Year

1994

Degree Name

Doctor of Philosophy

Department

Department of Civil and Mining Engineering

Abstract

In the design of reinforced or prestressed concrete tlat plates with spandrel beams, one of the most critical aspects that needs to be considered is the punching shear strength, Vu of the slab-column-spandrel connections. Research on this behaviour has been carried out in recent years by various engineering academics and professionals. One of the more encompassing analytical approach in determining Vu, is the procedure developed by Loo and Falamaki for reinforced concrete slab-column-spandrel connections at the edgeand corner-column positions. In th,e case of prestressed concrete tlat plates, there is as yet no reliable procedure for the determination of Vu' particularly for the above stated slab-column-spandrel connections. Thus, the main objective of the present study is to develop an analytical procedure for the prediction of Vu, for these types of structural connections. This procedure is an extension of the analytical approach developed by Loo and Falamaki* whereby the effect of prestress is taken into account and incorporated into the appropriate equilibrium equations.

The development albeit an extension of a reliable analytical method requires accurate test results from large-scale models with proper boundary conditions. Tests up to failure were carried out on four prestressed post-tensioned concrete flat plate models, two with spandrel beams of different widths and depths, while the other two have a torsion strip and a free edge respectively. These half-scale models, each weighing approximately 5 tonnes, represent two adjacent panels at the corner of a typical flat plate structure and were tested under simulated unifonnly distributed loads. For ease of construction, each of the flat plate models was supported on six concrete column sections, which were cast and rigidly connected onto prefabricated steel sections at the bottom instead of having concrete columns. Specially designed load cells were used to measure the three reaction components at the hinged base of each of the column supports. Strain gauges were also attached to the reinforcing bars and prestressed tendons of the slab. The strains and other electrical signals were logged using a Hewlett Packard 3054A data acquisition control system via a Hewlett Packard 9826 computer.

Besides the experimental work, three concurrent studies were also carried out. The first was a comparative study of the various methods of punching shear strength analysis of reinforced concrete flat plates with spandrel beams. It was found that the Wollongong Approach developed by Loo and Falamaki [1992] was superior to alternative methods including that recommended by the Australian Standard for Concrete Structures (AS 3600-1988). The second was a parametric study of the effect of spandrel beam on the punching shear strength analysis, using the Wollongong Approach. From this study, a range of parametric limitations were identified within which the Wollongong Approach may be applied.

Finally, based on the experimental results, a theoretical study was undertaken which led to the development of a prediction procedure for the punching shear strength, Vu of post-tensioned concrete flat plates with spandrel beams, the details of which are presented herein. As with the Wollongong Approach, the proposed procedure (referred to in this thesis as the "Modified Wollongong Approach") is applicable to the analysis of failures at the comer- and edge-column positions. In addition to the consideration of parameters such as the overall geometry of the connection, the concrete strength and the slab restraint on the spandrel, the procedure also takes into account the following parameters:

(1) the size and location of the prestressed tendons,

(2) the magnitude of the applied prestress, and

(3) the profiles of the draped tendons.

In comparing the accuracy and reliability of the proposed analytical procedure with the Australian Standard approach, the latter was found to be less reliable in that it consistently overestimates the value of Vu' especially at the corner-column positions. This is also consistent with the compared results of the comparative study on reinforced concrete flat plates with spandrel beams.

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