НАУЧНАЯ БИБЛИОТЕКА - РЕФЕРАТЫ - Alternative construction methods
Alternative construction methods
- 1. Alternative Construction Methods
- Adobe construction
- Cast earth construction
- Cordwood construction
- Earthship construction
- Experimental construction
- Rammed earth construction
- Straw bale construction
- Industial Construction Materials
- Construction Techniques
The need to be competitive in the emerging global economy is a hot topic in many countries today. Industrialization, such as the prefabrication of building components, is critical to competitiveness. Many prefabrication technologies deliver a better product because building is done in a quality controlled, sheltered environment. Just as importantly, prefabrication can dramatically improve productivity.
The productivity growth of labour intensive construction industry is declining and must be improved to survive in an internationally competitive market. Builders will have to develop new construction methods and adapt existing methods from other industries and countries.
An awareness of the current trends and latest innovations in prefabrication and industrialized construction is essential.
The destruction of urban Europe and Japan during the Second World War, combined with the post war baby boom, created a need for housing for millions of people.
The existence of a single large client (the state) and a need for rapid construction combined to provide fertile soil for a boom in the development of industrialized construction techniques. Japanese and European construction firms pioneered many new processes, and today they are still making significant progress in prefabrication and industrialized construction technology. New construction methods and materials, computers and robots are being developed to constantly improve productivity.
One Japanese firm, Sekisui, ushers home buyers into a facility where they use three dimensional computer images to "custom design" their own home. Sekisui builds over 70, 000 of these luxury houses a year using industrialized construction technology, and can deliver a finished home within three months.
Innovations in the areas of materials, computers and robotics are improving building quality. As construction evolves into an industrialized process, new construction methods and building systems are also being developed to assemble prefabricated components. World's builders can take advantage of these advances.
We'll try to examine some alternative methods in construction through this report.
1. Alternative Construction Methods
Adobe construction is one of the oldest forms of building technology, still being used in the United States today. This form of building has been used in the desert Southwest for nearly 1, 000 years, while its historical origins can be traced back to Rome, as early as the 1st century A. D. Adobe, an Arabic word, describes a construction method in which clay bricks are molded while still wet and cast small enough to shrink without cracking. These bricks were usually laid up with a mud mortar.
The desert Southwest played host to the largest concentration of adobe structures, for many reasons. The Spanish settlers who came to this area found the thick walls of the adobe structure were easy to build with indigenous materials, while the completed structure's thermal mass soaked up the solar heat, therefore keeping the houses cool during the day and warm at night.
Cast earth construction
Cast Earth construction is a method of construction similar to rammed-earth. It is the work of Michael Frerking, an architect and general contractor in Prescott, Arizona. He has been working with rammed-earth technologies in Arizona for over 20 years. Cast-earth construction, unlike rammed-earth, uses a mix of gypsum plaster in place of traditional portland cement. Cast-earth is cast into forms using current poured concrete techniques and tools.
Cast-earth can be batched in a local concrete plant, delivered using regular trucks, and pumped through regular concrete pumps into regular concrete forms. It is this regular use of a new technology that makes cast-earth an economical choice to rammed-earth and many other construction techniques. In addition to lower labor and materials charge, cast-earth is considerably stronger, the set time is shorter, therefore bringing an age old construction technique into the twentieth century.
Cordwood construction in its simplest state, is simply the stacking of wood logs with mortar between and a roof overhead. This simple building technology has been around indefinitely, with no known origin. The present state of cordwood building, with Rob Roy as its chief architect and engineer, has become a valuable form of environmental building technology. A cordwood masonry home can be built with simple tools and techniques, using short pieces of wood.
Cordwood buildings use short logs, stacked widthwise with a mortar mix between. The high thermal mass and energy efficient construction, coupled with its economical building process, make this a worthwhile building technology for the present and the future.
Earthships can be found in the desert outside of Taos, New Mexico. They are the vision and product of architect Michael E. Reynolds. Working with various environmental concerns in mind, Reynolds has come to the conclusion that Steel belted tires, of which the US disposes of 250 million a year, are the environmental solution to the worlds housing problem. Reynolds construction technique stacks the tires like bricks and packs them solid with dirt. At 300 pounds per tire, all walls are load bearing, and neither concrete or foundation are necessary to hold walls in place. The three-foot-thick walls provide so much thermal mass, Reynolds compares them to batteries. Earthships usually face south with rear walls bermed into a hill taking advantage of passive solar techniques. Earthships are finished with stucco, and resemble an adobe home when finished.
Experimental construction is a generic term for a building technology that is still in the works. Many building technologies are currently being experimented with, and may prove to be a viable alternative to traditional building techniques in the future.
Rammed earth construction
Rammed earth construction, the technique of pounding moist earth into a formwork to create monolithic walls of earth, has been used worldwide for thousands of years. This form of construction has been used off and on for 200 years in the US, but never with as much enthusiasm as now.
Rammed earth construction, as with adobe and most other forms of earth housing, benefits from the use of inexpensive local materials in a thick walled system that maintains a high thermal mass and high energy efficiency. Rammed earth is a mixture of soil, water, and usually portland cement, packed into a form using a hydraulic tamper.
Straw bale construction
Straw, grasses, and reeds have been used along with wood and earth to build structures for thousands of years. With the development of the modern baling machine in the early 1800's, many structures, made of bales stacked like bricks, began to pop up throughout the mid west. Straw bales, made from the leftover stems of harvested grain, are considered a waste product by American farmers. Enough straw is burned or buried yearly by American farmers, nearly two million tons, to build 5 million 2, 000 s. f. homes. Straw bale construction can be of either load-bearing or non load-bearing construction. In a load-bearing home, straw bales are stacked and tied together with threaded rods from bottom plate to top plate, compressing the bales.
Non load-bearing walls are also considered infill, where straw bales are filled in between a load bearing heavy timber structure. Straw bale homes are finished with a plaster or stucco coat. Straw bale construction appeals to many new home builders due to its ease of construction, flexibility of design, affordability, high insulation value, and low environmental impact.
Industial Construction Materials
Innovative building materials fall into two general categories: new and improved materials (such as high performance concrete composites), and prefabricated assemblies of materials (such as insulation and exterior cladding).
Precast concrete is one prefabrication system benefitting immensely from developments in materials science. Polypropylene, steel, or glass fibres can now be added to concrete to make a less brittle composite material. Because it is less prone to cracking, this concrete is easier to use in precast applications where the component must be moved to the site. Research is being done to improve other material properties such as early strength, which will reduce the time between precasting and transport to the building site. One concern about high performance concretes is that they are more sensitive to mixing errors than regular concrete. Precasting in a quality controlled industrial environment makes these errors less likely, and allows for easier testing of the finished product. Testing of construction materials will be a major part of future quality assurance programs as building owners demand higher quality construction.
The development of other new composite materials is allowing designers to replace heavier conventional structures with lighter, more durable structures that can be more easily prefabricated and transported to the site.composite materials, such as fibre reinforced gypsum, can also offer improved fire resistance, sound absorption, and corrosion resistance. They will be used more widely in all construction fields, including prefabrication, as more research is done on joining methods and long term mechanical behaviour.
New plastic applications are surfacing every year. The use of polyvinyl chloride (PVC) as a structural material is the latest trend. As research continues to improve the viability of PVC as a replacement for timber and steel, prefabricated PVC wall panels, interior partitions, and modular housing will be developed.
The joining of two (or more) materials such as exterior cladding and insulation to form a multi purpose assembly is a common innovation. These prefabricated assemblies reduce on site labour and perform better than equivalent site built assemblies. Other combinations include plastic coatings for cladding, concrete and steel girders, and glass block and translucent insulation for glass walls. Building product and material manufacturers have been the only sector of the construction industry to actively develop or look for new technology to improve their products, and there are no indications they will stop doing so in the future. Accordingly, more and more of these industrially manufactured materials will appear and their use should continue to grow.
Once fabrication of building components has started, it is difficult to make changes to the design. This means that the design must be at an advanced stage before construction starts.computers have helped speed up design considerably in recent years, and can allow designers to thoroughly analyze the building for different purposes before construction starts. When they were first adopted, Computer Aided Design (CAD) packages were simply used to replace tasks normally done by hand, such as drawing, and were not a cost effective investment. Now, CAD packages can be used for many tasks, ranging from analyzing buildings for heat loss to generating 3 D interior mock ups. As computer technology and software improve, building designers will be able to do more advanced design work before construction starts.
Prefabricated building components must fit together properly at the site. Some building systems require precise positioning of structural components (e. g., for piping connections). When prefabricated materials and components are manufactured with varying degrees of dimensional accuracy, it can cause problems. For example, a window opening in a prefabricated panel that is too large can create an even larger headache for the window installers. The adoption of Computer Aided Design and Computer Aided Manufacture (CAD/CAM) techniques has helped overcome these shortcomings.computer controlled cutting and joining tools ensure good dimensional control, and are widely used in the Japanese and Scandanavian prefabrication industries. In Japan, most prefabricated houses begin with 3 D steel structures, although timber use is growing.
Completely finished prefabricated kitchen and bathroom modules (often from different companies than the main house builder) are added at a later stage.computers play a large part in providing the dimensional accuracy needed in these "pop in" modules.
The Japanese and Europeans are also pursuing the development of robots for construction applications. Robots are faster and more precise than humans, ideal for dangerous jobs, and they don't get sick or go on strike. Robots are most suited for an industrialized construction setting, where prefabrication can be broken down into standard repetitive tasks that can be controlled by computer. Robots can cut and shape, position and connect members to form structural frames with amazing dimensional consistency. There are robots that will paint, trowel concrete, shotcrete, handle materials, and inspect finished prefabricated components for flaws.
Robots are also being developed for site assembly of prefabricated components. Research is being done in England to reduce the complexity and variations of construction joints, so that robots can be used to join panels. The Japanese are developing robotized tools for the building site, and installing rails on prefabricated panels to serve as guides for robots.
New building systems and construction methods are also appearing in the move toward prefabrication. Many innovations depend not on developments in materials science or computers, but on imaginative usage of existing construction technologies and attention to design.
Architectural precast panels are now being used, with only small modifications, as load bearing walls by some builders in the United States. The structural use of these panels requires close and early collaboration between the architect and engineer because of additional design complexities such as floor to wall connections and shear reinforcement. Buildings can be designed without a structural core, however, thus providing the architect with more flexibility for floor plans, and can be built for less money than conventional structures.computer Aided Design packages can simplify structural analysis and facilitate design communications between the architectural and engineering teams.
The Taisei Corporation of Japan has developed the T Up system, a high rise construction technique ideally suited to erection of prefabricated structures. Once the structural core of a building is completed a "hat" truss structure is assembled and mounted, where it will eventually become the top floor. Travelling cranes are attached on the underside of the "hat" and used to handle and assemble prefabricated floor slabs, beams, girders, and walls. The "hat" also provides shelter from adverse weather conditions, thereby preventing delays and improving working conditions and construction quality.
The attachment of concrete reinforcement to structural members before delivery to the site is another time saving innovation. Self forming steel members are used to construct composite steel concrete structures. A sandwich panel system developed in Austria and used in the U. S. features a welded wire fabric surrounding a foam insulation core. These lightweight panels are assembled to form the outer shell of a house and then shotcreted to obtain an exterior concrete finish.
In fact, a number of social factors are also pushing the construction industry toward industrialization of the construction process. The demand for high quality buildings is growing in the whole world and the rest of the world. As they become more educated about energy conservation, lighting, indoor air quality, and other health and comfort related issues, consumers (homebuyers and commercial property owners) increasingly want their buildings to be built to the highest standards. Prefabrication of building components using mechanized, computer controlled tools is one way to consistently achieve high quality. Almost all building materials will be manufactured industrially in the near future, and it is natural to expect more and more assembly of these materials in a controlled environment away from the building site.
Continued growth in communications technologies, consumer electronics, and other creature comfort systems will make building construction more complex.computer controlled heating and ventilation and multi room access to entertainment and communications are some of the features that will be incorporated in future "smart" houses and buildings. Assembling and installing these technologically advanced systems in an exposed, site built structure will not please the owner.
Construction labour force is aging and shrinking as progressively fewer young people enter the industry. If demand for labour remains the same and the supply decreases, costs will increase. This pressure will lead builders to industrialized construction, which requires fewer specialized trades and people.
Industrially produced buildings have come a long way from the repetitive boxes most people associate with the word "prefabrication". The move to industrial construction is inevitable, and designers and builders should pay attention to its opportunities now.
International Council for Building Research, Studies and Documentation (CIB). Trends in building construction techniques worldwide. Special report for CIB '89.
Gregerson, J., Architectural precast can play a structural role. Building Design & Construction, January 2002.
KDC Consultants. Construction a challenge for the european industry. Voorburg, The Netherlands, 2001.
http://irc. nrc-cnrc. gc. ca/practice/gen1_E.html (Originally published in "Construction Canada" 34 (3), May 1992, p.25-26, 28)