|Name||Sydney Harbour Bridge, Australia|
|Owner||Roads and Traffic Authority, New South Wales, Australia|
|Chief Engineer, Public Works Department, New South Wales.||John Bradfield - supervised the whole project. He campaigned for the bridge, prepared the specifications (but not the final form of the bridge) and oversaw its completion.|
|Design||Sir Ralph Freeman, as a consultant to Dorman Long|
|Steel Contractor||Dorman Long - the work on site was directed by a Director, Lawrence Ennis|
|Latitude||S 33 51' 07"|
|Longitude||E 151 12' 40"|
|Why||Links Sydney Central District (SCD) with North Shore across the harbour.|
|How to read the bridge||Read more.....|
|Overall type||2 pinned truss arch|
|Width||This bridge is very wide at 49 m. - 8 lanes traffic, 2 railway lines, a footpath and a bicycle track.|
|Spans||Main span: 503 m. Approach spans: North: 72.5 m. and 4 of 53.3 m. South: 5 of 51.8 m.|
|Top of arch||134 m. above sea level|
|Pylons (not part of structure)||Height above water about 88 m.|
|Materials||Bridge: Steel but with high tensile steel for the trusses, cross girder flanges and principal lateral bracings.
Pylons: Concrete faced with granite.
|How to read the bridge||Read more about the book metaphor...|
2 large N- frame trusses .
2 pairs of pylons/towers, at each end, are about 88 m. high and not part of the structure - they were added primarily to add visual balance.
Each of the 24 panels of the truss 18 m. wide and varying in height from 18 m. at the centre to 57 m. at the ends.
Two large metal hinges with pins 368 mm (14.5 inches) diameter and 4.16 m. long at the base of the bridge carry the massive horizontal thrust of around 20,000 tons from the arch acting at about 45 degrees from the horizontal.
A "saddle" steel forging was bored to fit the pin and machined to fit the faced end of the lower chord member of the arch. Each bearing was made in Darlington, England.
|Words||The individual struts and ties of the truss.
In turn these are made up of more components so that the book analogy needs more levels!
You may not be able to read the small print on the diagram below taken from the Reference by Freeman R (1934) However you will see that the members are made up of steel angles and plate which are rivetted into box sections. You can see these members even more clearly by visiting the bridge climb site and looking at the panoramic view.
Arch and deck: Steel.
Towers: Concrete faced with granite.
The image below taken from Reference Freeman R (1934) shows the compexity of a deck panel.
This paragraph is made of sentences which are cross girders (suspended from the hangers which hang from the arches), longitudinal beams that span between cross girders and troughed steel sheet that sits on these girders and carries the concrete deck.
You can also see the horizontal girders that make up the wind bracing.
|Sentences||Cross girders, longitudinal beams, lateral members, troughed deck and concrete slab.
|Words||Individual steel plates, rivets, angles that make up the girders.
|Letters||Steel but with high tensile steel for the trusses, cross girder flanges and principal lateral bracings.
Freeman (References 1934) quoted the additives in the high strength steel
as being 0.04% Phosphorus, 0.05% Sulphur, 1% Manganese, 0.32-0.42% Carbon and 0.15-0.35% Silicon.
|Paragraphs||Bearings: 4 main bearings
Foundations depth 12.2 metres of RC in a hexagonal formation.
|Grammar||Technically the bridge is a way of taking forces from up in the air down to the ground.
So imagine the flow of those forces through the structure.
Think of a truck standing on the brdge and how its weight is transmitted through the bridge to the ground.
The lightest form of bridge may have been a truss arch of uniform depth but the variable depth was more suitable for the erection process and the designer considered the possible savings as no more than 2% of weight (see References below Freeman, R 1934).
Likewise a 3 hinged arch would have been easier in many ways since it would have been statically determinate and some difficult erection processes could have been avoided.
A 2 - hinged arch is more rigid under moving loads, resists wind loading better but, most importantly, cost less.
Two independent systems of transverse bracing were used to resist wind - one in the plane of the lower chords and one between the upper chords and the end posts.
There was no sway bracing i.e. diagonal cross bracing between the two truss girders of the arch. All the cross girders of the bridge deck are supported on henagers and pins so that the loading on the hangers is axial.
A major consideration in deciding the dimensions of the bridge was the transportation of steel plates and sections by sea.
The maximum length for reasonable cost was restricted to 60 feet or 18.3 m.
This is why the panel lengths and the maximum depth of truss are approximately 18 m. The arches chords are both parabolas but the curvature of the upper chord is reversed over the last 3 panels at each end.
The designer decided that such a large bridge had to be built without falswork.
So two separate construction teams built each side of the arch as cantilever trusses. Wire cables anchored back through inclined U-shaped tunnels cut into the rock held the trusses in place.
Cranes at the ends of the cantilevers lifted each steel piece into position and the bridge builders riveted them into place. The cranes then 'crept' forward onto the new section and the whole process repeated. The southern end was worked on a month ahead of the northern end to detect errors and to learn lessons for the northern side.
When the cantilevers were completed the two sides were nearly touching. The cables were then slowly released and the two halves gradually brought together at the bottom of the truss and pinned together.
At this point the arch had effectively 3 pins - one at each end and one in the middle (see Chapter 3 for the significance of this). The two top chords of the truss were then jacked apart to a predetermined load that produced similar levels of stress in the top and bottom chords and the support cables removed.
The bridge then became a two pinned arch. The last stage was to connect the vertical suspenders to the arch and, starting at the centre to sling the bridge deck from them.
Freeman R, "Sydney Harbour bridge: Design of the Structure and Foundations", Proc Instn Civ Engrs, 1934
The bridge climb site where you can see a panoramic view.
New South Wales government official web site
A website for the bridge with more information and pictures.
The "Pylon Lookout" site with more information and pictures.
See picture of the bridge bearing.