Wood structure building group fire spread high-risk building identification method

Abstract

The invention discloses a wood structure building group fire spread high-risk building identification method, and relates to the technical field of building group fire spread prevention and control. The method comprises the following steps: firstly, on the basis of collecting building space vector data, obtaining building group fire spreading fire dynamic data; on the basis, a building group fire spreading network model is established in combination with a directed graph basic principle; in consideration of fire spreading characteristics of a wood structure building group, a method for identifying node importance, namely a high-risk building, based on path centrality is provided, and a building group high-risk building transformation sequence is given in combination with a node deletion technology. According to the method, the heterogeneity of all building nodes of the building group and the fire spreading influence of a multi-node fire scene can be fully considered, the pertinence and accuracy of fire spreading prevention and control are improved, meanwhile, the low-intervention prevention and control target is achieved, and important support is provided for disaster prevention planning and emergency plans of the wood structure building group.

Description

Technical Field

[0001] The present invention relates to the technical field of safety engineering, and particularly to a method for identifying high-risk buildings for fire spread in a wooden building complex. Background Art

[0002] Currently, the research on fire spread prevention and control technologies for wooden building complexes mainly focuses on the single-building level and the complex-building level. At the single-building level, modern technologies such as fire detection, fire retardant technology, fire extinguishing technology, personnel evacuation technology, fire-fighting Internet of Things, and GIS are mainly introduced to improve the fire fighting and rescue capabilities and fire safety management levels, and reduce the fire risks of single buildings. On the basis of renovating single buildings, the fire prevention and control at the complex-building level mainly controls the fire spread range through measures such as setting fire separation belts and dividing fire compartments. In addition, traditional rural building complexes have requirements for protecting traditional styles and features during the fire prevention and control renovation process, and it is necessary to try to keep them as old as possible. Large-scale renovations of the building complex are not allowed for fire spread prevention and control work. The methods of existing technologies to solve such problems include: (1) Taking single ancient buildings as the analysis object, based on the analysis of the fire characteristics, fire causes, and fire hazards of ancient buildings, an ancient building fire risk assessment system for evaluating the fire ignition probability and fire hazard of ancient buildings from three levels of people, objects, and environment is established, in order to prevent and control fires for single wooden buildings from three levels of people, objects, and environment; (2) Taking traditional villages as the analysis object, through setting up layout modules, acquisition modules, model construction modules, and evaluation modules, complex network modeling is carried out on fire prevention and control facilities. Based on the fire prevention simulation model, fire prevention and control efficiency evaluation indicators are analyzed, aiming to obtain the performance of fire prevention and control facilities of the fire protection system; (3) Taking the positions of each oil pipe in the oil tank area as the analysis object, by arranging sensor nodes at the positions of each oil pipe in the oil tank area, a weighted directed network for oil tank area spread is established. Using the fire development state and environmental data monitored by the sensor nodes, fire spread attributes are assigned to the nodes, and the structure growth and numerical update of the weighted directed graph are carried out to predict the fire spread situation.

[0003] However, in the traditional rural and urban fire protection improvement projects, the practice of individually reconstructing single buildings and dividing fire protection zones has the following problems: (1) The scope of reconstruction is large and it affects the traditional style. Individually reconstructing single buildings not only disrupts the traditional style of the building complex, but may also result in inefficient or ineffective protection measures, and increases the reconstruction investment and subsequent maintenance costs; (2) The differences in the fire spread risks and fire safety characteristics of different wooden building complexes are not considered, and the problems of insufficient protection and overprotection coexist. Therefore, under the dual goals of the current fire spread prevention and control requirements for wooden building complexes and the traditional style protection policy requirements, it is very necessary to adopt fire spread prevention and control measures with a low degree of intervention in wooden building complexes. (3) Analyzing single ancient buildings as the object is based on case and experience analysis, and does not reveal the fire development process of single buildings from the perspective of fire dynamics. The selection of evaluation indicators is based on the expert scoring method, which has a certain degree of subjectivity and affects the accuracy of the final evaluation results; although corresponding fire prevention and control measures can be proposed from the three levels of people, objects, and environment for each building in the later stage of fire prevention and control, improving each building requires a large amount of time and cost, and the transformation of objects and the environment will inevitably damage or affect the original traditional style, so it is not applicable to the fire prevention and control of wooden building complexes. (4) Taking traditional villages as the analysis object, the fire spread mechanism within traditional villages is not described. The selected network evaluation indicators cannot well explain the performance changes of fire prevention and control facilities after the failure of a certain fire prevention and control node, nor can they identify the locations of important prevention and control facilities in traditional villages, and the differences in different prevention and control facility nodes on the overall prevention and control effect are not considered. Therefore, the described method is not accurate or comprehensive enough for fire prevention and control guidance. (5) Taking the positions of each oil pipe in the oil tank area as the analysis object, the differences in the impacts of different oil pipes on the entire spread network are not considered, and the important nodes in the oil tank area network cannot be identified based on the complex network method, so the fire spread prevention and control goal of the oil tank area cannot be achieved well in a targeted manner. Therefore, the complex network method can provide a new perspective for the low-intervention prevention and control of fire spread in wooden building complexes. Summary of the Invention

[0004] To solve the above technical problems, this patent proposes a method based on path centrality to identify the buildings that have an important impact on the fire spread of the building complex. On this basis, targeted transformation is carried out, which can not only reduce the cost, but also the transformation effect does not affect the overall traditional style, and it is the best measure to achieve low-intervention fire spread prevention and control.

[0005] To implement the above technical solution, the steps are as follows:

[0006] S1. Construct the fire spread parameters of the building complex and divide the fire spread stages;

[0007] The fire spread parameters of the building complex include: the building parameters and fire parameters of the building complex;

[0008] The building parameters of the building complex include: the location, area, scale, and building geographical distribution characteristics of the individual buildings in the building complex;

[0009] The fire parameters include: the size of individual buildings, building styles, building opening ratios, and the amount of combustibles, as well as information on fire spread parameters;

[0010] The fire spread stages include: the indoor fire spread stage in buildings, the fire spread stage among different rooms in a building, and the fire spread stage between buildings;

[0011] S2. Construct a directed graph model of fire spread in the building complex based on the fire spread parameters and fire spread stages of the building complex, and determine the spread relationship between individual buildings in the building complex. The steps are as follows:

[0012] S2.1. Determine the semantic model of the nodes and edges of the directed graph of fire spread in the building complex. The steps are as follows:

[0013] S2.1.1. Define the individual buildings in the building complex as nodes, that is, an individual building is a node in the directed graph G; obtain the set of building nodes V, V = {1, 2,..., i,..., M}, where M represents the number of individual building nodes;

[0014] S2.1.2. Define the fire spread path between buildings as a directed edge to obtain the edge set E, E = {e 1 , e 2 ,... e N}, where N represents the number of edges;

[0015] S2.2. Analyze the directed graph network of fire spread between buildings. The analysis steps are as follows:

[0016] S2.2.1. Based on the physical quantities of the temperature and heat release rate of any node i at a certain moment t, establish the combustion relationship S i ;

[0017] The expression of S i is as follows:

[0018] S i = S i (t, t 0i , Q i , T i );

[0019] In the formula, t represents a certain moment; Q i represents the heat release rate of fire (HRR) of node i; T i represents the average temperature of node i; t 0i represents the ignition time of the node. Among them, for the initial ignition node, t 0i = 0; when t < t 0iWhen it indicates that node i is not ignited, both t and t 0i are 0; when t ≥ t 0i node i is in the burning state, and t and t 0i are functions of the burning time Δt i , and the expression is as follows:

[0020] Δt i = t - t 0i ;

[0021] S2.2.2. Set the initial conditions for the fire spread in the building complex;

[0022] The initial conditions for the fire spread in the building complex include: environmental conditions, simulation conditions, and node initial conditions;

[0023] Furthermore, the environmental conditions include: environmental wind speed and environmental temperature (T ∞ ), and the environmental temperature is the average temperature of node i;

[0024] Furthermore, the simulation conditions include: the number of nodes in the building complex, the simulation time step dt, and the total number of simulation time steps N t ;

[0025] Furthermore, the node initial conditions are: for the initially ignited node, its ignition time t 0i = 0, and the initial state is set to S i = S i (0, 0, 0, T ∞ ); for the unignited nodes, the expression of its ignition time is as follows:

[0026] t 0i = (N t + 1)dt;

[0027] For the unignited nodes, their initial state is set to S i = S i (0, (N t + 1)dt, 0, T ∞ );

[0028] S2.2.3. Update the node states at different simulation times t k , where k = 1, 2,..., N t ; The steps are as follows:

[0029] S2.2.3.1. Determine the HRR and temperature interpolation curves through field simulation, and determine Q 0i ≤ t k ) at time t k for all ignited nodes (satisfying t i and T i ;

[0030] S2.2.3.2. Calculate the heat radiation flux of each ignition node to each non-ignition node j at time t according to the heat radiation flux of fire spread between buildings k at that moment;

[0031] S2.2.3.3. Determine whether the non-ignition node j is ignited. If the node j is ignited, then t 0j =t k , and the status of the non-ignition node j is updated to S i =S i (0, t k , 0, T ∞ );

[0032] S2.2.3.4. Set a 1×M time vector as the ignition time vector during the simulation process, and record the process of building fire spread over time. The i-th element of the vector records the time when node i is ignited;

[0033] S2.3. Based on the directed graph model of building complex fire spread, determine the adjacency matrix A M×M , and combine with the directed graph node traversal algorithm to determine the fire spread matrix P M×M , the steps are as follows:

[0034] For a building complex with M nodes, considering only the different positions of the ignition nodes, assuming there are m initial ignition nodes, the total number of loss scenarios is ;

[0035] The determination steps are as follows:

[0036] S2.3.1.1. When only considering one initial ignition, that is, m = 1, there are a total of M loss scenarios. The method for establishing the adjacency matrix A M×M is as follows:

[0037] Determine the weight matrix of the edges, that is, construct the adjacency matrix A M×M to store the connection relationship data of each node in the network. This matrix is composed of M adjacency vectors. The elements of the adjacency vector are denoted as a(i, j), where (i = 1, 2,..., M; j = 1, 2,..., M). The value-taking method of a(i, j) is as follows:

[0038]

[0039] In the formula, (i, j) = 1 indicates that there is only one edge from the ignition node i to the non-ignition node j, which means that when the ignition node i catches fire, the non-ignition node j can be ignited. The relationship between the two nodes is ignition and being ignited, and the edge weight a(i, j) takes 1; otherwise, if it cannot be ignited, the edge weight is represented by 0;

[0040] S2.3.1.2. When there is more than one initial ignition node, the adjacency matrix A M×M is established as follows:

[0041] S2.3.1.2.1. For each set ignition node i, according to the fire spread simulation calculation, the process of the ignition building gradually igniting other buildings can be determined. At this time, an ignition time vector can be obtained Similarly, by setting other ignition nodes, the corresponding time vectors can be obtained

[0042] S2.3.1.2.2. For the time vector Sort the node numbers in ascending order according to the ignition time. The earlier the ignition time of the node, the earlier it is. For the node at the x-th sorting position, assuming its number is r, the node that ignites r exists among the nodes at the first x - 1 sorting positions;

[0043] S2.3.1.2.3. Select the node closest to r among the first x - 1 nodes and determine it as the node that directly ignites the node numbered r. If the number of this node is m, at this time A (i) (m, r) = 1;

[0044] S2.3.1.2.4. According to the sorting result, execute S2.3.1.2.3 successively to finally determine the adjacency matrix corresponding to the i-th fire spread scenario obtained from node i;

[0045] S2.3.1.2.5. After calculating all fire scenarios, obtain the adjacency matrix A of the fire spread of the building complex through Boolean operation T , and the expression is as follows:

[0046]

[0047] In the formula, ∪ represents the union operation on the elements in the corresponding positions of the matrix;

[0048] S2.3.2. Establish the fire spread matrix P through the node traversal algorithm M×M :

[0049] The node traversal algorithm is used to analyze the maximum range that may be ignited after a fire occurs at the ignition node i (single building). When all buildings in the entire building complex can be ignited, the set of all nodes can be obtained through the node traversal algorithm. When only some buildings are ignited, the traversal algorithm obtains the maximum connected subgraph with i as the source point or the maximum area that the building complex can be ignited;

[0050] The establishment process is as follows:

[0051] S2.3.2.1. Set an M×M auxiliary matrix D, initialize all element values of D to 0, and set the initial value of the traversal count variable F to 1;

[0052] S2.3.2.2. Start traversing from the fire - starting node i, and find the adjacency matrix A M×M of all column numbers y where the values in the i - th row a(i,j) are 1. Denote the set of nodes that meet the condition as J, record all node numbers that meet the condition in the auxiliary matrix D(F,y)=y, and at the same time set the elements in the y - th column of the adjacency matrix A M×M to 0;

[0053] S2.3.2.3. Increase the traversal count F by 1;

[0054] S2.3.2.4. Find the unvisited column number y in the node set J, start traversing from any node with column number y, and repeat S2.3.2.2 - S2.3.2.3 until J is an empty set;

[0055] S2.3.2.5. Obtain the spread matrix P M×M ;

[0056] Based on the traversal of the fire - starting node i, a node set V i can be obtained. V i is all the buildings that may be ignited when the initial fire - starting building is i, corresponding to the largest connected sub - graph with i as the fire - starting node or the fire spread loss scenario when the fire - starting building is i;

[0057] The expression for the values of the elements in the i - th row of the spread matrix P M×M is as follows:

[0058]

[0059] In the formula, the number of columns corresponding to the elements with value 1 in the i - th row of matrix P M×M represents all the node numbers that can be ignited after the fire - starting node i catches fire. The number of rows corresponding to the elements with value 1 in the y - th column represents the fire spread scenario that can ignite the un - ignited node j;

[0060] S3. Identify the high - risk buildings for fire spread in the building complex according to the results of S2, and the steps are as follows:

[0061] S3.1. Calculate the sum of the out - degree and in - degree of the fire - starting node i to determine the node connectivity C(i) value; the expression is as follows:

[0062]

[0063] In the formula, is the sum of the out - degrees of node i, representing the number of nodes that node i can directly ignite; It is the sum of the in-degrees of node i, representing the number of nodes that can directly ignite node i; the larger C(i) is, the higher the "hub status" of node i in the entire network, and the greater the influence of node i on the local or overall network;

[0064] S3.2. Calculate the frequency P ig (i) of the ignition node i appearing (being ignited) in different fire spread scenarios to determine the node risk value F(i); the specific steps are as follows:

[0065] S3.2.1. Determine the semantic definition of P ig (i), that is, P ig (i) is the frequency of the ignition node i appearing (being ignited) in different fire spread scenarios. The larger the value of P ig (i), the more scenarios the ignition node i is ignited by other fire spread scenarios; calculate the frequency of different fire spread scenarios appearing, and the expression is as follows:

[0066]

[0067] In the formula, s ig (i) is the number or area of fire spread scenarios that can directly or indirectly ignite node i, which can be expressed by the fire spread matrix as:

[0068] s ig (i) = P′ i S

[0069] In the formula, P' i is the i-th column of the spread matrix P M×M ;

[0070] S3.2.2. Determine the semantic definition of the node risk F(i) in fire spread, that is, if a certain node in the building complex causes greater fire spread losses as the initial ignition building, and the higher the frequency of this node being ignited in different fire spread scenarios, or the higher the correlation of this node with other spread loss scenarios, it indicates that the risk of this node in the building complex is higher; for this reason, use the product of the fire spread loss of fire spread scenario i and the frequency of the ignition node i being ignited in different fire spread scenarios to express the risk degree of the ignition node i in the building complex, and the calculation formula is as follows:

[0071] F(i) = L(i)P ig (i)

[0072] In the formula, L(i) is the number or area of buildings ignited by fire spread scenario i. The larger L(i) is, it means that when this node catches fire, the more buildings that can be directly or indirectly ignited, and the greater the spread loss; P ig(i) is the frequency of the ignition node i appearing (being ignited) in different fire spread scenarios as described above;

[0073] S3.3. Combine the fire spread matrix P M×M Determine the losses of different fire spread scenarios in the building complex, and determine the values of the path centrality index I(i) of different nodes;

[0074] The path centrality index of the ignition node i can be calculated by the following formula:

[0075] I(i) = F(i)·C(i) = L(i)·P ig (i)·C(i)

[0076] In the formula, F(i) is the node risk; C(i) is the node connectivity; L(i) is the number of buildings or area ignited in the fire spread scenario i; P ig (i) is the frequency of the ignition node i appearing (being ignited) in different fire spread scenarios;

[0077] Therefore, when a certain node i is the ignition point, if the value of the path centrality index I(i) is larger, it indicates that the connection degree of the node spread network is large, and the frequency of this node being able to ignite other node buildings is high, and the node risk is also high;

[0078] For the fire prevention and control of the building complex, this node is more important, and more fire prevention measures need to be invested to reduce its ignition probability. In addition, if the connection between this node and its adjacent nodes can be disconnected, the effect of effectively controlling the fire spread of the building complex can be achieved;

[0079] S3.4. Sort the path centrality indicators of all nodes to obtain the importance sequence of network nodes.

[0080] Advantages of the present invention:

[0081] While fully considering the fire spread characteristics of the building complex, the present invention meets the requirements of low intervention degree (i.e., small renovation range, no impact on the traditional style of the building complex, and appropriate protection) and effective fire spread prevention and control for the wooden structure building complex.

[0082] In the practice process of the present invention, the low-intervention and high-efficiency control of the fire spread of the building complex is realized by controlling the important nodes in the network: before the fire occurs, important buildings can be obtained by combining fire spread and network node importance analysis, and the fire spread risk of the whole building complex can be reduced by strengthening the protection of a few important buildings; during the fire, more efficient fire extinguishing and rescue strategies based on the fire scenario can be established by preferentially cooling or demolishing important buildings that have a great impact on the fire spread, so as to maximize the utilization of limited rescue resources; after the fire, important nodes can be determined by combining the on-site inspection spread network to provide decision-making support for post-disaster restoration and reconstruction. Brief Description of the Drawings

[0083] Figure 1 is the flowchart of the steps of the present invention;

[0084] Figure 2 is the schematic diagram of the network structure of the present invention;

[0085] Figure 3 is the UAV mapping diagram of a wooden structure building complex in a certain place in Yunnan Province;

[0086] Figure 4 is the layout diagram of a wooden structure building complex in a certain place in Yunnan Province;

[0087] Figure 5 is the directed graph of fire spread in multi-scenario building complexes;

[0088] Figure 6 is the statistical chart of the path centrality index of each node in the building complex. Detailed Description of the Invention

[0089] The present invention will be further described in detail below with reference to specific embodiments.

[0090] As Figure 1 and Figure 2 shown, a method for identifying high-risk buildings for fire spread in a wooden structure building complex includes the following steps:

[0091] S1. Construct fire spread parameters of the building complex and divide the fire spread stages;

[0092] The fire spread parameters of the building complex include: building parameters and fire parameters of the building complex;

[0093] Furthermore, the building parameters of the building complex are collected through UAV oblique photography technology (or open source map data), including: the location, area, scale and building geographical distribution characteristics of the individual buildings in the building complex;

[0094] Furthermore, the fire parameters of the building complex are obtained through on-site investigation methods, including: information on the fire spread parameters such as the size of individual buildings, building styles, building opening ratios and the quantity of combustibles;

[0095] The fire spread stages are divided into: the stage of fire spread in the building interior, the stage of fire spread in different rooms within the building, and the stage of fire spread between buildings;

[0096] This embodiment is selected from a certain ancient city block, and the building form is a typical through-tenon wooden structure building. The buildings in the building complex are closely connected and arranged in a continuous manner. There are a total of 215 buildings in the target area, as Figure 3 and Figure 4 shown;

[0097] Furthermore, a fire in a building complex generally goes through multiple development stages, such as smoldering, open fire appearance, fire growth, flashover, fire spreading from the fire - starting room to other rooms, fire spreading from the fire - starting building to other buildings, and finally extinguishing. It can be simply divided into three stages: the stage of fire spreading inside a building, the stage of fire spreading among different rooms within a building, and the stage of fire spreading between buildings.

[0098] The stage of fire spreading inside a building, that is, the fire heat release rate curve Q(t) of the entire single - building, is obtained by superimposing the fire heat release rates of each fire - starting room and the ignited rooms based on the ignition time of each room.

[0099] The fire spreading among rooms within a building, that is, the stage of fire spreading inside a building, is mainly a process in which the fire breaks through the room limit and spreads to adjacent rooms. When a fire breaks out in a certain room inside a building and the fire develops to the flashover state, it breaks through the room limit and spreads horizontally along paths such as wooden doors, windows, partition walls, and corridors, and spreads vertically along paths such as wooden floors, exterior wall windows, and stairwells.

[0100] In the stage of fire spreading between buildings, among them, thermal radiation, fire plumes, and flying fire are the main ways of fire spreading between buildings; when only considering heat transfer by thermal radiation between buildings and ignoring convective heat transfer, the fire - starting building is regarded as a surface radiation source, and when the fire breaks through the fire - resistance limit of the exterior wall of the irradiated building, it is considered that fire spreading between buildings has occurred.

[0101] Considering that the fire growth rate of a wooden - structure building is between medium - speed fire and fast - speed fire, and the fire - resistance limits of maintenance components such as partitions, floors, and doors and windows follow a uniform distribution within the range of 10 - 20 minutes (referring to the American National Standards Committee (NIST) NFPA914). Using the Monte Carlo simulation method, the fire growth factors and the fire - resistance limits of maintenance components during the fire growth process of the building are enumerated, and the fire heat release rate curves of the building under 1000 different combinations of growth factors and fire - resistance limits are obtained, and further the mean value of the heat release rate at each moment is calculated.

[0102] S2. Construct a directed graph model of the fire spreading in the building complex through the fire spreading parameters and stages of the building complex, and determine the spreading relationship between individual buildings in the building complex. The steps are as follows:

[0103] S2.1. Determine the semantic model of the network points and edges of the directed graph of the fire spreading in the building complex. The steps are as follows:

[0104] S2.1.1. Define the individual buildings in the building complex as nodes, that is, an individual building is a node in the directed graph G; obtain the building node set V, V = {1, 2, …, i, …, M}, where M represents the number of individual building nodes. In this embodiment, there are 215 buildings in the target area, that is, M = 215.

[0105] S2.1.2. Define the fire spread path between buildings as a directed edge to obtain the edge set E, where E = {e 1 , e 2 , … e N}, and N represents the number of edges;

[0106] S2.2. Analyze the directed graph network of building-to-building spread. The analysis steps are as follows:

[0107] S2.2.1. Based on the physical quantities of the temperature and heat release rate of any node i at a certain moment t, establish the building-to-building spread combustion relationship S i ;

[0108] S i has the following expression:

[0109] S i = S i (t, t 0i , Q i , T i );

[0110] In the formula, t represents a certain moment; Q i represents the heat release rate of fire (HRR) of node i; T i represents the average temperature of node i; t 0i represents the ignition time of the node. Among them, for the initial ignition node, t 0i = 0; when t < t 0i , it means that node i has not been ignited, and both t and t 0i are 0; when t ≥ t 0i , node i is in a burning state, and t and t 0i are functions of the burning time Δt i , and the expression is as follows:

[0111] Δt i = t - t 0i ;

[0112] S2.2.2. Set the initial conditions for the fire spread of the building complex;

[0113] The initial conditions for the fire spread of the building complex include: environmental conditions, simulation conditions, and node initial conditions;

[0114] Furthermore, the environmental conditions include: environmental wind speed and environmental temperature (T ∞ ), and the environmental temperature is the average temperature of node i;

[0115] Furthermore, the simulation conditions include: the number of nodes in the building complex, the simulation time step dt, and the total number of simulation time steps N t ;

[0116] Furthermore, the initial conditions of the nodes are as follows: for the initially ignited node, its ignition time t 0i = 0, and the initial state is set to S i = S i (0, 0, 0, T ∞ ); for the unignited nodes, the expression for their ignition time is as follows:

[0117] t 0i = (N t + 1)dt;

[0118] For the unignited nodes, their initial state is set to S i = S i (0, (N t + 1)dt, 0, T ∞ );

[0119] S2.2.3. Update the node states at different simulation times t k where k = 1, 2,..., N t ; The steps are as follows:

[0120] S2.2.3.1. Determine the HRR and temperature interpolation curves through field simulation, and determine Q 0i ≤ t k and T i at time tk for all ignited nodes (satisfying t i ) through interpolation;

[0121] S2.2.3.2. Calculate the heat radiation flux from each ignited node to each unignited node j at time t k according to the heat radiation flux of fire spread between buildings;

[0122] S2.2.3.3. Determine whether the unignited node j is ignited. If node j is ignited, then t 0j = t k , and the state of the unignited node j is updated to S i = S i (0, t k , 0, T ∞ );

[0123] S2.2.3.4. Set a 1×M time vector as the ignition time vector during the simulation process to record the process of building fire spread over time. The i-th element of the vector records the time when node i is ignited;

[0124] S2.3. Based on the directed graph model of building complex fire spread, determine the adjacency matrix A M×M, determine the fire spread matrix P by combining with the directed graph node traversal algorithm M×M , the steps are as follows:

[0125] For a building complex with M nodes, when only considering the different positions of the initial fire nodes, assuming there are m initial fire nodes, the total number of loss scenarios is ;

[0126] The determination steps are as follows:

[0127] S2.3.1.1. When only considering one initial fire, that is, when m = 1, there are a total of M loss scenarios, and the adjacency matrix A M×M The establishment method is as follows:

[0128] Determine the weight matrix of the edges, that is, construct the adjacency matrix A M×M Store the connection relationship data of each node in the network. This matrix consists of M adjacency vectors. The elements of the adjacency vector are denoted as a(i,j), where (i = 1, 2,..., M; j = 1, 2,..., M), and the value of a(i,j) is taken as follows:

[0129]

[0130] In the formula, (i,j) = 1 means there is only one edge from the fire node i to the non-fire node j, indicating that when the fire node i catches fire, the non-fire node j can be ignited, and the relationship between the two nodes is ignition and being ignited, and the edge weight a(i,j) takes 1; otherwise, if it cannot be ignited, the edge weight is represented by 0;

[0131] S2.3.1.2. When there is more than one initial fire node, the adjacency matrix A M×M The establishment method is as follows:

[0132] S2.3.1.2.1. For each set of fire node i, according to the fire spread simulation calculation, the process of the fire in the fire building gradually igniting other buildings can be determined. At this time, an ignition time vector can be obtained Similarly, for other set of fire nodes, the corresponding time vectors can be obtained

[0133] S2.3.1.2.2. For the time vector Sort the node numbers in ascending order of the ignition time. The earlier the node catches fire, the more forward its position. For the node at the sorting position x, assuming its number is r, the node that ignites r exists among the nodes at the first x - 1 sorting positions;

[0134] S2.3.1.2.3. Select the node closest to r among the first x - 1 nodes as the node that directly ignites the node numbered r. If the number of this node is m, at this time A (i)(m, r) = 1;

[0135] S2.3.1.2.4. Sequentially execute S2.3.1.2.3 according to the sorting result, and finally determine the adjacency matrix corresponding to the i-th fire spread scenario obtained from node i;

[0136] S2.3.1.2.5. After calculating all fire scenarios, obtain the adjacency matrix A of the fire spread in the building complex through Boolean operations T , and the expression is as follows:

[0137]

[0138] In the formula, ∪ represents the union operation on the elements in the corresponding positions of the matrix;

[0139] S2.3.2. Establish the fire spread matrix P through the node traversal algorithm M×M :

[0140] The node traversal algorithm is used to analyze the maximum range that may be ignited after a fire occurs at the ignition node i (single building). When all buildings in the entire building complex can be ignited, the set of all nodes can be obtained through the node traversal algorithm. When only some buildings are ignited, what the traversal algorithm obtains is the maximum connected subgraph with i as the source point or the maximum area where the building complex can be ignited;

[0141] The establishment process is as follows:

[0142] S2.3.2.1. Set an M×M auxiliary matrix D, initialize all element values of D to 0, and set the initial value of the traversal times variable F to 1;

[0143] S2.3.2.2. Start traversing from the ignition node i, and find the adjacency matrix A M×M The column numbers y of all elements with a value of 1 in the i-th row a(i, j) are found, and the set of nodes that meet the conditions is denoted as J. Use the auxiliary matrix to record all node numbers that meet the conditions D(F, y) = y, and at the same time set the elements in the y-th column of the adjacency matrix A M×M to 0;

[0144] S2.3.2.3. Increase the traversal times F by 1;

[0145] S2.3.2.4. Find the unvisited column numbers y in the node set J, start traversing from any node in the column numbers y, and repeat S2.3.2.2 to S2.3.2.3 until J is an empty set;

[0146] S2.3.2.5. Obtain the spread matrix P through node traversal analysis M×M ;

[0147] A node set V can be obtained based on the traversal of the ignition node ii , V i is all the buildings that may be ignited when the initial fire - starting building is i, corresponding to the maximum connected sub - graph with i as the fire - starting node or the fire spread loss scenario when the fire - starting building is i;

[0148] The spread matrix P M×M The value expression of the i - th row elements of

[0149]

[0150] In the formula, the matrix P M×M The column numbers corresponding to the elements with value 1 in the i - th row of represent all the node numbers that can be ignited after the fire - starting node i catches fire. The row numbers corresponding to the elements with value 1 in the y - th column represent the fire spread scenarios that can ignite the non - fire - starting node j;

[0151] Get the directed graph of all fire spread scenarios of the building complex as shown in Figure 5 In this embodiment, the number of fire spread scenarios of the wooden structure building is 129;

[0152] S3. Identify the high - risk buildings for fire spread in the building complex according to the results of S2, and the steps are as follows:

[0153] S3.1. Calculate the sum of the out - degree and in - degree of the fire - starting node i to determine the node connectivity C(i) value; the expression is as follows:

[0154]

[0155] In the formula, is the sum of the out - degrees of node i, indicating the number of nodes that node i can directly ignite; is the sum of the in - degrees of node i, indicating the number of nodes that can directly ignite node i; the larger C(i) is, the higher the "hub status" of node i in the whole network, and the greater the influence of node i on the local or whole network;

[0156] S3.2. Calculate the frequency P ig (i) of the fire - starting node i appearing (being ignited) in different fire spread scenarios to determine the node risk degree F(i) value; the specific steps are as follows:

[0157] S3.2.1. Determine the semantic definition of P ig (i), that is, P ig (i) is the frequency of the fire - starting node i appearing (being ignited) in different fire spread scenarios. The larger the value of P ig (i), the more scenarios in which the fire - starting node i is ignited by other fire spread scenarios; calculate the frequency of different fire spread scenarios appearing, and the expression is as follows:

[0158]

[0159] In the formula, s ig (i) is the number of fire scenarios or the area of scenarios that can directly or indirectly ignite node i, and can be expressed through the fire spread matrix as:

[0160] s ig (i) = P′ i S

[0161] In the formula, P' i is the i-th column of the spread matrix P M×M ;

[0162] S3.2.2. Determine the semantic definition of the node risk degree F(i) in fire spread, that is, if the fire spread loss caused by a certain node in the building complex as the initial ignition building is greater, and the frequency of this node being ignited in different fire spread scenarios is higher, or the relevance of this node to other spread loss scenarios is higher, it indicates that the risk degree of this node in the building complex is higher; for this reason, the product of the fire spread loss of fire spread scenario i and the frequency of the ignition node i being ignited in different fire spread scenarios is used to express the risk degree of the ignition node i in the building complex, and the calculation formula is as follows:

[0163] F(i) = L(i)P ig (i)

[0164] In the formula, L(i) is the number of building blocks or the area ignited by fire spread scenario i. The larger L(i) is, it indicates that when this node catches fire, the more buildings that can be directly or indirectly ignited, and the greater the spread loss; P ig (i) is the frequency of the ignition node i appearing (being ignited) in different fire spread scenarios as described above;

[0165] S3.3. Combine the fire spread matrix P M×M to determine the losses of different fire spread scenarios in the building complex and determine the values of the path centrality index I(i) of different nodes;

[0166] The path centrality index of the ignition node i can be calculated according to the following formula:

[0167] I(i) = F(i)·C(i) = L(i)·P ig (i)·C(i)

[0168] In the formula, F(i) is the node risk degree; C(i) is the node connectivity; L(i) is the number of building blocks or the area ignited by fire spread scenario i; P ig (i) is the frequency of the ignition node i appearing (being ignited) in different fire spread scenarios;

[0169] Therefore, in the case where a certain node i is the ignition point, if the value of the path centrality index I(i) is larger, it indicates that the node has a large connection degree in the spread network, and the frequency of this node being able to ignite other node buildings is high, and the node risk is also high;

[0170] Obtain the statistical results of the path centrality indicators of each node in the building complex as shown in Figure 6 the following.

[0171] For the fire prevention and control of the building complex, the more important this node is, the more fire prevention measures need to be invested to reduce its ignition probability. In addition, if the connection between this node and its adjacent nodes can be disconnected, the effect of effectively controlling the spread of the building complex fire can be achieved;

[0172] S3.4. Sort the path centrality indicators of all nodes to obtain the importance sequence of network nodes, as shown in the following table;

[0173] Table 1 Transformation sequence of important nodes

[0174]

[0175] According to this sorting, take targeted fire prevention measures. For nodes with high node importance, more fire prevention measures need to be invested and reasonable transformation should be carried out; for nodes with low node importance, it means that when they are ignition nodes, the loss caused by the small spread probability is also small, and relatively simple fire prevention measures can be used to avoid the occurrence of the spread of the building complex fire;

[0176] Adopt the importance indicators of each node obtained by path centrality calculation. According to the risk requirements of the spread of the building complex fire, when carrying out fire safety transformation, only some nodes that have a greater impact on the risk of the spread of the building complex fire need to be strengthened and transformed, and it is not necessary to strengthen and transform all buildings.

[0177] It can be seen from Table 1 that by sequentially carrying out fire protection transformation on the important node transformation sequence determined according to the path centrality method, the expected total loss of the spread of the building complex fire gradually decreases. The earlier the node with higher importance is transformed, the most obvious the effect is, and then the transformation effect gradually slows down. The expected loss of the spread of the building complex fire after transforming different numbers of nodes is shown in Table 2;

[0178] Table 2 Expected loss of the spread of the building complex fire after transforming different numbers of nodes (m 2 )

[0179]

[0180] The parameter description of the present invention is shown in Table 3:

[0181] Table 3 Description of each parameter

[0182]

[0183]

[0184]

[0185] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for identifying high-risk buildings for fire spread in a wood-structured building complex, characterized by: The following steps are involved: S1. Construct fire spread parameters for building complexes and divide fire spread stages; The fire spread parameters of the building complex include: building parameters and fire parameters of the building complex; The architectural parameters of the building complex include: the location, area, scale and geographical distribution characteristics of the individual buildings in the building complex; The fire parameters include: single building size, architectural style, building opening ratio and combustible material quantity fire spread parameter information; The fire spread stages include: the fire spread stage inside the building, the fire spread stage in different rooms in the building, and the fire spread stage between buildings; S2. Construct a directed graph model of fire spread in a building complex through fire spread parameters and fire spread stages of the building complex, and determine the spread relationship of each single building in the building complex; S3. Based on the results of S2, identify the buildings with high risk of fire spread in the building complex.

2. A method for identifying high-risk buildings for fire spread in a wood-structured building complex according to claim 1, characterized in that: The steps of constructing a directed graph model of fire spread of a building complex by using fire spread parameters and fire spread stages of the building complex, and determining the spread relationship of each single building in the building complex are as follows: S2.

1. Determine the semantic model of the points and edges of the directed graph network of the building complex fire spread; S2.2, analysis of the directed graph network of building sprawl; S2.

3. Based on the directed graph model of fire spread in building complexes, determine the adjacency matrix A M×M , combined with the directed graph node traversal algorithm to determine the fire spread matrix P M×M .

3. A method for identifying high-risk buildings for fire spread in a wood-structured building complex according to claim 1, characterized in that: The steps of identifying high-risk buildings for fire spread in a building complex according to the results of S2 are as follows: S3.

1. Calculate the sum of the out-degree and in-degree of the fire node i to determine the node connectivity C(i); S3.

2. Calculate the frequency P of fire node i in different fire spread scenarios ig (i) to determine the node risk F(i) value; S3.

3. Combined with the fire spread matrix P M×M Determine the losses of different fire spread scenarios of the building complex and determine the path centrality index I(i) values ​​of different nodes; S3.

4. Sort the path centrality indices of all nodes to obtain the importance sequence of network nodes.

4. A method for identifying high-risk buildings for fire spread in a wood-structured building complex according to claim 2, characterized in that: The steps of determining the semantic model of the network points and edges of the directed graph of fire spread in building complexes are as follows: S2.1.

1. Define individual buildings in the building complex as nodes, and obtain a building node set V, V = {1, 2, ..., i, ..., M}, where M represents the number of individual building nodes; S2.1.

2. Define the fire spread path between buildings as directed edges, and obtain the edge set E, E = {e1, e2, …e N }, N represents the number of edges.

5. A method for identifying high-risk buildings for fire spread in a wood-structured building complex according to claim 2, characterized in that: The steps of analyzing the inter-building sprawl directed graph network are as follows: S2.2.

1. Based on the physical quantities of temperature and heat release rate of any node i at a certain time t, establish the relationship S of the spread of combustion between buildings. i ; S i The expression is as follows: S i =S i (t,t 0i ,Q i ,T i ); In the formula, t represents a certain moment; Q i represents the fire heat release rate (HRR) of node i; T i represents the average temperature of node i; t 0i represents the time when the node is ignited, where for the initial ignition node, t 0i =0; when t <t 0i When t = t, it means that node i is not ignited, t and t 0i are all 0; when t≥t 0i When node i is in the burning state, t and t 0i is the combustion time Δt i The function is expressed as follows: Δt i =t-t 0i ; S2.2.

2. Set the initial conditions for the spread of fire in the building complex; The initial conditions for the spread of fire in building complexes include: environmental conditions, simulation conditions and node initial conditions; Environmental conditions include: ambient wind speed and ambient temperature (T ∞ ), the ambient temperature is the average temperature of node i; The simulation conditions include: the number of building cluster nodes, the simulation time step dt and the total number of simulation time steps N t ; Furthermore, the initial conditions of the nodes are: for the initial ignition node, its ignition time t 0i =0, the initial state is set to S i =S i (0,0,0,T ∞ ); For the unignited node, the ignition time expression is as follows: t 0i =(N t +1)dt; For the non-fired nodes, their initial state is set to S i =S i (0,(N t +1)dt,0,T ∞ ); S2.2.

3. Update different simulation times t k Node state, where k = 1, 2, ..., N t ; The steps are as follows: S2.2.3.

1. Determine the HRR and temperature interpolation curves through field simulation, and determine all the nodes that have caught fire (satisfying t 0i ≤t k ) at t k Q of the moment i and T i ; S2.2.3.

2. Calculate the heat radiation flux of all fire nodes for each unfired node j at t according to the fire spread heat radiation flux between buildings. k Thermal radiation flux at the moment; S2.2.3.

3. Determine whether the unignited node j is ignited. If the node j is ignited, then t 0j =t k , the state of the non-fired node j is updated to S i =S i (0,t k ,0,T ∞ ); S2.2.3.

4. Set a 1×M time vector As the ignition time vector in the simulation process, the vector records the process of building fire spreading over time. The i-th element of records the time when node i is ignited.

6. A method for identifying high-risk buildings for fire spread in a wood-structured building complex according to claim 2, characterized in that: Based on the directed graph model of building group fire spread, the adjacency matrix A is determined. M×M , combined with the directed graph node traversal algorithm to determine the fire spread matrix P M×M The steps are as follows: For a building complex with M nodes, only considering the different locations of the fire nodes, assuming that there are m initial fire nodes, the number of loss scenarios is indivual; The steps to determine are as follows: S2.3.1.1, when only one initial fire is considered, that is, when m = 1, there are a total of M loss scenarios, and the connection matrix A M×M The establishment method is as follows: Determine the edge weight matrix, that is, construct the adjacency matrix A M×M The matrix stores the connection relationship data of each node in the network. The matrix consists of M adjacent vectors. The elements of the adjacent vector are recorded as a(i,j), where (i=1,2,…,M; j=1,2,…M). The value of a(i,j) is as follows: In the formula, (i, j) = 1 means that there is only one edge from the burning node i to the unburned node j, which means that when the burning node i catches fire, the unburned node j can be ignited, and the relationship between the two nodes is ignition and being ignited, and the edge weight a(i, j) is 1; otherwise, if it cannot be ignited, the edge weight is 0; S2.3.1.

2. When there is more than one initial fire node, the connection matrix A M×M The establishment method is as follows: S2.3.1.2.

1. Each time a fire node i is set, the process of the burning building gradually igniting other buildings can be determined according to the fire spread simulation calculation. At this time, an ignition time vector can be obtained. Similarly, by setting other fire nodes, we can get the corresponding time vector S2.3.1.2.

2. For time vector Sort the nodes by ignition time from small to large. The earlier the node is, the earlier the ignition time is. For the node with sorting position x, assuming its number is r, the node that ignites r exists in the nodes with sorting position x-1 before. S2.3.1.2.

3. Take the node closest to r among the first x-1 nodes and determine it as the node that directly ignites the node numbered r. If the node numbered is m, then A (i) (m,r)=1; S2.3.1.2.4, execute S2.3.1.2.3 one by one according to the sorting results, and finally determine the adjacency matrix corresponding to the i-th fire spread scenario obtained by node i; S2.3.1.2.

5. After calculating all fire scenarios, the adjacency matrix A of the fire spread of the building complex is obtained through Boolean operations. T , the expression is as follows: In the formula, ∪ represents the union operation of the elements in the corresponding positions in the matrix; S2.3.

2. Establish the fire spread matrix P through the node traversal algorithm M×M : The node traversal algorithm is used to analyze the maximum range that may be ignited after a fire occurs at the fire node i. When the buildings of the entire building complex can be ignited, the node traversal algorithm can obtain the set of all nodes. When only some buildings are ignited, the traversal algorithm obtains the maximum connected subgraph with i as the source point or the maximum area of ​​the building complex that can be ignited. The establishment process is as follows: S2.3.2.

1. Set an M×M auxiliary matrix D, where all element values ​​of D are initially set to 0 and the initial value of the traversal count variable F is set to 1; S2.3.2.

2. Traverse from the fire node i and find the adjacency matrix A M×M The set of nodes that meet the condition is recorded as J, and the auxiliary matrix is ​​used to record the numbers of all nodes that meet the condition D(F,y)=y. M×M The elements in the yth column are set to 0; S2.3.2.3, the number of traversals F increases by 1; S2.3.2.

4. Find the unvisited column number y in the node set J, traverse from any node in the column number y, and repeat S2.3.2.2 to S2.3.2.3 until J is an empty set; S2.3.2.

5. Obtain the spreading matrix P through node traversal analysis M×M ; Based on the traversal of the fire node i, a node set V can be obtained i , V i It is all the buildings that may be ignited when the initial fire building is i, corresponding to the maximum connected subgraph with i as the fire node or the fire spread loss scenario when the fire building is i; Spread Matrix P M×M The expression for the value of the element in the i-th row is as follows: In the formula, the matrix P M×M The number of columns corresponding to the element with a value of 1 in the i-th row represents the numbers of all nodes that can be ignited after the fire node i catches fire. The number of rows corresponding to the element with a value of 1 in the y-th column represents the fire spread scenario that can ignite the unignited node j.

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