A prestressed wood structure tension loss evaluation method and device
By monitoring environmental temperature and humidity and using a multiphysics coupling model, the tension loss of prestressed timber structures is decomposed into multiple components, solving the problem of insufficient prediction accuracy in existing technologies and achieving high-precision tension loss assessment and optimization design support.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XIAMEN UNIV
- Filing Date
- 2026-01-24
- Publication Date
- 2026-06-05
Smart Images
Figure CN122154274A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method and apparatus for assessing the tension loss of prestressed timber structures. Background Technology
[0002] Prestressed timber structures, by introducing prestressing technology at joints, can effectively improve the problem of concentrated failure in joint areas under lateral loads in traditional timber structures, enhancing their seismic toughness and lateral bearing capacity, and enabling the structure to have a self-resetting mechanism under earthquakes. However, during long-term service, the performance of prestressed timber structures is affected by the coupled effects of multiple factors such as wood creep, changes in environmental temperature and humidity, and relaxation of prestressing materials, resulting in a significant time-varying decrease in effective tension. This loss of tension directly affects the seismic toughness of the structure during its service life, thus threatening its safety and durability.
[0003] Currently, assessment techniques for tension loss during the service life of prestressed timber structures generally suffer from insufficient consideration of the aforementioned multi-factor coupling effects, leading to limited prediction accuracy. Studies show that the creep coefficient in the transverse direction of wood can be 8 to 10 times that in the longitudinal direction, especially under transverse load-bearing conditions in floor slabs, where tension loss is even more significant. Existing methods often ignore this crucial influence. Furthermore, existing models often employ simplification when simulating wood moisture transport and environmental deformation, failing to distinguish the differences in environmental strain coefficients during moisture absorption and drying, thus failing to accurately reflect the material response under actual environmental conditions. This neglect of the influence of transverse creep and the oversimplification of moisture transport and environmental deformation models limit in-depth analysis of the coupling mechanisms among various factors of prestress loss, making it difficult for existing technologies to achieve high-precision prediction of tension loss based on environmental monitoring data. Therefore, to improve the safety assessment capability of prestressed timber structures throughout their entire life cycle, it is urgent to establish a tension loss assessment method that comprehensively considers transverse creep of wood, changes in environmental temperature and humidity, moisture transport and its induced environmental deformation, and the relaxation coupling effect of prestressing materials. Summary of the Invention
[0004] This invention provides a method for assessing the loss of tensile force during the service life of prestressed timber structures using environmental temperature and humidity monitoring data, which can effectively solve the above-mentioned problems.
[0005] This invention is implemented as follows: A method for assessing tension loss in prestressed timber structures includes the following steps: S1. Obtain key parameters of the prestressed timber structure and collect the temperature and relative humidity of the service environment; S2. Calculate the equilibrium moisture content of the wood surface based on the temperature and relative humidity, and use a one-dimensional moisture diffusion model combined with the equilibrium moisture content as a time-varying boundary condition to solve for the moisture content distribution inside the wood component. S3. Update the elastic flexibility of the wood according to the moisture content distribution, and calculate the elastic strain of the wood component in combination with the rate of change of prestress. S4. Decompose the creep strain into a pure creep component and a mechanical moisture-absorbing creep component, and calculate them separately; S5. Based on the direction of moisture content change, select the corresponding environmental strain coefficient to calculate the environmental strain caused by drying shrinkage and wetting expansion. Wherein: if the moisture content increases, the hygroscopic environmental strain coefficient is used; if the moisture content decreases, the desorption environmental strain coefficient is used. S6. The elastic strain, creep strain and environmental strain are superimposed to obtain the total strain, and the prestressing tendon tension is updated according to the change in the total strain to form a time-varying curve of tension force.
[0006] The beneficial effects of this invention are: (1) This invention achieves a high-precision, mechanistic dynamic assessment of long-term tension loss in prestressed timber structures by integrating environmental monitoring data with a multi-physics field coupled constitutive model of timber. Its beneficial effects are: it can not only accurately predict the time-varying attenuation curve of prestress based on the history of temperature and humidity, thus solving the prediction bias caused by the traditional method due to neglecting the anisotropic creep of timber, simplifying the environmental deformation model, and lacking multi-field coupling analysis; more importantly, by decomposing the total strain into four physically distinct components—elastic, pure creep, mechanical hygroscopic creep, and hysteretic environmental strain—and setting differentiated parameters for members with and without grain, it achieves, for the first time, a quantitative analysis of the contribution of each factor in the assessment, thereby revealing the main control mechanism of prestress loss and providing direct theoretical basis and decision support for structural optimization design and preventive maintenance. Attached Figure Description
[0007] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.
[0008] Figure 1 This is a flowchart of the present invention.
[0009] Figure 2 This is a comparison chart of the time-varying moisture content curve of the horizontally textured floor slab of this invention and the measured data.
[0010] Figure 3 This is a comparison chart of the curve of prestressed tension force of the horizontally textured floor slab over time and the measured data.
[0011] Figure 4This is a comparison chart of the curve of prestressed tension force of the non-roughed floor slab of the present invention versus time and the measured data.
[0012] Figure 5 This is a comparison chart of the time-varying moisture content curve of the non-roughed floor slab of the present invention and the measured data.
[0013] Figure 6 This is a schematic diagram illustrating the contribution percentage of each strain component to the total strain in Embodiment 1 of the present invention.
[0014] Figure 7 This is a schematic diagram showing the contribution ratio of each strain component to the total strain in Embodiment 2 of the present invention. Detailed Implementation
[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.
[0016] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.
[0017] Reference Figure 1-7 As shown, a method for assessing tension loss in prestressed timber structures includes the following steps: S1. Obtain key parameters of the prestressed timber structure and collect the temperature and relative humidity of the service environment; S2. Calculate the equilibrium moisture content of the wood surface based on the temperature and relative humidity, and use a one-dimensional moisture diffusion model combined with the equilibrium moisture content as a time-varying boundary condition to solve for the moisture content distribution inside the wood component. S3. Update the elastic flexibility of the wood according to the moisture content distribution, and calculate the elastic strain of the wood component in combination with the rate of change of prestress. S4. Decompose the creep strain into a pure creep component and a mechanical moisture-absorbing creep component, and calculate them separately; S5. Based on the direction of moisture content change, select the corresponding environmental strain coefficient to calculate the environmental strain caused by drying shrinkage and wetting expansion. Wherein: if the moisture content increases, the hygroscopic environmental strain coefficient is used; if the moisture content decreases, the desorption environmental strain coefficient is used. S6. The elastic strain, creep strain and environmental strain are superimposed to obtain the total strain, and the prestressing tendon tension is updated according to the change in the total strain to form a time-varying curve of tension force.
[0018] In step S2, the equilibrium moisture content of the wood surface is first calculated according to the Rasmussen formula using the monitored sequence, and this is used as a time-varying boundary condition.
[0019] Where W, s, s1, and s2 are all functions of temperature, and the specific values of the coefficients are given in the following formulas.
[0020]
[0021]
[0022]
[0023]
[0024] Subsequently, the moisture diffusion coefficient D and surface emissivity S were calculated. In Example 1, the influence of the adhesive layer was ignored, and the above parameters were determined solely based on the moisture content u.
[0025]
[0026] Subsequently, a one-dimensional water diffusion model was established based on Fick's second law:
[0027] The finite difference method is used to discretize the component into multiple nodes along the thickness direction, and the internal moisture content distribution at each time step and at each depth is obtained by iterative solution.
[0028] In this example, the spatial step size Δx is set to 5 mm and the time step size Δt is set to 3 hours.
[0029] For internal nodes, a difference equation is established using the current time step and the next time step:
[0030] For the boundary nodes, the difference equations for the boundary nodes are established using the central difference method, taking into account the surface water flux boundary conditions:
[0031]
[0032] By solving the above system of equations, the moisture content distribution vector of each node along the thickness direction of the wooden component at the current time step can be obtained. In step S4, the pure creep component is calculated using the generalized Kelvin model, and the total creep strain is calculated using the mechanical moisture-absorbing creep theory. The calculation formula is as follows:
[0033]
[0034]
[0035] For this example, Δu k Let the water content change be at time step k. This represents the cumulative absolute value of the change in moisture content from the loading time (τ) to the current time (t). For prestressed timber wall structures, J is taken as... ∞ = 0.90, C = 0.50; J is taken as 0.90 for prestressed timber structure floor slabs. ∞ = 0.58, C = 2.40. Where σ0 represents the initial compressive stress applied to the wooden component at the initial moment. In this example, the initial compressive stress is taken as 0.9050 MPa for the wall and 0.8589 MPa for the floor slab.
[0036] The generalized Kelvin model used in the pure creep calculation contains 6 Kelvin elements. The hysteresis time τ is taken as 0.1, 1, 10, 100, 1000, and 10000 days. The corresponding wall creep compliance parameter J... i The values are, in order: 0.0522, 0.0478, 0.0342, 0.0802, 0.0864, 0.2114; the corresponding floor slab creep compliance parameter J. i The values are, in order: -0.0238, 0.1075, 0.0028, 0.1720, 0.1681, 0.7676. J0(u ref The elastic compliance at the reference moisture content is used as the baseline compliance for creep calculation, and is used to convert the dimensionless creep parameter J. i and J ∞ This is converted into actual deformation. ref For reference moisture content, a value of 20% is used in this example. In the specific calculation, J0(u ref The same elastic compliance formula as in step S3 is used for calculation, but a constant reference moisture content u needs to be substituted in. ref .
[0037] In step S1, the key parameters include geometric parameters and material parameters: geometric parameters include: height of the wooden component ( h w ), Width of glued laminated timber components ( w w ), total thickness of glued laminated timber components ( w CLT ), number of layers of glued laminated wood ( N layer ), single-layer board thickness ( t lam ), unbonded length of prestressed tendons ( l PT ), total cross-sectional area of prestressed tendons ( A P Material parameters include: initial prestress level of the prestressing tendons (…). Pt ), elastic modulus of prestressed tendons ( E p ), Wood elastic modulus ( MOE Wood moisture diffusion coefficient ( D ), wood surface emissivity ( S ), average moisture content of wood ( W, s, s 1 , s 2) Wood pure creep parameters ( J i ), Wood mechanical moisture absorption creep parameters ( J ∞ , c ), Wood environmental strain coefficient ( α u ).
[0038] For a prestressed wood structure that includes both parallel-grain and transverse-grain load-bearing components, different mechanical moisture-absorbing creep parameters, as well as different moisture absorption environment strain coefficients and desorption environment strain coefficients, are set for the parallel-grain and transverse-grain load-bearing components, respectively.
[0039] Based on the moisture content distribution obtained in step S2, the elastic strain of the wooden component is calculated. This step considers the correction effect of moisture content changes on the elastic modulus of the wood. In this embodiment, the elastic compliance update formula is:
[0040] Among them, the moisture reduction factor ( k u Take 1.06.
[0041] The formula for calculating the increment of elastic strain is:
[0042]
[0043] The first term of the formula is the strain at the previous moment, the second term is the deformation caused by the stress increment, and the third term is the additional deformation caused by the change in stiffness.
[0044] In step S5, the environmental strain caused by shrinkage and expansion is calculated. The core of this invention lies in distinguishing between the moisture absorption and desorption processes. First, the moisture content increment is calculated: if the moisture content increment > 0, the moisture absorption environmental strain coefficient is used; if the moisture content increment < 0, the desorption environmental strain coefficient is used. Specific parameter values are as follows: For the prestressed wood structure wall in this example, α... u,abs =0.0197, α u,des = 0.0268; For the prestressed wooden floor slab in this example, α u,abs = 0.1830, α u,des = 0.2731, where the mechanical moisture absorption related parameter is taken as 1.3; since temperature changes have little effect on wood strain, the effect of thermal expansion is ignored in this embodiment, the coefficient of thermal expansion is taken as 0, and the environmental strain update formula is:
[0045]
[0046] Where b is a mechanical moisture absorption related parameter, α T is the coefficient of thermal expansion.
[0047] In step S6, based on the deformation compatibility principle, the strain components calculated in steps S3 to S5 are superimposed to obtain the total strain of the wall and the total strain of the floor slab. The tension of the prestressing tendons is then updated using the following formula:
[0048] In this example, the wall height is 1000 mm, the floor slab thickness is 100 mm, and the prestressing tendon length is 1200 mm.
[0049] Compare the currently calculated prestress value with the value calculated in the previous iteration step. If the absolute value of the difference is less than the allowable error (set to 0.1 kN in this embodiment), the calculation in the current time step is considered to have converged, the result is output, and the process proceeds to the next time step; otherwise, the stress is updated using the updated prestress value, and the process returns to step S3 to recalculate until convergence.
[0050] By repeatedly executing steps S2 to S6, the tension change curve for the entire cycle can be obtained.
[0051] To illustrate the content of this case in detail, the following examples are provided: Example 1 A prestressed orthotropic glued laminated timber (GLP-FLAP) shear wall has a cross-sectional dimension of 550 × 175 mm and a height of 1000 mm. The wall is composed of five layers of glued laminated veneer, each 35 mm thick, subjected to compression along the grain. At the bottom of the wall, an orthotropic glued laminated timber floor is installed, each 100 mm thick, composed of five layers of glued laminated veneer, each 20 mm thick, subjected to compression out of plane. The glued laminated timber is made of Canadian SPF No. 2 grade timber. A single unbonded prestressing tendon is placed at the center of the wall, with a total length of 1200 mm and a cross-sectional area of 141 mm². The initial tension of the prestressing tendon is 82.0 kN. The temperature and humidity sampling interval for monitoring the environment is set to 3 hours. The model input parameters are shown in Table 1 below.
[0052] Substituting the above parameters into step S2 of the analysis method, the time-varying distribution of moisture content inside the CLT was calculated using 500 days of monitored temperature and humidity data. Then, according to the formulas in steps S3 to S5, elastic strain, creep strain, and environmental strain were calculated respectively. Specifically, when calculating environmental strain, the program automatically determined the direction of moisture content change at each time step. For example, on day 258, monitoring data showed that the environment remained dry, and the program determined that the wood was in a desorption state, automatically calling the larger desorption coefficient from Table 1 for calculation, thus capturing significant shrinkage deformation. Finally, through iterative updates in step S6, the residual tension of the prestressed tendons after 500 days was obtained as 68.2 kN, meaning a tension loss of approximately 16.8%, which is highly consistent with the field measurement results. The calculated results are compared with the measured results for example... Figure 3 As shown.
[0053] Furthermore, in Example 1, Figure 2 The comparison between the calculated and measured moisture content shows that the model successfully predicted the 'wave-like' infiltration process of moisture content inside the wood caused by seasonal fluctuations in environmental humidity. Furthermore, by decomposing the total strain (refer to...) Figure 6 The contribution of each component can be quantified: at 500 days, environmental strain accounts for approximately 78.54% of the total strain, mechanical hygroscopic creep accounts for approximately 9.35%, pure creep accounts for approximately 12.06%, and elastic strain accounts for approximately 0.06%. This decomposition clearly shows that: 1) environmental swelling and shrinkage due to moisture is the most important driving source of strain (and thus prestress loss); 2) mechanical hygroscopic creep coupled with the history of moisture content changes makes a huge contribution and cannot be ignored; 3) pure viscoelastic creep makes a stable but relatively small contribution in the long term.
[0054] Example 2 A prestressed orthogonal glued laminated timber shear wall has a cross-sectional dimension of 550 × 175 mm and a wall height of 1000 mm. The wall is composed of 5 layers of laminated plywood, each layer being 35 mm thick. The stress direction is longitudinal compression. The glued laminated timber is made of Canadian SPF No. 2 grade timber. A single unbonded prestressing tendon is installed at the center of the wall, with a total length of 1100 mm and a cross-sectional area of 141 mm². 2 The initial tension of the prestressing tendons was 82.0 kN. The temperature and humidity sampling interval for the monitoring environment was set to 3 hours. The model input parameters are shown in Table 2 below.
[0055] Substituting the parameters from Experiment No. 2 into steps S2 to S6 of the analytical method, and using 500 days of monitored temperature and humidity data, the time-varying distribution of moisture content inside the CLT wall was calculated. Then, according to the formulas in S3 to S5, the elastic strain, creep strain, and environmental strain of the wall were calculated respectively. Since this specimen did not include the CLT floor slab, all strain components related to the floor slab were zero in the calculation, and the total deformation of the system was entirely contributed by the wall. When calculating the environmental strain, the program automatically determined the direction of moisture content change at each time step. For example, on day 258, the same as for specimen No. 1, monitoring data showed that the environment remained dry. The program determined that the wood was in a desorption state and automatically called the desorption coefficient of the wall in Table 2 for calculation. Finally, through force balance and iterative update in step S6, the remaining tensile force of the prestressing tendons after 500 days was obtained as 74.2 kN, meaning the tension loss was approximately 9.5%. This calculated result was highly consistent with the field measurement results. The comparison between the calculated and measured results is as follows: Figure 4 As shown.
[0056] Furthermore, the contributions of each component in Example 2 are as follows: At 500 days, the environmental strain accounts for approximately 48.78% of the total strain in this example, mechanical moisture-absorbing creep accounts for approximately 17.05%, pure creep accounts for approximately 34.31%, and elastic strain accounts for approximately -0.15%. The negative value indicates that slight elastic rebound mitigates a very small amount of prestress loss. Compared to the wall-floor specimen in Example 1 (loss of 16.8%), the prestress loss in the pure wall specimen in Example 2 is significantly reduced. This directly verifies that the enormous creep and environmental strain generated by the CLT floor slab under out-of-plane transverse pressure are the main factors leading to long-term prestress loss in the prestressed timber structure system. After removing the floor slab, the deformation contribution of the wall in the longitudinal direction is limited, thus greatly reducing the overall prestress loss of the system.
[0057] It should be noted that J in this case ∞It characterizes the limiting increase in flexibility that mechanical hygroscopic creep can achieve under infinite time or fully varied moisture conditions. It reflects the magnitude of the irreversible plastic flow potential of a material excited by changes in humidity. The microscopic mechanism of the difference between parallel and transverse grains is as follows: Along the grain: Wood cellulose microfibrils are arranged longitudinally along the cells, providing the main load-bearing framework. Under compression along the grain, deformation is mainly contributed by the tension / compression of the microfibrils themselves and the shear slip between the microfibrils, with elastic and viscoelastic components dominating, and permanent plastic flow induced by moisture being relatively limited. Therefore, along the grain... ∞ The value is relatively large, but the growth is slowing down; Cross-grain direction: The load primarily acts on the amorphous matrix composed of hemicellulose and lignin, and between the thin cell walls. Under cross-grain pressure, the intrusion of water molecules significantly softens the hemicellulose and lignin, and lubricates the interfaces between cell walls, leading to extensive, irreversible plastic collapse and cell wall wrinkling. Therefore, the J-axis of the cross-grain... ∞ The value is usually smaller than that for parallel grains, but it corresponds to a higher proportion of irreversible plastic components in the deformation, and is more easily "triggered" and accumulated under changes in moisture. Therefore, if a uniform J is adopted... ∞ This value will severely underestimate the irreversible deformation accumulated in the transversely strung components under long-term wet cycling, thus incorrectly predicting the prestress loss. The differentiated settings of this invention accurately characterize the essential differences in the plastic response of materials under different stress directions.
[0058] Furthermore, in this case, C is a rate-sensitive parameter, which determines the sensitivity of creep to changes in moisture content. A larger C value indicates that even small fluctuations in moisture content can more quickly drive mechanical hygroscopic creep towards its limit value (J). ∞ This means that the material responds more rapidly and drastically to changes in humidity. The response characteristics of parallel and transverse grain are as follows: In the transverse direction (e.g., floor slab C=2.40): the transverse dimensional changes of wood are extremely sensitive to moisture. The entry and exit of water molecules can rapidly alter the state of the cell wall matrix, acting as a "lubricant" to significantly reduce friction between cell walls and microfibrils. This results in a dramatic amplification of the rate and magnitude of deformation under stress. Therefore, the creep of transversely grained components exhibits a high sensitivity to humidity fluctuations; even short periods of dry or humid environments can trigger significant additional deformation. Along the grain (e.g., wall C=0.50): Deformation along the grain is more constrained by the microfiber skeleton, and the impact of moisture changes on its mechanical state is relatively slower and more profound. Its creep development depends more on long-term, stable moisture content changes, and its response to short-term humidity fluctuations is relatively slow. Therefore, under the same environmental history in the example, the floor slab (cross-grained) has a higher rate-sensitive parameter value, and its mechanical moisture-absorbing creep can accumulate a larger amount of deformation in a shorter time. This is the key dynamic reason why the prestress loss of the floor slab system (16.8%) is much higher than that of the pure wall system (9.5%). A uniform rate-sensitive parameter value will completely eliminate this crucial difference in time-varying characteristics.
[0059] Furthermore, in this case, α u It characterizes the pure environmental deformation (shrinkage and swelling) caused by a unit change in moisture content. It is the most direct macroscopic parameter representing the anisotropy of wood. The macroscopic laws governing the difference between parallel and cross-grain growth are as follows: Cross-grain direction (e.g., the desorption coefficient of floor slabs is 0.2731): The radial and tangential (collectively referred to as cross-grain) shrinkage and swelling rates of wood are extremely high. This is because moisture mainly exists in the amorphous regions of the cell walls, and its entry and exit directly lead to significant changes in cell wall thickness, which in turn cause substantial changes in the transverse dimensions of the components. Typically, the dimensional change rate of cross-grain can be 10 to 30 times or more than that of longitudinal grain.
[0060] Parallel direction (e.g., the desorption coefficient of the wall is 0.0268): Along the direction of cellulose microfibrils (parallel), the longitudinal dimension of the cell wall is constrained by the crystal structure of the microfibrils, and the rate of change is extremely small.
[0061] In addition to distinguishing directions, this case further differentiates between the hygroscopic and desorption processes. Due to the lag in water adsorption within the cell wall (desorption typically requires lower relative humidity to reach the same moisture content as hygroscopic adsorption, and at the same moisture content, the cell wall shrinkage is greater in the desorbed state), desorption > hygroscopic adsorption. Therefore, ignoring the anisotropy and path dependence of the wood's environmental strain coefficient will lead to a severe underestimation (for cross-grain components) or distortion (failing to reflect the lag effect of the wet-dry cycle). Thus, by setting differential coefficients in two dimensions (direction + path), the true physical picture of wood environmental deformation is fully reconstructed in the prestress loss assessment model.
[0062] A device for assessing the tension loss of prestressed timber structures, comprising: The parameter acquisition module is used to acquire key parameters of prestressed timber structures. The data acquisition module is used to collect the temperature and relative humidity of the service environment; The moisture content analysis module is used to calculate the equilibrium moisture content of the wood surface based on the temperature and relative humidity, and solve the one-dimensional moisture diffusion model to obtain the moisture content distribution. The strain calculation module is used to calculate elastic strain, creep strain and environmental strain based on the moisture content distribution, wherein when calculating the environmental strain, the corresponding environmental strain coefficient is selected according to the direction of moisture content change. The prestress update module is used to superimpose the strain components to obtain the total strain, update the prestressing tendon tension according to the change in the total strain, and output the time-varying curve of tension force. It also includes a temperature and humidity sensor that is communicatively connected to the data acquisition module.
[0063] A computer-readable storage medium having a computer program stored thereon that, when executed by a processor, implements a method for assessing the tension loss of a prestressed timber structure.
[0064] Principle: A refined, mechanistic multiphysics coupling analysis model is driven by long-term monitored environmental temperature and humidity data. This model first calculates the time-varying moisture content field within the wood based on moisture diffusion theory. Then, it decomposes the total deformation of the wood under the coupled effects of stress and humidity into four physically distinct strain components: elastic strain modulated by real-time moisture content, pure viscoelastic creep reflecting time hardening, mechanical hygroscopic creep coupled with the history of moisture content changes, and hysteretic environmental strain distinguishing between different paths of moisture absorption and desorption. Crucially, the model sets differentiated parameters for components with different stress directions (parallel and transverse) based on their microscopic deformation mechanisms. Finally, based on the principle of deformation coordination, these components are superimposed and coordinated to update the stress state of the prestressing tendons. This not only enables dynamic and high-precision prediction of the prestress loss curve but also quantitatively reveals the contributions of each physical mechanism and component, systematically addressing the shortcomings of existing technologies in considering wood anisotropy, environmental hysteresis effects, and multiphysics coupling.
[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.
Claims
1. A method for assessing tension loss in prestressed timber structures, characterized in that, Includes the following steps: S1. Obtain key parameters of the prestressed timber structure and collect the temperature and relative humidity of the service environment; S2. Calculate the equilibrium moisture content of the wood surface based on the temperature and relative humidity, and use a one-dimensional moisture diffusion model combined with the equilibrium moisture content as a time-varying boundary condition to solve for the moisture content distribution inside the wood component. S3. Update the elastic flexibility of the wood according to the moisture content distribution, and calculate the elastic strain of the wood component in combination with the rate of change of prestress. S4. Decompose the creep strain into a pure creep component and a mechanical moisture-absorbing creep component, and calculate them separately; S5. Based on the direction of moisture content change, select the corresponding environmental strain coefficient to calculate the environmental strain caused by drying shrinkage and wetting expansion. Wherein: if the moisture content increases, the hygroscopic environmental strain coefficient is used; if the moisture content decreases, the desorption environmental strain coefficient is used. S6. The elastic strain, creep strain and environmental strain are superimposed to obtain the total strain, and the prestressing tendon tension is updated according to the change in the total strain to form a time-varying curve of tension force.
2. The method for assessing tension loss in prestressed timber structures according to claim 1, characterized in that, In step S2, the one-dimensional water diffusion model is established based on Fick's second law, and its governing equation is: The finite difference method is used for decomposition.
3. The method for assessing tension loss in prestressed timber structures according to claim 1, characterized in that, In step S4, the formula for calculating the mechanical moisture absorption creep component is: 。 4. The method for assessing tension loss in prestressed timber structures according to claim 1, characterized in that, The key parameters include geometric parameters and material parameters: The geometric parameters include the height, width, total thickness, number of plywood layers, thickness of a single plywood layer, unbonded length of prestressing tendons, and total cross-sectional area of the wooden components. The material parameters include the initial prestress level of the prestressing tendon, the elastic modulus, the elastic modulus of the wood along and across the grain, the moisture diffusion coefficient, the surface emissivity, the pure creep parameter, the mechanical moisture-absorbing creep parameter, and the strain coefficient of the moisture-absorbing environment and the strain coefficient of the desorption environment.
5. The method for assessing tension loss in prestressed timber structures according to claim 1, characterized in that, For a prestressed wood structure that includes both parallel-grain and transverse-grain load-bearing components, different mechanical moisture-absorbing creep parameters, as well as different moisture absorption environment strain coefficients and desorption environment strain coefficients, are set for the parallel-grain and transverse-grain load-bearing components, respectively.
6. The method for assessing tension loss in prestressed timber structures according to claim 1, characterized in that, In step S3, the relationship between the elastic flexibility and the moisture content is as follows: 。 7. The method for assessing tension loss in prestressed timber structures according to claim 1, characterized in that, In step S5, the calculation of environmental strain further includes introducing a thermal expansion term, the calculation formula of which is: 。 8. A device for assessing the tension loss of prestressed timber structures, characterized in that, include: The parameter acquisition module is used to acquire key parameters of prestressed timber structures. The data acquisition module is used to collect the temperature and relative humidity of the service environment; The moisture content analysis module is used to calculate the equilibrium moisture content of the wood surface based on the temperature and relative humidity, and solve the one-dimensional moisture diffusion model to obtain the moisture content distribution. The strain calculation module is used to calculate elastic strain, creep strain and environmental strain based on the moisture content distribution, wherein when calculating the environmental strain, the corresponding environmental strain coefficient is selected according to the direction of moisture content change. The prestress update module is used to superimpose the strain components to obtain the total strain, update the prestressing tendon tension based on the change in the total strain, and output the time-varying curve of the tension force.
9. The device for assessing the tension loss of prestressed timber structures according to claim 8, characterized in that, It also includes a temperature and humidity sensor that is communicatively connected to the data acquisition module.
10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1 to 7.