Techno Consultants Ltd.
Technical Notes
Use of Digital Cameras  |  Product of Inertia Ixy

Use of Digital Cameras
NB: This note was written prior to year 2000.  Use of digital cameras has now become very common & its use obvious.  It was not so at the time this note was written.  It took a great deal of effort to educate myself and others around me at the time to realise its benefits.

any Architects and Engineers in our observation are not using Digital Cameras to their full benefit. Even those who happen to be up to date in their use of IT equipment are failing to grasp the effective use of this amazing tool in building design and construction.

The main reason for this failing is the user’s expectations and comparison of the digital camera with the conventional film cameras. From the technical benefit viewpoint, the two tools have many common elements in terms of use but they also have differences. Most users compare the image definition of the two cameras and conclude that definition of digital cameras is not good enough for their needs.

In our experience, the best use of the digital cameras is to regard them as a tool to take site notes and then store them on CD’s later in the office. When used in this way, the digital camera becomes an invaluable tool. They allow capturing site visit views and survey details, which are then downloaded on to the computer with ease, rapidity and minimal cost. Site personal can also take photographs and then transmit them to designers, suppliers and clients in any corner of the world by email for immediate feedback and action.

When writing reports and minutes after site visits, auto display of the images on the screen in your work background can help confirm or enhance site observations by a combination of glances and some keen zoom-in studies of these images. In addition, other members of the team in the office can also grasp the site facts from photos much easier than hard to repeat wordy descriptions or cryptic site notes.

In short, use digital cameras as a tool to record site facts. Store site images on CD’s. One CD can hold up to about 1000 images at a resolution of 1024x768 low compression. Just one CD may therefore be sufficient for most project needs. Distribute and recall stored images as and when necessary to enhance the productivity of your project team with wonderful results.

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Product of Inertia Ixy Property of Triangles and Circle Quadrants

In calculations for unsymmetrical bending, the product of inertial property Ixy is an important sectional property. Yet most engineering books and section property tables do not include this value for various unsymmetrical sections. In general, there are 3 shapes for which this property is missing. These shapes are a Triangle, Circle Quadrant and Rolled Steel Angles.

When performing calculations, it is also necessary to know the sign of this property. It can be negative or positive depending upon the orientation of the shape. The following sketches show the formulae and the sign for two of the shapes.

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The formulae for the quadrant are:


The formulae for the Triangle are:

For Rolled Steel Angles, the value needs to be calculated for each section from its dimensions. The sign of this value is however similar to the Circle Quadrants and Triangles shown above.

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Software Sections
Masonry           Reinforced Concrete
Structural Analysis              Units Conversion               Steelwork
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