Seismic Load Notation
Common notation used in seismic load definitions: E, Eh, Ev, QE, load combinations and direction subscripts.
Common notation
| Symbol | Meaning | Notes |
|---|---|---|
| E | Total seismic load effect | Combined horizontal and vertical effects |
| Eh | Horizontal seismic load effect | From horizontal ground motion |
| Ev | Vertical seismic load effect | From vertical ground motion |
| QE | Effect of horizontal seismic force | Used in some standards for the horizontal component |
| D | Dead load | Permanent loads including self-weight |
| L | Live load | Variable loads |
| Rx | Response in X-direction | After modal combination within X |
| Ry | Response in Y-direction | After modal combination within Y |
| Rz | Response in Z-direction | After modal combination within Z (vertical) |
| Sa | Spectral acceleration | At a given frequency and damping |
| ZPA | Zero-period acceleration | Peak ground acceleration; rigid plateau |
Load combinations
Seismic loads are combined with other loads using load combinations specified by the applicable standard. A typical combination for strength design is: 1.2D + 1.0L + 1.0E, where E = Eh + Ev (or E = Eh +/- Ev depending on the direction of vertical acceleration). The load factors and combination expressions vary by standard and must be confirmed against the current edition.
Notes
- Notation varies between standards — always confirm the meaning of symbols in the context of the specific standard being used
- Some standards use E for the total effect and separate Eh and Ev; others combine them differently
- The vertical seismic effect Ev may be additive or subtractive depending on whether it increases or decreases the total load
- Load combinations for allowable stress design differ from those for strength design