Seismic Strengthening of RC Building Structures

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1 Seismic Strengthening of RC Building Structures Dr. Basem ABDULLAH

2 History of Earthquake In Japan Tyfo FIBRWRAP Systems

3 Seismic-resistant Building Design Standards in Hong Kong Buildings in Hong Kong are currently not required by law to meet specific seismic-resistant design standards. The strongest earthquake ever recorded in Hong Kong measured intensity of VI to VII on the MMS. Internationally, Many major cities and economies located in areas of seismicity comparable to that of Hong Kong, including Shanghai, South Korea, Thailand, Australia, France, Germany and New York City, have all introduced seismic resistant design standards for new buildings.

4 Seismic Design Code for Building in Japan Seismic Design Code for Building was introduce for the first time in 1924 when the Urban Building Law was revised as a consequence of the 1923 Kanto great earthquake disaster. (Seismic coefficient =0.1) In 1950, the Building Standard Law replaced the Urban Building Law. (Seismic coefficient =0.2) The Seismic Design Code for Building was radically changed in 1981 in the largest revision since The Seismic Capacity Evaluation Standards and Guidelines for Seismic Rehabilitation of RC Buildings were introduced in 1977 and revised in 1990 and 2001.

5 Enhancing the Seismic Performance of Existing Buildings

6 Enhancing the Seismic Performance of Existing Buildings Lateral Load Capacity (C) Strength Upgrading Strength and Ductility Upgrading Existing Building Demand Seismic Performance Ductility Upgrading Ductility (F)

7 Strengthening Methods for Enhancing the Seismic Performance of Existing Buildings Strength (C) Strength Upgrading Strength and Ductility Upgrading Ductility Upgrading Demand Seismic Performance For Retrofitting Before Strengthening Ductility (F)

8 Strengthening Methods for Enhancing the Seismic Performance of Existing Buildings Tyfo FIBRWRAP Systems Strength Upgrading Adding Wall Infilling wall Adding wall for increasing thickness Infilling Opening Wing wall Adding Steel with boundary Frame Steel framed brace Steel framed panel Adding exterior steel frame Steel framed brace Adding structural frame Core wall Mega Frame Buttress Exterior Frame Others Shear wall with grid-shaped block Shear wall with precast panel Unbonded brace

9 Strengthening Methods for Enhancing the Seismic Performance of Existing Buildings Ductility Upgrading RC jacketing With wire fabric With welded hoop Steel jacketing With square steel tube With circular tube FRP Wrapping With Continuous fiber sheet With FRP shape

10 Strengthening Methods for Enhancing the Seismic Performance of Existing Buildings Prevention of Damage Concentration Improvement of vibration property Reduction of eccentricity Improvement of stiffness irregularity Reduction of pounding risk at expansion joint Improvement of extreme brittle member Installing seismic slit Improvement of failure mode

11 Strengthening Methods for Enhancing the Seismic Performance of Existing Buildings Reduction of seismic forces Mass Reduction Remove water tank on the building Remove roof concrete for water proofing Removing upper stories Seismic isolation Base isolation at grade level Base isolation below grade level Mid-story isolation Structural response control device Active mass damper (AMD) Tuned mass damper (TMD) Metallic damper Oil damper

12 Strengthening Methods for Enhancing the Seismic Performance of Existing Buildings Strengthening of foundation Strengthening of foundation beam Strengthening of pile

13 Strengthening Methods for Enhancing the Seismic Performance of Existing Buildings Ductility Upgrading Strength Upgrading

14 Strengthening Methods for Enhancing the Seismic Performance of Existing Buildings Tyfo FIBRWRAP Systems Infilling Wall Shear Wall with Opening Steel Framed Brace (Internal) Adding Seismic Slit Steel Framed Brace (External) Buttress Beam Strengthening Column Strengthening

15 Enhancing the Seismic Performance of Existing Buildings by Adding Infilling Wall

16 Enhancing the Seismic Performance of Existing Buildings by Steel Framed Brace

17 Enhancing the Seismic Performance of Existing Buildings by Steel Framed Brace (External) Tyfo FIBRWRAP Systems

18 Enhancing the Seismic Performance of Existing Buildings by Adding Buttress Tyfo FIBRWRAP Systems

19 Enhancing the Seismic Performance of Existing Buildings by Adding Installing Seismic Slit

20 Enhancing the Seismic Performance of Existing Buildings by Using Fiber Reinforced Polymers

21 Enhancing the Seismic Performance of Existing Buildings by Dampers Gum Steel Damper Oil Damper

22 Enhancing the Seismic Performance of Existing Buildings by Adding Shear walls with Grid-Shaped Block Tyfo FIBRWRAP Systems

23 Concept of Seismic Evaluation The Seismic Capacity Evaluation Standard and Guidelines for Seismic Rehabilitation of RC Buildings are used in conjunction with the guidelines for seismic retrofitting of RC buildings. The seismic capacity of the building is quantified by the seismic index Is. This index should be evaluated at each story and to each direction. Where : E o = Basic Seismic Index of Structure. S D = Irregularity Index I s = E o S D T T = Time Index ( to account for the degree of deterioration of the building)

24 Concept of Seismic Capacity Evaluation Tyfo FIBRWRAP Systems The Basic Seismic index of Structure E o The Eo index is a basic value that specifies the seismic performance of a building. The Eo index is the criteria used for evaluating the seismic performance of a building based on the strength and ductility of the building.) E 0 = n+1 n+i f C, F Where : C : is the strength index F : is the ductility index n+1 n i : is the shear-story modification factor n : is the number of stories i: is the story being analyzed

25 Horizontal Force Concept of Seismic Capacity Evaluation Tyfo FIBRWRAP Systems The Basic Seismic index of Structure E o Building A Many walls, considerably strong but low in ductility Building B Rigid-frame structure with less walls and not so strong but large in ductility Critical failure Point Seismic response Horizontal Displacement

26 Horizontal Force Concept of Seismic Capacity Evaluation Tyfo FIBRWRAP Systems The Basic Seismic index of Structure E o The basic seismic index is a function of the strength index C, and the ductility index F. E o = E 1 a b E o = E 2 c E o = E E2 2 Horizontal Displacement

27 Concept of Seismic Capacity Evaluation Tyfo FIBRWRAP Systems The Basic Seismic index of Structure E o Three level screening procedures are recommended to Estimate Is, which are dependable on the characteristics of the story to be analyzed. The first level screening procedures is the simplest, which used for stories with a large density of walls. The ultimate strength is estimated based on the concrete shear strength and cross section Area of the columns and walls The Second procedures requires the calculation of the ultimate strength capacity and ductility of columns and walls. The beams are usually assumed to be rigid. This procedure is used for weak column-strong beam frames The third procedures implies to calculate the ultimate capacity and ductility for the vertical members as well as beams. All the possible mechanisms of failure are taken into account. For general concrete building. I s 0.6

28 FRP for Seismic Strengthening of RC Buildings

29 Advantages of Using FRP as Strengthening Material for Concrete Structure Non destructive and easy to install Much lighter system / High strength to weight ratio. Does not require heavy or special equipment. Can be used in space constrained areas. Can incorporate different finishing coats.

30 FRP Performance Characteristics Increases bending strength of flexural elements. Increases shear strength of beams columns and walls. Increases vertical load capacity of columns. Increases ductility under cyclic loading. Does not corrode and can contain further corrosion.

31 Strengthening Applications for Concrete Structure Beam Strengthening Slab Strengthening Wall Strengthening Column Strengthening

32 JBDPA Guidelines for Strengthening with FRP The Japanese guidelines for seismic retrofitting of RC building with FRP materials (JBDPA, 1999 revised 2010) provide specification on the characteristics of the FRP materials used in Japan, their proper handling and installation. Design and detailing recommendations are provided in the guidelines, which mainly target the shear strength of either columns or beams. The guidelines are part of the Guidelines for Seismic Rehabilitation of RC Buildings (JPDPA, st revised nd revised 2001), a comprehensive publication that documents different retrofitting methods utilized in Japan.

33 JBDPA Guidelines for Strengthening with FRP Tyfo FIBRWRAP Systems Materials The JBDPA guidelines describe the properties of PAN-class high-strength carbon fiber sheets, and aramid fiber sheets. In its turn, aramid is subclassified as aramid 1 and aramid 2. Characteristic Carbon Fiber Aramid Fiber 3400 MPa Class Aramid 1 Aramid 2 Type of Fiber PAN-class High-Strength Homopolymer Copolymer Tensile Strength 3400 MPa 2060 MPa 2350 MPa Young Modulus 230 GPa 118 GPa 78 GPa Weight 300 g/m2 623 g/m2 525 g/m2 The viscosity of the adhesive resins influences the efficiency of the strengthening work. Thus, If sagging is likely to occur, a resin of high viscosity is recommended. Also, if smooth impregnation in the fiber is required, a resin with low viscosity should be used.

34 JBDPA Guidelines for Strengthening with FRP Tyfo FIBRWRAP Systems Design Approaches for Strengthening of Columns In order to determine the required amount of FRP strengthening, the Japanese guidelines provide expressions to calculate the flexural and shear strengths, and ductility index of RC members.

35 Design Approaches for Strengthening of Columns Tyfo FIBRWRAP Systems Ultimate Flexural Capacity of Columns The ultimate flexural capacity of RC column is calculated from the following expressions. For N max N > N b : M u = 0.5a g σ y g 1 D g g 1 bd 2 F c N max N N max N b For N b > N 0 : For 0 > N N min : M u = 0.5a g σ y g 1 D + 0.5ND 1 N bdf c M u = 0.5a g σ y g 1 D + 0.5Ng 1 D

36 Design Approaches for Strengthening of Columns Tyfo FIBRWRAP Systems Ultimate Flexural Capacity of Columns The ultimate flexural capacity of RC column is calculated from the following expressions. For N max N > N b : M u = 0.5a g σ y g 1 D g g 1 bd 2 F c N max N N max N b Balanced Axial Force: N b = g 1 bdf c Ultimate Axial Force in compression: N max = bdf c + a g σ y Ultimate Axial Force in Tension: N min = a g σ y Where: N : Axial force in the column, a g : overall area of the longitudinal reinforcement of the column;g 1 : Ratio of distance between the centers of longitudinal reinforcement in tension and compression to the column width; b, D: Dimensions of the column; σ y : specified yield strength of the longitudinal reinforcement. F C : Compressive strength of concrete; h 0 = clear height of column;

37 Design Approaches for Strengthening of Columns Tyfo FIBRWRAP Systems Ultimate Flexural Capacity of Columns The ultimate flexural capacity of RC column is calculated from the following expressions. For N b > N 0 : M u = 0.5a g σ y g 1 D + 0.5ND 1 N bdf c N b = g 1 bdf c Ultimate Axial Force in compression: N max = bdf c + a g σ y Ultimate Axial Force in Tension: N min = a g σ y Where: N : Axial force in the column, a g : overall area of the longitudinal reinforcement of the column;g 1 : Ratio of distance between the centers of longitudinal reinforcement in tension and compression to the column width; b, D: Dimensions of the column; σ y : specified yield strength of the longitudinal reinforcement. F C : Compressive strength of concrete; h 0 = clear height of column;

38 Design Approaches for Strengthening of Columns Tyfo FIBRWRAP Systems Ultimate Flexural Capacity of Columns The ultimate flexural capacity of RC column is calculated from the following expressions. For 0 > N N min : M u = 0.5a g σ y g 1 D + 0.5Ng 1 D N b = g 1 bdf c Ultimate Axial Force in compression: N max = bdf c + a g σ y Ultimate Axial Force in Tension: N min = a g σ y Where: N : Axial force in the column, a g : overall area of the longitudinal reinforcement of the column;g 1 : Ratio of distance between the centers of longitudinal reinforcement in tension and compression to the column width; b, D: Dimensions of the column; σ y : specified yield strength of the longitudinal reinforcement. F C : Compressive strength of concrete; h 0 = clear height of column;

39 Design Approaches for Strengthening of Columns Tyfo FIBRWRAP Systems Ultimate Flexural Capacity of Columns The shear force associated to the flexural capacity Mu can be computed as Q mu = αm u h 0 α = experimental value which equal to 2 Validation of the equation for Flexural Strength of Columns

40 Design Approaches for Strengthening of Columns Tyfo FIBRWRAP Systems Ultimate Shear Capacity of Columns The ultimate shear capacity of RC column is calculated from the following expressions. Q su = 0.053p 0.23 t 18 + Fc M Qd P w σ wy + 0.1σ 0 bj p w σ wy = p ws σ wys + p wf σ fd 10 MPa Where: σ 0 : Axial Stress (No larger than 8 MPa), M Q : Shear span ; b: width of the column after strengthening; d: effective depth (distance from the extreme compression fiber to centroid of longitudinal tension reinforcement); j: Distance between the tensile and compressive force resultants (j=0.8d), p t = Ratio of tensile reinforcement = a t bd % ; F C : Compressive strength of concrete; P ws = ratio od existing shear steel reinforcement to area of contract surface = a v bd (%); p wf = ratio of FRP reinforcement to area of contact surface = AreaFRP (%); bd σ wys : Specified yield strength of existing transversal reinforcement; σ fd = tensile strength for FRP for shear design.

41 Design Approaches for Strengthening of Columns Ductility Factors and Ductility Index of Columns The ductility index F is a function of the ductility factor μ, and can be expressed by the following relationships obtained from a degrading tri-linear hysteresis model. F = 2μ 1 = μ μ = 10 Q su Q mu 0.9, where 1 μ 5

42 Conclusions In this presentation the following were introduced The concept for enhancing the seismic performance of existing building Methods for strength and ductility upgrading of concrete structures The concept of Seismic Capacity Evaluation of RC building FRP for Seismic Strengthening of RC buildings JBDPA Guidelines for strengthening with FRP

43 Thank you