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International Concrete Abstracts Portal

Showing 1-5 of 16 Abstracts search results

Document: 

SP225-06

Date: 

May 1, 2005

Author(s):

A. Scanlon

Publication:

Symposium Papers

Volume:

225

Abstract:

Current practice related to design of concrete structures for deflection control is reviewed. The paper discusses the limitations of the current code procedures based on minimum thickness rules and deflection calculations. Results are presented to demonstrate the sensitivity of deflections to span to depth ratio, sustained live load, and extent of cracking.

DOI:

10.14359/14378


Document: 

SP225-02

Date: 

March 1, 2005

Author(s):

P. J. E. Sullivan

Publication:

Symposium Papers

Volume:

225

Abstract:

Three approaches to fire design are currently available: (1) The direct application of data from furnace tests on simply supported members heated at the ISO 834 Time/Temperature standard rate. (2) Conventional ultimate limit state design in bending for fire, taking into account idealised material losses in strength at elevated temperatures. (3) Complete analysis of structural members using iterative finite difference or finite element techniques to estimate temperature gradients and determining the resulting stress and strain resultants. Prescriptive design falls into the first category and the thickness of the protective cover to the steel together with the minimum dimensions of the element is tabulated in building codes. Performance design would be carried out by the other 2 methods, where the applied heat impinging the surface due to a fire is assessed, the temperature distribution evaluated and the deterioration determined. This method is more appropriate for important structures with indeterminate members.

DOI:

10.14359/14374


Document: 

SP225-12

Date: 

March 1, 2005

Author(s):

R. R. H. Zhu and T. T. C. Hsu

Publication:

Symposium Papers

Volume:

225

Abstract:

Inverted “T” bent caps are used extensively in concrete highway bridges because they are aesthetically pleasing and offer a practical means to increase vertical clearance. The problem is that at service load unacceptable diagonal cracks frequently occur at the re-entrant corners between the cantilever ledges and the web. In order to control the diagonal cracks, an extensive three-phase investigation was carried out. The first phase was to predict the diagonal crack widths at the interior portions of the bent caps. A 2-D analytical model, called Compatibility-Aided Strut-and-Tie Model (CASTM), was developed. This model was calibrated by testing seven full-size 2-D test specimens. The second phase was to predict the diagonal crack widths at the end faces of the exterior portions of bent caps. In this phase the CASTM was extended to 3-D analysis, which was calibrated by testing ten 3-D specimens. In the third phase, two whole-wholebent-cap specimens were tested to determine the effective distribution width in the vicinity of an interior applied load on the ledge. Crack control methods for the interior spans and the exterior end faces were recommended.

DOI:

10.14359/14384


Document: 

SP225-11

Date: 

March 1, 2005

Author(s):

D. T. Blackman and R. J. Frosch

Publication:

Symposium Papers

Volume:

225

Abstract:

Epoxy coated reinforcement is often used as a means of improving the durability of structures. The use of epoxy coating on reinforcement, however, has been shown to decrease bond strength resulting in increased crack spacing and crack widths relative to uncoated reinforcement. While the general influence of epoxy coating on cracking is recognized, there is scare data available to substantiate the magnitude of the effect. The objective of this research was to evaluate the influence of epoxy coating on crack spacing and crack widths. Ten specimens were subjected to a constant moment region, and the crack spacings and widths were measured over a range of reinforcement stress levels. Primary variables included the epoxy coating thickness, reinforcement spacing, and reinforcement stress. The results from this study showed that epoxy coating thickness affects both crack spacing and width. In general, as coating thickness is increased, crack width increased and crack spacing decreased. While crack control aimed at minimizing corrosion of reinforcing steel may not be of concern when epoxy coated steel is used, crack control remains an important design consideration for aesthetic reasons, for increasing structural durability, and for the design of water-retaining or other specialized structures.

DOI:

10.14359/14383


Document: 

SP225-13

Date: 

March 1, 2005

Author(s):

A. Schokker, J. West, E. Villari, J. Breen, and M. Kreger

Publication:

Symposium Papers

Volume:

225

Abstract:

A number of different crack width prediction equations have been proposed for use with partially prestressed concrete structures, but laboratory and field results for members with varying levels of post-tensioning are limited. A durability study at The University of Texas at Austin involved beams with varying combinations of bonded post-tensioning and non-prestressed reinforcement. This work included extensive crack width measurements at varied load levels. A follow-up study is now on-going at Penn State University to consider beams with a combination of pretensioning and post-tensioning (such as found in spliced girder applications). This paper presents and discusses the measured crack data from these studies, and compares the data to selected existing crack width prediction models. Comparison of measured and predicted crack widths did not reveal a single comprehensive crack width prediction formula for the range of variables considered.

DOI:

10.14359/14385


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