Sunday, April 8, 2018

3D Printed Bridges

Recently, a couple of firms have created short pedestrian bridges built with robots. The company MX3D created a steel bridge that was printed by a robot (with the help from ARUP and Autodesk). The bridge was built off-site and it will be carried to a river in Amsterdam where it will be assembled. The original design was to be printed at the site but it was so complicated they had trouble analyzing (or building) it. They scaled back their ambitions slightly for this somewhat more practical design (photo of steel bridge by Adriaan de Groot).
A similarly organic-shaped bridge was printed using microfibers and cement as ink. However, unlike the steel bridge, the concrete bridge has already been assembled on site in Alcobendas (northeast Madrid). The bridge was designed by the Institute of Advanced Architecture of Catalonia (IAAC) and constructed by Acciona using a machine that was designed and built by D-Shape (photo of concrete bridge by IAAC).

Both bridges turned out to require much more work (and more money) than was originally anticipated. However, such struggles should be expected when developing new technologies. What it means for me and other human bridge engineers is less certain.

Sunday, April 1, 2018

Humboldt County Bridges: Highway 101 Bridge across the Eel River at Rio Dell

September 2013 (40.50967-124.12001) Eel River Bridge
The Eel River Bridge (04 0016R) was built in 1940 with an unfortunate geometry, structure-type, and design for the site. It was originally a three span Pratt through truss bridge, but log jams during floods caused so much damage that the third truss span (and most of the girder spans) had to be replaced in 1964 (see photo below).
The piers were so vulnerable due to earthquakes that lead-rubber isolation bearings were eventually placed between the piers and bearings (in 1986) to reduce the inertia forces from the heavy truss spans.
Also, the remaining through truss spans were constantly in need of repair due to oversize loads damaging the cross-bracing (see photo below).
This bridge is now 78 years old, but it needed constant work to remain in service.

Sunday, March 25, 2018

Mendocino County Bridges: Route 271 Bridges across Big Dann and Cedar Creek

2000 (39.84861-123.70222) Cedar Creek Bridge
When State Highway 101 was completed, old State Route 271 was relinquished to the county. However local residents continued to use the Big Dann (10 0030) and Cedar Creek (10 0029) bridges (on 271) to get to and from their homes. The cost to seismically retrofit these big bridges would have been millions of dollars and so the residents agreed to the installation of seismic gates instead. When an earthquake occurs, the ground shaking will close the gates, preventing people from driving onto the bridges.

Sunday, March 18, 2018

Southwest Eighth Street Pedestrian Bridge Collapse in Miami, Florida

Like many of you, I was shocked and saddened by the news that a pedestrian bridge collapsed while it was being constructed across Southwest Eighth Street in Miami, Florida. As a bridge engineer I'm always worried about making a mistake that could result in similar damage.
This bridge was being built using accelerated bridge construction (ABC) techniques, which are meant to get bridges built faster and more safely. Hopefully we'll learn some lessons from this collapse that will make bridge design and construction even safer in the future.

Sunday, March 11, 2018

Mendocino County Bridges: Confusion Hill Bridges Carrying Highway 101 across the South Fork of the Eel River

August 2010 (39.92088-123.76359) Confusion Hill Bridges
The Confusion Hill Bridges are two structures that carry Highway 101 across the South Fork of the Eel River in Mendocino County. The bridges were designed and constructed to avoid a massive landslide on the south bank of the river.  The North Bridge (10 0299) was completed in July of 2009 and the South Bridge (10 0300) was completed in September 2009 and the bypass was opened in October of 2009.

The North Bridge is a 581 ft long continuous prestressed box girder bridge on sloping single column bents (see top photo). This shorter bridge was built using the traditional method of supporting the wet concrete and rebar on falsework.

The South Bridge is a long three span continuous prestressed box girder bridge on vertical single column bents. It has a total length of 1239 ft (348 ft, 571 ft, 436 ft). It was built segmentally using cantilever construction (where the weight of the cured concrete supports the cantilevered spans).

Both bridges were designed by Caltrans engineers and built by Finley Engineering Group out of Tallahassee, Florida and by MCM Construction of California.

Sunday, March 4, 2018

Mendocino County Bridges: Philo Greenwood Road Bridge across the Navarro River

August 2017 (39.08580-123.48450) Philo Greenwood Road Bridge
Continuing northwest from last week's Russian River Bridge, we arrived at the Philo Greenwood Road Bridge across the Navarro River. This is an open spandrel arch bridge (with timber approaches) that was built in 1951. The arch span is 130 ft long and the entire structure is 352 ft long.
The twin arches are founded in rock on each river bank and support a thin deck on spandrel columns. This is a local agency bridge (10C0032) supporting a county road.
The Navarro River is 28 miles long and flows northwest through the Coastal Range to the Pacific. Philo is the name of a town and Greenwood is the name of a ridge that are connected by the road.
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Sunday, February 25, 2018

Mendocino County, California Bridges: Highway 101 Bridge across the Russian River

August 2017 (38.95389-123.10167) Russian River Bridge
We've gone back to Mendocino County to look at bridges we missed during our last trip in August. California built a realignment of Highway 101 in 1933 that included this bridge over the Russian River. We can see in the photo above that the bridge has long (steel girder) approaches on both ends. The main span is a steel through truss bridge but with such a high skew that the portal and sway braces are attached to the previous panels. In the plan view below we can see more clearly how the end panels are cut to accommodate the skewed bracing.
The main span is 245 ft long and the total bridge is 1125 ft long over the Russian River flood plain. The Russian River is the second longest waterway in California with a length of 110 miles. It was originally called the Ashokawna by the First Nation people and then Slavyanka by Russian fur traders in 1817. It's a surprisingly wild river, especially during the winter. Beavers were once hunted along the river and even today 8 ft long sturgeons have been caught in its deeper regions.
The river flows south nearly parallel to Highway 101 causing the bridge to have its high skew. Past our bridge it eventually turns west for about 40 miles before emptying into the Pacific near Jenner. Despite the river being somewhat isolated I counted about 20 major bridges crossing the river including it's forks (the East Russian River) and tributaries (Austin Creek). You can look at some of these interesting bridges on my website or on the Bridgehunter website.
The vertical clearance of the through truss is limited by the cross bracing at the top. The minimum vertical clearance = 15' - 4", which makes the bridge structurally deficient (see photo below). We can also see in the photo below that the road is climbing out of the Alexander Valley and over the Mayacamas Mountains to the north (shown in the background).
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Sunday, February 18, 2018

Shasta County Bridges: Pedestrian Bridge across Big Chico Creek

February 2018 (39.731, -121.844) Big Chico Creek Bridge
I drove to Chico to visit my granddaughter who took me on a tour of Chico State University. Winding its way through campus is the Big Chico Creek with several bridges that carry students to class.
This week's structure is a prefabricated through truss pedestrian bridge made of Corten steel by Big R Bridges out of Greeley, Colorado. I though the red color went nicely with all the trees on campus. There is a sign by the bridge that states the maximum load is 72,000 lbs. That is the load of an AASHTO LRFD HL 93 truck whose three axles are 32 kips, 32 kips, and 8 kips. I would imagine that the allowable pedestrian load is much higher.
The bridge looks pretty strong and it's carrying a large utility load on both overhangs (see photo below). This bridge is a Pratt truss because it carries the load through diagonal members sloping toward the center of the bridge. I count 12 - 8 ft long truss panels.
There is a tab screwed onto the ends of the truss with the vehicle loading (HL-93), a serial number, and the date the bridge was manufactured (January 2016). It's funny they designed this pedestrian bridge for a vehicular load. Maybe in an emergency it must be able to carry a truck load.  Information on when it was placed at the site (and the bridge's name) wasn't available.
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Sunday, February 11, 2018

Monterey County, California Bridges: Pfeiffer Canyon Bridge South of Big Sur (2)

October 2017 (36.239, -121.775) Pfeiffer Canyon Bridge (44 0298)
It was a year ago that I wrote about the landslide that damaged the Pfeiffer Canyon Bridge and the efforts to accelerate construction of the new bridge. The new bridge was completed in October, seven months after the 49 year old bridge was demolished. The old bridge had to be demolished first because the new bridge was build at the same location. A video of the new bridge's construction is available from Caltrans.
In the photo above we can see the superstructure being assembled from behind the abutment. The girders were built with enough camber to allow it to span half the distance before coming to rest on the temporary shoring before being dragged to the opposite abutment.
The replacement bridge is a single span 308 ft long steel girder bridge without piers, which will hopefully prevent future slides from impacting the bridge. Note the walkways (above) needed to allow the bridge to be painted and inspected.
The new bridge cost $24 million and was built by the Golden State Bridge Company in Benicia California. The steel girders were fabricated in Vallejo California. The bridge has a new bridge number (44 0298) and a bridge inspection was done on October 18th, even though the overhangs and abutments were still supported by falsework and the joint seals still needed to be installed (see top and bottom photos).

Sunday, February 4, 2018

Bridges of Mexico: Puente Ticumán across the Rio Yautepec in the State of Morelos

October 2017 (18.7308, -99.11915) Puente Ticumán
Damage to the Puente Ticuman from the  9/19/2017 Mexico Earthquake was reported by GEER Main Team member Prof. Alesandra Morales from the University of Puerto Rico.
She wrote:
Its a  classic embankment failure. The bridge is in good condition. Minor cracking prior to the earthquake.

What the workers told her:
1) Bridge was designed by Japanese Consultants.
2) Bridge was NOT designed for heavy loads.
3) Bridge was being use for heavy loads (farming industry).
4) There's a steel bridge that runs parallel to this one and its the one that is currently being used by the locals (alternate route).
5) They will only fix the entrance/exit to the bridge so people can use it for the moment.
6) A total reconstruction of the bridge will take place next year and they are thinking about using drilled shafts.
7) Lots of bees! 
Alesandra wrote "It appears that the masonry wingwalls failed and the suddenly unrestrained embankment slid down the hill.'
Alesandra's report makes the bridge site sound like an agriculture area but the Google Photo above makes it seem more like a resort! This area near Jojutla had the most serious earthquake damage, mostly related to weak and unstable soil.

Sunday, January 28, 2018

Bridges of Mexico: Puente Xiotepec Carrying Highway 95D across Rio Apatlaco in the State of Morelos

September 2017 (18.7625, -99.2343) Xiotepec Bridge
While my team investigated earthquake damage in the State of Puebla, another team was studying damage in the State of Morelos. That team found quite a bit of damage related to weak soils. A single span 125 ft long highway bridge on the Mexico City-Acapulco Highway 95D, south of Cuernavaca (and 50 miles south of Mexico City) collapsed during the 9/19/2017 Mexico Earthquake.

In the photo above, we can see that the span moved away from the south abutment and fell onto the banks of the Rio Apatlaco. By the time the second reconnaissance team got to the site, the bridge had been removed (see photo below) in preparation for building a replacement bridge on the site.
Fortunately, there was another bridge less than 200 yards away. Although Puente Xiotepec collapsed, Puente Xochitepec continued to carry traffic on Highway 95D across the river. Also,  Highway 95 (a few hundred yards to the west) remained undamaged (see Google Earth photo below).
Recorded ground motion in the area was too low to damage engineered structures but the soil was weaker and could cause damage to structures for peak ground accelerations (pga) as low as 0.10g. (see USGS ShakeMap below). The team that went to Moreles found a lot of soil-related earthquake damage.
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Sunday, January 21, 2018

Bridges of Mexico: Undercrossing over Calzada de la Viga in Mexico City

September 2017 (19.3696, -99.12248) UC Eje 2 Ote Calzada de la Viga
My next few blogs include photos taken by other earthquake reconnaissance team members and collaborators. Professor Eduardo Miranda of Stanford shared some photos of an undercrossing (where a highway goes over a road) that had some damage from the 9/19/2017 earthquake. This is where the Circuito Interior Avenida Rio Churubusco goes over Eje 2 Ote Calzada de la Viga.
I really like all the information In Prof. Miranda's photos. The photos show the direction of the camera and whether it is level, the latitude, longitude, azimuth, and bearing, the elevation above sea level and the time. The only problem with so much information is that it's hard to see the bridge! If we look closely we can see the undercrossing is two parallel continuous box girder superstructures supported on wide piers with shear keys at the ends of the drop bent caps.
In the photo above we see that the ground is torn up, most likely from rocking of the foundations that support the piers.
The photo above shows a masonry abutment which was damaged due to banging of the superstructure against the shear walls. It's not a good idea to built masonry elements on bridges unless they are well reinforced. I don't see any reinforcement in this abutment.
In the photo above we can see that the undercrossing has a long center span over the roadway and two very short spans with masonry abutments at the ends. It seems like the piers and the abutments couldn't laterally support the long center span, which resulted in rocking of the piers and damage to the abutments.
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Sunday, January 14, 2018

Bridges of Mexico: Pedestrian Overcrossing across Blvd. Adolfo Ruiz Continues in Mexico City

September 2017 (19.2913, -99.1105)
There were just a couple of bridge collapses during the 9/19/2017 Mexico Earthquake. A Pedestrian Overcrossing across Blvd. Adolfo Ruiz Cortines (taken from Google Earth) is shown before the earthquake. The supports are slender single column bents with slotted bent caps to support the single girder spans.

The superstructure must have been made up of simple spans supported on a narrow seat. This allowed the bridge to come apart when it was shaken during the earthquake, unfortunately landing on a passing cab. Bridge designers must provide continuity or very large seats in order to protect human lives at locations where earthquakes can occur.