Time Lapse Movies of the Construction
The following are time lapse photos taken of the Memorial Bridge Construction Process. Helmar Herman has developed special software to collect and edit these high definition photos of the Memorial Bridge construction process. Thanks to Helmar for the work.
First half of April - Completing the North Tower and decking the North Truss Span
Last half of March - The North Counterweight
Floating in the North Span on March 6, 2013
Beginning to build the tower of the South Span (time lapse)
January 5 till the float in of the South Span (time lapse)
Floating in the South Flanking Span of the New Bridge
Finishing the Micropiles on Pier 3 through January 5, 2013
Continued preparation of the Piers through early December 2012
Preparing the Piers for the New Bridge
Floating Out the North Span
Removing the Towers on the North Span and Readying for Float Out
South Span leaves and begin taking down the tower of the North Span
The tower of the south span is removed and the span lifted onto the barge.
Early March - The cranes get ready and one needs repair
End of February and First of March Preparations
Miss Stacy's Great Adventure
The Towers are Decapitated and the Center Span Leaves
Center Span waits for Final Departure
Removing the Center Span
Preparing for the Float Out - Early February
Late January 2012
Early January 2012
New Design Selected - Many Technical Innovations
The New Memorial Bridge will look different. Some have characterized it as sleek, some as having a reference to the old bridge, and others have characterized it as lacking style and being downright ugly. What we know is that beauty is in the eye of the beholder. The old bridge has been characterized in many ways before and to this day. Not all of those characterizations have been complementary. What we can all agree on is that it has been familiar, and we have become comfortable with its design. But change we must. So lets focus on what we get for $81.4 million.
What is really interesting are the various technical innovations that are incorporated into the New Memorial Bridge. These range from innovative construction techniques, to design elements, materials, lighting, maintenance and operations. And this does not include the enhancements to the bridge's functionality. Here are just a few:
The New Memorial Bridge will be a significant improvement in function for all of us, whether we are on foot, in autos, or on the river. The roadways will be of similar width, but there will also be 5 foot bicycle pathways in each direction, going all the way across the bridge. Cyclists will not have to dismount and walk on the sidewalks because 1) there will be dedicated lanes, and 2) there will be a solid roadway (no steel grating) on the lift span. Pedestrians will gain as well. The sidewalks will be 6 feet on both sides of the bridge. The cyclists will be on the roadway, making the walkways more usable. The wooden planking will be replaced with non-slip treading, and the current obstructions will be gone.
NOTE: Updated plans include observation Belvederes (observation bump outs) on both the North and South Fixed Spans. In addition, there will be no guard rail between the road and the sidewalk. Instead, the guard rail will be adjacent to the structural members of the bridge.
Pedestrian Walkways are unobstructed
Roadway and Cyclist Lanes Improve the Traffic Flow
Maritime Traffic Improved
The traffic in the river will be pleased to find out that the New Memorial Bridge will have slightly increased vertical clearance when the bridge is in its lower position. The Old Memorial Bridge had a clearance of 19 feet above high tide, and the new bridge will have an additional two feet, bringing the clearance to 21 feet. This may not sound like much, but in will slightly reduce the number of lifts and will improve the flow of traffic in the river. The New Bridge will also operate 25% faster than the old bridge. This means that mariners will be able to move through the channel without having to wait as long for a lift. The vertical and horizontal clearances when the bridge is open will be the same as they are today.
Open Bridge has 150' Vertical Clearance
The winning contractor has committed to completing the New Memorial Bridge by July 3, 2013. Their schedule was almost six months faster than the other two competitors. How do they do it? Is the schedule a real reflection of what they can do? We will have to wait and see, but some of the construction techniques and design elements give us a clue to their ability to do the job so much faster. The first has to do with the piers that support the bridge, and the second focuses on the design of the three "truss" sections.
Can 90 year Old Piers support the New Bridge for another 100?
The existing four piers supporting the Old Memorial Bridge consist of granite blocks and poured concrete resting on bedrock at the bottom of the Piscataqua River, 90 feet down. All the surveys of the piers indicate they are in good shape, with two exceptions. There is some deterioration of the concrete at the top of the piers, and that will have to be repaired. But the engineering design codes have changed in the last 90 years, now requiring that the foundations be earthquake proof. Piers that just rest on the bedrock are insufficient. Work on the river bottom during fish migration seasons is also prohibited.
The solution to these problems is also innovative. By drilling down through each of the piers, and installing a series of seven reinforced columns in each pier, the New Memorial Bridge will actually rest on the seven new columns rather than the 90 year old piers. The piers provide both protection to the new columns, but they also provide environmental protection for the fishery during construction, allowing the work to proceed during migration season. They act as an in-place coffer dam. The columns will each be drilled into the bedrock providing the earthquake protection.
Truss Design or Girder Design?
We are all familiar with the truss design of the Old Memorial Bridge. But did you know that historical truss design contributes to problems. One of the statistics mentioned in the design presentation was that 5% of the bridges in the US are of a truss design, and that they represent about 20% of the bridge failures. Where they fail is in the gusset plates. The gusset plates hold the bridge components (chords) together. The picture below gives a good look at the number of gusset plates just at one junction of the Old Memorial Bridge. Not a pretty picture.
Rusting Gusset Plates on Old Memorial Bridge
The I-35 Bridge in Minneapolis failed because of under-designed gusset plates that twisted and broke under compound stresses. Gusset plates are one of the most stressed portions of a truss bridge. So how do you get a "truss" style bridge and eliminate the gusset plates? HNTB (the engineering design firm) has come up with a solution that retains the look of a truss, but which eliminates the bulk of the gusset plates. The only ones that remain have stresses, but they are much simpler, and they are mostly out of the way of the salt used on the roadways. Here is a top-down view of the new design that provides a contrast to the picture above.
Gusset Plates used only to Splice girders together
What remains is a bridge that is made from I-beam girders, that when assembled look like a truss bridge, but which are structurally a girder bridge. The girders are spliced together with gusset plates, but they are not subject to the twisting loads of a traditional truss bridge, and they can be easily repaired when needed.
Identical truss Spans yield speed and Reduced Cost
What has certainly not passed anyone's eye is that each of the spans is identical. In fact they have been designed to be identical so that the company providing the components can "mass produce" them. The company providing the components is Structal from Claremont, NH. They specialize in steel fabrication, with a focus on bridges. (They are hiring.)
Building identical spans means that we will benefit from their ability to reduce the cost of manufacture. Having the company be a New Hampshire company means New Hampshire (and probably Vermont) people are working. The piece parts will be transported to Portsmouth for assembly, probably at the State Pier next to the Sarah Mildred Long Bridge prior to being floated into place.
Three Identical Spans
New Materials will last longer
The New Memorial Bridge will not rust any time soon. At least that is the plan. The entire structure will be built from new steel formulations that naturally resist rust better than the old steel used in the old bridge. But any steel placed in the maritime environment is subject to salt water corrosion. And that is before you treat snow and ice with salt. So the new bridge will be coated with zinc. Galvanizing is typically done by dipping steel in molten zinc. That is impractical for bridge components, due to their size. So they are spraying molten zinc onto each of the components before it leaves the factory. Add a clear coat spray of polyurethane and you get an iridescent gray green color. The new bridge will have a completely new look. And it will be almost 50 years before they will have to touch up the zinc coating.
On the Old Memorial Bridge, there are sodium vapor street lights that cast a wide cone of light on the bridge itself, and illuminate much of Badgers Island. The lighting on the new bridge will use light emitting diodes. These LEDs will be much more efficient in terms of electric consumption, will last ten years or more, and will be highly directional. They will shine where they should (the road and walkways), and be less visible elsewhere. We might even be able to see the sky at night.
The question of "feature lighting" is still up in the air. Many people (stakeholders and others) would love to see the bridge lit, if only on special occasions. The lighting could be dramatic, and it would make our new, technically innovative design, an artistic feature of the community. Let's hope that this comes true.
Jim LaBranche has provided a picture of what "feature lighting" looks like on a truss bridge that spans the St. John's River in Jacksonville, Florida.
Memorial Bridge Design Options (Before the Contract was Let)
As the Memorial Bridge has gone through another emergency repair, just to maintain automobile traffic, we find ourselves captivated by the design issues. This note is to provide some context for the design options, and to make clear the impact that various design decision can have on the current published replacement for the Memorial Bridge.
NH DOT has proposed a design that is a "skyline replica" for the Memorial Bridge. Pictures of this proposed design can be seen below. The further the distance from this design, the more it looks just like the current bridge. The closer you get, the more you will see differences, including a solid surface on the lift section, wider bicycle lanes and less obstructed sidewalks. But you will also see that the lattice work of the current beams would be gone.
Recently some people have expressed an interest in a more modern design, citing some of the dramatic new designs that have been built in the past decade in Europe and Asia. (Here is a link to an article that will get you thinking.) All things being equal, I would love to have a new dramatic design for the bridge. But the selection of a design has implications on both time and cost.
All of the engineering assessments of the current bridge have agreed that the piers (foundations that support the bridge) are in good condition and can be used to support the new bridge. If we use the existing piers to support the new bridge, we gain cost and time, but we are limited in terms of the design options. If we want a design that requires changes to the piers, then we may get a striking design, but we sacrifice time, and probably money.
Why the trade-off? Several years ago the DOTs had completed the analysis and licensing process to rehabilitate the Memorial Bridge. That included, among other things an environmental review. There are other reviews, including historical and navigation reviews. But the environmental review typically takes the most time, is the most contentious, and the most expensive. If we do not disturb the piers, we will likely receive a "check list review" of the environmental impact, because we have already done the work. If we change the piers, there is a high probability we will need to go through a lengthy review process.
Two years ago I conducted a survey about the three bridges. One of the questions dealt with the design of the Memorial Bridge. Of the more than 550 who responded to the question, those who wanted to maintain the historical design outnumbered those who did not by more than 13 times. All this says is that two years ago, there was a strong preference for a bridge like that proposed by the NH DOT. It also says that there are people who would like something else.
As we approach the decision on the design of the Memorial Bridge replacement, what we do to the piers will determine when we will see the bridge completed. The piers limit the design options, and they can change the timing.
Let's make a wise decision.
Preliminary Design Renderings
These pictures may look like the real thing, but they were created using software, and are designed to give a first impression of what the replacement for the Memorial Bridge might look like. The first impression is it looks the same. But the closer you look, the more differences you will see.
Gone are the lattice beams that have led to the rusting. In their place are solid beams that will be easier to keep rust free. Gone is the steel grid center span. The bicycle lanes are 5' wide in both directions. The pedestrian walkways a full 6' wide. The bridge tender shelters are positioned to hang off to the side. The memorial plaque from the original bridge has a new home.
Remember, these are still in the early design phase, so there will be changes. But this should give you an idea of what is actually going to be built.
From the Portsmouth end of the bridge. Note the bike paths, new safety barriers, and the beams that replace the lattice work.
From the Harbor Place docks. Note the bridge tender house on the right.
From Prescott Park. Note the cantilevered bridge tender shelters opening the pedestrian walkways.