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Full text of "DTIC ADA068027: Design, Performance, and Installation of a Press-Lam Basement Beam in a Factory-Built House."

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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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