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| The building is strengthened by (1) the addition of 3,000 tons of structural steel primarily in two areas of the building, and (2) installation of a new shear wall structure inside the core of the old building. |
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| Structural steel is used in the core base upon which the core shear walls are built, and along the roof line of the 10th floor north and south wings. The whole is interconnected to form a single structure that will maintain the structural integrity of the building during earth movement; it insures that the north and south wings of the building move "in sinc" with the rest of the building during a seismic event. Major concentrations of structural steel are shown in red in the drawing lower right. |
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| The shear wall structure (seen in the drawing at upper right) works in concert with the structural steel, while resisting shear forces (torqueing) by providing a rigidity to the building needed for the building to maintain its shape during a seismic event. This shear wall structure could be its own stand alone building, so in order to construct this building within the old City Hall some internal parts of the old City Hall had to be demolished. |
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| The shear wall structure |
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| Structural steel placement |
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| The steel of the old structure in an area of the central core of the basement during initial excavation. The original steel was held together with 900,000 rivets. The new steel is welded in place. |
Additional steel supports added to an existing column in the basement. |
Massive structural steel beams in the basement support the new shear wall structure in the central core, where the shear walls grow upward to the top of the building. |
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| The original trusses holding up the tenth floor roof. |
10th Floor - Its located within City Hall, shown in red in the drawing. |
New structural steel reinforcing beams which are tied into the central core of the building to stabilize the wings during a seismic event. This is a horizontal truss that acts as a diaphragm i.e. it moves together. |
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| The traditional method of pouring concrete into forms was not used for the shear walls. |
Instead, the concrete was blown onto the walls in a process called "shotcreting" very similar to how concrete is applied in the construction of a home swimming pool. |
A completed shear wall next to the entrance to the Council Chambers on the 3rd floor. |
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| 2nd floor shear wall thickness. |
17th floor shear wall thickness - The thickness of the shear wall on a tower floor can be compared to the much thicker shear wall at left found on the lower floors (this is the 2nd floor). |
A section of the central core on the 11th floor which supports the structural steel roof truss for the north and south wings. |
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