Stiffness and Strength Analysis of Case Furniture

7.1Properties of Case Furniture

Unlike craft furniture, industrially manufactured furniture should be created according to a specific, repetitive technology, in the conditions of mechanised serial production. Also a number of important structural, technical, organisational and commercial requirements have to be fulfilled, unknown to crafts factories and furniture workshops. These requirements have become an essential stimulus to the overall mechanisation and technification of furniture production, which has also resulted in the need to prepare their design documentation. Engineering design methods, without which it is hard to imagine building, aviation and machine construction, have never been systematically or on a large scale introduced into furniture production. The implementation of engineering methods of construction requires the gathering of detailed information concerning:

• the function of the piece of furniture and maximum operational loads resulting from it, or also in extreme cases, unusual loads, especially when it concerns children’s and teenager’s furniture;

• elastic properties of materials used, taking into account the orthotropic char­acteristics of wood and wood materials, together with indicating maximum stresses; and

• elastic and durability properties of normalised glued and separable furniture joints and connectors, hinges and accessories carrying operational loads.

The structural development, ensuring durable and safe use, is one of the three components of the design process. Next to strength requirements, aesthetic and functional requirements are a part of them. Functional design is of the greatest practical importance, as it ensures the most effective possible fulfilment of the assumed operational functions. The purpose of aesthetic activities is shaping the

© Springer International Publishing Switzerland 2015 J. Smardzewski, Furniture Design,

DOI 10.1007/978-3-319-19533-9_7

proportions and spatial forms of the piece of furniture and the choice of surface colour, texture and drawing to the satisfaction of the most demands of the user. This part of the project in many cases clearly dominates the whole design works, shifting functional and durability features further away. In this situation, the functional requirements should have strong preference, sometimes at the expense of aesthetic or durability values.

In a properly planned furniture production process, the assessment of the stiff­ness of individual products should be begun already at the constructional design stage. This helps eliminate any furniture construction errors by setting the correct parameters for individual components, subassemblies and assemblies in accordance with the prescribed criteria of stiffness and durability. Formulating the engineering process of designing furniture in such a way will enable to limit destructive tests of finished products and shorten the cycle of implementing the piece of furniture to production, limit the number of complaints in continuous production and save a significant amount of time and material. Stiffness and strength of furniture can be assessed with the use of:

• theoretical analysis and the guideline details resulting from it for constructors

and technologists of furniture and

• damage tests of the prototype or finished product, as well as checking calcu­lations in order to justify the constructional errors found.

The first works concerning the stiffness of case furniture appeared in the year 1957-58 (Kotas 1957, 1958a, b, c). It demonstrates the deformations of furniture bodies and analyses examples of increasing stiffness of the entire construction and strength of joints. Static and strength problems were later extended in national and foreign literature (Chia-Lin and Eckelman 1994; Dzi^gielewski and Smardzewski 1989, 1990, 1992; Eckelman and Resheidat 1984; Eckelman and Rabiej 1985; Eckelman 1967; Ganowicz and Kwiatkowski 1978; Ganowicz et al. 1978; Joscak 1986; Joscak and Vacek 1989; Kuhne and Kroppelin 1978; Korolew 1970, 1973; Lapszyn 1968; Smardzewski and Dzi^gielewski 1994), focusing both on the global stiffness of the entire construction, as well as stiffness and strength of elements and joints.

Within the framework of the stiffness analysis, deformations of the furniture body and bends of bars, shelves, partitions, bottoms of drawers and containers, as well as deformations of wall joints are examined. While strength calculations pri­marily concern the strength of wall angular joints and suspending cupboards and bottoms, attempts to assess the stability of designed furniture constitute a separate group of analytical studies. The stability of furniture is the most essential part of quality studies on a finished product, and its loss may be a direct threat to the life or health of the user.