Civil engineering has never shied away from technical innovation or ground-breaking techniques. Indeed, by incorporating the latest methodologies and most recent theories, architects and engineers have been able to advance structural design at a staggering rate. From conceptual processes to sign off, every step of the development process has benefited from this creative and pioneering approach.

Ingenuity in civil engineering has manifested itself in a number of ways, ranging from specific improvements in insulation, building services and glazing, to more rudimentary considerations that have influenced design, building practicality and project management. In short, few aspects have been untouched in the relentless drive to modernise.

New technologies and the very latest techniques have opened up a host of possibilities in terms of functionality and, more importantly, safety. Nowhere has this been felt more strongly than in the design of suitable measures to protect buildings against natural events, particularly from subsidence and seismic activity.

One emerging technology is that of linear motion guides, which were initially developed to provide motion control for machinery and components. Originated in Japan, these adaptable and reliable mechanisms have a variety of uses, particularly where the technology has been applied to base-isolation units in order to dispel vibration from seismic events.

Linear motion guides

In general, linear motion guides move or position loads. This basic premise means they are extremely adaptable and have become a common component in machine tools where accuracy and reliability is key. Tough as well as practical, linear motion guides are typically constructed of rails, or raceways, and guide blocks, or platforms, on which materials or components are transported. Various techniques are used to support this mechanism although most contemporary systems use steel ball bearings housed within the block that run along a groove in the rail. As a result, linear motion guides can be installed on level surfaces, vertical planes, inverted positions, slopes or walls.

Developments in this field have the potential to influence a number of applications in civil engineering, ranging from earthquake-damage prevention techniques to sporting stadia and bridge design. It would therefore seem likely that the study of movement in buildings, and the propensity of linear motion guides to control it, could serve not only to protect structures, but also to enhance their functionality.

Unwanted movement

Our understanding of the effects of earthquakes on buildings is fundamental to saving lives and property and forms the basis on which new procedures and technologies are based, enabling the design of buildings that are better equipped against seismic events.

The majority of injuries caused by earthquakes are a result of collapsing buildings and other structures, therefore engineers are striving to create earthquake-resistant buildings that may suffer damage during a shock, yet remain capable of safeguarding the lives and property of those inside and outside the building.

Current techniques include base isolation that uses vibration-isolating elements sandwiched between the building and the foundations to counteract the effects of an earthquake. This practice is, however, becoming increasingly common in areas less prone to seismic events as pressure grows to construct buildings on brown-field sites that suffer from ground-borne vibration due to underground railways or busy roads.

In Japan, however, this principle has been extrapolated to new heights with linear motion guides acting as stabilising mechanisms between buildings and the ground. The premise of this application relies on the guide’s remarkable ability to support extreme loads while retaining an extremely low friction coefficient, which can be as little as 0.008.

Since ground movements are transferred to the ball bearings held within the guide’s block, the building remains static while the earth moves beneath it. This makes horizontal shifts less prevalent, thereby preventing damage to building faciltities and disruption to normal working conditions.

A similar concept is being applied to corridors that connect separate earthquake-resistant buildings. Instead of conveying seismic forces, the corridors flex in accordance with movements due to linear motion guides supporting the floor and enabling movement in the walls. The flexibility of the corridors ensures that the potential energy generated is dissipated rather than being spread to neighouring buildings.

Bridging the gap

The advent of linear motion guides in civil engineering projects extends way beyond the life-saving endeavours of base isolation and the flexibility of connecting corridors. For instance, bridge design could also benefit from the extreme load-carrying solutions provided by linear motion technology.

In this realm, however, the destructive forces of nature are joined by the man-made perils of traffic vibrations. Here, the crippling and relentless movements that span bridges often cause large-scale resonance oscillations that have the potential of simply shaking the bridge apart. As a result, bridge designers have sought effective ways of compensating for vibration induced by both vehicles and wind, as well as providing suitable earthquake protection.

One method of achieving this is introducing tuned mass dampers (TMDs), which add a mode of vibration to the base structure and feature a natural frequency just below that of the target mode of the base structure, i.e. the mode to be dampened. In simple terms, they add an additional vibration that counteracts that of the passing cars, wind or quake.

The key to the success of TMDs is the overall system design and specification of the system’s component parts. An important consideration is the means by which the mass of the TMD is to be moved. A smooth, non-resistive mechanism is crucial if the bridge is to reap the rewards of the weight/damping ratio mentioned previously. It is in this area that linear motion guides can provide high-load linear guidance with minimal resistance on vulnerable bridges.

Take your seats

Until recently, the large-scale transformation of buildings was reserved for facelifts or major reconstruction work that would render the premises temporarily uninhabitable or inoperable. If the layout was to be changed, the building would have to be emptied and the bulldozers called in.

While this remains the case for many building types, sporting arenas have been given a new lease of life with extendable, removable and adaptive seating. One of best known exponents of this new technology is the Stade De France, the largest sporting stadium in France with an 80,000 seating capacity.

Built in less than three years, the stadium is the biggest mobile, transformable stadium in the world. Its lowest grandstand, with a capacity of 25,000 seats, can be pulled back 15m underneath the middle stands to reveal an athletics track.

Interestingly, unlike the Stade De France, the Telstra Stadium’s moveable stands were built using concrete – undoubtedly the most cost-effective building material for projects of this size, but on a completely different scale in terms of weight. While conventional hydraulics, motors and drives are used to position these enormous structures, it is conceivable that linear guides could provide an alternative means of transport that would reduce maintenance requirements yet deliver more effective motion control, while providing a more ecological, efficient, smoother and quieter system.

This is attainable because of a number of developments in linear motion technology that have enabled greater efficiency levels and extraordinary control. An important innovation is a system that holds the linear guide’s ball bearings at an equal distance from each other by a specially designed cage that retains, guides and separates the balls. The construction promotes smoother movements, less friction and a propensity for the guide to retain lubricating grease between the balls leading to minimal variations in rolling resistance and, more importantly, long-term, maintenance-free operation.

Fast forward

The inherent characteristics of linear motion guides and the continual development of increasingly adaptable variants have already made them an important factor in a growing number of architectural designs. From the harshness of industrial processing and uncertainty of earthquake protection to the ingenuity of modern stadia and marvel of cutting-edge design, linear motion guides have a range of attributes ideally suited for mechanical and now civil engineering projects. Offering low-friction movements, longer lifespans, maintenance free and extreme load-carrying capacities, modern linear motion guides are a contemporary development with plenty of future potential.

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