An Experimental Investigation on Post Tensioned Beams · PDF fileBangalore- Karnataka, India 2 nd Dr. S.Vijaya Professor Department of Civil Engineering, Dr. Ambedkar Institute Of

8543 This work is published under Attribution-NonCommercial-ShareAlike 4.0 International License

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

Volume 4 Issue 12 August 2017 www.ijifr.com

Abstract

Reinforced Concrete is most commonly used material in Civil Engineering works. It is essential to have sufficient strength and stiffness in the existing structures, several Pre-stressed Concrete (PSC) are designed without proper code necessities so they provide inadequate structural performance in order to avoid this they have to be upgraded to increase load carrying capacity. In this experiment post-tensioned beam was strengthened by BFRP fabric. The objective of this work is to analyse the behaviour of post tension beams such as deflection, ultimate load carrying capacity and cracks. To accomplish this post tensioned beams of size 1300mmX150mmX200mm were casted according to IS 1343-1980 regulations and tested experimentally less than two point loading. The beams were allocated as Control beam, Post Tensioned beam, Strengthen beam and Retrofitted beam. The conclusion was discussed based on load deflection curve plotted. From experiment results the increase in load carrying capacity and the reduction in cracks and deflection for strengthen beams can be observed. Beam strengthens with double layer BFRP have additional load carrying capacity and reduction in deflection compared to other beams.

An Experimental Investigation on Post

Tensioned Beams with BFRP Fabrics

Paper ID IJIFR/V4/ E12/ 020 Page No. 8543- 8551 Subject Area Civil

Engineering

Key Words Post Tensioned Beams, Strengthening, Retrofitting, BFRP

1st Varun G

Post Graduate Student

Department of Civil Engineering,

Dr. Ambedkar Institute Of Technology,

Bangalore- Karnataka, India

2nd Dr. S.Vijaya

Professor




3rd Dr. B.Shivakumaraswamy

Professor & Head




8544

ISSN: 2347-1697

International Journal of Informative & Futuristic Research (IJIFR)

Volume - 4, Issue -12, August 2017

Continuous 48th Edition, Page No. : 8543- 8551

Varun G, Dr. S.Vijaya, Dr. B.Shivakumaraswamy :: An Experimental Investigation on Post Tensioned Beams with BFRP Fabrics

I. INTRODUCTION

Due to lack of construction methods, standard design, construction materials and effect of

natural disasters such as earthquake and deterioration of existing structures, numerous

Pre-stressed Concrete (PSC) structures so-called are unstable to sustain the loads from

structural members. As a result, many existing Pre-stressed Concrete (PSC) aren’t designed according to codal requirements and are frequently considered as inadequate

structural behaviour as a result of loss of pre-stress in strands. As we know that existing

structures cannot be replaced completely and there are cases where construction is also

not possible depending on location and economy of structure, the best option is for

strengthening of structure.

Strengthening of Pre-stressed Concrete (PSC) structures plays a vital role. The need of

strengthening the structures is due to increase loads, design errors etc. The critical zones

in PSC beams are shear and flexure, in order to keep these structures operational they can

be strengthened by Fiber Reinforced Polymer (FRP). These FRP’s acts as extra layer of

tensile reinforcement and they have high strength to weigh ratio, corrosion resistant and

they exhibit high tensile strength. These FRP’s are externally bonded with epoxy resins to

the concrete members.

The initial FRP material used was glass fibres embedded in polymeric resins that were

prepared by petrochemical industry. FRP systems were first applied to reinforced

concrete columns for providing supplementary confinement in Japan in 1980s. Sudden

drastic increases in use of FRP were witnessed in Japan after HyogoknNanbu earthquake

in 1995. The research activities lead to FRPs material in many fields. The countries like

Europe, Japan, Canada and United States in fields of retrofitting and rehabilitations

project using as FRPs used as construction material. FRP materials are now finding wider

acceptance in the characteristically conservative infrastructure construction industry [1].

In 1980’s the FRP’s were first applied to RC columns for additional confinement. The

initial FRP materials used was glass fibres embedded with polymeric resins and it was

made by petrochemical industry following World War II. Various researches have carried

out numerous experiments in countries like Japan, Canada and Unites States in

retrofitting of structures by means of FRP’s [2].

In this work the post-tensioned beams were strengthened with natural fibres i.e sisal fibre.

The beams were strengthen with natural laminate only for flexure zone and other beams

were strengthen with sisal fibres laminate throughout the length with the anchorages. The

strengthen beam with anchorages carried more loads compared to beams strengthen in

flexure zone. [5]

In this experimental work the post-tension beam were strengthened with CFRP and

GFRP. Here beams were wrapped with different types such as total length wrapping,

bottom wrapping and full length wrapping. The load carrying capacity of beams for full

length wrapping seems to be more for both CFRP and GFRP compared to control beams,

the latter is more. [8].

8545

ISSN: 2347-1697





In this experimental work the post tensioned beams are strengthened with BFRP and

analysis is carried out to know their flexural behaviour, deflection and load carrying

capacity under static loading. Where two beams are strengthen with single layer BFRP

and other two with Double layer BFRP.

II. EXPERIMENTAL STUDY

The experimental analysis was conducted on Post Tensioned beams cast and they were

tested under two point loading. This analysis is restricted only for flexure failure as the

beams are designed to fail in flexure. The reinforcement provided was #2-10ɸ on compression and tension side with a stirrups of 8ɸ@150mm c/c along length of specimen. For post-tensioned beams along with actual reinforcement, 2 number of 7mm

dia tendons are placed with an eccentricity of 50mm, stressed for a pre-stressing force of

48KN in each tendon individually. The clear cover of 40mm was provided from soffit of

beam and 25mm cover from sides. The beams are divided into as,

(a) Control Beams. (CB)

(b) Post-Tensioned Beams. (PTB)

(c) Strengthen Beams. (SB)

(d) Retrofitted Beams.(RB)

All the beams were strengthen with BFRP fabric and epoxy resin. Fabrics are attached to

soffit of beams for full length.

2.1 Casting of Beam specimen

Post-tensioned beams were cast using a flexible rubber tube of 11mm diameter along the

length of beam, during this high tensile steel tendons of 7mm diameters of two numbers

are inserted into the tube in order to avoid firmness of tube during casting. Concrete of

grade M40 was used and poured from height less than 1m, with help of vibrator it was

compacted uniformly as shown in Figure 1. After initial setting of concrete the tendons

are moved back and forth to confirm that there was no concrete in rubber pipe. After 24

hours the beam specimens are de-mould and they are cured for 28days and then the

specimens were tested.

2.2 Pre-stressing of Beams

Mild steel plates of 150mmX100mmX10mm were used as end bearing plates on both

sides of beam. Two holes were punched in each end bearing plate for the tendons to

accommodate. High tensile tendons were placed through the holes in mild steel plates in

respective ducts provided. At both the ends the barrels are first fixed and then two pieces

of wedges were inserted into barrels for each tendon. The tendon was sealed at one end

and at other end tendon was stressed by hand operated hydraulic jack up to designed pre-

stressing force and the elongation of tendons was measured. Each tendon of 7mm

diameter was pre-stressed individually with hydraulic jack of 7-metric ton capacity with

least count of 1KN as shown in Figure 2. In this work Gifford – Udall system is referred.

8546

ISSN: 2347-1697





Figure 1: - Post-tensioning of beams

2.3 Strengthening of Beams with BFRP fabric

In this experimental work the post-tensioned beams were strengthened with Single layer

(SBSL) and Double layer (SBDL) BFRP. The bottom surface of post-tensioned beam

should be free from oils, excess concrete and other materials. Lapox L-12 epoxy resin is

applied over the soffit of beam, BFRP should be cut to required shapes and size and then

it is pressed with roller to get rid of air bubbles and to gain proper bonding. Once the

strengthening work is done then it is allowed for drying up to four days to get proper

bonding.

2.4 Retrofitting of Beams with BFRP fabric

The post-tensioned beams are preloaded up to visible crack having a width of 1.5mm to

2mm, and then they are retrofitted with Single layer (RBSL) and Double layer (RBDL)

BFRP. Before retrofitting the bottom surface of beams were cleaned and deleterious

materials were removed, a layer of epoxy resin is coated on beam bottom surface first and

then BFRP cut into required size is pressed on it with help on rollers to remove entrapped

air and it is allowed for drying for four days to attain proper bonding.

2.5 Testing of Beams

The beam specimens were tested under 500KN capacity loading frame and all beams was

tested under static loading as shown in Figure 2. The loading were applied at an interval

of 10KN increments till the failure of beam i.e ultimate load. Deflections were measured

at mid span of the beams. At each loading, deflection was recorded with help of LVDT’s.

Figure 2: - Test setup on loading frame

8547

ISSN: 2347-1697





III. RESULTS AND DISCUSSIONS

3.1 Deflected Shapes of Beams

The figure below shows different types of test conducted on beams and their failure,

crack observed and deflected shape.

Figure 3: - Deflected shape of control beam

The beams failed in flexure only. The cracks obtained are almost perpendicular to axis of

beam. The initial crack was at 40KN load for Control beams.

Figure 4: - Deflected shape of post-tensioned beam

The initial crack is observed at 60KN load. The crack width was more at flexure zones.

The failure of beam is in flexure zone as there is maximum number of cracks in this

region.

Figure 5:- Deflected shape of strengthen beam with single layer

The initial crack is observed at 70KN load. The cracks appeared was flexure crack and

shear crack, but maximum number of cracks is observed at flexure zone. At last stages of

loading delamination of BFRP was observed. Crushing of concrete at mid span was

observed near to final stages of loading.

Figure 6: - Deflected shape of strengthen beam with double layer

The initial crack is observed at 70KN load. Delamination of BFRP was observed at final

stages of loading. Crushing of concrete was observed at left point of loading at ultimate

load.

8548

ISSN: 2347-1697





Figure 7: - Deflected shape of retrofitted beam with single layer

The initial crack is observed at 70KN load. Crushing of concrete was observed at left

point of loading at ultimate load.

Figure 8: - Deflected shape and delamination of retrofitted beam with double layer

The initial crack is observed at 150KN load. Crushing of concrete was observed at left

point of loading at ultimate load. Delamination of BFRP was observed at final loads.

3.2 Load v/s Deflection

The beams of size 1300X150X200mm were subjected for loading at 10KN intervals and

deflection were measured at mid-span of beam using LVDT’s and results are plotted as

load v/s deflection curve and the same is shown in figure – 9 ,

Figure 9: - Load v/s Deflection curve for CB and PTB

Figure – 9 shows the load v/s deflection curve of control beam and post-tensioned beam.

It can be obsereved from the figure that as load increases deflection also increases in

control beam as well as in post-tension beam. It can also be seen that maximum load

carrying capacity is more in post-tension beam compared to control beam, i.e 170KN in

post-tensioned beam and 130KN for control beam respectively. Also, the control beam

0

20

40

60

80

100

120

140

160

180

0 5 10 15 20 25

LOA

D (

KN

)

DEFLECTION (mm)

CB

PTB

8549

ISSN: 2347-1697





experiences deflection of around 20.8mm at 130KN load, where as post-tensioned beam

experiences deflection of around 13.2mm at 130KN load. That is post-tensioned beam

experiences less deflection with more load carrying capacity when compared to control

beam.

Figure 10: - Load v/s Deflection curve for CB, PTB, SBSL and SBDL

Figure – 10 shows the load v/s deflection curve of control beam, post-tensioned beam,

strengthen beam with single layer and double layer BFRP. We can conclude that as the

loads are increased, deflection also increases. It can also be seen that maximum load

carrying capacity is more in case of strengthen beam with double layer BFRP compared

to control beam, post-tensioned beam and strengthen beam with single layer BFRP, i.e

200KN in strengthen beam with double layer BFRP then 130KN for control beam,

170KN for post-tensioned beam and 190KN for strengthen beam with single layer BFRP.

Also the control beam experiences deflection of around 20.8mm at 130KN, post-

tensioned beam experiences deflection of around 13.2mm at 130KN, strengthen beam

with single layer BFRP experiences deflection of around 8.7mm at 130KN load and

strengthen beam with double layer BFRP experiences deflection of around and 8.2mm at

130KN. That is strengthen beam with double layer BFRP experiences less deflection with

more load carrying capacity when compared to control beam, post-tensioned beam and

strengthen beam with single layer BFRP.

Figure – 11 shows the load v/s deflection curve of control beam, post-tensioned beam,

retrofitted beam with single layer and double layer BFRP. We can observe that as load

are increased, deflection also increases. It can also be seen that maximum load carrying

capacity is more in case of retrofitted beam with double layer BFRP compared to control

beam, post-tensioned beam and retrofitted beam with single layer BFRP, i.e 172KN in

retrofitted beam with double layer BFRP then 130KN for control beam, 170KN for post-

tensioned beam and 170KN for retrofitted beam with single layer BFRP. Also the control

beam experiences deflection of around 20.8mm at 130KN, post-tensioned beam

0

50

100

150

200

250

0 5 10 15 20 25

LOA

D (

KN

)

DEFLECTION (mm)

CB

PTB

SBSL

SBDL

8550

ISSN: 2347-1697





experiences deflection of around 13.2mm at 130KN, retrofitted beam with single layer

BFRP experiences deflection of around 10.6mm at 130KN load and retrofitted beam with

double layer BFRP experiences deflection of around and 9.4mm at 130KN. That is

retrofitted beam with double layer BFRP experiences less deflection with more load

carrying capacity when compared to control beam, post-tensioned beam and retrofitted

beam with single layer BFRP.

Figure 11: - Load v/s Deflection curve for CB, PTB, RBSL and RBDL

IV. CONCLUSIONS

Based upon experimental results and observations, following conclusions were drawn,

1. Strengthening of post-tensioned beams with BFRP wrapping improves the load

carrying capacity and reduces deflection importantly and, also strengthened beams

and retrofitted beams provide better performance when compared with control beam.

2. The load carrying capacity of post-tensioned beam, strengthened beam with single

layer BFRP and strengthened beam with double layer BFRP is increased by 23.52%,

31.57% and 35.0% when it is compared with control beams.

3. The load carrying capacity of retrofitted beam with single layer and double layer

BFRP is increased by 23.52% and 31.57% when it is compared with control beams. .

4. We can also confess that the deflection of post-tensioned beams, strengthened beams

and retrofitted beams tends to be small when it is compared with control beam.

V. REFERENCES

[1] M. Di Ludovico, A. Prota, G. Manfredi, and E. Cosenza, “FRP Strengthening of Full-Scale

PC Girders”, ASCE Journal of Composites for Construction, Vol. 14, No. 5, (2010) , pp 510-

520.

[2] Owen Rosenboom, Tare K. Hassan, Sami Rizkalla, “Flexural behaviour of aged pre-stressed

concrete girders strengthened with various FRP systems”, Construction and Building

Materials Elsevier Ltd, (2007), pp 764-776.

0

20

40

60

80

100

120

140

160

180

200

0 5 10 15 20 25

LOA

D (

KN

)

DEFLECTION (mm)

CB

PTB

RBSL

RBDL

8551

ISSN: 2347-1697





[3] Owen Rosenboom, and Sami Rizkalla “Behavior of Prestressed Concrete Strengthened with

Various CFRP Systems Subjected to Fatigue Loading” ASCE Journal of Composites for

Construction, Vol. 10, (2006), pp 492-506.

[4] Yujin Liang, Changsen Sun, and Farhad Ansari “Damage Assessment and Ductility

Evaluation of Post Tensioned Beams with Hybrid FRP Tendons” Journal of composites for

construction. Vol.15, (2011), pp 274-283.

[5] Bharath G R, Dr. H N Jagannatha Reddy, “Strengthening of Post-Tensioned Beams by

Externally Bonded and Anchored Natural Sisal Fiber Reinforced Polymer Composites”,

International Research Journal of Engineering and Technology (IRJET), Volume: 02 (2015).

[6] Vathsala and H N Jagannath Reddy, “An Experimental and Analytical Investigation of Post-

Tensioned Concrete Beam Strengthened Using GFRP Sheet” International Journal of

Engineering Research & Technology (IJERT) Vol. 3 (2014).

[7] Yasmeen Taleb Obaidat, Susanne Heyden, Ola Dahlblom, Ghazi Abu-Farsakh and Yahia

Abdel-Jawad, “Retrofitting of reinforced concrete beams using composite laminates”,

Construction and Building Materials, pp 591-597, ( 2011).

[8] Vathsala, Jagannath Reddy and Malathesha, “Behaviour of Post-tensioned Beams

Strengthened by CFRP And GFRP Wrapping”, International Journal of Engineering

Research & Technology (IJERT), Vol. 2, (2013).

Authors Profile

Varun G received degree in Civil Engineering from Bangalore Institute

of Technology, VTU in 2015, and pursing Post Graduation in Structural

Engineering at Dr. A.I.T, Bengaluru. His interests include theoretical

and experimental studies on Pre-stressed concrete structures.

TO CITE THIS PAPER

Varun,G. , Vijaya,S. , Shivakumaraswamy,B. (2017) :: “An Experimental Investigation

on Post Tensioned Beams with BFRP Fabrics” International Journal of Informative &

Futuristic Research (ISSN: 2347-1697), Vol. (4) No. (12), August 2017, pp. 8543-8551,

Paper ID: IJIFR/V4/E12/020.

Available online through- http://www.ijifr.com/searchjournal.aspx

http://www.ijifr.com/searchjournal.aspx

An Experimental Investigation on Post Tensioned Beams · PDF fileBangalore- Karnataka, India 2 nd Dr. S.Vijaya Professor Department of Civil Engineering, Dr. Ambedkar Institute Of

Documents