# Influence Surface (Railroad) \[CSB]

Influence surface coefficients are the numerical values used to determine the influence of a unit load on a specific point of a structure, based on its position and orientation. These coefficients represent the contribution of a unit load at a specific point to the total response of the structure.

## General

**Stage:** During an influence surface-based live load analysis, the stiffness matrix and active elements are captured at the selected stage, followed by the placement of a unit load on the rail surface. The analysis then determines the influence surface coefficients that are used to assess the maximum load effect on the structure.

**Rail:** The chosen rail is used to determine the geometry of the influence surface.

**Live Load Category \[Gravity/Gravity and Centrifugal/Centrifugal/Hunting/Braking]:**

**Unit Load Spacing Long.:** The spacing of the unit loads in both longitudinal and transverse directions significantly affects the total analysis time. For each unit load, a finite element analysis must be conducted. This parameter allows the user to specify the unit load spacing in the longitudinal direction.

## Centrifugal

The parameters listed below, part of this tab, are applicable only if the Live Load Category parameter (under the General Tab) is set to either 'Gravity and Centrifugal' or 'Centrifugal.' Otherwise, these parameters will be marked as Not Applicable (N/A).

**Centrifugal Factor Comp. Method \[User Defined/AREMA 1.3.6.c]:** The centrifugal factor can be calculated according to the AREMA specification or manually defined by the user through the parameter options.

**Max. Design Speed:**

**Centrifugal Factor:** If the Centrifugal Factor Comp. Method parameter is set to 'User Defined,' this parameter can be specified. Otherwise, since the centrifugal force factor will be calculated according to AREMA, it will be shown as Not Applicable (N/A).

**Height of Application Point (from rail):**

## Hunting

**Hunting Force Factor (0-1):** The hunting force factor can be specified manually by the user using this parameter.


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