The Blueprint

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architecture, civil engineer, engineering, mechanics

If you have ever watched a house being built, or if you have ever had an addition put onto an existing house, you know that the standard method of communication is a big piece of paper called a blueprint. Blueprinting is the standard method used to copy large architectural and construction drawings. A blueprint used to consist of white lines on a blue background. A more recent process uses blue lines on a white background.

The term “blueprint” is usually used to describe two printing methods, the blueprint and the diazotype.

Blueprinting is the older method, invented in 1842. The drawing to be copied, drawn on translucent paper, is placed against paper sensitized with a mixture of ferric ammonium citrate and potassium ferricyanide. The sensitized paper is then exposed to light. Where the areas of the sensitized paper are not obscured by the drawing, the light makes the two chemicals react to form blue. The exposed paper is then washed in water. This produces a negative image, with the drawing appearing in white against a dark blue background.

In the diazotype method, the paper is light-sensitized with a mixture of a diazonium salt (used in the manufacture of dyes), a reactant, and an acid that keeps the diazonium salt and the reactant from reacting with each other. The semi-transparent original is placed on top of the sensitized paper, and a copy of the same size as the original is made by direct contact. Light destroys the diazonium salt. Ammonia gas or solution is used as a developer after exposure — it neutralizes the acid and allows the remaining diazonium salt to combine with the reactant to create a blue dye. The chemicals on the paper acquire color only in the areas not exposed to light. This diazotype method produces dark lines on a white background, and is the popular method used today for reproduction of large-format drawings.

The reason people still use blueprints is because it is an inexpensive process. Compared to the cost of creating a large-format copying machine, a diazotype machine is a great bargain.

The Arch Bridge

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architecture, civil, civil engineer, engineering, science, transportation

 

After more than 2,000 years of architectural use, the arch continues to feature prominently in bridge designs and with good reason: Its semicircular structure elegantly distributes compression through its entire form and diverts weight onto its two abutments, the components of the bridge that directly take on pressure.

Tensional force in arch bridges, on the other hand is virtually negligible. The natural curve of the arch and its ability to dissipate the force outward greatly reduces the effects of tension on the underside of the arch.

But as with beams and trusses, even the mighty arch can’t outrun physics forever. The greater the degree of curvature (the larger the semicircle of the arch), the greater the effects of tension on the underside of the bridge. Build a big enough arch, and tension will eventually overtake the support structure’s natural strength.

While there’s a fair amount of cosmetic variety in arch bridge construction, the basic structure doesn’t change. There are, for example, Roman, Baroque and Renaissance arches, all of which are architecturally different but structurally the same.

It is the arch itself that gives its namesake bridge its strength. In fact, an arch made of stone doesn’t even need mortar. The ancient Romans built arch bridges and aqueducts that are still standing today. The tricky part, however is building the arch, as the two converging parts of the structure have no structural integrity until they meet in the middle. As such, additional scaffolding or support systems are typically needed.

Modern materials such as steel and prestressed concrete allow us to build far larger arches than the ancient Romans did. Modern arches typically span between 200 and 800 feet (61 and 244 meters), but West Virginia’s New River Gorge Bridge measures an impressive 1,700 feet (518 meters)

Truss Bridge

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architecture, arts, beam bridges, bridge, civil, civil engineer, civil engineering, civilengineering, compression, engineering, road, science, stress, technology, tension, tops and bottoms, transportation, truss bridges

Truss Bridges: Beam Bridges With Braces

Travel around the world, and you’ll encounter dozens of variations on your standard beam bridge. The key differences, however, all come down to the design, location and composition of the truss.

During the early Industrial Revolution, beam bridge construction in the United States was rapidly developing. Engineers gave many different truss designs a whirl in an attempt to perfect it. Their efforts weren’t for naught. Wooden bridges were soon replaced by iron models or wood-and-iron combinations.

 

 

All these different truss patterns also factored into how beam bridges were being built. Some takes featured a through truss above the bridge, while others boasted a deck truss beneath the bridge.

A single beam spanning any distance undergoes compression and tension. The very top of the beam gets the most compression, and the very bottom of the beam experiences the most tension. The middle of the beam experiences very little compression or tension. This is why we have I-beams, which provide more material on the tops and bottoms of beams to better handle the forces of compression and tension.

And there’s another reason why a truss is more rigid than a single beam: A truss has the ability to dissipate a load through the truss work. The design of a truss, which is usually a variant of a triangle, creates both a very rigid structure and one that transfers the load from a single point to a considerably wider area.

While truss bridges are largely a product of the Industrial Revolution, our next example, the arch, dates back much further in time.

The Girder Bridge

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architecture, aviation, cars, civil, civil engineer, engineering, transportation

The Beam Bridge

Bridge building doesn’t get any simpler than this. In order to build a beam bridge (also known as a girder bridge), all you need is a rigid horizontal structure (a beam) and two supports, one at each end, to rest it on. These components directly support the downward weight of the bridge and any traffic traveling over it.

However, in supporting weight, the bream bridge endures both compressional and tensional stress. In order to understand these forces, let’s use a simple model.

If you were to take a two-by-four and lay it across two empty milk crates, you’d have yourself a crude beam bridge. Now if you were to place a heavy weight in the middle of it, the two-by-four would bend. The top side would bend in under the force of compression, and the bottom side would bend out under the force of tension. Add enough weight and the two-by-four would eventually break. The top side would buckle and the bottom side would snap.

Many beam bridges use concrete or steel beams to handle the load. The size of the beam, and in particular the height of the beam, controls the distance that the beam can span. By increasing the height of the beam, the beam has more material to dissipate the tension. To create very tall beams, bridge designers add supporting latticework, or a truss, to the bridge’s beam. This support truss adds rigidity to the existing beam, greatly increasing its ability to dissipate the compression and tension. Once the beam begins to compress, the force spreads through the truss.

Yet even with a truss, a beam bridge is only good for a limited distance. To reach across a greater length, you have to build a bigger truss until you eventually reach the point at which the truss can’t support the bridge’s own weight.

How Bridge Works

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cars, civil, civil engineering, climate, engineering, science, transportation

We are a species of bridge builders. Since time out of mind, humans have engineered structures to surmount obstacles, such as, say, Jiaozhou Bay. The body of water is now home to a 26.4-mile (42.5-kilometer) bridge that links the busy Chinese port city of Quingdao to the Chinese suburb of Huangdou.

We’ve tamed steel, stone, lumber and even living vegetation, all in an effort to reach the places, people and things we desire.

Although the concept itself is as simple as felling a tree across a creek, bridge design and construction entails serious ingenuity. Artists, architects and engineers pour vast resources into bridge construction and, in doing so, reshape the very environment in which we live.

As a result, we inhabit a planet of bridges, some as ancient as Greece’s 3,000-year-old Arkadiko bridge or as unchanged as India’s 500-year-old Meghalaya living bridges, which are coaxed into existence from growing tree roots (more on that later). Countless others have fallen into the ravines and rivers they span, as humans continue to tackle ever more ambitious bridges and construction.

In this article, we’ll get to know the bridges we so often take for granted (we literally walk and drive all over them), as well as the designs that make them possible. We’ll look at the fundamental principles of bridge engineering, the different types and how we attempt to thwart the physical forces and natural phenomena that perpetually threaten to destr

oy the world’s bridges.

First up, let’s get right down to the basics.

Cofferdam – Definition, Application, Limitations & Working of Coffer Dams

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civil, climate, construction economics, engineering, environment, execution area, work proceeds

The multiple-stage method of diversion over the tops of alternate low construction blocks or through diversion conduits in a concrete dam requires shifting of the cofferdam from one side of the river to the other during construction. During the first stage, the flow is restricted to one portion of the stream channel while the dam is constructed to a safe elevation in the remainder of the channel.

In the second stage, the cofferdam is shifted and the stream is carried over low blocks or through diversion conduits in the constructed section of the dam while work proceeds on the un-constructed portion. The dam is then carried to its ultimate height, with diversion finally being made through the spillway, penstock, or permanent outlets.

A cofferdam can be defined as “A watertight construction designed to facilitate construction projects in areas which are normally submerged”, such as bridges and piers.

A cofferdam is installed in the execution area and the water is pumped out in order to facilitate work for workers and enable them to work in dry conditions and can construct structural supports, enact repairs, or perform other types of work in a dry environment. In some regions of the world, a cofferdam is better known as a caisson. Working inside a cofferdam can be hazardous if it is installed improperly or not safely pressurized, but advances in engineering have led to increased safety for workers using this unique work environment.

A cofferdam is a temporary dam or barrier used to divert a stream or to enclose an area during construction. The design of an adequate cofferdam involves the problem of construction economics. When the construction is timed so that the foundation work can be executed during the low-water season, the use of cofferdams can be held to a minimum. However, where the stream flow characteristics are such that this is not practical, the cofferdam must be so designed that it is not only safe, but also of the optimum height.

Height Limitations for Cofferdam

The height to which a cofferdam should be constructed may involve an economic study of cofferdam height versus diversion works capacity. This may include routing studies of the diversion design flood, especially when the outlet works requirements are small. If outlet works requirements dictate a relatively large outlet conduit or tunnel, diversion flows ordinarily may be accommodated without a high cofferdam. It should be remembered that the floodwater accumulated behind the cofferdam must be evacuated in time to accommodate another storm.

The maximum height to which it is feasible to construct the cofferdam without encroaching upon the area to be occupied by the dam must also be considered. Furthermore, the design of the cofferdam must take into consideration the effect that excavation and de-watering of the foundation of the dam will have on its stability, and it must anticipate removal, salvage, and other factors.

Generally, cofferdams are constructed of materials available at the site. The two types normally used in the construction of dams are

 

1. Earthfill cofferdams and
2. Rockfill cofferdams

Whose design considerations closely follow those for permanent dams of the same type. Other less common cofferdam types are concrete cribs filled with earth or rock, and cellular-steel cofferdams filled with earth or rock. In this case, the major portion of the cofferdam consists of an earth and rock embankment, and steel sheet piling was used to affect final closure in swift water. Cellular steel cofferdams and steel sheet piling are adaptable to confined areas where currents are swift.

If the cofferdam can be designed so that it is permanent and adds to the structural stability of the dam, it will have a decided economic advantage. In some embankment dams the cofferdam can even be incorporated into the main embankment. In such instances, the saving is twofold-the amount saved by reducing the embankment material required and the amount saved by not having to remove the cofferdam when it is no longer needed.

The Earthquake-Proof Buildings

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architecture, aviation, civil, civil engineer, civilengineering, construction, engineering, science

The Earthquake-Proof Building That Is Built to Collapse

The Brilliant Idea: A replaceable, building-wide system to help hospitals, apartment buildings and office towers survive severe seismic shaking.

Innovators: Gregory Deierlein, Stanford University; Jerome F. Hajjar, Northeastern University

“Elastic high-strength steel cables run down the center of the system’s frame. The cables control the rocking of the building and, when the earthquake is over, pull it back into proper alignment.”

“A steel frame situated around a building’s core or along exterior walls offers structural support. The frame’s columns, however, are free to rock up and down within steel shoes secured at the base.”

“Steel fuses (in blue) at the frame’s center twist and contort to absorb seismic energy. Like electrical fuses, when they “blow out” they can be replaced, restoring the structural system to pre-earthquake conditions.”For decades, the goal of seismic engineers has seemed straightforward: Prevent building collapse. And so they add steel braces to a skyscraper’s skeleton or beefier rebar to concrete shear walls. After absorbing the brunt of seismic shaking, however, the compromised structures often must be demolished. “The building, in a sense, sacrifices itself to save the occupants,” says Gregory Deierlein, a Stanford University civil and environmental engineer. A team Deierlein led with Jerry Hajjar, a Northeastern University engineer, hopes to change that, designing a system that protects both people and the structures they live and work in.

Last fall, the engineers successfully tested a 26-foot-tall, three-story, steel-frame building outfitted with the new system, built atop the E-Defense shake table—the world’s largest earthquake simulator—in Miki City, Japan. Steel “fuses,” not structural elements, absorbed the shock of an earthquake greater than magnitude 7, and cables pulled the building back into plumb once the shaking stopped. After an earthquake of that scale, the deformed fuses could be replaced in about four days—while the building remained occupied. Jim Malley of the San Francisco firm Degenkolb Engineers calls the system the next step in the evolution of green building. “As structural engineers,” he says, “our sustainable design is the ability not to have to tear buildings down after earthquakes, but to use them for hundreds of years.”