Sloped Members

RedSpec™ considers only transverse loading in the analysis. The meaning of "transverse" is that the load acts perpendicular to the span of the member, and the load acts in the same plane as the depth of the member.

When the member is sloped, RedSpec™ adjusts input spans and loads for a transverse analysis.

Note that wind pressures generally act perpendicular to the building envelope. When entering wind pressures in RedSpec™, the user may judge it necessary to increase the input load by the cosine of the slope, thereby counteracting one element of the adjustments made by RedSpec™.

Point Load

Input point loads are assumed to act vertically. RedSpec™ multiplies the load magnitude by the cosine of the slope to account for decreased intensity in the transverse direction. This applies to both live and dead loads. The user is advised to account for this adjustment if the point load is known to act in the transverse direction rather than the vertical.

Analysis

With the adjustments to span and loads as described above, RedSpec™ analyzes the member as if it were a horizontal member subject to vertical loads. The member's allowable properties (i.e. resistances) are not adjusted for slope.

Results

Transverse values of design shear, moment, and deflection are reported. Allowables are not affected by slope, except allowable deflection as a ratio of span is based on the slope-adjusted span. An exception is made for open-web trusses: the embedded frame analysis returns vertical, rather than transverse, deflection, so the allowable deflection is based on horizontal span.

Reactions in the Supports section of the output are vertical. In other words, the reactions from the transverse analysis are divided by the cosine of the slope to obtain the vertical reactions. Required bearing lengths given in the notes are based on vertical reaction. This method is appropriately conservative where the likelihood of slope-cut ends exists.

Axial Forces

RedSpec™ considers only the transverse components of loads in the analysis. The axial components due to slope are neglected. It is important to note that RedSpec™ assumes the member is properly attached at each support to resist not only the vertical force but also the sliding force, if any. This would apply to any I-joist, beam, or open-web truss on beveled plate, as well as any I-joist or beam in a sloped hanger. It is not appropriate to use RedSpec™ exclusively, with no axial analysis, for the design of a rafter system with no vertical support at the high end. A joist that is vertically supported at the high end typically is connected via hanger to a ridge beam, whereas the unsupported joist is essentially leaning against a ridge board. This is analogous to a ladder leaning against a wall, where the only resistance to sliding is at the foot of the ladder. Please contact RedSpec� technical support for assistance in designing rafter systems with no vertical support at the ridge.