Renovating Resorts Atlantic City

Concrete International, Nov 2006 by Thomas, Jay, Eberhardt, Keith, Alkhrdaji, Tarek

Field discoveries tax project schedule

The adage "time is money" is certainly relevant to many industries, but it's particularly relevant for owners of buildings undergoing renovations, where downtime, interruptions to services, or inconveniences to customers come into play. To the casino industry, the phrase is even more literal, as interruptions to revenue-generating operations come at great expense.

When it opened in 1978, Resorts Atlantic City was the first casino on the East Coast and set the standard for casino gaming and entertainment. Situated on 11 acres (4.5 ha) overlooking the Atlantic Ocean, the 100,000 ft2 (9300 m2) casino's original structure was built in the 1920s and has undergone various renovations over the years. Recently, one of the two original towers was demolished, and a new, state-of-the-art hotel tower was constructed in its place. The final phase of this construction project was to connect the original hotel tower, lobby, check-in area, and casino with the new hotel's lobby by creating a new promenade between them. The access would allow customers to easily reach all casino services without having to walk outside between the two towers.

CHALLENGES

With the new tower open, the need for the new access was immediate. Because of different floor elevations in the two towers, however, the new walkway had to slope between the two areas. This required the removal of an existing intermediate slab in the old tower (Fig. 1 and 2). Although demolition of the intermediate slab wasn't complex, its removal resulted in columns that spanned two stories-further evaluation and remediation was therefore required.

A second challenge wasn't discovered until construction of the walkway had begun. The new walkway was designed to be supported by a series of supports resting on the original base slab below-a slab that was thought to be a slab-on-ground. During construction, an entrance hatch was discovered in the floor of the original base slab. Because this was thought to be a slab-on-ground, the discovery of an access hatch was confusing.

Further investigation revealed that this part of the base slab was actually a suspended slab over an old steam tunnel as shown in Fig. 2. Worse yet, the existing beams supporting the slab over the tunnel had never been maintained and had severely deteriorated over time. Not only would these beams be incapable of supporting the new loads, there were serious doubts about their ability to support the current loads. Temporary shoring was immediately installed to support the slab until remediation and strengthening plans could be established.

Severely deteriorated beams, slabs, and columns in a below-grade room called the Grease Recovery Unit (GRU) were also discovered. The GRU was adjacent to the steam tunnel and functioned as a processing room for the massive amounts of grease created daily by the many hotel restaurants. Shutting it down for any length of time to perform structural repairs would cause major disruptions.

Because these three areas needed to be repaired, strengthened, or both, before any portion of the new walkway could be completed, a timely evaluation, repair strategy, and installation process were essential. Recognizing the importance of proper and timely restoration, the owner required the project team to develop and implement strategies to repair the deteriorated structural concrete elements and strengthen them if needed. Accordingly, the scope of the project was redefined to include:

* Strengthening of the columns at the new walkway;

* Repair and strengthening of deteriorated beams in the steam tunnel; and

* Repair and strengthening of deteriorated beams, slabs, and columns in the GRU room.

BIGGER IS NOT BETTER-COLUMN STRENGTHENING

After removal of the existing intermediate slab in the old tower, a structural engineer conducted a survey of the existing conditions and determined that the columns were not made of reinforced concrete, as originally thought, but rather consisted of concrete-encased structural steel shapes. The concrete jackets on these columns had minimal reinforcement and, as a result, a structural evaluation was necessary to ensure that the steel columns that now spanned two stories were adequate to support the building loads. An analysis of the steel column showed that the doubling of the columns' unbraced length to 20 ft (6.1 m) resulted in an understrength condition under live load.

Traditional methods for strengthening columns involve installing a cast-in-place reinforced concrete jacket around the column to improve buckling strength. This was not a viable option, however, because it would increase the overall column size and reduce the width of the new corridor below code requirements for safe egress.

Another option was selected-the installation of very thin, high-strength, carbon fiber reinforced polymer (CFRP) sheets to strengthen the eight columns (Fig. 3). Both horizontal (hoop) sheets and continuous vertical sheets were externally bonded to each concrete column using epoxy adhesive. The resulting bidirectional composite jacket reinforced and confined the existing concrete to create a reinforced concrete member, thus providing buckling resistance for the steel column. While adding less than 1 in. (25 mm) to the column dimensions, the externally bonded composite jacket effectively upgraded the column with minimal impact on the schedule, building operations, and egress requirements.