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A source of inner strength

Posted 11-30-2010

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The white cliffs of concrete that now dominate the Albert Sherman Center (ASC) construction site draw their inner strength from a skeleton of steel reinforcing bars commonly called rebar.

“Rebar is the bones of the concrete,” said Kevin Sullivan, field engineer for Berry, the ASC construction manager and a division of Suffolk Construction. “It’s what gives the walls their rigidity.”

Before concrete is poured into the forms that give shape to the walls, a framework of rebar is built and positioned in between the forms. The rebar arrives on-site as individual pieces of steel in varying lengths and diameters. Ironworkers then assemble the pieces into specific panels and “cages” using steel “tie wire” to bind the rebar together.

Once assembled on the ground, the rebar panels and cages are lifted into place by a crane, so other ironworkers can wire them into place, making their way along the sheer faces of the rebar grid wearing safety harnesses like rock climbers. “They assemble the rebar by following very specific drawings that are approved by the design team,” Sullivan said. “Engineers then inspect the rebar in the field before the concrete is poured.”

In addition to giving the walls rigidity, the rebar framework is important for strengthening the corners and edges of the concrete walls to prevent them from chipping, Sullivan said.

A total of 837 tons of rebar will be used in the foundation walls and footings for the ASC. The rebar in the building weighs between 2 and 4 pounds per linear foot, depending on the diameter of the bars. That equates to more than 100 miles of rebar that will be embedded in the concrete of the ASC. If that rebar were laid end to end, it would stretch along the Massachusetts Turnpike from Stockbridge to Boston.