History of Prestressed Concrete in UK

Once reinforced concrete had been developed by Hennebique at the end of the 19th Century, it was realised that the performance could be improved if the bars could be placed in tension, thus keeping the concrete in compression. 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.

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 be 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.

Both Freyssinet's systems are shown in use here. The beam is an arch which formed part of the roof of a U-boat pen during WWII. 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. This photo is taken from Grote's book.

Mautner comes to England

Dr Mautner had been a director of Wayss & Freitag in the 1930s, and was also a professor at Aachen. 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. 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 the 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 complex, with 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.

Emergency Bridge Beams. 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. Some mention of their construction is made by C.S. 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.

Bridge over the LNER in North Yorkshire. With the assistance of Network Rail and North Yorkshire County Council it is now known that this bridge carried the Great North Road, now the A1, across the Leeds to Northallerton Railway at Sinderby.  It is at OS Grid Reference SE335811.  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. 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.  This bridge has now been removed, but was located at OS Grid reference SJ595948, where the A49 road crosses the West Coast Main Line in Newton-le-Willows.  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.  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.c. slab at the side were replaced in 1993.  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.c. deck slab and the p.s.c. griders are visible. I am grateful to St Helens 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 in 1949 in a brief note "An Exhibition of Prestressed Concrete", with spans of 25' up to 40'; Linford (Hants), Bury St Edmunds (Suffolk), Tilemill (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.

Adam Viaduct (1946) near Wigan carries the LMS railway from Wigan to the South West, over the River Douglas, at OS Grid Reference SD571051.  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. I am grateful to Brian of  wiganworld.co.uk for taking these two photos for me.

Nunn's Bridge (1948), at 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.  The bridge is located at OS Grid reference TF367415.

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.

Masonry Repair (1948).  In order to repair the masonry tower of St Luke's Church, Silverdale, near Newcastle-under-Lyme, Staffs from the effects of mining subsidence, it was prestressed using the Magnel system.

Airport Taxiway (1949).  A prestressed concrete taxiway was built at London Airport (Heathrow).  This was similar to a complete runway slab built by Freyssinet at Orly; the slab was only prestressed transversely, but was made up of a series of 45 deg triangles.  Vertical rollers were inserted in the joints, so as the slab contracted transversely it pushed against end abutments, thus inducing a longitudinal prestress as well.  This system neatly overcomes the friction that would arise if direct application of the longitudinal prestress were attempted.  The slab was 120' wide by 355' long.

Prestressed concrete in buildings (1949).  Beams for factory roofs were provided for the Heathcote Factory at Tiverton in Devon, and the HMSO warehouse at Sighthill in Edinburgh was the forerunner of precast, prestressed building construction.  The main beams were pretensioned in a factory, while the secondary beams were posttensioned on site.

Partially Prestressed Concrete. Paul Abeles was also a refugee who came to England just before WW2. He was a believer in what we now call partially prestressed concrete, in which additional untensioned reinforcement was included in the beam. The idea behind this was to increase the ultimate moment capacity in the beam, with the primary effect of the prestressing being to reduce the crack widths. He published a paper in 1940, which was criticised by Mautner. 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. These were discussed in a paper in 1952 (details needed).  His systems were openly criticised - there were many who said that rather than combining the advantages of reinforced and prestressed concrete it combined their disadvantages instead.

Conflicting systems.  In the years after WWII there were many conflicting prestressing systems.  The Freyssinet system, under the guidance of Mautner and later Alan Harris, were already established in the UK and held valid patents, but immediately after the war Prof Magnel of Ghent University was actively publicising his system, and Abeles was proposing the use of partially prestressed concrete.  Many other systems were developed; some to avoid the patents held by the early protagonists, but others with genuine improvements.  It was during this period that the systems, now almost universally used, of 7-wire strands held by 3-piece wedges, were developed.

The history after 1950 is well-documented - Concrete, The Structural Engineer and the Proceedings of the Inst. Civil Engineers all carry many papers relating to innovations or landmark prestressed concrete structures.

References.

Abeles P. Saving reinforcement by pre-stressing, Concrete Constr. Engng, 35, 328-333, July 1940, with discussion by Mautner in 36, 73, Feb 1941.

Andrew A.E. and Turner F.H., Post tensioning systems for concrete in the UK: 1940-1985. CIRIA Report 106, 1985. Brief description of history of psc but is primarily concerned with describing systems so that engineers will recognise them if they see them. It does not, however, make any reference to the Freyssinet two-wire system that was used on the earliest beams.

Anon, Prestressed Concrete Sleepers, Concrete Constr. Engng, 41, 168-170, June 1946.  Describes the Dowmac long-line prestressing system and refers to the first sleepers laid in 1942 on the LMS railway and seems to be derived from a paper by R S V Barber and D R Lester, entitled "The development of prestressed concrete units", read before the Society of Engineers.

Anon, A Prestressed Concrete Railway Bridge near Wigan, Concrete Constr. Engng, 42, 305-308, October 1947.  A description of the Adam Viaduct.  The manufacture of the beams themselves was described separately (43, 353-355, Nov 1948)

Anon, Prestressing applied to Strengthening a Church Tower in Staffordshire, Concrete Constr. Engng, 43, 280-283, Sept. 1948

Anon, An Exhibition of Prestressed Concrete, Concrete Constr. Engng, 44, 129, April 1949.  A description of an exhibition organised by the Ministry of Works, which mentions a number of applications, including the only reference known so far to the use of the war-time emergency beams.  An earlier paper, in the same journal (35, 267-279, June 1940) describes Reinforced Concrete Sleepers, but these clearly failed when placed in lines where high speeds were expected, and had a life of only a few years even in sidings.

Anon, An Experimental Prestressed Concrete Slab at London Airport, Concrete Constr. Engng, 44, 176-177, June 1949. Describes a proposal for a prestressed taxiway.

Anon.  Prestressed Concrete Roof Beams at Tiverton, Concrete Constr. Engng, 44, 50-52, Feb 1949.

Anon.  Prestressed Concrete beams in a Building at Edinburgh, Concrete Constr. Engng, 1949.  Describes building of HMSO building at Sighthill.

Grote J. and Marrey B., Freyssinet, Prestressing and Europe, Editions du Linteau, 2000. Primarily concerned with Freyssinet's contribution to prestressing but refers to how his systems were used by both sides during the war. In English, French and German.

Gueritte T.J., A revolution in the technique of the utilisation of concrete, presented at the Inst. of Structural Engrs 19 March 1936 (reference needs to be checked). This was a translation of a paper by Freyssinet, who attended the presentation.

Gueritte T.J., Recent developments of pre-stressed concrete construction with resulting economy in the use of steel, The Structural Engineer, 18, 626-642, July 1940. Contained also a technical appendix by Mautner.

Gueritte T.J., Further data concerning prestressed concrete: Comparison between calculated stresses and stresses registered during test. Procs Inst. Civ. Engrs., 91-136, 1941.

Leonhardt F.  Prestressed Concrete, Ernst and Sohn.

Harris A.J., Freyssinet, the genius of prestressing, The Structural Engineer, June 1997.

Paul A.A., The use of pre-cast pre-stressed concrete beams in bridge deck construction, Procs Inst.Civ. Engrs, 21, 19-30, Nov 1943.

Sriskandan K., Prestressed Concrete road bridges in Great Britain: a historical survey, Procs Inst. Civ. Engrs, 86, 269-303, 1989.

Sutherland R.J.M., Humm D. and Chrimes M., Historic Concrete - background to appraisal, Thomas Telford, 2001.  A comprehensive overview with extensive lists of references.  Largely based on a special issue of the Proc Inst. Civil Engineers, Structures and Buildings, 116, 255-482, 1996 on the same subject.

Taylor H.P.J., The railway sleeper: 50 years of pretensioned, prestressed concrete, The Structural Engineer, 71, 281-295, August 1993. Describes design principles of sleepers, as well as the history.

Taylor H.P.J., The precast concrete bridge beam - the last 50 years, The Structural Engineer, 76, 407-414, 1998.  An overview of precast beams.

Thomas F.G. (ed.), Proceedings of a conference on Prestressed Concrete held at the ICE, February 1949.  A comprehensive review of the state of the art at the time with a comprehensive list of references.

Walley F., The childhood of prestressing - an introduction, The Structural Engineer, 62A, 5-9, Jan 1984.