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Fédération Internationale du Béton Proceedings of the 2 nd International Congress June 5-8, 2006 – Naples, Italy ID 9-17 Session 9 – Seismic evaluation of concrete structures Lateral Force Resisting Mechanism of a Multi-story Shear Wall and Peripheral Members Sakashita, M., Kono, S., Watanabe, F. Department of Architecture, Kyoto University, Nishikyo, Kyoto, 615 – 8540 Japan Tanaka, H. Division of Earthquake Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611 – 0011 Japan INTRODUCTION In current design procedures [1,2], cantilever structural walls are normally assumed to stand on a solid foundation, and foundation beams, slabs and piles are designed separately without considering their interactions. This is because their interactions have not been thoroughly studied for their complexity. Also neglected in the practical design is the fact that shear transfer mechanisms along the wall base vary depending on the crack patters and inelastic deformation levels at the shear wall base. This study aims to experimentally clarify the variation of the lateral load resisting mechanisms considering the interaction between a shear wall, foundation beams, slabs and piles, and to establish more rational design procedures for each structural component. In our earlier studies [3,4], experiments using two 20% scale specimens and two 15% scale specimens were performed. From these experiments, it was clear that the shear transfer mechanism along the wall base varied according to the deformation of the shear wall. This mechanism could be simulated by a simple section analysis of the foundation beam. In this study, more realistic experimental conditions were set up than in earlier experiments, such as the scale of the specimen, the steel ratio of the longitudinal reinforcement in the foundation beam and the loading methods. As our earlier studies, this study focuses on clarifying the transition of the shear transfer mechanism from experiment and analysis. The specimen configuration in this experiment was determined from typical fourteen story residential buildings in Japan. They normally have multiple spans of a RC moment resisting frame in the longitudinal direction and a single span of shear wall system in the transverse direction. In this study, the assemblage consisting of the lowest three floors of shear wall with a foundation beam, the first floor slab, and two piles in the transverse direction was scaled to 25%. This scale enable to use deformed reinforcing bars in the shear wall and observe more realistic crack distributions in the shear wall. Keywords: shear wall, foundation beam, pile, interaction EXPERIMENTAL SETUP Specimens Figure 1 shows specimen configuration and Fig. 2 shows reinforcement arrangement. The first floor slab extended 750 mm on either side of the shear wall and the total width was 1500mm. The shear wall and the slabs had the same thickness of 70mm. Pile caps were omitted and the piles were extended to the midheight of the foundation beam to simplify the construction. The distance between the contraflexural points of the piles (the center points of supporting pin and roller) and the midheight of the foundation beam was set 1250mm and the shear span ratio of the piles was fixed as 1.84 although the shear span ratio is supposed to vary depending on the soil, axial force, and lateral force under earthquakes. The center-to-center distance of the piles was 3000mm.

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Fédération Internationale du Béton Proceedings of the 2nd International Congress June 5-8, 2006 – Naples, Italy ID 9-17 Session 9 – Seismic evaluation of concrete structures

Lateral Force Resisting Mechanism of a Multi-story Shear Wall and Peripheral Members Sakashita, M., Kono, S., Watanabe, F. Department of Architecture, Kyoto University, Nishikyo, Kyoto, 615 – 8540 Japan Tanaka, H. Division of Earthquake Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611 – 0011 Japan INTRODUCTION In current design procedures [1,2], cantilever structural walls are normally assumed to stand on a solid foundation, and foundation beams, slabs and piles are designed separately without considering their interactions. This is because their interactions have not been thoroughly studied for their complexity. Also neglected in the practical design is the fact that shear transfer mechanisms along the wall base vary depending on the crack patters and inelastic deformation levels at the shear wall base. This study aims to experimentally clarify the variation of the lateral load resisting mechanisms considering the interaction between a shear wall, foundation beams, slabs and piles, and to establish more rational design procedures for each structural component.

In our earlier studies [3,4], experiments using two 20% scale specimens and two 15% scale specimens were performed. From these experiments, it was clear that the shear transfer mechanism along the wall base varied according to the deformation of the shear wall. This mechanism could be simulated by a simple section analysis of the foundation beam. In this study, more realistic experimental conditions were set up than in earlier experiments, such as the scale of the specimen, the steel ratio of the longitudinal reinforcement in the foundation beam and the loading methods. As our earlier studies, this study focuses on clarifying the transition of the shear transfer mechanism from experiment and analysis.

The specimen configuration in this experiment was determined from typical fourteen story residential buildings in Japan. They normally have multiple spans of a RC moment resisting frame in the longitudinal direction and a single span of shear wall system in the transverse direction. In this study, the assemblage consisting of the lowest three floors of shear wall with a foundation beam, the first floor slab, and two piles in the transverse direction was scaled to 25%. This scale enable to use deformed reinforcing bars in the shear wall and observe more realistic crack distributions in the shear wall. Keywords: shear wall, foundation beam, pile, interaction EXPERIMENTAL SETUP Specimens Figure 1 shows specimen configuration and Fig. 2 shows reinforcement arrangement. The first floor slab extended 750 mm on either side of the shear wall and the total width was 1500mm. The shear wall and the slabs had the same thickness of 70mm. Pile caps were omitted and the piles were extended to the midheight of the foundation beam to simplify the construction. The distance between the contraflexural points of the piles (the center points of supporting pin and roller) and the midheight of the foundation beam was set 1250mm and the shear span ratio of the piles was fixed as 1.84 although the shear span ratio is supposed to vary depending on the soil, axial force, and lateral force under earthquakes. The center-to-center distance of the piles was 3000mm.

Proceedings of the 2nd Congress Session 9

June 5-8, 2006 – Naples, Italy Seismic evaluation of concrete structures

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Material properties are shown in Tab. 1. Table 2 shows types of reinforcement. In this study, the shear wall was designed to fail in flexure and the piles were designed to be elastic in order to focus on the shear transfer mechanism along the shear wall base.

Lat eral Column1F Floor Slab(Thickness 70mm)

Transverse Foundat ionBeam Foundat ion Beam

The cent er dist ance bet ween piles 3000mm

Shear wall(Widt h 70mm)

Loading Beam

Beam

Beam

The dist ance bet ween t he cont raf lexural point of t he pilesand t he midheight of t he foundat ion beam1250mm

Slab Widt h 1500mm

Fig. 1. Specimen configuration

2400

3600

390

44044080 80

2740

3800

70

810

660

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400

3730

80 80

260260 270270

2400

3600

2740260 260

3260

600 600

600

450

1500

450

(a) Elevation (b) Plan view

Fig. 2. Reinforcement arrangement (unit: mm)

Tab. 1. Material properties of concrete and reinforcement

(a) Concrete (b) Reinforcement

Compressivestrength (MPa)

Tensile strength(MPa)

Young'smodulus (GPa)

Foundation beam, Pile 45.7 3.41 25.9Wall, Column, Beam 60.3 3.32 30.4

Yield strength(MPa)

Tensile strength(MPa)

Young'smodulus

D6 377 532 179D10(SD295A) 378 511 183D10(KSS785) 919 1078 201

D13 351 505 175D16 337 502 191D22 341 525 183D32 387 585 188

Proceedings of the 2nd Congress Session 9

June 5-8, 2006 – Naples, Italy Seismic evaluation of concrete structures

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Tab. 2. Types of reinforcement Member Steel ratio(%)

Longitudinal 8-D13 1.50Transeverse 2-D10@100 (KSS785) 0.549Longitudinal 4-D10 (SD295A) 1.18Transeverse 2-D6@150 0.302

Vertical D6@150 0.302Horizontal D6@150 0.302

Longitudinal 8-D32 3.28Transeverse 2-D13@120 0.480Longitudinal 4-D22 1.26Transeverse 2-D10@150 (SD295A) 0.634

Longitudinal 8-D16 0.738

Transeverse 2-D10@150 (SD295A) 0.366

Longitudinal 8-D16 1.36Transeverse 2-D10@150 (SD295A) 0.272

Longitudinal D6@150 0.302

Type of barsColumn

(260×260mm)Beam

(140×200mm)Shear Wall

(70mm)Pile

(440×440mm)Foundation Beam

(150×880mm)Slab

(70mm)Transverse Foundation

Beam(260×880mm)Loading Beam(350×400mm)

In Japanese design guideline [5], the required amount of the longitudinal reinforcement in the foundation beam under shear walls are determined separately based on the following two external forces as shown in Fig. 3. • Moment from piles (Mp) • Axial force Q/2 (tensile force) [Q is the total lateral force applied to the shear wall.] As shown in Fig. 3 (b), large rotation of the shear wall makes the shear force Q transfer through the limited area under compression. In gerenal, the lateral force applied to piles that are subjected to tensile axial force is smaller than the lateral force applied to piles that are subjected to compressive axial force. Axial force Q/2 is given as the possible maximum axial force in the foundation beams at the ultimate state. As for Mp in Fig. 3 (a), foundation beam is modeled as a line element and Mp is calculated by the lateral load applied to the piles and the distance between the contraflexural point of the piles and the midheight of the foundation beam.

Ai Dist r ibut ion

Q2

Q

Mp=Q ×2 2h

Q1

h1 h2Mp=Q ×1 h1

Q/ 2 Q/ 2

Q

Q/ 2Tension

Ai Dist r ibut ion

Q

(a) Moment from piles (Mp) (b) Axial force Q/2

Fig. 3. Design of foundation beams

In experiment, monolithic action between foundation beam and peripheral members, such as a shear wall, slabs and piles, is expected and it restricts the damage of the foundation beam at least until the shear wall yields and the shear wall base begins to be separeted from the foundation beam. In this study, the amount of longitudinal reinforcement in the foundation beam was set smaller than the requirement of the Japanese design guideline [5]. Figure 4 shows moment distributions and reaction forces at Q=360kN. At this time shear

Proceedings of the 2nd Congress Session 9

June 5-8, 2006 – Naples, Italy Seismic evaluation of concrete structures

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wall yields in flexure and moment applied to the foundation beam from piles was 296kN ⋅m. Flexural yield strength of the foundation beam ignoring contributions of peripheral members was 230 kN ⋅m. The safety factor of the foundation beam was 230/296=0.78. According to this design guideline, the yielding of the foundation beam precedes the yielding of the shear wall. Japanese design guideline [5] allows that the required strength of foundation structure can be decreased using ductile pile system. The steel ratio of the longitudinal reinforcement in this study became closer to those designed by the Japanese guideline.

h=1250mm

Q=360kN

0.3Q=108kN

0.7Q=252kN

Mp=0.7Q× h =296kN

・m

Njack

Moment capacit y of shear wall=2455kN m・ Moment capacit y

of foundat ion beam=230kN m・

Njack

Fig. 4. Moment distributions and reaction forces at Q=360kN

Test Setup As shown in Fig. 5, lateral load Q was applied statically through a 1000kN horizontal jack (A) to the loading beam. Two 2000kN vertical jacks were adjusted to create appropriate column axial forces at the shear wall base, N1 and N2, which are a linear function of lateral load Q to simulate loading conditions of the prototype fourteen-story shear wall system under earthquakes.

1 2 2.27 353 (unit:kN)andN N Q= ± + (1)

3500mm3000mm1750mm

5095mm

2000kN jack

Pin Roller

1000kN Jack (A)

0.3Q+ -

Q +-

0.7Q

1145mm

1690mm

2260mm

1000kN Jack (B)

Loading beam

Fig. 5. Loading system

Proceedings of the 2nd Congress Session 9

June 5-8, 2006 – Naples, Italy Seismic evaluation of concrete structures

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At the roller support, 0.7Q was applied horizontally to the pile when Q was positive and 0.3Q was applied to the pile when Q was negative by a 1000kN jack (B) in the opposite direction to the 1000kN horizontal jack (A). As shown in Fig. 6 (a), the load was applied two cycles at each prescribed load stage until the first story drift angle reached 0.06%. Then the displacement control was used with two cycles at each prescribed displacement in Fig. 6 (b). The first story drift angle is hereinafter called α . In this experiment, it was difficult to measure the drift angles of the shear wall because of the rotation and the deformation of the foundation. So they were calculated from the flexural deformation and the shear deformation of the shear wall and the relative sliding of the shear wall base. They were measured with the multiple displacement gauges placed at the shear wall.

-300

-200

-100

0

100

200

300

0 1 2 3 4 5 6Cycle (times)

-3

-2

-1

0

1

2

3

6 8 10 12 14 16 18 20 22Cycle (times)

1F D

rift A

ngle

(%)

(a) Load control (b)Displacement control

Fig. 6. Loading Cycle TEST RESULTS Observed Damage Observed damage is as follows. • Figure 7 (a) shows crack distribution. Flexure-shear cracks of the shear wall penetrated the slabs

transversely and developed to the foundation beam. Bold lines showed flexure-shear cracks whose widths were especially wide in positive loading. In this experiment, the shear wall deformed along these cracks involving the parts of the foundation beam, the pile, the transverse foundation beam and the slabs.

• Concrete crushing was hardly observed at the base of the columns in this experiment. • Figure 7 (b) shows damage of the shear wall base. On the west side longitudinal bars of the column

buckled. From the midspan of the shear wall to the east column, vertical bars of the shear wall fractured. The first result stated above was different from those of common experiments of shear wall with basement. Lateral Load- First Story Drift Angle (α ) Relation Figure 8 shows the lateral load – first story drift angle (α ) relation and yielding points of the shear wall and the foundation beam. As shown in Fig. 8, contrary to the design based on the Japanese design guideline [5], the yielding of the shear wall preceded the yielding of the foundation beam. It is thought that the foundation beam acted monolithically with peripheral members containing the shear wall and the damage of the foundation beam became small. After α =2%, specimen was pushed monotonically to 3% in positive direction. As noted in observed damage, concrete crushing was hardly observed at the shear wall base. The lever arm of the shear wall was made constant and the reduction of the lateral load didn’t occur.

Proceedings of the 2nd Congress Session 9

June 5-8, 2006 – Naples, Italy Seismic evaluation of concrete structures

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Q +- WestEast

(a) Crack distribution

East West

Five longit udinal bars of t he column buckled.Ten vert ical bars of t he shear wall f ract ured.

(b) Damage of the shear wall base

Fig. 7. Damage after the loading test was finished

-400

-200

0

200

400

-4 -3 -2 -1 0 1 2 3 4

Late

ral L

oad

(kN

)

1F Dr i f t Angl e α ( %)

Shear Wall (0.094%, 313.4kN)

Shear Wall (-0.128%, -313.1kN)

Foundation Beam [Lower] (0.350%, 340.3kN)Foundation Beam [Upper] (0.350%, 340.3kN)

Foundation Beam [Lower] (-0.188%, -339.6kN)

Foundation Beam [Upper] (-0.374%, -358.3kN)

Fig. 8. Lateral load – first story drift angle (α ) relation

Strain Distributions of Longitudinal Reinforcement in the Foundation Beam and in the Slabs Figure 9 (a), (b) shows the strain distribution of longitudinal reinforcement in the foundation beam at seven representative loading stages. Location in the foundation beam in Fig. 9 (a), (b) is illustrated with Fig. 9 (d). Until α became 0.11% (at this time the shear wall yielded in flexure.), the strains were restricted to small values. This is due to the monolithic action with peripheral members. After α became 0.11%, strains began to increase rapidly. This is because the shear transfer mechanism varied and the foundation beam begins to behave independently as the deformation of the shear wall increases. Transition of strain distributions of the upper longitudinal reinforcement was larger than that of the lower longitudinal reinforcement.

Proceedings of the 2nd Congress Session 9

June 5-8, 2006 – Naples, Italy Seismic evaluation of concrete structures

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Figure 9 (c) shows the average strain distribution of longitudinal reinforcement in slabs. Compared with Fig. 9 (a), each point and each distribution at seven representative loading stages agreed with that of Fig. 9 (a) except strains at midspan of the foundation beam. As shown in Fig. 9 (d), the height of the longitudinal reinforcement in slabs was almost same as that of the upper longitudinal bars in the foundation beam. The foundation beam could be considered as T beam.

-0.1

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0

0.05

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0.2

0.25

0.3

-1000 -500 0 500 1000

データ 2 22: 04: 37 2006/ 01/ 12

Q=+150kN( 0. 00940%, 147. 0kN)Q=+250kN( 0. 0334%, 252. 7kN)α =+0. 06%( 0. 0653%, 285. 9kN)α =+0. 12%( 0. 132%, 320. 6kN)α =+0. 27%( 0. 269%, 336. 8kN)α =+0. 40%( 0. 394%, 342. 8kN)α =+0. 68%( 0. 637%, 354. 8kN)ε y

Location in foundation beam (mm)

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0

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データ 2 22: 07: 40 2006/ 01/ 12

Q=+150kN( 0. 00940%, 147. 0kN)Q=+250kN( 0. 0334%, 252. 7kN)α =+0. 06%( 0. 0653%, 285. 9kN)α =+0. 12%( 0. 132%, 320. 6kN)α =+0. 27%( 0. 269%, 336. 8kN)α =+0. 40%( 0. 394%, 342. 8kN)α =+0. 68%( 0. 637%, 354. 8kN)ε y

Location in foundation beam (mm) (a) Upper longitudinal bar (Foundation beam) (b) Lower longitudinal bar (Foundation beam)

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データ 2 22: 26: 12 2005/ 10/ 07

Q=+150kN( 0. 00940%, 147. 0kN)Q=+250kN( 0. 0334%, 252. 7kN)α =+0. 06%( 0. 0653%, 285. 9kN)α =+0. 12%( 0. 132%, 320. 6kN)α =+0. 27%( 0. 269%, 336. 8kN)α =+0. 40%( 0. 394%, 342. 8kN)α =+0. 68%( 0. 637%, 354. 8kN)ε y

Location in foundation beam (mm)

- 150 +150 +450 +750 +1050 +1350- 450- 750- 1050- 1350X

Location of the longitudinal barsin the foundation beam and in the slabs

Sout h Nort h

East West

Upper longitudinal barsin the foundation beam D22( )

Lower longitudinal barsin the foundation beam D22( )

Longitudinal barsin the slabs D6( )

(c) Longitudinal bars (Slabs) (d) Location in the foundation beam

Fig. 9. Strain distributions of longitudinal reinforcement

SIMULATION OF STRAIN DISTRIBUTIONS OF THE FOUNDATION BEAM Analytical Methods In the ultimate strength design based on Japanses design guideline [5] , as shown in Fig. 3, moment from piles (Mp) and axial force (N) were checked in the design of the foundation beams. This design procedure does not consider the variation of the shear transfer mechanism. In this study, two additional moment were considered. One is moment due to lateral force acting on the top surface of the foundation beam (Mq). The other is moment due to vertical longitudinal bars in the shear wall (Mw). The

Proceedings of the 2nd Congress Session 9

June 5-8, 2006 – Naples, Italy Seismic evaluation of concrete structures

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distributions of N, Mq and Mw vary as the shear wall rotates and the contact area between the shear wall and the foundation beam decreases. As for Mp, the distribution does not vary as shown in Fig. 11. Figure 10 shows a schematic figure of contact and detachment of the shear wall base. Numbers beside each figure indicate the degree of detachment (D). It is assumed that the shear wall rotates and applied Q is transferred uniformly through the contact region (shaded region in Fig. 10). Figure 12 shows the models of the distributions of N, Mq and Mw corresponding to the degree of detachment in Fig. 10. The foundation beam was replaced with a line element. Calculating moment and axial force at each section, the strain distributions of the longitudinal reinforcement in the foundation beam were computed by a simple section analysis at each loading stage. The foundation beam was considered as T beam with slabs from experimental results.

00.25

Column(Tension side)

Column(Compression side)

Whit e region has no cont act . No st ress t ransfer is assumed.

0.50

Shaded region is t he area of cont act .Shear st ress is assumed t o dist r ibut e uniformly.

750 750750750

0.751.0

Degree ofdet achment Shear wall

Shear Force

Fig. 10. Degree of detachment (D)

h’

Q

0.3Q 0.7Q

Mp=0.7Q× h' (0.3Q× h')

h' '

h’ :Dist ance bet ween t he cont raf lexural point of t he pile and t he cent roid of t he foundat ion beam

h' ' :Dist ance bet ween t he t op surface and t he cent roid of t he foundat ion beam

Fig. 11. Distribution of Moment from piles (Mp)

Q Q Q Q Q

Q Q Q Q Q

N N N N NN N N

N=0.3QTension Tension Tension Tension TensionCompression Compression Compression Compression

0.3Q 0.3Q 0.3Q 0.3Q 0.3Q0.3Q 0.3Q 0.3Q0.7Q 0.7Q 0.7Q 0.7Q 0.7Q (a) D=0 (b) D=0.25 (c) D=0.50 (d) D=0.75 (e) D=1.0

(1) Axial force due to lateral force (N)

Fig. 12. Distributions of the moment and axial force corresponding to the degree of detachment (D) (continue)

Proceedings of the 2nd Congress Session 9

June 5-8, 2006 – Naples, Italy Seismic evaluation of concrete structures

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Q Q Q Q Q

Q Q Q Q Q

Mq Mq Mq MqMq=Q× h''

0.3Q 0.3Q 0.3Q 0.3Q 0.3Q0.3Q 0.3Q 0.3Q0.7Q 0.7Q 0.7Q 0.7Q 0.7Q

h'' h' ' h' ' h' ' h' '

(a) D=0 (b) D=0.25 (c) D=0.50 (d) D=0.75 (e) D=1.0

(2) Moment due to lateral force acting on the top surface of the foundation beam (Mq)

Mw

T=MIN(Esw(ε y× (1500mm- X)/ 3000mm),Fsw)× Asw

0 0 0 0 0

Mw Mw Mw Mw

T=Fsw× Asw T=Fsw× Asw T=Fsw× Asw T=Fsw× Asw

- 1500 - 1500 - 1500 - 1500 - 15001500 1500 1500 1500 1500

750mm 1500mm 2250mm 3000mm

Esw:The modulus of elast icit y of t he shear reinforcement bar of t he wall ε y:The yield st rain of t he longit udinal bar of t he column

Asw:The area of t he shear reinforcement bar of t he wall Fsw:The yield st rengt h of t he shear reinforcement bar of t he wall (a) D=0 (b) D=0.25 (c) D=0.50 (d) D=0.75 (e) D=1.0

(3) Moment due to vertical longitudinal bars in the shear wall (Mw)

Fig. 12. Distributions of the moment and axial force corresponding to the degree of detachment (D)

Comparison between Computed and Experimental Results The comparison between the computed and experimental strain distributions are shown in Fig. 13, Fig. 14, Fig. 15 and Fig. 16 at 4 different loading stages. Figure 13 shows the distributions until the shear wall yielded and Fig. 14 shows immediately after the shear wall yielded. Figure 15 and Fig. 16 show after the shear wall yielded. As shown in Fig. 13, especially the strains of the upper longitudinal bars were restricted to smaller values than the computed strains. This is due to the monolithic action with peripheral members. When the shear wall yielded, the strain distribution began to agree with the computed strain distributions as shown in Fig. 14. The strains of the lower longitudinal bars near the pile with 0.3Q lateral force indicated by a break line circle were larger than the computed strains. This behavior is explained later.

Q

Q

0.3Q 0.7Q

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Exper i ment +0. 06%( 0. 0653%, 285. 9kN)Anal ysi s ( Degr ee of det achment =0)ε y

Location in foundation beam (mm)

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Exper i ment +0. 1%( 0. 0653%, 285. 9kN)Anal ysi s ( Degr ee of det achment =0)ε y

Location in foundation beam (mm) (a) D =0 (b) Upper longitudinal bar (c) Lower longitudinal bar

Fig. 13. Strain distributions of the foundation beam α =0.06%

Proceedings of the 2nd Congress Session 9

June 5-8, 2006 – Naples, Italy Seismic evaluation of concrete structures

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Q

Q

0.3Q 0.7Q

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Location in foundation beam (mm)

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Exper i ment +0. 12%( 0. 132%, 320. 6kN)Anal ysi s ( Degr ee of det achment =0)ε y

Location in foundation beam (mm) (a) D =0 (b) Upper longitudinal bar (c) Lower longitudinal bar

Fig. 14. Strain distributions of the foundation beam α =0.12%

As the deformation of the shear wall increased, the strain distributions varied. In analysis, as shown in Fig. 15 and Fig. 16, the transition of strain distributions could be simulated well near the pile with 0.7Q lateral force that was indicated by solid line circles. In this experiment, the flexural yield strength of the foundation beam was set smaller than the requirement of the Japanese design guideline [5]. Though Mq and Mw should be considered in addition to Mp and N, due to the compressive axial force as shown in Fig. 12 (1) and the contribution of the slabs, the foundation beam didn’t yield near the pile with 0.7Q lateral force until α =0.35%. In this study, degree of detachment was adjusted to agree with the experimental results. In order to utilize this analytical method in design, it is necessary to establish the procedure to determine appropriate degree of detachment corresponding to design conditions. As for the strain distributions near the pile with 0.3Q lateral force, the computed results could not agree with the experimental results. This seems to be related to the stress transfer mechanism from tensile pile to the foundation beam as shown in Fig. 17. Near the pile with 0.3Q lateral force, compression force is transferred to the foundation beam forming diagonal concrete strut. This mechanism makes lever arm of the foundation beam small and the tensile force acting on the lower longitudinal reinforcement in the foundation beam increase. This problem could not be clarified by a section analysis. The analysis considering the whole structure should be conducted.

Q

Q

0.3Q 0.7Q

Q

Q

0.3Q 0.7Q

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Exper i ment +0. 27%( 0. 269%, 336. 8kN)Anal ysi s ( Degr ee of det achment =0)Anal ysi s ( Degr ee of det achment =0. 25)ε y

Location in foundation beam (mm)

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Exper i ment +0. 27%( 0. 269%, 336. 8kN)Anal ysi s ( Degr ee of det achment =0)Anal ysi s ( Degr ee of det achment =0. 25)ε y

Location in foundation beam (mm) (a) D =0 and 0.25 (b) Upper longitudinal bar (c) Lower longitudinal bar

Fig. 15. Strain distributions of the foundation beam α =0.27%

Proceedings of the 2nd Congress Session 9

June 5-8, 2006 – Naples, Italy Seismic evaluation of concrete structures

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Q

Q

0.3Q0.3Q 0.7Q

Q

Q

0.3Q 0.7Q

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Exper i ment +0. 68%( 0. 637%, 354. 8kN)Anal ysi s ( Degr ee of det achment =0. 25)Anal ysi s ( Degr ee of det achment =0. 50)ε y

Location in foundation beam (mm)

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Exper i ment +0. 68%( 0. 637%, 354. 8kN)Anal ysi s ( Degr ee of det achment =0. 25)Anal ysi s ( Degr ee of det achment =0. 50)ε y

Location in foundation beam (mm) (a) D =0.25 and 0.50 (b) Upper longitudinal bar (c) Lower longitudinal bar

Fig. 16. Strain distributions of the foundation beam α =0.68 %

h’

Q

0.3Q 0.7Q

Mp=0.7Q× h (0.3Q× h')

Tension

TensionCompression

Compression

Lever Arm

Fig. 17. Stress distributions near the piles

CONCLUSIONS One 1/4-scale cantilever structural wall system was tested to clarify the variation of the lateral load resisting mechanisms considering the interaction between a shear wall, a foundation beam, slabs and piles. The main conclusions can be summarized as follows. • Contrary to the design, the yielding of the shear wall preceded the yielding of the foundation beam. This

is due to the monolithic action between a foundation beam and peripheral members. • From strain distributions of longitudinal reinforcement in the foundation beam in experiment, the

transition of the shear transfer mechanism was confirmed. • In the analysis of the foundation beam, it is assumed that the foundation beam is subjected to moment

from the piles (Mp), moment (Mq) and axial force (N) due to lateral force Q, acting on the upper edge of the foundation beam, and moment due to vertical longitudinal bars in the shear wall (Mw). The analytical method using degree of detachment of the interface between the shear wall base and the foundation beam made shear transfer mechanism clear.

Other minor conclusions can be summarized as follows. • Flexure-shear cracks of the shear wall penetrated the slabs transversely and developed to the

foundation beam and the shear wall deformed along these cracks involving the parts of the foundation beam, the pile, the transverse foundation beam and the slabs.

Proceedings of the 2nd Congress Session 9

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• Near the pile with 0.3Q lateral force, the tensile force acting on the lower longitudinal reinforcement in the foundation beam in experiment was larger than that calculated in analysis. This is because compression force is transferred forming the diagonal concrete strut from the pile to the foundation beam.

REFERENCES 1. Architecture Institute of Japan. AIJ Standard for Structural Calculation of Reinforced Concrete Structures

Based on Allowable Stress Concept, 1999:218-241. 2. Paulay, T. Priestley, M.J.N. Seismic Design of Reinforced Concrete and Masonry Buildings. John Wiley

& Sons, 1992:362-499. 3. Sakashita M, Bechtoula H, Kono S, Tanaka H, Watanabe F. A Study on The Seismic Force Resisting

Mechanism of A Multi-story Shear Wall System Considering The Interaction Between Wall, Slab, Foundation Beam, and Pile Elements. 13th World Conference on Earthquake Engineering Conference Proceedings, 2004:pdf.No.3482.

4. Sakashita M, Urabe A, Murakami K, Kono S, Tanaka H, Watanabe F. Lateral Load Resisting Mechanism of a Monolithic Shear Wall or a PCa Shear Wall and Peripheral Members Part1-2. Summaries of Technical papers of Annual Meeting Architectural Institute of Japan C-2 Structures 4, 2005:403-406. (in Japanese).

5. The building center of Japan. Design and Construction Guidelines for Multiple Story Frame Structures with Shear Wall, 1999:9-54, 179-334. (In Japanese)

6. Architecture Institute of Japan. Design Guidelines for Earthquake Resistant Reinforced Concrete Buildings Based on Inelastic Displacement Concept, 2001:91-240, 278-293, 320-327. (In Japanese)