Research on pre stressed reinforced frp strip in repairing and upgrading service capacity of old concrete bridge

VIETNAM NATIONAL UNIVESITY, HANOI VIETNAM JAPAN UNIVERSITY PHAM VAN GIAO RESEARCH ON PRE-STRESSED REINFORCED FRP STRIP IN REPAIRING AND UPGRADING SERVICE CAPACITY OF OLD CONCRETE BRIDGE MASTER’S THESIS 2020dsfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfjsfsdfsdfsdhhffsdfsd Hanoi, 2020 VIETNAM NATIONAL UNIVESITY, HANOI VIETNAM JAPAN UNIVERSITY PHAM VAN GIAO RESEARCH ON PRE-STRESSED REINFORCED FRP STRIP IN REPAIRING AND UPGRADING SERVICE CAPACITY OF OLD CONCRETE BRIDGE MASTER’S THESIS MAJOR: INFRASTRUCTURE ENGINEERING CODE: 8900201.04 QTD RESEARCH SUPERVISOR: Dr DANG VIET DUC Vdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdfsdf Hanoi, 2020gfgfgfgfgfgfgfdgdfgdfgdfgdHanoi, 2020fgdfgdfgdfgdfgdHanoi, 2020gdfgdfgdfgdfdgdf ABSTRACT Currently in Vietnam, the method bonded FRP material is becoming popular in repairing and upgrading old bridge, thanks to the advantages of CFRP materials, construction methods and extremely large demand since the large number of bridges need to be strengthened Nevertheless, this method has not yet promoted the maximum advantages of FRP materials The pre-stressed CFRP method is advanced method However, the addition of stress to pre-stressed concrete beams should be considered because the pre-stressed concrete structure has been stressed, if the stress value is unreasonable, the reinforcement will cause the structure to be failure This study focuses on stress change analysis in concrete, using Load Resistance Factor Rating Method and Finite Element Method to consider the feasibility of pre-stressed method when reinforced pre-stressed concrete structure i ACKNOWLEDGEMENTS First of all, I would like to thank Vietnam Japan University for creating the best conditions for me to study during the part time Here I have a chance to study and research with excellent lecturers in Vietnam and Japan Vietnam Japan University is place to help me change my mindset and vision I express my deepest thanks to my supervisor Dr Dang Viet Duc for his enthusiasm, patience, advice He took time to listen, guide and keep me on the correct path, his support has been priceless I would like to express my deepest thanks to Prof Nguyen Dinh Duc, Prof Hironori Kato, Dr Nguyen Tien Dung, Dr Phan Le Binh and Mr Bui Hoang Tan for always supporting, helping and giving me useful advices I would like to thanks to Japan International Cooperation Agency (JICA), VNU Vietnam Japan University (VJU) and the University of Tokyo and special the collaboration between Vietnam and Japan government for giving me great learning opportunity I am warmly thankful Dr Sakai Yuya and The University of Tokyo students for their enthusiasm, friendliness and kind help me during internship The last but not least, I would like to express my enthusiastic to thank my family, my friends This thesis could not have been done without their supporting and encouragement ii TABLE OF CONTENTS Page ABSTRACT i ACKNOWLEDGEMENTS ii TABLE OF CONTENTS iii LIST OF TABLES v LIST OF FIGURES vi LIST OF ABBREVIATIONS ix CHAPTER INTRODUCTION .1 1.1 Necessity of the study .1 1.2 The objective of the study 1.3 Scope of the study 1.4 Structure of thesis .3 CHAPTER LITERATURE REVIEW 2.1 The causes of pre-stressed concrete structure deterioration .4 2.1.1 Change of vehicle load 2.1.2 Construction issues 2.1.3 Service issues .5 2.2 The solution repairing and strength bridge in Vietnam 2.2.1 Application of conventional materials 2.2.2 Application of bonded steel plates 2.2.3 Strengthening external tendon system 2.2.4 Bonded FRP material 2.3 Overview of FRP material 10 2.4 Measures for pre-stressing of FRP strip 11 2.5 Enhance structure with pre-stressed CFRP 13 CHAPTER METHODOLOGY 17 3.1 General 17 3.2 Structural objectives .18 3.3 LRFR Method 25 3.3.1 Section properties 26 3.3.2 Load Determination .28 iii 3.4 Finite Element Method 31 3.5 Structural strengthening design 33 3.5.1 Assessment structural capacity 33 3.5.2 Criteria according to LRFR 36 3.5.3 CFRP design 36 3.5.4 Structural assessment after strengthening 38 CHAPTER RESULTS & DISCUSSIONS 39 4.1 Strengthening of T33 and T24.7 .39 4.1.1 LRFR assessment for old structures 39 4.1.2 LRFR for strengthen structures 40 4.2 Comparison of two structural analysis method 49 4.2.1 FEM assessment for old structures 49 4.2.2 FEM for strengthen structures .50 CHAPTER CONCLUSIONS & RECOMMENDATIONS .56 REFERENCES 57 iv LIST OF TABLES Table 3.1 Concrete property for old concrete beam design 21 Table 3.2 High tensile steel property for old concrete beam design 21 Table 3.3 CFRP specifications provided by Sika 22 Table 3.4 Cross section property without high tensile steel 27 v LIST OF FIGURES Figure 2.1 H30 arrangement according to old standard Figure 2.2 HL93 arrangement according to current standard Figure 2.3 Using epoxy to fill crack in concrete Figure 2.4 Using concrete mortar to patch surface beam Figure 2.5 Strength with steel plate Figure 2.6 Using external tension system Figure 2.7 Bonded FRP material 10 Figure 2.8 Stress - Strain relationship of composite polymer materials [1] 11 Figure 2.9 The method of creating pre-stressing for FRP strip [3] 12 Figure 2.10 The system was used according to research [5] 12 Figure 2.11 Pre-stressing system of CFRP strip [6] 13 Figure 2.12 Relationship between Moment – Deformation [3] 14 Figure 2.13 Load–deflection relationship Beam strength with bonded FRP [8] 15 Figure 2.14 Load–deflection relationship Beam strength with unbonded FRP [8] 15 Figure 3.1 The flowchart of the study 17 Figure 3.2 Bridge cross section T33 19 Figure 3.3 ½ T33 cross section 19 Figure 3.4 Section A-A 19 Figure 3.5 Section B-B 19 Figure 3.6 Bridge cross section T24.7 20 Figure 3.7 ½ T24.7 Cross section 20 Figure 3.8 Section D-D 20 Figure 3.9 Section E-E 20 Figure 3.10 CFRP Arrangement 24 Figure 3.11 Detail A 24 Figure 3.12 Detail B 24 Figure 3.13 The flowchart of the methodology 25 Figure 3.14 Special section of T shape 26 Figure 3.15 Truck HL93 29 Figure 3.16 Triaxial truck and Two-axle truck 30 Figure 3.17 Lane Loading distribution (9.3N/mm) 30 Figure 3.18 Finite Element Model T33m 32 Figure 3.19 Finite Element Model T24.7m 33 Figure 3.20 Flowchart brief rating factor method 34 Figure 4.1 Stress distribution T33 before repairing 39 Figure 4.2 Stress distribution T24.7 before repairing 40 vi Figure 4.3 Stress distribution before and after using pre-stressed CFRP under Dead loads + HL93 for Max case T33 41 Figure 4.4 Stress distribution before and after using pre-stressed CFRP under Dead loads for Max case T33 41 Figure 4.5 Stress distribution before and after using pre-stressed CFRP under Dead loads+HL93 for Max case T24.7 43 Figure 4.6 Stress distribution before and after using pre-stressed CFRP under Dead loads for Max case 24.7 43 Figure 4.7 Stress distribution before and after using pre-stressed CFRP under Dead loads+HL93 for Med case T33 45 Figure 4.8 Stress before distribution and after using pre-stressed CFRP under Dead loads for Med case T33 45 Figure 4.9 Stress distribution before and after using pre-stressed CFRP under Dead loads+HL93 for Med case T24.7 47 Figure 4.10 Stress distribution before and after using pre-stressed CFRP under Dead loads for Med case T24.7 47 Figure 4.11 Stress distribution before repairing at the top of beam under Dead load and Live load for T33 49 Figure 4.12 Stress distribution before repairing at the bottom of beam under Dead load and Live load for T33 49 Figure 4.13 Stress distribution before repairing at the top of beam under Dead load and Live load for T24.7 50 Figure 4.14 Stress distribution before repairing at the bottom of beam under Dead load and Live load for T24.7 50 Figure 4.15 Stress distribution after repairing at the top of beam under Dead load and Live load for T33 - Max case 50 Figure 4.16 Stress distribution after repairing at the bottom of beam under Dead load and Live load for T33 - Max case 51 Figure 4.17 Stress distribution after repairing at the top of beam under Dead load and Live load for T33 - Med case 51 Figure 4.18 Stress distribution after repairing at the bottom of beam under Dead load and Live load for T33 - Med case 51 Figure 4.19 Stress distribution after repairing at the top of beam under Dead load and Live load for T24.7 - Max case 52 Figure 4.20 Stress distribution after repairing at the bottom of beam under Dead load and Live load for T24.7 - Max case 52 Figure 4.21 Stress distribution after repairing at the top of beam under Dead load and Live load for T24.7 - Med case 53 Figure 4.22 Stress distribution after repairing at the bottom of beam under Dead load and Live load for T24.7 - Med case 53 vii Figure 4.23 CFRP arrangement according to the study [10] 55 Figure 4.24 Stress distribution in the bottom of beam according to the conventional method by FEM for T33 in the Max case 55 Figure 4.25 Stress distribution according to the conventional method by LRFR for T33 in the Max case 55 viii For T33: At the Med case T33 Choose to add pre-stress to achieve RF  and RF  Select the stress value to supplement via the CFRP strip:  Tf 33 m ed  6Mpa Determine the value of CFRP to supplement (Eq 3.40): FfTm33ed  1259(kN ) Determine the number of CFRP strips to add (take integers): T 33 n  FfTm33ed Fulti  1259  1.93( strips) 651 Select the number of CFRP strip to add: strips Tension for a strip of CFRP: f fTm33ed  FfTm33ed n1  1259  419.67(kN ) The degree to take advantage of the ability to work of CFRP Strip: T 33 n2m ed  ff Fulti 100%  419.67  64.5% 651 Check for RF coefficients after strengthening pre-stressed CFRP (Eq 3.31): Rating factor for T shape 33m: RFmTed33 LRFR  1.37  44 Stress before and after using prestressed CFRP under Dead loads+HL93 Stress (MPa) Distance (m) -3 10 15 20 25 30 -8 -13 -18 Stress in top of beam Non-CFRP Stress in bottom of beam Non-CFRP Tensile limit Compression limit Stress in top of beam Prestressed CFRP Stress in bottom of beam Prestressed CFRP -23 -28 Figure 4.7 Stress distribution before and after using pre-stressed CFRP under Dead loads+HL93 for Med case T33 Stress before and after using prestressed CFRP under Dead loads Stress (MPa) Distance (m) -3 10 15 20 25 30 -8 -13 -18 -23 -28 Stress in top of beam Non-CFRP Stress in bottom of beam Non-CFRP Tensile limit Compression limit Stress in top of beam Prestressed CFRP Stress in bottom of beam Prestressed CFRP Figure 4.8 Stress before distribution and after using pre-stressed CFRP under Dead loads for Med case T33 45 For T24.7: At the Med case T24.7 Choose to add pre-stress to achieve RF  and RF  Select the stress value to supplement via the CFRP strip:  Tf m24.7ed  6Mpa Determine the value of CFRP to supplement (Eq 3.40): FfTm24.7 ed  508(kN ) Determine the number of CFRP strips to add (take integers): T 24.7 n  24.7 FfTmax Fulti  508  0.78( strips) 651  508  508(kN ) Select the number of CFRP strip to add: strips Tension for a strip of CFRP: 24.7 f fTmax  24.7 FfTmax n1 The degree to take advantage of the ability to work of CFRP Strip: T 24.7 n2max  ff Fulti 100%  508  78% 651 Check for RF coefficients after strengthening pre-stressed CFRP (Eq 3.31): Rating factor for T shape 24.7m: RFmTed24.7 LRFR  1.28  46 Stress before and after using prestressed CFRP under Dead loads+HL93 Distance (m) Stress (MPa) -3 10 15 20 25 -8 -13 -18 Stress in top of beam Non-CFRP Stress in bottom of beam Non-CFRP Tensile limit Compression limit Stress in top of beam Prestressed CFRP Stress in bottom of beam Prestressed CFRP -23 -28 Figure 4.9 Stress distribution before and after using pre-stressed CFRP under Dead loads+HL93 for Med case T24.7 Stress before and after using prestressed CFRP under Dead loads Stress (MPa) Distance (m) -3 10 15 20 25 -8 -13 -18 -23 -28 Stress in bottom of beam Non-CFRP Stress in top of beam Non-CFRP Tensile limit Compression limit Stress in the bottom of beam Prestressed CFRP Stress in the top of beam Prestressed CFRP Figure 4.10 Stress distribution before and after using pre-stressed CFRP under Dead loads for Med case T24.7 Rating factor ( RFmTed33  1.37  , RFmTed24.7  1.28  ) in the Med case the RF value is close to 1, the number of CFRP strips needed to enhance is significantly less than in the Max case, for T33 the number of CFRP strips from to 3, for T24.7 from strips down to The CFRP tensile value reaches nearly from 60% to 80% of the material's maximum tensile value From fig 4.3 to fig 4.10 show that using the pre-stressed CFRP method 47 significantly improves the bearing capacity of the structure, helping to redistribute stress in the beams, when additional stress load effect in the beam still ensures the values are within authorized range Using the pre-stressed CFRP method in the bottom of the beam not only improves the tensile strength at the bottom of beam, but also improves the compressive strength at the top of beam In the middle of the beam, for Max case T33 compressive stress increased by 15 Mpa, tensile stress increased by 3.42 Mpa (fig 4.3 and fig 4.4); for Med case T33 compressive stress increased by Mpa, tensile stress increased by 1.37 Mpa (fig 4.7 and fig 4.8), for Max case T24.7 compressive stress increased by Mpa, tensile stress increased by 2.14 Mpa (fig 4.5 and fig 4.6), for Med case T24.7 compressive stress increased by Mpa, tensile stress increased by 1.36 Mpa (fig 4.9 and fig 4.10) After using pre-stressed CFRP, when there is no additional load-effect on the beam, the stress at the top and bottom of beam still ensures the ability to work within the tensile limit and compression limit From fig 4.4, fig 4.6, fig 4.8, fig 4.10 when no additional load is active, the value of the stress at the bottom of beam is closer to the allowable compression limit, reaching nearly 60% of the maximum compression value of concrete In the case of having large repair such as replacing the surface of the bridge, the effect of reducing the dead load, at the bottom of beam, the compression value will increase, so that the maximum compression value of the concrete after the pre- stressed CFRP (nearly 60% of the maximum compressive value of concrete) is reasonable The results of the study show that when strengthening the CFRP sheet with a tensile value above 60% of the maximum tension of the CFRP strips, a reasonable number of CFRP strips must be calculated, because if the number of tensile strips is too large a lot of additional stresses can damage the structure or be detrimental to the structure, this can be seen when comparing the two cases Max case and Med case in both structure T33 and T24.7 48 4.2 Comparison of two structural analysis method 4.2.1 FEM assessment for old structures Check for RF coefficients before using pre-stressed CFRP (Eq 3.30): T 33 Rating factor for T shape 33m ( RFbfT 33  FEM ): RFbf  FEM  0.67  T 24.7 Rating factor for T shape 24.7m ( RFbfT 24.7 FEM ): RFbf  FEM  0.76  The structure need to be repaired and upgraded to meet the current requirements For T33: Figure 4.11 Stress distribution before repairing at the top of beam under Dead load and Live load for T33 Figure 4.12 Stress distribution before repairing at the bottom of beam under Dead load and Live load for T33 49 For T24.7 Figure 4.13 Stress distribution before repairing at the top of beam under Dead load and Live load for T24.7 Figure 4.14 Stress distribution before repairing at the bottom of beam under Dead load and Live load for T24.7 4.2.2 FEM for strengthen structures For T33 Max case Figure 4.15 Stress distribution after repairing at the top of beam under Dead load and Live load for T33 - Max case 50 Figure 4.16 Stress distribution after repairing at the bottom of beam under Dead load and Live load for T33 - Max case For T33 Med case Figure 4.17 Stress distribution after repairing at the top of beam under Dead load and Live load for T33 - Med case Figure 4.18 Stress distribution after repairing at the bottom of beam under Dead load and Live load for T33 - Med case 51 Check for RF coefficients after strengthening pre-stressed CFRP for T33 at Max T 33 case (Eq 3.31): RFmax  FEM  2.94  Check for RF coefficients after strengthening pre-stressed CFRP for T33 at Med case (Eq 3.31): RFmTed33 FEM  1.49  For T24.7 Max case Figure 4.19 Stress distribution after repairing at the top of beam under Dead load and Live load for T24.7 - Max case Figure 4.20 Stress distribution after repairing at the bottom of beam under Dead load and Live load for T24.7 - Max case 52 For T24.7 Med case Figure 4.21 Stress distribution after repairing at the top of beam under Dead load and Live load for T24.7 - Med case Figure 4.22 Stress distribution after repairing at the bottom of beam under Dead load and Live load for T24.7 - Med case Check for RF coefficients after strengthening pre-stressed CFRP for T24.7 at Max T 247 case (Eq 3.31): RFmax  FEM  1.93  Check for RF coefficients after strengthening pre-stressed CFRP for T24.7 at Med case (Eq 3.31): RFmTed247 FEM  1.47  Stress distribution chart of LRFR Method and the FEM are quite similar The results of Rating factor before repair of both methods for the two types of structure are relatively equal RFbfT 33  LRFR  0.65 and RFbfT 33 ,  FEM  0.67 RFbfT 247 LRFR  0.78 and RFbfT 247 FEM  0.76 Nevertheless, the RF results of the FEM method are greater than that of the LRFR Method when using pre-stressed CFRP, 53 T 33 RFmax  LRFR  2.44 and T 247 T 247 T 33 RFmax RFmax RFmTed33 LRFR  1.37 and RFmax  LRFR  1.58 and  FEM  1.93 ,  FEM  2.94 , RFmTed33 FEM  1.49 , RFmTed247 LRFR  1.28 and RFmTed247 FEM  1.47 , The cause of the difference between the results can be explained as follows: the principle of calculating two different methods, the LRFR bringing about the 2D problem, considering the factors of safety, the truckload activity is calculated evenly distributed across the beams through the calculation of the horizontal distribution coefficient LRFR Method tend to be more secure than FEM FEM is based on a 3D problem that approximates the working model of the structure, especially the description of truck loading and actual loading arrangement FEM considers the effect of increasing structural stiffness through the deck-bridge description, and the horizontal beam system When using pre-stressed CFRP strips, the results from the stress distribution chart and the RF result between the two methods differ, because when modeling the 3D problem, the strengthening of the pre-stressed CFRP strips can both affect the other divisions of the bridge such as the horizontal beam system and the deck-bridge, this is difficult to show in the experiments for single beam like the 2D problem describes the effect on a single beam structure The author proposed to apply the Med case when applying the pre-stressed CFRP Method to bridge structure repair in Vietnam, especially in the two types of structures in the study T33 and T24.7 CFRP arrangement The author proposes the layout according to the model presented in fig 3.10 When performing a conventional CFRP arrangement - add the CFRP to a strip of equal length (Fig 4.23) Comparing stresses in beams of conventional methods (fig 4.24 and fig 4.25) and proposal method both LRFR Method and FEM At the position enhanced by conventional method, there is a sudden change in stress Fig 4.24 and fig 4.25 is stress distribution in the Max case T33, if strengthen conventional method with pre-stressed CFRP strips with long strips simultaneously At this position it is very likely that it is failure before reaching the breaking load The advantage of the proposal method helps to reduce the sudden change of stress (fig 4.3, fig 4.4, fig 4.7, fig 4.8, fig 4.15 to fig 4.18), significantly saving CFRP material, but still ensure implement adequate stress at the unfavorable position 54 Figure 4.23 CFRP arrangement according to the study [10] Figure 4.24 Stress distribution in the bottom of beam according to the conventional method by FEM for T33 in the Max case Stress after using prestressed CFRP under Dead loads+HL93 Distance (m) Stress (MPa) -30.00 -8 5.00 10.00 15.00 20.00 25.00 30.00 -13 -18 -23 -28 Stress in top of beam Stress in bottom of beam Tensile limit Compression limit Figure 4.25 Stress distribution according to the conventional method by LRFR for T33 in the Max case 55 CHAPTER CONCLUSIONS & RECOMMENDATIONS The objective of the thesis is to evaluate the effectiveness of the CFRP strip when used to enhance the pre-stressed structure and propose stress value to be added to the structure through CFRP strip, arrange CFRP strip to achieve to be most effective The results of the thesis indicate that after using pre-stressed CFRP in pre-stressed concrete beam according to old design, it significantly improves the working ability The structure after repairing and upgrading is capable of operating with the design load according to current standards The CFRP pre-stressed method redistributes stresses in the beam, increases the tensile capacity at the bottom of the beam and increases the compressive capacity at the top of beam Stress distribution area in the beam is always within the allowable range From the stress chart after increasing the live load of HL93, it can be seen that the stress is still in a safe range, so the structure may be able to withstand a load greater than the design load The results indicated both FEM and LRFR methods When comparing the CFRP strip arrangement of the conventional method and the proposal method, it is found that the proposal method is more effective, helping to limit the sudden change of stress at the point of reinforcement, ensures stress is added at the critical location and significant savings in CFRP material From the results of this study, proposed using pre-stressed CFRP method to repair and strengthen pre-stressed concrete structures in Vietnam, especially the old bridge structures to improve operating capacity, meet traffic demand, helping economic development, 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and Huo S (2005) Looking to load and resistance factor rating Public roads, 69(1) 58 ... small-sized reinforced concrete beams, the characteristics of pre- stressed reinforced concrete beams and pre- stressed reinforced concrete beams are different The pre- stressed reinforced concrete. ..VIETNAM NATIONAL UNIVESITY, HANOI VIETNAM JAPAN UNIVERSITY PHAM VAN GIAO RESEARCH ON PRE- STRESSED REINFORCED FRP STRIP IN REPAIRING AND UPGRADING SERVICE CAPACITY OF OLD CONCRETE BRIDGE MASTER’S... technology for being application repairing old bridge such as continuous-ization of simple span structures, external tensioning method, method of bonded FRP strip and reinforcing paste of steel plate