Evolution and state‐of‐the‐art of column stability criteria

The strength and stability of steel columns have been the subjects of a great many studies since the original work of Leonhard Euler in 1744 and 1759. Numerous examinations of elastic buckling of perfectly straight columns were conducted during the 19th century, the most famous being the studies of Engesser and Considère, with several series of column tests attempting to find agreement between theory and physical behavior. The research work continued in the 20th century, examining the influence of material and member imperfections, including the famous tangent modulus work of Shanley, and the resolution of the effects of material non‐linearity, residual stress and column out‐of‐straightness. The definitive solutions were only obtained in the 1970‐s, when modeling and numerical solutions allowed for the incorporation of all nonlinear effects. Since that time reliability and probabilistic solutions have provided state‐of‐the‐art criteria for limit state treatment of the column problem. These principles are now the bases of the design standards for columns in all of the countries in the world. The paper focuses on the major evolutions that have taken place, but especially the work over the past 40 years. Realistic treatment and representation of the strength of columns in actual structures have now been achieved by the engineering profession. Santrauka Plieniniu kolonu stiprumas ir pastovumas buvo daugelio tyrinejimu objektas, pradedant nuo originaliu Leonhardo Eulerio 1744 ir 1759 m. darbu. XIX a. buvo atlikta daugelis idealiai tiesiu kolonu tampriojo klupumo tyrimu, iš kuriu žymiausi buvo Engesero (Engesser) ir Konsideres (Considere) tyrimai, apeme kelias kolonu bandymu serijas. Jais siekta rasti derme tarp teorijos ir fizines elgsenos. Darbai buvo tesiami ir XX a., nagrinejant medžiagu ir elementu nuokrypiu poveiki, iskai‐tant gerai žinoma Šenlio (Shanley) liestines modulio darba, ir medžiagu netiesiškumo, liekamuju itempiu bei kolonu išklupimo poveikius. Galutiniai sprendiniai buvo gauti tik 1970 m., kai modeliavimas ir skaitiniai eksperimentai leido atsižvelgti i visus netiesinius poveikius. Nuo to laiko patikimumo ir tikimybiniai sprendiniai suteike šiuolaikinius kriterijus kolonu problemos ribiniu būviu traktuotei. Dabar šie principai yra visu pasaulio šaliu kolonu projektavimo normu pagrindas. Straipsnyje pristatytos pagrindines raidos kryptys, apžvelgiamas darbas, nuveiktas per pastaruosius 40 metu. Statybos profesionalai pasieke tikroviška dabartiniu statiniu kolonu stiprumo traktuote ir pateikima. First Published Online: 24 Jun 2011 Reikšminiai žodžiai: kolonos, plienas, pastovumas, stiprumas, teorija, bandymai, ribiniai būviai, patikimumas, projekta‐vimas, normo

Classification System for Semi-Rigid Beam-to-Column Connections

The current study attempts to recognise an adequate classification for a semi-rigid beam-to-column connection by investigating strength, stiffness and ductility. For this purpose, an experimental test was carried out to investigate the moment-rotation (M-theta) features of flush end-plate (FEP) connections including variable parameters like size and number of bolts, thickness of end-plate, and finally, size of beams and columns. The initial elastic stiffness and ultimate moment capacity of connections were determined by an extensive analytical procedure from the proposed method prescribed by ANSI/AISC 360-10, and Eurocode 3 Part 1-8 specifications. The behaviour of beams with partially restrained or semi-rigid connections were also studied by incorporating classical analysis methods. The results confirmed that thickness of the column flange and end-plate substantially govern over the initial rotational stiffness of of flush end-plate connections. The results also clearly showed that EC3 provided a more reliable classification index for flush end-plate (FEP) connections. The findings from this study make significant contributions to the current literature as the actual response characteristics of such connections are non-linear. Therefore, such semirigid behaviour should be used to for an analysis and design method

Mechanical Properties of High and Very-High Strength Steel at Elevated Temperatures and After Cooling Down

High-strength steels (HSS) are produced using special chemical composition or/and manufacturing processes. Both aspects affect their mechanical properties at elevated temperatures and after cooling down, and particularly the residual strength and the ductility of the structural members. As HSS equates the design of lighter structural elements, higher temperatures are developed internally compared to the elements designed with conventional carbon steel. Therefore, the low thickness members, along with the severe effect of high temperature on the mechanical properties of the HSS, constitute to the increased vulnerability of such structures in fire. Moreover, the re-use and reinstatement of these structures are more challenging due to the lower residual mechanical properties of HSS after the cooling down period. This paper presents a review of the available experimental studies of the mechanical properties of HSS at elevated temperatures and after cooling down. The experimental results are collected and compared with the proposed material model (reduction factors) of EN1993–1-2. Based on these comparisons, modified equations describing the effect of elevated temperatures on the mechanical properties of HSS are proposed. Also, the post-fire mechanical properties of HSS are examined. A comprehensive discussion on the effect of influencing parameters, such as manufacturing process, microstructure, loading conditions, maximum temperature, and others is further explored