Thin bed concrete composite slab

Abstract

The utility model discloses a kind of thin bottom concrete composite board, including steel truss, steel sheet net and the concrete thin bottom plate of thickness≤25mm. Steel truss is composed of upper chord, wave-shaped web and lower chord steel bar, and the top surface of lower chord steel bar is flush with the top surface of concrete thin bottom plate;Steel sheet net is welded into grid by incision or ribbed longitudinal, transverse thin steel belt, longitudinal thin steel belt is bent into L shape, its horizontal limb is buried into bottom plate, and inclined limb is welded with web trough, steel sheet net is 5-10mm from bottom surface of bottom plate. Upper chord has a variety of structures such as opening downward / upward groove type, thin-walled steel pipe, steel bar. The composite board is through composite anchoring and reinforcing system, improves steel-concrete bonding strength and overall stiffness, dead weight≤150kg / m², free support span≥2.5m, plate width≥1500mm, comprehensive cost reduces 20%-30%, applicable to fabricated building floor.

Description

Technical Field

[0001] This utility model relates to the field of building structure technology, specifically to a thin-bottomed concrete composite slab, which is suitable for floor slab structures of various buildings and can be widely used in floor construction of various projects. Background Technology

[0002] In the development of prefabricated buildings, lightweighting and efficient construction have become important requirements, posing numerous challenges to traditional floor decking systems. Open-faced floor decking increases decoration costs by 25%-35% due to its wavy bottom structure, requiring additional ceiling treatment; while closed-faced floor decking achieves a flat bottom surface, it increases material costs by 40%-50%, and both have redundant effective concrete thicknesses, with a conventional thickness ≥50mm, resulting in excessive self-weight of 180-220kg / m², making it difficult to meet the requirement of ≤150kg / m² for floor slab self-weight in the "Evaluation Standard for Prefabricated Buildings" (GB / T 51129).

[0003] While existing thin-bottom steel truss plates achieve some degree of lightweighting, with a bottom plate thickness of 15-20mm, they have significant technical drawbacks:

[0004] Weak structural anchorage: The anchorage depth of the outward bend of the steel truss web members (Φ5mm) is insufficient, the contact area ratio with the base plate is <15%, and the measured interface bond strength is ≤0.6MPa, which easily leads to detachment during the construction stage.

[0005] Poor reinforcement effect: The steel wire mesh (Φ2-3mm) embedded in the base plate has low tensile strength, generally only 100MPa. The bonding area with concrete is reduced by 60% compared with traditional steel mesh. It accounts for 20% of the thickness of the thin concrete slab. The combination effect between the steel wire mesh and the concrete slab is very poor, and it cannot effectively suppress the shrinkage cracks of the thin slab. The crack width > 0.3mm accounts for more than 65%.

[0006] Economic imbalance: Although steel fiber UHPC concrete can improve crack resistance, the material cost increases by 200%-300%, and UHPC can only be used as the bottom formwork of concrete, not as the concrete after it is stacked, which increases the thickness of the floor slab and the project cost.

[0007] Span and width are limited: Insufficient stiffness of steel trusses results in a maximum span without bracing of ≤1.5m. The lack of reinforcement in the vertical truss direction limits the slab width to within 1200mm, and the cracking rate of ultra-wide slabs exceeds 50%.

[0008] Industry data shows that the aforementioned defects have led to significant engineering problems, with severe cracking issues in composite slabs during use and frequent collapse accidents during construction. Therefore, there is an urgent need for a new type of composite slab that can address the technical bottlenecks of weak anchorage, insufficient stiffness, and uncontrolled cracking in thin-bottomed steel truss slabs.

[0009] This utility model addresses three major technical bottlenecks in thin-bottomed steel truss plates: weak anchorage, insufficient stiffness, and uncontrolled cracking. Through innovative composite structures, it breaks through the boundaries of traditional technologies and provides a safe, economical, and highly adaptable solution for prefabricated buildings. Utility Model Content

[0010] Utility Model Purpose

[0011] To address the technical problems of existing thin-bottomed steel truss slabs, this utility model provides a safe, reliable, economical, efficient, and highly adaptable thin-bottomed concrete composite slab. Through composite structure innovation, it improves structural performance and meets the requirements of prefabricated buildings for floor slabs.

[0012] Technical solution

[0013] A thin-bottomed concrete composite slab, characterized in that it comprises a steel truss, a steel mesh, and a thin-bottomed concrete slab:

[0014] Steel truss: Composed of top chord, web members, and bottom chord reinforcement. Web members are continuously bent into a wavy structure using steel bars, pipes, strips, or cold-formed steel. The bottom chord reinforcement is welded to the troughs of the web members, and its top surface is not lower than the top surface of the thin concrete slab. This ensures that the bottom chord reinforcement can participate in the load-bearing capacity of the thin slab, enhancing its strength, and also guarantees the load-bearing function of the reinforcement in later stages. If the surface of the reinforcement is lower than the top surface of the thin concrete slab, the protective layer thickness of the reinforcement perpendicular to the truss will increase, preventing it from effectively fulfilling its load-bearing function.

[0015] Steel mesh: A mesh structure formed by welding longitudinal and transverse thin steel strips. The longitudinal and transverse thin steel strips have indentations or ribs parallel to their extension direction in at least one direction to enhance adhesion to concrete and the bending strength of the steel strips. The longitudinal thin steel strips are bent into an L-shape, consisting of horizontal and inclined legs. The horizontal legs are embedded in the thin concrete base slab, and the inclination angle of the inclined legs matches that of the web members. The troughs of the web members are welded to the inclined legs. The thickness of the longitudinal and transverse thin steel strips is ≤1mm, and their width is 10mm-40mm. The distance between the steel mesh and the bottom surface of the thin concrete base slab is 5mm-10mm.

[0016] Thin concrete slab: thickness ≤25mm, with the steel mesh embedded inside to form a reinforced concrete thin slab structure.

[0017] Upper chord structure optimization:

[0018] Structure a: It is made of thin-walled steel plate bent into a channel-shaped section with the opening facing downward. The two sides of the section are inclined outward, with an angle of 0°-30° with the vertical direction. Multiple rows of steel bars perpendicular to the axis of the upper chord are welded to the upper edge. V-shaped or figure-eight shaped steel bar feet are welded below the steel bars. The channel-shaped section with the opening facing downward is provided with a 1-2mm deep indentation, and the end is provided with a connection hole.

[0019] By using thin steel plates bent into shape, the channel section has the widest unfolded width and the largest distance from the centroid of the lower chord of the truss, thus significantly increasing the moment of inertia and improving the bending stiffness and strength of the truss, all while using the same amount of steel. After the upper flange is unfolded, the spacing of the web members also increases, and the number of trusses can be reduced for the same width of composite plate.

[0020] The reinforcing bars are welded perpendicular to the axis of the top chord, forming a line-to-surface contact. This creates a fixed connection relative to the reinforcing bars, resulting in a hollow truss. This also creates another truss in the perpendicular direction, enhancing the external stiffness of the truss and preventing longitudinal cracks in the base plate due to excessive width. Since the truss spacing is generally greater than 400mm, the connection between two trusses by reinforcing bars alone is insufficient. Therefore, an additional reinforcing bar is added in the middle of the truss and connected to the transverse steel strip, increasing the stiffness of the transverse truss. This allows for the complete formation of a two-way truss spatial structure, significantly improving its overall integrity compared to traditional trusses.

[0021] Indentation can enhance the local stability of the upper chord of the channel section and increase the bond strength between the upper chord and the post-cast concrete, thereby fully utilizing the strength of the upper flange steel. The connecting holes are used to connect the longitudinally adjacent plates at the cross beam, thereby further utilizing the strength of the upper flange steel, reducing the amount of upper reinforcement, and saving steel consumption.

[0022] Structure b: A thin-walled steel plate is bent into an upward-opening channel-shaped section. The two sides of the section slope inward at an angle of 0°-30° to the vertical. The channel is filled with cement mortar, plaster, or rigid concrete. The upper edges of both sides are bent inward to form short rolled edges with a width of 5mm-10mm. This improves the stability of the section and the mutual anchoring effect of the internal filling, allowing the steel of the upper chord and the filling to work together to bear the load.

[0023] Structure c: Made of thin-walled steel pipes, with a cross-section that is trapezoidal, circular, or elliptical with a smaller top and a larger bottom.

[0024] Structure d: directly constructed of steel bars.

[0025] Steel truss arrangement: The steel truss is arranged in multiple parallel rows in at least one longitudinal or transverse direction, and a horizontal welding platform with a width of 10mm-30mm is provided at the trough or crest of the web members.

[0026] Innovation

[0027] Innovative composite anchoring structure: L-shaped longitudinal thin steel strips are welded to the web members and rationally arranged with the bottom chord reinforcement, which greatly improves the anchoring strength and reliability of the steel truss and the thin concrete base plate, effectively solving the problem of weak anchoring.

[0028] High-efficiency reinforcement system upgrade: The steel mesh made of notched / ribbed thin steel strips, combined with optimized size and embedding location design, significantly improves the steel-concrete bond strength and composite effect, enhances the strength of the base plate, and effectively inhibits the shrinkage cracks of the thin plate.

[0029] Diverse upper chord structures: Four different types of upper chord structures are available, which can be flexibly selected according to engineering load requirements, cost budget, etc., greatly enhancing the structural adaptability and economy.

[0030] Innovation in overall stress mechanism: By using connecting components such as steel bars and steel bar feet, the steel truss and steel mesh are constructed into a two-way stress truss system, forming a spatially coordinated stress structure and an efficient coordinated stress mechanism, which comprehensively improves the overall stiffness and load-bearing capacity of the composite slab.

[0031] Beneficial effects

[0032] Lightweight: The thickness of the concrete thin base slab is ≤25mm, which significantly reduces the self-weight and meets the requirements of the "Evaluation Standard for Prefabricated Buildings" for the self-weight of the floor slab.

[0033] High stiffness and crack resistance: Through optimized anchoring structure and reinforcement system, the stiffness variation coefficient of the composite plate is significantly reduced, the crack width is effectively controlled, and the proportion of cracks with a width > 0.3 mm is greatly reduced.

[0034] Convenient construction: The steel truss and steel mesh form an integral structure, which is convenient for on-site installation. The maximum span without supports can be increased to more than 2.5m. By adding transverse steel bars or transverse trusses, the plate width can be extended to more than 2500mm, reducing the amount of supports and improving construction efficiency.

[0035] Economic efficiency: Using thin-walled steel plates as the top chord of the truss increases the spacing between the bottom web members compared to ordinary steel trusses. For the same width of composite slab, the number of trusses can be reduced without affecting the bending strength and stiffness of the members. Reducing the number of trusses also allows for a reduction in the amount of bottom chord reinforcement, resulting in greater economic efficiency. Adding connection holes to the top flange allows the top chord to be used as surface reinforcement, reducing the amount of connecting reinforcement and further improving economic efficiency.

[0036] Safe and reliable: Improved structural performance effectively reduces collapse accidents during construction and cracking problems during use, enhancing the safety and durability of buildings. Attached Figure Description

[0037] Figure 1This is a schematic diagram of a steel truss structure for a thin-bottomed concrete composite slab (the upper chord has a downward-facing groove-shaped cross-section).

[0038] Figure 2 This is a schematic diagram of a steel truss structure for a thin-bottomed concrete composite slab (the upper chord has an upward-facing groove-shaped section).

[0039] Figure 3 This is a schematic diagram of a steel truss structure with a thin-bottomed concrete composite slab (trapezoidal cross section of the upper chord).

[0040] Figure 4 This is a schematic diagram of a steel truss structure for a thin-bottomed concrete composite slab (upper chord reinforcement).

[0041] Figure 5 A schematic diagram of the frame structure of a thin-bottomed concrete composite slab;

[0042] Figure 6 This is a schematic diagram of the skeleton structure of a thin-bottomed concrete composite slab;

[0043] Figure 7 This is a schematic diagram of the skeleton structure of a thin-bottomed concrete composite slab;

[0044] Figure 8 This is a schematic diagram of the skeleton structure of a thin-bottomed concrete composite slab;

[0045] Figure 9 This is a schematic diagram of the skeleton structure of a thin-bottomed concrete composite slab;

[0046] Figure 10 A schematic diagram of a thin-bottomed concrete composite slab;

[0047] Figure 11 A schematic diagram of a thin-bottomed concrete composite slab;

[0048] In the diagram: 1. Steel truss; 1-1. Top chord; 1-2. Web member; 1-3. Bottom chord reinforcement; 2. Steel mesh; 2-1. Longitudinal thin steel strip; 2-2. Transverse thin steel strip; 3. Thin concrete base plate; 4. Reinforcing bar; 5. Reinforcing bar foot; 6. Short rolled edge; 7. Horizontal welding platform; 8. Connecting hole. Detailed Implementation

[0049] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0050] Example 1: Please refer to the appendix Figure 1-11 This utility model provides a technical solution: a steel truss composed of an upper chord, web members, and lower chord reinforcing bars; the web members are formed by continuous bending of reinforcing bars, steel pipes, steel strips, or cold-formed steel; the lower chord reinforcing bars are welded at the troughs of the web members, and the top surface of the lower chord reinforcing bars is not lower than the top surface of the thin concrete base plate; a steel mesh is formed by welding longitudinal and transverse thin steel strips to form a grid structure; the thin concrete base plate has a thickness of ≤25mm, and the steel mesh is embedded inside; the steel truss and the steel mesh are fixed by welding to form an integral load-bearing structure.

[0051] In this embodiment, the bottom chord reinforcement can be partially embedded in the thin concrete base slab, which can improve the connection between the truss and the base slab and also enhance the strength of the base slab. If the bottom chord reinforcement is completely embedded in the concrete base slab, the protective layer thickness of the additional reinforcement perpendicular to the direction of the bottom chord reinforcement increases, which is not conducive to the bidirectional stress of the floor slab.

[0052] In this embodiment, steel mesh is used as the reinforcement of the thin concrete base plate. Compared with traditional wire mesh or fiber concrete, since the thickness of the steel mesh accounts for only 2% to 5% of the base plate thickness, the base plate and the steel mesh work together, and the strength of the base plate is significantly improved. Furthermore, the steel mesh is welded and fixed together with the trough of the web members of the truss, which not only facilitates production but also enhances the connection between the concrete base plate and the truss, overcoming the problem of insufficient connection between the base plate and the truss due to its thinness.

[0053] Furthermore, as a preferred option, a steel mesh formed by orthogonally welding longitudinal and transverse thin steel strips is embedded in the concrete base slab. The longitudinal and transverse thin steel strips are pressed with grooves or ribs parallel to the extension direction of the steel strips to enhance the bond strength with the concrete. The ribs can enhance the bending strength of the steel strips, thereby improving the local bending strength of the base slab.

[0054] Furthermore, as a preferred option, the longitudinal thin steel strip is bent into an L-shape, with its horizontal limb embedded in the thin concrete base plate. The inclination angle of the inclined limb is consistent with the inclination angle of the web member, and the trough of the web member is welded to the inclined limb to form an integral load-bearing structure. Compared with the traditional web member which is bent outward and then anchored in the thin base plate, the connection between the web member and the base plate is more reliable and the reinforcement effect on the base plate is better.

[0055] In this embodiment, the upper chord of the truss is made of thin-walled steel plate bent into a downward-facing channel-shaped section with both sides of the section inclined outwards at an angle of 0°-30° to the vertical direction. The thin steel plate is used as the upper flange, maximizing its spread and positioning its centroid as high as possible to increase the truss's moment of inertia and lateral stability. The channel-shaped upper flange has a width of 10-20mm on both sides, ensuring sufficient width for connection with the web members. This width covers the bending area of ​​the web members, and the connection is made with a straight member in the middle, thus ensuring maximum axial stiffness of the truss web members. The spread width of the thin steel plate increases the spacing between the web members, allowing the spacing at the bottom of the web members to be increased from 80mm to 150mm. For every 600mm wide floor slab, the number of trusses can be optimized from 3 to 2, saving 40% of the truss usage. The bottom chord reinforcement serves as the reinforcing steel in the concrete and also increases the stiffness of the truss. In existing technology, floor slabs use three trusses, each with three bottom chord members. This means the minimum spacing of the bottom reinforcement is 100mm, while the actual load-bearing capacity of the floor slab generally requires a spacing of 180mm. Therefore, the existing technology results in some waste of bottom slab reinforcement, which cannot fully utilize its function. Furthermore, each additional truss adds two more web reinforcement members. These web reinforcement members connect the upper and lower flanges during construction and do not participate in structural load-bearing after concrete pouring, thus also leading to steel waste.

[0056] Furthermore, as a preferred option, multiple rows of reinforcing bars perpendicular to the axis of the upper chord are welded to the upper edge of the channel-shaped cross-section, with the reinforcing bars spaced apart along the length of the steel truss.

[0057] Furthermore, as a preferred option, V-shaped or figure-eight shaped steel bar feet are welded below the steel bars. The lower end of the steel bar feet is welded and fixed to the transverse thin steel strip, and the upper end is welded and fixed to the steel bars. They are located between two adjacent steel trusses to enhance the overall structural integrity.

[0058] Because the upper edge of the channel section is relatively wide, generally greater than 40mm, the reinforcing bars are welded perpendicular to the axis of the upper chord to form a line-to-surface contact, which can form a fixed connection relative to the reinforcing bars, thus forming a hollow truss. This creates another truss in the vertical direction, enhancing the external stiffness of the truss and preventing longitudinal cracks from appearing in the base plate due to its excessive width. Since the truss spacing is generally greater than 400mm, the connection between two trusses by reinforcing bars alone is weak. Therefore, a reinforcing bar foot is added in the middle of the truss and connected to the transverse steel strip to increase the stiffness of the transverse truss. This allows for the complete formation of a two-way truss spatial structure, significantly improving the overall integrity compared to traditional trusses.

[0059] Furthermore, the preferred top chord with a downward-facing channel cross-section has a 1-2mm deep indentation and one or more connecting holes at the ends. To ensure the top chord functions effectively in the post-cast concrete and increase its bond with the concrete, indentations are added, thus saving steel. Connecting holes at both ends connect two slabs longitudinally. Since the beam spans the beam, holes are left at both ends of the upper flange to utilize the steel. Then, lapped steel is used to connect them, aligning the holes. Steel bars or bolts are inserted into the holes, and finally, the longitudinally adjacent top chords are connected together to form a continuous load-bearing steel structure. This significantly reduces steel consumption compared to traditional composite slabs with re-lapped reinforcement.

[0060] Example 2: Essentially the same as Example 1, except that the upper chord is made of thin-walled steel plate bent into an upward-facing channel-shaped section. The two sides of the section slope inwards at an angle of 0°-30° to the vertical, and the channel is filled with cement mortar, plaster, or rigid concrete. The inclination of the channel section can be the same as the inclination angle of the web members, allowing the upper chord and web members to fully contact and weld together, ensuring reliable connection. Filling the channel section with rigid materials such as plaster, concrete, and grout can increase the cross-sectional area of ​​the upper flange, thereby enhancing the truss stiffness and increasing the span of the composite slab.

[0061] Furthermore, as a preferred feature, the upper edges of both sides of the channel-shaped cross-section with the opening facing upward are bent inward to form short rolled edges, the width of which is 5mm-10mm. This increases the stability of the channel steel side plate and also enhances the connection between the channel steel and the rigid material, allowing the rigid material and the channel steel to share the load.

[0062] Example 3: Basically the same as Example 1, except that the upper chord is made of thin-walled steel pipe with a cross-section that is trapezoidal, circular or elliptical with a smaller top and a larger bottom.

[0063] Example 4: It is basically the same as Example 1, except that the upper chord is made of steel bars directly.

[0064] Example 5: Essentially the same as Example 1, except that the steel truss is arranged in multiple parallel rows longitudinally or laterally, and a horizontal welding platform is provided at the troughs or crests of the web members. The width of the horizontal welding platform is 10mm-30mm. When the plate width is small, only multiple rows of longitudinal trusses can be arranged; when the width is greater than 1200mm, trusses can also be arranged laterally to form a space frame structure. Bending the horizontal welding platform at the troughs facilitates the welding of the steel mesh to the truss, ensuring welding strength. Bending the horizontal welding platform at the crests facilitates the welding of the upper chord to the web members, ensuring welding strength.

[0065] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A thin-bottomed concrete composite slab, characterized in that, include: The steel truss (1) is composed of an upper chord (1-1), web members (1-2) and a lower chord steel bar (1-3); the web members (1-2) are formed by continuous bending of steel bars, steel pipes, steel strips or cold-formed steel. The lower chord reinforcement (1-3) is welded to the trough of the continuous bend of the web member (1-2), and the top surface of the lower chord reinforcement (1-3) is not lower than the top surface of the thin concrete bottom plate (3); Steel mesh (2) is formed by welding longitudinal thin steel strips (2-1) and transverse thin steel strips (2-2) to form a mesh structure; A thin concrete base plate (3) with a thickness of ≤25mm is embedded with the steel mesh (2). The steel truss (1) is fixedly connected to the steel mesh (2) to form an integral load-bearing structure.

2. The thin-bottomed concrete composite slab according to claim 1, characterized in that: At least one of the longitudinal thin steel strips (2-1) and the transverse thin steel strips (2-2) has indentations or ribs pressed on it, parallel to the direction of the steel strip's extension.

3. A thin-bottomed concrete composite slab according to claim 1, characterized in that: The longitudinal thin steel strip (2-1) is bent into an L-shape and consists of a horizontal leg and an inclined leg. The horizontal leg is embedded in the thin concrete base plate (3), and the inclination angle of the inclined leg is consistent with the inclination angle of the web member (1-2). The trough of the web member (1-2) is welded to the inclined leg.

4. A thin-bottomed concrete composite slab according to claim 1, characterized in that: The thickness of the longitudinal thin steel strip (2-1) and the transverse thin steel strip (2-2) is ≤1mm, and the distance between the steel mesh (2) and the bottom surface of the concrete thin base plate (3) is 5mm-10mm.

5. The thin-bottomed concrete composite slab according to claim 1, characterized in that: The upper chord (1-1) can be any of the following structures: (a) A thin-walled steel plate is bent into a channel-shaped section with the opening facing downwards. The two sides of the section are inclined outwards, with an angle of 0°-30° with the vertical direction. (b) A thin-walled steel plate is bent into a channel-shaped section with the opening facing upward. The two sides of the section are inclined inward, with an angle of 0°-30° with the vertical direction, and the channel is filled with cement mortar, gypsum or concrete. (c) Made of thin-walled steel tubes, with a cross-section that is trapezoidal, circular, or elliptical with a smaller top and a larger bottom. (d) It is made directly from steel bars.

6. The thin-bottomed concrete composite slab according to claim 5, characterized in that: The upper edge of the groove-shaped section is welded with multiple rows of steel bars (4) perpendicular to the axis of the upper chord (1-1), and the steel bars (4) are arranged at intervals along the length of the steel truss (1).

7. The thin-bottomed concrete composite slab according to claim 6, characterized in that: The steel bar (4) is welded with a V-shaped or figure-eight shaped steel bar foot (5). The lower end of the steel bar foot (5) is welded and fixed to the transverse thin steel strip (2-2), and the upper end is welded and fixed to the steel bar (4). The steel bar foot (5) is located between two adjacent steel trusses (1).

8. The thin-bottomed concrete composite slab according to claim 5, characterized in that: The upper chord (1-1) of the downward-facing groove-shaped section has indentations and one or more connecting holes (8) at its end.

9. The thin-bottomed concrete composite slab according to claim 5 (b), characterized in that: The upper edges of the two sides of the upward-facing groove-shaped cross-section are bent inward to form short rolled edges (6).

10. The thin-bottomed concrete composite slab according to claim 1, characterized in that: The steel truss (1) is arranged in multiple parallel rows along the longitudinal or transverse direction, and a horizontal welding platform (7) is provided at the trough or crest of the web members (1-2).

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