ewha womans university architectural structure laboratory investigation of rehabilitation effects on...

EWHA WOMANS UNIVER-SITY ARCHITECTURAL STRUCTURE LABORATORY

Investigation of Rehabilitation Ef-fects on Fire Damaged High Strength Concrete BeamsEun Mi Ryu 1, Ah Young An 1, Ji Yeon Kang 2, Yeong Soo Shin 3, Hee Sun Kim 3

1 : M.S., Ewha Womans University, Seoul, South Korea 2 : Ph.D, Ewha Womans University, Seoul, South Korea

3 : Professor, Ewha Womans University, Seoul, South Ko-rea

CONTENTSResearch backgrounds and ob-jectivesExperimental approach and resultsAnalytical approach and results

ConclusionParametric studies

EWHA WOMANS UNIVERSITY ARCHITECTURAL STRUCTURURE LABO-RATORY

3 Research backgrounds and ob-jectives When high strength reinforced concrete is ex-posed to high temperature due to fire, deterio-rations occur :

Reduction in strength and elastic modulus Cracking and spalling of the concrete Loss of bond between concrete and steel

< Fire incidents > < cracking and spalling after fire>


4 Research backgrounds and ob-jectives Types of repair materials

Fibre Reinforced polymer (FRP) Epoxy injection for structural cracks Polymeric mortar Concrete jacketing Steel Jacketing Shotcreteing


5 Experimental approach and results Experimental approach

Specimen- From the compressive test, averaged value is obtained as 54.39MPa- Mixture ratios for concrete are listed in Table- Width, depth and length of high strength concrete beams are 250mm, 400mm and 4700mm, respectivelycompressive strength(MPa) W/C(%) s/a(%) Weight per unit volume (kg/m3)W C S G AD54.39 31 41 168 542 666 974 1.6



Fire test and rehabilitation- Specimens are heated according to the ISO 834 standard time temperature curve- The beams are subject to four-point loading- After fire test, fire damaged U-shaped concrete cover is removed. And removed part is filled with polymeric ce-ment mortar.

< The horizontal heating furnace for fire test > < rehabilitated beam >



Test set-up- Specimens are simply supported with an effective span of 3750mm and subject to four-point loading Variable - cover thickness(40, 50mm), fire exposed time period(0, 1 hour), rehabilitation(or not)

< Test set-up and Detail of gages and LVDT >

Speci-men Cover Thick-ness(mm)Fire ex-posed time pe-riod(sec)

Rehabilita-tion H4BC 40 - -H4B1H 40 3600 -H4B1HR 40 3600 ○H5BC 50 - -H5B1H 50 3600 -H5B1HR 50 3600 ○


8 Experimental approach and results Experimental results

Specimen having cover thickness of 40 mm and 50 mm

< 40mm >

5.4 %(ultimate load) 0.7%(ultimate load)

< 50mm >


9 Experimental approach and results Experimental results

< Ultimate load and slope from FE analy-sis >< Experimental load-deflection curves >

Specimen Ultimate load(kN) Slope(kN/mm)Exp_H4BC 254.1 13.3Exp_H4B1H 220.1 9.4Exp_H4B1HR 268.0 14.3Exp_H5BC 248.0 13.2Exp_H5B1H 177.0 6.6Exp_H5B1HR 249.7 14.0

7.3 %(ultimate load)


10 Analytical approach and re-sults Analytical approachABAQUS version 6.10-3, is used. And three-dimensional FE models are with width, depth and length equal to experi-mental conditions

Step 1 Temperature analysis Step 2 Integrated temperature-structural analysis Step 3 Structural analysis of rehabilitated beams and damaged beams

< FE model >

Part Temperature Ratio of origi-nal strength Concrete lower than 500°C 90 %

Steel lower than 500°C 90 %< Properties of rehabilitated beam>


11 Analytical approach and re-sults Analytical results

Specimen having cover thickness of 40 mm and 50 mm

< 40 mm> < 50 mm>


12 Analytical approach and re-sults Analytical results

Stress contour of FE models for beam having cover thickness of 40mm- High stresses are distributed in rehabilitated part while low stresses are found in damaged concrete part.

(a) Stress contour of concrete part

(b) Stress contour of rehabilitated part


13 Parametric studies Approach of parametric studies

Parametric studies are performed in order to predict the structural behavior of high strength RC beam ac-cording to strength of polymeric mortar. Parameters are strength of two different polymeric cement mortar such as 59.7MPa and 44.4MPa.

Description Unit Mortar type A Mortar type BElastic modu-lus MPa 29210 25540Compressive strength MPa 59.72 44.40Poisson’s ra-tio 0.2 0.2Density kg/m3 20 20

Model Condition Cover thicknessH4B1HRA Rehabilitated with mortar type A 40mmH4B1HRB Rehabilitated with mortar type B 40mmH5B1HRA Rehabilitated with mortar type A 50mmH5B1HRB Rehabilitated with mortar type B 50mm

< Properties of polymeric cement mortar >

< List of models according to polymeric cement mortar >


14 Parametric studies Results of parametric studies

Specimen having cover thickness of 40 mm and 50mm

< 40 mm> < 50 mm>

11.4 %(ultimate load) 13.3%(ultimate load)


15 Conclusion The results obtained from experiments and FE analyses are summarized as follows:

In the experiments, the ultimate load of the rehabili-tated beam is similar to that of the control beam. So, high strength concrete beam can be reused if a damaged beam due to fire is rehabilitated with polymeric cement mortar. The load-deflection curves of the beams from the FE analyses are in good agreement with those of the experiments. The ultimate loads of the beams heated for 1hour are fully recovered regardless of strengths of poly-meric cement mortar. It is found that the ultimate loads and slopes of beams having cover thickness of 40mm are higher than those of beams having cover thickness of 50mm.

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