1 İnş. Yük. Müh.,Promer Müş. Müh. Ltd. Şti., Ankara

2 İnş. Yük. Müh.,Promer Müş. Müh. Ltd. Şti., İstanbul

3 Dr.İnş. Müh.,Buehler &Buehler Eng. Sacramento/California

4 Principal Str. Eng. Buehler & Buehler Eng. Sacramento California

Email: info@promerengineering.com.tr

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COMPARISON OF ALTERNATIVE RETROFITTING TECHNIQUES

FOR A TYPICAL R/C SCHOOL BUILDING

S. Yıldırım2, A. Sümer

3 , E.Fuller,

4 Y.İ. Tonguç

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ABSTRACT:

This study consist of 4 different retrofitting techniques on a 4 storey typical school building.

Moreover comparison result of classical retrofitting technique and seismic damper application is

included for an 8 storey administrative reinforced concrete building. All mentioned retrofitting

techniques were technically applicable. The building performance has reached to the level which The

aim of this study was to compare them economically. Compered retrofitting techniques were classical

(adding R/C shear walls and R/C jacketing of columns), Adding Braced Steel Frames, Adding

Buckling Restrained Bracing Frames (BRBF) and Base Isolation. Shear Wall addition and R/C

jacking of columns is studied using Turkish Earthquake codes (TEC) whereas Other 3 techniques are

studied using ASCE 41 due to lack of necessary criterias in TEC.

ANAHTAR KELİMELER : Retrofitting, Base Isolation, Inovative Retrofitting Techniques.

1. EXISTING BUILDING INFORMATION

Figure 1: Google Earth view. Photo 1: Front view.

District : Kadıköy Total Construction area : 3020m2

Campus Name : Gözcübaba High School Number of students : 600

Construction time : 1994 Concrete Quality : A Bl: 8.5 MPa; B

Bl: 7.1 MPa

Number of storey : 4

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2. RETROFITTING WITH SHEAR WALL ADDITION

The reason of using conventional techniques were;

Being more familier for engineers,

No need for high skilled workers,

Matearials can be found from Turkish Market.

More economical for this kind of typical buildings.

Disadvantages;

Building need to be evacuated,

8-10 months for construction,

High Architectural disturbance,

The following additions were done in this alternative.

Interior and Exterior R/C shear wall additions were done respectively,

4 Shear walls added and 2 existing shear walls were reconstructed for x-direction

4 Shear walls were added for y-direction

29 of 44 columns were jacketed at the Ground and 1 st Floor

14 of 42 columns were jacketed at the 2 nd Floor

4 of 42 columns were jacketed at the 3 rd Floor

Typical plan view of retrofitted building can be seen in Figure 2.

Figure 2: Typical Retrofitted Plan view.

Table 1: Compartive Results of Retrofitted Building.

Assessment of the retrofitted building using Shear walls and column jacketing can be seen in table 2.

There can be seen some beams in collapse and heavy damage region in both X and Y direction.

Because αs were higher than 75%, beams are considered as secondary members and not retrofitted as

per Ismep Guidelines 2008. Displacement, natural periods are decreased while mass and shear force

are increased as it is expected for Retrofitted Building. Retrofitted building satisfied conditions of

Turkish Earthquake Code (TEC 2007).

Approximate total structural cost for retrofitting with additional shear walls and R/C column jacketing

can be seen in table 4.

Table 2: Assessment of Retrofitted Building Using Additional Shear Walls X-Direction

Table 3: Assessment of Retrofitted Building Using Additional Shear Walls Y-Direction

Table 4: Structural Retrofitting Cost With Shear Wall Addition

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3. ALTERNATIVE RETROFIT SOLUTIONS

3.1 BRACED FRAME RETROFIT

A Preliminary Design and analysis that details can be seen in Figures 3,4,5 were performed by

Eric Fuller in order to get cost estimation of Braced Frame (OCBF) and Buckling Restrained

Bracing Frame (BRBF) Retrofitting.

Solution originally based on equivalent displacement to

concrete solution

Displacement requirements of this solution

reduced building functionality to the point where

it was unreasonable

Shifted to force based solution

Deleted all existing shear walls to eliminate

displacement compatibility issues

Design threshold at 75 percent of total base shear per

guidelines section 4.5.2.2

Beam performance ignored

Due to larger drifts jacketing of many columns required

Photo 2: OCBF Installation

Photo 3: OCBF Installation Photo 4: BRBF Installation

Ordinary Concentric Braced Frame solution (OCBF)

Buckling Restrained Braced Frame solution (BRBF)

Brace locations at perimeter when possible

Grade beam foundations kept linear

Minimizes demolition

Existing columns remain stable

Design Criteria:

R=4.0 , I=1.4, Cd=3.0

Interstory Drift:

1.6 cm OCBF

3.0 cm BRBF

0.6 cm Concrete (for comparison)

Figure 3: Section 1 OCBF Figure 4: Section 2 OCBF

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Figure 5: Foundation Plan View of Braced Framed Building

Figure 6: Details of Beam at Braced Frame Figure 7: Details of Brace Frame Footing

Table 5: Steel Bracing Addition Retrofitting Cost Summary Table.

3.2 BUCKLING RESTRAINED BRACING FRAME (BRBF) RETROFIT

Application of Buckling Restrained Bracing Frames are

very similar to OCBF. Differences are:

Core plate is allowed to yield without buckling

in both tension and compression

BRB elements are specified by core plate area

which defines capacity

Advantages of BRBF solutions over OCBF are

lower system demand and increased

predictability

Table 6: Buckling Restrained Bracing Frame Retrofitting Cost Summary Table

3.3 BASE ISOLATION RETROFITTING

A Preliminary Design which is seen at Figure 8 was done by Ian Aiken (Siecorp) in order to get cost

estimation for base isolation retrofitting.

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38 SLİDER 18 LEAD

RUBBER

Figure 8: LRB and Slider Application

Figure 9: Assumed Section of Base Isolation Application

Table 7: Base Isolation Application Cost Summary Table

Although Base Isolation Application has some advantages such as;

Minimum architectural disturbance,

Having minimum acceleration for upper structure

System has some disadvantages for this kind of typical school buildings in Turkey such as;

High cost,

Completely imported material,

Long time period and high cost for testing (No qualified, certified test center in Turkey).

Technical difficulties and cost of installing isolators under an existing building.

4. CONCLUSSIONS

Comparison Parameters of Retrofitting techniques are not only the cost for sure. The following

parameters can be considered in choosing retrofitting technique.

Total Cost,

Construction Time,

Material availability in Turkish Market,

Special conditions of the building such as historical buildings,

Possibility of evacuating the building.

Amount of architectural disturbance

For typical school buildings which is considered in this study the most important parameter between

these is the cost. Economical comparison chart can be seen in Figure 10.

Figure 10: Economical Comparison Chart of Alternative Retrofitting Techniques

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5. RESOURCES

Turkish Earthquase Code 2007.

ASCE 41-06. (2006), Seismic Rehabilitation of Existing Buildings. American Society of Civil

Engineers.

FEMA 273. (1997), Guidelines to the Seismic Rehabilitaion of Existing Buildings. Federal

Emergency Management Agency.

FEMA 356. (2000), Prestandard and Commentary for the Seismic Rehabilitation of Buildings.

Federal Emergency Management Agency.