Waterloo Engineering is mourning the loss of Dr. Sinnathamby Thambithurai (S.T.) Ariaratnam, one of the earliest members of the Department of Civil Engineering. He passed away on April 2, 2026. He was 92.
Ariaratnam joined the University of Waterloo in September 1962, recruited as one of the institution's first engineering professors when it was only a few years old. He taught in the department for nearly four decades until his retirement in 2001, and was named Distinguished Professor Emeritus in 2002.
Born in Madduvil, Sri Lanka, Ariaratnam was educated at Drieberg College in Jaffna and earned a first-class honours degree in engineering from the University of Ceylon. He went on to earn first-class honours in mathematics and a master's degree from the University of London, before completing his PhD at Trinity College, Cambridge in 1960.
His research interests included random vibration and stability, continuum mechanics, the plastic theory of structures, nonlinear mechanics and dynamic plasticity. He held visiting professorships at University College London, the Indian Institute of Technology Madras, and the University of Illinois at Urbana-Champaign.
Ariaratnam served on the editorial boards of the Journal of Applied Mechanics, Solid Mechanics Archives, and Dynamics and Stability of Systems, and was a Fellow of the American Academy of Mechanics. Those who knew him remembered a man of principle and quiet generosity who treated everyone he met with dignity and respect, and who never lost touch with his Sri Lankan Tamil roots.
Ariaratnam is survived by his wife, Ariarani; his four sons, Samuel, Daniel, Michael and Joel; and his grandson, Anton.
Dr. Sinnathamby Thambithurai