Evaluation of structural response under exceptional seismic actions - - PowerPoint PPT Presentation

Evaluation of structural response under exceptional seismic actions

Matej Fischinger1, Gaetano Della Corte2

1 Faculty of Civil and Geodetic Engineering

University of Ljubljana

2 Department of Structural Engineering

University of Naples “Federico II”

Urban Habitat Constructions under Catastrophic Events

Naples, Italy,16-18 September 2010

 Extreme conditions occur when both loading and

structural resistance are combined in such a way to reduce the safety level below acceptable values.

 This situation may arise either when the loading is

larger than expected (foreseen by the codes existing at the time of the design of the structure) or when the provided capacity was lower than anticipated by the modern standards.

Exceptional seismic actions

Research on structural response under exceptional seismic events

 To support the development of the PBD procedures  As a basis for the seismic risk studies  To gain information about innovative structural systems  To provide data for seismic rehabilitation of the systems

designed prior to the development of modern seismic design principles

 To enhance the ability of structures to withstand impact

and explosion loads

Overview

 State of the art  Contributions from COST members  Experimental studies – through collapse  Analytical studies  RC structures  Steel structures  Masonry structures

RC structures - Precast structures (contribution from COST members)

 PRECAST project (Fischinger et al. 2008,

Toniolo 2007 )

 Large rotations of columns (up to 10%)  Ibarra’s model (2005) was modified at UL

Modified Ibarra model

RC structures – Precast structures (contribution from COST members)

 Risk studies on RC precast structures with

strong connections (Fischinger at al. 2008) – PEER methodology

 Other vulnerability studies on RC structures

Kappos (2007)

RC structures - Precast structures (contribution from COST members)

 How the connections behave in such

conditions?

 SAFECAST project - Response of connections

at large rotations of columns

 Experiments on dowel connections (COST26 final

conference – Fischinger et al.) – large rotations

RC structures – Walls (contributions from COST members)

 Seismic response of

lightly reinforced walls - Fischinger et

• al. 2008

 Pushover

investigation of 3D wall systems with flexible foundation using capacity spectrum method – Apostolska et al., 2008

Blind prediction

• f the response
• f 7-story wall,

tested at UCSD MVLEM

RC structures (contributions from COST members)

 Experimental investigation of existing RC

buildings sesimically upgraded by means of several innovative techniques (e.g. FRP, eccentric braces and buckling restrained braces)

• Mazzolani et al., 2007

Controventi con leghe a memoria di forma Materiali Compositi (C-FRP) Controventi Eccentrici (EB) Controventi ad instabilità impedita (BRB) Isolamento con isolatori in gomma (BI) Prova di spinta sulla struttura in c.a. Pannelli a taglio (SSP)

5 6 4 3 2 1

RC structures (contributions from COST members)

 Full scale experimental tests on a real masonry-

infilled reinforced concrete two story frame building- Mazzolani et al., 2007

RC structures (contributions from COST members)

 Modelling of upgraded RC structures (non-

ductile mechanisms of the original structure as well as response of strengthen structure):

 Mazzoalni et al., 2007: advanced model for RC in

real masonry infilled building

 Bordea et al., 2007: modelling of enhacement of

ductility of RC columns strengthen by FRP

 Landolfo et al. 2008: Experimental and analytical studies

• f typical European steel beams up to severe strength

degradation

 Strength and stiffness degradation was measured in the

range of large plastic rotation demand

 Empirical formulas for characterization of ductility and

plastic overstrength were proposed

Steel structures (contributions from COST members)

 D’Aniello et al. 2008: Tests on buckling restrained braces

subjected to large displacements that far exceed the design values

 Design alternatives were proposed to maximize the

brace capacity under the extremly large deformations.

Steel structures (contributions from COST members)

 Stratan and Dubina 2008: Nearly full scale tests of

eccentricaly braced bare steel frames with removable steel shear links

 An appropriate detailing of end connections essential for

good performance

Steel structures (contributions from COST members)

 Landolfo et al. 2006, Della Corte et al. 2006, Dubina et al.

2007: Incremental dynamic analysis of different types of steel structures to investigate near-collapse response

 Dogariu et al. 2007: Test on masonry pannels under

monotonic and cyclic load

 Results can be used as the baseline to evaluate the

effectiveness of the retrofiting interventions

 Informations can be used for development of the

analytical model suitable for analysis of masonry shear pannels up to complete failure

Masonry structures (contributions from COST members)

 Krstevska et al. 2007: Large scale test of historical

mosque with a minaret

 Test on the original bare masonry model, with a small

intensity earthquake to produce small, repairable, damage

 Tests on the repaired and strengthened model, until

collapse of the minaret

 Tests on the strengthened mosque until collapse. The

strengthening systems were based on FRP materials

Masonry structures (contributions from COST members)

Masonry structures (contributions from COST members)

Two FEM numerical models

• f the original and

strengthen structure FEM models successfully used for the comparison of two structures Calibration with large-scale model steel needed

 De Matteis et al. 2008: Experimental and analytical

investigations of the cental part of Fossanova gothich church

 tests on the bare masonry, to produce moderate, repairable,

damage; 2) tests on the strengthened model (transverse FRP rods) , until severe damage (close to the collapse)

 Original structure PGA =0,14g, strengthen structure 0.4g

Masonry structures (contributions from COST members)

 Until a decade ago very few experimental and

analytical studies of the structural behaviour up to the collapse. Recently the interest has shifted towards near-collapse behaviour.

 Impressive (full-scale) experiments were performed

near to the collapse providing suitable data for the development of the adequate analytical models.

Conclusions and recommendations (1)

 Empirical calibrated macro-models are prevailing.

Although rather simple in concept they provide good physical understanding and consequently good control of the highly complex near-collapse

• mechanisms. Works performed within the COST C26

action have considerably contributed to these results.

 Since each collapse mechanism of a particular

structural element or structural system is so specific, general solutions are not to be expected. Long term solution is to perform sufficient experiments

Conclusions and recommendations (2)