Dr Andreas LampropoulosSchool of Environment and Technology, University of Brighton, UK

WG 7: Earthquake Resistant Structures

Working Group 7 Annual Meeting

Strengthening of existing structures using novel ultra high performance cementitious materials

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There is a need for strengthening the vast majorityof the existing structures in earthquake prone areas

Chi Chi Taiwan (1999) [EERI]

Golcuk, Turkey (1999) [EERI] 

Damaged after strong earthquakes

Designed Before the implementation of a seismic risk Code or under the provisions of old seismic Codes

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Strengthened elements with additional concrete layers/jackets  Cast in two phases – Composite Elements

Concrete to concrete interfaces

Shear stress < Shear strength

Increase shear strength

Roughening of the interface DowelsBent down bars to connect the reinforcement of the oldand the new concrete

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Concrete shrinkage Volume change in concrete due to loss of moisture

Tensile stresses

Slip at the interface Debonding

Cracks at the new layer

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Finite Element Modelling of strengthened elements

a) Concrete modellingb) Steel – concrete bondc) Concrete shrinkaged) Old – new concrete Interface

Calibration with Experimental results

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Interface

Concrete shrinkage

-100 -80 -60 -40 -20 0 20 40 60 80 100-200

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(kN

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Deflection (mm)-100 -80 -60 -40 -20 0 20 40 60 80 100

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(kN

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Deflection (mm)-100 -80 -60 -40 -20 0 20 40 60 80 100

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New sustainable materials with less shrinkage & higher strength can improve the performance of the strengthened elements

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Ultra High Performance Fibre Reinforced Concrete (UHPFRC)

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Direct tensile tests

Young’s modulus: 57.5 GPa Tensile strength: 11.5 MPa

Paschalis S, Lampropoulos A. Size effect on the flexural performance of Ultra High Performance Fiber Reinforced Concrete (UHPFRC). HPFRCC-7 7th RILEM conference (2015)

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Initial columnJacketed column

Columns strengthened with UHPFRC

Lampropoulos AP, Paschalis S, Dritsos SE. UHPFRC versus RC jackets for the seismic upgrade of columns. IABSE conference (2015)

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Jacket’s thickness effect

Column’s stiffness was increased 3-10 times as jacket’s thickness was increased from 25mm to 75mm

The respective increment of the ultimate load was found to be in the range of 2.6-3.8 times

Lampropoulos AP, Paschalis S, Dritsos SE. UHPFRC versus RC jackets for the seismic upgrade of columns. IABSE conference (2015)

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RC jacketed columns

Lampropoulos AP, Paschalis S, Dritsos SE. UHPFRC versus RC jackets for the seismic upgrade of columns. IABSE conference (2015)

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Stiffness improvement Ultimate load improvement

RC jacket: ~ 8 times higher UHPFRC jacket: ~ 10 times higher

(compared to the initial column)

UHPFRC jacket

Higher stiffness increment RC jacket

Higher ultimate load increment

RC jacket: ~ 5 times higher UHPFRC jacket: ~ 4 times higher

(compared to the initial column)Lampropoulos AP, Paschalis S, Dritsos SE. UHPFRC versus RC jackets for the seismic upgrade of columns. IABSE conference (2015)

Beams strengthened with UHPFRC

UHPFRC in the compressive side

UHPFRC in the tensile side

Three side UHPFRC jacket

Lampropoulos AP, Paschalis S, Tsioulou O.T. Dritsos SE., ICCRRR (2015).Lampropoulos AP, Paschalis S, Tsioulou O.T. Dritsos SE., Engineering Structures

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5. Conclusions

Significant improvement of the performance of the columns strengthened with UHPFRC jackets was highlighted

Stiffness was increased 3-10 times for jacket’s thickness 25mm to 75mm

The respective ultimate load increment was found to be 2.6-3.8 times

Jacket’s thickness effect:

Strengthened columns

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5. Conclusions

Regarding the comparisons of the two examined techniques (UHPFRC versus RC jacketing)

UHPFRC jacket was found to be almost 30% more efficient compared to the RC jacket in terms of column’s stiffness

In terms of ultimate load capacity, RC jacketing was found to be more efficient, since 26% higher ultimate load increment was observed compared to the respective results of UHPFRC jacketed columns

Strengthened beams

My and Mu increment for specimens strengthened with UHPFRC in the tensile side was found equal to almost 30%. For beams strengthened in the tensile side with an additional RC layer the increment was considerably higher (150% for My and almost 100% for Mu).

In case of beams strengthened in the compressive zone, the additional of UHPFRC resulted to an increment of My and Mu almost 30%, while the increment was slightly lower 20-25 % when normal concrete was used.

Highest moment increment was observed for a three side UHPFRC jacket. My and Mu were increased 160-180%.