【正文】 on, and absence of munication than by the idea of the design. If a contractor is uncertain, he will add costs to hedge the risk he will be taking. It is for this reason that both the architect and the engineer should be wellversed in the area of construction potentials if innovative designs ate to be petitively bid. At the least the architect must be capable of working closely with imaginative structural engineers, contractors and even fabricators wherever possible even if the architecture is very ordinary. Efficiency always requires knowledge and above all imagination, and these are essential when designs are unfamiliar.The foregoing percentages can be helpful in approximating total construction costs if the assumption is made that structural design is at least of average (of typical) efficiency. For example, if a total office building construction cost budget is ﹩5,000,000,and 25 percent is the “standard” to be used for structure, a projected structural system should cost no more than ﹩1,250, a very efficient design were realized, say, at 80 percent of what would be given by the “average” efficient design estimate stated above the savings,(20 percent),would then be﹩250,000 or 5 percent of total construction costs ﹩5,000, the ﹩5,000,000 figure is mitted, then the savings of ﹩250,000 could be applied to expand the budget for “other” costs.All this suggests that creative integration of structural (and mechanical and electrical) design with the total architectural design concept can result in either a reduction in purely construction design concept can result in either a reduction in purely construction costs or more architecture for the same cost. Thus, the degree of success possible depends on knowledge, cleverness, and insightful collaboration of the designers and contractors.The above discussion is only meant to give the reader an overall perspective on total construction costs. The following sections will now furnish the means for estimating the cost of structure alone. Two alternative means will be provided for making an approximate structural cost estimate: one on a square foot of building basis, and another on volumes of structural materials used. Such costs can then be used to get a rough idea of total cost by referring to the “standards” for efficient design given above. At best, this will be a crude measure, but it is hoped that the reader will find that it makes him somewhat familiar with the type of real economic problems that responsible designers must deal with. At the least, this capability will be useful in paring alternative systems for the purpose of determining their relative cost efficiency.3. Squarefoot EstimatingAs before, it is possible to empirically determine a “standard” persquarefoot cost factor based on the average of costs for similar construction at a given place and time. Moreorless efficient designs are possible, depending on the ability of the designer and contractor to use materials and labor efficiently, and vary from the average.The range of squarefoot costs for “normal” structural systems is ﹩10 to ﹩16 psf. For example, typical office buildings average between ﹩12 and ﹩16 psf, and apartmenttype structures range from ﹩10 to ﹩ each case, the lower part of the range refers to short spans and low buildings, whereas the upper portion refers to longer spans and moderately tall buildings.Ordinary industrial structures are simple and normally produce squarefoot costs ranging from ﹩10 to ﹩14,as with the more typical apartment building. Although the spans for industrial structures are generally longer than those for apartment buildings and the loads heavier, they monly have fewer plexities as well as fewer interior walls, partitions, ceiling requirements, and they are not tall. In other words, simplicity of design and erection can offset the additional cost for longer span lengths and heavier loads in industrial buildings.Of course there are exceptions to these averages. The limits of variation depend on a system’s plexity, span length over “normal” and special loading or foundation conditions. For example, the Crown Zellerbach highrise bank and office building in San Francisco is an exception, since its structural costs were unusually high. However, in this case, the use of 60 ft steel spans and freestanding columns at the bottom, which carry the considerable earthquake loading, as well as the special foundation associated with the poor San Francisco soil conditions, contributed to the exceptionally high costs. The design was also unusual for its time and a decision had been made to allow higher than normal costs for all aspects of the building to achieve open spaces and for both function and symbolic reasons. Hence the proportion of structural to total cost probably remained similar to ordinary buildings.The effect of spans longer than normal can be further illustrated. The “usual” floor span range is as follows: for apartment buildings,16 to 25 ft。 for office buildings,20 to 30 ft。 and garagetype structures span,50 to 60 ft, carrying relatively light(50～75 psf) loads(., similar to those for apartment and office structures).Where these spans are doubled, the structural costs can be expected to rise about 20 to 30 percent.To increased loading in the case of industrial buildings offers another insight into the dependency of cost estimates on “usual” standards. If the loading in an industrial building were to be increased to 500psf(., two or three times), the additional structural cost would be on the