Professor Constantin Christopoulos

Canada Research Chair in Seismic Resilience of Infrastructure

Structural Engineering IconStructural Engineering Research Group

Contact me

Constantin Christopoulos
Dept. of Civil Engineering
University of Toronto
35 St. George St.
Toronto, Ontario
Canada, M5S 1A4

Tel: 416-978-6238

c.christopoulos@utoronto.ca

Research Interests

Professor Christopoulos’ research is primarily focused on the development of advanced high-performance structural systems that enhance the dynamic response and seismic resilience of built infrastructure.

The main research areas are:

  • development of self-centering seismic resistant systems
  • use of steel castings to enhance the seismic performance of infrastructure
  • development of wind and earthquake damping systems for high-rise buildings
  • development of seismic isolation and energy dissipation devices
  • study of the non-linear dynamics of structures
  • development of design methodologies for structures incorporating damping and isolation devices
  • vibration-based health monitoring of structures

The research involves advanced large-scale testing of new structural systems in the Structures Laboratories, simulations using advanced finite element models and the development of new design methods for the implementation of advanced resilient seismic resistant systems.

Professional and Tech Transfer Activities

Professor Christopoulos also acts as a consultant on projects involving the implementation of advanced damping and isolation technologies in structures.

He is also actively involved in the development and transfer into the market of new technologies developed through research carried out at the University of Toronto. He is a co-founder of U of T spinoff companies Cast Connex which specializes in cast steel connections and casting design and Kinetica Dynamics which markets the viscoelastic coupling damper for high-rise buildings.

Education and Designations

B.A.Sc. (École Polytechnique de Montréal)
M.A.Sc. (École Polytechnique de Montréal)
Ph.D. (University of California San Diego)
P.Eng.

Teaching

Course Code Title & Description Instructor Session Location(s) Day(s) Start Time End
CIV312H1 Prof. Constantin Christopoulos Fall 2016 Scheduled by the Office of the Faculty Registrar.
CIV1171H Prof. Constantin Christopoulos Winter 2017 RS 208 Tuesdays 9:00 12:00

Research

Validation, design and implementation of new Self-Centering Steel Braces

Researcher: Hyunhoon Choi, Postdoctoral Fellow

In this research project the 2-D and 3-D seismic response of steel braced frames incorporating traditional and more advanced bracing systems is investigated using nonlinear time-history analyses. The study includes the design of 6 buildings of different configurations and heights located in a high seismic area using traditional braced systems, Buckling Restrained Braces (BRBs) and Self-Centering Energy Dissipative (SCED) braces.

The nonlinear finite element analyses are carried out using the program Ruaumoko on suites of records representing both far-field and near-field earthquakes to assess the performance of the three types of frames.

The study focuses on the nonlinear torsional response of these buildings with different eccentricities, the residual deformations sustained by the more traditional systems as well as on the validity of a proposed design methodology for new steel buildings incorporating SCED braces.

Friction-Damped, Post-tensioned, Self-Centering, Steel Moment Resisting Frames

Researcher: Hyungjoon Kim, Ph.D. Candidate

New connections for steel moment-resisting frames that incorporate posttensioning elements to provide a self-centering capacity along with energy dissipating mechanisms to dissipate energy have been studied and experimentally validated. The connection for SMRFs in the study introduces a bolt-prestressed friction mechanism as an energy dissipating device of which friction interface consists of stainless steel and new Non-Asbestos Organic (NAO) break lining pads. The experimental study shows that posttensioned connections are capable of developing similar stiffness and strength characteristics to welded connections and undergo large deformations with good energy dissipation capacity but without inelastic deformations in the beams or columns and without residual story drift.

SCFRcon_WEB_1813400

Friction-Damped, Post-tensioned, Self-Centering System
for Moment Resisting Frames

SCFRcon_video_WEB_357346

Finite Element Analysis of the Friction-Damped System (Post-tensioning bars not shown)
(Download .wmv file)

Development of a Passive Damping System for High-rise Coupled Structural Wall Buildings

Student: Michael Montgomery, Ph.D. Candidate

As buildings increase in height and slenderness they become increasingly sensitive to wind and seismic dynamic vibrations. Currently, when engineers are faced with vibration perception problems, they must either, reduce the height of the building, increase the lateral stiffness of the structural system, or use specialized vibration absorbers such as Tuned Mass Dampers (TMD). A new damper concept for high-rise buildings has been developed through collaboration with Halcrow Yolles of Toronto, which mitigates dynamic wind and seismic vibrations. The new damper configuration can be directly incorporated into existing structural configurations such as coupled structural wall buildings. This new configuration is non-obtrusive and will not affect usable space of the building.

Image
Tall Building Susceptible to Wind and Seismic Dynamic Vibrations (PCL 2006)
 

(Download .wmv file)

Dynamic Wind Response of Building Equipped with Visco Elastic Dampers

Development of Eccentric Braced Frames (EBF) and Moment Resisting Frames (MRF) with Replaceable Nonlinear Links

Student: Nabil Mansour, Ph.D. Candidate

Steel EBF and MRF structures designed according to the latest seismic design specification are expected to sustain damage during a design level earthquake through repeated inelastic deformation and localized buckling. Repair is therefore expected to be costly and disruptive, even if the structure has met its goal of providing life safety during an earthquake. Furthermore, it is difficult to assess the extent of this damage since no measure of the cumulative inelastic action that has taken place during an earthquake is usually possible, and hence whether the structure can survive another earthquake. The objective of this research is to address these drawbacks by introducing an innovative approach consisting of designing MRFs and EBFs with replaceable nonlinear links at the locations of expected inelastic action. The research program combines analytical and large-scale experimental studies to develop, assess and validate guidelines for the design of the replaceable nonlinear link and its connection.

Image
Full Scale Validation of the Replaceable Link Concept
in the U of T Structures Laboratories

Development of High-Performance Seismic Force-Resisting Systems for Mid-Rise Steel Buildings

Student: Lydell Wiebe, PhD Candidate

This research topic is in the field of innovative structural systems for the resistance of seismic loading. The objective is to significantly improve the performance of mid-rise steel buildings under seismic loads by applying new systems that are currently being developed at the University of Toronto . These systems use post-tensioning and energy-dissipation technologies to reduce or eliminate both damage to main structural elements and residual deformations. In this way, not only is life safety provided, but there is also a significant reduction in the disruption of building activities due to repairs after an earthquake. Reducing a building’s repair requirements following earthquakes of varying magnitudes yields economic benefits for both the owner and the tenants of the building. The end objective of this project is to put forward recommendations for the practical implementation of the system that could be used by practicing engineers in the context of a design office.

Cast Steel Connector for Tubular Braces in Seismic Building Applications

Student: J. Carlos de Oliveira, MASc Candidate

Hollow structural sections (HSS) are the most efficient structural shape available for carrying axial loads.  Unfortunately, designing and detailing HSS end connections to resist seismic type inelastic brace member loading has proven to be very difficult.  Consequently, brittle failure of HSS brace member end connections have been observed in recent earthquakes.  Because of the low structural redundancy in braced frames, brittle failures at brace member connections pose a serious threat to life safety.

This thesis presents the use of a cast steel connector as an alternative to the weld-fabricated member end connections currently used in practice.  The use of a pre-engineered cast connector that has been designed to connect to a range of HSS members offers improved safety by eliminating the shear-lag effects associated with slotted HSS connections.  Further, because every connection need not be individually designed and since cast connectors can be mass produced, the proposed solution may offer cost savings when compared to conventional weld-fabricated connections.

Old vs. New Brace Connection

Connector Animation
Stress Output from the Finite Element Analysis of a Connector-Brace Assembly Subjected to Tensile Loading

Advanced Numerical Evaluation of the Seismic Response of Existing Under-Designed Reinforced Concrete Buildings and of the Effectiveness of Retrofit Strategies

Student: Gulsah Sagbas, M.A.Sc. Candidate

This research project focuses on advanced numerical evaluation of the seismic response of existing under-designed reinforced concrete buildings and the effectiveness of retrofit strategies. A numerical evaluation of non-seismically designed beam-column subassemblies retrofitted by a low invasive retrofitting technique using VecTor2 will be performed. This research will be collaborative study between University of Toronto and University of Canterbury. The experimental study was performed at the University of Canterbury, and the analytical study at the University of Toronto. The failure modes of the as-built and retrofitted specimens, determined by the experimental studies carried at the University of Canterbury, in New Zealand, are shown below.

Experimental Tests
Experimental Study Photos

Vector2 Model
Vector 2 Finite Element Model

Cast Fuse Elements for Seismic Braces

Student: Michael Gray, MASc Candidate

The goal of this research program is to develop a cast steel-yielding element that will enhance the seismic performance of concentrically braced frame steel structures. The element is intended to be the source of the inelastic energy dissipation during an earthquake while remaining elastic under wind loads.  The casting’s performance will be verified using a combination of finite element analysis and laboratory testing.

Vibration Based Damage Detection through an Experimental Modal Analysis of a Fixed Fixed Steel Beam Using Impact Loading

Student: Stephanie D'Addese, BASc Candidate

This project was aimed at investigating a means of detecting damage within a beam through an experimental modal analysis. It used a commercial software package to model a steel tube so that modal properties such as natural frequency and mode shape could be obtained. Once the modal parameters of the tube were attained for both the undamaged and damaged states of the beam, they were examined for changes so that damage could be detected. Although damage was identified from slight variations in the modal frequencies and mode shapes of the steel tube, the location and severity of that damage is inconclusive from the modal analysis performed.

Impact Testing
Impact Testing of a Steel Beam to Detect Damage

The Small-Scale Shake Table

The Structural Dynamics and Earthquake Engineering Research Team at the University of Toronto has a small-scale demonstration shake table that is capable of simulating any single degree-of-freedom base excitation on structural models. The shake table can be used for demonstration of simple structural dynamics principals, or for research projects on scale structural models including excitation using real earthquake records.

Shake Table 1Shake Table 2
Demonstration Shake Table

Three such studies have been previously conducted using the shake table:

  1. Alex Chan (2004) conducted a study of Seismic Resistant Design of Steel Structures with Replaceable Nonlinear Elements, using the shake table to verify his concept for simple moment-resisting and eccentrically-braced aluminum frames.ImageSeismic Response of Frame Using Replaceable Nonlinear Elements
  2. Neil Warburton (2004) conducted an Investigation of a Base Isolation System that was tested by modifying the frames that Alex Chan had previously constructed to include a base isolator model.

    Experimental Setup

Closeup of the Seismic Response of the Base Isolator

  • Jeffrey Erochko (2006) conducted a study of Friction-Braced Frames also by modifying the original moment-resisting frame constructed by Alex Chan.

Image


Seismic Response of Friction Braced Frame

Publications

Books

  1. Christopoulos C. and Filiatrault, A., Principles of Supplemental Damping and Seismic Isolation, IUSS Press, Milan, Italy, 2006, 500 p.
  2. Filiatrault, A., Tremblay, R., Christopoulos, C., Folz, B. and Pettinga, D., Elements of Earthquake Engineering and Structural Dynamics, Third Edition, Polytechnic International Press, 2013, 900 p.

Journal Papers

Gray, M., Christopoulos, C. and Packer, J., 2013. “Cast Steel Yielding Brace System (YBS) for Concentrically Braced Frames: Concept Development and Experimental Validations, ASCE Journal of Structural Engineering, (under review).

Guo, W.W. and Christopoulos, C., 2012. “Performance-Spectra Based Method for the Seismic Design of Structures Equipped with Passive Supplemental Damping Systems”, Earthquake Engineering and Structural Dynamics, (in press).

Guo, W.W. and Christopoulos, C., 2012. “A Simplified Procedure for Generating Performance Spectra for Structures Equipped with Passive Supplemental Dampers”, Earthquake Engineering and Structural Dynamics, (in press).

Kyriakopoulos, N. and Christopoulos, C., 2012. “Seismic Assessment and Upgrade of Type 2 Steel MRFs Built In Canada Between the 1960s and 1980s Using Passive Supplemental Damping”, Canadian Journal of Civil Engineering, (under review).

Erochko, J., Christopoulos, C. and Tremblay, R., 2012. “Shake Table Testing of a Three-Story Self-Centering Energy Dissipative (SCED) Braced Frame,” Earthquake Engineering and Structural Dynamics, (in press).

Wiebe L., Christopoulos C., Tremblay R. and Leclerc M., 2012. “Mechanisms to Limit Higher Mode Effects in a Controlled Rocking Steel Frame”, Earthquake Engineering and Structural Dynamics, (in press).

Wiebe L., Christopoulos C., Tremblay R. and Leclerc M., 2012. “Large-Amplitude Shake Table Testing of Higher Mode Controlled Rocking Steel Frame”, Earthquake Engineering and Structural Dynamics, (in press).

Areemit, N., Montgomery, M., Christopoulos, C. and Hasan, A., 2012. “Experimental Identification of the Dynamic Properties of a Coupled Shear Wall Residential High-Rise Building in Toronto”, Canadian Journal of Civil Engineering, Vol. 39(6), pp. 631-642.

Sagbas, G., Vecchio, F.J. and Christopoulos, C., 2011. “Computational Modeling of the Seismic Performance of Beam-Column Subassemblies”, Journal of Earthquake Engineering, Vol. 15 (4), pp. 640-663.

Wiebe, L. and Christopoulos, C., 2010. “Using Bézier Curves to Model Gradual Stiffness Transitions in Nonlinear Elements: Application to Self-Centering Systems”, Earthquake Engineering and Structural Dynamics, Vol. 40 (14), pp. 1535–1552.

Shen, Y., Christopoulos, C., Mansour, N. and Tremblay, R., 2011. “Seismic Design and Performance of Steel Moment Resisting Frames with Nonlinear Replaceable Links”, ASCE Journal of Structural Engineering, ASCE Journal of Structural Engineering, Vol. 137(10), pp. 202-214.

Mansour, N., Christopoulos, C. and Tremblay, R., 2011. “Experimental Validation of Replaceable Shear Links for Eccentrically Braced Steel Frames”, ASCE Journal of Structural Engineering, Vol. 137(10), pp. 1141-1153.

Herion, S., de Oliveira, J.C., Packer, J.A., Christopoulos, C. and Gray, M.G., 2010. “Castings in Tubular Structures – State-of-the-Art”, Structures and Buildings, Institution of Civil Engineers, Vol. 163, Issue SB6, pp. 403–415.

Erochko, J., Christopoulos, C., Tremblay, R. and Choi, H., 2010. “Residual Drift Response of SMRFs and BRB Frames in Steel Buildings Designed According to ASCE7-05”, ASCE Journal of Structural Engineering, Vol. 137(5), pp. 589-600.

Nuta, E., Christopoulos, C. and Packer, J.A., 2010. “Methodology for Seismic Risk Assessment for Tubular Steel Wind Turbine Towers: Application to Canadian Seismic Environment”, Canadian Journal of Civil Engineering, Vol. 38(3), pp. 293-304.

**** Winner of 2012 - Sir Casimir Gzowski Medal ****

Wiebe, L. and Christopoulos, C., 2010. “Characterizing Acceleration Spikes due to Stiffness Changes in Nonlinear Systems”, Earthquake Engineering and Structural Dynamics, Vol. 39 (14), pp. 1653–1670.

Uma, S. R., Pampanin, S. and Christopoulos, C., 2010.” Development of Probabilistic Framework for Performance-Based Seismic Assessment of Structures Considering Residual Deformations”, Journal of Earthquake Engineering, Vol. 14(7), pp. 1092-1111.

Wiebe, L. and Christopoulos, C., 2009. “Mitigation of Higher Mode Effects in Base- Rocking Systems by Using Multiple Rocking Sections”, Journal of Earthquake Engineering, Vol. 13(S1), pp. 83-108.

Kim, H.-J. and Christopoulos, C., 2009. “Numerical Modeling and Ductile Ultimate Deformation Response of Post-Tensioned Self-Centering Moment-Resisting Steel Frames”, Earthquake Engineering and Structural Dynamics, Vol. 38(1), pp. 1-21.

Kim, H.-J. and Christopoulos, C., 2009. “Seismic Design Procedure and Seismic Response of Self-Centering Post-Tensioned Steel Moment-Resisting Frames”, Earthquake Engineering and Structural Dynamics, Vol. 38(3), pp. 355-376.

Martinez-Saucedo, G., Packer, J.A. and Christopoulos, C., 2008. “Gusset Plate Connections to Circular Hollow Section Braces under Inelastic Cyclic Loading”, ASCE Journal of Structural Engineering, Vol. 134(7), pp. 1252-1258.

Kim, H.-J. and Christopoulos, C., 2008. “Friction Damped Post-Tensioned Self- Centering Steel Moment Resisting Frames”, ASCE Journal of Structural Engineering Vol. 134(11), pp. 1768-1779. de Oliveira, C., Packer, J.A. and Christopoulos, C., 2008. “Cast Steel Connectors for CHS Brace Members in Seismic Applications”, ASCE Journal of Structural Engineering, Vol. 134(3), pp. 374-383.

Christopoulos, C., Tremblay, R., Kim, H.-J. and Lacerte, M., 2008. “The Self-Centering Energy Dissipative (SCED) Bracing System for the Seismic Resistance of Structures”, Journal of Structural Engineering, Vol. 134(1), pp. 96-107.

Tremblay, R., Lacerte, M. and Christopoulos, C., 2008. “Seismic Response of Multi- Storey Buildings with Self-Centering Energy Dissipative Steel Braces”, ASCE Journal of Structural Engineering, Vol. 134(1), pp. 108-120.

Pettinga, D., Christopoulos, C., Pampanin, S. and Priestley, M.J.N., 2007. “Effectiveness of Simple Approaches in Mitigating Residual Deformations in Buildings”, Earthquake Engineering and Structural Dynamics, Vol. 36, No. 12, pp. 1763-1783.

Pettinga, D., Pampanin, S., Christopoulos, C. and Priestley, M.J.N., 2006. “The Role of Inelastic Torsion in the Determination of Residual Deformations”, Journal of Earthquake Engineering, Vol. 11, No. 1, pp. 133-157.

Pampanin, S., Christopoulos, C. and Chen, T.-H., 2006. “Development and Validation of a Metallic Haunch Seismic Retrofit Solution for Existing Under-Designed RC Frames”, Earthquake Engineering and Structural Dynamics, Vol. 35, No. 14, pp. 1739-1766.

Christopoulos, C., Lopez Garcia, D. and Tsai, K.C., 2005. “Educational Reconnaissance of the Area Affected by the 1999 Chi-Chi Earthquake Three Years Later”, Earthquake Spectra, Vol. 20, No.1, pp. 1-22.

Christopoulos, C., 2004. “Frequency-Response of Flag-Shaped SDOF Hysteretic Systems”, ASCE Journal of Engineering Mechanics, Vol. 130, No. 8, pp. 894-903. A14.

Christopoulos, C. and Pampanin, S., 2004. “Towards Performance-Based Design of MDOF Structures with Explicit Consideration of Residual Deformations”, ISET’s Journal of Earthquake Technology, Vol. 41, No.1, pp. 172-193.

Christopoulos, C., Léger P. and Filiatrault, A., 2003. “Seismic Sliding Response Analysis of Gravity Dams Including Vertical Accelerations”, Journal of Earthquake Engineering and Engineering Vibration, Vol. 2, No. 2, pp. 189-200.

Christopoulos, C., Pampanin, S. and Priestley, M.J.N., 2003. “New Damage Index for Framed Systems Based on Residual Deformations: Part I – SDOF Systems”, Journal of Earthquake Engineering, Vol. 7, No. 1, pp. 97-118.

Pampanin, S., Christopoulos, C. and Priestley, M.J.N., 2003. “New Damage Index for Framed Systems Based on Residual Deformations: Part II – MDOF Systems”, Journal of Earthquake Engineering, Vol. 7, No. 1, pp.119-140.

Christopoulos, C., Filiatrault, A. and Folz, B., 2002. “Seismic Response of Self-Centering Hysteretic SDOF Systems”, Earthquake Engineering and Structural Dynamics, Vol. 31, pp. 1131-1150.

Christopoulos, C., Filiatrault, A., Uang, C.-M. and Folz, B., 2002. “Post-Tensioned Energy Dissipating Connections for Moment Resisting Steel Frames”, ASCE Journal of Structural Engineering, Vol. 128, No. 9, pp. 1111-1120.