Over Design, Dome and Ring Beam construction

In the mid 1960's I was working with Post Tension concrete projects in the southeast United States for Noble Concrete, Inc. Many of our large projects would be stressing Ring beams for dome concrete buildings. Domes exert a large lateral load on the walls of the buildings upon which they set. The Ring beam is what holds the walls from falling outward from the weight of the dome.

In concrete construction there is ordinarily a large safety factor built into the construction in the way of extra steel bars. Post Tension concrete is a limited different, too much of a good thing can cause trouble.

The manufacture engineer will note on the plans how much tension is required and suppliers like Noble Concrete would bid on the jobs and then make the shop drawings showing the placement and size of the cables required.

Over Design, Dome and Ring Beam construction

We got the covenant of a church dome in Jacksonville Florida and all was going well. When the concrete had been poured and reached the permissible vigor I loaded up the stressing equipment and headed south. Our time on the construction site for a job like this is ordinarily no more than a consolidate of days and this one could be completed in less than a day. Of policy there is always the question with the Unions. They insist on having one of their citizen do the work. However, they never have anyone trained in this type of work. We give them a call and they send us a consolidate of workers, we tell them just to stand there and watch and we faultless the job a fast as possible.

We were manufacture our second trip colse to the Ring beam bringing the stress up in stages to preclude damage to the columns. I had planned on connecting to each cable four times during the stressing procedure. Suddenly there was a large pop and all that I could see were workers scrambling down off the building!

We stopped the stressing and inspected the columns for cracks. I also climbed to the top of the sustain for the dome and checked the top of the form. We had raised the dome about one inch off the top of the form. The columns were pulled into the point that one of them had cracked!

I got on the phone to the engineer and asked him what we should do next. His reply was "is it keeping up the dome? Then your job is through." He had over designed the ring beam just as he over designs when using steel bars and if he was aware of what would happen, which I doubt, he did not warn us. We relayed the information to the contractor and packed up for home.

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