Mechanical Properties of Bolt
Figure 15 shows the distributions of bolt force and M — 9r curves, in cases changing grade of bolts as A325 and A490, in which those are for models of A2 and FE8, respectively. From this figure, it is observed that the bolt force is increased near ultimate state by taking higher grade bolts, connection moment capacity can be upgraded a little in the elasto-plastic region; and connection rotation also can be increased.
In this study, in order to investigate the interaction between column flange and top angle’s vertical leg and these effects including bolt action on M — 9r characteristics of top – and seat-angle connections, elasto-plastic finite element (FE) analysis was performed. Here, numerical analysis results together with the prediction by Kishi-Chen power model are compared with experimental ones to examine an applicability of the proposed analysis method and power model. In addition, to investigate the influence of connection parameters on prying force and moment-rotation behavior of top – and seat – angle connection, a parametric study was conducted by varying dimensions of connection models and magnitude of pretension force surcharged to the bolts. The following conclusions are obtained from this study:
(1) Proposed numerical analysis method can be applicable to estimate elasto-plastic nonlinear behavior of angle type connection;
(2) Power model is able to predict M — 9r curves of the connection satisfactorily and can be applicable for nonlinear analysis of steel frames with semi-rigid connections;
(3) Pretension force of bolts has no effect on prying action at the initial and ultimate level of loading, but gives some effects a little at the intermediate loading level;
(4) A prying action can be increased with decreasing of thickness of flange angle or increasing gage distance from the angle heel to the centerline of bolt hole;
(5) Depth of beam section has no effect on prying action;
(6) Use of stiffer bolts or weaker angles in connection may increase the prying action; and
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