forces. Generally, the bracing is arranged to form trusses composed of triangular configurations, because of the stability of such arrangements. The joints between members comprising a triangle cannot move relative to each other unless the length of the members changes. Figure 3.6a illustrates the use of X bracing in the center bay of a multistory building to form a vertical cantilever truss to resist lateral forces. Other forms of bracing, however, may be used as an alternative to reduce material requirements or to provide more space for wall penetrations, such as doors and windows. Figure 3.6b shows how a single diagonal can be used in the center bay to form a vertical truss. In large bays, however, the length of the diagonal may become too long for structural efficiency. Hence, two or more diagonals may be inserted in the bay instead, as shown in Fig. 3.6c to e. The type of bracing in Fig. 3.6c is known as K bracing; that in Fig. 3.6d, as V bracing; and that in Fig. 3.6e, as inverted V bracing. The V type, however, has the disadvantage of restricting deflection of the beams to which the diagonals are attached and thus compelling the diagonals to carry gravity loads applied to the beams. The bracing shown in Fig. 3.6a to e has the disadvantage of obstructing the bay and interfering with placement of walls, doors, passageways, and, for bracing along the building exterior, placement of windows. Accordingly, the inverted V type often is converted to knee bracing, short diagonals placed near beam-to-column joints. When knee bracing also is architecturally objectionable because of interference with room arrangements, an alternative form of wind bracing, such as rigid frames or shear walls, has to be adopted. Trusses also can be placed horizontally to stiffen buildings for less drift. For example, Fig. 3.6 shows a building with wind bracing provided basically by an internal vertical cantilever tube. A set of horizontal trusses at the roof and a similar set at an intermediate level tie the tube to the exterior columns. The trusses reduce the drift at the top of the building by utilizing bending resistance of the columns. A belt of horizontal trusses around the building exterior at the roof and the intermediate level also helps resist drift of the building by utilizing bending resistance of the exterior columns. When not considered architecturally objectionable, diagonal bracing may be placed on the building exterior to form a braced tube. The bracing may also serve as columns to transmit floor and roof loads to the ground. Figure 3.6g shows how multistory X bracing has been used to create a braced tube for a skyscraper. See also Arts. 3.3.5, 5.1819, and Secs. 7 through 10. (Council on Tall Buildings and Urban Habitat, Planning and Design of Tall Buildings, Vols. SC, SB, and CB, American Society of Civil Engineers, New York; E. Simiu and R. H. Scanlon, Wind Effects on Structures, John Wiley & Sons, Inc., New York; Minimum Design Loads for Tall Buildings and Other Structures ANSI/ASCE 7-98, American Society of Civil Engineers, New York.) Buildings should be designed to withstand minor earthquakes without damage, because they may occur almost everywhere. For major earthquakes, it may not be economical to prevent all damage but collapse should be precluded. Because an earthquake and a high wind are not likely to occur simultaneously, building codes usually do not require that buildings be designed for a combination of large seismic and wind loads. Thus, designers may assume that the full strength of wind bracing is also available to resist drift caused by earthquakes. The methods of protecting against high winds described in Art. 3.2.4 may also be used for protecting against earthquakes. Shaking of buildings produced by temblors, however, is likely to be much severer than that caused by winds. Consequently, additional precautions must be taken to protect against earthquakes. Because such protective measures will also be useful in resisting unexpectedly high winds, such as those from tornadoes, however, it is advisable to apply aseismic design principles to all buildings. These principles require that collapse be avoided, oscillations of buildings damped, and damage to both structural and nonstructural components minimized. Nonstructural components are especially liable to damage from large drift. For example, walls are likely to be stiffer than structural framing and therefore subject to greater seismic forces. The walls, as a result, may crack or collapse. Also, they may interfere with planned actions of structural components and cause additional damage. Consequently, aseismic design of buildings should make allowance for large drift, for example, by providing gaps between adjoining buildings and between adjoining building components not required to be rigidly connected together and by permitting sliding of such components. Thus, partitions and windows should be free to move in their frames so that no damage will occur when an earthquake wracks the frames. Heavy elements in buildings, such as water tanks, should be firmly anchored to prevent them from damaging critical structural components. Displacement of gas hot water heaters is a common cause of gas fires following

C Tight knots to 11/2 in. Knotholes up to 1 in across grain and some up to 11/2 in if total width of knots and knotholes is within specified limits. Synthetic or wood repairs and discoloration and sanding defects that do not impair strength permitted. Limited splits allowed. Stitching permitted. D Knots and knotholes up to 21/2-in wide across grain and 1/2 in larger within specified limits, limited splits, and stitching permitted. Limited to Exposure 1 or interior panels. the panels intended end use, such as APA Rated Sheathing or APA Rated Sturd- I-Floor. Veneer grades define veneer appearance in terms of natural, unrepaired-growth characteristics and allowable number and size of repairs that may be made during manufacture (Table 10.17). The highest quality veneer grades are N and A. The minimum grade of veneer permitted in Exterior plywood is C grade. D-grade veneer is used in panels intended for interior use or applications protected from permanent exposure to weather. Panels with B-grade or better veneer faces are always sanded smooth in the manufacturing process to fulfill the requirements of their intended end use applications such as cabinets, shelving, furniture, and built-ins. Rated Sheathing panels are unsanded since a smooth surface is not a requirement of their intended end use. Still other panels, such as Underlayment, Rated Sturd-I-Floor, C-D Plugged, and C-C Plugged, require only touch sanding for sizing to make the panel thickness more uniform. Unsanded and touch-sanded panels, and panels with B-grade or better veneer on one side only, usually carry the trademark on the panel back. Panels with both sides of B-grade or better veneer, or with special overlaid surfaces, such as High- Density Overlay, usually carry the trademark on the panel edge. 10.12.3 Plywood Group Number Plywood can be manufactured from over 70 species of wood. These species are divided on the basis of strength and stiffness into five groups under U.S. Product Standard PS 1-95. Strongest species are in Group 1; the next strongest in Group 2, etc. The group number that appears in the trademark on some APA trademarked panels, primarily sanded grades, is based on the species used for face and back veneers. Where face and back veneers are not from the same species group, the higher group number is used, except for sanded panels 3/8 in thick or less and decorative panels of any thickness. These are identified by face species if C or D grade backs are at least 1/8 in thick and are not more than one species group number larger. Some species are used widely in plywood manufacture, others rarely. OSB panels, being composed of flakes or strands instead of veneers, are graded without reference to veneers or species, and composite panels are graded on an OSB performance basis by end use and exposure durability. Typical panel trademarks for all three panel types and an explanation of how to read them are shown

The picture above shows the two most common areas which should have your attention. Plumbing When bricks are laid there has to be a guide to keeping the walling upright. By using a sprit level as shown in the bottom drawing above, one is said to be leveling the wall. This is extremely important when building the first section of walling. The drawing above shows a spirit being used at the end of a wall. Each time a row of bricks (known as a course) are laid it becomes necessary to straighten things up. By placing the spirit level against the 2 sides of the end you are able adjust the amount they learn in or learn out. By placing your foot at the bottom of the level it is possible to tap the bricks in or pull them out; this motion is becomes necessary after laying each course of bricks. You should aim toward the corners of your new first as this is where all the measuring plumbing and leveling takes place. Take care that the face of the level is kept clean from any mortar as it may rub off onto the face of your bricks.