PSI - Issue 78

Leonardo Casali et al. / Procedia Structural Integrity 78 (2026) 1269–1276

1274

3.2. Longitudinal stiffening Also in the longitudinal direction there are obviously the same needs for containing the horizontal deformations that have been expressed with reference to the transverse direction. However, the stiffening solution adopted is different and simpler, made possible in consideration of the substantially regular and repetitive configuration of the framed structural scheme in this direction. A longitudinal bracing system is envisaged which consists in the use of HE320A type profiles for the first two bracing fields in elevation and for bracing with a V configuration on the third bracing field. HE240A profiles are provided for the remaining fields up to roof level. The braces have been defined as capable of resisting both tensile and compression forces, checking their stability. Some bracing field have been configured in a reverse V shape, simple or stiffened, to ensure the necessary passage through the affected spans. A similar solution was not applicable in the present case with reference to the transversal direction of the building, in consideration of two aspects: the framed structural system was not continuous neither horizontally nor vertically; due to internal operational needs within the building it was not permitted to block the fields of the frame with braces. The strategy adopted for locating braces is to arrange the profiles so as to have the greatest inertia associated with the greatest free deflection length, therefore the flanges of the profile are arranged parallel to the longitudinal plane of the building. In fact, in this way the strong axis is associated with the out-of-plane bending of the bracing characterized by a greater span. On the contrary, in the orthogonal plane (the plane of the framing system) the free deflection length is substantially halved as the braces are connected to each other at the centre. Fig. 7 below reports views of some vertical alignments of the longitudinal frame systems affected by the insertion of braces.

Fig. 7 Examples of bracing placement: alignment B2 (left); alignment G (right)

4. Modelling The calculation model is a finite element model (FEM) in which the framed structural elements (beams, columns, and braces) are reproduced by one-dimensional "beam" type elements joining two nodes, each having 6 degrees of freedom. The decks are considered rigid in their plane, according to the provisions of Italian Code, in consideration of the construction methods that involve the casting of an upper slab. For the purposes of analysing the structure, the displacements in the two horizontal directions (X and Y) and the rotations around the vertical axis (Z) of all the nodes lying on a deck are considered mutually constrained by a rigid plane diaphragm reproduced with internal constraints. The internal constraints at the beam-column nodes are generally of the hinge type, however in cases where the stiffening crescent-shaped devices have been inserted in the transverse direction, the constraint is managed using link type elements characterized by a rotational stiffness, modelling the stiffness of the connection. Steel bracing elements with both tensile and compression capacity were inserted in the longitudinal direction of the building reproducing the actual braces present within the framed system. The numerical model also include the presence of the beams on which the overhead cranes move. In terms of internal constraints the beams were considered to be hinged (with reference to the two bending planes) in correspondence of the main columns of the structure. The reference structural heights adopted in the model coincide with the axes of the floor beams at the decks levels defined in the project sections (see example in Fig. 3). Axonometric views of the calculation model of Block A of PM3 building is shows in Fig. 8. The non-linearity associated with the application sequence of the loads and with the assembly of the structure shall be, and actually was, taken into consideration, with particular reference to the presence of the stiffening elements,