Documents disponibles écrits par cet auteur

Impact of residual stresses and initial imperfections on the seismic response of steel moment frames / Kapil Mathur in Journal of structural engineering, Vol. 138 N° 7 (Juillet 2012) 

Public ISBD [article]  in Journal of structural engineering > Vol. 138 N° 7 (Juillet 2012) . - pp. 942–951 Titre : Impact of residual stresses and initial imperfections on the seismic response of steel moment frames Type de document : texte imprimé Auteurs : Kapil Mathur, Auteur ; Larry A. Fahnestock, Auteur ; Taichiro Okazaki, Auteur Année de publication : 2012 Article en page(s) : pp. 942–951 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Direct  analysis  method  Steel  moment  frames  Connection  cyclic  strength  degradation Résumé : The 2010 AISC specification establishes the direct analysis method (DM) as the standard stability analysis and design procedure. Although the DM has important benefits over conventional stability design methods, the interface between the DM, the AISC seismic provisions, and the seismic design requirements in ASCE-7 is not fully established. Because the DM, which was developed for design scenarios that do not contain seismic loading, includes the effects of initial geometric imperfections and inelastic behavior owing to residual stresses, it is critical to explore the impact of these parameters on the seismic behavior of typical steel buildings. To examine these issues, a series of steel special moment-resisting frame models were subjected to monotonic pushover, cyclic pushover, and response history analyses. The observed behavior was used to draw comparisons between systems with and without residual stresses and initial imperfections. Cyclic strength degradation at beam-to-column connections was also considered to examine the potential interaction it may have with the other parameters. Whereas the well-known impact of strength degradation on cyclic stability was noted, residual stresses and initial imperfections did not have any appreciable effect on stability behavior for the systems considered. The analyses conducted in this study indicate no clear benefit to using the DM when designing regular ductile steel systems in high seismic regions and simpler design methods may be equally effective. ISSN : 0733-9445 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29ST.1943-541X.0000512 [article] Impact of residual stresses and initial imperfections on the seismic response of steel moment frames [texte imprimé] / Kapil Mathur, Auteur ; Larry A. Fahnestock, Auteur ; Taichiro Okazaki, Auteur . - 2012 . - pp. 942–951. Génie Civil Langues : Anglais (eng) in Journal of structural engineering > Vol. 138 N° 7 (Juillet 2012) . - pp. 942–951 Mots-clés : Direct  analysis  method  Steel  moment  frames  Connection  cyclic  strength  degradation Résumé : The 2010 AISC specification establishes the direct analysis method (DM) as the standard stability analysis and design procedure. Although the DM has important benefits over conventional stability design methods, the interface between the DM, the AISC seismic provisions, and the seismic design requirements in ASCE-7 is not fully established. Because the DM, which was developed for design scenarios that do not contain seismic loading, includes the effects of initial geometric imperfections and inelastic behavior owing to residual stresses, it is critical to explore the impact of these parameters on the seismic behavior of typical steel buildings. To examine these issues, a series of steel special moment-resisting frame models were subjected to monotonic pushover, cyclic pushover, and response history analyses. The observed behavior was used to draw comparisons between systems with and without residual stresses and initial imperfections. Cyclic strength degradation at beam-to-column connections was also considered to examine the potential interaction it may have with the other parameters. Whereas the well-known impact of strength degradation on cyclic stability was noted, residual stresses and initial imperfections did not have any appreciable effect on stability behavior for the systems considered. The analyses conducted in this study indicate no clear benefit to using the DM when designing regular ductile steel systems in high seismic regions and simpler design methods may be equally effective. ISSN : 0733-9445 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29ST.1943-541X.0000512

Nonlinear finite-element analysis of critical gusset plates in the I-35W bridge in Minnesota / Minmao Liao in Journal of structural engineering, Vol. 137 N° 1 (Janvier 2011) 

Public ISBD [article]  in Journal of structural engineering > Vol. 137 N° 1 (Janvier 2011) . - pp. 59-68 Titre : Nonlinear finite-element analysis of critical gusset plates in the I-35W bridge in Minnesota Type de document : texte imprimé Auteurs : Minmao Liao, Auteur ; Taichiro Okazaki, Auteur ; Roberto Ballarini, Auteur Année de publication : 2011 Article en page(s) : pp. 59-68 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Connections  Finite-element  method  Nonlinear  analysis  Bridge  failure Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Reported evidence suggests that failure of gusset plates initiated the collapse of the I-35W Bridge in Minneapolis, Minnesota. The particular gusset plates were at a panel point designated as U10. Therefore, an analytical investigation was conducted on the condition of the U10 gusset plates at the time of bridge collapse. The forces delivered to panel point U10 were reproduced using available information of the bridge. These forces were introduced to detailed nonlinear three-dimensional finite-element models to calculate stress and strain states of the gusset plates. The results indicate that substantial portions of the U10 gusset plates were yielded at the time of collapse, confirming earlier findings from federal and state investigations. Weight increase due to past deck reconstruction and construction material and equipment staged on the day of collapse, along with insufficient thickness of the gusset plate, were identified as the main contributing factors to the substantial yielding. The results also suggest that the interaction of compression and shear played an important role in the gusset plate failure. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v137/i1/p59_s1?isAuthorized=no [article] Nonlinear finite-element analysis of critical gusset plates in the I-35W bridge in Minnesota [texte imprimé] / Minmao Liao, Auteur ; Taichiro Okazaki, Auteur ; Roberto Ballarini, Auteur . - 2011 . - pp. 59-68. Génie Civil Langues : Anglais (eng) in Journal of structural engineering > Vol. 137 N° 1 (Janvier 2011) . - pp. 59-68 Mots-clés : Connections  Finite-element  method  Nonlinear  analysis  Bridge  failure Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Reported evidence suggests that failure of gusset plates initiated the collapse of the I-35W Bridge in Minneapolis, Minnesota. The particular gusset plates were at a panel point designated as U10. Therefore, an analytical investigation was conducted on the condition of the U10 gusset plates at the time of bridge collapse. The forces delivered to panel point U10 were reproduced using available information of the bridge. These forces were introduced to detailed nonlinear three-dimensional finite-element models to calculate stress and strain states of the gusset plates. The results indicate that substantial portions of the U10 gusset plates were yielded at the time of collapse, confirming earlier findings from federal and state investigations. Weight increase due to past deck reconstruction and construction material and equipment staged on the day of collapse, along with insufficient thickness of the gusset plate, were identified as the main contributing factors to the substantial yielding. The results also suggest that the interaction of compression and shear played an important role in the gusset plate failure. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v137/i1/p59_s1?isAuthorized=no

Reduced link sections for improving the ductility of eccentrically braced frame link-to-column connections / Jeffrey W. Berman in Journal of structural engineering, Vol. 136 N° 5 (Mai 2010) 

Public ISBD [article]  in Journal of structural engineering > Vol. 136 N° 5 (Mai 2010) . - pp. 543-553 Titre : Reduced link sections for improving the ductility of eccentrically braced frame link-to-column connections Type de document : texte imprimé Auteurs : Jeffrey W. Berman, Auteur ; Taichiro Okazaki, Auteur ; Heidrun O. Hauksdottir, Auteur Année de publication : 2011 Article en page(s) : pp. 543-553 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Eccentrically  braced  frames  Reduced  beam  sections  Finite-element  analysis  Link-to-column  connections  Ductility  Steel  frames Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Eccentrically braced frames (EBFs) are desirable seismic load resisting systems as they combine the high elastic stiffness of concentrically braced frames with the ductility and stable energy dissipation of moment resisting frames. EBFs with links attached to the columns are particularly appealing for architectural flexibility as they provide multiple locations for placement of doors and hallways. However, previous research has shown that link-to-column connections are prone to failure at low drift levels, due to their susceptibility to fracture at the link flange-to-column welds. This paper investigates the application of the reduced beam section concept for links in eccentrically braced frames to enhance the ductility of link-to-column connections. A design procedure for link section reduction is proposed and preliminary finite-element analyses are conducted on a shear link with various reduced section geometries. A parametric study performed on an array of links having various cross sections and lengths suggests that the reduced link section may substantially reduce the plastic flange strains at the link ends, which can improve the fracture life. The reduction in plastic flange strains is found to be significant for all links, with larger reductions for intermediate and flexural links. Furthermore, the detrimental kinking deformation of the flanges, caused by the large rotation demands in shear links, is moved away from the column face when reduced sections were used. While the analysis results show promise, experimental verification is recommended before the proposed design procedure can be implemented in practice. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v136/i5/p543_s1?isAuthorized=no [article] Reduced link sections for improving the ductility of eccentrically braced frame link-to-column connections [texte imprimé] / Jeffrey W. Berman, Auteur ; Taichiro Okazaki, Auteur ; Heidrun O. Hauksdottir, Auteur . - 2011 . - pp. 543-553. Génie Civil Langues : Anglais (eng) in Journal of structural engineering > Vol. 136 N° 5 (Mai 2010) . - pp. 543-553 Mots-clés : Eccentrically  braced  frames  Reduced  beam  sections  Finite-element  analysis  Link-to-column  connections  Ductility  Steel  frames Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Eccentrically braced frames (EBFs) are desirable seismic load resisting systems as they combine the high elastic stiffness of concentrically braced frames with the ductility and stable energy dissipation of moment resisting frames. EBFs with links attached to the columns are particularly appealing for architectural flexibility as they provide multiple locations for placement of doors and hallways. However, previous research has shown that link-to-column connections are prone to failure at low drift levels, due to their susceptibility to fracture at the link flange-to-column welds. This paper investigates the application of the reduced beam section concept for links in eccentrically braced frames to enhance the ductility of link-to-column connections. A design procedure for link section reduction is proposed and preliminary finite-element analyses are conducted on a shear link with various reduced section geometries. A parametric study performed on an array of links having various cross sections and lengths suggests that the reduced link section may substantially reduce the plastic flange strains at the link ends, which can improve the fracture life. The reduction in plastic flange strains is found to be significant for all links, with larger reductions for intermediate and flexural links. Furthermore, the detrimental kinking deformation of the flanges, caused by the large rotation demands in shear links, is moved away from the column face when reduced sections were used. While the analysis results show promise, experimental verification is recommended before the proposed design procedure can be implemented in practice. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v136/i5/p543_s1?isAuthorized=no