CN113858348A - Low-quality-speed raw wood glued wood beam fire resistance improving technology based on tree species mixing - Google Patents
Low-quality-speed raw wood glued wood beam fire resistance improving technology based on tree species mixing Download PDFInfo
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Abstract
The invention belongs to the technical field of fire resistance of wood structures, in particular to a technique for improving the fire resistance of a low-quality fast-growing glued wood beam based on tree species mixing, which specifically comprises the following steps: and (3) grading the strength of the laminate: the method is characterized in that high-quality structural wood with high density and high strength grade is adopted in a region with large tensile stress borne by the bottom of the glued wood beam, and low-quality fast-growing wood with low density and low strength grade is adopted in a region with compression on the top, shearing on the middle and small tensile stress on the bottom of the glued wood beam; preparing and maintaining a glued wood beam; fire tests, wherein the glued wood beams are subjected to fire on two side surfaces and the bottom surface in the fire tests; measuring the residual bearing capacity after the fire, wherein the residual bearing capacity of the glued wood beam after the fire is measured according to a bending resistance test method; and (4) comparing the calculated residual bearing capacity of the glued wood beam after fire with the test value. The aim of guaranteeing the fire safety of the building is fulfilled while a large amount of domestic fast-growing wood is utilized and the material is saved.
Description
Technical Field
The invention relates to the technical field of fire resistance of wood structures, in particular to a technique for improving the fire resistance of a low-quality fast-growing glued wood beam based on tree species mixing.
Background
In order to avoid global temperature rise and ecological environment deterioration, international major countries successively promise to take carbon reduction measures, and the national government also establishes the (double-carbon) targets of '2030C peak reaching and 2060C neutralization'. The infrastructure construction of China mostly adopts traditional building materials such as cement, steel and the like, and the yield of the building materials reaches over 50 percent of the world. Because the energy consumed by the construction industry every year accounts for more than 30% of the total energy consumption in China, and the discharged carbon dioxide accounts for more than four times of the total discharge, the energy saving and carbon reduction of the construction industry are the main paths for ensuring the realization of the double-carbon target. Compared with a concrete structure and a steel structure, the wood structure is environment-friendly, energy-saving and reproducible, and the wood structure member can be prefabricated in a factory, so that the construction site can be assembled quickly, the construction period is greatly shortened by avoiding on-site wet operation, and the prefabricated wood structure belongs to an assembled green building. 3-5 m for each construction2Wood structure building can absorb CO only2The quantity reaches 1 ton, so the modern wood structure is vigorously developed and accords with the national strategy of double carbon in China.
Compared with the traditional wood structure adopting log or square wood components and tenon-and-mortise joint nodes, the modern wood structure mostly adopts a node form of connecting glued wood beam-column components and metal parts. The laminated wood is formed by performing pressure gluing through key processes of finger joint length extension, transverse width splicing, thickness superposition and the like after removing natural defects influencing the wood strength controllably according to stress characteristics. Therefore, the glued wood structural member has become a structural member replacing the conventional raw wood and square wood structural members, and is widely used in the wood structural engineering.
At the present stage, because the integrity of the wood structure industrial chain in China is not high, compared with the traditional concrete and steel structure, the wood structure industrial chain has relatively high manufacturing cost, so that the wood structure industrial chain is more applied to east and southeast coastal areas with developed economy in China, and in view of the fact that the areas are few and many people exist, the multi-story and high-rise wood structure building has larger development space. Meanwhile, different from foreign countries, most of the wood structure building applications in China require more exposed wood elements, the measure gives consideration to the integrated design of structure decoration and the decoration-free of buildings, and can further reduce the comprehensive construction cost of the buildings, which is an important means for improving the competitiveness of the wood structure buildings.
But the fire hazard of the wood structure building is high due to the inherent combustible property of the wood. A large number of researches and engineering cases prove that when a fire disaster happens, wood is heated to burn, a large amount of heat and combustible gas are released, the fire behavior is promoted, the mechanical properties of solid wood and structural composite wood are remarkably degraded at high temperature, the effective section of a wood component is reduced at high temperature, the rigidity is reduced, the bearing capacity is reduced, the deformation is increased under the load effect, the structural safety is endangered, and the safety of the declaration of fire fighters and the fire extinguishing rescue work are threatened. The fire resistance of wood structure buildings is a bottleneck limiting the scale development and application thereof.
The fire resistance of a building element characterizes the ability of the element to perform an insulating or structural support function during a fire, usually expressed in terms of the fire resistance limit. The fire endurance of a building element is determined by fire tests under standard fire conditions or standard temperature rise curve conditions. National standard "method for testing fire resistance of building elements part 1: the standard fire curve specified in the general requirements (GB/T9978.1-2008) is ISO 834 curve.
The cutting of natural forests in China is forbidden, and at present, all domestic wood structure buildings are built by high-quality structural wood imported from abroad, which is a resource bottleneck for developing wood structures in China. With the increase of domestic application of wood structures, the feasibility of applying large-scale domestic fast-growing wood in building structures is widely concerned, and the total area of the artificial forest in China is at the first place in the world; according to the eighth forest general survey data in China, the Chinese fir is the dominant tree species with the largest forest land area of the artificial forest, the occupation ratio of the Chinese fir in the total area of the artificial forest is respectively as high as 19 percent, and the Chinese fir is a potential material resource for the wood structure building engineering in China.
The outer side of the laminated wood member is firstly carbonized under the action of high temperature to form a carbonized layer in a fire, and the carbonized layer has no strength; the strength of the secondary outer layer is reduced by the action of high temperature. The deterioration of the mechanical properties of the stressed member in the wooden structure is mainly caused by the loss of strength of the carbonized layer and the strength reduction of the heated area. Glued wood beams are the most common flexural structural members in buildings, and in the design of wood building structures, their cross-sectional dimensions are largely determined by the modulus of elasticity. The height of the cross-section of the component is a decisive parameter for its fire resistance compared to its width.
Compared with natural forest wood, the fast-growing wood has the advantages of low density, loose material, low strength grade, high carbonization rate in fire, high reduction speed of the cross section size after fire, and difficulty in being used as a structural stress member, so that the fast-growing wood cannot be used as a material for a structural stress member of a building. With the large-scale development of wood structure buildings in China, particularly the increase of the application of multi-story high-rise wood structure buildings, the fire resistance problems of wood resources and wood structures are gradually highlighted, and a glued wood member with remarkably improved fire resistance based on domestic fast-growing wood is urgently needed to be provided according to actual requirements. Meanwhile, in consideration of the high occurrence and the hazard of fire, the design is carried out in advance according to the fire resistance of the residual bearing capacity of the glued wood member after the fire happens, and the design is a necessary guarantee for fire safety of the wood structure building.
The fire resistance of the wood structure building member is determined according to the carbonization rate of the wood structure building member by the national and international main national standard specifications and the technical manual of the industry association, the carbonization depth, namely the thickness of a carbonization layer, is determined according to the fire receiving time, and the residual bearing capacity of the fired member is finally obtained. Suggested values of carbonization rates of different tree species are given in domestic and foreign standards, as shown in table 1.
TABLE 1 charring speed of wood and laminated wood specified in domestic and foreign standards
Thus, according to European Standard EN 1995-1-2:2004, considering the rounding effect of the section after the fire of the wood, i.e. the greater the charring depth of the corner of the section due to the greater fire, the effective charring depth of the member is calculated according to equation (1):
def＝βn·t+7·k0 (1)
in the formula: defThe effective carbonization depth of the wood is mm; beta is anThe nominal carbonization speed of the wood is mm/min; k is a radical of0In order to consider the coefficient of the thickness influenced by the high temperature in the wood carbonization layer, the coefficient can be calculated by the formula (2); and t is the fire time of the wood for min.
Australian standard AS 1720-:
def＝βn·t+7.5 (3)
βn＝0.4+(280/ρ)2 (4)
in the formula: rho is the density of the wood with the water content of 12 percent, kg/m3The carbonization rate beta in the formula (3)nDetermined by equation (4).
The effective carbonization depth of the fire-bearing wood member is calculated according to the following formula (5) as specified in the technical manual NDS 1997 of the association of forest papers and the chinese standard "design standards for wood structures" (GB 50005-2017):
def＝1.2·βn·t0.813 (5)
in the formula: beta is anThe nominal carbonization speed of the wood, mm/min, American technical manual and Chinese standard suggest values of 0.635mm/min and 0.633mm/min respectively.
The article of lime paste plastering and static test research on stress performance of wooden beam after fire in No. 7-79, volume 32, No. 2011, in the academic journal of building structures, reports that lime paste plastering is carried out on the surface of the fire exposing side of the wooden beam to improve the fire resistance of a component, but after the surface of the component is plastered, no wood grain exists, the decorative effect of the wood structure and the exposed wood grain is lost, and the lime paste plastering and static test research does not exist in the practical engineering of the wood structure building in ChinaHas application feasibility. An article of 'three-side fire-affected wood beam fire endurance test research' in the book of 12 th 127 and 130 th pages of the book of 12 th 127 in 2012 reports the fire endurance research of three-side fire-affected douglas pine log wood beams, wherein the fire endurance of the wood beams with the size of 150mm multiplied by 300mm multiplied by 4000mm is 37min under the load bearing ratio of 50%; adopts the ball shield B60-2 expanded wood structure fire-proof coating, the dosage of the fire-proof coating is 450-2The fire endurance of a component with the roller coating thickness of 1mm is 48min under the same working condition, the fire endurance of the wood beam adopting the fireproof coating is improved by 29.7 percent, and the improvement effect is smaller. An article of 'research on fire endurance test of glued wood beam with three surfaces treated by different flame retardant coatings' in No. 10, 73-78 and 97 of volume 48 of 2018, reports that the flame retardant coating is coated on the exposed side surface of the glued wood beam to improve the fire endurance, and the test shows that when the load holding ratio is 30%, the ultimate load of the pinus sylvestris beam with the size of 100mm × 200mm × 4000mm (width × height × length) is 24min, after the flame retardant coating is coated on the surface, the residual bearing capacity after fire is 28min, the lifting amplitude is 16.7%, and the lifting effect is limited. "study on bending resistance of Larix Gmelini wood under fire conditions" in 2016 (Nature science), volume 38, volume 5, of Nanjing university of Industrial science ", reported the deterioration law of bending strength and elastic modulus of Larix Gmelini wood under the action of 20-280 deg.C; "research on high-temperature douglas fir structure grain along with grain compressive strength test" article reported the deterioration law of douglas fir wood compressive strength at 20-280 ℃ in "proceedings of university of science and technology in huazhong (nature science edition) 2019, volume 47, phase 8; journal of Materials in Civil Engineering 2021 "Mechanical properties testing using Douglas fiber wood floor under improved treated wood control" (DOI:10.1061/(ASCE) MT.1943-5533.0004072) reported the Mechanical properties of the pyrolysis layer wood under the protection of the outer carbonization layer; the residual bearing capacity of the glued wood member after being ignited can be calculated according to the degradation condition of the mechanical property of the pyrolysis layer, but the calculation is time-consuming and the process is complex.
Disclosure of Invention
The present invention develops against the following three problems:
(1) in the aspect of improving the fire resistance of the glued wood member, the mode of plastering gypsum or fire-retardant coating on the surface of the wood member is adopted. However, the two modes have limited improvement range of fire resistance of the wood members, and are generally less than 50%; secondly, fireproof coating is carried out on the surface of the wood member, so that the construction difficulty of hidden parts such as wood structure nodes and the like is high and the hidden parts are difficult to operate after the installation of the member is finished, the surface fireproof coating is generally coated firstly, and then construction and installation are carried out, but in the hoisting and construction scheme at the present stage, the surface of the member is often collided, rubbed or extruded to cause local loss of the surface fireproof coating, so that potential safety hazards are caused; thirdly, when the wood member normally works, the moisture content gradient is generated in the wood member due to the ambient temperature and humidity conditions, when the temperature and humidity change remarkably, the moisture content gradient in the wood member is increased, so that the size of the wood member is changed, and the gypsum or the fireproof coating coated on the surface of the wood member is weak in tension resistance, so that the coating is peeled off and loses the fireproof effect. Meanwhile, the mode of plastering with gypsum is adopted, the natural texture of wood is covered, the architectural decoration effect is reduced, the fireproof coating is adopted for plastering, most of the fireproof coating is petroleum polymer resin, the wood is a porous material, the liquid fireproof coating has the functions of suction and permeation, the fireproof coating is used in large quantity, and the environmental protection performance of the wood structure is difficult to guarantee.
(2) In the aspect of materials for glued wood members, because domestic fast-growing wood has small density and low strength grade, the carbonization rate in a fire scene is high, the residual cross-sectional area after fire is small, and the residual bearing capacity is low, the glued wood members cannot be used as materials for building structure stress members. At present, all the timber for the timber structure building is imported high-quality natural forest timber.
(3) In the aspect of calculating the residual bearing capacity of the fire-receiving glued wood component, the carbonization rates of the wood with larger density difference are different, but the related national standard specifications are uniformly specified as a certain fixed value, and the fire-resistant design is carried out according to the specification; when a material with higher density is adopted, the actual carbonization rate is low, but the design is more conservative, so that the material is larger and the economical efficiency is lower due to the adoption of a larger cross-sectional area. The carbonization depth of the fire-affected glued wood member specified in part of national standards does not consider the reduction of the residual bearing capacity of the member by the pyrolysis layer, or the influence of the specified pyrolysis layer on the residual bearing capacity of the fire-affected member is too large, so that the calculation precision is low, and the accuracy of the building safety performance evaluation of the fire-affected wood structure is difficult to ensure.
According to the three technical problems of the existing modern wood structure, the invention provides a low-quality-rate-of-growth-wood glued wood beam fire-resistant performance improving technology based on tree species mixing and a residual bearing capacity calculating method thereof, and fully utilizes the glued wood laminating and gluing preparation process, domestic fast-growing wood is arranged in the areas with the pressed top, the sheared middle and the small tensile stress at the bottom of the glued wood, the using amount of the domestic fast-growing wood is not less than 50%, high-density high-quality structural wood with higher strength grade is arranged in the area with the high tensile stress at the bottom of the glued wood beam, and structural wood components are arranged at the bottom due to the small carbonization rate of the structural wood. Compared with the full-low-quality fast-growing wood laminated wood beam, after fire is applied to three sides, the bottom tension area is provided with the laminated wood beam of high-density, high-strength and high-quality structural wood, the reduction range of the section height and the width of the section bottom tension area is reduced, and the degree of arc formation of the corner part of the member bottom tension area is reduced, so that the residual effective section area of the member is increased, the residual bearing capacity of the fired member is improved, and the fire resistance is improved; meanwhile, the technology comprehensively considers the influence of the strength degradation of a high-temperature decomposition layer in a fired component and the arc of the corner part of the bottom of the section, provides a method for calculating the residual bearing capacity by reducing the residual section area based on the carbonization rate, adopts the method based on the thickness of the carbonization layer for the residual section area, and effectively improves the calculation precision. The technology of the invention realizes multiple targets of utilizing domestic fast-growing wood in large quantity, saving materials and ensuring fire safety of the wood structure building.
In order to achieve the purpose, the invention provides the following technical scheme: low-quality-speed raw wood glued wood beam fire resistance performance improving technology based on tree species mixing specifically comprises:
and (3) grading the strength of the laminate: the method is characterized in that high-quality structural wood with high density and high strength grade is adopted in a region with large tensile stress borne by the bottom of the glued wood beam, and low-quality fast-growing wood with low density and low strength grade is adopted in a region with compression on the top, shearing on the middle and small tensile stress on the bottom of the glued wood beam;
preparing and maintaining a glued wood beam;
fire tests, wherein the glued wood beams are subjected to fire on two side surfaces and the bottom surface in the fire tests;
measuring the residual bearing capacity after the fire, wherein the residual bearing capacity of the glued wood beam after the fire is measured according to a bending resistance test method;
and (3) comparing the calculated residual bearing capacity of the glued wood beam after being fired with a test value, calculating the residual bearing capacity of the glued wood beam after being fired according to the thickness of the charring layer at the exposed side of the member, the thickness of the pyrolysis layer and the degree of circular arc of the corner of the pulled area at the bottom of the member, and calculating the influence of the circular arc of the corner of the pyrolysis layer and the pulled area at the bottom of the member in the glued wood beam after being fired on the residual bearing capacity by 9% of the thickness of the charring layer.
And (3) reducing the residual bearing capacity of the glued wood beam after the fire, and controlling and calculating the thickness of the member exposed side carbonized layer, the thickness of the pyrolysis layer and the degree of corner rounding of the pulled region at the bottom of the member. The carbonized layer does not contribute to the strength of the member, and is not considered in the calculation of the residual bearing capacity of the glued wood beam after being fired according to the strength of 0; the influence of the corner rounding of the pyrolysis layer and the member bottom tension area in the glued wood beam after being ignited on the residual bearing capacity is calculated by 9% of the thickness of the carbonization layer, and the residual bearing capacity calculation formula of the glued wood beam after being ignited is calculated according to the following formula.
In the formula, PtThe residual bearing capacity of the mixed tree species glued wood beam after being fired is represented by kN; e is the elastic modulus of wood, in MPa; i is the moment of inertia in mm4；fmAfter the timber beam is firedBending strength in MPa; l is the span of the beam and is in mm; b and h are the width and height of the section of the wood beam and mm; y in formula (6)nDetermined by equation (7).
Furthermore, the thickness of the laminated board for the laminated wood beam is in the range of 25-45mm, and in the preparation of the laminated wood beam, resorcinol-phenolic resin adhesive is adopted for bonding the laminated boards.
Furthermore, the number of the high-quality structural wood laminated plates in the area with larger tensile stress borne by the bottom of the glued wood beam is more than or equal to 2.
Furthermore, the tree species of the high-quality structural wood arranged in the area with larger tensile stress borne by the bottom of the glued wood beam are more than or equal to 1.
Further, when the wood species are more than or equal to 2, the farther the configuration of the wood species is from the neutral axis of the laminated wood beam, the higher the density of the wood and the higher the strength grade.
Furthermore, the air-dry density of the high-quality structural wood arranged in the area with larger tensile stress at the bottom of the laminated wood beam when the water content is 12 percent is more than or equal to 0.45g/cm3。
Furthermore, the strength grade of the high-quality structural wood arranged in the area with larger tensile stress borne by the bottom of the laminated wood beam when the water content is 12% is not less than C22.
Furthermore, the low-quality and high-speed raw wood laminated plates are adopted in the areas with compression on the top, shear on the middle and tension stress on the bottom of the glued wood beam, and the ratio of the number of the low-quality and high-speed raw wood laminated plates in the total number of the laminated plates of the member is more than or equal to 50%.
Furthermore, the air-dry density of the low-quality and high-speed raw wood laminate adopted in the area with the compressed top, the sheared middle and the small tensile stress at the bottom of the laminated wood beam is less than or equal to 0.40g/cm when the water content is 12 percent3。
Furthermore, the strength grade of the low-quality and high-speed raw wood laminate adopted in the area with the compressed top, the sheared middle and the small tensile stress at the bottom of the laminated wood beam is less than or equal to C16 when the water content is 12 percent.
Compared with the prior art, the invention has the beneficial effects that:
on the basis of the glued wood beam with the domestic fast-growing wood usage amount not less than 50%, the domestic fast-growing wood is effectively combined with high-quality structural wood, and efficient utilization of the domestic fast-growing wood is achieved. Compared with the single low-quality domestic fast-growing wood laminated wood beam, after the high-density high-quality structural wood is mixed, the fire resistance of the laminated wood beam is obviously improved. The cross-sectional area of the structural member for the wood structure building can be designed to be smaller, a large amount of low-quality domestic fast-growing wood with lower price is adopted in the structural member, the current situation that a large amount of high-quality wood needs to be imported in China is relieved, the cost is saved, and the construction cost is reduced. The fire resistance of the low-quality raw wood glued wood beam is improved by configuring high-density and high-strength-grade high-quality structural wood at the bottom of the cross section, the appearance effect of the wood structure building is wood texture, the negative influence of gypsum smearing on the building effect is avoided, and the negative influence on the environment and the physical and mental health of building users caused by the traditional adoption of chemical substances such as high-molecular fireproof paint is also avoided.
The residual bearing capacity of the three-surface fire-glue wood beam calculated according to the existing standard specification or the technical manual of the industry association is low in precision. The method for calculating the residual bearing capacity based on the equivalent effective residual section area effectively improves the calculation precision, can avoid the waste of resources during structural design, and can also reduce the potential safety hazards such as casualties or property loss and the like caused by insufficient mechanical properties of components during fire. The aim of guaranteeing the fire safety of the building is fulfilled while a large amount of domestic fast-growing wood is utilized and the material is saved.
Drawings
FIG. 1 is a schematic view of a tree species hybrid low mass green wood laminated wood beam.
Fig. 2 is a schematic cross-sectional view of the whole low-quality fast-growing wood glued wood beam remaining after being fired.
FIG. 3 is a schematic cross-sectional view of a tree species hybrid low mass fast growing glued wood beam with a structural wood disposed in the bottom tension zone after fire.
FIG. 4 is a schematic view of the remaining cross section of a hybrid low-mass-rate-of-growth laminated wood beam of a tree species with two types of structural wood arranged in the bottom tension zone after fire.
In the figure: 1-glue joint, 2-low-density fast-growing wood, 3-high-density structural wood, 4-exposure side fast-growing wood pyrolysis layer, 5-exposure side carbonization layer, 6-fire load, 7-exposure side high-density structural wood pyrolysis layer, 8-higher-density structural wood, and 9-exposure side higher-density structural wood pyrolysis layer.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention.
Referring to fig. 1-4, the present invention provides the following technical solutions: low-quality-speed raw wood glued wood beam fire resistance performance improving technology based on tree species mixing specifically comprises:
and (3) grading the strength of the laminate: the method is characterized in that high-quality structural wood with high density and high strength grade is adopted in a region with large tensile stress borne by the bottom of the glued wood beam, and low-quality fast-growing wood with low density and low strength grade is adopted in a region with compression on the top, shearing on the middle and small tensile stress on the bottom of the glued wood beam;
the density of the wood is measured according to the method for measuring the density of the wood (GB/T1933-2009);
the strength grade of the laminate is determined according to the specification of structural laminated material (GB/T26899-2011) and is determined according to the specification of EN 338: 2016;
preparing and maintaining a glued wood beam;
the fire test is carried out according to a standard temperature rise curve in ISO 834-1999;
the residual bearing capacity of the glued wood beam after being fired is measured according to a bending resistance test method A in structural laminated wood (GB/T26899-2011);
and (3) comparing the calculated residual bearing capacity of the glued wood beam after fire with a test value: the residual bearing capacity of the glued wood beam after being fired is controlled by the thickness of a charring layer on the exposed side of the member, the thickness of a pyrolysis layer and the degree of corner rounding of a pulled area at the bottom of the member, and for convenience of calculation, the influence of the corner rounding of the pyrolysis layer in the glued wood beam after being fired and the pulled area at the bottom of the member on the residual bearing capacity is calculated by 9% of the thickness of the charring layer.
Preferably, the thickness of the laminated plate for the laminated wood beam is in the range of 25-45mm, and the adhesive for bonding the laminated plates is resorcinol-phenolic resin in the preparation of the laminated wood beam.
Preferably, the number of the high-quality structural wood laminated plates in the area with larger tensile stress borne by the bottom of the laminated wood beam is more than or equal to 2.
Preferably, the high-quality structural wood is arranged in the area with larger tensile stress borne by the bottom of the laminated wood beam, and the tree species of the high-quality structural wood are more than or equal to 1.
Preferably, when the wood species are more than or equal to 2, the farther the configuration of the wood species is from the neutral axis of the laminated wood beam, the higher the density of the wood and the higher the strength grade.
Preferably, the high-quality structural wood is arranged in the area with larger tensile stress at the bottom of the laminated wood beam, and the air-dry density of the high-quality structural wood is more than or equal to 0.45g/cm when the water content is 12 percent3。
Preferably, the strength grade of the high-quality structural wood arranged in the area with larger tensile stress at the bottom of the laminated wood beam is more than or equal to C22 when the water content is 12%.
Preferably, the low-quality and low-speed raw wood laminates are adopted in the areas with compression at the top, shear at the middle and tension stress at the bottom of the laminated wood beam, and the ratio of the number of the low-quality and low-speed raw wood laminates in the total number of the component laminates is more than or equal to 50 percent.
Preferably, the laminated wood beam has a top compression area, a middle shearing area and a bottom tension stress area which are lessThe air-dry density of the low-quality quick-growing wood laminate adopted in the field is less than or equal to 0.40g/cm when the water content is 12 percent3。
Preferably, the strength grade of the low-quality and high-speed raw wood laminate adopted in the area with the compressed top, the sheared middle and the small tensile stress at the bottom of the laminated wood beam is less than or equal to C16 when the water content is 12 percent.
Taking a laminated wood beam with the size of 100mm multiplied by 200mm multiplied by 2000mm (width multiplied by height multiplied by length) as an example for implementation, the components are all formed by 6 wood laminated plates with the thickness of 33.3mm through the bonding action of resorcinol-phenolic resin, and are cured under the environment that the temperature is not lower than 20 ℃ and the relative humidity is 60-80% until the components are fully cured.
The laminated wood beam with all low-quality Chinese-made fast-growing fir wood is set as a comparison component. According to GB/T1933-3The fir wood strength grade determined according to GB/T26899 & 2011 and EN 338 & 2016 is grade C16.
The fire resistance test is carried out on the glued wood beam by adopting a standard temperature rise curve specified in ISO 834-1999, three surfaces of the glued wood beam are set to be subjected to fire, namely two side surfaces and the bottom surface, the furnace door is opened after the test piece reaches the specified fire time, and the dry powder fire extinguisher and the water are immediately adopted to extinguish the fire to prevent the test piece from continuing to burn. According to GB/T26899-.
When the fire is not fired, the flexural limit bearing capacity of the all-low-quality domestic fast-growing fir glued wood beam is 47.19kN, and when the fire is fired for 10min or 20min, the residual limit bearing capacity of the all-low-quality domestic fast-growing fir glued wood beam is 39.91kN and 25.52kN respectively.
The high-density structural wood arranged in the tension area at the bottom of the domestic fast-growing fir glued wood beam takes high-quality douglas fir imported from North America and high-quality Xingan larch imported from Russia as examples, and the average air-dried density of the douglas fir and the larch is measured to be 0.457g/cm according to GB/T1933-3And 0.605g/cm3The strength grades of Douglas fir and Larix Gmelini determined according to GB/T26899 & 2011 and EN 338 & 2016 are C22 and C30, respectively.
The present invention will be described in detail with reference to examples.
Example 1:
the method is based on the technology for improving the fire resistance of the low-quality fast-growing glued wood beam mixed by tree species and the calculation method of the residual bearing capacity of the low-quality fast-growing glued wood beam, the size of the glued wood beam is 100mm multiplied by 200mm multiplied by 2000mm (width multiplied by height multiplied by length), and the glued wood beam is composed of 6 wood laminates with the thickness of 33.3 mm.
2 layers of plywood on the outermost layer of the tension area at the bottom of the glued wood beam are larch structure wood, and the rest 4 layers of plywood are all low-quality domestic fast-growing Chinese fir.
After the fire exposure time is 10min, according to a GB/T26899-2011 bending test method A, a three-point loading test is carried out on the extinguished glued wood beam, the residual bearing capacity is 73.61kN, and compared with the full-low-mass fast-growing fir glued wood beam, the residual limit bearing capacity is improved by 84.4% after the fire exposure time is 10 min.
Calculated according to the formula specified in mainstream documents such AS Australian standard AS 1720-. According to the formula (6), the fire time is 10min, the theoretical calculated value of the residual bearing capacity of the fir glued wood beam with larch arranged in the bottom tension area is 76.79kN, the error from the test value is 4.3 percent, and the theoretical calculated value precision is higher than the theoretical calculated value precision specified in the international main national standard or industry association technical manual.
Example 2:
the method is based on the technology for improving the fire resistance of the low-quality fast-growing glued wood beam mixed by tree species and the calculation method of the residual bearing capacity of the low-quality fast-growing glued wood beam, the size of the glued wood beam is 100mm multiplied by 200mm multiplied by 2000mm (width multiplied by height multiplied by length), and the glued wood beam is composed of 6 wood laminates with the thickness of 33.3 mm.
2 layers of plywood on the outermost layer of the tension area at the bottom of the glued wood beam are douglas fir structural wood, and the rest 4 layers of plywood are low-quality domestic fast-growing Chinese fir.
After the fire exposure time is 10min, according to GB/T26899-.
Calculated according to the formula specified in mainstream documents such AS Australian standard AS 1720-. According to the formula (1), the fir glued wood beam with Douglas fir in the bottom tension area and the fire time of 10min has the theoretical calculated value of the residual bearing capacity of 65.67kN and the error from the test value of 9.2 percent, which is higher than the theoretical calculated value precision specified in most international main national standards or technical handbooks of industry associations.
Example 3:
the method is based on the technology for improving the fire resistance of the low-quality fast-growing glued wood beam mixed by tree species and the calculation method of the residual bearing capacity of the low-quality fast-growing glued wood beam, the size of the glued wood beam is 100mm multiplied by 200mm multiplied by 2000mm (width multiplied by height multiplied by length), and the glued wood beam is composed of 6 wood laminates with the thickness of 33.3 mm.
2 layers of plywood on the outermost layer of the tension area at the bottom of the glued wood beam are larch structure wood, and the rest 4 layers of plywood are all low-quality domestic fast-growing Chinese fir.
After the fire exposure time is 20min, according to GB/T26899-2011 bending test method A, the three-point loading test is carried out on the extinguished glued wood beam, the residual bearing capacity is 62.63kN, and compared with the full-low-mass fast-growing fir glued wood beam, the residual limit bearing capacity is improved by 145.4% after the fire exposure time is 20 min.
Calculated according to the formula specified in mainstream documents such AS Australian standard AS 1720-. According to the formula (1), the fire time is 20min, the theoretical calculated value of the residual bearing capacity of the fir glued wood beam with larch arranged in the bottom tension area is 62.66kN, the error from the test value is 0.1 percent, and the theoretical calculated value precision is higher than the theoretical calculated value precision specified in the international main national standard or industry association technical manual.
Example 4:
the method is based on the technology for improving the fire resistance of the low-quality fast-growing glued wood beam mixed by tree species and the calculation method of the residual bearing capacity of the low-quality fast-growing glued wood beam, the size of the glued wood beam is 100mm multiplied by 200mm multiplied by 2000mm (width multiplied by height multiplied by length), and the glued wood beam is composed of 6 wood laminates with the thickness of 33.3 mm.
2 layers of plywood on the outermost layer of the tension area at the bottom of the glued wood beam are douglas fir structural wood, and the rest 4 layers of plywood are low-quality domestic fast-growing Chinese fir.
After the fire exposure time is 20min, according to GB/T26899-2011 bending test method A, the three-point loading test is carried out on the extinguished glued wood beam, the residual bearing capacity is 57.92kN, and compared with the full low-mass fast-growing fir glued wood beam, the residual limit bearing capacity is improved by 127.0% after the fire exposure time is 20 min.
Calculated according to the formula specified in mainstream documents such AS Australian standard AS 1720-. According to the formula (1), the fir glued wood beam with Douglas fir in the bottom tension area and the fire time of 20min has the theoretical calculated value of the residual bearing capacity of 53.40kN, the error from the test value is 7.8 percent, and the theoretical calculated value is higher than the theoretical calculated value precision specified in most international main national standards or technical handbooks of industry association.
Example 5:
the method is based on the technology for improving the fire resistance of the low-quality fast-growing glued wood beam mixed by tree species and the calculation method of the residual bearing capacity of the low-quality fast-growing glued wood beam, the size of the glued wood beam is 100mm multiplied by 200mm multiplied by 2000mm (width multiplied by height multiplied by length), and the glued wood beam is composed of 6 wood laminates with the thickness of 33.3 mm.
2 layers of plywood on the outermost layer of the tension area at the bottom of the glued wood beam are douglas fir structural wood, and the rest 4 layers of plywood are low-quality domestic fast-growing Chinese fir.
And after the fire time is 27min, carrying out a three-point loading test on the extinguished glued wood beam according to a GB/T26899-2011 bending test method A, wherein the residual bearing capacity is 47.40 kN.
Calculated according to the formula specified in mainstream documents such AS Australian standard AS 1720-. According to the formula (1), the fir glued wood beam with Douglas fir in the bottom tension area and the fire time of 27min has the theoretical calculated value of residual bearing capacity of 44.85kN and the error from the test value of 5.4 percent, which is higher than the theoretical calculated value precision specified in the technical manual of the international main national standard or industry association.
Example 6:
the method is based on the technology for improving the fire resistance of the low-quality fast-growing glued wood beam mixed by tree species and the calculation method of the residual bearing capacity of the low-quality fast-growing glued wood beam, the size of the glued wood beam is 100mm multiplied by 200mm multiplied by 2000mm (width multiplied by height multiplied by length), and the glued wood beam is composed of 6 wood laminates with the thickness of 33.3 mm.
2 layers of plywood at the outermost layer of the tension area at the bottom of the glued wood beam are made of dahurian larch structural wood, and the rest 4 layers of plywood are made of low-quality domestic fast-growing Chinese fir.
And after the fire time is 27min, carrying out a three-point loading test on the extinguished glued wood beam according to a GB/T26899-2011 bending test method A, wherein the residual bearing capacity is 54.943 kN.
Calculated according to the formula specified in mainstream documents such AS Australian standard AS 1720-. According to the formula (1), the fire time is 27min, the theoretical calculated value of the residual bearing capacity of the fir glued wood beam with larch arranged in the bottom tension area is 53.18kN, the error from the test value is 3.2 percent, and the theoretical calculated value precision is higher than the theoretical calculated value precision specified in the international main national standard or industry association technical manual.
While there have been shown and described the fundamental principles and essential features of the invention and advantages thereof, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing exemplary embodiments, but is capable of other specific forms without departing from the spirit or essential characteristics thereof; the present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein, and any reference signs in the claims are not intended to be construed as limiting the claim concerned.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (10)
1. Low-quality-speed raw wood glued wood beam fire resistance can improve technique based on tree species mixes, its characterized in that specifically includes:
and (3) grading the strength of the laminate: the method is characterized in that high-quality structural wood with high density and high strength grade is adopted in a region where the tensile stress is large at the bottom of the glued wood beam, and low-quality fast-growing wood with low density and low strength grade is adopted in a region where the top of the glued wood beam is pressed, the middle of the glued wood beam is sheared and the tensile stress at the bottom of the glued wood beam is small;
preparing and maintaining a glued wood beam;
in the fire test, the laminated wood beam is subjected to fire on three sides, namely two side surfaces and a bottom surface;
measuring the residual bearing capacity after the fire, wherein the residual bearing capacity of the glued wood beam after the fire is measured according to a bending resistance test method;
and comparing the calculated residual bearing capacity of the glued wood beam after being fired with the test value, wherein in the theoretical calculation of the residual bearing capacity of the glued wood beam after being fired, the influence of the corner rounding of the high-temperature decomposition layer in the glued wood beam after being fired and the pulled area of the bottom of the member on the residual bearing capacity is calculated by 9 percent of the thickness of the carbonization layer.
2. The low-mass-velocity-of-growth-wood-glued-beam fire-resistance improvement technology based on tree species mixing of claim 1, wherein: the thickness of the laminated board for the laminated wood beam is within the range of 25-45mm, and resorcinol-phenolic resin adhesive is adopted for bonding the laminated boards in the preparation of the laminated wood beam.
3. The low-mass-velocity-of-growth-wood-glued-beam fire-resistance improvement technology based on tree species mixing of claim 1, wherein: the number of the high-quality structural wood laminated plates in the area with larger tensile stress borne by the bottom of the glued wood beam is more than or equal to 2.
4. The low-mass-velocity-of-growth-wood-glued-beam fire-resistance improvement technology based on tree species mixing of claim 1, wherein: the high-quality structural wood is arranged in the area with larger tensile stress borne by the bottom of the glued wood beam, and the tree species of the high-quality structural wood are more than or equal to 1.
5. The low-mass-velocity-of-growth-wood-glued-beam fire-resistance improvement technology based on tree species mixing of claim 4, wherein: when the wood species are more than or equal to 2, the farther the configuration of the wood species is away from the neutral axis of the laminated wood beam, the higher the density and the higher the strength grade of the wood.
6. The low-mass-velocity-of-growth-wood-glued-beam fire-resistance improvement technology based on tree species mixing of claim 1, wherein: the air-dry density of the high-quality structural wood arranged in the area with larger tensile stress borne by the bottom of the glued wood beam when the water content is 12 percent is more than or equal to 0.45g/cm3。
7. The low-mass-velocity-of-growth-wood-glued-beam fire-resistance improvement technology based on tree species mixing of claim 1, wherein: the strength grade of the high-quality structural wood arranged in the area with larger tensile stress borne by the bottom of the glued wood beam when the water content is 12% is not less than C22.
8. The low-mass-velocity-of-growth-wood-glued-beam fire-resistance improvement technology based on tree species mixing of claim 1, wherein: the low-quality and high-speed raw wood laminated plates are adopted in the areas with the compressed top, the sheared middle and the low tensile stress at the bottom of the glued wood beam, and the ratio of the number of the raw wood laminated plates in the total number of the laminated plates of the member is more than or equal to 50 percent.
9. The low-mass-velocity-of-growth-wood-glued-beam fire-resistance improvement technology based on tree species mixing of claim 1, wherein: the air-dry density of the low-quality and high-speed raw wood plywood adopted in the area with the compressed top, the cut middle and the small tensile stress at the bottom of the glued wood beam is less than or equal to 0.40g/cm when the water content is 12 percent3。
10. The low-mass-velocity-of-growth-wood-glued-beam fire-resistance improvement technology based on tree species mixing of claim 1, wherein: the strength grade of the low-quality and high-speed raw wood laminate adopted in the area with the compressed top, the sheared middle and the small tensile stress at the bottom of the glued wood beam is less than or equal to C16 when the water content is 12 percent.
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