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Er Robert F. Mast Developer of Unified Design Provisions for Flexure and AF in ACI 318

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Dr. N. Subramanian
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PostPosted: Fri Sep 18, 2020 1:04 am    Post subject: Er Robert F. Mast Developer of Unified Design Provisions for Flexure and AF in ACI 318 Reply with quote

Er Robert F. Mast Developer of Unified Design Provisions for Flexure and AF in ACI 318

I am sorry to report the passing away of ACI Past President (1995-96) and Honorary Member Er Robert F. Mast, at the age of 86. Born May 20, 1934,  Robert F. Mast received his bachelor's degree in architectural engineering from the University of Illinois at Urbana-Champaign in 1957.  He went on to serve in the US Army. n 1959, Bob joined Anderson, Birkeland, and Anderson as the "M" in the firm later known as ABAM before the 1998 merger when it became BergerABAM.  He became a partner of the firm in 1963, serving it as the President during 1972-86 and as Chairman during 1986-98. He retired as Senior Principal and Director of Engineering Development of BERGER/ABAM Engineers Inc., Federal way, WA.

Association with ACI

He joined ACI in 1959 and became Honorary Member in 2004. He was a member of ACI Committee 318, Structural Building Code during the 1971 code cycle, and was a very active and influential member of the committee for decades. He also served on the ACI Technical Activities Committee and many other Committees.

Awards and Recognition

He received the ACI Arthur J. Boase Award in 1997 and the ACI Arthur R. Anderson Award in 2003.
The National Academy of Engineering recognized him in 1989;
He received the American Society of Civil Engineers Outstanding Projects and Leadership (OPAL) award in 2002, the T.Y. Lin Award in 1969, 1973, and 2002;
The Consulting Engineers Council of Washington Engineer of the Year Award in 2000;
The Precast/Prestressed Concrete Institute's Medal of Honor in 2001, the Martin P. Korn Award in 1992 and 2001, and the Charles C. Zollman Award, 2002.  
The Washington State Academy of Science lists Robert Mast as a member of the 2011 Founding Class.

He also served as the Prsident of the Structural Engineers Association of Washington (SEAW) in 1969 and SEAW Southwest President in 1967.

In 2014, Puget Sound Engineering Council (PSEC) named Robert Mast as Engineer of the Year, acting on his nomination by SEAW.

Notable Works
His work on the monorail for the Seattle World's Fair, especially on its curved beams is notable.  According to him "Alweg's original design for the monorail beam bearings used machined bronze.  These were very expensive, and required tight tolerances.  Working with a bearings specialist, E Terry Dalton out of Lake Oswego, OR, we developed an alternative using laminated pads and stainless steel.  I believe that was a new concept in 1960-61."One of his his favorite projects is Space Mountain, on which he worked in the 1970s for Disney World in Orlando, Florida.

Contribution to Structural Design

His contributions to the structural engineering include his development of the concept of shear friction in 1968 (see Ref.1), which had applications in prestressed and reinforced concrete and became widely used in 1971 and relied on by engineers around the world. More information on Shear Friction may be had from my paper (Ref.3)

In 1992, Robert Mast (Ref.2) published a paper proposing a unified design provision for reinforced and prestressed concrete beams and column members. The main concept of Mast’s proposal is the unification of requirements for determination of strength reduction factors φ and moment redistribution. The unification of these requirements is based on the net tensile strain—the tensile strain in the reinforcement at nominal strength, exclusive of strains due to effective prestress, creep, shrinkage, and temperature change. With this proposal, net tensile strain replaced the reinforcement ratio as the primary limiting parameter for reinforcement design. Mast’s paper defined sections as tension-controlled when the net tensile strain is greater than 0.005 and compression-controlled when the net tensile strain is less than 0.002. A linear transition of the strength reduction factor occurs between these limits (see Fig.1). The net tensile strain at a section is also used to define when redistribution of moment is permissible. The net tensile strain approach resolved several issues in the ACI Code, such as calculation of reinforcement ratios for members with thin webs. With these changes, limits on reinforcement ratios and prestressing reinforcement indices are no longer necessary.

These concepts enumerated in Mast’s paper were adopted into an Appendix of the 1999 ACI 318 Building Code and fully adopted in the 2002 ACI 318 Building Code with several minor modifications.


  1. Mast, R. F. (1968) “Auxiliary Reinforcement in Precast Concrete Connections,” Proceedings, ASCE, V. 94, ST6, June, pp.1485-1504.
  2. Mast R.F. (1992) “Unified Design Provisions for Reinforced and Prestressed Concrete Flexural members and Compression Members,” ACI Structural Journal, V. 89, No. 2, Mar.-Apr., pp. 186-199.
  3. Subramanian, N., (2020) “Shear-friction and Collapse of Pedestrian Bridge at Miami, USA”, Journal of the Indian Concrete Institute, Vol. 20, No.4, Jan.-Mar., pp. 22-30.
  4. Mast, R. F., 1968, “Auxiliary Reinforcement in Concrete Connections,” Journal of the Structural Division, V. 94, June, pp. 1485-1504.
  5. Mast, R. F., 1998, “Analysis of Cracked Prestressed Concrete Sections: A Practical Approach,” PCI Journal, V. 43, No. 4, July-Aug., pp. 80-91.
  6. Mast, R. F., 2001, “Vibration of Precast Prestressed Concrete Floors,” PCI Journal, V. 46, No. 6, pp. 76-86.

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