seismic strengthening of rc building...

Tyfo® FIBRWRAP® Systems

FYFE Japan Co., Ltd.

Seismic Strengthening of RC Building

Structures

Dr. Basem ABDULLAH



His

tory

of

Ear

thq

uak

e In

Jap

an



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.



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 1924.

The Seismic Capacity Evaluation Standards and Guidelines for Seismic Rehabilitation of RC Buildings were introduced in 1977 and revised in 1990 and 2001.



Enhancing the Seismic Performance of Existing Buildings



Ductility (F)

Lateral Load Capacity (C)

Strength Upgrading

Ductility Upgrading

Strength and Ductility Upgrading

Enhancing the Seismic Performance of Existing Buildings

Existing Building

Demand Seismic Performance



Ductility (F)

Strength (C) Strength Upgrading

Ductility Upgrading

Strength and Ductility Upgrading

Strengthening Methods for Enhancing the Seismic Performance of Existing Buildings

Before Strengthening

Demand Seismic Performance For Retrofitting



Str

eng

then

ing

Met

ho

ds

for

En

han

cin

g t

he

Sei

smic

Per

form

ance

of

Exi

stin

g B

uil

din

gs

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




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




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




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




Strengthening of foundation

Strengthening of foundation beam Strengthening of pile




Strength Upgrading

Ductility Upgrading



Infilling Wall

Steel Framed Brace (Internal)

Steel Framed Brace (External)

Buttress Beam

Strengthening Column

Strengthening

Shear Wall with Opening

Adding Seismic Slit

Str

eng

then

ing

Met

ho

ds

for

En

han

cin

g t

he

Sei

smic

Per

form

ance

of

Exi

stin

g B

uil

din

gs



Enhancing the Seismic Performance of Existing Buildings by Adding Infilling Wall



Enhancing the Seismic Performance of Existing Buildings by Steel Framed Brace



Enhancing the Seismic Performance of Existing Buildings by Steel Framed Brace (External)



Enhancing the Seismic Performance of Existing Buildings by Adding Buttress



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



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



Enhancing the Seismic Performance of Existing Buildings by Dampers

Steel Damper Gum

Oil Damper



Enhancing the Seismic Performance of Existing Buildings by Adding Shear walls with Grid-Shaped

Block



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.

𝐼𝑠 = 𝐸𝑜 ∗ 𝑆𝐷 ∗ 𝑇 Where : 𝐸𝑜 = Basic Seismic Index of Structure. 𝑆𝐷 = Irregularity Index 𝑇 = Time Index ( to account for the degree of deterioration of the building)



Concept of Seismic Capacity Evaluation

The Basic Seismic index of Structure 𝐸𝑜

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.)

𝐸0 =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





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

Horizontal Displacement

Ho

rizo

nta

l F

orc

e Critical failure Point

Seismic response





The basic seismic index is a function of the strength index C, and the ductility index F.

Horizontal Displacement

Ho

rizo

nta

l F

orc

e a

b

c

𝐸𝑜 = 𝐸1

𝐸𝑜 = 𝐸2

𝐸𝑜 = 𝐸21 + 𝐸

22





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 ………. 𝐼𝑠 ≥ 0.6



FRP for Seismic Strengthening of RC Buildings



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.



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.



Strengthening Applications for Concrete Structure

Beam Strengthening Slab Strengthening

Wall Strengthening

Column Strengthening



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, 1977 1st revised 1990 2nd revised 2001), a comprehensive publication that documents different retrofitting methods utilized in Japan.




Materials

The JBDPA guidelines describe the properties of PAN-class high-strength carbon fiber sheets, and aramid fiber sheets. In its turn, aramid is sub-classified 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.




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.




Ultimate Flexural Capacity of Columns

The ultimate flexural capacity of RC column is calculated from the following expressions.

For 𝑁𝑚𝑎𝑥≥ 𝑁 > 𝑁𝑏 :

𝑀𝑢 = 0.5𝑎𝑔𝜎𝑦𝑔1𝐷 + 0.024 1 + 𝑔1 3.6 − 𝑔1 𝑏𝐷2𝐹𝑐𝑁𝑚𝑎𝑥 −𝑁

𝑁𝑚𝑎𝑥 − 𝑁𝑏

For 𝑁𝑏 > N ≥ 0 :

𝑀𝑢 = 0.5𝑎𝑔𝜎𝑦𝑔1𝐷 + 0.5𝑁𝐷 1 −𝑁

𝑏𝐷𝐹𝑐

For 0 > 𝑁 ≥ 𝑁𝑚𝑖𝑛 :

𝑀𝑢 = 0.5𝑎𝑔𝜎𝑦𝑔1𝐷 + 0.5𝑁𝑔1𝐷






For 𝑁𝑚𝑎𝑥≥ 𝑁 > 𝑁𝑏 :

𝑀𝑢 = 0.5𝑎𝑔𝜎𝑦𝑔1𝐷 + 0.024 1 + 𝑔1 3.6 − 𝑔1 𝑏𝐷2𝐹𝑐𝑁𝑚𝑎𝑥 −𝑁

𝑁𝑚𝑎𝑥 − 𝑁𝑏

𝑁𝑏 = 0.22 1 + 𝑔1 𝑏𝐷𝐹𝑐

Balanced Axial Force:

Ultimate Axial Force in compression:

𝑁𝑚𝑎𝑥 = 𝑏𝐷𝐹𝑐 + 𝑎𝑔𝜎𝑦

Where: N : Axial force in the column, 𝑎𝑔: overall area of the

longitudinal reinforcement of the column;𝑔1: Ratio of distance between the centers of longitudinal reinforcement in tension and compression to the column width; 𝑏, 𝐷: Dimensions of the column; 𝜎𝑦: specified yield

strength of the longitudinal reinforcement. 𝐹𝐶 : Compressive strength of concrete; ℎ0 = clear height of column;

Ultimate Axial Force in Tension:

𝑁𝑚𝑖𝑛 = −𝑎𝑔𝜎𝑦






For 𝑁𝑏 > N ≥ 0 :

𝑀𝑢 = 0.5𝑎𝑔𝜎𝑦𝑔1𝐷 + 0.5𝑁𝐷 1 −𝑁

𝑏𝐷𝐹𝑐

𝑁𝑏 = 0.22 1 + 𝑔1 𝑏𝐷𝐹𝑐













For 0 > 𝑁 ≥ 𝑁𝑚𝑖𝑛 :

𝑀𝑢 = 0.5𝑎𝑔𝜎𝑦𝑔1𝐷 + 0.5𝑁𝑔1𝐷

𝑁𝑏 = 0.22 1 + 𝑔1 𝑏𝐷𝐹𝑐












The shear force associated to the flexural capacity Mu can be computed as

𝑄𝑚𝑢 =𝛼𝑀𝑢ℎ0

α = experimental value which equal to 2

Validation of the equation for Flexural Strength of Columns




Ultimate Shear Capacity of Columns

The ultimate shear capacity of RC column is calculated from the following expressions.

𝑄𝑠𝑢 =0.053𝑝𝑡

0.2318 + 𝐹𝑐

𝑀𝑄𝑑 + 0.12

+ 0.85 𝑃𝑤 𝜎𝑤𝑦 + 0.1𝜎0 𝑏𝑗

Where: 𝜎0 : 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), 𝑝𝑡 = Ratio of tensile reinforcement =𝑎𝑡 𝑏𝑑 % ; 𝐹𝐶 : Compressive strength of concrete; 𝑃𝑤𝑠= ratio od existing shear steel reinforcement to area of

contract surface = 𝑎𝑣 𝑏𝑑 (%); 𝑝𝑤𝑓= ratio of FRP reinforcement to area of contact surface =𝐴𝑟𝑒𝑎𝐹𝑅𝑃

𝑏𝐷(%);

𝜎𝑤𝑦𝑠: Specified yield strength of existing transversal reinforcement; 𝜎𝑓𝑑 = tensile strength for FRP for shear

design.

𝑝𝑤𝜎𝑤𝑦 = 𝑝𝑤𝑠𝜎𝑤𝑦𝑠 + 𝑝𝑤𝑓𝜎𝑓𝑑 ≤ 10 MPa




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

∅ =1

0.75 1 + 0.05𝜇

𝜇 = 10𝑄𝑠𝑢

𝑄𝑚𝑢− 0.9 , where 1 ≤ 𝜇 ≤ 5



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



Thank you

seismic strengthening of rc building...

Documents