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International Concrete Abstracts Portal

Showing 1-10 of 17 Abstracts search results

Document: 

SP231-16

Date: 

October 1, 2005

Author(s):

R.W. Furlong, Ph.D., FACI, HonMASCE

Publication:

Special Publication

Volume:

231

Abstract:

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.

10.14359/14932


Document: 

SP231-15

Date: 

October 1, 2005

Author(s):

H.R. Hamilton III, T. Labonte, and M.H. Ansley

Publication:

Special Publication

Volume:

231

Abstract:

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.

10.14359/14931


Document: 

SP231-14

Date: 

October 1, 2005

Author(s):

A. Al-Mayah, K. Soudki, and A. Plumtree

Publication:

Special Publication

Volume:

231

Abstract:

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.

10.14359/14930


Document: 

SP231-13

Date: 

October 1, 2005

Author(s):

R. El-Hacha, T.I. Campbell and C.W. Dolan

Publication:

Special Publication

Volume:

231

Abstract:

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.

10.14359/14929


Document: 

SP231-12

Date: 

October 1, 2005

Author(s):

M. Iqbal

Publication:

Special Publication

Volume:

231

Abstract:

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.

10.14359/14928


Document: 

SP231-11

Date: 

October 1, 2005

Author(s):

D.K. Merritt and B.F. McCullough

Publication:

Special Publication

Volume:

231

Abstract:

Prestressed pavement is perhaps one of the most important yet underusedinnovations in prestressed concrete in the past century. Generally in the form of post-tensioning, prestress significantly reduces the required slab thickness and greatlyimproves pavement performance by reducing the occurrence of cracking. While thefirst reported use of prestressed concrete for pavements occurred in the late 1930s andearly 1940s in Missouri, Michigan, and Maryland, the prestressing techniques commonto today’s practices were first used in the 1940s in France. Domestic applicationsfollowed in 1953 at the U.S. Navy’s Patuxent River Naval Air Station. In 1971, theFederal Highway Administration (FHWA) initiated a new series of demonstration projectsat Dulles International Airport; Hogestown, Pennsylvania; Brookhaven, Mississippi; andTempe, Arizona. Later, in 1985, research at The University of Texas at Austin led theconstruction of a one-mile test section on Interstate 35 near Waco, Texas, which is stillin excellent condition after 20 years. Despite the success of these and other morerecent projects, prestressed pavement is still not widely used. New FHWAdemonstration projects, however, are currently applying prestressed pavementtechnology to precast concrete pavement construction. Recent projects in Texas andCalifornia have demonstrated the viability of prestressed precast pavements for notonly improving performance and reducing slab thickness, but also for expeditingpavement construction.

10.14359/14927


Document: 

SP231-10

Date: 

October 1, 2005

Author(s):

E. Baran, C.K. Shield, and C.E. French

Publication:

Special Publication

Volume:

231

Abstract:

This paper presents a description and comparison of several experimentaltechniques used to determine the effective prestressing force in pretensionedprestressed concrete girders. The effective prestressing force was determined by threemethods: (1) using vibrating wire strain gages that were embedded in the girders duringfabrication; (2) load testing the girders to determine flexural cracking and crack re-opening loads and then back calculating the losses; and (3) exposing a length ofstrand, attaching resistance strain gauges on the strands, and flame-cutting theinstrumented strands.Several instruments were used to determine the flexural crack initiation and crack re-opening loads. These included crack detection gages, concrete surface strain gauges,and LVDTs, as well as visual observations. Use of data from the strain gauges placed atthe bottom surface of the girders was determined to be the most effective way ofdetecting flexural crack initiation and re-opening. Cracking loads determined fromvisual observation were significantly larger than those determined from the straingauge data.The back-calculated prestress losses determined from the measured flexural crackinitiation and re-opening loads of the girders were significantly larger than thosedetermined from other experimental methods and those predicted by the PCICommittee and AASHTO LRFD methods. Losses determined by the other experimentalmethods and the predictions correlated more closely with those back-calculated usingvisually-observed cracking loads.These results indicate that prediction of losses based on the measured flexuralcracking and crack re-opening loads using the basic theory of mechanics results in anoverestimation of prestress losses. Consequently, girders may undergo flexuralcracking and crack re-opening at lower loads than predicted using the basic theory ofmechanics.

10.14359/14926


Document: 

SP231-09

Date: 

October 1, 2005

Author(s):

J.F. Stanton

Publication:

Special Publication

Volume:

231

Abstract:

In post-tensioned systems, friction during stressing and slip-back due tosetting the wedge anchors cause loss of prestress. If the tendon is long or containssharp curvatures, these losses can be significant. This paper summarizes methods forcalculating the losses and provides an evaluation of the numerical coefficientssuggested by ACI 318-05 for friction. Equations are provided where closed formmethods are possible, and numerical methods are outlined for other cases.

10.14359/14925


Document: 

SP231-08

Date: 

October 1, 2005

Author(s):

P.R. Gupta

Publication:

Special Publication

Volume:

231

Abstract:

Friction losses contribute about 50% of the total losses in post-tensionedconstruction. The original loss coefficients that were derived for earlier post-tensioningsystems are still being used in the ACI recommendations for unbonded construction.Some of these systems have not been used in the industry for almost 30 years.This paper presents a review of the current ACI recommendations of friction losses inunbonded construction. The paper also describes the theoretical development of asimple field technique to determine the curvature and wobble coefficients under fieldconditions. Results from initial testing are compared with the ACI recommendations andindustry practice.

10.14359/14924


Document: 

SP231-07

Date: 

October 1, 2005

Author(s):

A.E. Naaman

Publication:

Special Publication

Volume:

231

Abstract:

Assuming the prestressing force remains constant with applied externalload, the analysis of beams prestressed with unbonded tendons under service loads,where the section is uncracked, is no different than the analysis of beams with bondedtendons. However, after cracking, significant differences emerge, the most importantof which is that the stress in the unbonded tendon is member dependent, that is, itdepends on the deformation of the member, while the stress in the bonded tendon issection dependent, that is, it depends on the curvature of the section. This causes thestress in unbonded tendons to be significantly smaller than that for bonded tendons,and that is particularly important at nominal bending resistance.This paper summarizes the analysis procedure for beams prestressed with unbondedtendons at service and ultimate limit states; it focuses in particular on three problems:1) how to analyze a beam in the elastic uncracked range of behavior; 2) how to analyzea beam in the elastic cracked range of behavior; and 3) how to analyze a beam atnominal bending resistance.

10.14359/14923


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