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Comparison of pre stressed concrete partially pre stressed

Early attempts worked, with the beams showing reduced tendency to crack in tension, but after a few months the cracks reopened. A good description of this early work is given in Leonhardt. No satisfactory answer was found until it was realised that creep occurred.

  1. On the other hand, unbonded reinforcements are considered as separate components acting on the structure. Finite Elements Software for Plates and Shells.
  2. The first major application of his techniques is believed to be the reconstruction of railway bridges for the electrification of the LNER railway out of Liverpool St Station in London.
  3. The tension stiffening effect occurs in two intervals. The implemented numerical model assumes a non-linear material behavior and concrete cracking, geometric nonlinearity, cyclic loading, and composite construction.

Freyssinet's discovery of Creep Boutiron Bridge is one of three similar bridges built by Freyssinet over the River Allier, near Vichy, in France, in the mid 1920s. It is a three-span reinforced concrete arch, with open spandrels. The river carries a high volume of melt-water in the spring when the snows melt in the Massif Central. When an arch is being constructed it has to rest on falsework until it is complete; normally, wedges underneath the falsework are knocked out at that time, which drops the falsework away and transfers the deadweight to the arch.

The presence of the wedging makes the falsework fragile, and the act of dropping it away from the arch can be dangerous. Freyssinet decided to avoid these problems and installed jacks between the two halves of each arch span.

The jacking pockets are still visible today. By jacking the two arches against each other, the arches lifted slightly, away from the falsework, which could then be safely removed. In-situ concrete was used to fill the gap between the arches. A few months after construction, Freyssinet said that he was cycling to work over the bridge when he realised that the parapet was no longer straight, but was dipping at the mid-span of each arch.

He concluded that the arch must have shortened, but he was able to reinstal the jacks, push the arches apart again, and make good the structure.

This led him to realise that concrete creeps under load. He did tests to confirm this and concluded that the early attempts at prestressing had failed because concrete of too poor a quality had been used which increased the amount of creep and steel bars with too little prestress had been used which meant that the creep strains removed the prestress. At about the same time, in England, Glanville was pursuing laboratory studies of concrete and coming to similar conclusions.

It is disputed which man actually discivered creep first, but it is not disputed that Freyssinet was the first to capitalise on the discovery. Freyssinet then decided that to make prestressed concrete work, very high quality concrete was needed, with very high tensile steel wires, stressed as highly as possible.

Creep would still occur, but the prestress that would be left after these losses would still comparison of pre stressed concrete partially pre stressed worthwhile. He set up a company to produce telegraph poles, using thin concrete tubes made with mortar, and prestressed with piano wire.

This company was set up during the depression and was a financial failure. Freyssinet's practical systems Freyssinet then went on to produce practical systems utilising two larger diameter wires typically 5 or 6 mm clamped by means of a single wedge between the wires pushing them against an external block.

He patented this in France and elsewhere, and licensed it to a number of companies, including Wayss and Freitag in Germany. I believe the first description of his work in the UK was by Gueritte in 1936.

A development of the orginal anchorage is this system, which can grip 12 wires of 5 mm diameter. The central wedge is grooved to hold the wires and is made of high-strength mortar.

The barrel is also made of mortar but with external and internal spirals of steel. The barrel is cast into the structure and connected to the duct for the tendon. After the concrete has hardened, the 12 wire strand is inserted and jacked, using the wedge to grip the tendon.

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Both Freyssinet's systems are shown in use here. The horizontal tie is formed of prestressed concrete. These beams were designed to be placed side by side, and the full depth then filled with concrete to resist bomb attack. The lower wires visible on the end of the beam are the original 2-wire system; these were pretensioned. When the power of bombs increased, the roofs were made deeper, which required more prestress.

This was provided with the newer 12-wire system, which was placed outside the concrete and post-tensioned. The ends of these wires are also visible.

  • It looks as though the handrail has recently been replaced but the beams appear to be in good condition with no evidence of rust staining;
  • He concluded that the arch must have shortened, but he was able to reinstal the jacks, push the arches apart again, and make good the structure;
  • It is not known how many beams were made, nor, to a large extent, is it known where they were used;
  • The results of this technique are more accurate compared with those obtained using Simpson's integration technique;
  • Figure 33 shows a table with the results of the forces corresponding to normal stress, shear strength, and flexural moment along the element.

This photo is taken from Grote's book. He was of Jewish descent, but despite holding the Iron Cross as a result of his distinguished service in WWI, he was rounded up with other Jewish professionals and placed in Buchenwald concentration camp in 1938. At that time, however, it was possible to buy oneself out of the camps and with the help of the Mouchel Company in England, and probably also of the British Secret Services, he came to England in 1938.

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He brought with him details of Freyssinet's work, to which, as a licensee, Wayss and Freitag had been privy. With Mouchel he formed the Prestressed Concrete Company, which produced demonstration beams in prestressed concrete which were tested at Southall in 1938. With the Dowsett Company they set up a plant at Tallington near Stamford in Lincolnshire to produce prestressed concrete beams and railway sleepers.

War-time construction in England Monkton Farleigh Mine. This was an old limestone mine from which a seam of high quality stone was extracted in the 18th and 19th centuries to construct the city of Bath. During WWII it was used to store very large amounts of ammunition and other ordnance. It had its own internal railways, and a tunnel linking it to the GWR.

Some parts of the roof were apparently unstable, so short pretensioned prestressed beams were installed over part of the area in 1940.

Grote says that 3000 beams, each 5m long, were used, and includes sketches. The mine is no longer used to store ammunition, but some parts have been taken over for various commercial uses, including wine storage.

It is believed that these beams are still in place, although they are no longer accessible and their present condition is unknown. They are described in Gueritte's paper in comparison of pre stressed concrete partially pre stressed Structural Engineer in 1940; although he does not mention the mine by name it is clear that these are the beams to which he refers. There is an unofficial web page that gives many details of the Monkton Farleigh mine complexwith many photos, but none that I can see which shows the prestressed beams.

Railway Sleepers from 1942. Prestressed concrete railway sleepers have been in use in the UK for over 60 years.

Taylor describes the development of the first commercial sleepers in 1943, and the construction of a long-line plant to make them, following unsuccessful attempts to use reinforced concrete sleepers, which failed after only 10 days service on the main line.

During the early part of WWII, a number of prestressed concrete beams were made, to be stored for emergency use. It is not known how many beams were made, nor, to a large extent, is it known where they were used.

  • An uneven number of thin horizontal planes of any width is distributed along the cross-sectional symmetry vertical axis;
  • Passive reinforcement tendons were distributed in six layers, as shown in Figure 30 , with a 2.

Some mention of their construction is made by C. Chettoe in his discussion on Gueritte's 1941 paper. A paper published in the Civils in 1943 refers to two bridges built with these beams, but perhaps for reasons of security, precise locations were not given. The A1 was dualled in the 1950s by adding two further carriageways to the west of the existing road. The railway line has now been closed, and the void beneath the bridges has been filled in with earth and concrete, but the bridge deck, and presumably the bridge beams, remain in position.

The long-term future of the bridge is uncertain since the A1 is soon to be upgraded to motorway standard and the bridge will cease to have any use. The photos here were taken in February 2004 and the drawings have been taken from the Civils paper by Paul. According to Thomas, this may have succeeded the LMS bridge below since it is said to have incorporated ties to stop the beams spreading, which had occurred on the other bridge. The bridge at Sinderby, looking north.

The road forms the southbound exit slip road from the A1, and provides access to industrial buildings in the old station area. The only part of the beams that are exposed is this section about 2m long at the north east corner.

History of Prestressed Concrete in UK

This may be a fascia panel since the beams themselves are shown as I-beams both on the orginal drawings and the NYCC plans. The concrete is in very good condition, with no sign of cracking, erosion, or corrosion. Earth has been banked up against the beams elsewhere up to the bottom of the parapet. Bridge over the LMS in Lancashire. The bridge was officially known as Mill Lane Railway Bridge, but unofficially as the Bloodystone Bridge since nearby was a monument to the murder by a returning crusader of his wife's lover.

The bridge was unusual in that the beams are skew to both the road and railway, since they were not the correct length for the skew span.

  • As a parabolic profile was considered for the active reinforcement plotted in the normal force, prestressing moment and total moment graphs, the curve is clearly identified in the prestressing tendons;
  • The softening behavior of concrete after peak strength fc is modeled by a stress-linear strain ratio, as shown in equations 2 and 3 , respectively, for concrete stress and tangent modulus of elasticity;
  • Freyssinet's discovery of Creep Boutiron Bridge is one of three similar bridges built by Freyssinet over the River Allier, near Vichy, in France, in the mid 1920s.

It appears that the bridge was assessed, and a 7 tonne weight limit applied, which is a disadvantage on a trunk road. The original steel parapet beam and the r.

The prestressed girders were replaced in 1997. It is notable that the bridge at Sinderby, above, has no weight limit, despite having similar spans and prestress, but it does not have the disadvantage of the skew area under the footpath, and with narrower beams the amount of prestress per unit width of the bridge is higher.

The underside of the bridge, clearly showing the skew angle between the original metal edge beam on the left and the prestressed boxes on the right. Some patch repairs to both the r. I am grateful to St Comparison of pre stressed concrete partially pre stressed Council for this photograph and for information about the later history of the bridge.

After WWII, the emergency stock of beams was used to tackle the back-log of bridge repairs that had built up. It is said that these beams were so cheap that the manufacturers could not compete, which may imply that there were many of them. No central record exists of where these beams were used, but four locations were mentioned comparison of pre stressed concrete partially pre stressed 1949 in a brief note "An Exhibition of Prestressed Concrete", with spans of 25' up to 40'; Linford HantsBury St Edmunds SuffolkTilemill Berks and Newport Fronbridge Pembs.

Detailed locations of these bridges, and any others made with the same beam stock, together with photos and condition reports, are still sought. It has 4 spans of about 29' each, with 16 I-beams in each span. It was prestressed with the Freyssinet system.

The advantages were claimed to be the speed of erection; ballasted track could be used and the heavier beams meant that the bridge was less lively. This bridge is still in use and has recently 1999 been listed by English Heritage. Adam viaduct in 2005 Adam viaduct seen from below. The beams appear to be in reasonable condition although water is clearly getting through the deck, especially near the edges. The beams seem to be tied together, but all the features seen here appear to be original.

Nunn's Bridge 1948at Fishtoft near Boston in Lincolnshire, is the first application of post-tensioning in the UK, in 1948. The bridge has 5 beams 70' long, 3'7" deep below an integral top slab.

Each beam has 12 Freyssinet 12-wire draped tendons. The bridge is illustrated in the "Historic Concrete" and was the subject of a paper in Concrete in August 1948. Nunn's Bridge, photographed in July 2004. It looks as though the handrail has recently been replaced but the beams appear to be in good condition with no evidence of rust staining.