GIBA part II: Things are really shaking on the bridge

■ BY MARCY SHORTUSE       giba logo

The April 20 quarterly meeting of the Gasparilla Island Bridge Authority had so much information jam-packed into three hours, we just couldn’t run it all in one week. This is part two of that meeting’s proceedings, see part one regarding the weight restriction conversation in last week’s Boca Beacon.

According to Gasparilla Island Bridge Authority Engineering Chairman Peter Strong, the new Boca Grande Swing Bridge may have a resonance problem. Then again, it may not.

At the April 20 quarterly meeting of the GIBA Board Strong said there’s a quirk regarding the bridge vibrating sporadically when it is opening, which is called mechanical resonance. It is the tendency of a mechanical system to vibrate or sway when the frequency of its oscillations matches the system’s natural frequency of vibration. While it can cause catastrophic failure in improperly-constructed structures including bridges, buildings and airplanes – a phenomenon known as resonance disaster – Strong doesn’t believe that will be the case with our bridge.

“During the construction process in February and March there was a lot of difficulty with the bridge resonating,” Strong said. “Like a bell when you hit it, it has a particular pitch. If you change the shape of the bell, the pitch is different. Our bridge would kind of ring like a bell. You could feel it when you were standing on it as it opened.”

Strong rode the bridge numerous times as it was opening, and said there is no set pattern to when the resonance begins, which leads him to believe it could possibly be related to anything from the wind, to the tide, to some small part of the structure that needs adjustment.

“It’s not a safety issue, but we have to address it to make sure bridge has good long-term stability,” Strong said. “This is common among large structures, and hard to predict during engineering. We are looking at various solutions, and we did bring out a resonance expert from Washington state who crawled under the bridge and gave us some good input as to what to do to eliminate it.”

The engineering committee meeting, which was held just days prior to the April 20 quarterly meeting, are not available at this time according to GIBA officials, but board members who attended said that Strong told everyone in the meeting there were no structural problems with the bridge at all.

The board also touched on the issue of a large “change” order that will soon be negotiated currently with bridge contractor firm GLF. Strong said bridge construction slowed in the summer, then almost stopped after difficulties of elevations of the tip ends of bridge were found, and it being balanced.

“A lot of subtle technical difficulties delayed construction for several months,” Strong said. “It costs an auxiliary amount of $17,000 a day every day they are late. Several months of delay has a significant impact. It’s their fault, but that’s what negotiation is all about. We hope to get it resolved before next board meeting in June.”

Strong said they may or may not come to a figure that is even appropriate to bring to the board at a later date.

Strong also told the board that a new generator would be in place and ready to go some time this summer. They realized the old generator wasn’t going to be optimal some time months ago, particularly with the modern technology the new bridge utilizes.

He also discussed the new back-up bridge opening method, which now only takes two men in a boat to open instead of four very large men wheeling the entire bridge around.

“If things shut down on the old bridge you could open it by putting a key through the deck and having guys wheel it around,” Strong said. “We had conceived of that thought for the new bridge, but there were difficulties. It took four beefy guys to rotate it and it wasn’t practical. The new system that allows one or two guys going across by boat and into electrical system underneath the bridge to open it.”

Board member David Hayes also gave his report regarding causeway landscaping from the south bridge northward.

Hayes said they sent out their request for proposals to trim and clean up all existing trees that are there now, to eliminate pepper trees once and for all

and place trees such as cabbage palms in groups to create an entrance to the causeway. Hayes said they will be careful not to impede the view of the water from the road too much.

The winning bidder was a company called Cintron, who has offices in Fort Myers. The approximate cost for the project is $70,000 and artist renderings should be available over the summer. Watkins said nine local companies were offered the job, and only three came in person to observe the causeway firsthand.

The dirt pile that has graced the side of the roadway for so long may be soon be disappearing as well. When Board Chairman Ginger Watkins mentioned the county couldn’t use it because it was filled with concrete pieces, local hauling contractor Kevin Kelley (who attended the meeting for other reasons) said there was a good chance he could get rid of it for no cost to the GIBA. That plan is still in the works.

In an update from GIBA Executive Director Kathy Banson-Verrico she said traffic for the first six months of the fiscal year was up five percent compared to last year. March was highest traffic month with 121,000 vehicles crossing the bridge, the highest month since she took over the executive director position. Of the totals, 68 percent of the vehicles used GIBA passes, and 32 percent paid in cash. She said approximately 94 percent of that figure included regular passenger vehicles, not trucks or tour buses. Commercial vehicles and vehicles pulling trailers made up five percent of that number.

She also said from February to the end of March GIBA opened 199 new bridge pass accounts. This summer GIBA employees will be working on a program where postcards will be sent out to those whose accounts are going to expire.

Banson-Verrico said that the engineering firm of Hardesty & Hanover was correct in their earlier assumptions that GIBA would experience a decrease of approximately 50 percent in their bridge openings once the new bridge was fully functional and the old bridge was out of the way.

“At the beginning of the year we were down by 43 percent,” she said. “We will have some pilings in the water, so it’s single-channel traffic only and that takes a little more time. Sometimes people are running the red lights and getting caught between the bridge gates, which makes it take even longer.”

She also said that traffic lanes at the tollbooth continue to be restricted because there isn’t enough room to merge the three lanes of traffic consistently. She reminded everyone that GIBA employees coordinate with each other during and after bridge openings to try to make sure all three tollbooths don’t open at once.

“Once we are completely done the lanes will be configured a bit differently,” she said. “While we don’t have a median barrier wall we will continue with these restrictions, but keep in mind that we are not holding up traffic for no reason when the bridge is open, and we don’t randomly open the bridge when there are no boats waiting to pass.”

Banson-Verrico also said the new bridge tender house has started to record data again just as it used to, collecting weather and wind speed data, and that the GIBA would be partnering with the Boca Grande Historical Society to create an exhibit on the history of the bridge.

The next general board meeting will be held in November.