Your base (foundation level) often has a mass value if you have a basement slab or ground floor. In elevated structures (e.g., podium slabs), ensure mass is not double-counted between the base and first floor.

This article is intended for educational purposes. Always verify with the latest CSI ETABS documentation and your local building code.

Code base shear ($V = C_s \cdot W$) uses this $W$. If the Mass Summary shows incorrect $W$, the design base shear will be wrong, leading to unsafe or over-conservative designs.

| Pitfall | Consequence | Fix | | :--- | :--- | :--- | | | Ignored live load and SDL; unconservative base shear | Define custom mass source (Dead + SDL + % Live) | | Duplicated Mass | Artificially high seismic forces | Check for overlapping shells or duplicate area loads | | Zero Rotational Mass | No torsional periods; inaccurate mode shapes | Assign diaphragm constraints to all floors | | Mass at Pinned Base | Building wants to lift off during analysis | Release base restraints or ignore (static only) |

Etabs Mass Summary By Story Work <Validated>

Your base (foundation level) often has a mass value if you have a basement slab or ground floor. In elevated structures (e.g., podium slabs), ensure mass is not double-counted between the base and first floor.

This article is intended for educational purposes. Always verify with the latest CSI ETABS documentation and your local building code. etabs mass summary by story

Code base shear ($V = C_s \cdot W$) uses this $W$. If the Mass Summary shows incorrect $W$, the design base shear will be wrong, leading to unsafe or over-conservative designs. Your base (foundation level) often has a mass

| Pitfall | Consequence | Fix | | :--- | :--- | :--- | | | Ignored live load and SDL; unconservative base shear | Define custom mass source (Dead + SDL + % Live) | | Duplicated Mass | Artificially high seismic forces | Check for overlapping shells or duplicate area loads | | Zero Rotational Mass | No torsional periods; inaccurate mode shapes | Assign diaphragm constraints to all floors | | Mass at Pinned Base | Building wants to lift off during analysis | Release base restraints or ignore (static only) | Always verify with the latest CSI ETABS documentation