Engineering

Precast Prestressed Concrete Bridges

PPC Precast Prestressed conrete bridge

In the particular county where I work, precast, prestressed concrete (PPC) bridges make up about 75% of the bridges on the local system.  These bridges are simple to construct, cost effective, and very durable.  I believe they are a great option for traversing small streams or grade separations.  One of the biggest enemies to any concrete bridge is salt.  In this part of the country, we do not use much road salt, so the degradation of the concrete is a very small issue.  The bridges are inspected every two years, and the deterioration of the beams is always checked.  If salt were to decay the concrete causing the exposure and degradation of the prestressing cables, then there would be major issues.  In areas where much road salt is used, precast, prestressed concrete beam construction may not be the best option.

 

PPC Deck Beam Bridge

For the most part, the construction of the PPC deck beam bridges is very simple.  Its pretty much a block of concrete over piling, with precast, prestressed beams on top.  There aren’t many pieces to the puzzle.  Soil borings are taken to determine the depth of the bedrock that the piling should rest upon.  Hydraulic surveys are done, taking into account the design year of the high water elevation. There are a few factors, including average daily traffic, that determine if the flood year to be considered is the 15 year high water, 20 year high water, etc.  One hundred year high water elevations are also determined.  Keeping these records is vital, as these elevations can be useful in determining the base flood elevation in the future if a floodplain is near the bridge. These type of bridges can also be used for railroad crossings. One of the major design concerns is for seismic activity.  Depending on which region the bridge will be in determines the design parameters.  In many cases, there is no need to purchase additional right of way, unless the road will be raised to an extent that would require the slopes be rebuilt to safer design criteria, or if the road needs to be realigned.

Once the plans have been approved, and the job has been bid, the construction is pretty straightforward.  Any old structure is removed, and piling is driven.  In cases where bedrock is shallow, piling may have to be drilled into the rock, or a spread footing wall may be built. The abutments are really just big blocks of concrete.  No matter if the bridge is 25 feet long or 80 (about the limit of single-span bridges of this type), the abutment designs are very similar.  They are reinforced with steel reinforcement bars.  In the cases of multi-span bridges, concrete piers are built.  Riprap can then be placed in necessary places before the beams are put on.  In areas of high velocity flows, it is important that the riprap be big enough not to wash away.  I have seen 150 pound riprap wash as far as 50 feet downstream.  After the abutments have cured for a week, the beams are placed on.  The first beam is always a nail biter.  If the bridge was not laid out properly, this is where it will show.  The beams are put on bearing pads, which are really just pieces of neoprene. Most of our bridges are 24′ wide, which may be either 6 four foot wide beams, or 8 three foot wide beams.  The beams are connected laterally so they act as one unit.  They are also ‘pinned’ into the abutments with large reinforcement bars the are set down into holes drilled into the abutments.  At this point any bridge rail may be installed, as well as pouring the last of the concrete which will act as a back wall.  The beams have ‘keys’ which will then need to be filled with grout.  One thing that we have always done, is place ‘flowable fill’ behind the abutments.  This keeps the dirt from settling, and creating a future speed bump.  Flowable fill is really nothing more than sand with some cement in it.  It goes in like quicksand, and gets hard like concrete.  But instead of having a strength of 3000 psi plus, its strength is more like 300 psi.  It can easily be dug out if necessary. The road can then be reconstructed with rock, asphalt, or oil and chip, depending on the existing surface.  Besides some tidying up and other item such as seeding if necessary, that is about it.  Where time constraints have been an issue, we have torn out a bridge and built a new one in two weeks-start to finish-before.  The only difference was a fast-setting concrete was used.

ppc deck beam precast prestressed railroad bridge

For many bridge replacements, in particular on local agency systems, I believe prestressed precast concrete deck beam bridges are a logical and economical choice.  When all factors are considered, in areas that are not susceptible to deterioration due to road salt, PPC bridges are a good fit due to their cost, quick construction time, and durability.

Vacate of Public Roads by Abandonment in Illinois

abandonment

Abandonment vs. Vacate

A fairly common question/concern that our office faces is what to do with a road that has been ‘abandoned’.  Some landowners want roads that are no longer being used to be permanently vacated to restrict access to their property.  Sometimes these old rights-of-way can become an issue of a property dispute when accessing private property.  Some people put gates on the road.  The road may be totally grown over with trees and brush.  In some instances, the road was platted out, but never actually built.  In Illinois, a road is considered public until it goes through the legal vacate process. Illinois does not consider ‘non-use’ to be a sufficient enough reason to consider a road vacated.

Anyone contesting that a road  is not open to public travel because it has been abandoned by non-use, has to have the issue resolved either through the local highway authorities or in the courts.   The simpler process is to go through the local highway authorities and proceed with a formal vacate process.  If it goes to court, the court is the entity that determines whether a roadway has been abandoned. The Illinois Department of Transportation has no policy or guidance in this area.  Issues of this nature are referred to the county engineer and the county state’s attorney.  IDOT would not be involved in any legal proceedings regarding this matter, since this is handled between the highway authority, the public, and the courts.  The courts would then consider three factors in determining if a road has been abandoned by non-use.

1. Non-use of the road for a period of time (the length of time is not defined; it is up to the court to decide that based on each case);

2. Whether or not the public acquired the legal right to use another route, either new or existing, for access;

3. Whether the necessity for the road has ceased to exist.  When a court finds that a highway has indeed been abandoned, the highway reverts to the original property owners.

The Vacate Process

For the complete process, please visit the Illinois Department of Transportation’s website.  This link will take you to the document that outlines the process of formally vacating a road.   The vacate process can be found in Chapters 10 through 20.

An important thing to remember is that the vacate process shall not deny anyone access to their property.  Even if the road is not being used, if it provides the only way of access to a property, then it cannot be vacated.  Once the road is vacated, the property should go back to the original owner if possible.  If this is not possible, then the property should be split equally and given to the owners on each side of the road.  This property should then be added to the tax rolls.   In a ruling that was passed in 2005, if the property owners refuse the rights, then the highway authority may sell the vacated property to a third party at fair market value.

So as a reminder, at least in the state of Illinois, abandonment or non-use of a public road does not mean it has been vacated.  Check with your local highway authorities, County Engineer, and possibly with your county’s mapping office on the ownership of a property before deciding if you wish to have a road vacated.

 

 

Bridge Load Rating Checklist

In the state of Illinois on April 15, 2016 Circular Letter 2016-10 was sent to all agencies concerning Load Ratings for bridges.  New truck configurations are being allowed, causing there to be more load per axle.  This letter stated that new load ratings are to be assigned for ALL bridges.  Engineering judgement is no long an acceptable form of bridge rating, and new ratings are to be assigned based on actual calculations.

bridge-load-rating-checklist

To help identify the structures that need in-depth analysis, a checklist has been established for all structures.   In response to changes in the AASHTO Manual for Bridge Evaluation (MBE), a September 29, 2011 FHWA memo allowed assigned load ratings so long as the following conditions are met.  The checklist is due for all identified structures by December 31, 2016.  IDOT has set up an Inspection Date Notification System in which the following checklist may be answered.

1. The bridge was designed and checked using either the AASHTO Load and Resistance Factor Design (LRFD) or Load Factor Design (LFD) methods to at least HL-93 or HS-20 live loads, respectively; and

2. The bridge was built in accordance with the design plans; and

3. No changes to the loading conditions or the structure condition have occurred that could reduce the inventory rating below the design load level; and

4. An evaluation has been completed and documented, determining that the force effects from State legal loads or permit loads do not exceed those from the design load; and

5. The checked design calculations, and relevant computer input and output information, must be accessible and referenced or included in the individual bridge records.

Question Number 4 was done by IDOT and results complete on October 5, 2016.   Our county alone has almost 200 structures that need the checklist submitted.  If all 5 conditions cannot be met, bridge plans MUST be electronically submitted to IDOT.   Item 5 is very difficult for our agency in general to locate because most of our bridges were built using IDOT’s standard bridge plans which have since been retired, or by using consultants.  Access to calculations which may be 40-50 years old in some cases just isn’t feasible.  That leaves the only option of submitting bridge plans.  The main issue will be FINDING the existing bridge plans.  This could potentially be a logistical nightmare.    Some of the older plans were large-format (24″x36″), and access to a copier/scanner that large may not be an option for some agencies.  And some agencies plain and simple may not have bridge plans for older structures.  There will be THOUSANDS of sets of bridge plans that will be submitted.  I cannot imagine who will be responsible for sifting through all of these, not to mention the space it will take to electronically store them.

There are approximately 26,000 bridges in Illinois.  Lets guess that half of them have the information available.  That leaves 13,000 bridges that must have plans submitted.  The bulk of that will be up to local agencies that may not have the personnel or equipment to make copies of everything.  My point of view is this:  Isn’t every set of bridge plans submitted to IDOT? Why don’t they already have copies?

I have sent a couple of e-mails to the IDOT Bureau of Bridges and Structures with questions about this last item.  So far no one has returned my message, but when I find something out for certain, I will update this post.

UPDATE 10/17/2016

The IDOT Bureau of Bridges and Structures has responded to my email.  They say if plans identify the loads as HS-20 or HL-93 and have the stamp of a Licensed Structural Engineer (Licensed Professional Engineer before 1989), then conditions One and Five are met.  If Standard Plans were used, they are considered signed by a Structural Engineer.

Right of Way

There are many questions that arise when referring to right of way.  Who has ownership?  What is the difference between fee simple and common law ownership?

Right o

 

First of all, Right of Way can be defined as follows:  The land, interest therein, acquired for and devoted to a highway.  The problem in this definition can be what constitutes ‘acquired’.  I will address this issue with respect to the state of Illinois;  Check your local and state regulations before making any kind of final decision on right of way.

Right of Way can be dedicated to a highway authority through a statutory or common law process.  Statutory dedication would of course be the preferred method.  This would consist of a platting process, and the end result is the fee simple (ownership) interest in the public jurisdiction to which the right of way is dedicated.   The landowner and highway authority will agree to a purchase price, and the process is recorded to make it legal.

Common law dedication occurs when there has been public use over a prolonged period of time.  Many times this may consist of privately owned property.   This would actually result in a right of way easement: the landowner still owes (and pays taxes on!) the property, but has transferred the authority to the highway authority for as long as it remains a road.  Some landowners do not realize this.  They think that by owning this, THEY have authority over the property.  Utilities can be an exception here.  When a utility company wants to install or repair utilities on ROW, they must contact and may even have a permit from the highway authority.  If the property in question is of a common law dedication, they MUST also have the permission of the land owner.

The land in a common law dedication may be quit-claimed to the highway authority, making the public body the landowner for that property.

Before doing any work in the right of way, the local highway authority MUST approve of any work performed.  This includes fences, culverts, mailboxes, signs, and even plants.  Each state or local agency may have its own rules for ‘setbacks’, or how far from the right of way construction should be.

To find out what the right of way is contact the proper highway department.  Many times a township may not know what the answer is, and might consult with the County Engineer for their county.  A search should be done for any dedicated right of way.  Some counties have mapping systems, or GIS, that map out where the right of way is.  In Illinois, the Illinois Department of Transportation has a field report record for every road that shows the right of way.  There can be conflicts between one or all of these methods, and the final answer can be engineers judgement at times.  To be conservative, I would say in case of conflict, use the smallest right of way.  In Illinois, the absolute minimum right of way by law is 40 feet.   This is for both dedicated and prescriptive right of way.   I have seen subdivision plats showing 30 feet, but that is in violation of the law, even if accepted by the local government.

I hope this has cleared up the differences in the kinds of right of way.  It is not always an easy answer, or one that a landowner wants to hear.

 

Culvert Collapse: Not Only Bridges Can Fail

When you think of a ‘collapse’, you normally think of a bridge. This is not always the case. Pipe culverts can collapse also, leading to devastating consequences. Just because there may not be a ‘structure’, does not mean there cannot be a collapse. I think when we imagine a culvert, we are thinking of a small pipe. But these pipes can be up to 10 feet in diameter, and maybe even bigger. So if a 10 foot pipe culvert would collapse, that could mean a 10 foot hole in the road! There are several factors that can lead to the failure of a culvert, with some failures happening suddenly, and some happening over time.

Culvert Collapse

Culvert Collapse

Some pipe culverts collapse due to material weakness. Metal culverts can become corroded from either chemicals from runoff, or from water sitting in them for extended periods. After time, the bottom may rust, then the culvert may fail.  Even though these culverts are typically designed for a 50 to 75 year service life, and have some type of corrosion protection (galvanization, asphalt coating,) corrosion may take plus much sooner.  This can be sudden, or may take years. Concrete culverts have a tendency to separate at the joints. One section may start to separate, maybe even causing a chain reaction. Sometimes an end section or even more than one, may fall completely off. This can lead to the road being too narrow and steep at the culvert. Groundhogs can even make the joints weak by burrowing on top of them.  Plastic culverts (HDPE, etc.) may also fail from joint separation, or possible material weakness. They can be affected by different factors such as sunlight.  Proper cover must be over the culverts as well, or loads can be transferred directly to the pipe without being distributed properly over the soil/road on top of the pipe.

Culverts that become obstructed can also pose a problem.  If debris is blocking a culvert, the water will find the path of least resistance.  The water may try to go around the culvert, or even under it.  In these instances, the pipe may be intact, but the soil around the culvert may wash out, creating a hazardous situation.  This could happen during a flood, at which point the soil may wash out and cause a sudden collapse of the road.

It is a good idea to set up some kind of inspection schedule and inventory when it comes to pipe culverts. If you notice a dip in the road, or cracking above a culvert, it probably needs to be inspected.

 

The Power of Water

This is an older post I have written, but with the recent hurricane Harvey affecting the Gulf coast, I thought it would be a relevant reminder.  Please, everyone affected by flooding, heed the officials call to evacuate, and do NOT try to drive through flooded roads!!

Last week I wrote an article on flooding.  Today I am giving a specific example of just what too much water too fast can do.

This occurred during a heavy spring rain.  There was over 4-1/2″ of rain in just a few hours.  This location had a 10′ diameter pipe that had over 3 feet of earth and rock cover over the top.

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This was the hole that was left after the wash out.  Notice the traffic control by a local resident.

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Finally, this is where the culvert ended up.  Again, this culvert was 10′ in diameter, and 20 feet long.  That put its weight at over 3,000 pounds.  Adding two feet of dirt adds 67,000 pounds and a foot of rock adds another 34,000 pounds.  That is a total of 104,000 pounds, or 52 tons.  It didn’t just move the culvert; it ended up about 60 feet downstream.  According to the EPA, the weight of the average car is 4,079 pounds or just over two tons.  So the water at this location moved 13 times that much material.

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Please do not underestimate the power of moving water when trying to drive through flooded roads!

Types of Road Oil

I have written a little review here of the different kinds of road oil our county uses for oil and chip projects.  I explain the differences between Rapid Set, High Float Emulsion, and High Float Polymer.

Feel free to comment on any kind you might use, or any suggestions for oil and chip roads in particular.

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