Note: Descriptions are shown in the official language in which they were submitted.
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..vKGROUND TO TH~ INVENTIO~
This invention relates to beams for sh~ring structures, ~he main
use of such structures being to serve as a temporary support during
the formation of collcrete slabs.
The beams ior shoring structures must first of all be strong
enough, so that they will not fail under the weight of the concrete
even under abusive conditions. Apar~ from that paramount
requirement, the beams should be light iTl weight ior easy assembly
and removal of the shoring structure as the building progresses: and
since many beams are needed to support a large concrete slab, each
beam also should be inexpensive in itself, and should be easily
manufactured in production quantities.
PRIOK AR~
An examplc of a typical stringer that has ~een use~d hitherto is
tllat shown in Canadian ~atent l~o. 1,1~,127 (JOHN~rr~, 4 August
1~81). The beam is forme-l as an aluminum extrusion. ~`lle
cross-sectional shape of the extrusion inclucles a boLtolrl flange
having a wide, flat, tllin base; a comparaLively slender we~; and a
challnel-shaped top section in the form ol an inverted top hat. A
strip of wood Lits in~o the upper top hat channel and is provided
for the purpose of receiving nails or screws so tha~ a declcing board
may be nailed do~.7rl to the top oL the beam. ~`he~ scrip of ~ood is
secured in the top hat channel by screws which pass through the si~es
of the channel. This JO~ TOi~' stringer is, itself, an improved and
more robust design compared with those sho~n in AV~Y U.~. ~atents
27 4,144,690 (i~larch 2~, 1479), 3,89~,152 (August 12, 1975) an~ 3,787,~2
~23L~2~
(January 22, 1974).
In U.S. Patent 4,159,604 (BURRELL, 3 July 1979) the wooden
strip is secured by barbs formed in the sides of the trough. It is
plain that in such arrangements the capacity of the wood to
contribute to the structural strength and stiffness of the beam is
quite limited: when the beam deflects under load, there is some
relative movement between the wood and the metal permitted by such
jointing means as those illustrated.
It is a]so known from U.S. 4,191,000 (HENDERSON, 04 March
1980) to provide a composite beam for shoring structures in which
the beam is made entirely of wood. The top and bottom flanges are
rectangular sections of wood in which the grain runs along the
length of the beam. The flanges are joined by a web of wood that is
"tailed'in" to both flanges, i.e., slots are cut in the flanges and
complementary tails on the web are a tight fit in the slots, and
are glued into the slots. In this case, the joint between the web
and the flange is a very strong one: now, the wood of a flange
cannot deflect or flex independently of a corresponding flexure in
the web. the strength of the web therefore complements that of the
flange, and vice versa.
BRIEF DESCRIPTION OF THE INVENTION
It is recognized by the present invention that the performance of a
beam as a shoring support can be enchanced by a combination of
features from the two types of previous construction as described
above. It is recognized that wood is well-suited for taking
compressive forces: its bulk ensures that it resists buckling under
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., .
~ pression, and the disruptive induced shear sLresses which woul~ ~e
incurred during such buckling.
ln a beam, it is bad practice on the other hand to employ wood
in tension: wood can have knots in it which seriously reduce its
tensile strength (though they hardly afLect its rigidity under
cornpression.) ~ince the beam cannot be allowed to fail, the designer
must allow a huge factor of safety, which is not neecled when the woo~i
is only in compression.
~ ther materials have other characteristics: aluminum, or other
extruded materials, cannot have a thick and bulky section as that
would be too expensive. lt is uneconolnical for extruded shapes to be
anything but thin, though, of course, the shapes can be intricate.
These shape characterisLics mean that whilst an extruded shape is
MUCh superior Lo WoO(I in supporting tensile forces, wood is the one
that is l-nore suiLt(l ~o takirlg coml~ressive rorces, at leas~ with the
type of loadiTlg and the n-lanller of use enco-lllLered in ~eams for
shoring strucLu1-e~s.
In ~he inve~Tltiorl~ the top flange of the beanl (whicll is uTlder
coml)ressioll wherl lhe beam is loaded) is wood, ancl the bottonl flange
(which is under Lension) is extruclecd. l`he flanges are joined by a
web t~lat renders ~I-le beam a unitary whole. ~ucll a beam ccln be used
in the same rnanner as the knowl- beanls with ~he all-extruded secLion
an(l a wood insert, since a wooclen surface is preseTlted on top for the
nailirlg down of boal-(ls, and the extruded shape of the bottor;l flange
can include Lhe c~lstomary T-s]ots for retaining bolts.
Preferably, the ~wo flanges are joined to the web by tailing-in
27 the web, which is conveniently of a lamil-lated or sandwich
construction. The tails can be provided on the bottom flange by
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,., ~. .,
~ropriate shaping of the extruded sectin.
DETAILE~ SC~IPTI~N ()l THE PR~F~K~D ~i~lB~Dl~ T
An exemplary embodiment of the invention will now be described
with reference to the accompanying drawing, in which:
Figure 1 is a cross-section oc a beam that emboclies the invention.
The beam of Figure 1 includes a top flange 4, a ~ottom flange 5
and a web 6. The top flan~e 4 is of wood, arranged with its grain
disposecl along the length of the beam, i.e., perpenclicular to the
plane of the ligure. The bot~om flange 5 is of aluminum and the
cross-section shown in the Figure has the shape in whicl-l ~he aluminum
was extrude(l.
The extruded shape oi- the bottom flange S inclucles a wi~e base
50 comprised by the two lirnbs 51, 5~. I.ach linlb has a respective
beacl 53, 57 at its extremity. The extrucled shape inclucles a T-shaped
slot 5~ that runs the length of the beam. t'rotrudillg upwarus from the
material on top of the slot 5~ are two tails 5~.
The top flange 4 is made of woocl of a rectangular section. Four
slots 4~ are cut in the undersurface of the flan~e 4. The slots 4
are slightly tapered.
The web 6 has seven plies, in the plics ~() the grain runs
vertically, whereas in t-he plies 61, 62, ~3 the grain runs along the
length of the beam. The lengthwise-grained plies ~1, 62, 63 are cut
away at the top of the web, so as to leave tails ~4 that extend from
27 the plies 6~. Par~ of the vertically-grained plies 6~ are also cut
away to leave the tails slightly tapered. The two outer
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~ gthwise-grainecl plies 61,63 are cut away at the bottom of the
beam, to leave slots 67.
To assemble the beam, the tails 64 on top of the wer~ 6 are
inserted into the slots 40 in the top flange 4. The tails 54 on the
bottom flange 5 are inserted into the slots 67 in the bottom of the
web 6. Each tail is made a goocl tight fit in its respective slot so
that the components of the beam have to be pressed together to bed
down the tails fully into the slots. The tails and slots are glued
during assembly. This manner of joining components oc beams togetl,er
is ~nown as "~ailing-in". It produces a joint of generally greater
strength than ~he materials of the components (i.e., if the beam
fails, it very rarely does so at the joints). The slots and tails
shoulc] be accura~ely made to ensure a good fit, but there is little
problern in Lhis regard once a production set up has been made: the
woo(3en cooponents can be milled to shape using suitable jigs and
Eixtures whilst the extrucled component is precise enough as extruded.
I~hen made properly, the joint permits absolutely no relative
rnovement ~etwcerl its components: any flexure of the one must be
accornpaniecl by a commensurate flexure of the other.
It is recognizecl in ttle invention that tailing-in an extrudcd
component to a wooden coponerlt produces a joint between the two of
tlle require(3 strerlgtll and reliability, yet with no great expense.
In use, quantities of beams are assembled in such a way that
flat l)oards may be laid on top, and nailed down to tne beams. The
top-f]ange 4, being of wood, readily accepts nails or screws. lf
desired, cross-braces can be installed between beams and nailed to
27 the exposecl sides of the rectangular shape of the top flange 4. (ln
tne all-extruded beam of the prior art, even with the wood insert,
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assembly had to be carried out on the basi.s that cross-braces
could not be attached between the beams, because the sides of the
wood insert were not exposed.)
l`he beams of the invention are light enough for them to ta~e
their place in shoring structures of the flying variety. Iierè, the
beams are assembled to provide a shoring structure on whici-l a
concrete floor is poured, in the usual way; but when the concrete has
set, the shoring structure is not dismantled but is caused ~o slide
bodily horizontally until clear of the floor on top of it. It is then
lifted by crane, and laid upon an upper floor so as to be ready to
shore another concrete floor without dèlay.
Since ~he flying shoring structure has to be lifted
substantially at thè limit of the crane's reach, it is very important
that the structure should be light; and the strength-to-weight ratio
o the beam o the invention is very good as compared with prior art
beanls. The stress i.n a shoring structure whilst it is being flown
from the crane can cause the structure to distort: thc ability of the
beam of the invention to receive cross-braces or bridging-braces
between the beanls means that the structure can easily be given the
required stiflness that i.t needs to survive the flying operation
without damage.
0ther refinements oL the beam of the inventiorl include the
provision of the beads 53,57 at ~he extremities of the base 5~. These
beads receivc clamping clips to hold the beam down onto another beam
acting as a stringer running cross-wise below, or on~o other suitable
supports; or for securing otller parts such as pan-forms to the beam.
27 The beads 53, 57 also act to concentra~e the mass of the base at the
edges, for good strength and stability.
231~7~
The undersur~ace of the base 50 may be slightly concave to
ensure good stability of the base.
The T~slot 5~ is provided to receive tlle head of a bolt, also
for holding the beam down onto its support, or for mounting and
hanging other parts from the beam.
With the invention, some degreee of versatility is providecl.
The extruded shape of the bottom flange 5, being extruded might be
difficult to change, but the top flange and the web can be readily
changed. Similarly, if the wooden parts deteriorate, the extruded
part can be fitted with new wooden parts. The web 6 itself has a good
deal of bulkiness as compared with the slender web of the
all-extrucled beam, which means that the web can be taller, without
the web being liable to a buckling failure.
The beam has been described when used horizontally and wilh the
wood flange upmost. In shoring structures, sometimes the beams need
to be clisposecl vertically or horizontally witl- the flanges at the
sides. This can be appropriate when shorirlg walls or columns for
instance. I`he beam of the invention can still be used in such
circumstances, though it should of course be arranged that tl~e
properties of the beam are used to the best advantage in that the
bulky wooclen flange is the one that is preclorninantly in com~ression
and the comparatively slim-sectioned extrudecl flange is the one that
is predominantly in tension.
The material of the extrusion may be other than aluminum. It
could be titanium, or it could be a glass-filled plastic resin. The
matcrial of the web may be other than plywood, in that the plies that
27 cornprise the tails could be of metal or plastic. There may be more or
fewer plies than seven. Likewise, instead of the two tails 5~, a
2~Z~
~ .lgle extruded tail coulc~ be accommodated in a single machined slot
at the lower end of the web.
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