Evolution in Concrete Buildings

Preface 

Around 200 years back, in 1818 with the formation of the Institution of Civil Engineers formal journey of Civil Engineering profession started in London. Though engineering has been an essential attribute of human life almost for last 5,000 years and very much in use in Mesopotamia (Iran, Syria, and Turkey), Indus Valley Civilization (Northeast Afghanistan to Pakistan and northwest India), Ancient Egypt, Mayan (Parts in Mexico and southward through Guatemala, Belize, El Salvador and Honduras), Ancient China, Ancient Greece, Persia (Iran), Ancient Rome, Aztecs (Mexico), Inca (Ecuador, Peru and Chile). Other than construction of shelter for civilized people, followed by the discovery of wheel and sailing transportation also became very important.

The term “Civil Engineering” was probably invented by first self-proclaimed Civil Engineer John Smeaton (1724 – 1792) to differentiate it with oldest form of engineering, known as Military Engineering. Smeaton also formed the oldest the Society of Civil Engineers in 1771 which still exists in the name of the Smeaton Society of Civil Engineers, though mainly as a dining and discussion club of senior distinguished engineers.

Under the leadership of first president and eminent Scottish Civil Engineer, Thomas Telford, the Institution of Civil Engineers received a Royal Charter in 1828. Thus, formally recognising Civil Engineering as a profession with following definition:

the art of directing the great sources of power in nature for the use and convenience of man, as the means of production and of traffic in states, both for external and internal trade, as applied in the construction of roads, bridges, aqueducts, canals, river navigation and docks for internal intercourse and exchange, and in the construction of ports, harbours, moles, breakwaters and lighthouses, and in the art of navigation by artificial power for the purposes of commerce, and in the construction and application of machinery, and in the drainage of cities and towns.

With the establishment of new profession and to meet the demand of Industrial revolution several Colleges and Private Institutes were set up in different places:

• 1794: The School of Survey, Guindy, Tamil Nadu, India; became the Civil Engineering School in 1858
• 1824: The Rensselaer School, New York, USA; became The Rensselaer Institute in 1834
• 1838: The Royal Polytechnic Institution, Central London, UK (now the University of Westminster)
• 1839: The College for Civil Engineers, Putney, West London, UK
• 1847: College of Civil Engineering, Roorkee, Uttarakhand, India (now the Indian Institute of Technology, Roorkee)
• 1854: Poona Engineering and Mechanical School, Pune, Maharashtra, India (now the College of Engineering, Pune)
• 1856: Calcutta Civil Engineering College, Kolkata, West Bengal, India (now Indian Institute of Engineering Science and Technology, Shibpur)

However, it will be worthy to note Buildings, mainly private Buildings were not included as major subject for many years as initial attempts were experimental and there was no proven theory or guidelines. 

First Concrete Buildings

Perhaps the earliest known occurrence of cement is from twelve million years ago. A deposit of cement was formed after an occurrence of oil shale located adjacent to a bed of limestone burned due to natural causes somewhere around 1,20,00,000 BC in Palestine. These ancient deposits were investigated in the 1960s and 1970s. In 3,000 BC Cementous material with different admixture was used by Egyptians to build the Pyramid or by Chinese to build the Great Wall.

Around 300 BC Romans used slaked lime a volcanic ash called pozzolana, found near Pozzouli by the bay of Naples. They used lime as a cementitious material. Notable Roman author Pliny the Elder reported a mortar mixture of 1-part lime to 4-parts sand. Another Roman Author cum Engineer Marcus Vitruvius Pollio reported a 2 parts pozzolana to 1-part lime along with admixtures like animal fat, milk, and blood. In 193 BC, Porticus Aemilia was built in ancient Rome, which was one of the largest commercial structures of its time and functioned as a storehouse and distribution centre for goods entering the city via the Tiber river. Constructed in 200 AD, the a former roman temple – Pantheon's dome is still the world's largest unreinforced concrete dome.

First Reinforced Concrete Building

In 1740s, Englishman Benjamin Huntsman invented early modern crucible steel. In 1824, another Englishman Joseph Aspdin invented Portland cement by burning finely ground chalk and clay in a kiln until the carbon dioxide was removed. It was named “Portland” cement because it resembled the high-quality building stones found in Portland, England. 

A French industrialist Fran?ois Coignet was regarded as pioneer in the development of structural, prefabricated and reinforced concrete. He observed that the coefficient of thermal expansion for Steel and Concrete are almost same and these two materials can be used together.

In 1853, Coignet built the first iron reinforced concrete structure, a four-story house at 72 rue Charles Michels in the suburbs of Paris. However, Coignet's descriptions of reinforcing concrete suggests that he did not do it for means of adding strength to the concrete but for keeping walls in monolithic construction from overturning. 

In 1854, English builder William B. Wilkinson reinforced the concrete roof and floors in the two-storey servant cottage he was constructing. His positioning of the reinforcement demonstrated that, unlike his predecessors, he had knowledge of tensile stresses.

Though before 1877, there was no proven scientific theory, unless an American Inventor Thaddeus Hyatt published a report titled An Account of Some Experiments with Portland-Cement-Concrete Combined with Iron as a Building Material, with Reference to Economy of Metal in Construction and for Security against Fire in the Making of Roofs, Floors, and Walking Surfaces based on his experiments.

First Post-Tensioned Concrete Building

Use of prestressing concept in structures is more than a century old. Initial use of prestressing was found in structures like, wooden barrels (liquid containers), wooden cartwheels, small slabs. The first known use of Pretsressing in RCC slabs was recorded in 1886 by Mr. Jackson – a German Engineer. However, the ‘prestress’ introduced in the reinforcement bars was completely lost due to use of low-strength concrete and rebar.

In 1872 P. Jackson, obtained a patent in California. Used tie rods to construct beams or arches from individual blocks. In1888 C. W. Doehring (Germany) obtained a patent for prestressing slabs with metal wires. In early 1900 J. Lund of Norway and G. R. Steiner of USA made renewed attempts at prestressing with no success.

The concept of post-tensioning and its application were understood by the engineers as early as 1860s. But, none of the applications were successful. Research by Dohring, Mandle, M. Koenen, Steiner, Emererer, Dischiner etc. strengthened observations about loss of prestress, due to shrinkage, creep of concrete, relaxation of steel.

Dramatic increase in the effective capacity of strand after initial stress losses has made prestressing an economical and practical proposition. Around 1910 R E Dill of Nebraska recognized the loss of prestressing due to shrinkage and creep and constructed members with “successive” post-tensioning using “unbonded” rods. In early 1920 W. H. Hewett of Minneapolis developed prestressing for circular tanks. Many circular tanks were subsequently built.

In 1926-1928 Frenchman Eugene Freyssinet used high strength steel to overcome long-term losses and constructed the successful prestressed members. He also explained the use of this technology in structures like slabs, vaults, arches, small bridges etc. In 1940, Freyssinet introduced the now well-known and well-accepted Freyssinet system comprising the conical wedge anchors for 12-wire tendons. Further research and Development of Design Technology by Guyon, Leonhardt, T. Y. Lin, Magnel, Bijan O. Aalami and many more practicing engineers made the use of prestressed technology a boon for the field of structural engineering. Major reason of successful application of Prestressing is availability of high strength Reinforcement and Prestressing Steel. 

It wasn’t until the early 1950s and the introduction of lift slab construction (precast slab units) in the USA that the pioneering engineers revisited the application of prestressing to eliminate cracks and reduce deflections in thin flats slab in buildings. However, initially like Reinforced Concrete, Prestressing in different forms, namely Precast and Post Tension were practiced by a group of developers mainly based on precedence and experience due to absence of any theory. In 1950, famous Chinese Structural Engineer, Tung-Yen Lin introduced Load Balancing Theory.

Starting in late 1950s, simple load balancing enabled engineers to engage in design of prestressed buildings, using the skill sets they had for conventionally reinforced structures. Simple load balancing unravelled the potential of prestressing and led to a mushroom growth of its application in building construction- initially in California and later in other parts of the United States and subsequently all over the World. However, Irregular and complex floor slabs with non-aligned columns, steps, and exotic architectural features, characteristic of the luxurious buildings, were not practical to be analysed simple load balancing.

After 1980, four significant events brought the application of post-tensioning to building structures to full maturity and widespread acceptance. 

• Development of effective hardware for stressing and anchoring of single and multi-strand tendons
• Development of easy to use computer programs for effective design of post-tensioned floor systems (ADAPT Corporation, 1981)
• Extension of simple load balancing to complex and non-uniform floor slabs - typical of real life structures (Aalami Bijan O, 1985)
• Development of a universal structural modelling technique for the analysis and design of floor systems (Aalami Bijan O, 2005)

Closing Note

Post Tensioning in Building structure is becoming common all over the world including in India with an estimated growth of 18%. Post Tensioning offers many benefits which includes direct cost reduction, superior structural performance, construction efficiency and sustainability. However, it must be noted that to implement such a sophisticated technology successfully, it is essential to use advanced tools and techniques besides complying with the safe practices by experienced engineers. 

Reference:

1. Wikipedia (https://en.wikipedia.org)
2. https://www.concreteconstruction.net/
3. Aalami, B.O., Critical Milestones in Development of Post-Tensioned Buildings, a look back at the last 50 years of progress, Concrete International, Oct 2007, pp 52-56
4. Sengupta, Amlan K and Menon, Devdas, Prestressed Concrete Structures, Aug 2008
5. Dinges, Tyson, The history of prestressed concrete: 1888 to 1963, 2009, Kansas State University
6. Roy, Partha P., Prestressed Concrete: History and Applications, Dec 2013, National workshop on Innovation in Concrete Technology, C. E. Dept. of BESU, Shibpur
7. Roy, Partha P., Evolution in Concrete Buildings, International Conference on Theoretical and Experimental Advances in Civil Engineering, SRM University, Chennai, 2018.