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Calgary, Canada

Ghali A.,University of Calgary | Gayed R.B.,Krupp Canada Inc.
Canadian Journal of Civil Engineering

Drift and internal forces due to lateral forces on multi-storey concrete buildings composed of flat plates, columns, and shear walls are considered. For analysis, the structure should be idealized by a model composed of all monolithic components: shear walls, slabs, and columns. All components affecting the structure's stiffness should be considered in design; this is required by codes. However, for seismic design, codes allow, as alternative, a lateral force-resisting system composed of the shear walls only, but require that the design for the moment and the shearing force, transferred between the column and the slab, be based on the calculated drift. The study in this paper shows that this alternative can greatly overestimate the drift, the unbalanced moments transferred between the columns and the slabs and the bending moments on the shear walls. The design forces depend upon the natural period of vibration, whose value would be overestimated by ignoring the contribution of the slabs and columns to the stiffness of the structure. This paper recommends that the design be based on the analysis of a structural model composed of the shear walls, the slabs, and the columns; the paper also gives guidance on the design of flexural and punching shear reinforcements in the slabs. Source

Ghali A.,University of Calgary | Gayed R.B.,Krupp Canada Inc.
Journal of Structural Engineering (United States)

Modern structures must be designed for satisfactory serviceability over a long lifespan: 100 years or more. The camber or the deflection must not be excessive during the design lifespan. The present paper concerns the state-of-the-art technology on prediction of the most probable long-term deflection. © 2014 American Society of Civil Engineers. Source

Ghali A.,University of Calgary | Dilger W.,University of Calgary | Gayed R.B.,Krupp Canada Inc.
Journal of Structural Engineering (United States)

Slabs having a low flexural reinforcement ratio can fail when a pattern of yield lines forms a mechanism. When a local pattern of flexural yield lines forms a mechanism, any limit on angular rotation is bound to be reached, triggering a secondary failure by punching. The ultimate strength is the maximum load reached before failure by flexure or punching. The flexural-failure load can be predicted by yield-line analysis. Unlike flexural failure, secondary failure by punching exhibits a sudden drop in load and noticeable damage to the concrete. The established facts are that the ease of installation, the low cost of the finished product, and its effectiveness make HSSR the most used type of slab shear reinforcement. In the radial arrangement, it is very difficult to avoid interference of the studs with the top and bottom orthogonal flexural bars. The installed studs can end up in positions shifted away from the design, and a small shift can result in significant reduction in the efficacy of the shear reinforcement. Source

Ghali A.,University of Calgary | Gayed R.B.,Krupp Canada Inc. | Dilger W.,University of Calgary
ACI Structural Journal

The basic requirements for punching shear in concrete slabs are the same in the ACI 318-14 code and the guides ACI 421.1R-08, ACI 421.2R-10, and ACI 352.1R-11. However, the equations and the details of the shear reinforcement to satisfy the basic requirements are different in ACI 352.1R-11 from the ACI 421 guides. The agreements and differences of the requirements in the four references are summarized. The comparisons, the discussions, and the recommendations in the present paper could improve future editions of the code and the guides to enhance safety and effectiveness of shear reinforcement. Copyright © 2015, American Concrete Institute. All rights reserved. Source

Elbadry M.,University of Calgary | Ghali A.,University of Calgary | Gayed R.B.,Krupp Canada Inc.
Journal of Bridge Engineering

The models for prediction of creep in codes and design guides are mainly based on tests in which the load is sustained for a number of years, rarely exceeding 10; however, most models predict that creep reaches its extreme after approximately 30 years. An exception is the frequently accepted Model B3; it predicts indefinite increase of creep with the logarithm of the number of days of sustained loading. Analysis of deflection using Model B3 of a large number of bridges agrees with measured deflection in terms of magnitude and continued increasing tendency. Modern design requires satisfactory serviceability sustainable for a long life span. The absolute value of camber or deflection must not be excessive. This paper shows that by adopting Model B3, combined with appropriate prestressing, it is possible to satisfy this requirement for 125 years. © 2013 American Society of Civil Engineers. Source

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