|Title:||Bolted moment connections in cold-formed steel beam-column sub-frames|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Steel framing (Building) -- Testing
Steel, Structural -- Testing
|Department:||Department of Civil and Structural Engineering|
|Pages:||1 v. (various pagings) : ill. ; 30 cm|
|Abstract:||Scope of work This thesis reports the findings of a two-year research project in which an experimental investigation and a numerical study on the structural performance of bolted moment connections in cold-formed steel beam-column sub-frames were performed. The objective of the research project is to demonstrate the high structural performance of bolted moment connections between cold-formed steel sections in practical framing. A total of twenty-five tests with different connection configurations in both internal and external beam-column sub-frames subject to lateral and gravity loads were carried cut. Advanced finite element analysis method was also proposed to predict the structural behaviors of the beam-column sub-frames with semi-rigid connections. Experimental investigation A total of twenty-five full-scale tests on beam-column sub-frames with bolted moment connections of different configurations were carried out under both lateral and gravity loads. Four different modes of connection failure were identified among the tests: - BFcsw: Bearing failure in section web around bolt hole; - FFcs: Flexural failure of connected cold-formed steel section; - FFgp: Flexural failure of connected gusset plate; - LTBgp: Lateral torsional buckling of gusset plate. The moment resistances of the proposed connection configurations were found to range from 62% to 97% of the moment capacities of the connected sections. Among the four failure modes, the flexural failure of connected cold-formed steel section was considered to be the most favourable as over 85% of the moment capacity of the connected section was readily mobilized in the connection. Numerical study After data analysis on the test results to generate the moment joint-rotation curves of bolted moment connections, the non-linear finite element analysis program GMNAF was used to model the overall lateral load-deflection curves of the beam-column sub-frames incorporating both geometrical non-linearity and connection flexibility. An incremental-iterative Newton-Raphson procedure was adopted for solution. All of beam-column sub-frames which were failed by flexural failure of connected cold-formed steel section were examined. The comparison of the numerical results with the test results showed that the finite element models with semi-rigid connections was able to predict correctly the overall behavior of the beam-column sub-frames up to failure. A semi-empirical design rule is also proposed for the connection configurations to generate the moment joint-rotation curves of the connections; the rotational stiffness of the connections were calculated by summation of the flexibilities of individual components. Conclusions Based on the findings of the experimental investigation and the numerical study, it is concluded that bolted moment connections between cold-formed steel sections may be readily achieved using the proposed connection configurations. The bolted moment connections are demonstrated to be effective in transmitting moment between the connected sections under both lateral and gravity loads, and thus enabling effective moment framing in cold-formed steel structures. The proposed non-linear finite element analysis with semi-rigid joints may be used to predict the overall behavior of cold-formed steel beam-column sub-frames with bolted moment connections correctly up to failure. Engineers are encouraged to build short to medium span cold-formed steel portal frames with bolted moment connections for improved buildability when compared with timber or reinforced concrete frames.|
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