Stochastic optimum design criterion of added viscous dampers for buildings seismic protection

Giuseppe Carlo Marano,Francesco Trentadue,Rita Greco 국제구조공학회 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.25 No.1

In this study a stochastic approach for linear viscous dampers design adopted for seismic protection of buildings is developed. Devices optimal placement into the main structure and their mechanical parameters are attained by means of a reliability-based optimum design criterion, in which an objective function (O.F.) is minimized, subject to a stochastic constraint. The seismic input is modelled by a non stationary modulated Kanai Tajimi filtered stochastic process. Building is represented by means of a plane shear type frame model. The selected criterion for the optimization searches the minimum of the O.F., here assumed to be the cost of the seismic protection, i.e., assumed proportional to the sum of added dampings of each device. The stochastic constraint limits a suitable approximated measure of the structure failure probability, here associated to the maximum interstorey drift crossing over a given threshold limit, related, according with modern Technical Codes, to the required damage control.

Stochastic optimum design of linear tuned mass dampers for seismic protection of high towers

Marano, Giuseppe Carlo,Greco, Rita,Palombella, Giuseppe Techno-Press 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.29 No.6

This work deals with the design optimization of tuned mass damper (TMD) devices used for mitigating vibrations in high-rise towers subjected to seismic accelerations. A stochastic approach is developed and the excitation is represented by a stationary filtered stochastic process. The effectiveness of the vibration control strategy is evaluated by expressing the objective function as the reduction factor of the structural response in terms of displacement and absolute acceleration. The mechanical characteristics of the tuned mass damper represent the design variables. Analyses of sensitivities are carried out by varying the input and structural parameters in order to assess the efficiency of the TMD strategy. Variations between two different criteria are also evaluated.

Stochastic optimum design of linear tuned mass dampers for seismic protection of high towers

Giuseppe Carlo Marano,Rita Greco,Giuseppe Palombella 국제구조공학회 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.29 No.6

This work deals with the design optimization of tuned mass damper (TMD) devices used for mitigating vibrations in high-rise towers subjected to seismic accelerations. A stochastic approach is developed and the excitation is represented by a stationary filtered stochastic process. The effectiveness of the vibration control strategy is evaluated by expressing the objective function as the reduction factor of the structural response in terms of displacement and absolute acceleration. The mechanical characteristics of the tuned mass damper represent the design variables. Analyses of sensitivities are carried out by varying the input and structural parameters in order to assess the efficiency of the TMD strategy. Variations between two different criteria are also evaluated.

Stochastic optimum design criterion of added viscous dampers for buildings seismic protection

Marano, Giuseppe Carlo,Trentadue, Francesco,Greco, Rita Techno-Press 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.25 No.1

In this study a stochastic approach for linear viscous dampers design adopted for seismic protection of buildings is developed. Devices optimal placement into the main structure and their mechanical parameters are attained by means of a reliability-based optimum design criterion, in which an objective function (O.F.) is minimized, subject to a stochastic constraint. The seismic input is modelled by a non stationary modulated Kanai Tajimi filtered stochastic process. Building is represented by means of a plane shear type frame model. The selected criterion for the optimization searches the minimum of the O.F., here assumed to be the cost of the seismic protection, i.e., assumed proportional to the sum of added dampings of each device. The stochastic constraint limits a suitable approximated measure of the structure failure probability, here associated to the maximum interstorey drift crossing over a given threshold limit, related, according with modern Technical Codes, to the required damage control.

Stochastic Approach for Analytical Fragility Curves

Giuseppe Carlo Marano,Rita Greco,Mauro Mezzina 대한토목학회 2008 KSCE JOURNAL OF CIVIL ENGINEERING Vol.12 No.5

One of the main problems is the assessment of "residual reliability" or "vulnerability" of a single existing structure, or of a given class of similar structures, against seismic actions. The fragility curves describe the probability of a structure to suffer a given damage level when it is subject to a given seismic excitation level. This research work is focused on an analytical method for constructing fragility curves of existing structures based on a stochastic approach. Analysed structure is modelled by a simple one degree of freedom system subject to a nonstationary Kanai-Tajimi process. The numerical values of the parameters of its constitutive law, here suitably described by means of a hysteretic model, are selected using an identification procedure with the non linear pushover analysis performed on the real assessed structure. To develop fragility curves, a displacement based damage index is adopted. Fragility curves are obtained in terms of probability of exceeding a given damage level by using an approximate crossings theory of stochastic processes.

New analytical model for the hoop contribution to the shear capacity of circular reinforced concrete columns

Francesco Trentadue,Giuseppe Quaranta,Rita Greco,Giuseppe Carlo Marano 사단법인 한국계산역학회 2014 Computers and Concrete, An International Journal Vol.14 No.1

The paper is concerned with the analytical description of a resistance mechanism, not considered in previous models, by which the hoops contribute to the shear capacity of RC columns with circular cross sections. The difference from previous approaches consists in observing that, because of deformation, the hoops change their original shape and, as a consequence, their slope does not match anymore the original one in the neighborhood of a crack. The model involves two parameters only, namely the crack inclination and the hoop strain in the neighborhood of a crack. A closed-form analytical formulation to correlate the average value of the crack width and the hoop strain is also provided. Results obtained using the proposed model have been compared with experimental data, and a satisfactory agreement is found.

Structural Optimization of Hollow-section Steel Trusses by Differential Evolution Algorithm

Alessandra Fiore,Giuseppe Carlo Marano,Rita Greco,Erika Mastromarino 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.2

This paper deals with the weight minimization of planar steel trusses by adopting a differential evolution-based algorithm. Square hollow sections are considered. The design optimization refers to size, shape and topology. The design variables are represented by the geometrical dimensions of the cross sections of the different components of the truss, directly involving the size of the structure, and by some geometrical parameters affecting the outer shape of the truss. The topology is included in the optimization search in a particular way, since the designer at different runs of the algorithm can change the number of bays keeping constant the total length of the truss, to successively choose the best optimal solution. The minimum weight optimum design is posed as a single-objective optimization problem subject to constraints formulated in accordance with the current Eurocode 3. The optimal solution is obtained by a Differential Evolutionary (DE) algorithm. In the DE algorithm, a particular combination of mutation and crossover operators is adopted in order to achieve the best solutions and a specific way for dealing with constraints is introduced. The effectiveness of the proposed approach is shown with reference to two case-studies. The analysis results prove the versatility of the optimizer algorithm with regard to the three optimization categories of sizing, shape, topology as well as its high computational performances and its efficacy for practical applications. In particular useful practical indications concerning the geometrical dimensions of the various involved structural elements can be deduced by the optimal solutions: in a truss girder the cross section of the top chord should be bigger than the one of the bottom chord as well as diagonals should be characterized by smaller cross sections with respect to the top and bottom chords in order to simultaneously optimize the weight and ensure an optimal structural behaviour.

Strength deterioration of reinforced concrete column sections subject to pitting

Rita Greco,Giuseppe Carlo Marano 사단법인 한국계산역학회 2015 Computers and Concrete, An International Journal Vol.15 No.4

Chloride induced reinforcement corrosion is widely accepted to be the most frequent mechanism causing premature degradation of reinforced concrete members, whose economic and social consequences are growing up continuously. Prevention of these phenomena has a great importance in structural design, and modern Codes and Standards impose prescriptions concerning design details and concrete mix proportion for structures exposed to different external aggressive conditions, grouped in environmental classes. This paper focuses on reinforced concrete column section load carrying capacity degradation over time due to chloride induced steel pitting corrosion. The structural element is considered to be exposed to marine environment and the effects of corrosion are described by the time degradation of the axial-bending interaction diagram. Because chlorides ingress and consequent pitting corrosion propagation are both time-dependent mechanisms, the study adopts a time-variant predictive approach to evaluate residual strength of corroded reinforced concrete columns at different lifetimes. Corrosion initiation and propagation process is modelled by taking into account all the parameters, such as external environmental conditions, concrete mix proportion, concrete cover and so on, which influence the time evolution of the corrosion phenomenon and its effects on the residual strength of reinforced concrete columns sections.

Optimum shape and length of laterally loaded piles

Fenu, Luigi,Briseghella, Bruno,Marano, Giuseppe Carlo Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.68 No.1

This study deals with optimum geometry design of laterally loaded piles in a Winkler's medium through the Fully Stressed Design (FSD) method. A numerical algorithm distributing the mass by means of the FSD method and updating the moment by finite elements is implemented. The FSD method is implemented here using a simple procedure to optimise the beam length using an approach based on the calculus of variations. For this aim two conditions are imposed, one transversality condition at the bottom end, and a one sided constraint for moment and mass distribution in the lower part of the beam. With this approach we derive a simple condition to optimise the beam length. Some examples referred to different fields are reported. In particular, the case of laterally loaded piles in Geotechnics is faced.

Simplified method to design laterally loaded piles with optimum shape and length

Luigi Fenu,Bruno Briseghella,Giuseppe Carlo Marano 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.71 No.2

Optimum shape and length of laterally loaded piles can be obtained with different optimization techniques. Inparticular, the Fully Stress Design method (FSD) is an optimality condition that allows to obtain the optimum shape of the pile,while the optimum length can be obtained through a transversality condition at the pile lower end. Using this technique, the structureis analysed by finite elements and shaped through the FSD method by contemporarily checking that the transversality condition issatisfied. In this paper it is noted that laterally loaded piles with optimum shape and length have some peculiar characteristics,depending on the type of cross-section, that allow to design them with simple calculations without using finite element analysis. Some examples illustrating the proposed simplified design method of laterally loaded piles with optimum shape and length areintroduced.