The "InERD" Project presentation held @ Associazione - - PowerPoint PPT Presentation

mauro.sommavilla@arcelormittal.com

Innovative Earthquake Resistant Design

The "InERD" Project

presentation held @ Associazione Tecnologici per l’Edilizia ATE

• Milan year 2009

PRF208 INERDSOFT – User friendly software for INERD Earthquake Design

InERD Research: Start : 01-07-2001 End : 30-06-2004 InERD Software: Start : 01-03-2006 End : 31-12-2008

• Dott. Ing. Mauro SOMMAVILLA

1

Post Earthquake in l’Aquila (Italia) RaiTre TV channel on the 14/04/2009

Observed Damage: collapse of an entire single storey

“Soft-storey” mechanism in RC MRF

PROBLEM:

• Izmit Turkey 1999 – M 7.4-7.9

InERD concept: additional & independent system for checking accidental actions which can be applied to concrete frame structures (MRF) to assure “Robustness” required by NTC & prEN 1991-1-7:2006 § 1.5.14 1) DUE TO the non homogeneity in the placing of the partition walls often not fully predictable @ design stage (infills & wide openings) 2) DUE TO difficulties in the checking of the quality of the employed materials

(production control)

3) DUE TO the level of approximation in determining the real seismic axial force in the vertical members (Vertical Seismic action + struts) WHY ? Because concrete structures designed according the criteria of EC2 & EC8 require of additional “Robustness” measures

(in spite of the fact that seismic actions are NOT classified as accidental actions)

3

Structural Analysis VS Real Behaviour

Weakened Columns from shear + moment combination at extremities

Plastic hinges

N V M N V M

4

Objective:

• Increasing the structural safety & reliability of new concrete MRF;
• Stimulate the consumption of steel, very ductile material, on markets suffering
• f seismic problems (Italy, Greece, Turkey, etc);

Solution:

Incorporating steel “light” sections (at least) in the base columns of new MRF concrete buildings without modifying the traditional construction practice of such a buildings & without necessarily pursuing Standard prescriptions of composite structure (e.g. EC4).

The InERD Project (preventing, protecting, strengthening)

“Design handbook for earthquake resistant steel structures”

5

Piano Primo Piano Terra

For both configurations C1 & C2:

• Welded plate at profile ends for transferring tensile & compression stresses between concrete and steel
• Horizontal stiffeners welded to the column to mobilise the profile shear panel (not in all specimens)

C1 The InERD Project

C1 C2

6

The InERD Project

To improve the concrete MRFs behaviour to resist seismic forces also avoiding the possible formation of « Soft Storey » mechanisms through the addition of “ad hoc” steel profiles in the vertical concrete structural members of the lower storeys. Such a steel profile is not considered in the usual static design of a concrete MRF but it is considered relevant as a “safety fuse” which activate ONLY in case of a problematic/unpredicted response of the concrete structure undergoing seismic actions The “light” steel sections constitute “safety fuses” economically & technically acceptable for the concrete construction world practice

Scope:

7

Improvements:

• The resistance of the “composite” column is less sensitive to

uncertainties on the axial local action thanks to the M-N interaction resistance domain of the steel column

• The mechanical characteristics of the employed materials

are no more subjected to uncertainties thanks to the strict quality directives applied to the steel production chain of ROLLED sections in conformity to EN 10025:2004 (& NTC)

The solution with the steel profile exhibits a higher rotational capacity and, if a “soft- storey” mechanism is likely to occur, it would NOT be of a brittle mode like that observed in pure concrete structures.

The InERD Project

8

8 cycles before failure 12 cycles before failure Efailure=33kJ

+

Reinforced concrete Composite section Efailure=168kJ

Test Response to seismic forces

Columns designed according both static & seismic DCL/DCM configurations

9

with masonry infills

Infill

NSd = constant = 0,2 NRd,RC

• Max. vertical load: - 900 KN
• Max. horizontal load:

900 KN

• Max. horizontal displacement:

200 mm

The InERD Project

10

The InERD Project

Irrigi dime nti Infill

First storey CLS

• nly

Joint mechanisms activation Steel Profile added Plastic HINGE

12

• With steel profiles, ductility of the structural elements is increased (i.e. their energy dissipation

capacity at any degree of horizontal force applied)

• The new concept increase the column strength in both flexion MRd and shear VRd;

assures a greater rotational capacity in the plastic field

pl improving ductility u/ y

• Steel profiles enhance the column resistance and hence allow to satisfy the “strong column-weak

beam” concept adopted by Eurocode 8

• Stiffeners help the transmission of stresses in the joint BUT also in their absence (saving of €€€)

the beneficial “InERD behaviour” of the beam-to-column joint is shown

• A new effective calculation method has been developed & implemented into a software

The InERD Project

13

Software InERD download: www.arcelormittal.com/sections

• n line registration

software

14

Criteria for the CHOICE of the steel profile

(software implementation):

• NRd steel

NEd ( gG +

EiQ) with g=1.0 &

Ei= 2i<<1

(Seismic Load)

• MRd steel

MRd RC*MIN (qRC,3.6RC,DCM

DCH)/3.6

(under N=0) VRd steel VRd RC

• (EICOMP-EIC)/EIC*100

30%

• rmajor/rminor

1 [MRd,comp / MRd,Rconcrete]major axis [MRd,comp / MRd,Rconcrete]minor axis

Criterion I: after an earthquake, the steel section alone must provide resistance to the

axial load related to the seismic combination (i.e. seismic MASS only)

Criterion II: the steel section alone must compensate the loss in resistance of the

damaged concrete column being able of resisting flexural moment & shear related to the seismic combination (i.e. seismic FORCES)

Criterion III: the steel section alone must NON modify significantly the LOCAL flexural

stiffness EI of the concrete columns (i.e. force distribution + period of vibrations)

Criterion IV: the change in the mechanical properties of the columns must be of the

same magnitude order in both main loading axes (i.e. frame properties)

Technical Advisory Italy - ArcelorMittal Commercial Long

mauro.sommavilla@arcelormittal.com

Thanks

• Dott. Ing. Mauro SOMMAVILLA