IABSE ANNUAL MEETING, LONDON, 19TH SEPTEMBER 2011

SEISMIC APPROACH DESIGN COMPARISON BETWEEN IBC AND ITALIAN DM2008IBC AND ITALIAN DM2008

Ing. Luca Zanaica Ing. Francesco CaobiancogSenior Structural Engineer

gSenior Structural Engineer

1WORKING GROUP 7: “EARTHQUAKE RESISTANT STRUCTURES”

OUTLINES• The two codes’ frameworks• Study case project• Seismic input parameters’ definition

El ti t & D i t• Elastic spectra & Design spectra• Results for the case project• Results for the case project• Cantilever walls investigationg• Final results• Force-based Vs. Displacement-base

2SEISMIC APPROACH DESIGN COMPARISON BETWEEN IBC AND ITALIAN DM2008WORKING GROUP 7: “EARTHQUAKE RESISTANT STRUCTURES”

THE TWO CODES’ FRAMEWORKS

DM 2008Decreto Ministeriale

14/01/2008

IBC 2009International Building

Code 200914/01/2008 Code 2009

EN 1998-1-1:2005ASCE 7

Minimum Design LoadsEN 1998 1 1:2005 Eurocode 8 - Design of

structures for earthquake i t

Minimum Design Loadsfor Buildings andOther Structures

resistance Part 1: General rules,seismic actions and

ACI 318Building Codeseismic actions and

rules for buildingsBuilding Code

Requirements for Structural Concrete

3SEISMIC APPROACH DESIGN COMPARISON BETWEEN IBC AND ITALIAN DM2008WORKING GROUP 7: “EARTHQUAKE RESISTANT STRUCTURES”

CASE PROJECT

Milit f ilit• Military facility• Shear wall• Shear wall

seismic i t tresistant

structure• Asymmetric

l hplan shape• Short walls• Short walls

4SEISMIC APPROACH DESIGN COMPARISON BETWEEN IBC AND ITALIAN DM2008WORKING GROUP 7: “EARTHQUAKE RESISTANT STRUCTURES”

SEISMIC INPUT PARAMETERSDM 2008 IBC 2009Use Class II: Occupancy Category II:structure with regular crowd CU=1

p y g ybuildings not designated as essential nor representing a substantial hazard to human life in the event of failure

Nominal Service Life VN=50years Seismic Importance Factor I=1Mapped parameters: PGA; horizontal spectral

l ti lifi ti f t F tMapped spectral response accelerations: SS& Sacceleration amplification factor FO; spectrum

constant-velocity period start TC*& S1

Site Class C: Site Class D: coarse-grained thickener soil or fine-grained stiff soil (180≤vs≤360 m/s)

stiff soil (180≤vs≤360 m/s)

Seismic-force-resisting system: Seismic-force-resisting system: g yshear walls

g yspecial reinforced concrete shear walls

Structural Factor q=3 Response Modification Factor R=6

Over strength factor Ω0=MINq; 1,2 for squat walls

Over strength factor Ω0=2.5

5SEISMIC APPROACH DESIGN COMPARISON BETWEEN IBC AND ITALIAN DM2008WORKING GROUP 7: “EARTHQUAKE RESISTANT STRUCTURES”

ELASTIC & DESIGN SPECTRA0,8

DM 14/01/2008 q=1

IBC R 1

0.797g

0 777g 0 7

0,8

DM 14/01/2008 q=3

IBC R=6

0,6

0,7 IBC R=10.777g

0,6

0,7 IBC R=6

0,5 0,5

0,4 0,4

0,2

0,3

0,2

0,3 0.259g

0,1 0,1

0.133g

00 1 2 3 4

00 1 2 3 4

6SEISMIC APPROACH DESIGN COMPARISON BETWEEN IBC AND ITALIAN DM2008WORKING GROUP 7: “EARTHQUAKE RESISTANT STRUCTURES”

RESULTS FOR THE CASE PROJECTDM 2008 IBC 2009

Design Base shear: Design Base shear:Design Base shear:4150 kN

Design Base shear:4400 kN

REASONS:• Structure high stiffness: very low period

moves the study onto the PGA zonemoves the study onto the PGA zone• Facility study case is not well representative

for this CODES’ comparisonFurther study is required• Further study is required…

7SEISMIC APPROACH DESIGN COMPARISON BETWEEN IBC AND ITALIAN DM2008WORKING GROUP 7: “EARTHQUAKE RESISTANT STRUCTURES”

CANTILEVER WALLS INVESTIGATION

• m = 60 tons• P = 200 kN• ∆hstorey = 3m

TA=0.3s TA=0.7s TA=1.6s TA=2.6s TA=3.3s TA=4.0s

[Priestly, Calvi, Kowalsky “Displacement-Based Seismic Design of Structures”]

8SEISMIC APPROACH DESIGN COMPARISON BETWEEN IBC AND ITALIAN DM2008WORKING GROUP 7: “EARTHQUAKE RESISTANT STRUCTURES”

CANTILEVER WALLS’ FINAL RESULTS D

M20

08

Vbase

DM20

08

Mbase

IBC

20

16

12

8

4

2

IBC

20

16

12

8

4

2

∆VbaseDM2008‐IBC0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400

Base Shear [kN]

∆ΜbaseDM2008‐IBC0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000

Base Moment [kNm]

mbe

r

20

umbe

r

20

16

Storey

Nu 16

12

8

4

Storey

Nu 16

12

8

44

22

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300

Base Shear [kN]

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000

Base Moment [kNm]

9SEISMIC APPROACH DESIGN COMPARISON BETWEEN IBC AND ITALIAN DM2008WORKING GROUP 7: “EARTHQUAKE RESISTANT STRUCTURES”

FORCE-BASED VS. DISPLACEMENT-BASEDFORCE-BASED METHOD CRITICISMSStiffness is estimated to determine the

period T. Stiffness is dependent on strength which cannot

be know until the end of the design processbe know until the end of the design processAllocating seismic force between elements based on initial stiffness is illogical becausebased on initial stiffness is illogical because

different elements might not yield simultaneously

The assumption that unique force-reduction factors are appropriate for a given structural

t d t i l i t l t di t bltype and material is at least disputable.

[Priestly, Calvi, Kowalsky “Displacement-Based Seismic Design of Structures”]

Displacement check is performed at last

10SEISMIC APPROACH DESIGN COMPARISON BETWEEN IBC AND ITALIAN DM2008WORKING GROUP 7: “EARTHQUAKE RESISTANT STRUCTURES”

[ y, , y p g ]

FORCE-BASED VS. DISPLACEMENT-BASEDSEISMIC CODES PROVIDE A VARIETY OF DESIGN DISPLACEMENT

[Priestly, Calvi, Kowalsky “Displacement-Based Seismic Design of Structures”][ y y p g ]

… why not starting straight from a design displacement?

11SEISMIC APPROACH DESIGN COMPARISON BETWEEN IBC AND ITALIAN DM2008WORKING GROUP 7: “EARTHQUAKE RESISTANT STRUCTURES”

FORCE-BASED VS. DISPLACEMENT-BASEDEstimate Structural

Dimensions:Calculate yield

Calculate the effective stiffness Ke(me,Te)

DISPLACEMENT-BASED REMARKS

Constant yield curvature behaviour for a given geometrical sectionCalculate yield

displacement ∆y

S l t th d tilit l lCalculate the design forces and

moments: e g K ∆d & K ∆d H

Empirical calculation (through calibrated laws) of ξhyst

U f l ti di l t t ith

a given geometrical section

Select the ductility level µand the max permitted drift Θ

moments: e.g. Ke∆d & Ke∆d H

Capacity design with particular attention to material properties

Use of elastic displacement spectra with adequate damping:

NO R or q force reduction factor

Th d i i d t th tCalculate the design displacement ∆d=minΘH;µ∆y

attention to material properties, over strength factors and P-∆

Calculate the updated plastic

The design is made onto the secant stiffness Ke

Calculate the design ductility µd=∆d/∆y

p pdisplacement for the obtained

section: ∆d,ls

Y

Calculate the secant-stiffness equivalent damping ξeq= ξel+ ξhyst

∆d,ls=∆d

NEND

Y

Calculate the effective response period Te(∆d,ξe)

Calculate the updated design displacement ∆d

NEW=minΘH;∆d,ls

12SEISMIC APPROACH DESIGN COMPARISON BETWEEN IBC AND ITALIAN DM2008WORKING GROUP 7: “EARTHQUAKE RESISTANT STRUCTURES”

FORCE-BASED VS. DISPLACEMENT-BASED

DO YOU THINK ADIRECT DISPLACEMENT-BASED METHOD

IS GOING TO BE THE FUTURE FOR SEISMICIS GOING TO BE THE FUTURE FOR SEISMICDESIGN OF NEW STRUCTURES?

…IN ANY CASE IT APPEARS MORE RATIONAL…

13SEISMIC APPROACH DESIGN COMPARISON BETWEEN IBC AND ITALIAN DM2008WORKING GROUP 7: “EARTHQUAKE RESISTANT STRUCTURES”

IABSE ANNUAL MEETING, LONDON, 19TH SEPTEMBER 2011

THANK YOU!THANK YOU!

14SEISMIC APPROACH DESIGN COMPARISON BETWEEN IBC AND ITALIAN DM2008WORKING GROUP 7: “EARTHQUAKE RESISTANT STRUCTURES”