US2373072A - Rigid frame bridge and method of making the same - Google Patents

Description

April 3, 1945. E.- M. \INICHERT RIGI D FRAME BRIDGE AND METHODS OF MAKING THE SAME 4 Sheets-Sheet 1 Filed Aug. 19, 1941 INVENTOR April 3, 1945. E. M. WICHERT 2,373,072

RIGID FRAME BRIDGE AND METHODS OF MAKING THE SAME Filed Aug. 19, 1941 4 Sheets-Sheef 2 INVENTVOR Ernest M W2C]! eff kh m April 1945- E. M. WICHERT 2,373,072

RIGID FRAME BRIDGE AND METHODS 0F MAKING THESAME Filed Aug. 19, 1941 4. Sheets-Sheet 3 INVENTOR Ap 1945. E. M. WICHERT 2,373,072

RIGID FRAME BRIDGE AND METHODS OF MAKING THE SAME Filed Aug. 19, 1941 4 Sheets-Sheet 4 m WW4 mm mm i 23 ii "T22 lllmlllllllllllll ihn fiiiimll g 23 i; E Wm H IHlllllllilllllll @iMZMuIH W 25 i 25 .ii lilllilllllllllllllll :2 'ah wilmnll I MENTOR fr nestM VVz'dzert i gw v Patented Apr. 3, 1945 RIGID FRAME BRIDGE AND METHOD OF MAKING THE SAME Ernest M. Wichert, Pittsburgh, Pa.

Application August 19, 1941, Serial No. 407,437

11 Claims.

This invention relates to rigid frame bridges and the fabrication and construction thereof. It relates more particularly to rigid framebridges made up of fabricated structural shapes. (ordinarily of metal, which will be taken as an example material, although other materials may be employed) and reinforced cast' material such as concrete and to methods of making such bridges, whereby a rigid frame bridge for a given duty may be made at a great saving of materialand cost.

While the invention is of broad application it is perhaps most typically applied to continuous bridge structures with single openings such as are most frequently used for highway overpasses.

A rigid frame as herein referred to is a continuous structure of generally inverted U shape comprising opposed generally vertical supporting portions and a generally horizontal portion spanning the space between said generally vertical supporting portions and meeting each of said generally vertical supporting portions adjacent its upper end, applied external forces or loads producing vertical and horizontal reactions at the lower ends of said generally vertical supporting portions. either entirely of reinforced concrete or of a plurality of rigid frames of fabricated structural metal shapes in side-by-side parallel relationship with a concrete slab superimposed upon all of the frames, the generally vertical supporting portions being encased in concrete. When a bridge is made by erecting a plurality of rigid frames of fabricated structuralmetal shapes and superimposing a concrete slab thereupon, whether or not the generally vertical supporting portions are enclosed in concrete, each of the materials of the structure (metal and concrete) functions independently.

The present invention in certain of its aspects relates to composite rigid frame bridges made of fabricated structural shapes and reinforced concrete and in other of its aspects relates to any rigid frame bridge. Referring first to composite rigid frame bridges made for example, of fabricated structural metal'shapes and reinforced concrete, the metal portion of such a bridge is first erected. after which the reinforcin bars are set in place and the concrete is poured about the structural metal shapes and the reinforcing bars. In rigid frame bridges made of fabricated structural metal shapes with a superimposed reinforced concrete slab and concrete encased vertical support: as heretofore conventionally made the metal structure has had to sustain all the loads to which the bridge is subjected including the load of the superimposed concrete slab. The slab merely performs the function of spanning transversely the space between the metal rigid frames without participating in the primary longitudinal stresses. As a result an undesirably great quantity of metal has to be used in a rigid frame bridge'of this type.

In all conventional rigid frame bridges as hereill tofore made it has been impossible to calculate with any degree of accuracy the ambiguous stresses at the knees of the bridge where the gen erally vertical supporting portions meet the generally horizontal portion which spans the space between the generally vertical supporting portions. Consequently if it is to be made certain that the bridge will be strong enough to perform 7 the intended duty a very large factor of safety must be employed, resulting in use of a far greater quantity of material than is actually necessary. Moreover the employment of such a great Weight of material has necessitated large and expensive foundations.

I provide a rigid frame bridge and a method 25 of making the same which bring about a great Ordinarily rigid frame bridges are made saving in the amount of material used for construction of, a bridge for performing a given duty. In the construction of a composite rigid frame bridge made of fabricated structural metal shapes and reinforced concrete I take full advantage of the structural properties of the component materials so that they interact compositely as will presently be described. I also provide for constructing rigid frame bridges so that the ambiguous stresses at the knees are eliminated, making it possible to calculate the stresses in the structure with a relatively high degree of accuracy and to avoid the conventional practice of using a far greater amount of material than necessary to insure adequate strength. This results not only in a great saving of materials and cost in the bridge proper, but likewise reduces the cost of the foundation since the vertical and horizontal reactions, in a rigid frame bridge as herein described, are much smaller than in conventional rigid frame bridges designed for the same loading condition. I can effect economies of from 25 to 50% in the cost of rigid frame bridges designed for a given duty.

I have found that by bonding to each other the metal or like material and reinforced concrete in a rigid frame bridge to such an extent as to insure cooperative interaction thereof as a composite unit I can effect a substantial saving in t1. amount of material used both in the generall;

horizontal span portion and in the generally vertical supporting portions. Composite metal and concrete beams in which the metal and concrete are bonded together have heretofore been employed for floor joists. The stress distribution in a composite rigid frame bridge is such that, I have found, I can substantially reduce the weight not only of the span portion but of the supporting portions as well while providing for performance of a predetermined duty by the bridge.

A composite rigid frame bridge as herein re-' ferred to is a continuous structure made up of-a continuous fabricated skeleton of structural shapes and reinforced cast material, the structure being of generally inverted U shape comprising opposed generally vertical supporting portions and a generally horizontal portion spanning the space between said generally vertical supporting portions and meeting each of said generally vertical supporting portions adjacent its up per end, the structural shapes and reinforced cast material being bonded to each other to such an extent as to insure cooperative interaction thereof as a composite unit, applied external forces or loads producing vertical and horizontal reactions at the lower ends of said generally vertical supporting portions. The reinforced cast material forms what I call a continuous monolith," which term is used herein as a term of broad definition and not of limitation and contemplates a structure of reinforced cast material embodying discontinuities in the reinforced cast material (either in the cast material itself or in I the reinforcing therein or in both the cast material and the reinforcing therein) which do not destroy the strength of properties of the structure. Advantages of my invention may be obtained even though discontinuities in the structure somewhat impairior reduce its strength or properties.

The bonding together of the structural metal shapes and the reinforced cast portions of the rigid frame bridge may be effected in various ways. Preferably the metal span portion is provided with a series of projections which extend into and are embedded in the reinforced concrete. While similar provision may be made for bonding the reinforced concrete to the metal supporting portions I find that in most cases the bond of the concrete on the surface of the metal in the supporting portions or legs of the bridge is sufficient because the shearing stresses there tending to cause the concrete and metal surfacesthe concrete is cast thereagainst and the concrete in the legs will in most cases, as above indicated, bond to the surface of the metal sufficiently so that when the metal and concrete of the span portion are bonded together in'the manner above referred to the entire bridge including the metal span portion, the concrete span portion, the metal leg portions and the concrete leg portions will act cooperatively as one unit to carry loads applied to the bridge. The result, is that a composite rigid frame bridge employing predetermined quantities of metal and concrete will carry a much greater load than when the metal and concrete do not cooperatively interact as above explained. Consequently, if a bridge of given load bearing capacity is to be constructed the amount, and therefore the cost, of the materials employed may be greatly reduced relatively to the amount and cost of materials heretofore employed in metal and concrete rigid frame bridges of the same load bearing capacity. By making the metal and concrete rigid frame bridge composite as described above I can effect a saving in materials of from 25 to 30%.

The reference in the claims to the two components of the rigid frame bridge (skeleton and monolith) being effectively bonded to each other throughout the extent of both components contemplates that the bond between said components will remain unimpaired after the bridge has been subjected to its design load and also that the bond between said components may be discontinuous at portions of the bridge where discontinuities in the bond do not destroy the strength or properties of the structure. Advantages of my invention may be obtained even though discontinuities in the bond between the components of the rigid frame bridge somewhat impair or reduce its strength or properties. The materials of the respective components are utilized in such quantities and relative proportions that the bonding thereof together assures that when the bridge is subjected to its design load each of the materials is stressed substantially to itsv design capacity.

A characteristic of a rigid frame bridge is that when external forces or loads are applied thereto they produce vertical and horizontal reactions at the lower ends of the supporting portions or legs. This is because of the rigid construction at the knees producing continuity between the span portion and the leg portions. When, for example, a live load is superimposed upon the span portion of a rigid frame bridge the tendency of such loads is to cause the midsection of the span portion to bow downwardly. This in turn tends to cause the leg portions to bow out-. wardly and the lower ends of the leg portions thus produce horizontal as well as vertical reactions to the live load. The lower ends of the legs in a rigid frame bridge are mounted upon footings, rock foundations or other supports and restrained from lateral movement. This characteristic together with the rigidity at the knees brings aboutthe peculiar stress distribution in a rigid frame bridge which can be taken advantage of as described herein by making the bridge composite, that is, by bonding to each other the metal and reinforced concrete of the bridge to such an extent as to insure cooperative interaction thereof as a composite unit with the beneficial results explained above.

I have also discovered that a further important saving in material in a composite rigid frame bridge may be effected by controlling the stresses vin the metal portion of the bridge while the concrete is being cast. I preferably place the metal portion of the rigid frame bridge, both in the vide a temporary support or supports under the metal span portion and while such temporary support or supports is or are in place cast the concrete about the metal part of the frame. While it is desirable to exert substantial upward pressure against the metal span portion during casting of the concrete, due to the peculiar stress distribution in a rigid frame bridge I obtain definitely beneficial results by simply holding the metal span portion against sagging upon application of the concrete without actually pressing it 'upwardly prior to commencement of During of the concrete. In either case the temporary supmetal .of the bridge so that the entire structure as a unit acts as a continuous load supporting member.

I prefer, as above indicated, to positively press upwardly the metal span portion prior to pouring the concrete as this causes beneficial contrastresses in the composite rigid frame bridge after calculated with a relatively high degree of accuracy and the use of an unnecessary amount of material to compensate for inability to accurately calculate the stresses is obviated. A result similar to that obtained by the provision of the elements as above described may be obtained in other ways, as, for example, by cutting out or interrupting portions of. the metal structure at the knees. v

The concrete portion of a composite rigid frame bridge should also be partly interrupted at the knees since it acts compositely with the metal portion to transmit stresses. The concrete portion may have openings extending transversely of the bridge formed through it at the knees. or non-structural materials, such, for example, as cork, rubber, asphalt plank or the like, may be embedded in the concrete in predetermined positions at the knees to prevent transmission of stresses therethrough and insure concentration and localization of the stresses in the concrete similarly to the stress distribution in the metal portion of the bridge asabove explained.

the concrete has hardened and the temporary support has been removed so thatbefore any external load is applied to the composite rigid frame bridge the, generally horizontal portion and the generally vertical portions are stressed in a direction opposite that of the stresses produced by dead load, live loadsand other forces. The contrastressing may be, and preferably is, carried to the point where the structural metal frame is stressed to /1 of the elastic limit of the metal. I am thus enabled to effect a considerable saving in material over and above the saving effected by simply making therigid frame bridge composite so that the metal and concrete cooperatively interact as a composite unit. Theadditional saving in material brought about by contrastresslng brings the total saving due to my improved structure and method tobetween 30% and 50%. In other words, by employing the features above referred to I can build a rigid frame bridge for performing a predetermined duty at a saving of as much as 50%. r

The stress which is impressed in the metal rigid frame prior to concreting as described above is herein referred to as contrastress. The presence of the contrastressinthe finished bridge structure is evidenced by the fact that the load bearing capacity of such structure is greater than the load bearing capacity of an identical but not contrastressed'structure by the amount of contrastress impressed into the metal rigid frame.

I prefer to provide each of the supporting portions or legs of the metal part of the rigid-frame bridge with two elements or members which are spaced apart longitudinally of the frame at their upper ends and relatively close together at their lower ends'and to connect the upper end of each of such elements to the metal span portion and to interrupt the continuity of the skeleton be- I As above mentioned. the metal span portion of the rigid frame bridge is preferably provided with a series of projections which extend into and are embedded in the reinforced concrete. I p"eferably form the primary metal span portion with a generally horizontal flange at its topfor instance an I beam may be u ed. Instead of individually forming or apply ng the series of projections inor to the primary metal span portion I preferably apply thereto a sepa ate member embodying the projections. When the p:i-

mary metal span portion has a flange at its top I preferably superimpose the member having the projections upon such flange and fasten the same thereto. Preferably such applied member has a solid plate po'tlon connected to the flange w th projections extending therefrom. The p'ovision of such member materially strengthens the metal span portion aside from the effect of the projections since the result is in effect to thicken the upper flange of the metal span portion. This results in a further sav ng of material since the weight of the prlma=y metal span portion may be reduced.

Other details, objects and advantages of the invention will'become apparent as the following description of certain present preferred embodiments thereof and certain present preferred methods of practicing the same proceeds.

In the accompanying drawings I have shown certain present preferred embod ments of the invention and certain present preferred methodsof practicing the same, in which Figure l is a plan view of a rigid frame bridge;

Figure 2 is an elevational view of the bridge shown inFigure 1;

Figures 3 to 8, inclusive, are diagrammatic elevational sketches illustrating a method of erection of a contra-stressed composite rigid frame bridge;

Figures 9 t .12. inclusive, are sketches simi a to Figures 3 to 8, inclusive, illustrat ng another method of erection of a contrastressed composite rigid frame bridge;

Figure 13 is a fragmentary vertical transverse cross-sectional 1719'.) through the upper part of the metal span portion of a rigid frame bridge; and

Figure 14 is a plan view of a horizontal fragment of the structure shown in Figure 13.

Referring now more particularly to the drawings, the rigid frame bridge shown in Figures 1 and 2 illustrates the type of bridge employed for highway overpasses at grade separation intersections. One highway. designated H passes under the bridge and a second highway designated H passes over the bridge, vertical planes through the center lines of the two highways extending at approximately right angles to each other at the bridge. The bridge comprises a span portion designated generally by reference numeral 2 shown as comprising four transversely spaced I beams or girders 3. Each of tire I beams 3 is connected to a generally vertical metal supporting portion at each end of the bridge in such manner that the I beam and the generally vertical metal supporting portion act as a continuous unit. Each of the I beams 3 together with the gene:al!y vertical metal supporting portions at its ends and the reinforced ccnc ete applied thereto as herein described makes up a composite rigid frame so that the bridge shown in Figures 1 and 2 may be considered. as comprising four' such rigid framcs disposed in parallel relation. The frames are cross connected with cliaphragms in any preferred manner. The bridge roadway surface 4 is bounded by curbs 5 and railings 6. The generally vertical supporting portions of the rigid frames are not shown in Figures 1 and 2 since in the completed structure they are covered with facing concrete. 8. Their structure will be explained in connection with other figures of the drawings.

The structure of a preferred form of composite rigid frame bridge and the method of making or erecting the same may perhaps best be explained in connection with the diagrammatic sketches Figures 3 to 8, inclusive. In these sketches the deflections and distortions of the members are greatly exaggerated for the sake of illustration. In Figure 3 the surface of the ground is designated at 9. A pair of spaced footings III are provided to each of which is anchored V a generally vertical metal supporting portion or leg II destined to become an integral part of a rigid frame. Each of the metal supporting portions or legs I I has a pair of upwardly projecting members or elements I2 whose upper ends are spaced apart longitudinally of the frame. Each inner element I2 is shown in Figure 3 as being vertical and each outer element I2 is shown as being inclned to the vertical. However, the relaiive position and orientation of the elements may be widely varied.

While the supporting portions of the rigid frame are herein referred to as being generally vertical" this term is to be construed as one of bro-ad definition and not of limitation; The sup- .porting portions or legs of the rigid frame may I3 fastened to the footing by anchor bolts I4. Thus the two elements I2, the connection I3 and the footing It] at each end of the frame are essentiaily unitary. The inner elements I2 are shown as terminating at a different elevation than the outer elements I2. This is for the purpose of obtaining thedesired moment distribution in the finished structure as will presently appear.

The legs II having been erected as shown in Figure 3, the metal span portion of the frame is next set in place. The metal span portion is shown in Figure 4 and designated by reference numeral I5. As shown it is in the form of an I beam. It may be set in place upon the legs I I by a crane whOse work supporting chains are shown'at I6 in Figures 4. Since the outer elements I2 as shown in Figure 4 extend above the inner elements the metal span portion I5 rests upon the outer arms as shown, being initially spaced above the upper ends of the'inner arms. The ends of the metal span portion I5 are connected to the tops of the outer elements. Strap bolts I! are connected within the upper ends of the inner elements I2 and extend about the metal span portion I5 as shown in Figure 4. After the ends of the portion I5 have been fastened to the outer elements I2 the strap bolts I! are drawn up to deflect the'met-a-l span portion I5 as shown in Fig-v ure 5 and engage the bottom of the metal span portion I5 upon the tops of the inner elements I2.

After the legs II and metal span portion I5 have been erected and rigidly connected together as above described a jack I8 is placed on the ground under the centerof the metal span portion I5, as shown in Figure 6. A temporary supporting member I9 is set in place upon the jack I8 and extends-upwardly into engagement with the under surface of the metal span portion I5 at its longitudinal center. The jack I8 is then preferably operated to raise the member I9 and deflect the metal span portion I 5 as shown in Figure 6. Such deflection of the metal span portion I5 is accompanied by deflection of the legs I I, but such deflection of the legs is comparatively small and no attempt has been made to show it in the drawings. Impressing the upward deflection in the metal span portion I5 creates horizontal reactions which are deductible from the normal horizontal reactions.

Before completing the description of the method of erection of the composite rigid frame bridge illustrated in Figures 3 to 8, inclusive, reference is made to Figures 13 and 14 which are, respectively, a fragmentary vertical transverse crosssectional view through the upper part of the metal span portion I5 with a superimposed member designated by reference numeral 20 mounted thereon and a plan view of a horizontal fragment of such structure. The upper flange of the I beam constituting the metal span portion I5 is shown at 2|. The superimposed member 20 has a solid plate portion 22 which is preferably at least approximately as wide as the flange 2| and is shown as being somewhat wider. Connected with the solid plate portion 22 and preferably integral therewith and extending upwardly and laterally therefrom are opposed series of projections 23. The member 20 may be connected with stantial width of the solid plate portion 22 of the member 20 results in substantial strengthening of the metal span portion when the member 20 has been fastened to the portion I5. Also, the wide solid plate portion 22 provides a walkway upon the metal span portion l facilitating erection.

When the member 20 has been connected to the metal span portion IE it becomes in effect integral therewith and a part thereof. The projections 23 are for the purpose of extending into and being embedded in the reinforced cast material, as concrete, which is applied to the metal frame portionin making the composite rigid frame bridge.

The member 20 may be applied to the metal span portion l5 at any convenient time during fabrication or erection. Consequently, although the member 20 is not specifically shown in Figures 4, 5 and 6, which are mainly diagrammatic sketches, it is to be, understood that such member may be joined to the metal span portion l5 prior to setting of the same upon the legs I I.

Referring now to Figure 7, reinforcing bars and concrete forms are set in place and concrete 26 is poured about the reinforcing bars and the contrastressed metal frame structure so as to embed the projections 23. Such projections are shown purely diagrammatically in Figure '7. The concrete also preferably substantially embeds the legs II as shown in Figure 7. Care should be taken that the metal of the legs ll before pouring of the concrete should be clean and free from oil and grease. This is to insure a good bond between the metal of the legs and the concrete to resist shearing stresses which tend to cause the contacting surfaces of the metal and concrete to slide relatively to one another. The projections 23 of the member 20 which are embedded in the reinforced concrete resist the horizontal shearing forces between the concrete slab atop the metal frame and the metal of the span portion l5. Thus the metal frame comprising the legs II and the metal span portion I 5 and the reinforced concrete applied thereto interact cooperatively as a composite unit.

The elements I! may be encased separately, or, if the two elements l2 are formed into one encased unit, the concrete between the upper ends of the elements l2 should be interrupted by an actual opening or the insertion of a non-structural material like cork, rubber or asphalt plank 28, thus making the generally horizontal portion a 3-span continuous beam.

After the concrete has hardened the jack I8 is lowered and the temporary support I9 is re-' moved. The composite rigid frame bridge then assumes a shape such as indicated in Figure 8.

Figures 9, 10-, l1 and 12 correspond in a general way to Figures 3, 4, 5 and 6 to illustrate a modified method of erecting the composite rigid frame bridge. In Figure 9 the legs II are the same as in Figure 3 but a temporary support 21 is erected at thepoint where the center of the rigidframe bridge is to be. The support 21 is a predetermined distance higher than the elements l2. The metal span portion I5 is applied as shown in Figure 10 with its center resting upon the temporary support 21. The ends of the meal span portion l5 are drawn down and connected with the outer elements I! as shown in Figure 11, after which the metal span portion I5 is further drawn down by the strap bolts l1 upon the inner elements l2 as shown in Figure .12. The structure as shown in Figure 12 is the equivalent of that shown in Figure 6 although erected 'by a different procedure. The reinforced concrete is applied to the thus contrastressed structure as above described and after the conremoved I find the two erection methods above described to have particular advantages from the standpoint of facility of operation although the metal frame may be contrastressed or the stresses therein controlled in other ways.

In order to obtain maximum economy ranging from to %as above indicatedthe metal portion of the rigid frame bridge should be contrastressed as above explained. It is recommended in a composite rigid frame bridge comprising structural steel to oontrastress the steel to the extent of about three-fourths of the elastic limit of the steel. For instance for carbon steel with elastic limit of 36,000 pounds per sq. in. the steel should be contrastressed about 27,000 pounds per sq. in. Adding to this the customary 18,000 pounds per sq. in. working stress under normal loading, the steel would take care of-a total stress of 45,000 pounds per sq. in. withoutbeing stressed under normal loading to any greater extent than is the case in such structures wherein the concrete and structural steel work independently.

When for example the contrastressing method of Figures 3 to 8, inclusive, is tofbe employed the designing engineer may show on the construction drawings the desired elevations at the outer and inner elements of the generally vertical supporting portions of the metal frame structure and at the temporary support. These elevations are obtained from deflections calculated to produce the desired contrastress. If preferred the reaction at the temporary support which will produce the desired contrastress may be calculated and shown on the construction drawings and such 40 If a double check is desired it is possible to calculate the necessary deflection and reaction and then measure both the deflection ordinates and the magnitude of the reaction.

All exposed portions of the structural metal. frame .in my composite rigid frame bridge may be painted, encased in concrete or gunited, if desired.

Advantages of my composite rigid frame bridge are:

(l) Full utilizatlonof the structural properties of the component materials so that they function cooperatively throughout the structure, including the generally horizontal portion and the generally vertical supporting portions thereof, resulting in substantial saving of material in both the generally horizontal portion and the generally vertical supporting portions,

2) Obtaining of additional substantial savings by controlling the stresses in the structural metal portion of the composite rigid frame b'rid e, preferably by contrastressing, before concreting.

(3) Since the composite rigid frame bridge produces much smaller vertical and horizontal reactions than a conventional rigid frame bridge a further important saving is effected in the cost of foundations. This is particularly true when the structure is supported on piles.

(4) The composite rigid frame lbridge may be fabricated, constructed and erected in a much inated since the stresses must pass through the,

four points of connection between the generally horizontal portion and the generally vertical supporting portions.

(7) My rigid frame bridge obtains important economies over conventional rigid frame bridges even for span lengths less than one-half the span length which has heretofore been considered the lower limit from the economical or practical standpoint and for span lengths more than twice the span length which has heretofore been considered the upper limit from the economical or practical standpoint.

(8) My rigid frame bridge lends itself readily to esthetic treatment, a great variety of architectural effects being obtainable with little or no sacrifice in economy.

The feature of connecting the generally horizontal portion of a rigid frame bridge to the upper ends of the generally vertical supporting portions at four spaced points at the knees, thus making the generally horizontal portion virtually a three-span continuous beam, is broadly applicable to all rigid frame bridges.

It has been widely recognized by outstanding authorities that the actual stresses in conventional rigid frame bridges are at great variance with the expected stresses derived from presently used formulas, particularly the stresses in the corners or knees which by actual test have been found to vary from the calculated stresses-by more than 100%. I largely or entirely eliminate the ambiguous stresses at the knees of rigid frame bridges so that the stresses can be'calculated rather accurately and an important saving in material can be effected. By the employment of the structure as herein disclosed the generally horizontal portion of the rigid frame bridge is connected with the upper ends of the generally vertical supporting portions at four different points, making the generally horizontal portion of the bridge virtually a 3-span continuous beam.

The expression fabricated skeleton of struc-' tural shapes as used herein means a structure fabricated out of shapes such, for example, as I-beams, plates and angles, channels, flat bars, etc., commonly used for structural purposes, and excludes reinforcing bars, whether round, square, deformed, twisted or of any other shape, commonly used as reinforcements in concrete or similar cast material.

While I have shown and described certain present preferred embodiments of the invention and certain present preferred methods of practicing the same it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the. scope of the following claims.

I claim:

1. A composite rigid frame bridge comprising two components one of which comprises a continuous fabricated skeleton of structural shapes,

the skeleton being of generally inverted U shape and having opposed generally vertical supporting portions and a generally horizontal portion spanning the space between said generally vertical supporting portions and meeting each of said generally vertical supporting portions adjacent its upper end, the other of such components comprising a continuous monolith of reinforced cast material shaped to conform to said skeleton and effectively bonded to said skeleton throughout the extent of both components, said bonding together of said components assuring cooperative participation of both components in the distribution of all primary stresses, the material of the respective components being utilized in such quantities and relative proportions that said bonding assures that when the bridge is subjected to its design load each of said materials is stressed substantially to its design capacity, external vertical forces or loads applied to said composite rigid frame bridge producing vertical and horizontal reactions at the lower ends of said generally vertical supporting portions.

2. A composite rigid frame bridge comprising two components one of which comprises a continuous fabricated skeleton of structural shapes. the skeleton being of generally inverted U shape and having opposed generally vertical supporting portions and a generally horizontal portion spanning the space between said generally vertical supporting portion and meeting each of said generally vertical supporting portions adjacent its upper end. the other of such components comprising a continuous monolith of reinforced cast material shaped to conform to said skeleton and effectively bonded to said skeleton throughout the extent of both components, each of said generally vertical supporting portions having an inner and an outer element spaced apart longitudinally of the structure at their upper ends and relatively closetogether at their lower ends. each connected with said generally horizontal portion and each capable of sustaining both compressive and tensile forces, the continuity of the skeleton between the connections of said respective inner and outer elements with said generally horizontal portion being interrupted, external vertical forces or loads applied to said composite rigid frame bridge producing vertical and horizontal reactions at the lower ends of said generally vertical supporting portions.

3. A composite rigid frame bridge comprising two components one of which comprises a continuou fabricated skeleton of structural shapes, the skeleton being of generally inverted U shape and having opposed generally vertical supporting portions and a generally horizontal portion spanning the space between said generally vertical s pporting portions and meeting each of said generally vertical supporting portions adjacent its upper end, the other of such components comprising a continuous monolith ofreinforced cast material shaped to conform to said skeleton and effectively bonded to said skeleton throughout the extent of both components. all of said portions of said skeleton having impressed therein stresses opposed to stresses to which the structure is sublected in use. external vertical forces or loads applied to said composite rigid frame bridge producing vertical and horizontal reactions at the lower ends of said generally vertical supporting I portions.

of reinforced cast material of generally inverted U shape and having opposed generally vertical primary load supporting portions which are of greater dimension longitudinally of the bridge at their upper ends than at their lower ends and a generally horizontal portion spanning the space between said generally vertical supporting portions and meeting each of said generally vertical supporting portions adjacent its upper end, the reinforced cast material being partly interrupted in the general plane of the bridge at the knees where said generally horizontal portion meets each of said generally vertical supporting portions, external vertical forces or loads applied to said rigid frame bridge producing vertical and horizontal reactions at the lower ends of said generally vertical supporting portions.

5. A method of making a composite rigid frame bridge comprising assembling fabricated structural shapes into a continuous structure of generally inverted U shape having opposed generally vertical supporting portions and a generally.horizontal portion spanning the space between said generally vertical supporting portions and meeting each of said generally vertical supporting portions adjacent its upper end, applying means to place said structure under stress opposed to stress to which it is subjected in the composite rigid frame bridge when in use, while said structure is thus contrastressed applying to it reinforced cast material, effectively bonding said structure and the reinforced cast material so that they interact cooperatively to transmit stresses as a composite unit and thereafter rendering inoperative said means to place said structure under stress.

6. A method of making a composite rigid frame bridge comprising providing opposed generally vertical supporting portions each having a pair of generally upwardly extending elements spaced apart longitudinally of the frame at their upper ends and relatively close together at their lower ends and a generally horizontal portion spanning the space between said generally vertical supporting portions and connected to both elements of each thereof whereby to form a rigid structure of generally inverted U shape. applying means to place said structure under stress opposed to stress to which it is subjected in the composite rigid frame bridge when in use, 'while said structure is.

vertical supporting portions each having a pair of generally upwardly extending elements spaced apart longitudinally of the frame at their upper end and relatively close together at their lower ends and a. generally horizontal portion spanning the space between said generally vertical supporting portions and connected to both elements of each thereof whereby to form a rigid structure of generally inverted U shape, applying means to place said structure under stress opposed to stress to which it is subjected in the composite rigid frame when in use. while said structure is thus contrastressed applying to it reinforced cast material, effectively bonding said structure and the reinforced cast material so that they interact cooperatively to transmit stresses. as a composite unit, partly interrupting the reinforced cast material inthe general plane of the bridge at the knees where said generally horizontal portion meet; each of said generally vertical supporting portions and after said applying and bonding of the reinforced cast material rendering inoperative said means to place said structure under stress. I

8. A method of making a composite rigid frame bridge comprising assembling fabricated structural shape into a continuous structure of generally inverted U shape having opposed generally vertical supporting portions and a generally horizontal portion spanning the space between said generally vertical supporting portions and meeting each of said generally vertical supporting portions adjacent its upper end, placing a temporary support under and in supporting relationship to said generally horizontal portion, while said temporary support is thus positioned applying to said structure reinforced cast material, effectively bonding said structure and the reinforced cast material so that they interact cooperatively to transmit stresses as a composite unit, said temporary support developing in said structure stress opposed to stress to which it is subjected when in use, and after the cast materialhas hardened removing said temporary support.

9. A method of making a composite rigid frame bridge comprising assembling fabricated struc-- tural shapes into a continuous structure of gen-- erally inverted U shape having opposed generally vertical supporting portions and a generally horizontal portion Spanning the space between said generally vertical supporting portions and meeting each of said generally vertical supporting portions adjacent its upper end, placing a temporary support under and in supporting relationship to said generally horizontal portion, raisin said support and thereby placing said structure,

under stress opposed to stress to which it is sub- .iected in the composite rigid frame bridge when in use. while said structure is thus contrastressed applying to it reinforced cast material, effectively bonding said structure and the reinforced cast material so that they interact cooperatively to transmit stresses as a composite unit and after the cast material has hardened removing said temporary support.

10. A method of making a composite rigid frame bridge comprising assembling fabricated structural shapes into a continuous structure of generally inverted U shape having opposed generally vertical supporting portions and a generally horizontal portion spanning the space between said generally vertical supporting portions and meeting each of said generally vertical supporting portions adjacent its upper end, placing a temporary support under and in supporting relationship to said generally horizontal portion, while said temporary support is thus positioned applying to said structure reinforced cast material which hardens after application. effectively bonding said structure and the reinforced cast material so that they interact cooperatively to transmit stresses as a composite unit, aid temporary support inducing during hardening of the cast material stresses at and near the point of support which are opposed to stresses to which the structure is subjected when in use, and after the cast material has hardened removing said temporary support,

resulting in material decrease in the stresses,

throughout the finished structure when in use.

- 11. A composite rigid frame bridge comprising two components one of which comprises a con- 10 ing portions.

skeleton throughout the extent of both components, stresses opposed to stresses to which the bridge is subjected in use being impressed in the central part of said generallyhorizontal portion and in the upper parts of said generally vertical supporting portions, external vertical forces or loads applied to aid composite rigid frame bridge producing vertical and horizontal reactions at the lowerends of said generally vertical'support- ERNEST M. WICHERT.

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