# Weight Reduction of a Ship Crane Truss Structure Made of Composites
## 1 Introduction  
One of the features of modern structural design is the use of advanced manufacturing technologies and new types of structural materials. The use of composite materials makes it possible to achieve required mechanical and operational properties at the design stage [1]. The introduction of new technologies in design leads to the complex problems of structural mechanics. The general goal in designing ship cranes is to develop a structure that performs all specified operations and uses a minimum amount of material. The use of fiber-reinforced plastic (FRP) as a structural material [2; 3], as well as modern technological processes for their production [4; 5], removes a number of substantial restrictions, increasing the number of design options and making the development process more complicated. That makes the use of modern computer simulation and optimization tools crucial for designing hosting mechanisms. There are also certain difficulties associated with the use of FRP. In particular, it is well known that in case of FRP, the material and structure are formed simultaneously in the same technological cycle. Therefore, the mechanical properties of the finished structure are inextricably linked with the process technology, which requires experimental confirmation of the declared characteristics as they may strongly depend on the process conditions and on the equipment used. However, despite the difficulties of designing structures made of FRP in comparison with those made of metals, the use of FRP can be justified by decisive advantages inoperation. One example of such an application is a ship's crane manipulator (CM). The advantages of FRP that may strongly increase the performance of certain types of cranes include low weight, resistance to extremely low temperatures, resistance to aggressive climatic and chemical influences, and low sensitivity to physical fields (low magnetism). The use of FRP in marine engineering should be regulated by appropriate documents of classification societies, for example, Det Norske Veritas (DNV) [6]. These regulations cover hull structures and some ship equipment from FRP, but do not cover ship cranes. Despite that, the design of cranes could benefit from the replacement of some solid metallic parts with truss structures made of FRP. In such a design, cross sheets (frames) can be also made of FRP [7]. Several books and articles are devoted to optimization problems for truss structures. Paper [8] presents algorithms suitable for optimization of the truss structure with discrete admissible diameters of the rods. The authors emphasize the convergence problems of new methods in relation to specific engineering problems. Papers [9; 10] present efficient integer programming models for truss topology optimization problems. However, a crane boom has a standardized topology structure. Paper [11] describes a new machine-learning-combined method for constructing a composite framework. Despite the efficiency of the method proposed by the authors, its parameters adjustment and implementation in engineering practice is quite tricky. Articles [12; 13] present methaheuristic algorithms for solving optimization problems of truss structures. However, there is no algorithm that could be used for efficient optimization of the entire crane boom structure. The use of the considered algorithms and methods to solve the optimization problem for such structures is difficult due to the large number of variables, unknown parameter correlation functions, several calculation cases, and the large number of additional constraints and dependencies imposed by the production technology. So, a universal methodology for engineering use is needed. In this paper, we present an engineering technique for optimizing a design of the CM boom made of FRP. In the first part, the description of the crane design and a comparison of the boom made of metal and of FRP are presented.