L’Ambiance CollapseL’Ambiance Collapse

Group 15

David Lawlor

Emma Quinn

Daniel O’Sullivan

Cian O’Sullivan

IntroductionIntroduction Bridgeport, ConnecticutBridgeport, Connecticut April 23, 1987April 23, 1987 Sixteen-story building, Thirteen Sixteen-story building, Thirteen

apartment levels, topping three apartment levels, topping three parking levelsparking levels

Consisted of two offset rectangular Consisted of two offset rectangular towers towers

Elevator

DesignDesign

Seven inch thick posttensioned, concrete Seven inch thick posttensioned, concrete slabs slabs

Steel columns comprised its Structural Steel columns comprised its Structural FrameFrame

Lift-Slab method of constructionLift-Slab method of construction Hydraulic lifting apparatus used to put slabs Hydraulic lifting apparatus used to put slabs

into positioninto position Two shear walls in each tower – Lateral Two shear walls in each tower – Lateral

Resistance (except top two floors)Resistance (except top two floors)

CollapseCollapse

Building little more than halfway completedBuilding little more than halfway completed First the West Tower, then the EastFirst the West Tower, then the East Took five seconds for entire building to collapseTook five seconds for entire building to collapse 28 construction workers died in collapse28 construction workers died in collapse Unusually prompt legal settlement ended all Unusually prompt legal settlement ended all

investigationsinvestigations Consequently – the exact cause of the collapse Consequently – the exact cause of the collapse

has never been establishedhas never been established Number of deficiencies – which was the trigger?Number of deficiencies – which was the trigger?

Theory 1Theory 1

National Bureau of Standards (NBS) National Bureau of Standards (NBS) “An overloaded steel angle welded to a shearhead arm channel “An overloaded steel angle welded to a shearhead arm channel deformed, causing the jack rod and lifting nut to slip out and the collapse deformed, causing the jack rod and lifting nut to slip out and the collapse to begin”to begin”

Theory 2 Theory 2 Thornton-Tomasetti Engineers Thornton-Tomasetti Engineers

“The instability of the wedges holding the twelfth floor and roof package “The instability of the wedges holding the twelfth floor and roof package caused the collapse”caused the collapse”

Theory Theory 33 Schupack Suarez Engineers Inc

“The improper design of the posttensioning tendons caused the collapse”

                                                                                                                                                  

General Layout of Posttensioning

Theory 4Theory 4 Occupational Safety and Health Occupational Safety and Health

Administration (OSHA) Administration (OSHA) “Questionable weld details and substandard welds could have caused “Questionable weld details and substandard welds could have caused the collapse” the collapse”

Theory Theory 55 Failure Analysis Associates

(FaAA) “The sensitivity of L’ambiance Plaza to lateral displacement caused its collapse”

                                                                  

Wedged Slab-to-Column Connection

Other factors contributing to Other factors contributing to disasterdisaster

Gross negligence on part on Gross negligence on part on managementmanagement

Variations in control of lifting operationsVariations in control of lifting operations Cutting corners to save money (use of Cutting corners to save money (use of

broken rock fill under certain footing-broken rock fill under certain footing-instead of direct bearing on rock)instead of direct bearing on rock)

Building regulations not adhered to for Building regulations not adhered to for innovative “lift-slab” methodinnovative “lift-slab” method

ConclusionsConclusions

Insure lateral stability and safety during Insure lateral stability and safety during construction when using lift-slab methodconstruction when using lift-slab method

Responsibility for each aspect of design Responsibility for each aspect of design should be clearly allocatedshould be clearly allocated

Ensure a high standard of structural safety Ensure a high standard of structural safety during construction by constant during construction by constant monitoring by engineermonitoring by engineer

Independent Engineers from building Independent Engineers from building authorities to check progressauthorities to check progress