DAMPER IN CIVIL CONSTRUCTION

                                             A tuned mass damper (TMD), also known as a harmonic absorber or seismic damper, is a device mounted in structures to reduce the amplitude of mechanical vibrations. Their application can prevent discomfort,damage, oroutright  structural failure. They are frequently used in power transmission, automobiles, and buildings.

                 Tuned mass dampers stabilize against violent motion caused by harmonic vibration. A tuned damper reduces the vibration of a system with a comparatively lightweight component so that the worst-case vibrations are less intense. Roughly speaking, practical systems are tuned to either move the main mode away from a troubling excitation frequency, or to add damping to a resonance that is difficult or expensive to damp directly. An example of the latter is a crankshaft torsional damper. Mass dampers are frequently implemented with a frictional or hydraulic component that turns mechanical kinetic energy into heat, like an automotive shock absorber.

Friction Damper

Friction dampers are designed to have moving parts that will slide over each other during a strong earthquake. When the parts slide over each other, they create friction which uses some of the energy from the earthquake that goes into the building.

This is a Pall Friction Damper installed in the Webster Library of Concordia University in Montreal, Canada. The damper is connected to the centre of some cross-bracing.

The damper is made up from a set of steel plates, with slotted holes in them, and they are bolted together. At high enough forces, the plates can slide over each other creating friction. The plates are specially treated to increase the friction between them.

FIREFIGHTING ROBOTS

WILL FIREFIGHTING ROBOTS 

EVER REPLACE HUMAN FIREFIGHTERS

Not on a large scale in the near future, but there have been advances in technology in recent years that has resulted in them being used on actual fires. There is no question that they could be useful in certain types of incidents where the environment would be very dangerous for humans, such as hazardous materials, radioactivity, or a propane tank that could explode.

Most of the fire fighting robots in development or being used today are controlled remotely, are tethered by a fire hose which supplies water, and they have infrared and standard cameras which transmit images back to the operator.

The Thermite  robot, pictured above, is small enough to be able to go through an average sized door in a structure. The video below features this machine.

Being used now in New South Wales, Australia is a much larger robot made in Germany, called a Turbine Aided Firefighting machine (TAF 20).

The $310,000 TAF 20 can spray water mist or foam from 60 meters (196 feet) and blast water up to 90 meters (295 feet). It was used last week at a factory fire in Sydney where NSW Emergency Services Minister David Elliot said it proved its effectiveness, according to ABC news.

“It will be of great use for our firefighters in battling other large and complex fires, including bushfires,” Mr Elliot said.

Lockheed Martin, which recently demonstrated a flying firefighting robot is also developing a ground-based machine they call the Fire Ox.

he Fire Ox is self-sufficient, in that it is not dependent on a tethered fire hose since it has an on-board water tank. It appears to be designed for wildland fires and haz-mat incidents. It can be operated with a game-style controller, programmed to follow a predetermined course, or can follow a person walking in front of it.

ASPHALT ROAD SURFACE

A road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a roador walkway. In the past, gravel road surfaces, cobblestone and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete laid on a compacted base course. Road surfaces are frequently marked to guide traffic. Today, permeable paving methods are beginning to be used for low-impact roadways and walkways. Pavements are crucial to countries such as US and Canada, which heavily depend on road transportation. Therefore, research projects such as Long-Term Pavement Performance are launched to optimize the life-cycle of different road surfaces.

Asphalt

                                                       Asphalt (specifically, asphalt concrete), sometimes called flexible pavement due to the nature in which it distributes loads, has been widely used since the 1920s. The viscous nature of the bitumen binder allows asphalt concrete to sustain significant plastic deformation, although fatigue from repeated loading over time is the most common failure mechanism. Most asphalt surfaces are laid on a gravel base, which is generally at least as thick as the asphalt layer, although some 'full depth' asphalt surfaces are laid directly on the native subgrade. In areas with very soft or expansive subgrades such as clay or peat, thick gravel bases or stabilization of the subgrade with Portland cement or limemay be required. Polypropylene and polyester geosynthetics have also been used for this purpose and in some northern countries, a layer of polystyrene boards have been used to delay and minimize frost penetration into the subgrade.

Depending on the temperature at which it is applied, asphalt is categorized as hot mix, warm mix, or cold mix. Hot mix asphalt is applied at temperatures over 300 °F (150 °C) with a free floating screed. Warm mix asphalt is applied at temperatures of 200–250 °F (95–120 °C), resulting in reduced energy usage and emissions of volatile organic compounds.Cold mix asphalt is often used on lower-volume rural roads, where hot mix asphalt would cool too much on the long trip from the asphalt plant to the construction site.

An asphalt concrete surface will generally be constructed for high-volume primary highways having an average annual daily traffic load greater than 1200 vehicles per day. Advantages of asphalt roadways include relatively low noise, relatively low cost compared with other paving methods, and perceived ease of repair. Disadvantages include less durability than other paving methods, less tensile strength than concrete, the tendency to become slick and soft in hot weather and a certain amount of hydrocarbon pollution to soil and groundwater or waterways.

In the mid-1960s, rubberized asphalt was used for the first time, mixing crumb rubber from used tires with asphalt. While a potential use for tires that would otherwise fill landfills and present a fire hazard, rubberized asphalt has shown greater incidence of wear in freeze-thaw cycles in temperate zones due to non-homogeneous expansion and contraction with non-rubber components. The application of rubberized asphalt is more temperature-sensitive, and in many locations can only be applied at certain times of the year.

Study results of the long-term acoustic benefits of rubberized asphalt are inconclusive. Initial application of rubberized asphalt may provide 3–5 decibels (dB) reduction in tire-pavement source noise emissions; however, this translates to only 1–3 decibels (dB) in total traffic noise level reduction (due to the other components of traffic noise). Compared to traditional passive attenuating measures (e.g., noise walls and earth berms), rubberized asphalt provides shorter-lasting and lesser acoustic benefits at typically much greater expense.