The Ingalls Building, built in 1903 in Cincinnati, Ohio

Cincinnati, Ohio

Cincinnati is a city in the U.S. state of Ohio. Cincinnati is the county seat of Hamilton County. Settled in 1788, the city is located to north of the Ohio River at the Ohio-Kentucky border, near Indiana. The population within city limits is 296,943 according to the 2010 census, making it Ohio's...

, was the world's first reinforced concrete

Reinforced concrete

Reinforced concrete is concrete in which reinforcement bars , reinforcement grids, plates or fibers have been incorporated to strengthen the concrete in tension. It was invented by French gardener Joseph Monier in 1849 and patented in 1867. The term Ferro Concrete refers only to concrete that is...

 skyscraper

Skyscraper

A skyscraper is a tall, continuously habitable building of many stories, often designed for office and commercial use. There is no official definition or height above which a building may be classified as a skyscraper...

. The 15 story building was designed by the Cincinnati architectural

Architecture

Architecture is both the process and product of planning, designing and construction. Architectural works, in the material form of buildings, are often perceived as cultural and political symbols and as works of art...

 firm Elzner & Anderson and was named for its primary financial investor, Melville E. Ingalls

Melville E. Ingalls

Melville Ezra Ingalls , commonly abbreviated M.E. Ingalls, was a Massachusetts state legislator who went on to become president of the Cleveland, Cincinnati, Chicago and St. Louis Railroad .-Career:...

. The building was considered a daring engineering

Structural engineering

Structural engineering is a field of engineering dealing with the analysis and design of structures that support or resist loads. Structural engineering is usually considered a specialty within civil engineering, but it can also be studied in its own right....

 feat at the time, but its success contributed to the acceptance of concrete construction

Construction

In the fields of architecture and civil engineering, construction is a process that consists of the building or assembling of infrastructure. Far from being a single activity, large scale construction is a feat of human multitasking...

 in high-rise buildings in the United States.

The Ingalls building is bordered by East 4th Street and Vine Street in the Cincinnati Central Business District

Central business district

A central business district is the commercial and often geographic heart of a city. In North America this part of a city is commonly referred to as "downtown" or "city center"...

.

Overcoming skepticism

Prior to 1902, the tallest reinforced concrete structure in the world was only six stories high. Since concrete

Concrete

Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

 possesses very low tensile (pulling) strength

Tensile strength

Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...

, many people from both the public and the engineering community believed that a concrete tower as tall as the plan for the Ingalls Building would collapse under wind loads or even its own weight. When the building was completed and the supports removed, one reporter allegedly stayed awake through the night in order to be the first to report on the building's demise.

Ingalls and engineer Henry N. Hooper were convinced, however, that Ernest L. Ransome

Ernest L. Ransome

Ernest Leslie Ransome was an English-born engineer, architect, and early innovator in reinforced concrete building techniques. Ransome devised the most sophisticated concrete structures in the United States at the time....

's system of casting twisted steel bars

Rebar

A rebar , also known as reinforcing steel, reinforcement steel, rerod, or a deformed bar, is a common steel bar, and is commonly used as a tensioning device in reinforced concrete and reinforced masonry structures holding the concrete in compression...

 inside of concrete slabs as reinforcement (patented in 1884) and casting slab, beams and joists as a unit would allow them to create a rigid structure. The architects also prized the cost savings and fireproofing advantages of concrete over steel

Steel

Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 frame construction. Finally, after two years of convincing, city officials issued Ingalls a building permit and the work began.

Construction

Hooper designed a monolithic "concrete box of eight-inch [200 mm] walls, with concrete floors and roof, concrete beams, concrete columns, concrete stairs -- no steel. It consists merely of bars embedded in concrete, with the ends interlaced." (Ali)

The amount of concrete produced during construction -- 100 cubic yards (76 m³) in each ten-hour shift -- was limited by the rate at which the builders could place it. An extra wet mix was used to insure complete contact with the rebars and uniform density in the columns. Floor slabs were poured without joints at the rate of three stories per month. Columns measured 30 by 34 inches (760 by 860 mm) for the first ten floors and 12 inches (300 mm) square for the rest. Three sets of forms were used, rotating from the bottom to the top of the building when the concrete had cured. Completed in eight months, the finished building measures 50 by 100 feet (15 by 30 m) at its base and 210 feet (64 m) tall.

The exterior concrete walls are eight inches thick (200 mm) in unbroken slabs 16 feet (5 m) square with a veneer

Masonry Veneer

Masonry veneer walls consist of a single non-structural external layer of masonry work, typically brick, backed by an air space. The innermost element is usually structural, and may consist of wood or metal framing or masonry...

 4 to 6 inches (100 to 150 mm) thick. The Beaux Arts Classical exterior is covered on the first three stories with white marble

Marble

Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite.Geologists use the term "marble" to refer to metamorphosed limestone; however stonemasons use the term more broadly to encompass unmetamorphosed limestone.Marble is commonly used for...

, on the next eleven stories with glazed gray brick

Brick

A brick is a block of ceramic material used in masonry construction, usually laid using various kinds of mortar. It has been regarded as one of the longest lasting and strongest building materials used throughout history.-History:...

, and on the top floor and cornice with glazed white terra cotta

Glazed architectural terra-cotta

Glazed architectural terra-cotta is a ceramic masonry building material popular in the United States from the late 19th century until the 1930s, and still one of the most common building materials found in U.S. urban environments...

.

Landmark status

Still in use today, the building was designated a National Historic Civil Engineering Landmark in 1974 by the American Society of Civil Engineers

American Society of Civil Engineers

The American Society of Civil Engineers is a professional body founded in 1852 to represent members of the civil engineering profession worldwide. It is the oldest national engineering society in the United States. ASCE's vision is to have engineers positioned as global leaders who strive toward...

. In 1975, it was added to the National Register of Historic Places

National Register of Historic Places

The National Register of Historic Places is the United States government's official list of districts, sites, buildings, structures, and objects deemed worthy of preservation...

.