Static structures (e.g. – buildings) – With transporting feature
Reexamination Certificate
2000-01-25
2002-10-22
Safavi, Michael (Department: 3673)
Static structures (e.g., buildings)
With transporting feature
C052S334000, C052S414000
Reexamination Certificate
active
06467223
ABSTRACT:
BACKGROUND—FIELD OF INVENTION
This invention relates to a single or multistory modular compound composite concrete and steel floor for modular buildings. The objective is not only to provide an economical, structurally efficient, higher quality and more durable modular building, but to be able to handle, transport and install it economically as well.
BACKGROUND—DESCRIPTION OF PRIOR ART
Theoretically, an item built in mass production in a controlled environment ought to be able to be produced at a lower cost and higher quality than the same item built on a custom basis out in the elements. This is experienced in the auto industry, the computer industry and many others. This has not, however, been experienced as successfully in the building construction industry. It is true that structural members, plumbing, mechanical, electrical and other building components have adopted mass production, but their complete assembly into a building has not. The bulkiness of buildings generally does not allow them in whole to be built in a factory or easily shipped and installed. As a result, buildings were divided into sections or modules, mass production was attempted to be applied and the modular building process was created. But even this industry has not achieved the economical and quality benefits the production process ought to provide. In most areas of the country commercial modular buildings are generally no less expensive than a building built on site. And the durability, quality and aesthetics of the modular product often does not match that of conventional. So if value is the measure of quality versus cost, unlike other industries, the modular production process has provided less value than conventional construction. As a result the modular industry has managed to capture only a relatively small part of the construction market. Namely, that part of the market that must be relocatable. If a commercial building can be built conventionally, modular generally has not been considered an option. Reasons for the inability of the industry to provide more value than conventional construction include: shipping restrictions, architectural paradigms and quality gaps, shipping and handling costs and, apparently, a lack of expertise to overcome these characteristics.
The most obvious characteristic of modular construction is that the modules must be transportable. This poses challenges in several ways. Transportability is mainly a function of road and bridge geometry and strength. As a result, modules have to fit within maximum rectangular volume and weight constraints regulated by the department of transportation or some other governmental agency. Roads in the US have relatively liberal widths but other factors such as telephone poles and signs on street corners make it difficult in some cases to maneuver wide or very long modules. But this is much less of a problem than the height limitations imposed by bridges, power lines, trees and other obstacles.
In addition, over the long history of building construction has evolved distinct architectural, safety and non discriminatory building paradigms. In the more populated areas and therefore major market areas, the market has demanded and even empowered local governments to create building ordinances to ensure some or all of these paradigms are adhered to. The more basic ones include, for example, high pitched roofs in residential areas, high ceilings in all construction, fire resistive construction and minimum requirements for egress and handicap access in commercial construction. And in recent years, local planning ordinances require minimum percentages of masonry on the exterior facade. These paradigms, desirable or mandatory, again pose challenges to the modular production process. Shipping height restrictions limit the height of roofs and the use of high or cathedral ceilings. Fire resistive materials tend to increase weight. In the past, in order to minimize weight, modular buildings have been built of wood products. However, because wood is combustible, building codes restrict the size of wood buildings and require fire rating and sprinkler systems when the floor area reaches a certain size. Wood is subject to termites and rot and is a relatively weak material whose strength diminishes when it gets wet. In areas where basements are generally not used, the lowest portion of the typical wood framed floor structure is required to be set a minimum of a half of a meter above grade so that moisture cannot cause it to deteriorate so quickly. This necessitates skirting the exterior walls to the ground, steps at all doors and a handicap ramp at least at one main door. These are large expenses if constructed of the more accepted poured on site concrete with steel handrails and relatively expensive and unappealing if constructed of the typical pressure treated wood. And finally masonry materials are very heavy and almost all but thin veneers such as stucco are almost impossible to attach to the building for shipping.
Also, as with any other manufactured product there are shipping, handling and installation costs. Although it is true materials have to be shipped to the conventional site, there is a well established infrastructure and materials have to delivered to the modular plant, as well. Shipping the modules is above and beyond this. And of course, the cost is proportional to size, weight, distance and quantity. The largest modules require escorts in addition to the equipment to pull it. Heavier modules require larger or stronger equipment to pull and handle them. Trucking company's charge by the mile and of course this is multiplied by the number of modules there are. Installation cost is a function of the number of modules. And material has to be applied to protect the modules from the elements until they are installed.
Further, shipping and handling a module can require applying forces on it in different locations or in larger magnitudes than would be experienced in the installed position on the foundation. Therefore, packaging not only includes protecting the product from the elements, but providing the appropriate structure or mechanism to withstand the stresses, deflections, vibrations and impacts induced by handling and the dynamics of traveling down the road. None of which may be experienced in conventional construction. These loads have been supported in an array of ways by the addition of columns, beams and braces in some manner or another. Since bending resistance is proportional to the cross sectional height of a member to the third power, the taller the beam the less it has to weigh and the more economical it will be. As height is one of a modules most valuable commodities, the tendency is to compress structural member height as much as possible. This has made it a challenge to incorporate strong efficient economical modules and packaging structures. The inverse of the beam strength characteristic is; to maintain strength, for very small reductions in height you have to add a lot of weight. As a result, short heavy inefficient members have been used. Resolving this issue would contribute the majority of the solutions to most of the other challenges as well. This requires a design that makes height restricted beams their most efficient. The solution lies in distributing as much of the cross sectional area that makes up the beam to the very top or bottom of the beam height limitations, as possible, and using the most suitable material in those top and bottom flanges.
In summary, all of these challenges contribute significant costs to a modular building that a conventionally built building would not have. But, they cannot be completely eliminated because a modular building has to be shipped. However, a properly designed system and production process should generate economic benefits that far outweigh the costs of shipping and installation, while providing the quality demanded by architectural paradigms. Only when costs and quality meet or exceed that of conventional construction can market share increase. This can only be accomplished b
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