Artur Duchaczek

The influence of a cracking mode on fatigue crack propagation in steel girders in military bridges

This article is presented a way of taking into account mixed mode cracking in fatigue analyses of steel girders in military bridges. The influence of the angle size of the direction crack propagation φ on the evaluation of fatigue life of steel girders is also described. The conducted analyses showed that taking into account mixed mode cracking and the value of the direction of crack propagation φ has a positive influence on the accuracy of calculations related to the determination of fatigue life of steel structural elements due to decreasing a value of the equivalent stress intensity factor Keq. The work is also presented the results of calculations of fatigue cracks propagating in the main steel girders developing in the direction away from assembly openings. The analysis was conducted using the FRANC2D software for two adopted models of physical material. The calculation results of fatigue crack propagation in the case of material models which are either ideally elastic or ideally elastic with linear plastic strain hardening are also described. The conducted analyses showed that adoption of particular material properties has a significant influence on the value of the obtained calculation results.

Evaluation of probability of bridge damage as a result of terrorist attack

Abstract The paper presents an approach for evaluation of the likelihood of damage to the transportation infrastructure in the context of the terrorist attacks on the example of a number of bridges located in Wrocław (Poland). Assuming that there will be only one bridge destroyed in a given area, in order to determine the probability of damage to one of the objects, there was one of multi-criteria optimization methods used, i.e. the method of Analytical Hierarchy Process (AHP). The main advantage of the analysis carried out was that the accepted hierarchy of decision-making options could be easily explained in a scientific manner, not only with reference to personal knowledge, experience, and intuition.

Determination of the value of stress intensity factor in fatigue life of steel military bridges

In the case of bridge structures the ability to determine the life of a damaged bridge span as a function of load cycles is fairly essential. It allows the person who is responsible for the service of such a structure to make decisions related to the necessity of its possible repair. One of the basic parameters used in the analysis of service lifecycle of steel structures with a damage of a particular size, is the stress intensity factor K, which is used in a large number of formulas describing the growth rate of fatigue cracks. The work presents an assessment of a possible use of the finite elements method to calculate using the stress intensity factor K directly. The obtained results were compared with the results obtained with three other methods based on the FRANC2D software and with laboratory own tests results. Taking into account the results of these analyses presented in the paper it was found out that the FRANC2D software is a very useful and practical tool in strictly engineering tasks.

The Use of the Generalised Knapsack Problem in Computer Aided Strategic Management

There are many methods and tools in the literature that are helpful in strategic management. Some of them are related to the aspect of sustainability in terms of controlling and balancing the level of fulfilment of the different, sometimes conflicting, objectives which must be considered while building strategies. These tools include product portfolio methods. However, their use is often intuitive and detached from the quantitative aspects of management, such as cost-related restrictions or other quantitative restrictions imposed by the market or by internal circumstances. This article presents a proposal for the modification of portfolio methods aimed at enforcing the portfolio’s quantitative aspect through the use of a discrete optimisation problem, namely the knapsack problem. Interacting with the decision maker, the quantitative parameters of the situation and the strategic goals are determined. Following this, a proposal solution is generated by a computer system in which the respective algorithms for the generalised knapsack problem (also called the generalised assignment problem) are embedded. The decision maker can accept the solution or change the parameters if the solution does not suit them or if they simply want to have other solutions for comparison. The outline of the system and the interaction between the decision maker and the system is illustrated by means of an example of constructing strategies for a university.

Application of the AHP method in modeling the trust and reputation of software agents

Given the unique characteristics of cyberspace and, in particular, the number of inherent security threats, communication between software agents becomes a highly complex issue and a major challenge that, on the one hand, needs to be continuously monitored and, on the other, awaits new solutions addressing its vulnerabilities. An approach that has recently come into view mimics mechanisms typical of social systems and is based on trust and reputation that assist agents in deciding which other agents to interact with. The paper offers an enhancement to existing trust and reputation models, involving the application of the AHP method that is widely used for decision support in social systems, notably for risks analysis. To this end, it is proposed to expand the underlying conceptual basis by including such notions as self-trust and social trust, and to apply these to software agents. The discussion is concluded with an account of an experiment aimed at testing the effectiveness of the proposed solution.

Fuzzy analysis of project duration in situations of risk

The duration of project activities is usually not deterministic. Thus, it may be modeled by means of fuzzy numbers. In the literature there exist several fuzzy approaches to the modeling of project activities duration. In this paper a new one proposed, which will permit to determine the critical path taking into account several risk factors and expert opinions. A Finally, a case study will be presented and analysed: the project of constructing a shopping mall in Poland.

Risk assessment as a safety element in temporary bridge exploitation

The world financial crisis, which started in the real property market, suppressed voices of risk analysis critics. Most entrepreneurs do not question its necessity, however, only few of them use it in practice. The reasons for this situation include financial ones or lack of organisational culture. Risk identification in bridge facilities exploitation encompasses specification and hierarchisation of potential threats. These threats may hamper transport or even make it impossible. Correct specification and accurate quantity description of risk factors influence the effectiveness of risk assessment of a particular facility. This allows to avoid or decrease problems in various logistical undertakings. The article presents an analysis of risk assessment possibilities for temporary bridges. It was assumed that bridges are very important elements of road infrastructure. Thus, the problem of risk assessment in road transport was directly correlated with a possible bridge infrastructure fault. Moreover, the article presents an original method of analysis of one bridge exploitation risk factor, i.e. the fatigue risk factor. The analysis was conducted on the example of temporary bridges based on one of the selected method of multicriteria optimisation, i.e. the Analytic Hierarchy Process.

The Impact of Cross Beam on Stresses of Girders in Low Water Bridges

Low water bridges are classified to a group of military bridges, most frequently made of materials obtained at their construction site (steel sections and wood). They are characterised by similar structural solutions as civilian bridges, commonly called detour or temporary ones. However, low water bridges are structures that are not expected to enable the conduct of shipping and the runoff of ice floes. The aim of this study is to determine the impact of the number of cross beams and their rigidity as well as assembly connections made on the stress distribution in spans of low water bridges. The carried out numerical analyses (FEM) have shown that either the number of girders or the number of cross beams significantly affect the stress distribution in main girders. Moreover, these analyses have proved that the rigidity of cross beams and the manner of assembly connections execution with the sufficiently rigid wood plate have little effect on the stress distribution in the major structural elements of low water bridges. The analyses have shown, however, a very large impact of the way of modelling assembly connections in a steel grate on the stress distribution in the wood plate.

Identification of the risk of disturbances of operation of transport infrastructure in crisis conditions

The paper contains a specification of the notions of risk, transport infrastructure and crisis situation. The study also presents selected methods of identification of risks to transport infrastructure facilities, based on the example of a bridge facility.

Statistical methods for classification of unmanned aerial vehicles

When making decisions regarding multiple objects, researchers often face the problem of choosing the appropriate method for grouping objects with similar characteristics [1]. The present article proposes the use of agglomeration methods to search for links between individual unmanned aerial vehicles (UAVs). An undoubted advantage of the application of agglomeration methods is the possibility of searching for similarities even between many objects to describe which numerous characteristics can be used. The aim of this article is to investigate interrelations between the selected UAVs. For the study purposes the cluster analysis was employed comprising algorithms for grouping objects so that the degree of linkage between elements from the same group was as high as possible, while with elements from the other groups as low as possible. Identification of similar objects, merging them into homogeneous groups, gives the opportunity to organize and classify them.