A window usually consists of transparent glass or plastics (glazing) held in place by light framing, called sash. The window is fitted into a frame secured to the walls (Fig. 1.5a). For sliding windows, the frame carries guides in which the sash slides. For swinging windows, stops against which the window closes are built into the frame. Hardware is provided to enable the window to function as required. For movable windows, the hardware includes grips for moving them, locks, hinges for swinging windows, and sash balances and pulleys for vertically sliding windows. The main purposes of windows are to illuminate the building interior with daylight, to ventilate the interior, and to give occupants a view of the outside. For retail stores, windows may have the major purpose of giving passersby a view of items displayed inside. (See also Sec. 11.) Doors are installed in exterior walls to give access to or from the interior or to prevent such access. For similar reasons, doors are also provided in interior walls and partitions. Thus, a door may be part of a system for enclosing a building or a component of a system for enclosing interior spaces. Systems for Enclosing Interior Spaces. The interior of a building usually is compartmented into spaces or rooms by horizontal dividers (floor-ceiling or roof-ceiling systems) and vertical dividers (interior walls and partitions). (The term partitions is generally applied to non-load-bearing walls.) Floor-Ceiling Systems. The basic element of a floor is a load-carrying deck. For protection against wear, esthetic reasons, foot comfort, or noise control, a floor covering often is placed over the deck, which then may be referred to as a subfloor. Figure 1.6a shows a concrete subfloor with a flexible-tile floor covering. A hollowcold- formed steel deck is incorporated in the subfloor to house electric wiring.

Construction offices and shanties should be equipped with adequate portable extinguishers. So should each floor in a multistory building. Lightning, a high-voltage, high-current electrical discharge between clouds and the ground, may strike and destroy life and property anywhere thunderstorms have occurred in the past. Buildings and their occupants, however, can be protected against this hazard by installation of a special electrical system. Because an incomplete or poor installation can cause worse damage or injuries than no protection at all, a lightning-protection system should be designed and installed by experts. As an addition to other electrical systems required for a building, a lightningprotection system increases the construction cost of a building. A building owner therefore has to decide whether potential losses justify the added expenditure. In doing so, the owner should take into account the importance of the building, danger to occupants, value and nature of building contents, type of construction, proximity of other structures or trees, type of terrain, height of building, number of days per year during which thunderstorms may occur, costs of disruption of business or other activities and the effects of loss of essential services, such as electrical and communication systems. (Buildings housing flammable or explosive materials generally should have lightning protection.) Also, the owner should compare the cost of insurance to cover losses with the cost of the protection system. 3.6.1 Characteristics of Lightning Lightning strikes are associated with thunderstorms. In such storms, the base of the clouds generally develops a negative electrical charge, which induces a positive charge in the earth directly below. As the clouds move, the positive charges, being attracted by the negative charges, follow along the surface of the earth and climb up buildings, antennas, trees, power transmission towers, and other conducting or semiconducting objects along the path. The potential between clouds and earth may build up to 106 to 109 V. When the voltage becomes great enough to overcome the electrical resistance of the air between the clouds and the ground or an object on it, current flows in the form of a lightning flash. Thus, the probability of a building being struck by lightning depends not only on the frequency of occurrence of thunderstorms but also on building height relative to nearby objects and the intensity

5. Structures with all of the following characteristics: located in an area with SD1 of 0.2 or greater located in an area assigned to Site Class E or F with a natural period T of 0.7 seconds or greater, as determined in equivalent lateral force procedure Model analysis procedure. A sitespecific response spectrum shall be used but the design base shear shall not be less than that determined from simplified procedure period (SS) and at 1-second period (S1) and they need to be adjusted for site class effects, by site coefficient Fa and Fv. (See Tables 5.15 and 5.16.) The corresponding design spectral response accelerations at short periods and at 1 second are: 2 S  F S (5.309) DS 3 a a 2 S  F S (5.310) D1 3 v 1 The general design response spectrum curve is developed as Fig. 5.113, in which and T is the fundamental period (in seconds) of the structure. TABLE 5.15 Values of Site Coefficient Fa as a Function of Site Class and Mapped Spectral Response Acceleration at Short Periods (SS)