St. Pete Pier Shoring

Pierhead Building Construction Engineering

St. Pete Pier, Florida’s newest landmark attraction, ends with a five-story high pinnacle pierhead building that required an innovative construction engineering solution from McLaren Engineering Group. Perched on the waters of Tampa Bay in St. Petersburg, Florida, this highly anticipated “pier for everyone” promises to be a destination location for both the Central Florida community and tourists.

The 0.6-mile pier features exploration and activity areas, children’s play spaces, fishing spots, education centers, local vendors, and a massive 5-story pierhead building at the end. The building’s construction called for uniquely thick, and heavy, post-tensioned concrete slabs creating a distinct challenge in its construction (the 4^th level slab with a 36” thickness and the 5^th level slab at 30” thick). The pier’s marine deck under the building at the pierhead was designed for a 100 psf live load for cost efficiency and was not designed for the heavy shoring loads that would result from supporting the upper-level slabs during construction. This meant that the heavy shoring loads from supporting the weight of the fluid concrete for the 4^th and 5^th floor slabs above exceeded the available load capacity of the pier deck below.

The typical way to support these slabs during construction would be to shore from lower slabs up, but the marine deck below the building did not have the live load capacity from which to borrow to support the 4^th and 5^th floor building slabs during construction.

The McLaren Difference: Applied Ingenuity

Working with the contractor, McLaren devised a plan to support the shoring for the construction of the heavy upper floors of the pier head building. Holes were formed in the pier’s marine deck to allow for steel H-piles to be driven through the deck later. The upper floors were constructed prior to lower floors, to avoid interferences with shoring at lower floors and to allow clearance for removing the steel framing providing support for the shoring.

Preparing for Construction

To prepare for the construction of the pier head building upper floors, McLaren worked with the contractor to establish lanes along the pier for construction vehicle traffic and for emergency vehicle access if needed. Mobile crane and concrete pump truck locations were identified to provide the best access for placement of concrete. The reinforced concrete pier deck between pile bents and the precast concrete piles at pile bents were analyzed for loading from construction vehicles, emergency vehicles, mobile crane outrigger loads, and concrete pump truck outrigger loads. These analyses confirmed that the pier was adequate for the intended construction loading and established maximum allowable speeds for construction and emergency vehicles.

Building Up then Down

Instead of constructing the building from the bottom floors up, the supporting concrete elevator shafts, stair cores, and columns were built first, followed by the 4^th floor, and then the 5^th floor. The shoring and steel framing acting as the shoring support were then removed, and steel H-piles were cut off below the mudline and removed. The 2^nd and 3^rd floors, which are a more conventional slab thickness, were then shored from the pier’s marine deck for concrete placement. McLaren provided a temporary steel bracing design for the longer unbraced length of the concrete elevator shafts, stair cores, and columns for the period where the 4^th and 5^th floors were constructed but the 2^nd and 3^rd floors were not. The bracing design prevented buckling of these elements while also staying clear of the 2^nd and 3^rd floors to be constructed.

The dramatic and impressive 4^th floor concrete placement took place overnight and lasted 8½ hours, taking 80 workers, 77 concrete trucks, and 767 cubic yards of concrete. Successful concrete placement of the 5^th floor, 2^nd floor, and 3^rd floor took place in the following months. The value engineering efforts for the independent system of steel framing supporting the shoring for the 4^th and 5^th floor concrete placement included assessment of alternate materials, pile types, pile layouts, beam layouts, and member sizes. Value engineering efforts during the design process for supporting the shoring for the 4^th and 5^th floor concrete placement resulted in a cost savings to the City of St. Petersburg of approximately $1.2M over initial concepts to reinforce the pier’s marine deck and over initial pile layouts, beam layouts, and member sizes for the temporary steel support system.