Smart structures can be subdivided into two general categories. The first is structures that would perform 'smartly' during a specific event, e.g. earthquake events. The second category is the structures that would perform 'smartly' during any normal and/or abnormal event. The second category includes structures sensitive to vibration levels, structures which are exposed to wind, since wind can affect the structure from numerous directions and bridges, since loads on a bridge can have an arbitrary location at a given time. the distinction between the two structural types will have an important effect on both the optimal sensor number and locations. Recently, researchers have presented several methods for optimal number and location of sensors. These methods are based on different optimization techniques. In most of these published studies, many variable shave been investigated. These include the number and location of sensors, number of structural degrees of freedom, number of tests, and number of structural modes. All these studies assume that the location and the magnitude of damage are known a priori, before locating the sensors. In addition, in most of the published studies, the variability of the location of the loading source has not been well studied. This paper present a simple approach, which address the above issues. First, the stress ratio concept is used to logically estimate the expected location and magnitude of structural damage. Second, the load factor approach in combination with the goal programming algorithm will be presented as a means to find the optimal sensor location when dealing with structures with multiple loading conditions. The examples in this study demonstrate these techniques.