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International Concrete Abstracts Portal

Showing 1-5 of 13 Abstracts search results

Document: 

SP161-11

Date: 

April 1, 1996

Author(s):

R. Ganeswaran and B. V. Rangan

Publication:

Symposium Papers

Volume:

161

Abstract:

Presents the results of a study on long-term deformations of high-strength concrete. Shrinkage and creep deformations of high-strength concretes, as well as deflections of beams and one-way slabs made of high- strength concrete are reported. The measured deformations are compared with the values predicted by the ACI method, the CEB-FIP Model Code, and the Australian Practice. The comparison shows several discrepancies between measured and predicted values.

DOI:

10.14359/1505


Document: 

SP161-10

Date: 

April 1, 1996

Author(s):

P. R. Chakrabarti

Publication:

Symposium Papers

Volume:

161

Abstract:

In this project, an attempt is made to study the instantaneous load- deflection behavior of partially prestressed beams with unbonded post- tensioning tendons. Thirty-three beams with the following variables were tested: different mixes of reinforcing and prestressing steel, T-beams and rectangular beams, normal and high-strength concrete, low and high ratios of span/depth, and different effective stresses in tendons. Cracking was observed and deflections measured at precracking and postcracking stages. A suitable method for deflection calculation at precracking and postcracking stages is proposed. The proposed deflections and the deflections obtained by current ACI 318-89/92 code equations are compared with the measured deflections.

DOI:

10.14359/1503


Document: 

SP161-09

Date: 

April 1, 1996

Author(s):

N. J. Gardner and J. Zhang

Publication:

Symposium Papers

Volume:

161

Abstract:

North American design codes offer two methods to insure deflection serviceability. The design engineer can calculate the live load and sustained load deflections and check that they are less than code specified limits. Alternatively, the codes give maximum span/depth ratios for which serviceability can be assumed to be satisfied and deflections do not need to be calculated. However, the span/depth provisions of ACI 318-89 and CSA A23.3- M84 do not consider many of the factors which influence the deflection behavior of reinforced concrete beams and may not be consistent with the code specified deflection limits. The immediate and long term deflections of reinforced concrete beams were calculated using a layered, nonlinear finite element model. The long term deflections were calculated by a hybrid technique using an effective reduced modulus for concrete creep and a conventional finite element, time-dependent load vector for shrinkage and tensile cracking. The modelling technique was verified using the extensive experimental data of Christiansen. Span/depth ratios are proposed, which include the effects of concrete strength, tension steel ratio, and compression steel ratio, for incremental deflection criteria of span/500 and span/250. Long term deflection multipliers are given for sustained moments of 30, 50, and 70 percent of the design ultimate moment.

DOI:

10.14359/1449


Document: 

SP161-05

Date: 

April 1, 1996

Author(s):

Y. L. Mo and H. C. Lai

Publication:

Symposium Papers

Volume:

161

Abstract:

Although structures with elastic response are fairly well understood, structures with inelastic response are more difficult to analyze. Furthermore, in studies of inelastic response, attention has generally been paid to the response of reinforced concrete structures with relatively little attention being given to pounding of reinforced concrete buildings. Generally, the mutual collisions, or pounding, result from excessive deflections of adjacent buildings. In this paper, an algorithm is described for computing the pounding response of reinforced concrete buildings. In this situation, the buildings are idealized as two-dimensional multi-degree-of-freedom systems with nonlinear force-deformation characteristics. Collision between adjacent masses can occur at any level and are simulated by means of impact elements. Using real earthquake motions, the effect of deflection is investigated. In this study, the following conclusions are found. 1. Pounding can cause high overstresses, mainly when the colliding buildings have excessive deflections. 2. The code-specified separation distance is adequate to prevent pounding. 3. Pounding problems of adjacent buildings with large difference in mass are common.

DOI:

10.14359/1443


Document: 

SP161

Date: 

April 1, 1996

Author(s):

Editors: Edward G. Nawy and Debrethann R. Cagley

Publication:

Symposium Papers

Volume:

161

Abstract:

SP-161 All the papers presented in this publication were reviewed by recognized experts in accordance with the ACI review procedures. It is hoped that designers, constructors, and codifying bodies will be able to draw on the material presented in this volume in conjunction with the ACI 435 Committee Report "Control of Deflection in Concrete Structures", in improving the long-term deflection behavior and performance of concrete constructed facilities.

DOI:

10.14359/14201


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