Task 3 - Vulnerability and damageability of constructions under - - PowerPoint PPT Presentation

COST C26 Final Conference:

“Urban Habitat Constructions under Catastrophic Events”

Naples, Italy, 16-18 September 2010

Task 3 - Vulnerability and damageability of constructions under impact and explosion

Florea Dinu Romanian Academy, Timisoara, Romania

WG3 - Impact and explosion resistance

Introduction

• Impact and explosion resistance (WG3)

– to analyse the behaviour of constructions from urban environment under very strong accidental actions, such as gas explosions, bomb blast, or impact from projectiles or vehicles out of control. – these phenomena are characterized by a large amount of energy that is released in a very short period of time – The main research activities:

• Assessment of degradation and damage
• Modeling
• Structural analysis

MoU, Cost C26

Research in WG3, Task 3

• The research focused on tools to assess

vulnerability and robustness of structural systems to blast and impact:

– Performance expectations for constructions – Threat and risk assessment – Progressive collapse – Available tools and approaches – Furthure developments

Performance expectations for constructions

Murrah Federal Building Khobar Tower

TNT Equivalent 20,000 lb. TNT Equivalent 4,000 lb. Standoff 80 feet Standoff 15 feet

DoD Antiterrorism Standards for Buildings

Threat characterization

Performance expectations for constructions

Ufundi House formerly 8 stories US Embassy

DoD Antiterrorism Standards for Buildings

Incorporation of prescriptive measures

Threat and risk assessment

• Maintaining adequate stand-off is effective in

reducing the risks from blast but may not be enough

• Risk mitigation strategies must be aimed at

three basic levels

where: P(C) = probability of structural collapse due to abnormal load, H, λH = rate of occurrence of the abnormal load or hazard, P(LD|H) = probability of local damage given that the abnormal load occurs P(C|LD) = probability of collapse given that local damage occurs.

Progressive collapse

• The approaches for reducing the risk of

progressive collapse are categorized as follows:

– Event control – Indirect design – Direct design

Reaction

• CEN/TC 250 decides to form an Ad-hoc Group

“Robustness”

• Improved definition and quantification of

robustness

• Clearer description of accidental actions needed

– EN 1991-1-7 (external blast ?)

• Development of sets of material dependant

(prescriptive) measurements in dependency of the consequence classes to ensure robustness

Design approach

• Structural design strategies for structures

designed to resist blast and mitigate progressive collapse, fall into two general categories:

– the indirect method – the direct methods

• providing specific local resistance for the abnormal

load - such an approach provides resistance to only

• ne hazard
• developing alternate load paths - is intuitively more

attractive because it focuses the attention of the designer on the behavior of the structural system

The indirect method

• In the indirect method, it is used a prescriptive

approach to increase the overall robustness of the structure.

• This is accomplished by incorporating general

structural integrity measures (selection of structural system, layout of walls and columns, member proportioning, detailing of connections).

• The indirect method is recommended for

facilities that are characterized as requiring a very low level of protection.

The indirect method

Different types of ties incorporated to provide structural integrity

Specific local resistance

• In the specific local resistance method, the

designer explicitly designs critical load bearing building components to resist the design level threat, such as blast pressures.

• Thus, it is a threat specific approach.
• This method is also referred to as key

element design

• The specific local resistance direct design

approach is often the only rational approach when retrofitting an existing building

Specific local resistance

• Key elements are defined as structural elements

whose notional removal would cause collapse of an unacceptable extent

• They should therefore be designed for accidental

loads, which are specified in several standards as 34 kPa. Such accidental design loading should be assumed to act simultaneously with 1/3 of all normal characteristic loading:

D + L /3 + Wn/3

where D = dead load, L = live or imposed load, and Wn = wind load, The difficulty with strengthening key elements is that it must be done with a specific threat in mind!

Specific local resistance

Reinforced concrete column without/with composite wrap

• 8 units are overlapping

with each other.

• 10 very strong mechanical

floors to stop unexpected progressive collapse.

Specific local resistance

THE TAIPEI 101

Alternate load path method

• The load carried by the lost element must find an

alternate load path to the building supports without initiating structural collapse.

• Large deformations are permitted before the onset of

failure of an element.

• This method reduces the risk of progressive collapse

by ensuring structural redundancy

• The method does not require characterization of the

threat causing loss of the element, and is, therefore, a threat independent approach.

Alternate load path method

The amplification of the gravity loadings applies only to the section of the structure directly below the failed element!

Alternate load path method

Load Application for Alternate Path Analysis (UFC 4-023-03, 2004)

Available tools and aproaches

• Vulnerability of urban area configurations to blast

effects

– Single buildings – Rectangular urban layout

• Robustness analysis of constructions to impact

– Bridge response to train collision – Response of RC frames to impact loading

• Robustness analysis of buildings to blast

– Tying force method – The specific local resistance method – The alternate load path method

Assessment of explosion effects in railway stations

• Blast waves resulted from

the detonation of a solid high-explosive charge (a TNT equivalent).

• Waiting hall area about

50×30×12 m, long corridor about 100×10×8 m

• The full simulation of the

explosion is performed using an Eulerian formulation for the ex- plosive and for the fluid representing the air

Geometrical finite element model of structure consisting of a main hall and a long corridor

Structural response at four time instants using the pressure-time functions approach

Top view of death risk contours for the main hall and corridor

Response of RC frames to impact loading

• The study aims

– To calculate the qualitative changes

• f the RC framed structures, under

impact loading – To evaluate risk level for such abnormal situations

• The impactor was modeled as

a rigid 197 kg weight of cylindrical body with the density

• f 7830 kg/m3, with an elastic

modulus 159 GPa and Poisson’s ratio of 0.2

RC framed structure

1,3 1,5 1,7 1,9 2,1

0,1 0,11 0,12 0,13 0,14 0,15 0,16 0,17 0,18 0,19 0,2

Time (ms) Point of risk level D D (A) D (B) D (C)

Comparison the point of risk level. Indicated to parentheses in RC slab state

Robustness evaluation of a multistory building in case of column loss

• The 26 story designed to withstand seismic

forces up to 0.24g

• Overstrength conditions for non-dissipative

critical members (columns, joints, ) + ductility for dissipative members

• Alternate load path to evaluate the robustness of

the structure

• In order to develop a multilevel evaluation,

different extension of damage was considered

• Columns are removed one by one and 3D

dynamic nonlinear analyses are employed

Structural configuration

Alternate load path

C6 C5 C4 C3 C2 C1

Column removal locations

Load Time (sec) (1/20)T 10

Application of vertical load in the dynamic analysis

Results

• 120
• 100
• 80
• 60
• 40
• 20

0.00 0.10 0.20 0.30 0.40 0.50 Time (sec) Displacement (mm) C3 C4-5

Linear response Nonlinear response

Plastic hinge & axial force diagram for loss

• f two columns at a time – case C4-5.

Vertical deformation vs. time

Results

1 1.2 1.4 1.6 1.8 2 1 2 3 4 5 6 Normalised plastic rotation DIF numerical DOD, 2009

Dynamic increase factors for different loss scenarios

Further developments

• Accounting for accidental actions from man-made hazards (blast, impact) in

the codes

• Improved requirements for structural robustness (eg. prevention of

progressive collapse from terrorist attacks)

• Risk oriented design rules for important facilities
• Design of new buildings and assessment of existing buildings under blast and

impact

– methods of analysis (direct and indirect methods) – acceptance criteria – structural detailing for structures subjected to blast, impact (principles, type of connections, tying systems) – possible extension of seismic design principles and details

• New materials and construction techniques

– unobtrusive and aesthetic facades – nonfrangible glass for facades

• Performance based format for multi-threat assessment (eg. blast and fire).

Blast load/ explosions – The Risk Matrix Recommended practice for the design of offshore facilities against fire and blast loading API RP 2FB First Edition 2006

Contributors

–

• C. Pérez-Jiménez, M. Minguez-Fica & J. De la Quintana, Labein Tecnalia-saix,

Bilbao, Spain –

• G. Solomos, F. Casadei, G. Giannopoulos, European Commission-Joint

Research Centre, Via E. Fermi 2749, 21027 Ispra (VA), Italy; M. Larcher Institut für Mechanik und Statik, Universität der Bundeswehr München, 85577 Neubiberg, Germany –

• I. Björnsson & S. Thelandersson, Lund University, Division of Structural

Engineering, Lund, Sweden –

• J. Vaiciunas & V. Dorosevas, Faculty of Civil Engineering and Architecture,

Kaunas University of Technology, Lithuania –

• J. Mediavilla, TNO Defence, Security and Safety, Rijswijk, The Netherlands; F.

Soetens & J.W.P.M. Brekelmans, TNO Built Environment and Geosciences, Delft, The Netherlands. – M.P. Byfield & S. Paramasivam, School of Civil Engineering and the Environment, University of Southampton, Southampton, United Kingdom –

• F. Dinu, Romanian Academy, Timisoara Branch, Centre for Advanced and

Fundamental Technical Sciences & D. Dubina, The “Politehnica” University of Timisoara, Romania.