Mid-America Earthquake Center

Hybrid Simulation for the Assessment of Semi-Rigid Partial-Strength Steel Frames in

Seismic RegionsQuake Summit 2012

July 11, 2012Boston, 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 DesignIntroduction Exp. Module Ana. Module Results Conclusions

Moment

Rotationkq1

kq2

Rotational spring

Subassembly FEM Analysis

Frame with rotational springsIdealized M-q

Experimental Testing

Realistic M-q

Current Limitations

Structure DesignIntroduction Exp. Module Ana. Module Results Conclusions

• 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 DesignIntroduction Exp. Module Ana. Module Results Conclusions

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 DesignIntroduction Exp. Module Ana. Module Results Conclusions

Hybrid Simulation Approach

{F}

Computational: FEA

Measure forces

SimulationCoordinator

Experimental: LBCB

Target Disp.

Measured forces

{u}

Calc. forces

Structure DesignIntroduction Exp. Module Ana. Module Results Conclusions

Small-Scale Setup

Steel

Small-Scale Setup

Rubber

Small-Scale Validation

Structure DesignIntroduction Exp. Module Ana. Module Results Conclusions

Small-Scale Validation

Structure DesignIntroduction Exp. Module Ana. Module Results Conclusions

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

LBC

B2

Control Development

[T]

[T]-1

Y

X

Y

q

qX

Structure DesignIntroduction Exp. Module Ana. Module Results Conclusions

• 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

Structure DesignIntroduction Exp. Module Ana. Module Results Conclusions

Full-Scale Setup

Structure DesignIntroduction Exp. Module Ana. Module Results Conclusions

Control Instrumentation

Control Development

Structure DesignIntroduction Exp. Module Ana. Module Results Conclusions

• 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

Structure DesignIntroduction Exp. Module Ana. Module Results Conclusions

Cyclic Loading of the Model

Structure DesignIntroduction Exp. Module Ana. Module Results Conclusions

• The Loma Prieta, PGA = 0.26 g

• USGS 1662 Emeryville, 77 km from the epicenter

• Soft soil (Vs = 199 m/s)

Record Selection

Structure DesignIntroduction Exp. Module Ana. Module Results Conclusions

Hybrid Results

Structure DesignIntroduction Exp. Module Ana. Module Results Conclusions

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)

Structure DesignIntroduction Exp. Module Ana. Module Results Conclusions

| 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 DesignIntroduction Exp. Module Ana. Module Results Conclusions

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 DesignIntroduction Exp. Module Ana. Module Results Conclusions

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

Structure DesignIntroduction Exp. Module Ana. Module Results Conclusions

• 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.)

Structure DesignIntroduction Exp. Module Ana. Module Results Conclusions

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