BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of precast concrete construction. More specifically, the present invention discloses a reinforced concrete beam assembly having a cross-section with a lower flange extending between the lower edges of two vertical webs, and a two upper flanges extending laterally outward from the upper edges of the webs.
2. Statement of the Problem
A wide variety of precast concrete slabs and beams have used for many years. The simplest type of precast concrete beam has a generally rectangular cross-section and may include reinforcing strands embedded in the concrete to increase the tensile strength of the slab. This configuration has the disadvantage of being structurally inefficient. In other words, this asymmetrical beam cross-section is not proportioned to achieve its optimum load-bearing capacity.
FIG. 1 shows the cross-section of a typical double-T beam 10 that has been widely used for many years in the industry, primarily for medium-duty floor or roof joist construction. The double-T beam has an upper flange 15 and two downwardly-extending webs 12 and 13. Reinforcing strands 15 are often embedded in the lower portions of the webs 12, 13 to increase tensile strength. This cross-section is more efficient than a simple slab, but has a number of significant limitations.
First and foremost, the absence of a lower flange means that the neutral axis is relatively high in the cross-section of a double-T beam, which increases camber (i.e., bowing over the length of the beam). A degree of camber may be acceptable in some structures, such as bridges, walkways and parking garages. But, camber has been a major obstacle to use of precast concrete tees in other types of construction, particularly where a flat floor surface is required. One response to the problem of camber has been to construct a raised floor over double-T beams using a grid of variable-height risers to support the floor panels and compensate for variations in the elevation of the upper surfaces of the double-T beams. However, this approach increases construction costs by increasing the structural depth.
FIG. 2 shows the cross-section of a typical hollow-core beam 20 that has also been widely used for many years in the industry. A hollow-core beam 20 typically has a plurality of vertical webs 21, 22 and 23 extending between its upper and lower flanges 25 and 24. The voids 28 between the webs 21, 22, 23 and flanges 24, 25 are either filled with air or a light-weight material, such as Styrofoam, having negligible structural properties. It should be noted that a hollow-core beam can be viewed as a series of I-beams in parallel to one another. More specifically, each of the vertical webs 21, 22, 23 in the hollow-core beam can be viewed as the web of an I-beam. The adjacent portions of the upper and lower flanges 25, 24 of the hollow-core beam can be viewed as the upper and lower flanges of the I-beam. An L-beam is a very efficient structural shape, and therefore hollow-core beams are also very efficient.
Nonetheless, hollow-core beams have a number of drawbacks. One of the most significant limitations is the difficulty in forming voids 28 within a concrete slab. Hollow-core beams can be made using an extrusion process, but this requires the use dry-cast concrete to minimize sagging and the risk of collapse of the voids as the concrete sets. The maximum length of extruded beams is also limited due to the difficulties in handling long beams and the limitations of dry-cast concrete. Another approach has been to suspend pieces of foam in the wet concrete as the beam is being cast to create voids. This is unexpectedly difficult due to the large amount of buoyancy associated with foam in wet concrete.
FIG. 3 shows a cross-section of another type of beam 30 that has been used in the industry for many years, primarily for road and bridge construction. This cross-section is commonly referred to as a “tub” section. Two vertical webs 32 and 33 extend generally upward from the ends of the lower flange 34. Reinforcing strands 15 can be embedded in the lower flange 34. Tub section beams are typically used to support a horizontal deck spanning the upper ends of the vertical arms 32, 33. In this configuration, the deck forms the fourth side of a box-shaped cross-sectional structure to complete the structural section.
3. Solution to the Problem
Nothing in the prior art discussed above shows a concrete beam assembly having the structure of the present invention. In particular, the present invention employs a beam cross-section having two vertical webs with a horizontal first flange extending between one set of edges of the webs, and horizontal second and third flanges extending laterally outward from the other edges of the webs. For example, in one embodiment, the beam has a horizontal lower flange extending between the lower edges of the vertical webs and two horizontal upper flanges extending laterally outward from the upper edges of the webs. Reinforcing strands can be embedded in the lower flange. A flooring structure can be placed atop an assembly of the beams to provide a relatively flat floor surface.
The present beam cross-section has the advantage of approximating the structural properties of the a hollow-core beam, without the difficulties associated with forming voids in a hollow-core beam. More specifically, the present beam cross-section can also be viewed as a series of I-beams in parallel to one another, in the same manner this analogy can be applied to a hollow-core beam. The vertical webs are analogous to I-beam webs, and the upper and lower flanges of the present beam cross-section are analogous to the upper and lower flanges of the I-beams. This provides the present beam cross-section with superior structural properties. In addition, the location of the neutral axis in the beam cross-section can be readily adjusted to meet the needs of a particular job by changing the dimensions and spacing of the webs and flanges.
SUMMARY OF THE INVENTION
This invention provides a concrete beam assembly having a concrete beam with two vertical webs spaced apart from one another that extend along the length of the beam. A horizontal first flange extends between the first edges of the webs, so that the webs and first flange define a channel extending along the length of the beam. Horizontal second and third flanges extend laterally outward in opposing directions from the second edges of the webs. A flat flooring structure is supported by the upper surfaces of the beam.
These and other advantages, features, and objects of the present invention will be more readily understood in view of the following detailed description and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention can be more readily understood in conjunction with the accompanying drawings, in which:
FIG. 1 is a cross-sectional view of a double-T beam 10.
FIG. 2 is a cross-sectional view of a hollow-core beam 20.
FIG. 3 is a cross-sectional view of a tub section 30.
FIG. 4 is a cross-sectional view of a beam 40 implementing the present invention.
FIG. 4
a is a cross-sectional view of another embodiment of a beam 60 implementing the present invention.
FIG. 5 is a cross-sectional view of the completed assembly of the beam 40 shown in FIG. 4 with a flat flooring structure.
FIG. 6 is a cross-sectional view of the completed assembly of the beams 60a and 60b shown in FIG. 4a with a flat flooring structure.
FIG. 7 is a cross-sectional view of another assembly of beams 40a and 40b with a raised flooring structure.
FIG. 8 is an exploded perspective view of a beam 40 showing an insert 50 being dropped into the channel 48 between the vertical webs 42, 43 of the beam 40.
FIG. 9 is an exploded perspective view of another embodiment of beams 60a, 60b and 60c assembled with inserts 50 being dropped into the channels formed between adjacent beams.
FIG. 10 is a side elevational view of a beam 40 with a number of weights 90 placed along its length to minimize vibration.
DETAILED DESCRIPTION OF THE INVENTION
Turning to FIG. 4, a cross-sectional view is provided showing a beam 40 implementing the present invention. The beam 40 has two vertical webs 42 and 43 that are parallel to, and spaced apart from one another. These webs 42, 43 preferably extend over the entire length of the beam, although this is not required. A lower flange 44 extends between the lower edges of the webs 42, 43 to define a channel 48 that faces upward. The depth of the channel 48 depends on the height of the webs 42 and 43 and the thickness of the lower flange 44. The channel 48 preferably extends along the entire length of the beam 40. Two upper flanges 45 and 46 extend laterally outward in oppose directions from the upper edges of the webs 42, 43. Reinforcing strands 15 can be embedded in the lower flange 44 or the lower portions of the vertical webs 42, 43 for increased strength. For example, these reinforcing strands 15 can be prestressed, post-tensioned, or simply rebar.
The beam 40 can have any desired length and other dimensions, subject to structural limitations and job requirements. It should also be understood that the cross-sectional pattern of the beam 40 could be extended laterally for more than two vertical webs 42, 43 (and therefore the resulting beam would have more than one channel 48). For example, the beam could have four vertical webs and two channels.
Some types of construction require a relatively flat floor. FIG. 5 is a cross-sectional view of the completed assembly of the beam 40 shown in FIG. 4 with a flat flooring structure on top of the beam 40. In this embodiment, the flooring structure includes an insert 50 that is placed in the channel 48 to provide a relatively flat upper surface. FIG. 8 is an exploded perspective view showing an insert 50 being dropped into the channel 48 between the vertical webs 42, 43 of the beam 40. The insert 50 can be a substantially planar sheet of metal, wood or plastic. It can also incorporate a number of legs, ridges or risers to help support the insert 50 above the floor of the channel 48. The embodiment of the insert 50 shown in FIGS. 5, 8 and 9 fits entirely within the channel 48 to create an upper surface that is relatively flush with the upper surfaces of the adjacent upper flanges 45, 46 of the concrete beam 40. Two opposing lips can be formed in the edges of the channel 48 to receive the edges of the insert 50 and thereby create a flush upper surface. Alternatively, the underside of the insert 50 could rest on the upper surfaces of the upper flanges 45, 46.
A thin concrete topping layer 55 can be poured on top of the assembly to create a relatively smooth, flat floor surface covering the concrete beam 40 and insert 50. The channel 48 can be used for carrying pipes 80, ducts or wiring that are concealed beneath the flooring structure, as shown in FIG. 5.
FIG. 4
a is a cross-sectional view of another embodiment of a beam 60 implementing the present invention. The configuration of the beam 60 in this embodiment is generally inverted from the beam 40 in FIGS. 4 and 5. As in the first embodiment, this beam 60 has two vertical webs 62 and 63, but the upper flange 64 extends between the upper edges of the webs 62, 63, and the lower flanges 65 and 66 extend laterally outward from the lower edges of the webs 62, 63. Please note the reinforcing strands 15 are now embedded in the lower flanges 65 and 66. The channel 68 faces downward in this embodiment.
FIG. 6 is a cross-sectional view of the completed assembly of the beams 60a and 60b shown in FIG. 4a with a flat flooring structure. It should be noted that the edges of each beam form a half channel, so that two adjacent beams 60a, 6b form a complete channel between them, as shown in FIG. 6. FIG. 9 is an exploded perspective view of two inserts 50 being dropped into the channels formed between adjacent beams 60a, 60b and 60c. A thin concrete topping layer 55 can then be poured on top of the assembly to create a relatively smooth, flat floor surface as shown in FIG. 6.
FIG. 7 is a cross-sectional view of another assembly of beams 40a and 40b with a raised flooring structure. In this embodiment, the flooring structure includes a grid of floor panels 75 supported above the upper surfaces of the beams 40a, 40b on risers 70. The lower ends of the risers 70 rest on the upper surfaces of the beams 40a, 40b. The risers 70 may require a variety of heights to compensate for the uneven upper surfaces of the beams 40a, 40b and thereby result in a flat and level grid of floor panels. For example, this can be accomplished either with adjustable-height risers 70 or risers that are individually cut to the proper height on the job site. Here again, the region beneath the raised flooring and above the beams 40a, 40b (e.g., the channels 48) can be used as a plenum for carrying pipes 80, ducts or wiring that are concealed beneath the floor panels 75. The floor panels 75 can be easily removed to provide access to the pipes, ducts or wiring for repair or maintenance.
It should be expressly understood that the various embodiments of the present invention can be generalized in the following terms. The vertical webs 42, 43 are spaced apart from one another and in a generally parallel relationship extending along the length of the concrete beam. Alternatively, the webs 42, 43 could be non-parallel or extend along only a portion of the length of the beam, although this may complicate manufacture. Each web 42, 43 has upper and lower edges extending along their lengths.
A horizontal first flange extends between either the upper or the lower edges of the vertical webs depending on the embodiment of the concrete beam. In the embodiment depicted in FIG. 4, the first flange is the lower flange 44 that extends between the lower edges of the webs 42, 43. In the embodiment shown in FIG. 4a, the first flange is the upper flange 64 that extends between the upper edges of the webs 62, 63. In both embodiments, these edges of the webs can be generalized as the “first edges.”
It should also be noted that the webs and first flange define a channel 48, 68 extending along the length of the concrete beam. In FIG. 4, this channel 48 is on the upper surface of the beam and therefore faces upward. In FIG. 4a, channel 68 is on the lower surface of the beam and faces downward.
Horizontal second and third flanges extending laterally outward in opposing directions from the other edges of the webs. In FIG. 4, the second and third flanges are the upper horizontal flanges 45 and 46 extending laterally outward from the upper edges of the webs 42, 43. In FIG. 4a, the second and third flanges are the lower horizontal flanges 65 and 66 extending from the lower edges of the webs 65, 66. Here again, these edges of the webs can be generalized as the “second edges.”
The horizontal flanges 44, 45 and 46 in FIG. 4 (or flanges 64, 65 and 66 in FIG. 4a) define the upper and lower surfaces of the concrete beam 40, 60. As illustrated in FIGS. 4-9, these upper and lower surfaces are uneven due to the vertical offset between the horizontal flanges provided by the vertical webs. However, a flat flooring structure can be supported by the upper surfaces of the concrete beam as previously discussed.
In addition to the channel 48, 68 formed between the vertical webs 42, 43 (or 62, 63 in FIG. 4a), two half channels are formed on the opposite side of the beam 40 by the vertical webs and the second and third horizontal flanges. These half channels extend along the length of the concrete beam, as shown in FIG. 6. In the embodiment shown in FIG. 4, the half channels are on the underside of the beam 40 and face downward. In FIG. 4a, the half channels are on the top of the beam 60 and face upward. Two half channels can be effectively combined to create a complete channel by placing two beams adjacent to one another in a parallel relationship with their lateral edges abutting, as shown in FIGS. 6 and 9. This process can be extended with additional parallel beams to create an assembly of any desired width having a plurality of parallel channels spaced at intervals across the width of the assembly.
It is important to recognize the structural advantages of the present invention. As previously mentioned, the present beam cross-section emulates the structural properties of a hollow-core beam, which in turn can be viewed as a series of I-beams in parallel to one another. The vertical webs in the present beam are analogous to I-beam webs, and the upper and lower flanges of the present beam are analogous to the upper and lower flanges of the I-beams. Although the vertical alignment of the flanges and webs is different in the present cross-section, this is largely irrelevant for the purposes of structural analysis. In particular, the presence of lower flanges allows the present invention to offer structural properties similar to a hollow-core beam, but without its manufacturing difficulties. This provides a high span-to-depth ratio and a high moment of inertia for the beam cross-section. In addition, reinforcing strands 15 can be embedded in the lower flanges to increase the strength and stiffness of the concrete beam.
The location of the neutral axis in the beam cross-section can also be readily adjusted to meet the needs of a particular job by changing the dimensions and spacing of the webs and flanges. The dimensions of the flanges and webs, as well as the horizontal spacing between the webs can be used to adjust the neutral axis of the beam cross-section, and thereby control camber to meet the needs of a particular job. It should be noted that this camber adjustment can be made even without changing the overall area of the beam cross-section or its weight.
The present beam cross-section does have the disadvantage of creating an uneven upper surface for flooring. However, this can be addressed by using a flooring structure on top of the concrete beams, as shown for example in FIGS. 5-9. In addition, the channels in the concrete beams can be used as plenums for wiring, pipes and ducts 80.
FIG. 10 is a side view of a beam 40 with a number of weights 90 placed along its length to minimize vibration of the beam 40. Dynamic loads may be of particular concern due to the relatively shallow depth of the beam cross-section in the present invention. The mass of the detuning weights 90 and their locations along the beam 40 can be designed by computer modeling to determine the dynamic properties (i.e., eigenvalues and eigenvectors) of a given beam. The weights 90 can then be positioned on the beam to detune the beam, by shifting its eigenvalues out of the range of frequencies of concern. The weights 90 can also be placed to reduce the amplitude of selected vibrational modes.
The above disclosure sets forth a number of embodiments of the present invention described in detail with respect to the accompanying drawings. Those skilled in this art will appreciate that various changes, modifications, other structural arrangements, and other embodiments could be practiced under the teachings of the present invention without departing from the scope of this invention as set forth in the following claims.
Patent Application
20100287859
