CN-117513648-B - Normal temperature and fire-resistant design method for U-shaped recycled concrete composite beam

Abstract

The invention relates to a normal temperature and fire resistance design method of a U-shaped recycled concrete composite beam, which comprises the following steps of A1 determining the load effect and fire resistance grade of the U-shaped recycled concrete composite beam, A2 designing the section size, A3 analyzing the carrying capacity and normal use capacity of the U-shaped recycled concrete composite Liang Changwen and designing a reinforcement, A4 designing the fire resistance of the U-shaped recycled concrete composite beam by adopting a simple design method or a complex design method, A5 designing the roughness and the reinforcement of a composite interface according to the analysis in A3 by adopting the simple design method or the complex design method, and A6 selecting an optimized construction method of the U-shaped recycled concrete composite beam. Compared with the prior art, the method has the advantages that the fireproof property of the recycled concrete and the excellent mechanical property of the high-strength concrete are fully exerted, the bending-resistant bearing capacity and the ductility of the recycled concrete beam can be effectively improved at normal temperature, the bursting phenomenon of the fire-receiving surface is reduced at high temperature, and the temperature field in the beam is obviously reduced.

Inventors

• XIAO JIANZHUANG
• CHEN ZIXUAN

Assignees

• 同济大学

Dates

Publication Date

20260512

Application Date

20231115

Claims (1)

1. 1. The normal temperature and fire resistance design method of the U-shaped recycled concrete composite beam is characterized by comprising the following steps of: a1, determining the load effect and the fire resistance grade of the U-shaped recycled concrete composite beam; a2, designing the cross section size of the U-shaped recycled concrete composite beam; a3, analyzing the carrying capacity and the normal use capacity of the U-shaped recycled concrete combination Liang Changwen, and designing reinforcement of the U-shaped recycled concrete combination beam; a4, performing refractory design of the U-shaped recycled concrete composite beam, and adopting a simple design method or a complex design method; A5, according to analysis in A3, carrying out roughness and reinforcement design of a combined interface, and adopting a simple design method or a complex design method; A6, selecting an optimized construction method of the U-shaped recycled concrete composite beam according to the analysis results obtained in A2 to A5; The U-shaped regenerated concrete composite beam in A2 is designed to meet the requirements of the structural design specification (GB 50010-2010) on the size of a component, the dimensional parameters of the U-shaped regenerated concrete composite beam can meet the engineering design requirements, and the reinforcement design of the U-shaped regenerated concrete composite beam in A3 is designed to meet the requirements of the concrete structural design specification (GB 50010-2010) on the bending bearing capacity and the oblique bearing capacity of the positive section of the concrete beam; the simple design method in A4 means that the minimum value of the thickness of the protective layer of the simple beam or the continuous Liang Liangkuan and the longitudinal tension steel bar (21) in the technical regulations of refractory design of building concrete structures (DBJ/T15-81-2022) is met, the influence of the reduction of the heat conductivity coefficient of the recycled concrete is not considered, and the method is only used as a safety reserve; The complex design method in A4 refers to nonlinear overall process analysis under fire conditions, wherein a general finite element program is adopted to calculate a time-varying internal temperature field of a concrete member and a structure, and the influence of reduction of the thermal conductivity coefficient of the recycled concrete is considered, so that high-temperature mechanical analysis of the member and the structure is carried out on the basis, and whether the fire resistance limit of the member or the structure meets engineering design requirements is judged; In A5, the simple design method is that the design interface is a rough interface, the roughness degree of the rough interface is not lower than the corresponding roughness degree under the condition that half of coarse aggregate is exposed, or a natural pouring surface which is not smoothed, interface steel bars are arranged and constructed, and the steel bar arrangement rate of the interface steel bars is not lower than the steel bar arrangement rate of stirrups; In A5, the complex design method is to analyze the high-temperature safety of the combined interface by adopting nonlinear overall process analysis under the fire condition, and the strength and rigidity loss of the interface bearing capacity under the high-temperature effect should be considered, and the degradation rules of the interface tensile bearing capacity and the shearing bearing capacity under the high temperature should be tested by a test; the designed U-shaped recycled concrete composite beam comprises a precast concrete shell (11) and cast-in-situ compression zone concrete (12); the prefabricated concrete shell (11) is a recycled concrete shell, the cross section of the prefabricated concrete shell (11) is U-shaped, and the strength grade of the prefabricated concrete shell (11) is not higher than C40; The cast-in-situ compression zone concrete (12) is high-strength concrete arranged in a U-shaped groove body of the precast concrete shell (11), and the cast-in-situ compression zone concrete (12) is concrete with a strength grade of C50-C80; The U-shaped recycled concrete composite beam is internally provided with a reinforcement cage serving as a framework, the reinforcement cage is arranged in a precast concrete shell (11) and comprises a horizontally arranged tension reinforcement (21), a vertical reinforcement (23) and a vertically arranged stirrup, the stirrup is used for restraining the tension reinforcement (21), the stirrup is of a U-shaped structure, the top of the stirrup is provided with a bending part, the upper surface of the bottom of the stirrup is abutted with the tension reinforcement (21), and the lower surface of the bending part of the stirrup is abutted with the vertical reinforcement (23); The cross section size of the U-shaped recycled concrete composite beam is not smaller than 200 mm, the width b is not smaller than 300 mm, the thickness h 1 of the bottom of the precast concrete shell (11) is not smaller than 80mm, the widths b 1 and b 3 of the side face of the precast concrete shell (11) are not smaller than 45mm, and the width b 2 of the cast-in-situ compression zone concrete (12) is not smaller than 100mm; the concrete (12) of the cast-in-situ compression zone and the concrete slab are cast at the same time, the heights of two sides of the precast concrete shell (11) are set to be h 1 + h 2 , the height h 3 above the precast concrete shell is cast at the same time as the concrete (12) of the cast-in-situ compression zone, the height h 3 is made of the same concrete material as the concrete (12) of the cast-in-situ compression zone, and the height h 1 , h 2 , h 3 is the bottom thickness of the precast concrete shell, the core height of the concrete of the cast-in-situ compression zone and the top height of the concrete of the cast-in-situ compression zone respectively.

Description

Normal temperature and fire-resistant design method for U-shaped recycled concrete composite beam Technical Field The invention relates to the field of building structures and construction, in particular to a normal-temperature and fire-resistant design method of a U-shaped recycled concrete composite beam. Background In order to realize the sustainability of civil engineering structures, disaster prevention and reduction are quite important matters in structural design. With the development of high-rise structures and large-span structures, high-strength concrete and high-performance concrete are increasingly widely applied. However, the compact microstructure of the high-strength concrete ensures that the high-strength concrete has higher internal stress under the action of high temperature, concrete burst easily occurs, so that internal steel bars are exposed, the temperature of the steel bars is rapidly increased, and the fire resistance of the structure is obviously reduced, which restricts the application of the high-strength concrete in building structures. The method of adding fireproof paint and the like improves the construction cost, increases the construction procedures, and brings the maintenance problem of long-term use of the building structure. In contrast, recycled concrete prepared from recycled aggregate generated by crushing waste concrete has been demonstrated to have good fire resistance. The recycled concrete has the characteristics of loose and porous interior because the surface of the recycled aggregate is rich in old mortar. The thermal conductivity of the recycled concrete is lower than that of common concrete under the same water cement condition, and the recycled concrete is not easy to burst at high temperature. However, the application of the recycled aggregate reduces the bearing capacity and rigidity of the recycled concrete member at normal temperature to a certain extent, which restricts the application of the recycled concrete structure and also restricts the exertion of the excellent thermal performance of the recycled concrete material. Patent CN208329371U discloses a T shape steel rib recycled concrete composite beam, including the concrete composite beam case, spacing fixed plate has been placed to the bottom of concrete composite beam case, and evenly distributed's joint groove has been seted up at the top of spacing fixed plate, and the stirrup that is located the inner chamber of concrete composite beam case and evenly distributed has been placed at the top of spacing fixed plate, and the spacing fixed plate that is located the inner chamber of concrete composite beam case has been placed at the top of stirrup, and the inside top and the bottom of stirrup all are provided with the reinforcing bar. Through the cooperation of steel rib and flange board, make the bearing capacity of the device stronger, the extensibility of the better utilization T shape steel of being convenient for has saved the use of template, has improved the efficiency of construction, is convenient for fill the inside at this composite beam with old and useless concrete simultaneously, has both protected the environment and can the waste recycling. However, the design greatly increases the usage amount of steel in the concrete beam, has a complex structure and increases the construction cost. In addition, steel such as a limit fixing plate is arranged on the surface of the concrete beam, performance degradation is rapid after fire, and recycled concrete is applied to the middle of the concrete beam, so that excellent fire resistance of the recycled concrete cannot be fully utilized. Disclosure of Invention The invention aims to overcome the defects of the prior art and provide a normal temperature and fire resistance design method of the U-shaped recycled concrete composite beam, which fully exerts the fire resistance characteristic of recycled concrete and the excellent mechanical property of high-strength concrete, can effectively improve the bending bearing capacity and ductility of the recycled concrete beam at normal temperature, reduces the bursting phenomenon of the fire-receiving surface at high temperature, obviously reduces the temperature field in the beam, fully exerts the heat insulation performance of the recycled concrete, protects the internally stressed steel bars, avoids the weakening of the structural section size caused by the bursting of the high-strength concrete, and can effectively reduce the on-site pouring workload and accelerate the engineering progress in a construction mode. The aim of the invention can be achieved by the following technical scheme: the invention provides a U-shaped recycled concrete composite beam, which comprises a precast concrete shell and cast-in-situ compression zone concrete; The precast concrete shell is a recycled concrete shell, the cross section of the precast concrete shell is U-shaped, the refractory performance is good, the precast co