By the 1850s engineers were making calculations for nearly every aspect of building design; foundations, columns, beams, floor structures, roof trusses, and heating and ventilation systems. They were also calculating construction costs based on estimates of quantities of materials, the manpower and construction plant required and the duration of building activities.
The art in engineering design calculations lay and still lies in the ability to make simplifications, and approximations that reduce the difficulty and time needed to carry out the calculations to a realistic level, while still adequately representing the engineering behavior of the materials and structures being considered.
As early as 1800 it was well known that the combined effects of several forces on an object could be calculated graphically using the triangle of forces or parallelogram of forces method. These methods were limited by their analysis of only one joint at a time however in 1864 James Clerk Maxwell (1831-79) devised the so-called “reciprocal diagrams”. Maxwell’s diagrams combined the separate equilibrium diagrams for each joint into a single diagram for the whole truss, with the same number of lines as there are members in the structure representing forces.
Although Maxwell’s reciprocal diagrams provided much needed detail of the combined forces to research scientists, they proved too challenging for less mathematically gifted engineers. It was Robert Henry Bow (1827-1909) who simplified the method of notation which makes the creation of a reciprocal diagram much simpler and straightforward. In doing so, Bow,
Following are two graphical representations of (A) Shear Forces in a beam and (B) Bending Moment Forces in a beam. To the right of each are "reciprocal diagrams", from Bow's book, of the loaded truss in each.
Meanwhile, in continental Europe, graphical statics was being developed to a high degree of sophistication. The prime mover in the development of the graphical methods was German Karl Culmann (1821-81) and he disseminated his ideas through lectures and in his book “Die Graphische Statik”. Culmann’s books methodically analyzed the graphical methods that could be used to solve numerous problems in statics including suspension bridges, retaining walls, simple and long span beams, arches, trusses and many others. Culmann was the first to make regular use of bending moment and shear force diagrams that show so vividly how a beam is working as a structure. Much of his work dealt with statically indeterminate structures in which the distribution of loads is affected by the stiffness of the materials and structural members.
It would be difficult to overestimate the impact of graphical statics on the world of structural engineering; it was certainly no less significant than the impact of the computer in the late twentieth century. The use of graphical methods to represent engineering data continued to grow in the middle of the nineteenth century.
An even more ingenious and sophisticated graphical means of calculating was developed by the French mathematician Maurice Ocagne (1862-1938) in the 1880s, a technique he called "nomography." Its purpose was to solve all all equations of a given type by means of one diagram. Nomograms formed an important part of design methods in many branches of building engineering well into the 1980s.
The following nomogram can be used to choose a correctly sized hose:
By the 1850s the use of cast iron internally for columns and beams im mills ad warehouses was well established. So too was the use of wrought iron for roof trusses. All these buildings howeever had external walls of masonry for some very good reasons. The masonry walls:
The skeleton frame has no masonry wall and the structure needs a means for carrying wind loads and providing stability against overturning. This is provided by one of three means:
All these solutions had long been used in the iron frame's ancestor, the timber frame.
Perhaps the first iron building that used rigid connections between column and beam to provide stability was Hungerford Fish Market, London, designed by Charles Fowler, one of the first architects to exploit the sculptural qualities of cast iron. This was little more than a roof covering the market stalls and being open-sided, lacked the walls that would usually provide stability for a building. This form became the pattern for many thousands of canopies over the platforms of small railway stations during the following decades.
The experience gained in the development of the skeleton frame proved extremely valuable when the firm Fox Henderson won the contract to build the Crystal Palace in London's Hyde Park.
The engineering of the building is pervaded by ingenious devices that were not only innovations in srtrucural engineering, but also enabled the uilding to be constructed very economically and in incredibnly quick time--from first arriving on site on 30 July 1850, the entire building covering 70,000 square meters of Hyde Park, was constructed in just twenty seven weeks. The main features of the design were these:
The fame of the Crystal Palace spread worldwide almost instantaneously, helped very much by the reports of its design and construction in the Illustrated London News-one of the first newspapers to feature engraved illustrations. Subsequent international exhibitions in France, Germany and the U.S. all strove to match the achievements of Paxton and Fox and Henderson and many succeeded. To this day, similar exhibitions (or "expositions") are seen as an opportunity to show off innovative architecture and building engineering at their best.
The middle of the nineteenth century witnessed yet another cycle of industrial growth as manufacturing industries in Europe and the United States accelerated production to meet the increasing demand for goods both at home and abroad. Civil and building engineers saw a corresponding increase in opportunities as they provided the infrastructure to transport these goods: railways, bridges, tunnels, harbors, and dock facilities as well as their associated buildings…railway stations and warehouses at transport interchanges.
The spinning and weaving industries continued to grow rapidly in Britain as the textile trade spread worldwide, and many hundreds of mills were constructed to the well-established pattern using cast iron columns and beams and masonry jack arches and external walls. Alongside the construction of multistory mills were a growing number of engineering works producing iron machinery of every kind, not only for the textile mills but for shipyards, steam engines, railroad engines and cars, and hundreds of types of machine tools. All these industries were housed in large single-story buildings that were above all functional and economical and from the 1850’s on, made mainly of wrought and cast iron rather than masonry and timber.
The typical works or fabricating shops had three bays—two single-height areas on either side of a central double height space that contained one of more large gantry cranes for handling the heavy raw materials and finished artifacts. The main structure consisted of cast iron or wrought columns, wrought iron beams or trussed girders, and a roof of wrought iron trusses supporting a covering of corrugated iron and including, perhaps, roof lights to illuminate the working areas beneath. In the early nineteenth century, the walls were often still made of brick or stone, but in the second half of the century, these two would be replaced by iron columns supporting a curtain wall of corrugated iron.
Between the 1830s and 1880s, tens of thousands of engineering workshops and factories were constructed of wrought iron in every industrial country of the world. Once these skills were mastered for the construction of small buildings, they could be applied to larger and larger structures.
By the 1860s the world’s railways and steamships were transporting growing numbers of people and goods and this had a considerable effect on the ease and rapidity with which ideas spread from one country to another. New ideas and achievements in civil and building engineering spread throughout Europe, America and major cities throughout the world. No longer was it ignorance of technical ideas that inhibited new developments; it was more likely the lack of engineers with practical experience to apply these ideas.
Railway stations were highly visible and with their often massive and impressive scale, were regarded by many architectural historians as the cathedrals of the nineteenth century. No building type contributed more to spreading an awareness of iron construction than the railway station, and none more than St. Pancras Station (1865-68) engineered by William Henry Barlow & Rowland Mason Ordish
Starting with the Crystal Palace, the growing number of national and international exhibitions provided opportunities for showcasing the iron frame. One of these was the first major contract for Gustave Eiffel (1832-1923) who later built two of the world’s best known monuments, the Statue of Liberty (1880-1884) and the Eiffel Tower (1889). Railway stations, exhibition buildings and the pervasive market building were all well suited to iron construction because they were single-story buildings that required no fireproofing. The last 1800’s saw the building of Paris’ first of its grand department stores, Le Bon Marche which featured exposed iron on an impressive scale. It was the work of architect Louis Charles Boileau (1837-1914) and engineer Armand Moisant (1838-1906), While designing Le Bon Marche, Monsant was collaborating with architect Jules Saulnier (1817-81) for a new mill and factory building at the Menier Chocolate Factory (1872) which incorporated a unique and remarkable frame comprising a wrought iron lattice that stretched the full length and height of each wall and was infilled with brickwork. By the early 1870’s wrought iron frame construction had become an acceptable choice for virtually and type of building--banks, libraries, art galleries, and even churches.
Steel became cheaper to manufacture and its quality improved following the development of two new methods for making it—the Bessemer process, developed in Britain in 1856 and the Siemens-Martin process developed in Germany in 1863-64. Steel first began to replace wrought iron in the railway industry and later for high pressure boilers for steam engines, then finally, from the early 1870’s on in the building industry.
The first use of steel for a large building was in Ferdinand Dutert's design for Galerie des Machines at the 1889 Exposition Universale in Paris where it stood alongside the Eiffel Tower which was made of wrought iron.
By the 1860s, machine-made detail paper-commonly light buff in color-was available in large sizes from a roll. It included hemp or other fibers to enhance its strength, making it especially suitable for working or "shop" drawings. Paper premounted on muslin and often bound along the edges with fabric or tape, was also available. Finished drawings could be made on inexpensive tracing paper, and copied using the new "cyanotype" process.
The cyanotype or "blueprint" photographic process was first introduced by the astronomer John Herschel in 1842, although not commonly used by architects and engineers until the late 1850s. The copy paper was impregnated with a mixture of ferric ammonium citrate and potassium ferricyanide, and placed under the original. When exposed to bright light, the two chemicals reacted and turned blue; the paper shielded by the ink or pencil lines of the drawing remained white.
Early blueprints were rather laborious to make. The sensitized paper, with the translucent original on top of it, was placed in a glass-fronted printing frame that was then placed in the sun. After the paper had been adequately exposed, it was removed from the frame, thoroughly washed, and hung up to dry. In the 1860s, linen cloth made from flax became a more durable alternative to tracing paper, but fell out of favor by the 1930s because of its cost. The copying process was mechanized around 1900 using artificial ultraviolet and a rotating drum that transported the original and copy paper.
In the early 1870s, the "hectograph" (from hekaton, the Greek word for one hundred) was developed as a way of copying drawings. Descended from James Watt's copying process, it was much improved by the use of special pencils or ink that contained water-soluble aniline dyes, usually purple or bright blue. A drawing was pressed against a damp gelatin pad or "graph," which absorbed the dyes. After the original was removed, sheets of blank paper were pressed against the image on the graph; up to fifty prints could be produced before the ink was exhausted. Although the process was initially used mainly for copying correspondence or specifications, by 1900 aniline-dye inks and pencils were being sold in many colors so that colored drawings could be copied.
Despite the replacement of timber construction by various forms of so called fireproof construction during the 1840s and 1850s, fire remained a major cause of death and of damage to buildings in the late nineteenth century. As construction boomed in large cities in Europe and America, the numbers of patented fireproofing systems for buildings proliferated. The importance of ensuring that columns did not fall in a fire was well recognized and many types of fireproof columns were also patented. In 1860 John Cornell Patented the idea pf making columns using two concentric cast iron tubes and filling the space between with fire-resistant clay. Probably the best known and most commercial successful column though not inherently a fireproof one was the Phoenix column patented in 1862 by Samuel Reeves of the Phoenix Iron Company. It was originally used as a way of making large compression members for iron bridges by riveting together four, eight, or more segments along their longitudinal flanges. The use of Phoenix columns spread into iron frame buildings in the 1870s and fire protection was afforded by terra-cotta tiles held in place by wrought iron bands.
With so many patentees claiming to have invented fireproof materials and construction methods, the authorities in several countries, including Germany and Austria from the mid-1880s on and the United States starting in about 1890, began undertaking fire tests to investigate the claims. In 1896 the National Fire Protection Association was formed and by 1903 Underwriters Laboratories was testing construction systems, building materials, electrical products and fire protection equipment
The circumstances that led to this period of remarkable innovation by both architects and engineers were rooted in the economic climates of the two cities.
The huge demand for new building following both the Civil War and the Chicago fire, however, created enormous pressure to build more cheaply and more rapidly than traditional masonry construction allowed. This coincided with the pressure to generate higher financial returns on the capital investment in building, which meant improving the net-to-gross ratio (i.e., increasing the usable floor area for a given building footprint). This was achieved both by reducing the proportion of the building plan taken up by load-bearing masonry walls and, in those days before electric lighting, by increasing the depth to which daylight penetrated inside the building. The latter was done by using light wells, increasing story heights, and increasing the amount of glazing in the external envelope.
One of the first buildings to benefit from a reappraisal of these methods was the Equitable Life Assurance building in New York, designed in 1867 and completed in 1870. After the scheme for the building had been chosen, the young project architect, George B. Post (1837-1913), who had trained as a civil engineer, set about redesigning the internal structure of the building following precepts more typical of multistory mill buildings than of architect-designed buildings in New York. His redesign was said to have halved the cost of the internal structure.
Here, George Post created an even more radical structural solution.
Although radical in many respects, the Produce Exchange was conservative in a significant way:
The Coal and Iron Exchange in New York, was designed by Richard M. Hunt (1828-95) and completed around 1873. The inefficiency resulting from the large amount of floor area occupied by load-bearing masonry columns and walls was overcome in three steps. The first was to carry the internal floor loads on iron columns of a much smaller cross section. The large size of the masonry walls and columns can be seen in the basement and first few stories. In the fourth floor and above, some of the internal masonry columns are replaced by iron columns of much smaller sections. Another notable feature of this building is the use of inverted arches in the foundations to distribute the loads over a larger area of soil-a technique that, in turn, increased the height to which buildings could be constructed. In 1871, when this building was being designed, ten stories was unusually tall for a building in New York. The Coal and Iron Exchange building may have been the first in the U.S. to use inverted arches.
Displayed here is a building section showing thick load bearing masonry walls and piers, and inverted arches in the foundation.
The second step toward replacing masonry construction was taken by William LeBaron Jenney (1832-1907) in 441 the First Leiter Building in Chicago (1878-79). He was the first engineer in the U.S. to place iron columns just inside the facade to carry the floor beams. While this followed the precedent set in many industrial workshops and, indeed, in the Crystal Palace, as discussed in the previous chapter, Jenney was the first to apply the idea to mainstream commercial office building. Since the masonry facade now had to carry only its own weight, it could be thinner, creating additional useful floor area in 440 the lower stories. This type of construction came later to be known as "cage construction," or the "cage frame."
The Home Insurance Building, completed in 1885, was a landmark in the history of building construction. In it, Jenney took the third and final step in reducing the floor area occupied by masonry: Each story of the masonry facade was supported by beams at the floor level of that story. The maximum height of masonry was thus reduced to single-story height. Not only did this design, later called "skeleton-frame construction," greatly increase the usable floor space, it also avoided the problem of the different rates of expansion of iron and masonry. The building authorities, however, refused to allow Jenney to use iron columns in the party wall for fear of disturbing the neighboring building
Another breakthrough was Jenney's use of rolled steel I-beams, manufactured by Carnegie Steel through the Bessemer process, instead of wrought iron above the sixth floor. This marked the first time in the U.S. building industry that permission was given to use Bessemer steel in building construction. The Home Insurance Building's iron-and-steel-frame structure weighed onethird that of an all masonry structure in a similarly designed building. This resulted in a huge saving in the cost of materials compared to traditional masonry construction. In addition, the foundations could be smaller, creating highly valuable basement space for the building services plant. Finally, Jenney's use of the skeleton frame meant that buildings could now be taller.
Now that the envelope of the building was non-load-bearing, entirely new methods had to be devised for supporting the windows and other elements of the facade. Because developers still wanted these buildings to have the appearance of masonry, the design of the facade involved much intricate detailing. Rather than load-bearing partition walls to support the floors also led to simplified building plans and a rationalized approach to the distribution of services throughout the building. The stairs, elevators, and risers that carried the services vertically through the building were clustered together to simplify construction and rationalize the layout of offices. The horizontal distribution of electricity and gas for lighting, and air for ventilation, was usually located above the ceilings in corridors that required less headroom than the offices themselves.
The Fort Dearborn Building (1893-95) by Jenney & Mundie provide us with examples of many of these new methods.
The foundations for tall buildings was an issue of particular significance in Chicago as beneath the city was a layer of highly conpressible clay. 15 meters deep and that severely limited the loads that could be placed on conventional masonry foundations.
The engineer who took the first step in this crucial branch of building engineering was John Wellborn Root (1850-91), better known perhaps as one half of the firm Burnham and Root. Root met Daniel Burnham during his first job as a draftsman, and they formed their partnership in 1873. Root recognized the importance of technical and engineering issues to the design of increasingly large buildings in 1880s Chicago. He summarized the technical process of design as a nine-part set of goals:
1 The design should provide the largest floor area and most spacious building consistent with financial success;
2 The floor plan must provide maximum daylight for rooms; an L-shaped plan would usually achieve this;
3 Lifts should be located centrally, either side of an entrance hall;
4 The building services-heating and ventilation equipment, electrical equipment and distribution, gas or electric lighting should be located to allow easy use, maintenance and alteration;
5 The height of each story should be standardized at the optimum-10 feet 6 inches (3.2 meters);
6 Walls should contain as many openings as are consistent with their structural function;
7 The structural steel frame and fireproofing of the columns and beams should reflect not only the loads they need to carry, but also the soil conditions beneath;
8 In Chicago's notorious wet and sandy soil, foundations for walls or columns should be built on a grillage of steel rails embedded in concrete;
9 Construction of building should progress with equal speed over the whole area of foundations to avoid unequal settlement.
The Montauk Building (1881-82) in Chicago was the first of Burnham and Root's many commercial buildings designed and constructed following the new approach that Root had articulated.
It should not be imagined however that Root's approach was his own invention; it was developed in response to the requirements of a property developer, Peter Brooks a shipping enterpreneur from Boston seeking a profitable investment in Chicago. The partners designed that building for Peter Brooks. It was THe Montauk Building.
The Montauk Buildings greatest innovation was its foundations. As buildings increased in height and weight, their loads needed to be spread over a greater area of the comparably weak soil underlying Chicago; this was accomplished by increasing the area of the foundations. In the Loop district of central Chicago, the ground consists of a number of layers. The top few meters are of sandy silt covered with a variety of fill materials imported during the development of the first settlements in Chicago.
In the case of the Montauk Building, it was found that the traditional footings would serioiusly obstruct not only the basement but the ground floor. Root's response was to propose buying secondhand steel rails and laying them as a grillage to spread the loads over a large area without the need for massive stone footings. To prevent the steel from tusting the bottom layer of erails was placed on a bed of concrete; the upper layers wre encased in concrete. Foundation (d) in display.
Foundation types for Chicago buildings:
(a) Typical footing of dimension stone-rectangular blocks of hard limestone, with concrete mortar.
(b) Rubble stone pier.
(c) Section of a pier of Jenney's Home Insurance Building (1883-85)
(d) Section of a pier of The Montauk Building
Although Root intended this foundation design to be a one off at The Montauk Building, they found it effective at a subsequent project and realized that the steel-rail and concrete grillage could be of more general use. This idea alone enabled high-rise buildings to progress beyond the limit of about ten stories, and by 1892 heights had reached twice that number. The idea was taken up by Adler & Sullivan, Jenney, and Holabird & Roche, the firm of William Holabird and Martin Roche (1853-1927). In their Tacoma Building, Holabird and Roche further refined this idea by replacing the secondhand rails with I-beams of new steel. Steel grillage foundations became the preferred solution for all tall buildings in the Loop district of Chicago until the introduction of deep-pile foundations and caissons, after about 1890, and reinforced concrete foundations, after about 1905.
Holabird & Roche's thirteen-story Tacoma Building was interesting for a number of reasons.
As more and more large buildings were constructed during the 1870s, a new attitude to building design developed. Individual designers as well as architecture and engineering firms gained the confidence, step by step, to take on increasingly complex challenges.
This was no better illustrated than in the Auditorium Building designed by Adler & Sullivan at the end of the 1880s. The complexity of the building structure and the building services, not to mention the highly loaded foundations, would have made the project almost inconceivable only a few years earlier. That it was undertaken and completed is a measure of the degree to which engineering design and construction skills had progressed over the preceding decade. The firm that undertook this remarkable project was one of the most influential in American architectural history.
By the 1880s, most Chicago architectural firms had at least one partner with an engineering background. In Adler & Sullivan, formed in 1881, that partner was Dankmar Adler (1844-1900). His first independent commission was the Central Music Hall, completed in 1879. Constructed using masonry walls, with internal columns of cast iron and beams and floor girders of wrought iron, the Central Music Hall was not especially advanced for its time, however The Central Music Hall became especially famous for its excellent acoustics, and established Adler as a leading acoustics engineer of his day. It was the multidisciplinary experience Adler gained on this project that put him in a position to take on the Auditorium Building.
In 1879 Adler's firm recruited the twenty-three-year-old Louis Sullivan, who had trained as a draftsman in Jenney's office and studied at the Ecole des Beaux-Arts in Paris. (Sullivan stayed there for only a year, finding it too academic and sterile, and lacking in practical construction detail.) Sullivan must have shown his talents quickly, for he was made a partner in 1880, and in 1881 the practice was renamed Adler & Sullivan. Together Adler and Sullivan would go on to design over a hundred major buildings in Chicago
Early in their collaboration the firm was commissioned to design what would become known as the Auditorium Building. This enormous structure, which occupied an entire block, comprised a 4200 seat theater, a 10 story commercial office block, a 10 story hotel and a tower with some 15 stories of high-rent office space.
The foundations of the Auditorium Building presented particularly severe problems because of the large area of the site, the wide variation of the loads carried on each foundation, and the use of both discrete footings and continuous foundations beneath the load-bearing masonry walls that surrounded the theater auditorium. There was serious danger that the different foundations would settle at significantly different rates, which could lead to cracking of both nonstructural elements, such as windows and plastered partition walls, and the load-bearing masonry walls. At that time the prediction of founda-tion settlement was based on rather crude tests of the soil properties, and the effect of water on the behavior of soils under loads was not at all well understood.
Beneath the theater and the 10-story parts of the building, Adler designed the structure and foundations to exert a uniform pressure on the soil of 4,000 pounds per square foot (190 kN/m2); he predicted that this would result in a total settlement of the building under full load of 450 mm.
Beneath the 19-story tower, however, he was not able to reduce the load on the soil to less than about 4,500 pounds per square foot (215 kN/m 2). To minimize the differential settlement between the tower and the rest of the building, he used a form of prestressing. Prior to the start of construction he loaded the soil where the tower would stand with kentledge of brick and pig iron equal to the weight of the building, to induce the pre-dicted maximum settlement. Then, as construction proceeded, the kentledge was removed at the same rate as the weight of the building grew. To accommodate the in-evitable difference in settlement that would likely occur, the water and waste pipes were fitted with flexible lead pipe connections.
Despite the care Adler took, there was indeed significant differential settlement across the site, and movement of the building was monitored carefully. Although no serious problems arose, by the 1940s, when it had reached its final equilibrium state, the settlement of the hotel foyer floor varied from about 75mm to nearly 750mm in different areas.
By the late 1880s buildings of twelve stories were common in both New York City and Chicago, and some were a few stories higher. Their external walls were still generally of load-bearing masonry, while the internal load-bearing structures comprised columns of cast or wrought iron and beams of wrought iron. Some of the internal walls might also be of load-bearing masonry, and there would be non-load-bearing internal partition walls of brick or concrete block. In essence, this was the same structural system used in the earliest five- or six-story mills and warehouses in eighteenth-century England.
Wind loads impinging on the external masonry walls were conveyed horizontally through the floor structures to the end walls, where they could be carried down to the foundations. The external walls acted as shear walls. The sheer weight of the masonry and upper stories also served to prestress the walls in compression, which added to their stability, just as it had in medieval cathedrals.
Two further charac-teristics of buildings in New York and Chicago were signif-icant: Their location in city streets afforded some protection from extreme winds, and the heights of the buildings were not large compared to their widths-they were rarely taller than twice their width. All these factors together led engineers at the time to continue assuming that wind loads required no special consideration.
In the late 1880s a number of developments altered this picture as the interoduction of the cage frame reduced the size and weight of the external masonry walls. Although enabling the construction of taller buildings it also seperated the external wall from the main building structure, making it less practical to use external walls as shear walls so additional dedicated structural elements wouldbe needed.
On the other hand, columns of cage frame were made of wrought iron and capable of carrying bending loads unlike the former cast iron columns designed to carry only compressive loads and to which girders or ofloor beams were seldom joined by rigid connection. THe cage frame and the skeleton frame that follower it allowed for the first time the structure of a tall building to be braced by useing the rigidity of the connections between columns and beams. The wrought iron cage frame also made it easier to incorporate diagonal bracing as an alternative, lightweight means of conducting wind loads down to the foundations.
From the late 1880s to around 1910, wind bracing was incorporated into all new iron and steel-framed tall builsings. Two forms of bracing were used,
The earliest example of a tall building incorporating structural elements to carry wind loads was probably the Tower Building in New York, completed in 1889. The very narrow footprint of the building and its exposed location on Broadway, in Lower Manhattan, were undoubtedly why engineer William Harvey Birkmire (1860-1924) felt that such elements were necessary.
Two sixteen-story buildings in Chicago designed during 1889-the Monadnock Building and the Manhattan Building, one using portal-frame bracing, the other diagonal cross bracing.
Even though the Monadnock Building had a load-bearing masonry structure (the last of its kind in Chicago), its extreme height and slenderness led engineer John Wellborn Root to introduce a wind bracing 459 structure. The portal framing consisted of girders 325 mm deep riveted to the wrought iron columns.
The wind bracing structure for the Manhattan Building (1889-91), designed by the engineer Louis E. Ritter, comprised both portal-frame bracing and crossed diago-nal wrought iron rods fitted with turnbuckles. This light pre-tensioning ensured that the frame would carry ten-sion loads, in even the lightest winds. Despite the ex-pense incurred by using additional steel, many engineers employed portal bracing to create a fluid passageway throughout an entire building floor.
Thje Metropolitan Life Insurance Company Tower in New York briefly the tallest building in the world (1909 til 1913) at fifty floors was one of the first buildings to integrate this new understanding of portal bracing. Up to the twelfth floor the wind bracing consisted of deep girders with riveted connections to the columns; above the twelfth floor where bending was less acute, bracing was provided by lightweight gusset plates and knee braces.
The use of reinforced concrete to form the columns, beams, and floor structures of the structural frame of a building began in the 1880s.
From the 1750s, when the benefits of hydraulic cement were studied and publicized by John Smeaton, "mass concrete" (concrete without re-inforcement) was widely used in building foundations as a replacement for timber or stone.
From the 1830s, experimental houses were constructed using mass concrete in many European countries and in the United States. In fact, the very first paper presented at the newly formed Royal Institute of British Architects in 1836 was devoted to the nature and properties of concrete and its application to construction up to that time.
During the following four decades, many patents were granted for fire-proof flooring systems that consisted of various forms of iron rods or strips embedded in concrete or encased by precast concrete blocks; the purpose of the iron, however, was often ambiguous-it served partly to carry forces and partly to act as a frame to hold the concrete in place until construction was complete. W. B. Wilkinson (1819-1902) had patented his fireproof flooring system using iron cables in 1854, and advertisements described his firm as designers and constructors of concrete staircases and fireproof floors of all descriptions, with as little iron as possible and that wholly in tension, thereby preventing waste.
In 1867 a French gardener by the name of Joseph Monier (1823-1906) obtained a patent for a system similar to that of Joseph-Louis Lam bot for making pots for ornamen-tal flowers and shrubs and various waterproof vessels and pipes. Like the systems developed by Lambot and by Francois Coignet, the iron rods in his cement armé were used to provide an armature for the concrete. However, Monier soon realized the potential for his idea in the building industry and obtained several more patents in the 1870s and 1880s, including one in 1886 for a system of cement and iron construction for permanent or movable houses that would be hygienic and economical.
Initially, there was no evidence that his designs included place-ment of the iron where it could carry the tensile stresses that would develop in the structures. Instead, he concentrated on exploiting the waterproof qualities of cement armé, building a large number of reservoirs for storing water on farms, some with a capacity as large as 50 cubic meters.
Monier continued to promote his iron and concrete system for house construction, but few were built. In the early 1870s Monier began experimenting with different arrangements of the iron reinforcement, and soon found the benefits of using the iron to carry tensile forces. His patent of 1878 shows this idea developed to its full maturity, and the now familiar arrangement of reinforcing bars to carry tension and shear forces is clear to see.
The American mechanical engineer William E. Ward (1821-1900), who ran a factory making bolts and screws, designed and built for himself a large fireproof concrete house in Port Chester, New York (1873-76). As he wrote in a paper in 1883, "All the beams floors and roofs were exclusively made of beton, re-enforced [sic] with light iron beams and rods. "12 The reason for placing the iron beam so near the bottom of the mold was to utilize its tensile quality for resisting the strain below the neutral axis, the beton above this line was relied on for re-sisting compression. Ward also recognized the importance of the bond between the iron and concrete, both to ensure composite action of the two materials and for controlling the shrinkage of the concrete.
Until the mid-1880s, however, all the examples of reinforced concrete had been isolated experiments by individuals without the commercial backing of a contractor that would ensure their widespread adoption.
During the 1880s and 1890s, two contractors changed this situation and became largely responsible for the growth of reinforced concrete construction in Europe. One was the German firm founded by Gustav Wayss (1851-1917), which later became Wayss and Freytag; in 1885 this firm bought the rights to exploit Monier's system, patented in 1878. The other was the French firm founded by Francois Hennebique (1842-1921).
By 1902, four firms dominated the U.S. market in reinforced concrete construction. One of them, the Ferro Concrete Construction Company of Cincinnati, Ohio, designed and built what can truly be called the first reinforced concrete skyscraper, the Ingalls Building in Cincinnati (1902-1903). At sixteen stories and 65 me-ters high, though just half the height of the tallest steel-2,493 framed building at the time, it was the world's tallest reinforced concrete building. As is typical of building
As is typical of building height records, it did not hold this title for long, and in 1909 the Hennebique company was soon proud to fea-ture in its publicity the Royal Liver Building in Liverpool (1908-11) as the tallest concrete building in the world. Its crowning Liver bird statue stands 94 meters above street level.
Some architects were quick to see the design opportunities that reinforced concrete offered. This collaboration between the French architect Anatole de Baudot and structural engineer Paul Cottancin offered the opportunity to use the new material to echo the curved forms of masonry ribs and vaults.
Cottancin's system of reinforcing concrete used a woven mesh of steel wires, usually about 4 mm in diameter and about 100 mm apart, rather than individual reinforcing bars. In many of his buildings, Cottancin used both own system for reinforced concrete and his related system for reinforced brickwork. The bricks he argued carried compression stresses in the same way that the concrete did.
The Belgian-born architect Auguste Perret (1874-1954), who would become the best-known architect to work in concrete in the 1920s, began working with the Hennebique firm to develop new building forms, including those for factories, a garage, and a showroom for automobiles.
Among the examples of Peret's early work of which the Hennebique company was especially proud was the new Theatre des Champs-Elysees (1911-13), cited as a demonstration of how the firm's framing system created a fully integrated monolithic, sculptured structure, in contrast to the discrete beams and columns of a steel frame building.
After the early prominence of French engineers in developing the use of reinforced concrete during the 1890s, the lead was soon taken by engineers from German-speaking countries. In the first decade of the new century they successfully experimented with virtually every form of reinforced concrete construction; the main exception was the thin concrete shell, which they developed in the 1920s.
The main reason for the remarkable progress of these engineers was simple: They realized that the successful design of concrete structures demanded a thorough understanding of the theoretical basis of structural analysis much better than what was being learned by young engineers in any other country. The investment, so to speak, in developing structural theory during the second half of the nineteenth century finally paid off hand-somely. Structural analysis had been unnecessarily complex for many of the structures being designed in iron and steel during this period, and for this reason had not been widely taught in France, Britain, or the United States. For understanding and designing concrete structures, however, it was essential.
One company, Dyckerhoff and Widmann, was central to progress in this area. Only six years after they began using reinforced concrete in 1903, the firm had designed and constructed the enormous
At 265 meters long and 35 meters wide, the building is reminiscent of a cathedral or one of the grand Roman baths, both for its scale and its sense of drama. One side of the transverse hall is formed from six reinforced con-crete arches, each spanning some 45 meters, which open onto the station platforms.
Many dozens of buildings of similar scale were built in Germany during the period, including factories, museums, and crematoriums. Smaller gems include the platform canopy, 8.4 meters wide, at Sonneberg Station in Thuringen from 1910
and an elegant factory roof in Nurnberg, from 1918, spanning over 25 meters.
The most remarkable building from this period is the Jahrhunderthalle in Breslau, in modern Poland. To form the dome, thirty-two primary ribs spring from a ring beam supported by four arches each 20 meters high and spanning 41 meters.
Writing in 1928, the structural engineer Franz Dischinger said of this building, "With its 65-meter ribbed dome, it is not only the widest-spanning concrete roof in the world, but also the most remarkable and statically-interesting work in reinforced concrete." Coming from the man who developed the thin concrete shell in the 1920s, this was indeed a tribute.