# TR.31.2.18 CFE (Comisión Federal De Electricidad) Seismic Load

The purpose of this command is to define and generate static equivalent seismic loads as per Manuel de Diseño por Sismo - Seismic Design Handbook Comisión Federal De Electricidad - Electric Power Federal Comission - October 1993 (Chapters 3.1, 3.2, 3.3 and 3.4) specifications. Depending on this definition, equivalent lateral loads will be generated in horizontal direction(s). This is a code used in the country of Mexico.

The seismic load generator can be used to
generate lateral loads in the X & Z directions
for Y up or X & Y for Z up. Y up or Z up is the
vertical axis and the direction of gravity loads (See the
`SET Z UP` command in
TR.5
Set Command Specification). All vertical coordinates of the floors above the
base must be positive and the vertical axis must be
perpendicular to the floors.

## General Format

DEFINE CFE (ACCIDENTAL) LOAD

`cfe-spec`

`weight-data`

Refer to Common Weight Data for information on how to specify structure weight for seismic loads.

Where:

cfe-spec = { ZONE f1 QX f2 QZ f3 GROUP f4 STYP f5 (REGULAR) (TS f6) (PX f7) (PZ f8) }

The optional parameter
`REGULAR` is entered to consider
the structure as a regular structure. By default,
all structures are considered as
irregular.

## Generation of CFE Seismic Load

To provide a CFE Seismic load in any load case:

`LOAD i`

`CFE LOAD {X | Y | Z} (f)`

Where:

Parameter | Description |
---|---|

LOAD i | load case number |

CFE LOAD { X | Y | Z | f | factor to multiply horizontal seismic load. Choose horizontal directions only |

## Methodology

Seismic zone coefficient and parameter values are supplied by the user through the `DEFINE CFE LOAD` command.

Program calculates the natural period of building T utilizing Rayleigh-Quotient method. If time period is provided in the input file, that is used in stead of calculated period.

The acceleration a is calculated according to the following:

Where:

- c = Seismic coefficient is extracted from table 3.1
- a
_{0}, T_{a}, T_{b}, and r are obtained form table 3.1

The ductility reduction factor Q’ is calculated according to section 3.2.5.

If not regular, then Q’ = Q’ x 0.8

If the period T_{s} of the soil is known and the soil type II or III T_{a} and T_{b} will be modified according to section 3.3.2.

Lateral loads for each direction are calculated for:

When T ≤ T_{b}, Eq. 4.5. Section 3.4.4.2 is used:

When T > T_{b}, Eq. 4.6/7/8. Section 3.4.4.2 is used:

Where:

${K}_{1}=\frac{q[1-\text{\hspace{0.17em}}r(1-q\left)\right]\Sigma {W}_{i}}{\Sigma ({W}_{i}/{h}_{i})}$ |

${K}_{2}=\frac{1.5rq(1-q)\Sigma {W}_{i}}{\Sigma ({W}_{i}/{h}_{i}^{2})}$ |

q = (T_{b}/T)^{r} |

The base shear are distributed proportionally to the height if T ≤ T_{b} or with the quadratic equation mentioned if T > T_{b}.

The distributed base shears are subsequently applied as lateral loads on the structure.

## Example

UNIT KGS METER DEFINE CFE LOAD ZONE 2 QX .5 QZ 0.9 STYP 2 GROUP B TS 0.2 SELFWEIGHT MEMBER WEIGHT 1 TO 36 41 TO 50 UNI 300 JOINT WEIGHT 51 56 93 100 WEIGHT 1440 101 106 143 150 WEIGHT 1000 FLOOR WEIGHT YRA 11.8 12.2 FLOAD 400 - XRA -1 11 ZRA -1 21 LOAD 1 ( SEISMIC LOAD IN X DIRECTION ) CFE LOAD X 1.0 LOAD 2 ( SEISMIC LOAD IN -Z DIRECTION ) CFE LOAD Z -1.0