Behavior of Partially Confined Strengthened Reinforced Concrete Columns under Vertical and Lateral Loads
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Presentation of Ph.D. Thesis Reinforced concrete jacketing has been used widely for strengthening RC columns. In some cases, such as corner and edge columns, it is impossible to strengthen a column using a full jacket. Many studies have focused on fully strengthened reinforced concrete columns. However additional study is required for partially strengthened RC columns from two and three sides. So, this research focused on studying the effectiveness of strengthening the corner and edge columns under vertical load and under the combination of vertical and lateral loads. Also, the research illustrated the behavior of RC columns strengthened by RC jackets from two, three, and four sides of the perimeter and it investigated the effect of using the different interaction methods between original columns and strengthening jackets such as friction, dowels, and stirrups' welding. A new design equation was developed from this study to calculate the capacity of a partially strengthened column under vertical load. An analytical approach was introduced to predict partial strengthened R.C. column capacity for axial and eccentric loading. By the aid of this analytical approach, flow charts were created to get the capacity of corner and edge columns subjected to vertical and lateral loads. Recommendations for column behavior after strengthening were presented to help structural engineers to capture the best efficiency from the full and partial strengthening. an analytical study and experimental program were performed. The experimental study consisted of group of specimens having 1000 mm height, 100x100 mm cross section, and main reinforcement 4Γ10 mm with stirrups 9Γ4 mm. The specimens were divided into fifteen study cases. Different parameters such as strengthening sides, surface connections, jacket to column stirrups connection type, and loads directions due to the column location. The results were compared with some of the design equations in various codes and the results from finite element analysis.
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Behavior of Partially Confined Strengthened Reinforced Concrete Columns under Vertical and Lateral Loads
- 1. Port Said University Faculty of Engineering Civil Engineering Department Behavior of Partially Confined Strengthened Reinforced Concrete Columns under Vertical and Lateral Loads by Dr. Khaled Mohamed Mahmoud Ahmed Ph.D. in structural engineering Khaled.mahmoud@eng.psu.edu.eg +201003915088 Supervisors: Prof. Dr. Hassan Mohamed Hassan Ibrahim Professor of Concrete Structures Vice President of Port Said University for Community Service and Environmental Development Port Said University Dr. Ezzaat Ahmed Sallam Associate Professor Civil Engineering Department Faculty of Engineering Port Said University
- 2. Chapter 1 Introduction Chapter 2 Literature Review Chapter 3 Experimental Work Chapter 4 Experimental Results and Discussion Chapter 5 Theoretical Study Chapter 6 Analytical Prediction of Partially Jacketed Columns Chapter 7 Conclusions and recommendations INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Thesis Outline
- 3. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. INTRODUCTION The reasons of columns strengthening: β’ Errors in design or bad detailing. β’ Improper quality control measures (poor construction materials and workmanship). β’ Unexpected loading, like earthquakes, strong winds, impact and explosive loading. β’ Functional changes in the service of the structure. β’ Deterioration by time. β’ Columns can sustain two main types of loads, the axial loads and the lateral loads. β’ Columns have a high axial load capacity compared to their lateral load capacity. β’ Building elements like columns are constructed to resist both internal and lateral loads from actions as wind and earthquakes.
- 4. First type : Based on the column height, the RC jacket can be as follow 1- The global jacket confines the column's whole height. 2- The local jacket is used to confine a part of the column's full height, such as a quarter, one third, half, two thirds, or three-quarters of the column's full height. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Partial Strengthening of R.C. Columns (1) (2) Second type: The strengthening from two or three sides of the perimeter. Edge column Corner column
- 5. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. In some cases, full jacketing can't be executed in the case of corner and edge columns due to the following reasons: PROBLEM STATEMENT β’ The column that want to be strengthened is adjacent to an existing building. β’ Distortion of the building facade
- 7. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. PROBLEM STATEMENT ο± The partial strengthening of columns from the perimeter need to be studied experimentally ο± There is no available strength prediction equations to predict axial load capacity of partially jacketed columns ο± An analytical procedure is needed to calculate and predict lateral load capacity of partially jacketed columns considering slip between the column core and jacket.
- 8. ο± Study experimentally and analytically the behavior of strengthened and partially strengthened RC columns to identify the effected factors on the strength of partial strengthened RC columns. ο± Compare the jacketed columns capacity which had been obtained from the analytical study, the experimental study, the numerical study and the equations from various codes to present the most effective method to calculate the strengthened columns capacities. ο± To propose new equations to design the strengthened and partial strengthened columns subjected to vertical loads and those that subjected to vertical and lateral loads. ο± To identify the best case of partially jacketing and the best method to make the strongest bond interacting between the column and the jacket surfaces. ο± To provide engineers with valuable recommendations on this kind of structural strengthening. ο± To help structural engineers at design the strengthened columns and partial strengthened columns. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. OBJECTIVES
- 9. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. METHODOLOGY LAYOUT Methodology Experimental Work Vertical Load Lateral Load Theoretical Study Modelling of Columns Using ANSYS Analytical Analysis and Strength Prediction Searching of new Equation and Analytical Procedure
- 12. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. First Program
- 13. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Specimen No. Column dimensions(mm) Main reinforcement Stirrups Remarks C0 100x100 4Γ10 9Γ4 Control column Specimen No. Column dimensions after strengthening(mm) Jacket main reinforcement Jacket stirrups Remarks C1 200x200 4Γ10 9Γ6 Full jacketed column C2, C3, C4 200x150 4Γ10 9Γ6 Jacketed columns from three sides C5, C6, C7 150x150 3Γ10 9Γ6 Jacketed columns from two sides First Program Specimens Experimental Work
- 15. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Specimen No. Specimen type Surfaces bonding Stirrups connection C0 Control N/A N/A C1 Full jacketed Friction N/A C2 Three sides jacketed Friction N/A C3 Friction Welded stirrups C4 Friction + dowels N/A C5 Two sides jacketed Friction N/A C6 Friction Welded stirrups C7 Friction + dowels N/A The factors affect on the bonding of the original column and the jacket surfaces Materials Concrete strength of the core 23 MPa Concrete strength of the jacket 40 MPa Nominal diameter (mm) Average yield strength (MPa) Average tensile strength (MPa) Elongation (%) 4 280 390 28.65 6 320 410 27 10 445 550 23.6 First Program Specimens Experimental Work
- 16. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Testing Procedures Universal testing machine Experimental Work
- 17. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Experimental Results Failure Modes of the Specimens at First Program (a) Control column elevation Co CA specimen C2 specimen C3 specimen C4 specimen C0 specimen C1
- 18. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. specimen C5 specimen C6 specimen C7 Failure Modes of the Specimens at First Program Experimental Results
- 19. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. The ultimate capacities of the strengthened columns under vertical loads Strengthening type Column Failure load (kN) Gained capacity percentage Strengthened column from three sides C2 580.05 153% C3 800.2 249% C4 769.5 236% Strengthened column from two sides C5 471.9 106% C6 535.17 133% Experimental Results Strengthening type Column π·ππππππππππππ π·π΄πππππππππ Strengthened column from three sides C2 60% C3 82.5% C4 79% Strengthened column from two sides C5 62% C6 70% C7 68%
- 20. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. The ultimate capacities of the strengthened columns under vertical loads ππ’ β ππππ ππππ π΄π Experimental Results
- 21. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Second Program
- 22. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Specimen No. Column dimensions(mm) Main reinforcement Stirrups Remarks C0 100x100 4Γ10 9Γ4 Control column Concrete strength of the core 14 MPa Concrete strength of the jacket 26 MPa Materials Second Program Specimens Specimen No. Column dimensions after strengthening(mm) Jacket main reinforcement Jacket stirrups Remark. CA 200x200 4Γ10 9Γ6 Full jacketed column CC 200x150 Jacketed columns from three sides CD CE CB 150x150 3Γ10 Jacketed columns from two sides CBB Experimental Work
- 23. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. (a) Control column elevation Co CA CC, CD, CE CB, CBB (b) Strengthened columns elevations Second Program Specimens Experimental Work
- 24. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Axial and lateral loading system 1 5 3 2 4 6 7 Experimental Work Testing Procedures
- 25. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Specimens loads directions Loading of Second Program Experimental Work
- 26. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. (a) Control column elevation specimen CC specimen CD specimen CE specimen C0 specimen CA Failure Modes of the Specimens at second Program Experimental Results
- 27. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Failure Modes of the Specimens at second Program specimen CB specimen CBB Experimental Results
- 28. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. The ultimate capacities of the strengthened columns under vertical and lateral loads Strengthening type Group Experimental max. capacity due to lateral load (kN) under constant axial load (45 kN) Control column (core) C0 14.5 Strengthened column from all sides CA 174.5 Strengthened column from three sides CC 136.75 CD 92.25 CE 102.5 Strengthened column from two sides CB 99 CBB 76.5 Experimental Results
- 30. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Theoretical Study Numerical model for strengthened columns under vertical loads Modelling of the elements Concrete Solid 65 Steel Beam 188 Base plate Solid 185 Connection Combin 39 Strengthening type Column Experimental Capacity (KN) Numerical Capacity (KN) Numerical Gained capacity percentage Strengthened column from three sides C2 580.05 568 138 % C3 800.2 771 223 % C4 769.5 739 209 % Strengthened column from two sides C5 471.9 465 95 % C6 535.17 531 122 % C7 515.31 475 99 %
- 31. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. C0 C4 C3 C2 C1 C7 C6 C5 Numerical model for strengthened columns under vertical loads Theoretical Study
- 32. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Numerical model for strengthened columns under vertical and lateral loads Theoretical Study Strengthening type Group max. Experimental capacity due to lateral load (KN) under constant axial load max. numerical capacity due to lateral load (KN) under constant axial load Numerical gained capacity percentage Strengthened column from three sides CC 136.75 183 843 CD 92.25 106 536 CE 102.5 135 607 Strengthened column from two sides CB 99 112 583 CBB 76.5 101 428
- 33. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. C0 CE CC CBB CB Numerical Experimental Numerical model for strengthened columns under vertical and lateral loads Principle Plastic tensile strain CA Theoretical Study
- 34. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Numerical model for strengthened columns under vertical and lateral loads C0 CA CE CD CC CB Theoretical Study
- 35. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Numerical model for strengthened columns under vertical and lateral loads Theoretical Study
- 36. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. The compression between the analytical and the experimental capacity specimen Experimental capacity (kN) Analytical capacity By ANSYS (kN) π·ππππππππππππ π·ππππππππππ C2 580.05 568.00 0.98 C3 800.20 771.00 1.04 C4 769.50 738.72 0.96 C5 471.90 465.00 1.01 C6 535.17 531.00 1.01 C7 515.31 475.00 1.08 First program Second program Specimen Laboratory capacity due to lateral load (kN) under constant axial load (45 kN) Analytical capacity due to lateral load (kN) under constant axial load (45 kN) π·ππππππππππππ π·ππππππππππ CC 136.75 183 0.75 CD 92.25 106 0.87 CE 102.5 135 0.76 CB 99 112 0.88 CBB 76.5 101 0.76 Theoretical Study
- 37. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Analytical Study and Proposed Strength Prediction
- 38. ANALYTICAL PREDICTIONS OF PARTIALLY JACKETED COLUMNS A new equation to calculate the capacity of Partially strengthened RC columns subjected to axial load πππππ = 0.67 β πππ’π β (π΄π β π΄π π) + ππ¦π β π΄π π πππππππ‘ = 0.67 β πΉππ’π β (π΄π‘ β π΄π β π΄π π) + πΉπ¦π β π΄π π Pstrengthened = πππππ + πΎ β πππππππ‘ Number of strengthened sides Surfaces bonding Stirrups connection K Three sides jacketed Friction N/A 0.53 Friction Welded stirrups 0.87 Friction + dowels N/A 0.82 Two sides jacketed Friction N/A 0.49 Friction Welded stirrups 0.62 Friction + dowels N/A 0.58 INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom.
- 39. ANALYTICAL PREDICTIONS OF PARTIALLY JACKETED COLUMNS The Capacity of Strengthened RC Columns subjected to vertical and lateral loads Given N, Mx, My Compute the stiffness matrix Ks (x) Get the section flexibility matrix by invert the stiffness matrix [fs] = [Ks]-1 Get section strains [dx]=[Ξ΅a Ξ³x Ξ³y] Get section resistance [R] Check convergence End yes No Start Next load level π΅ = πΊ. π¬. π π¨ πΊ = πΊπ β πΈπ. π β πΈπ. π π΅ = πΊπ. π¬. π π¨ β πΈππ. π¬. π π¨ β πΈπ. π. π¬. π π¨ π΄π = β π. π. π π¨ = β πΊπ β πΈππ β πΈππ . π¬. ππ π¨ π΄π = β πΊπ. π. π¬. π π¨ + πΈπ. ππ . π¬. π π¨ + πΈπ. π. π. π¬. π π¨ π΄π = β πΊπ. π. π¬. π π¨ + πΈπ. π. π. π¬. π π¨ + πΈπ. ππ . π¬. π π¨ π«(X)=Ks(x).d(x) Ks(π) = π¬π π¨ β ππ¬π π¨ β π¬ππ π¨ β ππ¬π π¨ ππ π¬π π¨ πππ¬π π¨ β ππ¬π π¨ πππ¬π π¨ ππ π¬π π¨ INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom.
- 40. ANALYTICAL PREDICTIONS OF PARTIALLY JACKETED COLUMNS The general formula of the strain due to slip as follow: πΊπ = πΊπ β πΈπ β ππππ β πΈπ β ππππ πΊππππ = πΆ β πΊπ πΊπ = πΊπ β πΈπ β π β πΈπ β π β πΊππππ π« = π²π+π πΊπ πΈπ πΈπ β π²π πΆπΊπ π π The Capacity of Strengthened RC Columns subjected to vertical and lateral loads INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom.
- 41. ANALYTICAL PREDICTIONS OF PARTIALLY JACKETED COLUMNS Validation of the slip factor To calculate the capacity of the strengthened or partial strengthened columns by the previous method, it should be known the value of the slip factor. For this a lot of trials were made to get it. By the experimental results from this research and by another research βKaliyaperumal, Seismic retrofit of columns in buildings for flexure using concrete jacket, ISET Journal of Earthquake Technology, Vol. 46, No. 2, June 2009, pp. 77β107β, the models of the same strengthened columns were solved by the previous method with various slip factor till the result of the modeling agree with the result of the experimental result. the closet slip factor value was 0.25 from the validation. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Get the jacketed column properties from experimental work Model the jacketed column using a new slip factor Compare the result with the experimental results (if Pu = Puexperimental) Get the value of slip factor Yes No
- 42. ANALYTICAL PREDICTIONS OF PARTIALLY JACKETED COLUMNS INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Start Given: N, Mx, My Compute nominal Pucore , and the Core is loaded with 50% Pucore as a permanent load Put the resident load of the core + the additional loads N,M on the full section of strengthened column Get Numax,Mumax END Solve Solve Reducing loads Load history After jacketing ( 1 ) ( 2 )
- 43. ANALYTICAL PREDICTIONS OF PARTIALLY JACKETED COLUMNS Nominal failure surfaces for jacketed columns For Corner column To draw the chart - Pure normal (e/t = 0) - Pure moment (e/t = β) - Balanced point INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom.
- 44. ANALYTICAL PREDICTIONS OF PARTIALLY JACKETED COLUMNS For Edge column Nominal failure surfaces for jacketed columns INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom.
- 45. ANALYTICAL PREDICTIONS OF PARTIALLY JACKETED COLUMNS Nominal failure surfaces for jacketed columns For full strengthened column INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom.
- 46. ANALYTICAL PREDICTIONS OF PARTIALLY JACKETED COLUMNS o First, the core subjected to a ratio from the vertical load then the residual loads were put on the full strengthened column section. o The moment-flexural rigidity chart was drawn and the EIs was obtained from the value of service moment. o The reduction of rigidity was obtained by calculated the ratio between EIs and EImax. The reduction of the flexural rigidity INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Load the core with the percentage of the permanent load Load the full section with the residual load From moment- rigidity chart obtain the rigidity of Mservice, and the max. rigidity Get the reduction of the rigidity = πΈπΌπ /πΈπΌπππ₯.
- 47. ANALYTICAL PREDICTIONS OF PARTIALLY JACKETED COLUMNS The reduction of the flexural rigidity INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom.
- 49. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. Conclusions Based on the experimental and analytical results of partially strengthened columns using concrete jackets and subjected to vertical or both vertical and lateral loads, the following conclusions were obtained: οΌ Using two or three side jackets could increase columns capacities if good connection between jacket and column is established. οΌ The best results of columns strengthening from two and three sides have been obtained from using welding between core and jacket stirrups. So, using welding is recommended at partially strengthening of columns. οΌ Using dowels at columns strengthening improves the behavior of strengthened columns from two and three sides. but it is not recommended for gravel columns, because the dowels in gravel columns make it weak due to the holes which had been made to fix the dowels. οΌ The strengthening of columns without using dowels or welding increases the capacities of columns and achieves satisfied results. οΌ Increasing number of strengthening sides increases column gained capacity for columns subjected to both axial and lateral loadings. It was noticed that the gained capacity depends on loading direction with respect to jacket location.
- 50. INTRO Exp. work Exp. results Theoretical study Analytical prediction Conc. & Recom. οΌ The results of the finite element models agree with an acceptable margin to the experimental results, and it achieved an accuracy of 98% in case of vertical loads, and 82 % in case of the combination of lateral loads. οΌ In the case of full strengthening of the RC columns, the jacket alone carries the lateral load, and the core doesnβt carry any lateral load. So, the slip value has no effect at this case. οΌ Structural engineers can use the new equation to design the strengthened RC column that subjects to vertical load. οΌ Structural engineers can use the charts of the nominal failure surfaces for jacketed columns to design the strengthened RC column that subjects to vertical and lateral loads. Conclusions
- 51. INTRO Exp. work Exp. results Theoretical study Conc. & Recom. Future Work As a result of this work, several items should be considered in future research: ο± Study the strengthening of any number of columns sides of the perimeter of various columns shape as T, and L sections. ο± Study the strengthened corner and edge columns by using steel cages and try to get design equations. Analytical prediction ο± Study the partially strengthened columns using various types of concrete jackets such as shotcrete jackets or concrete with fibers jackets. ο± Study various types of jackets for partially strengthening as ferrocement jackets.
- 52. The Published Papers from the research
- 53. The Published Papers from the research
- 54. Dr. Khaled Mohamed Mahmoud Consultant Engineer for Design of Concrete Structures Consultant Engineer for Strengthening and Restoration of Buildings Best regards Email: khaled.mahmoud@eng.psu.edu.eg Cell phone: +201003915088