Table 2 Durability Levels Protected Grade Bricks are usually used for internal walls above a damp proof course. General Purpose Grade Bricks are suitable for use in external walls in mild exposure environments and normal (non-wet area) interior walls. Exposure Grade Bricks are suitable for saline environments and should always be used below the damp- proof course and in other locations of severe exposure. Figure 1 Salt attack damage to masonry unit Figure 2 Salt attack damage to mortar Design Considerations Brick Technical Manual 59 5.1.3 Mortar The resistance of mortar joints to degradation during the life of a building is related to surface hardness, which is strongly related to cement content. Low hardness will lead to progressive erosion of the surface of the joints by physical damage, wind action, insect attack and the effects of salt crystallisation. Mortar is classified in AS 3700 as grades M1, M2, M3 or M4. These grades are used for durability requirements as well as for strength properties. Mortar of type M1 can only be used for restoration work to match existing construction and therefore has no corresponding durability provisions. Refer to Mortar section 2.5 in this manual for more details.

TABLE 13.6 Diameters of Circular Ducts in Inches Equivalent to Rectangular Ducts Side 4 8 12 18 24 30 36 42 48 60 72 84 Air filters come in a number of standard sizes and thicknesses. The filter area should be such that the air velocity across the filters does not exceed 350 ft /min for low-velocity filters or 550 ft /min for high-velocity filters. Thus, the minimum filter area in square feet to be provided equals the airflow, ft3 /min, divided by the maximum air velocity across the filters, ft /min. Most air filters are of either the throwaway or cleanable type. Both these types will fit a standard filter rack. Electrostatic filters are usually employed in industrial installations, where a higher percentage of dust removal must be obtained. Check with manufacturers ratings for particle-size removal, capacity, and static-pressure loss; also check electric service required. These units generally are used in combination with regular throwaway or cleanable air filters, which take out the large particles, while the charged electrostatic plates remove the smaller ones. See also Art. 13.6. After air discharge grilles and the air handler, which consists of a heat exchanger and blower, have been located, it is advisable to make a single-line drawing showing the duct layout and the air quantities each branch and line must be able to carry. Of the methods of duct design in use, the equal-friction method is the most practical. It is considered good practice not to exceed a pressure loss of 0.15 in of water per 100 ft of ductwork by friction. Higher friction will result in large power consumption for air circulation. It is also considered good practice to stay below a starting velocity in main ducts of 900 ft /min in residences; 1300 ft /min in schools, theaters, and public buildings; and 1800 ft /min in industrial buildings. Velocity in branch ducts should be about two-thirds of these and in branch risers about onehalf. Too high a velocity will result in noisy and panting ductwork. Too low a velocity will require uneconomical, bulky ducts. TABLE 13.7 Size of Round Ducts for Airflow*

A flat slab is a two-way slab generally of uniform thickness, but it may be thickened or otherwise strengthened in the region of columns by a drop panel, while the top of the column below the slab may be enlarged by a capital (round) or bracket (prismatic). If a drop panel is used to increase depth for negative reinforcement, the minimum side dimensions of this panel are L3 /3 and L2 /3, where L1 and L2 are the center-to-center spans in perpendicular directions. Minimum depth of a drop panel is 1.25h, where h is the slab thickness elsewhere. A waffle flat slab or waffle flat plate consists of a thin, two-way top slab and a grid of joists in perpendicular directions, cast on square dome forms. For strengthening around columns, the domes are omitted in the drop panel areas, to form a solid head, which also may be made deeper than the joists. Other variations of waffle patterns include various arrangements with solid beams on column centerlines both ways. Standard sizes of two-way joist forms are given in Table 9.21. The drop panel increases shear capacity. Hence, a solid flat slab can ordinarily be designed for concrete for lower strength than for a flat plate. Also, deflection of a flat slab is reduced by the added stiffness that drop panels provide. The depth of drop panels can be increased beyond 1.25h to reduce negativemoment reinforcement and to increase shear capacity when smaller columns are desired. If this adjustment is made, shear in the slab at the edge of the drop panel may become critical. In that case, shear capacity can be increased by making the drop panel larger, up to about 40% of the span. See Fig. 9.31 for bar details (column