| Name | Puente de Alamillo (Harp Bridge) Seville, Andalusia, Spain |
|---|---|
Who |
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| Owner | Regional Government of Andalucia |
| Concept Design |
S Calatrava |
| Construction Design |
C Alonzo, J R Atienza |
| Advice | A C Aparicio, J R Casa, J C Traversaro |
| General Contractor |
UTE-Formento de Construcciones y Contratas-Dragados y Construcciones |
| Stays System | Dywidag-Systems International |
Where |
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| Latitude | N 37-24'-48" |
| Longitude | W 5-59'-26" |
Why |
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| Constructed for Expo'92 | on island of La Cartuja |
| Crosses the San Jeronimo meander | of the Guadalquivir River |
| Carries Ring Road around Seville | Ronda de Circunvalacion SE-30 |
What |
Read more..... |
How to read the bridge |
Read more..... |
How was it built? |
Read more..... |
Back |
References and links |
| What | |
|---|---|
| Overall type | Hanging-cable stayed - as slideshow pictures 1-4 and 40-44 |
| Width | 32 m. 6 lanes, 1 central walkway on a higher level than the traffic |
| Length | 250 m. |
| Main span | 200 m. |
| Height of tower | 134.25 m. |
| Angle of tower | 32 degrees from vertical |
| Materials | Tower: composite steel/concrete Deck: steel box and reinforced concrete slab Cables: steel |
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| How to read the bridge | Read more about the book metaphor... |
|---|---|
| Chapter 1 | Suspension system |
| Paragraphs | Leaning tower: An irregular roughly heaxagonal cross section with average dimensions 12 m. * 8 m. See slideshow pictures 10-18 Bridge deck: A complex beam comprising of the sentences described below. See slideshow pictures 5-7 and 32-39 Supporting cables: 13 pairs of stays every 12 m. See slideshow pictures 8-9 and 16-22 |
| Sentences | Leaning Tower: outer jacket: consists of stiffened steel plate Leaning Tower: concrete fill: provides weight and strength to the tower Leaning Tower: staircase: provides access up the middle to platform at top Bridge Deck: central box girder: is a steel hexagonal box beam 4.4 m. deep, 5.6 m. wide Bridge Deck: transverse steel ribs: are 12 m. long and positioned at every 4 m. along the bridge Bridge Deck: concrete slabs: on each side support a 230 mm. deep concrete slab. The ribs are structurally connected to the reinforced concrete slab. In other words they act together as one beam because the horizontal shear force between them is resisted by shear connectors  Click on the image of the deck cross section above to open a larger version in a new window Cables: strands:Transmit tension and consist of 60 steel strands (mostly - the longest stays have 45) each 15 mm. diameter. They are protected by an epoxy resin coating and encased in a two-layer high density polyethylene sheath. See slideshow pictures 26,29 Cables: anchorages: connect the cable to the deck at one end and the tower at the other. |
| Words | Leaning Tower: outer jacket: plate: forms the outer layer Leaning Tower: outer jacket: stiffeners: are welded to the plate to stiffen it  Click on the image above to open a larger version in a new window. It is taken from A C Aparicio, J R Casa, (1997) The Alamillo cable-stayed bridge:special issues faced in the analysis and construction, Proc. Instn Civ Engrs Structs & Bldgs, 122, Nov., 432-450 and shows part of the inside of the tower Leaning Tower: outer jacket: horizontal truss: stiffens the whole tower and helps to transmit shear forces between the steel plate and the concrete fill 
 Click on the images above to open a larger version in a new window. The left hand diagram is taken from A C Aparicio, J R Casa, (1997) The Alamillo cable-stayed bridge:special issues faced in the analysis and construction, Proc. Instn Civ Engrs Structs & Bldgs, 122, Nov., 432-450 and shows the position of the horizontal trusses. The right hand diagram is a sketch showing the way the trusses are connected to the steel outer plate. Leaning Tower: outer jacket: shear connectors: are stud bolts welded to the plate also to transfer shear forces. Bridge Deck: central box girder: plate: The box girder comprises welded steel plates with Bridge Deck: central box girder: stiffeners: to help prevent buckling of the relatively thin plate and Bridge Deck: central box girder: shear connectors: to transmit shear force to the concrete slab Cables: strands: individual strand: is made from steel grade 270 ASTM A-416 standard Cables: anchorages: deck: See slideshow pictures 30-31 Cables: anchorages: tower: See slideshow pictures 17-21 |
| Letters | Steel: Iron, carbon with other additives such as chromium etc Concrete: Cement, sand, aggregate and water Reinforced concrete: Concrete is strong in compression but weak in tension where it has to be reinforced with steel bars |
| Chapter 2 | Foundations |
| Paragraphs | Bearings: See slideshow pictures 23, 28
Piled: 54 piles transmit the forces to the lower ground strata. |
| Sentences | Piled: Each reinforced concrete pile is 2 m in diameter and 47.5 metres long |
| Words | Piles: reinforcement: steel reinforcing bars are tied together to make a cage which is lowered into a bore hole and then Piles: concrete: concrete is poured around the steel |
| Letters | Steel: Iron, carbon with other additives such as chromium etc Concrete: Cement, sand, aggregate and water Reinforced concrete piles: Concrete is strong in compression but weak in tension where it has to be reinforced with steel bars |
| 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 weight of the traffic and pedestrians bears down on the bridge deck which is just a sophisticated plank or beam. The beam works by bending but can only do that if it is supported - by bearings at the far end from the tower, by cables at intervals along its length and by the foundations under the tower that clamp the deck, tower and foundations together. The bearings sit on the foundations. The cables are inclined so the deck is also compressed by a horizontal force that increases along the length towards the tower with each pair of cables. The tension in the cables also pulls on the tower. These forces are balanced, not by some back stays as is usual, but by the weight of the considerable backwards lean of the massive tower. The resultant of the cable forces and the weight of the tower acts along the axis of the tower down to the bridge deck. The horizontal component of this force is balanced by the horizontal compression in the bridge deck - it is internally self balanced As a consequence the net forces onto the foundations are mainly vertical. Unfortunately this only works for one set of external forces on the bridge and to achieve this balance they have to be known quite precisely. In practice this is impossible. Variations in the weight of the deck due to construction tolerances, the actual forces in the stays as distinct from the theoretical ones and other factors all contribute. The bridge is very sensitive to small changes in geometry or weight because its structural configuration relies on setting to zero the difference between two large bending moments. The forces on and in the deck change as traffic crosses, as the wind blows and as the temperature changes. A scale model of the bridge was tested in a wind tunnel. Maintaining only an axial force in the tower would require the weight and inclination of the tower to change too - something that is clearly not feasible. When all loadings and variations were considered by the construction designers and advisors and when they calculated the envelope of the possible maximum and minimum internal forces in the bridge they realised that they had to design bridge deck, the tower and the foundations to cope with very large bending moments. They realised that small variations in the weight of the tower and the forces in the cable stays could affect the safety of the bridge Consequently adopted a sophisticated quality control system to check the weights as built and to measure the forces in the cables. They used the actual measured values in a computer programme to check against the performance of the actual bridge so they could be sure they understood how the bridge was behaving as it was built. They realised that they must also allow for creep and shrinkage of the concrete in the tower. A huge foundation had to be built with a large number of very large piles of big dimensions and a huge capping plate on top to connect them. Direct evidence of the structural inefficiency of this type of bridge is that the maximum bending moment in the deck is around 60 % of the bending moment of a simply supported beam with the same span. Of course the impact of the bridge is largely architectural - read more about bridges as public art |
| The diagram shows the nature of the internal forces - click on it to open a larger version in a new window with further explanation |
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| Construction | The concept design was based on the balanced cantilever method. It was intended to erect segments of the bridge deck and the tower
so that they balanced - so as the deck grew outwards from the tower so the tower grew upwards. The construction designers and advisors
showed that this was too risky - proper safety levels could not be reached. They realised it was possible to backfill part of the river
underneath the bridge and erect temporary supports. The sequence was as follows: 1. Construct the foundations and the lower concrete part of the tower. 2. Backfill part of the river 3. Construct temporary piers 4. Erect the steel box girder using the temporary suports. 5. Weld into place the steel ribs onto the box (in parallel with step 4). 6. Construct the four lower segments of the tower (see diagram below). 7 Continue to erect the tower and tension the cables The total construction time was 2 years. |
| The diagram shows a simplified sequence for the erection of the tower in segments and the stressing of the cables to balance the forces at each stage - click on it to open a larger version in a new window |
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| Links | 1. Wikipedia 2. Structurae database 3. Calatrava home web site 4. Calatrava unnoffical web site |
| References | 1. A C Aparicio, J R Casa, (1997) The Alamillo cable-stayed bridge:special issues faced in the analysis and construction, Proc. Instn
Civ Engrs Structs & Bldgs, 122, Nov., 432-450 2. J R Casas (1994) A combined method for measuring cable forces: The cable stayed Alamillo Bridge, Spain, Structural Engineering International Vol 4, 235-240 |
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