BEHAVIOUR OF REINFORCED CONCRETE TEE- BEAMS...

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International Journal of Civil Engineering and Technology (IJCIET)

Volume 8, Issue 11, November 2017, pp. 620–630, Article ID: IJCIET_08_11_065

Available online at http://http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=8&IType=11

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

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BEHAVIOUR OF REINFORCED CONCRETE

TEE- BEAMS RETROFITTED USING

FERROCEMENT

P. Raghunathapandian

Assistant Professor, Dept of Civil Engineering, Meenakshi College of Engineering,

K.K Nagar, Chennai, Tamilnadu, India

Dr. B. Palani

Professor, Dept of Civil & Structural Engineering,

Annamalai University, Chidambaram, Tamilnadu, India

Dr. D. Elango

Professor and Head, Dept of Civil Engineering,

Valliammai Engineering College, Kanchipuram (Dt), Tamilnadu, India

ABSTRACT

Reinforced concrete structural components are found to exhibits distress, even

before their service period that is often due to several causes. Such unserviceable

structures require immediate attention, enquiry into the cause of distress and suitable

remedial measures, so as to bring the structures back to their functional use again.

This strengthening and enhancement of the performance of such deficient structural

elements in a structure or a structure as a whole is referred to as retrofitting. All the

important issue to be addressed in retrofitting is for life safety. Ferrocement is most

commonly used as retrofitting material due to their easy availability, economy,

durability, and their property of being cast to any shape without needing significant

formwork. Ferrocement as a retrofitting material can be pretty useful because it can

be applied quickly to the surface of the damaged element without the requirement of

any special bonding material and also it requires less skilled labour, as compared to

other retrofitting solutions presently existing. The Ferrocement construction has an

edge over the conventional reinforced concrete material because of its lighter weight,

ease of construction, low self weight, thinner section as compared to RCC and a high

tensile strength which makes it a favorable material for prefabrication also.

The present investigation on Preloaded Reinforced Concrete Tee Beams is

retrofitted using Ferrocement to increase the strength Soffit of Beam and along the

side faces of web, by placing the wire mesh along the longitudinal axis of the beam.

From the study it is seen that the ultimate load carrying capacity of Reinforced

concrete Tee beam elements retrofitted by Ferrocement is significantly increased

when Welded Wire mesh are used for retrofitting.

Key words: Ferrocement, Retrofitting, Wire Mesh, orientation.

P. Raghunathapandian, Dr. B. Palania and Dr. D. Elango


Cite this Article: P. Raghunathapandian, Dr. B. Palania and Dr. D. Elango, Behaviour

of Reinforced Concrete Tee-Beams Retrofitted using Ferrocement. International

Journal of Civil Engineering and Technology, 8(11), 2017, pp. 620–630.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=11

1. INTRODUCTION

Reinforced concrete is one of the most abundantly used construction material, not only in the

developed areas, but also is the remotest places. The Reinforced Cement Concrete structures

constructed in the developed area are often found to exhibit distress and suffer changes, even

before their service period that is often due to several causes such as improper design, faulty

construction, change of usage of the building, change in codal provisions, over loading,

earthquakes, explosion, corrosion, wear and tear, flood, fire etc. such unserviceable structures

require immediate attention and enquiry into cause of distress and suitable remedial measures,

for bringing the structure into its functional use again. In the last few decades several attempts

have been made in India and abroad to study these problems and to increase the life of the

structures by suitable retrofitting and strengthening techniques. Among the plate bonding

techniques FRP plate are quite popular now a days. But it is observed that the use of FRP is

restricted is many developed countries and urban areas of the developing countries due to

higher initial cost and requirement of skilled labour for their application. Thus there is a need

to develop an alternative technique, which is economical and can be executed at site even

with less skilled labour available at site.

2. LITERATURE REVIEW

Many Experimental studies have been conducted in recent year to strengthen flexural

members by using various materials Andrew et.al (1998) studied the flexural performance of

reinforced concrete beams repaired with conventional method and Ferrocement. They

concluded that beams repaired by Ferrocement showed superior performance both at the

service and ultimate load. The flexural strength and ductility of beams repaired with

Ferrocement was reported to be greater than the corresponding original beams and the beams

repaired by the conventional methods. Beams rehabilitated with Ferrocement jackets shows

better performance in terms of ultimate strength, first crack load, crack width, ductility and

rigidity of the section. It was observed that the cracking and ultimate strength increases by

10% and 40% in case of rehabilitated beams, where as these increases were 10 – 30% and 40

– 50% in case of composite section. The jacketing increase the rigidity of the beams and leads

to a reduction in deflection by 37% and a reduction in crack width by 29%.

Kaushik et.al. (1994) studied the addition of thin layer of ferrocement to a concrete beam

and found to be enhancing its ductility and cracking strength Composite beams reinforced

with square mesh exhibit better performance than the composite beams reinforced with

hexagonal mesh. Increasing the number of layers improves the cracking stiffness of the

composite beams in both cases. Nassif et.al. (1998) in this Study ferrocement shell improves

the flexural behavior of RCC beams, however there is no increase in the moment carrying

capacity of under reinforced beams. but, the moment carrying capacity increased by 9% &

15% for balanced and over reinforced section respectively. Seshu et.al. (2000) evaluated the

ultimate strength of the reinforced concrete beams, which failed due to overloading and were

repaired using ferrocement laminate, is affected by the level of damage sustained prior to

repairing. However, ultimate strength, ductility ratio and energy absorption have been

improved after the repair in all cases. The steel ratio used in the repair layer has a great

influence on the amount of gain in the resisting moment, ductility ratio, and energy

absorption. The higher the steel ratio the higher the gain in resisting moment and energy

Behaviour of Reinforced Concrete Tee-Beams Retrofitted using Ferrocement


absorption: conversely, the ductility ratio was found to be decreased with increase in steel

ratio. Fahmy et.al. (1997) studied the flexural behavior of reinforced concrete T-beams

strengthened with thin ferrocement laminate attached to the tension face using L-shaped mild

steel round bars as shear connectors. From the experimental investigation it was concluded

that the performance of the Strengthened beams improved substantially in terms of strength,

flexural rigidity and first crack load, provided the connectors are adequately spaced and the

surface to receive the laminate roughened to ensure sufficient bond strength for composite

action. Paramasivam et.al. (1994) examined the shear transfer between composite layers in

beams. They concluded from this study that full composite action between both layers cannot

be attained based on rough surfaces without shear studs and a minimum of five studs should

be used to ensure full composite action. Shear studs with hooks exhibited better pre cracking

strength compared to all other type of studs. It was also concluded that beam with square

mesh are better than beams with hexagonal mesh for controlling cracks. The addition of

ferrocement laminates to the soffit of the beams delays the first crack load, restrains cracks

from further widening and increases the flexural stiffness and load capacities of the

strengthened beam. The improvement in mid-span deflection and load capacities are lower in

beams where the composite action was lost between the original beam and the strengthening

ferrocement laminates. Thus it is suggested that the surface of the beam to receive the

ferrocement laminate to be roughened and provided with closely spaced shear connectors in

order to ensure full composite action. Jumaaet et.al. Studied that the shear connectors used for

the purpose of strengthening of beam also affects the formation of first crack, mid-span

deflection and also the load capacity of the beam. The improvements in reducing the cracking,

deflection and ultimate load was greater with smaller shear connector spacing. They also

concluded that the performance of the strengthened beam with higher volume fraction of

reinforcement in ferrocement laminates was slightly better than the one with lower volume

fraction results.

3. EXPERIMENTAL PROGRAMME

Table 1 Properties of Materials

Properties of Cement

Sl.no Property Experimental Value Indian Standards

1 Grade 53 IS:12269 - 2013

2 Soundness Test 2mm IS:4031 (Part-3)2005

3 Fineness of Cement 8% IS:4031 (Part-2)2005

4 Consistency of Cement 30% IS:4031(Part-4)2005

5 Initial Setting Time 45mins IS : 12269:2013 Clause 6

6 Final Setting Time 230mins IS : 12269:2013 Clause 6

7 Specific gravity 3.15 IS:4031(Part-3)2005

Compressive strength of cement mortar cubes (N/mm2

)

8 3 Days 29.31 IS : 12269:2013 Clause 6

9 7 Days 38.12 IS : 12269:2013 Clause 6

10 28 Days 54.36 IS : 12269:2013 Clause 6

Properties of Fine Aggregates

11 Fineness modulus 2.9 IS:2386(Part-1)2002

12 Specific Gravity 2.59 IS: 2386 (Part-3)2002

13 Water Absorption 1% IS: 2386 (Part-3)2002

Properties of Coarse Aggregates (10 – 20 mm)



14 Water Absorption 0.5% IS: 2386(Part-3)2002.

14 Specific Gravity 2.74 IS: 2386(Part-3)2002.

15 Impact test 46.53% IS:2386(Part-4)2002

16 Specific Gravity 2.74 IS: 2386(Part-3)2002.

17 Fineness modulus 8.44 IS: 2386(Part-1)2002

Table 2 Summary of Strengthening Plan

Sl. No Beam

Group Beam Code

Pre – Loading

Level (%)

Type of

Strengthening

Steel Ratio

(%)

Volume fraction of

Ferrocement (%)

1

BC

BC – 1 100

Nil

0.425 1.61

2 BC – 2 100 0.425 1.61

3 BC - 3 100 0.425 1.61

4

BRB

BRB 1- 1

60

At Soffit only 0.425 1.61

5 BRB 1 – 2 At Soffit only 0.425 1.61


7 BRB 2 – 1

70




10 BRB 3 – 1

80


11 BRB3 - 2 At Soffit only 0.425 1.61

12 BRB3 - 3 At Soffit only 0.425 1.61

13

BRS

BRS 1- 1

60

Along the faces of

beam only 0.425 1.61

14 BRS1 – 2 Along the faces of




16 BRS2 – 1

70

Along the faces of






19 BRS3 – 1

80

Along the faces of


20 BRS3 - 2 Along the faces of


21 BRS3 - 3 Along the faces of


To carry out the investigation, Material used and its Properties are tabulated M25 Grade of

concrete mix was used for preparation of specimen and Twenty one Reinforced Concrete Tee

beams are casted. The specimens of reinforced under reinforced, balanced flanged concrete

beam. The specimen consists of flange of size 510*100 mm and web of 150 mm*300 mm

reinforced with conventional steel and the length of the beam is 3000 mm. Main

reinforcements of Tee beams were high yield strength deformed steel bars of 3 numbers of

10mm diameter bars and four number 8mm diameter bars are used for stirrups. Out of these

fourteen beams, three were used as control beams and tested for failure to find out the safe

load carrying capacity and also ultimate load carrying capacity corresponding to the allowable

deflection as per IS 456 - 2007. The cross sectional geometries and longitudinal

reinforcements were the same for all the specimens. Longitudinal reinforcement consist of

three 10 mm diameter steel rebar‟s in the bottom of the beam. Strengthening was not applied

to control beam.



Section Details of RC T beams

Compaction is done with the help of needle vibrator in all the specimens and care is taken

to avoid displacement of the reinforcement inside the form work. Then the top surface of the

concrete is leveled and smoothened by metal trowel and wooden float. Remaining beams

were stressed to 60%, 70%, and 80% of the ultimate load obtained from the testing of the

control beams and were then retrofitted with 15mm thick ferrocement made with 1:2 cement

sand mortar and w/c ratio 0.40.

The Ferrocement was reinforced with one layer of weld mesh. In Case I: Totally Nine

Numbers of Preloaded Level (60%, 70%, and 80%) respectively were used with Retrofitted

Soffit of beam (BRB). Similarly, Case II: Totally Nine Numbers of Preloaded Level (60%,

70%, and 80%) respectively were used with Retrofitted on along the side faces of beam (BRS).

Control beam were designated as BC whereas, beams retrofitted with weld mesh at soffit of

beam designated as BRB. Retrofitted beam with weld mesh at along the side faces of Beam

only designated as BRS respectively

Figure 1 Preparation of Steel Reinforcement for Beams. Figure 2 Tee beam mould before casting



Figure 3 Pouring of Concrete on Tee Beam Mould Figure 4 Concreting of Tee beam mould

Figure 5 Demoulded RC Tee Beams Figure 6 RC Tee Beams under Curing

All the beams were tested with an effective span of 2.8 m. Two concentrated loads were

applied at 1m spacing from both supports (Fig 6). The beams were tested using hydraulically

operated Jacks connected to a data acquisition system through the load cells with an increase

in load

Figure 7 Schematic Diagram for Testing Arrangement



Figure 8 Flexural Tested on Tee Beam

The deflections in the beams were noted using three dial gauges placed at the quarter span

points. The load is applied almost at a uniform rate load and deflections were recorded at

regular intervals for each step.

4. PROCESS OF RETROFITTING ON PRE LOADED BEAM

The beams were stressed up to a specified limit as above and then retrofitted by applying weld

mesh and then plastering it with cement mortar up to the thickness of 30 mm for all 18 beams.

Effect of three different stress levels of 60%, 70% and 80% has been studied. First of all

surface of beams were cleaned by sand blasting techniques. One layer of weld mesh stretched

and attached to soffit of beams and also alongside faces of beams. The nail and visor used for

bonding between beam and mesh. Then 15mm plaster in the form of 1:2 Cement mortars is

applied on faces of beams. After remolding the beam were subjected to curing for 28days.

Figure 9 Beams are retrofitting at Soffit beam (BRB) Figure 10 Beams are retrofitting alongside faces (BRS)

5. TEST RESULTS AND DISCUSSION

The control beams were tested up to failure. The remaining 18 beams were stressed to various

levels i.e., 60%, 70% and 80% of the average ultimate load of control beams. Subsequently

the retrofitting of beams using orientations of weld mesh in the ferrocement was carried out.

These retrofitted beams were then loaded to failure and the data was recorded in the form of

load and deflection. Fig 11, 12 and 13 shows the load deflection behaviors at the mid span

points of the control as well as beams retrofitted with welded wire mesh orientations. It is

observed from the curves in fig 11, 12 and 13 shows that with an increase in load there is a

considerable increase in deflection for all the beams. It was also noted that the Maximum



ultimate load carrying capacity of Retrofitted beams with 60% Pre Loaded levels achieved

higher values. Table 3 Ductility of Tested Beams

Table 4 Energy Absorption of Tested Beams

Beam

Group Beam Code

Ductility

ratio

Average

Ductility

ratio

Increase in

ductility %

BC

BC – 1 4.25

4.68 - BC – 2 4.64

BC - 3 4.99

BRB

BRB 1- 1 7.08

7.28 55.55 BRB 1 – 2 7.63

BRB 1 – 3 7.13

BRB 2 – 1 6.12

6.20 32.47 BRB 2 – 2 6.02

BRB 2 – 3 6.15

BRB 3 – 1 5.23

5.42 15.81 BRB 3 - 2 5.69

BRB 3 – 3 5.34

BRS

BRS 1- 1 7.48

7.21 54.05 BRS 1 – 2 7.19

BRS 1 – 3 6.98

BRS 2 – 1 6.05

6.15 31.41 BRS 2 – 2 6.12

BRS 2 – 3 6.29

BRS 3 – 1 5.05

5.16 10.42 BRS 3 - 2 5.15

BRS 3 - 3 5.27

Beam

group Beam code

Energy

absorptio

n N-m

Average

Energy

absorption

Increase in

Energy

absorption

%

BC

BC – 1 2980

2903.33 - BC – 2 2840

BC - 3 2890

BRB

BRB 1- 1 3930

3896.67 34.21 BRB 1 – 2 3910

BRB 1 – 3 3850

BRB 2 – 1 3730

3726.67 28.36 BRB 2 – 2 3720

BRB 2 – 3 3730

BRB 3 – 1 3600

3593.33 23.77 BRB 3 - 2 3550

BRB 3 – 3 3630

BRS

BRS 1- 1 3350

3345.00 15.21 BRS 1 – 2 3355

BRS 1 – 3 3330

BRS 2 – 1 2970

3003.33 13.44 BRS 2 – 2 2980

BRS 2 – 3 3060

BRS 3 – 1 2689

2994.35 3.21 BRS 3 - 2 2739

BRS 3 - 3 2670



Figure 11 Load – Deflection Relationships of CB, BRB, and BRS on 60% Pre-loaded Beams.



6. CONCLUSIONS

Based upon the test results of the experimental study undertaken, the following conclusions

were drawn:

The failure of the composite is characterized by development of flexural cracks over the

tension zone.



All the beams retrofitted using ferrocement exhibit higher flexural strength when compared

with control beams.

Beams pre-loaded up to 60% of their ultimate load and retrofitted using ferrocement achieved

higher ultimate load levels when compared with beams pre-loaded up to 70% and 80%.

In flexure, the beams retrofitted at bottom of web give more strength when compared to the

beams retrofitted at along the side faces of web Portions.

Beams retrofitted using ferrocement at soffit only, achieved on ultimate load which is 16.57%

higher than that of control beams. Similarly beams retrofitted along the side faces of web

achieved on ultimate load which is 6.35% higher than that of control beams.

All the retrofitted beams showed significant increase in ductility ratio and considerable

increase in energy absorption.

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