Green's Mill Historical Bridge

Green’s Mill Bridge – An Engineering Treasure

An Engineering Treasure

Green’s Mill Bridge is eligible for listing on the National Register of Historic Places “as a nationally significant example of a self-anchored bridge”.

The fourth self-anchored suspension bridge built in America was constructed August 1,1933 by Clinton Bridge Works, Clinton, Iowa and Missouri State Highway Department: T.H. Culter, Chief Engineer; N.R. Sack, Bridge Engineer; Howard Mullins, Bridge and Resident Engineer for just under $37,000”. Information from Engineering News-Record, vol. 111, No. 13, September 28, 1933

Green’s Mill Bridge was one of five bridges constructed when the Lake of the Ozarks, Missouri was created by constructing BagnelI Dam on the Osage River. Each of the five bridges spanned one of the five rivers that shape and sent water into the “Dragon Lake” of the Ozarks. Four of those five bridges have been demolished and replaced. Green’s Mill Bridge is the only one remaining.

Green’s Mill Historical Bridge, Inc, was organized in 2018 to preserve and maintain the bridge in its original location. To provide a public pedestrian attraction at the confluence of the Lake of the Ozarks and the ‘scenic flat-water floating and fishing Little Niangua River’. To make bridge and Ozarks history accessible to visitors by supporting Bridge engineering history and education. 

Green’s Mill bridge is a unique bridge in itself. A Self-Anchored Suspension Bridge is a bridge that is anchored to the deck and is held up by the towers.

The winning bid to build the bridge was accepted on June 7,1932 for just under $37,000. Construction started August 1,1932 and was completed March 25, 1933. At the time of construction, it was one of four self-anchored suspension bridges. The others are located in Pittsburg, Pa. and are known as the Three Sister Bridges. They span over the Allegany River.

The bridge design, a prototype, represents a daring exploration of structural design by the state highway department and ranks among Missouri’s most important early highway bridges. The bridge has been determined eligible for listing on National Register of the Historic Places under Criterion C for engineering as a nationally significant example of a self-anchored suspension bridge. **

^{** Clayton Fraser, Missouri Historic Bridge Inventory (Draft), “Little Niangua River Bridge Data Sheet,” Loveland, Colorado: Fraser design, 1996, available at Historic Preservation Section, Missouri Department of Transportation, Jefferson City, Missouri.}

 ^{*Howard Mullins, MO Highway Department, 1933, Engineering News -Record, Vol. 111, No. 13, September 28, 1933}

History

Meandering from Dallas County headwaters to the Lake of the Ozarks at Green’s Mills Bridge, the Little Niangua River invited visitors to quiet contemplation of Ozarks life and history. 

The Osage word “Niangua” means “many springs”. The quiet flat-water river sheltered the legendary Osage people; attracted early traders and trappers; welcomed Westward Expansion settlers from Kentucky and Tennessee.

For two centuries, life along five Ozark rivers flourished. Fording the Little Niangua to meet neighbors and established trade, families prospered in its fertile valleys. Locals recall the villages of Nonsuch, on the river’s west bank, and Coelleda, across the river, which boasted both a store and a one-room school. Green’s Mill, upstream from the site of its namesake bridge, was a center of community life. As early logging ventures accelerated, rough trails and tiny villages developed into gravel roads and towns. Small boats, ferries, and log tie rafts plied the rivers.

In 1929, work began on the hydroelectric Bagnell Dam on the Osage River. Fed by five tributaries, the Osage River basin created the famed Lake of the Ozarks!

The lake’s rising water breached riverbanks, destroyed shallow river fords, and submerged valleys. Ozarker’s migrated to the hills to re-imagine their lives.

 Five new bridges were constructed across the wide river-arms of the ‘Dragon Lake’ in the Ozarks. Today, propelled by boating and recreation, lake living and health care, education and entertainment, perpetual traffic prevails, so: Four of the Lake’s original bridges have been destroyed.

One remains – GREEN’S MILL HISTORICAL BRIDGE

Engineering Background

Green’s Mill Bridge is a self-anchored suspension bridge, as opposed to an externally anchored suspension bridge. This means the supports are connected to its deck, instead of being placed off of the bridge; a difference that has implications on various aspects of the bridge including construction staging, aesthetics and forces.

STAGE 1: The west bank of the Little Niangua River was used to stage construction and begin with the driving of a falsework timber trestle. Substructure construction began on August 1,1932 beginning with the east abutment. Work proceeded toward the west utilizing the trestle. Work on the superstructure started on February 1, 1933. Two towering piers were installed. The towers extended over 57 feet high. The bridge abutments on each side were put in place, but soil conditions don’t allow the abutments to take the tension load from the proposed cables. The abutments are designed to take the vertical load.

The girders and deck were built on top of the timber trestle falsework.

STAGE 2: At this point, the entire construction load of the bridge was supported by timber falsework trestle as ironworkers attached steel links and the 4 unit- 1-1/4 inch each main cable.

With main cables in place, ¾ inch hangars could be attached to the side stringers and to the main cable support. Forces flow from hangar to main cable, and the force is split between the tower piers and a lateral compressive force applied at each end of the stiffening stringers.

With the self-anchored suspension system in place, the construction team was free to demolish the falsework trestle below the deck and add in the finishing details like bridge railing and roadway signage.  Superstructure construction was completed March 25, 1933.

In 1997, the aging timber deck was placed with a rigid steel grid deck. *

*Taken in part by Tufts University student CEE 1292023 Joshua Callahan

 Adopting a Bridge

The idea of adopting a bridge started to sprout roots August 22, 2017, when a group of like-minded residents of Camden County answered a call posted by Karen Daniels, Sr. Historic Preservation, MoDOT Design Division in Jefferson City, Missouri to the possibility of adopting the Little Niangua River Bridge (S-391). A meeting was held with MoDOT, the State Historic Bridge Foundation, Camden County Historical Society and the State Highway Patrol Office.

The idea gained momentum in 2018 when Green’s Mill Historical Bridge, Inc. was formed with the intent of preserving this important piece of Camden County bridge history.  Our idea is to make Green’s Mill Bridge a historical destination as well as a venue for public gatherings.

In January 2020, the organization devised a Feasibility plan to submit to the Federal Highway Department with a detailed plan of what our organization wanted to do, the cost, how we were going to pay for it and the time it would take to complete. The organization was notified in March 2023 that MoDOT and the Federal Highway Department was accepting our bid to adopt this magnificent bridge.

Construction of a new bridge spanning the Little Niangua River was completed in August 2019. At that time, vehicle traffic was barred from crossing Green’s Mill Bridge. However, we encouraged pedestrians to visit this iconic bridge, walk across its unique roadway, take in the beautiful scenery surrounding it and breath in the pure unchanged atmosphere of history past.

    Why It Matters — Preserving Our Past For Future Generations

The self-anchored construction method so expertly used by the Green’s Mill Bridge is largely gone from modern bridge construction. Green’s Mill Historical Bridge stands unique as an aesthetic snapshot in time in the timeline of American steel bridge construction.

*^{Taken in part from Tuffs University student Joshua Callahan.}

Our Mission

To provide the preservation and the beautification of the Green’s Mill Historical Bridge and its environment so that the public may enjoy the benefits of an historic pedestrian bridge for education, recreation, exercise, access to river views, community and cultural for future generations.