"Trying to get all those alignments to fit in is very difficult," Dave Nazare, technical support manager for the Utah Department of Transportation (UDOT), told ROADS & BRIDGES. "I’ve been told it’s like having a bunch of wires in a coffee can. If you try to move one wire they all kinda want to pop right out and spill all over the place. That’s a lot of the challenges that [Wasatch Constructors] has, where you have all those multi-levels. If you change alignments and profiles at all on any one level it affects all the others. That was very challenging for them, no doubt."
So far the challenges haven’t been the ones calling the shots. To date, 81 bridges are currently under construction and 23 are completed. The I-80/I-15/SR 201 section, located on the south end of the project, is expected to be finished next September.
"There are 15 flyover structures in that interchange and we have started construction on all but three of them," Jeff Ellis, segment structures project manager for the Jordan Segment, told ROADS & BRIDGES. "They’re all at various stages."
Wasatch is starting to do bridge deck work on the I-80 flyover that runs through the valley and the I-80 westbound to I-15 northbound. Steel girders and columns were starting to be put in place on the I-80 westbound to I-15 southbound.
"The new feature we’re adding is dedicated lanes that will tie I-15 and I-80 directly to State Route 201, so that it’s separate from 21st Street (2100 South)," said Ellis.
Shaking and settling
The day will come when the earth cracks in Salt Lake City, which lies on a major fault line. It will not, however, be a day when the bridges crumble. That’s the holding hope of UDOT and Wasatch Constructors after the two dedicated a load of man hours to seek out ways to avoid construction catastrophe after a seismic event. According to the American Association of State Highway & Transportation Officials, one is supposed to look at a seismic event that has a 10% chance of occuring in 50 years. The I-15 reconstruction team decided they should consider one that has a 10% chance of occuring in 250 years.
"In a major event we don’t want the bridges to fail," said Nazare. "We want the damage to be repairable, and that’s pretty much the strategy that’s employed."
One player in the Wasatch strategy is the plastic moment hinge, which are being inserted at the top and bottom of the column and is allowed to yield in a major earthquake, but won’t fail.
There has been some confusion as to how long the bridges will last once constructed. In proposals, UDOT asked Wasatch to supply a 75-year life-cycle cost analysis for the bridge types so there would be an idea as to what types of maintenance would have to be performed in a 75-year life. Nobody expects the bridges to go maintenance free during that time, and UDOT is anticipating to do a bridge replacement in 45 to 50 years.
Extra steps are being taken to give the bridges durability in the salty environment. Wasatch is using 5% silica fume on the top decks, epoxy-coated rebar and salt sealants.
Tackling the soft soil was another major issue in the early stages. Wasatch is using some stone columns for soil reinforcement in liquification areas, which will stabilize the soil and reduce the liquification potential in seismic events. The use of lime cement columns also were used in the effort to gain some soil strength, "but the contractor found the production of those were not meeting what they had expected when they put their bid together, so they weren’t used very extensively," according to Nazare.
It’s your call
Because this is a design-build project, most of the responsibility is placed in the contractor’s hands. The concept is new to UDOT. "They’re doing things a little bit differently than we’d probably do as a department to accelerate the process," said Nazare.
"We brought a lot of experienced people that have been involved in the design-build process. It is that experience with facilitating the design coordination, and actually starting construction prior to final design, that is contributing to our success," said Ellis. "It is more of a coordination issue than anything else, but the process is faster and more flexible than the traditional design-bid-build process."
In fact, UDOT felt Wasatch’s presence right from the start. In an effort to save time on a particular bridge, the contractor made a complete design for the structure, but then drew up the foundation and released it to construction before they finished drawing up the rest of the bridge. All this in an effort to save time.
"They’d do a complete design of a bridge and just draw up the foundations so they could get the foundation work in a hurry," said Nazare. "Then they would go back and draw the deck and the superstructure."
Building precast concrete girders, which have precast deck panels produced by Basic Precast in Salt Lake City, was another break from the norm. Wasatch is using four sizes of concrete girders—1,050-, 1,450-, 1,850- and 2,400-mm (spliced girders) deep—which tend to have narrower webs and wider flanges. Wasatch also is post-tensioning some of these pre-stressed girders, putting three together and then post-tensioning to get one span. Concrete girders are prominant around the single-point urban interchanges, where ramps come under a bridge and are controlled by just one traffic signal underneath. The areas require "quite a bit of sight distance," according to Nazare. The idea is more cost-effective than using steel.
Flyovers, like the ones saturating the 1-80/I-15/SR 201 zone, are structural steel girder bridges.
How they do it
Despite all the complexity and coordination involved during the design-build process, the actual construction of the bridges is quite elementary. The lake bed sediment doesn’t support a lot of load on a spread footing, and for that reason all bridges are on driven piles. After driving the piles they put on a pile cap and construct the columns. On top of the columns and pedestals are beam seats, then comes the superstructure, which is either concrete beams or steel girders. The bridge deck is constructed next, and in the case of the precast deck forms another 4 in. of concrete is applied on the deck to form the riding surface. Roadway barriers or 15-ft noise walls are the last to be put in place.
Wasatch is using two types of concrete on the bridge structures—one is 35,000 kpa (5,000 psi) and the other is 28,000 kpa (4,000 psi). The contractor determines which is used on what bridges. The concrete mix is composed of fine and coarse aggregate, Type 2 Mountain Cement, WRDA 64 water reducer, DARACEM 19 high-range water reducer and DARAVAIR 1000, which is an air-entrained admixture. All of the concrete admixtures are produced by WR Grace. Steel at 36 and 50 ksi is being used for the steel girders.
Grove (Models RT635C and RT865B) and Manitowoc (Model 227, 777, 3900W) cranes are being used to perform the lifting duties of the construction, while vibratory hammers and hydraulic impact hammers from American Pile Driving Equipment are handling the work of placing the foundations for the columns. A fleet of Schwing concrete pumps delivered the mix and either a Bid-Well or Gomaco C-700 bridge deck finisher smoothed out the surface on bridges.
Sticking with the Salt Lake City theme, Wasatch and UDOT decided to carve a mountain ridge across the top of bridges hanging over the expressway and on noise walls. UDOT also required a second color in staining
. High mast lighting was going to be used on only the ramps on the interchanges, but further consideration led to full corridor lighting. Some of the lighting is already complete on the north end of the project and on the I-80 junction.
Make sure to put a coat on
Utah Department of Transportation (UDOT) was very concerned about the highway project’s long-term maintenance needs, as well as ultimate public approval of the finished appearance of the work. The state had never before specified a coating for concrete, but a call for a chemical stain was included in the final I-15 specification. The stain would be applied to the concrete portions of the highway’s new bridges, as well as to soundwalls and other concrete barriers.
Bruce Toews, Sherwin-Williams industrial and marine group sales manager, and Dee McNeill, Sherwin-Williams corrosion engineer, demonstrated to UDOT how the company’s H&C Concrete Stain, combining silicone and acrylic, bonds to the concrete so the surface cannot peel, crack or chip. The coating, when used with HB-150, is said to reduce water absorption by more than 85% and chloride ion intrusion by more than 92%, assuring longer lasting concrete.
McNeill also explained how adding color to the project would improve the roadway’s overall aesthetics, and that the opaque silicone-acrylic formulation would hide graffiti and enhance the project’s design. Inventory would be held at the many Sherwin-Williams stores in the overall project area so any graffiti could be quickly covered with matching stain without leaving unsightly patches.
"You can cover over any graffiti with just two coats without having to sandblast it off. You can apply up to 50 coats before you need to sandblast, up to 3 mil thickness." said Wasatch Constructor’s contract administrator Bill Saumier, referring to the H&C Stain.
The concrete painting contractor was Scott Derr Painting of Webster, Texas. For the concrete part of the work, Scott Derr said Sherwin-Williams was chosen as the sole supplier to ensure overall consistency of appearance. To protect the bridges from salt damage, the concrete in splash zones was first prepped with the Sherwin-Williams HB 150, which Derr noted can go either over or under the color coat. Then, two coats of stain were applied to concrete areas such as retaining walls, barriers, slope paving, columns and exterior girders.
The steel portions of the bridges were first blasted with steel grit to remove slag and allow for uniform surface adhesion before primer was applied. Later, in the field, the steel was spot blasted at bolts and welds by Interstate Coatings Inc., Seattle, then spot primed and pressure washed. Stripe coats along bolts and edges gave extra protection before the contractor applied a full intermediate coat of Sherwin-Williams Recoatable Epoxy, topped with a Corothane II Satin that was chosen for its durability.
Galvanized downspouts on the bridge’s new drainage system were to be coated with a DTM wash primer from Sherwin-Williams, followed by applications of the same Recoatable Epoxy and Corothane II used on the steel.
Purple mountains’ majesty
In the I-15 project, color selection was a priority. Chris Petracca of Sherwin-Williams’ color and design marketing department assisted the I-15 project members in choosing colors picked up from the natural terrain. "The area had a great palette to chose from," said Petracca. The plum colors of the mountains were used on the steel and grayed to a subdued purple hue called "Mountain Dusk." The concrete is a sage green called "Desert Sage," with a darker variant of the green used to give the concrete another design element.
"The colors blend the bridge infrastructure in with the surroundings and soften the sterility of the concrete and steel," said Petracca.
Since this was new construction, Sherwin-Williams was able to use its photo imaging process to take the engineers’ drawings and apply the actual colors used so the project team could see precisely how the colors would look.
The bridge painting on I-15 is expected to be 20% accomplished by the end of 1999 and completed by summer of 2001. But the care taken in bridge design, product selection and application gives the new I-15 bridges a life expectancy to 2076.