The Analysis of Shear Forces Flow around the Supports of Flat Slabs

2020 ◽  
Vol 309 ◽  
pp. 216-221
Author(s):  
Simona Šarvaicová ◽  
Viktor Borzovič
Keyword(s):  
Cross Section ◽  
Shear Resistance ◽  
Linear Analysis ◽  
Punching Shear ◽  
Shear Forces ◽  
Flat Slab ◽  
Flat Slabs ◽  
Eurocode 2 ◽  
Non Linear ◽  
Linear Shear

This paper deals with both linear and non-linear analysis of shear forces distribution in the area near the supports of the flat slabs. With a cross-section ratio of cmax / cmin > 3, the main amount of the shear stress is concentrated near the column or wall corners bases. As a consequence of this phenomenon, it is necessary to reduce the control perimeter when evaluating the punching shear resistance of a flat slab. The fragments of the flat slabs with the thickness of 200 mm supported by a wall with various loading conditions were analyzed. The results according to the Eurocode 2 were compared to a non-linear shear resistance evaluation that was calibrated based on the results from the previous experiments. Based on thus evaluated punching shear resistances, the theoretical reduced control perimeter was determined and subsequently it was compared to design model Eurocode 2. The physical basis for determining reduced control perimeters is based on the shear force concentration near the support.

scholarly journals NON-LINEAR ANALYSIS TO IMPROVE PUNCHING SHEAR STRENGTH IN FLAT SLAB USING Z-SHAPE SHEAR REINFORCEMENT

2019 ◽  
Vol 7 (1) ◽  
pp. 65-70
Author(s):  
Abdulnasser M. Abbas
Keyword(s):  
Shear Strength ◽  
Three Dimensional ◽  
Linear Analysis ◽  
Punching Shear ◽  
Stress Concentrations ◽  
Structural Behaviour ◽  
Shear Forces ◽  
Construction Time ◽  
Flat Slab ◽  
Non Linear

Currently, flat slabs become one of the widely used structures due to its architectural benefits such as uncomplicated formwork, flexibility and minimum construction time. However, these structures are relatively weak to resist the punching shear due to a considerable lowering in stiffness induced from the development of cracks that resulting from axial and seismic loads. Moreover, the punching failure is considered a brittle failure caused by the transferring of unbalanced moments and shear forces between the structural members. Unfortunately, this may cause a catastrophic collapse, especially in the region of the slab-column. Therefore, many experimental and theoretical studies were done to improve the punching strength of the flat slab. In the current work; a finite element three-dimensional non-linear analysis has simulated by ABAQUS tool to investigate the structural behaviour of flat slab. Two specimens have considered, the first is a flat slab reinforced by ordinary steel reinforcement. While in the second one, a Z-shape shear rebar improvement has been added to the slab-column connection. The proposed model has reflected a reasonable enhancement to the flat slab. The analysis considers different parameters such as punching shear forces, deformations, and stresses of Von-Mises. The outcomes indicate that punching shear strength is increased by approximately 11.1%, and the deflections are decreased by 77.3% when the Z-shape reinforcement is used. In the meantime, stress concentrations were reduced and move from the slab-column connection.

Reconstruction Effectiveness of Locally Supported Flat Slabs to Increase in Shear Resistance

2020 ◽  
Vol 309 ◽  
pp. 246-251
Author(s):  
Mária Bolešová ◽  
Katarína Gajdošová ◽  
Marek Čuhák
Keyword(s):  
Shear Stress ◽  
Numerical Models ◽  
Shear Resistance ◽  
Reconstruction Method ◽  
Detailed Calculation ◽  
Shear Reinforcement ◽  
Flat Slab ◽  
Advantages And Disadvantages ◽  
Flat Slabs ◽  
Eurocode 2

The most used horizontal load-bearing systems in concrete buildings are flat slabs. The effective and economic reconstruction of a locally supported flat slab of an existing building creates a complex task. Shear stress arises near the column and it becomes critical in design with increasing slab slenderness and requires a more detailed calculation. Increasing in the shear resistance of the flat slab can be achieved in various ways. Each method brings different effectiveness, advantages and disadvantages. The most widely used methods of the reconstruction are the increase in the size of the column (therein increasing the control perimeter for displaying the shear stress), the increase in the thickness of the flat slab or reinforcing the slab with shear reinforcement. Bolts and screw anchors (using different mounting angles) can be used as shear reinforcement. Each mentioned reconstruction method should be subjected to numerical calculations and verification of its efficiency. The parametric study presented in this paper is focused on the reconstruction techniques and their verification according to various numerical models. The results from Eurocode 2, fib Model Code 2010 and the new generation of Eurocode 2 are compared to show the differences between them. The aim of this paper is to bring a demonstration of the reconstruction methods that will increase in the shear resistance of the locally supported flat slabs and trying to choose the most effective one.

scholarly journals Experimental verification of punching shear resistance of flat slab fragments

2021 ◽  
Vol 30 (4) ◽  
Author(s):  
Simona Šarvaicová ◽  
Viktor Borzovič
Keyword(s):  
Reinforced Concrete ◽  
Experimental Verification ◽  
Shear Resistance ◽  
Linear Analysis ◽  
Punching Shear ◽  
Test Results ◽  
Loading Test ◽  
Design Models ◽  
Flat Slab ◽  
Standard Design

The paper deals with the loading test results of an experimental reinforced concrete flat slab fragment, which was supported by an elongated rectangular column. The slab specimens were 200 mm thick and were designed without any shear reinforcement. By experimentally obtained punching shear resistance, the accuracy of the standard design models for prediction punching resistance was compared. The results of the experiments were also compared with the results of a numerical non-linear analysis performed in the Atena program.

scholarly journals Theoretical prediction of punching shear capacity of flat slabs without shear reinforcement strengthened by concrete topping

2021 ◽  
Vol 1203 (2) ◽  
pp. 022108
Author(s):  
Daniel Čereš ◽  
Katarína Gajdošová
Keyword(s):  
Shear Resistance ◽  
Design Guidelines ◽  
Shear Capacity ◽  
Reinforcement Ratio ◽  
Punching Shear ◽  
Shear Reinforcement ◽  
Model Code ◽  
Flat Slabs ◽  
Eurocode 2 ◽  
Model Code 2010

Abstract The main reasons for strengthening flat slabs are the change of the use of a building, increase in the value of loads, degradation of the concrete cover layer, or insufficient reinforcement. This paper is focused on the assessment of punching shear capacity of the strengthened flat slabs without shear reinforcement. One of the possibilities how to enhance punching shear capacity is the addition of reinforced concrete topping. The main goal of this paper is to compare the possibilities for calculation of the increase in the punching shear capacity by investigation of the influence of different thicknesses of concrete toppings and different reinforcement ratio. A reference specimen is represented by a fragment of a flat slab with the thickness of h = 200 mm supported by circular column with the diameter of 250 mm. Three different thicknesses (50 mm, 100 mm, 150 mm) of concrete toppings were considered together with three different reinforcement ratios for each thickness of concrete overlay. Theoretical predictions of the punching shear resistance of flat slabs were evaluated by design guidelines according to the relevant standards: Eurocode 2 (EN 1992-1-1), Model Code 2010 and draft of the second generation of Eurocode 2 (prEN 1992-1-1). The differences in the influence of reinforcement ratio are significant. In Model Code 2010 the reinforcement ratio in concrete topping was considered in equation of moment of resistance. This is unlike in both of the mentioned Eurocodes, where the reinforcement ratio was assumed as a geometric average value of the original reinforcement ratio in the slab before strengthening and of the reinforcement ratio of concrete topping. All the predicted theoretical calculations are based on the perfect connection and bond between the original and new layer of concrete. These predictions should be verified by experimental investigation, which is going to be prepared shortly. By the additional increase in the thickness of concrete topping or in the amount of added reinforcement the attention should be payed to the limitation of the punching shear resistance by the value of the maximum punching shear resistance in the compression concrete strut.

scholarly journals The influence of a column shape cross-section on the punching capacity

2019 ◽  
Author(s):  
Simona Sarvaicova ◽  
Viktor Borzovic ◽  
Tomas Augustin
Keyword(s):  
Cross Section ◽  
Shear Failure ◽  
Shear Crack ◽  
Rectangular Cross Section ◽  
Linear Analysis ◽  
Linear Modeling ◽  
Model Code ◽  
Eurocode 2 ◽  
Non Linear ◽  
Comparison Of The Results

The article deals with non-linear modeling of slab-column connection which represents a fragment of flat slab supported by a column and loaded up to the punching shear failure. The aim of this parametrical study is the analysis of the length of reduced control perimeters in the case of columns with significantly elongated rectangular cross-section. The non-linear analysis was performed in program Atena and calibrated by test results obtained from the laboratory experiments carried out at Slovak University of Technology in Bratislava. The results of non-linear analysis are compared with the values of shear resistance calculated according to the current Eurocode 2 model; fib Model Code 2010 and model proposed for the second generation of Eurocode 2 based on the Critical shear crack theory. The reliability of the models is evaluated by comparison of the results of numerical analyses and previously mentioned design models.

scholarly journals Design considerations on the influence of slab continuity on punching resistance of flat slabs

2020 ◽  
Vol 13 (6) ◽  
Author(s):  
Fernanda Gabriella Batista Santos Oliveira ◽  
Luis Fernando Sampaio Soares ◽  
Robert Lars Vollum
Keyword(s):  
Shear Crack ◽  
Floor Plate ◽  
Punching Shear ◽  
Fe Modelling ◽  
Flat Slab ◽  
Design Considerations ◽  
Flat Slabs ◽  
Shear Design ◽  
Eurocode 2 ◽  
Modelling Assumptions

abstract: This paper assesses the influence of slab continuity on the punching resistance of a realistically proportioned flat slab floor plate without shear reinforcement. The edge column punching resistance of a symmetric flat slab extending bays in each direction was assessed by means of NLFEA with TNO DIANA, MC2010 levels II, III, IV, Eurocode 2 and NBR 6118. Both Eurocode 2 and NBR 6118 are seen to give similar predictions for punching resistance, while MC2010, which is based on the Critical Shear Crack Theory and depends on how rotations are calculated and FE modelling assumptions, varies significantly with its levels of approximation with Level IV agreeing reasonably well with predictions from NLFEA. Direction for the critical rotations is shown to vary and can also be influenced by the reinforcement over the span. For EC2, NBR 6118 and MC2010 LoA II and III punching shear design are independent of span, unlike the results obtained with MC2010 LoA IV.

scholarly journals Strengthening flat slabs without shear reinforcement against punching shear by concrete overlay

2021 ◽  
Vol 1209 (1) ◽  
pp. 012056
Author(s):  
D Čereš ◽  
K Gajdošová
Keyword(s):  
Parametric Study ◽  
Shear Crack ◽  
Shear Resistance ◽  
Shear Capacity ◽  
Reinforcement Ratio ◽  
Punching Shear ◽  
Flat Slab ◽  
Model Code ◽  
Eurocode 2 ◽  
Model Code 2010

Abstract Research in this paper presents a theoretical study of increasing in punching shear capacity of the strengthened flat slab by concrete overlay. The parametric study is based on comparison of three different relevant standards design models and presents results how Eurocode 2 (EN 1992-1-1), Model Code 2010 and draft of second generation of Eurocode 2 (prEN 1992-1-1) take into account strengthening by concrete overlay. A reference specimen is represented by a fragment of a flat slab supported by circular column. Influence of concrete toppings depends on thickness and also on reinforcement ratio. In Eurocode 2 and new generation of Eurocode 2 the increase of punching shear resistance of the slab with concrete topping can be taken into account only by reinforcement ratio and thickness of the slab considering the perfect connection and bond between the original slab and new layer of concrete overlay. Model Code 2010 is based on Critical shear crack theory and the reinforcement ratio in concrete topping was considered in equation of moment of resistance and punching shear resistance is calculated by considering the rotation and deformation of the slab. Estimation of results by parametric study are compared by non-linear model from Atena software.

scholarly journals Slabs strengthened for punching shear with post-installed steel and CFRP connectors

2019 ◽  
Vol 12 (3) ◽  
pp. 445-478
Author(s):  
M. J. M. PEREIRA FILHO ◽  
M. V. P. FREITAS ◽  
D. F. A. SANTOS ◽  
A. J. C. NASCIMENTO ◽  
M. P. FERREIRA
Keyword(s):  
Shear Resistance ◽  
Experimental Results ◽  
Punching Shear ◽  
Design Codes ◽  
Shear Reinforcement ◽  
Shear Strengthening ◽  
Flat Slab ◽  
Design Recommendations ◽  
Eurocode 2 ◽  
Shear Failures

Abstract Structural accidents due to punching shear failures have been reported in flat slab buildings. Design recommendations presented by codes can lead to entirely different punching shear resistance estimates for similar situations. Furthermore, design codes do not present guidelines for the design of punching shear strengthening of existing slabs. This paper uses a database with 118 experimental results to discuss the performance of theoretical estimates of punching shear resistance using ACI 318, Eurocode 2 and ABNT NBR 6118 in the case of slabs without shear reinforcement. Another database with results of 62 tests on slabs strengthened with post-installed steel and CFRP dowels is used to evaluate the performance of these strengthening techniques and to propose adaptations in codes to allow their use in punching shear strengthening situations of existing slab-column connections.

Design of Flat Slabs Height

2015 ◽  
Vol 1106 ◽  
pp. 221-224
Author(s):  
Ľudovít Fillo ◽  
Jana Labudková ◽  
Ján Hanzel
Keyword(s):  
Shear Resistance ◽  
Punching Shear ◽  
Shear Forces ◽  
Flat Slabs

Results of latest experiments have revealed that the maximum punching resistance defined from crushing of concrete struts at the perimeter of a column is an insufficient criterion for limitation of maximum shear forces at the vicinity of the columns. Therefore further limitation has been recommended by CEN TC250 SC2 and introduced in STN EN 1992-1-1/NA [1]. The paper will deal with the new requirements concerning the maximum punching shear resistance, based on the kmax factor and design of min flat slabs height.

scholarly journals Non-linear analysis of slab-column connections with openings

2019 ◽  
Author(s):  
Ludmila Kormosova ◽  
Tomas Augustin ◽  
Jaroslav Halvonik
Keyword(s):  
Cross Section ◽  
Linear Models ◽  
Linear Analysis ◽  
Transverse Reinforcement ◽  
Flat Slab ◽  
Analysis And Design ◽  
Non Linear ◽  
Testing Accuracy ◽  
Rectangular Columns ◽  
General Method

This paper is focused on the assessment of punching capacity of the slab-column connections without transverse reinforcement with openings located close to a column. Non-linear analysis and design equations from the relevant codes of practise are used for the prediction of the punching resistance of flat slab specimens supported by the rectangular columns with different ratio h/d of the column’s cross-section. The non-linear models were calibrated using experimental results from the laboratory tests. The main goal of the study is an investigation of the effect of the openings on the punching capacity and as well as testing accuracy of the design equations for the prediction of the punching resistance. Several methods for the reduction of the control perimeter length accounting for presence of the openings were tested in order to find the most general method for the estimation of the punching capacity. However, standard methods introduced in the relevant codes of practise provide very inconsistent results concerning of the model’s safety for different position of the openings as well as for different cross-section of the columns. Therefore modification of the methods was proposed and verified using obtained results.

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