Investigation into the Resilience of Concrete Flat Slabs against Progressive Collapse

Justin Russell Supervisors: Dr. John Owen Dr. Iman Hajirasouliha

Contents

- Project Background - Project Aim - Preliminary Investigations

- Future Work

- Conclusions

Oklahoma City bombing , 1995

- Project Background

Case Studies

Rowan Point, 1968

Piper’s Row Car Park, Wolverhampton 1997

Case Studies

Sampoong Department Store, Korea, 1995

Copenhagen Gas Explosion

Case Studies

Oklahoma City bombing , 1995

Case Studies

World Trade Centre Buildings 1 and 2 World Trade Centre Building 7

Project Background Issues with Concrete Slabs

* Mitchell, D and Cook, W. D (1984) Preventing progressive collapse of slab structures. Journal of Structural Engineering

Punching shear failure**

Nonlinear behaviour of slabs*

** Yaser Mirzaei (2010) Post-Punching Behavior of Reinforced Concrete Slabs. Ph.D Thesis

- Slabs are a economical structural system which are very popular

- They also have complex failure mechanisms that are not fully understood

- However full analysis is often complicated by their nonlinear behaviour at high deflections

- Progressive failure by due to punching shear has been identified as a serious risk Piper’s Row Car Park, Wolverhampton 1997

Current Design Approach

Eurocode 1990: -Basic requirement “A structure shall be designed and executed in such as way that it will not be damaged by events such as: explosion, impact and the consequences of human error to an extent disproportionate to the original cause”

Building Regulations 2004: Approved Document A - Classifies buildings by size and use - Outlines prescriptive requirements for horizontal and vertical ties

Building Regulations 2004: Approved Document A - Classifies buildings by size and use - Outlines prescriptive requirements for horizontal and vertical ties - Alternatively consider notional removal of any column or beam

- If damage greater than 15% of floor area or 70m2 then element is ‘key’ - ‘Key’ elements must be able to withstand accidental force of 34kN/m2

Contents

- Project Background - Project Aim - Preliminary Investigations

- Future Work

- Conclusions

Project Aim

Aim

Investigate the influence of the nonlinear and dynamic effects in the analysis of a flat slab structure after a column loss scenario

Objectives

- Conduct numerical simulations of column loss to consider the potential for progressive collapse

- Collect data from scaled RC slab elements for both static and dynamic conditions - Validate the numerical model against results from the experimental tests

- Analyse a range of structure layouts and designs under sudden column loss

Contents

- Project Background - Project Aim - Preliminary Investigations

- Future Work

- Conclusions

Preliminary Investigations

- Conducted extensive parameter study into key issues

- Investigated a multi-storey RC flat slab structure after a column is removed

- Static push down tests were compared to dynamic column removals

- Factors considered included: Number and position of columns removed Span to depth ratio of slab Size of structure (no. of bays and floors) Slab aspect ratio Level of loading

- Displacements and forces through the structure recorded

-Allowed identification of critical influencing factors and their effects

Preliminary Investigations

Preliminary Investigations

Preliminary Investigations

Preliminary Investigations

Dynamic Test Static Test

Normalised Displacement

Shear force ratio (Demand/design)

Moment ratio (Demand/design)

--- indicates change from hogging to sagging

Experimental Work Experimental Program

- Investigate the behaviour of a reinforced concrete slab after a column loss

- Identify critical failure mechanisms

- Observe the level of damage experienced

Objectives

Test Details

- 4.1m by 2.1m, 80mm depth, reinforced concrete slab built at 1/3 scale

- Simulates a column loss by adding an imposed dead load with a missing support

- All supports considered as pinned

Experimental Work Static Load Test

Experimental Work Static Load Test

Experimental Work Static Load Test

Experimental Results

0

1

2

3

4

5

6

7

0 20 40 60 80 100 120 140 160 180

UDL

(kN

/m2)

Displacement (mm)

Force against Displacement

Experimental Results Cracking Pattern

Contents

- Project Background - Project Aim - Preliminary Investigations

- Future Work

- Conclusions

Future Work Experimental Program

- Conduct a dynamic column loss test on a scaled slab and compare to the static case

- From all tests data will be collected including:

Strain in steel and concrete

- Data will then be used to validate the numerical models

- Repeat both static and dynamic tests for a corner column loss scenario.

- Conduct further tests to consider changes in reinforcement layout

Vertical displacement and rotation of the slab Reaction forces Accelerations (where applicable) Cracking progression and patterns

Finite Element Simulation

- Model the experimental case with Finite Element software

- Using ABAQUS to provided detailed analysis of the nonlinear behaviour

- Once behaviour of an single floor element understood, the entire structure can be assessed

- Potential for progressive collapse can then be determined

Finite Element Simulation

Contents

- Project Background - Project Aim - Preliminary Investigations

- Future Work

- Conclusions

Conclusions

- Previous catastrophic failures demonstrate progressive collapse is a key issue for the design of all structures - There is currently no suitable analysis or design method for concrete flat slab systems

- Material and geometric nonlinearity must also be considered to accurately consider failure mechanisms of the structure

- Dynamic effects need to be understood and included to analyse the structure successfully

- The complex behaviour experienced during these conditions can be predicted from simplified models if the key factors are understood

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