a steel frame building Dr. J. Mediavilla J.W.P.M. Brekelmans BSc - - PowerPoint PPT Presentation

Damage and blast response of a steel frame building

• Dr. J. Mediavilla

J.W.P.M. Brekelmans BSc

(presenting author)

• Prof. F. Soetens

2

Content presentation

• Introduction
• Objectives
• Problem description / case study
• FEM model
• Blast loading
• Results
• Conclusions
• Recommendations

3

Introduction

• Blast explosive loading of buildings
• Steel frame buildings
• Finite element modelling
• Global versus local failure

4

Objectives

Gain insight into the dynamic response and failure of a typical multi-storey frame building under blast loading in

• rder to:
• 1. assess the type and extent of damage (qualify and

quantify)

• 2. assess the risk of collapse (progressive collapse)
• 3. design mitigation measures: effective structural

designs (redundancy to avoid progressive collapse, bracings), retrofit

• 4. improve design codes

5

Problem description / case study

• Geometry and dimensions of steel multi-storey building
• Steel frame dimensioned for typical load combinations,

not for blast, without bracing (deep beams and columns), rigid / full strength joints

• Floors: steel concrete composite slabs
• Facade: glass / reinforced concrete parapet
• Blast scenarios considered:

1. Backpack (5 kg) at 1m distance

• 2. Private car (100 kg) at 10m distance
• 3. Truck (1000 kg) at 25 m distance

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Case study: steel frame multistory building

7200 7200 6 x 4500 4000 column Technical installations parapet Modular ceiling glass

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Case study: blast scenarios

m (kg of TNT) equivalent distance (m) 5 backpack 1 100 private car 10 1000 truck 25

d m

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FEM Model

• Simulations structural response: nonlinear finite

element model, LS-DYNA

• Simple blast loading model based on CONWEP
• accounts for the angle of incidence of the blast wave
• no shadowing or confinement effects
• Boundary conditions
• foundation: fixed hinges
• joints:

rigid / full strength

• Columns and beams:

beam elements

• Façade, floor and roof: shell elements
• Implicit static analysis → explicit dynamic response

(dead load) → (blast load)

• Failure criteria

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Failure criteria

• Concrete /

Reinforcement: strain limit

• Glass: strength limit
• Steel: strain limit

mm2 mm2 mm2 mm2 mm2 mm2

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Blast loading

• Theory
• Pressure contour plots
• Pressure points / time history plots

pressure-time curve for free air blast wave

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Blast load scenario “truck”

Pressure contour plots: side-front and side-back

0.026s 0.036s 0.065 s

0.065 s 0.073 s

Side- Front Side- Back

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Blast load scenario “truck”

Pressure time history plot

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Results

• Damage to the façade
• Damage to the steel structure
• Energy absorption
• Internal forces
• Front column: foundation
• Front column: Joint / member
• Failure modes

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Damage to the façade

Scenario “truck”

t=0.16 s t=0.17 s t=0.19 s t=0.35 s

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Damage to the steel structure

Scenario “truck”

plastic strain plot

Glass: ft=80 MPa

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Energy absorption

Scenario “truck”

Internal energy (concrete parapets already failed)

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Internal forces

Front column: Foundation

Rstat Rdyn = 2,5 times Rstat -> possible failure in compression

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Internal forces

Front column: Joint / member

Check joint failure due to M-N, V interaction Check member failure due to local instability / global failure

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Conclusions

• FEM modelling suitable → validation of model still

needed → avoid tests → parametric studies possible

• Correct modelling parapet is crucial in case study
• CONWEP → not suitable for short distance blast

scenarios

• Simple failure criteria have been used →

no information about collapse due to instability criteria → no M-N, V interaction of joints and members

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Recommendations

• Further study needed to:
• include other failure modes (local instability, load

interaction)

• investigate global failure / progressive collapse
• determine design mitigation measures
• Improve FEM modelling for:
• short distance blast loading
• failure modes
• determining lower vibrations modes
• Validation FEM model