الفهرس 
LITERATURE REVIEWOnly 14 pages are availabe for public view
Abstract
This research presents an experimental and numerical investigation to study the behavior of post-tensioned concrete slabs at pocket locations with a different amount of additional steel at each pocket.
The experimental phase consisted of three specimens with the same dimensions of 400 cm x 120 cm x 15 cm. Each contains two stressing pockets with dimensions of 80 cm x 40 cm x 15 cm. A concrete mix of 50 MPa was used and the same mesh of three bars of 10 mm diameter in both directions up and down was used for all three specimens. The parameter that was changed is the amount of additional reinforcement around each stressing pocket. S1 had zero additional reinforcement, S2 had a 1.70 % of the area of the cross-section as additional reinforcement (4 bars of 18 mm diameter) and S3 had a 3.40 % of the area of the cross-section as additional reinforcement (8 bars of 18 mm diameter).
As for the numerical investigation in this study, an analytical model using the finite element method was developed for the tested specimens using the nonlinear package “ANSYS 13”. The model was also validated through comparisons with experimental results and a good agreement was obtained.
The specimens were tested under flexural to obtain the optimum results and behavior of stressing pockets. All specimens of the experimental program were tested at the laboratories of the Housing and Building National Research Center.
The modes of failure, the ultimate capacities and the general deformational behavior of the specimens. Also, the cracking behavior of specimens was presented. The analyses and comparison of the experimental test results were also introduced.
Also, a comparative study was conducted using different parameters on a number of post-tensioned reinforced concrete slabs and the behavior of the inner stressing pockets and the slabs was studied.
7.2 Conclusions
The current study had elaborated on the behavior of the stressing pockets and the post-tensioned slabs, the following points summarize the conclusions of this investigation:
1- The crack patterns of the three post-tensioned reinforced concrete specimens were different, as it was affected by the additional steel reinforcement. The third specimen (S3) and the second specimen (S2) had an increased first crack load in comparison with the first specimen (S1). Although (S2) and (S3) had a slightly different value of first crack load, (S3) had a higher value than (S2) by 9%.
2- The load of failure at S1 (131.4 kN) was so low compared with that of S2 (203.3 kN) and S3 (202.8 kN). Which means that not only the additional reinforcement at S2 and S3 affected the behavior of the stressing pockets, but also the maximum load capacity of the slabs.
3- Displacement-based ductility and energy-based ductility both indicates the improvement of the ductile behavior upon addition of reinforcement at the pocket locations. The two methods clearly state that the second specimen (S2) had an improved ductile behavior than the third and the second specimen.
4- With zero additional reinforcement in S1, the failure took place at the edge of the right pocket, while at S2 the crushing failure was at mid-span and S3 had a bearing failure. Which indicates that the additional reinforcement had an impact on the failure of each specimen depending on the percentage of the additional reinforcement.
5- The second specimen (S2) had more number of cracks and density than both the first specimen (S1) and the third specimen (S3), but the cracks at the stressing pockets of the first specimen (S1) was severe in comparison with the second and the third specimens, indicating the impact of the additional reinforcement on the crack pattern.
6- The strain gauge on the additional reinforcement at S2 and S3 clarified that the S2 had higher strain than S3 which was the predicted case, the difference in the strain was 31%. But this percentage won’t be justified if the cost of the additional steel and the mode of failure was taken into consideration.
7- As established from the previous points that the additional reinforcement had notable impact on both the behavior of the inner stressing pockets and the total behavior of the slab, the difference between the maximum load capacity between S2 and S3 is less 1 kN in favor of S2 which have a less percentage of reinforcement (1.70 %) at its stressing pockets in comparison with S3 (3.40 %). It should be noted that these changes in the load capacity is due to the special loading conditions discussed through this study. It would be safe to conclude that 1.70 % of additional reinforcement will be both effective in enhancing the behavior of the stressing pockets and maintain the ductile behavior of the slab.
8- As established from chapter 6, the results obtained from the experimental program and finite element models are in good agreement except for the first specimen (S1) which had an error during testing.
9- The comparative study of different post-tensioned reinforced concrete slabs recommended the usage of 1.70 % and 3.40 % of the cross section as additional reinforcement depending on the behavior required from the post-tensioned concrete slab.
7.3 Recommendations for Future Research Work
The following recommendations are suggested for future research work:
1. Studying the behavior of stressing pockets in different locations on the slab, preferably near columns to study its impact on punching shear.
2. Conducting the same experiment on larger spans to minimize the effect of the additional steel on the whole slab.