Calculation method of fire resistance of bolted connections between steel plate and timber-tube column

Abstract

This invention discloses a method for calculating the fire resistance limit of bolted connections between steel plate beams and columns embedded in a wood-bamboo structure. The method includes: calculating the design shear force of each shear facet of a single bolt in the bolted connection; assuming the fire resistance limit of the bolted connection is t, calculating the carbonization depth of the wood-bamboo material at time t after exposure to fire, and determining the remaining cross-sectional thickness of the connected wood-bamboo components; calculating the temperature distribution of the bolt at time t after exposure to fire; determining the pin bearing compressive strength distribution of the bolt at time t after exposure to fire; calculating the shear bearing capacity of each shear facet of a single bolt at time t after exposure to fire; comparing the shear bearing capacity of the bolted connection at time t with the design shear force; if the shear bearing capacity of the bolted connection at time t is greater than the design shear force, increasing the fire exposure time; if the shear bearing capacity of the bolted connection at time t is less than the design shear force, decreasing the fire exposure time; until the shear bearing capacity of the bolted connection equals the design shear force, determining the fire resistance limit of the bolted connection.

Description

Technical Field

[0001] This invention relates to a method for calculating the fire resistance limit of bolted joints in beam-column connections of wood-bamboo structures, and particularly to a method for calculating the fire resistance limit of bolted joints in beam-column connections with embedded steel plates in wood-bamboo structures. Background Technology

[0002] Embedded steel plate beam-column bolted connections are a typical type of joint where steel plates are embedded inside the wood-bamboo beam-column components, and a reliable connection is achieved through a group of bolts. They offer advantages such as high load-bearing capacity, high stiffness, and convenient construction, and are widely used in multi-story and large-span wood-bamboo structures. However, wood and bamboo are solid combustible materials; they ignite when the surface temperature reaches 200–400℃, gradually forming a charred layer on the surface. The charred layer almost completely loses its strength, while the mechanical properties of the uncharred internal areas are relatively less affected by fire.

[0003] For bolted connections between embedded steel plate beams and columns, the stress distribution in the joint area is complex and the structure is concentrated. Furthermore, due to the high thermal conductivity of the steel plate, it heats up rapidly during a fire and transfers heat to the surrounding wood and bamboo materials, creating a "thermal bridge" effect. This results in a significantly higher carbonization rate for the wood and bamboo materials in the joint area compared to ordinary wood and bamboo components. Simultaneously, the localized areas around the bolt holes are more prone to premature failure at high temperatures due to stress concentration and cross-sectional weakening. As the core component for load transfer in wood and bamboo structures, the fire resistance rating of the joint directly determines the overall structural safety and collapse resistance during a fire. If the joint fails prematurely during a fire, even if the beams and columns still possess some residual load-bearing capacity, the entire structure may still experience progressive collapse due to joint failure. Therefore, accurately calculating the fire resistance rating of bolted connections between embedded steel plate beams and columns is of crucial engineering significance for scientifically assessing the fire resistance performance of wood and bamboo structures and guiding fire protection design.

[0004] Currently, for complex structural forms such as embedded steel plate bolted connections, there is a lack of methods for calculating the fire resistance limit that takes into account the thermal bridging effect of the steel plate, local carbonization of bolt holes, and the synergistic effect of multiple bolts, which cannot meet the needs of fire-resistant design for wood-bamboo structures. Therefore, it is urgent to propose a method for calculating the fire resistance limit of embedded steel plate beam-column bolted connections in wood-bamboo structures, so as to provide a scientific basis for fire safety assessment and fire protection design of wood-bamboo structures. Summary of the Invention

[0005] To address the aforementioned technical problems in existing technologies, this invention aims to propose a scientific, accurate, and effective method for calculating the fire resistance limit of bolted connections between steel plate beams and columns in wood-bamboo structures. This calculation method can be applied to the fire-resistant design of wood-bamboo structures, laying a theoretical foundation for the fire performance evaluation of bolted connections between beams and columns in wood-bamboo structures.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for calculating the fire resistance limit of bolted connections between steel plate beams and columns embedded in a wood-bamboo structure includes the following steps:

[0008] Step S1: Calculate the design shear force F1 for each shear plane of a single bolt in the bolted connection node;

[0009]

[0010]

[0011] Where M is the design value of the bending moment of the node under the ultimate limit state of fire resistance bearing capacity; V is the design value of the shear force of the node under the ultimate limit state of fire resistance bearing capacity; the rotation center O2 is located at the intersection of the beam-column contact surface and the center line of the lowest row of bolts of the beam; Let be the distance from bolt i to the rotation center O2; , Let O2 be the absolute value of the x and y coordinates of bolt i when O2 is the origin; n is the total number of bolts in the bolt group; n v This represents the number of shear surfaces of the bolts in the node. The angle between the direction of the load and the direction parallel to the grain;

[0012] Step S2: Assuming the fire resistance limit of the bolted connection joint is t, calculate the char depth d of the wood or bamboo at time t after being exposed to fire. n = ,in The carbonization rate is determined; the remaining effective cross-sectional thickness t of the connected wood and bamboo components is determined. n =t1- d n Where t1 is the thickness of the connected wooden and bamboo components on one side before being exposed to fire;

[0013] Step S3: Calculate the temperature of the screw at time t after it is heated. , where x is the distance from a point inside the remaining effective section to the edge of the remaining effective section;

[0014] Step S4: Determine the pin bearing compressive strength distribution of the screw at time t after being exposed to fire;

[0015]

[0016]

[0017] in, The angle between the load and the wood grain is The compressive strength of pin bearings for wood and bamboo at room temperature; The compressive strength of the pin shaft along the grain of wood and bamboo at room temperature; This refers to the cross-grain compressive strength of wood and bamboo at room temperature.

[0018] Step S5: Calculate the shear capacity of each shear facet of a single bolt at time t after exposure to fire;

[0019]

[0020] Step S6: Compare the shear capacity Z(t) of the bolted connection at time t after being exposed to fire with the design shear force F1. If they are equal, the fire resistance limit of the bolted connection is determined to be t. If the shear capacity Z(t) of the bolted connection at time t after being exposed to fire is greater than the design shear force F1, the fire exposure time is increased. If the shear capacity Z(t) of the bolted connection at time t after being exposed to fire is less than the design shear force F1, the fire exposure time is decreased.

[0021] Step S7: Repeat steps S2 to S6 until the shear bearing capacity of the bolted connection is equal to the design value of the shear force, and determine the fire resistance limit of the bolted connection.

[0022] Preferably, in step S2, Determined based on the type of wood and bamboo.

[0023] Preferably, in step S4, the longitudinal and transverse compressive strength of the pins of wood and bamboo at room temperature can be determined according to the formula given by the pin bearing compressive strength test or the specification.

[0024] Preferably, in step S6, the bisection method can be used for iterative solution.

[0025] The beneficial effects of this invention are as follows: It establishes a pin bearing compressive strength distribution model around the bolt hole, which can quantify the accelerated carbonization and strength degradation caused by heat flow intrusion and stress concentration at the hole edge, thereby more realistically reflecting the actual bearing capacity attenuation process of the node under fire and achieving higher calculation accuracy.

[0026] Additional aspects and advantages will be set forth in part in the description which follows, and will become apparent from the description or may be learned by practice of the invention. Attached Figure Description

[0027] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0028] Figure 1 This is a flowchart illustrating the method for calculating the fire resistance limit of bolted connection nodes of steel plate beams and columns embedded in a wood-bamboo structure according to the present invention.

[0029] Figure 2 This is a front view of the bolted connection node of the beam-column structure in the fire resistance limit calculation method of the bolted connection node of the steel plate embedded beam-column structure in the present invention.

[0030] Figure 3This is a top view of the bolted connection node of the beam-column structure in the method for calculating the fire resistance limit of the bolted connection node of the steel plate embedded beam-column structure in the present invention.

[0031] Figure 4 This is a front view of the bolted connection node of the wood-bamboo structure beam-column in the fire resistance limit calculation method of the bolted connection node of the wood-bamboo structure embedded with steel plate beam-column in one embodiment of the present invention.

[0032] Figure 5 This is a top view of the bolted connection node of the beam-column structure in the method for calculating the fire resistance limit of the bolted connection node of the steel plate beam-column embedded in the wood-bamboo structure in one embodiment of the present invention.

[0033] In the diagram, 1 represents a wooden or bamboo beam, 2 represents a wooden or bamboo column, 3 represents an embedded steel plate, and 4 represents a bolt. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Figure 1 The flowchart illustrates the method for calculating the fire resistance limit of bolted connection nodes of steel plate beams and columns embedded in wood and bamboo structures according to the present invention.

[0035] See Figure 1-3 A method for calculating the fire resistance limit of bolted connections between steel plate beams and columns embedded in a wood-bamboo structure includes the following steps:

[0036] Step S1: Calculate the design shear force F1 for each shear plane of a single bolt in the bolted connection node;

[0037]

[0038]

[0039] Where M is the design value of the bending moment of the node under the ultimate limit state of fire resistance bearing capacity; V is the design value of the shear force of the node under the ultimate limit state of fire resistance bearing capacity; the rotation center O2 is located at the intersection of the beam-column contact surface and the center line of the lowest row of bolts of the beam; Let be the distance from bolt i to the rotation center O2; , Let O2 be the absolute value of the x and y coordinates of bolt i when O2 is the origin; n is the total number of bolts in the bolt group; n v This represents the number of shear surfaces of the bolts in the node. The angle between the direction of the load and the direction parallel to the grain;

[0040] Step S2: Assuming the fire resistance limit of the bolted connection joint is t, calculate the char depth d of the wood or bamboo at time t after being exposed to fire. n = ,in The carbonization rate is determined; the remaining effective cross-sectional thickness t of the connected wood and bamboo components is determined. n =t1- dn Where t1 is the thickness of the connected wooden and bamboo components on one side before being exposed to fire;

[0041] Step S3: Calculate the temperature of the screw at time t after it is heated. , where x is the distance from a point inside the remaining effective section to the edge of the remaining effective section;

[0042] Step S4: Determine the pin bearing compressive strength distribution of the screw at time t after being exposed to fire;

[0043]

[0044]

[0045] in, The angle between the load and the wood grain is The compressive strength of pin bearings for wood and bamboo at room temperature; The compressive strength of the pin shaft along the grain of wood and bamboo at room temperature; This refers to the cross-grain compressive strength of wood and bamboo at room temperature.

[0046] Step S5: Calculate the shear capacity of each shear facet of a single bolt at time t after exposure to fire;

[0047]

[0048] Step S6: Compare the shear capacity Z(t) of the bolted connection at time t after being exposed to fire with the design shear force F1. If they are equal, the fire resistance limit of the bolted connection is determined to be t. If the shear capacity Z(t) of the bolted connection at time t after being exposed to fire is greater than the design shear force F1, the fire exposure time is increased. If the shear capacity Z(t) of the bolted connection at time t after being exposed to fire is less than the design shear force F1, the fire exposure time is decreased.

[0049] Step S7: Repeat steps S2 to S6 until the shear bearing capacity of the bolted connection is equal to the design value of the shear force, and determine the fire resistance limit of the bolted connection.

[0050] In step S2 Determined based on the type of wood and bamboo.

[0051] In step S4, the longitudinal and transverse compressive strength of the pins of wood and bamboo at room temperature can be determined according to the formula given by the pin bearing compression test or the specification.

[0052] In step S6, the bisection method can be used for iterative solution.

[0053] The following is a further explanation using a specific embodiment:

[0054] by Figure 4-5The following example illustrates a bolted connection between a laminated bamboo structure and its embedded steel plate beams and columns. In a newly constructed laminated bamboo structure, the cross-sectional dimensions of the laminated bamboo beams are 150mm × 250mm, and the cross-sectional dimensions of the laminated bamboo columns are 200mm × 250mm. The beams and columns are connected using embedded steel plate bolts. The thickness of the embedded steel plate is 10mm, and the slot thickness is 12mm. Six 14mm diameter bolts are used to connect the beams, with two shear surfaces. The bolt end-to-end distance along the grain is 130mm, and the end-to-end distance across the grain is 75mm. The column spacing is 75mm, and the row spacing is 100mm. The design bending moment of the joint is 13.6kN·m, and the design shear force is 17kN. The carbonization rate of the laminated bamboo is also considered. =0.9 mm / min.

[0055] according to Figure 1 The calculation steps for its fire resistance limit are as follows:

[0056] Step S1: Calculate the design shear force F1 for each shear plane of a single bolt in the bolted connection node;

[0057] kN

[0058] =70.34 。

[0059] Step S2: Assuming the fire resistance limit of the bolted connection is 45 min, calculate the char depth d of the wood and bamboo after 45 min of exposure to fire. n = =40.5mm;

[0060] Determine the remaining cross-sectional thickness t of the connected wooden and bamboo components. n =t1- d n =28.5mm;

[0061] Step S3: Calculate the temperature of the screw after 45 minutes of exposure to heat;

[0062]

[0063] Step S4: Determine the pin bearing compressive strength distribution of the screw at 45 minutes after exposure to fire;

[0064] The compressive strength of the pins along the grain and across the grain of the laminated bamboo at room temperature is determined based on the pin bearing compression test or results: the compressive strength of the pins along the grain is 46.2 MPa, and the compressive strength of the pins across the grain is 27.0 MPa.

[0065] =27.9 MPa

[0066]

[0067] Step S5: Calculate the shear capacity of each shear facet of a single bolt after 45 minutes of exposure to fire;

[0068]

[0069] =6.75 kN

[0070] Step S6: Compare the shear capacity Z(t) of the bolted connection at the time of 45 minutes of exposure to fire with the design shear force F1. It is found that the shear capacity Z(t) of the bolted connection at the time of 45 minutes of exposure to fire is less than the design shear force F1, so the fire exposure time is reduced.

[0071] Step S7: Use the bisection method to iteratively solve the problem, repeating steps S2 to S6 until the shear bearing capacity of the bolted connection node is equal to the design value of the shear force, and determine that the fire resistance limit of the bolted connection node is 41.4 min.

[0072] The above are preferred embodiments of the present invention. Those skilled in the art can make various modifications or improvements based on these embodiments. Without departing from the overall concept of the present invention, such modifications or improvements should fall within the scope of protection claimed by the present invention.

Claims

1. A method for calculating the fire resistance of a bolted connection of a steel plate beam embedded in a timber-bamboo structure, characterized in that, Includes the following steps: Step S1: Calculate the design shear force F1 for each shear plane of a single bolt in the bolted connection node; Wherein, M is the moment design value of the joint under the fire resistance bearing capacity limit state; V is the shear design value of the joint under the fire resistance bearing capacity limit state; is the distance from the bolt i to the rotation center O2; , is the absolute value of the horizontal and vertical coordinates of the bolt i with O2 as the origin; n is the total number of bolts in the bolt group; n v is the number of bolt shear planes in the joint; is the angle between the load direction and the grain direction; Step S2: Assuming the fire resistance limit of the bolted connection joint is t, calculate the char depth d of the wood or bamboo at time t after being exposed to fire. n = ,in The carbonization rate is determined; the remaining cross-sectional thickness t of the connected wood and bamboo components is determined. n =t1- d n Where t1 is the thickness of the connected wooden and bamboo components on one side before being exposed to fire; Step S3: Calculate the temperature distribution of the screw at time t after being heated. , where x is the distance from a point inside the remaining effective section to the edge of the remaining effective section; Step S4: Determine the pin bearing compressive strength distribution of the screw at time t after being exposed to fire; in, The angle between the load and the wood grain is The compressive strength of pin bearings for wood and bamboo at room temperature; The compressive strength of the pin shaft along the grain of wood and bamboo at room temperature; This refers to the cross-grain compressive strength of wood and bamboo at room temperature. Step S5: Calculate the shear capacity of each shear facet of a single bolt at time t after exposure to fire; Step S6: Compare the shear capacity Z(t) of the bolted connection at time t after being exposed to fire with the design shear force F1. If they are equal, determine the fire resistance limit of the bolted connection as t. If the shear capacity Z(t) of the bolted connection at time t after being exposed to fire is greater than the design shear force F1, increase the fire exposure time. If the shear capacity Z(t) of the bolted connection at time t after being exposed to fire is less than the design shear force F1, decrease the fire exposure time. Step S7: Repeat steps S2 to S6 until the shear bearing capacity of the bolted connection is equal to the design value of the shear force, and determine the fire resistance limit of the bolted connection.

2. The method for calculating the fire resistance limit of bolted connection nodes of steel plate beams and columns embedded in a wood-bamboo structure according to claim 1, characterized in that, In step S1, the rotation center O2 is located at the intersection of the beam-column contact surface and the center line of the lowest row of bolts on the beam.

3. The method for determining the remaining cross-section of a wooden or bamboo component after combustion, considering the effect of cracking, as described in claim 1, is characterized in that... In step S2 Determined based on the type of wood and bamboo.

4. The method for determining the remaining cross-section of a wooden or bamboo component after combustion, considering the effect of cracking, as described in claim 1, is characterized in that... In step S4, the longitudinal and transverse compressive strength of the pins of wood and bamboo at room temperature are determined according to the formula given by the pin bearing compression test or the specification.

5. The method for determining the remaining cross-section of a wooden or bamboo component after combustion, considering the effect of cracking, as described in claim 1, is characterized in that... In step S6, the bisection method is used for iterative solution.

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