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

Duct

ility

lim

it

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

Sudden

column loss

Ongoing Research ProjectsDHS Project

• Significance of uplift under external blast

196 January 2011 GEMS 2011 Meeting