Gee & Jenson West Palm Beach, Florida A hazard poses the threat that an unwanted event, possibly a catastrophe, may occur. Risk is the probability that the event will occur. Inasmuch as all buildings are subject to hazards such as hurricanes, earthquakes, flood, fire, and lightning strikes, both during and after construction, building designers and contractors have the responsibility of estimating the risks of these hazards and the magnitudes of the consequences should the events be realized. After the risk of a hazard has been assessed, the building designers and contractors, guided by building-code, design standards, zoning-code, and health-agency specifications and exercising their best judgment, should decide on an acceptable level for the risk. With this done, they should then select a cost-effective way of avoiding the hazard, if possible, or protecting against it so as to reduce the risk of the hazards occurring to within the acceptable level. Studies of building failures provide information that building designers should use to prevent similar catastrophes. Many of the lessons learned from failures have led to establishment of safety rules in building codes. These rules, however, generally are minimum requirements and apply to ordinary structures. Building designers, therefore, should use judgment in applying code requirements and should adopt more stringent design criteria where conditions dictate. Such conditions are especially likely to exist for buildings in extreme climates or in areas exposed to natural hazards, such as high winds, earthquakes, floods, landslides, and lightning. Stricter criteria should also be used for buildings that are *Revised and updated from Sec. 3, Protection Against Hazards by the late Frederick S. Merritt, Consulting Engineer. tall and narrow, are low but very large, have irregular or unusual shapes, house hazardous material or critical functions, or are of novel construction. Furthermore, building codes may not contain provisions for some hazards against which building designers nevertheless should provide protection. Examples of such hazards are vandalism, trespass, and burglary. In addition, designers should anticipate conditions that may exist in buildings in emergencies and provide refuge for occupants or safe

 where G  modulus of rigidity v  unit shearing stress   unit shearing strain It is related to the modulus of elasticity in tension and compression E by the equation E where  is a constant known as Poissons ratio. 5.2.5 Poissons Ratio Within the elastic limit, when a material is subjected to axial loads, it deforms not only longitudinally but also laterally. Under tension, the cross section of a member decreases, and under compression, it increases. The ratio of the unit lateral strain to the unit longitudinal strain is called Poissons ratio. For many materials, this ratio can be taken equal to 0.25. For structural steel, it is usually assumed to be 0.3. Assume, for example, that a steel hanger with an area of 2 in2 carries a 40-kip (40,000-lb) load. The unit stress is 40,000/2, or 20,000 psi. The unit tensile strain, taking the modulus of elasticity of the steel as 30,000,000 psi, is 20,000/ 30,000,000, or 0.00067 in / in. With Poissons ratio as 0.3, the unit lateral strain is 0.3
0.00067, or a shortening of 0.00020 in / in. 5.2.6 Thermal Stresses When the temperature of a body changes, its dimensions also change. Forces are required to prevent such dimensional changes, and stresses are set up in the body

Figure 10 Example showing bed course location for wall ties placed at a vertical spacing of 600mm centres and a horizontal spacing of 450mm centres 76mm Designa Basalt 162mm Designa Basalt 450mm Designa Basalt 450mm Design Considerations Brick Technical Manual 69 In a stretcher bonded brick veneer wall or cavity class region is dictated by their horizontal spacing as wall, when wall ties are place at a vertical spacing of shown below. 450mm centres, the grade of wall ties in each wind Table 6 Wall Tie Spacing - 450mm vertical centres Maximum horizontal spacing (mm) General area Within 1200mm of corners Wind class 300 450 600 300 450 600 Note: L = light duty, M = medium duty, H = heavy duty, - = no ties suitable. Refer to Table 3.5 of AS 3700 for mean tie strength for each duty rating. Figure 11 Example showing bed course location for wall ties placed at a vertical spacing of 450mm centres and a horizontal spacing of 600mm centres 76mm Designa Basalt 162mm Designa Basalt 600mm Designa Basalt 600mm