Punching Capacity of UHPC Post Tensioned Flat Slabs with and Without Shear Reinforcement: An Experimental Study

Abstract

Punching capacity is one of the main items in the design of both pre-stressed and non-pre-stressed flat slabs. All international design codes include provisions to prevent this type of failure. Unfortunately, there is no code provision for UHPC yet, and hence, the aim of this research is to experimentally investigate the impact of column dimensions and punching reinforcement on the punching capacity of post-tensioned slabs and compare the results with the international design codes’ provisions to evaluate its validity. The test program included five slabs with a compressive strength of 120 MPa: one as a control sample, two to study the effect of column size, and the last two to study the effect of punching reinforcement. Comparing the results with the design codes showed that ACI-318 is more accurate with an average deviation of about 5%, while EC2 is more conservative with an average deviation of about 20%. Besides that, punching reinforcement reduces the size of the punching wedge by increasing the crack angle to 28° instead of 22° for slabs without punching reinforcement. Also, the results assure that both ductility and stiffness are enhanced with the increased column dimensions and punching reinforcement ratio. Doi: 10.28991/CEJ-2023-09-03-06 Full Text: PDF

Machine learning base models to predict the punching shear capacity of posttensioned UHPC flat slabs

“…Phase-1 was concerned in developing a typical FEM model for PT-UHPC flat slab considering concrete compressive strength (Fcu), strands layout (in terms of the average pre-stressing stress in the punching zone) (Fps), shear reinforcement capacity (Ash.Fy) and the aspect ratio of the column (L/B). Then the developed model was validated using the experimental results from the previous research work 2 , 3 .…”

“…The developed typical FEM model will be validated against the experimental results of monotonic testing of nine PT-UHPC flat slabs from previous studies by the same research group 2 , 3 . The dimensions of all tested slabs were 1000 mm × 1000 mm in plan and thickness of 120 mm, they all had four 0.5″ posttensioning strands in each direction stressed up to net effective stress of 800 MPa after losses.…”

“…In compression, concrete is linear elastic and defined by the concrete Young’s modulus according to experimental tests and concrete Poisson’s ratio (ν) 2 , 3 .…”

“…Punching shear behaviour of the Column-slab connection using the normal reinforced concrete is usually sudden brittle failure due to the stress concentration at the small area surrounding the column. Thus, continuous research effort is performed to validate the current design recommendations available by different international design codes to make advantage of the advanced construction materials and the construction methods in such critical failure criterion 1 – 3 . The most common methods to avoid the brittle failure in the column-slab connections are to increase the slab or/and column dimensions using various strategies including the column head and/or drop/up panel which is not always effective especially in large spans or heavy loads in industrial buildings, bridges and even raft foundations.…”

“…Afifi et al 3 compared the results of the experimentally testes post-tensioned UHPC flat slabs with the predicted ultimate punching shear using the available equations in ACI and EC2 that showed the significant difference between the predicted and the experimental results. The ACI.…”