Joint design stiffening joints

From the standpoint of long life and freedom from maintenance, dished, hemispherical and cone bottoms are the best for cylindrical tanks, and are the designs of necessity if a vessel is to be "prestressed" (see Chapter 47), or if there is a desire or necessity to eliminate expansion joints. Flat bottoms, unless provided with properly designed expansion joints, will heave upward with brick growth. In addition, adequate and frequent stiffening is required if flexing and... 

However, the fabricator is a cautious man and, although he is confident that he will need no preheat, he designs his joint simulation test so that he can include test welds made with some preheat. He therefore makes the fabricated beam 2 m long, so that he can include three stiffeners staggered on either side of the beam as shown in Fig. 2.9. He also selects the plates which have the maximum CE of... 

Fig. 4.2. Common engineering joints and joint designs, (a) The lap joint and its variants, b) Containment joints for plates, extrusions and pultrusions. (c) Ways of minimising peel in laps, doublers and stiffeners.

There are many versions of software programs available for the analysis and design of composite laminates and laminated structural elements. ESAComp is one such version, initiated by the European Space Agency, covering fiber/matrix mechanics, plies, laminates, plates and stiffened panels, beams and columns, bonded joints and mechanical joints. The software can interface with the widely nsed finite element software packages. 

Major type of use Unstressed joints designs with caps, overlaps, stiffeners Stressed joints at sUghtly elevated temp Unstressed joints on lightweight materials joints in flexure Where highest and strictest end-service conditions must be met sometimes regardless of cost, as military uses... 

Thin to large wall Designing around TP problems is the joint responsibility of the product and mold designers. For example, one way to handle the problem of thin to large area walls is by the inclusion of long ribs into the product in the direction of plastic flow. These ribs are not a functional requirement of the product but they act as auxiliary runners attached to the product to facilitate plastic flow in difficult to fill areas. In some instances the ribs may be used as a surface decoration like a corrugation or they may be on the concealed side of the product where they are stiffeners. 

The designer assumed that the columns were axially loaded and no allowance was made for the bending of the columns due to the stiffness of the joint. The bending moments due to wind loading were calculated as though the top and bottom column joints at each storey were rigid. The tops of the second storey columns were assumed to be partially restrained in position because of the stiffening sidesway provided by the central columns and stairs. 

Thermoplastic adhesives are not ordinarily recommended for use at above 66°C, although they can be used up to 90°C in some applications. These materials have poor creep resistance and fair peel strength. They are used mostly in stressed joints and designs with caps, overlaps, and stiffeners. The materials most commonly bonded are non-metallic material, especially wood, leather, plastics, and paper. With the exception of some hot-melt adhesives, thermoplastic adhesives are not generally used for structural applications. Examples of thermoplastic adhesives are shown in Table 4.2. ... 

Thermoplastic adhesives soften and melt when heated (provided that they do not decompose). In other words, they do not cross-link during cure. These adhesives are single-component and harden upon cooling by evaporation of a solvent or water vehicle. They have poor creep resistance, fair peel strength, and are used mostly in unstressed joints and designs with caps, overlaps, and stiffeners. The most common application is to bond nonmetallic materials such as wood, leather, cork, and paper.In general, thermoplastic adhesives are not used for structural applications or at temperatures above 66°C (150°F). Thermoplastic adhesives includeit t ... 

While a rigid metal component may accommodate these stresses easily, a more flexible plastic part of the same cross section may require extra stiffening in the form of ribs, inserts, or bosses. Much of the design simplicity of molded parts can be lost in making provision for mechanical assembly. By contrast, a bonded joint requires no extra design provision other than a check to ensure that enough joint area is available and that the adhesive meets service requirements. 

O Figure 47.16 shows the design of the aluminum ceiling panel intended for use on the latest intercity coaches (Seeds 1984). The requirement is to fasten the top-hat stiffeners to the upper side of the panel without damaging the epoxy-paint finish on the underside. Two-part separate application acrylic adhesive met the requirements of the joint and a light abrasion plus a solvent wipe gave adequate preparation. 

---