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Alexandria UniversityFaculty of EngineeringStructural Engineering Department3nd Year

PRESTRESSED CONCRETE HISTORY & EXAMPLES

Presented by: Ibrahim Ali Hassan  – Sec 1 No.11Ahmed Said Al-Abassy  – Sec 1 No.36Khaled Mohammad Al-Yamany  – Sec 3 No.122Sherif Hosney Abd-Elmohsen  – Sec 4 No.144

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INTRODUCTION

Prestressing means deliberately inducing a self-equilibrated state of stress in an object or structure beforeit is placed in service that is essential for the functionality or the stability of a structure. It may simplifyconnections and improve performance by increasing stiffness or limiting cracking. Prestressing may also preclude stress reversals under normal load conditions and thus allow use of tension-only or compression-only elements. It is often useful for rehabilitation, for strengthening or stabilizing a structure by providing

confining forces.

HISTORY OF PRESTRESSED CONCRETE 

The concept of prestressing could betraced back to Egyptian boats, builtapproximately 3500 years ago, inwhich the hull, posts and ropesformed structures to prevent“hogging,” or negative curvature inhulls. These boat structures were

 prestressed by twisting ropes, asshown in Fig. 1.

In Gothic cathedrals, added weight has also been used to create a beneficial prestress where the weight of pinnacles helped prevent sliding failures in buttresses. A weighted central rod or wooden pendant wasused along the axis of spires to stabilize spires under lateral loads. An unusual prestressing techniqueinvolves using buckled elastic struts, utilizing the fact that the axial load increases slightly above the Euler bifurcation load with increasing axial deformation. This principle was used for a design of the deployablemast to support the solar panels for the international space station.

The concept of prestressed concrete appeared in 1888 whenP.H. Jackson was granted the first patent in the United States

for prestressed concrete design. Jackson’s idea was perfect, but the technology of high strength steel that exhibited lowrelaxation characteristics was not yet available. It was notuntil Eugene Freyssinet defined the need for these materialsthat prestressed concrete could be used as a structural buildingmaterial. In 1948, Gustave Magnel wrote the first book ofdesign in prestressed concrete, Le Béton Précontraint(Prestressed Concrete). Magnel designed and built thelegendary Walnut Lane Bridge in Philadelphia.

Simultaneously, Urlich Finsterwalder, the German bridge

 builder and designer revolutionized the construction meansand methods for prestressed concrete bridges by inventing thefree cantilever construction method of prestressed concrete bridges, which allowed long span bridges to be constructedwithout stabilized shoring. He then designed stress-ribbon bridges which allowed prestressed concrete to span distancesonly steel suspension bridges could achieve. In 1939 Paul Abeles and his peer, H. von Emperger studiedand tested prestressed concrete that the idea of “partial prestressing” emerged.  

Figure 2. The Walnut Lane Memorial Bridge, a prestressedconcrete girder bridge in Philadelphia, Pennsylvania,

designed by Belgian Engineer Gustave Magnel. Opened in

Figure 3. Double Cantilever Method (Magnel 1954)

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Initially, Freyssinet and Magnel were adamant that prestressed concrete should not be allowed to exhibitany tensile forces at sustained loading. Later, the Roebling family developed the first stress--relieved wirefollowed by the first stress--relieved strand.

In 1957, T.Y. Lin organized the First Prestressed Concrete World Conference. Shortly after thisconference, Lin published a technical paper in the Prestressed Concrete Institute (PCI) Journal thatintroduced a new Load Balancing technique which allowed most structural engineers to design prestressed

concrete easily.

Lake Pontchartrain Causeway Bridges in Louisiana, USA: 

Lake Pontchartrain Causeway in Louisiana, USA is considered one of the historic civil engineeringlandmarks in USA according to ASCE. It was listed by Guinness world records as the longest bridge overwater in the world till July 2011, Jiaozhou bay bridge in China now took that name.

On Jan. 20, 1955, construction on the causeway began. An onsite precast, prestressed concrete plantmanufactured the various components which were then barged to the bridge site where large cranes wereused for installation. The assembly line process resulted in high levels of quality control and rapid production. Construction of the structure, from first pile to completion, was a mere 14 months.

On May 10, 1969, a second bridge opened at a cost of $33 million. As part of the construction project,low-level bascules on the original bridge were removed and replaced with both a high-level, fixed-span atthe south navigation channel and a high-level bascule at the north navigation channel. Seven crossoverswere built to allow access from one bridge to the other and to accommodate vehicle emergencies.

Each of the Lake Pontchartrain Causeway’s two bridges have 28 -footwide roadways with 18-inch curbson either side. The two spans are approximately 84 feet apart.

In 1995, the GNOEC established a rehabilitation program to provide systematic repairs on the agingstructures. The commission increased causeway tolls by $0.50 to pay for repair and maintenance. The $79million program is currently underway and is scheduled to be finished in 2008.

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Precast concrete plant: 

Prior to construction of the original bridge, a precast, prestressedconcrete plant was built on Lake Pontchartrain’s north shore.Virtually the entire causeway was manufactured at this plant. The

deck and girders were monolithically cast and prestressed, formingone unit for each span. 

Piles: 

The twin bridges are supported by more than 9,000 hollow, precast,concrete pilings that are 54 inches in diameter. At the time of thefirst span’s construction, they were the largest piles ever driven.Plans are underway to restore damaged pilings  

Boukei Bridge in Hokkaido, Japan:

The world’s first application of the prestressing with highly eccentric external tendon to a continuous -span girder was in the construction of the Boukei Bridge in Hokkaido, Japan. Considering the siteconditions, the bridge was designed with a two-span continuous and unsymmetrical girder having a totallength of 57 m as shown in Figure 6. The effective width of the bridge varies from 3.0 m at the abutmentsto 6.0 m at the central pier.

The characteristic of this innovative bridge is that the external tendon layout takes the similar shape of the bending moment diagram as shown in Figure 8. The structure was designed to form a pseudo truss, withthe main girder made of concrete as compression chords, the external tendons as tension chords, and thesteel deviators as diagonal members. This allowed the girder height to be reduced significantly, thusmaking the bridge lightweight. The external tendons are placed below the girder in the midspan region bymeans of steel struts, the function of which is similar to a truss. At the intermediate support region, it is placed above the bridge deck and covered with a fin-shaped concrete web member. The combination ofthe subtended tendons and the fin-shaped concrete web makes this bridge a unique one with aesthetically pleasing appearance.

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Bicycle wheel: A simple example which reflect the Prestressing Concept:

  Wire spokes are strong in tension but weak incompression (due to buckling)

  Spokes must be kept in tension

 

When the wheel is assembled, spokes aretightened up uniformly by the turnbuckles at therim

  Under a downward load on the wheel, the spokesin the lower part of the wheel tend to be subjectedto compression

  Tensile prestress in the spokes must be higherthan the compression force to keep all the spokesin tension

Other types of loading on the wheel: due to braking and due to taking a sharp cornerForces due to braking:

  Could not be resisted if thespokes were arrangedradiating from the center ofthe hub.

  Spokes are set at an angle tothe radii, each pair forming atriangulated system which isable to generate tensile and

compression forces whichoppose the braking force.

  Tensile prestress ensures thatall spokes are in tension andactive

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References: 

  The Prestressing of Structures: a Historical Review, by Dario Gasparini

www.arct.cam.ac.uk/Downloads/ichs/vol-2-1221-1232-gasparini.pdf

  The History of Prestressed Concrete: 1888 to 1963, by Tyson dingeswww.krex.k-state.edu/dspace/handle/2097/1439

  A presentation about Lake Pontchartrain Causeway by Mils bingham & Cary Bourgeoisin Louisiana Civil Engineering Conference 13th of Sep - 2013

  Structural Engineer Websitewww.gostructural.com/article/4298/the_lake_pontchartrain_causeway

  Recent technology of prestressed concrete bridges in Japan by Hiroshi Mutsuyoshi & Nguyen DucHai, Saitama University

www.iabse-bd.org/old/43.pdf

  Basis of structural design by Aurel Stratan.www.ct.upt.ro/users/AurelStratan/bsd%5Cc04-bsd.pdf