What is allowable strength?
The allowable stress or allowable strength is the maximum stress (tensile, compressive or bending) that is allowed to be applied on a structural material. The allowable stresses are generally defined by building codes, and for steel, and aluminum is a fraction of their yield stress (strength):
Permissible stress design (in USA construction more commonly called allowable stress design) is a design philosophy used by civil engineers. The designer ensures that the stresses developed in a structure due to service loads do not exceed the elastic limit.
- In aerospace engineering, the ultimate load is a statistical figure used in calculations, and should (hopefully) never actually occur. Strength requirements are specified in terms of limit loads (the maximum loads to be expected in service) and ultimate loads (limit loads multiplied by prescribed factors of safety).
- Limit load is the maximum load that a structure can safely carry. It's the load at which the structure is in a state of incipient plastic collapse. As the load on the structure increases, the displacements increases linearly in the elastic range till the load attains the yield value.
- Vertical Hitch Working Load Limit X Number of Legs* X Sling Angle Factor = WLL at specified angle. The Working Load Limit for the sample sling above, in a 60° basket hitch would be calculated as follows: 500 lbs. (Vertical WLL) x 2 (num. of legs) x .866 (sling angle factor from table) = 866 lbs.
A factored load is a load multiplied by a certain factor designated by codes of practice to drermine the strength of a structural members such as reinforced concrete. Whereas the unfactored loads are used to meet the elastic or linear limit state (below the yield limit) of structural members.
- An Axial load is a force administered along the lines of an axis. Axial loading occurs when an object is loaded so that the force is normal to the axis that is fixed, as seen in the figure. Taking statics into consideration the force at the wall should be equal to the force that is applied to the part.
- Permissible stress design (in USA construction more commonly called allowable stress design) is a design philosophy used by civil engineers. The designer ensures that the stresses developed in a structure due to service loads do not exceed the elastic limit.
- The service load is the best estimate of the actual load that a concrete member may be called on to support. The current way, Ultimate Strength. The design load is the service load increased by specified load factors in order to provide a factor of safety. Traditional Examples: Service Load = Dead Load + Live Load.
Updated: 20th September 2018