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The Structural Engineering and Materials program offers graduate studies and research opportunities focused on the broad advancement of structural engineering and the built environment. Click on the links to the right to learn more about specific topics.

The Virginia Cooperative Center for Bridge Engineering seeks to advance the state of Bridge Engineering in the U. S. with a strategic emphasis on the Commonwealth of Virginia. The Center is jointly administered by Virginia Tech and the Virginia Transportation Council with the following objectives:

  • Increase the number of multidisciplinary graduates at BS, MS, and PhD levels entering the practice of bridge engineering
  • Advance the practical technology base for bridge engineering and design
  • Transfer new and relevant bridge engineering technologies to the US and Commonwealth of Virginia transportation officials
  • Work cooperatively with VTRC and VDOT to address bridge engineering issues of immediate importance to the Commonwealth.
  • Provide continuing education opportunities for US and Commonwealth bridge engineering officials (via distance learning and strategic short courses)

Faculty Member: Dr.  Ioannis Koutromanos

CONCRETE AND MASONRY STRUCTURES – Constitutive models, performance assessment, retrofit techniques

Constitutive modeling of quasibrittle materials.

The behavior of concrete and masonry structures under cyclic loading is complicated, because a number of different mechanisms can affect the structural response. The occurrence of large cracks is common for older concrete and masonry construction, due to the possibility for shear cracking. Additionally, localized mode-I crack opening and shear (mode-II) slip is expected to occur along the masonry mortar bed joints. Numerical simulation is a powerful tool for the performance assessment of such systems, allowing the determination of the response for a variety of structural configurations, material properties and loading scenarios. To this end, constitutive models must be developed to account for the inelastic behavior of quasibrittle materials (materials whose behavior is affected by cracking processes) under multi-axial stress states.

The finite element simulation of strongly localized damage (large strains concentrated over very narrow bands) with continuum elements leads to an overestimation of the strength and ductility. To avoid such overestimations, discrete cohesive crack interface elements must be introduced in a finite element model to obtain the correct deformation patterns and the strength degradation associated with strongly localized damage.

Specific research topics include:

  • Formulation and numerical implementation of constitutive models to describe the stress-strain behavior of materials characterized by cracking processes.
  • Numerical analyses of inhomogeneous quasibrittle materials at the meso- or micro-scale to elucidate the effect of the constituent interaction on the observed macroscopic behavior.
  • Formulation and implementation of discrete crack interface elements to accurately simulate the effect of strongly localized damage.
Constitutive modeling of quasibrittle materials.
Constitutive modeling of quasibrittle materials.
Constitutive modeling of quasibrittle materials.

Seismic Performance Assessment of Reinforced Concrete and Masonry Buildings Using Computational Models

Reinforced concrete and masonry structures constitute a significant portion of the building inventory in various earthquake-prone areas around the world. The determination of the seismic performance of such systems is of uttermost importance for the hazard assessment of the built environment.

Detailed nonlinear finite element models can capture the cyclic load-displacement response and failure mechanisms of concrete and masonry buildings for any earthquake loading scenario. Finite element modeling can also determine the improvement in performance of older construction due to the application of retrofit techniques.

Research topics include:

  • Validation of detailed analytical models using the results of experimental tests.
  • Performance assessment for archetype structural configurations, subjected to collections of ground motions scaled to various intensity levels.
  • Investigation of the effect of retrofit techniques on the seismic performance of old construction.
Seismic Performance Assessment of Reinforced Concrete and Masonry Buildings Using Computational Models
Seismic Performance Assessment of Reinforced Concrete and Masonry Buildings Using Computational Models
Seismic Performance Assessment of Reinforced Concrete and Masonry Buildings Using Computational Models

Faculty Member: Dr.  Roberto Leon

EARTHQUAKE ENGINEERING-  conducting computational simulations and experiments to better understand seismic behavior and improve design provisions for steel and composite structural systems.

Composite Structural Systems

Composite steel-concrete structures offer significant benefits in terms of strength, stiffness and ductility for design in seismic areas.  This form of construction is popular in Japan, China, and the rest of Southeast Asia for tall buildings, and is recognized by USA codes. However, it is not commonly used because of the perceived lack of design provisions, particularly with respect to connections.

Specific research experimental topics include:

  • Shear transfer between steel and concrete under large cyclic deformation reversals.
  • Effect of composite diaphragm action, including:
    • the appropriate values of stiffness and strength to be used in analysis,
    • the presence of openings in the floor slab, any preexisting slab cracking, and the modeling of connections to chord and collectors,the interactions between in-plane and out-of-plane forces at the local level, and
    • the degree of ductility and load path redundancy that can be obtained from diaphragms and their connections.
  • Behavior and design of circular and rectangular concrete-filled tube columns with high strength concrete and slender tube sections under large cyclic load reversals.
  • Behavior and design of composite connections between composite steel-concrete beams and concrete filled tubes with emphasis on local force transfer between steel and concrete.

Specific research modeling and simulation topics include:

  • Shear and bearing force transfer between steel and concrete under large cyclic deformation reversals.
  • Local buckling of composite sections.
  • Plastic hinge length and rotational capacity.
  • Advanced analytical models of connection behavior and performance, including combinations of shape-memory alloys and similar advanced materials to re-center connections and improve energy dissipation capacity.
  • Incremental dynamic analysis of archetypes structures in support of development of structural system factors (R, Cd,and W0).
Composite Structural Systems
Composite Structural Systems
Composite Structural Systems

Innovative Braces

In conventional seismic systems, the primary lateral resisting structural elements deform inelastically to dissipate energy during a large seismic event.  This inelastic deformation, a direct consequence of the use of ductility concepts in design, often leads to a large residual interstory drift, severe damage to structural and nonstructural elements, costly repairs, and large indirect economic losses after a major earthquake. The main thrust of this research is the development of a brace in which (1) the need for energy dissipation does not lead to residual deformations, and (2) the reuse of the re-centering component and easy replacement of the energy dissipating components damaged in an event are easily achievable. This device uses conventional buckling restrained struts to dissipate energy and superelastic shape memory alloy (SMA) wires to recenter the structure. These innovative robust hybrid braces considerably reduce permanent drift and are assembled from easily replaceable damageable elements – (Joint work with Drs. Walter Yang and Reginald Desroches – Georgia Tech)

Innovative Braces
Innovative Braces

Reinforced Concrete Beam-Column Joints

Evaluation of older reinforced concrete frames has focused on weaknesses related primarily to shear capacity of beams and columns as well as insufficient anchorage of reinforcement.  In general little has been done to model large levels of joint shear strength and deformation for older frames where joint shear failure and pullout of the bottom bars is a possibility.  Analytical studies are underway to develop an OpenSEES joint model capable of tracking this type of phenomenon.

Reinforced Concrete Beam-Column Joints

Retrofit of Older Reinforced Concrete Moment Frames

This experimental work is  will evaluate the efficacy of a new class of innovative systems with recentering and/or high damping capabilities, and will develop a framework for their design and implementation to retrofit reinforced concrete (RC) buildings. Five retrofit measures will be investigated to achieve this goal, consisting of novel bracing systems, beam-column connection elements, or columns wraps. Common advantageous characteristics of the systems include the ease of application (requiring little-to-no heavy machinery), scalability and adaptability, passive nature, and need for little-to-no maintenance through the life-cycle. Tests will be carried out on unretroffitted and retrofitted slices of a building using a large shaker (Joint work with Drs. Yang Wang and Reginald DesRoches – Georgia Tech)

Retrofit of Older Reinforced Concrete Moment Frames

Modern Sensors for Crack Detection in Steel Bridges

A wireless strain sensing system is under development to exploit the operation principle of a passive (batteryless) radio frequency identification (RFID) system.  The system consists of an RFID reader and an RFID tag, where the tag includes an antenna and an integrated circuit (IC) chip.  The reader emits interrogation electromagnetic signal to the tag (at power level P1), so that the tag is activated and reflects signal back to the reader (with power level P1′).  This reflection is also called backscattering.  The system is classified as passive because the RFID tag does not require its own power supply, i.e. the tag receives its operation power entirely through the electromagnetic emission from the reader (Joint work with Drs. Yang Wang and Manos Tentzeris – Georgia Tech).

Modern Sensors for Crack Detection in Steel Bridges

Field Testing of Structures and Post-Earthquake Performance Assessment

Full-scale testing of structures and assessment of their service performance throughout their life cycle is an integral part of the code improvement process.  This work is important for curved and skewed bridges and buildings with irregularities in strength and stiffness.  Only high quality field data should be used to calibrate and validate models that can then be used for larger parametric studies.

Similarly, post-earthquake investigations, particularly those aimed at comparing levels of performance between different detailing approaches, are an important tool to assess the real strength and deformation capacity of structural systems.  Work in this area in countries with construction practices similar to the USA (Chile and New Zealand, for example) is particularly valuable

Composite Structural Systems
Field Testing of Structures and Post-Earthquake Performance Assessment

Faculty Member: Dr. Zack Grasley

Research in sustainable infrastructure materials incorporates the following aspects:

  • Quantification of durability through novel experimental techniques
  • Modeling of environmentally-induced deformation in cementitious materials
  • Development of novel cementitious materials using nanometric modifiers and inclusions
  • Coupling of thermodynamics, mechanics, and chemistry to uncover mechanisms linking environment, reactions, and deformation of reacting media
  • Development of high-damping materials for more resilient infrastructure
  • Computational materials science applications to material sustainability and behavior
Carbon nanofibers bridging cracks in portland cement paste
Carbon nanofibers bridging cracks in portland cement paste
Atomic force microscopy image of calcium silicate hydrate phase of portland cement paste
Atomic force microscopy image of calcium silicate hydrate phase of portland cement paste
Computational analysis of geometry dependent clustering of nanometer inclusions
Computational analysis of geometry dependent clustering of nanometer inclusions
Dynamic pressurization apparatus for measurement of radial permeability based on poromechanical principals
Dynamic pressurization apparatus for measurement of radial permeability based on poromechanical principals

Faculty Member: Dr. Cris Moen (with colleagues from the College of Engineering)

THIN-WALLED STRUCTURES –  interfacing structural mechanics, computational simulations, and experiments to better understand the physical behavior of thin-walled structural members

Cold-Formed Steel Framed Buildings

Cold-formed steel is a popular construction material in low and midrise commercial and residential building construction that gains it stiffness and strength through its shape. Recent advances in thin-walled structural analysis is motivating broad sweeping changes to design approaches and codes, especially for components (e.g., studs, joists) and systems (e.g., sheathed walls, pre-manufactured metal buildings) facing wind and seismic loads.

Specific research topics include:

  • Buckling and capacity of cold-formed steel members with holes
  • Cold work of forming and plasticity
  • Initial imperfection characterization with non-contact measurements
  • Computational simulations to collapse of cold-formed steel members and systems
  • Mechanics-based design methods and tools
  • Seismic design of cold-formed steel framed buildings
Cold-formed steel framing is used to construct midrise buildings
Cold-formed steel framing is used to construct midrise buildings
Cold-formed steel structural stud buckling modes including the influence of holes: (a) local buckling, (b) distortional buckling, (c) flexural-torsional buckling
Cold-formed steel structural stud buckling modes including the influence of holes: (a) local buckling, (b) distortional buckling, (c) flexural-torsional buckling

Aluminum Structures

Aluminum is a popular material used in naval structures because of its light weight and corrosion resistance.  Most design methods for naval structures were developed in the WWII era and are currently being updated with modern thin-walled analysis and tools.

Research topics include:

  • Buckling deformation and strength of L-stiffened aluminum ship wall and deck panels
  • Influence of friction stir welding on the structural behavior of thin-walled ship hulls
  • Multi-physics structural performance of thin-walled ship hulls at high temperatures

Multi-Functional Thin-Walled Structures

Multi-functional materials such as carbon fiber composites and those created with additive manufacturing (3D printing) can benefit many aspects of our society – from better bridge construction materials to more fuel efficient commercial aircraft to deep space vehicles that are resistant to space radiation.

Research topics include:

  • Tow steered composite tailoring to maximize capacity of thin-walled cylindrical tubes for aerospace applications
  • Multi-functional material structures – for example, lightweight cellular structures with zero coefficient of thermal expansion constructed with additive manufacturing
Tailored tow steered carbon fiber composites can increase buckling capacity of thin-walled elliptical cylinders
Tailored tow steered carbon fiber composites can increase buckling capacity of thin-walled elliptical cylinders