An Experimental Study on the Effect of Fibre Reinforced Concrete on the Behaviour of the Exterior

Beam-Column Joints Subjected to Cyclic Loading

A BRIEF INTRO ON BEAM COLUMN JOINT

╠ During a strong earthquake, beam-column joints are subjected to cyclic loading.

╠ They constitute one of the critical regions.

╠ They must be designed and detailed to dissipate large amounts of energy without

appreciable loss of strength and stiffness.

╠ The ductile behaviour of reinforced concrete structures dominantly depends on the

reinforcement detailing at the beam-column joints.

╠ It is subjected to high shear and bond-slip deformations under earthquake loading.

╠ Failure of the joint region can not only damage the column load paths but also

adversely affect the ductility and energy dissipation capacity of the frame as whole.

In exterior joints the beam longitudinal reinforcement that

frames into the column terminates within the joint core.

After a few cycles of inelastic loading, the bond

deterioration initiated at the column face due to yield

penetration and splitting cracks which on further loading,

progresses towards the joint core.

Repeated loading will aggravate the situation and a

complete loss of bond up to the beginning of the bent portion

of the bar may take place.

The longitudinal reinforcement bar, if terminated straight,

will get pulled out due to progressive loss of bond. The pull

out failure of the longitudinal bars of the beam results in

complete loss of flexural strength. This kind of failure is

unacceptable at any stage.

Hence, proper anchorage of the beam longitudinal

reinforcement bars in the joint core is of utmost importance.

The horizontal ties in the form of transverse

reinforcement in the joint provide effective restraints against

the hook when the beam bar is in compression

a) Forces b) poor detail c) sufficient detail

Forces acting in the exterior joint during earthquake

Overall Review of the Study on RC Beam-Column Joints

• Mustafa GENCOLGU et al (2002), reported that for the

ductile behaviour of beam-column joints, closely spaced transverse

reinforcement is required by earthquake codes. However, placement

of this reinforcement in joints always causes some difficulties due

to a lack of qualified workmanship.

• According to these evaluations, it is shown that the usage of

fibre reinforcement concrete in beam-column joints can be an

alternate solution for minimizing the density of transverse

reinforcement.

The general arrangement of the experimental setup and the beam tip displacement transducers (from 2 to 16). - Mustafa

GENCOLGU et al (2002)

STRAIN CONTROLLED LOADING - Mustafa GENCOLGU et al (2002)

• IDAYANI BINTI SALIM et al (2007) reported the casting of the beams and slabs at a particular floor level together with the beam-column connection zone using the same lower grade of concrete. The columns above and below the beam column joint were cast with markedly higher grade of concrete. Such casting sequence forms beam-column connection zones with significantly lower concrete strength than that in the upper and lower columns.

• The results show that lower concrete strength (Grade C30) in the connection zone reduces its ultimate capacity and shear stress. It was also found that additional links in the connection zone cast with Grade C30 concrete improves the shear capacity of the joint beyond that achieved by the specimen with Grade C80 concrete with out additional link in the zone.

• K.R.Bindhu et al (2008) studied on the effect of cross inclined

bar at the joint as confining reinforcement on the behaviour of exterior

reinforced concrete beam-to-column connections subjected to earthquake

loading.

• The author sorted four exterior beam-column joint sub

assemblages in to two groups. Group-A comprises of 2 joint assemblages

with joint detailing as per ductile detailing code in India (IS 13920:1993)

with 2 axial load cases and Group-B comprises of 2 specimens with

cross inclined bars as confining reinforcements.

• The dimension of the column is 1000x150x100 mm and that of

beam is 550x100x150 mm. The experimental results are compared with

analytical results using Finite Element Software ANSYS.

• The conclusions drawn are all the specimens failed by developing

tensile cracks at interface between beam and column. The joint region of

specimens of group-B is free from cracks except some hairline cracks,

which show the joints had adequate shear resisting capacity.

• The increase in column axial load improves the load carrying

capacity and stiffens the joints. Also, this increases the energy absorption

capacity of the specimens with cross-incline bars.

• From the enhanced performance of the detailing of joints with

cross inclined bars (Group-B), it is suggested that the same can be

adopted for beam-column joints in low to moderate seismic risk regions.

Continued….

•To study the effect of different fibers on the given type of

reinforcement configuration (detailing) of the beam column joint.

•To study the increase in strength of the joints and increase in

ductility due to the addition of different fibres.

OBJECTIVES OF THE CURRENT INVESTIGATION

FACTORS EFFECTING PROPERTIES OF FIBRE REINFORCED CONCRETE

Fibre reinforced concrete is the composite material containing fibres in the cement matrix in an orderly manner or randomly distributed manner.

Its properties would obviously, depend upon the efficient transfer of stress between matrix and the fibres, which is largely dependent on the,

Type of fibre

Fibre geometry

Fibre content

Orientation and distribution of the fibres

Mixing and compaction techniques of concrete

Size and shape of the aggregate.

Parameters which are chosen as variables

I) Type of fibres

There are different type of fibre which may be used as concrete

admixtures.

1. Glass fibre (Used for Study)

2. Steel fibre

3. Nylon fibre

4. Polyester fibre (used for study)

5. Natural fibresII) Volume fraction of fibres

Fibres added with concrete in four volume fractions 0.25%, 0.5%, 1.0% and 1.5% weight of concrete.

And hence 9 specimens were cast including one control specimen.

PROPERTIES OF FIBRES

•Glass fibre (Discrete glass fibres)Tensile strength : 1020 to 4080 N/mm2

Trade name : CEM-FILAlkali resistance : GoodDurability : High

•Polyester fibre (Recron 3s) Cut length : 6mm or 12 mm Shape of fibre : special for improved holding of

cement aggregatesTensile strength : 400-600 N/mm2

Dispersion : Excellent Acid resistance : Excellent

Alkali resistance : Good Melting point > 250oC

METHODOLOGY

i.Material testing

a) coarse aggregate

b) fine aggregate

ii.To prepare the design mix for the model

iii. Instrumentation

a). Measurement of load and deflection

b). Measurement of joint shear distortion

c). Measurement of strain

1. Displacement ductility

• Effect of reinforcement detailing on displacement ductility

• Effect of confinement on displacement ductility

Displacement ductility = maximum displacement

displacement at first yield

2. Stiffness behaviour

• Effect of reinforcement detailing on stiffness behaviour

• Effect of confinement on stiffness behaviour

3. Crack pattern

Preparation of BEAM-COLUMN joint model:•The test specimen is a typical exterior beam column joint. •The height of column is 1200 mm and the length of beam is 800 mm from the face of the column.•The same dimensions were adopted for all the test specimens.

Column Detail

Beam Detail

BEAM-COLUMN joint model

Materials unitPlain

concrete

Glass fibre reinforced concrete

Polyester fibre

reinforced concrete

Cementkg/m3 430 430 430

Aggregate (12mm)

kg/m3 910 910 910

Sandkg/m3 445 445 445

Waterkg/m3 180.6 180.6 180.6

Fibrekg/m3 ___

0.25% - 60.5% - 121.0% - 241.5% - 36

0.25% - 60.5% - 121.0% - 241.5% - 36

Characteristics of the concrete mixtures

Reinforcement bar – Designed as per IS:13920-1993

Plywood mould prepared for the beam-column joint specimen

Reinforcement bar just placed inside the mould

Specimen after finishing work

Completed specimen sample

Experimental setup

CONCLUSION

From the studies of previous researchers, it has been found that

the ductility provisions increases the moment carrying capacity in the

joints and so the addition of the fibres which are having good tensile

strength increases the strength further and acting as a crack control

admixtures. It may be expected that the ultimate load carrying

capacity will become constant beyond certain percentage increase of

fibres and so an economic and optimum value may be obtained for a

better joint strength.

REFERENCES:-1. Mustafa Gencoglu, Ilhan Eren, “An experimental study on the effect of steel fibre reinforced concrete on the behaviour of the Exterior Beam-Column joints subjected to Reversal Cyclic loading”, Turkish J.eng. Env. Sci , 493-502, Feb – 2002. 2. H.J.Pam , J.C.M. Ho, “An overview of research at HKU on HSRC columns and beam-column joints for Low-Medium seismic risked Regions”, EJSE Special Issue 2008. 3. Fumio KUSUHARA, Keiko AZUKAWA, “Tests of reinforced concrete interior beam-column joint sub assemblage with eccentric beams”, 13th World Conference on Earthquake Engineering, Canada, Page No. 185, August 1-6, 2004. 4. K.R.Bindhu and K.P.Jaya, “Performance of exterior Beam Column Joints with Cross-Inclined bars under seismic Type loading”, Journal of Engineering and Applied Sciences 3(7): 591-597, 2008. 

5. Jaehong Kim and James M. LaFave, “Joint shear behaviour prediction in RC beam-column connections subjected to seismic lateral loading”, The 14th World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China. 6. L. Caladoa, L. Simões da Silvab, “Cyclic behaviour of steel and composite beam-to-column joints”, University of Coimbra, Portugal. 7. Yoshiko Tsunehara, “Seismic performance of full-scale reinforced concrete beam-column joints”, university of California, Los angels.