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Abstract

In general practice, composite beams are designed with either simple connections or fully rigid moment connections due to lack of information on semi-rigid connections. But, semi-rigid composite connections will offer several advantages like strength, stiffness and economy to the system when compared to simple or moment connection. Although several researchers have reported the advantages of semi-rigid frames, information for their optimal design is currently not available. In this study, 4, 8 and 12-storey composite plane frames in different seismic zones are designed and their capacity curve is compared with corresponding curves for rigid frames to study the limitations and economy of semi-rigid frames. It is shown that semi-rigid frames perform better in low to moderate seismic zones but may not be advantageous in severe seismic zones.

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... The nonlinear connection was designed such that the ultimate moment of the connection is reached within 20 mrad. Connections were modelled as linear rotational springs for linear static analysis and as a multi-linear plastic element (nonlinear spring) for nonlinear analysis [29]. Modeling of elements with hinges is shown in Fig. 6. ...
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The actual behavior of beam to column connections in steel frames is seldom fully rigid or fully pinned. The true behavior of the connections is usually semi-rigid. Neglecting the real behavior of the connection in the analysis may lead to unrealistic predictions of the response and reliability of steel frames. This paper considers the effects of semi-rigid behavior of the connections in the finite element analysis and in the reliability analysis of steel frames. Assuming that the loads and the resistance of members are random variables, then the Monte Carlo simulation technique is used for the best estimation of the probability of failure of the frame system. Some examples are presented, which illustrate the importance of the effect of the semi-rigid behavior of the connections in the calculation of the overall reliability of the total system of the steel frames.
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This paper presents a simplified approach for the design of semi-continuous composite beams in braced frames, where specific attention is given to the effect of joint rotational stiffness. A simple composite beam model is proposed incorporating the effects of semi-rigid end connections and the nonprismatic properties of a 'cracked' steel-concrete beam. This beam model is extended to a sub-frame in which the restraining effects from the adjoining members are considered. Parametric studies are performed on several sub-frame models and the results are used to show that it is possible to correlate the amount of moment redistribution of semi-continuous beam within the sub-frame using an equivalent stiffness of the connection. Deflection equations are derived for semi-continuous composite beams subjected to various loading and parametric studies on beam vibrations are conducted. The proposed method may be applied using a simple computer or spreadsheet program.
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The design and analysis of partially restrained frames for seismic loads present some interesting and challenging issues to practicing engineers. The most important are how to determine the moment-rotation characteristics for the connections, the effect of floor slabs, and the influence of the partially-restrained connections on the dynamic characteristics of the frames. The use of databases for the determination of the appropriate moment-rotation curves is discussed and found lacking. A more rational, mechanistic approach to the problem is described and its merits discussed. The influence of floor slabs is shown to be important and simplified techniques to handle this effect are proposed. The behavior of FR frames under seismic loads is shown to be equivalent to that of PR frames once the dynamic characteristics are properly modeled. The design of PR frames will require both the development of new preliminary design approaches and advanced analysis tools because the conventional equivalent lateral load analysis cannot account for the dynamic effects properly.
Design criteria for composite Structures in Steel and concrete, Design guide for partially restrained composite connections
aScE task committee, "Design criteria for composite Structures in Steel and concrete, Design guide for partially restrained composite connections", Jl. of Struct. Engg., aScE, Vol. 124, (10), 1998, pp 1099-1114.
Stability design of semi-rigid frames
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chen, W.f., goto, y, richard liew, J.y., "Stability design of semi-rigid frames", John Wiley and Sons, inc, 1996.
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fEMa-356, "Prestandard and commentary for the Seismic rehabilitation of Buildings", ASCE for the Federal Emergency Management Agency, Washington, D.c., 2000.