Repetitive construction processes scheduling using mixed-integer linear programming

Many construction projects contain several identical or similar units, such as floors in multistory buildings, houses in housing developments, sections of pipelines or highways. Repetitive processes arise from the subdivision of a generalized construction process into specific activities associated with particular units. In many cases it is possible to perform individual processes (repeated in each units) in alternative ways (modes). Regardless of the construction project procurement system, duration and cost are the key factors determining project’s economic efficiency and fulfillment of the owner’s needs and requirements. Minimizing project duration and cost are the most important criteria for schedule optimization. Processes that repeat from unit to unit are realized by specialized crews. Uninterrupted resource utilization becomes an extremely important issue for scheduling repetitive processes to minimize employment costs. In this paper, the problem of selecting appropriate modes and minimizing the total project cost and with a constraint on project duration is presented with respect to the continuity of the crews’ work. The paper uses the mixed integer linear programming to model this problem and uses a case study to illustrate it

Selection of subcontractors using ordinal ranking methods based on Condorcet approach

A choice of a subcontractor may have critical impact on realization of the project, it has influence on the cost, duration, and quality. Selection of the best sucontractor can be defined as multiple criteria decision making problem (MCDM) of choosing a proper offer from set of alternatives evaluated by using set of criteria. Decision maker should determine the criteria as objective and measurable. Significance of decision making problem is presented by large amount of theories and methods developed for solving MCDM problems and number of criteria considered in these problems. A Condorcet method (formulated over two centuries ago) is commonly accepted for democratic (majority of criteria determines the winner) and fair election – a Condorcet winner is the alternative which is preferred in all pair-wise comparisons. According to social choice theory where a Condorcet winner cannot be obtained from a set of alternatives, the best solution is close to being a Condorcet winner. The paper presents four selection methods of the best alternative that is as close as possible to being a Condorcet winner and contains examples of a subcontractor selection using only ordinal scales of evaluation of alternatives.A choice of a subcontractor may have critical impact on realization of the project, it has influence on the cost, duration, and quality. Selection of the best sucontractor can be defined as multiple criteria decision making problem (MCDM) of choosing a proper offer from set of alternatives evaluated by using set of criteria. Decision maker should determine the criteria as objective and measurable. Significance of decision making problem is presented by large amount of theories and methods developed for solving MCDM problems and number of criteria considered in these problems. A Condorcet method (formulated over two centuries ago) is commonly accepted for democratic (majority of criteria determines the winner) and fair election – a Condorcet winner is the alternative which is preferred in all pair-wise comparisons. According to social choice theory where a Condorcet winner cannot be obtained from a set of alternatives, the best solution is close to being a Condorcet winner. The paper presents four selection methods of the best alternative that is as close as possible to being a Condorcet winner and contains examples of a subcontractor selection using only ordinal scales of evaluation of alternatives

Metoda projektowania struktury systemu wykonawczego przedsięwzięcia budowlanego z zastosowaniem algorytmu ewolucyjnego

The paper discusses the problem of designing a construction project’s organisation structure at the operating level, where tasks and processes are of “complex of operations” type. Such a system includes heterogeneous operating units (crews, teams) of a general contractor and cooperating external ones – subcontractors, that create a temporary organisation. Its structure changes according to the project schedule as the project advances. The author identified the problem of designing a construction project operating system structure from the point of a general contractor, built the system’s model and formalised it mathematically. The contractor selection process (i.e. the selection of the system’s elements) is described as the problem of triple-criteria optimisation of the schedule. The assessment of possible variants of the system’s structure is made according the criteria crucial for the project’s efficiency and the general contractor’s objectives (i.e. minimisation of project duration and cost, and keeping subcontracting to minimum – as the general contractor is assumed to be interested in making full use of their own resources). To solve the problem, a method that uses metaheuristic approach has been worked out. An evolutionary algorithm (using stochastic processes) was adapted for solving the triple-criteria schedule optimisation problem in deterministic conditions. The author developed also a heuristic algorithm to allocate limited resources of variable availability. The solutions are generated by means of an achievement scalarising function, which is based on Tchebycheff utility function. The selection of final solution can be done by analysing the approximation of whole set of non-dominated solutions on the basis of total decision maker’s preferences, or by means of Steuer’s interactive method.W artykule podjęto problem projektowania struktury systemu wykonawczego przy harmonogramowaniu realizacji przedsięwzięcia budowlanego typu „kompleks operacji”. System ten złożony jest z niejednorodnych jednostek operacyjnych generalnego wykonawcy oraz kooperujących jednostek zewnętrznych – podwykonawców. Tworzą oni tymczasową organizację. Jej struktura zmienia się w czasie zgodnie z harmonogramem realizacji przedsięwzięcia. Autor dokonał identyfikacji modelu i formalizacji matematycznej problemu projektowania struktury systemu wykonawczego przedsięwzięcia budowlanego. Proces doboru wykonawców (elementów systemu) opisano jako problem optymalizacji trójkryterialnej harmonogramu. Ocena możliwych wariantów budowy struktury systemu wykonawczego dokonywana jest przy zastosowaniu kryteriów decydujących o efektywności przedsięwzięcia i działalności generalnego wykonawcy (minimalizacja czasu i kosztu realizacji oraz kosztu robót zleconych podwykonawcom). Do rozwiązania analizowanego problemu opracowano metodę wykorzystującą podejście metaheurystyczne. W tym celu zaadaptowano algorytm ewolucyjny (wykorzystujący procesy stochastyczne) do rozwiązywania zagadnień trójkryterialnej optymalizacji harmonogramów w warunkach deterministycznych oraz opracowano heurystyczny algorytm rozdziału ograniczonej i zmiennej w czasie liczby jednostek zasobów i wykonawców. Rozwiązania generowane są z wykorzystaniem funkcji skalaryzującej osiągnięcia celów optymalizacji, bazującej na metryce Czebyszewa. Wybór rozwiązania końcowego może być dokonany poprzez analizę przybliżenia całego zbioru rozwiązań niezdominowanych (na podstawie preferencji globalnych decydenta) lub z wykorzystaniem ineraktywnej metody Steuera

Hemispheric asymmetry in the efficiency of attentional networks

Advantage in conflict resolution was observed, which may indicate hemispheric asymmetry of the executive network. No VF effect for alerting was found. The results, consistent with the common notion of general right hemisphere dominance for attention, provide a more detailed account of hemispheric asymmetries of the attentional networks than previous studies using the LANT task

CFD Analysis of the Fluid Particles Distribution by Means of Aviation Technique

Abstract The article describes a computational study, using CFD models, of droplet spray dispersal in the wake of a 'Turbo Kruk' airplane up to 500 m downstream. The CFD Reynolds-averaged Navier-Stokes (RANS) models use a Lagrangian (droplet phase) and Eulerian (fluid phase) procedure to predict the droplet trajectories trough the turbulent aircraft wake. The methods described in the work have the potential to improve current models for aerial spraying and will help in the development of new spraying procedures. In this study, the CFD models are used to describe the phenomenon of sprays released from atomizers mounted on the plane. A parametric study of the aircraft model examines the effects of crosswind on the aircraft's vortex structures and the resulting droplet trajectories. The study shows, that such influence is underestimated in the current models. A comparison of the present results to AGDISP predictions is provided

Simulation modelling construction project with repetitive tasks using Petri nets theory

Resources selection and allocation at the project planning stage is an important issue for reducing project cost, duration and risk. Existing planning and scheduling methods overlook aspects of limited production capacity of construction companies (contractors) due to the fact that they are simultaneously engaged in realization of some projects. This paper presents a new methodology for project scheduling with repetitive processes using Petri nets based approach. The paper starts with an overview of current developments in the Petri nets theory. We then propose an efficient computational method based on simulation of Petri net model for construction project planning and subcontractor agreement analysis. An example of construction project simulation research is presented to illustrate the method of project planning and resources allocation. First published online: 14 Oct 201

Dobór elementów deskowania ścian z uwzględnieniem kryteriów ekonomicznych

Planning formwork (selecting systems, designing layout of formwork members) affects the economy of in situ concrete structures. Formwork rental cost, and labor cost of formwork installation and removal,  have a significant share in total cost. The paper investigates into the problem of minimizing wall shuttering cost. A mathematical model of the problem of panel layout is proposed, and its operation is illustrated by the case with two optimization criteria.Racjonalne planowanie deskowania konstrukcji (dobór systemu, zaprojektowanie układu elementów) wpływa na koszty wykonania obiektów realizowanych w technologii monolitycznej. Istotny udział w strukturze kosztów stanowią koszty dzierżawy elementów systemu, a przede wszystkim robocizny przy ich montażu i demontażu. W artykule jest rozważany problem ustalania planu zadeskowania ścian kondygnacji obiektów  w aspekcie minimalizacji ww. kosztów. Opracowano model matematyczny zagadnienia projektowania układu tarcz oraz rozwiązano przykład jego rozwiązania dla dwóch kryteriów optymalizacji.&nbsp

Assignment problem and its extensions for construction project scheduling

The assignment problem consists of allocating renewable resources (construction equipment, crews, or contractors) of limited availability to a set of activities. The classical model for this problem minimizes the total time or cost of completing all activities with the assumption that each activity is assigned to one particular resource. This paper systematizes and describes extensions of these assumptions, considering the effects of task sequence: parallel, serial and hybrid (modeled by means of network methods). This study proposes algorithms for the solution of presented models, which can be used in construction project scheduling

Zespół kruchości u pacjenta dializowanego otrzewnowo — implikacje kliniczne i terapeutyczne

Zespół kruchości (FS) to wyczerpanie rezerw fizjologicznych, osłabienie, wątłość, związane ze starzeniem się i wyeksploatowaniem organizmu. U pacjentów ze schyłkową niewydolnością nerek, leczonych nerkozastępczo, objawy zespołu kruchości występują znacznie częściej oraz w znacznie młodszym wieku w porównaniu z populacją ogólną. Celem niniejszej pracy jest omówienie problematyki zespołu kruchości w grupie chorych dializowanych otrzewnowo, ze szczególnym uwzględnieniem dostępnych narzędzi diagnostycznych oraz wyboru asystowanej dializoterapii otrzewnowej jako preferowanej opcji terapeutycznej