Performance-based aseismic design method for steel frame-wood support mixed structure

Abstract

The invention relates to the technical field of building earthquake resistance, and discloses a performance-based earthquake resistance design method for a steel frame-wood support mixed structure, which comprises the following steps: acquiring building basic information; a double-level-double-index performance target system is established, double levels comprise rare earthquake performance limit and frequent earthquake normal use, and double indexes comprise interlayer displacement angles of the overall structure of the building and strain of local components; determining structural performance constraints according to related laws and regulations, and selecting structural performance targets according to building requirements; establishing an initial structure model, and carrying out preliminary design and verification on the initial structure model to enable the initial structure model to meet structural performance constraints, so as to obtain a target structure reference model; establishing a mixed structure model based on the target structure reference model, and performing performance optimization on the mixed structure model until a structure performance target is met, so as to obtain a required complete structure model; the method has the advantages of being complete and reliable in design, clear and specific in performance target and sufficient in target quantification.

Description

Technical Field

[0001] This invention relates to a performance-based seismic design method for steel-frame-timber hybrid structures, belonging to the technical field of building seismic resistance. Background Technology

[0002] The destructive power of earthquakes lies not only in the instantaneous collapse of structures, but also in the residual deformation and plastic damage they cause, leading to functional degradation and even obsolescence of building structures. Therefore, studying the seismic performance of structures and developing scientific seismic design theories and methods are of great significance for improving the seismic resistance of buildings and mitigating the consequences of disasters. Structural seismic design methods have evolved from static methods based on bearing capacity to dynamic analysis methods considering ductility and energy dissipation. In recent years, Performance-Based Seismic Design (PBSD) has become a hot topic in international structural seismic research due to its better reflection of structural response capabilities under different seismic damage levels, and is gradually being incorporated into relevant design codes in my country.

[0003] Currently, among novel composite structural systems, steel-wood hybrid structures have attracted significant attention due to their high degree of prefabrication, superior seismic performance, and environmental friendliness. Existing research largely focuses on steel-frame-wood shear wall systems, but compared to these, steel-frame-wood bracing systems exhibit more significant advantages and broader application potential in terms of building layout flexibility, structural lightweighting, and post-earthquake repairability. However, systematic research and development of design methods for this advantageous system remain significantly insufficient.

[0004] Existing performance-based seismic design methods are primarily geared towards traditional building systems such as steel and concrete structures, and have established relatively fixed design processes and evaluation systems. However, when these mature methods are directly applied to emerging steel-wood hybrid structures, their fundamental limitations become apparent. Current theories have not established a systematic design framework that effectively integrates the high ductility of steel with the energy-dissipating properties of wood. Traditional design processes adhere to the model of "first elasticity under small earthquakes, then verification under large earthquakes," a process completely conflicting with the collaborative working mechanism of this new type of structure: it cannot utilize the unique advantages of the steel frame providing foundation toughness and the wood supports as adjustable energy-dissipating modules. Designers, in their pursuit of meeting the excessive requirement of no cracking under small earthquakes, fall into an ineffective cycle of repeatedly reinforcing components. This not only stifles the energy-dissipating potential of the wood supports but also makes it difficult to achieve a balance between economy and safety in the final design, thus preventing the full realization of the mechanical advantages of this new composite structure.

[0005] To address this, Chinese patent application CN202410969810.1 discloses a method and system for testing the seismic performance of prefabricated steel-wood composite structures. The method includes: generating simulated steel-wood composite samples using a connection structure simulation system, including samples with different composite structures and varying wood structure proportions; conducting vibration detection to obtain a vibration detection dataset; extracting vibration absorption indices for the wood structure; establishing a mapping relationship between the composite structure, the wood structure proportion, and the vibration absorption indices; training a prediction model; acquiring information about the structure to be tested; inputting the data into the model to predict the vibration absorption indices; and outputting a seismic performance report. This method can accurately assess the seismic performance of prefabricated steel-wood composite structures with different steel-wood composite ratios. When applied to performance-based seismic design methods, by training the model using structural simulation and vibration detection data, it enables automatic detection and prediction of seismic performance, thereby helping to fully leverage the mechanical advantages of steel-wood composite structures and improving the accuracy of seismic testing.

[0006] However, the above solution has the following problems in actual use: 1. It lacks in-depth guidance on the structural design process and does not take into account the impact of factors such as site type, seismic fortification category and functional importance level on the seismic performance of the structure, resulting in insufficient design depth.

[0007] 2. It only evaluates seismic performance through vibration absorption index, without clearly defining the specific performance requirements under different seismic levels, resulting in problems of vague performance targets and insufficient quantification. Summary of the Invention

[0008] To address the aforementioned problems in existing technologies, this invention provides a performance-based seismic design method for steel-frame-timber hybrid structures.

[0009] The technical solution of the present invention is as follows: A performance-based seismic design method for steel-frame-timber hybrid structures, which can be implemented using finite element analysis software (such as ABAQUS), includes the following steps: Step 1: Obtain basic building information, specifically the structural geometric parameters of the target building (such as floor height, number of floors, structural type, etc.), site type, seismic fortification category, and functional importance level.

[0010] The second step involves applying performance-based design to propose a dual-level, dual-index framework. This simplifies the traditional fortification target into two key levels: the "normal use" state for dealing with frequent earthquakes and the "performance limit" state for dealing with rare earthquakes. It also establishes a dual-level, dual-index performance target system that assesses the overall structural response by inter-story drift angle and assesses local component damage by component strain.

[0011] Step 3: Based on the information obtained in Step 1 and relevant regulatory requirements, determine structural performance constraints. Select structural performance targets according to the actual needs of the building. These constraints represent the minimum ultimate seismic performance under rare earthquakes. Specifically, this includes the minimum required overall structural performance index based on inter-story drift angle and the minimum required component damage index based on material strain under rare earthquake intensity. The structural performance targets must be comprehensively higher than or equal to the structural performance objectives, representing customized seismic performance under rare earthquakes and normal seismic performance under frequent earthquakes. Specifically, this includes overall structural performance indicators based on inter-story drift angle that meet building requirements and component damage indicators based on material strain that meet building requirements under rare earthquake intensity, and overall structural performance indicators based on inter-story drift angle that meet normal use requirements and component damage indicators based on material strain that meet normal use requirements under frequent earthquake intensity. It should be noted that the intensity of a rare earthquake is greater than that of a frequent earthquake.

[0012] Step 4: Conduct preliminary design and verification of the steel frame benchmark based on rare earthquakes. This includes establishing an initial structural model containing only the first type of components, which are steel frame components. Therefore, the initial structural model is a finite element model of the initial steel frame containing only the main steel beams and columns. Elastoplastic time history analysis is then performed on this model to evaluate its true elastoplastic response. Based on the analysis results, the structural layout or component sections are iteratively adjusted until a benchmark steel frame is designed, and this benchmark steel frame is verified to meet the first target performance. This yields the target structural benchmark model, which only possesses basic collapse resistance under rare earthquakes.

[0013] Step 5: Based on the target structural model obtained in Step 4, optimize and fully verify the second type of components, which are timber-supported components. By adding the second type of components to the target structural model to establish a hybrid structural model, and then optimizing the performance of the hybrid structural model to achieve the structural performance target determined in Step 3, a complete finite element model of the steel frame-timber-supported structure is obtained, i.e., the complete structural model. The method for optimizing the performance of the hybrid structural model is as follows: simultaneously perform elastoplastic time history analysis under rare earthquakes and elastic response spectrum analysis under frequent earthquakes on the hybrid structural model. Based on these results, optimize the performance by adjusting at least one of the following: the arrangement, quantity, and cross-sectional dimensions of the second type of components, until all performance indicators of the hybrid model fully meet the structural performance target.

[0014] The present invention has the following beneficial effects: 1. This invention adopts a "major earthquake first, minor earthquake later" design logic, that is, it first considers rare earthquakes and then considers frequent earthquakes. Through two-stage setting of structural performance constraints and structural performance targets, it first establishes a target structural model of the first type of component (i.e., steel frame component) structure under rare earthquakes, which only has the basic collapse resistance capacity (i.e. meets the minimum ultimate seismic performance of rare earthquakes). Then, by adding adjustable second type of component (i.e., wooden support component) into the target structural model, the structural performance constraints are raised to the structural performance targets required by the project. Compared with the traditional roundabout verification process of "minor earthquake first, major earthquake later", this invention has a clear logic and a direct path, which can fundamentally avoid the ineffective cycle of over-design to meet the requirements of minor earthquakes, and has the advantage of greatly improving design efficiency.

[0015] 2. This invention considers various basic information about the building and establishes a dual-level, dual-index performance target system that evaluates the overall structural response by inter-story drift angle and assesses local component damage by component strain. This provides an accurate quantitative scale for the damage state of the structure in the model. At the same time, this target system, through the level settings of performance limits in rare earthquakes and normal use in frequent earthquakes, can perfectly correspond to the collaborative working mechanism of "steel frame to maintain the whole and wood support to control damage" in steel-wood hybrid structures, making the design evaluation more scientific and reliable. Compared with the existing technology, it has the advantages of complete and reliable design, clear and specific performance targets, and sufficient quantitative targets.

[0016] 3. This invention positions the first type of component (i.e., steel structure component) as a frame to ensure the structure does not collapse (i.e., to meet the minimum seismic resistance performance required for rare earthquakes), and positions the timber support as a regulator to improve performance and dissipate energy (i.e., to improve the hybrid structure model so that it can meet the structural performance objectives). This allows for a clear division of labor between the first and second types of components. This clear functional division enables designers to use the more cost-effective timber support to meet diverse performance objectives without unnecessary reinforcement of the expensive main steel frame. Thus, while ensuring high safety, it achieves the optimization of construction costs. Compared with existing technologies, it has the advantage of achieving a high degree of unity between structural safety and economy. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the process of the present invention; Figure 2 This is a schematic diagram (mm) of the steel frame according to an embodiment of the present invention; Figure 3 This invention provides the moment-strain curves and damage level definitions for steel components in this embodiment. Figure 4 This is the inter-story drift angle curve of the steel frame under the initial design scheme in the embodiments of the present invention; Figure 5This is the inter-story drift angle curve of the steel frame after dimensional adjustment under a rare earthquake in an embodiment of the present invention; Figure 6 This is a PEEQ diagram of the steel frame after adjusting the cross-sectional dimensions in an embodiment of the present invention; Figure 7 This is the inter-story drift angle curve of the structure under frequent earthquakes in this embodiment of the invention; Figure 8 This invention provides the stress-strain curves and damage levels of wooden components under compressive stress in embodiments of the invention. Figure 9 This is the inter-story drift angle curve of the structure under a rare earthquake in an embodiment of the present invention; Figure 10 This is a structural stress cloud diagram under a rare earthquake in an embodiment of the present invention; Figure 11 This is the inter-story drift angle curve of the structure under frequent earthquakes in this embodiment of the invention; Figure 12 This is a structural stress cloud diagram under frequent earthquakes in an embodiment of the present invention. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0019] Example: Traditional performance-based seismic design processes suffer from limitations when applied to novel systems such as steel-wood hybrid structures, including rigid processes, low efficiency, and difficulty in synergistically leveraging the advantages of different materials. Therefore, this embodiment provides a scientific, systematic, and quantifiable performance-based seismic design method for steel-wood hybrid braced structures. The aim is to accurately achieve multi-level seismic performance targets through an innovative process of "major earthquakes first, then minor earthquakes," providing solid technical support for the application of this type of novel structure.

[0020] Please refer to Figure 2 This embodiment employs a performance-based seismic design method for a steel-frame-timber hybrid structure, comprising the following steps: The first step involves obtaining basic building information, including structural design parameters, site type, seismic fortification category, and functional importance level. In this example, the target building is a 20-story steel-framed office building with a floor height of 4m and a column spacing of 6m. Based on the engineering geological survey report and building codes, its seismic design parameters are determined as follows: fortification intensity of 8 degrees (design basic seismic acceleration of 0.30g), site category II, design seismic group I, and site characteristic period of 0.35s.

[0021] Based on steps two and three, the improved performance-based design theory of this invention is applied to establish a concise dual-level performance target and a quantifiable dual-index evaluation system for this embodiment, ensuring the relevance and rationality of subsequent design. Level one corresponds to frequent earthquakes, and level two corresponds to rare earthquakes. To meet different building functions and personalized needs, the performance levels are specifically designed into four optional categories: A, B, C, and D, with each category assigned clear quantitative indicators and performance descriptions, as shown in Tables 1 and 2. According to the building requirements, the structural performance target of this embodiment must reach "Performance Target D".

[0022] Table 1 Performance Targets for Steel-Timber Hybrid Frame-Bracket Structures

[0023] Table 2 Classification and Quantification of Levels

[0024] Following step four, a trial design of the pure steel frame under rare earthquake loading is conducted based on the design information from step one. The local performance objective at this stage is "collapse prevention" (i.e., the structural performance constraint in step three). Based on the "strong column, weak beam" principle, moderate damage is allowed for the frame beams, while only minor damage is allowed for the frame columns. The preliminary beam and column sections are shown in Table 3, and the material is Q235B H-beams. The strain-based evaluation criteria for the steel components are shown in Table 4.

[0025] Table 3 Initial Structural Design Scheme

[0026] Table 4. Strain-based evaluation criteria for steel components

[0027] The performance of this design scheme under three types of seismic waves was calculated using ABAQUS finite element analysis software, and the results are as follows: Figure 4 As shown in Table 5, the analysis results indicate that the maximum inter-story drift angle of the structure reaches 0.021 rad, exceeding the "collapse prevention" performance level limit.

[0028] Table 5 Performance evaluation of components under rare earthquake loading (for components with maximum cumulative plastic strain)

[0029] Based on the above analysis results, a systematic optimization was carried out on the weak points of the structure. The cross-sectional dimensions of the original beams and columns were optimized and adjusted, and the specific adjustment scheme is shown in Table 6. The performance of the structure was calculated again, and its maximum inter-story drift angle was significantly reduced to approximately 0.0186 rad, meeting the performance target requirement of "preventing collapse". Meanwhile, under rare earthquake loading, the frame beams and frame columns experienced minor and moderate damage respectively, both meeting the preset performance requirements. Figure 5 , Figure 6 As shown.

[0030] Table 6 Adjusted Structural Design Scheme

[0031] The structural performance objective of this embodiment requires that the structure not collapse under rare earthquakes and remain functionally intact under frequent earthquakes. Therefore, specific inter-story drift angle limits and component strain limits need to be set for "functional integrity".

[0032] Based on step five, and having already met the requirement of "not collapsing under major earthquakes," performance optimization and verification under frequent earthquakes are performed using timber supports. The ABAQUS finite element analysis software is used to calculate the steel frame structure under frequent earthquake loads. Figure 7 As shown, the maximum inter-story drift angle under this condition is 0.004 rad, slightly exceeding the limit of 0.00333 rad corresponding to the "functionally sound" performance level. Deformation control failed to fully meet the expected performance requirements. Timber supports are needed to improve the lateral stiffness of the structure. The strain-based evaluation criteria for timber components are as follows: Figure 8 As shown in Table 7.

[0033] Table 7 Performance Evaluation Criteria for Timber Components

[0034] In this embodiment, 100mm × 100mm herringbone timber supports are symmetrically arranged at the mid-span of the steel frame. The optimized steel-timber hybrid structure undergoes rare earthquake time history analysis and frequent earthquake response spectrum analysis to verify whether it simultaneously meets the two requirements of "performance objective D". The analysis results are shown below. Figures 9-12 .

[0035] During the calculation process of structural analysis software, the calculation results can identify potential weak points in the building structure. For example, if some components have strain exceeding the limit, the cross-section needs to be strengthened or the arrangement changed, and the design needs to be optimized and adjusted. After adjustment, the verification analysis is performed again. This process is repeated until the structure fully meets the final seismic performance design requirements.

[0036] As can be seen from the above design and implementation process, the present invention can effectively realize the seismic performance design of steel frame-wood braced hybrid structures, improve the safety and stability of buildings in earthquakes, and reduce project costs.

[0037] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A performance-based seismic design method for steel-frame-timber-braced hybrid structures, characterized in that: Includes the following steps: Obtain basic building information; Establish a dual-level, dual-index performance target system. The dual levels include the performance limit for rare earthquakes and normal use during frequent earthquakes. The dual indices include the inter-story drift angle of the overall building structure and the strain of local components. Structural performance constraints are determined according to relevant regulations, and structural performance targets are selected based on building requirements. An initial structural model composed of the first type of components is established. This initial structural model is then preliminarily designed and verified to meet the structural performance constraints, thereby obtaining the target structural reference model. A second type of component is added to the target structural baseline model to establish a hybrid structural model. The performance of the hybrid structural model is optimized until the structural performance target is met, thereby obtaining the required complete structural model.

2. The performance-based seismic design method for steel-frame-timber-supported hybrid structures according to claim 1, characterized in that: The acquisition of basic building information includes obtaining the target building's geometric parameters, site type, seismic fortification category, and functional importance level.

3. The performance-based seismic design method for steel-frame-timber-braced hybrid structures according to claim 1, characterized in that: The first type of component is a steel frame component, and the second type of component is a wooden support component.

4. The performance-based seismic design method for steel-frame-timber-braced hybrid structures according to claim 1, characterized in that: The structural performance constraints are the minimum ultimate seismic performance under rare earthquakes as stipulated by relevant regulations, and the structural performance objectives are the customized seismic performance required by the building under rare earthquakes and the normal seismic performance under frequent earthquakes.

5. The performance-based seismic design method for steel-frame-timber-braced hybrid structures according to claim 4, characterized in that: The minimum ultimate seismic performance under rare earthquakes includes the minimum required overall structural performance index based on inter-story drift angle and the minimum required component damage index based on material strain under rare earthquake intensity. The customized seismic performance of buildings under rare earthquakes and the normal seismic performance under frequent earthquakes include the overall structural performance index based on inter-story drift angle that meets building requirements and the component damage index based on material strain that meets building requirements under rare earthquake intensity, as well as the overall structural performance index based on inter-story drift angle that meets normal use and the component damage index based on material strain that meets normal use under frequent earthquake intensity.

6. The performance-based seismic design method for steel-frame-timber-braced hybrid structures according to claim 1, characterized in that: The preliminary design and verification of the initial structural model includes the following steps: performing elastoplastic time history analysis on the initial structural model under rare earthquakes to evaluate its true elastoplastic response, and designing and verifying based on the analysis results.

7. The performance-based seismic design method for steel-frame-timber-braced hybrid structures according to claim 1, characterized in that: The performance optimization of the hybrid structure model includes the following steps: simultaneously performing elastoplastic time history analysis under rare earthquakes and elastic response spectrum analysis under frequent earthquakes on the hybrid structure model, and optimizing the performance based on the results.

8. The performance-based seismic design method for a steel-frame-timber-braced hybrid structure according to claim 7, characterized in that: The performance optimization of the hybrid structure model also includes the following steps: adjusting at least one of the arrangement, quantity, and cross-sectional dimensions of the second type of components.

9. The performance-based seismic design method for steel-frame-timber-braced hybrid structures according to claim 1, characterized in that: The design method described can be implemented using finite element analysis software.

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