International Concrete Abstracts Portal

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.

Career highlights are presented regarding Ned H. Burns, now recognized asa “Legend of the Prestressed Concrete Industry.” Dr. Burns’ childhood, family,marriage, military service, and education are described briefly. His development inresearch and teaching is chronicled as awards began to accumulate. Leadershippositions are indicated while awards continued in recognition of his excellence instructural engineering education and practice.

Post-tensioned concrete is a popular material used in the construction ofparking facilities due to economy and durability it offers. The flooring system in post-tensioned parking facilities generally consists of one-way post-tensioned slabssupported by post-tensioned beams cast monolithic with concrete columns formmoment frames. However, the building codes have restricted the use of post-tensionedconcrete as primary lateral load systems in high seismic regions due to concerns aboutductility, anchorage, bond, transfer lengths, grouting, characteristics of high strengthprestressing steel and level of prestressing. Until recently, building codes have insistedon the ductile non-prestressed steel as the sole reinforcement and have not permittedthe use of prestressing in ductile moment frames. This paper summarizes issues,advances and historical developments of code requirements concerning theprestressed or post-tensioned frames, followed by performance of parking facilitiesduring recent major earthquakes. Next, the paper provides an overview of the currentstate of seismic design process for post-tensioned parking facilities and its structuralsystems, subsystems and elements.

This paper provides an overview of the ACI 440.4R-04 document on“Prestressing Concrete with FRP Tendons” reported by ACI Committee 440 on “Fiber-Reinforced Polymer Reinforcements”. The document is one of the Emerging TechnologySeries published by ACI. The paper outlines the content of the document and thephilosophy of applying FRP technology as opposed to conventional steel forprestressing. The document offers general information on the history and use of FRP forprestressing applications, and a description of the unique material properties of FRP. Italso focuses on the current state of design, development, and research needed tocharacterize and ensure the performance of FRP as prestressing tendons in concretestructures. The proposed guidelines are based on knowledge gained from worldwideexperimental research, analytical work, and field applications of FRPs used asprestressed tendon. Current developments in the document include a basicunderstanding of flexural and axial prestressed members with FRP tendons, FRP shearreinforcement, bond of FRP tendons, and unbonded or external FRP tendons forprestressing applications. The document concludes with a list of research needs.