Milo Smith Ketchum Jr.

A pioneer and promoter of thin-shell concrete and space-frame roof structures, Milo S. Ketchum Jr. was a leader in bridging the gap between precomputer and computer methods for analyzing complex structures. A renowned educator, researcher, and practitioner, he made landmark advances in the field of photoelasticity and precomputer systems for predicting the behavior a wide array of structural types. He was an inspiring teacher of, and role model for, countless engineers around the country in the latter half of the twentieth century. 

Milo S. Ketchum, Jr. (Courtesy of Martin/Martin, Inc.)

Milo S. Jr. was born on March 8, 1910, in Denver, Colorado, the third child of Milo S. and Mary Esther (Beatty) Ketchum. His older siblings were sisters Martha Esther and Elizabeth Jane. His father, an eminent early-twentieth-century educator and engineer, was Dean of Engineering at the University of Colorado in Boulder when Milo Jr. was born. During his first nine years—including his early grade school days—Milo Jr. spent his time “listening to news of the war [World War I] and playing in the campus’s open irrigation ditches.”

With a twinkle in his eye while he was “holding court,” Ketchum delighted in saying that he came from a long line of American WASPs—white Anglo-Saxton Protestants. The Ketchums-in-America date back to the 1630s. They were part of the Massachusetts Bay Colony, settling in Greenwich, Connecticut, in 1635. In the early 1800s, Milo Jr.’s great-grandfather, Eddy Ketchum, who was born in Pennsylvania, moved to Ohio, where he married Harriett Smith and where Milo Jr.’s grandfather Smith A. Ketchum was born on January 7, 1840. Twelve years later, Eddy and Harriett moved their family of eleven to a farm near Henry, Illinois.

It was there that Smith A. met and married Milo Jr.’s grandmother Martha Clement in 1865. Born in Ontario, Canada, she and her family lived on a farm next to the Ketchums. According to Milo Jr., his grandfather, in addition to being a farmer, was “a lay preacher in the Primitive Baptists, who did not believe in a paid clergy and other somewhat liberal ideas.” He also added, “My grandfather was a giant of man. My father was six feet four inches tall, but his father was even taller.”

Smith A. and Martha would have seven children. Milo Smith (Milo Jr.’s father), born on January 26, 1872, was their third. Milo S. and Mary (Milo Jr.’s parents) met while both were teaching at the University of Illinois at Urbana—she, domestic science, and he, civil engineering. They were married on September 17, 1903, and moved to Colorado in 1905, where he became a professor of civil engineering at the University of Colorado. One year later, the thirty-three-year-old Illinois native was named the institution’s dean of engineering.

In 1919, Milo Sr. resigned as dean at Colorado, and the five Ketchums moved to Philadelphia, where the head of the family took the position of department head for civil engineering at the University of Pennsylvania. In 1922, they moved to Illinois, where Milo Sr. was named dean of engineering at the University of Illinois in Urbana. It would be there that Milo Jr. and his sisters would spend the last years of their youth.

After high school, Milo Jr. immediately enrolled at the University of Illinois, where he earned bachelor’s (1931) and master’s (1932) degrees in civil engineering. In addition to his famous father, the dean of engineering, one of Milo Jr.’s other influential professors was the legendary Hardy Cross.

Cross’s iterative methods—in particular, his recently published moment distribution method—were revolutionizing the field of structural engineering. The methods allowed structural engineers to analyze and design difficult indeterminate structures—feats previously unheard of in the precomputer days. The main reason was because of the impossibly large number of simultaneous equations involved. Without computers, Cross’s methods were the only practical way it could be done. Under the tutorage of his father and Cross, Ketchum’s life-long thinking habits about the structural analysis of complex structures evolved.

In 1934, Milo Jr. moved to Colorado to work for the U.S. Bureau of Reclamation. One of his assignments was surveying and laying out U.S. Route 24 in Yellowstone National Park. He next worked for the Portland Cement Association in Chicago. In 1937, he moved to Cleveland, Ohio, becoming an engineering professor at Case Institute of Technology.

While in Cleveland, two major events occurred that would forever affect Ketchum’s life. First, he met and married Gretchen Allenbach, a marriage that would endure until her death in 1990, and would produce four children—David, Marcia, Matthew, and Mark. The pair would stay in Ohio until after World War II, when they moved to Colorado—she, for the first time, and he, as the returning native.

The second influencing event was the construction of the first thin-shell concrete structures in the United States—a small planetarium in New York City in 1934, and a large sports arena Hershey, Pennsylvania, in 1936. Both projects had many in the engineering community abuzz, especially educators, theorists, and researchers.

Thin-shell construction had been introduced into the United States in the mid-1930s by the legendary German-born, Austrian structural engineer Anton Tedesko. Tedesko came to the United States specifically to work for Roberts and Schaefer (R&S) in Chicago and introduce thin-shell concrete construction to the country.

Tedesko’s first full-scale, thin-shell concrete roof in America was the 1934 Hayden Planetarium at the Museum of Natural History in New York City, a three-inch-thick hemisphere. His second—the first large-scale thin-shell project built in the United States—was the 1936 Hershey Arena in Hershey, Pennsylvania, a three-and-a-half-inch-thick concrete barrel shell with an impressive clear span of 222 feet.

According to Tedesko, “Many shells were built during World War II, including industrial plants, military installations, and airplane hangars. Structural efficiency and performance were important requirements during these years, with the architect playing a minor role. There was no emphasis on appearance, but the structures built turned out to be clean and simple, based on function and not on architectural dreams. The shell boom continued after the war. At this point, a second firm of engineers [Ammann and Whitney (A&W) in New York] entered the field and, by the end of this first period, shells were the domain of two recognized engineering firms who at times associated themselves with local firms.”

The second period of shells in the United States came with the publication, in 1952, of the ASCE Manual 31, Design of Cylindrical Concrete Shell Roofs (primarily based on the work of Alfred L. Parme). According to Tedesko, “This ended the technical domination by the two [firms, R&S and A&W,] and, with the help of the Portland Cement Association (PCA), enabled more engineers to design cylindrical shells. Other firms of engineers entered the field and the purity of the shell form became more generally accepted. PCA’s promotional support shifted from the two pioneering firms to small, local engineers.”

Ketchum was one of those engineers. Shortly after the thirty-five-year-old founded his structural engineering company in Denver—Milo S. Ketchum Consulting Engineer—he became an enthusiastic promoter of thin-shell concrete roof construction in the Rocky Mountain region.

In due time, he convinced his architectural clients that thin-shell construction was a great solution for buildings needing vast column-free spaces. Among his trademark thin-shell concrete roof types were folded-plates, circular barrels, and hyperbolic paraboloids. The analysis of such structures involved solving large sets of simultaneous equations, unsuitable for design practice in the precomputer days. Ketchum utilized the iterative schemes he learned at Illinois—and the newly published ASCE Manual 31—to successfully deal with the problem.

St. Louis Planetarium, Forest Park, Missouri (Courtesy of Martin/Martin, Inc.)

Noteworthy among Ketchum’s numerous thin-shell projects in Colorado were Boulder’s Casey Middle School, First National Bank, and Colony Supermarket; Denver’s Ideal Cement Hangar and Fan Fair Supermarket; and Colorado Springs’s International Center at the Broadmoor Hotel, a major hyperbolic paraboloid structure. Outstanding thin-shells that Ketchum was involved with beyond Colorado included two award-winners in Missouri—the TWA Hangar in Kansas City and the St. Louis Planetarium in Forest Park.

Prominent non-thin-shell projects his Denver-based firm completed while he was active in it—or served as a consultant to it—included Denver’s Currigan Convention Center, McNichols Sports Arena, and City Center Marriott Hotel; Colorado Springs’s Antlers Hotel and Holly Sugar Tower; and Boulder’s monumental Engineering Science Center complex at the University of Colorado.

In 1962, after building his Denver firm for twenty years, Ketchum moved to Old Saybrook, Connecticut, not far from where the Ketchums originally landed in America 330 years earlier. He established and operated a branch office of his firm until 1967, when he took a position as professor of civil engineering at the University of Connecticut at Storrs. He retired from the university in 1978, returning to Denver in 1980, where he often served as a consultant to the company he first founded in the mid-1940s.

Ketchum was the author of several seminal technical papers. His book Handbook of Structural Details for Buildings became a widely used desk reference for many engineering firms prior to the advent of CADD. In his papers and lectures, he actively promoted thin-shell concrete roof construction to all who would listen. 

Hyperbolic paraboloid roof, International Center at the Broadmoor Hotel, Colorado Springs, Colorado (Courtesy of Martin/Martin, Inc.)

He was honored with numerous awards throughout his life, including a Distinguished Alumnus Award from the University of Illinois, an honorary doctorate from the University of Colorado, and the Turner Medal from the American Concrete Institute (ACI). He was an honorary member of ASCE and ACI, and a member of the National Academy of Engineering.

About working as a consulting engineer to architects, Ketchum said: “Because the engineer is essentially a subcontractor, to be successful as a consultant takes the type of person that can adjust to this secondary role and play it down. Eventually any creative ideas the engineer has will become the architect’s own.” An engineer in this type of business must be content with—and receive satisfaction from—such a situation.

A great believer in the value of professional engineering societies, Ketchum was cofounder of the Structural Engineers Association of Colorado and the Consulting Engineers Council of Colorado (now the American Council of Engineering Companies of Colorado). He served as president of both groups in their formative years. He also believed in lifelong education for engineers. Said Ketchum, “Engineers should join and participate in a professional organization, keep up with progress, and get as much education as they can absorb … and be ethical.”

His main hobbies were building and sailing sailboats.

Ketchum died in Denver on December 6, 1999. He was eighty-nine years old.