Structural Design Methods


  1. Working stress method (WSM)

This was the customary technique for configuration for reinforced cement, as well as for auxiliary steel and timber design outline. The technique essentially accept that the basic material acts as a direct versatile way, and that sufficient security can be guaranteed by reasonably limiting the stresses in the material incited by the normal “working loads” on the structure. As the predetermined reasonable stresses are kept well beneath the material quality, the presumption of linear versatile conduct is viewed as legitimate. The ratio proportion of the quality of the material to the passable stress is frequently alluded to as the factor of safety.

Notwithstanding, the primary presumption linear elastic and the inferred supposition that the stresses under working burdens can be kept inside the ‘passable stresses’ are not observed to be reasonable. Many variables are in charge of this, for example, a long haul exertion of creep and shrinkage, the impacts of stress concentration, and other optional impacts. Every such impact coming about noteworthy nearby increments in a redistribution of the ascertained stresses. The plan generally brings about moderately huge areas of auxiliary individuals, in this manner bringing about better serviceability execution under the standard working stresses.

  1. Ultimate Load Method (ULM)

With the developing acknowledgment of the inadequacies of WSM in reinforced concrete design, and with expanded comprehension of the conduct of reinforced concrete at extreme loads, a definitive heap of configuration is advanced and turned into another option to WSM. This strategy is in some cases additionally alluded to as the load factor strategies are a definitive quality. In this strategy, the stresses condition at the site of approaching breakdown of the structure is dissected, and the non straight stess strain bends of concrete and steel are made utilization of.

The idea of ‘modular ratio’ and its related issues are kept away from completely in this strategy. The security measure configuration is presented by a suitable decision of the load factor, characterized as the proportion of a definitive load to the working load. A definitive load technique makes  feasible for various sorts of burdens to be appointed diverse load factors under joined loading conditions, in this manner conquering the related weakness of WSM.

This technique by and large outcomes in more slim areas, and frequently prudent plans of pillars and sections, especially when high quality strengthening steel and cement are utilized. Be that as it may, the agreeable “strength” execution at extreme burdens does not ensure attractive “serviceability” execution at the typical service loads.

The design now and then outcome in over the top diversions and break widths under administration loads, attributable to the thin areas coming about because of the utilization of high quality strengthening steel and cement. The circulation of stress resultants at extreme load is taken as the dissemination at the administration loads, amplified by the load factors(s); at the end of the day, examination is still in view of direct flexible hypothesis.

  1. Limit State Method (LSM):

The philosophy of the limit state technique of design symbolizes a definite advancement over the old customary design philosophies. Different than the  WSM which based the calculations on service load conditions only, and also not like the ULM, which based the calculations on final load conditions only, LSM targets for an extensive and balanced solution to the design complications, by putting into consideration the safety at vital loads and serviceability at the working loads.

The LSM philosophy utilizes different safety factors format which tries to give sufficient safety at final loads and also ample serviceability at the service loads, by putting into consideration all the potential ‘Limit State’.