DOWNTOWN / UNIVERSITY / 4TH AVE

Solar Art

On February 19 at 8:45 a.m., a propeller blade will project onto the image of a 1910s airplane embossed into the sidewalk of the Luis G. Gutierrez Bridge, newly opened to pedestrians and bicyclist.

No other time or day during the year will the propeller align with the plane. It’s a magical moment, one that the bridge’s designers purposely fashioned to make the new bridge for the Cushing Street extension to the West Side an actual destination.

Such was the case at 8:45 a.m. on Oct. 14, when people gathered around a sandblasted sidewalk image of the Tucson Pressed Brick Co. as the solar projection of the TPCO brick stamp inched onto the sidewalk image.

“I was out there and there were people watching for it to happen,” said Claudia Perchinelli, a bridge engineer and owner of Structural Grace, the local bridge engineering firm that designed the bridge. “It was very exciting. They all had their cameras and they were waiting.”

That’s exactly what the bridge’s architect, David Dobler of Structural Grace, wanted to achieve with the 12 solar icons laser-cut into the shade canopies above the sidewalks. Each sidewalk image and accompanying text depicts a specific moment or event that defines Tucson.

“I wanted to create something in my mind to get people here for other reasons than just cross the river. I wanted to create a destination,” Dobler said.

How hard is it to have the sun project an image on a precise spot at a precise time on a specific date? We always know where the sun will be. Sundials easily tell the right time. But Dobler had to wrestle with many more variables to make sure the 12 images were embossed into the exact locations on the sidewalk.

The bridge follows a rounded camber across the Santa Cruz. Plus it’s rounded side-side, too. In addition, the canopy with the image to be project is curved. All this needed to be incorporated into the 3D modeling.

The light poles that carry the canopies had to be exactly vertical and the crossbars with the canopies at a precise height. Even the sidewalk benches needed adjustments. The image and text for Juan Bautista de Anza wrap around one bench.

On top of all that, the Luis G. Gutierrez Bridge has undergone considerable design changes since 2007. There was the name change from Cushing Street Bridge. The bridge was narrowed by about a dozen feet, and has gone from three spans to two spans. Most significantly, there was a major realignment to have the bridge cross the Santa Cruz River at an angle to preserve Pima County’s Theresa Lee Public Health Center.

The bridge is aligned 22º39’50” askew in a southeast to northwest slant. Designers learned by chance that this alignment was only half a degree off from where the sun rises and sets on the winter and summer solstices, Dec. 21 and June 21. To the lay person, that’s a rising and setting sun right down the middle of the street.

That triggered the Indiana Jones in David Dobler’s psyche. Since “Raiders of the Lost Ark,” he’s been intrigued by the tomb scene, where Jones attaches a gem on a staff and the sun projects onto the secret spot.

“I bought a statue of St. John the Baptist, stuck it on a staff, and on the summer solstice 2008, I held it up on the bank of the Santa Cruz River and checked the shadow,” Dobler recalled.

Of course, the shadow fell exactly where Dobler expected.

Dobler and Structural Grace’s computer aided design modeler Mike Lichtenstein created a 3D computer model with the bridge specifics and then ran it with specific dates and times to see if a projected image would project onto a sidewalk image at a precise time. Then Dobler built a real life model with the image of the Spanish flag projecting onto a rough presidio drawing and set it up in the Structural Grace parking lot on Aug. 8, 2008.

“At the allotted time, which I think was high noon, the image didn’t align where we expected it to,” Dobler said. “We just sat there and waited. An hour later, it aligned perfectly.”

The Google shade and shadow program they used did not account for Arizona not recognizing Daylight Saving Time. Dobler and Lichtenstein took the results of this parking lot experiment to astronomer at UA: Science Flandrau to confirm their premise. They got a thumbs-up from the astronomers.

Dobler and Lichtenstein then entered exact geometrics of all the bridge elements into the 3D modeling program to align canopy and sidewalk images.

The image in the canopy would be in a fixed position, and Dobler had specific historic dates in mind for all 12 images. So the variables were moving the sidewalk image and finding an ideal time for the canopy image to project onto the sidewalk.

“Mike and I sat down and did the modeling. You just literally plug in different times. We would then move the sidewalk image to align at a specific time.”

It took one week at the end of 2009 to establish times and sidewalk placements. But they were not done.

“As the bridge design changed, the alignments had to be adapted by shifting the images by the respective narrowing amount,” Dobler said.

They had to go through the 3D modeling exercise two more times to establish the precise positions of the sidewalk images you see today.

Fast forward to August 2012. The bridge is essentially done – but there are square holes at the base of each canopy where the lazer-cut images would go. Armed with a carpenter’s crayon, Dobler made precise measurements from the center lines of each light pole and from barrier separating the side walkfrom the roadway. Then he drew two squares, six inches apart, one for the sidewalk image, one for the text.

“I crawled on the ground. It was hot. I was out here eight hours doing this,” Dobler said.

“The most important chapter of the bridge’s story is the story of collaboration between engineer, architect and artist.”

Bridge artist Brenda Semanick heartily agrees.

“Dave and I worked together on this for four years,” Semanick said. “It was a beautifully collaborative project.”

For the solar art, Semanick designed the canopy panels that project onto the sidewalk images, which were drawn by her artist husband, David Johnson Vandenberg. Semanick also designed the laser-cut cottonwood leaves that give the canopy an artistic perforated look.

The staircases down to the river are embedded with 200 shards of replica Hohokam pottery. Semanick based the designs on pottery excavated from the Santa Cruz River. She hand-painted each one.

“I went there and worked with the guys who built the staircases and said ‘put one here, put one there.’ I even put a few in myself,” Semanick said. “It was summer. It was brutal work for those guys.”

Semanick also added ducks, fish and bats to the center pier that holds up the bridge. She carved 20 bats out of clay and then made molds and cast each in concrete. The bats can be found high on the pier under the bridge.

“ I went up there with the guys,” Semanick said. “I wanted each bat placed a certain way.

Calendar: Solar events for the Luis G. Gutierrez Bridge

This article appears courtesy of the Downtown Tucson Partnership and DowntownTucson.org