Frequently Asked Questions

Where does the "Dr." come from in Dr. Beam and Dr. Stress? The "Dr." is supposed to indicate expertise and consultation, along with a bit of gender-neutral anthropomorphism.

 Dr. Beam

Why doesn't Dr. Beam plot stresses? Currently Dr. Beam is cross-section neutral--i.e., there is no knowledge of the details of the cross-section beyond the moment of inertia. Computing stresses requires additional information about a cross-section, and to do this in a general manner is beyond the scope of the current release.

 

How can I change the sign convention for the plotting of moments, shears, etc.? Double-click on the scale button to the right of the plot in question, and simply add a negative sign to the relevant scale value.

 

How many levels of undo does Dr. Beam support? Dr. Beam currently has 10 levels of undo (and re-do). This can be a simple way to sequence a presentation of a series of steps in an analysis: do the steps ahead of time, and then undo back to the starting configuration--during the presentation, simply replay the steps using the re-do command.

 

Dr. Stress

Why do the stress state dots in Dr. Stress's Mohr's circle plots always stay in the upper half plane? Mohr's circle shows the magnitude of normal and shear components on the block faces. In two dimensions, the shear components happen to align with coordinate axes, and so signs can be assigned. In three dimensions, this is not the case, and so it only makes sense to plot magntiudes without accomodating signs, which boils down to plotting absolute values.

 

How does the mouse-based rotation work? It's not like other 3D program I'm used to. The block rotations in Dr. Stress all occur relative to the block faces themselves rather than to an arbitrary global reference frame. By default, dragging the mouse "up and down" causes rotation about the green face, while dragging the mouse left and right causes rotation about the red face. The Rotations sub-menu under the Options menu allows you to change the rotation faces. (Mac only: holding down the "r", "g", or "b" key while dragging the mouse will constrain the rotation to the red, green, or blue faces respectively.)

 

Why do the traction vectors appear to "jump" sometimes while the block is being rotated? Normal stresses that are compresive are depicted by arrows pointing toward the block, while tensile normal stresses are depicted by arrows pointing away from the block. When showing total traction vectors rather than separate components, as the normal component of the traction vector changes sign, the location of the arrow's head and tail will swap, and this causes the visual jump.