spSlab/spBeam Moment Redistribution Applications
The solve options in spSlab/spBeam offer users the flexibility to customize design options, punching shear options, and deflection calculations options. However, it is crucial to exercise sound engineering judgment and remain aware of how these options are implemented within the software to ensure the most accurate representation of the physical model and its conversion to an analytical model. It is also important to understand the consequences of each solve option and how it impacts the analysis and design results.
This technical article examines the implications of activating the moment redistribution solve option under design and investigation run modes in spSlab/spBeam. Unlike the design run mode, the applications of moment redistribution while investigating existing as-built beams and slabs requires added care and has limitation imposed by the program. By reviewing scenarios documented in this article, engineers and designers can distinguish between several conditions based on the relationship of the required moment to the moment capacity of the member. The scenarios discussed in this article are shown in the following figure, based on the selection between longitudinal beams or one-way slabs. This will provide insights to make informed decisions for optimal structural analysis and design outcomes using the moment redistribution feature. StructurePoint encourages the reader of this article to return their opinions and thoughts on this important topic and engage our engineering and development team in a constructive discussion of any constructive feedback.
References
• “spSlab/spBeam” Engineering Software Program Manual v5.50, STRUCTUREPOINT, 2015
• “Continuous Beam Design with Moment Redistribution (ACI 318-14)” Design Example, STRUCTUREPOINT, 2018
• “Continuous Beam Design with Moment Redistribution (ACI 318-11)” Design Example, STRUCTUREPOINT, 2018
• “Continuous Beam Design with Moment Redistribution (CSA A23.3-14)” Design Example, STRUCTUREPOINT, 2018
• Contact “Support@StructurePoint.org” to obtain supplementary materials (spBeam models: B1D2, B2I2, B2I2R, S1D2, S2I2, and S2I2R)
Case A: “Longitudinal Beams” under “Design” run mode to be considered.
Required Moment – Moment Capacity Relationship | Moment Redistribution Results | |
Required moment is always LESS THAN moment capacity in “Design” run mode. | Moment redistribution is always performed. Adjustment factor obtained from the program is calculated using the required moment (Mu). | |
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Case B1: “Longitudinal Beams” under “Investigation” run mode to be considered.
Required Moment – Moment Capacity Relationship | Moment Redistribution Results | |
Required moment is LESS THAN moment capacity. | Moment redistribution is not needed. The program provides the following note: “Required moment is less than capacity, redistribution is not needed.” | |
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Case B2: “Longitudinal Beams” under “Investigation” run mode to be considered.
Required Moment – Moment Capacity Relationship | Moment Redistribution Results | |
Required moment is MORE THAN moment capacity. | Moment redistribution is needed. Adjustment factor obtained from the program is calculated using moment capacity (Mn) based on the reinforcement provided. | |
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Case C: “Slabs/Flanges” under “Design” run mode to be considered.
Required Moment – Moment Capacity Relationship | Moment Redistribution Results | |
Required moment is always LESS THAN moment capacity in “Design” run mode. | Moment redistribution is always performed. Adjustment factor obtained from the program is calculated using the required moment (Mu). | |
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Case D1: “Slabs/Flanges” under “Investigation” run mode to be considered.
Required Moment – Moment Capacity Relationship | Moment Redistribution Results | |
Required moment is LESS THAN moment capacity. | Moment redistribution is not needed. The program shall provide the following note: “Required moment is less than capacity, redistribution is not needed.” | |
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Case D2: “Slabs/Flanges” under “Investigation” run mode to be considered.
Required Moment – Moment Capacity Relationship | Moment Redistribution Results | |
Required moment is MORE THAN moment capacity. | Moment redistribution is needed. Moment redistribution is not performed due to a program limitation that will be removed in a future release. | |
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