The objective of this paper is to provide a state-of-the-art review for the structural application, manufacturing, material properties, and modeling of a new material: steel foam. Foamed steel includes air voids in the material microstructure and as a result introduces density as a new design variable in steel material selection. By controlling density the engineering properties of steel components may be altered significantly: improvement in the weight-to-stiffness ratio is particularly pronounced, as is the available energy dissipation and thermal resistivity. Full-scale applications of steel foams in civil structures have not yet been demonstrated. Therefore, existing applications demonstrating either proof-of-concept for steel foam, or full-scale use of aluminum foams in situations with clear civil/structural analogs are highlighted. Adoption of steel foam relies on the manufacturing method, particularly its cost, and the resulting properties of the steel foam. Therefore, published methods for producing steel foam are summarized, along with measurements of steel foam structural (modulus, yield stress, etc.) and non-structural (thermal conductivity, acoustic absorption, etc.) properties. Finally, existing models for predicting foamed steel material properties are summarized to highlight the central role of material density. Taken in total the existing research demonstrates the viability of steel foams for use in civil/structural applications, while also pointing to areas where further research work is required. © 2011 Elsevier Ltd. All rights reserved.
Smith BH, Arwade SR, Szyniszewski S, Schafer BW, Hajjar JF (2012) Material characterization and microstructural simulation of hollow spheres and PCM steel foams, Structural Stability Research Council Annual Stability Conference 2012 pp. 602-619
The objective of this research is to characterize the mechanical properties of hollow spheres and PCM steel foams under compressive and tensile loading, and to develop and validate microstructural computational models for such foams that account for micro-scale buckling of the cell walls and localized material yielding. Such models allow the virtual investigation of the relationship between microstructural design parameters and macroscopic material properties. Steel foams are a new class of structural materials that have the potential to provide enhanced energy dissipation, stiffness, and buckling mitigation by virtue of their unusual mechanical properties. Through physical experiments we characterize some previously unreported properties of the material such as the compressive unloading modulus and its evolution with increasing plastic deformation, the Poisson's ratio of the material in the plastic range, and the tensile yield and fracture strengths. Our three dimensional finite element models are among the first to treat the material microstructure as random while incorporating both material and geometric nonlinearity at the micro-scale. The experimental characterization of the material properties feeds directly into work being performed to develop candidate applications of steel foam in civil structures, and the computational work is being used to suggest novel microstructural designs that lead to improved macroscopic material properties.
This paper provides the methodology for an energy-based progressive collapse assessment of multistory buildings. The progressive collapse of steel-framed buildings is analyzed based on an energy flow perspective. The energy based assessment of structural members is introduced, and compared with conventional force and deformation approaches discussed in the literature. Consecutively, the advantages of energy flow analysis in interpretation of extreme dynamic events are discussed. On the global level, a building can arrest the collapse, and achieve its stable configuration only if the kinetic energy is completely dissipated by the structure. Otherwise, the remaining kinetic energy will cause the collapse to continue. In a conventional building, kinetic energy is dissipated within structural members by the transformation into their deformation energy. Structural members can dissipate finite amounts of energy before becoming unstable. The column deformation energy was shown to be a better stability indicator under dynamic loading than the maximum dynamic force. The energy flow analysis is illustrated with a collapse assessment of a typical steel building. © 2012 Elsevier Ltd.
This paper characterizes mechanical properties of hollow sphere (HS) steel foam, and applies calibrated Deshpande-Fleck plasticity to mechanical simulations of steel foam components. Foamed steel, steel with internal voids, provides enhanced bending rigidity, exceptional energy dissipation, and the potential to mitigate local instability. The experimental characterization of the hollow sphere foam encompasses compressive yield stress and densification strain, compressive plastic Poisson's ratio, compressive unloading modulus, as well as tensile elastic modulus, tensile unloading modulus, tensile yield stress, tensile fracture strain, and shear yield stress and fracture strain. Since HS steel foam is compressible under triaxial pressure, Deshpande-Fleck plasticity of compressible metals was calibrated and employed in simulations. Plastic Poisson's ratio, measured in a uniaxial test, is an important metric of foam compressibility, and it affects the response of the foam to multi-axial loadings significantly. This work is part of a larger effort to help develop steel foam as a material with relevance to civil engineering applications. © 2013 Elsevier Ltd.
Ryan SM, Szyniszewski S, Ha S, Ha S, Xiao R, Nguyen TD, Sharp KW, Weihs TP, Guest JK, Hemker KJ (2015) Damping behavior of 3D woven metallic lattice materials, Scripta Materialia 106 (September 2015) pp. 1-4
© 2015 Acta Materialia Inc. Cu and NiCr metallic lattice materials of two different micro-architectures were manufactured with a 3D weaving process. Dynamic mechanical analysis experiments demonstrated that the damping properties of these materials are much greater than their bulk counterparts and were found to have damping loss coefficients comparable to polymers, but with much higher maximum use temperatures. The magnitude of the damping phenomenon is characterized experimentally, and the importance of Coulomb (frictional) damping and inertial damping are investigated using a finite element model.
Szyniszewski S, Ryan S, Ha S, Zhang Y, Weihs T, Hemker K, Guest JK (2014) Simulation of frictional damping in metallic woven materials, EURODYN 2014: IX INTERNATIONAL CONFERENCE ON STRUCTURAL DYNAMICS pp. 3857-3859 EUROPEAN ASSOC STRUCTURAL DYNAMICS
Li Z, Szyniszewski S (2013) Finite prism elastic buckling analysis and application in steel foam sandwich members, Structural Stability Research Council Annual Stability Conference 2013, SSRC 2013 pp. 654-668
The objective of this research is to develop a layer-wise finite prism method for studying the elastic buckling of steel foam sandwich members. Foamed steel, literally steel with internal voids, enables lightweight and stiff components. Steel foam sandwich panels (steel face sheets and low-density, highly porous foam core) exhibit higher bending rigidity and plate buckling strength in comparison to slender, steel plates with the same weight. Analytical sandwich plate buckling solutions are not applicable to buckling analysis of cold-formed sandwich members with interaction between local and global buckling modes. Finite element analysis (either solid 3D or shell representation) provides the most reliable solution; however, its use is complicated, computationally expensive, and not practical for engineers. The proposed layer-wise finite prism solution is an alternative, easy-to-use tool, which builds upon the shape functions available in the literature, and is verified against eigenbuckling finite element solutions implemented in LS-DYNA software. Future research is needed to incorporate the elastic buckling solutions in the direct strength design of sandwich panel members. Copyright © (2013) by the Structural Stability Research Council (SSRC).
Physics based collapse simulations of moment resisting steel frame buildings are presented with an emphasis on the development of energy flow relationships. It is proposed that energy flow during progressive collapse can be used in evaluation of moment resisting, steel frame building behavior and specifically, localized failure. If a collapsing structure is capable of attaining a stable energy state through absorption of gravitational energy, then collapse will be arrested. Otherwise, if a deficit in energy dissipation develops, the unabsorbed portion of released gravitational energy is converted into kinetic energy and collapse propagates from unstable state to unstable state until total failure occurs. The energy absorption of individual members provides very transparent information on structural behavior as opposed to oscillating internal dynamic forces in structural members. Therefore, critical energy absorption capacity is hereby proposed as a stable failure criterion in progressive collapse analysis. Energy flow quantification is shown to be readily available from the dynamic finite element simulations. The proposed dynamic, energy based approach to progressive collapse, provides insight and a simple yet robust analysis for producing structures capable of resisting abnormal loadings and/or unexpected hazards. © 2009 ASCE.
In this paper a design method for the compressive capacity of sandwich panels comprised of steel face sheets and foamed steel cores is derived and verified. Foamed steel, literally steel with internal voids, provides the potential to mitigate many local stability issues through increasing the effective width-to-thickness of the component for the same amount of material. Winter's classical effective width expression was generalized to the case of steel foam sandwich panels. The provided analytical expressions are verified with finite element simulations employing brick elements that explicitly model the steel face sheets and steel foam cores. The closed-form design expressions are employed to conduct parametric studies of steel foam sandwich panels with various face sheet and steel foamed core configurations. The studies show the significant strength improvements possible with steel foam sandwich panels when compared with plain steel sheet/plate.
Szyniszewski S (2009) Probabilistic approach to progressive collapse prevention. Physics based Simulations, Proceedings of the 2009 Structures Congress - Don't Mess with Structural Engineers: Expanding Our Role pp. 2836-2843
Physics based collapse simulations of moment resisting steel framed buildings are presented.Survival probability of a building occupant is proposed as a single scalar measure to quantify resistance to progressive collapse of a particular structure at hand. Practical procedure for the survival probability calculations by means of physics based simulations and theorem of total probability is shown in the paper. Simulations of structural response to the sudden removal of a key structural member have been carried out for a number of failure scenarios. Such analysis is at the forefront of civil engineering modeling because it involves material nonlinearities, large deflections, finite strains, and certainly requires dynamic analysis. Saving human lives in the case of abnormal loadings and/or unexpected hazards is equivalent to minimizing the area of collapsed floors. Such approach should also minimize the financial loss to a building owner.The area of collapsed floors can be extracted from the physics based simulations. It is proposed to quantify the goodness of design with the survival probability of a building occupant. Such single scalar measure provides an opportunity to employ optimization algorithms to produce the safest and the most economic structural design. © 2009 ASCE.
Liu Z, Jacques CC, Szyniszewski S, Guest JK, Schafer BW, Igusa T, Mitrani-Reiser J (2015) Agent-Based Simulation of Building Evacuation after an Earthquake: Coupling Human Behavior with Structural Response, NATURAL HAZARDS REVIEW 17 (1) ARTN 04015019 ASCE-AMER SOC CIVIL ENGINEERS
Smith BH, Szyniszewski S, Hajjar JF, Schafer BW, Arwade SR (2012) Erratum: Steel foam for structures: A review of applications, manufacturing and material properties (Journal of Constructional Steel Research (2012) 71 (1-10)), Journal of Constructional Steel Research 72
Szyniszewski ST (2011) Expected building damage using stratified systematic sampling of failure triggering events, Vulnerability, Uncertainty, and Risk: Analysis, Modeling, and Management - Proceedings of the ICVRAM 2011 and ISUMA 2011 Conferences pp. 865-872
Expected building damage is proposed as a measure of building performance against structural collapse. The proposed novel concept is illustrated with a case study of a typical steel framed building subjected to a bomb explosion and the resulting column removal. Stratified approach to systematic sampling was used to assign appropriate weights to sampled damage scenarios. Finally, an overall expected building damage resulting from randomly located explosions was analytically derived. The analytical expected damage gives a mean building failure as a function of the explosion reach. The presented expected damage is a scalar performance measure and thus it lends itself to a comparison of alternative designs. Expected damage function is a collapse signature of a given building that takes into account copiousness of explosion locations and feasible detonation magnitudes. Copyright © ASCE 2011.
Szyniszewski S (2010) Effects of random imperfections on progressive collapse propagation, Structures Congress 2010 pp. 3572-3577
Progressive collapse is an increasing concern in the structural engineering community, especially after the collapse of the World Trade Centre Towers. While numerous papers have been published on the subject, the effects of random imperfections on failure paths have not yet been studied. The presented simulation study investigated the effects of random geometric imperfections on the formation of alternative paths after the removal of the first story column(s). Eccentricities and curvatures were introduced as independent random variables for each structural element. Gaussian distributions with means and standard deviations selected on the basis of a handbook of construction tolerances were applied to represent the real life imperfections. The selected, representative seismic building was repeatedly simulated under the same column(s) removal scenario with different imperfections randomly introduced in each simulation. The presented design exhibited competing failure modes. The dominant failure mode was observed in 80% of the simulations, while the secondary failure mode manifested itself in the remaining 20% of the simulations (the same column(s) removal scenario). The presented probabilistic study revealed that real-life imperfections may result in the alternate failure paths. Monte Carlo simulations shall be employed to detect such secondary load redistribution paths and/or collapse modes. © 2010 American Society of Civil Engineers.
Szyniszewski S, Schafer BW, Smith BH, Arwade SR, Hajjar JF (2012) Local buckling strength of steel foam sandwich panels, Structural Stability Research Council Annual Stability Conference 2012 pp. 620-637
In this paper a design method for the compressive capacity of sandwich panels comprised of steel face sheets and foamed steel cores is derived and verified. Foamed steel, literally steel with internal voids, provides the potential to mitigate many local stability issues through increasing the effective width-to-thickness of the component for the same amount of material. Further, steel foams have exceptional energy dissipation and deformation capacity. A design methodology for the compressive capacity of steel foam sandwich panels (plates) is needed to facilitate application of such panels and in the civil engineering domain. Winter's classical effective width expression was generalized to the case of steel foam sandwich panels. The generalization requires modification of the elastic buckling expressions to account for shear deformations. Further, an equivalent yield stress is introduced to provide a single parameter description of the yielding behavior of the steel face sheets and steel foam core. The provided analytical expressions are verified with finite element simulations employing brick elements that explicitly model the steel face sheets and steel foam cores. The closed-form design expressions are employed to conduct parametric studies of steel foam sandwich panels with various face sheet and steel foamed core configurations. The studies show the significant strength improvements possible with steel foam sandwich panels when compared with plain steel sheet/plate. The design expressions and related parametric study provide insights on the optimal balance between face sheets and core. Given the success in defining optimal targets the obvious next step is assembly and testing of full-scale steel foam sandwich panels. This will complement existing efforts on material characterization of steel foam itself. This work is part of a larger effort to help develop steel foam as a material with relevance to civil engineering applications.
The objective of this paper is to provide and verify a new design method for the in-plane compressive strength of steel sandwich panels comprised of steel face sheets and foamed steel cores. Foamed steel, literally steel with internal voids, provides enhanced bending rigidity, exceptional energy dissipation, and the potential to mitigate local instability. In this work, Winters effective width expression is generalized to the case of steel foam sandwich panels. The generalization requires modification of the elastic buckling expressions to account for panel non-composite bending rigidity and shear deformations. In addition, an equivalent yield stress is introduced to provide a single parameter description of the yielding behavior of the steel face sheets and steel foam core. The provided analytical expressions are verified with finite element simulations employing three-dimensional continuum elements and calibrated constitutive models specific to metallic foams. The developed closed-form design expressions are employed to conduct parametric studies of steel foam sandwich panels, which (a) demonstrate the significant strength improvements possible when compared with solid steel, and (b) provide insights on the optimal balance between steel face sheet thickness and density of the foamed steel core. This work is part of a larger effort to help develop steel foam as a material with relevance to civil engineering applications. © 2012 Elsevier Ltd. All rights reserved.
The objective of this paper is to unveil a novel damping mechanism exhibited by 3D woven lattice
materials (3DW), with emphasis on response to high-frequency excitations. Conventional bulk
damping materials, such as rubber, exhibit relatively low stiffness, while stiff metals and ceramics
typically have negligible damping. Here we demonstrate that high damping and structural stiffness
can be simultaneously achieved in 3D woven lattice materials by brazing only select lattice joints,
resulting in a load-bearing lattice frame intertwined with free, ?floating? lattice members to
generate damping. The produced material samples are comparable to polymers in terms of
damping coefficient, but are porous and have much higher maximum use temperature. We shed
light on a novel damping mechanism enabled by an interplay between the forcing frequency
imposed onto a load-bearing lattice frame and the motion of the embedded, free-moving lattice
members. This novel class of damping metamaterials has potential use in a broad range of weight
sensitive applications that require vibration attenuation at high frequencies.