I AD-A066 027 FOREST PRODUCTS LAB MADISON WIS F/6 13/13
(J DESIGN* PERFORMANCE* AnD INSTALLATION OF A PRESS-LAM BASEMENT B«—ETC(U)
1976 J A Y0UN60UIST* D S 6R0MALA
UNCLASSIFIED FSRP-FPL-316 NL
6-79
SDA068027
DESIGN, [RESEARCH
* PAPER
PERFORMANCE, fplsis
AND INSTALLATION
OF A PRESS-LAM
BASEMENT BEAM
IN A F/CTORY-BUILT
HOUSE
' FOREST PRODUCTS LABORATORY
FOREST SERVICE
U.S. DEPARTMENT OF AGRICULTURE
MADISON, WIS.
1978
5 III
Abstract
Press-Lam and other parallel-laminated-
veneer products exhibit distinct advantages
when utilized in applications that require well-
defined material properties.
A Press-Lam basement beam was de-
signed and manufactured for a model prebuilt
house. Design stresses were determined in
conjunction with another Press-Lam study. The
finished beam was installed by a regular con-
struction crew using no special equipment or
techniques
Performance of this beam is expected to
be comparable to other design alternatives,
and to exceed design requirements for the life
of the structure
M j ' * S'/” S * Si
I r'eSec.^W c.^/s
DESIGN, PERFORMANCE,
AND INSTALLATION OF
A PRESS-LAM BASEMENT JBEAM i
IN A JACTORY-JgUILT HOUSE 1 . (
rr
to J. A^foUNGQUIST,
D. S./GROMALA,
R. W./JOKERST, .
R. C./MOODY,
xl
j j, l./tschernitz /
TorestlProducts Laboratory/ Forest Service
U S. Department of Agriculture ^
Introduction ( ) j fS i I
(7/ ji/' •
As supplies of large, high-quality sawtim-
ber decline, additional raw material supplies
must be sought for the manufacture of struc-
tural-size timbers for items such as basement
beams Small or low-grade logs can fill that de-
mand if they can be processed into engineered
wood products Press-Lam. a process devel-
oped at the Forest Products Laboratory (FPL),
offers that potential
Press-Lam is a parallel-laminated-veneer
product, made by peeling logs on a veneer
lathe, drying the veneer in a heated press, ap-
plying an adhesive, layering and pressing again
into a continuous sheet of laminated wood Re-
search at FPL has examined the effects of ve-
neer peeling, press drying, and laminating on
product performance (4)'. Other aspects of
PLV research have been explored by the USDA
Forest Service's Southern Forest Experiment
Station and by the Canadian Forest Products
Laboratories
Research conducted in cooperation with Wausau Homes
Inc . Wausau Wis
Maintained at Madison Wis in cooperation with the Uni-
versity of Wisconsin
Numbers in parentheses refer to literature cited at the end
ot this report
J-C
Because the physical dimensions of the
continuous sheets are limited only by produc-
tion equipment, sheets can be ripped and
cross-cut to meet desired end-product require-
ments Extensive test programs at FPL on ex-
perimentally produced parallel-laminated ve-
neer have established that the mechanical
properties of this product can be closely con-
trolled. Markets for which PLV may be well
suited include mobile home center beams and
truss chords, components for manufactured
housing, door rails and stiles, tension lamina-
tions for glulam beams, and root decking sup-
port systems
The beam project described in this report
covers one of four chosen FPL demonstration
uses of parallel-laminated veneer for structural
and/or specialty products Other reported
demonstration uses include railroad ties (7),
electrical distribution crossarms (8), and bridge
timbers and decking (9)
To demonstrate the feasibility of incorpo-
rating Press-Lam into a house design, the FPL
entered into a cooperative agreement with
Wausau Homes, Incorporated, of Wausau,
Wis., to supply a Press-Lam basement beam for
installation and use in a prebuilt house
V
Preparation of Material for Beam
Peelable Coast Douglas-fir No. 2 sawlogs
were shipped to the Forest Products Labora-
tory, cut to 52-inch bolt lengths, and rotary
peeled on a 4-foot lathe to a thickness of 0.42
inch. This veneer was then clipped to 21-inch
widths and press dried at 375° F at 50 psi to an
average moisture content of 15 percent. Drying
time was either 5.5 minutes or 11 minutes, de-
pending upon whether sapwood or heartwood
was being processed. Because the drying
press was not in the same building as the lami-
nating equipment used in producing this mate-
rial, the dried veneer had to be reheated in a
conventional veneer drier prior to glue appli-
cation and lamination. The reheating process
reduced the moisture content of the veneer to
about 1 1 percent. This press-dried veneer was
then assembled into a continuous sheet of 4-
ply step-pressed dimension stock, using a
phenol resorcinol adhesive. Veneer placement
was staggered in each layer to allow for a 12-
inch spacing between adjacent butt joints. The
wood was at a minimum temperature of 200° F
prior to adhesive application and was lami-
nated using pressures of 150 psi for approxi-
mately 6 minutes Dimension material, 1 'A by 20
inches in cross-section was then cut to lengths
of 21 feet. Both the length and width of these
Press-Lam components were constrained by
laboratory equipment limitations.
Dimension boards were abrasive planed
and cold-laminated into structural-size timbers
for use in concurrent studies aimed at deter-
mining the properties of large Press-Lam mem-
bers
Establishing Design Stresses
Eighteen beams were loaded to failure (9)
in two-point edgewise bending in accordance
with ASTM D 1 98 ( 1 ). Load and midspan deflec-
tion were monitored continuously to failure.
Test beams, 416 inches wide by 20 inches deep,
were tested on spans ranging from 17.5 to 19
feet. The average modulus of rupture (MOR)
was 5,450 psi, with a coefficient of variation of
about 9 percent.
An additional 18 beams were similarly
loaded to evaluate their moduli of elasticity
(MCE). The average MOE for the 36 beams was
1.7 million psi, with a coefficient of variation of
less than 7 percent.
The allowable bending stress was derived
by methods outlined in ASTM D 2915 (2). The
near-minimum strength of the population (5th
percentile) was divided by a factor of 2.1 to ac-
count for long-term loading and the possibility
of accidental overloading of the member. The
resultant allowable bending stress was 2,200
psi. This value was then multiplied by factors to
account for duration of load (1.15) and size ef-
fects (1 .06) to arrive at the final allowable stress
of 2,680 psi. Deflection calculations were
based on the average MOE (1.7 million psi), as
specified in the National Design Specification
(NDS) (3).
Because none of the test beams failed in
shear, it is difficult to assess the allowable
shear stress for these members. The average
shear stress at failure was calculated to be 330
psi. If these beams had failed in shear, the de-
sign shear stress would be 130 psi. This value
was chosen to represent a conservative esti-
mate of allowable shear stress.
Basement Beam Design
Because the Press-Lam basement beam
was to be installed as a minor modification in a
factory-designed house, its dimensions were
necessarily made compatible with the existing
design (fig. 1). The primary constraint from a
design standpoint was that the beam depth
could not exceed 12 inches. This restriction
produced a beam that was less material-effi-
cient than a deeper member.
Design Requirements
The design loadings currently employed by
the commercial designers involved in this proj-
ect are:
Floor Load: 40 psf live; 8 psf dead
Roof Load: 30 psf live; 8 psf dead
Maximum allowable deflection is 1 /240th of the
span under full load and 1 /360th of the span
under live load only.
The standard basement beam for this
model would be either four glue-nailed 2 by 8's
over five intermediate supports (fig. 2a), or a
steel beam, 8 inches deep, over three interme-
2
Figure 1.— Basement floor plan of test house.
M 146 565
diate supports (fig. 2b) The Press-Lam beam
was intended to provide an alternative to the
steel beam when three intermediate supports
are specified (fig. 2c).
Design Calculations
The final beam was designed to be 6
inches wide by 12 inches deep. Two sections
were manufactured. Beam sections A and B
(fig. 3) were field-spliced over a support with an
array of nails. These nails provide little transfer
of bending moment at small joint rotations. For
this reason, the joint over the column at R3 (fig.
2) was considered to be nonrigid and was as-
sumed to be a simple support for design pur-
poses However, a rigid structural joint was pro-
vided over the column adjacent to the longest
span (R4, fig. 2) to minimize deflections on the
long span. The final beam dimensions and lap-
joint configuration are shown in figure 3.
An evaluation of the design strength and
stiffness of the three beams shown in figure 2 is
given in the appendix.
Verification of Lap-Joint Design
As noted, beam section B (fig. 3) was de-
signed to be structurally continuous over one
oi the column supports, and assurance of the
adequacy of the joint design was required. As
outlined in the appendix, the joint was designed
such that bending stresses in a ply, rather than
the torsional shear stresses in the lap, would be
critical.
A beam section 5'/2 inches wide by 10
inches deep by 9'/2 feet long with a lap joint at
midspan was tested to examine its failure
mode. It was loaded in center point bending on
a 9-foot span. The specimen failed in a bending
mode, similar to other Press-Lam members with
butt joints The MOR on the gross section was
3,150 psi, and the MOE was 2.0 x 10 psi. As-
suming that the outer four plies (the last leg of
the lap joint) cannot transmit bending stresses
the MOR on the net section becomes 4.200 psi
This value is 23 percent less than the mean
strength of 5,450 psi found for the beams with-
out a lap joint.
Even with this reduction in strength the
joint exhibited nearly twice the required design
strength and failed in a bending mode Based
on these considerations, the structural lap joint
was considered adequate.
The measured MOE in this test also served
to verify the hypothesis that butt or lap joints
did not reduce the gross section bending stiff-
ness
ED
a.)
GLUE-NAILED
2 xB's
1 1 1 1 1
Rl
t r
R2 R3
t
R4
1
RS
R6
R7
b.)
B“
WIDE
FLANGE STEEL
BEAM
1 1 1
r
Rl
R2
f
R3
R4
R5
c.)
12 “
DEEP PRESS- LAM
1
f
<ri
R2
T
R3
R4
R5
Figure 2.— Three typical basement beam designs.
M 146 566
22 /£
le'-io'/t
28-41/1“
BEAM A
* INTERNAL SPLICE-- RIGID LAP JOINT AT POINT C.
(SUPPORTED AT R4)
Figure 3.— Plan view of beam section dimensions and lap joint configuration.
BEAM B
M 146 $64
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Installation of Basement Beam
The beam was delivered in January, 1977,
to the Wausau Homes plant in Wausau, Wis., in
two sections— section A measuring 18 feet,
IOV 2 inches; section B measuring 28 feet, 41/2
inches. Each had one staggered end (fig. 3) to
allow for the field splice.
At the erection site near Wausau, the two
sections of the beam were removed from the
truck and placed at ground level on the edge of
the foundation. The sections were connected
with an array of nails. The top course of the
foundation served as a leveling device to align
the splice. When the two pieces were joined,
the finished beam measured a nominal 6 inches
wide by 12 inches deep by 47 feet, 6'/2 inches
long. A deflection line was installed on the
beam at that time The beam was then installed
in precut pockets in the concrete block foun-
dation (fig 4). Steel shims were used to level
the beam. Although the construction crew had
had no prior experience with beams of this
length, no erection problems were encoun-
tered.
As various housing components were as-
sembled on the structure, beam deflection
measurements were taken. With all of the exte-
rior and interior walls in place, the floor panels
secured, and the roof panels in place, no beam
deflection was detectable The owner's impres-
sions oi overall beam performance will be mon-
itored periodically.
Figure 4.— Press-Lam beam installed in test house.
Summary
A main basement beam, manufactured of
Press-Lam. was designed for a specific loading
configuration and installed as the main sup-
porting member for a factory-built house. The
beam was installed by the regular construction
crew using no special equipment or tech-
niques The structural continuity of the Press-
Lam beam provides greater effective span snff-
ness. resulting in a larger column-free base-
ment area than is possible using the standard
giue-nailed beams In designs where the addi-
tional beam depth can be tolerated, Press-Lam
can be used as an alternative to a steel beam.
Literature Cited
1 . American Society for Testing and Materials
1967. Standard tests of timbers in struc-
tural sizes. ASTM Stand. Desig. D 198-
67. ASTM. Philadelphia. Penn.
2. A nerican Society for Testing and Materials.
1974. Evaluating allowable properties for
grades of structural lumber ASTM
Stand. Desig. D 2915-74. ASTM, Phila-
delphia, ~enn.
3. National Forest Products Association.
1977. National design specification for
wood construction. NFPA, Washington,
DC.
4. Schaffer, E. L., R. W. Jokerst, R. C. Moody,
C. C. Peters, J. L. Tschernitz, and J. J. Zahn.
1977. Press-Lam: Progress in technical
development of laminated veneer struc-
tural products. USDA For. Serv. Res.
Pap. FPL 279. For. Prod. Lab., Madison,
Wis.
5. Schaffer, E. L., J. L. Tschernitz, C. C. Peters,
R. C. Moody, R. W. Jokerst, and J. J. Zahn
1972. Feasibility of producing a high-yield
laminated structural product: General
summary. USDA For. Serv. Res Pap.
FPL 175. For. Prod. Lab., Madison, Wis.
6 Seely, F. B , and J. O. Smith.
1932. Advanced mechanics of materials.
John Wiley and Sons, Inc.. New York.
7 Tschernitz. J. L . E L Schaffer, R. C Moody.
R W Jokerst. D S (iromala. C C Peters,
andW T Henry
1979. Hardwood Press Lam crossties:
Processing and performance USDA
For Serv. Res Pap FPL 313 For Prod
Lab., Madison, Wis
8. Youngquist. John. Frank Brey. Joseph
Jung.
1977 Structural feasibility of parallel-lam-
inated veneer crossm as USDA For
Serv. Res. Pap FPL 303 For Prod
Lab., Madison, Wis
9. Youngquist, J. A . D. S Gromala, R W
Jokerst, R. C. Moody, and J L Tschernitz
1978. The design, fabrication, testing, and
installation of a Press-Lam bridge
USDA For Serv. Res Pap FPL 332.
For. Prod. Lab . Madison. Wis.
Appendix
Bending Stresses and Deflections
The design of this house was based on a
24-foot bay width (dimension perpendicular to
the beam axis). Half of this width contributes
load to the beam, while the rest is distributed
between the foundation walls.
Thus, design loads convert to uniform dis-
tributed loads as follows:
Floor: 40psfx12ft = 480 Ib/linear ft,
live
8 psf x 12 ft = 96 Ib/linear ft,
dead
Roof: 30 psf x 12 ft = 360 Ib/linear ft,
live
8 psf x 12 ft = 96 Ib/linear ft,
dead
The 1 8-foot, 1 0Vj-inch span nearest the ga-
rage is subject to floor loads only, as a ridge
beam across the living room carries the roof
load above this span. All other spans are be-
neath a load-bearing partition and carry both
floor and roof loads.
NDS permits a 1 5 percent increase in nom-
inal design stresses when designing for snow
loads. The snow load is 35 percent of the total
load for this design, thus it is the critical design
case.
Analyses were performed on the three
beam configurations with the following
assumptions:
(a) Glue-nai'ed 2 by 8 s:
Allowable bending stress =
1 650 psi ;
Increase for snow duration
= 1.15 x 1650 = 1900 psi
Modulus of elasticity (MOE)
= 1 7 million psi
All spans simply supported.
(b) 8-inch wide-flange steel beam:
Yield stress (fy) = 36.000 psi
Allowable bending stress =
0.6 x f y = 21,600 psi
MOE = 29 million psi.
No 2 Douglas-lif repetitive use
7
(c) 12-inch-deep Press-Lam beam:
Allowable bending stress =
2330 psi
Increase for snow duration
= 1.15 x 2330 = 2680 psi
MOE = 1 .7 million psi
Conventional engineering mechanics for-
mulae were used to analyze the beams. Maxi-
mum bending stresses and deflections ex-
pressed as a fraction of the allowable are
shown for the three design alternatives in figure
A1 . For each beam section, stresses and de-
flections shown are for the most critical loading
combination.
Design of Lap Joint
The lap joint was designed such that the
theoretical strength of a single glueline with an
area of b (lap length) times h (beam depth)
would transmit bending stresses equal to the
moment capacity of a single leg of the joint (4
plies). These stresses are transmitted through
torsional shear in the joint.
Both bending and torsional shear stresses
are linear functions of the applied moment at
the joint:
= M = 1 M
S’ ,x 6S
(1A)
where
= maximum bending
stress (psi)
M rnax = maximum bending
moment (inch-pounds)
S = section modulus =
(in.) 6
t = beam width (in.)
h = beam depth (in.)
b = lap length (in.)
7,„,, x = maximum torsional
shear stress (psi)
(i = factor tabulated in me-
chanics text dependent upon
joint geometry.
It was assumed that the ratio of bending
strength to shear strength of this Press-Lam
material is about 12 to 1 , i.e..
I
O
111.) v
12 7,,.
(2A)
X
Then, substituting values of <7 tabulated in
mechanics of materials textbooks (e g., 6), and
iterating yields
bmm = 15 in.
(3A)
Assuming that one leg of the joint (4 plies)
is ineffective in resisting bending stresses at
the joint, the bending stress is
too
„ _ M ma , 21 ,660 Ib-ft _ 9 4nn
S 108 in. 1 - 2 40 °P SI
(4A)
This stress is less than the allowable value
previously derived, and the lap length of 15
inches is adequate.
PRESS- LAM
100 L
Figure A1 .—Normalized stresses (a) and deflections (fi) for 3 beam configurations expressed as a
percentage of the allowable.
Ml 46 567
US GOVE RNMFN T PRINTING OFFICE 1478 750126 T6
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