study of r.c column strengthened by steel angles and ...c. analytical work using finite element...

Study of R.C Column Strengthened by Steel Angles and Strips Using ANSYS

Varsha R

P.G Student, Dept. of Civil Engineering

Vimal Jyothi Engineering College, Chemperi

Kannur, Kerala, India

Anuragi P Assistant professor, Dept. of Civil Engineering

Vimal Jyothi Engineering College, Chemperi

Kannur, Kerala, India

Abstract—The purpose of the paper is to study the behavior

and efficiency of reinforced concrete square column

strengthened by steel angle and strips. Finite element package

ANSYS 16.1 is used for the analysis. The column is a key

element that carries load from upper story down to

foundations. Sometimes, columns have not enough strength

due to inadequate shear reinforcements or splice length or bad

construction workmanship. Column capacity can also be

deteriorated by previous seismic action or fire. In these cases,

columns have to be locally strengthened to ensure life safety

using one of the following approaches; Additional reinforced

concrete layer, Ferro-cement jacketing, Fiber reinforced

polymer wrapping, Steel jacketing etc. Among them steel

jacketing is comparatively easy to install at site and also

effective to increase load capacity and the coefficient of

thermal expansion of steel and concrete are approximately

same. Finite element package ANSYS Workbench is used for

the analysis.

Keywords—Reinforced concrete column, Steel angles, Steel

strips

I. INTRODUCTION

Reinforced concrete is one of the most abundantly used construction material not only in the developed world, but also in the remotest parts. Column is one of the most important structural elements, which is designed to support mainly the compressive load. Losing load carrying capacity in the column, caused by strength deterioration or material deficit, may lead to catastrophic failure of structures. Column strengthening is therefore a very important aspect in a building structure. At present, rehabilitation considers as one of the most important and widespread aspects of civil engineering. Rehabilitation is a process, which is used to bring the deficient structure or any structural component to the pre-established performance level. Two main categories can be noticed in rehabilitation: repairing and strengthening. Strengthening is defined as the increase in the current capacity of the non-damaged structural component to another specified level. Now a days retrofitting, repairing, and restoring are the important aspect for structural engineering community. Retrofitting can be done by using the approach of local strengthening of structural elements (i.e. beams, columns) or global strengthening of structure (i.e. insertion of bracing or shear wall). Steel jacketing consists of four angles attached to corners of column and discrete steel plates with a specific spacing which are welded to the angles. Steel plates are termed as strips or also battens. Study has been carried out on column strengthened with steel angles and horizontal steel strip. But column strengthening with steel angles and inclined steel strips hasnot been studied yet. The purpose of the paper is to study the behaviour and efficiency of reinforced concrete square

column strengthened using steel angles and inclined strips. Finite element package ANSYS Workbench is used for the analysis.

A. Objectives

To conduct analytical investigation of R.C column strengthened with steel angles and strips

To evaluate the effectiveness of column strengthening using steel angle and strips

To compare the square column strengthened with steel angle and inclined strip with reference column and column strengthened with steel angles and horizontal strips

B. Scope

It is difficult to rebuild the column that may not have enough strength and it is also time consuming and uneconomical. The scope of the paper is,

To understand the efficiency of the column strengthened using steel angles and strips

To use this method for column strengthening

II. ANSYS

Ansys develops and markets finite element analysis software used to simulate engineering problems. Most Ansys simulations are performed using the Ansys Workbench software.

III. STRENGTHENING OF COLUMN

A. Specimen Details

The analytical work consisted of a total 11 square column. Concrete columns were cast satisfying the condition for short column (l/b<12).M25 grade concrete were used for casting column. All column were of the same size 250x250x1000mm, this were designed as per IS 456-2000.The columns consist of 4nos of 20mm diameter longitudinal bars which were tied using 6mm bars at a spacing of 120mm.The column is fixed at one end and free at the other end.

Fig 1. Steel angle

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 14, Number 12, 2019 (Special Issue) © Research India Publications. http://www.ripublication.com

Page 90 of 94

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The columns were strengthened by four steel angles and steel strips which were welded to the longitudinal angles at equal intervals. Steel angle is shown in Fig.1. The gap left between the steel angles and strips was filled with cement grout. The angles used were 50mm equal angles having thickness of 5mm.The strips used were of size 50x250mm having 5mm thickness.

B. Study case

The case examined here is that of a concrete member with a square cross-section with side b strengthened with steel angles with side L1, and thickness t1 and with steel battens with height S2 and thickness t2 placed at pitch S. The whole length of the column is L. The columns were subjected to an axial load N. The presence of pre-existing of n longitudinal bars of diameter db and transverse stirrups of diameter φst placed at pitch Sst was also considered. Detailed and useful geometrical rules for the design of steel caging are: L1 ≥ 0.2b and t1 ≥ 0.1L1= 0.02b. Eurocode 8 prescribes that the spacing between two successive steel strips should be at least b/2.

C. Analytical Work Using Finite Element Model

The finite element package Ansys workbench 16.1 was used for the study by introducing a numerical model. A total of 8 finite element models were developed to study the behaviour of these columns by using static structural. All are square column of size 250x250x1000mm fixed at one end and free at other end. An axial load of 1500kN is acting on the column. The steel angle used for strengthening is hot rolled equal steel angle of size 50x50mm having 5mm thickness. And the strips used are of size 50x250mm with 5mm thickness. Total deformation and shear stress of different columns models are compared and studied.

IV. MODELLING AND ANALYSIS

Details of models are given in Table 1. TABLE 1. DETAILS OF MODELS

Model

Name

Representation

Model 1

Reference column

RC

Model 2

Column strengthened by steel angle and horizontal strips @ 125mm spacing

SC 90

Model 3

Column strengthened by steel angle and inclined strips at an angle of 600 @ 125mm spacing

SC 60

Model 4


SC 70

Model 5


SC 80

Engineering properties of concrete, structural steel for reinforcement and structural steel for steel angles and strips are shown in Table 2, Table 3 and Table 4 respectively.

TABLE 2. ENGINEERING PROPERTIES FOR CONCRETE

Density (kg/m3)

Young’s modulus (MPa)

Poisson

ratio

Tensile ultimate Strength (MPa)

Compressive

ultimate strength (MPa)

2500

25000

0.2

3.125

25

TABLE 3. ENGINEERING PROPERTIES FOR REINFORCEMENT STEEL

Young’s modulus (MPa)

Poisson

ratio

Tensile yield stress (MPa)

Compressive

yield Strength (MPa)

Tensile ultimate strength (MPa)

2.1x105

0.3

415

415

485

TABLE 4. ENGINEERING PROPERTIES FOR STEEL ANGLES AND STRIPS

Yield strength

(MPa)

Tensile strength

(MPa)

310

461.9

Models are created in geometric sections. Properties of the materials are assigned for geometry in the step, model in Ansys Workbench. Meshing of the column is done to get more accurate results which is shown in Fig 2. One end of the column is restrained in all three directions and other end is free. 1500kN concentrated load is applied on top face. Boundary condition and method of loading is shown in Fig 3

Fig 2. Meshing of model

Fig 3. support and loading condition


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V. RESULTS

A. Total Deformation

The total deformations for models are shown in Table 5 and in Fig 4 to Fig 8.

TABLE 5. TOTAL DEFORMATION

Fig 4. Total deformation- RC

Fig 5. Total deformation- SC 90



Model

Total deformation

(mm)

RC

0.82918

SC 90

0.69965

SC 60

0.70209

SC 70

0.70136

SC 80

0.70063


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The comparison diagram of total deformation is shown in Fig 9

Fig 9. Comparison diagram of Total deformation

B. Shear Stress

Obtained shear stress values are shown in Table 6 and Fig 10 to Fig 14

TABLE 6. SHEAR STRESS

Model

Shear

stress(MPa)

RC

189.63

SC 90

140.77

SC 60

109.55

SC 70

109.75

SC 80

111.99

Fig 10. Shear stress- RC

Fig 11. Shear stress- SC 90


0.6

0.65

0.7

0.75

0.8

0.85

RC SC 90SC 60SC 70SC 80

Tota

l def

orm

atio

n (m

m)

Model

Total deformation (mm)

Total deformation(mm)


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The comparison diagram of shear stress is shown in Fig 15

REFERENCES [1] Ade Lisantono, Agung Budiman and Paulinus Haesler Boantua

Sidauruk,“Experimental investigation of reinforced concrete column embedded with the steel shapes”,Science direct.Procedia Engineering,2016,vol.125, pp. 879-884

[2] A.M. Tarabia and H.F. Albakry, “Strengthening of R.C columns by steel angles and strips”, Alexandria Engineering Journal,2014,vol.53, pp. 615-626

[3] Giuseppe Campione,“Strength and ductility of R.C columns strengthened with steel angles and battens”,SciVerse Science direct,2012,vol.35, pp. 800-807

[4] Hamza M. Salman and Mohannad H. Al-Sherrawi, “Finite element modeling of a reinforced concrete column strengthened with steel jacket”,Civil Engineering Journal,2018, pp. 916-925

[5] Hatem M.Mohamed, Mahmoud F.Belal and Sherif A.Morad, “Behaviour of reinforced concrete columns strengthened by steel jacket” ,HBRC Journal,2015, vol.11, pp. 201-212

[6] IS 456-2000 [7] Steel hand book

Fig 15. Comparison diagram of shear stress

VI. CONCLUSIONS The following conclusions can be drawn from the present study. 1. The decrease in total deformation is approximately

same for all columns strengthened by steel angles and strips inclined at different degree.

2. The decrease in shear stress is more when column encased with steel angle and strip inclined at 600

3. In the case of column strengthened with steel angle and strips inclined at 600 shear stress decreased to 42.23%% and 22.178% when compared with reference column and column encased with steel angle and horizontal strips

4. The number of steel strips required for column strengthening is less when strips are inclined than the number of horizontal strips

5. Confinement played a larger role in improving the strength of the column

020406080

100120140160180200

RC SC90

SC60

SC70

SC80

Shea

r stre

ss( M

Pa)

Model

Shear stress( MPa)

Shear stress(MPa)


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study of r.c column strengthened by steel angles and ...c. analytical work using finite element...

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