Structural Design Actions

Introduction

In the world of engineering and construction, understanding structural design actions is of paramount importance. Applied loads can create stresses and deformations within a structure, which, if not properly accounted for, can lead to failure. To ensure the safety and integrity of any construction project, it is crucial to identify and analyze all the loads that act on a structure before embarking on the design phase. In Australia, these aspects are covered in the AS/NZS 1170 series, which provides guidelines and standards for structural design. These standards can be accessed on the Standards Australia Website.

Permanent, Imposed and Other Actions

AS/NZS 1170.1:2002 is a crucial standard that addresses various types of loads. Permanent load (G) refers to actions that are likely to act continuously throughout the design working life of a structure with relatively small variations in magnitude over time. This includes the self-weight of structural elements, partition walls, and other removable items like floor finishing. Imposed load (Q), on the other hand, represents variable actions resulting from the intended use or occupancy of the structure. Some examples of imposed load include floor actions due to people/crowd, plant/equipment, storage, and vehicles. Additionally, other actions like liquid pressure, ground water, rainwater ponding, and earth pressure must also be considered during the structural design process.

Wind Load

In AS/NZS 1170.2:2021, comprehensive wind actions for structures subject to wind forces are detailed. To design for wind pressure on structures, engineers must consider factors such as regional wind speed, terrain type, structure shielding, topography, and the aerodynamic shape factor of the building. For structures that are particularly sensitive to wind, the dynamic response factor needs to be taken into account, as outlined in Appendix G of the standard. Wind load analysis is essential for ensuring the stability and safety of structures in areas prone to strong winds.

Figure 3.1A Wind Regions Source: AS/NZS 1170.2:2011

Snow and Ice Actions

For structures located in regions with cold climates, the design for snow and ice actions becomes critical. AS/NZS 1170.3:2003 provides guidelines for determining snow and ice loads suitable for the structure’s type, intended use, and exposure to such conditions. The actions may be assessed for ultimate or serviceability purposes using relevant annual probability of exceedance. Alpine and Subalpine regions require special attention when considering snow and ice actions due to their higher vulnerability to these loads.

Earthquake Action

Earthquakes remain a major concern for structural engineers, as they can cause significant damage to buildings and infrastructure. To estimate earthquake loads, engineers need to consider the expected earthquake coefficient, soil settlement statistics, and the types of seismic waves that could impact the structure. Seismic coefficients, which define the ratio of earthquake acceleration to gravity acceleration, help evaluate the seismic acceleration for the design. AS1170.4:2007 provides essential earthquake actions and general detailing requirements for designing structures to withstand seismic forces..

Conclusion

By comprehensively understanding and implementing the various structural design actions discussed above, engineers can ensure the creation of safer, more resilient, and reliable structures for diverse applications in Australia. Adherence to the relevant standards, such as those provided in the AS/NZS 1170 series, is essential to achieving successful engineering projects that stand the test of time and environmental challenges. Proper load identification, analysis, and design are the cornerstones of constructing structures that prioritize safety and longevity.