Keywords: connection, semi-rigid, seismic, steel frame, nonlinear, time history analysis, pushover analysis.

In the analysis and design of steel frame buildings, it is customary to represent joint behaviour by an idealized model, either as a rigid or as a pinned joint. However, typical connections in actual structures do not behave in either a perfectly rigid or a perfectly pinned manner. Previous investigations show that most connections in real steel structures have characteristics between these simplified extremes [1]. Pinned connections exhibit some rotational stiffness, while rigid connections possess some degree of flexibility, and consequently, these assumptions can lead to unrealistic predictions of the response and strength of steel structures.

Connections in braced simple steel frames using angle sections do not behave in a perfectly pinned manner and exhibit some rotational stiffness. The current study evaluates the effects of this partial rigidity of the beam-to-column connection on the behaviour and seismic response of steel frame buildings. For this purpose, a particular class of braced steel buildings, those composed of three and five stories are modeled as two-dimensional frames, and an initial static analysis is performed. Then the structural members are designed subject to gravity and lateral loads, according to the specifications of AISC-ASD 2005 [2]. The connection type used in the present study is a double web angle connection which is a customary type and it is used in most practical cases. The Kishi and Chen power model is used for modeling of non-linear moment-rotation behaviour of the connection [3]. This model is suitable for practical purposes since the key parameters of this model are physically meaningful and may be determined analytically with acceptable accuracy. Particular attention is devoted to inelastic modeling of framework components for accurate representation of the frame behaviour. Nonlinear static pushover analysis and nonlinear time history analysis are applied for comparing the idealized model with the real state of the structure.

Results indicate that the use of bracing elements reduces the sensitivity of the structural response to differences in connection behaviour. Also in some cases, considering the real behaviour of connections instead of ideally pinned connections can lead to some differences in evaluating the seismic response of the braced simple steel frames.

1

A. Abolmaali, A.R. Kukreti, H. Razavi, "Hysteresis Behavior of Semi-rigid Double Web Angle Steel Connections", Journal of Constructional Steel Research, 59(8), 1057-1082, 2003. doi:10.1016/S0143-974X(03)00005-1

2

AISC, "Specification for Structural Steel Buildings", ANSI/AISC 360-05, American Institute of Steel Construction, Chicago (IL), 2005.

3

N. Kishi, W.F. Chen, "Moment-Rotation Relations of Semirigid Connections with Angles", Journal of Structural Engineering, 116(7), 1813-1834, 1990. doi:10.1061/(ASCE)0733-9445(1990)116:7(1813)

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