Steel moment frames column loss analysis: The influence of time step size

Abstract

Time history analysis Time step size a b s t r a c t This paper applies two well-known structural dynamics computational algorithms to the problem of disproportionate collapse of steel moment frames applying the alternate load path method. Any problem of structural dynamics strongly depends on the accuracy and the reliability of the analysis method since the parameters involved in the selection of the appropriate algorithm are affected by the nature of the problem. Disproportionate collapse is herein simulated via a time history analysis used to ''turn off'' the effectiveness of an element to the structure. For this kind of problem the time step size of the computational algorithm is of major importance for the accuracy of the method and thus, remains a variable throughout the present analyses. Two plane steel moment frames are used for the numerical examples, while all the analyses are performed independently. Firstly the β-Newmark method is applied and secondly the linear Hilbert-Hughes-Taylor a-method is applied and the respective results are compared and discussed in the last part of the paper.

Evaluation of wind load integration in disproportionate collapse analysis of steel moment frames for column loss

“…Gerasimidis and Baniotopoulos have shown in Gerasimidis and Baniotopoulos (2011) that regardless the computational algorithm used for the dynamic analyses, the time step size of the algorithm must be sufficiently small in order to capture the phenomenon. An appropriate value of time step size has found to be Dt off =300, where Dt off is the time interval of the column removal.…”

“…That is why the calculation of the resistance of a structure to disproportionate collapse is a very tedious task since the phenomenon is strongly related to abnormal conditions and rare events. Such events that have been identified so far by the researchers are gas explosions, terrorist attacks, accidental impact of vehicles, unpredicted fire, extreme wind and many others (National Institute of Standards and Technology, 2007;Deodatis, 1997;Papadopoulos and Deodatis, 2006;Baker et al, 2008;Ellingwood et al, 2007;Ellingwood and Leyendecker, 1978;Ellingwood and Dusenberry, 2005;Izzuddin et al, 2007;Starossek, 2009;Gerasimidis et al, 2008Gerasimidis et al, , 2009Dubina et al, 2010;Frangopol and Curley, 1987;Kwasniewski, 2010;Foley et al, 2007;Kim and Kim, 2009;Gerasimidis and Baniotopoulos, 2011;Gerasimidis, 2011). The uncertainties related to such type of abnormal events are apparently significant and therefore relevant loading simulations are very hard to be produced.…”

Loss-of-stability induced progressive collapse modes in 3D steel moment frames

“…The latter used an energy-based approach and identified buckling-initiated failure mechanisms. Gerasimidis and Baniotopoulos (2011) performed linear dynamic analysis studying the effect of the time step, while Fu (2012) performed nonlinear dynamic analysis under consecutive column-removal scenarios and suggested measures to mitigate yielding-type failure mechanisms. The former considered material nonlinearities only, while the latter considered also geometric nonlinearities and performed a hybrid 2D simulation, modelling a planar frame with the ability to develop out-of-plane buckling.…”

Horizontal bracing to enhance progressive collapse resistance of steel moment frames

“… The continuity between the beams and the columns kept constant. Increasing yield strength caused by suddenly remove of a column is omitted. Fixed support conditions at the foundation are considered. Concrete slabs do not represent in the analytical model and the beams carry slabs load directly. The maximum displacement of the structure has occurred in the first vibration, so damping has a small effect in response and is not considered in the analysis Steel reinforcement after yielding is not considered. …”