Mid-America Earthquake Center
Hybrid Simulation for the Assessment of Semi-Rigid Partial-Strength Steel Frames in
Seismic RegionsQuake Summit 2012
July 11, 2012
Boston, Massachusetts
Hussam N. Mahmoud, Ph.D.
Colorado State University
• Introduction• Structure Design• Hybrid Simulation Approach
- Experimental module
- Analytical module
• Experimental Results and Observations • Conclusion• Questions
Overview
• Numerous examples of brittle fracture of welded moment connections, Northridge (1994), Kobe (1995)
• Fracture initiation at the connection (backing bar detail)- Poor design practice- Poor toughness
Damage to Welded Connections
Structure DesignStructure DesignIntroductionIntroduction Exp. ModuleExp. Module Ana. ModuleAna. Module ResultsResults ConclusionsConclusions
Moment
Rotationkq1
kq2
Rotational spring
Subassembly FEM Analysis
Frame with rotational springs
Idealized M-q
Experimental Testing
Realistic M-q
Current Limitations
Structure DesignStructure DesignIntroductionIntroduction Exp. ModuleExp. Module Ana. ModuleAna. Module ResultsResults ConclusionsConclusions
• The structure is 2-story, 4-bay longitudinal and 2-bay transverse
• The lateral load resisting system is SMRF designed using IBC 2006
• Load combination of 1.0 DL + 10 psf (partitions) + 0.25 LL + EQ
Specimen Design
SMRF, Typ.
30 ft 30 ft 30 ft 30 ft
W 18 x 40
Experimental Component
Structure DesignStructure DesignIntroductionIntroduction Exp. ModuleExp. Module Ana. ModuleAna. Module ResultsResults ConclusionsConclusions
Connection Capacity d
(in) T
(in) k
(in) La (in)
ts (in)
ta (in)
l (in)
ga (in)
p (in)
G (in)
W (in)
70% Mpbeam 17.9 1-3/16 3 8 1 5/8 16 2-3/4 5-1/2 3 1-1/4
50% Mpbeam 17.9 1-3/16 3 8 3/4 1/2 14 2-3/4 5-1/2 3 1
30% Mpbeam 17.9 1-3/16 3 8 1/2 3/8 14 2-3/4 5-1/2 3 1
Specimen Design
• Connection is designed as top-and seat-angles with double web-angles
• According to EC 3 with capacity of 70%, 50%, and 30% of the beam plastic moment
Ks
Kt
la
Web Angle
Flange Angle
tt = t
f(Fastener Dia.) = W
ls
lt = l
ga
p Seat Angle
Top Angle
ts (thickness of seat angle) and ta (thickness of web angle)
Structure DesignStructure DesignIntroductionIntroduction Exp. ModuleExp. Module Ana. ModuleAna. Module ResultsResults ConclusionsConclusions
Hybrid Simulation Approach
{F}
Computational: FEA
Measure forces
SimulationCoordinator
Experimental: LBCB
Target Disp.
Measured forces
{u}
Calc. forces
Structure DesignStructure DesignIntroductionIntroduction Exp. ModuleExp. Module Ana. ModuleAna. Module ResultsResults ConclusionsConclusions
Small-Scale Setup
Steel
Small-Scale Setup
Rubber
Small-Scale Validation
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Small-Scale Validation
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SIMCOR Space
(3 control points)
LBCBs Space
(2 control points)
x1,y1,dq1
x2,y2,dq2
x3,y3,dq3
(x1+dx1, y1+dy1, dq1)
(x2+dx2, y2+dy2, dq2)(x3+dx3, y3+dy3, dq3)
Fixed B.C.
LBCB1
LB
CB
2
Control Development
[T]
[T]-1
Y
X
Y
q
qX
Structure DesignStructure DesignIntroductionIntroduction Exp. ModuleExp. Module Ana. ModuleAna. Module ResultsResults ConclusionsConclusions
• Elastic deformation- Problem Definition
- LBCB platform movement controlled internally- LBCB frame, reaction wall/floor have finite stiffness- Internal actuator displacements include both specimen and external
deformations
Inelastic specimen
Rigid actuator
Elastic box
x
u1
u2
F
F = f1(u1)
F = f2(u2)
F
K2
K1
- Solution- An external measurement and feedback system was developed- 3 DOF (x,y, rz) for each LBCB for a total of 6 DOFs- System of 6 high tension string pots with low friction connections- Precisely monitors and accounts for the movement of the LBCB platform in
space
Control Development
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Full-Scale Setup
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Control Instrumentation
Control Development
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• Global- Still images and videos - Global drift - Global strain- M-q
• Local- Still images and videos- Bolt slip- Localized strain- Angle deformation relative
to the beam and column
Instrumentation
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Cyclic Loading of the Model
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• The Loma Prieta, PGA = 0.26 g
• USGS 1662 Emeryville, 77 km from the epicenter
• Soft soil (Vs = 199 m/s)
Record Selection
Structure DesignStructure DesignIntroductionIntroduction Exp. ModuleExp. Module Ana. ModuleAna. Module ResultsResults ConclusionsConclusions
Hybrid Results
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65.2% Mpbeam
82% Mpbeam
43.6% Mpbeam
ki
(kips.in/rad) ku
(kips.in/rad) kdeg (%)
| M |Max (kips.in)
%Mpbeam qMax (rad)
Energy Dissipated (kips.in.rad)
70% Mpbeam 510,683 390,827 23.47 3,222 82.0 0.0196 195.18
50% Mpbeam 494,314 266,718 46.04 2,556 65.2 0.0271 177.45
30% Mpbeam 306,521 203,565 33.59 1,708 43.6 0.034 109.56
Hybrid 30% Mpbeam
Hybrid Simulation Results (local)
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| 2nd |Max (in)
| 1st |Max (in)
| Base Shear |Max (kips)
70% Mpbeam 6.48 2.89 281.6
50% Mpbeam 7.17 3.35 253.6
30% Mpbeam 7.13 2.84 202.8
Hybrid Simulation Results (global)
Structure DesignStructure DesignIntroductionIntroduction Exp. ModuleExp. Module Ana. ModuleAna. Module ResultsResults ConclusionsConclusions
IDR limit of 5%
IDR limit of 2.5%
1
(%)
stMaxIDR 1
41
stMax
DBEASCE
IDRIDR
1
41
stMax
MCEASCE
IDRIDR
2
(%)
ndMaxIDR 2
41
ndMax
DBEASCE
IDRIDR
2
41
ndMax
MCEASCE
IDRIDR
70% Mpbeam 1.61 0.322 0.644 2.32 0.464 0.928
50% Mpbeam 1.86 0.372 0.744 2.42 0.484 0.968
30% Mpbeam 1.58 0.316 0.632 2.70 0.540 1.080
Hybrid Simulation Results (global)
Structure DesignStructure DesignIntroductionIntroduction Exp. ModuleExp. Module Ana. ModuleAna. Module ResultsResults ConclusionsConclusions
A new Hybrid simulation approach for the seismic evaluation of semi-rigid steel frames is executed
Conclusions
• Three simulations were conducted• Large hysteretic loops characterize the connection
behavior• No failure in any of the connection components• The maximum moment sustained by the 70%
Mpbeam, 50% Mpbeam, and 30% Mpbeam connections is 3,222 kips.in (82% Mpbeam), 2,556 kips.in (65% Mpbeam), and 1,708 kips.in (43% Mpbeam), respectively
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• The corresponding rotations are 0.0196 rad, 0.0271 rad, and 0.3400 rad, respectively
• The procedure used to scale the records does not allow for direct comparison with the interstory drift limits in ASCE 41-10
• The 50%Mpbeam and 70% Mpbeam frame are deemed acceptable for LS limit state (DBE) while the 30%Mpbeam violates the requirements as its roof drift ratio is calculated to be 2.70%, which is slightly higher than the limit of 2.5% for DBE
• For the expected maximum period elongation, the demand is always higher than the DBE and in some cases even higher than the MCE
Conclusions (cont.)
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Acknowledgements
Mid-America Earthquake Center
• Dr. Elnashai, Dr. Spencer, and Dr. Kuchma• Fellow former graduate students at UIUC • NEES staff at UIUC (MUST-SIM)• The analytical and experimental investigations
on the steel frames were supported by the MAE Center
• The experimental investigation was supported by NEES (shared-use)
Questions
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