PRACTICAL DEMONSTRATION OF THE USE OF JOINT FLEXIBILITY IN STEEL FRAME DESIGN

摘要

In the case of the braced frame, the material saving for the alternative with rigid joints was 9.7% in comparison with the one with pin connections. It is, however, necessary to make complicated and costly joint stiffening, that will decrease the total cost saving of the rigid jointed frame. In the case of a semi-rigid jointed frame we obtain a material saving of up to 17.7% compared to the frame with pinned joints. This difference is already considerable, even though the total cost will also decrease by something, because the fabrication of a semi-rigid joint is usually more expensive than the fabrication of a pinned one. In the case of the unbraced frame, the material saving for the alternative with welded semi-rigid joints was 7.1 % in comparison to a rigid jointed frame. In the case of a bolted semi-rigid jointed frame we obtain a material saving of up to 14% compared to the frame with rigid joints. The total cost saving of the frame with semi-rigid joints will even increase, because there is no need to make complicated and costly joint stiffening. So, when minimum cost of steel structures is of interest, we can use two different strategies: 1. in the case of braced frames - we can reduce the profile dimensions, i.e. reduce the material costs, but increase the fabrication cost of joints in comparison with a frame with simple joints, 2. in the case of unbraced frames - we can simplify the joint detailing, i.e. reduce the fabrication costs. The connections can be designed without expensive stiffeners. By an appropriate choice of joint types and their properties we can influence the magnitude of critical loads and buckling lengths, what, in this case, did not influence the design of column sections. We can affect the distribution and possible redistribution of internal forces and moments from the beams to the columns and vice versa, as well as the frame deformation. We can not only reduce the beam profiles but also decrease the cost of fabrication and thus find an optimal design with the lowest overall cost. This paper was published under the Grant Research Project VEGA No 1/7139/20, which is financially supported by the Research Grant Agency of the Ministry of Education of the Slovak Republic and by the Slovak Academy of Sciences.