Work to build stairs for the library's new 5th and 6th floors in its central stairwell officially began today (Wednesday, July 22). As a result the stairwell is expected to be closed for use for 3 to 4 weeks, which is an ambitious time frame given the work that will be required to cast the stairs in place.
Each section of the upper floor central stairs to be built will be large and very heavy, and their construction will be a complex undertaking. A number of options for building or installing the stairs were explored. The first required an elaborate but too-disruptive plan to crane-hoist precast stair sections weighing 15 tons apiece into the building through the openings for the buck hoist external elevator then cabled them diagonally across the floor to where they will be fitted into place within the stairs using a complex system of pulleys and other equipment. This would have required additional work to reinforce the 5th floor with a few dozen temporary shoring posts set underneath on the 4th floor in areas including the Music & Media Center and LAL book stacks. Another option involved having precast stairs delivered in smaller, less load-sensitive pieces from the manufacturer, but this was determined to be unfeasible. A later plan would have cut a hole in the roof above the stairwell to lower the precast stair pieces directly into place from overhead by crane; this option was determined to be feasible but, the part of about cutting a hole in the new roof was decided to be something to avoid if another way could be found.
In the end, casting the stairs in place was found to be by far the safest and least disruptive option. The work will include within the stairwell the erection of scaffolding and structural supports as well as the concrete forms for the stairs themselves. Once rebar is laid and the concrete is poured and dried within the forms, the forms will be removed and then the stairs will need detailed finish work.
To reduce the scope of the work within the period in which the stairwell will be closed, the construction contractor no longer plans to include the installation of new handrails for the central stairs on floors 1-4. The handrails will be installed later in a separate phased effort that won’t necessarily require closure of the entire stairwell.