PIOPIEtI NAIIING Or CAIP LACING
SCHOOL OF FOR[ST'Y t[IBRARY
UNIYERSITY OF FLORIDOA
UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST PRODUCTS LABORATORY
In Cooperation with the Univenrsity of Wisconsin
P-OP? ::AILI::G 0o CAR 3BRACI:G'
L.J. I.'A?.'.'?2T, Senior Engineer
J.11. GA -'AI:, Assistant Engineer
The ease with which wood can be cut, fitted, and fastened, in addition
to its light wei.-L and availability, has made it an efficient and practical
material for car bracing. Yet the very ease and simplicity of using wood often
causes some of thie basic principles of nailing to be overlooked, with the re-
sult that the bracing: may not measure up to its full possibilities for strength
:he nailing of car bracing frequently requires the exercise of hudgmert
as 5:. best practice, especially when in oome particular i:-stsnce it is impossi-
ble to meet ioeal conditions. For example, what is the best detail for nail-
ing a 2-inch cleat to the 2-inch car floor w: it is known that, in _e.-eral,
the penetration in the piece receiving the point of the nail should be at least
twice that through which the nail passes? Again, is there any ai-antage in
having the nail pass entirely through both pieces being joined?
before discussing nailing in detail, it is well to recount the several
ways nails ....' be called on to f-unction. 17'-ils ma, be s'ubjected to direct with-
drawal, to lateral displacement, or to a combination of both. Resistance to
withdrawal, as the name implies, is the reaction to forces tending to pull the
nail out in the director of its length, whereas, lateral resistance is the re-
action to forces tending to bend the -ail or push it sidewise.
It is known that resistance to withdrawal is related to the density or
hardness of the wood. The dense woods hold nails rach better than do the light
weight woods. In fact, resistance to direct withdrawal (as opposed to lateral
resistance) varies about as the second power of the specific &ravity of the
wood. This does not imply that light or low density species are not entirely-
suitable for car b ac .'' "' L ;tJ -
suitable for car braci-. o :.t the same nail strength with the softer woods,
however, "requires more, larger, or improved nails. resist'!mce to withdrawal
also depends on tl,.-, area of contact of the nail with the vood, and hence in-
creases directly with the diameter of nail and with depthl of penetration as
long as no splitting of the wood occurs.
Lateral resistance for a nail of given size Increases with the density
of the wood, but not quite so raoidly. It also increases about as the 3/2
power of the nail diameter. >.s, the safe lateral lo'd for a 20d rail in
white pine is nearlyT twice that 8pon 8d. For white oak the ratio is about the
same but, because of its higher d nity, the loads -ir. about 50 percent ..4J'.,c1
than for the ine.
;omie Important Details in C)r racingn .
To obtain ;o&d nai in, the foIlowir- genera details should ee o --
lse no. .Is of proper ].enfrth Wherever possible' the noils should be
lor e 'no:h so h;"'.t Kin softwoods approximately t'wo-thirds of the leng 4,-,, oes
into th.o .e b-er rec 1,ring the point. This neans thl.t the length of the nail
should be at least 2 ree times the thickness of the outer piece (fig. 1).
'Tere te t sickness of the "embers does 'ot perrit thi s sI.7ested depth of
,','-tion a suf iciert number of shorter nails should be usd: to pro-ide
equivalent area of contact in the wood member receiKinf the point.
Driwe nails so that the points do not co'e out of tihe side of the
piece. I 'se "s minors" as they ',re called not only result i weakened jnts
but are also a cause of injury,
Be suro. the n ils yen, use do not snlit the wooS. rT ittinrg *' rtl'y
wealcens the joint. If the ,'ood bondss to split b.aly use a thinner nail.,
blunt the points, or, tctter still, purchase n .nFt. In' nails. ''ien prac-
ti.cal, borin- lead holes sli 'tlr smaller in riaeter than E. djiamleter of
the shank of -he ri] is eOrellent practice.
TUs'e p]h:,, of noils. The stren'4h increases directly as the number
of nails used.
"'"eneuer Oos.::. Ie, do not use nal. s in direct toenslon, hut use the
preferably in l.ateral resistane., .en .ais i.n di rect pension, rien way,
they usually fail. :ud denlv ando .,, cause injury or da '.,;, The rsistan rice
to withdrawal is 1iflu.:ced: reratly byl the srrfac. c n-' on of the nail. or
temporary ser-rice, cere -ccated ... nails ma,' v e .*... 1ed 7at ri:1y to increase
the '-oldin- power wt a .r...r. naet and .r.r %'cre re a.ay fe obtained
with special' nails r',!vin 0: n'"c pited o eLce surface
Do not Yoc- o- nailed jo'at s w':irren us,' re wool that will later
dry out. "'ails -3 _' in green ;ood thot laer rics out quite cor: :only lose
ost of rh.ir ,',i-.f' pover. ence, use dry lui'ner.
I'e s'stance to Latoril r" re
Jails .re n'or.e_. _i'iciont vdhen 'rivreu into irica .:rt. 'f r'. wc'd than
when Ori>e-w i ': -., r:y .ra o
Tlie leral resir, dance of rails is exprewsed by c:: f'otnIa i -m I '
'. re, P re'r3)r c' s :.he l'-b1im e '.K OP 'e ora,' in "o':4 s; c To ro-
^(3p_-^ o as in ';e''o '"15nT o *'":c' se c o 4 ^^ wod <'a n,<',* *-[:Ilier'' "'::it~e
itne 4,r 00 s tr' l 'e r' a c':', 1',c' .. ... >e dr o
the nail ic in p hes.
Thu accompanying table based on this formula gives recommended
values of safe lateral resistance, expressed in pounds per nail, for common
wire nails, driven perpendicular to the grain of wood at 15 percent moisture.
The bracing material should be free of knots and cross grain at the
places ,':.,re it is to be nailed. Wood splits easily when nailed near a knot
or -./h:r cross-grained at the nailing ends, with the result that the effective-
ness of the nailing is either seriously impaired or perhaps entirely lost.
Table l.--Safe lateral resistance1 of nails
Species Pounds per nail size of
4d 6d 8d lOd 12d 16d 20d 30SOd 40d
"-orthern white pine, pon-
derosa pine, and spruce .. 28 34 43 51 51 :59 76 85 96
Southern yellow pine, Doug-
las-fir, and western
larch .................... 43 52 65 78 78 90 116 130 147
Oak, sl.vi-r maple, birch,
beech, and ash............ 53 65 81 97 97 111 143 160 181
'These safe loads are recommended for permanent nailed construction,
and consequently for temporary nailing such as in car bracing, higher values
may be used. When ultimate loads are required for design, they may be con-
servatively considered as five times the safe loads given in the table. The
actual ultimates are from six to eleven times the safe loads.
Some Special Problems in Car Bracing
Let us consider some of the special problems of bracing carload
shipments, assuming nominal 2 by 4 inch to 2 by 10 inch bracing. lumber,
sheathing, or car lining ranging from 1-1/4 to 1-3/4 inches, and car floors
1-1/4 to 2-1/2 inches thick.
-ai1 Sizes.--What size of nail should be used? First, we must se-
lect a size and type of point that does not split the wood, and when used with
sheathing or flooring, a length sufficient to completely penetrate the piece
holding the point. With stanchions and very thick material two-thlirds of the
length should be in the member holding the point. With these conditions ful-
filled, the size of nail makes little difference as long as the same total
weight of nails is used and provided the nails do not bend in driving. The
slight advantage in this instance is in favor of the smaller diameter nail
used in greater quantity.
i:ails Penetrating TI',Cr.!' Members.--When nails penetrate through a
piece of wood they frequently tear off a sliver when the point emerges. .igh-
est resistance to withdrawal results with nails just short enough so that they
do not come through the member receiving the point. On the other hand, the
shock, or repetition of shock required to tear the bracing entirely off is
^rreatest for a long nail that protrudes some distance through the piece.
Figure 2-Dialgrammatic sketch of "K" brace sorn o'
Figure 1-Nall Joint sawed open to expose lengths of nail. Above:
Good practice. Nail of proper length, about two-thirds of the length
being in the block receiving the point. Below: Poor practice. Nail
too short, giving Insufficient length in block.
Z M P8312 F
ircct in ~rf :ail.-Slant driving of nails does not give any advantage
over straight driving. In fact, when the points doe not pass entirely through
all members, the straight driving is preferable because a -reater portion of the
length will be in the place receiving the points. When the nail extends through
the member receiving the point but little difference is evident.
Position of Cleat.-It is important to place wall cleats so that the
nails go into the stanchions rather than into the sheathing or siding alone, A
nail -r.ay then be chosen which will more nearly meet the desired condition of
havir.g about two-thirds of its length in the members to which the cleat is
_'ur'ber of IFails.--A dry 2 by 6 placed with its edge against a load will
require three to six 20d nails in the cleat at each end to develop the full
stre.. ;th of the 2 by 6, dcpcndine upon the arrangement of the cleat and the
quality of the 2 by 6.
Let us assume that one of the diagonals of a K brace (fig. 2) is a 2 by
6 of Dou.ls-fir, 6 feet lon;-. This brace acts as a long column and the
cripplin, load it should take is about 6,000 pounds. Part of the load is taken
by thrust against the side of the car, part by friction, and the balarcc by
thrust against the cleats. If it is estimated that 3,000 pounds of the total
thrust is taken by the cleat, and that the ultimate lateral resistance load
for a 20d nail is 580 pounds (safe load 116 x 5), it is evident that at least
five 20d nails should be used to develop the strength of the car brace. If
thi. brace were only 4 feet long, and of good grade and quality of material,
double the above number of nails in the cleat would be required to hold it.
Quality of the Wood.--The effective nailing scheme to fit any problem
in carx bracing cannot be applied if the lumber to be used consists of indis-
criminately mixed species and mixed grades. However, the use of mixed material
is not objectionable provided it is first segregated into groups of species
having the same nailing properties. Furthermore, if low-grnde material is other-
wise permissible, none of the defects, as previously pointed out, should be
allowed at the point of nailing.
L UNIVERSITY OF Fl ORIDA
II 111111262 08929 0703
3 1262 08929 0703