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 Dott. Ing. Mauro SOMMAVILLA InERD Software: Start : 01-03-2006 mauro.sommavilla@arcelormittal.com End : 31-12-2008
- Izmit Turkey 1999 – M 7.4-7.9 PROBLEM: “Soft - storey” mechanism in RC MRF Observed Damage: collapse of an entire single storey Post Earthquake in l’Aquila (Italia) RaiTre TV channel on the 14/04/2009 1
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 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) 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)
Structural Analysis VS Real Behaviour N V M N V M Weakened Columns from shear + moment combination at extremities Plastic hinges 3
The InERD Project (preventing, protecting, strengthening) Objective: • Increasing the structural safety & reliability of new concrete MRF; • Stimulate the consumption of steel, very ductile material, on markets suffering of 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). “Design handbook for earthquake resistant steel structures” 4
The InERD Project C2 C1 C1 Piano Primo Piano Terra For both configurations C1 & C2: Welded plate at profile ends for transferring tensile & compression stresses between concrete and steel - 5 Horizontal stiffeners welded to the column to mobilise the profile shear panel ( not in all specimens) -
The InERD Project 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: 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. 6
The InERD Project 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. 7
Test Response to seismic forces 8 cycles before failure 12 cycles before failure E failure =33kJ E failure =168kJ + Composite section Reinforced concrete Columns designed according both static & seismic 8 DCL/DCM configurations
The InERD Project Max. vertical load: - 900 KN Max. horizontal load: 900 KN Max. horizontal displacement: 200 mm N Sd = constant = 0,2 N Rd,RC with masonry infills Infill 9
The InERD Project Infill CLS Plastic HINGE only First storey Joint Steel Profile mechanisms added Irrigi activation dime 10 nti
The InERD Project - 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 M Rd and shear V Rd ; 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 12
Software InERD download: www.arcelormittal.com/sections 13 on line registration software
Criteria for the CHOICE of the steel profile (software implementation): Criterion I: after an earthquake, the steel section alone must provide resistance to the - N Rd steel N Ed ( g G + Ei Q) with g =1.0 & (Seismic Load) Ei = 2i <<1 axial load related to the seismic combination (i.e. seismic MASS only) - M Rd steel M Rd RC * MIN (q RC ,3.6 RC,DCM (under N=0) DCH )/3.6 Criterion II: the steel section alone must compensate the loss in resistance of the V Rd steel V Rd RC damaged concrete column being able of resisting flexural moment & shear related to the seismic combination (i.e. seismic FORCES) - (EI COMP -EI C )/EI C *100 30% 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) - r major /r minor 1 [M Rd,comp / M Rd,Rconcrete ] major axis Criterion IV: the change in the mechanical properties of the columns must be of the [M Rd,comp / M Rd,Rconcrete ] minor axis same magnitude order in both main loading axes (i.e. frame properties) 14
Thanks ArcelorMittal Commercial Long Technical Advisory Italy - Dott. Ing. Mauro SOMMAVILLA mauro.sommavilla@arcelormittal.com
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