Why Load Path Reactions May be Different Than Boise Member Report in BC Framer®

There are sometimes differences in reactions shown in BC Framer® when comparing the Bearing symbols, the Load Path labels, the MiTek Member Report and the Boise Member Report.

For example: Load Path Label and selected bearing symbol showing 3853 Snow and 1241 Dead load.

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Boise Design report showing 4124 Snow and 1255 Dead load.

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BC Framer® and the related MiTek Sapphire platforms execute a top down load distribution routine using an assumed member self-weight to generate the loads applied to each member in the structure so that they can be analyzed. Additionally, slightly different rules for load patterns and other assumptions are made as compared to the member-by-member analysis in the Boise Design Engine (BDE) and MiTek design engines.  The alternative approach is to analyze each member in the structure and then transfer the resulting reactions to the members below, which can be terribly inefficient in a platform where multiple analysis engines are employed (MiTek Truss, MiTek lumber, BDE) and structural configurations are complex.  These minor differences were deemed an acceptable trade-off for the overall time savings in the design process and are in alignment with standard load distribution practices.

The result is that users will find the reaction summary table in a BC Framer® member report or MiTek member report have reactions that differ from the loads associated with the bearing symbols in the BC Framer® model. The design engines are generally a bit more conservative and thus the reaction summary table results can be a little higher than the BC Framer® model’s bearing symbol values. When performing manual load transfer for sizing members outside of BC Framer® or sizing components such as hangers or other connectors, the values from the BC Framer® member report should be used to avoid any confusion.

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