnails/4.jpg)
Triangles & TrussesA triangle is the strongest
geometric shapeWhich bridge is stronger?
![Page 5: Wooden Bridge Construction](https://reader035.vdocuments.site/reader035/viewer/2022062411/56816945550346895de0ceca/html5/thumbnails/5.jpg)
Types of TrussesVarious types of trusses are used
in bridge design/construction◦Designed & tested by bridge &
mechanical engineers
![Page 6: Wooden Bridge Construction](https://reader035.vdocuments.site/reader035/viewer/2022062411/56816945550346895de0ceca/html5/thumbnails/6.jpg)
8 Common Types1. King Post/Queen Post
Simplest type of truss Contains the fewest members Used for simple roofs or short span bridges
2 angled supports leaning into a common vertical support
A bridge would require 2 king post trusses with a road surface or bridge way between them
![Page 7: Wooden Bridge Construction](https://reader035.vdocuments.site/reader035/viewer/2022062411/56816945550346895de0ceca/html5/thumbnails/7.jpg)
2. Warren Truss• One of the simplest yet strong• Consists of longitudinal members joined
by angled cross members• Forms alternately inverting triangles• Ensures all members are not subject to torsion –
only compression and tension• Equilateral triangles
8 Common Types
![Page 8: Wooden Bridge Construction](https://reader035.vdocuments.site/reader035/viewer/2022062411/56816945550346895de0ceca/html5/thumbnails/8.jpg)
• Members alternate between tension and compression
• Members in the centre are subject to compression and tension (compensate for live loads)
8 Common Types
Centre Load Spread LoadRed = tension Blue = compression Green = no load
![Page 9: Wooden Bridge Construction](https://reader035.vdocuments.site/reader035/viewer/2022062411/56816945550346895de0ceca/html5/thumbnails/9.jpg)
3. Pratt Truss• Includes vertical members and diagonals • Opposite to Howe Truss
• Shorter, vertical members are in COMPRESSION
• Often used in railway bridges • Good use of iron
• Typically uses more iron• Iron beams for diagonal members
• Many variations
8 Common Types
Centre Load Spread Load
![Page 10: Wooden Bridge Construction](https://reader035.vdocuments.site/reader035/viewer/2022062411/56816945550346895de0ceca/html5/thumbnails/10.jpg)
4. Howe Truss• Includes vertical members and diagonals • Opposite to Pratt Truss
• Longer, angled members are in COMPRESSION
• Suitable for longer spans• Typically uses more wood
• Wooden beams for diagonal members
8 Common Types
Centre Load Spread Load
![Page 11: Wooden Bridge Construction](https://reader035.vdocuments.site/reader035/viewer/2022062411/56816945550346895de0ceca/html5/thumbnails/11.jpg)
5. K –Truss• Shorter compression members than other
truss designs• Shortened vertical members (compression)• Shorter compression members = more resistance
to buckling• Most complicated and hardest bridges to
build
8 Common Types
Centre Load Spread Load
![Page 12: Wooden Bridge Construction](https://reader035.vdocuments.site/reader035/viewer/2022062411/56816945550346895de0ceca/html5/thumbnails/12.jpg)
6. Bollman Truss• Type of suspension truss• Inefficient due to each panel functioning on is own
rather than aiding each other like the previous types of trusses
• Extremely stable• Stiff deck – good for railway bridges • Easy to assemble
8 Common Types
![Page 13: Wooden Bridge Construction](https://reader035.vdocuments.site/reader035/viewer/2022062411/56816945550346895de0ceca/html5/thumbnails/13.jpg)
8. Fink Truss• Most common roof design truss• V-shaped members• Overlapping king post trusses connected by smaller
member in BLANK• Capable of spanning longer distances
• Single = 33ft, double = 54 ft• Quick, cheap, capable of carrying large loads,
relatively long life span
8 Common Types Cont.
![Page 14: Wooden Bridge Construction](https://reader035.vdocuments.site/reader035/viewer/2022062411/56816945550346895de0ceca/html5/thumbnails/14.jpg)
Making TrussesWhen making a truss:1. Make a full size drawing on grid paper.2. Cut the pieces to fit the drawing.3. Tape the drawing to a table.4. Glue the pieces in place to the drawing
gluing the joints. Use glue sparingly.5. Glue joints. Use glue sparingly.6. When dry, pull the paper off and
remove carefully.