An improved soft-kill BESO algorithm for optimal distribution of single or multiple material phases

Finding the optimum distribution of material phases in a multi-material structure is a frequent and important problem in structural engineering which involves topology optimization. The Bi-directional Evolutionary Structural Optimization (BESO) method is now a well-known topology optimization method. In this paper an improved soft-kill BESO algorithm is introduced which can handle both single and multiple material distribution problems. A new filtering scheme and a gradual procedure inspired by the continuation approach are used in this algorithm. Capabilities of the proposed method are demonstrated using different examples. It is shown that the proposed method can result in considerable improvements compared to the normal BESO algorithm particularly when solving problems involving very soft material or void phase

The ESO method revisited

This paper examines the evolutionary structural optimisation (ESO) method and its shortcomings. By proposing a problem statement for ESO followed by an accurate sensitivity analysis a framework is presented in which ESO is mathematically justifiable. It is shown that when using a sufficiently accurate sensitivity analysis, ESO method is not prone to the problem proposed by Zhou and Rozvany (Struct Multidiscip Optim 21(1):80–83, 2001). A complementary discussion on previous communications about ESO and strategies to overcome the Zhou-Rozvany problem is also presented. Finally it is shown that even the proposed rigorous ESO approach can result in highly inefficient local optima. It is discussed that the reason behind this shortcoming is ESO’s inherent unidirectional approach. It is thus concluded that the ESO method should only be used on a very limited class of optimisation problems where the problem’s constraints demand a unidirectional approach to final solutions. It is also discussed that the Bidirectional ESO (BESO) method is not prone to this shortcoming and it is suggested that the two methods be considered as completely separate optimisation techniques

Applications of topology optimization techniques in seismic design of structure

During the last two decades, topology optimization techniques have been successfully applied to a wide range of problems including seismic design of structures. This chapter aims to provide an introduction to the topology optimization methods and a review of the applications of these methods in earthquake engineering. Two well-established topology optimization techniques will be introduced. Several problems including eigenfrequency control of structures, compliance minimization under periodic loading, and maximizing energy absorption of passive dampers will be addressed. Numerical instabilities and approaches to overcome them will be discussed. The application of the presented approaches and methods will be illustrated using numerical examples. It will be shown that in seismic design of structures, topology optimization methods can be useful in providing conceptual design for structural systems as well as detailed design of structural members

Effects of thickness of roof layers on optimum design of truss bolt system using finite element modeling techniques

In underground excavations, optimum design of reinforcement systems is largely based on geological features of the surrounding rock such as in-situ stress distribution, rock strength properties, thickness of the layers, etc. In current design of truss bolt systems these parameters are yet to be considered. In this study, effects of changing thickness of roof layers on optimum design of truss bolt have been investigated using three stability indicators, namely reduction in the loosened area above the roof, number of plastic points and horizontal movement on the first bedding plane. Total of 7 different bedding configurations have been generated and 100 different truss bolt designs have been tested on each bedding configuration. Results showed that by changing the thickness of the roof layers, the optimum design of truss bolt changes drastically. In highly laminated formations, it has been demonstrated that a gently inclined bolt angle is more effective, while by increasing the thickness of roof layers, truss bolt systems with a higher bolt angle and longer bolts, i.e. similar to systematic rock bolt systems, responds better

Shape optimization of metallic yielding devices for passive mitigation of seismic energy

Bi-directional Evolutionary Structural Optimization (BESO) is a well established topology optimization technique. This method is used in this paper to optimize the shape of a passive energy dissipater designed for earthquake risk mitigation. A previously proposed shape design of a steel slit damper (SSD) device is taken as the initial design and its shape is optimized using a slightly modified BESO algorithm. Some restrictions are imposed to maintain simplicity and to reduce fabrication cost. The optimized shape shows increased energy dissipation capacity and even stress distribution. Experimental verification has been carried out and proved that the optimized shape is more resistant to low-cycle fatigue

An improvement technique for Bi-directional Evolutionary Structural optimisation (BESO) method

Bi-directional Evolutionary Structural optimisation (BESO) method is now a well-known and popular method in topology optimisation. A new interpretation of this method is presented in which the method is viewed as a two-step procedure. Based on this interpretation, a simple heuristic improvement technique is introduced to improve BESO results. The proposed improvement technique is tested and verified through numerical examples and its performance is compared with the averaging sensitivity stabilisation technique proposed in [1]. It is shown that the proposed improvement is robuster than the averaging sensitivity technique. REFERENCES: [1] X. Huang and Y. M. Xie. Convergent and mesh-independent solutions for the bi-directional evolutionary structural optimization method. Finite Elements in Analysis and Design, 43 (14), 1039–1049, 2007

Data on use of a computer-marked on-line assessment in engineering education over the course of five years

<p>This fileset presents the data obtained though implementing an on-line computer-marked assessment in a second-year core civil engineering course in an Australian university. The data is gathered on-line in five years from the first year of implementing this quiz in 2011 to 2015. Students were allowed to attempt the quiz multiple times over a certain period of time, longer than a week. A large question bank was constructed with several variants for each question. Students faced randomly selected variants of questions in each attempt. At the end of assessment period, the best score of each student was recorded as their mark for the quiz. An anonymous on-line survey was conducted every year after the end of the assessment period in which students were asked to answer a number of questions and provide their opinion about the quiz.</p><p><br></p><p> The data presented here includes students’ marks in each attempt, the time they spent on each attempt, and anonymous survey results.<br></p

Flexural performance of FRP-reinforced geopolymer concrete beam

Fibre-reinforced polymer (FRP) rebar and geopolymer concrete (GPC) are relatively new construction materials that are now been increasingly used in the construction sectors. Both materials exhibit superior structural and durability properties that also make them a sustainable alternative solution. Due to the absence of any design standard for an FRP-reinforced GPC beam, it is important to validate the efficacy of available standards and literature related to other materials, e.g., FRP-reinforced conventional concrete or GPC alone. Four theories/design standards are considered for this comparison&mdash;ACI440.1R-15, CAN/CSA S806-12, parabolic stress block theory, and equivalent rectangular stress block theory for GPC under compression. The accuracy of these four approaches is also examined by studying the flexural performance of both the glass FRP (GFRP) and carbon FRP (CFRP). The FRP-reinforced beams are designed against the actual load they will be subjected to in a real-world scenario. It is concluded that parabolic stress block theory over-estimates the capacity, whereas CSA S806-12 yields the most accurate and conservative results. In addition, the flexural performance of the FRP-reinforced beams is evaluated in terms of ultimate, cracking, and service moment capacity, along with serviceable, ultimate, and residual deflection

Evaluating temporal changes in hydraulic conductivities near karst-terrain dams: Dokan Dam (Kurdistan-Iraq)

Dam sites provide an outstanding opportunity to explore dynamic changes in the groundwater flow regime because of the high hydraulic gradient rapidly induced in their surroundings. This paper investigates the temporal changes of the hydraulic conductivities of the rocks and engineered structures via a thorough analysis of hydrological data collected at the Dokam Dam, Iraq, and a numerical model that simulates the Darcian component of the seepage. Analysis of the data indicates increased seepage with time and suggests that the hydraulic conductivity of the rocks increased as the conductivity of the grout curtain decreased. Conductivity changes on the order of 10-8m/s, in a 20-yr period were quantified using the numerical analysis. It is postulated that the changes in hydraulic properties in the vicinity of Dokan Dam are due to suspension of fine materials, interbedded in small fissures in the rocks, and re-settlement of these materials along the curtain. Consequently, the importance of the grout curtain to minimize the downstream seepage, not only as a result of the conductivity contrast with the rocks, but also as a barrier to suspended clay sediments, is demonstrated. The numerical analysis also helped us to estimate the proportion of the disconnected karstic conduit flow to the overall flow

Simultaneous pattern and size optimisation of rock bolts for underground excavations

Designing a rock bolt reinforcement system for underground excavation involves determining bolt pattern, spacing, and size. In this paper, a topology optimisation technique is presented and employed to simultaneously optimise these design variables. To improve rock bolt design, the proposed technique minimises a displacement based function around the opening after bolt installation. This optimisation technique is independent of the material model and can be easily applied to any material model for rock and bolts. It is also extremely flexible in that it can be applied to any mechanical analysis method. To illustrate the capabilities of this method, numerical examples with non-linear material models and discontinuities in the host rock are presented. It is shown that the complexity of systems optimised using this approach is only restricted by limitations of the method used to analyse mechanical system responses