annual report 2011 - Office for Research - Northwestern University

Members of the Bažant research group in the lab. From left: Jan Vorel, visiting scholar from Czech Technical University, Prague; Mija Hubler, doctoral candidate;
Bažant; Christian Hoover, doctoral candidate; Roman Wendner, visiting scholar from Universität für Bodenkultur Wien, Vienna; Mahendra Gattu, graduate
research assistant; Kyung-Tae Kim, doctoral candidate; and Kedar Kirane, graduate research assistant. Missing from the photo are Jorg Unger, visiting scholar
from University of Weimar, Germany and Steve Albertson, lab technician.
Zdenĕk P. Bažant
McCormick School of Engineering and
Applied Science
Analyzing Structural Failure, Safety,
and Durability
A fifth-generation civil engineer, Zdeněk P. Bažant, civil and
environmental engineering, is known as a world leader in
scaling research in solid mechanics. His research focuses
on the effect of structure size on structural strength as
it relates to the failure behavior of structures. He has
also made outstanding advances in structural stability,
fracture mechanics, the micromechanics of material
damage, concrete creep, drying, thermal and corrosive
effects in concrete, finite-strain continuum mechanics, and
probabilistic mechanics of structural strength and of long
time deformation.
At Northwestern he focused first on concrete creep and
hygrothermal effects (i.e., heat and humidity). What he
calls his “cleanest simple result,” the AAEM method (Age-
Adjusted Effective Modulus Method), is now featured in
virtually all design codes and standard recommendations.
The method makes possible an easy approximate
assessment of aging and drying influences on longtime
deformations of concrete structures.
Of all his work, Bažant is probably best known for his size-
effect law, a deceptively simple formula that explains why
the strength of large quasi-brittle structures is lower than
predicted by the classical strength theory and reflects the
fact that quasi-brittle failure of structures is decided by both
material strength and energy dissipated by fracture. He
revolutionized the scaling theory by deriving his simple law
of broad applicability, bridging asymptotically the scaling
laws of plasticity and classical fracture mechanics. Bažant
demonstrated theoretically that, in quasi-brittle failure that
is preceded by large stable growth of localized fracture or
distributed cracking damage, the size effect is not statistical
but is caused mainly by stress redistribution and localization
of cracking damage associated with the release of energy
stored in the structure. He showed that the neglect of size
effect in design was a significant contributing factor in many
famous structural failures, including the Malpasset and St.
Francis dams, the giant Sleipner oil platform, the viaducts in
Oakland and Kobe earthquakes, the Schoharie Creek Bridge,
and other structures.
Bažant’s groundbreaking concepts have been applied to
numerous disciplines, including the design of concrete
structures, ship and aircraft engineering, arctic ice
engineering, geotechnical and mining engineering,
petroleum engineering, nuclear safety, earthquake-resistant
design, blast, groundshock and impact, and the assessment
of the danger of snow avalanches. He was the first to
explain the 9/11 gravity-driven collapse of the World Trade
Center. Bažant recently has been studying the fluid pressure
effects in nano-porous solids, the scaling of strength of
polycrystalline metals on approach to the nanoscale, and
the probability distribution of strength and lifetime of quasi-
brittle structures from atomistic concepts.
Excellence in Research | Annual Report 2011 29
Andrew Campbell