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Structural Dynamics is the study on the response of structures to loads that vary with time with respect to one or more of (i) position, (ii) direction or (iii) magnitude. This important topic, however has not received much attention in the engineering curricula until recent times. For several decades, structural engineering students have been taught (only) static methods to analyse and design structures such as building, bridges, pipelines, multi-purpose towers, etc. This was because knowledge of structural dynamics was not common and the subject was difficult to teach. The effects of dynamics were included through Dynamic Load Allowances, (DLAs), Impact Factors (IFs) or Dynamic Amplification Factors (DAFs). For example, the bridge design codes provide charts which relate the DLA to be provided with respect to the first flexural natural frequency of the bridge. The first natural frequency is estimated in the absence of dynamic analysis. In the design of crane girders, structural engineers use an IF to allow for the dynamic effects due to the crane movement. These simplified procedures in education and application obviously do not promote best practice. With the advent of advanced computing facilities and sophisticated experimental methods, there has been an increase in knowledge on the behaviour of structures subjected to dynamic loads. The time has hence arrived for structural dynamics to be included in engineering curricula and be taught in universities. In addition, there are three major issues with structural engineering in the new millennium. They are: (i) vibration problems in very tall and/or slender structures which have emerged as a consequence of new materials technology and aesthetic requirements (Thambiratnam et al., 2012), (ii) increased vulnerability of structures to random loads such as impact, blast and seismic loads (Thambiratnam & Perera, 2012; Jayasooriya et al., 2011; Thillakarathna et al., 2010) and (iii) safety concerns of aging structures, which suffer deterioration and/or subjected to increased loading (Chan & Thambiratnam, 2011). Real world examples of the consequences of these three issues are illustrated in Figures 1, 2, 3 and 4. Figure 1 shows the slender and aesthetically pleasing Millennium footbridge bridge in London. This bridge was closed on its opening day as it exhibited high levels of (lateral) vibration which the design engineers did not expect. It has since then been retrofitted with dampers at a cost similar to the cost of original construction. Figures 2 and 3 show the building damage caused by an earthquake and the damage of a bridge column by vehicular impact respectively. Figure 4 shows the aging (almost 70 year old) Story bridge in Brisbane which needs continuous monitoring of its structural health as it is now subjected to increased and faster moving loads and in addition, might have suffered deterioration due to environmental effects.
Figure 2. Seismic damage of buildings
Figure 3. Impact damage of bridge column
Figure 4. 70 year old (aging) story bridge, Brisbane