The present paper is devoted to the proposal of appropriate numerical modelling able to provide a suitable description of the mechanical behavior of a composite geopolymer. Reference is made to a natural sisal-fiber-reinforced geopolymer. The study is based on the results of appropriate experimental investigations for compressive, flexural and splitting loadings, taking into account different weight percentages of fibers to evidence their role in the mechanical behavior. The main objective of the paper is to calibrate the microplane constitutive model, available in ANSYS software version 18.1, where the numerical analyses are performed. Therefore, the present study is structured in two different steps. Firstly, the mechanical behavior of geopolymers reinforced with sisal fibers is experimentally investigated, and subsequently, the gathered test data are interpreted and utilized to calibrate the relevant constitutive model to be used in the numerical stage. The obtained results are compared with experimental data, yielding good correlations. The paper’s results supply the parameters required to obtain an affordable numerical model of the reinforced geopolymer for different percentages of fibers to be adopted for material design with assigned mechanical properties.

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.