L’Ambiance Collapse Group 15 David Lawlor Emma Quinn Daniel O’Sullivan Cian O’Sullivan

Introduction Bridgeport, Connecticut Bridgeport, Connecticut April 23, 1987 April 23, 1987 Sixteen-story building, Thirteen apartment levels, topping three parking levels Sixteen-story building, Thirteen apartment levels, topping three parking levels Consisted of two offset rectangular towers Consisted of two offset rectangular towers Elevator

Design Seven inch thick posttensioned, concrete slabs Seven inch thick posttensioned, concrete slabs Steel columns comprised its Structural Frame Steel columns comprised its Structural Frame Lift-Slab method of construction Lift-Slab method of construction Hydraulic lifting apparatus used to put slabs into position Hydraulic lifting apparatus used to put slabs into position Two shear walls in each tower – Lateral Resistance (except top two floors) Two shear walls in each tower – Lateral Resistance (except top two floors)

Collapse Building little more than halfway completed Building little more than halfway completed First the West Tower, then the East First the West Tower, then the East Took five seconds for entire building to collapse Took five seconds for entire building to collapse 28 construction workers died in collapse 28 construction workers died in collapse Unusually prompt legal settlement ended all investigations Unusually prompt legal settlement ended all investigations Consequently – the exact cause of the collapse has never been established Consequently – the exact cause of the collapse has never been established Number of deficiencies – which was the trigger? Number of deficiencies – which was the trigger?

Theory 1 National Bureau of Standards (NBS) “An overloaded steel angle welded to a shearhead arm channel deformed, causing the jack rod and lifting nut to slip out and the collapse to begin” National Bureau of Standards (NBS) “An overloaded steel angle welded to a shearhead arm channel deformed, causing the jack rod and lifting nut to slip out and the collapse to begin”

Theory 2 Thornton-Tomasetti Engineers “The instability of the wedges holding the twelfth floor and roof package caused the collapse” Thornton-Tomasetti Engineers “The instability of the wedges holding the twelfth floor and roof package caused the collapse” Theory 3 Schupack Suarez Engineers Inc “The improper design of the posttensioning tendons caused the collapse” General Layout of Posttensioning

Theory 4 Occupational Safety and Health Administration (OSHA) “Questionable weld details and substandard welds could have caused the collapse” Occupational Safety and Health Administration (OSHA) “Questionable weld details and substandard welds could have caused the collapse” Theory 5 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 disaster Gross negligence on part on management Gross negligence on part on management Variations in control of lifting operations Variations in control of lifting operations Cutting corners to save money (use of broken rock fill under certain footing- instead of direct bearing on rock) Cutting corners to save money (use of broken rock fill under certain footing- instead of direct bearing on rock) Building regulations not adhered to for innovative “lift-slab” method Building regulations not adhered to for innovative “lift-slab” method

Conclusions Insure lateral stability and safety during construction when using lift-slab method Insure lateral stability and safety during construction when using lift-slab method Responsibility for each aspect of design should be clearly allocated Responsibility for each aspect of design should be clearly allocated Ensure a high standard of structural safety during construction by constant monitoring by engineer Ensure a high standard of structural safety during construction by constant monitoring by engineer Independent Engineers from building authorities to check progress Independent Engineers from building authorities to check progress