General Introduction 1

Buildings, bridges, roads, and waterworks, in all ages, have been among the principal embodiments of community culture. They have, as a rule, been most actively constructed in times of comparative security and economic well-being although for centuries they were created almost wholly by slave labor or by the unaided strength of free men. In recent years, mechanical devices and scientific understanding of the forces of nature and the properties of materials have, with some exceptions, enlarged and are continuing to expand greatly man's capacity to create works and structures for his use and convenience.

As an industry construction is not always sharply defined but is generally understood to include the design and production of domestic shelter; enclosed space for commercial, manufacturing, public, and other purposes; substantial changes in the earth's topography; and fixed works for transportation and for the transmission of commodities such as water, gas, and electrical energy. The products of this industry ranging from single-family houses to bridges, dams, water purification and distributing systems, and streets and roads, are conspicuous in the differences in their technical development and in the physical conditions and geographic areas in which they are created.

The technological changes in many cases in recent years have been notable, in others almost wholly absent. The movement of large quantities of earth, for example, for roads, railroads, dams, and other works which 15 to 20 years ago required the use of many horse- or mule-team wagons or scrapers may now be done by large mechanical-driven bucket graders having a capacity of 5 to 15 times that of the dump wagons or fresno scrapers formerly used. The building of houses, however, as is well known, remains largely a handcraft operation. Lumber, brick, cement, roofing, pipe, and fixtures are for the most part still delivered to the site in much the same form and installed in much the same manner as they have been for many years. Recent developments in small-house construction may eventually have far-reaching effects but thus far have been used only to a limited extent. Geographic, topographic, and other conditions also introduce widely different problems. Tunnel con

The contributions of the several authors are indicated in the footnotes to the individual sections.

1 Prepared by Lowell J. Chawner, Chief, Construction Economics Section, U. S. Bureau of Foreign and Domestic Commerce.

struction in congested areas of large cities presents peculiar difficulties in the disposal of excavated materials and requires special care in the use of explosives and in the protection of foundations to large buildings. In remote mountain areas the greatest problems are usually those of transporting men, materials, and equipment to the project. In building construction, soils of different physical and chemical composition and depth to rock at the site of a project make necessary essentially different types of foundations. Similar differences influence the design of a plant for the purification of water to remove turbidity, unpleasant taste, or pathogenic bacteria. In terms of its finished products, construction is thus principally a nonduplicating industry.

Contracting as a business is, furthermore, essentially mobile. Administrative and technical personnel, equipment, and to an important although lesser extent skilled mechanics often move over wide areas. Productive plant is not permanently situated as in most manufacturing industries but must be set up at each particular project. Increasing shop fabrication of materials and the use of mechanical equipment are, however, tending somewhat to fix the situs of employment of a larger portion of the total number of workers directly or indirectly dependent upon construction for their livelihood.

General Trends in Design, Materials, and Construction Methods

The rational engineering design of structures in the United States is hardly more than 70 years old even in its simplest forms. Recently these methods have been greatly perfected and extended. Models are now extensively used in the design of bridges, tall buildings, river channels, dams and many other works and structures; elaborate mathematical procedures are available for the analysis of stresses in building frames, arches, and monolithic concrete domes; and actual stress measurements upon completed structures under known loads are often made. These improvements in methods of design have been accompanied in many branches of engineering by extensive laboratory tests upon materials which have made possible increased safety and economy in many structures.

New materials such as glass brick, high-strength and rust-resisting steels, reinforced brickwork, fire-resisting treatments of lumber products, and the scientific proportioning of portland cement concrete have been

developed, in many cases quite extensively, during the past few years. A fuller description of these and other new materials is given in the sections of this report relating to the various types of construction.

In its broadest sense, construction includes both activities at the site of an improvement as well as in the manufacture and fabrication of essential materials. Although the several branches of construction have shown wide differences, especially during the past 15 years, there has been a general tendency to reduce the job-site operations and to deliver to the construction site materials more and more highly fabricated. This has been due in part to improved manufacturing and transportation facilities which have made possible some reduction in the costs of construction as well as increases in the size of the units which could be handled. Special efforts toward speeding up the erection of structures, in the case of building construction in the central areas of large cities, has also tended toward the use of highly fabricated units. Steel columns which 20 years ago were built up, sometimes on the site, using plates and angles are now rolled in large sections of sufficient size except for the heaviest loads. A similar development has taken place in steel bridge construction, where the members, and in many cases the completed trusses or girders, are completely shopfabricated. The proportioning of concrete at a central plant, the transporting of it in trucks as large as 4 cubic yards in capacity, and delivery ready for placing; the fabrication of wallboard panels of wood, vegetable fiber, asbestos-cement, or gypsum; ready-cut structural members for small houses; and the complete shop fabrication of removable interior partitions, especially for office buildings, are further examples of this development.

The methods of construction on the site itself have also experienced important technical changes in many operations. Equipment such as trenching machines, concrete pavers, caterpillar-tread power shovels, and pneumatic-tired trucks have come into wide use during the past 15 or 20 years. Two of the most recent developments are the actual pumping of concrete at the rate of 40 to 60 cubic yards per hour and the drilling by continuous rotary methods of large caissons of 5 feet to 12 feet in diameter for bridge and building foundations.

Primary Effects

of Technological Change

Technical improvements in construction are related, in important respects, to costs and to the size of the works and structures which are technically feasible. These two primary effects appear to be associated in many cases with secondary changes such as the enlargement of the volume of activity and employment, the stimulation of other industries, improved community

health, and variations in the rate of urban growth. Single cause and effect in economic and social actions is, of course, exceedingly rare and the social effects of technological changes in construction are no exception to this general observation. It is believed, however, that some of the secondary changes just mentioned, even though not dominated by technology, are often determined by it to an important degree.

Long-term trends in construction costs frequently reflect the technical improvements in various types of construction. The differences in some of these trends are shown by the indexes which appear in chart 1. Although a number of factors such as labor productivity, contractor's profits, the prices of labor and materials, and the size of projects included from year to year enter into indexes of construction costs, they do not show the systematic differences between the various types which are clearly evident in the case of the technological factors. The construction of buildings during the past 15 years has experienced a number of technical improvements but, excepting those of the past year or two, they have not been conspicuous. However, grading and excavation for highways and railroads, as has already been observed, has seen a notable series of developments in the introduction of new equipment such as wheel scrapers, pneumatic-tired trucks of large capacity, loading machines, and heavy tractors. Power shovels have also increased greatly in mobility, ruggedness, speed, and economy of operation as well as in size. The largest shovels are actually much too large for most construction operations (they have a capacity only slightly less than that of an ordinary freight car) and are used for stripping purposes in open-pit coal mining operations. The index for bridge construction costs shown on figure 72 relates, subsequent to 1922, to structures built by State highway departments and is not based upon any single span or type of structure. Major improvements in highway bridge structures both concrete and steel are well known, but, excepting in the longer and heavier spans, have not been as notable as have been the technical changes in grading and excavating. The differences in the trends in the costs shown in this chart are very largely attributable to differences in technological developments.

New technical developments or improvements frequently make possible works and structures of a type or extent which otherwise would be impossible. Long span suspension bridges, such as the George Washington Bridge across the Hudson River at New York City, were made possible by the development of cold-drawn steel wire of high strength. Treatment plants for the purification of large quantities of turbid, bacterialaden water for domestic use have been made possible only as chemistry and biology have developed the re

quired processes. Modern reinforced concrete buildings and bridges have depended heavily upon new methods for the stress analysis of rigid structures, power equipment for mixing the concrete, and recent developments in the chemistry of cement. Subaqueous tunnels in soft materials required compressed air and the air lock before they could become a reality. For many years work under high pressures was retarded by inadequate knowledge of the physiological effects of compressed air.

General Economic and Social Effects

The secondary influences of technological changes in construction are more obscure as has already been observed. In many cases technical improvements have doubtless sustained activity and employment at levels which, very likely, would not otherwise have been maintained.

Through their effects upon costs, technical improvements have also enlarged the physical volume of works possible with a given allocation of funds particularly by public agencies. According to the estimates of the Bureau of Public Roads, the expenditure, which in 1922 built 100 miles of highway, would have built 124 miles

INDEX

180

160

CONSTRUCTION WAGE RATES

140

120

of that same type of highway in 1930 and 170 miles in 1932. This was possible, not at the expense of wage rates which were substantially higher in 1930 than in 1922 and approximately the same in 1932 as they were 10 years before, but almost wholly through technical improvements in the various processes of highway construction.

The wide cyclical fluctuations in construction activity are influenced by many factors (not identical for all types of construction) such as the rate of increase in population in a given locality, interest rates, levels of prices and income, earnings of industrial corporations, the physical volume of production, the fiscal policies of governments, and many others. Technological change is only one of these factors. It may be observed, however, that the types of construction which have experienced the widest fluctuations during the past 15 years-factory, commercial, and residential building-are those in which technological change has been slight. Conversely, the types of construction in which technical development has been the greatest― highways, bridges, and dams-are those in which the volume of activity has been most nearly sustained at normal levels (see figure 73). It should not be maintained that the relatively moderate fluctuations in the latter types as well as those in waterworks and sewerage construction are the direct and sole result of technical progress in construction; but it is clear that this technical progress has not to any degree increased the fluctuations in the major types of construction

FIGURE 72. Indexes of construction costs, materials prices, and wage rates, 1919-36. 1919-100.

1. Construction wage rates, reported by the Engineering News-Record as actually paid in 20 cities in the United States. Arithmetic means of indexes of skilled and unskilled rates.

2. Station and office buildings, actual costs, United States Interstate Commerce Commission (1936 not yet available).

2. Building materials prices, United States Bureau of Labor Statistics. 4. Bridges, trestles, and culverts; grading and excavation; actual unit costs of completed work; 1922 to 1936, United States Bureau of Public Roads; 1915 to 1922, United States Interstate Commerce Commission.

activity in recent years. Probably the most apparent difference disclosed by figure 73 is that between public and private construction. Sustained revenue from gasoline taxes and general public approval of expenditures for highways, waterworks, and sewage treatment plants, as well as Government policy favorable toward public works in periods of depression, have been very important factors in moderating the fluctuations in these types of construction during the past few years.

Related Trends In Other Industries

Technical trends in other industries, in many cases, also influence construction. For example, improvements in farming have lessened the proportion of our population required for the production of basic agricultural commodities. A century ago, more than threefourths of the working population of this country was required to provide food and other necessaries from a reluctant soil and only a very few could be spared for the production of other conveniences of life. This condition has given way gradually to an age in which, according to the census of 1930, less than one-fourth of all gainfully employed persons in the United States were required on farms to provide basic agricultural commodities even in abundance. This change has resulted for many years in a shift of population from farm to city areas, particularly to the satellite communities of large metropolitan districts. This shift has been met by a movement away from the centers of these metropolitan areas because of unsanitary and congested housing conditions. These migrations, which the automobile and rapid-transit lines have largely made possible, have resulted in periods of marked building activity in the outskirts of urban areas, such as occurred from 1922 to 1928. The volume of residential building has been tremendously influenced by this process of urbanization and other types of construction have also been directly affected.

There appears to be no adequate justification for assuming that a sustained reversal of the long-time movement is to be expected, although the growth of cities is likely to be at a somewhat slower rate than that experienced in recent decades. The development to a commercially practicable stage of chemical processes which will further utilize products of the soil in the manufacture of essential industrial commodities such as fuel alcohol from specially developed starchy grains; oils from the tung tree or the soybean; or a wide variety of fabrics and plastic materials from young-growth timber may further retard the movement of population from the farm to the larger cities. In any event the rebuilding and modernization of cities, rather than the provision of shelter for new population, will probably represent a larger portion of urban construction activity than has been true in the past.

The phenomenal technical developments in the automobile industry during the past 25 years have also influenced construction in many ways. Indeed, the construction of highways and the manufacture of trucks and motorcars are particularly dependent one upon the other for their development. The introduction of new processes in chemical, steel, electrical machinery, and other industries is also frequently reflected in factory building activity.

In view of the important differences in the developments in the various types of construction several of them are discussed in some detail in the following pages. Not all types have been included. Railroad construction, for example, is not treated separately, but comments upon earth handling and bridge structures for highways are, in many important respects, applicable to railroads. Furthermore, the major technical developments affecting railroad transportation in recent years have not been in the construction of road and track but in rolling stock such as electric and Diesel-electric locomotives and lightweight streamlined trains. These improvements are discussed in the chapter of this report dealing with Technology and Transportation. It may be observed here, however, that the recent increases in train speed resulting from these mechanical improvements may also soon require construction changes in alinement, superelevation of curves, and improved smoothness of track. Although not all types of works and structures are included in the following pages, those which are discussed cover a wide range from small houses in which structural changes have been slight to highways in which recent technical progress has been particularly rapid.

Houses 2

The provision of domestic shelter has been one of the slowest of the arts to respond to the widespread technical progress of recent times. To be sure, houses, in spite of their slow improvement, had for many years provided fairly adequately for the protection of human life against the hazards of severe weather and had made possible some privacy of individual and family life. Nevertheless, prior to the past 2 or 3 decades they had afforded, except for a very few, little convenience or comfort and, with the possible exception of very recent developments, have experienced little change in methods of fabrication on the site for a century or more.

From the point of view of technical improvement a distinction must be made between the housing structure, the facilities with which it is provided, and the community utilities with which it is served. Structurally, the detached houses which were built in the

2 Prepared by Lowell J. Chawner, U. S. Bureau of Foreign and Domestic Commerce.

largest number in 1936 were not essentially different, as has just been observed, from many of those built in urban areas 100 years or more ago. In both 1936 and 1836 the materials: Brick, stone, sawed lumber, sand, and lime were delivered to the site in much the same form and erected in much the same manner, although the materials themselves are now produced by methods far in advance of those formerly used. Architecturally, the 1936 house may or may not have differed from its predecessors in appearance, depending in part upon the section of the country in which it was built. In plan, the interior today probably puts space to more sustained use and provides better light and outlook than did the 1836 house, but in general the architectural features of small houses have shown no notable changes. The facilities included, however, have experienced substantial improvements. Central heat, hot and cold running water, interior water closets, and installed baths, which were rarely provided 100 years ago are commonplace essentials in millions of houses today. Also community planning, frequently ignored in the hasty urban growth of the United States, has recently received increasing attention of designers. Light, air and open space, parks and playgrounds; protection against the noise and dangers of heavy traffic on streets and highways; and the arrangement of houses or other dwelling units in the interest of economy in providing for utilities are essential technical considerations of modern housing.

The technical availability as well as the extensive use of these facilities should not obscure the extent to which they are still economically unavailable to large groups of our people. For a surprising number of families, housing is still little more than shelter. Recent statistical inquiries into the condition of urban residential property have provided detailed measures of housing conditions not heretofore available. The most extensive of these inquiries, conducted during the early months of 1934 in 64 cities throughout the United States disclosed a wide range of data on the crowding, facilities provided, the age and condition of structures, and other housing information. "Crowded" conditions (from one to two persons per room) were disclosed in 15.6 percent of the dwelling units surveyed. About one-fourth of the units in the 64 cities were without installed bathing facilities and almost one-fifth without private indoor water closets. In several of the cities the units which were without installed baths or water closets ran as high as half of the standing dwelling units. A number of these urban areas also showed more than one-fourth of the units to be without running water. These proportions, which may be accepted as roughly representative of all urban

Real Property Inventory, 1934, Department of Commerce, Bureau of Foreign and Domestic Commerce, Washington, D. C.

areas, although many of the oldest cities and poorest housing were not included, indicate that approximately 4 million urban American families are still without the barest essentials of "modern improvements" such as running water, private indoor water closets, and bathing facilities, in addition to possibly twice that number in rural areas. The wide technical advance in production methods which has brought the price of adequate clothing, books, a wholesome variety of foodstuffs, even of radios and automobiles in normal times within the range of nearly all persons still finds "modern" houses (not necessarily new ones) beyond the means of one-third to one-half of the families of the United States.

Facilities

During the past 15 years the technical developments in housing facilities have consisted largely in the gradually increasing adoption of the features which have already been mentioned and in the wider use of improved heating units, electricity, gas, elevators in multi-family units, refrigeration, and the use of domestic labor-saving devices largely powered by electricity. Insulation against heat transfer through walls and roof has also developed extensively since about 1930. This is also true of devices for air circulation, cleansing, and humidity control which are being installed in many new homes today. Air refrigeration is technically available but at present is within the reach of but few families.

Further technical developments in the insulation, heating, ventilation, and air cooling of houses and other buildings will undoubtedly be made during the next few years. One of the most interesting possibilities is the perfection of the electrically powered heat pump. It is theoretically possible, as was observed by Lord Kelvin in 1852, to reverse a refrigeration process and to use it for heating purposes. In moderate climates (where temperatures seldom go below 30° to 40° Fahrenheit) the efficiency of such a device may be as high as 300 to 500 percent; that is, a unit of electrical or mechanical energy may, by reversing the principles of the heat engine, transmit heat energy from a low temperature source to a higher temperature body in an amount three to five times that of the original electrical or mechanical energy applied. A few heat pumps of this type have actually been installed in England and in this country. A combined installation for cooling in summer and heating in winter is attractive to contemplate and appears altogether possible in

Refrigeration, A. R. Stevenson, Jr., Journal of the Franklin Institute, vol. 208, pp. 143-187, August 1929.

Two-Mill Commercial Heat, by Reversing Refrigeration Cycle, W. R. Chawner, Electrical West, Apr. 1, 1931, pp. 177-179.

The Heat Pump, T. G. N. Haldane, Engineers and Engineering, March 1930, pp. 64-72.