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Home > Tools > Frequently Asked Questions
Q. Are stiffness modifiers mandatory for structural elements when designing buildings for gravity loads only, as per ACI 318? A. No, stiffness modifiers are not mandatory. Analysis methods and details are beyond the scope of the ACI 318 Code, particularly for serviceability analysis or second-order analysis related to sway effects. Stiffness modifiers in Table 6.3.1.1 are permitted but not required; they are suggested as a method to satisfy Section 6.3.1.1 for specific types of analysis. The title of the table states, “…areas permitted for…,” indicating they are optional. Designers are free to use other approaches as long as they meet the requirements of Section 6.3.1.1. It is crucial to thoroughly understand how commercial software implements these analyses to ensure they align with design goals. For additional guidance on lateral load analysis, refer to Section 6.6.3.1.2 and commentary in R6.6.3.1.2. References: ACI 318-19 Topics in Concrete: 318 Building Code
Q. Are stiffness modifiers mandatory for structural elements when designing buildings for gravity loads only, as per ACI 318?
A. No, stiffness modifiers are not mandatory. Analysis methods and details are beyond the scope of the ACI 318 Code, particularly for serviceability analysis or second-order analysis related to sway effects. Stiffness modifiers in Table 6.3.1.1 are permitted but not required; they are suggested as a method to satisfy Section 6.3.1.1 for specific types of analysis. The title of the table states, “…areas permitted for…,” indicating they are optional. Designers are free to use other approaches as long as they meet the requirements of Section 6.3.1.1.
It is crucial to thoroughly understand how commercial software implements these analyses to ensure they align with design goals. For additional guidance on lateral load analysis, refer to Section 6.6.3.1.2 and commentary in R6.6.3.1.2.
References: ACI 318-19
Topics in Concrete: 318 Building Code
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