Post on 28-Mar-2018
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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