A slotted prestressed concrete composite floor slab and a design configuration method

Abstract

The application provides a slotted prestressed concrete composite floor and a design configuration method. The composite floor comprises a prefabricated bottom plate, a composite cast-in-situ layer, additional steel bars and a key groove. The side edge of the prefabricated bottom plate is provided with a chamfer, the chamfers of adjacent prefabricated bottom plates are in contact with each other to form a V-shaped gap, and a concrete reinforced area is formed in the key groove of the bottom plate; the additional steel bars are located in the key groove in the concrete reinforced area. The design configuration method determines the structural parameters of the prefabricated bottom plate through the size of the composite plate, then calculates the bending moment and shear force of the composite plate according to the load combination of the permanent load control, and calculates the maximum deflection in the span of the composite plate according to the quasi-permanent load combination, and finally, the bending steel bars of the composite plate are designed, and the maximum deflection in the span of the composite plate and the shear bearing capacity of the oblique section of the support of the composite plate are respectively checked. The application has the advantages of excellent joint force transmission performance of the composite floor, low steel content of the structure, high deflection calculation accuracy in the design method and the like.

Description

Technical Field

[0001] This invention relates to the field of prefabricated concrete structures, and more particularly to a slotted prestressed concrete composite floor slab and its design and configuration method. Background Technology

[0002] Composite concrete slabs are crucial horizontal structures in prefabricated concrete buildings, accounting for approximately 50% of the total structural weight. Their selection directly impacts the building's structural quality and construction ease. Composite slabs consist of a precast base slab and a cast-in-place concrete layer. Current standards recommend two types of precast base slabs and their joint combinations, resulting in two types of composite slabs with different load-bearing properties after being combined and cast in place, suitable for one-way and two-way slabs respectively. Existing composite slabs suffer from drawbacks such as limited applicable spans, insufficient load transfer at separated joints, complex construction at integral joints, and low production and assembly efficiency. Specifically:

[0003] The first type of composite floor slab has no reinforcing bars on the side of the precast base slab, which can achieve mold standardization and high production efficiency. During assembly, the adjacent base slabs are pressed together and straight additional reinforcing bars are placed on the base slab around the joint, which constitutes the so-called "separated joint" or "closed joint". Its joint structure is simple and construction is efficient. However, under load, the composite surface is prone to lifting and tearing failure. The reasons are: (1) The additional reinforcing bars are placed directly on the precast base slab, and the surrounding area cannot be fully wrapped by the cast-in-place concrete, making it easy to pull out and thus difficult to exert its material strength; (2) The flat direct joint weakens the effective height of the section and affects the positive bending bearing capacity of the section. In summary, the force transmission performance of the separated joint is poor and it is not suitable for two-way slab composite floor system. The second type of composite floor slab has straight reinforcing bars on both sides of the precast base slab, which are then lapped and anchored into the post-cast strip between adjacent base slabs. Combined with other structural measures, it forms a so-called "integral joint". Due to the superior force transmission performance of the integral joint, it is designated as the slab-side connection of two-way composite floor slabs. However, its base slab has problems such as high production cost, complex structure, cumbersome process, mutual interference of reinforcing bars on the slab side, and low construction efficiency during the prefabrication and assembly stages.

[0004] Furthermore, both of the aforementioned traditional concrete composite slabs employ pre-embedded truss reinforcement or stirrups in the bottom slab to resist shear slip at the composite surface. While truss reinforcement has a complex structure and cumbersome manufacturing process, and stirrups, although relatively simple in shape, both of these shear-resistant measures significantly increase the steel content of the composite slab's structural reinforcement, resulting in high material costs and increasing the difficulty and complexity of component production.

[0005] Furthermore, the maximum applicable span of traditional concrete composite floor slabs is generally no more than 6m. However, large public building projects, in order to pursue building headroom, layout of large spaces, and flexible partitioning, have put forward higher requirements for the span of floor slabs. Existing concrete composite floor slabs are usually difficult to verify through deflection and crack width under normal serviceability limits. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a slotted prestressed concrete composite floor slab and its design and configuration method for improving the bending resistance and force transmission performance of composite floor slabs and the accuracy of deflection calculation.

[0007] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0008] A slotted prestressed concrete composite floor slab includes a precast base slab and a composite cast-in-place layer located above the precast base slab. It also includes additional reinforcing bars arranged at the joints of the composite slab and keyways provided on the side of the precast base slab. The side edge of the precast base slab is chamfered, and the chamfers of adjacent precast base slabs contact each other to form a V-shaped notch and form a concrete reinforcement zone with the keyways. The additional reinforcing bars are located in the keyways within the concrete reinforcement zone.

[0009] As a further improvement to the above technical solution:

[0010] The slotted prestressed concrete composite floor slab also includes non-prestressed steel bars arranged along the non-prestressed direction of the precast base slab. The ends of the non-prestressed steel bars extend from the bottom surface of the keyway and obliquely extend to the composite cast-in-place layer on the opposite side. The extended ends of the non-prestressed steel bars of adjacent precast base slabs are staggered along the joints of the composite floor slab.

[0011] The bending angle of the non-prestressed steel bars is directly proportional to the thickness of the composite floor slab, and the distance from the bending point of the non-prestressed steel bars to the side edge of the precast base plate is inversely proportional to the thickness of the composite floor slab.

[0012] The slotted prestressed concrete composite floor slab also includes cold-formed thin-walled C-shaped steel arranged along the prestressing direction of the precast base slab. The lower flange of the cold-formed thin-walled C-shaped steel is located in the precast base slab, and the upper flange is located in the composite cast-in-place layer. The web of the cold-formed thin-walled C-shaped steel is provided with through holes for non-prestressed steel bars to pass through. The through holes are corresponding to the keyways.

[0013] The design and configuration method for the above-mentioned slotted prestressed concrete composite floor slab includes the following steps:

[0014] Step S01. Estimate the cross-sectional dimensions of the composite slab, and determine the material properties of the composite slab, the bend-up angle of the non-prestressed steel bars in the precast base slab, and the distance from the bend-up point of the non-prestressed steel bars to the side edge of the precast base slab based on the estimation results.

[0015] Step S02. Determine the dimensions and arrangement of the keyway and cold-formed thin-walled C-shaped steel based on the dimensions of the precast base plate;

[0016] Step S03. Calculate the design load values ​​under the load combinations controlled by permanent loads respectively. and the design value of load under quasi-permanent load combination ;

[0017] Step S04. Based on the load design value under the load combination controlled by the permanent load. Calculate the bending moment M and shear force V of the composite slab, and based on the quasi-permanent load combination. Calculate the maximum deflection within the span of a one-way composite slab. ;

[0018] Step S05. Design the reinforcement of the bottom slab bending steel, the reinforcement of the joints within the span, and the reinforcement of the support joints according to the bending moment M of the composite slab.

[0019] Step S06. Determine the current flexural reinforcement of the composite slab, the shear capacity of the support inclined section, and the maximum deflection within the span of the composite slab. If all requirements are met, the final configuration parameters are obtained; otherwise, the thickness of the composite plate is adjusted and the process returns to step S01.

[0020] As a further improvement to the above technical solution: In step S02, determining the size and arrangement of the keyway includes:

[0021] The length of the keyway meets the requirements , The anchorage length of the reinforcing bars should be 200mm-250mm wide and 20mm deep. The spacing between adjacent keyways should be 80mm, and the minimum spacing between the keyway and the outer edge of the precast base plate should be 20mm.

[0022] As a further improvement to the above technical solution: In step S02, determining the dimensions and arrangement of the cold-formed thin-walled C-shaped steel includes:

[0023] The length of the cold-formed thin-walled C-shaped steel is determined by the span of the precast base plate; the height of the through hole is 60mm, and the width and arrangement correspond to the keyway; the lower edge of the through hole 11 is 10mm from the lower flange of the steel section; the spacing between adjacent steel sections in the precast base plate is no more than 400mm, and the distance between the outermost steel section and the side edge of the base plate is no more than 200mm.

[0024] As a further improvement to the above technical solution: In step S03, the design value of the load under the quasi-permanent load combination Including the design value of dead load under quasi-permanent load combination and the design value of live load under quasi-permanent load combination :

[0025] ,

[0026] Design values ​​of dead load under quasi-permanent load combination The calculation expression is:

[0027] ,

[0028] in, Indicates the number of constant loads participating in the combination. This represents the standard value of the i-th dead load;

[0029] Design value of live load under quasi-permanent load combination The calculation expression is:

[0030] ,

[0031] in, Indicates the first Quasi-permanent value coefficient, Indicates the first A standard value for live load, This indicates the number of live loads participating in the combination.

[0032] As a further improvement to the above technical solution: In step S04, based on the quasi-permanent load combination Calculate the maximum deflection of a one-way laminated plate. The calculation formula is:

[0033]

[0034]

[0035]

[0036] in, Indicates the total thickness of the composite plate. Indicates the thickness of the composite cast-in-place layer. Indicates the thickness of the precast base plate. This represents the short-term stiffness of the composite slab in the non-prestressed direction. This represents the stiffness reduction factor in the non-prestressed direction. This indicates the elastic modulus of the composite concrete layer. This indicates the elastic modulus of the prestressed concrete in the base slab. For the moment of inertia of the composite cast-in-place layer section, This represents the moment of inertia of the entire cross section of the composite slab. This represents the coefficient considering the long-term effect of load on the increase of deflection, where, when hour, ;when hour, ;when hour, Values ​​are obtained using linear interpolation. The cross-section is the ratio of compression reinforcement. The tensile reinforcement ratio of the cross section is given. This indicates the maximum deflection of the composite plate. This represents the design value of the load under the quasi-permanent load combination. Indicates the span of the composite slab. This indicates the long-term stiffness of the composite slab in the non-prestressed direction.

[0037] As a further improvement to the above technical solution: In step S05, when designing the reinforcement of the joints within the span, if the additional reinforcement is under tension, the reinforcement design shall be carried out according to the following formula:

[0038]

[0039] in, This represents the cross-sectional area of ​​non-prestressed steel reinforcement in the precast base slab. Indicates the cross-sectional area of ​​the additional reinforcing bars. Indicates the total thickness of the composite plate. Indicates the thickness of the composite cast-in-place layer. Indicates the thickness of the concrete cover on the top of the slab;

[0040] When the additional reinforcing bars are under compression, the cross-sectional area of ​​the additional reinforcing bars satisfies:

[0041]

[0042] Compared with the prior art, the advantages of the present invention are as follows:

[0043] This invention features chamfered edges on the sides of the precast base slab, with adjacent chamfers combining to form a V-shaped notch, creating a concrete reinforcement zone within a keyway at the top of the base slab. Simultaneously, additional reinforcing bars are arranged at the joints of the composite slab and located within the keyway in the concrete reinforcement zone. The V-shaped notch in the concrete reinforcement zone ensures that the additional reinforcing bars are completely bound to the cast-in-place layer at the joint, significantly enhancing the connection strength and load transfer performance between the additional reinforcing bars and the composite cast-in-place layer, thereby greatly improving the bending resistance of the composite slab. Furthermore, the invention achieves localized slab reduction through the keyway, and the placement of the additional reinforcing bars within the keyway increases the effective calculated height of the joint section, further improving bending resistance and load transfer performance, providing a structural foundation for constructing a two-way composite slab system. Moreover, the keyway and the composite cast-in-place layer form a mechanical interlocking effect, further enhancing the shear resistance of the composite surface.

[0044] As can be seen, the present invention, through the combination of V-shaped notches and additional reinforcing bars, ensures that the additional reinforcing bars are always wrapped in the composite cast-in-place layer and are always wrapped in the surrounding new and old interface concrete, giving full play to their material strength, ensuring that the bending bearing capacity of the joint section reaches or is close to that of the cast-in-place layer, and improving the bending and force transmission performance, increasing the applicable span of the composite floor slab, and expanding the application space and scope of the composite floor slab.

[0045] The design and configuration method of this invention can effectively optimize the bending bearing capacity and other properties at the joint, reduce the steel content of the shear resistance measures on the composite surface, and also reduce the implementation cost; the design and configuration method of this invention further introduces a stiffness adjustment coefficient. It can more realistically reflect the anisotropic stiffness distribution caused by the prestressing applied to the composite slab and the weakening of the joint section. Therefore, the calculated deflection is closer to the actual stress characteristics of the floor slab and is suitable for deflection verification of the new composite slab under normal service limit state. Attached Figure Description

[0046] The invention will now be described in more detail with reference to embodiments and the accompanying drawings.

[0047] Figure 1 This is a structural schematic diagram of the slotted prestressed concrete composite floor slab of the present invention;

[0048] Figure 2 yes Figure 1 A sectional view of section AA;

[0049] Figure 3 yes Figure 1 A sectional view of section BB;

[0050] Figure 4 This is a schematic diagram showing the connection relationship between adjacent precast base plates of the present invention;

[0051] Figure 5 This is a schematic diagram showing the positional relationship between the precast base plate and the support beam of the present invention;

[0052] Figure 6 yes Figure 5 Detailed view at point C;

[0053] Figure 7 yes Figure 5 Detailed view at point D;

[0054] Figure 8 yes Figure 5 Detail drawing at point E;

[0055] Figure 9 This is a front view of the cold-formed thin-walled C-shaped steel of the present invention;

[0056] Figure 10This is a schematic diagram illustrating the implementation process of the design and configuration method for slotted prestressed concrete composite floor slabs according to the present invention.

[0057] Figure 11 This is a schematic diagram of the load-deflection curve of the composite plate A obtained by using the finite element method in a specific application embodiment of the present invention.

[0058] The labels in the diagram represent:

[0059] 1. Cold-formed thin-walled C-shaped steel; 11. Through hole; 2. Prestressed steel reinforcement; 3. Non-prestressed steel reinforcement; 4. Keyway; 5. Precast base plate; 51. Chamfer; 6. Additional steel reinforcement; 7. Top surface reinforcement; 8. Composite cast-in-place layer; 9. Support beam; 10. Concrete reinforcement zone. Detailed Implementation

[0060] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments, but this does not limit the scope of protection of the present invention.

[0061] Figures 1 to 8 An embodiment of the slotted prestressed concrete composite floor slab of the present invention is shown. In this embodiment, the slotted prestressed concrete composite floor slab includes a precast base slab 5, a composite cast-in-place layer 8, additional reinforcing bars 6, and a keyway 4. The composite cast-in-place layer 8 is located above the precast base slab 5. The additional reinforcing bars 6 are arranged at the joints along the non-prestressed direction of the precast base slab 5. The keyway 4 is located on the side of the precast base slab 5. Chamfers 51 are provided on both sides of the precast base slab 5. The chamfers 51 of adjacent precast base slabs 5 contact each other to form a V-shaped notch, which combines with the keyway 4 to form a concrete reinforcement zone 10. The additional reinforcing bars 6 are located within the keyway 4 in the concrete reinforcement zone 10 to strengthen the connection between the additional reinforcing bars 6 and the composite cast-in-place layer 8. Its structure is simple, easy to assemble, and highly efficient.

[0062] At this point, the V-shaped notch in the reinforced concrete zone 10 allows the additional reinforcing bar 6 to be completely wrapped by the composite cast-in-place layer 8 at the joint, greatly enhancing the connection strength and force transmission performance between the additional reinforcing bar 6 and the composite cast-in-place layer 8, and significantly improving the bending resistance of the composite floor slab. Simultaneously, this invention achieves a partial slab drop by setting the keyway 4. The additional reinforcing bar 6, placed in the keyway 4, increases the effective calculated height of the joint section, thereby improving bending resistance and force transmission performance, providing a structural foundation for constructing a two-way composite floor slab system. Furthermore, the keyway 4 and the composite cast-in-place layer 8 form a mechanical interlocking effect, further improving the shear resistance of the composite surface.

[0063] As can be seen, the present invention, through the combination of V-shaped notches and additional reinforcing bars 6, ensures that the additional reinforcing bars 6 are always wrapped within the composite cast-in-place layer 8 and are always wrapped within the surrounding new and old interface concrete, fully utilizing their material strength. This ensures that the flexural bearing capacity of the joint section reaches or is close to that of the cast-in-place layer, and improves the flexural and load-bearing performance, increasing the applicable span of the composite floor slab (e.g., the maximum applicable span of the composite floor slab can be expanded to 9 meters), thus expanding the application space and scope of the composite floor slab. The present invention improves the installation efficiency of the precast base slab 5, and after stacking, it can form a bidirectional load-bearing mechanism, reasonably reducing the slab thickness.

[0064] Furthermore, such as Figures 4 to 6 As shown, the slotted prestressed concrete composite floor slab also includes non-prestressed steel bars 3. These non-prestressed steel bars 3 are arranged along the non-prestressed direction of the precast base slab 5. The ends of the non-prestressed steel bars 3 extend from the bottom surface of the keyway 4 and obliquely extend to the cast-in-place layer 8 on the opposite side. The protruding ends of the non-prestressed steel bars 3 of adjacent precast base slabs 5 are staggered along the joints of the composite floor slab. In this embodiment, the spacing of the non-prestressed steel bars 3 is 20mm to 40mm, and the specific staggered spacing can be determined according to the actual reinforcement configuration.

[0065] Compared to existing composite floor slabs, the non-prestressed steel bars 3 of this invention can extend obliquely to the opposite composite cast-in-place layer 8 for effective anchoring. Specifically, by using the non-prestressed steel bars 3 that intersect obliquely on the slab side, the precast base slab 5 and the opposite composite cast-in-place layer 8 are tightly connected. This limits the separation effect between the precast base slab 5 and the composite cast-in-place layer 8 under stress, effectively limiting the lifting effect of old and new concrete at the joint and preventing tearing damage under stress. Furthermore, it effectively avoids the problem of interference between the straight reinforcing bars on both sides of the traditional precast base slab 5, facilitating the standardization of precast molds. Simultaneously, the ends of the non-prestressed steel bars 3 extend from the bottom surface of the keyway 4, effectively avoiding the problem of opening holes and slots in the side molds of the precast base slab 5, thus improving mold production efficiency and reducing costs.

[0066] Preferably, the bending angle α of the non-prestressed steel bar 3 is related to the thickness of the composite floor slab. The distance 'a' from the bend point of the non-prestressed steel bar 3 to the side edge of the precast base slab 5 is directly proportional to the thickness of the composite floor slab. The ratio is inverse; please refer to Table 1 for details.

[0067]

[0068] In this embodiment, the thickness of the precast base plate 5 is 70mm, and the chamfer 51 of the precast base plate 5 is 30°. The length of the keyway 4 meets the following requirements. , For the rebar anchorage length, the width of the keyway 4 is 200mm-250mm, with the width determined by a 10mm modulus based on actual engineering conditions. The depth of the keyway 4 is 20mm, the spacing between adjacent keyways 4 is 80mm, and the minimum distance between the keyway 4 and the outer edge of the precast base slab 5 is 20mm. The distance 'a' from the bend point of the non-prestressed rebar 3 to the side edge of the precast base slab 5 is not less than 30mm and not more than 50mm; the bend angle α of the non-prestressed rebar 3 is not less than 30° and not more than 60°. In other embodiments, the component dimensions can be set according to the actual dimensions of the composite floor slab.

[0069] In this embodiment, the concrete strength grade of the precast base slab 5 is not lower than C30, and the concrete strength grade of the composite cast-in-place layer 8 is not lower than C25.

[0070] Furthermore, such as Figure 3 , Figure 4 , Figures 7 to 9 As shown, the slotted prestressed concrete composite floor slab also includes cold-formed thin-walled C-shaped steel 1, which is arranged along the prestressing direction of the precast base slab 5. The lower flange of the cold-formed thin-walled C-shaped steel 1 is embedded in the precast base slab 5, and the upper flange is located in the composite cast-in-place layer 8. The web is provided with through holes 11 for the reinforcing bars to pass through. The cold-formed thin-walled C-shaped steel 1 embedded in the precast base slab 5 is fully anchored to the composite cast-in-place layer 8, forming a shear slip-resistant structure on the composite surface, which effectively suppresses relative slippage at the interface between the new and old concrete. At the same time, the use of cold-formed thin-walled C-shaped steel 1 to replace the traditional truss reinforcement reduces the steel content of the shear reinforcement in the components, lowers material costs, eliminates the need for formwork construction, and improves assembly efficiency.

[0071] In this embodiment, the length of the cold-formed thin-walled C-shaped steel 1 is determined by the slab span, the spacing between adjacent cold-formed thin-walled C-shaped steel 1 is no greater than 400mm, and the distance from the outermost C-shaped steel to the side edge of the precast base slab 5 is no greater than 200mm. Simultaneously, the upper flange of the cold-formed thin-walled C-shaped steel 1 is located below the top reinforcing bar 7, the concrete cover thickness of the lower flange of the cold-formed thin-walled C-shaped steel 1 is 15mm, the height of the through hole 11 is 60mm, the width and arrangement of the through hole 11 correspond to the keyway 4, and the lower edge of the through hole 11 is 10mm from the lower flange of the C-shaped steel. In other embodiments, the dimensions of the C-shaped steel can be set according to the actual dimensions of the composite floor slab.

[0072] Furthermore, such as Figure 7 and Figure 8 As shown, the additional reinforcing bar 6 located in the outermost precast base slab 5 is anchored into the post-cast concrete of the support beam 9 and extends beyond the centerline of the support beam 9. When the additional reinforcing bar 6 is under compression, the anchorage length extending into the support beam 9 should not be less than 15d (d is the diameter of the additional reinforcing bar 6 at the support joint); when the additional reinforcing bar 6 is under tension, the anchorage length extending into the support beam 9 should not be less than .

[0073] In this embodiment, the diameter of the additional reinforcing bars 6 of the outermost precast base plate 5 is not less than 12mm, and the spacing between adjacent additional reinforcing bars 6 is not greater than 120mm.

[0074] In this embodiment, the composite floor slab also includes prestressed steel bars 2, which are arranged along the prestressing direction of the precast base slab 5. The prestressed steel bars 2 and non-prestressed steel bars 3 are perpendicularly connected to each other and are located within the precast base slab 5. This effectively improves the crack resistance of the composite floor slab under normal serviceability limits, ensuring that the maximum applicable span of the composite floor slab is up to 9m.

[0075] In this embodiment, the diameter of the additional reinforcing bar 6 is not less than 12mm, the spacing between adjacent additional reinforcing bars 6 is not greater than 120mm, and the anchorage length of the reinforcing bar is... .

[0076] In this embodiment, the total thickness of the composite floor slab should not be less than 150mm and should not be greater than 300mm. When the composite floor slab is designed as a one-way slab, the span-to-thickness ratio should not be greater than 30; when it is designed as a two-way slab, the span-to-thickness ratio should not be greater than 40. When the total thickness of the composite floor slab is not greater than 200mm, the spacing of the non-prestressed steel bars 3 should not be greater than 150mm; when the total thickness of the composite floor slab is greater than 200mm, the spacing of the non-prestressed steel bars 3 should not be greater than 1.5 times the total thickness of the composite floor slab; the spacing of the prestressed steel bars 2 should not be greater than 200mm, and the lateral distance between the outermost prestressed steel bar 2 and the precast base slab 5 should not be less than 50mm and not greater than 100mm.

[0077] In this embodiment, the non-prestressed steel bar 3 can be HRB400, HRB500, HRBF400, or HRBF500, while the prestressed steel bar 2 can be prestressed steel wire, steel strand, or prestressed threaded steel bar.

[0078] This embodiment further provides a design and configuration method for the above-mentioned slotted prestressed concrete composite floor slab, such as... Figure 10 As shown, the steps include:

[0079] Step S01. Estimate the cross-sectional dimensions of the composite slab, and determine the material properties of the composite slab, the bending angle of the non-prestressed steel bars 3 in the precast base slab 5, and the distance from the bending point of the non-prestressed steel bars 3 to the side edge of the precast base slab 5 based on the estimation results.

[0080] Step S02. Determine the dimensions and arrangement of the keyway 4 and the cold-formed thin-walled C-shaped steel 1 based on the dimensions of the precast base plate 5;

[0081] Step S03. Calculate the design load values ​​under the load combinations controlled by permanent loads respectively. and the design value of load under quasi-permanent load combination ;

[0082] Step S04. Based on the load design value under the load combination controlled by the permanent load. Calculate the bending moment M and shear force V of the composite slab, and based on the quasi-permanent load combination. Calculate the maximum deflection within the span of a one-way composite slab. ;

[0083] Step S05. Design the reinforcement of the bottom slab bending steel, the reinforcement of the joints within the span, and the reinforcement of the support joints according to the bending moment M of the composite slab.

[0084] Step S06. Determine the current flexural reinforcement of the composite slab, the shear capacity of the support inclined section, and the maximum deflection within the span of the composite slab. If all requirements are met, the final configuration parameters are obtained; otherwise, the thickness of the composite plate is adjusted and the process returns to step S01.

[0085] In specific application embodiments, the following assumptions are also made:

[0086] (1) When the length-to-width ratio of a prestressed concrete composite floor slab is not greater than 2, it shall be designed as a two-way slab; when the ratio of the long side to the short side is greater than 2, it shall be designed as a one-way slab.

[0087] (2) The prestressed concrete composite floor slab prevents the precast base slab 5 and the composite cast-in-place layer 8 from lifting and relative slippage through structural measures. The additional steel reinforcement 6 can fully utilize its material strength, and the entire cross section of the composite slab is effective. Therefore, the flexural bearing capacity of the composite slab and the shear bearing capacity of the oblique section can be calculated.

[0088] (3) The close-fitting joints have a weakening effect on the flexural bearing capacity of the cross section. Therefore, when designing the reinforcement of the additional steel bar 6, the design value of the bending moment of the joint section is 8% larger than the design value of the bending moment of the entire cross section of the composite slab, and the calculated height of the section is taken as the distance between the additional steel bar 6 and the point of action of the resultant force of the compression steel bar on the top surface of the composite layer.

[0089] (4) The close-fitting joints have a weakening effect on the shear control section at the edge of the support. Therefore, only the contribution of the composite cast-in-place layer 8 to the shear bearing capacity of the inclined section is considered.

[0090] In this embodiment, step S01 also includes initial configuration such as cross-sectional dimension estimation and preliminary selection of material properties. When estimating the cross-sectional dimensions, the composite slab system is applicable to spans from 2.1m to 9m, and the cross-sectional dimensions are based on... ( For the estimation of secondary beam spacing; when initially selecting material properties, the concrete grade can be initially selected based on the total thickness of the composite slab, while the steel reinforcement grade can be selected based on engineering experience first, and then verified and confirmed based on the internal force analysis results.

[0091] In step S02 of this embodiment, determining the size and arrangement of the keyway 4 includes:

[0092] Keyway 4 length meets , The anchorage length of the reinforcing bar is 200mm-250mm (the value can be taken as a module of 10mm according to the actual project situation), the depth is 20mm, the spacing between adjacent keyways 4 is 80mm, and the minimum spacing between keyway 4 and the outer edge of the precast base plate 5 is 20mm.

[0093] In this embodiment, step S02, determining the size and distribution of the cold-formed thin-walled C-shaped steel 1 includes:

[0094] The length of the cold-formed thin-walled C-shaped steel 1 is determined by the span of the precast base plate 5; the height of the through hole 11 in the web of the steel is 60mm, and the width and arrangement should correspond to the keyway 4. The lower edge of the through hole 11 is 10mm away from the lower flange of the steel; the spacing between adjacent steel sections in the precast base plate 5 is no more than 400mm, and the distance between the outermost steel section and the side edge of the base plate is no more than 200mm.

[0095] In step S03 of this embodiment, the design value of the load under the load combination controlled by the permanent load is... Design values ​​of dead loads under load combinations controlled by permanent loads and the design value of live load under load combinations controlled by permanent loads. .

[0096] Specifically, the design value of dead load under the load combination controlled by permanent loads. The calculation expression is:

[0097] (1)

[0098] in, This represents the partial factor for the i-th constant load. This represents the standard value of the i-th constant load.

[0099] Design value of live load under load combination controlled by permanent load The calculation expression is:

[0100] (2)

[0101] in, Indicates the first Live load partial factor, Indicates the first An adjustment factor for each variable load considering the design service life. Indicates the first Live load combination coefficient, Indicates the first A standard value for live load, This indicates the number of live loads participating in the combination.

[0102] Then according to the formula Design values ​​of loads under load combinations controlled by permanent loads are obtained. As shown in equation (2) above, this embodiment forms the adjustment coefficient by fully considering the service life of each variable load. And considering the coefficients of each live load combination value Taking into account the various live load partial factors and standard value of live load Obtain the design value of live load under load combination This approach can improve the accuracy of determining the design value of live load by integrating multiple influencing factors.

[0103] In this embodiment, the design load value under the quasi-permanent load combination Including the design value of dead load under quasi-permanent load combination and the design value of live load under quasi-permanent load combination The design value of dead load under quasi-permanent load combination The calculation expression is:

[0104] (3)

[0105] in, Indicates the number of constant loads participating in the combination. This represents the standard value of the i-th constant load.

[0106] Design value of live load under quasi-permanent load combination The calculation expression is:

[0107] (4)

[0108] in, Indicates the first Quasi-permanent value coefficient, Indicates the first A standard value for live load, This indicates the number of live loads participating in the combination.

[0109] Then according to Obtain the design values ​​of the loads under the quasi-permanent load combination. .

[0110] In step S04 of this embodiment, the composite slab adopts a load combination controlled by permanent load. Perform internal force analysis and calculate the combination of quasi-permanent loads. The maximum deflection within the span of a one-way composite slab is calculated. This is based on the quasi-permanent load combination. Calculate the maximum deflection of a one-way laminated plate. The calculation formula is:

[0111] (5)

[0112] (6)

[0113] (7)

[0114] in, Indicates the total thickness of the composite plate. Indicates the thickness of the composite cast-in-place layer. Indicates the thickness of the precast base plate. This represents the short-term stiffness of the composite slab in the non-prestressed direction. This represents the stiffness reduction factor in the non-prestressed direction. This indicates the elastic modulus of the composite concrete layer. This indicates the elastic modulus of the prestressed concrete in the base slab. For the moment of inertia of the 8 sections of the superimposed cast-in-place layer, The moment of inertia of the entire cross section of the composite slab, This represents the coefficient considering the long-term effect of load on the increase of deflection, where, when hour, ;when hour, ;when hour, Values ​​are obtained using linear interpolation. The cross-section is the ratio of compression reinforcement. The tensile reinforcement ratio of the cross section is given. This indicates the maximum deflection of the composite plate. This represents the design value of the load under the quasi-permanent load combination. Indicates the span of the composite slab. This indicates the long-term stiffness of the composite slab in the non-prestressed direction.

[0115] As shown in equation (5) above, considering the weakening effect of close-fitting joints on the bending stiffness of the composite slab in the non-prestressed direction, this embodiment introduces a stiffness reduction factor into the calculation formula for the bending stiffness of the composite slab in the non-prestressed direction. This allows for the reflection of the weakening effect of the prestressed bending stiffness, and adjustment of the short-term stiffness of the composite slab in the non-prestressed direction. At the same time, based on the tensile reinforcement ratio of the cross-section... Determine the influence coefficient of long-term load on deflection increase. Then, the long-term stiffness of the composite slab in the non-prestressed direction was calculated. Considering the long-term stiffness of the composite slab in the non-prestressed direction The long-term effect of load on deflection can be considered to accurately calculate the deflection of one-way composite slabs. .

[0116] In a preferred embodiment, step S04 of this embodiment further includes determining the stiffness reduction factor in the non-prestressed direction. The steps include:

[0117] Step S401. Use the finite element analysis method to obtain the load-deflection curves of the current composite slab under different structural conditions. The load-deflection curves are curves showing the relationship between load and deflection.

[0118] Step S402. Take the secant stiffness corresponding to the deflection reaching L / 200 in the load-deflection curve as the equivalent stiffness D1 of the composite plate under normal serviceability limit state;

[0119] Step S403. Calculate the flexural stiffness D0 of the cast-in-place slab with the same thickness as the current composite slab. Compare the equivalent stiffness D1 of the composite slab under the normal serviceability limit state with the flexural stiffness D0 of the cast-in-place slab with the same thickness to obtain the non-prestressed directional stiffness reduction factor. .

[0120] In step S05 of this embodiment, the design of the positive cross-section within the span of the composite slab includes:

[0121] (1) Single-reinforced section design: When calculating the reinforcement of the bottom slab tensile reinforcement in the positive section according to the single-reinforced rectangular section design method, the preset maximum and minimum reinforcement ratio requirements must be met; if the reinforcement ratio of the bottom tensile reinforcement does not meet the preset maximum reinforcement ratio requirements, the positive section reinforcement calculation shall be carried out according to the double-reinforced rectangular section design method.

[0122] (2) Double-reinforced section design: When calculating the reinforcement of the positive section according to the double-reinforced rectangular section design method, it may meet the preset maximum and minimum reinforcement ratio requirements. If the reinforcement ratio of the tensile reinforcement at the bottom of the slab still does not meet the maximum reinforcement ratio requirement, the design should be adjusted, that is, the estimated total thickness of the composite slab should be increased, and then the positive section design should be carried out again until the reinforcement ratio requirement is met.

[0123] In this embodiment, when designing the reinforcement of the joint within the span in step S05, the reinforcement design is performed according to the following formula when the additional steel bar 6 is under tension:

[0124] (8)

[0125] in, This represents the cross-sectional area of ​​the non-prestressed steel reinforcement in the precast base slab 5. Indicates the cross-sectional area of ​​the additional reinforcing bars. Indicates the total thickness of the composite plate. Indicates the thickness of the composite cast-in-place layer. This indicates the thickness of the concrete protective layer on top of the slab.

[0126] When the additional reinforcing bar 6 is under compression, the cross-sectional area of ​​the additional reinforcing bar satisfies:

[0127] (9)

[0128] When the additional reinforcement is under tension, the reinforcement ratio of the additional reinforcement 6 per unit width of the slab should be greater than the reinforcement ratio of the non-prestressed reinforcement 3 in the precast bottom slab 5. In this embodiment, by designing the reinforcement of the joint within the span according to the above formula (8), and combining the constraint condition of the cross-sectional area of ​​the additional reinforcement 6 under compression, the reinforcement design of the joint within the span can be effectively made to meet the requirements and optimize the reinforcement design of the joint within the span.

[0129] In this embodiment, when designing the reinforcement of the composite slab support cross section in step S05, since the joint at the support completely isolates the precast base slab 5 and the support beam 9, the effective height of the support cross section is taken as the distance between the additional steel bar 6 and the point of action of the resultant force of the compression steel bar on the top surface of the composite layer. The additional steel bar 6 serves as the bottom steel bar of the cross section.

[0130] The composite slab does not have stirrups, and the reinforcing bars in the precast base slab 5 cannot be bent upwards. The shear force of the composite slab's control section is borne by the composite layer concrete. In this embodiment, step S04 optimizes the shear capacity of the composite slab's support by verifying the shear capacity of the inclined section. Specifically, the following formula for verifying the shear capacity of the inclined section can be used: , In the formula: The influence coefficient of section height, when At that time, take , This represents the design value of the tensile strength of the composite concrete layer. The width of the board is in mm. V represents the effective height (mm) of the composite cast-in-place layer, and V is the design value of shear force under the load combination controlled by permanent load. If the shear resistance of the inclined section does not meet the requirements, the estimated total thickness of the composite slab can be increased, or high-strength concrete can be used.

[0131] In this embodiment, step S06 involves verifying the maximum deflection of the composite plate, which can optimize the deflection of the composite plate and improve structural durability. Specifically, if the deflection verification does not meet the requirements, the estimated total thickness of the composite plate is increased.

[0132] To verify the performance of this invention, in a specific application embodiment, the above-described method of this invention was used to calculate and analyze the key mechanical parameters of a single-joint slotted prestressed concrete C-shaped steel composite slab with inclined reinforcement (hereinafter referred to as composite slab A). Correspondingly, a cast-in-place slab and a standard composite slab were compared and analyzed. The geometric dimensions, peripheral support conditions, and longitudinal reinforcement ratio of the bottom stress reinforcement of the cast-in-place slab are the same as those of composite slab A in this embodiment. The concrete strength grade is C30, and it is cast in one piece without joints or overlapping surfaces; it is simply referred to as cast-in-place slab A. The bottom plate dimensions, composite layer thickness, peripheral support conditions, concrete strength grade, joint location, and additional reinforcement 6 at the joint of the standard composite slab are the same as those of composite slab A in this embodiment. The only difference is the use of a separated joint structure, with no reinforcement on the side of the precast concrete bottom plate; it is simply referred to as composite slab B.

[0133] Specifically, the composite slab A is a single-section slab with simple support on all four sides. In this embodiment, a 1m slab width is taken as the research object, with specific dimensions of 4000mm × 1000mm × 150mm. It is constructed by closely splicing two 2000mm × 1000mm × 70mm slotted, obliquely reinforced prestressed concrete C-shaped steel precast base slabs. The thickness of the composite cast-in-place layer 8 is 80mm. The precast base slab 5 uses C40 concrete, and the composite cast-in-place layer 8 uses C30 concrete. The non-prestressed steel bars 3 in the composite slab use HRB400 grade steel bars; the prestressed steel bars 2 use... Spiral ribbed steel wire , , The live load was taken as 3.5 kN / m2, and the concrete cover thickness was 20 mm.

[0134] According to the method of this invention, the load combination controlled by permanent load is calculated as: p = 1.3 × 25 × 0.15 + 1.5 × 4 × 0.7 = 9.08 kN / m, which is then used for the reinforcement design of the floor slab section; and the quasi-permanent load combination is calculated as follows: This is then used for the serviceability limit state verification of floor slabs.

[0135] Then, the stiffness reduction factor is solved according to the method of this invention. :

[0136] (1) The load-deflection curve of the composite plate A under loading was simulated using ABAQUS finite element software. The specific analysis results are as follows: Figure 11 As shown.

[0137] Will Figure 11 The mid-span displacement in the load-deflection curve reaches L Secant stiffness at / 200 is converted to the actual bending stiffness of the composite slab. and the flexural stiffness of cast-in-place floor slabs of equal thickness Compared to the obtained non-prestressed direction stiffness adjustment coefficient .

[0138] The internal force calculations and reinforcement design of the in-span sections were performed, and the results are shown in Table 2.

[0139]

[0140] The test results and theoretical calculation results of the above composite slab A, cast-in-place slab A, and composite slab B are compared, and the results are shown in Tables 3 and 4. Table 4 compares the calculated deflection values ​​with the experimental values. When using formula (7) of this invention to calculate the theoretical deflection of the composite slab, the increase factor of long-term load on the deflection is not considered, and the following is set... Right now .

[0141]

[0142]

[0143] As shown in Table 3, the test and calculated values ​​of the flexural bearing capacity of the composite slab A of the present invention are close to those of the cast-in-place slab A and much greater than those of the composite slab B. This is because: (1) the grooved and lowered slab of the precast bottom plate 5 of the composite slab A of the present invention, which places additional steel bars 6, effectively increases the effective calculated height of the joint section; (2) the cross-anchoring of the diagonal reinforcing bars on the side of the slab effectively limits the lifting effect between the precast and composite concrete at the joint, ensuring that the additional steel bars 6 will not be pulled out or slip under stress; (3) the chamfer 51 on the side of the slab ensures that the additional steel bars 6 are fully wrapped in the post-cast concrete at the joint section, and can fully exert their tensile strength. The above comprehensive measures ensure that the joint structure of the present invention can achieve the same flexural bearing capacity as cast-in-place slabs, and based on the reliable force transmission mechanism, it can also be applied to two-way slabs with a length-to-width ratio of no more than 2.

[0144] The separated joint (composite slab B) lacks structural integrity and has poor force transmission performance, which led to brittle failure of the joint section during the test due to concrete uplift and slippage. Its flexural bearing capacity is far from being equivalent to that of cast-in-place slabs, and the theoretical calculation method for the flexural bearing capacity of cast-in-place slabs cannot be used. Its test value is the actual bending moment borne by the mid-span joint section when the composite slab experiences brittle failure.

[0145] As shown in Table 4, the deflection test value of the composite slab A of the present invention increased by 10.5% compared with that of the cast-in-place slab A. This indicates that the close joints of the composite slab of the present invention do indeed change its stiffness distribution along the span direction, resulting in a significant increase in deflection under load. Directly applying the design method of the cast-in-place slab would lead to dangerously biased deformation calculation results. In addition, the test results show that the standard composite slab B will experience brittle failure due to slippage of the composite surface under the design load, making it impossible to calculate or measure its deflection.

[0146] By introducing a stiffness reduction factor, this invention considers the weakening of cross-sectional discontinuous stiffness caused by the distribution of joints in the non-prestressed direction. The calculated deflection value of composite plate A is very close to the experimental value, indicating that the method of this invention can objectively reflect the real structural characteristics of the new composite plate, and the accuracy fully meets the engineering requirements.

[0147] On the other hand, Table 4 lists the steel content of the shear resistance measures at the joint surface of composite slab A and composite slab B. The cold-formed thin-walled C-shaped steel 1 used in composite slab A of the present invention as the shear resistance measure at the joint surface not only completely restricts the relative slippage between the precast base plate 5 and the composite layer under stress, but also reduces its steel content by 80% compared with traditional truss reinforcement, which greatly reduces the production cost of composite slab. That is, the structure and method of the present invention can effectively reduce costs.

[0148] In summary, the joint structure of the composite slab of this invention exhibits superior force transmission performance compared to the standard separated joint. The flexural bearing capacity at the joint is essentially equivalent to that of cast-in-place concrete, and the steel content of the shear resistance measures on the composite surface is effectively reduced, while also lowering implementation costs. Furthermore, this invention more accurately reflects the anisotropic stiffness distribution caused by prestressing of the composite slab and weakening of the joint section, resulting in a calculated deflection that more closely approximates the actual stress characteristics of the floor slab. This makes it suitable for deflection verification of the new composite slab under normal serviceability limits.

[0149] Preferred embodiments have been described for the present invention, but various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of the invention. In particular, the technical features mentioned in the various embodiments can be combined in any manner as long as there is no structural conflict. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A design and arrangement method for a slotted prestressed concrete composite floor slab, the slotted prestressed concrete composite floor slab comprising a prefabricated bottom plate (5) and a composite cast-in-place layer (8) above the prefabricated bottom plate (5), further comprising additional steel bars (6) arranged at the joint of the composite slab, and a keyway (4) provided on the side of the prefabricated bottom plate (5), the side edge of the prefabricated bottom plate (5) is provided with a chamfer (51), the chamfers (51) of adjacent prefabricated bottom plates (5) are in contact with each other to form a V-shaped gap, and form a concrete reinforced area (10) with the keyway (4); the additional steel bars (6) are located in the keyway (4) in the concrete reinforced area (10), characterized by the steps of Comprise: Step S01. Estimate the size of the laminated slab section, and determine the material properties of the laminated slab, the bending angle of the non-prestressed steel bar (3) in the prefabricated bottom plate (5), and the distance from the bending point of the non-prestressed steel bar (3) to the side edge of the prefabricated bottom plate (5) according to the estimation results; Step S02. Determine the size and arrangement of the key groove (4) and the cold-formed thin-walled C-shaped steel (1) based on the size of the prefabricated bottom plate (5); Step S03. Calculate the load design value under load combination of permanent load control respectively and load design value under load combination of quasi-permanent load ; Step S04. Load combination design value under the permanent load control Calculate the bending moment of the composite slab With shear And load design value under load combination according to quasi-permanent load Calculate the maximum deflection of the one-way composite slab across ; Step S05. According to the bending moment of the laminated slab The bottom plate bending resisting steel reinforcement, the cross joint spanning reinforcement and the support joint reinforcement are respectively designed. Step S06. judging whether the bending reinforcement of the current composite slab, the shear capacity of the bearing oblique section, and the maximum deflection of the composite slab within the span meet the requirements If yes, the final configuration parameters are obtained, otherwise the thickness of the composite slab is adjusted and the step S01 is returned. In step S04, the load design value under the quasi-permanent load combination is calculated The calculation formula of the maximum deflection of the one-way slab composite slab is: The calculation formula of the maximum deflection of the one-way slab composite slab is: ， wherein, denotes the total thickness of the composite slab, denotes the thickness of the cast-in-situ layer, denotes the thickness of the precast bottom slab, denotes the short-term stiffness of the composite slab in the non-prestressed direction, denotes the reduction factor of the non-prestressed stiffness, denotes the elastic modulus of the composite layer concrete, denotes the elastic modulus of the prestressed concrete of the bottom slab, is the sectional moment of inertia of the cast-in-situ layer, denotes the total sectional moment of inertia of the composite slab, denotes the factor considering the effect of the load long-term action on the deflection increase, wherein when , ; when , ; when , is obtained by linear interpolation, is the sectional reinforcement ratio of the compression reinforcement, is the sectional reinforcement ratio of the tension reinforcement, denotes the maximum deflection of the composite slab, denotes the load design value under the quasi-permanent load combination, denotes the span of the composite slab, denotes the long-term stiffness of the composite slab in the non-prestressed direction.

2. The design configuration method according to claim 1, wherein In the step S02, the size and arrangement of the key groove (4) include: The length of the keyway (4) satisfies 1.2 , The length of the keyway (4) satisfies 1.2 The length of the keyway (4) satisfies 1.2 3. The design configuration method of claim 1, wherein In the step S02, the dimensions and arrangement of the cold-formed thin-walled steel (1) are determined to include: Cold-formed thin-walled The length of the profiled steel (1) is determined by the slab span of the prefabricated bottom plate (5); the height of the through hole (11) is 60 mm, the width and arrangement of the through hole (11) correspond to the key groove (4), and the lower edge of the through hole (11) is 10 mm away from the lower flange of the profiled steel; the distance between adjacent profiled steels in the prefabricated bottom plate (5) is not greater than 400 mm, and the distance between the outermost profiled steel and the side edge of the bottom plate is not greater than 200 mm.

4. The design configuration method according to any one of claims 1 to 3, characterized by, In step S05, the design of the joint in the span is as follows: ， wherein, Apsrepresents the cross-sectional area of the non-prestressed reinforcement in the prefabricated slab (5), Apsaddrepresents the cross-sectional area of the additional reinforcement, Apsrepresents the total thickness of the composite slab, Apsrepresents the thickness of the cast-in-situ layer of the composite, Apsrepresents the thickness of the concrete cover on the top of the slab; When the additional steel bar is in tension, the cross-sectional area of the additional steel bar satisfies:

5. The design configuration method according to any one of claims 1 to 3, characterized by, Also comprising a non-prestressed steel bar (3) arranged in the non-prestressed direction of the prefabricated bottom plate (5), the end of the non-prestressed steel bar (3) extends from the bottom surface of the key groove (4) and extends obliquely to the opposite laminated cast-in-place layer (8); The extension end of the non-prestressed steel bar (3) of the adjacent prefabricated bottom plate (5) is arranged staggered along the joint of the composite floor.

6. The design configuration method according to any one of claims 1 to 3, characterized by, The bending angle of the non-prestressed steel bar (3) is proportional to the thickness of the composite floor, and the distance from the bending point of the non-prestressed steel bar (3) to the side edge of the prefabricated bottom plate (5) is inversely proportional to the thickness of the composite floor.

7. The design configuration method according to any one of claims 1 to 3, characterized by, Also comprising a cold-formed thin-walled C-shaped steel (1) arranged in the prestressed direction of the prefabricated bottom plate (5), the lower flange of the cold-formed thin-walled C-shaped steel (1) is arranged in the prefabricated bottom plate (5), and the upper flange is arranged in the laminated cast-in-place layer (8), the web of the cold-formed thin-walled C-shaped steel (1) is provided with a through hole (11) for the non-prestressed steel bar (3) to pass through, and the through hole (11) is arranged corresponding to the key groove (4).

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