Note: Descriptions are shown in the official language in which they were submitted.
Z83
Truss Shoring System ancl Apparatus Therefor
Thi.s invention relates to a truss shoring method and an
apparatus therefor u-tilizecl in the pouring of concrete floors.
Such systems and apparatus are already known and the latter
basically consist of various braced structural members supporting
wooden panels on to which the concre-te is poured, such arrangements
being termed structural units which, after the floor has set, are
removed or "flown" to a higher position in the building being erec-ted.
However one disadvantage with these known arrangements has been
among others, tha-t the provisions for "rolling" the units out from
under a poured and se-t floor to a position for "flying" have not,
for one reason or another, proved to be too satisfactory. Another
disadvantage has been that the integers of such units have not been
too easily interchangeable so that quite large stocks of integers
have had to be maintained. Hence, it is the object of the present
invention to overcome the above disadvantayes by providing a more
universal system and apparatus directed to the pouring of concrete
for the particular purpose just described.
According to one broad aspect therefore, the present invention
relates to apparatus utilized in the pouring of concrete floors, said
apparatus including (a) a pair of spaced and braced substantially
rectangular interconnectable modular truss-sections connected
together to form a structural unit, each said section at least
including (i) a pair of upper and lower longitudi.nally extending
chords, (ii) at least a pair of longitudinally spaced vertically
extending connectors serving to connect and space said chords apart,
(iii) at least one vertically ex-tending load-bearing member, inter-
mediate said pair of vertical connectors, secured to the side faces
of said chords and also serving to connect and space said chords
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apart; and (iv) at least one diagonally extending member connected to
said pair of chords and located between a said verti.cal connector and
said load-bearing member, said diagonal member also serving to space
said chords apart; (b) a plurality of screw-jacks located below said
load-bearing members to support said section in their operative
position and capable of pivotal movement when ~equired; and (c)
a plurality of beam members detachable secured to the upper portions
of said sections and extending a-t least from side to side thereof.
According to another broad aspect, the present invention
relates to a method of assembling a structural unit employed in the
pouring of concrete floors, said method including the steps of (a)
connecting at least a pair of substantially rectangular interchange-
able modular truss-sections together in transverse spaced relation
to form a structural unit, each said section at least including
(i) a pair of upper and lower longitudinally extending chords,
(ii) at least a pair of longitudinally spaced vertically extending
connectors serving to connect and space said chords apart,(iii) at`
least one vertically extending load-bearing member, intermediate said
pair of vertical connectors, secured to the sides faces of said
chords and also serving to connect and space said chords apart; and
(iv) at least one diagonally extending member connected to said pair
of chords and located between a said vertical connector and said load-
bearing member, said diagonal member also serving to space said chords
apart; (b) locating a plurality of scre~jacks below said load-bearing
members to support said sections in their opera-tive position and
capable of pivotal movement when required; (c) detachably securing a
plurality of beam members secured to the uppor portions of said
sections so as to extend at least from side -to s.ide thereof; and (d) ;
detachably securing a plurality of panels to said beams so as to
receive poured concrete -thereon.
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The inven-tion is illustrated, by way of example and
diagrammatically, in the accompanyiny drawings, in which:
Figure l is a side view of a basic modular truss-
section;
Figure lc is a cross-section through the upper chord of
a modular truss-section taken on the line lc-lc of ~IG. 2;
Figure 2 is a side view of another modular truss-section;
Figure 3 is a side view of an end-piece;
Figure 4 is a part end view of an assembled modular truss-
section;
Figures 5 and 6 are, respectively, front and side elevations
of a pivotable screw-jack;
Figures 7-9 are end elevations of three forms of beams;
Figures lO and ll are side elevations of two forms of
detachable clamps;
Figure 12 is an elevation of a connecting sleeve;
Figure 13 is an elevation of an extension leg;
Figure 14 is a side elevation of leg-connec-ting means;
Figure 15 is a plan view of a hingeable brace-clamp;
Figure 16 is an end view of two forms of modular truss-
sections;
Figures 17 and 18 are perspective views of two forms of
splicing or connecting plates;
Figure l9 is a side view of an alternate modular truss-
section;
Figures 20 and 21 are side views of alternative forms of fence
posts to which a sa:Eety fence may be anchored;
Figure 22 is a side elevation of a spandrel extension;
Figure 23 is a side eleva-tion of a connecting bracket,
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Figure 2~ is a side elevation of a ceiling roller and
bracket;
Figure 25 is a perspective view of a truss-supporting dolly;
Figure 26 is a perspective view of a floor roller;
Figure 27 is a side elevation of a positioning bracket;
Figure 27a is a plan view of ~'igure 27;
Figure 28 is a perspective view of a further positioning
dolly;
Figure 29 is a perspective view of a complete modular truss
unit with a spandrel extension;
Figure 30 is a diagrammatic view of a modular unit with a
spandrel extension;
Figure 31 is a diagrammatic view of a modular unit with a
pair of mutually opposed spandrel extensions;
Figure 32 is a diagrammatic view of a modular unit with a
spandrel extension showing a phase in the "rolling" or "flying"
operation of the unit; and
Figure 33 is a view similar to Figure 29 but omitting the
spandrel extension.
Referring to the drawings, the invention includes a pair
of substantially rectangular interconnectable modular-truss-sections
each of which consist of vertically disposed pairs of upper and
lower longitudinally extending truss chords 1,2 each of hollow box-
like cross-section spaced apart and connected by load-bearing mem-
bers 3 also of hollow box-like cross-section extending vertically
on -the outer sides of said chords 1,2 and longitudinally spaced tubu-
larconnectors 4 extending vertically between said
chords, each said member 3 being intermed.iate a pair of connectors 5.
Diagonally extending members 5 also connect the chords together
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at least one of said members 5 being located be-tween each adjacent
pair of members 3 and connec-tors 4. Cross-braces 6 also transversely
connect the diagonal members 5 of one -truss-section with those o~
the opposite truss-section through connection studs 7 carried by the
members 5 and, if desired, also connect them together in a horizontal
plane through connection studs 8 projecting upwardly from the lower
chord 2. The upper chord 1 is, as will be seen from Figure lc,
provided with a pair of side flanges 9 projecting from either side of
its upper horizontal surface.
If desired, the end of each modular truss-section may be
provided with an end-piece such as that shown in Figure 3 and, as
will be appreciated, the truss-sections of each module are connected
in end-to-end (or longitudinal) relation by means of splice plates
(Figs. 17 and 18) bolted to the upper and lower chords 1,2 of a pair
of end-to-end abuttinq truss-sections.
Load-bearing adjustable screw-jacks 10 (see Figures 5 and 6)
are capable of being pivotally mounted to, and support, the lower
ends of the load-bearing members 3 (see Figure 4), said jacks being
of the type described and claimed in our copending Application Serial
No. 366,301 filed December 8th, 1980.
Beam members 11, Figures 7 and & (of the type described and
claimed, respectively, in our Canadian Patent No.1,045,348 which
issued on January 2nd, 1979 or in our copending Canadian
Application No. 368,473 filed January 14th, 1981) having a lower
T-shaped slot 12, stub flanges 13 and a wooden insert 14 are then
secured to the upper surfaces of the upper truss chords 1 respectively
by the type of clamps 15 or 16 shown in Figures 10 and 11 and which
are described and claimed in our copending Application Serial No.
368,630 filed January 15th, 1981. The beams may also be of the type
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which omi-t the slot 12 and which are shown in Figure 9 such beams
being described and claimed in our British Patent No. 1,501,783
published on February 22nd, 1978. The clamps secure the stub
flanges 13 of beams 11 to the side flanges 9 of the upper chord 1.
The beams 11 are spaced apart throughout the length of the
chords and extend transversely thereto. Plywood panels P (see
Figures 29-33) are then detachably secured to the wooden inserts 14
by nails in order to receive the poured concrete.
Should the height of -the modular truss-unit be insufficient,
primary extension legs 17 of substantially box-like cross-section
(Figure 13) can be inserted in the lower ends of the vertical side
connectors 3 and maintained at the required height by means of open
ended U-bolts 18 (see Figure 14) passing through holes (not shown)
provided in the lower ends of the load-bearing members 3 and holes
19 spaced throughout the length of said legs 17. The stirrup-bar 20
extending across each U-bolt 18 serves -to define a hand-grip and also
serves as a limiting stop to prevent said bolts 18 from being over-
inserted into the cooperating and aligned holes in the legs. Screw-
jacks 10 are then positioned below the lower ends of the primary
extensible legs 17 to support the latter. The right hand side of
Figure 16 illustrates this arrangementO
Should the height of -the modular truss unit still be insufficient,
connecting sleeves 26 (Figure 12) of box-like cross-section are slidden
on to the lower ends of the primary extension legs 17 and the upper
ends of secondary extension legs 27 (Figure 16) of substan-tially box-
like cross-section are sliddcn into the opposite ends of said sleeves
26 which are then bolted to each pair of primary and secondary legs
17, 27 extending in aligned relationship. Vertically spaced pairs of
- ` hingeable clamps 2L ~Figure 15) are secured to each vertically aligned
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3L~2QZ83
pair of legs 17,27, one on each said leg.
Each clamp includes a pair of members 22,23 pivoted
together at 24 and each having threaded means 25 projecting there-
from. In operation, the members 22,23 are pivoted away from one
another so as to permit the clamp to embrace a primary extension
leg 17 and to be tightened thereon. Apertured ends of transverse
and longitudinal cross-braces 6' (Figure 16) are then secured to
the clamps 21 by the threaded means 25. The screw-jacks 10 are
then positioned below the lower ends of the secondary extension
legs 27 to support the latter. The left hand side of Figure 16
illustrates this arrangement. The clamps (informally known as
Case 18) form the subject of a divisional application.
Longitudinally aligned modular truss-sections are
connected together by pairs of upper and lower splice plates 28
(Figure 17).
In cases where the underside of the floor to be poured
is non-planar, longitudinally aligned modular truss-sections of
different heights must be employed. However, in this case, whereas
the lower chords 2 will be longitudinally aligned, the upper chords
1 will not, so that angled or drop-splice plates 29
(Figure 18) must be employed to connect said aligned sections
together and such an arrangement of truss-sections is shown in side
view in Figure 19.
Obviously, and for safety purposes, a safety fence must
be provided in order to prevent workers from falling. This can be
achieved in ~wo ways. The first is to provide fence post brackets
30 (see Figure 20) of box-like cross-section secured to extensions
31 which are adapted -to be placed alongside outer ends of the upper
chords 1 and bolted thereto. The brackets 30 are adapted to receive
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arld support. ve~tic~ L timber ~osts 32 to which ho.ri~ontal timber rails
33 are attached and which extend from at least one side of a -truss-
unit to the other. The second alternative, is to provide vertical
steel posts 34 (Figure 21) which, at their lower ends, are
hingeably connected -to ex-tensions 35 capable of being slidden into
the outer ends of the upper chords 1 and bolted thereto. Each post
34 carries at least a pair of vertically spaced hoops 36 to which a
pre-formed mesh safe-ty fence 37 (see Figures 29 and 33) can be
detachably secured, such a type of fence being described and
illustrated in our Canadian Patent No. 906,324 which issued on
August 1st, 1972.
Often as not, the spandrel i.e. the perimeter of a
floor, requires some form of special attention such as, for example,
a depth which is greater than the depth of the general area of the
floor, such depth depending from the floor and requiring special
formwork prior to the concrete being poured. Obviously, such form-
work must be erected from special staging and, heretofore, this has
been separate from the "flying" unit and has involved much time and
effort. However, the present invention overcomes such problems
in a quick and relatively easy manner. With prior knowledge that a
portion, or all, of a perimeter of a floor will require a greater
depth than the remainder o~ the area of the floor, the unit is
provided with all adjlls~ble spalldrel extens:ion ill~icated genc:rcl~.ly
at 37 in Fic~ure 22 and a spalldrel connecto:r 44 (E~igure 23).
The extension,indicated generally at 37, projects from one
end of the modular truss unit and includes pairs of vertically
disposed upper and lower chords 38, 39 spaced apart by vertical
side members 40 each of the latter being disposed between a pair of
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diagonal side braces 41. Preferably, -the overall length of each
lower chord 39 is less -than tha-t of the upper chords, 38 and the
upper surface of the latter is provided with side flanges 9' (see
Figure 30).
The inner ends of the upper and lower chords 38,39 of
hollow box-like cross-section are provided with pairs of side plates
42 welded at one end thereof to -the innermost side member 40.
Each pair of plates 42 is adapted to embrace an associated
vertically extending and bored connector 44 of hollow box-like
cross-section and provided with horizontally extending stub
extensions 45. Bolts 43 are adapted detachably and adjustably to
secure the side plates 42 to the connectors 44 and the extensions
45 are adapted to projec-t into the upper and lower primary chords 1,2
of the modular truss unit. The extensions 45 are retained ln situ
within the chords 1,2 by bolts 45' passing through holes 77
(Figure 35) in the extensions and corresponding holes (not shown)
formed inthe sides of said upper and lower chords 1,2,
It will thus be apparent that the spandrel extension 37
is vertically adjustable on the connectors 44 so that i-ts upper
horizontal surface can be varied in relation to the upper horizontal
surface of the adjacent and connected modular truss unit.
A plurality of cross-beams 11 such as, for example, those
described and claimed in British Patent No. 1,501,783 published
February 22nd, 1978 or -that shown in Canadian Patent No. 1,045,348
of those shown in Figures 7-9 herewith (all of which beams include
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wooden inserts to which the plywood panels P can be nailed) are
`, placed in spaced relation to one another and extend from one upper
chord 38 of the spandrel extension to the other in order to support
- the staging required to pour the spandrel S. Obviously, the free
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portion of the plywood panels P (to the lef-t as viewed in Figure 30)
forms a walkway ~ which will support a numbex of wor]cmen and -the
ancillary equipment required in the pouring of a spandrel S which
projects and depénds from the outer perimeter of -the floor F and
which is of greater depth than the latter.
The extension 37 is also capable of bearing vertically
extending fence posts which serve to carry a safety fence as will be
described hereinafter. Moreover, and if desired, the lower chords
39 may carry detachable or integral hingeable vertical supports
45' and the lower ends of the latter may be supported by any sui-table
and vertically adjustable jack means.
P~eferring now to Figure 31, it will be seen that a
pair of modular truss-units (with the beams and attendant integers
omitted for greater clarity) connected by a filler panel indicated
generally-at FP and each uni-t is provided with spandrel extension 37
at its end remote from said panel FP.
; As will be appreciated from references to Figures 29-32
the workers can stand on the walk-way F to erect the forming
required to pour the spandrel S (See Figures 30 and 31).
If required, the spandrel extension 37 can be provided
with separate or integral and pivotally mounted leg support means 45
(Figures 29 and 30) supported at the lower end by any suitable
jack means and being capable of vertical adjustment. The spandrel
extension and its components (informally known as Case 21) forms the
subject of a further divisional application.
Figure 24 illustrates what is termed as a ceiling roller
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assembly, indicated generally at 46, employecl in "rolling" themodular uni-t in a longitudinal horizontal plane and as will be
described hereinaf-ter. It will be seen that the assembly 46 includes
a vertically adjustable support 47 the upper end of which carries a
roller 48, the support 47 being mounted in a holder 49 having an
ear 50 capable of insertion in the open end of the top chords 1 of
the truss-unit. The ceiling roller assembly (inEormally known as
Case 22) forms the subjec-t of another divisional application.
Figure 25 shows a wheeled roll-out stand or dolly
indicated generally at 51 (and employed in "rolling" of a modular
unit) which includes vertically adjustable support means 52 the upper
end of which carries detachable roller means 53 (shown more clearly
in Figure 26) mounted on a base plate 54 having a pair of holes 55,56
of different diameters. The roll-out stand and roller means (infor-
mally known as Case 25) forms the subject of yet another divisional
application.
Figure 27 shows a support bracket, indicated generally
at 57, utilized in the moving of modular unit in a transverse
horizontal plane. The bracket 57 includes a pair of spaced upper
cheeks 58(see Figure 27a) adapted to embrace avertical tubular
connector 4 and to be detachably secured in this operative position
by means of nuts and bolts 59 as well as a vertically extending body
portion 60 of hollow box-like cross-section carrying a lower support
plate 61. The support bracket 57, as will be described hereinafter,
is adapted to operate in conjunction with the wheeled pivot dolly
indicated generally at 62 in Figure 28 which is provided with a
vertically adjustable support column 63 having an upper end 64.
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After the floor has been poured, and the concrete set, it :is
then necessary to remove the unit from beneath the poured and set
floor and to "fly" it to a higher location by a crane in order that
a further floor may be poured upon it. Before "flying" however, the
uni-t must be "rolled" outwardly so that it projects a predetermined
distance beyond the perimeter of the floor so that a crane can be
connected to it. ~owever, before "rolling" can occur, the height
of the unit has to be reduced. This is done in various ways,
through the use oE hydraulic or mechanical jacks, etc.
as will now be described. The procedure is slightly dlfferent,
depending upon whe-ther the screw-jacks 10 are pivotally mounted to
the lower ends of the load-bearing members 3, or support the lower
ends of the primary ex-tension legs 17, or support the lower ends of
the secondary extension legs 27 and whether the three types of unit
just described are provided with one or more spandrel extensions 37.
Accordingly, the sequential steps of the rolling-out and flying
procedures comprise:-
(i) Unit without e~tension legs
(a) placing at least two hydraulic dollies of any
suitable low-rise type (not shown) beneath the lower
chords 2 of the modular unit and supporting the
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(b) securiny the inner end oE the unit to any suitable loca-
tion by means of cables (not shown) and known in the trade as
tie-back or safety lines in order to ensure that the unit is not
rolled ou-twardly too far;
(c) slac~ening the jacks 10 (pivotally moullted to -the
lower ends of the load-bearing members 3), pivoting them
upwardly and thereaEter securing them in thcir non-
operative position as is deseribed more fully in -the
abovementioned Canadian Application No. 366,301.
(d) placing at least four rollers 53, two either side,
under the lower chords 2;
(e) eausing the hydraulie jaclis to lower the modular unit
until it is supported on said rollers 53; and
(assuming that the eeiling roller assemblies 46 are
not utilized)
(f) pushing the unit outwardly from -the building until
it approximately reaches its fulcrum-point where slings
65 are placed around the upper chords 1 and eonnected
to the c~ble 66 of a crane whereupon said uni-t is
~ushed (or "rolled") fully outwardly where the erane
will "fly" the unit upwardly to a higher location.
It is possible, of course, that the particular shape of
the building will recluile the utiliz.ation oE tlle ce:iLinq rol:Lcr
assemblies 46 as will now be deseribecl. 'l`he use of such
assemblies ensurcs that the poured and set Eloor immediately above
the modular unit will not be damaged during a rolling operation
and, moreover, will permi-t the modular unit to be rolled out,
withou-t tipping, beyolid its fulerum-point due to the surfaee
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engagement between the ceiling rollers 48 and the underside ofsaid poured and set floor. If the use oE the assemblies 46 is
required, then an additional s-tep (e') will be required i.e.
(e') inserting each ear 50 of each assembly 46 into the open
inner end of each upper chorcl 1.
Thus, a rolled-out uni-t, using assemblies 46, is shown
diagrammatically in Figure 32.
ii Unit with primary extension legs
(a) placing at least two hydraulic jacks of any
suitable high-rise type beneath the lower chords 2 of
the modular unit and supporting the latter thereon;
(b) placing at least four roll-out stands 51 under the
lower chords 2 at pre-de-termined locations and at pre-set
elevations;
(c) slackening the jacks 10 supporting the primary
extension legs 17 and removing and securing them in any
suitable location on the modular truss unit;
(d) removing the U-bolts 18 connec-ting the primary extension
legs 17 to the load-bearing members 3 and pushing
the legs 17 upwardly until they are contained within the
load-bearing members 3 when said bolts 18 are re-inserted to
retain said legs 17 in their inoperative position;
(e) if the type of dolly 51 is not employed, placing at
least four floor rollers 53 (Fig. 26), two either side,
under the lower chords 2;
(f) causing -the hydraulic jacks to lower the modular unit
until it is supported on said rollers 53;
(g) if the ceiling roller assemblies 46 are employed,
inserting -the ears 50 of said assemblies into the open
inner end of each upper chord l;
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(h) securin~3 the inner encl oL th~ U~ Lo any suitabl
location by means o~ a tie-bac~ or sa~ety line; and
(i) pushing -the unit outwardly and flying i-t in
aecordance with step (f) oE method (i) described above.
lt will be appreeiated tha-t step (b) of method (ii) will not be
required if floor rollers of the type shown in Figure 26 are em-
ployed because the lower chords 2 will be sitting on the rollers 53
; thus enabling -the unit to be rolled outwardly on said floor rollers,
the use of which depends upon the height between the two ad~acent
floors and any possible obs-tructions in the roll-out path. Qui-te
obviously, the making use of said step (b) a dis-tinct saving in man-
power time will be achieved.
(iii) Unit with both primary ancl secondary extension legs
~ The height between the two adjacent floors dietates
t whether primary ~ el~sion legs 17, eaeh having at least one
seeondary extension leg 27, are used. ~owever, when sueh legs
are used, the heicJht is -too great for the u-tilization of the
high-rise hvdraulic jae~;s so that the lowering proeedure is dif~(r-
ent i.e. the modular unit is supported from above through the
20 intermediary o~ winehes loeated on the floor above and eooperating
eables passing through holes formed in said floor and fastened
to the truss unit. The holes are eonstituted by sleeves around
which the concrete of the upper of the two floors is poured
during a pouring o~era-tion and the winches are placed in pOSiti
on saicl upper Eloor whell the latter has set. 'L`hc lowering
proeedure woulcl then inelude -the following steps:-
(a) seeuring the wineh eables to the upper ehord 1 of
~ the mc~clular -truss unit;
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(b) rcmov.incJ t}le pivot jacks 10 suppo.r-~:ing the lower
ends of the secondary e~tension legs 27 and securing
said jacks 10 to -the -truss unit;
(c) removing the cross-braces 6', clam~s 21, sleeves 26
and secondary c~tc~nsioll legs 27;
(d) removing the U-bolts 18 connecting the pri.mary
extensiOn legs 17 to the 1.oad-bearing members 3 and pushing
said lec3s upwardly until they are contained within said
members 3 when said bol-ts 18 are reinserted -to retain
the legs 17 in their inoperative positlon;
(e) either placing roll-out stands under the lower chords
2 of the unit or the floor rollers 53 (Fig. 26) on the
floor under said chords;
(f) lowering said modular unit, by means of the winches,
down on to said roll-out stands or the said floor rollers 53;
(g) inserting the ceiling roller assemblies 46 (if
required) into the open inner ends of the upper chords
1 of the truss unit;
(h) securing the inner end of the unit to any suitable
location by means of tie-backs or safety lines;
(i) disconnecting the winch cables from the truss
uni-t; and .
(j) pushing the unit outwardly and flying it in
accorcl.lnce with stcp (f) o~ Inetllocl (i) clcscri.bed above.
If, due -to a projection depending from -the underside of the
: upper floor, i-t is required to move a truss uni-t sideways or
t~ransversely in a horizontal plane prior to a rolling-out
operation, this can be achieved by the use of the dolly 62 shown
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in Figure 28 and the positioning of such a dolly depends upon
whether primary ~-t~nsion legs 17 are used or not.
Assuming that primary c~ n~ion legs 17 ~re not
employed and it is required to move the truss-uni-t sideways, support
brackets 57 are detachably secured to the tubular connec-tors 4
with the support plates 61 located beneath the lower chords 2,
whereby, after the jacks 10 have been pivoted upwardly and
secured in their non-opera-tive position, dollies 62 can be positioned
beneath the brackets 57 and vertically adjusted until their upper
ends 64 are accommodated within the open lower ends of said
brackets 57. Thus, as the wheeled dollies 62 are moved, the
truss unit will follow due to being supported by said dollies.
Alternatively, and assuming the primary extension legs
17 are employed and have been slidden upwardly and secured within
the load-bearing members 3, the dollies 62 can be positioned beneath
the open encls of said legs 17 and vertically adjusted until their upper
ends 64 are accommodated wi-thin said open ends and thereby support
the modular truss unit for sideways movement.
Finally, it is to be noted from the drawings that the
diagonal members 5, of each associated pair thereof, extend down-
wardly towards one another and to their point oE connection with
the lower chord 2, either from adjacent the upper end of a vertical
load-bearing member 3 or from an adjacent upper end of a tubular
connector 4. This means -that the modular -truss unit can be
supported at the points of in-tersection o-f said members 3 and con-
nectors 4 with the lower chord 2, as well as a-t the points of inter-
section of the diagonals 5 with said chord 2, said points preferably
being 2'-6" apart. ~his is distinctly advantageous over ~nown
prior art where the load-bearing members ~rc spaced 5'-0" and 10'-0"
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apart and the diagonals meet at their point of connection with one
another as well as their intersection with the upper chord. This is
distinctly advantageous because of the whip and play of the prior art
units during "rolling" opera-tions due to -the great distance between
the lower connection points and particularly when such a unit
assumes the posi-tion such as that of the instant invention in
Fig. 32.
The present invention is also advantageous in that
in the arrangement shown and described above, the substantially
rectangular truss sections permit the modular truss uni-ts formed
thereby to be spliced together at their extremities whereas, in at
least one known arrangement, the units are spliced together at mid-
span because the sections are substan-tially parallelogram shaped due
to the chords being of different lengths.
Moreover, as the load-bearing members 3 of the present
invention are box-like cross-section, as opposed to known art, where
they are of I-bea~ construction, the unit is much stronger and has
a greater rigidity.
.,
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