Alpine Gives Guidance on Reading a Component Drawing
Originally published by: Alpine, an ITW Company — March 20, 2017
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Editor’s Note: Alpine recently provided this component drawing training guide to component manufacturers through its March Inside VIEW email.
A) Loading Criteria
Top & Bottom Chord live and dead loads. Non-concurrent Bottom Chord Live Load (NCBLL). Soffit Load. Load Duration Factor (an adjustment of allowable design values of lumber & fasteners). On-center component spacing.
B) Wind Criteria
Includes the ASCE Wind Load Standard. Wind Design Speed (mph), Building Type (Closed, Open, Partially Enclosed). Building Usage Risk Category. Mean Height of roof. TCDL (Roof dead load). BCDL (Ceiling dead load used in wind analysis). Wind Load pressure Analysis - Main Wind Force Resisting System (MWFRS) and Components & Cladding (C&C). Load Duration Factor used for wind load cases.
C) Snow Criteria
Ground Snow Load (Pg) varies by location - refer to ASCE GSL map. Thermal Factor (Ct) of the building. Exposure Factor (Ce) from ground surface, vegetation & constructed features. Category (CAT) or Importance Factor based on occupancy. Snow Duration Factor used solely for snow load cases.
D) Code / Misc. Criteria
Building Code & Truss Plate Institute (TPI) Standard used in the component design. Repetitive Factors or Load Sharing. Fabrication (FT) and Rotation Tolerances (RT) and Max. (#) indicates override values. Plate type(s) used in iDesign.
E) Deflection / CSI Criteria
Panel Point (PP) Deflection for the absolute maximum vertical deflection distance, the span/deflection ratio & the limits used for the design. Dead Load Creep Factor used in the component analysis. Maximum CSI (Combined Stress Index = combined maximum axial & bending stress with associated component type) acting on a member. Camber applied by manufacturer to the component design.
F) Maximum Reactions
* R = Maximum vertical reaction from a gravity load case.
* U = Maximum uplift reaction from a wind load case.
* Rw = Maximum downward reaction from a non-gravity load case (e.g. Wind or Drag load).
* Rh = Maximum horizontal reaction from a gravity load case.
* RL = Maximum horizontal reaction from a non-gravity load case (e.g. Wind or Drag load).
* W = Bearing Width.
G) Maximum Top Chord Forces per Ply (lbs.)
Maximum Tension and Compression forces for each top chord member, where member forces exceed 375 lbs.
H) Maximum Bottom Chord Forces per Ply (lbs.)
Maximum Tension and Compression forces for each bottom chord member, where member forces exceed 375 lbs.
I) Maximum Web Forces per Ply (lbs.)
Maximum Tension and Compression forces for each web member, where member forces exceed 375 lbs.
Size, Species, and Grade for each member used in the analysis.
Web bracing requirements are noted and referenced by a letter in parenthesis on the component drawing.
L) Loading & Wind Notes
Loading notes indicating additional loading conditions analyzed for the truss, including unbalanced loads, non-concurrent loads, drag loads, mechanical loads, etc.
M) Heel Height
The vertical measurement of the component from the bottom of the bottom chord to the top of the top chord at the outside edge of the heel.
N) Member Label
The member number (e.g. T# = Top Chord, B# = Bottom Chord, W# = Web) as specified by the member label in the Lumber note (refer to item J above).
O) Joint Label
All joints of the component are identified by a unique letter.
P) Connector Plate
Size and orientation of connector plate. Orientation indicates direction of slots on connector.
The vertical rise in inches for every 12 inches of horizontal run.
R) Overall Component Height
The vertical dimension including the overhang of the component.
S) Component Span & Panel Dimensions
Horizontal measurements that provide both panel point dimensions and the running total of component span based on out-to-out dimensions of the top and bottom chord of the component.
T) Engineers Seal
Seal of the registered professional responsible for the design.
U) Panel Splice
The location within top chord and/or bottom chord panels where two chord members are joined together by a connector plate.