Dimitrios Lignos

Biography

Prof. Lignos joined the École Polytechnique Féderale de Lausanne (EPFL) in 2016 from McGill University in Canada where he was a tenured Associate Professor and a William Dawson Scholar for Infrastructure Resilience. He holds a diploma (National Technical University of Athens, NTUA, 2003), M.S. (Stanford University, 2004) and Ph.D. (Stanford University, 2008). In addition, he was a post-doctoral scientist at Stanford University (2009) and in Kyoto University (2010). Prof. Lignos teaches graduate and undergraduate courses in seismic design, nonlinear behaviour of steel and composite structures as well as supplemental damping systems, Structural Stability, Nonlinear Analysis and Performance-based Earthquake Engineering. His awards for teaching, research and service in Civil Engineering include the 2011 Outstanding Teaching Award (Faculty of Engineering, McGill University), as well as the Outstanding reviewer (2012, 2013) award from ASCE, the 2013 State-of-the-Art in Civil Engineering Award by ASCE and the 2014 Christophe Pierre Award for Research Excellence - Early Career. Just recently, he received the 2019 Walter L. Huber Civil Engineering Research Prize from ASCE for significant contributions in developing state of the art methods to simulate extreme limit states in steel structures.Prof. Lignos is a member of ASCE and the Earthquake Engineering Research Institute. He acts as an Associate Editor for Metal Structures and Seismic Effects of the ASCE Journal of Structural Engineering. He joined the Editorial Board of Earthquake Spectra and Earthquake Engineering and Structural Dynamics International journals. He serves as an acting member of the CEN/TC 250/SC 8/WG 2 and has been selected as a member of the Project Team (PT2) for the Eurocode 8-Part 1 Current Revisions for Steel and Composite Structures. He is also a member of the Canadian Standards Association (CSA) S16 technical committee for Steel Structures. Prof. Lignos is involved as a NEHRP consultant in numerous research-to-practice projects related to the behaviour and nonlinear modelling and analysis of structures applicable to the engineering practice through the Applied Technology Council (ATC). Detailed Curriculum Vitae (last update September 2018)

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Related publications (142)

Seismic Assessment and Retrofit of Pre-Northridge High Rise Steel Moment Resisting Frame Buildings with Bilinear Oil Dampers

Dimitrios Lignos

This paper presents quantitative information on the effectiveness of seismic retrofit solutions using bilinear oil dampers for seismically deficient existing tall steel buildings. For this purpose, a benchmark 40-story steel space moment-resisting frame building is studied that represents 1970s design practice in North America. Rigorous seismic performance assessment based on ASCE 41 recommendations reveals a high collapse risk for the existing building. The local engineering demand parameters are comprehensively assessed to quantify the impact of seismic retrofit on steel columns and column splices, which are particularly vulnerable due to the time of construction. Multiple retrofit schemes are explored with numerous damping levels and vertical damping distribution methods. The dampers are designed via a recently developed multi-degree-of-freedom performance curves method. A new balanced vertical damping method is proposed to account for the effects of frame inelasticity. This strongly depends on the supplemental damping level, and it determines the effectiveness of the employed vertical damping distribution method. The results indicate that the proposed retrofit strategies can minimize the collapse risk of the tall building. It is shown that the balanced vertical damping distribution method provides the most uniform drift distribution along the building height. Despite the reduction in story drift ratios, the axial force demand in exterior columns remains relatively high in the bottom stories regardless of the seismic retrofit solution. On the other hand, bilinear oil dampers produce relative constant forces despite exhibiting higher velocity demands than expected.

MDPI2023

This paper summarizes a series of analytical studies that were conducted in connection with an improved approach for the design of acceleration-sensitive nonstructural elements. In the new approach, bracing to secure nonstructural elements to the structure is designed and detailed to experience nonlinearities to limit forces acting not only in the nonstructural elements but also in the attachments to the structure and in the attachment(s) to the nonstructural element. The project was sponsored by the Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe (SERA) and involved shake table testing at the University of Bristol to validate the proposed novel approach as well as analytical studies. Prior to the testing, a series of analytical studies were conducted to examine the feasibility of the proposed approach and for selecting motions to be used in the shake table tests. By using exclusively motions recorded in instrumented buildings in California it is shown that acceleration demands in nonstructural elements can easily exceed 2 or 3g, but that by allowing nonlinearity to occur in the bracing element, acceleration and forces can be greatly reduced even with small levels of nonlinearity. In particular, it is demonstrated that given the frequency content of floor motions, which correspond to ground motions amplified and filtered by the structure, the reductions in accelerations and forces are much larger than those that are produced under ground motions for similar levels of nonlinearity. Furthermore, it is shown that the proposed approach not only results in large reductions in forces and accelerations, especially for elements tuned to any of the modal frequencies of the supporting structure but, simultaneously, it can also achieve substantial reductions in lateral deformations with respect to those that would occur on nonstructural elements remaining elastic. Yet, another important advantage of the proposed approach is that force and deformation demands become far less sensitive to the period of vibration of the nonstructural element.

Applied Technology Council, Sponse2022

Assessment of stiffener spacing design requirements for intermediate EBF links via nonlinear finite element analysis

Dimitrios Lignos

Links in eccentrically braced frames (EBFs) with intermediate length are designed with transverse web stiffeners. Web stiffening is required because the common failure modes are associated with web buckling as well as flange and lateral torsional buckling. Current design stiffener spacing requirements for intermediate length have been based on preliminary work that dates back to early 1990s. This paper assesses, through nonlinear continuum finite element analyses, the stiffener spacing design requirements per AISC- 341-16 of intermediate length EBF links.

ETAM2022

Applied Technology Council, Sponse2022