where Rn is the nominal resistance, Qi is the load effect, and F is the factor of safety.
The main disadvantages of the ASD methods are: (1) F is applied only to the resistance
part of the equation without heeding the fact that varying types of loads have different
levels of uncertainty, (2) F is only based on judgment and experience, and (3) no quantitative
measure of risk is incorporated in F.
The design of spread footings using LRFD requires evaluation of the footing performance
at various limit states. The primary limit states for spread footing design include
strength limits such as bearing capacity failure or sliding failure and service limits such as
excessive settlements or vibration.
The goal of LRFD is to design, without being conservative as to be wasteful of
resources, a foundation that serves its function without reaching the limit states
where Rn is the nominal resistance, Qi is the load effect, and F is the factor of safety.The main disadvantages of the ASD methods are: (1) F is applied only to the resistancepart of the equation without heeding the fact that varying types of loads have differentlevels of uncertainty, (2) F is only based on judgment and experience, and (3) no quantitativemeasure of risk is incorporated in F.The design of spread footings using LRFD requires evaluation of the footing performanceat various limit states. The primary limit states for spread footing design includestrength limits such as bearing capacity failure or sliding failure and service limits such asexcessive settlements or vibration.The goal of LRFD is to design, without being conservative as to be wasteful ofresources, a foundation that serves its function without reaching the limit states
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