A New Design Problem in the Formulation of a Special Moment Resisting Connection Device for Preventing Local Buckling

Abstract

In the present paper an improved formulation devoted to the optimal design problem of a special moment resisting connection device for steel frames is proposed. This innovative device is called a Limited Resistance Plastic Device (LRPD) and it has been recently proposed and patented by some of the authors. It is thought to be preferably located at the extremes of the beam, connecting the beam end cross section with the relevant column. The typical device is a steel element characterized by symmetry with respect to three orthogonal barycentric planes and constituted by a sequence of three portions with abrupt cross section changes. The main novelty of the present proposal is related to the design of special geometry for the optimal device ensuring that it possesses a reduced resistance with respect to the relevant connected beam element, is characterized by an equivalent bending stiffness equal to the one of the connected beam elements and exhibits full plastic deformations avoiding any local instability phenomenon. The optimal design is formulated as a minimum volume one and is subjected to suitable constraints on the geometry of the device and on its elastic and plastic behavior. The optimization problem is a strongly non-linear programming one and it is solved by adopting an interior-point algorithm that is available in the MATLAB Optimization Toolbox. The numerical simulations are devoted to the most used standard steel profiles (IPE, HE) and the results prove the great reliability of the proposed device. In addition, the relevant elastic and plastic domains of the designed devices are defined, and the expected behavior of the device is verified by appropriate 3D finite element models in the ABAQUS environment.

Experimental analysis of new moment resisting steel connections

“…The specimen is constituted by three different parts, two corresponding to the flanges (equal each other) and the other one for the web. Each part has been derived by a S275 steel slab, shaped following the results of the optimal design reported in [15] with an assigned ultimate bending moment equal to 0.67 of the corresponding one of HEB240 (dimensions in Fig. 1).…”

“…The overall assembly has been obtained by factory welding the single parts and it has been performed by Tecnozinco s.r.l., whose contribution is gratefully acknowledged. The mechanical characterization of the material constituted the slab has been performed by tensile tests on suitable specimens following [15] and the results are reported in Table 1. Assuming the geometrical characteristics of the specimen, the mean value of 𝑓𝑓 𝑦𝑦 , the consequent ultimate bending moment of LRPD is equal to 241.8 kNm corresponding to a load of 306 kN.…”

“…In the recent past, the authors proposed a new moment resisting connection for steel frame elements, called LRPD (Limited Resistance Plastic Device) [8][9][10][11][12][13][14][15]. Mainly, LRPD is thought as a steel device replacing a part of the structural elements with the aim to obtain a connection between structural members with preset mechanical and kinematical behaviour.…”

“…Mainly, LRPD is thought as a steel device replacing a part of the structural elements with the aim to obtain a connection between structural members with preset mechanical and kinematical behaviour. The detailed description of the geometrical description of LRPD can be found in [15], while its leading features are those of the same elastic flexural stiffness as the original selected member, to possess a bending moment resistance reduced with respect to that of the original beam, to avoid any local instability phenomenon. In many papers [8][9][10][11][12][13][14][15] authors proposed different optimal design for LRPD as well performed a lot of numerical analyses to verify the LRPD behaviour and the related computational aspects.…”

“…The detailed description of the geometrical description of LRPD can be found in [15], while its leading features are those of the same elastic flexural stiffness as the original selected member, to possess a bending moment resistance reduced with respect to that of the original beam, to avoid any local instability phenomenon. In many papers [8][9][10][11][12][13][14][15] authors proposed different optimal design for LRPD as well performed a lot of numerical analyses to verify the LRPD behaviour and the related computational aspects. In the present paper a first step of experimental campaign on the mechanical behaviour of LRPD is presented by performing the four-point bending test to apply a pure bending moment without shear force in central zone of the specimen.…”