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International Concrete Abstracts Portal

Showing 1-5 of 12 Abstracts search results

Document: 

SP203-01

Date: 

August 1, 2001

Author(s):

A. Scanlon, D. R. Cagley Orsak, and D. R. Buettner

Publication:

Symposium Papers

Volume:

203

Abstract:

AC1 Building Code requirements for deflection control are critically reviewed. Provisions for minimum thickness, deflection computations, and permissible computed deflections are reviewed. Differences in the approaches to deflection control for one-way and two-way construction are identified. Limitations in the application of the prescribed deflection calculation method are discussed. Results of a survey of consulting firms concerning deflection control in design offkes are presented. The paper concludes by suggesting possible directions for future changes in building code requirements for deflection control.

DOI:

10.14359/10801


Document: 

SP203-07

Date: 

August 1, 2001

Author(s):

H. H. Nassif, M. Sanders, and W. Cao

Publication:

Symposium Papers

Volume:

203

Abstract:

Current concrete design codes use an effective stiffness model to calculate the deflections of T-Beams. Based on the effective flange width, an effective moment of inertia, as well as section properties is computed. This effective flange width is limited by a criterion that is not consistent between various codes and which directly affects the computed deflections, moments, shears, and torques for the beam. In particular,the effect of flange width on serviceability limit states such as deflection, fatigue, cracking, and vibration is evident. There is a need to use more rational as well as realistic effective flange width criteria that would lead to more accurate predictions of beam deflections. An analytical and experimental study has been initiated to assess the contribution of the flange width to the calculation of deflection in concrete T-beams. This paper presents part of the results of an analytical study to model the exact behavior of T-beams with various effective flange widths. The Finite Element Method (FEM) is utilized to model the overall pre-cracking, cracking, and post-cracking, non-linear behavior. Actual data for material properties are used to model concrete and reinforcing steel. The FE Model is validated using available test results from literature and then used to analyze T-beams with various parameters. The beams are incrementally loaded to failure under a two point loading system. The load-deflection relationships are determined. A parametric study is undertaken to determine the effect of overall flange width. and other parameters such as reinforcement ratio, and concrete compressivestrength, on deflections. Results show that deflections for beams subjected to service loads (service load ranging between cracking and 30-40% of ultimate loads) are mainly affected by using the effective flange width rather than full flange width. It is observed that using the actual flange width would provide a better estimate of deflection at service loads.

DOI:

10.14359/10807


Document: 

SP203-05

Date: 

August 1, 2001

Author(s):

M. C. C. Guarda, J. S. lima, and 1. M. Pinheiro

Publication:

Symposium Papers

Volume:

203

Abstract:

This paper presents an overview of the requirements for deflection of beams and slabs in the draft Brazilian Code for concrete structures, NBR 6116:2000. Firstly, the Brazilian Code recommendations for deflection computations and allowable limits are described, and then these provisions are compared with those of section 9.5 of ACI 316-99. The paper also includes a numerical example to illustrate how the new proposals are applied to structural design. It is observed that the general criteria of the two codes are similar, but some differences are pointed out regarding minimum thickness requirements, load conditions, effective moment of inertia for continuous beams and the values of modular ratio, modulus of rupture and allowable deflections.

DOI:

10.14359/10805


Document: 

SP203-11

Date: 

August 1, 2001

Author(s):

B.-S. Choi and A. Scanlon

Publication:

Symposium Papers

Volume:

203

Abstract:

Research has shown that design expressions previously developed for material properties such as modulus of elasticity, modulus of rupture and creep coefficient used in the calculation of beam deflections may not be appropriate for high-performance-high-strength concrete. Also, the uncertainties associated with regular and high-performance concrete material properties as characterized by probability distribution functions may be different. Since high strength concrete may be used to reduce the size of structural members, assessment of deflections will be an increasingly important design consideration. This paper discusses these issues and demonstrates through Monte Carlo simulation techniques some differences between the variability of deflections in beams made with regular and high-strength concretes.

DOI:

10.14359/10811


Document: 

SP203-10

Date: 

August 1, 2001

Author(s):

R. I. Gilbert

Publication:

Symposium Papers

Volume:

203

Abstract:

An experimental program of long-term testing of large-scale reinforced concrete flat slab structures is described and the results from the first series of tests on five continuous flat slab specimens are presented. Each specimen was subjected to sustained service loads for periods up to 500 days and the deflection, extent of cracking and column loads were monitored throughout. The measured long-term deflection is many times the initial short-term deflection, due primarily to the loss of stiffness associated with time-dependent cracking under the combined influences of transverse load and drying shrinkage. This effect is not accounted for in the current code approaches for deflection calculation and control. Recently proposed procedures to improve deflection calculation (1) are evaluated against the test results and good agreement between the measured and calculated deflections is obtained.

DOI:

10.14359/10810


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