Optimization of force-limiting seismic devices connecting structural subsystems

This paper is focused on the optimum design of an original force-limiting floor anchorage system for the seismic protection of reinforced concrete (RC) dual wall-frame buildings. This protection strategy is based on the interposition of elasto-plastic links between two structural subsystems, namely the lateral force resisting system (LFRS) and the gravity load resisting system (GLRS). The most efficient configuration accounting for the optimal position and mechanical characteristics of the nonlinear devices is obtained numerically by means of a modified constrained differential evolution algorithm. A 12-storey prototype RC dual wall-frame building is considered to demonstrate the effectiveness of the seismic protection strategy

Optimization of shoring/reshoring levels in high-rise building construction

Formwork system is a significant constituent and a basic requirement for high-rise cast-in-place reinforced concrete buildings. Usually, the builders are confronted with the decision to choose the safe, optimum number of levels of shores/reshores for a predetermined safety factor and given grade of concrete, giving due consideration to the cost of formwork system. In this study, MATLAB program is developed to calculate the load distribution between the interconnected slabs and levels of shore/reshore of a slab formwork based on a simplified method. This program is further modified by incorporating genetic algorithm for the optimization of cost of construction for high-rise building. The cost of level of shores and reshores per floor is defined as a function of cycle time which directly reflects the increase in the cost of construction. Various combinations of shore and reshore levels with several grades of concrete for various safety factors are checked to minimize the cost of construction. The optimization equation is solved using genetic algorithm considering appropriate constraints to practically ensure feasible solutions. The case of one level of shores and numerous levels of reshores is better than one level of reshores and numerous levels of shores. The result of certain combination of shore and reshore levels is not the same when the level numbers are reversed. A comparative study is carried out to check the optimum cost for various safety factors. The program is useful for the designers to decide the levels of shores and reshores with minimized cost without compromising the safety of construction

Design optimisation of steel portal frames using modified distributed genetic algorithms

Distributed genetic algorithms have been modified in this study to improve their quality, performance, and convergence to the optimum solution for structural steel frames. This was achieved by introducing some novelties of the main algorithm of distributed genetic algorithms and applying them in structural optimisation. Among these are the creation of new mutation schemes, adding a crossover scheme, definition of a penalty function, properties of twins, and definition of the reproduction scheme. Many optimisation problems have been designed to minimise the weight of a steel structure and are well documented in the literature. However, having a frame controlled by displacement will necessitate choosing a different approach for the objective function. In addition to weight minimisation, attempts have been made to investigate displacement maximisation and this also forms part of the novelty of this study. Various steel frames in terms of geometry and loading conditions are considered during the optimisation process and they are assumed to have rigid and/or semi-rigid connections. The design optimisations are conducted according to therequirements of both BS 5950 and EC3 codes of practice. A stiffness matrix is developed for a non-prismatic member that is involved in the analysis process

Structural optimization in steel structures, algorithms and applications

L'abstract è presente nell'allegato / the abstract is in the attachmen

Framework to Explore the Design Space for Design of Tall Buildings

Design of tall buildings is undergoing a resurgence that is driven by a variety of factors – economical growth, scarcity of land in urban areas, high land costs, increased population density, technological advancements and man’s desire to build taller structures. Considerable research work has been done in the last two decades to meet this demand. Computer-based tools that help design engineers explore design alternatives are indispensable in tackling this complex problem. In addition, a framework that finds the near optimal design, adds value to this exploratory work. In this paper, we develop a general framework for the design optimization of buildings using sizing, shape, and topology design variables. Sizing optimization can be carried out using discrete design variables (from a database of available sections) or continuous design variables (cross-sectional dimensions of custom wide flange sections). Similarly, shape optimization can be carried out using either discrete or continuous design variables. And finally, topology optimization can be carried out using boolean design variables. Allowable stress design guidelines are used as constraints along with displacement, inter-story drift, total structural weight, and frequency constraints. The finite element model is made of three-dimensional beam elements. A typical function evaluation involves a linear, static analysis with multiple load cases, a linear, modal analysis to extract the lowest few eigenpairs, and a linear, buckling analysis to find the buckling capacity. An optimization toolbox that contains gradient-based and population-based optimizers, is a part of the framework. Numerical results how that the framework is capable of producing efficient designs effectivel

Impacto de la rigidez de las uniones en el coste global de pórticos a dos aguas de acero

This paper studies the influence of joint stiffness value combinations in gabled steel frames. Twelve different joint stiffness values were combined for the column base, knee joint and ridge joint. Ten different geometries were combined for gabled steel frames (8-20 m span, 3.5-10 m column height and 10-20% roof slope). Finally, three different load levels for snow and wind were considered, with constant values of permanent and maintenance loads. A total of 46656 cases were analyzed using specific software for steel structure design, obtaining in each case the total cost. Graphical cost representation was obtained for each joint stiffness value combination. Joints represent an average of 17% of the total cost of gabled steel frame structures. In general, lower cost structures were obtained with low joint rigidity values. It is possible to reduce the total cost by around 18% on average, with appropriate selection of joint stiffness combinations.En este artículo se presenta un estudio sobre la influencia de la rigidez de las uniones en pórticos a dos aguas de acero. Se combinan doce valores diferentes de rigidez de placa de anclaje, hombro y cumbrera. Se combinan diez geometrías (8- 20 m de luz, 3.5-10 m de altura de pilares y 10-20% de pendiente de cubierta). Se consideran tres niveles de carga de nieve y viento con valores constantes de carga de mantenimiento. Se analizan un total de 46656 supuestos utilizando un programa informático de cálculo de estructuras para obtener en cada caso su coste total. Se obtiene la representación gráfica del coste para cada combinación de rigideces. En general, los costes más bajos de las estructuras se corresponden con valores bajos de rigidez. Es posible reducir el coste total un 18% de media, con la selección apropiada de la combinación de valores de rigidez de las uniones

Comprehensive Review of Optimal and Smart Design of Nonlinear Building Structures With and Without Passive Dampers Subjected to Earthquake Loading

The optimal and smart design of nonlinear building structures with and without passive dampers subjected to earthquake loading is of great concern in the structural design of building structures. The research started around 1980 and many investigations have been conducted. A comprehensive review on this subject is made in this article. After the description of essential features of the optimal design problem of nonlinear building structures under earthquake ground motions, analysis types of optimization problems are explained and the significance of the dynamic pushover analysis is discussed from the viewpoint of analysis of limit states under earthquake ground motions of magnitude larger than the code-specified level. Then, the categorization by the response of frames and dampers was made. In this categorization, several subjects are discussed first: 1) Optimal design of bare nonlinear building frames under seismic loading, 2) Optimal design of nonlinear dampers for elastic building frames under seismic loading, 3) Optimal design of linear dampers for nonlinear building frames under seismic loading, 4) Optimal design of nonlinear building frames with specified nonlinear dampers under seismic loading, 5) Optimal design of nonlinear dampers for specified nonlinear building frames under seismic loading, 6) Simultaneous optimization of elastic-plastic building structures and passive dampers. Finally, the classification of researches in view of solution strategies is conducted for providing another viewpoint

Approximation of the critical buckling factor for composite panels

This article is concerned with the approximation of the critical buckling factor for thin composite plates. A new method to improve the approximation of this critical factor is applied based on its behavior with respect to lamination parameters and loading conditions. This method allows accurate approximation of the critical buckling factor for non-orthotropic laminates under complex combined loadings (including shear loading). The influence of the stacking sequence and loading conditions is extensively studied as well as properties of the critical buckling factor behavior (e.g concavity over tensor D or out-of-plane lamination parameters). Moreover, the critical buckling factor is numerically shown to be piecewise linear for orthotropic laminates under combined loading whenever shear remains low and it is also shown to be piecewise continuous in the general case. Based on the numerically observed behavior, a new scheme for the approximation is applied that separates each buckling mode and builds linear, polynomial or rational regressions for each mode. Results of this approach and applications to structural optimization are presented

A parametric investigation into the development of cold formed steel free form grid shells

In recent years, the adoption of parametric design approaches to geometric modelling allows to describe and investigate large complex systems with few variables [1]. Form finding techniques such as the force density and dynamic relaxation methods help in defining efficient free form structures [2]. There is therefore potential to design free form grid shells which can be optimized for basic parameters like support conditions, grid topology, load conditions, material and section properties. This work explores the possibility to use cold-formed steel section for free form shells, making advantage of their structural efficiency and versatility that allows the realization of light constructions. Three free form shells, having different geometries, configurations and grid topology, are investigated, and the viability of adopting cold formed steel members to create lightweight and stable grid shells through parametric modelling is analysed