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Broadway Avenue Minnesota River Bridge

Photos 

View from south

Photo taken by David Erickson in November 2008

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BH Photo #127199

Map 

Street Views 

Statement of Significance 

From Minnesota Historic Property Record

Spanning the Minnesota River on Minnesota Trunk Highway 99 (formerly TH 21), Bridge No. 4930 connects the city of St. Peter in Nicollet County, on the west, with rural Oshawa Township in Le Sueur County, on the east. In the St. Peter street system, the bridge stands on Broadway, just east of the downtown district. Locally, it is known as the Broadway Bridge. The crossing is 402 feet in length, consisting of two, rigid-connected, Pennsylvania, through-truss spans on a concrete substructure. The spans display conventional, built-up detailing -- two laced channel sections with cover plate in the upper chord, two laced channel sections in the lower chord, and four laced angle sections in the vertical and diagonal members. The bridge's overall design, however, is unconventional, largely because the current of the Minnesota River twists in mid-channel at the site. This hydraulic peculiarity dictated the construction of a skewed pier, so as to offer the least resistance to the flow of the water. Because of the oblique placement of the pier, the two truss spans required a skewed configuration at the end supported by the pier. This goal was achieved by designing each span with truss webs of unequal length and slightly different profile. In the west span, the north web is a ten-panel, 195-foot truss with inclined endposts at each end, while the south web is a nine-panel, 176-foot truss with an inclined endpost at the abutment and a vertical endpost at the pier. In the east span, the situation is exactly reversed. Although the east and west spans are structurally independent of each other, they are visually integrated by an ornamental linkage that joins their top chords together over the pier. Because of the linkage, the two spans appear to be part of a single, continuous truss, when they are in fact two, simply supported trusses.

The Broadway Bridge has a concrete deck with a 30-foot roadway. Outside the truss webs on the south side, there is a sidewalk supported on metal brackets cantilevered from the bridge's flooring system. An ornamental, metal, lattice-work railing borders the sidewalk on the river side. The bridge also has an ornamental lighting system, consisting of four metal light standards, positioned on concrete posts at the four corners of the crossing. The light standards are detailed in the Classical Revival Style, with fluting on the shaft and consoles at the base. In the mid-1960s, the state highway department raised the bridge's portals and overhead sway bracing to provide greater vertical clearance for traffic. The remodeling retained the original configuration of the features and did not significantly affect the bridge's historical integrity.

In August 1929, a heavily laden grain truck collided with the east end of the Broadway Bridge in St. Peter and tumbled a span of the 1883 structure into the Minnesota River. Since the crossing was part of Minnesota Trunk Highway 21, its maintenance was the responsibility of the Minnesota Highway Department, which already had the bridge's replacement under consideration. In the fall of 1929, the state highway department developed preliminary plans for a new two-span, through truss crossing, but civic leaders in St. Peter balked at the design. The city had just invested heavily in an ornamental lighting system for the central business district, and its merchants wanted the new Broadway Bridge, which was the eastern gateway for the downtown, to be a suitably attractive structure, preferably of concrete-arch construction. The state engineers resurveyed the bridge site and reconsidered their design. But foundation conditions on the shore were not suitable for a concrete arch, and there was not sufficient vertical clearance at the site for a deck truss. In the end, the state highway department adhered to its original recommendation for a two-span, steel, through truss, and in August 1930, the St. Peter City Council gave its approval. In covering the city's bridge story, the St. Peter Herald found consolation in the fact that the new Broadway Bridge would be no ordinary steel-truss structure, but rather a "unique engineering feat" of "special design." The state highway department did indeed face a major challenge in the design of the new Broadway Bridge. Because the current of the Minnesota River twisted in mid-channel at the bridge site, the structure's pier would have to be placed on an oblique alignment, which dictated a skewed configuration for the ends of the truss spans at the pier. In strictly engineering terms, the design of a long-span, skewed, through truss was a demanding proposition. And in aesthetic terms, it was something of a nightmare, because the structural logic tended to impose asymmetrical massing and visually contorted lines. In the case of the Broadway Bridge, the state's design called for each span to use two different truss configurations. One web would be 196 feet in length, consisting of ten panels and terminating in inclined endposts at each end; the other web would be nine panels and 176 feet, with an inclined endpost at the abutment, but a vertical endpost at the pier. Because of the different endpost configurations, the two spans would meet at the pier in a most ungainly manner -- one span ending with a diagonal line, the other with an abrupt vertical line. As a means of visually integrating the two sections of the bridge, the state engineers decided to insert a strictly ornamental member to join the upper chords of the two spans over the pier. This device not only eliminated the unsightly gap between the two dissimilar trusses, but created a flowing upper line for the entire crossing. The result was a unified, double arched profile that made the bridge appear to be a single, continuous truss, when, in fact, it consisted of two, independent, simply supported spans. By way of further ornamentation, the state equipped the bridge with a metal lattice-work railing and Classical Revival Style street lamps, which matched the lighting system recently installed in the city's downtown. In the fall of 1930, the state highway department awarded, on a low-bid basis, a construction contract for the Broadway Bridge to the Minneapolis Bridge Company. The total cost was $99,000, which included $3,500 for building a temporary crossing during construction, and $2,500 for removing the old bridge. Favored by unusually mild weather, the contractor worked throughout the winter and completed the crossing a month ahead of schedule, in June 1931. "The new St. Peter bridge is the most elaborate and the largest in this locality," reported the St. Peter Herald. "An ornamental lighting system is now being installed that will fit in nicely with St. Peter's fine new white way. . . . Thus the approach to St. Peter from the east will be a model gateway."

The Broadway Bridge is eligible for the National Register under Criterion C in the area of engineering, within the historic context of "Iron and Steel Bridges in Minnesota." The Multiple Property Documentation Form (MPDF) associated with this context states, in Registration Criterion 12, that a bridge may eligible under Criterion C if it "exhibits exceptional engineering skill to meet unusual site conditions." With its skewed, through-truss design, the Broadway Bridge satisfies this criterion. The Broadway Bridge is also eligible under Criterion C for its high aesthetic qualities, as provided for by the MPDF in Registration Criterion 11.

Facts 

Overview
Pennsylvania through truss bridge over Minnesota River on MN 99 in St. Peter
Location
St. Peter, Le Sueur County, Minnesota, and Nicollet County, Minnesota
Status
Open to traffic
Future prospects
This bridge is one of 24 historic bridges in the state chosen by MnDOT for long-term preservation. At this point, it sounds like the bridge will be moved a few hundred feet from its current location and restored for bicycle and pedestrian traffic.
History
Built 1931
Design
Pennsylvania through truss
Dimensions
Length of largest span: 196.2 ft.
Total length: 402.3 ft.
Deck width: 29.9 ft.
Vertical clearance above deck: 15.6 ft.
Recognition
Posted to the National Register of Historic Places
Also called
Broadway Bridge
Approximate latitude, longitude
+44.32475, -93.95303   (decimal degrees)
44°19'29" N, 93°57'11" W   (degrees°minutes'seconds")
Approximate UTM coordinates
15/424009/4908385 (zone/easting/northing)
Quadrangle map:
Saint Peter
Inventory numbers
MN 4930 (Minnesota bridge number)
BH 20513 (Bridgehunter.com ID)
Inspection (as of 05/2015)
Deck condition rating: Fair (5 out of 9)
Superstructure condition rating: Fair (5 out of 9)
Substructure condition rating: Satisfactory (6 out of 9)
Sufficiency rating: 50.5 (out of 100)
Average daily traffic (as of 2008)
5,077

Update Log 

  • September 3, 2013: Updated by Jason Smith: Changed the name of the bridge
  • August 29, 2012: New photos from Jason Smith
  • March 10, 2011: Essay added by Nathan Holth
  • August 19, 2010: Updated by Matthew Lohry: Removed "Arched Cantilever Truss" category: This is a two-span, simply-supported Petit (Pennsylvania) through truss.
  • April 21, 2010: New Street View added by Nathan Holth
  • February 15, 2010: Updated by Matthew Lohry: Updated county location and span configuration
  • September 29, 2009: New photos from Jason Smith
  • November 6, 2008: New photo from David Erickson

Sources 

  • David Erickson
  • Jason Smith - flensburg [dot] bridgehunter [dot] av [at] googlemail [dot] com
  • Matt Lohry
  • Nathan Holth

Comments 

Minnesota River Bridge
Posted March 10, 2011, by Nathan Holth (form3 [at] historicbridges [dot] org)

I added some information from the DOT that explains the what and why of this unusual design.

Minnesota River Bridge
Posted October 21, 2009, by Matthew Lohry (mmlohry [at] comcast [dot] net)

It is beautiful, and is one of my favorites in the state. On an even happier note, it is one of 24 historic bridges chosen by MNDOT for long-term preservation, so it looks like this bridge will be around for many more decades for the enjoyment of us historic bridge fanatics! :>D

Minnesota River Bridge
Posted October 21, 2009, by Anthony Dillon (spansaver [at] hotmail [dot] com)

Thanks Matthew for the clarification on this bridge. It is really hard to make out the end posts in these pictures, even on high definition. It certainly had me fooled, and I would suspect some others as well. A very beautiful and unique bridge either way!

Minnesota River Bridge
Posted October 20, 2009, by Matthew Lohry (mmlohry [at] comcast [dot] net)

Although at first glance this bridge may appear to be a continuous through truss, it is indeed a Pennsylvania through truss with two independent spans. Notice that this bridge's abutments are perpendicular to the roadway, while the center pier is at the same angle as the sharply skewed river, resulting in two spans, each of which have trusses of different lengths. The south truss of the first span is the same length as the north truss of the second span, and vice versa. At the center pier, each span has one truss with a vertical end post, while the other has an inclined end post. This resulted in a very awkward looking truss structure. To fix this, a redundant horizontal member was added to each side of the bridge between the spans. That horizontal member gives it the look of a continuous truss, but actually serves no structural purpose. Hope this helps!!

Minnesota River Bridge
Posted September 30, 2009, by Anthony Dillon (spansaver [at] hotmail [dot] com)

The only other continuous truss bridge that I know of is the Zoar Bridge in Tuscarawas County, Ohio. It is a 3 span Pratt built in 1883 by the Wrought Iron Bridge Company. I'm sure there are other examples out there that I'm not familiar with.

Minnesota River Bridge
Posted September 30, 2009, by Robert Elder (robertelder1 [at] gmail [dot] com)

I see that Anthony has already considered it a continuous span. That would make sense given that there are not true endposts supported by the center pier.

Minnesota River Bridge
Posted September 30, 2009, by Robert Elder (robertelder1 [at] gmail [dot] com)

In the past, I have wondered whether the spans of this bridge should be considered continuous or simple. Although I have crossed this brige previously, I never had an opportunity to photograph it so I am glad to see these pictures here.

Simple? Continous? Any suggestions?

Minnesota River Bridge
Posted September 29, 2009, by Anthony Dillon (spansaver [at] hotmail [dot] com)

WOW......this is a very unique span indeed! Basically it is a continuous 2-span through truss. I thought maybe it just had vertical endposts on the adjoining ends, but indeed it appears to have been built as one.

Minnesota River Bridge
Posted September 29, 2009, by Todd aka. "bridgebuilder" (mrwalk08 [at] aol [dot] com)

This is one unique bridge. It looks well maintained. I like the design of how the two spans meet midstream. The two color paint scheme stands out too.