When St. Paul officials began making plans two years ago to address cracked pier caps and leaking expansion joints on a heavily traveled bridge linking downtown to the East Side, they figured they could make the fix for $3 million.

But when a consultant this summer discovered that the traffic and structural loads on the bridge’s long support arms exceeded federal standards not in place when the bridge went up in the early 1980s, the repair work nearly tripled — to $8 million or more.

The steep jump now has the city weighing the option of building a new Kellogg Boulevard-3rd Street bridge — conservative estimates run from $30 million to $40 million — that would meet pent-up demand for a more attractive and multifunctional structure.

It also raises questions about how a bridge built only 32 years ago could be deteriorating so rapidly.

City Engineer John Maczko said the pier caps were showing pronounced stress, which he said starts with the bridge design — OK in 1980 but considered defective today.

“The bridge itself could not be [built] under today’s code of specifications because of the cantilever,” which causes stress on the bridge’s outer lanes, he said.

The bridge is considered “structurally deficient” by engineers, which doesn’t mean that it is unsafe or likely to fall, but instead has elements that need to be monitored and repaired.

Nevertheless, in a state where memories of the stunning Interstate 35W bridge collapse in 2007 remain fresh, MnDOT has taken notice.

State Bridge Engineer Nancy Daubenberger said that she has asked district engineers to go through their inventories and see if there are other bridges in similar straits; so far nothing has been found. While the Kellogg bridge has a common hammerhead-pier design, its cantilevered arms are uncommonly long and take on more load “than what we’d normally see,” she said.

The Kellogg bridge, which covers nearly a half-mile between the edge of downtown and Mounds Boulevard, carries an average of 10,300 vehicles daily. It’s the 12th busiest bridge in the city among spans of more than 1,000 feet.

MnDOT built the $5.8 million bridge in 1982 and turned it over to St. Paul the following year. Daubenberger said that MnDOT didn’t “know of anything that would have happened in construction that would have pointed to the stress happening.”

An early hint of problems with the bridge surfaced in a city report nearly two years ago.

According to a Public Works Department funding request in January 2013, the main problem with the bridge was identified as cracking in the ends, or caps, of the concrete piers used to support the spans.

The cracking “accelerate[ed] and worsen[ed]” due to leaking from the deck expansion joints above the pier caps, the report said.

At the time, city officials believed the bridge could remain serviceable “for another 50 years” if the pier caps were repaired and leaks plugged, a fix they said would cost less than 10 percent that of replacing the bridge with a new one.

Public Works also reported in January 2013 that the structural sufficiency of the bridge rated 54.1 on a scale of zero to 100. Nine months later, a MnDOT inspection report gave the bridge a 78 sufficiency rating. But this July, a month before the MnDOT consultant found the bridge didn’t meet federal standards, its sufficiency rating plummeted to 37.4.

Repair or rebuild?

Earlier this week, city officials announced that they will restrict traffic on the bridge beginning next week in order to reduce wear on its outer lanes. At the same time, officials must decide in coming months whether to repair or rebuild the structure, and how to pay for it.

Both Mayor Chris Coleman and City Council President Kathy Lantry favor a new bridge.

“Just start doing the math,” Lantry said Thursday. “By the time we did the $8 million repair, the bridge is a year older. And you still won’t get people down to the Vento Nature Sanctuary, it still wouldn’t have bike lanes or be better lit or carry more cars or accommodate [bus rapid transit].”

“Do you invest $8 million to keep the wheels on it? Or is this the opportunity to say this bridge hasn’t functioned well for the way we use it, so maybe we ought to just start over?”

While the bridge is considered structurally deficient, the bigger factor in deciding whether or not to build anew has to do with the bridge’s designation as “functionally obsolete” — which means it falls short of modern standards for transportation demands.

Maczko said the city has several options, ranging from simply making needed repairs — which would extend the bridge’s life for 25 to 30 years — to putting a wider deck on the existing piers, to building entirely new.

The city will use $300,000 it had earmarked for planning repairs and instead hire consultants to draw up a list of bridge alternatives and costs.

While the city would bear the cost of repair work, a new bridge would require significant funding from the state and federal government. Lantry and Coleman said they have been in touch with state and federal partners, and state Rep. Sheldon Johnson, a DFLer who represents part of the East Side, said he will lobby for state support.

The bridge, which carries four lanes of traffic, will be closed starting at 9 a.m. Friday through the weekend so it can be re-striped and fitted out with new signs. Come 6 a.m. Monday, motorists will be limited to three lanes in the center, two westbound and one eastbound. Cyclists and pedestrians will have to share a narrower path.

The current bridge “doesn’t handle bikes and pedestrians and can’t handle [bus rapid transit],” Maczko said. “Is it really wise for us to put $8 million into rehabbing the bridge and have all the other needs unmet?”