International Concrete Abstracts Portal

A survey of the first uses of precast, prestressed or post-tensioned foldedplates roofs show that this structural system start in the 1950’s and end in the 1970’s Ahistoric perspective of this structural system will be presented starting in the 1950’s andending in the 1970’s. While prestressed concrete was making a break-through in theUnited States with the Walnut Lane Bridge in Philadelphia, PA, Europe was usingprestressed concrete in various types of structural systems. One of these systems wasthe folded plate roof system. Approximately a decade later in the United States, theCloverleaf Lanes Bowling Alley in Dade County, Florida used the same application inwhich the corrugated slab spanned 120 feet and extending transversely 286 feet. In1962, this system of folded plate shells went from long span structures to being used inroof structures for dormitories at Washington State University. The main beams for thedormitories were pretensioned in a factory, while the secondary beams were post-tensioned on site. During the 1970’s, precast folded plate structures were beingconstructed throughout the United States for various types of buildings, one notablestructure is the Hangar for Allegheny Airlines at Logan Airport, Boston, Massachusetts.Then they disappeared in the United States. Some Possible reasons why folded plateconstruction stopped are numerous but the two main factors are the architecturalsolution, and the lack of understanding of folded plate structures on the part ofengineers and architects.

In the early 1940’s Prof. G. Magnel performed extensive researchprogrammes on real scale prestressed concrete beams at Ghent University (Belgium) inorder to elaborate design methods for this new material. He also developed his ownanchorage system which was used until the mid 60’s in Belgium. He gave manylectures in several countries in which he explained in a simple way the principles ofprestressed concrete. He was also instrumental in the design of the first prestressedconcrete bridge in the USA, the Walnut Lane Bridge in Philadelphia and he was theauthor of the first English textbook on prestressed concrete. He designed one of thefirst PC railway bridges in Europe and the first statically indeterminate PC bridge in theworld. In the 1950’s many engineers from abroad spent some time in Magnels lab inGhent to perform research and to get acquainted with practical realizations.

The initial impetus to the application of prestressed concrete in the UnitedKingdom was heavily driven by the conditions imposed by the Second World War.Refugees from Germany, particularly Mautner and Abeles, brought skills andknowledge of tests carried out in France and Germany. The need to provide emergencystructures, both for military purposes and to meet civilian needs, together withshortages of many materials, especially steel, led to the construction of beams on ascale, and at a speed, which would not have taken place in more normal times. Thepaper covers developments in the UK from the outbreak of the war in 1939 up to theearly 1950s, when more normal times returned. This period of development is still notproperly documented because security conditions prevented the publication of fulldetails of the applications.

The successful implementation of carbon fiber reinforced polymer (CFRP)rods in prestressed applications depends on the anchor system. Finding a properanchor is a challenging problem due to the weakness of the CFRP tendon in thetransverse direction. This paper presents a finite element study conducted toinvestigate the contact pressure distribution in a wedge anchor system for CFRP rods.The effect of the thickness variation of the barrel on the contact pressure distributionwas investigated. The thickness of the barrel was reduced at the loading end of therod. Different thickness reductions were investigated. It was found that as thereduction of the thickness increased the contact pressure decreased at the loading endof the rod. This leads to the elimination of the stress concentration on the carbon fiberrod which results in the avoidance of the premature failure of the rod. Also, highershear stress was observed on the rod-sleeve surface than on the wedge-barrel surface.Tensile load-displacement relationship was modeled for different barrel thicknessreductions. For a given displacement, higher tensile load was carried by the anchorwith less barrel thickness reduction.

Self-consolidating concrete (SCC) is a relatively new approach to makingconcrete and is characterized by its high flowability and resistance to aggregatesegregation in the plastic state. SCC has become a popular alternative for commercialprecast elements and is being evaluated for use in precast bridge girders. This paperoutlines structural testing of six precast, pretensioned, AASHTO Type II girders. Threewere constructed using SCC, and three using a conventional mix. The major tasksincluded performing plastic and hardened property tests, constructing SCC beamswithout vibrating, determining the prestress transfer length, monitoring the camber,and finally testing the beams in such a manner as to produce flexure and sheardominated failure modes. Results of the construction and testing are presented.