# TR.31.2.18 Japanese Seismic Load

The purpose of this command is to define and generate static equivalent seismic loads as per Japanese specifications using a static equivalent approach similar to those outlined by UBC. Depending on this definition, equivalent lateral loads will be generated in horizontal direction(s). The implementation is as per Article 88 in the "Building Codes Enforcement Ordinance 2006".

## General Format

DEFINE AIJ (ACCIDENTAL) LOAD

`AIJ-spec`

`weight-data`

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

Where:

AIJ-spec = { ZONE f_{1}CO f_{2}TC f_{3}ALPHA f_{4}}

where:

## Generation of AIJ Seismic Load

General format to provide Japanese Seismic load in a primary load case:

`LOAD i`

AIJ LOAD {X | Y | Z} (f_{5}) (ACC f_{6})

Where:

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

LOAD i | load case number |

AIJ LOAD { X | Y | Z } f5 | optional factor to multiply horizontal seismic load. |

ACC f6 | multiplying factor for Accidental Torsion, to be used to multiply the AIJ accidental torsion load (default = 1.0). May be negative (otherwise, the default sign for MY is used based on the direction of the generated lateral forces). |

If the `ACCIDENTAL` option is specified, the accidental
torsion will be calculated per the AIJ specifications. The value of the accidental
torsion is based on the "center of mass" for each level. The "center of mass" is
calculated from the SELFWEIGHT, JOINT WEIGHTs and MEMBER WEIGHTs you have specified

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.

## Methodology

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

Program calculates the natural period of building *T*utilizing the
following equation:

T = h(0.02 + 0.01α) |

= | ||

= |

Design spectral coefficient, R_{t}, is calculated utilizing T and
T_{c} as follows:

_{c} | = |

α_{i} is calculated from the weight values provided in the
Define AIJ Load command.

α_{i} = W_{i} / W |

_{i} | = | |

= |

The seismic coefficient of floor, C_{i}, is calculated using:

C_{i} = Z R_{t}
A_{i} C_{o}

= | ||

_{o} | = |

Seismic load shear force, Q_{i}, of each floor is calculated by
C_{i} and W_{i}:

Q_{i} =
C_{i}W_{i}

_{i} | = |

Load value of each floor Pi is calculated by seismic load shear force Qi.

P_{i} = Q_{i}–
Q_{i+1}

The total lateral seismic load is distributed by the program among different levels.