The working stress approach and the limit state approach are two distinct methodologies in structural design, each with its own advantages and limitations.
The working stress approach utilizes service loads throughout the design process, without fully exploiting the material’s ultimate strength. Stresses within structural members are calculated based on elastic behavior, and the design ensures these stresses remain below predefined allowable values. Since structures typically experience loads far below their ultimate capacity during their lifespan, this approach is aptly named the “working stress” method. However, this conservative approach may not always yield the most cost-effective design, as it doesn’t fully utilize the material’s potential. Consequently, it is now primarily employed in the design of temporary structures.
In contrast, the limit state approach assigns partial safety factors to each material and load, accounting for their specific properties and probabilities of occurrence. This approach allows for a more refined and accurate structural analysis, as it assesses each load and material characteristic individually. By doing so, it enables the utilization of material strength to its maximum potential while considering the likelihood of various load scenarios. Due to its ability to optimize material usage and minimize construction costs, the limit state approach has become the preferred method for most reinforced concrete designs.
In conclusion, the working stress approach prioritizes safety and simplicity, while the limit state approach emphasizes a more accurate and efficient utilization of materials. The choice between these methods depends on the specific project requirements, structural type, and desired level of conservatism. Understanding the strengths and limitations of each approach is crucial for making informed design decisions that balance safety, performance, and cost-effectiveness.