## Tuesday, February 25, 2014

### STRUCTURES: TORSION

Torsion is very common in machines but less common in building structures.  The examples here include a small detail and an entire garage.

1 Door handle

2 Tuck-under parking

Note: The torsion moment is the product of base shear v and lever arm e, the distance from  center of mass to center of resistance (rear shear wall). In the past, torsion of tuck-under parking was assumed to be resisted by cross shear walls.  However, since the Northridge Earthquake of 1994 where several buildings with tuck-under parking collapsed, such buildings are designed with moment resistant  beam/column joints at the open rear side.

## Tuesday, February 18, 2014

### STRUCTURES: SHEAR STRESS

Shear stress occurs in many situations, including the following examples, but also in  conjunction with bending, described in the next chapter on bending.  Shear stress  develops as a resistance to sliding of adjacent parts or fibers, as shown on the following  examples.  Depending on the number of shear planes (the joining surface [A] of connected elements) shear is defined as single shear or double shear.

A Shear plane
B Shear crack

## Tuesday, February 11, 2014

### STRUCTURES: AXIAL STRESS

Axial stress acts in the axis of members, such as columns.  Axial tension is common in rods and cables; wile axial compression is common in walls and columns.  The following  examples illustrates axial design and analysis.  Analysis determines if an element is ok;  design defines the required size.  The equation, fa = P/A, is used for analysis.  The  equation A = P/Fa, is used for design.  Allowable stress, Fa, includes a factor of safety.

1  Crane cable design

2  Suspension hanger analysis (Hong Kong-Shanghai bank)

3 Post/footing analysis

4  Slab/wall/footing, analyze a 1’ wide strip