Connecting element for a composite beam

In a composite beam, a connecting element interconnects a concrete slab and a downwardly depending structural steel member. The connecting element is L-shaped having an elongated base member which is secured by one or more fastening elements to the structural steel member and an elongated anchor strap extending angularly from the base member and incorporated into the concrete slab. Supporting webs are secured to and extend between the base member and the anchor strap. The part of the base member encircling the openings through which the fastening elements pass is deformed to provide rounded recesses. The anchor strap can be made more rigid by forming a corrugation-like recess extending in the elongated direction of the strap. When a force is applied to the anchor strap causing it to move angularly away from the base member, the support webs cause the adjacent surfaces of the base member to act as deformation zones relieving the force on the connection between the base member and the structural steel member.

SUMMARY OF THE INVENTION 
The invention is directed to a connecting member for providing 
interconnection between the concrete slab portion and downwardly depending 
structural steel member of a composite beam and, more particularly, it is 
directed to a L-shaped member having a base member through which fastening 
elements are driven into the structural steel member and an anchor strap 
which extends substantially at right angles to the base member and is 
incorporated into the concrete slab. 
In composite beams, the upper chord of the beam is formed of a reinforced 
concrete slab and its lower chord consists of a structural steel member, 
that is, a structural steel section or a lattice truss or girder. A 
shear-resistant connection is required between the upper and lower chords 
so that the full moment of inertia of the beam can be utilized. 
To provide the desired interconnection, it has been known to secure 
connecting elements to the lower chord, that is, to the structural steel 
member which form an anchorage for the concrete slab to be cast onto the 
structural steel member. Since longitudinal changes occur between the 
upper and lower chords of the composite beam under load, the projections 
provided by the connecting elements must be able to absorb bending 
stresses to insure the bonding action. 
Further, it has been known to use rolled sections and round bolts welded to 
the structural steel member as connecting elements. While such elements 
are satisfactory in absorbing bending stresses, it is problematical 
whether an effective fastening to the steel section or lattice truss or 
girder is achieved. One of the primary problems involved is that the 
structural steel member is usually covered with an anticorrosive coat 
which has an adverse effect on the welded joint. Even timeconsuming 
cleaning of the welded joint does not substantially improve its quality, 
because the humid environment, e.g., the weather conditions, in which the 
welded joint must be produced has a negative effect on it. 
The use of bolts inserted by means of explosive charge driven setting guns 
into the structural steel member as connecting elements does not provide 
the desired effect, because the connecting elements, though simple to 
secure, do not withstand the bending stresses which occur. These elements 
break under the plastic bending deformations which develop and lead to a 
failure of the bond between the upper and lower chords of the composite 
beam. 
The object of the invention is to provide a connecting element for optimum 
interconnection which can withstand both the expected bending stresses and 
deformations. 
In accordance with the present invention, the problems experienced in the 
past are overcome by providing supporting webs attached between the base 
member and anchor strap of the connecting element with the webs located 
outside the area of the base member through which the fastening elements 
extend. The part of the base member extending between the supporting webs 
and the openings through which the fastening elements are secured, provide 
deformation zones for absorbing certain of the forces developed when there 
is differential movement between the different parts of the composite 
beam. 
In carrying out the invention, the connecting element is secured to the 
structural steel member by means of fastening elements driven into the 
steel member by an explosive charge driven setting gun. Openings are 
provided through the connecting element surrounded by recessed surfaces 
through which the fastening elements are anchored into the structural 
steel member. The fastening elements pass through the base member of the 
connecting element and an anchor strap extends angularly from the base 
member and is also connected to it by supporting webs, the anchor strap 
absorbs the shearing forces in the concrete slab. Due to the supporting 
webs, the anchor strap is not merely bent relative to the base member by 
the shearing forces, rather these forces are transmitted to the base 
member over the supporting webs. Depending upon the direction of the 
stress applied to the anchor strap, either the supporting webs or the base 
member absorb the stresses. If the stress is directed toward the base, the 
supporting webs are bent slightly inwardly or outwardly and permit a 
deflection of the anchor strap which can be controlled by corresponding 
dimensioning of the strap. If the stress is directed away from the base 
member, the supporting webs pull the base member slightly upwardly, 
however, due to the provision of the deformation zones in the base member 
this pulling action has no deleterious effect on the fastening elements. 
Further, the deflection of the anchor strap can be controlled by suitably 
dimensioning the deformation zone portions of the base member. 
If the deflection of the anchor strap can not be absorbed in the 
deformation zones of the base member, that is, by the combination of the 
base member and the supporting webs, no harmful stress is developed in the 
fastening elements, because the base member is lifted around one of its 
edges with the result that the fastening elements are stressed only in 
tension. As a result, shearing and bending stresses which are harmful to 
the fastening elements do not appear. To counteract the tensile stresses, 
the base member has specially shaped surfaces for the fastening elements 
with the surfaces spaced apart in the longitudinal direction of the base 
member where two or more fastening elements are used. 
To prevent the shearing forces which act directly on the base member from 
exerting any shearing stress on the fastening elements, the surfaces 
encircling the openings through which the fastening elements are driven, 
are preferably formed as frusto-conically shaped stampings or recesses 
with the concave surface of the recess facing toward the surface of the 
structural steel member into which the fastening element is inserted. 
These recesses provide cavities at the point at which the fastening 
elements are driven into the structural steel member into which material 
can flow from the steel member, which is displaced during the driving of 
the fastening element. In this way, a form-locked connection is obtained 
between the base member and the structural steel member which is capable 
of absorbing any shearing forces which develop. 
To provide sufficient rigidity in the elongated direction of the base 
member for absorbing tilting moments and for ensuring uniform distribution 
of the forces acting on the supporting webs, a supporting web is provided 
along each of the long sides of the base member with the web extending for 
the full length of the long side. The deformation zones in the base member 
can be controlled, depending on the distance between the location of the 
openings through which the fastening elements are inserted and the 
supporting webs extending along the edges of the base member. 
The rigidity of the anchor strap can be varied in accordance with the 
length over which the supporting webs are attached to the anchor strap. If 
the supporting webs are secured over the entire length of the anchor 
strap, the rigidity of the strap is so great that for practical purposes 
the entire deformation takes place in the base member. If the supporting 
webs extend only over a portion of the length of the anchor strap, a part 
of the bending stress can be absorbed by the strap itself and its rigidity 
can be increased by providing a longitudinally extending corrugation-like 
recess in the strap. 
Further, to increase the holding values of the anchor strap in the concrete 
slab, the end of the anchor strap away from the base member can be bent at 
substantially right angles. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its use, reference 
should be had to the accompanying drawing and descriptive matter in which 
there is illustrated and described a preferred embodiment of the invention 
.

DETAIL DESCRIPTION OF THE INVENTION 
In FIG. 1 a connecting element 1 is illustrated consisting of an elongated 
base member 2 and an elongated anchor strap 3 connected to one end of and 
extending upwardly from the base member. A supporting web 4, 5 extends 
along each of the long sides or edges of the base member and the webs 
extend upwardly and are secured to the edge surface of the anchor strap 
which faces toward the base member. While the supporting webs 4, 5 extend 
along the full length of the base member they only extend along a portion 
of the length of the anchor strap. At the upper end of the anchor strap 3 
spaced from its connection to the base member 2, there is a bent edge 6. 
Furthermore, a corrugation-like recess 9 is formed in the surface of the 
anchor strap and extends in the elongated direction, the recess affords 
additional rigidity to the strap. Spaced inwardly from the long and short 
sides or edges of the base member 2 are points of attachment 7 in the form 
of frusto-conically shaped stampings or recesses each with a centrally 
located hole 8. The fastening elements 12 are driven downwardly through 
the openings or holes 8 for securing the base member 2 to a structural 
steel member. 
In FIG. 2, the structural steel member is a steel section girder 11 with 
the connecting elements 1 anchored to the upper surface of its top flange. 
With the connecting elements secured in the manner represented in FIG. 2, 
a concrete slab, not shown, is poured over the steel section girder 11 
incorporating the connecting elements. 
In FIGS. 3 and 4 a connecting element 1, as illustrated in FIG. 1, is 
secured on the upper surface of a girder 13 by means of a fastening 
element 12. As is clearly shown in FIG. 3, a certain amount of the 
material 13a forming the girder 13 has been displaced as the fastening 
element 12 was driven in with the material flowing upwardly into the 
frusto-conical cavity formed by the point of attachment 7 of the base 
member. As can be seen in FIG. 3 the downwardly facing surfaces of the 
points of attachment 7 have a concave configuration while the upwardly 
facing surfaces have a convex configuration. The flow of the material 13a 
of the girder 13 into the recess provides a formlocking connection between 
the girder and the base member 2 of the connecting element 1. Washers 14 
are provided around the fastening elements in contact with the convex 
surfaces of the points of attachment so that the base member is prevented 
from being displaced over the heads of the fastening elements 12. 
To illustrate the deformation of the connecting element 1 under the 
application of stress, a force is shown applied in the direction of the 
arrow A, note FIG. 3, against the anchor strap 3 which is provided with 
the elongated corrugation-like recess 9 and the bent upper edge 6. Due to 
the application of the force, anchor strap 3 has undergone a slight 
deflection, increasing the angular relationship between the surfaces of 
the base member and the anchor strap and this deflection is transmitted to 
the supporting webs 4, 5. As can be seen in FIG. 4, the action of the 
anchor strap on the supporting webs, causes the webs to pull the elongated 
edges of the base member 2 slightly upwardly from the upper surface of the 
girder 13, note FIG. 4. Due to the deformation regions or zones 2a of the 
base member 2, the fastening elements securing the base member to the 
girder are only stressed to such an extent that the anchoring values are 
not reduced. By dimensioning the deformation zones 2a of the base member 2 
by the proper selection of the material thickness and the extent of the 
deformation zones, it is possible to control the deflection of the anchor 
strap 3. This control can be enhanced by the shape and material thickness 
of the supporting webs which must substantially counteract the bending 
forces in case stress is applied as shown particularly in FIG. 4. 
The deflection of the anchor strap 3 itself can be controlled by its 
rigidity, which can be influenced by the design of the elongated 
corrugation-like recess 9 and the extent of the height of the supporting 
webs 4 and 5 along the anchor strap. 
While a specific embodiment of the invention has been shown and described 
in detail to illustrate the application of the inventive principles, it 
will be understood that the invention may be embodied otherwise without 
departing from such principles.