This page is devoted to frequently asked questions (FAQ) related to Cracking.
Why do linear and nonlinear long-term cracked-analysis results differ?
Extended Question: Since my load pattern, coefficients, and all other parameters are the same, why would I not get the same results?
Answer: The principle of superposition does not apply during nonlinear analysis, therefore results will be different between linear and nonlinear applications. Additional information on long-term cracked-section analysis is available through the Cracked-section analysis article.
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Should cracking factors be applied to floor slabs?
Answer: Cracking factors need not be applied to floor slabs unless special conditions exist, such as when shear walls are close to one another and the shell object acts as a coupling/link beam. However, this is rarely the case in that floor slabs typically do not contribute to the lateral capacity of the system. In fact, ACI prohibits such behavior in high seismic areas because flexural contribution from floor slabs may increase lateral stiffness to an unconservative extent. Floor slabs should however behave as diaphragms to transfer in-plane forces.
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Can I overwrite the resultant design slab reinforcement to reduce deflection?
Answer: Yes, various options are available for the redefinition of design reinforcement.
To begin, select Run > Cracking Analysis. Here, rebar from finite-element design is the default setting, which may be revised using either of the following methods:
- Use the Quick Rebar Top/Bottom option to specify a fixed amount of reinforcement throughout the slab.
- Use the Draw > Draw Slab Rebar option to model the reinforcement as required. Use the User-Specified Rebar option to analyze slab deflection.
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To what demand does SAFE design the reinforcement?
Extended Question: Does SAFE design the reinforcement to match demand parameters, or does it exceed these values by a certain margin? Further, is there a way to specify reinforcement such that demand is 85-90% of capacity?
Answer: SAFE designs the reinforcement according to ultimate demands, as is common in practice. Resistance factors could be modified through Design > Design Preferences to provide for a lower demand/capacity (D/C) ratio.
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