US3237912A - Mold bed for stressed concrete structural members - Google Patents

Description

MOLD BED FOR STRESSED CONCRETE STRUCTURAL MEMBERS Filed June 23. 1960 4 Sheets-Sheet 1 A V ,r j A V "I 0 L2 /5 /0 /5 Z/ 52 Z5 INVENTOR 9 f 22 3 6'42! 1 Milky? ATTORNEYS March 1, 1966 c. H. HUTCHINGS MOLD BED FOR STRESSED CONCRETE STRUCTURAL MEMBERS Filed June 23, 1960 4 Sheets-Sheet 2 March 1, 1966 c H HUTCHlNGs 3,237,912

MOLD BED FOR STRESSED CONCRETE STRUCTURAL MEMBERS Filed June 23, 1960 4 Sheets-Sheet 5 ATTORNEYS March 1, 1966 c. H. HUTCHINGS 3,237,912

MOLD BED FOR STRESSED CONCRETE STRUCTURAL MEMBERS Filed June 25. 1960 4 Sheets-Sheet 4.

' z I I 'u/ 99 7&7 5/55 52 19 a; a5 99 I NV E N TOR Qrl/Zflzdah'rgs mdam ATTORNEYS United States Patent 3,237,912 MOLD BED FOR STRESSED CONCRETE STRUCTURAL MEMBERS Carl H. Hutchings, 864 9th Ave. SE, Rochester, Minn. Filed June 23, 1960, Ser. No. 38,290 2 Claims. (Cl. 249-125) This invention relates to stressed concrete structural elements and to the molds in which they are formed, and particularly to such elements and molds wherein the elements have more than one leg and the legs are angularly related to one another.

Stressed concrete structural members, both prest-ressed and post-tensioned, are coming into wide-spread use, and are being used in many instances where steel girders were employed before. These members have within them tensioned cables which put into compression those portions of the concrete element which otherwise would take an imposed load in tension. This overcomes the notorious weakness of concrete when subjected to loads which put the lower chord of a horizontal beam in tension.

It has been a comparatively simple matter to form stressed rectilinear members, as the stressing cables could be strung along a straight mold bed, tensioned and held in tension during the casting and curing of the concrete. If a post-tensioning operation was desired, the tubes or other conduits could be laid in the bed having cables through them, and after casting the cables could be tensioned. These operations are well known. However, these practices cannot be followed where the element is to be an angular one with the bend being in the direction in which stressing is desired. In other words, with known practices and mold beds, it has not been possible to lay and stress cables where the cables must follow a dog-leg path and be held in that position. Therefore, the use of stressing methods and the benefits of its use has been confined to straight beams, girders, etc.

A more specific object of the invention is to provide a mold bed having two angularly related sections in continuation of one another with means at the juncture of the two sections to support one or more stressing cables intermediate their ends, while the ends are held at the remote edges of the two sections of the bed.

Other objects of the invention will become apparent from the following description of several practical forms of the invention when taken in conjunction with the drawings which accompany, and form part of, this specification.

In the drawings:

FIGURE 1 is a plan view of a mold bed for casting stressed concrete structural members embodying the principles of the present invention;

FIGURE 2 is a longitudinal section through the mold bed, taken on the line 22 of FIGURE 1;

FIGURE 3 is an enlarged transverse section of the mold at the juncture of the two angularly related sections, and is taken on the line 3-3 of FIGURE 2;

FIGURE 4 is a detail section of the mold showing the manner in which bolt holes are formed in portions of the cast member;

FIGURE 5 illustrates the manner in which two of the prestressed concrete units cast in the mold may be used to form a roof span;

FIGURE 6 is an enlarged section taken on the line 66 of FIGURE 5 illustrating how the cast units are interconnected to form a continuous roof, or other surface;

FIGURE 7 is an enlarged section through one of the rafter forming flanges of the units shown in FIGURES 5 and 6 showing the disposition of the stressing cables at the angle of the structural element;

3,237,912 Patented Mar. 1, 1966 FIGURE 8 is a detail view illustrating the manner of joining abutting rafter sections at the ridge of the roof;

FIGURE 9 is a view similar to FIGURE 7 but showing a modified arrangement of stressing cables;

FIGURE 10 shows still another cable and reinforcing arrangement;

FIGURE 11 is a view similar to FIGURE 6 but illustrating the alternate use of rafter units and roof slabs to form a roof;

FIGURE 12 is a side view of another mold bed having means for stressing individually the cables of the respective leg sections of the elements cast;

FIGURE 13 is a partial view looking down on one side of the mold shown in FIGURE 12;

FIGURE 14 is a transverse section through the mold shown in FIGURES 12 and 13, and is taken on the line 1414 of FIGURE 13;

FIGURE 15 is a longitudinal section through a structural element cast in a mold such as shown in FIGURES 12 to 14;

FIGURE 16 is a top plan view of a mold bed for making stressed concrete trusses;

FIGURES 17 is a transverse section through the mold bed of FIGURE 16, taken on the line 17-17 of FIG- URE 16 and illustrating a cable positioning member to serve as direction changer for the cables used;

FIGURE 18 shows an arrangement where separate rafter members are used with roof slabs to complete a roof; and

FIGURE 19 is a perspective view of a mold bed for casting a single prestressed rafter of the type shown in FIGURE 18.

Referring first to FIGURES 1 to 4, there is shown a mold bed 1 having a bottom 2 which inclines from the ends of the bed to form two inclined surfaces 3 and 4 which meet at an intermediate point to form an apex line 5. The angular relation of the two surfaces to one another may vary in accordance with the shape of the structural element to be cast.

While the bed may be constructed to form but a single rafter, or similar member, as will be described, the bed shown in FIGURES 1 to 4 provides for the simultaneous casting of a plurality of channel shaped members combining a pair of spaced rafters, joists, or studs and an interconnecting web which forms a roof, floor or wall (see FIGURE 6). To accomplish this, the bed is provided with end walls 6 and 7 adjacent the free ends of the inclined bottom sections, and a plurality of spaced, parallel partitions 8 which rise vertically from the bottom and extend from one end wall to the other. The partitions are higher at the juncture of the two inclined sections of the bed than at the end walls so that the cast member will have its rafter members taper from the apex of the angle to the outer ends. A core 9 is attached to the bed bottom intermediate each pair of partitions. The cores have their sides inclined to provide tapering recesses 10 between the partitions and cores to form the rafter elements of the cast units. The tops of the cores are flat, and parallel to but spaced below the tops of the partitions whereby a web will be formed interconnecting the rafter elements when the space between adjacent partitions is filled with a dry mix concrete and struck off flush with the partition tops.

The present invention is concerned primarily with means on the bed for holding stressing cables at the apex of the angle so that stressing cables may be laid to follow the angular pattern of the bed, stressed in that pattern, and held stressed while the mold is filled with concrete and the concrete sets. In order to do this, aligned holes 11 are provided in the partitions and holes 1 in the cores to permit a rod 13 to be inserted in one side of the mold bed and continue across the entire bed. To facilitate insertion and removal of the rod 13, it may be made in sections threadedly coupled together, as at 14. As the rod is threaded through the various holes to traverse the bed, sleeves 15 are slipped over the rod to span the recesses 10. The sleeves will form permanent parts of the cast members and provide a perch around which the stressing cables pass.

In setting up the mold for casting a prestressed member, a section of the rod 13 will be threaded through the openings 11 and 12 While sleeves 15 .are positioned as required. When a first section of rod is inserted, another is threaded to it and the insertion continued until the entire mold has been spanned. Cables 16 are laid over the sleeves 15 and have their ends threaded through openings 17 and 18 in the end walls 6 and 7. These openings may be spaced vertically so that several cables may be used and they will lie in a flaring pattern from the sleeves 15 to the end walls of the mold. One end of the cables may be anchored to the adjacent end wall, and jacks connected to the other ends of the cables and, using the end wall as a jackhead, operated to place the cables under desired tension. If preferred, jacks may be applied to both ends of the cables. As the desired angle is maintained in the cables by the fixed sleeves, they may be tensioned as though they extended straight from end to end. The concrete may then be poured and allowed to set, after which the jacks and anchors may be removed, releasing the tension to the cast members. The rod 13 may then be removed, but the sleeves will remain embedded in the concrete. The prestressed cast members are then ready for removal from the mold bed.

The webs formed above the cores of the bed may be suitably reinforced if desired. Appropriate reinforcing members 19 may be positioned above the core and held off of the core by spacers 20.

It is usually desirable to provide bolt openings in the rafter elements for interconnecting the members. This can be done by using core pins 21 having studs 22 projecting from their ends. The partitions and center cores may be slotted as at 23 and 24 (see FIGURE 4) to receive the studs, and, if necessary, the slots may be closed by filler strips 25 to prevent concrete from entering the slots. When the cast member is removed from the mold the core pins will be carried with it. The pins may be withdrawn easily, leaving the bolt holes open.

Two of the rafter members formed in the mold bed are shown in erected position in FIGURE 5. It will be seen that each member 26 has a pair of angularly related legs 27 and 28, and that the two members can form a hip roof or an arch which can extend over a considerable span without bracing. Referring to FIGURE 6, the unit is seen to consist of a pair of spaced rafter members 29, which were formed in the recesses of the mold, and an interconnecting web 30, which serves as a roof slab and was formed in the space in the mold bed above the cores 9. This provides a structural member of channel shape in which at least the rafter portions are stressed by the cables 16. As many of these units as may be required are attached together, by bolts 31 through holes 32 in the rafter portions, to span the roof of the structure under construction. When the cast members are put together end to end, as in FIGURE 5, they will have their adjacent ends bolted together, as at 33, the opposite ends will be suitably attached to the tops of walls, a footing, etc.

In FIGURE 9 a cast member 34 is shown having a somewhat different arrangement of stressing cables. The unit contains a sleeve section 35 at the juncture of the angularly related arms 36 and 37, and a plurality of stressing cables 38 are trained over the sleeve and extend along the respective arms. Each of the cables has a bridge wire 39 connected to it across the sleeve 35. In other words, the bridge wires will have one end connected to a cable at a point on one side of the sleeve and to a point on the opposite side of the sleeve. A turnbuckle 40 is used in the center of each bridge wire to permit the wires to be shortened so that the cables can be pulled to desired locations. The bridge wires also serve to strengthen the unit at the angle by holding the material in the angle under compression to prevent cracking.

In FIGURE 10 the unit 41 is provided with a sleeve 42 to support a stressed cable 43 as in the forms previously described. In addition to the stressing cables, reinforcing 44 in any desired form may be imbedded in the unit to provide additional strength.

FIGURE 11 shows a slight modification of the units as previously described. Here, the channel shaped units 45 have stressing cables 46 in the rafter portions 47 and cables 48 in the webs 49. These units are recessed along their upper corners to provide seats 50 upon which the side edges of roof, or floor, slabs 51 may rest to form a continuous, flat surface. The slabs may be stressed by cables 52. Any suitable connector such as the angle and bolt arrangement 53 may be used to hold the elements together.

Referring now to FIGURES 12 to 15 inclusive, a slightly different type of mold bed and a modified structural unit are shown. The mold bed 54 is shown as having its angularly related legs 55 and 56 positioned at right angles to one another, but it is contemplated that other angles may be used. In this form of the bed, each leg is recessed to provide a cavity 57 to form a slab 58 of some width and extending the full length of the leg. The bottom of the bed is recessed still deeper along transversely spaced lines to provide cavities 59 in which the rafter portions 60 of the structural unit will be cast.

In the modified bed, the stressing cables 61 are not continuous, but extend only the length of the leg in which they are imbedded. In order to provide for tensioning the cables, the end walls 62 and 63 of the two legs of the bed are apertured, as at 64 and 65, and the cables are threaded through them and are provided with anchors 66 which will bear against the end walls as the cables are jacked. At the apex of the bed the side walls 67 and 68 are provided with upstanding pillow blocks 69 and 70. Jackheads 71 and 72 span the bed and seat upon the blocks 69 and 70. They may be bolted, or otherwise secured, to the blocks. Each jackhead is provided with openings 73 through which the cables are threaded. Jacks (not shown) can be attached to the cable ends and bear against the jackheads to tension the cables. When the proper tension is applied anchors 74 may be put on the cables and the jacks released to let the anchors seat on the jackheads to hold the cables tensioned. It will be evident that the two sides, or legs, of the cast member will be independently stressed in this arrangement, with each being stressed as if it were a separate structure. This form of the invention will have some advantages, particularly in casting, but it will not have the advantage of the continuous cables at the apex.

In FIGURES 16 and 17 a mold bed is shown in which trusses having stressed elements may be cast as a unitary member. The bed will be of desired shape to produce a preselected truss. In the bed shown the base 75 will have perimetric side walls which include a straight wall 76 along what will be the base of the truss, short end walls 77 and 78 at right angles to the wall 76 and walls 79 and 80 at the desired angle to the base wall to form the inclined chords of the truss. Suitable core members 81 will be positioned on the bottom of the bed to provide channels between the core members and the bed walls into which concrete may be poured to form the truss base 82, top chords 83 and 84, diagonal struts 85 and 86 di verging from the base center, and suitable additional brace members 87 and 88. The core members are also arranged to provide a central channel 89 extending at right angles from the base wall. Jackheads 90 are arranged adjacent the ends of the bed, and jackheads 91 are located adjacent the side walls 79 and 80 forming the top chords in alignment with the diagonal struts 85 and 86.

In using the bed shown in FIGURES 16 and 17, a bridge member 92 is placed upright in the central channel 89 with its ends spaced from the side walls of the bed. The bridge member is shown as a girder-like member but may have any shape which will withstand the strains which will be imposed upon it. When the bridge member is in place, cables 93 are placed around one end of it and carried along the channels which will form the top chords 83 and 84. The ends of the cables are threaded through holes 94 in the end walls 77 and 78 and holes 95 in the jackheads 90. Other cables 96 are stretched around the opposite end of the bridge member and along the channels forming the diverging struts 85 and 86. The cable ends project through holes 97 in walls 79 and 80 and holes 98 in jackheads 91. Additional cables 99 are strung along the base channel and have their ends extending through the end walls 77 and 78 and the jackheads 90. When the cables are in place they can be jacked to tension them. The stresses placed upon cables 93 and 96 will be equal, so that the bridge member will be held accurately in position. The bridge member will serve as a permanent member around which the cables turn, and one cable will offset the other. After all of the cables are stressed, the concrete will be put in the mold and allowed to set. The resulting truss will be monolithic and have all of its principal members stressed.

FIGURE 18 shows a slightly diflierent arrangement of rafters and roof slabs. In this embodiment, the rafters 100 are separate members and the roof slabs 101 seat upon them. The roof slabs will have stepped matching edges to provide stepped joints 102 at the centers of the rafters. The roof slabs may have angles 103 fixed to them, and these may be joined to the rafters and to each other by means of bolts 104.

FIGURE 19 shows a mold bed in which individual rafters, such as shown in FIGURE 18, may be cast. This includes a base 105, side walls 106, and end Walls 107. The end walls are apertured, as at 108, to permit threading of the cables. The side walls have co-axial openings 109 at the apex of the angle formed by the bed to receive a pin 110 on which a sleeve 111 will be mounted. This bed will be used similarly to the one first described, in that the cables will be threaded through the end walls and pass around the sleeve 111. The ables used will be tensioned and the mold filled with concrete. After setting, the cables will be released and the pin 110 withdrawn. The sleeve will remain in the rafter to form a permanent post around which the cables turn.

It will be noted that in all of the structures disclosed that the structural element contains at least one angle to provide two angularly related legs and that the legs of the member have stressing cables extending their full lengths.

While in the above several practical embodiments of the invention have been disclosed, it will be understood that the details of structure shown and described are merely by way of illustration and the invention may take other forms within the scope of the appended claims.

What is claimed is:

1. A mold bed for concrete trusses having stressing cables therein comprising, means defining a base mold cavity, means defining top chord cavities extending from the ends of the base cavity and joined at an apex, means defining a center strut cavity from the base cavity to the apex, and strut cavities diverging from the juncture of the center strut cavity to the top chord cavities, cable-supporting means positionable in the center strut cavity of sufiicient length to have its ends at the apex and in the base cavity, means for anchoring stressing cables at the ends of the base cavity, and means for anchoring stressing cables at the top chord cavities at the juncture of the diverging strut cavities and the top chord cavities, whereby stressing cables may be strung along the top chord cavities and around one end of the cable-supporting means and along the diverging strut cavities and around the other end of the cable-supporting means.

2. A mold bed for concrete trusses as claimed in claim 1 wherein the cable supporting means comprises a rectangular girder.

References Cited by the Examiner UNITED STATES PATENTS 903,909 11/1908 Steiner 25-118 1,630,839 5/1927 Fisher et al 25-118 2,413,990 1/1947 Muntz 251 18 2,435,998 2/ 1948 Cueni.

2,483,175 9/ 1949 Billner 251l8 2,689,999 9/1954 Petersen M 251 18 2,786,349 3/1957 Coff 128 2,787,042 4/1957 Breguet 251 18 2,921,354 1/1960 Pankey et al 25-418 3,055,146 9/1962 Lobato 25--1l8 FOREIGN PATENTS 838,421 5/ 1952 Germany.

144,193 6/1920 Great Britain.

630,329 10/1949 Great Britain.

OTHER REFERENCES Foundation wall, fig. lower left, Engineering News Record, June 18, 1959, p. 62.

J. SPENCER OVERHOLSER, Primary Examiner.

MICHAEL V. BRINDISI, ROBERT F. WHITE,

NEDWIN BERGER, Examiners.

Claims (1)

1. A MOLD BED FOR CONCRETE TRUSSES HAVING STRESSING CABLE THEREIN COMPRISING, MEANS DEFINING A BASE MOLD CAVITY, MEANS DEFINING TOP CHORD CAVITIES EXTENDING FROM THE ENDS OF THE BASE CAVITY AND JOINED AT AN APEX, MEANS DEFINING A CENTER STRUT CAVITY FROM THE BASE CAVITY OF THE APEX, AND STRUT CAVITIES DIVERGING FROM THE JUNCTURE OF THE CENTER STRUT CAVITY TO THE TOP CHORD CAVITIES, CABLE-SUPPORTING MEANS POSITIONABLE IN THE CENTER STRUT CAVITY OF SUFFICIENT LENGTH TO HAVE ITS ENDS AT THE APEX AND IN THE BASE CAVITY, MEANS FOR ANCHORING STRESSING CABLES AT THE ENDS OF THE BASE CAVITY, AND MEANS FOR ANCHORING STRESSING CABLES AT THE TOP CHORD CAVITIES AT JUNCTURE OF THE DISVERING STRUT CAVITIES AND THE TOP CHORD CAVITIES, WHEREBY STRESSING CABLES MAY BE STRUNG ALONG THE TOP CHORD CAVITIES AND AROUND ONE END OF THE CABLE-SUPPORTING MEANS AND ALONG THE DIVERGING STRUT CAVITIES AND AROUND THE OTHER END OF THE CABLE-SUPPORTING MEANS.

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