Bridges – Truss – Arrangement
Patent
1995-12-15
1997-10-28
Lisehora, James
Bridges
Truss
Arrangement
14 6, 14 74, E01D 100, E01D 600
Patent
active
056806647
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a building structure and relates particularly, but not exclusively, to a bridge.
2. Description of the Prior Art
In recent years the superstructures of bridges for many major estuarine crossings around the world have been constructed in pre-stressed concrete. This is in spite of determined efforts by the steel bridge industry to compete in this arena, once its almost exclusive domain. In most cases, the concrete solutions were selected in preference to steel solutions on the basis of lower capital cost and lower perceived maintenance costs. Although structural steel solutions offer advantages of lightness, speed of construction and more reliable build quality, the conventional concepts and technologies being used in their design and fabrication make the solutions being offered unable to cross the critical cost divide.
At the same time, there is an increasing realisation that segmental concrete superstructures, be they pre-cast or in situ are less durable and maintenance free than previously believed. Now that an increasing number of such structures are entering into middle age, it is becoming apparent that the construction procedures adopted to protect ducted post-tensioned cables against corrosion are proving to be considerably less effective than anticipated by their designers. Furthermore, the resistance of concrete to long-term deterioration in aggressive marine and industrial atmospheres is proving to be unsatisfactory. By contrast, many steel or iron structures dating from last century which have been properly designed, constructed and maintained have exceeded their design life without the need for costly structural repairs.
One particular problem with steel bridges is the need for painting for maintenance purposes which can be expensive.
A further problem which is present for bridges of all types is aerodynamic performance. The wind can exert considerable direct forces and fatigue stresses on bridges and can cause significant oscillations. Aerodynamic performance is an important factor in determining bridge strength and design.
SUMMARY OF THE INVENTION
According to the invention there is provided a building structure comprising a space frame enclosed in a housing shell.
The space frame is thus protected from the environment by the shell.
The building structure may be of any type but suitably is a bridge or the like.
The space frame may be made of any suitable material and may be made principally from metal, preferably iron or steel. In this case, as the space frame is housed, ordinary grades of structural steel may be utilised without the need for costly painting or other protective coatings against corrosion. By comparison, in current practice only more costly grades of self weathering steel such as "corten" are used without protective coating. The space frame may include pre-stressing cables. Such cables afford significant savings in weight and cost of the space frame and increase the reliability and fatigue resistance of the space frame in particular at joints. The cables, of course, are also protected by the shell. The cables may run alongside elongate members of the space frame or may run inside elongate members of the space frame.
The housing shell is preferably aerodynamically shaped. A space frame by its nature is not aerodynamically shaped inducing high levels of turbulence. By using an aerodynamically shaped housing wind loads and fatigue stresses can be reduced. The aerodynamically shaped shell will also have an aesthetically pleasing appearance. Preferably then the housing shell is smooth over the majority of its surface. The housing shell may be convex on one side. Preferably, the housing shell is smooth over its lower surface and preferably convex over its lower surface. The shell may be symmetrical about a vertical plane.
The housing shell may be made from any suitable material and may be made at least partly from plastics material. The plastics material may be reinforced plastics material such as GRP.
REFERENCES:
patent: 3859682 (1975-01-01), Sulkiewicz
patent: 4620400 (1986-11-01), Richard
patent: 4993094 (1991-02-01), Muller
Lisehora James
Maunsell Structural Plastics Ltd.
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