Pezhman Sharafi

Heuristic Approach for Optimum Cost and Layout Design of 3D Reinforced Concrete Frames

AbstractThis paper presents a new methodology for cost optimization of the preliminary layout design of three-dimensional (3D) reinforced concrete (RC) frames. This approach is capable of being easily employed for the optimal layout design of a realistic large RC structure that accounts for constraints imposed by design standards. The new approach considers modeling, structural analysis, concrete member design, and discrete optimization together with data on the cost of systems and materials. The methodology is comprised of two parts. First, using the cross-sectional action effects as design variables, a heuristic cost function is presented as an alternative to traditional cost functions for layout optimization of RC structures. Using the presented cost function, a structural optimization problem is formulated for column layout design of 3D RC frames. Then, an ant system algorithm, a discrete method, is proposed to solve the cost optimization problem. Two comparative design examples are included to demons...

Nodal ordering for bandwidth reduction using ant system algorithm

Purpose – For the solution of equations with sparse matrices, the problem of bandwidth reduction is an important issue. Though graph theoretical algorithms are available, the purpose of this paper is to examine the feasibility of ant systems (AS).Design/methodology/approach – For band optimization an ant colony algorithm based on AS is utilized. In this algorithm a local search procedure is also included to improve the solution.Findings – AS algorithms are found to be suitable for bandwidth optimization.Originality/value – Application of AS to the bandwidth reduction is the main purpose of this paper, which is successfully performed. The results are compared to those of a graph theoretical bandwidth optimization algorithm.

Geometric Design Optimization for Dynamic Response Problems of Continuous Reinforced Concrete Beams

AbstractThis paper presents a computer-aided design method for conceptual geometric layout optimization of multispan RC beams for any type of dynamic responses. A key feature of the paper is the development of a new cost-optimization method for geometric layout problems that take both cost parameters and dynamic responses into account to achieve an optimum design along with acceptable dynamic performance of RC beams. This method takes advantage of employing a new optimization formulation that considerably simplifies the preliminary layout design computations. It focuses on minimizing the structural cost subject to constraints on eigenfrequencies, modal shapes, and the static and dynamic equilibrium. The proposed structural optimization problem is solved employing an ant colony optimization (ACO) algorithm. To verify the suitability of the methodology and illustrate the performance of the algorithm, solved examples are presented.

Ant colony optimization for finding medians of weighted graphs

Purpose – Medians of a graph have many applications in engineering. Optimal locations for facility centers, distribution of centers and domain decomposition for parallel computation are a few examples of such applications. In this paper, a new ant system (AS) algorithm based on the idea of using two sets of ants, named active and passive ants is proposed for the problem of finding k‐medians of a weighted graph or the facility location problem on a network.Design/methodology/approach – The structure of the algorithm is derived from two known heuristics; namely, rank‐based AS and max‐min ant system with some adjustments in pheromone updating and locating the ants on the graph nodes. The algorithms are designed with and without a local search.Findings – An efficient algorithm for location finding, and the novel application of an ant colony system can be considered as the main contribution of this paper.Originality/value – Combining two different tools; namely, graph theory and AS algorithm results in an effi...

Conceptual design optimization of rectilinear building frames: A knapsack problem approach

This article presents an automated technique for preliminary layout (conceptual design) optimization of rectilinear, orthogonal building frames in which the shape of the building plan, the number of bays and the size of unsupported spans are variables. It adopts the knapsack problem as the applied combinatorial optimization problem, and describes how the conceptual design optimization problem can be generally modelled as the unbounded multi-constraint multiple knapsack problem. It discusses some special cases, which can be modelled more efficiently as the single knapsack problem, the multiple-choice knapsack problem or the multiple knapsack problem. A knapsack contains sub-rectangles that define the floor plan and the location of columns. Particular conditions or preferences for the conceptual design can be incorporated as constraints on the knapsacks and/or sub-rectangles. A bi-objective knapsack problem is defined with the aim of obtaining a conceptual design having minimum cost and maximum plan regularity (minimum structural eccentricity). A multi-objective ant colony algorithm is formulated to solve the combinatorial optimization problem. A numerical example is included to demonstrate the application of the present method and the robustness of the algorithm.

Optimum Column Layout Design of Reinforced Concrete Frames Under Wind Loading

The geometric layout optimization of a structure is a significant stage in a design process, and selecting an appropriate geometric layout can impact all the subsequent stages of the design procedure and the relevant costs. This study presents a heuristic approach for the optimum layout design of two-dimensional reinforced concrete frames in order to optimize the total cost and controls the application under wind loadings. The aim is to find the optimum column layout design for 2D frames under wind loadings considering the involved cost elements. A heuristic methodology is developed in order to achieve a new design space and an objective function for the cost and layout optimization problem. The proposed method has the capability to make use of action effects of the structure as alternative design variables in place of the commonly used cross-sectional ones. Such a feature provides the method the ability to be easily employed in large and realistic structural optimization problems, and helps the optimization algorithms to take less time, in an iterative optimization process. Then, an Ant System based algorithm is proposed to solve the presented optimization problem. Examples are included to illustrate the robustness of the methodology.

Optimum spans' lengths of multi-span reinforced concrete beams under dynamic loading

In the design of continuous beams, say bridges, achieving an economical layout is one of the primary objectives, and requires simultaneous consideration of cost and layout variables. This study aims to figure out an explicit methodology for the optimum layout design of multi-span reinforced concrete beams under dynamic loadings in order to optimize the total cost. The aim is to determine the optimum spans lengths for continuous beams under dynamic loadings considering the involved cost elements. For this purpose a new methodology is developed in order to shift from the traditional design space to a new one. Then, an objective function for the cost and layout optimization problem is formulated in the new space. The proposed method employs action effects of the beams as alternative design variables in lieu of the cross-sectional ones. This ability enables the method to be easily used in realistic structural optimization problems rather than simple models, and helps the layout design procedure to take less time, in an iterative optimization process. In order to solve the formulated optimization problem, an Ant Colony Optimization algorithm is proposed. The robustness of the methodology is illustrated through a number of examples.

Cost optimization of column layout design of reinforced concrete buildings

A new layout optimization methodology is proposed for the cost optimization problem for reinforced concrete (RC) buildings. A new cost function is presented, as an alternative to traditional objective functions. The methodology and the new cost function have the potential of being easily employed in layout optimization of RC structures. Using the alternative cost function, an ant colony optimization (ACO) algorithm is formulated to determine the optimal column layout for buildings in order to minimize the cost. An example is included to demonstrate the effectiveness of the new methodology and excellent convergence of the ACO algorithm.

A new model for bridge management: Part A: condition assessment and priority ranking of bridges

Abstract Due to substantial role of bridges in transportation networks and in accordance with the limited funding for bridge management, remediation strategies have to be prioritised. A conservative bridge assessment will result in unnecessary actions, such as costly bridge strengthening or repairs. On the other hand, any bridge maintenance negligence and delayed actions may lead to heavy future costs or degraded assets. The accuracy of decisions developed by any manager or bridge engineer relies on the accuracy of the bridge condition assessment which emanates from visual inspection. Most of the bridge ranking systems are commonly based on structural condition. Parameters such as functionality and client preferences are used in an isolated fashion. The developing prioritisation method described herein is an important step in adding more holism and objectivity to the current approaches. To achieve this goal, all important parameters have been identified, weighted and finally synthesised in an index introduced as Priority Index (PI). PI is expressed as a number which enables the decision-makers to simply understand and compare the overall condition of a variety of bridges in the network. It embraces three factors: structural efficiency, functional efficiency and client impact factor. The proposed model was tested through case studies and qualified experts (senior bridge inspectors, engineers and asset managers) from about 30 private and public transportation authorities.

A new model for bridge management: Part B: decision support system for remediation planning

Abstract Bridges are fundamental elements in any road network and characterize a major capital asset of community resources. Because of their strategic location over obstacles, any failure may limit and restrict road traffic and cause inconvenience and economic loss. It is therefore important to manage bridge assets, to ensure that all the bridges are maintained in a safe condition, with the most cost-efficient use of resources. Most of the existing bridge management systems are to some extent subjective and based on cost optimization which does not address the indirect impact of the remedial actions. The subjective nature of decision-making in bridge remediation could be replaced by the application of a multi-criteria decision support system that supports decision-makers through balanced consideration of multiple criteria. The main goal of this paper is to present a requirements-driven decision support methodology for remediation of concrete bridges with the aim of maintaining bridge assets within acceptable limits of safety, serviceability and sustainability. The simplified analytical hierarchy process is used as a multi-criteria decision-making technique. A method for selection of the best remediation plan in terms of fund allocation for top-ranked bridges of the network is also proposed using the outputs of the previous procedures considering the budget as the main constraint.