Imperial CollegeLondon

Assessment of Building Structures under Extreme Loading

Bassam A. Izzuddin

Department of Civil & Environmental Engineering

Buildings under Extreme Loading

• Modelling capabilities

• Progressive collapse

• Ongoing research

26 January 2011 GEMS 2011 Meeting

Modelling Capabilities

• Computational Structural Mechanics Group– 2 academic staff (Izzuddin, Macorini)– 2 RA’s, 8 PhD students– http://www.imperial.ac.uk/csm

• Focus on structures subject to extreme loading– Developments in computational mechanics– Applied structural engineering research– Novel modelling solutions for engineering practice

• Development of advanced program ADAPTIC

36 January 2011 GEMS 2011 Meeting

• Advanced structural analysis program developed at Imperial College over past 20 years

• Blast, fire, earthquake and extreme static loading

• Steel, reinforced concrete and composite structures

• Whole building response: frame, slabs, walls, connections,…

• Geometric and material nonlinearity

• Robust and efficient solution procedures

• Modelling of large scale structures using HPC

46 January 2011 GEMS 2011 Meeting

Modelling CapabilitiesADAPTIC

Modelling CapabilitiesSimplified Methods

• Framework for progressive collapse assessment

• Steel beams subject to fire and blast loading

• Steel/composite beams with partial strength connections

• Membrane action in slabs

• Influence of material rate sensitivity

56 January 2011 GEMS 2011 Meeting

Modelling CapabilitiesIntegrated Building Response

• Frame/slab substructure under sudden column loss

66 January 2011 GEMS 2011 Meeting

Modelling CapabilitiesIntegrated Building Response

• Composite (ribbed) floor slab system under fire

76 January 2011 GEMS 2011 Meeting

Modelling CapabilitiesConnection Failure

• Detailed connection models with/without rate effect

86 January 2011 GEMS 2011 Meeting

Modelling CapabilitiesSlab failure

• Mechanics-based models for slabs subject to membrane action and reinforcement rupture

96 January 2011 GEMS 2011 Meeting

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Modelling CapabilitiesMasonry Structures

• Multi-scale modelling of masonry structures under extreme loading

106 January 2011 GEMS 2011 Meeting

Modelling CapabilitiesPartitioned Modelling on HPC

• Hierarchic partitioned approach for targeted model refinement and parallelisation on HPC

116 January 2011 GEMS 2011 Meeting

Progressive Collapse AssessmentDesign-Oriented Framework

• Robustness limit state– Prevention of collapse of upper

floors

– Stretching design envelope from strength to ductility limit

• Two stages of assessment– Nonlinear static response

accounting for ductility limit

– Simplified dynamic assessment

126 January 2011 GEMS 2011 Meeting

Progressive Collapse AssessmentDesign-Oriented Framework

• Maximum gravity load sustained under sudden column loss

• Multi-level framework

• Reduced model where deformation is concentrated

• Columns can resist re-distributed load

• Floors identical in components and loading

• Planar effects are neglected

136 January 2011 GEMS 2011 Meeting

Progressive Collapse AssessmentNonlinear Static Response

• Sudden column loss similar to sudden application of gravity load to structure without column– Maximum dynamic response can be approximated using

amplified static loading (d P)

146 January 2011 GEMS 2011 Meeting

• Need models beyond conventional strength limit, including hardening, tensile catenary and compressive arching actions

• Based on conservation of energy

• Work done by suddenly applied load equal to internal energy stored

• Leads to maximum dynamic displacement (also to load dynamic amplification)

• Definition of “pseudo-static” response

Progressive Collapse AssessmentSimplified Dynamic Approach

156 January 2011 GEMS 2011 Meeting

Ongoing Research Projects

• Robustness of composite buildings under localised fire (EU project: Liege, Imperial, Coimbra, …)

• Influence of material rate sensitivity on building robustness (Imperial, Trento)

• Keeping our structures standing and our people alive – The next 25 years (DHS project: Texas, Imperial, PEC, WPM)

166 January 2011 GEMS 2011 Meeting

Ongoing Research ProjectsDHS Project

• Testing of 3D floor systems to failure under column loss

176 January 2011 GEMS 2011 Meeting

Ongoing Research ProjectsDHS Project

• Sudden column loss vs blast damage– Column loss is an upper bound thus useful for design

186 January 2011 GEMS 2011 Meeting

Suddencolumn loss

Ongoing Research ProjectsDHS Project

• Significance of uplift under external blast

196 January 2011 GEMS 2011 Meeting