Winter Shenanigans

Yesterday, the power went off for about four hours. The high winds, and the colder air can cause problems with the power lines, and if it's a big enough problem, restoring power is a multi-step  process to keep the large breakers from throwing. Four hours is understandable, but a little inconvenient for my all electric home. 

Last night, at about 11:00, the power went out again. This time, the problem was from the big company power supplier, which turned out to be the original problem. The big difference was it was 16 hours before it came back on. 

So, the power is back on, the house is a toasty 67 degrees, and I had a chance to run my generator to keep it well maintained. Tomorrow I'll change the oil, put some fresh gasoline, cover it back up, and hope I won't have to use it again tonight. If I do, I won't wait long to fire it up. It's supposed to drop to about freezing, and the wind is still high.

Building a Bridge - Engineering Part 3

 Altogether, the posts on building a bridge will be numerous posts. I'm doing this to keep from a large volume, and hopefully, keep those interested from being bored. 

The next phase in engineering the building a bridge involves the drawing of plans, final funding, and the specifications for construction. How much goes on in the background is beyond my experience, but I have a feeling many projects are shot down before construction due to politics, and lack of funding. 

The plans are drawn by draftsmen using CAD programs. In the past, there drafting was done with pencils, and the drafting tools used for the craft. In my experience, AutoCad is the leading software package. It's expensive, especially when many of the plug-ins are purchased. Those proficient in the use of the software have my admiration. I base my opinion on what little experience I've had with simple two dimensional CAD programs. AutoCad is much more robust, more complicated, and can be used for some amazing, scaled three dimensional drawings. Considering the complexities, many of the drawings I've seen for construction projects are probably simple drawings for the more experienced draftsman.

With most bridge projects plans I've dealt with, the centerline proposed for the construction is the main control. Regardless of service roads, or surrounding structures, the centerline is the best baseline, since it eliminates any crossover stationing. I ,once, bid on parts of a project designed by a consulting firm, which had a very confusing conglomeration of stationing. Since the project involved many sections of highways with existing stationing, including the stationing was probably their solution to the complex problem of converting all stationing to one baseline. Their job was probably easier, but to the contractor, examining the plans was tedious. 

With a baseline, there is a starting point, which on a new project will be station 0+00. With tie-ins, or renovations of an existing road, the stationing for the project may start at some station as 256+58.5 which would be part, or a continuation, of a project point that had 256 one hundred feet stations, plus 58 feet 6  inches, which is 6/12 or .50 feet. I have worked with metric, when TxDot dabbled in metrics, and found the English units too entrenched to stay at metrics. Metrics are easier to use for calculations, but many manufacturers have English dimensioning, and these dimensions don't quite match the metric dimensions. Soft metrics can be used, but in reality, manufacturers aren't going to spend millions to convert, and in engineering, the calculations don't quite match. Since materials strengths, and dimensions require accurate calculations, errors in converting data can lead to problems. 

In stationing, and the centerline is used for the baseline, offsets are used to indicate future, or existing sections. With a 60 feet wide road, the edges would be defined by left and right offsets. At station 100+00, the far right edge would be station 100+00 - 30 feet right (100 feet from the starting point, and 30 feet perpendicular from that point). The left edge 100+00 - 30 feet left. It's an easy method to determine locations, and when it comes down to existing utilities, it's important to the owners to understand where, and how far to move any obstructing utilities. Utilities are usually moved before projects are let, since the operation can take a long time. Contractors charge for downtime, and justifiably so. Equipment, labor, and time add costs, which a contractor must learn how to handle. Failing to fall procedures outlined in the specifications, which are part of the contract, can lead to monetary losses by the contractor, and a bad working relationship between the engineers and contractor.

The plans are not just drawings of the future bridge. With TxDot, and most Texas municipal drawings that usually follow TxDot standards, included are a multitude of pages with standard drawings, paving designs, drainage structures, elevations views, existing utilities, typical design sheets, phasing, traffic control, environmental protection requirements, quantities, typical sections, and any special design features. There are more, but to really understand the requirements, you would have to examine the TxDot website that details the necessary requirements. Last, but not least, are the specifications for the project, which reference what is commonly called the "Bible". Txdot occasionally updates their standard specification book, which has all the standard construction, and material requirements. An important reference is always available for approved material suppliers. These suppliers provide materials that were tested by TxDot, and in some situations, a contractor can have a problem by bidding using a material not supplied by an approved supplier. The cost difference may be substantial, and lead to financial woes for the contractor.

Usually, there's a pre-bid meeting. The bidders may just meet at the office of the owner, an onsite meeting may be all that's required, or both may occur at the pre-bid. It's at this point questions are asked, answers are produced, or the engineer will answer the questions in writing before the bid date. If an addendum is required, it will be issued before the bid date. Acknowledging the receipt of addendums is usually part of the bid documents, and failing to acknowledge the addendum will lead to a bid being thrown out.

When all is compiled, checked, and approved, the project is released for bids. This leads to the contractor to examine the plans, and specifications, figure out the costs associated to perform the work, add a profit, fill out all the blanks correctly, notify the bonding company, and cross their fingers.

Bidding is once a month for TxDot projects, and at council meetings for cities. The bids are checked for following the rules of bidding, and any numerical irregularities. Whether the bid is local, or let in a multiple bid letting, some allow electronic bidding. It's at this point the contractor finds out if they won the bid, and can now start worrying about what they left out. Some are so far out of balance, the contractor is consulted, and allowed to remove their bid. This can come at a price, if the project requires a bid bond. The contractor forfeits the bond, and the bonding company frowns upon such things. 

The engineers might find they substantially underpriced the project, and wonder why. That, and if their track record with the contractor usually ends up with change orders for all their mistakes, they may wonder what their exposure will be, and how much it will cost. It's now their job to go through all the paperwork of the bid, and the contractor  will eventually be given a contract to sign. After signing, the contractor has to start submitting material sources, subcontractors, schedules, and have all prepared before the pre-construction meeting. When the start construction date is set, time is started on the project. Whether its a few months, or a few days, the contractor submitted schedule is used as a club, when the project falls behind.

Now it's time to start the project, and a new post.

Building a Bridge - Engineering Part 2

 I've worked on, or built, a few bridges during my career. Most were beam and girder, with one being a large cable stay bridge. When looking at the design, the fact they were built is a testament to wonders of modern engineering. The fact they stand for so long shows the design wasn't a foolish whim of a demented person, and after working on some older structures, the fine tuning of the design of newer bridges indicates some designs are now obsolete; even though the less desirable designs are still in use and safe. 

Not all bridges make it to the construction phase. We had a local bridge designed to the point a three dimensional model was made to scale. A historical society, and government officials, became involved with preserving the existing swing bridge, and the new bridge was cancelled. The old bridge was refurbished at a tremendous cost, was still an old, untenable, high maintenance bridge, and regardless of how ridiculous the effort was, remains as something that taxpayers shouldn't have to pay to maintain. 

The final design of a bridge requires knowledge of materials, the distances to be spanned, and the cost. Steel is one of the best materials, but requires coatings, which can be expensive over time. There is a steel that corrodes on the outside, but will not have deep corrosion. It's substantially more expensive than regular structural steel, but I have seen it used on overpasses. It's uglier than homemade soap, when the rust "bleeds" onto the concrete caps, and columns, supporting the girders made from the steel. Still, steel is the best material for the type of design, and the long spans required for flyovers, and other long spans in urban freeway congestion. 

Steel can be designed to span long distances, where concrete can't without overhead supports. What girders are used depends on the span distance, whether there is a typical wider flange beam that can handle the load, or specially fabricated girders with camber to offset deflection of the weight of the deck. On larger spans, the design can be a multitude of different steel configurations, including trusses, arches, and box beams. Regardless of the bridge design, steel will be used somewhere in the construction.

Concrete usually requires less maintenance, but concrete has limitations. The biggest limitation is how brittle it is. If a span has nothing but concrete, it will stay together for awhile, but the expansion and contraction will eventually cause large sections to crack, and fail. That's where reinforcing steel is necessary, and planned joints needed for temperature changes in the concrete. 

The "rebar" holds the concrete together, and distributes the load evenly. The more rebar, the more strength. This allows some of a bridge decks to be as thin as 8 inches, and still handle the weight of a full loaded semi at highway speeds. Concrete can be used for long span girders, but the only application I've seen is box girders with substantial dowels, or stay cables. What makes this design convenient is that huge sections can be precast, hauled to the site, and placed by cranes. Still, the concrete has to be reinforced, and maintenance requires constant monitoring of the concrete for corrosion of the reinforcement. Concrete always has cracks, and water will migrate to, and along, the reinforcement steel. Over time, the rust will expand, concrete will spall, and eventually a major section will fail.

For shorter spans, concrete girders can be used. These are prestressed before the concrete is poured with steel cable tendons. Camber is also cast in the girders. The camber required for the deck deflection is predetermined by years of testing, and even with the best of designs, the deflection may not be as wanted. I've driven over bridges that have a "lope" between spans, where the girders didn't deflect as designed. On one bridge, the inspector was constantly harassed about "his" bridge, which had this problem. Subsequent examination showed all elevations before the deck pour were accurate. The girders just didn't deflect as designed. 

With the design finally determined, the next phase is plans, specifications, final anticipated costs, and the approval of the highest powers involved. This can be very time consuming, but if many standard designs are involved, and the project is relatively small, the time can be very short. That requires another post.

Feeding the Mushrooms

 After reports of the Supreme Court hearing on jab mandates, I realized they are like mushrooms: Kept in the dark and fed crap. It's no wonder the nation is in such terrible shape, if the highest court in the land is full of what can only be described as functional idiots.

Building a Bridge - Engineering Part 1

 I've worked with many engineers during my career. Like all professions, engineers have years of school under their belt, and before they can officially stamp a set of plans, they have to become licensed. Licensing requires years of working under those that already secured their license, and tests specific to the branch of engineering they pursue. Not all engineers pass the test, and some spend their careers performing the tasks required to design, or build, but never have the legal authority to place a stamp signifying they take full responsibility for the design. Regardless of licensing, I worked with a brilliant engineer without a license that not only designed offshore semi-submersible platforms, he sailed with them on their maiden voyage to insure the "bugs" were shaken out of the platform, and the function was as required. He was an exception, and even some with licenses were far over their heads, and to make things worse, oblivious of the fact their efforts were not only sometimes foolish, they were dangerous as well.

Engineers that design bridges are usually civil engineers. In my circumstances, most of those I worked with were employed by the state of Texas. The hierarchy of responsibility has a small board in charge of the entire state, statewide engineers, with staff in Austin, districts with a chief engineer, and subordinate engineers on staff to support the workload. Some are more than qualified, and some are (to me) functional idiots. All usually are hired as graduate engineers, and some are contractually bonded to five years of service to the state for financial help while going to college. 

With a bridge, and the basic needs understood, rough design drawings start the process. The amount of lanes, the maximum span needed, and approaches are drawn to start the process from conception to completion. This determines the final weight, how the environment will affect the structure, and since it requires access, how existing roads will be modified for use. It's a start, but there's a long way to go.

In the past, airplanes were used to take aerial photographs of certain areas. Photos were used to build a collage of photos, which were used to create larger photos that could be shrunk to a size for ease of use. Surveyed marks were placed on paving for matching photos. You probably have seen these. They are large crosses, and circles, painted on paving painted white. Today GPS is used. It's very handy, but has some inherent problems. One being that an overhead view doesn't scale correctly to actual ground measurements. Changes in elevations, and the curvature of the Earth over a large distance, add up to differing quantities during actual construction. That, and locations shown on plans don't match-up in the field. Regardless of what is used, accurate plans require field surveys to have an accurate scale for measurement. 

During the initial design survey, samples of the existing soil are taken, and bore holes are made to acquire cores for analysis of the substrate. The cores are analyzed by a soils engineer, who specializes in determining the bearing of the existing soil, and what is underneath suitable for bearing the proposed structure. Sometimes, there is available data for some of the area, but bore holes are necessary (when possible) where bearing structures will be placed. Bedrock is the best for bearing, but even bedrock needs analyzing to determine the strength. When there is no bedrock, the soil needs analyzing to determine the length, and type of piling for construction. 

In my experience, which was mostly locally, the substrate is a mixture of clay and sand. The soil is analyzed to determine what bearing a driven, or drilled pile, will provide with friction. With the right diameter, number, and length, the piles can carry a tremendous amount of weight, and provide a firm base for a bridge designed to move. While movement can be small, it's necessary to handle the dynamic load of what the bridge will be used for. On some bridges I worked on , the movement was very noticeable, and while inside a cable stay bridge, I had a few moments of vertigo as heavy traffic passed overhead. 

With the information for the subgrade, the depth of a channel -if any- is now used for determining any construction to take place under the existing water, or the necessary span to satisfy the requirements. Determining the depth may be as easy as using a grade rod, or soundings from a small boat, to a marine survey using sonar mapping. I've never seen an attempt for soil bores in a channel, but have seen soil bores as near to the channel as the drilling rig allowed. Usually, the channel is designed to be free of obstructions to allow water traffic, or to maximize the drainage. If underwater construction is required, the design of a cofferdam is a necessary step. Cofferdams can be anything from dirt piles to allow pumping to the bottom, to elaborate sheet pile configurations to contain the water at deep depths. Whether they still use caissons is out of my knowledge, but they were used successfully in the past.

I have to add that all the efforts to determine underground conditions are not always successful. Years ago, I bid, but didn't win, the emergency repairs for a small bridge. One of the interior spans fell a few feet after a one hundred year flood. Long story short, piling driven for the pile cap reached refusal before the depth required. All involved theorized the sand was much stiffer at the interior bent, so when refusal (I'll explain "refusal" later) was reached, the driving was stopped, and the pile was cut off to grade. After a high volume of water eroded the bottom to a depth below the bottom of the piling, the piling settled, and the pile cap went down. Underwater examination at the now exposed bottom found a sandstone. The piling, which compacted the few feet of sand above the sandstone, successfully supported the bridge for decades, but when the and washed away during the flood, there was nothing under the piling for a few feet. I don't know how the successful contractor performed their repair, but my bid included a drilling rig to drill into the sandstone, and cased piling.  

The soil engineer passes the information to other engineers, including the paving engineer. The paving engineer is responsible for designing a paving to handle the dynamic load of future traffic. Many things are considered, including materials for the paving, the bearing of the existing soil, and the requirement for any fill to bring the subgrade to the elevation needed for the final paving structure. 

The design of the bridge is now well on the way, but there are multiple tasks required to finally get the project to the bidding process. I'll write about that next.