Post on 11-Jan-2020
transcript
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
2
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
4
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
5
Concrete shrinkage Volume change in concrete due to loss of moisture
Tensile stresses
Slip at the interface Debonding
Cracks at the new layer
6
Finite Element Modelling of strengthened elements
a) Concrete modellingb) Steel – concrete bondc) Concrete shrinkaged) Old – new concrete Interface
Calibration with Experimental results
7
Interface
Concrete shrinkage
-100 -80 -60 -40 -20 0 20 40 60 80 100-200
-150
-100
-50
0
50
100
150
200
Load
(kN
)
Deflection (mm)-100 -80 -60 -40 -20 0 20 40 60 80 100
-200
-150
-100
-50
0
50
100
150
200
Load
(kN
)
Deflection (mm)-100 -80 -60 -40 -20 0 20 40 60 80 100
-200
-150
-100
-50
0
50
100
150
200
Load
(kN
)
Deflection (mm)
New sustainable materials with less shrinkage & higher strength can improve the performance of the strengthened elements
9
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)
10
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)
11
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)
12
RC jacketed columns
Lampropoulos AP, Paschalis S, Dritsos SE. UHPFRC versus RC jackets for the seismic upgrade of columns. IABSE conference (2015)
13
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
15
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
16
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%.