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Seismic regulations impact building process
By Holly Fisher
Supplements Editor
Changes to building codes can result in stronger structures, but they can also increase the bottom line and lengthen a project’s timeline.
Last year South Carolina adopted the 2003 International Building Code, which significantly increased the seismic requirements for residential and commercial buildings.
Architect Stephen Russell realizes how challenging it can be to incorporate the added requirements into the design and construction process. His firm, Stephen Russell & Associates Ltd., designed a new two-story office building in Mount Pleasant under the strengthened earthquake requirements.
Still under construction, the Acker Office Building at 321 Wingo Way required a more extensive foundation than it would have needed under previous building codes.
Designers, engineers and builders must consider a process called “liquefaction” when selecting a foundation that can withstand an earthquake.
Simply, liquefaction is sand turning to water, similar to what you see on the beach as the ocean washes over the sand. Generally, sand provides good support for a structure, Russell said, but when the earth moves, the sand turns to more of a liquid substance.
Prior to the revised building code, Russell said a spread footing foundation would have adequately supported the 5,300-square-foot building on Wingo Way. But with the new seismic requirements, Russell had to more carefully assess the soil conditions at the building site.
For this project, there were two options: a deep pile foundation that would reach 90 to 120 feet down to the bedrock or a floating slab foundation. A floating slab, which Russell likened to a concrete raft below the soil, is designed to work independently of the structure.
“In a seismic event, when you have liquefaction, this slab will move and maintain the structural integrity as the building moves with it,” Russell said. “In theory, the building and the foundation stay intact.”
One downside, he noted, is the structure may not be level following an earthquake. But if it stays intact, there are ways to work with the foundation to level the building—something that would not be possible with a spread footing foundation, which breaks apart in an earthquake.
Geotechnical engineers recommend foundation options based on soil tests, Russell said. Some areas would be suitable for a floating slab; other areas would not.
A pile foundation would have been significantly more expensive, particularly for a smaller project like this office building, Russell explained, so the developer opted for a 12-inch floating slab with about 7 tons of reinforcing steel.
While constructing a secure foundation is important, it is not the only consideration. Russell noted the upper portions of the building have to be secured with bracings; the ceiling tiles have to be secure, as does the overhead heating/AC units.
When Russell first started designing the Acker Office Building, several elements of the building code were not in effect. As the plans went before the town for approval, new codes were being enforced, and Russell had to make adjustments.
The changes led to more work in designing the building, as well as in the construction plans and drawings, which added to the final cost.
In addition, the owner must pay for an independent inspector not affiliated with the contractor or architect to inspect the facility to ensure code requirements are being met, Russell said. That means more expense as well as downtime for the contractor who has to prepare for the inspection and meet with the inspector.
It is not only the seismic requirements with which builders have to contend. Wind has become a major issue, Russell said.
Five years ago, buildings were constructed to withstand 100 mph winds; today they must be ready for winds of 130 mph. That, coupled with new seismic regulations, is driving up construction costs.
The added seismic requirements added about $5 per square foot to the cost of the Acker building.
“It affects building costs significantly,” Russell said. “These are things people don’t see and yet there’s no way around it. A lot had to go on behind the scenes to make drastically different buildings.”
Yet, the main focus of the building code is to protect the general public—a benefit for everyone, Russell points out.
“A building has to maintain a minimum level of structural integrity so people inside are protected. We can all lament the existence of the code, but that’s the rational behind it,” Russell said. “Many of us—architects, engineers, contractors—can go back five years and we
didn’t have to meet (these requirements). It’s change, and no one likes change. It has been a challenge, but without it, you open up the possibility of those who make individual judgments (and possibly do less).”
Holly Fisher is the supplements editor for the Business Journal. E-mail her at hfisher@charlestonbusiness.com.
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