الفهرس 
LITERATURE REVIEWOnly 14 pages are availabe for public view
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Abstract
The main objective of the thesis is to provide more information and investigate the behavior of ultra-high performance concrete (UHPC) in punching shear failure.
In this research, four specimens of slab-column internal connections were constructed and were tested to investigate the failure of the ultra-high performance reinforced concrete slabs behavior on punching shear. All the four slabs had dimensions 1350*1350*80mm, whilst four main parameters were determined to be studied, which were the effect of concrete strength, column shape, column size (column aspect ratio), and flexural reinforcement ratio. The result of the experimental work was presented in terms of ultimate loads, punching cone angle, deflection, reinforcement strain, concrete strain, stiffness, ductility, and absorbed energy. The finite element model ABAQUS was adapted to reduce the gap between reliable simulations of punching phenomena of concrete slabs and experimental observations. ABAQUS/Explicit, the concrete damaged plasticity model (CDPM), was used explicitly in this thesis. The concrete was divided into length, width, and depth into brick elements (C3D8R) to avoid the shear local effect and hourglassing effect, while the reinforcement is modeled wire truss by (T3D2) embedded into the solid concrete elements.
Conclusions
UHPC displays crucially enhanced material properties compared with normal and HPC.
The mixing procedure used in this study produced compressive strength of 70MPa, while adding micro steel fibers exceeded compressive strength twice and a half times, implying that adding micro straight circular steel fibers has an aspect ratio of 65 with a volume ratio of 2% of concrete.
In order to prepare UHPC, a Pan mixer instrument must be used, which ensures that the inflow and fulfillment are very homogeneous without the addition of additional water or superplasticizer to the design mix.
UHPC is a very sensitive material and any change or disturbance in partial quantity or mixing procedures leads to chill way to gain the required concrete strength.
The cost of UHPC is quite high at initiation time, while in the long-time run, the cost will be normal and when it becomes more commonly used, the price will go down.
The flexure reinforcement yield in all specimens is diminutive as opposed to high values in concrete strain. These differences can be explained by the enormous concrete tensile strength in the UHPC relieved flexure reinforcement bar yielding and resisting the tension force that was produced inside the specimen which was announced in the concrete strain.
Using the UHPC with micro steel fiber in the flat slab structural system changes the punching behavior from pure brittle shear failure to mostly ductile shear failure, which is represented in a ductility ratio from 2.77 to 3.57 and gives a vast warning before failure occurs.
Decreasing the aspect ratio of the column increases the punching shear capacity in a slab, which means there is an inversely proportional relationship between aspect ratio and punching shear capacity.
For UHPC, the diameter of the punching cone perimeter was larger than that of conventional concrete and the location of the critical shear crack at the tension surface is far away from the face of the column, while the punching cone angle for UHPC was less than conventional concrete. The average punching cone angles for four specimens were 15.7ᵒ.
The critical shear perimeter is proposed to be taken at 2d from the face of the column, and can be defined as: bo=2(a+b+2πd) for rectangular column, bo=3(D+πd) for circular column, and bo=4(w+πd) for square column.
As expected for UHPC, the presence of micro steel fiber in all specimens changed the average ultimate load that was increased by 81% relative to the first crack.
The increasing of concrete strength for specimens SB1 and SB4 increased load-defection at “d/2” from columns by about 22.7% and 11.4% respectively relative to other specimens.
The average value between deflection at the first crack, ultimate deflection, and fracture deflection at ”d/2” from columns face for four specimens had a huge difference. The average ultimate deflection value exceeded by 67.5% compared to deflection at the first crack. However, the difference between fracture deflection and ultimate deflection was 58%. While the difference between fracture deflection and deflection at the first crack was about 86.75%.
Specimen SB1 has the highest initial stiffness, ultimate stiffness, and energy absorption by an increasable 40.62%, 24.48%, and 41.4% respectively compared to the other specimens, because specimen SB1 included high strength with a high flexural reinforcement ratio.
The numerical model results give a very good agreement compared to experimental results. The difference between the numerical result and experimental result in the ultimate load of four specimens was 2.6% and the deflection that happened at a distance “d/2” from the column face was 7%.
The average difference between ACI analytical results and Eurocode analytical results to the laboratory experimental results of the maximum capacity load of four specimens was increased by 30% and 20.5% respectively. This huge difference is due to using punching conventional concrete formulas and didn’t compute the presence of micro steel fibers in the compound and punching shear phenomena mainly depending on the tensile strength, friction force, and local synthesis.
Future Work and Recommendations
The following are suggestions for further studies on the punching shear behavior of ultra-high performance concrete (UHPC) slab-column connections:
Endeavor more mixing designs of UHPC to gets high compressive strength with low budget.
Study the different systems of connection bond between UHPC and conventional concrete.
Study the effect of gravity static load with pseudo seismic loading on the internal slab-column connections.
Study the effect of different steel bars fabrication of UHPC slab-column internal connections such as:
The effect of special fabrication of flexure steel reinforcement.
The effect of shear reinforcement in the punching shear zone like stirrups, bent up bars, and shear studs.
Investigate the influence of different parameters on the punching shear behavior of UHPC slab-column internal connections such as:
The eccentric load effect is symmetric or unsymmetric.
The size effect of slab thickness.
Open in the periphery of critical punching shear with the change in location and size of the open.
Study the punching shear behavior of UHPC flat slab structural system slab-column edge and corner connection.