Tag: Bridges

The Flow of the River: What 2D Hydraulic Modeling Can Teach us about Movement

GIF image of 2D hydraulic modeling showing water under a bridge

Imagine trying to measure water in a beaker or in a measuring cup; it is stagnant and easy to follow the line of meniscus to see if it’s a ½ cup or 3/4. Then imagine measuring water in a river in order to build safer bridges; it tumbles over rocks, it changes speed, it experiences different water levels throughout a season.

Believe it or not, water movement is one of the most difficult phenomenon to solve. Yes, you can apply mathematics or numerical methods to solve complicated differential equations, but there are always some unknowns about turbulent flows (class 4 rapids) where general assumptions are made.

Rivers require intricate numerical models for river-type engineering problems, and I have been accepted to present on these intricate models at this years biennial National Hydraulic Engineering Conference (NHEC) in Columbus, Ohio. The Conference spans a week from 8/27 to 8/31, and I will be presenting on Friday, August 31st.

Per the NHEC website (https://www.ohio.edu/engineering/nhec/), the conference is themed “Advancing Hydraulic Engineering through Innovation and Resilient Design,” and will address the challenges that transportation agencies face to construct, maintain, sustain, and improve hydraulic structures in the physical, natural, social, and economic environments of today and tomorrow. At this conference, I will be presenting on Two-Dimensional (2D) Hydraulic Modeling with Tidal Boundary Conditions.

Modelers typically use computer software packages where you input topography, flows, roughness parameters, and hydraulic structures. The software package uses the input to solve mathematical equations. It seems simple enough, but a modeler needs to have a conceptual understanding of numerical methods and know the limitations of the software package being used.

Whenever you hear the term “3D,” you think of an object in a space that has 3-dimensions, right? Similarly, water moves within a 3-dimensional space, where there is a z-component (up, down), y-component (left, right), and x-component (back, forth). What if I were to tell you that the movement of water in the z-direction (up, down) is not considered?

What would that mean? Well, what that means is that mathematically, we are simplifying a very complicated problem:  we are restricting movement of water to flow/move in 2D, 2-directions (x and y) and that is what 2D hydraulics is all about. Similarly, a one-dimensional (1D) hydraulic model is defined when the y-direction is neglected and water is confined to moving in the x-direction.

2D hydraulic modeling is not that new and has been available in an academia setting since the 80s. But in recent years, tools to develop 2D models have been readily available to engineers. A 2D model can’t be developed for every problem that we tackle, but it allows us to accurately represent actual real world conditions, make less assumptions and judgment calls, and communicate and show visualizations of flow movement to stake holders.

What Droughts can Teach us about the Importance of Proper Culverts

hillsboroughnh-stonearch

July 2016 struck New England with an extreme drought and dry weather patterns for an entire year in most of the region. Many people are seeing the drought disappear as heavy rainfall replenishes those dry wells. Showers are taken a little less guiltily.

Yet ironically, the seacoast areas of Maine and (some) of New Hampshire are still considered abnormally dry for this time of year. The drought.gov website says that the percent of dry conditions for the Northeast is a total of less than 10 percent. In general, around 90 percent have no dry conditions at all. Despite this time of year being dryer for the coast, long-term totals actually appear normal.

So, why the pesky persistence with this abnormally dry issue?

“Much of the Northeast remains drought free with the exception of coastal Maine, which has been plagued by below-normal precipitation over the summer,” Deborah Bathke reported in the National Drought Summary for August 8, 2017.

Lack of rainfall may seem relatively insignificant in the engineering world to some. Too much rainfall can cause road erosion, mud slides, sewage overflows, and building floods (among other glorious things). Too little rain? Aside from a crispy lawn, what could go wrong?

Well, for starters, a dry season can mean that ground water levels are low. Low water levels mean that engineered structures, like culverts, don’t work like they are supposed to. Which can lead to problems for an entire ecosystem.

Culverts are a great example. Culverts allow for water passage — such as streams, creeks and brooks — to move under roads. Many aquatic species migrate during their lifetimes, so in order to do that, they need to be able to swim or wade through water freely. The National Oceanic and Atmospheric Administration (NOAA) explains that incorrectly engineered or installed dams and culverts can contribute to declining fish populations by not allowing continuous water flow and creating a physical barrier to fish passage. Throughout the watershed, there can be several examples of perched road crossing culverts (where a drop in elevation exists between the end of the culvert and the water body) and culverts that are too narrow, steep or collapsed.

As rain levels increase and droughts are ending, aquatic life has the chance to move more freely through these constricted passageways.

The importance of culverts can be partly attributed to the way the water flows.

culverts

 

The New England states have turned their attention to the importance of designing culverts that are eco-friendly for the past two decades, with regulations in place in each of the five states that require certain levels of flows, both high and low, to be maintained through culverts in order to protect migrating organisms. From an article by the US Fish & Wildlife Service of Alaska comes the challenge to make roads more fish-friendly:

“What’s under our roads should ideally mimic what’s upstream and downstream,” the article says. “This helps ensure a seamless transition for fish passing underneath. … So how wide is wide enough? To answer that, we must understand the stream’s range of flows. A stream gauge that tracks water level and documents flood events over time can help.”

When accurate stream gauge data is not available, particularly for the smaller creeks or brooks, engineers must examine the existing conditions and develop assumptions on flows, typically using hydrologic models that are standard industry practice.

In short, as you drive from place to place during your day, take time to notice the road culverts you pass over. They have an important role in keeping an ecosystem functioning at its best, even under drought conditions.

14 Steps for Preserving Steel Structures

Piermont, NH-Bradford, VT Steel Bridge

Preventative maintenance is defined as scheduled work at regular intervals with the goal to preserve the present condition and prevent future deficiencies. On bridge structures, this work is typically performed on structures rated in ‘fair’ or better condition with significant service life remaining. Minor repairs may be necessary to maintain the integrity of the structure and prevent major rehabilitation. Structures that are not maintained are more likely to deteriorate at a faster rate and require costlier treatments sooner than maintained structures; therefore, it is more cost effective to maintain structures to avoid replacement or major rehabilitation needs.

New England’s weather causes extreme conditions for steel bridge trusses, such as flooding, ice and snow. Corrosive de-icing agents are used in the winter, which can accelerate deterioration of exposed bridge elements. Preventative maintenance is critical for steel truss bridges to reach their intended design service life and, therefore, attain the lowest life-cycle cost of the bridge investment. Presented are minimum recommended guidelines for preventative maintenance of steel truss bridges.

Here are 14 actionable maintenance tasks to preserve historic truss bridges:

  1. General: Remove brush and vegetation around structure. Annually.
  2. Bridge Deck & Sidewalks: Sweep clean sand and other debris. Power wash with water to remove salt residue. Annually.
  3. Wearing Surface: Check for excessive cracking and deterioration. Annually. 
  4. Expansion Joint: Power wash with water to remove debris, sand and salt residue. Annually.
  5. Bolted Connections: Inspect for excessive corrosion or cracking of the steel fasteners. Check for any loose or missing bolts. Annually.
  6. Welded Connections: Check for cracking in the welds. Annually.
  7. Truss Members: Power wash with water to remove sand, salt and debris, particularly along the bottom chord. Give specific attention to debris accumulation within partially enclosed locations such as truss panel point connections or tubular members. Annually.
  8. Bridge Seats: Clean around bearings by flushing with water or air blast cleaning. Annually.
  9. NBIS Inspection: Complete inspection of all components of the steel truss bridge. Every 2 years unless on Red List.
  10. Painted Steel: Scrape or wire brush clean, prime and paint isolated areas of rusted steel. Every 2 to 4 years.
  11. Steel Members: Check for rust, other deterioration or distortion around rivets and bolts, and elements that come in contact with the bridge deck which may be susceptible to corrosion from roadway moisture and de-icing agents. Every 3 to 5 years.
  12. Bearings: Remove debris that may cause the bearings to lock and become incapable of movement. Check anchor bolts for damage and determine if they are secure. Every 3 to 5 years.
  13. Exposed Concrete Surfaces: Apply silane/siloxane sealers after cleaning and drying concrete surfaces. Every 4 years.
  14. Bridge & Approach Rail: Inspect for damage, loose or missing bolts, sharp edges or protrusions. Every 5 years.

Actions to Avoid

  • Do not bolt or weld to the structural steel members.
  • Do not remove any portion of the structure.
  • CAUTION! Paint may contain lead.

Additional resources can be found through the New Hampshire Division of Historical Resources website.

Pi vs. Chocolate Cream

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Pi… I did not forget the “e”, I am referring to the mathematical constant, π, for the value 3.141592…, a ratio of the circumference of a circle to its diameter. For some it was junior high and others it was high school, but almost everyone is taught the concept of Pi in geometry class in America. The staggering question asked by so many students over the years is “how do we use this in ‘real’ life?” Well we have answered that question for all of you as it relates to engineering:

When designing bridges many of the structures utilize reinforced concrete to provide the strength necessary to support its daily use by vehicles. For many of our bridge projects, the circle is most often representing the area of reinforcing steel used in the reinforced concrete beam.  We determine the total amount of the (steel) reinforcing to determine the capacity of a structural member such as a beam, deck or slab.

In associated roadway design, Pi is used in a slightly different manner, to calculate curvature. A maximum curvature (minimum radius) is used to ensure adequate sight distance at differing speed limits. This promotes safe vehicular travel by providing a level of comfort and expectation to the driver.

Another application for the mathematical constant is in airfield markings. Their purpose is simple – to safely guide pilots during aircraft take-offs and landings, and while taxiing around the airfield. To create these markings, Pi is utilized when calculating the amount of airfield paint required for runway designation markers, taxiway centerlines and edge lines.

Pi is also used extensively in the calculation of areas of gravity sewers, wastewater force mains, water main pipes, storm drains, drainage culverts and other types of utility pipes. These calculations are used to establish the area of the pipe for the purpose of determining flow velocities and flow volumes as well as other types of hydraulics calculations.

Now that we have proved your mathematics teacher correct, and that someday you may need to know the value of Pi, the obvious question remaining is “what does pi and pie have in common?” My answer is Pi is focused on circles, radius and diameters… and so does pie! If you want a great Chocolate Cream Pie recipe check this out!