Refractory concrete trepanned composite beam partially coated with honeycomb profile steel and construction method

Abstract

The invention discloses a fire-resistant concrete perforated composite beam partially coated with honeycomb profile steel and a construction method. The composite beam comprises the honeycomb profile steel and fire-resistant concrete. The refractory concrete is ultra-high performance concrete doped with polyvinyl alcohol fibers, is located between an upper flange and a lower flange of the honeycomb profile steel and completely wraps the web, the honeycomb profile steel is laterally placed and then poured, the pouring process is completed at a time, and turning is not needed; a plurality of concrete holes are formed in the refractory concrete, and the concrete round holes are communicated with honeycomb holes in the honeycomb type steel web. According to the invention, the internal steam pressure of the UHPC at high temperature is evacuated by using fine pore channels formed after the PVA is melted at high temperature, so that the high-temperature burst behavior of the UHPC is reduced. On one hand, the honeycomb profile steel improves the flexural capacity of the beam, and on the other hand, the honeycomb holes are used as connecting channels for side pouring of the prefabricated concrete, so that the pouring process of the PEC beam concrete is simplified, and conditions are provided for trepanning of the concrete beam web.

Description

Technical Field

[0001] The invention belongs to the field of building technology, and particularly relates to a partially encased cellular steel fire-resistant concrete perforated composite beam and a construction method thereof. Background Art

[0002] The partially encased steel-concrete composite beam (PEC beam) is developed on the basis of the traditional steel-concrete composite beam. By pouring concrete in the area between the upper and lower flanges on both sides of the steel section, it solves the problem of poor stability of the traditional steel structure. At the same time, the concrete, as an insulation layer, improves the fire resistance of the structure. However, the steel sections of traditional PEC beams often use solid-web steel sections, which are difficult to perforate the concrete on both sides. At the same time, the pouring of the concrete on both sides requires reverse pouring, which makes the construction process cumbersome and the construction period longer. At the same time, traditional PEC beams often use ordinary-grade concrete, which has poor compressive and tensile properties and low durability. However, if ultra-high performance concrete (UHPC) is used, due to its dense microstructure, there are often serious spalling phenomena in the structure in case of fire or high-temperature environment, resulting in a decline in the mechanical properties of the structure. Summary of the Invention

[0003] In order to overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a partially encased cellular steel fire-resistant concrete perforated composite beam and a construction method thereof. The fire-resistant concrete adopts ultra-high performance concrete (UHPC) doped with polyvinyl alcohol fiber (PVA fiber). It uses the fine pores formed after the PVA melts at high temperature to evacuate the internal steam pressure of the UHPC at high temperature, thereby reducing the high-temperature spalling behavior of the ultra-high performance concrete. At the same time, the steel section uses cellular steel. On the one hand, the material distribution is far from the neutral axis, increasing the moment of inertia of the cross-section, which has a significant effect on improving the flexural bearing capacity of the beam. On the other hand, the honeycomb holes serve as the connection channels for the precast concrete to be placed and poured laterally, which not only simplifies the concrete pouring process of the PEC beam but also provides conditions for perforating the concrete web. In addition, the longitudinal reinforcement in the present invention can be used as another guarantee for the fire resistance of the structure, providing double guarantees for the fire resistance of the structure through reasonable design.

[0004] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0005] A partially encased cellular steel fire-resistant concrete perforated composite beam includes a cellular steel section and fire-resistant concrete; the fire-resistant concrete is ultra-high performance concrete doped with polyvinyl alcohol fiber, located between the upper and lower flanges of the cellular steel section and completely covering the web. After the cellular steel section is placed laterally, the pouring process is completed at one time without the need for reverse pouring; a number of concrete holes are opened in the fire-resistant concrete, and the concrete round holes communicate with the honeycomb holes on the web of the cellular steel section.

[0006] In one embodiment, longitudinal bars and stirrups are also distributed between the upper and lower flanges of the cellular steel section. Both the longitudinal bars and stirrups are embedded in the refractory concrete. The stirrups are C-shaped stirrups, with both upper and lower sides bent by a certain length and welded to the inner sides of the upper and lower flanges of the cellular steel section.

[0007] In one embodiment, longitudinal stiffeners are welded to both sides of the web of the cellular steel section. The longitudinal stiffeners are located on both upper and lower sides of the concrete holes and are closely attached to the upper and lower edges of the cellular holes.

[0008] In one embodiment, the concrete holes are coaxial with the cellular holes they communicate with, and the diameter of the concrete holes is smaller than the inner diameter of the cellular holes, preferably connected to the edges of the cellular holes.

[0009] In one embodiment, the volume fraction of polyvinyl alcohol fibers in the ultra-high performance concrete is 0.5 - 1.0%.

[0010] The present invention also provides a construction method for the partially encased cellular steel section refractory concrete open-hole composite beam, and the steps are as follows:

[0011] Place the cellular steel section horizontally and fix it, set up formworks at both ends, reserve the concrete holes with a mold, and then pour the refractory concrete and carry out steam curing;

[0012] The horizontal placement means that the upper and lower flanges of the cellular steel section are in the vertical position and the web is in the horizontal position.

[0013] In one embodiment, the cellular steel section is made by cutting and welding steel plates, and stirrups and longitudinal stiffeners are welded, and the longitudinal bars are fixed.

[0014] In one embodiment, the mold for reserving the concrete holes has the same shape as the cellular holes on the web of the cellular steel section, and the reserved mold also serves as a permanent formwork to avoid formwork removal.

[0015] When the partially encased cellular steel section refractory concrete open-hole composite beam of the present invention is applied to a building structure, stud bolts are welded to the outer side of its upper flange. During on-site construction, the composite floor slab is fixed first, and then the cast-in-place part is constructed.

[0016] The partially encased cellular steel section refractory concrete open-hole composite beam of the present invention can also be used as a crane beam. At this time, the concrete holes are removed. During prefabrication, holes are drilled in the upper flange of the cellular steel section and bolts are installed. The tails of the bolts are embedded in the inner side of the upper flange, and the rails are installed on-site through the bolts and pressing plates.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] 1. Improved fire resistance

[0019] The present invention utilizes the low melting point of polyvinyl alcohol (PVA) fibers. When a fire occurs, the organic fibers melt first to form fine channels inside the structure, avoiding the accumulation of steam pressure inside the structure, and fundamentally solving the problem of high-temperature bursting of ultra-high performance concrete (UHPC). The longitudinal reinforcement can be reasonably designed as the second barrier of structural fire resistance. When the external steel fails due to high temperature, the structure will not collapse suddenly, which will buy time for fire fighting and provide the possibility for structural reinforcement after the fire.

[0020] 2. Convenient construction

[0021] The present invention adopts honeycomb steel with holes in its web. On the one hand, it serves as a connecting channel for the side pouring of precast concrete, realizing the single pouring of concrete on the side of the PEC beam, avoiding the problem of secondary flipping and pouring caused by traditional solid-web steel, reducing the concrete curing time by half, and improving the prefabrication efficiency of the factory; on the other hand, the holes in the web of the steel provide conditions for the holes in the web of the concrete beam, which is convenient for the layout of pipelines.

[0022] 3. Improve overall stress performance

[0023] In the present invention, concrete on both sides of the steel web is formed at one time, and the concrete at the honeycomb hole position can be used as a connector between the steel and the precast concrete to bear the longitudinal shear resistance, thereby greatly improving the overall performance of the structure.

[0024] 4. Save materials

[0025] The structure of the present invention adopts honeycomb steel. Compared with solid steel, its cross section is more expanded and the cross-sectional inertia moment is larger under the same material, especially for the significant effect of improving the bending bearing capacity. In addition, the present invention eliminates the shear connector on the concrete web in the traditional structure, and uses the concrete at the opening position to resist the longitudinal shear force, which greatly saves steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the structure of the present invention.

[0027] Figure 2 Schematic diagram of different opening structures of the present invention.

[0028] Figure 3 It is a schematic diagram of an application scenario of the present invention.

[0029] Figure 4 It is a schematic diagram of another application scenario of the present invention. DETAILED DESCRIPTION

[0030] The embodiments of the present invention are described in detail below with reference to the accompanying drawings and examples.

[0031] like Figure 1As shown in the figure, the present invention is a partially clad cellular steel fire-resistant concrete open-combination beam, mainly including fire-resistant concrete 1 and cellular steel 2. Among them, the fire-resistant concrete 1 is ultra-high performance concrete (UHPC) doped with polyvinyl alcohol (PVA) fibers. The fire-resistant concrete 1 is located between the upper and lower flanges of the cellular steel 2, completely covering the web, but not covering the upper and lower flanges of the cellular steel 2, that is, keeping the outer sides and side ribs of the upper and lower flanges exposed. This is the meaning of the partial cladding of the present invention. This cladding method is different from the "fully clad" form in the prior art where small steel is completely placed inside the concrete. The outer dimensions of the cellular steel 2 are much larger than those of the small steel in the "fully clad" form.

[0032] At the same time, the fire-resistant concrete 1 can adopt a pouring method different from the "fully clad" form in the prior art. Specifically, after the cellular steel 2 is placed sideways for pouring, the upper and lower flanges of the cellular steel 2 are used as formworks, and the pouring process can be completed at one time without the need for turning over. Although the upper flange still needs to be wrapped due to the construction of the upper flange floor later, the side ribs of the upper flange and the large area of the lower flange are still in an exposed state.

[0033] A number of concrete holes 6 are provided in the fire-resistant concrete 1 of the present invention. The concrete round holes 6 communicate with the cellular holes 7 on the web of the cellular steel 2 and are used for the passage of equipment pipelines.

[0034] The design of the fire-resistant concrete 1 of the present invention can utilize the fine pores formed after the high-temperature melting of PVA to evacuate the internal steam pressure of UHPC at high temperatures, thereby reducing the high-temperature spalling behavior of ultra-high performance concrete and significantly enhancing the fire resistance of the structure. In a further embodiment of the present invention, the volume fraction of polyvinyl alcohol fibers in the ultra-high performance concrete is preferably 0.5 - 1.0%, and the water-cement ratio is adjusted from 0.18 to 0.19 compared with the original UHPC mix without PVA fibers. When the size of the cellular holes 7 is small or the steel reinforcement ratio is large, a volume fraction of 0.5% is recommended to ensure the workability of the concrete. In addition, for the construction of the fire-resistant concrete 1, it is recommended to use a full-bridge forced mixer with a greater mixing force for mixing.

[0035] The present invention uses cellular steel 2. On the one hand, the material distribution is far from the neutral axis, increasing the moment of inertia of the cross-section, which has a significant effect on improving the flexural bearing capacity of the beam. On the other hand, the cellular holes 7 serve as the connection channels for the precast pouring of the fire-resistant concrete 1, which not only simplifies the pouring process of the PEC beam concrete but also provides conditions for opening holes in the beam web. For example, the cellular steel 2 can be formed by cutting a solid web steel and butt-welding it in a staggered manner, and it is preferably a cellular steel with equal upper and lower flanges.

[0036] In a further embodiment of the present invention, longitudinal bars 3 and stirrups 4 are also distributed between the upper and lower flanges of the cellular steel section 2, and both the longitudinal bars 3 and the stirrups 4 are embedded in the fire-resistant concrete 1. Among them, the longitudinal bars 3 not only act as stress-bearing steel bars at normal temperature to share part of the load, but also serve as a double guarantee in adverse environments. For example, after the outer steel flange suffers significant damage in a highly corrosive or high-temperature environment, it can bear the load under normal service conditions of the structure and its own weight, providing internal support for structural reinforcement and preventing sudden structural failure. Specifically, due to the thermal inertia of the concrete, the inward propagation of temperature is greatly reduced. Therefore, when the lower steel flange fails due to fire, the longitudinal bars 3 can serve as another guarantee for structural fire resistance, providing double guarantee for structural fire resistance design through reasonable design.

[0037] In a further embodiment of the present invention, the stirrups 4 are C-shaped stirrups, with a certain length bent and welded on the inner sides of the upper and lower flanges of the cellular steel section 2, and the longitudinal bars 3 are tied at the corners at both ends of the C-shaped stirrups.

[0038] In a further embodiment of the present invention, longitudinal stiffeners 5 are welded on both sides of the web of the cellular steel section 2. The longitudinal stiffeners 5 are located on both sides of the concrete holes 6 and are close to the upper and lower edges of the honeycomb holes 7 to reduce the stress concentration phenomenon at the hole edges. Since the beam cross-section changes suddenly here, large stress concentrations will form on both sides of the honeycomb holes 7, causing tearing at the corner edges of the cellular steel section 2. Adding longitudinal stiffeners is equivalent to reinforcing this weak part and avoiding premature yielding of the steel at the edges of the honeycomb holes 7.

[0039] In a further embodiment of the present invention, the concrete holes 6 are coaxially designed with the communicating honeycomb holes 7, and the diameter of the concrete holes 6 is smaller than the inner diameter of the honeycomb holes 7, and is further preferably connected to the edges of the honeycomb holes 7.

[0040] The construction method of the partially clad cellular steel fire-resistant concrete open-hole composite beam of the present invention is as follows:

[0041] Step 1, process the cellular steel section 2 in the factory. For example, the cellular steel section 2 is made by cutting and welding steel plates, and the stirrups 4 and longitudinal stiffeners 5 are welded according to requirements, and the longitudinal bars 3 are fixed.

[0042] Step 2, in the factory, place the cellular steel section 2 horizontally and fix it, set up formworks at both ends, reserve the concrete holes 6 with a mold, and then pour the fire-resistant concrete 1 and carry out steam curing.

[0043] In the present invention, placing horizontally means that the upper and lower flanges of the cellular steel section 2 are in a vertical position, serving as the side formwork of the fire-resistant concrete 1, and the web is in a horizontal position, dividing the fire-resistant concrete 1 into upper and lower layers. Since honeycomb holes 7 are opened in the web, during pouring, the fire-resistant concrete 1 flows into the lower layer from the honeycomb holes 7.

[0044] Such as Figure 2As shown, in one of the embodiments, for different purposes, the cellular steel section 2 can adopt various forms such as stagger butt welding, directly opening regular hexagonal holes, circular holes, rectangular holes, etc. Among them, the form of stagger butt welding can save steel as much as possible in the steel plate cutting stage; while directly laser opening holes on the whole plate can reduce complex welding work, improve the mechanical performance of the structure at the same time, and avoid the generation of large thermal stresses. Among them, opening circular holes is beneficial to avoid stress concentration, as Figure 2 shown in (a) of Figure 2 ; opening rectangular holes is beneficial to opening rectangular holes in concrete, as shown in (b) of

[0045] Figure 3 shown is the application of the partially clad cellular steel fire-resistant concrete opening composite beam of the present invention in a building structure. Studs can be welded on the outside of its upper flange. During on-site construction, the composite floor slab is first fixed, and then the in-situ casting part is constructed.

[0046] Optionally, the connectors on the outside of the upper flange can be in various forms such as PBL connectors and bolts.

[0047] Figure 4 shown is the application of the present invention in a crane girder. When used as a crane girder, the concrete holes 6 can be removed flexibly. Since its upper flange is a steel section, during prefabrication, holes are opened on the upper flange of the steel section and bolts are installed. The tails of the bolts are embedded inside the upper flange of the steel section. The track is installed on-site through bolts and press plates.​​

Claims

1. A partially clad cellular steel fire-resistant concrete open-web composite beam, characterized in that, It includes cellular steel (2) and refractory concrete (1); the refractory concrete (1) is ultra-high performance concrete doped with polyvinyl alcohol fibers, which is located between the upper and lower flanges of the cellular steel (2) and completely covers the web. It is poured after placing the cellular steel (2) on its side, and the pouring process is completed at one time without the need for turning over; a number of concrete holes (6) are provided on the refractory concrete (1), and the concrete round holes (6) communicate with the cellular holes (7) on the web of the cellular steel (2).

2. The partially clad cellular steel-reinforced fire-resistant concrete open-web composite beam according to claim 1, wherein Longitudinal bars (3) and stirrups (4) are also distributed between the upper and lower flanges of the cellular steel (2), and both the longitudinal bars (3) and stirrups (4) are embedded in the refractory concrete (1). The stirrups (4) are C-shaped stirrups, and the upper and lower sides are bent by a certain length and welded to the inner sides of the upper and lower flanges of the cellular steel (2).

3. The partially clad cellular steel fire-resistant concrete open-web composite beam according to claim 1, characterized in that, Longitudinal stiffeners (5) are welded on both sides of the web of the cellular steel (2), and the longitudinal stiffeners (5) are located on the upper and lower sides of the concrete holes (6) and are close to the upper and lower edges of the cellular holes (7).

4. The partially covered cellular steel fire-resistant concrete open-web composite beam according to claim 1, wherein The concrete holes (6) are coaxial with the cellular holes (7) they communicate with, and the diameter of the concrete holes (6) is smaller than the inner diameter of the cellular holes (7), preferably in contact with the edge of the cellular holes (7).

5. The partially clad cellular steel fire-resistant concrete open-web composite beam according to claim 1, wherein The volume content of the polyvinyl alcohol fibers in the ultra-high performance concrete is 0.5 - 1.0%.

6. The construction method of the partially clad cellular steel fire-resistant concrete open-web composite beam according to claim 1, characterized in that, The steps are as follows: Place the cellular steel (2) on its side and fix it, set up formworks at both ends, reserve the concrete holes (6) with a mold, and then pour the refractory concrete (1) and carry out steam curing; The "placing on its side" means that the upper and lower flanges of the cellular steel (2) are in the vertical position and the web is in the horizontal position.

7. The construction method according to claim 6, characterized in that, The cellular steel (2) is made by cutting and welding steel plates, and the stirrups (4) and longitudinal stiffeners (5) are welded, and the longitudinal bars (3) are fixed.

8. The construction method according to claim 6, characterized in that, The mold for reserving the concrete holes (6) has the same shape as the cellular holes (7) on the web of the cellular steel (2), and the reserving mold also serves as a permanent formwork to avoid formwork removal.

9. Application of the partially clad cellular steel refractory concrete open-hole composite beam described in claim 1 in building structures. Studs are welded on the outer side of its upper flange. During on-site construction, the composite floor slab is fixed first, and then the cast-in-place part is constructed.

10. Application of the partially clad cellular steel refractory concrete open-hole composite beam described in claim 1 as a crane beam. Remove the concrete holes (6). During prefabrication, holes are drilled on the upper flange of the cellular steel (2) and bolts are installed. The tails of the bolts are embedded inside the upper flange. The track is installed on-site through the bolts and press plates.

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