Patent Publication Number: US-2007094960-A1

Title: Composite structural member with longitudinal structural haunch

Description:
This is a continuation of co-pending Application Ser. No. 10/001,055, filed Nov. 21, 2001. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to structural members, and more particularly, to a composite structural member having a concrete deck section with a longitudinal concrete structural haunch molded thereto to which is attached a steel structural member.  
      2. Description of the Prior Art  
      In the prior art there are a wide variety of structural members, both prefabricated and fabricated in place. These structural members include single element members, such as steel or concrete beams, and composite structural members with molded materials reinforced with, or supported by, metal bars or structural beams, girders or other elements. A typical molded material for the deck portions of these structures is concrete. To compensate for the deflection of the beams caused by their self-weight and the weight of the moldable material, a varying depth, longitudinal corrective haunch is used.  
      In forming structural members for spanning between two supports, it has often been found desirable to utilize a steel or wooden form beneath a molded concrete deck surface. First, the steel supports, such as wide flange girders, are erected. Then the forms are disposed around, and supported by, the girder or girders. The girder top elevations are then measured, and the varying depths for the longitudinal corrective haunch are computed and the necessary formwork built. Next, the concrete is poured into the mold such that the concrete fills the mold and extends over the girder. When the concrete is hardened, the forms are disassembled from around the girders, and the concrete then rests on the girders. In most instances, these wide flange girder-supported concrete structural members are formed in place. This is usually advantageous so the concrete surface can better fit into the finished structure because of the longitudinal corrective haunch. The concrete deck portion is attached to the beams by shear connectors which are molded into the concrete.  
      In such composite structures, the concrete deck portion must be sufficiently thick to support the load applied thereto. Such loads include the weight of the concrete itself and any external loads which are applied, such as traffic on a bridge.  
      The present invention utilizes a longitudinally extending structural haunch beneath a concrete deck portion, and a steel member is connected to the haunch. Preferably, the haunch has a substantially constant depth or height. The intent of the structural haunch is to increase the structural properties of the composite member, and more importantly, to reduce the steel beam weight required for a specified total structural depth or height, whereas in the prior art, the varied depth corrective haunch served only to compensate vertically for dead load deflections. As a result, for a structure having a given total depth or height and deck thickness, the steel beam weight in the present invention will be reduced as the haunch depth increases, or for a constant steel weight, the section properties increase as the haunch depth increases.  
      The present invention can be built in place or off-site with continuous shoring but includes an embodiment utilizing end supports and a single temporary support at or near the centerline of the span as disclosed in U.S. Pat. No. 5,144,710. In either case, the beam or beams can be elevated at the temporary supports during the casting process to compensate vertically for dead load deflections and do not require a variable depth haunch.  
     SUMMARY OF THE INVENTION  
      The present invention is a composite structural member with a molded longitudinal structural haunch. The invention is particularly well adapted for bridge structures, but is not intended to be so limited.  
      Generally, the invention can be described as a structural apparatus comprising a plurality of girders extending in a longitudinal direction and a molded deck portion disposed above the girders. The girders are spaced from one another in a transverse direction with respect to the girders. The molded section comprises a deck portion disposed at least partially above the girders and a plurality of longitudinally extending structural haunches extending downwardly from the deck portion. Each haunch is attached to a corresponding girder. The haunches preferably have a substantially constant depth or height.  
      Preferably, the deck portion and haunches are integrally molded and made of concrete.  
      Also, the girders are preferably supported at their ends and by a single temporary support at or near the centerline of the span or by multiple shores along the length of the girders.  
      The structure may further comprise a shear connector attached to each of the girders with the haunches molded around the shear connectors. If the haunches are greater than about 4 inches deep, a hat bar is preferably added adjacent to the shear connectors. An upper portion of the hat bars extends into, and is molded in, the deck portion.  
      The configuration of the present invention allows for the thickness of the deck portion and the total height of a haunch having a measurable height plus the girder height to be selected along with a girder weight, and that structure will have an increasing ultimate resisting moment as the haunch depth or height increases and the beam depth decreases the same amount. If the ultimate resisting moment is constant, then the girder weight will drop as the haunch depth increases and the beam depth decreases the same amount.  
      Numerous objects and advantages of the invention will become apparent as the following detailed description of the preferred embodiment is read in conjunction with the drawings which illustrate such embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a side elevation view of a prior art composite structural member having a molded deck portion, a variable depth corrective haunch and a steel supporting member.  
       FIG. 2  is a transverse cross section of the prior art structure taken along lines  2 - 2  in  FIG. 1 .  
       FIG. 3  is a side elevational view of a first embodiment of the composite structural member with longitudinally extending structural haunch of the present invention.  
       FIG. 4  is a transverse cross section taken along lines  4 - 4  in  FIG. 3 .  
       FIG. 5  shows a specific example of the prior art structure.  
       FIG. 6  shows a corresponding example of the first embodiment of the structural member of the present invention.  
       FIG. 7  is a transverse cross section of a second embodiment of the invention.  
       FIG. 8  shows an example of the second embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Referring to  FIGS. 1 and 2 , a prior art composite structure is generally designated by the numeral  10 . In the embodiment shown, prior art member  10  is a bridge structure adapted for extending between a pair of abutments or supports  12  and  14  disposed on opposite sides of whatever is to be bridged, such as a river (not shown).  
      Member  10  comprises a plurality of longitudinally extending girders  16  which generally have an I-beam configuration. A pair of girders  16  are shown, but more may be used. Girders  16  are positioned and supported on abutments  12  and  14  adjacent to longitudinally opposite ends  18  of the girders. As best seen in  FIG. 2 , each girder  16  has a vertically extending central portion  20  with horizontal upper and lower flange portions  22  and  24 .  
      Disposed above girders  16  is a molded deck portion  26  which is made of a moldable material such as concrete. Deck portion  26  has an upper surface  28 . A lower surface  30  of deck portion  26  is spaced above upper flange  22  of girder  16  by a downwardly extending variable depth corrective haunch  32 . Haunch  32  is an integral part of deck portion  26  and varies in thickness from a thinnest portion adjacent to ends  18  tapering to a thickest portion at the longitudinal center of girder  16 . Haunch  32  is a “variable depth corrective” haunch which is used to compensate for the downward deflection of girders  16  as a result of their own weight and the weight of deck portion  26 . The object of these corrective haunches is simply to keep upper surface  28  for the structure substantially close to the required grade line of the roadway even though girders  16  deflect somewhat.  
      Extending upwardly from the top of girders  16  are a plurality of shear connectors  34 . Shear connectors  34  are fixedly attached to the top of upper flanges  22  of girders  16 . Each shear connector  34  preferably has a shank portion  36  with an enlarged head portion  38  at the outer end thereof. Other kinds of connectors are also generally known. Deck portion  26  is formed and placed on girders  16  such that the molded material forming the deck portion is molded around shear connectors  34  thus forming a locking attachment between deck portion  26  and girders  16 . Once the molded material has hardened, a composite structure is formed.  
      Referring now to  FIGS. 3 and 4 , a first embodiment of the composite structural member with longitudinally extending structural haunch of the present invention is shown and generally designated by the numeral  50 . The illustrated embodiment shows structural member  50  as a bridge. Structural member  50  which may also be referred to as a structural apparatus  50  is also positioned on a pair of known supports or abutments  52  and  54  which are of a conventional type. During construction of structural member  50 , a single temporary support  53  with a jack  55  on it is used at the center of the span which allows for vertical adjustment for girder  56 . Alternatively, several temporary supports  53  may be used along the length of girder  56  to continuously shore and adjust the girder  56 .  
      Member  50  comprises a plurality of longitudinally extending girders  56  which are supported on abutments  52  and  54  adjacent to longitudinal ends  58  of the girders. Each girder  56  has a vertically extending central portion  60  with upper and lower horizontal flange portions  62  and  64  on opposite sides thereof.  
      Structural member  50  also comprises a molded section  66  made of a moldable material, such as concrete. Molded section  66  comprises an upper deck portion  68  with a plurality of longitudinally extending haunches  70  positioned on a corresponding upper flange  62  of each girder  56 .  
      Haunches  70  may be attached to girders  56  by a plurality of shear connectors  74  extending from upper flanges  62  in a manner similar to prior art shear connectors  32  previously described. An inverted hat bar  72  is preferably added at about the same spacing as the shear connectors  74  for depths or heights of haunches  70  greater than about 4 inches. Each hat bar  72  is molded in a corresponding haunch  70 . Upper, outwardly extending leg  76  on hat bars  72  extend into deck portion  68 . Thus a composite structure is formed.  
      Deck portion  68  of molded section  66  of structural member  50  is substantially the same thickness as deck portion  26  in corresponding prior art structural member  10  designed for the same application. Also, the overall height of structural member  50  from the top of deck  66  to the bottom of beams  56  is the same for the corresponding prior art structural member  10 .  
      Because of haunch  70 , it will be seen that the height of girder  56  is significantly smaller than girder  16  in prior art structural member  10 . The key aspect of the present invention is that structural member  50  is a composite unit which, for the same weight of girder, has a higher ultimate resisting moment than the corresponding prior structural member  10 , or, if structural members  50  and  10  have the same ultimate resisting moment, beam  56  will be lighter than beam  16 . Haunch  70  is a structural haunch which adds significant strength and other material properties to the entire structure unlike the corrective haunches used in the prior art. The latter, since their depth varies and depends on the existing camber of the girders, does not operate as a structural haunch. The advantage of the present invention is that it allows the use of a smaller girder  56  than prior art girder  16  in a structure designed for the same application and which will fit in the same space and location. The cost of constant depth, molded haunches  70  is considerably less than variable depth haunch  32 . Therefore, with the girder savings, there is a sizable savings using structural member  50  instead of prior art member  10 . Thus, the need for a strong, but less expensive structure, is met.  
     EXAMPLE 1  
      Referring to  FIGS. 5 and 6 , examples of a prior art structure and a corresponding example of the first embodiment of the present invention are shown. Prior art structural member  10 , as seen in  FIGS. 1 and 2 , has a thickness of 8 inches for deck portion  26  with girder  16  being a W30×124 I-beam (30-inch height, 124 pounds per foot) giving an overall height of 38.17 inches compared to structural member  50  of the present invention having a deck portion  66  thickness of 8 inches with a 6.11 inch haunch  70  mounted on a girder  56  which is a W24×104 I-beam, giving an overall height of 38.17 inches as well. This example confirms that for a constant total depth or height, deck thickness and required ultimate resisting moment, as the haunch depth or height increases the required beam weight decreases. Likewise, it confirms by logic, that if the beam weight is constant, the ultimate resisting moment increases as the haunch depth increases. 
 
 Ultimate Resisting Moment Calculation—Prior Art  
             C   =     T   =       A   b     ·     F   Y                     C   =     T   =         (   36.60   )     ⁢     (   2   )     ⁢     (   50   )       =     3   ,   660   ⁢           ⁢   k                     a   =       C   -       A   R     ·     F   Y           ϕ   ·     f   c   ′     ·     W   S                     a   =         (       3   ,   660     -     9   ⁢     (   0.2   )     ⁢     (   60   )         )       0.85   ⁢     (   4   )     ⁢     (   11.5   )     ⁢     (   12   )         =     7.570   ⁢           ⁢   inches                   MA   =     d   -       y   b     _     -     a   2                   MA   =       38.17   -     30.17   2     -     7.57   2       =       19.30   ⁢           ⁢   inches     =     1.608   ⁢           ⁢   feet                       M   U     =     C   ·   MA                   M   U     =       3   ,   660   ⁢     (   1.608   )       =     5   ,   886.5   ⁢           ⁢   ft   ⁢     -     ⁢   lb   ⁢     /     ⁢     in   2                   
 
 Ultimate Resisting Moment Calculation—Present Invention, First Embodiment  
             C   =     T   =       A   b     ·     F   Y                     C   =     T   =         (   30.90   )     ⁢     (   2   )     ⁢     (   50   )       =     3   ,   090   ⁢           ⁢   k                     a   =       C   -       A   R     ·     F   Y           ϕ   ·     f   c   ′     ·     W   S                     a   =         (       3   ,   090     -     9   ⁢     (   0.2   )     ⁢     (   60   )         )       0.85   ⁢     (   4   )     ⁢     (   11.5   )     ⁢     (   12   )         =     6.355   ⁢           ⁢   inches                   MA   =     d   -       y   b     _     -     a   2                   MA   =       38.17   -     24.06   2     -     6.355   2       =       22.9625   ⁢           ⁢   inches     =     1.914   ⁢           ⁢   feet                       M   U     =     C   ·   MA                   M   U     =       3   ,   090   ⁢     (   1.914   )       =     5   ,   912.8   ⁢           ⁢   ft   ⁢     -     ⁢   lb   ⁢     /     ⁢     in   2                   
 
 Where: 
 
      M U =Ultimate Resisting Moment  
      C=Compression Force part of Moment Couple  
      T=Tension Force part of Moment Couple  
      F Y =Steel Yield Stress (50 ksi for structural steel and 60 ksi for reinforcing steel)  
      MA=Moment Arm  
      a=Depth of Compression Block  
      d=Distance from bottom of beam to top of slab  
      A B =Area of beam  
      A R =Area of reinforcing steel in concrete slab  
      W S =Width of concrete slab  
      φ=Strength Reduction Factor  
      f c ′=28 Day Breaking Strength of Concrete  
       Y b   =Distance from bottom of flange to centroid of beam (  
         h   b     2         
 for W beams) 
 
      Referring now to  FIG. 7 , a second embodiment of the present invention is shown and generally designated by the numeral  80 . Structural member  80  which may also be referred to as a structural apparatus  80  is also positioned on a pair of known supports or abutments of conventional type in a manner similar to first embodiment apparatus  50 .  
      Member  80  comprises a plurality of longitudinally extending t-shaped beams or girders  82 . Each girder  82  has a vertical central web portion  84  extending upwardly from a horizontal flange portion  86 .  
      Structural member  80  also comprises a molded section  88  made of a moldable material, such as concrete. Molded section  88  comprises an upper deck portion  90  with a plurality of longitudinally extending haunches  92  positioned on flange portion  86  of a corresponding girder  82  such that web portion  84  thereof is molded in the haunch. A plurality of shear connectors  94  may be attached to each web portion  84  and also molded in haunch  92 .  
      A hat bar  96  is preferably added at about the same spacing as shear connectors  94  such that it straddles central web portion  84  of girder  82 . Such a hat bar  96  is preferably used for depths or heights of haunches  92  greater than about 4 inches. Each hat bar  96  is attached to a pair of longitudinal bars  98  by any means known in the art, such as welding or tying. Longitudinal bars  98  are disposed on opposite sides of the corresponding central web portion  84  of girder  82 . Bars  98  may be made of, for example, a section of conventional reinforcing rod, but the invention is not intended to be so limited.  
      Deck portion  90  of second embodiment structural member  80  is substantially the same thickness as deck portion  66  of the first embodiment member  50 . Also, the overall height of structural member  80  is substantially the same as first embodiment  50 .  
      As with first embodiment member  50 , the key aspect of second embodiment structural member  80  is that it is a composite unit which has a higher ultimate resisting moment than the corresponding prior structural member  10 . Haunch  92  is a structural haunch which adds significant strength and other material properties to the entire structure in a manner similar to haunch  70  in the first embodiment. The advantage of the second embodiment is that it allows the use of an even smaller and lighter girder which has significant cost savings associated with it.  
     EXAMPLE 2  
      Referring to  FIG. 8 , an example of the second embodiment of the present invention is shown. In this example, structural member  80  of the present invention has a deck portion  90  thickness of 8 inches with a 23.31 inch haunch  92  mounted on a girder  82  which is a WT6×76 T-shaped beam, giving an overall height of 38.17 inches. This second embodiment structure has an even higher ultimate resisting moment than the first embodiment shown in Example 1. 
 
 Ultimate Resisting Moment Calculation—Present Invention, Second Embodiment  
             C   =     T   =       A   b     ·     F   Y                     C   =     T   =         (   22.35   )     ⁢     (   2   )     ⁢     (   50   )       =     2   ,   235   ⁢           ⁢   k                     a   =       C   -       A   R     ·     F   Y           ϕ   ·     f   c   ′     ·     W   S                     a   =         (       2   ,   235     -     9   ⁢     (   0.2   )     ⁢     (   60   )         )       0.85   ⁢     (   4   )     ⁢     (   11.5   )     ⁢     (   12   )         =     4.533   ⁢           ⁢   inches                   MA   =     d   -       y   b     _     -     a   2                   MA   =       38.17   -   1.43   -     4.533   2       =       34.4735   ⁢           ⁢   inches     =     2.873   ⁢           ⁢   feet                       M   U     =     C   ·   MA                   M   U     =       2   ,   235   ⁢     (   2.873   )       =     6   ,   420   ⁢           ⁢   ft   ⁢     -     ⁢   lb   ⁢     /     ⁢     in   2                   
 
 Where: 
 
      M U =Ultimate Resisting Moment  
      C=Compression Force part of Moment Couple  
      T=Tension Force part of Moment Couple  
      F Y =Steel Yield Stress (50 ksi for structural steel and 60 ksi for reinforcing steel)  
      MA=Moment Arm  
      a=Depth of Compression Block  
      d=Distance from bottom of beam to top of slab  
      A B =Area of beam  
      A R =Area of reinforcing steel in concrete slab  
      W S =Width of concrete slab  
      φ=Strength Reduction Factor  
      f c ′=28 Day Breaking Strength of Concrete  
       Y b   =Distance from bottom of flange to centroid of beam (  
         h   b     2         
 for W beams) 
 
      It will be seen, therefore, that the composite structure with longitudinal structural haunch of the present invention is well adapted to carry out the ends and advantages mentioned as well as those inherent therein. While presently preferred embodiments of the apparatus have been described for the purposes of this disclosure, numerous changes in the arrangement and construction of parts may be made by those skilled in the art. All such changes are encompassed within the scope and spirit of the appended claims.