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International Concrete Abstracts Portal

Showing 1-5 of 8 Abstracts search results

Document: 

SP198-07

Date: 

March 1, 2001

Author(s):

S. A. Mirza

Publication:

Symposium Papers

Volume:

198

Abstract:

The CSA Standard A23.3-94 permits a moment magnifier approach for design of slender composite steel-concrete columns. This approach is strongly influenced by the effective flexural stiffness (EI) of the columns. However, the EI expressions given in CSA A23.3-94 are quite approximate when compared with the values of EI derived from axial load-moment-curvature relationships. This study was undertaken to determine the influence of different variables on EI of slender tied rectangular composite columns in which steel sections are encased in concrete. The columns studied were subjected to uniaxial bending in symmetrical single curvature under short-term loads. Approximately, 8,000 simulated columns, half of which subjected to bending moment about the major axis and the remaining half subjected to bending moment about the minor axis of the steel section, were used to generate the stiffness data. The EI expressions were then developed for use in slender composite column designs. A design equation is proposed in this paper.

DOI:

10.14359/9993

Document: 

SP198-06

Date: 

March 1, 2001

Author(s):

F. M. Bartlett

Publication:

Symposium Papers

Volume:

198

Abstract:

In 1988, the collapse of a supermarket roof in Burnaby, Canada, highlighted the need to distinguish between the specified strength and the actual strength of a material when evaluating existing structures. It is unsafe to calculate resistances using the actual strength instead of the specified strength in conven-tional resistance equations with customary resistance factors. This is the rationale behind current criteria for the evaluation of existing bridges in Canada, that require in-place strength data to be converted to equivalent specified strengths. In this paper, the statistical relationship between the specified strength and the actual in-place strength of concrete is examined. A method is summarized which enables concrete core compression strength data to be converted to an equivalent specified strength for structural assessment purposes. The method is illustrated by a case study involving 1200 40-year-old precast stringer bridges in Alberta, Canada.

DOI:

10.14359/9992

Document: 

SP198-05

Date: 

March 1, 2001

Author(s):

J. E. Breen

Publication:

Symposium Papers

Volume:

198

Abstract:

This Symposium honors a man who through a broad range of contributions, clearly carved a worldwide leadership position in the field of Structural Engineering. It is a fitting place to discuss the characteristics of leadership in the formulation of codes of practice and particularly building codes for structural concrete. In our North American democracies, the tradition of developing a clear consensus in support of a proposed change is the rule in formulating concrete design codes. Such a consensus means overwhelming agreement of a committee of strong-willed persons representing a myriad of conflicting interests after consideration and judgment of the merit of every dissenting opinion. In order to obtain such a consensus, code recommendations must not only be technically sound, but they must be practical, workable, and necessary. Above all, they must be patiently and painstakingly presented, defended, revised and re-presented to the committee. Those who shepherd the proposals that ultimately become part of the standards that guide practice and protect the citizenry must be effective leaders.

DOI:

10.14359/9991

Document: 

SP198-04

Date: 

March 1, 2001

Author(s):

W. H. Dilger and P. Langohr

Publication:

Symposium Papers

Volume:

198

Abstract:

For long span continuous concrete bridges, haunched box girders are the preferred choice of the structural engineers because they not only look most graceful, but they are also more efficient structurally, and more economical. It is therefore not surprising that the designers of the 12.9 km (8 mile) long Confederation Bridge in Eastern Canada chose the haunched girder configuration for the 43 girders of the 250 m (820 ft) long marine spans as well as 21 girders of the approach spans. In the paper it is demonstrated that the conventional approach to shear design of haunched girders is on the unsafe side. This is so because the compression force, the vertical component of which reduces the shear force in the web, is smaller than the bending moment M, divided by the internal lever arm d,. The relevant equations are derived on the basis of equilibrium in a web with diagonal cracks, sloped at an angle 8. As an example the shear design for the Confederation Bridge is presented.

DOI:

10.14359/9990

Document: 

SP198-03

Date: 

March 1, 2001

Author(s):

D. Mitchell

Publication:

Symposium Papers

Volume:

198

Abstract:

This paper describes some of the important aspects of code requirements for the design of structural members made with high-strength concrete. The provisions of the 1994 CSA Standard for the Design of Concrete Structures are highlighted. Comparisons are made between the provisions of the 1999 ACI Code and the 1994 CSA Standard. Some aspects of design from the 1990 CEB-FIP Model Code and the 1995 New Zealand Standard are also discussed.

DOI:

10.14359/9989

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