Agata Czarnigowska

Rezerwa kosztów przedsięwzięcia budowlanego jako część jego budżetu jest planowana w oparciu o doświadczenie i ilościową analizę ryzyka. Artykuł analizuje metody i narzędzia szacowania rezerwy kosztowej przedsięwzięć budowlanych na bazie 43 publikacji z lat 2006–2025. Mimo gwałtownego rozwoju metod analizy danych badana próba publikacji nie wskazuje jeszcze na przełom w technice planowania rezerw (dominują: lekko modyfikowana technika symulacji Monte Carlo i stosunkowo proste modele uczenia maszynowego). Co więcej, zarówno pojęcie rezerwy kosztu, jak i cechy przedsięwzięć traktowane jako predyktory kosztu traktowane są w badanych źródłach bardzo rozmaicie.

The selection of the target market (i.e., country) is a key decision that affects the contractor’s development prospects and determines success or failure in the competitive international construction environment. Despite its importance, the problem of market selection has been the subject of limited research and few tools have been proposed to help reduce the risk of making the wrong choice. Availability of several compromising/conflicting criteria, the difficulty in articulating and capturing them, and the ambiguities that may arise in their interpretation make the market selection for a construction enterprise a complicated task. This paper addresses this research gap and presents a tool based on a modified Fuzzy Group Analytic Hierarchy Process, which employs a type-2 fuzzy envelope of extended hesitant linguistic term set (EHFLTS) to aggregate the decision-maker’s judgments. Using extended hesitant linguistic terms, the comparative linguistic expressions (CLEs) generated using context-free grammar (CFG) enable the decision-maker(s) to express their preferences in a way that resembles a natural language. They also help to capture the hesitation in prioritizing the available options. The process of computing with word (CWW) with CLEs is implemented through EHFLTS envelopes. To illustrate the method’s principles of operation, a hypothetical case of selecting the best market for the construction enterprise is introduced.

Decision-making for the refurbishment of multi-family residential buildings is a complex and computationally difficult task. Therefore, the authors have developed a model that supports modernization planning in a long-term and comprehensive manner, i.e. from assessing the building to indicating the optimal scope of modernization. The comprehensive scope of the model includes the acquisition and provision of relevant knowledge to the model. The original methods proposed for its acquisition are derived from common expert knowledge based on linguistic terms. The methods adopted are not mandatory and may be replaced by others that provide more reliable knowledge. The fundamental aim of the proposed approach, however, is to select the optimal modernization option and allocate it over the planned modernization time horizon. An innovative optimisation approach based on decision matrices is used, allowing the selection of possible scenarios of repair options at each stage. These matrices are a set of constraints written in binary variables allowing the optimisation calculus to maintain a fixed sequence of repairs. In addition, the solutions used in the optimisation modules make it possible to take into account assumptions regarding the assumed assessment of the building’s condition and financial constraints. The developed model provides a practical and versatile tool that can be used by managers at the maintenance stage of residential buildings.

The paper puts forward a mixed integer linear programming model to support the long-term planning and budgeting for renewal and capital improvements of residential buildings, i.e., to select the optimal sequence of repair and improvement actions over a predefined planning horizon. The input is provided by the evaluation of the building performance according to a set of criteria. Then a set of possible repairs, replacements and improvements needs to be proposed together with the estimates of their cost and benefits; the latter are expressed by increments of building performance ratings according to predefined criteria. The renewal and modernization measures are not mutually independent: at least some of them are complementary and should be carried out in a specific order. The optimization problem was to define the order of renewal/improvement measures resulting with the highest benefits available within the budget, or to achieve the required levels of building performance at the lowest cost. A unique feature of the model is the approach to the constraints on sequential relationships between the measures and to their selection. The model can be used to construct long-term renewal and capital improvement plans.

BACKGROUND: Achieving sustainability of agricultural production is one of the key challenges for humanity. Minimizing the use of chemicals and replacing them with biological plant protection is, firstly, fully in line with the agriculture's development strategy and, secondly, confirmed to be achievable in practice. For instance, many researchers point to the potential of using Trichogramma spp. to control Ostrinia nubilalis in maize. However, the application methods for preparations containing Trichogramma spp. are still at the stage of development. So far, ground application proved time and energy consuming. Aerial application using ultralight aircraft is a new option.RESULTS: The present study presents the results of tests on the effectiveness of applying Trichogramma spp. from the board of an ultralight gyroplane. A 6‐year experiment was conducted on a maize monoculture located in south‐western Poland. The results indicate that the low‐height aerial application allows precise dosing and satisfactory distribution of the biopesticide. The efficacy of 60–85% (depending on the year) of the gyroplane‐based spraying operations was comparable with that observed for ground application.CONCLUSION: Considering the speed and high efficiency of the treatment, using a gyroplane as a carrier of the biopesticide application system is a good alternative to the other methods. © 2020 Society of Chemical Industry

The selection of suppliers is one of the key issues of supply logistics of any business entity. Due to the globalization of the economy and the rapid technological progress, the choice of products and the number of vendors is growing, which makes the selection process difficult. The specific character of the construction projects (one-off contracts with no incentives of the steady orders from one client, the need to adjust the batch size to the pace of the construction works whereas this pace is affected by risks and uncertainties, short time for planning, etc.) poses extra challenges to the suppliers’ production and transportation capacities and defines what “capable suppliers” mean for the project success. Therefore, the criteria of a construction project supplier selection go far beyond the obvious “price”. They need to refer to the supplier’s bid as well as the supplier’s own qualities (financial standing, reputation, flexibility). Though the selection process is expected to be based on unequivocal and objective input, in practice, it rests upon opinions and artificial measures used in lieu of the complete information. This input is, thus, fuzzy by nature and ignoring this fact may lead to wrong decisions. Therefore, the authors analyze the ways of quantifying supplier selection criteria and the methods of using them in the decision-making process presented in the literature. Then, they present a numerical example of supplier selection based on AHP with the fuzzy input, juxtaposing it with the results of the “classical” AHP with a crisp input. The results are different. Though this difference cannot be generalized, it indicates that the method of analysis may strongly affect the decision-makers choices.

The Monte Carlo simulation has become a standard tool in the practice of planning risk-affected projects. In particular, it is frequently applied to testing the impact of risk on schedule networks with deterministic structures and random activity durations defined by distribution functions of any type. The accuracy of simulation-based estimates can be improved by increasing the number of replications or by applying variance reduction methods. This paper focuses on the latter and analyzes the impact of the variance reduction method on the scale of the standard error of the estimated mean value of project duration. Three methods of variance reduction were examined: the Quasi-Monte Carlo with Weyl sequence sampling, the antithetic variates, and the Latin Hypercube Sampling. The object of the simulation experiment was a sample network model with the activity durations of triangular distributions. This type of distribution was selected as it is often applied in the practice of construction scheduling to capture the variability of operating conditions in the absence of grounds for assuming other types of distribution. The results of the sample simulation provided an indirect proof that applying variance reduction measures may reduce the time of the simulation experiment (reduced number of replications) as well as improve the confidence in the estimates of the model’s characteristics.

The approach used by construction companies to determine bid prices is an element of their strategy used to win jobs in competitive tenders. Such strategies build upon an analysis of the contactor's potential and capabilities (am I able to deliver? am I eligible to participate in the tender?), and the analysis of the economic environment, including the expected behavior of competitors. The tender strategy sets out both the guidelines and the procedure in deciding whether or not to bid as well as the rules for determining the price. The price, on the one hand, should be high enough to cover expected direct and indirect costs as well as risk-adjusted profit. On the other hand, it needs to be low enough to be considered most attractive (typically: the lowest) among the prices offered by the competitors. The paper focuses on the price definition component of the bidding strategy. It provides a brief overview of the existing methods that support bidding decisions by comparing their demand for input and limitations in practical applications and presents a simulation-based method supporting the determination of the profit ratio. This probabilistic method assumes the existence of a positive correlation between the prices offered by the competitors. Its application is illustrated by means of a numerical example. The outcomes of the simulation prompt the amount of the profit margin that maximizes the expected value of the contractor's profit.

Despite strict safety regulations and general awareness of risks related with work at height, scaffoldings are associated with many accidents. The scale of the problem of unsafe scaffolding can be indirectly analysed on the basis of individual accident reports and statistics. However, the total number, types, purposes, sizes, and condition of scaffoldings used in the practice of Polish construction sites have not been assessed do far. The authors intend to fill this gap by conducting regular observation of scaffoldings erected in selected Polish urban areas. This paper presents the methodology of data collection and compares scaffoldings observed in two big cities, Warsaw and Poznań. Although the method misses scaffoldings out of sight of the assessor and, due to urban locations, focuses on building and not industrial or infrastructure projects, it gives a good idea of the qualities of scaffoldings in use, and enables estimating changes in the number of scaffoldings over the year. As comes from the analysis, frame scaffoldings are the most popular type used in Polish construction. Users commonly choose the narrowest option (less than 70 cm of usable width of the platform) and apply them to a variety of works, be it placing concrete, cladding walls with ETICS or even heavy stone elements, or providing access to roofs. Modular scaffoldings are second most popular, whereas the tube and fitting type is used in extremely rare cases. Small projects (individual housing, small-scale repairs) frequently rely on combination of elements of systems scaffoldings and are often incomplete. Interestingly, "bad scaffoldings" do not appear only in remote suburbs. As for the changes of the number of scaffoldings over the year, the pattern is not as clear as could be expected in the case of a cold climate country. The findings indicate that occupational safety culture is still low.