Effect of Impact load on Fibre Reinforced Plastic(FRP) wrapped RC Beams By

J. Pradeep(03CE3001)

Under the guidance of

Prof.S.K.Bhattacharyya

Introduction to FRPFRP is polymer reinforced with fibres like glass, carbon, aramid etc .., retaining the element properties yet functioning like a single element. High strength to weight ratioCorrosion resistanceEasy installation

FRP consists of Fibre material embedded in a layer of Resin matrix to obtain a layer of FRP composite called lamina.

The fibre composites are being used for repair and retrofit of structures in conjunction with steel, concrete and masonry.

Loading on a StructureStructure undergoes various types of loading during its service life.

Impact Load is any sudden load that may occur on the structure due to collisions, falling loads etc.

The characteristics of impact loading are different from static and dynamic loading, for the same structure .

Effect of impact loading on RC structural elements has been studied earlier.

Studies on fibre composites have been carried out on static loading.

Introduction to Work

Study on the effect of impact loading on Structures strengthened with FRP is relatively sparse.

Project explores the use of composites in strength enhancement of RC beams under impact loading.

Fibre reinforced Plastics are considered in the wrapping of the RC beams.

Objective of the Work

To study the effect of the impact loading on the RC beams wrapped with FRP and compare with Normal RC beams.

To Experimentally observe the Impact resistance improvement in RC beams strengthened with different layers of FRP wrapping.

Current literatureImpact loading on RC beams with varying material properties and configurations are studied.

The absorption capacity and type of failure of RC beams under varied energy impacts.

FRP materials are studied for mechanical response, damage and type of failure of fibres under low velocity impact.

RC beams strengthened with CFRP laminates were studied for strength improvement under static loading.

Current literature..Impact loading on beams strengthened with CFRP Laminates was studied for stiffness of structure and crack properties.

No exclusive work on impact loading of RC beams with FRP wrapping has been found.

Scope of the WorkTo get an estimate of the energy absorption capacity of the concrete beam under the impact load.

Fabrication and casting of the beam specimens with and without FRP layer wrapping.

To develop the experimental set up required carrying out test of impact loading on the specimens.

Scope of the Work(contd.)

To carry out impact tests on the prepared specimens and acquire data for characterization.

To make a comparison of the experimental results with related studies in the field.

Fig : Simple detail of experiment setup

Impact loading Impulsive loading given to the structure by the impactor.

The loading is given on a simply supported beam by a impact hammer from a determined height .

Kinetic energy of the impactor transfers into the energy stored in the Beam and energy is dissipated through the supports.

Energy of the ImpactEnergy applied to the beam by the impactor is spent as :

Local deformation of the beam at the contact pointElastic energy in the beam Plastic energyEnergy dissipation by wave propagation

The impact resistance of beam is dependent on structural properties of the beam and energy imparted.

Experimental Study :The experiment is performed in stages:

Casting of the specimens

Wrapping of the RC beam specimens with single layer and double layer FRP.

fabrication of the Experimental setup

Configuration of the specimens with the setup for the testing.

Dimensions of the experimental setup

Casting of the specimenTwo batches of RC beams are cast , three beams each.

1150 mm x 150 mm x 100 mm size of each beam.

In a batch ,a control specimen, a Single FRP wrapped RC beam ,a Two layer FRP wrapped RC beam.

RC Beam Details

Beam specifications Design for M20 concrete with the specifications from IS 10262:1982

Maximum aggregate size of 20 mm

3 beams with 6 cylinders and 6 cubes were cast in a batch.

Static tests were performed on the cubes and cylinders to obtain the concrete strength of the batch.

Wrapping of RC BeamsSingle layer and Double layer FRP wrapping.

E-Glass fibre cloth (0.32 mm thickness) is treated with resin

The resin used is a 9:1 mixture of Araldite CY-230 and hardener HY-951

Hand lay up technique used to wrap the Beams.

Fabrication of test setupThe Impact hammer is a solid steel cylinder with a mass of 16 kg and dimensions 150 mm x 125 mm.

A steel sphere of 50 mm diameter is fit at the bottom to give a hemispherical head .

Support system for the specimen to avoid jumping ,during the impact.

Instruments used in Experiment:UTM (300 ton)

Drop weight test apparatus

Accelerometers along with spectrum analyzer

Electrical strain gauges

Load cell

Hi-Speed Camera

Computers to capture data

Position of gauges on the beam.

Support Conditions : Beam is simply supported on two ends.

A bracing mechanism is provided at the right support to avoid jumping.

A Load cell is installed at the left support.

Left end of beam loosely tied to the support to avoid jumping.

Setup (contd.)Hi-speed camera is placed in the location and focused to capture the impact event at the center as the drop occurs at the centre of the beam.

Placing all these gauges and the acquisition connected to three computers separately

Drop was given to acquire the data.

Beam with all gauges in Place

Testing of an Unwrapped RC Beam8 drops were imparted on the beam.

The beam failed after 8th drop due to spalling of concrete .

Maximum reaction observed at 7th drop.

Maximum strain observed at the strain gauge ,Sg2 of value 0.081.

Residual flexural strength observed as 4.6 tons

Reaction at the support

Deflection vs. number of blows

Strain distribution vs. Number of blows

Strain Profile on beam with blows

Position of gauges on the beam.

Strain at the bottom surface(Sg5,Sg6)

Spalling of concrete

Failure after 8th drop

Failure after 8th drop..(top view)

RC Beam with single layer of FRP:

Maximum deflection and maximum reaction observed at 11th drop.

Acceleration decreased considerably after 10th drop.

No appreciable change is observed in the data after 15 drops.

A clear bulge appeared at the transverse face of the beam.

Residual flexural strength observed as 6.1 tons

Acceleration at A2 vs. Number of blows

Reaction at support (singly wrapped FRP)

Deflection vs. Number of blows(singly wrapped FRP)

Strain distribution pattern at Sg2,Sg3

Crack pattern at the 8th blow

Crater after 10th drop

Localized bulge after 15th drop

RC beam wrapped with two layers of FRP:Maximum reaction at the support is observed at 12th drop.

No appreciable change is observed in the data after 20 drops.

A clear , wider bulge appeared at the transverse face of the beam.

Residual flexural strength observed as 6.9 tons

Reaction at support

Deflection at the centre

Bulging observed after 13th blow

Wider bulging after 21st blow

Comparison: Reaction at support

Comparison : Deflection at centre

Comparison : Residual strength

Comparison with Laminates : The number of blows resisted by specimens increased significantly.

For the same impact energy , reaction force increased with thickness and weight of laminates.

The deflection of the beams decreased with increase in stiffness of laminates.

Cracking of the beams is not well prevented by the laminates .

Spalling of concrete is not well controlled by the laminates .

Conclusions : The impact resistance increases as shown by the number of blows the specimens can resist after the FRP wrapping.

The residual flexural strength shows substantial increase in flexural strength due to wrapping , even after large number of blows .

The excessive spalling of the concrete gets checked with the wrapping of FRP layers.

Conclusions(contd.)Cracking of the RC beam , both formation and propagation are effectively controlled by wrapping.

These results show the superiority of FRP wrapped RC beams under impact loading.

References:A.Bentur,S.Mindess and N.Banthia, The behavior of concrete under impact loading : Experimental Procedures and method of analysis

Barbero,E.J, Introduction to composite material design,2nd edition, 1999 ,Taylor and Francis, Philadelphia, Pennsylvania.

B.R Hughes and H.Al-Dafiry, Impact Energy Absorption at contact zone and supports of Reinforced plain and fibrous concrete Beams,Construction and Building Materials,Vol.9,No.4,pp. 239-244,1995.

References..Cantwell,W.J.Smith,K.(1999).The static and dynamic response of CFRP-strengthened concrete structures.,J.Mat.Sci.Letters,18,pp 309-310.

N Lt Col Chakraborty,Low velocity impact on FRP encased concrete beams, Indian Institute of Technology Kharagpur, May 2007.

D.L.Grote,S.W.Park,M.Zhou, Dynamic behavior of concrete at high strain rates and pressures : I. Experimental Characterization, International Journal of Impact Engineering,25,pp 869-886,2001.

ReferencesErki.M.A and Meier.U, Impact loading of concrete beams Externally strengthened with CFRP laminates,J.Comp.Constr.,ASCE,3(3),pp 117-124,1999Jerome,D.M. and Ross.C.A, Dynamic response of concrete beams externally reinforced with carbon fiber reinforced plastic(CFRP) subjected to impulsive loads, Structures Under Extreme Loading Conditions, ASME , PVP 325,pp 83-94,1996Juan C. Serrano-Perez, Uday K. Vaidya, Nasim Uddin , Low velocity impact response of autoclaved aerated concrete/CFRP sandwich plates ,Composite Structures , 80 , pp 621-630,2007.

References.Suaris,W. and Shah,S.P, Properties of concrete subjected to Impact, J.Struct.Eng., ASCE, 109(7), pp 1727-1741,1983.

Tang T. and Saadatmanesh.H, Behavior of concrete beams strengthened with fiber-reinforced polymer laminates under impact loading.J.Comp.Constr. 7(3), pp 209-218, 2003.

Thank You

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