# General guide

## Introduction

At a glance: Some concepts and the meaning of some words are explained here although “loading” and “distortion” are explained in the following section.

Go to the head of the General volume.

### Geometric data measurement systems

The measurement systems used are:

• The inch pound system sometimes also called customary units. The maximum dimension is 320 inches or 26’ 8” and the resolution is 0.01 inch.
• Metric units with large dimensions. The maximum dimension is 32 metres and the resolution is 1 mm.
• Metric units with small dimensions. The maximum dimension is 3.200 metres and the resolution is 0.1 mm.

The geometric data is stored in a 32 bit integer form. That is each X and Y is fitted in to 32 bits of memory. To achieve this the maximum dimension depends on the meaning of the least significant digit in the decimal representation. The meaning of that least significant digit is referred to as the “resolution”.

### “Desktop”, “Mobile”

Herein the expression “desktop device” means Mac or PC and the expression “mobile device” means Android phone, iPhone or iPad.

### The meaning of some words

Some words have a specific meaning in this user guide.

“Component” The word “component” has the significance that it is the name of one of the entity kinds. In that use “component” means a part of a structural member. The ACI 318 uses the word “element” to mean a part of a structural member. In that context what is referred to as an element is called a component in the context of this application. However, in this context the word “component” also means a number of steel bars that are all of the same grade of steel and all of the same size.
Another use of the word “component” is in the description of a bending moment and of a curvature. Both a bending moment and a curvature are viewed as a vector in the plane of a cross-section. Relative to given orthogonal axes these can be described as Cartesian coordinates; that is as the component about each of the axes.

strain” means a slight change in a dimension of a body. See Distortion for an elaboration on this.

“other” is used in two contexts; in the expression “other distortions” and in the expression “other axis”.

“other distortions” means distortions from causes other than stress. (See Distortion – Stage, Other, Stress and Load-case distortion defined.)

other axis” means an axis other than the axis of interest. The orthogonal axes in the plane of the cross-section used to describe the cross-section are referred to as “the X, Y axes”. The axis of interest in a particular analysis may be anywhere on the plane of the cross-section. To accommodate this, this application uses a second set of orthogonal axes. The axis of interest is referred to as the “reference axis” and the axis at right angles to that axis as the “other axis”. (See Load Cases)

“restrained” and
unrestrained” relate to the circumstances of the structural member being analyzed. It indicates whether or not curvature about the “other” axis is restrained. Usually the expression “biaxial analysis” refers to an unrestrained case. (See Load cases)

Curvature deviation” means the angle between the axis of a bending moment and the axis of the curvature caused by that bending moment. (See Load cases)

### Stress-strain or stress/strain?

The combination of the word “stress” and the word “strain” has two distinct meanings. To clarify this the following convention has been adopted:

Stress-strain means a strain caused by stress.

Stress/strain means a relationship between stress and strain. In certain contexts it means a pair of numbers representing a stress value and the corresponding strain value in the stress/strain relationship of a material.

A meaning of strain is set out under Distortion. Also under that heading is the need for the expression “stress-strain”.