Through the course of my research into historic buildings, I frequently encounter interesting or novel materials used in their construction. While looking into a historic building with a reinforced concrete frame in downtown Minneapolis, I found out that “M/B Bars” were the type of steel reinforcement used in the construction. Searches for material on “M/B Bars” turned up several advertisements, which have provided me with some information on them.
M/B Bars were cold-twisted square steel bars manufactured by the William B. Hough Company of Chicago. The design of the bars is identical to Ernest Ransome’s 1884 patent. Ransome is often credited as pioneering commercial reinforced concrete construction in America. He recognized that because deformed steel reinforcement resisted slippage in concrete more than smooth reinforcement, it developed strength at a greater rate. Cold-twisting of steel did have a drawback; in that the ductility of the bar was decreased which in turn increased its brittleness. C.A.P. Turner, a nationally prominent engineer who lived in Minneapolis at the time decried the twisting of reinforcement for this reason. The M/B advertisements boast of the bars’ high ductility, proclaiming that they “bend double cold without fracture.” It is unclear how the William B. Hough Company achieved this increased ductility, however I consider it likely to be from the use of high quality steel.
A search for patents by William B. Hough revealed that he invented several methods for securing and/or spacing of reinforcement. From the quantity of buildings in which M/B Bars were used (provided in advertisements), it is clear that his company was successful, however I have not been able to find very much information of Hough or his company. An article in Concrete-Cement Age (Vol 3, Dec. 13, 1913), describing the collapse of a reinforced concrete building being constructed in Cedar Rapids, IA, mentions that Hough’s company both designed the building and supplied the reinforcement. The article blames the collapse on inadequate formwork; however other engineers at the time blamed the collapse on premature removal of formwork in cold weather.
Although M/B Bars and other twisted steel bars are no longer used for concrete reinforcement today, they were an important step towards the hot rolled deformed reinforcement used today. Without early advancements in the development and use of reinforced concrete by Ransome, Turner, Hough and countless other engineers and scientists, it could not have evolved into the mature structural system currently used.