Abstract:
A beam assembly contains a substantially straight beam, which is arranged between two bearings and extends in a longitudinal direction. The beam assembly contains at least three segments, which are arranged one behind the other in the longitudinal direction and which are connected to each other by two head plate joints. The three segments include a middle segment and two outer segments. The bearings are prevented from moving in the longitudinal direction. The beam assembly permits controlled relief of thermal constraining forces while the load-transferring function is simultaneously maintained and while external dynamic forces are evenly distributed within the construction. Accordingly, this is achieved in that the middle segment has a middle segment head plate at each of the two ends of the middle segment and each of the two outer segments has an outer segment head plate at the end of the outer segment directed toward the middle segment.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This is a continuation application, under 35 U.S.C. §120, of copending international application No. PCT/EP2013/067676, filed Aug. 27, 2013, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German patent application No. DE 10 2012 215 151.6, filed Aug. 27, 2012; the prior applications are herewith incorporated by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The invention relates to a beam assembly having a generally rectilinear beam which is arranged between two bearings, extends along a longitudinal direction and is made up of at least three segments, that is to say a central segment and two outer segments, which are arranged one behind the other in the longitudinal direction and are connected to one another via two head-plate joints. The bearings are obstructed from displacement in the longitudinal direction. The invention also relates to a construction, in particular a steel construction, erected with such a beam assembly. 
         [0003]    It is often the case that steel beams cannot be produced, and transported to the use location, in one piece in the length which is necessary for the intended use purpose. Rather, prefabricated segments of smaller length are connected to one another on the building site. This often takes place using so-called head-plate or end-plate joints, in the case of which head plates which are formed, or joined, onto the ends of the actual beam profiles are screwed to one other. It is usually the case that such head plates are oriented perpendicularly to the longitudinal direction of the beam. 
         [0004]    Steel constructions in nuclear facilities, but also in other fields of use, in particular main beams which are subjected to high levels of loading, often have to be configured to withstand pronounced constraint effects resulting from the influences of temperature. On the other hand, they have to be configured, and mounted, such that all of the external loads, such as imposed loads and induced vibration, e.g. from earthquakes, can be dissipated as uniformly as possible. This is often incompatible with the desire for mounting which is as free from constraint as possible so as to compensate for thermal expansion. In general, the reduction in strength also involves a reduction in load-bearing capacity. 
         [0005]    It has therefore been the case in the past that thermal constraining forces have been taken into account predominantly by axial displace ability of the connection (constraint-free mounting) being realized using movable bearings or floating supporting bearings. In the case of external dynamic stressing, this type of connection lacks a sufficient amount of axial strength in order to distribute the loads homogeneously throughout the system. As a result, these constructions are unsatisfactory from an economic point of view. 
       SUMMARY OF THE INVENTION 
       [0006]    It is an object of the invention to specify an alternative beam assembly which allows a controlled reduction of thermal constraining forces while, at the same time, maintaining the load-dissipating function and with external forces being distributed uniformly within the construction. 
         [0007]    Accordingly, a beam assembly has a generally rectilinear beam disposed between two bearings and extends along a longitudinal direction. The rectilinear beam is made up of at least three segments, that is to say a central segment and two outer segments, which are arranged one behind the other in the longitudinal direction and are connected to one another via two head-plate joints. The bearings are obstructed from displacement in the longitudinal direction. The central segment has a central-segment head plate at each of its two ends and each of the two outer segments has an outer-segment head plate at its end directed toward the central segment. The respective outer-segment head plate is oriented in a complementary manner in relation to the central-segment head plate located opposite it, such that, together, they form a head-plate joint. The two head plates of each head-plate joint are connected to one another via connecting screws or connecting bolts which are guided through apertures in the head plates. The apertures in at least one of the head plates of each head-plate joint are configured in the form of slots. The two head-plate joints are inclined in opposite directions in relation to a plane normal to the longitudinal direction and the slots are arranged, and oriented, such that, in the case of thermal expansion or contraction of the segments, the central segment can be displaced laterally relative to the two outer segments, that is to say transversely to the longitudinal direction. 
         [0008]    The problem on which the invention is based is thus solved by a straightforward and cost-effective steel construction. All that is required is to have metal sheets, rolled profiles and screws in a slot connection; there is no need for any special components. The straightforward combination of the aforementioned components achieves constraint-reducing mounting under the action of temperature and, at the same time, maintains the load-bearing capacity for external loads. The axial expansion of the segments under thermal loading is compensated for by lateral yielding of the construction in a direction perpendicular to the longitudinal direction. The high constraining forces here overcome the static friction between the head plates, the static friction being realized by partial prestressing of the screw-connection. Lateral yielding of the central segment of the beam as a result of external static and/or dynamic loads, in contrast, is not possible, for design reasons. After the action of temperature has ceased, the segments contract again, and this results automatically in a laterally directed restoring force, which pushes the central segment back again into the starting position. 
         [0009]    The customary scenario will be one in which the segments of the beam, at normal ambient temperature, are in line/alignment, and in which the central segment pushes out sideways in the case of a significant increase in temperature. It is also possible, however, to have a system design which reacts correspondingly to decreases in temperature, and thus to contractions of the segments, and in which, to a certain extent, the displaced state is the basic state. If, in the basic state, the connecting screws or connecting bolts are located approximately in the center of the slots and the central segment, accordingly, has been pushed some way out of alignment, there is—depending on the kind of change in temperature—freedom of movement in both directions. 
         [0010]    It is advantageously the case that the inclination axis of the respective central-segment head plate—and, accordingly, also the inclination axis of the outer-segment head plate located opposite it in the head-plate joint—is oriented perpendicularly to the longitudinal direction. Furthermore, the inclination axes of the two central-segment head plates are oriented preferably parallel to one another, and the two central-segment head plates are preferably at an equal angle of inclination in relation to a plane normal to the longitudinal direction. This angle of inclination preferably ranges between 30° and 60° and is preferably 45°. This provides optimal assistance for the above described, automatic lateral displacement of the central segment as a result of thermal expansion of the segments, while the load-bearing capacity is maintained in the best manner possible. Relatively small deviations from the aforementioned details relating to direction and angle are nevertheless possible, for example as a result of slight twisting or torsion of the inclination axes or as a result of slightly different inclination of the head-plate joints. 
         [0011]    The slots acting, during lateral displacement of the central segment, and to a certain extent as guide rails for the connecting screws or connecting bolts of the respective head-plate joint are, of course, arranged, and oriented, in the corresponding head plate so as to provide for the displaceability. In expedient coordination with the above described geometry, the slots are oriented perpendicularly to the inclination axis of the respective central-segment head plate. 
         [0012]    In a preferred variant, the apertures in the central-segment head plates of a head-plate joint are configured in the form of slots and those in the outer-segment head plates are configured in the form of round holes. However, the reverse may also be the case. The connecting screws or connecting bolts here are guided/inserted expediently through the two apertures, that is to say through the two head plates of the head-plate joint, and secured from the outside by nuts and/or by screw heads which engage laterally over the peripheries of the apertures and rest on the head plates. In a possible modification, however, the connecting bolts may also be formed, or jointed (for example welded), onto at least one of the two head plates of a head-plate joint, inserted through the slots in the other head plate and secured from the outside by a nut. 
         [0013]    The slots are advantageously closed over the entire circumference, that is to say they are surrounded on all sides by the head plate and are not open for example in the direction of their outer surrounding. This limits the lateral displaceability of the central segment, and the central segment cannot fall laterally out of the beam. The maximum lateral displacement path of the central segment here lies within a design-compatible range. This ensures that the stability and load-bearing capacity of the beam are not lowered below a critical value. 
         [0014]    As already indicated the two head plates of a head-plate joint, during installation of the beam, are expediently braced or clamped against one another by releasable force-fitting connecting elements. For this purpose, use is made preferably of connecting bolts, in particular in the form of threaded bolts and/or in the form of cap screws or similar elements which are suitable for forming a screw-connection and have an essentially cylindrical stem which is secured customarily by associated nuts—possibly in combination with washers—or, as an alternative, by a dowel pin or the like and are subjected to tensile loading in the process. The two head plates are advantageously braced against one another so as to maintain, for example by appropriately firm tightening of the screws or of the nuts, the lateral displaceability of the central segment under the action of temperature (partial prestressing). 
         [0015]    In an expedient configuration, the beam is a steel beam, of which the individual segments are produced for example in the form of rolled profiles with head plates formed or joined, in particular welded, onto the end sides. As an alternative, it is also possible for the beam, or at least individual constituent parts thereof, to be produced from other materials, in particular from modern composite materials or the like. The individual beam segments, for their part, may be segmented in a customary manner, that is to say may be made up of originally separate sub-segments—for example with head-plate joints oriented perpendicularly to the longitudinal direction. It is also possible, in principle, to produce a beam which is made up, for example, of five segments and in which the second and fourth segments, as seen in the longitudinal direction, are designed for lateral displace ability in the manner described. Since, in this case, the combination of the first to third segments or the combination of the third to fifth segments may be considered to be a single segment, such a configuration is also covered by the wording of the claims. 
         [0016]    The head plates have preferably planar contact surfaces which allow tilt-resistant and torsionally rigid support in relation to their respective connecting partner, and also connection thereto, and which form sliding surfaces when the central segment of the beam is displaced laterally. In an alternative configuration, the contact surfaces may also have a stepped formation oriented along the displacement direction, and this creates a guide rail for the lateral displacement. In particular in the case of solid beams, or in the case of closed box profiles, the head plates may have flanges projecting laterally beyond the beam profiles, in order to facilitate the fitting of the connecting elements and access thereto for installation and maintenance purposes. As an alternative, in the case of closed and/or solid profiles, it is also possible for appropriate access openings to be introduced into the material. 
         [0017]    The beam assembly described is expediently a constituent part of a steel construction or of a structure, in particular of a steel platform or of a supporting frame, for example in a nuclear facility or in some other industrial plant. 
         [0018]    The concept according to the invention is suitable for new steel constructions and also for upgrading existing ones. The geometry of the structure here is not influenced in practical terms, and the beam connection can be largely prefabricated in the workshop. 
         [0019]    The advantages achieved by the invention reside, in particular, in that the segmented configuration of a beam of which the individual segments are connected to one another by partially prestressed head-plate joints with slot/screw-connections and with a specific connection geometry makes it possible for a controlled reduction in stressing caused by thermal constraint effects to be realized by lateral yielding, with the bending load-bearing capacity for external loads being simultaneously maintained, in constructions which are subjected to thermal, static and dynamic loading, to be precise using straightforward steel-construction principles without any special components. 
         [0020]    This results in a) a flexurally rigid, load-bearing connection in the operating or installation position, b) an additional design option for reducing constraint-induced stressing in steel constructions, c) a more cost-effective design than has been the case hitherto, on account of the amount of material used in the construction as a whole being reduced, and d) a single construction combining expansion under thermal stressing and the load-bearing capacity for external loads being maintained at the same time. 
         [0021]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0022]    Although the invention is illustrated and described herein as embodied in a beam assembly and a construction erected therewith, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0023]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0024]      FIG. 1  is a diagrammatic, longitudinal sectional view through a first configuration of a beam according to the invention at ambient temperature; 
           [0025]      FIG. 2  is a sectional view through the beam according to  FIG. 1  taken along the section line designated therein by II-II; 
           [0026]      FIG. 3  is a sectional view through the beam according to  FIG. 1  taken along the section line designated therein by III-III; 
           [0027]      FIG. 4  is a longitudinal sectional view through the beam according to  FIG. 1  in a second configuration, at increased temperature; and 
           [0028]      FIG. 5  is a sectional view through the beam according to  FIG. 4  taken along the section line designated therein by V-V. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    The same parts are provided with the same designations in all of the figures. Referring now to the figures of the drawings in detail and first, particularly to  FIG. 1  thereof, there is shown a beam  2  illustrated in a longitudinal section at ambient temperature (ΔT=0), is configured in the form of an elongate, rectilinear steel beam which, in the example here, is clamped in vertically between an upper bearing  4  and a lower bearing  6 . The overall length of the beam  2  in a longitudinal direction  8  is designated by L. The two bearings  4 ,  6  are obstructed from displacement in the longitudinal direction  8 , for example by a surrounding construction or anchoring means. In particular, the bearings may be fixed bearings. In other designs, it would also be possible for the beam  2  to be arranged horizontally or obliquely. 
         [0030]    The beam  2  is constructed from three originally separate segments  10 ,  12 ,  14 , that is to say a central segment  10 , an upper outer segment  12  and a lower outer segment  14 , which are prefabricated in a workshop and put together, and connected to one another, at the construction site. Each of the three segments  10 ,  12 ,  14  has a beam element  16  formed for example from a symmetrical I-beam profile. The profile of the beam  2  is constant essentially over the entire length of extent. Of course, it is also possible to use other profiles. If appropriate, the three segments  10 ,  12 ,  14  may also have different profiles and/or profiles which vary in the longitudinal direction. 
         [0031]    In order to create the connections, the central segment  10  is provided, at both ends, with a respective flat central-segment head plate  18 , which is welded onto the beam element  16 . The two outer segments  12 ,  14 , of corresponding design, have an outer-segment head plate  20  in each case at their end which is directed toward the central segment  10 , this giving rise, in the definitively installed state, to two head-plate joints  22 . In each of the two head-plate joints  22 , the outwardly directed contact surfaces of the connecting partners involved rest flatly on one another over the entire lateral extent. 
         [0032]    So that, while maintaining a high bending load-bearing capacity, the beam  2  is mounted between the two bearings  4 ,  6  in a manner which is as free from constraint as possible, the head-plate joints  22  are configured with a specific inclination. To be precise, the two central-segment head plates  18  are arranged in a state in which they are inclined/tilted in opposite directions in relation to the horizontal about an imaginary inclination axis  24  in each case. The two inclination axes  24  run parallel to one another and perpendicularly to the longitudinal direction  8 , here, in  FIG. 1 , perpendicularly to the image plane and through the axis of symmetry of the beam profile. Each of the two central-segment head plates  18  assumes an angle of inclination α of 45° in relation to the horizontal (and thus also in relation to the vertical) or, expressed in more general terms, in relation to a plane normal to the longitudinal direction  8 . As a result of being inclined in opposite directions, in the section view according to  FIG. 1  the two central-segment head plates  18  would form a V lying on its side if they were extended appropriately to the left. The outer-segment head plates  20  are inclined in a coordinated, complementary manner. For this purpose, the beam elements  16  of the three segments  10 ,  12 ,  14  are cut in an appropriately inclined manner (in a manner similar to miter-cut corner connections) at the end connections, and the head plates  18 ,  20  are welded onto the end edges of the beam elements  16 . Accordingly, in  FIG. 1 , the central segment  10  has the outline of an isosceles, symmetrical trapezoid. 
         [0033]    The head plates  18 ,  20 , which are located opposite one another in the respective head-plate joint  22 , are connected on a permanent basis by screw-connection. For this purpose, the head plates  18 ,  20  according to the illustration in  FIGS. 2 and 3  are provided with suitably positioned apertures  26  or bores, through which threaded bolts  28 , preferably with two oppositely directed threaded portions in the two end regions, are inserted and are secured from both sides by screwed-on nuts  30 , which engage laterally over the apertures and rest on the head plates. As an alternative, it is also possible to use cap screws, each secured by a single nut. 
         [0034]    In specific terms, in the present exemplary embodiment, the apertures  26  in the respective outer-segment head plate  20  are configured in the form of round holes  32  with the diameter which is slightly larger than the diameter of the threaded bolt  28 , or screw stem, which is to be inserted through in each case ( FIG. 2 ). The apertures  26  in the respective central-segment head plate  18  are configured in the form of slots  34 , of which the width is likewise slightly larger than the diameter of the threaded bolt  28 , or screw stem, which is to be inserted through in each case, the length of the bolt or screw stem nevertheless being considerably larger than the width ( FIG. 3 ). 
         [0035]    In the definitively installed position, the longitudinal direction  36  of the slots  34  in the respective central-segment head plate  18  runs perpendicularly to the inclination axis  24  of the central-segment head plate, in this case parallel to the image plane of  FIG. 1 . The slots  34  are positioned in relation to the round holes  32  such that, in the case of the configuration which is illustrated in  FIG. 1 , and in which the three segments  10 ,  12 ,  14  are located in line/alignment, as seen in the longitudinal direction  8 , the threaded bolts  28  or screw stems tend to be positioned at that end of the slots  34  which is directed toward the long base side of the trapezoid, that is to say at the right-hand end in  FIG. 2 . 
         [0036]    As a result of the construction described, in the case of an increase in temperature (ΔT&gt;0), the accompanying attempts, on the part of the three segments  10 ,  12 ,  14  to be expanded in the longitudinal direction  8  and the fact that the two outer segments  12 ,  14  are clamped in firmly between the two bearings  4 ,  6  give rise to the central segment  10  being subjected to a resultant force in a direction transverse to the longitudinal direction  8 , in the direction of the long base side of the trapezoid—that is to say to the right in this case. 
         [0037]    In the case of the prestressing of the screw-connections being set at an appropriate level, this means that, when a minimum temperature difference ΔT in relation to the initial state on which  FIG. 1  is based, the minimum temperature difference being necessary to overcome the static friction between the head plates  18 ,  20  of the two head-plate joints  22 , is exceeded, the central segment  10  is displaced in the aforementioned direction, that is to say it yields laterally. The touching contact surfaces of the head plates  18 ,  20  here, on the one hand, give rise to force deflection in a direction transverse to the longitudinal direction  8  and, on the other hand, form mutual sliding surfaces. The slots  34  in the central-segment head plates  18  provide for the necessary degree of translator-movement freedom and, in addition, form a guide rail for the threaded bolts  28  or screw stems which are being displaced relative to them in the direction of the free space depicted in  FIG. 2 , that is to say in the left in this case. 
         [0038]    The higher the temperature difference ΔT, the greater the lateral displaceability of the central segment. The displacement distance is limited by the finite longitudinal extent of the slots  34 , which are closed at both ends. 
         [0039]    The state of maximum displacement is illustrated in  FIG. 4  (ΔT&gt;&gt;0). The threaded bolts  28  or screw stem, in this case, are located at those ends of the slots  34  which are directed toward the short base side of the trapezoid, wherein the remaining material crosspieces between the slots  34  and the outer surround of the central-segment head plates  18  act as end stops ( FIG. 5 ). The sum of the overall length of the three segments  10 ,  12 ,  14 , measured in each case along the axis of symmetry of the beam profile, has increased from originally L1+L2+L3 to what is now (L1+ΔL1)+(L2+ΔL2)+(L3+ΔL3). The difference between these two length dimensions is designated in  FIG. 4  by f a . However, the lateral displacement of the central segment  10  by the distance f a  causes the overall length L of the beam  2  to remain the same. In the present, special case, L1=L3 and it is therefore the case, at least approximately, that ΔL1=ΔL3, but this symmetry is not generally imperative. 
         [0040]    It is only if the temperature were to increase further that the beam  2  would be subjected to a significant level of constraint, which could result in corresponding pinching compression or bending deformation of the beam  2  or in the bearings  4 ,  6  loosening or in the threaded bolts  28  or screw stems shearing. 
         [0041]    The displacement of the central segment  10  is reversible. It is also possible for the configuration illustrated in  FIG. 4  to be used as an initial state for a subsequent decrease in temperature and corresponding contraction of the segments  10 ,  12 ,  14  which then results in the configuration illustrated in  FIG. 1 . 
         [0042]    The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:
     2  Beam     4  Upper bearing     6  Lower bearing     8  Longitudinal direction (of the beam  2 )     10  Central segment     12  Upper outer segment     14  Lower outer segment     16  Beam element     18  Central-segment head plate     20  Outer-segment head plate     22  Head-plate joint     24  Inclination axis     26  Aperture     28  Threaded bolt     30  Nut     32  Round hole     34  Slot     36  Longitudinal direction (of the slots  34 )   Δ Angle of inclination