Santi Rizzo

Numerical analysis of masonry structures via interface models

The present paper is devoted to the theoretical formulation and numerical implementation of an interface model suitable to simulate the behavior of mortar joints in masonry structures. The interface laws are formulated in the framework of elasto-plasticity for non-standard materials in order to simulate the softening response which occurs along the decohesion process in presence of shear and tension tractions. A variable material dilatancy parameter is introduced together with a further geometrical dilatancy related to the roughness of contact surfaces after joint fracture. An asperity model is adopted with the aim to describe the evolution of the contact surface shape during the loss of cohesion process and sliding. The interface laws are expressed both in rate and discrete incremental form. Details regarding the numerical implementation and the related algorithms are presented. Finally, the results obtained from the application to two case-studies show the capabilities of the proposed interface model and the effectiveness of the computational strategy herein presented.

A design algorithm for the optimization of laminated composite structures

This paper is devoted to the optimal design of laminated composite structures. The goal of the study is to assess the quality and the performance of an algorithm based on the directional derivative method. Particular attention is paid to the one‐dimensional search, a critical step of the process, performed by cubic splines approximation. The optimization problem is formulated as weight minimization, under constraints on the mechanical behavior of the structure. The assumed design variables are the ply thicknesses, treated as continuous design variables, constrained by technological requirements. The structural analysis is performed making use of quadrilateral four‐node composite elements, based on the first order shear deformation theory. The algorithm is applied to the optimization of a rectangular laminated plate. The results obtained are compared with those obtained by other similar studies and show the effectiveness and accuracy of the proposed approach.

Optimal design of laminated composite plates

The results of a study on the discrete structural optimization of laminated composite plates are presented. Evolution strategies, in their multi-membered variant, are used to solve the optimal design problem. The objective of the design is weight minimization, under constraints on the mechanical behavior of the structure. Using a parallel drawn from biological evolution, laminated plates are driven to the optimal solution using random operators, like mutation and recombination. A comparison of the result with those obtained by other methods is presented. The robustness of the method and the high computational cost of the feasibility check, performed by means of the Finite Element Method, is pointed out.

SHAKEDOWN OPTIMUM DESIGN OF REINFORCED CONCRETE FRAMED STRUCTURES

Structures subjected to variable repeated loads can undergo the shakedown or adaptation phenomenon,-which prevents them from collapse but may cause lack of serviceability, for the plastic deformations developed, although finite, as shakedown occurrence postulates, may exceed some maximum values imposed by external ductility criteria. This paper is devoted to the optimal design of reinforced concrete structures, subjected to variable and repeated loads. For such structures the knowledge of the actual values taken by the plastic deformations, at shakedown occurrence, is a crucial issue. An approximate assessment of such plastic deformations is needed, which is herein provided in the shape of quadratic constraints, by the so-called perturbation method. By suitable finite element discretization, the optimal shakedown problem is formulated as a convex nonlinear mathematical programming one. The M-N (bending moment-axial force) interaction is accounted for in the aim to provide the optimal shakedown design. The...

Shakedown optimal design of reinforced concrete structures by evolution strategies

Approaches the shakedown optimal design of reinforced concrete (RC) structures, subjected to variable and repeated external quasi‐static actions which may generate the well‐known shakedown or adaptation phenomenon, when constraints are imposed on deflection and/or deformation parameters, in order to simulate the limited flexural ductility of the material, in the presence of combined axial stress and bending. Within this context, the classical shakedown optimal design problem is revisited, using a weak upper bound theorem on the effective plastic deformations. For this problem a new computational algorithm, termed evolution strategy, is herein presented. This algorithm, derived from analogy with the biological evolution, is based on random operators which allow one to treat the areas of steel reinforcements at each RC cross‐section of the structure as design variables of discrete type, and to use refined non‐linear approximations of the effective bending moment – axial force M‐N interaction diagrams of each RC cross‐section. The results obtained from case studies available in the literature show the advantages of the method and its effectiveness.

Interface Models for the Analysis of Time-Dependent Effects in Masonry Structures

The present paper is devoted to the theoretical formulation and numerical implementation of an interface model suitable to simulate the behavior of cementitious joints at long term. The interface laws are formulated in the framework of viscoplasticity for non standard materials in order to simulate the time-dependent softening response which occurs along the decohesion process in presence of shear and tension tractions. The interface model parameters identification is discussed on the base of experimental data reported in the literature. The optimization problem related to the parameters evaluation is approached by a heuristic algorithm. Finally some examples show the capabilities of the proposed model and the effectiveness of the computational strategy herein presented.