Page 1 of 8

Journal for Studies in Management and Planning

Available at

http://edupediapublications.org/journals/index.php/JSMaP/

e-I SSN: 2395-0463

Vol ume 02 I s s ue 10

Oc tober 2016

Available online: http://edupediapublications.org/journals/index.php/JSMaP/ P a g e | 86

Retrofitting and strengthening of masonry structures

with advanced composite fiber wrap system

M. Saroja Lolitha1

, Mr. D. Aditya Sairam, M-Tech2

Mandava Institute of Engineering and Technology,

Jaggaiahpeta-521175

lolitha.6@gmail.com1

, dasairam102@gmail.com2

Abs tract:

A large number of masonry structures exist all over

the world. These structures need strengthening due to

many reasons such as lack of strength, stiffness,

ductility and durability. Generally the old structures

are not designed for earthquake loads, and hence

many such important structures have suffered during

the past earthquakes all over the world. Along with

loss of human lives and socio-economic problems,

damages and collapse of historically important

structures take place due to earthquake. Apart from

earthquake requirements, buildings need

strengthening due to modifications done in existing

structure or change in use of the building.

Deterioration of material strength on aging is another

significant reason for need of strengthening or

retrofitting. There are various methods for

strengthening of Masonry Structures among which

the use of FRP has received increased attention due

to the advantages of FRP, mainly lower specific

weight, resistance to corrosion, ease of application

and cost effectiveness. One of the important features

of FRP that makes it suitable for Masonry is its

adaptability to curved and rough surfaces. The use of

FRP material for strengthening of reinforced

concrete material is well established. As compared to

concrete less work has been done on masonry. A

large number of masonry structures including

historic monuments are required to be strengthened

or retrofitted in India and FRP can be a better option;

however research work is required in this context.

Effectiveness of FRP wrapping to masonry structural

elements to enhance the performance, is required to

be assessed experimentally. The present work

focuses on the experimental investigations of FRP

wrapped masonry load bearing members. The

experimental program consists of testing on FRP

strengthened masonry columns and FRP retrofitted

masonry walls. The enhancement in load carrying

capacity of masonry columns due to confinement by

FRP strips has been found. An ‘Advanced Composite

Fiber Wrap System’ with combination of vertical and

horizontal FRP strips has been proposed. Behaviour

of un-strengthened and FRP strengthened masonry

columns subjected to uniaxial compression has been

studied. The contribution of FRP anchors in

enhancement of load carrying capacity has been

quantified. In the next phase six masonry walls have

been tested.

Finite element analysis for un-strengthened

masonry elements and FRP retrofitted walls has been

done using the ANSYS software. The experimental

and analytical results are compared. CNR-DT-200 42

provides guidelines for the strengthening of masonry

structures using FRP. As no Indian Standard code is

available till now for the application of FRP on

masonry structures, the applicability of CNR-DT- 200, for the experimental work carried out in present

study was checked by evaluating the results as per

provisions of CNR-DT-200 and comparing with

experimental results. A mathematical model has been

proposed using the experimental results for

predication of compressive strength of brick masonry

column confined with FRP for Indian conditions.

Further the estimation of load carrying capacity of

FRP confined masonry columns with different strip

widths has been done by using proposed

mathematical model. The same model has been used

to compare performance of ‘Advanced Composite

Fiber Wrap System’ and ‘Continuous Wrapping

System’. This study reflects, FRP wrapping is an

effective strengthening and retrofitting technique for

the load bearing members of brick masonry

structures. ‘Advanced Composite Fiber Wrap

System’ is found to be is more effective and

economical as compared to Continuous wrapping

system. Substantial increase in load carrying capacity

of masonry columns was obtained by proposed

discontinuous fiber wrap system. FRP anchors were

effective in delaying the failure of specimens as well

as enhanced the load carrying capacity of columns by

16-18% in case of both the composite materials;

GFRP and CFRP. In case of masonry walls, different

failure modes were observed for different FRP

patterns. In case of Masonry Walls, lateral load

carrying capacity was increased significantly due to

discontinuous wrapping technique using composite

materials. The results of Finite Element Analysis

using ANSYS for masonry columns and masonry

walls are in line with experimental results. .

Page 2 of 8

Journal for Studies in Management and Planning

Available at

http://edupediapublications.org/journals/index.php/JSMaP/

e-I SSN: 2395-0463

Vol ume 02 I s s ue 10

Oc tober 2016

Available online: http://edupediapublications.org/journals/index.php/JSMaP/ P a g e | 87

Keywords

Finite Element Analysis, Retrofitting, masonry

structures, composite fiber wrap system, FRP.

1. Introduction

Masonry structures are one of the oldest forms of

construction though not obsolete and are still in

practice all over the world. The Egyptian Pyramids,

the Colosseum in Rome, the Taj Mahal in India and

the Great Wall of China are some of world’s

monuments that have been built in masonry. The

smallest residential buildings, built by Romans in the

first four centuries A.D., consisted of masonry walls,

that supported a timber loft and roof covered with

fired clay tiles. A multi-storeyed version of the small

domestic dwelling was also built by the Romans

during first century A. D. 1 ‘Mondanock Tower’ is

an example of multistored masonry building which is

16 storey high constructed in 1893 in Chicago.

Through civilization, engineers and architects

adopted masonry construction for residential

buildings, churches, temples, forts and bridges.

The masonry consists of two different materials;

masonry units and mortar joint. The common

masonry units are stone, clay bricks, calcium silicate

bricks and concrete blocks. Stones are the first

masonry units used for construction. Stone structures

are most durable and stand for centuries. Clay bricks

are the most common masonry units and have been

in use for at least last 10,000 years. By 3000 BC the

bricks were being made by hand in a mould with

cattle dung or straw added to increase the strength.

The mechanical production of bricks started in 1858

with introduction of the Hoffman kiln 1. Calcium

silicate bricks were made by moulding lime mortar in

brick shape and air drying. Concrete units were

introduced in mid 1800s. Now hollow concrete

blocks are used for reinforced masonry construction.

During ancient period mortars were made up of mud,

clay, bitumen or clay-straw mix. Egyptians /used

calcined gypsum a few thousand years ago while the

Greeks and Romans added lime, water and crushed

stone or bricks to make mortar 1. In eighteenth

century much research work was carried out on

cement all over the world and their after the use of

cement mortar started. Cement-lime mortars are also

used to combine advantages of cement and lime.

After more than 6000 years, masonry is still used

today for construction due to its advantages such as

aesthetics, heat and sound insulation, fire resistance

and economic considerations. Although masonry is

very strong in resisting compression but very weak in

resisting tension it is used in case of load bearing as

well as framed structures and a large inventory of

masonry structures exists all over the world. In

masonry structures the load bearing elements are

columns or piers, walls and arches.

‘Strengthening’ means the act of increasing

strength of something and ‘Retrofitting’ means the

process of modifying something after it has been

manufactured. Hence both terms are most of the

times used as synonymous in context of structures.

Also the term ‘Retrofitting’ is usually referred for

upgrading the seismic resistance of an existing

structure so that it becomes safe under the recurrence

of likely future earthquakes 2, hence used as

‘Seismic Retrofitting’.

A large number of masonry structures exist all

over the world. It has been reported by Arya 3 that as

per data of Indian Census 2001, the masonry houses

constitute 84.7% of the total housing units whereas

concrete and other units constructed using materials

such as wood, metal/asbestos sheets and bio-mass

material put together constitute 15.3%. The data of

past earthquakes have shown that masonry structures

are most vulnerable to earthquake forces. During the

last century, human casualties during earthquakes

were mainly caused by structural damage, being the

failure of unreinforced masonry structures

responsible of more than 60% of them 4. More than

15 lakh people have died due to collapse of buildings

during earthquakes in last 100 years, all over the

world. In 1976, earthquake in China caused loss of

approximately 2.4 lakh lives mainly due to collapse

of brick masonry structures 5.

More than 2000 deaths during Killari

(Maharashtra) earthquake in 1993 and more than

8000 deaths in Bhuj (Gujrat) earthquake (2001) is

attributed to collapse of masonry structures 6. Along

with loss of human lives and socio-economic

problems, damages and collapse of historically

important structures takes place due to earthquakes.

Preservation of Monuments is important as these are

identification of culture, region, country and having

artistic value. Seismic retrofitting of Historic

Monuments is a specialized task because many

conventional techniques cannot be applied, as, prime

objective of this type of retrofitting is to preserve

aesthetics of these structures. Archaeological Survey

of India has reported that there are at present more

than 3650 ancient monuments and archaeological

sites in nation. Generally the old structures are not

designed for earthquake loads and hence need

retrofitting. Even in some cases due to subsequent

updating of code and design practice or subsequent

upgrading of seismic zone, retrofitting of structures

is essential for survival of structures in next

earthquake. Prior to the introduction of modern

seismic codes in the late 1960s for developed

countries (USA, Japan etc) and late 1970s for many

other parts of the world including India, many

Page 3 of 8

Journal for Studies in Management and Planning

Available at

http://edupediapublications.org/journals/index.php/JSMaP/

e-I SSN: 2395-0463

Vol ume 02 I s s ue 10

Oc tober 2016

Available online: http://edupediapublications.org/journals/index.php/JSMaP/ P a g e | 88

unreinforced masonry structures were designed4.

Hence these structures were definitely not designed

to resist seismic forces and are not safe during

earthquake.

The existing masonry structures need

strengthening or retrofitting due to many reasons

such as lack of strength, stiffness, ductility and

durability. Apart from earthquake requirements,

buildings need strengthening due to modifications

done in existing structure or change in use of the

building. Deterioration of material strength on aging

is another significant reason for need of

strengthening or retrofitting. The building evaluation

showed that 96 % of the unreinforced masonry

(URM) buildings in California needed to be

retrofitted7. Also in a study, it has been observed that

retrofitting an existing building makes it 30% more

efficient, and makes a better case environmentally

than building a new structure with the same

efficiencies 8. Thereby, the development of effective

and affordable retrofitting techniques for URM

elements is needed.

Figure 1.1: Research Methodology

2. Experimental setup and Results

Experimental investigations have been carried out

on Fiber Reinforced Polymers (FRP) strengthened

masonry columns and FRP retrofitted masonry walls.

The experimental program has been presented in two

parts; first part on masonry columns and second part

on masonry walls. The enhancement in load carrying

capacity of masonry columns due to confinement by

FRP strips has been found out. An ‘Advanced

Composite Fiber Wrap System’ with combination of

vertical and horizontal FRP strips has been proposed.

Behaviour of unstrengthen and FRP strengthened

masonry columns subjected to uniaxial compression

has been studied. The contribution of FRP anchors in

enhancement of load carrying capacity has been

quantified. In the next phase masonry walls has been

tested. The behaviour of un-retrofitted and FRP

retrofitted masonry walls subjected to in-plane lateral

load along with pre-compression has been studied

experimentally. Evaluation of performance of

various FRP strip patterns for masonry walls has

been carried out.

Mas onry column s pecimen :

Specimen sizes were finalized considering the

provisions given in codes and sizes of bricks and

mortar joints. As per IS 1905:1987 47, a masonry

column has been defined as a vertical member, the

width of which does not exceed 4 times the

thickness. The same definition is also given by

British Standard CP III: Part2: 1970 113. National

Building Code of Canada114 and Recommended

Practice for Engineered Brick Masonry 1969 115,

defines the columns as a member whose width does

not exceed 3 times the thickness. Considering the

mortar joint thickness as 10 mm and size of bricks

210 x 100 x 70 mm, total 15 brick masonry solid

column specimens of 210 mm x 210 mm in cross

section and 480 mm of height were cast.

Figure 2.1: Masonry Column Specimens

Figure 2.2: Columns in Existing Masonry Buildings

Three column specimens were tested without FRP

wrapping to serve as control specimens under