Stressing jack in place - ready to tension the tendon.
The detailed shoring shown close to project completion.
The completed opening - still enclosed in the barrier walls.
Tendons prior to stressing and the concrete pour.
Tendons extending from the cut floor slab.

Post-Tensioned Slab Modification

Project Description 

The Owner of a downtown Baltimore, Maryland office building agreed to construct a new lobby with escalators for its main tenant . To build the new lobby, a 60 foot by 60 foot opening would have to be made in a post-tensioned slab. The goal for the owner during construction was to maintain a strict schedule, kept dust, debris and inconvenience for tenants to an absolute minimum, and ensure the work was unnoticeable to those outside of the building.

A first step was to design shoring and the phasing plan. Shoring was placed under the slab opening, not under adjacent slabs because that placement would result in reduced capacity as the cables were de-tensioned. A specific phasing plan was developed to determine the order in which the cables would be de-tensioned. This lock-off phasing plan allowed the crews to de-tension individual PT tendons while maintaining the structural integrity of the entire floor system.

Additionally, to address the goals of the owner, the project was phased in small sections and most of the work was performed at night in order to minimize disruption to the existing businesses. Because the owner did not want any outside the building to know construction work was occurring on the inside, the workspace was completely enclosed by building interior walls with a transition room at the access point with two doors and poly sheets hung within it in order to create a dust blocking effect. Further, any tasks creating noise were performed on weekdays between the hours of 10 p.m. and 6 a.m. No noise could be made from Friday night through the end of the weekend because of the increased business hours of one of the tenants -- a seafood restaurant.

In addition to confining all signs of the work as the Owner requested, work progressed at a pace that met the Owner’s strict requirement and was completed in 49 working days – allowing the Owner to meet the ultimate goal of providing new space for its most important tenant.