Buildup composite beam structure

This invention relates to the construction of a composite beam structure in a composite steel deck floor system. A T-shaped beam is welded through the valleys of the steel deck onto the top flange of the supporting beam. After concrete pouring, the T-beam is buried within the concrete slab to act as the shear transferring device to achieve the composite beam action. The T-beam also serves to strengthen the supporting beam in resisting the load during the concreting operation and to facilitate the placement of the concrete shrinkage control wire mesh.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the construction of composite beams in a 
composite steel deck floor system. 
2. Description of the Prior Art 
The utilization of composite action between a concrete floor slab and the 
floor supporting beam is well known in the art. To achieve the composite 
beam action, it is required to install a shear transferring device such 
that a compressive bending force can be developed within the cured 
concrete slab. This type of design is known as a composite beam design. If 
there is no shear transferring device provided, the floor supporting beam 
must be designed to resist the total imposed load and is known as a 
non-composite beam design. It is well known in the art that the beam 
strength and stiffness are greatly increased in a composite beam design as 
compared to a non-composite beam design. Therefore, the composite beam 
design has been continuously gaining popularity in the building industry. 
Shear studs are commonly used in the composite beam design and are 
installed in the following procedures. The first step is to secure the 
steel decks to the supporting beams. The second step is to weld the shear 
studs at the valleys of the steel deck profile through the steel deck onto 
the top flange of the supporting beam. The third step is to place the 
concrete shrinkage control wire mesh at 1 inch (25.4 mm) below the 
finished concrete slab. The fourth step is to pour and to finish the 
concrete slab. 
In the selection of the beam size in a composite beam design, the following 
two factors must be considered. First, the non-composite strength of the 
beam must be adequate to resist the dead weight of the floor and the 
construction loads. Second, upon curing of the floor slab, the composite 
strength of the composite beam must be adequate to resist the total 
imposed loads including the dead load and the design live load on the 
floor. 
The drawbacks of the prior art composite beam design include the following 
items. 
1. In most cases, the beam size is governed by the required non-composite 
beam strength during the erection period. 
2. The efficiency of the shear stud is affected by the concrete rib 
geometry formed by the valleys of the steel deck profile. The wider the 
concrete rib, the higher the stud efficiency. The deeper the steel deck, 
the lower the stud efficiency. In some cases, only a partial composite 
design can be achieved due to a reduction of the stud efficiency induced 
by the steel deck profile or the available rib locations for stud welding. 
3. The concrete shrinkage control mesh is supported by spaced apart plastic 
chairs. The plastic chairs can be easily knocked down during the 
concreting operation resulting in ineffective concrete shrinkage control 
due to mislocated wire mesh. 
SUMMARY OF THE INVENTION 
The objectives of this invention include the following items. 
1. To provide a shear transferring device such that the efficiency of shear 
transfer is not affected by the steel deck profile. 
2. To utilize the shear transferring device to strengthen the noncomposite 
strength of the beam such that the beam size can be reduced to effectively 
reduce the building height. 
3. To utilize the shear transferring device to secure the concrete 
shrinkage control mesh without using plastic supporting chairs. 
4. To utilize the shear transferring device to strengthen the inplane shear 
resistance to improve the seismic resistance of the floor system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a plan view of a typical bay of a floor system incorporating the 
composite beam design of this invention. The composite steel deck slab 10 
spans between composite beams 11 of this invention. The composite beams 11 
span between building columns 13 or composite girders 12 of this 
invention. 
FIG. 2 shows a typical cross-section of the composite beam of this 
invention taken along line 2--2 of FIG. 1. The composite concrete slab 10 
comprises steel decks 14 and an overlaying concrete layer 15. The steel 
decks 14 are supported on the top flange of the supporting beam 16. A 
continuous piece of T-beam 17 is structurally connected to the supporting 
beam 16 by welds 18 penetrating through the bottom flange 19 of the steel 
deck 14. The concrete shrinkage control mesh 20 is secured at the top 
flange 21 of the T-beam 17. Upon curing of the overlaying concrete 15, the 
supporting beam 16, the T-beam 17, and the overlaying concrete 15 will act 
together in a composite fashion to establish the composite beam of this 
invention. Many advantages ar achieved by this invention as compared to 
the studded composite beam design of the prior art as itemized below. 
1. In a studded composite beam design, the studs do not contribute any beam 
strength before the curing of concrete. Thus, the supporting beam 16 must 
be sized to resist the weight of the steel deck 14, the weight of the 
concrete 15, and the imposed construction load during the concreting 
operation. In the buildup composite beam design of this invention, the 
supporting beam 16 is required only to resist the weight of the steel deck 
without the weight of concrete while the combined strength of the 
supporting beam 16 and the T-beam 17 is available to resist the total load 
during erection. Therefore, the combined size of the supporting beam 16 
and the T-beam 17 is equivalent to a single supporting beam of the studded 
composite beam design. It becomes apparent that a saving in the ceiling 
height equaling the height of the T-beam 17 is achieved by this invention, 
since the entire T-beam 17 is buried within the depth of the floor slab. 
For a highrise building, the saving in the ceiling height of each floor 
will result in a significant reduction of building height. Segments of the 
T-beams 17 can be strategically located at the regions of high bending 
moment rather than covering the entire length of the supporting beam 16. 
2. In a studded composite beam design, the resistance against slab buckling 
relies on the enlarged stud head to hold down the concrete slab. In the 
buildup composite beam design of this invention, the floor slab is 
continuously locked under the long extended top flange 21 of the T-beam 
17. Therefore, significant improvement in the hold down capability is 
achieved allowing the development of high strain in the concrete slab 
without composite failure. The common problem of longitudinal concrete 
cracks on top of a studded composite beam is eliminated by this invention. 
3. The top flange 21 of T-beam 17 serves to automatically position the wire 
mesh 20 without the use of mesh supporting plastic chairs. 
4. In the buildup composite beam design of this invention, the upward 
movement of the slab is restrained by the top flange of the T-beam 17 and 
the lateral movement of the slab is restrained by the vertical leg of the 
T-beam 17. Therefore, the in-plane shear resistance, which is a direct 
measurement of the seismic resistance is greatly improved by this 
invention. Other structural shapes, such as an angle or a channel, can be 
used in place of T-beam 17. 
FIG. 3 shows a typical cross-section of the composite beam of this 
invention taken along line 3--3 of FIG. 1. The wire mesh 20 is positively 
secured to the top flange of the T-beam 17 by spaced apart tack welds 22 . 
The wire mesh 20 can be stretched between the T-beams 17 before applying 
the tack welds 22. In this manner, the proper wire mesh location is 
ensured during the concreting operation without the labor of placing the 
mesh supporting chairs. The T-beam 17 is notched as shown by the dashed 
line 23 to prevent interference with the profile of the steel deck 14. The 
bottom end of the T-beam 17 is structurally connected to the top flange of 
the supporting beam 16 by the welds 18 penetrating through the bottom 
flange of the steel deck 14. Even though the bottom of the T-beam 17 is 
connected to the supporting beam 16 in a spaced apart fashion at the 
valleys of the steel deck 14, these connections are integral parts of the 
T-beam 17. Therefore, the longitudinal shear transferring capacity is 
limited only by the strength of the welds 18 and is not affected by the 
geometry of the deck profile. The stud efficiency problem of a studded 
composite beam design is eliminated by this invention. 
FIG. 4 shows a typical cross-section of the composite beam design of this 
invention in a girder application taken along line 4--4 of FIG. 1. In a 
girder application, the corrugations of the steel deck 14 are parallel to 
the longitudinal direction of the girder. Therefore, to incorporate this 
invention into the composite girder design, it is necessary to layout the 
steel deck 14 such that one of the steel deck valleys will be positioned 
on top of the bottom supporting girder. Similar to the previously 
explained composite beam design of this invention, the composite girder is 
formed by a T-beam 17 being connected to the bottom supporting girder 24 
using welds 18 and an overlaying concrete slab 15 above the steel deck 14. 
The wire mesh 20 is supported on top of the T-beam 17. In the girder 
application, the T-beam 17 need not be notched. 
FIG. 5 is an isometric view of a segment of the T-beam 17 useful in this 
invention. Notches 25 on the vertical leg 26 of the T-beam 17 are provided 
to prevent interference with the steel deck profile. 
FIG. 6 shows a typical supporting beam profile 27 which is optimal for use 
in this invention. The optimal supporting beam profile 27 consists of a 
top flange 28, a web 29, and a bottom flange 30. The construction loading 
history of the buildup composite beam of this invention includes the 
following two stages. The first stage loading is during the erection of 
the steel decks and is resisted by the supporting beam. The second stage 
loading is during the concreting operation and is resisted by the combined 
action of the T-beam and the supporting beam. The second stage loading is 
much larger than the first stage loading and is mainly resisted by the 
bending strength provided by the top flange of the T-beam and the bottom 
flange of the supporting beam with little contribution by the top flange 
of the supporting beam. Similarly, the top flange of the supporting beam 
has little contribution to the bending strength of the composite section 
due to its proximity to the composite neutral axis. Therefore, the optimal 
profile of the supporting beam will have a thinner and narrower top flange 
as compared to the bottom flange. A thinner top flange will also 
facilitate the use of selfdrilling self-tapping screws for fastening the 
steel deck to the top flange of the supporting beam. 
FIG. 7 shows another typical optimal supporting beam profile 31 useful for 
the buildup composite beam design of this invention. This optimal beam 
profile 31 consist of a regular symmetrical wide flanged beam 32 with 
thinner flanges and a stiffening steel plate 33 being structurally 
connected to the bottom flange of the beam 32 by welds 34. 
While I have illustrated and described several embodiments on my invention, 
it will be understood that these are by way of illustration only and that 
various changes and modifications may be contemplated in my invention and 
within the scope of the following claims.