I beam

In the following, we shall consider a single cantilever beam, of square section, and will analyse the material requirements to minimise the weight for a given stiffness. The results are quite general in that they apply equally to any sort of beam of square section, and can easily be modified to deal with beams of other sections tubes, I-beams, box-sections and so on. 

The flexural stiffness of the beam will be proportional to El. So converting the section to an equivalent I beam as in the previous example... 

A third method is to convert the structural foam cross-section to an equivalent I-beam section of solid resin material (Fig. 6-22). 

The designer can use conventional plastics that are available in sheet form, in I-beams or other forms, as is common with many other materials. Although this approach with plastics has its place, the real advantage with plastic lies in the ability to process them to fit the design shape, particularly when it comes to complex shapes. Examples include... 

Procedures for calculating vent area ratios for various structural configurations which have been used for suppressive shields are presented in Fig. 36. The procedures shown in Fig. 36 are believed to be self-explanatory, except possibly for the interlocked I-beams. The vent areas number 2 and 3 for this case are to take account of the two equal spaces b associated with each I-beam. 

In a sandwich structure, the foam is used as the core with two skins of reinforced resin sheets firmly stuck on the foam to obtain high rigidity. The sandwich composite behaves as an I-beam see Figure 6.11. 

The most severe damage was on the front wall. The displacement was such to impact against the walkways and I-beam supports. Supporting I beams, 15-20 cm flange to flange, were twisted and deformed. A concrete walkway on the fifth floor was moved about 1 m and essentially demolished. 

The crystal structures of all amphibole minerals, including the asbestiform varieties, are most easily understood as variations on a basic structural unit called an I-beam. The term I-beam alludes to the cross-sectional shape of the three-part structure consisting of corner-linked (Si04) and/or (A104) tetrahedra (T) linked together into a double-tetrahedral chain that sandwiches a layer of edge-shared and R Og octahedra (O). R elements, which... 

Variations in the stacking of I-beams have been studied with single crystal x-ray diffraction. The stacking character distinguishes the different amphibole mineral series (Hawthorne, 1981), Such studies show that tetrahedra in the T sheet are rotated and tilted to accommodate the variations in the anion... 

Fig. 2.8 Cleavage in the amphiboles. (A) Schematic representation of the characteristic stacked amphibole I-beams in the three-dimensional structure. A tetrahedral portion of an I-beam is labeled "silica ribbon." The octahedral portion is labeled "cation layer" and represented by solid circles. One of the possible cleavage directions (110) along planes of structural weakness is indicated by the line A-A stepped around the I-beams in the lower part of the diagram. (B) Cross section of the stacked I-beams with the directions of easy cleavage indicated. There is a lower density of bonds between I-beams in the crystallographic directions (110) and (110). These directions, parallel to the c axis and the length of the chains, are the planes of cleavage. The minimum thickness of a rhombic fragment produced through cleavage is 0.84 nm.

Fig. 2.9 High-resolution electron micrographs of anthophyllite. Displacive fault termination or "zippers," and an interpretation based on the I beam structure of the amphiboles.

The equilibrium ground-state spectra of the parent six-coordinate and deoxy five-(or four-)coordinate species were obtained using a Tungsten lamp placed before the I /I beam splitter. Earlier work in our laboratory (3,4) has established that the experimental spectra of transient protoproducts can be resolved as they sequentially evolve during the dissociation process. At relatively long delays > 20 psec after excitation, the spectrum of the stable photoproduct... 

Thermoplastic structural foams with bulk densities not less than 50% of the solid resin densities are considered. Cellular morphology, uniform-density cell behaviour, the I-beam concept in designing, core-density profile and the role of the skin, mechanical properties, and ductile-brittle transitions are discussed. 63 refs. 

---