The main span of Scotswood Bridge is a tied arch. Normally, arches require an abutment to generate the horizontal component of the springing force. Because the central span is built on intermediate piers rather than end abutments, the only way to restrain the arch horizontally here is to include a tie holding the ends of the arch together. Note how slender the arch ribs are and how much wind bracing is required to withstand horizontal forces. In Newcastle, the 50 years return period three second wind gust is 45m/sec. This applies a horizontal load of about 0.7kN/m2.
Pedestrian bridge, Wolston, Warwickshire
The bridge below spans the upper reaches of the River Severn. Its interest lies in the way in which the handrail and the main trusses have been incorporated into one fabrication. The bridge deck comprises concrete supported on corrugated steel sheets which comprise permanent formwork. The corrugations add bending stiffness which allows the deck to span the short distance between the truss/handrail fabrications. Note the circularconcrete column supports which are an upward extension of the concrete pile foundations.
Victoria Ground, Hartlepool
For a football club which plays in the Third Division of the UK's Nationwide League, Hartlepool United have a remarkably accommodating stadium. It was developed in the mid nineties using Football Trust grants and funding from the local Development Corporation. The cantilever stand shown below is constructed from steel sections with corrugated steel sheet roofing and precast concrete steps supporting the seats. The wind bracing comprises tubular steel diagonal bracing. Most of the remaining steel comprises Universal Beams and angle sections, connected by welding and by bolts. Since reconstructing the stadium, the team has improved significantly. Stadium improvements always lead to enhanced levels of support which allows the club to pay higher wages to the players. Also, players prefer to play in a modern stadium.
Collingwood Mansions, North Shields
Formerly a tavern of ill repute, Collingwood Mansions is as close as North Shields gets to a riverside yuppie residential development. The new wing of the development comprises 4 storeys of structural steelwork supporting precast concrete floor panels. An interesting feature is the deep steel beams spanning from front to back. The development includes an undergraound car park. Because of the confines of the site, no columns could obstruct parking, so the ground floor needed a clear spa. Another interesting and little known fact is that the steelwork was originally installed 200mm too low. This meant that the new window heads and sills would not have aligned with those on the refurbished historic part,. To correct this, the whole of the steelwork was jacked up, column by column and steel plates were placed between the columns and their foundations. The procedure w=as lengthy because each column could be jacked by only 20mm relative to its neighbours to avoid overstressing the beams spanning between the columns.
NASA Aircraft Landing Test Facility
In the 1970's NASA (the US National Aeronautical Space Administration) constructed a facility to allow the testing of aircraft tyres as they landed. This was because they feared that the high landing speed of the space shuttle would cause the tyres to disintegrate. The facility comprises a 2km long test track and a special vehicle which can be propelled up to 270mph, at which time it automatically drops an aircraft wheel to replicate a landing event. The vehicle is very interesting. It weighs 60tons (so it can force a wheel down just like an aeroplane- a 747 wheel transmits 22 tons to the ground). It has to be accelerated to speed very quickly. Being NASA, they developed the world's largest water pistol which squirts an 18 inches diameter jet of water under a pressure of 3150psi (sorry for the imperial units, it is America) at the vehicle developing a thrust of two million pounds, causing it to accelerate to 270mph over a distance of 400ft in 2 seconds. The structural design of the vehicle is interesting because when something accelerates at 20g, everything is 20 times heavier than normal - and the weight is now acting horizontally. The water under pressure is stored in the three horizontal tanks shown below. When the spherical valve is opened, the water goes over the curved white tube, then down to the shed and then is squirted towards the vehicle. The vehicle has a bucket which catches the jet of water and turns it through 180 degrees, so transferring the energy from the water to the vehicle. The vehicle is eventually stopped by second hand aircraft carrier arrestor gear, using vanes rotating in drums of oil which becomes hot as the energy is lost from the vehicle. If this fails, the vehicle goes into a 1km deep forest which should stop it, although no-one has yet done the calculations to determine the bending resistance of trees acting as cantilevers.
The Reebok Stadium, Bolton, UK
Bolton Wanderers FC moved from their town centre Burnden Park ground to the out-of-town Reebok Stadium in 1997. The stadium is interesting in that the stand roofs are suspended from a tension structures which takes the loads to earth at the stadium corners. The structure is also used to mount the corner floodlights.
The Stadium of Light, Sunderland, UK
Sunderland FC moved from their traditional Roker Park to The Stadium of Light in 1997. The new Stadium is notable for having been constructed over the old Monkwearmouth coal mine. Potential ground movement led to piled foundations. The pitch is 7m below ground level and this reduces the visual impact of the stadium locally. All of the stands have cantilevered roofs offering uninterrupted views. Initially, the stadium held 42,000 people but is being extended year by year until eventually it will hold 56,000.
The next two pictures illustrate how an artist attempted to distinguish between tensile and compressive forces. The arrows drawn on the photograph are incorrect. They denote compression whereas the members are in tension. Tension should be illustrated by the internal forces pointing towards each other. This is because the internal forces are the reactions to the externally applied tensile forces which point away from each other. (See main Elementary Structural Design notes on this web site)
Steel Sculpture, Rotterdam
The picture below shows an interesting sculpture in Rotterdam. The wind loads on the tall steel members are the predominant loads and a significant moment is developed at the base of each member.
Newcastle United Football Stadium - St. James' Park
In the lecture, we have seen the recently developed stands. The pictures below show how it used to be. The original main stand included a unique curved press box in the roof. The cantilever concrete stand on the popular side has been incorporated into the new development and can still be picked out amongst the now larger stands.
Click here to view two 15 second movies from the England v Albania international game at St. James Park.
Aircraft Boarding Bridge, Amsterdam Airport
The structure below is a typical aircraft boarding bridge in which the weight of the walkway and the pedestrians is taken by the triangulated structure. The forces are principally ones of tension and compression and the structure can be analysed by the process of resolving forces at the joints once the support reactions have been found.
Structural Shoring Systems
Sometimes a building needs to be supported temporarily. The first two pictures illustrate the shoring of a wall in Clayton Street, Newcastle upon Tyne. The structure behind the wall has been removed in readiness for a new building but the façade will remain. The wind load would blow the wall over and the shoring is tied to the wall to prevent this. The intesting structural point is the fact that the steel shoring is triangulated above the footway but is a rigid structure relying upon bending at ground level. This allows pedestrians to continue to use the footway. The diagram below is an early computer drawing of the deflected shape of the shoring, made in 1977.
The picture below shows timber shoring supporting a stone abutment on a historic church at Coppergate, York, UK. Tension has developed in the masonry as a result of settlement of the foundation.
Old Trafford Stadium, Trafford Park, Manchester, UK
The two pictures below show the first of the four extended stands at this stadium. When stands reach this size, it is better to slope the roof down towards the pitch to keep the spectators seated near the front as dry as possible (this is Manchester). For smaller structures, the roof slopes the other way to provide sufficient height of viewing for spectators near the back. The structure is cantilevered to provide uninterrupted viewing.
The following three pictures should serve as a warning to budding civil engineers. The bridge piers were eroded by floodwater in the first case.
Below, this is the result of an earthquake in Los Angeles. The highway bridge had been designed to withstand horizontal earthquake shaking but unusually, the earthquake shook vertically. The vertical acceleration exceeded gravity so the bridge deck left its supporting columns and came crashing down onto them. Earthquake codes in California have been revised as a result of this eqrthquake.
Several people were killed when a span of a bridge connecting the shore to a ship collapsed at Dover Harbour whilst passengers were boarding. A steel pin locating one end of the span had corroded and snapped, so allowing the span to slip off its bearing. The span fell onto a pontoon 12 metres below.
These next two pictures show two early examples of reinforced concrete. The first illustrates a fully rigid framework in which the stability is provided by moment connexions between beams and columns. Note how the structural concrete is exposed. In the early days of reinforced concrete, this was acceptable.
The building below, a warehouse in Swansea is credited as being the UK's first multi-storey reinforced concrete building. The cantilever at the right is a noteworthy feature.