Effect Of Wire Mesh Orientation On Strength Of Beams Retrofitted Using Ferrocement Jackets

Abstract

Various retrofitting techniques are used in field and out of all plate bonding technique is considered as the best. In this technique, the plates of different materials viz CFRP, GFRP, ferrocement etc are bonded to the surface of structural member to increase its strength. Ferrocement sheets are most commonly used as retrofitting material these days due to their easy availability, economy, durability, and their property of being cast to any shape without needing significant formwork. In the present work, effect of wire mesh orientation on the strength of stressed beams retrofitted with ferrocement jackets has been studied. The beams are stressed up to 75 percent of safe load and then retrofitted with ferrocement jackets with wire mesh at different orientations. The results show that the percent increase in load carrying capacity for beam retrofitted with ferrocement jackets with wire mesh at 0, 45, 60 degree angle with longitudinal axis of beam, varies from 45.87 to 52.29 percent. Also a considerable increase in energy absorption is observed for all orientations. However, orientation at 45 degree shows higher percentage increase in energy absorption followed by 60 and 0 degree respectively.

Full text

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Prem Pal Bansal, Maneek Kumar, S.K.Kaushik
International Journal of Engineering, Volume (2) : Issue (1) 8
Effect Of Wire Mesh Orientation On Strength Of Beams
Retrofitted Using Ferrocement Jackets



Prem Pal Bansal*, B.E. Civil, M.E, Civil (Structures)
Lecturer, Department of Civil engineering,
Thapar University, Patiala,
INDIA 147 004
* Corresponding Author
Dr. Maneek Kumar, B.E. Civil, M.E, Civil (Structures),
Ph.D.
Professor & Head, Department of Civil engineering,
Thapar University, Patiala,
INDIA 147 004

Dr. S.K. Kaushik, B.Tech. Civil, M.E, Civil (Structures),
Ph.D.
Formerly Professor and Head, Department of Civil
Engineering,
Indian Institute of Technology, Roorkee
INDIA
prempalbansal@yahoo.co.in
prempal@gmail.com
maneek@tiet.ac.in







Abstract

Various retrofitting techniques are used in field and out of all plate bonding
technique is considered as the best. In this technique, the plates of different
materials viz CFRP, GFRP, ferrocement etc are bonded to the surface of
structural member to increase its strength. Ferrocement sheets are most
commonly used as retrofitting material these days due to their easy
availability, economy, durability, and their property of being cast to any shape
without needing significant formwork. In the present work, effect of wire mesh
orientation on the strength of stressed beams retrofitted with ferrocement
jackets has been studied. The beams are stressed up to 75 percent of safe
load and then retrofitted with ferrocement jackets with wire mesh at different
orientations. The results show that the percent increase in load carrying
capacity for beam retrofitted with ferrocement jackets with wire mesh at 0, 45,
60 degree angle with longitudinal axis of beam, varies from 45.87 to 52.29
percent. Also a considerable increase in energy absorption is observed for all
orientations. However, orientation at 45 degree shows higher percentage
increase in energy absorption followed by 60 and 0 degree respectively.

Keywords: ferrocement, retrofitting, jacket, wire mesh, orientation, beams.

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Prem Pal Bansal, Maneek Kumar, S.K.Kaushik
International Journal of Engineering, Volume (2) : Issue (1) 9
1.0 INTRODUCTION

Reinforced concrete is one of the most abundantly used construction material, not only in
the developed world, but also in the remotest parts of the developing world. The RCC
structures constructed in the developed world are often found to exhibit distress and suffer
damage, even before their service period is over due to several causes such as improper
design, faulty construction, change of usage of the building, change in codal provisions,
overloading, earthquakes, explosion, corrosion, wear and tear, flood, fire etc.
Such unserviceable structures require immediate attention, enquiry into the cause of distress
and suitable remedial measures, so as to bring 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. Of the various retrofitting techniques available, plate bonding is one of the most
effective and convenient methods of retrofitting. Among the plate bonding techniques FRP
plates are quite popular now-a-days. But it is observed that the use of FRP is restricted to
developed countries or 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 with the help of semi-
skilled labour available at site. Ferrocement jacketing is found to be one such attractive
technique due to its properties such as good tensile strength, lightweight, overall economy,
water tightness, easy application and long life of the treatment.
Many experimental studies have been conducted in recent years to strengthen flexural
members by using various materials. Andrew and Sharma (1998) in an experimental study
compared 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 method.
Beams rehabilitated with ferrocement jackets show 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 percent and 40 percent in case of
rehabilitated beams, whereas these increases were 10-30 percent and 40-50 percent in case
of composite sections. The jacketing increases the rigidity of the beams and lead to 37
percent and 29 percent reduction in deflection. The crack width of the composite beams and
rehabilitated beams decreases on an average by 42 percent and 36 percent respectively
[Kaushik, S.K. and Dubey, A.K., 1994].
The addition of thin layer of ferrocement to a concrete beam enhances its ductility and
cracking strength. Composite beams reinforced with square mesh exhibit better overall
performance compared to composite beams reinforced with hexagonal mesh. An increase in
the number of layers improves the cracking stiffness of the composite beams in both cases.
[Nassif, H.H et al, 1998, Vidivelli, B. et al, 2001, Nasif, N.H. et al 2004].
A ferrocement shell improves the flexural behaviour of RCC beams, although there is no
increase in the moment carrying capacity of under reinforced beams. However, the moment
carrying capacity increased by 9 per cent and 15 per cent for balanced and over reinforced
sections respectively [Seshu, D.R., 2000].
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
reported to improve 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
absorption; conversely, the ductility ratio was found to be decreased with increase in steel
ratio [Fahmy, Ezzat H. et al, 1997].
Paramasivam, P. et al (1994) 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 after strengthening the performance of the beam improved substantially in terms of
strength, flexural rigidity and first crack load, provided the connectors are adequately spaced

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Prem Pal Bansal, Maneek Kumar, S.K.Kaushik
International Journal of Engineering, Volume (2) : Issue (1) 10
and the surface to receive the laminate roughened to ensure sufficient bond strength for
composite action.
Thus, ferrocement is a viable alternative material for repair and strengthening of reinforced
concrete structures. It has been accepted by the local building authority in Singapore for use
in upgrading and rehabilitation of structures. The National Disaster Mitigation Agency
(NDMA), Government of India, also accepted the use of ferrocement for this purpose.
The behaviour of ferrocement in flexure depends upon various parameters such as mortar,
type of wire mesh, orientation of wire mesh etc.; hence the behaviour of ferrocement jackets.
In the present paper the effect of wire mesh orientation on the strength, toughness and
ductility of the retrofitted beams is presented.

2.0 EXPERIMENTAL PROGRAMME

To carry out the investigation, eight prototype beams of size 127mm x 227mm x 4100mm
reinforced with two bars of 10 mm diameter in tension and two bars of 8mm diameter in
compression were cast using the proportioned mix as shown in Fig.1. Out of these eight
beams, two were used as control beams (Type- A) and tested to failure to find out the safe
load carrying capacity corresponding to the allowable deflection as per IS:456-2000 i.e. span
/250. The other six beams were stressed to 75 percent of the safe load obtained from the
testing of the control beams and were then retrofitted with 15 mm thick ferrocement jackets
made with 1:2 cement sand mortar and w/c ratio 0.40 as shown in Fig. 2. The jacket was
reinforced with single layer of 40mm x 40mm square welded wire mesh. The three wire mesh
orientation viz. 0, 45, 60 degree were used in the ferrocement jackets.
The set of beams (two each) were divided into four categories depending upon the orientation
of wire mesh in the jacket. Control beams were designated as type-A, whereas, beams
retrofitted with welded wire mesh oriented at 0 degree were designated as type – B beams.
Retrofitted beams having welded wire mesh oriented at 45 degrees and 60 degrees were
designated as type – C and type-D, respectively. The same are shown in Plate 1


Fig. 1 Longitudinal and Cross-Section of Unretrofitted Under Reinforced Beams
(All Dimensions are in mm)

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Prem Pal Bansal, Maneek Kumar, S.K.Kaushik
International Journal of Engineering, Volume (2) : Issue (1) 11

Figure 2: Longitudinal and Cross-Section of Retrofitted Beams



(a) 00 Orientation (b) 450 Orientation


(c) 600 Orientation

Plate 2 Different Wire Mesh Orientations

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Prem Pal Bansal, Maneek Kumar, S.K.Kaushik
International Journal of Engineering, Volume (2) : Issue (1) 12
2.1
The properties of various materials used in the experimental study are reported in Tables 1 to
4
Materials

Sr. No. Characteristics Test Values Values as per IS:1489 (Part 1)
1 Standard consistency 34 -
2 Fineness of cement as retained on 90-
micron sieve (%)
Setting time (mins)
1. Initial
2. Final
Specific gravity
(Specific gravity bottle)
Compressive Strength (MPa)
1. 7days
2. 28 days
Soundness (mm)
(by Le-Chatelier’s method)
0.5 < 10
3

84
300
3.07

> 30
< 600
- 4
5
30.0
43.0
2.0

22.0
33.0
6 < 10 (Fresh Cement)
< 5 (Old Cement)

Table 1: Physical Properties of Portland Pozzolana Cement



Table 2: Physical Properties of Fine Aggregates



Table 3: Physical Properties of Coarse Aggregates


S. No. Characteristics

Value
1. Specific gravity (oven dry basis) 2.52
2. Bulk density loose (kN/m3) 14.8
3. Fineness modulus 2.36
4. Water Absorption (%) 2.67
5. Grading Zone Zone II
Value Sr. No. Characteristics

CA-I CA-II
1. Type Crushed Crushed
2. Maximum Nominal Size (mm) 12.5 4.75
3. Specific gravity 2.68 2.70
4. Total water absorption (%) 1.45 1.643
5 Fineness modulus 7.45 6.21