Ayse T. Daloglu

Reliability-based optimisation of offshore jacket-type structures with an integrated-algorithms system

Reliability-based optimisation (RBO) is a powerful tool for including uncertainties in the optimisation process, in which structural and reliability analyses and optimisation algorithms based on mathematical or evolutionary computation concepts have to be combined effectively. This process is rather complicated and difficult to carry out for large structural systems such as steel offshore structures. In this paper, a calculation system of integrated algorithms for the RBO of the offshore towers is presented. The calculation process is composed of a structural analysis package (SAPOS) based on the finite element method, a reliability analysis program based on the first-order reliability method and an optimisation program based on sequential quadratic programming using the International Mathematics and Statistics Library. In the RBO analysis, multiple limit states based on different criteria are used to check a probable failure condition and to identify the limit state criterion. An offshore jacket-type structure is considered as an example to demonstrate the applicability of the implemented algorithm to realistic structural systems.

An integrated framework including distinct algorithms for optimization of offshore towers under uncertainties

A reliability analysis is usually required to carry out design optimization of large structural systems to incorporate the uncertainties on the parameters such as material properties, external loads, manufacturing condition, etc. This procedure is called Reliability Based Design Optimization (RBDO), and requires a structural analysis program, a reliability analysis and optimization tools to couple effectively. In this paper, an integrated framework is proposed to implement the RBDO of the offshore towers. It has two distinct approaches to evaluate the probabilistic constraints; namely Reliability-Index based Approach (RIA) and Performance Measure Approach (PMA). The proposed framework also suggests Sequential Quadratic Programming (SQP) and Differential Evolution (DE) as optimization methods. Examples of monopod, tripod, and jacket towers under the reliability constraints based on limit states of the critical stress, buckling, and the natural frequency are presented to demonstrate the applicability of the implemented algorithm to realistic structural systems.

Application of the Modified Vlasov Model to the free vibration analysis of thick plates resting on elastic foundations

The Modified Vlasov Model is applied to the free vibration analysis of thick plates resting on elastic foundations. The effects of the subsoil depth, plate dimensions and their ratio, the value of the vertical deformation parameter within the subsoil on the frequency parameters of plates on elastic foundations are investigated. A four-noded, twelve degrees of freedom quadrilateral finite element (PBQ4) is used for plate bending analysis based on Mindlin plate theory which is effectively applied to the analysis of thin and thick plates when selective reduced integration technique is used. The first ten natural frequency parameters are presented in tabular and graphical forms to show the effects of the parameters considered in the study. It is concluded that the effect of the subsoil depth on the frequency parameters of the plates on elastic foundation is generally larger than that of the other parameters considered in the study.

Optimum weight design of steel space frames with semi-rigid connections using harmony search and genetic algorithms

In this paper, an optimization process using MATLAB-SAP2000 Open Application Programming Interface (OAPI) is presented for optimum design of space frames with semi-rigid connections. A specified list including W-profiles taken from American Institute of Steel Construction (AISC) is used in the selection of suitable sections. The stress constraints as indicated in load and resistance factor design of AISC, lateral displacement constraints being the top- and inter-storey drift and geometric constraints are considered in the optimization process. Genetic algorithm method based on biological principles and harmony search algorithm method based on the processes of musical harmony are used for optimum designs. Two different space frames are solved for the cases of rigid and semi-rigid connections, separately. A computer program is coded in MATLAB for the purpose interacting with SAP2000 OAPI. Results obtained from the analyses show that type of semi-rigid connections plays a crucial role in the optimization of steel space frames and increases the optimum weight.

Optimum Design of Braced Steel Space Frames including Soil-Structure Interaction via Teaching-Learning-Based Optimization and Harmony Search Algorithms

Optimum design of braced steel space frames including soil-structure interaction is studied by using harmony search (HS) and teaching-learning-based optimization (TLBO) algorithms. A three-parameter elastic foundation model is used to incorporate the soil-structure interaction effect. A 10-storey braced steel space frame example taken from literature is investigated according to four different bracing types for the cases with/without soil-structure interaction. X, V, Z, and eccentric V-shaped bracing types are considered in the study. Optimum solutions of examples are carried out by a computer program coded in MATLAB interacting with SAP2000-OAPI for two-way data exchange. The stress constraints according to AISC-ASD (American Institute of Steel Construction-Allowable Stress Design), maximum lateral displacement constraints, interstorey drift constraints, and beam-to-column connection constraints are taken into consideration in the optimum design process. The parameters of the foundation model are calculated depending on soil surface displacements by using an iterative approach. The results obtained in the study show that bracing types and soil-structure interaction play very important roles in the optimum design of steel space frames. Finally, the techniques used in the optimum design seem to be quite suitable for practical applications.

Genetic Algorithms for Optimization of 3D Truss Structures

Various optimization techniques have been applied to find the optimum solutions of structural design problems in the last 50 or 60 years. Simple structural optimization problems with continuous design variables have been solved initially using mathematically diverse techniques. New approaches called meta-heuristic techniques have been emerging along with the progress of traditional methods. This chapter first introduces the mathematical formulations of optimization problems and then gives a summary and development process of the preliminary techniques such as genetic algorithm (GA) in obtaining the optimum solutions. The mathematical formulations of the structural optimization problems are associated with the design variables, loads, structural responses, and constraints. Strategies are proposed to improve the performance of the technique to reduce the number of search and the size of the problem. Finally, some examples related to 3D truss structures are presented.

YAPI ZEMİN ETKİLEŞİMİNİN BETONARME YAPILARIN TASARIMINA ETKİSİ

Betonarme yapilarin tasarimi sirasinda genellikle temel zemini rijit bir ortam olarak dikkate alinarak tabanda kolonlarin ankastre oldugu kabulu ile yapi-zemin etkilesimi ihmal edilmektedir. Oysaki zemin, ust yapidan aktarilan yukler altinda sekil degistiren, gerilmelere maruz kalan ve maruz kaldigi etkilere karsi tepki olusturan bir ortamdir. Bu nedenle zemin etkileri dikkate alinmadan yapilan bir ust yapi tasariminin eksik kalabilecegi soylenebilir. Bu calismada, yapi-zemin etkilesiminin betonarme yapilarin tasarimina etkisi incelenmektedir. Bu amacla daha once literaturde incelenmis olan 8 katli bir yapi ornegi dikkate alinmistir. Yapinin oturdugu zemin, rijit yapi-zemin kabulunun yaninda Winkler ve Gelistirilmis Vlasov Modelleri de kullanilarak modellenmistir. Sayisal sonuclar SAP2000 paket programi ile MATLAB’te kodlanan bir yazilimin es zamanli kullanilmasiyla elde edilmistir. Bu sayede SAP2000 paket programina kendi icerisinde var olmayan Gelistirilmis Vlasov Modeli ile cozum yapma kabiliyeti kazandirilmistir. Cozumden elde edilen periyot, taban kesme kuvveti, kolon normal kuvvetleri, kolon egilme momentleri ve kolonlarin boyuna donati oranlari her bir zemin modeli icin karsilastirilmistir. Calismanin sonunda yapi-zemin etkilesiminin betonarme yapilarin tasarimina etkisinin ihmal edilemeyecek duzeyde oldugu gorulmustur

Optimization of Jacket Type Offshore-Tower Under Uncertainties

In this work, economical design implementation of a jacket tower, which is subjected to some uncertainties associated with the loads, the material properties, and environmental data etc., is presented. In order to fulfill the defined task, reliability based design optimization (RBDO) concept combining the reliability analysis and optimization is performed with reliability constraints including stress, buckling, and the lowest natural frequency. The probabilistic constraints are evaluated by using Reliability Index Approach (RIA) and Performance Measure approach (PMA). The mass of the tower is considered as being the objective function; the thickness and diameter of the cross-section of the jacket members are taken as being design variables of the optimization.Copyright