1

Seismic test and finite element analysis of a high-performance dual-core self-centering brace with a friction gusset connection

Ping-Ting Chung1) and Chung-Che Chou2)

1), 2) Department of Civil Engineering, National Taiwan University, Taiwan

2) cechou@ntu.edu.tw

ABSTRACT

The steel dual-core self-centering brace (DC-SCB) is a new structural member that provides both energy dissipation and self-centering properties in seismic-resisting systems, reducing residual drift of structures in major earthquakes. The axial deformation capacity of the steel DC-SCB is doubled by two inner cores, one outer box and serial axial deformation of two sets of tensioning elements in a parallel arrangement. However, the post-tensioning (PT) force of high-strength tendons is decreased when the strain of PT elements exceeds the yield strain. Recently, a high-performance DC-SCB that combines a DC-SCB and a friction gusset connection (FGC) together is proposed to eliminate the loss of PT force or damage of PT elements in extremely large earthquakes. This paper presents cyclic tests of a high-performance DC-SCB subassemblage (5 m-long) and a full-scale one-story, one-bay steel frame with a high-performance DC-SCB. The high-performance DC-SCB performed well under an increasing cyclic loading tests without failure. The maximum axial force of the high-performance DC-SCB was near 3700 kN at an interstory drift of 3.4%. Moreover, a three-story dual-core self-centering brace frame (DC-SCBF) with a single-diagonal high-performance DC-SCB was designed and its first-story, one-bay DC-SCBF subassembly specimen was tested in multiple earthquake-type loadings. The one-story, one-bay subassembly frame specimen in tests performed well up to an interstory drift of 2.5%, with yielding at the column base and local buckling of the steel beam; no damage of the high-performance DC-SCB was found after all tests. The maximum residual drift of the braced frame specimen caused by beam local buckling was 0.5% in 2.5% drift tests.

1. INTRODUCTION

A buckling-restrained braced frame (BRBF) is designed to limit plastic deformation in a brace under earthquake motions. A strong gusset connection which considers both

1)

Research Assistant 2)

Professor (Corresponding author)

2

the brace and frame action effects on the gusset is proposed to ensure stable energy dissipation of the BRB (Chou and Chen 2010, Chou and Liu 2012, Chou et al. 2012a, 2012b). However, the BRBF under severe earthquakes is prone to lateral residual deformation over the building height (Uang and Kiggins 2003, Tremblay et al. 2008, Chou et al. 2014). A single brace that uses a PT technology provides both self-

centering (SC) and energy dissipation properties and also eliminates the restraint of

columns or the frame expansion in lateral movement (Chou et al. 2008, Herning et al. 2009). Chou et al. (2014) proposed a steel dual-core self-centering (DC-SCB), which is composed of three conventional steel bracing members, two friction devices and two sets of tensioning elements that are in a parallel arrangement. These parallel structural members in the DC-SCB are used to double the axial elongation capacity of the self-centering energy-dissipation (SCED) brace (Christopoulos et al. 2008) when the same PT elements are used in both braces. The proposed DC-SCB exhibits a flag-shaped hysteretic response with minimal residual deformation (Chou et al. 2014, Chou and Chen 2015). The self-centering behavior of the DC-SCB is provided by the initial post-tensioning force; however, the surpassing yield strain of PT elements under large deformation causes loss of PT force (Chou et al. 2016). Erochko et al. (2015) presented a high-capacity SCED (HC-SCED) that positions the SCED and an external friction device in a series arrangement. The external friction device of the HC-SCED is mobilized to eliminate loss of PT force when the axial load exceeds the design strain of PT elements. This work investigates a possibility of using a friction gusset connection in a series with a DC-SCB that uses typical high-strength steel tendons as tensioning elements to provide the self-centering property.

The objective of this work is to develop a high-performance DC-SCB that is composed of a DC-SCB and a friction gusset connection (FGC) in a series arrangement. Since the DC-SCB uses high-strength steel tendons as tensioning elements to maintain its self-centering property, the axial strain in PT elements should be lower than the elastic limit to avoid loss of PT force. The high-performance DC-SCB can sustain in a major earthquake due to the slippage of the gusset connection when the brace force exceeds the friction force of the gusset connection to prevent yield of PT elements. In this work, the mechanics and hysteretic response of the high-performance DC-SCB are first introduced; finite element analysis is then used to verify the mechanics of the high-performance DC-SCB. Test results of a high-performance DC-SCB subassemblage (5-m long) and a full-scale one-story, one-bay steel frame with a high-performance DC-SCB are presented.

2. MECHANICS AND RESPONSE OF THE HIGH-PERFORMANCE DC-SCB

The high-performance DC-SCB (Fig. 1) is composed of a dual-core SCB (DC-SCB) and a friction gusset connection (FGC). The DC-SCB consists of three steel box members, inner and outer sets of PT elements, an energy dissipative device and four end plates in this study. The three steel box members are designated as the first core, the second core and the outer box; the second core is placed inside two other box members. The outer tendons are anchored to the left inner end plate and the right outer end plate; the inner tendons are anchored to the left outer end plate and the right inner

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end plate. Both ends of tendons are anchored to the ends of different bracing members to double the elongation capacity of the brace by serial deformations of PT elements (Chou and Chung 2014). These tendons are post-tensioned to compress all bracing members against end plates and are elongated to provide the SC capacity when the brace deforms axially. An energy dissipative device (EDD), which is located at one end of the brace, is activated by the relative movement between the first core and the outer box. The FGC that has a brass slim plate bolted between the brace end and the gusset plate slides when the brace force exceeds the frictional resistance of the gusset connection. Fig. 1(a) to (c) shows the kinematics and hysteretic response of the high-performance DC-SCB with the FGC in tension. When the axial force of the DC-SCB exceeds the initial PT force and the frictional resistance of the EDD, the outer box and the first core begin to move with respective to the second core. The FGC is not activated so that the slippage between the brace end and the gusset plate is zero (Fig. 1(b)). The relative displacement δ between the outer box and the second core and between the first core and the second core result in an axial displacement of 2δ in the brace, which doubles the elongation of the outer and inner sets of tendons. Two steel tendon sets with increasing δ are in tension, providing elastic restoring force to the DC-SCB in tension. When the brace force exceeds the frictional resistance of the gusset connection, a relative displacement, δfgc, between the brace end and the gusset plate occurs (Fig. 1(c)). Meanwhile, the axial deformation of the brace maintains 2δ without variation. When the load is removed, the bracing members return to their original position due to non-yielding of PT elements. The residual displacement of the brace occurs during movement of the FGC to prevent yielding of steel tendons. A similar behavior is observed when the high-performance DC-SCB is in compression.

Fig. 2 shows the simplified model of the high-performance DC-SCB. The cyclic response is composed of the DC-SCB response and the FGC response. The DC-SCB response is attributed to the bi-linear elastic behavior of PT elements with bracing members and the rigid plastic behavior of the EDD. The FGC response is a rigid plastic behavior that is associated with the relative movement between the brace end and the gusset connection.

The response of a high-performance DC-SCB remains the self-centering property before the activation of the FGC. Once the tensile activation load Fdt of a DC-SCB is exceeded, the outer end plates moves in opposite directions, resulting in a brace deformation twice that of the tendon elongation δ (Fig. 1(b)). The tensile activation load Fdt is expressed as:

indt dt f f

nTF =P +P = +P

2 (1)

where Pdt is the initial PT force in the tendons, Pf is the friction force of the EDD, n is the total number of tendons, and Tin is the initial PT force in one tendon. In order to prevent yielding of steel tendons that causes loss of the initial PT force, the yield strain in PT elements corresponds to the ultimate axial displacement of the brace δbu:

bu y in yδ = 2 ε - ε L (2)

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where εy is the tendon yield strain, εin is the initial tendon strain, and Ly is the length of the inner tendons. The maximum brace deformation δbu is corresponding to the ultimate axial force of the brace Fut that activates the FGC:

ut dt m,pt bu dtF =F +K δ -δ (3)

where Km,pt is the post-elastic axial stiffness of the brace, δdt is the axial activation displacement of the DC-SCB (Chou et al. 2016), corresponding to its activation force Fdt. The activation force Fdt and the activation displacement δdt occur where the first core and the outer box of the DC-SCB start moving, causing energy dissipation in the EDD. When the brace force reaches the frictional resistance of the FGC, Ffgc, slippage occurs between the brace end and the gusset connection, corresponding to the ultimate axial force of the brace Fut. The relationship between the maximum axial deformation of the high-performance DC-SCB, δut, and a design inter-story drift angle α is (Chou et al. 2014):

but bu fgc

L αδ = sinθ =δ +δ

2 (4)

where Lb is the length between working points chosen at the intersection of the centerlines of the column, brace and beam, θ is the angle of the brace, and δfgc is the slippage between the brace end and the gusset connection. The axial deformation of the high-performance DC-SCB is the summation of the brace deformation and the FGC slippage in series. However, the slippage δfgc is zero before the activation of the FGC. 3. TEST OF THE HIGH-PERFORMANCE DC-SCB

3.1 Test program

Fig. 3(a) shows a proposed high-performance DC-SCB specimen that had a first core of T320 × 300 × 10 mm, a second core of T270 × 250 × 12 mm, and an outer box of T420 × 370 × 10 mm tested at NCREE. The brace specimen had 24 seven-wire ASTM A416 Grade 270 steel tendons, and only twelve were anchored outside the outer end plates need for the initial PT work (Fig. 3(a)). The specimen was placed in the test setup (Fig. 3(b)), which included one steel box column pin-supported to the laboratory floor and attached to two 1000-kN hydraulic actuators. The high-performance DC-SCB specimen was positioned at an incline of θ (=60o) that the top end of the brace welded to dual gusset plates and the bottom end of the brace bolted to a dual gusset plate connection with a specified frictional strength. Positive drift means that actuators push the column to the right so the brace is in compression.

The initial PT force in the twelve steel tendons was set to 690 kN. The EDD that was placed between the first core and the outer box in the brace were set to produce a friction force of 967 kN. The FGC that was placed between the brace end and the base was designed to move at a friction force of 3352 kN. At a target drift level of 1.37%, the brace tensile force was about 2728 kN, less than the friction force of 3352 kN in the

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FGC. At a target drift level of 2.74%, the brace force was about 3352 kN based on the tendon strain of 0.82%. The activation of the FGC caused slippage between the brace end and the gusset plate connection, maintaining the same brace force. Table 1 lists brace force at each drift level. The high-performance DC-SCB specimen was subjected to one phase test. The loading protocol that was modified based on AISC seismic provisions (2010) consisted of two cycles per column drift of 0.06%, 0.11%, 0.23%, 0.46%, 0.69%, 1.37%, 2.06%, 2.74% and 3.43%. The actuator displacement rate was 0.8 mm/s for each column drift.

3.2 Test result

The high-performance DC-SCB without the EDD revealed a bilinear elastic response; the first change of stiffness occurred at a load equal to the initial PT force and the second change of stiffness occurred at the activation of the FGC. Fig. 4(a) shows the actuator force versus the displacement response of the brace in the phase test. Fig. 4(b) shows the corresponding axial force versus axial displacement response of the brace with slippage of the FGC. The axial deformation is measured from displacement transducers (marked as the L series) that were positioned on both ends of the high-performance DC-SCB, and between the brace end and the gusset plate at the base (Fig. 3(b)). The brace force obtained from the summation of the PT force and the EDD friction force in the brace. Fig. 4(c) shows the response of the brace without the FGC, the flag-shaped hysteretic response of the brace exhibits good self-centering behavior without yielding of the tendons. Fig. 4(d) shows the friction responses of the FGC and the EDD, respectively. The symmetric displacement response of the EDD is different from the response of the FGC because the FGC slippage when the brace is in tension and compression occurs at drifts of 2.06% and 3.43%, respectively (Fig. 5(a)). The residual deformation of the high-performance DC-SCB is caused by the slippage of the FGC when the brace force reaches the FGC friction force (Fig. 4(b)). Fig. 5(b) shows energy dissipation computed for the final cycle in each drift cycle; the corresponding equivalent viscous damping ratio is computed based on:

h heq

m m e

A Aξ = =

2πF Δ 4πA (5)

where Fm is the average of positive and negative peak brace forces, Δm is the average of positive and negative peak brace displacement, Ah is the energy dissipation in one cycle, and Ae is the elastic strain energy. The high-performance DC-SCB specimen provides stable energy dissipation in each drift cycle, without any sign of energy degradation. The energy dissipation of the DC-SCB without the FGC gradually increases as the drift increases except for the last drift cycle because the axial deformation and the axial force of the brace had no variation when the brace force reached the FGC friction force (Fig. 4(c) and Fig. 5(a)). The energy dissipation of the FGC increases from the drift of 2.06% to 3.43%; the behavior exhibits that the hysteretic response is a rigid plastic behavior (Fig. 4(d)).

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4. FINITE ELEMENT ANALYSIS OF THE HIGH-PERFORMANCE DC-SCB An analytical study using the finite element (FE) computer program ABAQUS (2010)

was conducted to study the self-centering behavior of the DC-SCB with the FGC. A model to simulate sliding of the FGC (model 1) is different from the gusset connection without sliding (model 2). The elastic modulus of steel was 203 GPa, and the von Mises yielding criterion was adopted. The actual material properties of bracing members and tendons that were obtained from coupon tests were used to calibrate parameters of the isotropic hardening model. All steel bracing members and end plates were modeled using eight-node solid elements, C3D8R, and tendon elements were modeled using truss elements, T3D2. Based on the previous works (Chou and Chung 2014), an interaction between the steel bracing members and the end plates was used with a hard contact behavior, allowing separation of the interface in tension and no penetration of that in compression. The activation of the FGC was modeled with slippage between the extended plate from the outer box and the gusset plate connection. The interaction that produces a friction force by applying the clamping force to the friction surface with a friction coefficient of 0.31 used in the EDD and the FGC.

The axial displacement of the brace, PT force and the friction force of the EDD and the FGC from the test were used as parameters in the finite element analysis. Fig. 6(a) shows FE models of the high-performance DC-SCB (model 1) and conventional DC-SCB (model 2). The difference between these two models is that model 1 allows slippage between the brace end and the gusset connection. The hysteretic response of model 1 differs from model 2 because model 1 has the residual deformation after slippage of the gusset connection but model 2 has loss of the PT force and residual deformation due to yielding of tendons. The FGC keeps the maximum axial force below the design value so that tendon yielding is excluded in model 1, eliminating loss of tendon force and axial capacity of the brace. Model 1 shows good self-centering behavior and small residual deformation in the brace, verifying the force-transfer mechanism of the high-performance DC-SCB.

5. ONE-STORY HIGH-PERFORMANCE DC-SCBF SUBASSEMBLY TEST

5.1 Test program The test program for a one-story, one-bay DC-SCBF with the FGC (DC-SCBF 1, Fig.

7(a)) had two phases: the first test excluded the EDD and the second test included the EDD in the brace. The braced frame had columns H414×405×18×28 mm and a beam H500×200×10×16 mm. The test results of the DC-SCBF without the FGC (DC-SCBF 2, Fig. 7(b)) was used as benchmark data (Chou et al. 2016). Both DC-SCBF tests used the same size of the DC-SCB with a first core of T250×280×8 mm, a second core of T210×240×10 mm and an outer box of T340×340×8 mm (Fig. 7(c)). The column panel zone was designed to remain elastic in all tests. The DC-SCB had 12 seven-wire ASTM A416 Grade 270 steel tendons, of which six were anchored outside the outer end plates. The initial PT force in six steel tendons was 425 kN. The EDD and the FGC used C2680 brass shim plates sandwiched by 20 and 24 mm-diameter F10T bolts, respectively. The EFD of DC-SCBF 1 was placed on the bottom gusset plate, and the EDD of both braces were placed in the opposite location (Fig. 7(a) and 7(b)). The DC-

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SCB was connected to framing members using a dual-gusset plate configuration, which was designed to remain elastic based on the past work (Chou et al. 2012a).

The subassembly DC-SCBF 1 specimen without the EDD in the brace used six F10T 24 mm-diameter bolts to stress the FGC to provide the frictional resistance at the target drift. The braced frame was tested to a drift of 0.5% to evaluate the initial PT force, Pdt, and then reloaded to a drift of 2% to evaluate its cyclic behavior in the first test. The subassembly frame specimen was then used two F10T 20 mm-diameter bolts to stress the EDD of the brace to dissipate seismic energy, and restarted testing to a drift of 2.5% in the second test. The first test of the DC-SCBF 1 without the EDD was subjected to a standard loading protocol that consisted of two cycles at a column drift of 0.09%, 0.18%, 036%, 0.5%, 1%, 1.5% and 2%. The second test of the DC-SCBF 1 with the EDD used the same loading protocol of the first test but to a column drift of 2.5%. The objective of the two phase test was to evaluate the seismic performance of the system, damage progress in the brace, beam and column and sliding behavior of the FGC.

5.2 Test result

Fig. 8(a) shows the axial force versus axial displacement responses of the brace with slippage of the FGC and Fig. 8(b) shows the brace response after removing slippage of the FGC. The slippage of the FGC was measured using displacement transducers that were positioned between the extended plate of the brace and the gusset plate. The initial PT force of the brace was 425 kN obtained in the first test of the DC-SCBF 1 without the EDD. The DC-SCB in two frame tests (DC-SCBF 1 and DC-SCBF 2) reached the activation force at an inter-story drift of 0.36%; the column base and the beam yielded after an inter-story drift of 1%, observed by whitewash flaking on the member face. The steel beam showed a sign of flange local buckling at an inter-story drift of 1.5%. The one-story, one-bay subassembly frame with the FGC performed well in the second test and no damage was found in frame members, DC-SCB or tendons after completing all tests. The test result of the high-performance DC-SCB in the frame shows good self-centering behavior and small residual deformation of the brace (Fig. 8(b)), which uses slippage of the FGC at the target drift to prevent loss of PT force associated with yielding of tendons. The DC-SCB 1 with the FGC and the DC-SCB 2 without the FGC (Chou et al. 2016) had the same initial PT force and bracing member size, but the maximum tendon strains in both braces were 0.59% at 2.5% drift and 0.67% at 2% drift, respectively, which were lower than the nominal yield of 0.8%. At a larger drift, the DC-SCB 1 with the FGC had smaller tendon strain due to slippage of the FGC (Fig. 8(a)). The energy dissipation and the equivalent viscous damping ratio of two DC-SCBs have similar responses (Fig. 8(c) and 8(d)).

6. CONCLUSIONS Typical seismic-resisting systems in earthquakes dissipate energy through beams

or braces, leading to structural damage or residual drifts that are difficult and expensive to repair. A steel dual-core self-centering brace (DC-SCB) was proposed to provide both energy dissipation and self-centering properties to structural systems. A high-

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performance DC-SCB that has a DC-SCB and a friction gusset connection (FGC) in series can prevent loss of PT force or damage of PT elements in extremely large earthquakes because of slippage of the FGC. The FGC that has a brass shim plate bolted between the brace end and the gusset plate is activated when the brace force exceeds the frictional resistance of the FGC. The force-transfer mechanism of the high-performance DC-SCB was also confirmed by finite element analyses. The high-performance DC-SCB performed well under an increasing cyclic tests without failure. The maximum axial force of the high-performance DC-SCB was near 3700 kN at an inter-story drift of 3.43%. Moreover, a single-diagonal high-performance DC-SCB was designed in a first-story, one-bay DC-SCBF subassembly specimen. The one-story, one-bay subassembly frame specimen with the FGC in tests performed well up to an inter-story drift of 2.5% with yielding at the column base and local buckling in the steel beam; no damage of the high-performance DC-SCB was found after tests. The maximum residual drift of the high-performance DC-SCBF caused by beam local buckling in these tests was 0.5% during 2.5% drift cycle. ACKNOWLENGMENT The authors would like to thank the Ministry of Science and Technology, Taiwan for financially supporting this research under Contract No. NSC 102-2221-E-002-101-MY3 and MOST 104-2625-M-002-028. The experimental work was conducted at the National Center for Research on Earthquake Engineering (NCREE) in Taiwan. Assistance from the technical staff is acknowledged. REFERENCES 1. AISC. (2010). “Seismic provisions for structural steel buildings,” Chicago, IL:

American Institute of Steel Construction. 2. ABAQUS. (2010). “Standard user’s manual version 6.10,” Providence, RI, USA:

Dassault Systems Simulia Corp. 3. Chou C-C, Chung P-T, and Cheng Y-T. (2016). “Experimental evaluation of large-

scale dual-core self-centering braces and sandwiched buckling-restrained braces,” Eng. Struct., 116, 12-25.

4. Chou C-C, Wu T-H, Beato Ovalle R. A., Chung P-T, Chen Y-H. (2016). “Seismic design and tests of a full-scale one-story one-bay steel frame with a dual-core self-centering brace,” Eng. Struct., 111, 435-450.

5. Chou C-C and Chen Y-C. (2015). “Development of steel dual-core self-centering braces: quasi-static cyclic tests and finite element analyses,” Earthquake Spectra, 31(1), 247-72.

6. Chou C-C and Chung P-T. (2014). “Development of cross-anchored dual-core self-centering braces for seismic resistance,” J. Constr. Steel Res., 101, 19-32.

7. Chou C-C, Chen Y-C, Pham D-H, and Truong V-M. (2014). “Steel braced frames with dual-core SCBs and sandwiched BRBs: mechanics, modeling and seismic demands,” Eng. Struct., 72, 26-40.

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8. Chou C-C and Liu J-H (2012). “Frame and brace action forces on steel corner gusset plate connections in buckling-restrained braced frames,” Earthquake Spectra, 28(2), 531-551.

9. Chou C-C, Liu J-H, and Pham D-H. (2012a). “Steel buckling-restrained braced frames with single and dual corner gusset connections: seismic tests and analyses,” Earthquake Eng. Struct. Dynam., 7(41), 1137-1156.

10. Chou C-C, Liu G-S, and Yu J-C. (2012b). “Compressive behavior of dual-gusset-plate connections for buckling-restrained braced frames,” J. Constructional Steel Research, 76, 54-67.

11. Chou C-C, Chen S-Y. (2010). “Subassemblage tests and finite element analyses of sandwiched buckling-restrained braces,” Engineering Structures, 32, 2108-2121.

12. Christopoulos C, Tremblay R, Kim HJ, and Lacerte M. (2008). “Self-centering energy dissipative bracing system for the seismic resistance of structures: development and validation,” J. Struct. Eng., ASCE, 134(1), 96-107.

13. Chou C-C, Weng C-Y, and Chen J-H. (2008). “Seismic design and behavior of post-tensioned connections including effects of a composite slab,” Eng. Struct, 30, 3014-23.

14. Erochko J, Christopoulos C, and Tremblay R. (2015). “Design, testing, and detailed component modeling of a high-capacity self-centering energy-dissipative brace,” J. Struct. Eng., 141(8): 04014193.

15. Herning g, Garlock MM, Ricles J, Sause R, and Li J. (2009). “An overview of self-centering steel moment frames,” In: Proceedings of the structures congress, Austin, TX.Tremblay R., Lacerte M., and Christopoulos C. (2008). “Seismic response of multistory buildings with self-centering energy dissipative steel braces,” J. Structural Eng., ASCE, 134(1), 108-120.

16. Uang C-M and Kiggins S. (2003). “Reducing residual drift of buckling-restrained braced frames,” Int. Workshop on Steel and Concrete Composite Construction, National Taiwan University, Taiwan, Report No. NCREE-030026.

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Table 1 Design and test strength of the high-performance DC-SCB Parameter 1.37% Drift Ratio 2.74% Drift Ratio

PT Force (kN)

Tendon Strain (%)

EDD Force (kN)

FGC Force (kN)

Brace Peak Force Tendon Strain (%)

Brace Peak Force Tendon Strain (%)

Tension (kN)

Compression (kN)

Tension (kN)

Compression (kN)

690 (690)

0.2 (0.2)

967 (850)

3352 (3381)

2728 (2523)

2362 (2313)

0.56 (0.47)

3352 (3188)

3352 (3381)

0.82 (0.69)

( ): value from the test

(a) (b) (c)

Fig. 1 Kinematics and hysteretic response of the high-performance DC-SCB

Fig. 2 Simplified model of the high-performance DC-SCB

F/2

F/2

??

? ?

Left Outer

End Plate

F/2

F/2

F/2

F/2

Right Outer

End PlateEDD

1st Core

Outer Box

Left Inner

End Plate

Anchorages

Inner

Tendons

Outer

Tendons

F

?

F

?

F

?

F/2

F/2

Gussets

F/2

F/2

F/2

F/2

?ef

FGC

2nd Core

Right Inner

End Plate

DC-SCB with

only PT Elements

Friction Gusset

Connection

Energy

Dissipative Device

End Plate

(Rigid Element)

Fdt=Pdt+Pf

Fdc

2PfF

fgc

F

?

F

?

F

?

Fdt

2Pf

Fut

Fdc

Fuc

High-Performance DC-SCB FGC Response DC-SCB Response

External Force

or Displacement

External Force

or Displacement

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` (a) A Proposed High-Performance DC-SCB

(b) Test Setup

Fig. 3 Component test of the high-performance DC-SCB (Unit: mm)

(a) Actuator Response (b) DC-SCB plus FGC Response

(c) DC-SCB Response (d) FGC and EDD Responses

Fig. 4 Test of the high-performance DC-SCB

3560 (2nd Core)

3910 (Inner Tendons)

3940 (Outer Tendons)

3910 (1st Core and Outer Box)

4150

5275

1

1

2

2

AnchorageFriction Gusset Connection

Enery Dissipative Device

D16 Steel Strand (ASTM A416-1860(270K))

855 1855 2855 3855 4855 5855 6855 7855 8855 9855 10855 11855

55

00

4560

60줩

58

50

(Unit: mm)

Lateral Support

Positive

3910

4150

5275

4427

L1

L3

L4

L2

L5

DC-SCB

Friction Gusset

Connection(L

6)

LVDT

Bolts

2nd Core

(T270⊥250×12)

Section 1-1

Section 2-2

Inner

Tendons

Outer

Tendons

1st Core

(T320⊥300⊥10)

Outer Box

(T420⊥370⊥10)

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(a) Axial Force (b) Energy Dissipation

Fig. 5 Characteristics of the high-performance DC-SCB

(a) Model 1 and Model 2

(b) Model 1 Response

(c) Model 2 Response

Fig. 6 Finite element analysis of the high-performance DC-SCB

Gussets with sliding friction for Model 1

Gussets without sliding friction for Model 2

Energy Dissipative Device

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(a) DC-SCBF 1 with the FGC (b) DC-SCBF 2 without the FGC

(Chou et al. 2016)

(c) Cross Section (d) Test Setup of DC-SCBF 1

Fig. 7 Tests of two one-story, one-bay DC-SCBF subassembly specimens

(a) Brace Response with the FGC (b) Brace Response without the FGC

(c) Energy Dissipation (d) Equivalent Viscous Damping Ratio

Fig. 8 Responses of braces and one-story, one-bay braced frames

250 1250 2250 3250 4250 5250 6250 7250 8250 9250 10250 11250 12250 13250 14250 15250

9000

4140

24줩

Beam H500x200x10x16

DC-SCB

Column H414x405x18x28

Unit: mm

Positive

3960

1600

4204023

Friction Gusset

Connection

1

1

2

2

Energy

Dissipative

Devices

250 1250 2250 3250 4250 5250 6250 7250 8250 9250 10250 11250 12250 13250 14250 15250

9000

41

40

24줩

Beam H500x200x10x16

DC-SCB

Column H414x405x18x28

250 1250 2250 3250 4250 5250 6250 7250 8250 9250 10250 11250 12250 13250 14250 15250

9000

24줩

Unit: mm

DC-SCB

Unit: mm

Positive

39

60

16

00

39

60

16

00

4204023

External

Friction Devices

41

40

Beam H500x200x10x16 Column H414x405x18x28

Positive

4204023

1

1

2

2

1

1

2

2

Energy

Dissipative

Devices

Energy

Dissipative

Devices

Section 1-1 Section 2-2

2nd Core (T210⊥240×10)

Inner Tendons

BoltOuter Tendons

Outer Box (T340⊥340⊥8)

1st Core (T250⊥280⊥8)