Therefore it is crucial to check for punching shear and to provide sufficient reinforcement to take care of it. Reinforcements should be provided in addition to the main reinforcements. This punching shear must not be neglected though it is less critical than the beam shear. The kind of reinforced concrete slab is a punching shear that is governed by high localized force. In the case of flat structures, this happens at column support points.
For determining maximum punching shear stress, the applied shears and moments, along with the shape of the punching shear failure cone, are utilized.
Punching shear failure is a type of failure occurs in a soil of very high compressibility. This type of failure is characterized by very large settlement. This type of failure mostly found in flat slabs. Some examples of poor drainage include short downspouts clogged gutters , or lack of waterproofing. Join Join TheConstructor to ask questions, answer questions, write articles, and connect with other people.
The program considers as many as nine different punching shear perimeters for each column in the model. We look at the interior, four edges, and four corner cases and determine which configuration produces the largest code check and present that in the results.
Here the program will also check out any EDGE punching shear perimeter considerations. The two below would be the most likely ones for this given geometry. In most cases these odd situations will not govern. However, large moments in a given direction can cause punching shear perimeters with larger areas to govern in specific cases.
The one below would be the most likely for this given geometry. Whichever configuration produces a maximum code check will be reported in the punching shear results. When the program tests all different cases to determine whether a corner or edge situation governs, it bases the controlling case on the maximum code check produced. There are cases where an edge case is governing that by inspection you might think it would be a corner case. See the images below:. In these two punching shear scenarios shown above, by inspection you would likely expect the corner condition to control over the edge ones.
Punching shear capacity is based on a minimum of three equations in the ACI code. One of these equations has an alpha term in it, where alpha is smallest for a corner condition. If this equation governs, this would guarantee the corner condition would have the smallest capacity.
However, if this equation does not govern then these capacities may not be as different as you might expect. Also, the demand portion of the equation will be different based on the geometry of the shear perimeter. It is possible that the edge cases produce a larger maximum stress than the corner cases.
In flat slab structures, this occurs at column support points. The failure is due to shear. This type of failure is critical because no visible signs are shown prior to failure. In this release, the designer can check if the required longitudinal slab or foundation reinforcement is adequate to resist the local shear force at the support. Moreover, the designer can proceed with the calculation and design the required shear reinforcement around the support, if necessary. The main components of the model are concrete slab, loading steel plate and subsoil.
The finite element mesh has regular shape and consists of cubical elements. It is formed by a generator. The load is induced by force. The created calculation model is shown in Fig. The modelled reinforcement is shown on Fig. The obtained set of nonlinear equations is solved using the arc-length method.
The solution of one option of the calculation task took 6—8 h. Following the nonlinear analysis the total load capacity and failure mode can be evaluated. Selected graphical results are provided in Fig. The achieved total slab load capacity for the different options is indicated in Table 4. Detailed analysis of the graphical results leads to a statement that the slab collapse mode is similar to that observed in the experiment.
The concrete slab suffered punching shear failure. The crack development for 3D visualization just before the collapse can be seen in Fig. The slab load capacity ranged between and kN. The maximum difference in the slab load capacity due to different subsoil load capacity was about 25 kN.
The difference is more remarkable in case of input parameters for concrete in which case a difference up to 88 kN was observed. The article deals with research in the field of analysis of concrete slabs with low thickness exposed to high load in interaction with subsoil. In these cases the typical approach to the concrete structure designing using verification models may not be optimal. The article and research presented comprise test of concrete slab followed by calculation of total load capacity in options based on existing design model code EC2 and nonlinear analysis using the finite element method.
The tested slab failed by punching shear at a force of kN and an average distance of 1. The irregular shape can be a result of inhomogeneous subsoil or also quicker progress of cracks on one side of the slab at higher load intensities.
The test is documented in detail using record of deformation measurements. This is followed by detailed analysis of the slab failure for which purpose the slab was cut to eight pieces.
The theoretical calculated value according to EC2 for the punching shear resistance was The real value of shear resistance is, as expected, larger than according to Eurocodes and the crack is in lower distance than according to Eurocodes. This means that Eurocodes are on the safe side. In this case the real resistance was more than five times higher than the calculated value.
However the foregoing facts confirm that the design punching shear resistance according to Eurocodes is very safe, maybe too safe. The approach using the calculation of load capacity of tested slab with influence of contact surface is also described. The application of verification models was followed by the advanced nonlinear analysis to determine the total load capacity. The analysis comprised application of 3D calculation model and fracture-plastic material. The use of created numerical model enabled a very good simulation of real behaviour of the slab.
The calculated total slab load capacity for mean values was very similar to that observed in the experiment. The collapse mode was also covered very well in the numerical model. The differences between the experiment and numerical modelling results can be attributed to the spread and uncertainties in the input concrete and subsoil parameters. The use of relations for specific concrete properties described in Model Code proved useful.
However, it should be noted that the calculations required by the nonlinear analysis are time and computationally consuming. For numerical computations, it is so ideal to use HPC High-performance computing. Because of that the nonlinear analysis is fit only in specific cases such as reconstructions and optimized designs where the use of typical verification models would not be appropriate.
It is also important to reflect the design and project criteria using, for example, global safety format, etc. Aboutalebi, M. Structural behaviour and deformation patterns in loaded plain concrete ground-supported slabs. Structural Concrete, 15 1 , 81— Article Google Scholar. Alani, A. Mechanical properties of a large scale synthetic fibre reinforced concrete ground slab. Construction and Building Materials, 41, — Finite element analysis of reinforced concrete.
State of the Art Rep. Barzegar, F. Layering of RC membrane and plate elements in nonlinear analysis. Journal of the Struct. Bazant, Z. Microplane model M4 for concrete.
I: Formulation with work-conjugate deviatoric stress. Fracture and size effect in concrete and other quasibrittle materials. Google Scholar. Determination of the punching cross-section of reinforced concrete flat slabs.
Periodica Polytechnica Civil Engineering. Cajka, R. Comparison of the calculated and experimentally measured values of settlement and stress state of concrete slab on subsoil.
Applied Mechanics and Materials, , — Cervenka, V. Pratur: Cervenka Consulting. Cervenka, J. Three dimensional combined fracture-plastic material model for concrete.
International Journal of Plasticity, 24 12 , — Halvonik, J. The maximum punching shear resistance of flat slabs. Procedia Engineering, 65, — Hegger, J.
Investigations on the punching behaviour of reinforced concrete footings. Engineering Structures, 29, — Experimental investigations on punching behavior of reinforced concrete footings. ACI Structural Journal, , — Hoang, L. Punching shear capacity of reinforced concrete slabs with headed shear studs. Magazine of Concrete, 68 3 , — Husain, M. Alternatives to enhance flat slab ductility.
International Journal of Concrete Structures and Materials, 11 1 , — Ibrahim, M. Three-dimensional finite element analysis of reinforced concrete slabs strengthened with epoxy-bonded steel plates. Advances in Concrete Construction, 2 2 , 91— General principles on reliability for structures, ISO Probabilistic model code.
Modelling of soil-structure interaction.
0コメント