[Title 24 CFR 3280.402]
[Code of Federal Regulations (annual edition) - May 1, 2001 Edition]
[Title 24 - HOUSING AND URBAN DEVELOPMENT]
[Subtitle B - Regulations Relating to Housing and Urban Development]
[Chapter Xx - OFFICE OF ASSISTANT SECRETARY FOR HOUSING--FEDERAL HOUSING]
[Part 3280 - MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS]
[Subpart E - Testing]
[Sec. 3280.402 - Test procedure for roof trusses.]
[From the U.S. Government Printing Office]


24HOUSING AND URBAN DEVELOPMENT52001-05-012001-05-01false3280.402Sec. 3280.402HOUSING AND URBAN DEVELOPMENTRegulations Relating to Housing and Urban DevelopmentOFFICE OF ASSISTANT SECRETARY FOR HOUSING--FEDERAL HOUSINGMANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDSTesting
Sec. 3280.402  Test procedure for roof trusses.

    (a) Roof load tests. The following is an acceptable test procedure, 
consistent with the provisions of Sec. 3280.401, for roof trusses that 
are supported at the ends and support design loads. Where roof trusses 
act as support for other members, act as cantilevers, or support 
concentrated loads, they shall be tested accordingly.
    (b) General. Trusses may be tested in pairs or singly in a suitable 
test facility. When tested singly, simulated lateral support of the test 
assembly may be provided, but in no case shall this lateral support 
exceed that which is specified for the completed manufactured home. When 
tested in pairs, the trusses shall be spaced at the design spacing and 
shall be mounted on solid support accurately positioned to give the 
required clear span distance (L) as specified in the design. The top and 
bottom chords shall be braced and covered with the material, with 
connections or method of attachment, as specified by the completed 
manufactured home.
    (1) As an alternate test procedure, the top chord may be sheathed 
with \1/4\ inch by 12 inch plywood strips. The plywood strips shall be 
at least long enough to cover the top chords of the trusses at the 
designated design truss spacing. Adjacent plywood strips must be 
separated by at least \1/8\ inch. The plywood strip shall be nailed with 
4d nails or equivalent staples not closer than 8 inches on center along 
the top

[[Page 135]]

chord. The bottom chords of the adjacent trusses may be either:
    (i) Unbraced,
    (ii) Laterally braced together (not cross braced) with 1" x 2" 
stripping not closer than 24 inches on center nailed with only one 6d 
nail at each truss, or
    (iii) Covered with the material, with connections or methods of 
attachment, as specified for the completed manufactured home.
    (2) Truss deflections will be measured relative to a taut wire 
running over the support and weighted at the end to insure constant 
tension or other approved methods. Deflections will be measured at the 
two quarter points and at midspan. Loading shall be applied to the top 
chord through a suitable hydraulic, pneumatic, or mechanical system, 
masonry units, or weights to simulate design loads. Load units for 
uniformly distributed loads shall be separated so that arch action does 
not occur, and shall be spaced not greater than 12 inches on center so 
as to simulate uniform loading.
    (c) Nondestructive test procedure--(1) Dead load plus live load. (i) 
Noting figure A-1, measure and record initial elevation of the truss in 
test position at no load.

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[GRAPHIC] [TIFF OMITTED] TC17OC91.008

    (ii) Apply load units to the top chord of the truss equal to the 
full dead load of roof and ceiling. Measure and record deflections.
    (iii) Maintaining the dead load, add live load in approximate \1/4\ 
design live load increments. Measure the deflections after each loading 
increment.

[[Page 137]]

Apply incremental loads at a uniform rate such that approximately one-
half hour is required to establish the total design load condition. 
Measure and record the deflections five minutes after loads have been 
applied. The maximum deflection due to design live load (deflection 
measured in step (iii) minus step (ii)) shall not exceed L/180, where L 
is a clear span measured in the same units.
    (iv) Continue to load truss to dead load plus 1.75 times the design 
live load. Maintain this loading for 12 hours and inspect the truss for 
failure.
    (v) Remove the total superimposed live load. Trusses not recovering 
to at least the L/180 position within 12 hours shall be considered as 
failing.
    (2) Uplift loads. This test shall only be required for truss designs 
which may be critical under uplift load conditions.
    (i) Measure and record initial elevation of the truss in an inverted 
test position at no load. Bottom chord of the truss shall be mounted in 
the horizontal position.
    (ii) Apply the uplift load as stated in Sec. 3280.305(c) to the 
bottom chord of the truss. Measure and record the deflections 5 minutes 
after the load has been applied.
    (iii) Continue to load the truss to 1.75 times the design uplift 
load. Maintain this load for 3 hours and inspect the truss for failure.
    (iv) Remove applied loads and within three hours the truss must 
recover to at least L/180 position, where L is a clear span measured in 
the same units.
    (d) Destructive test procedure. (1) Destructive tests shall be 
performed on three trusses to generally evaluate the truss design.
    (2) Noting figure A-1, apply the load units to the top chord of the 
truss assembly equal to full dead load of roof and ceiling. Measure and 
record deflections. Then apply load and record deflections in \1/4\ 
design live load increments at 10-minute intervals until 1.25 times 
design live load plus dead load has been reached.
    (3) Additional loading shall then be applied continuously until 
failure occurs or the factor of safety times the design live load plus 
the dead load is reached.
    (4) Assembly failure shall be considered as design live load 
deflection greater than the limits set in Sec. 3280.305(d), rupture, 
fracture, or excessive yielding.
    (5) The assembly shall be capable of sustaining the dead load plus 
the applicable factor of safety times the design live load (the 
applicable factor of safety for wood trusses shall be taken as 2.50).
    (e) Trusses qualifying under the nondestructive test procedure. 
Tests Sec. 3208.402(c) (1) and (2) (when required), shall be subject to 
a continuing qualification testing program acceptable to the Department. 
Trusses qualifying under the destructive test procedures, Tests 
Sec. 3280.402 (c)(2) (when required), and (d), shall be subject to 
periodic tests only.

[40 FR 58752, Dec. 18, 1975, as amended at 42 FR 961, Jan. 4, 1977. 
Redesignated at 44 FR 20679. Apr. 6, 1979, as amended at 58 FR 55008, 
Oct. 25, 1993]