الفهرس 
Punching Shear Failure
Previous Researches for Punching Failure UHPC SlabsOnly 14 pages are availabe for public view
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Abstract
Not for a long time, there is a growing interest in a new generation of concrete
to make huge development in construction. A relatively new sophisticated
construction material of cementations complex, ultra-high performance concrete
(UHPC) was used. The mechanical property of UHPC is supreme of
conventional concrete. The compressive strength is more than 124 MPa and
tensile strength is greater than 5 MPa. The modulus of elasticity ranged between
42 to 55GPa, concrete density ranged between 2,400 to 2,500 kg/m3, and tensile
strength was more than 6.2MPa. In this thesis, the punching of flat slabs with
UHPC was studied to increase the information of slab-column connections
against punching shear failure.
Reinforced concrete flat slabs are commonly used today because of the
preferences they offer; for example; decrease of floor height, simple formwork
construction, and pleasant appearance. However, the critical problem of this
system is the high-stress region slab-column connections resulting in a column
is essentially pushed through the slab, (known as punching shear failure). To
overcome this failure, there are many ways to increase the punching shear
capacity of the reinforced concrete flat slabs such as; increasing slab thickness
in the area adjacent to the column, increasing the dimension of a column which
is always against the architectural desire, preparing a slab around columns with
shear reinforcement, and finally development concrete strength.
The development of concrete strength is one of the most influential methods to
avoid punching shear failure in a slab. Therefore, this research was aimed to
examine slab-column connection with UHPC to increase punching shear capacity. It should be noted that UHPC is a new material, it is still limited to a
few structural applications due to its high cost, limited design codes, and the
high factors of safety adopted in the design.
To investigate the advantages of UHPC in the highly stressed region of slab-
column connections, four slabs specimens with dimensions 1350*1350*80mm
were prepared. All specimens contain steel fibers which enable tension to be
carried across opened cracks, give ductility and energy absorption for concrete.
The average strength for the specimens test ranged between 193MPa to 164MPa
for compression strength and 13.1MPa to 9.6MPa for tensile strength.
The experimental study and numerical analysis were used to examine the
punching shear strength of four UHPC specimens which have been tested under
concentrated vertical load, using various parameters such as concrete strength,
column aspect ratio, column shape, and flexural reinforcement ratio. The
experimental setup is a hydraulic jack acting at the center of the column stub. A
steel I-beam frame supported the specimen at the edges. The load was applied
gradually with a constant incremented rate of 10 KN. The numerical analysis
was accomplished by a nonlinear finite element analysis (ABAQUS software)
and performed with the concrete damaged plasticity model (CDPM),
ABAQUS/Explicit. The compressive behavior and the tension behavior of the
concrete were modeled by Hognestad Parabola and Bilinear tensile stress versus
crack width respectively. The concrete was divided into brick elements (C3D8R)
to avoid the shear local effect and hour glassing effect, while the reinforcement
is modeled as a wire truss by (T3D2) embedded into the solid concrete elements.
As a result, greater efficiency of UHPC was shown against punching shear
failure. Provided the maximum load capacity for the four specimens which gives
failure loads a 30% increase relative to the ACI punching formula. The average
ultimate load for four specimens was increased by 81% relative to the load at the
first crack. In addition, the average deflection value at the ultimate stage for the