Cable-Stayed Bridges - Sundial Bridge (8)

One last look at the Sundial Bridge. What I called a crackled glaze on the pedestal supporting the tower actually looks like broken pieces of white ceramic pottery grouted onto the surface. This was a technique used to great effect by Calatrava's countryman Antonio Gaudi in Park Guell (and in many other works).

This is a nice view of the bridge from under the deck, reinforcing yesterday's statement that you can't take a bad photo of this bridge.

The watercolor below must have been an early conceptual sketch Caltrava made to visualize the forces in his bridge. Writing this blog reminded me of some of the recent posts from the Tall Bridge Guy on painting, painted bridges, and on 3D computer graphics.

It's apparent that Calatrava is expert in all three forms of expression. His video of the Calgary Bridge was a thoughtful exploration of how the bridge would look at different times of day and at different times of the year. His roughest sketches are full of thought and feeling, And even though this bridge is painted white, it has elements of mosaic and sculpture.

Cable-Stayed Bridges - Sundial Bridge (8) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Cable-Stayed Bridges - Sundial Bridge (7)

The completed Sundial Bridge is very pretty, due to the perseverance of the investors, engineers, fabricators, builders, as well as due to Calatrava's design. It's hard to take an ugly photo of the bridge. This is largely because all the details and transitions have been carefully thought out.

Are all Calatrava's bridges white? It's a nice color for them since it accentuates the clean lines of the structure. Note how the end of the barrier rail has a crackle glaze, which is most often seen on Asian pottery. The tower supports have the same crackle texture.

The thin trapezoidal slots in the tower are repeated in the lights at the ends of the rails as well as in the metal railings. I like how the metal rails project outward from the deck before coming back in.

I wonder what it's like riding a bike on the glass surface? I don't like riding my bike on the metal grating of movable bridges, especially when it's wet. I imagine wet glass is even worse!

Cable-Stayed Bridges - Sundial Bridge (7) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Cable-Stayed Bridges - Sundial Bridge (5)

A composite view of the tower model, the tower during construction, and the tower on the completed bridge. I imagine the back bearings are in tension and the front bearing is in compression to resist the overturning force of the cables pulling on the tower. However, it's possible that since the tower leans backward and has such a heavy base that all three bearings stay in compression (and shear). Also the large tower base can resist the bending and shear from the cables pulling on the tower.

The cables are in a harp-arrangement. They are attached to steel arms on the side of the tower and to the vertical elements in the superstructure segments. They call this kind of bridge a 'cantilever spar' to differentiate it from cable-stayed bridges that support the superstructure by balancing the load on each side of the tower.

Note the vertical slots along the edge of the tower. Its possible they have a structural function, but I doubt it. They look more like ornamentation, like the openings they used to put in the sides of a Buick. Also, the glass deck looks nice on the bridge. However, at first, the tiles were prone to shattering whenever a hard object was accidentally dropped on them.

The tower points north and is used as a sundial in the park surrounding the bridge. The shadow moves fast enough so that you can perceive the Earth spinning on it's axis.

Cable-Stayed Bridges - Sundial Bridge (5) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Cable-Stayed Bridge - Sundial Bridge (4)

The superstructure that carries foot (and bicycle) traffic on the Sundial Bridge is built from triangular segments with a central spoke, similar to the vertebrae that supports human beings. Calatrava's work is often inspired by the human figure or by human structural elements.

In this photo we can see the unpainted tower behind the assembled superstructure with additional superstructure elements in the foreground. Cable stays are in rolled-up coils beside them. All that remains to do is put the remaining superstructure elements together and hang them from the tower.

Cable-Stayed Bridges - Sundial Bridge (4) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Cable-Stayed Bridge - Sundial Bridge (3)

A view under the tower of the Sundial Bridge. Note the concrete pedestals, which were used to jack the tower into place. Afterwards, the tower was painted and the columns were removed.

I was a little surprised that the tower sat on bearings. I imagined a strong earthquake could easily knock it over. Apparently its self-weight provides a sufficient restoring moment to keep it stable for seismic and wind loads.

Also note how the superstructure is attached to the tower at this location. To the west are cables that descend from the tower and support the superstructure. Unlike a conventional cable-stayed bridge, there is no back span to balance the tower and support the main span. Instead the tower slopes backward to support the main span.

Cable-Stayed Bridge - Sundial Bridge (3) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Cable-Stayed Bridges - Sundial Bridge (2)

Since we looked at a Calatrava-like bridge yesterday, I thought we might as well look at the real thing today.

I visited Calatrava's Sundial Bridge while it was being constructed (it's located on the Sacramento River just south of Redding in Turtle Bay). The engineer in charge felt that this project was different from a regular bridge construction project. For one thing, no one had any idea how much the bridge would cost. The owners just kept providing money until it got built. Also, the engineer complained that Calatrava provided very little engineering support for the project. Most of the details and much of the analysis was done by the project engineer. Finally, there were a lot of delays with the fabrication of the steel segments used to assemble the tower. The geometry of the sections and how they fit together must have been a matter of some concern since there were several models of the tower constructed of cardboard on the engineer's desk. I don't think Caltrava ever visited the site while the bridge was being constructed. Despite all of the problems, the owners were fortunate that they persevered and got an original Caltrava-designed bridge in the end.

In this photo, the tower is sitting on three bearings on the east side of the river while the skeletal superstructure is being assembled. Once the east side of the bridge was assembled, they had to take apart the crane and rebuild it on the west side of the river. We'll take another look at this interesting bridge tomorrow.

Cable-Stayed Bridges - Sundial Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Arch Bridges: Lake Redding Bridge

The Lake Redding Bridge was built in 1996 to replace the 1915 Diestelhorst Bridge as a vehicle crossing over the Sacramento River. The Diestelhorst Bridge is a historic structure that remains in place as a pedestrian bridge.

Both bridges are multi-span, open spandrel arch bridges. However, the Diestelhorst bridge has spandrel piers while the new Lake Redding Bridge has narrow open arches supporting a wide, prestressed concrete deck.

The Lake Redding Bridge is another attractive structure by Mark Ketchum and OPAC Consultants. It is a five span, 659 ft (200 m) long, 44 ft (13.4 m) wide bridge. The arches are supported on spread footings in bedrock and abutments on piles to resist the longitudinal arch forces. Steel piles also supported the construction trestle and the concrete formwork.

Arch Bridges: Lake Redding Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution 3.0 United States License.

Cable-Stayed Bridges: The Sundial Bridge

Redding, California is an unusual location for a bridge designed by the famous architect/engineer Santiago Calatrava. Normally, only the richest cities can afford a work by this visionary artist. However, a group of the city's supporters were able to provide sufficient funding to ensure that the Sundial Bridge was eventually built (in 2004).

Much of the engineering was done by the engineers hired to oversee its construction. Moreover, there was no agreement with the contractor over the price. It was a 'force' contract, where money was provided until the bridge was built. The cost eventually rose to over 23 million dollars or $1400 per square foot for the 700' long by 23' wide bridge (pedestrian bridges typically cost about $200 per square foot).

However, the Sundial Bridge has lured millions of visitors to the little nature center at Turtle Bay. It is an unusual cable-stayed bridge with a single tower supporting the superstructure from one end of the bridge. The bridge deck is made of glass panels that turned out to be easily broken when items were dropped onto it. On a sunny day, the shadow cast by the 217' tower moves a foot a minute across the dial constructed on the north side of the Sacramento River.

Cable-Stayed Bridges: The Sundial Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution 3.0 United States License.