We Dare You To Step Out!
Today we decided to look at the amazing glass ledges on the side of the Sears Towers building. The glass and steel ledges are suspended on the 103rd floor which is roughly 413m above the ground and are constructed of 3 glass layers measuring one and a half inches thick, and will bear the weight up to five tons.
Sears Towers now renamed Willis Tower but still referred to as Sears Towers is one of the tallest buildings in the United States reaching 110 stories high. The glass ledges measure 1.3 x 1.3m by 3.6m high and now offer the highest observation point in Chicago.
The ledges are known as Sky decks and visitors can experience the building swaying on a windy day as well as feeling the sensation of vertigo from within the glass boxes!
The sky decks were open to the public in July 2009 and are now one of the biggest attractions in Chicago attracting 25,000 visitors on clear days each paying around £9.00 to experience the amazing views. Imagine being able to experience un obstructive 360-degree views of up to 50 miles — including Michigan, Indiana, Illinois and Wisconsin!
The architects of course need to be praised for these amazing boxes, but the construction wouldn’t have been possible without glass specialists who were needed for the architects design & realization to take place.
Without getting too bogged down in all the technical elements which needed to be addressed before the boxes were constructed, let’s such take a quick look at the challenges MTH Industries had to face when they were instructed to design the glass and steel boxes for the tower.
- All glass elements had to be brought up to site using the internal elevators, which restricted the size of the boxes.
- The observation boxes had to be moveable. This was required to allow the facade maintenance equipment to operate along the facade without interruptions. But, even more difficult, it was decided that the glass boxes were to be retracted an additional 1200mm into the floor space, so that glass maintenance and cleaning could be done from inside the building.
- There were tenants at the floor below the Sky deck, so all the glass box loads had to be hanged and framed from the ceiling above.
- The frame and glass box had to be stiff enough to allow the movement of the box without creating large deformations or stresses at the glass connections.
- The details around the glass box had to include weather seals in both the extended and retracted position, allowing for the movement of the tower.
- The architect’s intention was to obtain maximum transparency, minimizing the visible structural steel elements.
- Safety and protection of the glass was requested. Safety issues excluded the option of double glass, and laminated glass was the solution. This meant the visitor wouldn’t have the need to protect or remove shoes on entering the ledges.
- A heating system was required to overcome the risk of condensation on the glass, or worse allow the formation of ice shards outside the ledges, which could fall onto the walk way below.
A tough brief I would say, but the team carried out intensive planning and testing of the boxes before they were happy with the end result.
To protect the boxes from every day wear and tear the team used an anti-graffiti film on the vertical glass sides, and in case the floor should get scratched, cracked or damaged a removable top made from a laminated 6mm sacrificial layer of fully tempered heat-soaked glass was put in place.
The laminated glass units forming the walls and the roof have 3 tempered 12mm lites of PPG’s Starphire low-iron glass. The walls and roof are laminated with clear PVB.
The extra-clear glass flooring uses tempered, low-iron glass laminated with 1,52mm DuPont’s SentryGlas Plus interlayers.
There were many more hurdles the team had to overcome, but I think it goes without saying they managed to deliver 4 amazing strong, unique and safe glass boxes.
Take a look at the images below they say it all!