Chapter 10- L’Ambiance Plaza Apartments

Question 1

76. What is the lift-slab technique that was being used in 1978 to construct the 16 storey L’Ambiance Plaza apartment building in Bridgeport, USA

Answer 1

The lift slab technique consists of casting all of a buildings posttensoined slabs on the ground, one on top of the other then lifting them on one or more slabs at a time up the columns with hydraulic jacks at a rate of 1.5m/h. This is done until each slab reaches its final postion.

Question 2

77. In a lift-slab building what does not, and what does provide lateral stability and resistance to the actions from wind and seismic forces

Answer 2

Shear walls, which are concrete walls, provide lateral stability and resistance against wind and seismic forces.

Question 3

78. What had the contractors on the L’Ambiance Plaza not done that was then practiced elsewhere following the collapse of a Canadian lift-slab building in a sudden windstorm, and what weakness of the lift-slab technique was this practice to overcome

Answer 3

The contractor had not stretched temporary diagonal steel cables between columns. The shear walls were not locked in place they building had little resistance and was unstable.

Question 4

Shearheads are an integral component to the lift-slab technique. What are they? On examining one of the shearheads what did the investigators find that fitted in with what one of the workers (a Mr Sheppard) had apparently heard when the building started to collaps

Answer 4

a shearheads is an reinforcement between slabs and columns. It actings as a point of a lifting mechanism and a means of transferring vertical loads from the slabs to the columns.
* When investigating a shearhead had a bent lifting angle with scarring markings, suggesting that the nut had slipped out of the slot provided for it.
* What the victims heard was the lifting rod slipping out of the lifting angle and hitting the column

Question 5

80. Why did the L’Ambiance Plaza apartment building collapse with progressive failure after the initial failure and what two mandatory safety measures used in California might have provided the structural integrity to prevent complete collapse after a single shearhead failure

Answer 5

The building collapsed progressively as the concrete slabs fell one at a time on top of each other. They were overloaded in the Center and collapsed downwards.
* there was then safety measures then introduced which included:
* Placing cribbing, temporary posts to support the slab before the attachment to the column is completed. Sway bracing , cables to keep the stack of floors from shifting sideways.