Defining Members
==================

Sequence
------------

The following sequence of steps for building a model in BRIDG is not the only method.
In fact, this sequence assumes that you are starting from scratch.
Copying an existing similar bridge model and modifying it is another great way to start.

Also, do not think of these steps as a single pass operation.
It should be an iterative approach, with each pass adding more complexity
to the model, until the bridge is completely defined within the scope of
this program.  Suggestions for the first few passes are described below.


Terminology
-------------

.. rubric:: Line Member
..

    Line Members (aka Stringers) directly support the road surface. 
    Line Members are the members that the trucks load.
    They are analyzed at multiple locations along their length and 
    may have multiple property changes along their length. 

.. rubric:: Truss Member
..

    Truss members support Line Members. They are only analyzed at their ends.

First Pass
--------------

#. Enter geometry for Line Members using COGO commands.
#. Enter basic line member placement.
#. Enter enough truss members to check general geometry.
#. Enter a minimal set of materials and shapes.
   These need not be the real data, but only needed in this pass so that the
   entries that references these tables have some thing to reference.


Geometry Definition
----------------------

See  :ref:`COGO Command Command Descriptions` entry sheet is used to create all of the necessary spatial coordinates and paths.
The following **minimum** data is required:

* A point at the beginning and end of all members
* A point at all boundary condition locations
* A path that defines the center line of traffic.
  Multiple lanes will be centered about this path.