CA1058386A

CA1058386A - Method of constructing a pre-stressed concrete circular wall

Info

Publication number: CA1058386A
Application number: CA218,999A
Authority: CA
Inventors: Chester I. Williams
Original assignee: Individual
Current assignee: Individual
Priority date: 1974-02-19
Filing date: 1975-01-30
Publication date: 1979-07-17
Also published as: US3869530A; GB1470471A

Abstract

A B S T R A C T
A procedure for constructing circular wells in sectors, including pre-stressing peripheral reinforcing rods to each sector as segments in a continuous peripheral tension system, and including provision for grouting the pre-stressed rods through the use of hollow rods and vented couplings.

Description

~058386 This invention is generally concerned with a method - for constructing poured concrete walls and more specifically con- -~
cerned with a method of constructing circular walls from concrete.
This invention relates to a method of constructing a -. circular pre-stressed reinforced concrete wall, said method in- -: cluding placement of spaced form sectlons and pouring concrete between said spaced sections, wherein the improvement comprises: .
placing spaced form sections including end panels to form a first sector of a circular wall; placing a shielding tube around rein-, 10 forcing rod means having threaded ends, and placing said tube and :~
rod means peripherally in the space between said form sections, ,, with said ends projecting from said end panels; pouring concrete :~
between said form sections including submerging said tube and rod ,. means, and permitting said concrete to set; exposing at least 1 part of the ends of said set concrete, and applying bearing J plates over said rod means ends, and nut means to said threaded ~:~ ends; applying tension to said rod means between said plates, and ~, .
1 securing said nut means; placing form sections to form an adja- i.
'',.~
~ cent sector of said wall with an end of said set concrete of said ,~, 20 first sector defining one end of the space between said form .. sections, the opposite end of said space being defined by an end ,~i panel; placing a shielding tube around reinforcing rod means , having threaded ends, and placing said tube and rod means per-- ipherally in the space between said form sections, and coupling .1; one end of said rod means of said adjacent sector to said rod .~, means of said first sector, the opposite end of said adjacent sector rod means projecting from said opposite end panel; pouring . concrete in said space between said form sectlons submerging said tube, rod means and coupling, and permitting said latter concrete - . ~

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to set to form said adjacent sector; exposing at least part of the end of said concrete of said set concrete of said adjacent sector defined by said opposite end panel and applying a bearing plate over the end of said rod means projecting from said oppo-site end and nut means to said latter threaded end; applying tension to said latter rod means; repeating the steps for con-structing said adjacent sector to form successive adjacent sec-tors of said wall; placing form sections to form a closure sec-tor of said wall, the space between said form sections being defined by the ends of the set concrete of said first sector and the last of said adjacent sectors; placing a shielding tube around reinforcing rod means having threaded ends, one of said i l , threaded ends being of opposite hand to the threaded end of said , rod means projecting from said first sector, placing said latter :;. tube and rod means in said space between said form sections, :'.1 ' ~ coupling said latter rod means to the rod means projecting from said last adjacent sector, and applying a turnbuckle coupling ' connecting said rod means of said first sector and the rod means ::

; of said closure sector, and boxing out a space between said form sections surrounding said turnbuckle coupling, said space pro-~, viding access from the exterior of said wall; pouring concrete :~~ between said form sections, including submerging said tube and ,'J, rod means and permitting said concrete to set to form said ~-... .
closure sector; and tightening said turnbuckle coupling to apply tension to the rod means of said closure sector.
It is standard practice to construct poured concrete ::
:, ~ i~
walls through the use of spaced form sections interconnected by :

ties of sufficient strength to resist the pressure of the poured .' ~ .

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concrete. The form sections are usually metal or plywood panels reinforced by parallel stiffening beams commonly referred to as "studs". Another set of beams, usually referred to as "walers"
extends transversely to the studs, and bears against them to -~
.~ .
transfer the accumulated stresses to the tie assemblies. These tie assemblies usually include a central tie rod that remains imbedded in the concrete, and has threaded ends inter-engaged , with bolts extending to an adjustable member bearing against the ,j ~! walers. The bolts traverse holes in the form panels, and these assemblies are usually identical with each of the form sections.
:, -'' The tie systems are frequently used additionally to control the spacing of the forms. When the concrete is poured in the space :~? ' ~;~ between the form panels, and is permitted to set, the result is a concrete wall with dimensions that are controlled by the accuracy of placement of the form system. This standard con-struction procedure is used for walls that are both linear and i~;ff ;
~`1 curved in plan, and with or without reinforcement.

`~ The reinforcement of concrete walls and other struc-tures is normally accomplished through the use of steel bars ~ 20 having a corrugated surface for maximum inter-engagement between ?i''~? the rods and the surrounding concrete. Concrete is very strong .i~,l -:
in compression, but notoriously unreliable in tension. The placement of reinforcing rods is usually selected so that the rods can take over the function of providing strength in tension.

.f~ Since material cannot develop tensile stress without ij` 'r 1~
':' ~. "'':

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~058386 e~ongation, it is preferable that the reinforcing rods be pre-stressed so that the concrete is not required to stretch be-fore the imbedded rods can develop tensile strength. This ob- `~
viously dictates that the pre-stress must be applied before the concrete is poured, unless special provision is made to prevent bonding of the concrete to the reinforcing rods. So-icalled "post-tensioning" involves the application of pre-i .. .
.~stress tension to the rods through the use of hydraulic ~acks, ~r other force-generating equipment. Performing this opera-tion prior to pouring the concrete obviously requires that pre-stress forces be transmitted through the form system, which is ordinarily impractical in the field. While the iso-lation of reinforcing rods from surrounding concrete ha~ been accomplished by surrounding the rod with a shielding tube or coating, this principle has not been effectively applied to the construction of pre-stressed successive wall sectors, to applicant's knowledge.
~Wherever reinforcing rods are used, it is usually t~considered advisable to assure that they are ult~mately im~
20 bedded in a cementitious material, which can either be con; ;~
crete or an initially more flowable material referred to as "grout". The intimate engagement of the reinforcing rods by ~-grout or concrete protects the rods from the effects of mois-ture or other corrosive influences, as well as providing some degree of stress transfer where this is not interfered with by a shielding material. In any event, it is always desirable to eliminate any voids that may exist in a concrete structure.
Standard procedures in the construction of concrete walls do not conveniently provide the features of pre-stress and grout~
ability, particularly where the walls are circular in plan.
The invention will now be described in reference to r. ~
'', ' ' ' ,~ ' ' ' ~ ' lOS8386 . the accompanying drawings, wherein:
Figure 1 is a perspective view o~ a circular con-crete structure cast in successive sectors, Figure 2 is a plan view of the structure shown in Figure 1, on an enlarged scale;
- ;7 Figure 3 is a fragmentary section on a horizontal plane of the area indicated at 3-3 in Figure 2, on an en-larged scale;
Figure 4 is an enlarged fragmentary section illus-trating the application of pre-stress tension (post-tension-ing) at the end o~ a wall sector;
Figure 5 is a section on a horizontal plane at the ~. junction between successive wall sectors, Figure 6 is a section similar to Figure 5, at the junction of a closure sector of the wall with the initial sec-tor;
Figure 7 shows the preferred arrangement for place- ~
ment o~ the reinforcing rods in the space between the form : ;
panels prior to the pouring of the concrete;
Figure 8 shows the arrangement for shielding the re-~ inforcing rods with a plastic tube; and Figure 9 shows a modification of the arrangement shown in Figure 6.
The wall structure generally indicated at 10 in Fig-; ure 1 is constructed of successively-placed sectors as indi- :`cated at 14-21. Referring to Figure 7, each of the sectors is :. constructed by the use of a form system including the spaced panels 22 and 23 reinforced, respectively, by parallel vertical studs 24 and 250 The walers 26-27 bear against the outer sur~
. 30 faces of the studs 24, and the walers 28-29 against the outer surfaces of the studs 250 Bolts referred to commonly as "she~

,;

~058386 ., ;, bolts" as shown at 30 and 31 traverse the panels 22 and 23, and are inter-connected by the inner tle-rod 32 in threaded -~
engagement with both o~ the bolts. The pre~sure of the con-- crete poured between the panels 22 and 23 is thus placed in opposition, and equalized. When the concrete between the ~`~
panels 22 and 23 has set, the bolts 30 and 31 are unscrewed by the application of a wrench to the end flats 33 and 34, leaving conical recesses in the spaces previously occupied by the ends 35 and 36 of the bolts, Stresses are transferred from the bolts to the walers by ad~ustable wedges as shown at 37 and 38 whlch bridge across the walers, and engage forged or broached flats (not shown) at an intermediate point on the bolts.
The form system for constructlng the wall sectors includes end panels as shown at 39 in Figure 7 for defining the end of the space between the panels 22 and 23. The end panels are provided with holes for receiving the ends of re-`; inforcing rods as shown at 40. These may be of a type common-ly referred to as "rebar", having a corrugated periphery as ~ 20 shown in Figure 6~ or the rods may be smooth on the outer sur-; face. In either case, they are preferably hollow. A small-diameter passage shown at 41 extends throughout the length of these rods. The ends of the rods are exteriorly threaded as shown at 42 and 43 in Figure 6. The rods are covered by a preferably plastic shielding tube as shown at 44, and this as-sembly of rod and tube may be supported conveniently on the central tie rods 32 of the tie system. An anti-rotat~on off-set as shown at 45 normall~ present on these tie rods may be used as a locating point for the reinforcing rod and tube to assure placement at the central portion of the space between the form panels 22 and 23. If the offset 45 is positioned up-~ `` 10583~6 wardly, it may also be used as a means of plac mg the rein forcing rods either radially inward or outward frDm the center of the space, as may be desired according to s~ress conditions~
` When the concrete of the initial wall sector 21 has been constructed as previously described, at least the end panels 39 are preferably removed. Bearing plates as shown at 46 and 47 are slipped over the ends of the rod 40, and the nut 48 is run down against a washer (optional), so that all loose~
ness is removed between the nut and the bearing plate 46. At the opposite end o~ the rod, the projecting threaded end 49 o~
the rod 40 is connected by a temporary coupling 50 to the pis-ton rod 51 o~ the hydraulic jack 52. A set of struts as shown at 53 and 54 exposes the coupling 50 and the end 49, so that the base 55 of the ~ack bears against the bearing plate 47.
The central portion o~ the base 55 is provided with a standard cutout area so that the nut 56 can be run down onto the kear-ing plate 47 after the pre-stress loading has been applied to the rod 40 by the hydraulic ~ack 52. The coupling 50 is then disconnected, and the ~ack removed.
After the pre-stress has been applied, grout is in-~ected at the end 49 by the application of standard fittingsJ
utilizing technique and equipment common in the installation of rock-bolts. Grout is pumped into the central passage 57 o~
the rod 40 after this passage has been blocked at the opposite end 42 by the insertion o~ a small peg. The rod 40 associated with the ~irst sector of the wall is provided with the cross-drilled hole 58 ~ust inside the bearing plate 46, and the grout continues down through the passage 57 to this point.
From here it moves laterally outward into the space between the rod 40 and the shielding tube 44, and continues back to the opposite end of this tube where it appears around the ::

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:1~58386 opening in the bearing plate 47 traversed by the rod 40. The space around the rod at the bearing plate 46 must not provide a substantial opening for the emergence of grout. After this grout has set, this particular pour sector of wall may be con-sidered as complete.
The formation of the ad,jacent sector 20 of the wall begins with the erection and securing of the forms as shown in Figure 7, with the end 59 of the first sector defining one end of the space between the form panels, and ~hus replacing one of the end panels 39. When the cross-tie systems have been installed, the hollow reinforcing rod 59 is placed in position, and connected to the end 49 of the rod 40 by the coupling 60.
(Refer to Figure 5.) This can be accomplished either by threading the coupling 60 down onto the end 49 beyond its nor-mal position, and then back-rotating it onto the threaded end - of the rod 59, or by placing the coupling 60 initially in its correct axial position with respect to the end 49, and then rotating the rod 59 into the correct engagement with the coupling. In either case, care should be taken to assure that ` 20 the ends of the rod do not obstruct the lateral ports 61 and 62 of the coupling~ which are provided by a cross-drilled - hole. The shielding tube 63 is then slipped axially into the , position shown in Figure 5, in which the coupling 60 is cover-edJ and the end of the tube 63 is fairly well blocked by the presence of the washer 64 and the nut 56. The concrete is then poured to form the wall sector 20, as previously describ-ed, When this concrete has set, the end panel of the form system is removed, and a be~ring plate slipped over the pro-,~ecting end of the rod 59, in the position of the plate 47 in Figure 4. Note that a bearing plate at the opposite end of the rod is unnecessary. The ,jack is then applied to the rod . . , . . .

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: 1~)5~33~36 ~ .
59 to generate the necessary tension9 which is secured by running a nut down onto the ~earing plate as before, When the tensioning operation has been completed, g~ ut is inJected at the pro~ecting end of the rod 59 as it was in the end of the rod 49. In this case, howeverg the grout proceeds through the central passage to the coupling 609 where it emerges through the lateral ports 61 and 62 which ~-ta~e over the function o~ the cross drilled hole 58 in the rod 40. It is usually somewhat easier to manufacture the couplings 60 with the ports 61 and 62 than it is to provide the cross-drilling operation in the rein~orcing rods, and the latter is therefore usually restricted to the rods of the ini-tial sector, where passage out through a coupling is not pos-sible, In,~ection continues until the grout emerges at the bearlng plate ad~acent the end of the rod where the grout is being in~ected. When this grout sets, the second wall sector may be considered as completed. Tnis procedure is continued around until the next step is the formation of the closure sec-tor 14.
'~ 20 The forms are erected for the closure sector, with .
the ends of the space between the panels defined by the oppo-site ends of the last-formed sector and the first sector. In other words, the forms are simply clamped to the inner and outer faces of the sectors, without the necessity of end-plates ; 39. When the cross-tie systems have been installed, the rein-forcing bar for the closure sector is installed as previously described. The coupling at the closure end of the reinforcing rod for the closure sector is different from the couplings 5~.
The threaded end 43 of the rod of the closure sector is of op-posite hand to that of the threaded end 42 of the fir~t sector9 and the closure coupling 64 is thus able to function as a .. ~9_ .

, ~0583~6 turnbuckle, In the installation of the last rod9 it wl~l usually be advisable to f~rst engage the turnbuckle coupling 64 with at least three or four threads of engagement9 and then engage the opposite coupling by back rotation to a degree suf ~icient ~or the transfer of stresses. The space around the turnbuckle coupling 64 and the ends 42 and 43 of the reinforc-ing rods is "~oxed out" by conventional form procedures to de-fine an access opening that will remain free of the concrete poured to form the closure wall sectorO Conceivably, this 10 opening could have been formed in the initial sector. The concrete is then poured, and permitted to set. A wrench may then be applied to the turnbuckle coupling 64 to a predeter-mined degree of torque, resulting in the application of the necessary pre-stress. The tightening of the turnbuckle coupl-ing completes a peripherally-continuous tension system includ-; ing the rods and couplings, with the bearing plates now being of secondary importance. The presence of the grout prevents 7 the rods from shifting position to release ring tension. The turnbuckle coupling 64 is provided with a threaded lateral 20 opening centrally along its length for receiving the grout-injection ~itting 65. This fitting is installed after the turnbuekle has been appropriately tightened. The injection of grout at this point causes it to flow via the central passage of the rod 669 and back through the space between this rod and its shielding tube 67 via the lateral ports in the coupling at i the opposite end of the rod 66 from that shown in Figure 6, Figure 9 shows an alternative arrangement to that shown in Figure 6. The hollow rod 68 of a first wall sector terminates short of the end of the sectora and is connected to 30 the short length o~ solid rod 69 (threaded at both ends) by the coupling 70 similar to the coupling 60 in Figure 5. The ,, -10 , .

i058386 lateral ports 71 and 72 serve the function of the hole 58 in Figure 60 The Figure 9 arrangement removes the need for the inconvenient cross-drilling operation, and maintains the full strength of the rodO It may also be noted in passing that the first wall sector can be grouted by the use of a tube tra~ers-ing a convenient hole in one of the bearing plates, and com-munic~ting with the space between the rod and the shielding tube. This practice is comparable to so-called up-grouting of rock bolts extending upwardly from the point of emergenceO
This practice i6 not considered as efficient as either of the above procedures in the present caseO
The components of the form system can be stripped at r~ any convenient time, and the removal of the components defin-ing the boxed-out space shown in Fieure 6 will permit this space to be filled with either grout or concrete, as may be preferred, The sequence of wall sectors is then co=pletcd, . .

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of constructing a circular pre-stressed reinforced concrete wall, said method including placement of spaced form sections and pouring concrete between said spaced sections, wherein the improvement comprises: placing spaced form sections including end panels to form a first sector of a circular wall; placing a shielding tube around reinforcing rod means having threaded ends, and placing said tube and rod means peripherally in the space between said form sections, with said ends projecting from said end panels; pouring concrete between said form sections including submerging said tube and rod means, and permitting said concrete to set; exposing at least part of the ends of said set concrete, and applying bearing plates over said rod means ends, and nut means to said threaded ends; apply-ing tension to said rod means between said plates, and securing said nut means; placing form sections to form an adjacent sector of said wall with an end of said set concrete of said first sector defining one end of the space between said form sections, the opposite end of said space being defined by an end panel;
placing a shielding tube around reinforcing rod means having threaded ends, and placing said tube and rod means peripherally in the space between said form sections, and coupling one end of said rod means of said adjacent sector to said rod means of said first sector, the opposite end of said adjacent sector rod means projecting from said opposite end panel; pouring concrete in said space between said form sections submerging said tube, rod means and coupling, and permitting said latter concrete to set to form said adjacent sector; exposing at least part of the end of said concrete of said set concrete of said adjacent sector defined by said opposite end panel and applying a bearing plate over the end of said rod means projecting from said opposite end and nut means to said latter threaded end; applying tension to said lat-ter rod means; repeating the steps for constructing said adjacent sector to form successive adjacent sectors of said wall; placing form sections to form a closure sector of said wall, the space between said form sections being defined by the ends of the set concrete of said first sector and the last of said adjacent sec-tors; placing a shielding tube around reinforcing rod means hav-ing threaded ends, one of said threaded ends being of opposite hand to the threaded end of said rod means projecting from said first sector, placing said latter tube and rod means in said space between said form sections, coupling said latter rod means to the rod means projecting from said last adjacent sector, and applying a turnbuckle coupling connecting said rod means of said first sector and the rod means of said closure sector, and boxing out a space between said form sections surrounding said turn-buckle coupling, said space providing access from the exterior of said wall; pouring concrete between said form sections, in-cluding submerging said tube and rod means and permitting said concrete to set to form said closure sector; and tightening said turnbuckle coupling to apply tension to the rod means of said closure sector.

2. A method as defined in claim 1, wherein said rod means are hollow, and the rod means of said first sector is pro-visded with a transverse hole adjacent one end thereof, said couplings having lateral apertures, and additionally including the steps of injecting grout via said hollow rod means after the application of tension thereto, said grouting being injected in said rod means of said closure sector at said turnbuckle aperture, and in said rod means of said first sector at the end thereof opposite from said transverse hole.

3. A method as defined in claim 1, additionally in-cluding the steps of securing said form sections with tie systems traversing the space between said sections, and at least partially supporting said tubes and rod means on said tie systems.

4. A method as defined in claim 3, wherein said sys-tems have a central offset, and said tubes and rod means are en-gaged with said offsets to locate said rod means laterally in the space between said form sections.

5. A method as defined in claim 1, wherein the rod means of said adjacent and closure sectors are hollow, and the rod means of said first sector is hollow over a major portion of its length, and includes a coupling connecting said major portion to a solid rod threaded at its opposite ends, said couplings having lateral apertures, and additionally including the steps of injecting grout via at least certain of said rod means after the application of tension thereto, said grouting being injected in said rod means of said closure sector at said turnbuckle aperture.

6. A method as defined in claim 5, where said grout-ing is continued in each sector until grout appears at the end of said shielding tube adjacent the point of injection of said grout.

7. A method as defined in claim 6, additionally in-cluding the steps of stripping said form sections and end panels from set concrete as each of said sectors is constructed, and also stripping said boxed-out portion and filling said access space with cementitious material.