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Research Paper

International Journal of Informative & Futuristic Research ISSN (Online): 2347-1697

Volume 2 Issue 9 May 2015

Abstract During an earthquake, a brittle punching failure can arise in flat plate-column connections due to poor transfer capacity of shearing forces and unbalanced moments. To increase the shear capacity of the slab, various types of shear reinforcement can be used in the slab around the connection. The aim of the project is to study the response of slab column connections containing with various slab shear reinforcement when subjected to combined gravity and cyclic lateral loading. At first a calibration model was developed to simulate the tested flat plate-column joint using finite element analysis program MASA. This model was used to predict the load displacement behaviour. The results showed that the model predicts the load level excellently but significantly over estimates the stiffness of the joint compared to that observed by James Lee & Ian Robertson. Since the present study is to compare the relative behaviour of slab-column joints provided with various slab shear reinforcement, the error in the estimation of joint stiffness will not alter the comparative conclusions drawn. Thus, the developed model was validated for application to various types of column slab connection behaviour.

Study On Behaviour Of Flat Plate

Column Connection With Various Types

Of Slab Shear Reinforcement Paper ID IJIFR/ V2/ E9/ 007 Page No. 2988-2999 Subject Area

Structure

Engineering

Key Words Lateral Cyclic Loadings, Flat Plate, Slab Column Joint, Punching Shear, Drift

S. Kavitha 1

M.Tech Scholar Department of Structure Engineering ACS College Of Engineering , Bengaluru, Karnataka-India

Umadevi. R 2

Assistant Professor Department of Structure Engineering ACS College Of Engineering , Bengaluru, Karnataka-India

Sugandha. N 3

Assistant Professor Department of Structure Engineering ACS College Of Engineering , Bengaluru, Karnataka-India

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ISSN (Online): 2347-1697 International Journal of Informative & Futuristic Research (IJIFR)

Volume - 2, Issue - 9, May 2015 21st Edition, Page No: 2988- 2999

S.Kavitha, Umadevi. R and Sugandha. N :: Study on Behaviour of Flat Plate Column Connection with Various Types of Slab Shear Reinforcement

1. Introduction

Flat plate is one of the most common floor systems for large span commercial buildings. The

advantages of a flat-Plate floor system are numerous. It provides architectural flexibility, more clear

space, less building height, easier form work, and, consequently, shorter construction time. Low

floor to floor heights reduce the total building height, thus reducing lateral loads, cost of building

cladding, cost of vertical mechanical and electrical lines, and air conditioning/heating costs. For

vertical loads, the structural performance and design of flat plates are well established. Under lateral

loads, many aspects of the behavior of flat plates are uncertain. A serious problem that can arise in

flat plates is brittle Punching Shear failure due to poor transfer capacity of shearing forces and

unbalanced moments between slabs and columns. In seismic zones, a structure can be subjected to

strong ground motions, and, for economical design, a structure is considered to undergo

deformations in the inelastic range, therefore, in addition to strength requirement, slab-column

connections must undergo these inelastic deformations without premature punching or shear failure.

In other words slab column connections must have adequate ductility.

2. Methodology

Literature review on studies of slab column joints and Finite element analysis of reinforced

concrete structures.

Developing of calibration model to simulate the tested flat plate-column connections.

Developing of finite element model to study the behavior of flat plate-column connections

without slab shear reinforcement.

Come up with recommendations to improve the ductility of flat plate column joint under

seismic loads.

3. Various Types Of Shear Reinforcements

Table 1: Types Of Shear Reinforcements

Sl.no. Abbreviation Description

1 NS No slab shear reinforcement (Fig .5)

2 SLS_I Single leg stirrups spread over a width equal to the column width in both the

directions. (Fig 6)

3 SLS_II Single leg stirrups spread over a width equal to six times the column width in

both the directions. (Fig 7)

4 LCY_I Inclined leg lacing type shear reinforcement as shown in Fig 8.

5 LCY_II 5 Inclined leg lacing type shear reinforcement spread over a width equal to six

times the column width in both the directions as shown in Fig 9.

6 VLCY Vertical leg lacing type shear reinforcement spread over a width equal to six

times the column width in both the directions as shown in Fig 10.

3.1 Analysis model

An interior flat plate column connection is considered for the analysis. The geometry and the

reinforcement details are as shown in the figures 1 and 2 respectively. M30 grade of concrete, Fe

415 grade of steel for main reinforcement and Fe 250 grade steel for shear reinforcement are adopted

in the analysis. The column is modeled with linear elastic material so as not to yield prior to slab

flexural yielding. Finite element modeling package, FEMAP is used to model the Flat plate column

joint. Following are the steps involved in the modeling of joint.

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Solid elements are used to model concrete and bar elements are used to model

reinforcement.

Slab is allowed to translate in loading direction alone and constrained in other (Y & Z)

directions. Gravity load is applied on the slab in the form of point loads.

Bottom of the column is hinge supported and the predetermined cyclic lateral displacement

routine is applied at the top of the column.

The Bond to the reinforcement is modeled by inputting Bond-Slip curve in the analysis.

The finite element model developed in FEMAP is transferred to MASA for the analysis.

The finite element mesh for the analysis model is as shown figure 3. The location of constraints and

points of loading are shown in the figure 4. The figures from 5 to 10 show the reinforcement layout

for models with various types of slab shear reinforcement

Plan view

Figure 1: Geometry of Slab column connection

Column Slab

Figure 2: Reinforcement details for the analysis model

Side view

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Side View Isometric View

Figure 3: Finite element mesh for the Analysis Model

Figure 4 : Loading and Constraints

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Figure 5 :Reinforcement Layout for model Figure 6: Reinforcement Layout for model

without slab shear reinforcement (NS) with single leg stirrups (SLS_I)

Figure 7: Reinforcement Layout for model

with single leg stirrups (SLS_II)

Figure 8 Reinforcement Layout for model

with inclined-leg Lacing (LCY_I)

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The cyclic lateral displacement routine is applied at the top of the column for all models.

The lateral displacement routine used in the analysis is shown figure 11.

Figure 11: Lateral displacement routine used in the analysis

4. Results Of Analysis Model

The hysteretic load deformation curves for Flat plate-column models with various types of

Slab shear reinforcement is plotted as shown below.

Figure 9 : Reinforcement Layout for model with

inclined-leg Lacing (LCY_II) Figure 10: Reinforcement Layout for model with

vertical-leg Lacing (VLCY)

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Figure 12 : Load deflection hysteretic curve for model without slab shear reinforcement (NS)

Figure 13: Load deflection hysteretic curve for model with single leg stirrups (SLS_I)

Figure 14 : Load deflection hysteretic curve for model with single leg stirrups (SLS_II)

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Figure 15 : Load deflection hysteretic curve for model with inclined-leg Lacing (LCY_I)

Figure 16: Load deflection hysteretic curve for model with inclined-leg Lacing (LCY_II)

Figure 17: Load deflection hysteretic curve for model with vertical-leg Lacing (VLCY)

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The figure 18 shows the deformed Shape for the model without slab shear reinforcement (NS).

Side view

Figure 18 Deformed Shape for the model without slab shear reinforcement (NS)

The figures 19 and 20 show the crack pattern and stresses in reinforcing bars at the joint respectively

observed in the model without slab shear reinforcement.

Figure 19 : Crack pattern for the model without slab shear reinforcement (NS)

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Figure 20: Stresses in reinforcing Bars at the joint (NS)

Analysis results from MASA are shown in table 4.2. This table shows lateral load sustained by the

various models and corresponding displacement both at peak and at the ultimate.

Table 2: Analysis results for FE models with various types of slab shear reinforcement

Type of Shear

Reinforcement

Cycle Peak

Lateral

Load

Displacement

at Peak Load

Lateral Load

at Ultimate

Displacement at

Ultimate Load

(kN) (mm) (kN) (mm)

NS Positive 18.07 12.00 12.22 24.00

Negative -15.84 -8.00 -6.48 -24.00

SLS_I Positive 21.81 16.00 17.74 28.00

Negative -17.34 -12.00 -9.68 -24.00

SLS_II Positive 21.50 16.00 21.14 20.00

Negative -17.23 -12.00 -12.70 -32.00

LCY_I Positive 19.48 12.00 15.54 20.00

Negative -16.72 -12.00 -9.82 -32.00

LCY_II Positive 19.84 12.00 11.89 28.00

Negative -16.61 -8.00 -14.92 -24.00

VLCY Positive 20.59 12.00 12.66 28.00

Negative -16.61 -8.00 -12.72 -28.00

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5. Conclusions

Three calibration models are developed to validate the finite element modeling and analysis

software’s FEMAP and MASA respectively. Six interior flat plate-columns connections with various

types of slab shear reinforcement are modeled and analysed under combined gravity and cyclic

lateral loading. Based on comparison of the results of these models, the following conclusions are

drawn:

Punching shear failure can arise in case of flat plate-column joint without slab shear

reinforcement. It is brittle failure which reduces lateral load carrying capacity of

connection suddenly.

All types of slab shear reinforcement, namely, single-leg stirrups (SLS_I & SLS_II) and

lacing type shear reinforcement (LCY_I, LCY_II & VLCY), are effective in resisting

punching shear failure of the flat plate-column joint under combined gravity and cyclic

lateral loading.

Use of Slab shear reinforcement improves the overall behaviour of the connection in

terms of ductility, energy dissipation capacity, resisting punching failure and drift

capacity.

The ductility of the joint under monotonic loads is significantly higher than that under

cyclic loading. Under Monotonic loading use of slab shear reinforcement does not affect

much the behaviour of connection.

Grade of steel of slab shear reinforcement does not affect much the behaviour of the

connection.

Both lacing type and single leg stirrups are effective in improving the overall behaviour

of the connection but lacing type shear reinforcement is recommended since it is easy to

install and does not require welding which suits Indian site conditions.

References

[1] ACI Committee 318 (2005), “Building Code Requirement for Reinforced Concrete and Commentary,”

American Concrete Institute, Farmington Hills, USA.

[2] Amin Ghali., and Ramez B. Gayed. (2006), “Seismic-Resistant Joints of Interior Columns with

Prestressed Slabs,” ACI Structural Journal, Vol. 103, No.5, September-October 2006, pp. 710-719.

[3] Austin D. Pan., and Jack P. Moehle. (1992), “An Experimental Study of Slab-Column Connections,” ACI

Structural Journal, Vol. 89, No.6, November-December 1992, pp.626-638.

[4] Carl Erik Broms. (2007), “Flat Plates in Seismic Areas, Comparison of Shear Reinforcement Systems,”

ACI Structural Journal, Vol. 104, No.6, November-December 2007, pp. 712-721.

[5] Carl Erik Broms. (2007), “Ductility of Flat Plates, Comparison of Shear Reinforcement Systems,” ACI

Structural Journal, Vol. 104, No.6, November-December 2007, pp. 703-711.

[6] Fanning P. (2001), “Nonlinear Models of Reinforced and Post-tensioned Concrete Beams,” Electronic

Journal of Structural Engineering.

[7] Fee Kiong Lim., and B. Vijaya Rangan. (1995), “Studies on Concrete Slabs with Stud Shear

Reinforcement in Vicinity of Edge and Corner Columns,” ACI Structural Journal,Vol. 92, No.5,

September-October 1995, pp. 515-525.

[8] Hong-gun Park., Kyung-soo Ahn., Kyoung-kyu Choi., and Lan Chung., (2007)“Lattice Shear

Reinforcement for Slab-Column Connections,” ACI Structural Journal,Vol. 104, No.3, May-June 2007,

pp. 294-303.71

[9] Ian N. Robertson., Tadashi Kawai., James Lee., and Brian Enomoto. (2002), “Cyclic Testing of Slab-

Column Connections with Shear Reinforcement,” ACI Structural Journal, Vol. 99, No.5, September-

October 2002, pp. 605-613.

[10] Ian N. Robertson. (1997), “Analysis of Flat Slab Structures Subjected to Combined Lateral and Gravity

Loads,” ACI Structural Journal, Vol. 94, No.6, November-December1997, pp. 723-729.

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[11] IS 456 (2000), “Indian Standard Code of practice for plain and reinforced concrete,”Bureau of Indian

Standards, New Delhi.

[12] IS 1893 (part 1): (2002), “Indian standard Code of practice for Earthquake Resistant design of

structures,” Bureau of Indian Standards, New Delhi.

[13] IS 13920 (1993), “Indian Standard Code of practice for ductile detailing of Reinforced Concrete

structures subjected to seismic forces,” Bureau of Indian Standards, New Delhi.

[14] John F. Brotchie. (1980), “Some Australian Research on Flat Plate Structures,” ACI Journal, January-

February 1980, pp. 3-11.

[15] Ožbolt J. (2005), “MASA 3 Manual,” Institute für Werkstoffe im Bauwesen Universität Stuttgart 70550

Stuttgart, Germany.

[16] Sami Megally., and Amin Ghali. (1994), “Design Considerations for Slab-Column Connections in

Seismic Zones,” ACI Structural Journal, Vol. 91, No.3, May-June 1994, pp. 303-314.

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