Nevada County, California Bridges: Independence Trail Bridges

November 2013 (39.29299 Degrees, -121.09459 Degrees) Independence Trail Bridges

We recently went for a hike along the Excelsior Canal, which was built in 1859 to carry water from the South Yuba River to hydraulic gold mining operations 25 miles away in Smartsville. The canal was a trench along steep hillsides with wooden flumes spanning across the ravines.

Considerable work was required to repair the flumes and turn the trench into a wheelchair accessible trail. The flumes have been turned into footbridges supported on tall timber piers with 'X' bracing.

The 'Independence Trail' is a part of the South Yuba River Project, which will eventually extend from Malakoff Diggins State Park to the confluence of the South Fork and Yuba Rivers. Today's visit was of the East Trail. I'm hoping to explore the West Trail (which has more elaborate flumes/bridges) soon.

Nevada County, California Bridges: Independence Trail Bridges by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

Ecuador's Bridges: Puente Rio Cupa (2)

The Rio Cupa bridge gets a surprising number of visitors in the course of a day. The heavy traffic explains why they first tried to build a vehicular bridge at this site.

The towers are 9.2 meters high and the deck is 1.3 meters wide. I'm standing at the west anchorage.  It's 23.9 meters to the west tower, 85.1 meters to the east tower, and 19.8 meters to the east anchorage. The east anchorage is 2 meters higher than the west anchorage.

The site was surveyed and a preliminary design was proposed by Walter in July of 2004. The design was checked by Toni Ruttimann and the bridge was built by Walter and the community of 5 de Agosto, Union Manabi later that year.

Ecuador's Bridges: Puente Rio Cupa (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Ecuador's Bridges: Puente Rio Baba (6)

This photo shows one of the anchorages for Puente Rio Baba. Walter (the designer and builder) is standing with one foot on the suspension cable and Zoe (from Bridges to Prosperity) is sitting next to him.

A metal frame made from pipes is embedded in the concrete of the anchorage and a length of cable is wrapped around the metal frame and extends outside the concrete. Walter weaves this cable into the suspension cable (he showed me how to do it, but now I can't remember).

Walter took me deep into the jungle to see how he surveyed the riverbanks near a village to see if he could build a bridge at the site. We traveled up and down the river in a dugout canoe with campesinos using machetes who clear a path for us.

Everyone was very grateful for Walter's work. Sometimes farmers would cut down bunches of bananas and other fruit and throw them into the back of Walter's truck. Once, we spent several hours surveying, and then Walter had to tell the villagers that the river was too wide for one of his bridges.

Ecuador's Bridges: Puente Rio Baba (6) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Ecuador's Bridges: Puente Rio Baba (5)

A view of the bottom of one of the towers for Puente Rio Baba. The pins for each tower (and a metal frame for each anchorage) are placed in the concrete before it is cured. Then the towers can be raised (usually with the help of a truck) and the suspension cables are attached to the top of the tower saddles and to the anchorages. Two or three struts provide lateral stability to the towers.

As I previously mentioned, the suspension cable has the same angle on each side of the tower so that the longitudinal force on each side of the tower is equal.  Also note that the hangers are made from a single cable that descends from one suspension cable, goes through a hole in one side of the floor beam, back up through a hole in the other side, and back up to the other suspension cable.

Ecuador's Bridges: Puente Rio Baba (5) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Ecuador's Bridges: Puente Rio Baba (4)

I've mentioned that a bridge looks very different from under the deck. Some bridges are more attractive from below, but they are usually not suspension bridges. However, the underside provides a lot of information on how the bridge works.

The floor beams for Puente Rio Baba are steel pipes hanging from the suspension cables. Timber stringers are staggered from side to side so that both ends of the stringers can be supported on the floor beams.

I believe that the villagers were responsible for supplying the timber used on Walter's bridge. After he completes his survey, he provides the villagers with a list of what he needs and if it's not there when he returns, he just drives on to the next village and the next bridge project.

Building these bridges is a communal process. It is quite common for villagers to have heated debates about the pros and cons of building a bridge. A firm commitment from the villagers is needed before Walter will begin a project. Because, the river can become dangerous or impassable during the rainy season, the standard of living for most people in the village will improve once they are able to safely cross the river.

Ecuador's Bridges: Puente Rio Baba (4) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Ecuador's Bridges: Puente Rio Baba (3)

After the anchorages and tower foundations have been poured and cured for one of Walter's bridges, then it can be assembled in a couple of days. The suspension cables are draped over the towers and attached to the anchorages. Then one or two people sit up on the suspension cables and attach precut stays every two meters. Floor beams are connected to each pair of stays and timber stringers are supported on the floor beams. Finally, wooden planks are laid on top of the timber stringers, hand railing and fencing is attached to the stays, and the bridge is complete.

For Puente Rio Baba, the deck also had to be anchored to the side of the cliff and steps were laid to help people get to the top. This isn't a bad solution when one bank is 40 meters higher than the other.

The deck is 102 meters long but the towers are 130 meters apart. The lower tower is 6.8 meters tall and the upper tower is only 3.9 meters tall. The anchorage is 23 meters behind the lower tower but only 9 meters behind the upper tower.

Toni wrote some software that Walter uses to determine the sizes of the towers and the lengths of the cables so he can cut everything out before construction begins.

We'll take another look at this interesting bridge tomorrow.

Ecuador's Bridges: Puente Rio Baba (3) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Ecuador's Bridges: Puente Rio Baba (2)

This bridge is a somewhat unusual design for Walter because it has one tower 40 meters above the other on a cliff on the other side of the river.

Walter began building bridges with Toni Ruttimann who had a strong desire to help the poor. Because neither Walter nor Toni were engineers, they came up with a very safe bridge design. As long as they maintained some simple geometric relationships and kept the span length below about 100 meters, they knew their bridges would be very safe. The towers were pinned and the force on each side of the tower was kept equal by making the angle of the cable the same on each side of each tower.

I called this bridge Puente Rio Baba but looking at my notes, I found that Walter called it Puente Santa Marianita, which is the name of the community that helped build the bridge. This bridge is in the country of Ecuador, the province of Pichincha, the canton of Santo Domingo, the parish of El Esfuerzo, and the community of Santa Marianita.

The Catholic Church plays a large role in rural life in Ecuador. We were sometimes accompanied by a priest to visit a bridge and then we would drive slowly because so many people would run out of their house to say hello or ask something from the priest.

We'll take another look at this bridge tomorrow.

Ecuador's Bridges: Puente Rio Baba (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Ecuador's Bridges: Puente Rio Baba (1)

I thought we might continue traveling south to look at some interesting bridges that I photographed in Ecuador.


In September The Happy Pontist devoted several blogs to voluntary organizations that provide bridges to help the rural poor. Coincidentally, I had recently spent some time in Ecuador for Bridges to Prosperity studying inexpensive bridges constructed (from used oil-drilling pipe and cable) by Walter Yánez. 


If a village wants a bridge, they can write to the provincial government. A vehicular bridge is preferred, but if that's not possible, Walter will come and perform a survey with an EDM and hand level to see if he can build a footbridge.  


He gives the villagers instructions on where to dig the holes and returns in about a month to pour the foundations and anchorages for the bridge. Then he'll return with the pipe and cable and work with the village to construct a suspension bridge up to 100 meters in length.


We'll take a closer look at Walter's bridge tomorrow.

Ecuador's Bridges: Puente Rio Baba (1) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

New York City's Bridges: Ward's Island Bridge

The Harlem River flows along the east side of Manhattan, north of Ward's Island. At the river's mouth is Ward's Island Bridge (sometimes referred to as the Harlem River Pedestrian Bridge), the only footbridge across the Harlem River. This rather spindly-looking structure was designed by Othmar Ammann in 1939, but because steel wasn't available until after the war, construction didn't begin until 1949.

It's a lift bridge with counterweights to raise the 330 ft long center span to the top of the towers. In fact, the bridge is only used from April to October and the center span is left in the raised position for the rest of the year.

The bridge consists of four ramps carrying pedestrians across FDR Drive on the Manhattan side, three spans across the Harlem River, and a gradual descent onto Ward's Island.

It has a modern, streamlined appearance, but because it is 937 ft long with tall towers and only 12 ft wide, it lacks a dramatic presence and appears flimsy.

New York City's Bridges: Ward's Island Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.