A design method of a temporary support system for a post-cast strip area of a frame structure

Abstract

The present application relates to a kind of frame structure post-cast strip area temporary support system design method, especially applicable to the temporary support of main girder in the process before and after the frame structure construction site is left post-cast strip provides the reference of force.This design method is through four kinds of control methods of maximum crack equivalence, maximum deflection equivalence, fixed end bending moment equivalence, fixed end equivalence, back to solve the optimal support force required to meet target performance, to realize the quantitative design and field controllable of temporary support, guide the quantitative value and implementation of temporary support in post-cast strip area.Through the mechanical design and specification reference of theoretical level, avoid the quality risk of secondary crack, leakage and secondary redistribution of internal force caused by insufficient support or excessive jacking of temporary support component in construction site.

Description

Technical Field

[0001] This invention relates to the field of building structural support systems, specifically a design method for a temporary support system for the post-cast strip area of ​​a frame structure. Background Technology

[0002] In modern construction engineering, frame structures are widely used due to their advantages such as high load-bearing capacity and flexible spatial division. However, during the construction of large-span or long strip frame structures, in order to effectively release the structural internal forces caused by early concrete shrinkage, temperature stress, and uneven settlement, it is usually necessary to reserve post-pouring strips according to specifications. As a temporary construction joint, the post-pouring strip breaks the continuous beam-slab structure, changing the stress characteristics and stiffness distribution of the structure during the construction phase. After the main structure is completed and the shrinkage tends to stabilize, a second pour is carried out to ensure the final integrity and safety of the structure.

[0003] In the existing frame structure construction process, the temporary support scheme for the main beams in the post-cast strip area mainly relies on empirical methods. Specific technical implementations typically include using plain concrete columns to be poured simultaneously with the main beams and floor slabs as rigid supports, or erecting a steel pipe scaffolding support system under the post-cast strip and pre-tightening and lifting it using top supports.

[0004] The inventors of this application have discovered the following technical problems with the above-mentioned technology: In the implementation of existing technical solutions, the support position and tightening force are usually determined solely based on the experience of construction personnel. Due to the lack of quantitative design based on mechanical models, the force path and stiffness distribution in the post-cast strip area during the construction stage deviate from the design expectations, easily leading to inappropriate support force values. Insufficient support force can cause excessive deflection at mid-span of the main beam and trigger severe early shrinkage cracks, compromising the structure's durability. Excessive jacking of the support can alter the internal force distribution at the beam-column joint, generating a reverse additional bending moment, which can lead to secondary cracks on the beam surface, leakage, and secondary redistribution of internal forces, among other quality risks. Furthermore, because existing technology cannot accurately reverse-engineer non-mid-span post-cast strips and complex load combinations, the design of the support system lacks a scientific mechanical basis, making it difficult to achieve optimal support force configuration while ensuring that structural performance does not deteriorate. Summary of the Invention

[0005] This invention addresses the problems of altered force paths in main beams, difficulty in accurately controlling internal forces and deformations, and lack of unified mechanical basis for temporary support design during the construction phase of frame structures with post-cast strips. It proposes a design method for a temporary support system in the post-cast strip area of ​​a frame structure. By establishing a mechanical equivalence relationship between the baseline working condition without post-cast strips and the construction condition with post-cast strips, and using the non-deterioration of cracks, deflection, and end moments of the main beam during the construction phase as the control objective, it achieves quantitative back-calculation and reasonable determination of the temporary support force.

[0006] This invention takes the main beam, which is integrally cast with columns at both ends, as the research object, and simplifies its construction phase to a span of... The equivalent beam model with fixed ends is used to uniformly consider the uniformly distributed load obtained from the floor slab load. and concentrated loads transferred from secondary beams to main beams. The combined effects of these factors are considered. Under the premise of satisfying linear elasticity and small deflection constraints, a basic mechanical model suitable for different construction conditions is constructed.

[0007] In the basic mechanics model, the bending moment influence lines of fixed-end-fixed-end beams and fixed-end-hinged support beams under unit concentrated loads are established based on structural mechanics theory. This serves as a unified calculation platform for subsequent linear superposition analysis of uniformly distributed loads, concentrated loads, and temporary support forces, thereby ensuring the consistency and comparability of internal force and deformation calculations under different working conditions.

[0008] Construction of the baseline load case without post-tensioning strips:

[0009] Under the complete stress condition without post-cast strips, the calculated loads are substituted into the foundation mechanics model to calculate the bending moments at both ends of the main beam under this reference load condition. Maximum deflection within the span The corresponding maximum crack width is determined based on the selected crack calculation formula. The aforementioned bending moment, deflection, and crack indices together constitute the performance reference values ​​of the main beam under normal stress conditions, serving as a benchmark for comparison to determine whether the construction phase, including post-cast strip conditions, achieves equivalence and does not deteriorate.

[0010] Establishment of a construction stage model including post-pouring strips:

[0011] During the construction phase of the post-cast strip, the post-cast strip is placed at or near the mid-span of the main beam. This is considered as a weakening of the beam's stiffness and an interruption of the force path at that location. Temporary supports that only provide vertical reaction forces are then installed below the post-cast strip to introduce vertical support forces. As unknowns, a stress model for the construction stage including post-pouring strips is established.

[0012] Based on the influence line of bending moment and the principle of linear superposition, uniformly distributed loads... Concentrated loads and vertical support force The effects of the loads are superimposed to obtain the bending moment expression for the control section of the main beam under the supported condition. Intraspan deflection expression and the expression for beam end bending moment This provides a mechanical basis for subsequent performance equivalence control calculations.

[0013] Multidimensional performance equivalent control and support force inverse calculation:

[0014] Based on the construction stage model including post-pouring strips, this invention constructs the equivalent control relationship of temporary support force from multiple structural performance dimensions such as cracks, deflection and bending moment.

[0015] Among them, the maximum crack width under the benchmark condition without post-cast strips To control the target, the bending moment of the control section under the supported condition is... Substituting into the crack calculation formula, a functional relationship between crack width and supporting force is established. And by applying crack non-deterioration constraints The supporting force components that satisfy the crack control requirements are obtained by reverse calculation. .

[0016] Maximum in-span deflection under the benchmark condition without post-cast strip To control the performance indicators, the in-span deflection under the support condition will be included. In comparison, construct a deflection non-deterioration constraint relationship. The supporting force components that satisfy the deflection control requirements are obtained by reverse calculation. It is used to limit the deflection and additional deformation of the main beam during the construction phase.

[0017] Meanwhile, to address the issue that temporary supports near the post-cast strip may cause changes in the end bending moment at the beam-column joint, equivalent control conditions for the end-fixed moment are established by comparing the end bending moment levels under the supported condition and the baseline condition without post-cast strips. Inversely, the supporting force components that do not cause the stress on the node are obtained. .

[0018] Furthermore, considering the case where the support location can be equivalent to a fixed end under specific working conditions, based on the mechanical model of the beam with fixed ends at both ends, equivalent control conditions for the fixed-end bending moment are further constructed. Thus, the corresponding supporting force component is obtained. .

[0019] Comprehensive determination of design support force:

[0020] Under the aforementioned equivalent control conditions, the cracks were respectively satisfied. Deflection Bending moment and fixed end The supporting force components required by the stress distribution. By comprehensively comparing the various supporting force components, the supporting force with the greatest control is selected as the basic design supporting force for temporary supports, and a safety factor is introduced on this basis. Determine the final design support force for use on the construction site. .

[0021] This invention transforms the traditional support design method, which relies on empirical values ​​or single control indicators, into a systematic design process based on structural mechanics models and using equivalent constraints from multiple performance indicators for inverse mechanical analysis. This method establishes a complete stress benchmark without post-cast strips to obtain key performance indicators such as maximum crack width, maximum in-span deflection, and fixed-end moments at both ends of the main beam, which serve as control targets. Then, in the construction phase with post-cast strips, a temporary vertical support force is introduced to construct a functional relationship between the aforementioned performance indicators and the support force. This allows for the inverse calculation of a reasonable support force that ensures the structural performance does not deteriorate during construction.

[0022] This invention can simultaneously consider the combined effect of uniformly distributed loads transmitted from floor slabs and concentrated loads transmitted from secondary beams. It is applicable to complex conditions where the post-cast strip is not located in the middle of the main span. Furthermore, it can correct for construction preloading effects, concrete aging effects, and load variations during construction by introducing correction coefficients, facilitating the formation of tabular, parameterized, and process-oriented engineering design methods. By incorporating multi-dimensional performance indicators such as node negative bending moment, cracks, and deflection into a unified equivalent control system, it can effectively avoid the risks of additional cracks, leakage, and secondary redistribution of internal forces caused by insufficient temporary support or excessive jacking. This improves the controllability and safety of structural stress during the construction phase of the post-cast strip, demonstrating good engineering applicability and promising prospects for widespread application. Attached Figure Description

[0023] Figure 1 This is a simplified model diagram of the fixed-end support at the end of the main beam under the condition of no post-cast strip in an embodiment of the present invention.

[0024] Figure 2 This is a simplified model diagram of the fixed-end hinged support at the end of the main beam in the case of post-cast strip in an embodiment of the present invention;

[0025] Figure 3 This is a simplified model diagram of the cantilever end of the main beam in the case of post-cast strip in an embodiment of the present invention;

[0026] Figure 4 This is a simplified diagram of load transfer calculation for a continuous two-way slab-supported beam according to an embodiment of the present invention.

[0027] Figure 5 This is a simplified diagram of the main beam with post-cast strip under the condition of no secondary beams in an embodiment of the present invention;

[0028] Figure 6 This is a simplified diagram of the main beam with post-cast strips under the secondary beam construction condition in an embodiment of the present invention;

[0029] Figure 7 The bending moment caused by a unit load on the fixed end of the fixed-end hinged support beam in this embodiment of the invention. Influence line diagram;

[0030] Figure 8The bending moment caused by a unit load on the left end of the fixed-end beam in this embodiment of the invention. Influence line diagram;

[0031] Figure 9 The bending moment caused by a unit load on the right end of the fixed-end beam in this embodiment of the invention. The influence line diagram. Detailed Implementation

[0032] Specific embodiments of the invention will now be described in detail. Although the invention is described in conjunction with these specific embodiments, it should be understood that the invention is not intended to be limited to these specific embodiments. Rather, these embodiments are intended to cover alternative, modified, or equivalent embodiments that may be included within the spirit and scope of the invention as defined by the claims. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. The invention may be practiced without some or all of these specific details. In other instances, well-known processes have not been described in detail so as not to unnecessarily obscure the invention.

[0033] When used in conjunction with the terms "comprising," "method comprising," or similar language in this specification and appended claims, the singular forms "a," "some," and "the" include plural references unless the context clearly indicates otherwise. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0034] Example 1

[0035] A design method for a temporary support system in the post-cast strip area of ​​a frame structure is proposed. In this embodiment, the main beam with a post-cast strip in the frame structure is taken as the research object. A quantitative design method for the temporary support force in the post-cast strip area is proposed to ensure that the structural performance of the main beam does not deteriorate during the construction stage. By constructing an equivalent control relationship between the complete stress benchmark working condition without post-cast strip and the construction working condition with post-cast strip, the temporary support force that meets the control requirements of cracks, deflection and internal force can be obtained in reverse.

[0036] I. Determination of the load on the upper part of the main beam:

[0037] First, obtain the geometric dimensions, material parameters, and relevant load information of the main beams, secondary beams, and floor slabs, including permanent actions, variable actions, and additional loads that may occur during the construction phase.

[0038] Based on current structural design codes, the above loads are combined and calculated according to a quasi-permanent combination to obtain the design values ​​of the construction stage effects. :

[0039] ;

[0040] in, For the first Standard value of permanent load Calculated load effect values;

[0041] For the first Standard value of variable load The calculated load effect value is the control term in the variable load effect;

[0042] For the first A coefficient for the quasi-permanent value of a variable load;

[0043] The number of permanent loads participating in the combination;

[0044] The number of variable loads participating in the combination.

[0045] Furthermore, based on the simplified load transfer diagram of a continuous two-way slab supported beam, the floor load is converted into an equivalent load acting on the main beam, including a uniformly distributed load along the length of the main beam. and concentrated loads transferred from secondary beams to main beams. ,like Figure 4 .

[0046] The above uniformly distributed load With concentrated load This serves as the basic input condition for subsequent main beam stress analysis and back-calculation of support force.

[0047] II. Establishment of a complete stress benchmark without post-cast strips:

[0048] Without setting a post-cast strip, the main beam is regarded as a continuous bending member with fixed supports at both ends, and a complete stress reference case without a post-cast strip is established. Figure 1 ;

[0049] Under this reference working condition, calculate the uniformly distributed load respectively. With concentrated load Substituting into the basic mechanical model, the key mechanical response indicators of the main beam during the construction stage are calculated respectively:

[0050] Beams with fixed supports at both ends under uniformly distributed loads The fixed-end moment under the action is:

[0051] ;

[0052] Fixed support-hinged support beam under uniformly distributed load The fixed-end moment under the action is:

[0053] ;

[0054] When the unit concentrated load moves along the span of the main beam, the expressions for the influence lines of the fixed-end moments, based on the influence line method, are as follows:

[0055] Influence line of fixed bending moment at the left end of the fixed end beam, such as Figure 8 :

[0056] ;

[0057] Influence line of fixed bending moment at the right end of the fixed end beam, such as Figure 9 :

[0058] ;

[0059] Influence line of bending moment at the fixed end of the beam supported by hinged joint, such as Figure 7 :

[0060] ;

[0061] in, The x-coordinate is taken along the span of the beam from the fixed end of the main beam. Calculate the span of the main beam. . In order to be in The ordinate of the influence line of the bending moment at the fixed end caused by a unit downward moving load applied at the point; The bending moment caused by a unit load at the left end of the fixed-end beam; The bending moment caused by a unit load on the right end of the fixed-end beam; The bending moment caused by a unit load on the fixed end of a fixed-end hinged support beam.

[0062] By using actual concentrated loads By superimposing the above influence lines, the fixed-end bending moment effect under concentrated load is obtained.

[0063] Under the complete stress reference condition without post-tensioning strips, the following performance indicators were calculated and used as control target values ​​for the construction stage:

[0064] Maximum crack width within the main beam span ;

[0065] Maximum deflection within the main beam span ;

[0066] Fixed-end negative bending moments at both ends of the main beam .

[0067] III. Construction of the mechanical model for the post-tensioning strip construction condition:

[0068] When a post-cast strip is installed, the continuity of stress in the main beam is interrupted at the location of the post-cast strip. For example... Figure 2 Based on the different locations of the post-pouring strip and the different support conditions during the construction stage, corresponding mechanical models for construction conditions are established.

[0069] In this embodiment, a temporary vertical support is provided below the main beam at the location where the post-cast strip is disconnected, in order to provide adjustable vertical support force. and the vertical support force As an unknown variable, it is introduced into the stress analysis model of the main beam, such as Figure 5 .

[0070] Based on different performance control objectives, the main beam is analyzed using the following mechanical models under the construction condition of setting post-cast strips:

[0071] Fixed-end hinged support beam model;

[0072] Fixed-end cantilever beam model;

[0073] Fixed-end beam model.

[0074] When the secondary beam transfers concentrated loads to the main beam, its stress relationship during the construction stage is as follows: Figure 6 As shown.

[0075] By changing the value of the vertical support force, a functional relationship between the key mechanical response indicators of the main beam and the support force was established.

[0076] IV. Equivalent control of maximum crack width and inverse calculation of support force:

[0077] In the crack control step, based on the complete stress benchmark condition without post-cast strips, the maximum crack width during the main beam construction stage was calculated. Calculate according to the following formula:

[0078] ;

[0079] In the formula, The maximum crack width; The stress characteristic coefficient of the component is 1.9, which is taken as 1.9 for bending components; The coefficient of non-uniformity of strain (or stress) in the longitudinal tensile reinforcement between cracks; The stress in the reinforcing steel at the crack section; Elastic modulus of steel reinforcement; The longitudinal tensile reinforcement ratio is calculated based on the effective tensile concrete cross-sectional area.

[0080] Under the construction condition of setting post-cast strips, the main beam is analyzed as a fixed-end hinged support beam model, and vertical support force is introduced at the break point of the post-cast strip. Based on the influence line of the fixed-end bending moment, the relationship between the bending moment of the control section and the support force is established, and the maximum crack width under the construction condition is calculated. .

[0081] By applying the following equivalent control conditions:

[0082] Inverse calculations are used to obtain the minimum vertical support force required to prevent crack deterioration. .

[0083] V. Equivalent control of maximum deflection and inverse calculation of support force:

[0084] In the deflection control step, the maximum deflection within the main beam span is calculated based on the complete stress benchmark condition without post-cast strips. As a deflection control target.

[0085] The deflection of the main beam is calculated according to the following formula:

[0086] ;

[0087] ;

[0088] ;

[0089] ;

[0090] ;

[0091] in, For the stiffness of the bending member; For short-term stiffness; The ratio of the elastic modulus of steel reinforcement to that of concrete. ; This refers to the reinforcement ratio of longitudinal tensile reinforcement; This refers to the reinforcement ratio of the longitudinal compression steel bars; It is the ratio of the cross-sectional area of ​​the compression flange to the effective cross-sectional area of ​​the web; This refers to the width of the flange in the pressure zone; This refers to the flange height in the pressure zone. This is the deflection amplification factor; The deflection coefficient is related to the load type and support conditions; The calculated span of the beam; This represents the deflection limit of the beam.

[0092] In construction conditions where post-cast strips are installed, vertical support is introduced at the disconnection point. Calculate the maximum deflection of the main beam under different support force conditions. .

[0093] By applying the following equivalent control conditions:

[0094] The vertical support force that satisfies the deflection control requirements can be obtained by reverse calculation. .

[0095] VI. Equivalent control of fixed-end moment and inverse calculation of support force:

[0096] In the bending moment control step, based on the complete stress reference case without post-cast strips, the fixed-end negative bending moment at the main beam support is determined. As a target for bending moment control.

[0097] like Figure 3 Under the construction condition of setting post-cast strips, the main beam is analyzed as a fixed-end cantilever beam model, and the fixed-end bending moment under cantilever conditions is calculated. .

[0098] By constructing the following equivalent control relationship:

[0099] M′+ =M;

[0100] Inverse calculations are performed to obtain the vertical support force that satisfies the requirement of avoiding stress deterioration at the beam-column joint. .

[0101] VII. Equivalent Control and Inverse Calculation of Support Force at Fixed End

[0102] In the fixed-end equivalent control step, based on the complete stress reference case without post-cast strips, the fixed-end bending moments under the condition of fixed supports at both ends of the main beam are determined. As an equivalent target.

[0103] Under the construction condition of setting post-cast strips and introducing vertical support forces, the main beam is analyzed as a fixed-end-fixed-end support beam model, and the fixed-end bending moment under the corresponding support force conditions is calculated. .

[0104] By constructing the following equivalent control relationship:

[0105] ;

[0106] The vertical support force that satisfies the requirement of no deterioration of fixed-end moment can be obtained by reverse calculation. .

[0107] VIII. Comprehensive Determination and Engineering Application of Supporting Force:

[0108] In engineering applications, the support forces obtained meet the requirements for crack control, deflection control, bending moment control, and equivalent control at the fixed end, respectively. , , and .

[0109] Taking into account the structural safety and performance control requirements during the construction phase, the control value among the above-mentioned support forces is selected as the design support force for the temporary support in the post-pouring strip area.

[0110] In addition, the design support force can be corrected by introducing corresponding correction coefficients based on the preloading effect, concrete aging effect, or load changes during the construction stage, so as to improve the consistency between the calculation results and the actual construction conditions.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation methods of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A design method for a temporary support system in the post-cast strip area of ​​a frame structure, characterized in that, Includes the following steps: Establish a basic mechanical model: taking an equivalent beam with fixed ends as the research object, and uniformly distributed loads on the floor slab are considered uniformly. Concentrated loads on secondary beams Based on the combined effects of linear elasticity and small deflection, the moment influence lines under different support conditions are derived. Constructing a baseline load case without post-cast strips: Calculating the baseline maximum crack width of the main beam under complete stress conditions. Maximum deflection within the span and the fixed-end moments at both ends , which serves as the target control value to prevent performance degradation during the construction phase; Construct a construction stage model including the post-pouring strip: Establish a stress-disconnected model at the post-pouring strip location and introduce vertical temporary support forces. As unknowns, a functional relationship is established between the supporting force, bending moment, deflection, and end bending moment based on the principle of influence line superposition, to obtain the bending moment of the control section under the supporting condition. Deflection and end moment The expression; Multi-dimensional equivalent control calculation: Using the crack, deflection, and end moment indices corresponding to the baseline condition without post-cast strips as constraints, constraint equations between performance indices and support forces are constructed through equivalent control of maximum cracks, maximum deflection, fixed-end moment, and fixed end moment, respectively. These equations are then solved in reverse to obtain the support force components that meet the requirements for non-deterioration of various performance characteristics. , , and ; Comprehensive determination of design support force: The components of the support force are compared and selected as the basic design support force, and a safety factor is introduced. The final design support force was calculated. .

2. The design method for a temporary support system in the post-cast strip area of ​​a frame structure according to claim 1, characterized in that, In the fundamental mechanical model, linear elasticity and small deflection theory are used to derive the influence lines of fixed-end bending moments under a unit concentrated load for fixed-end beams and fixed-end beams with hinged supports, respectively, serving as a calculation platform for the superposition of internal forces and deformations.

3. The design method for a temporary support system in the post-cast strip area of ​​a frame structure according to claim 1, characterized in that, The equivalent control of the maximum crack includes: Bending moment of control section under supported working conditions Substituting into the crack calculation formula, a functional relationship between the maximum crack width and the supporting force is constructed. ; Maximum crack width under the benchmark condition without post-cast strip As an upper limit constraint, apply Inversely, the supporting force that satisfies the equivalent crack performance can be obtained. .

4. The design method for a temporary support system in the post-cast strip area of ​​a frame structure according to claim 1, characterized in that, The equivalent control of maximum deflection includes: The expression for in-span deflection under supported conditions Compared with the reference deflection By making comparisons, a constraint relationship is established between deflection and support force. Build Given the deflection non-deterioration constraint condition, the support force that satisfies the deflection control requirement is obtained. .

5. The design method for a temporary support system in the post-cast strip area of ​​a frame structure according to claim 1, characterized in that, The equivalent control of the fixed-end moment is achieved through the following methods: The expression for the end moment under the support condition End bending moment under reference working condition Compare; form The control formula is used to inversely calculate the support force that will not cause the stress on the node to deteriorate. .

6. The design method for a temporary support system in the post-cast strip area of ​​a frame structure according to claim 1, characterized in that, The fixed-end equivalent control includes: Calculate the fixed-end moment under the supported condition based on the mechanical model with both ends fixed. ; form The equivalent control formula is used to inversely calculate the supporting force. .

7. The design method for a temporary support system in the post-cast strip area of ​​a frame structure according to claim 1, characterized in that, The final calculation formula for the design support force is: ； in, For safety, the value is set to 1.

2.

8. The design method for a temporary support system in the post-cast strip area of ​​a frame structure according to claim 1, characterized in that, The method further includes: calculating the uniformly distributed load transmitted from the slab to the main beam based on the simplified load transfer diagram of the continuous two-way slab-supported beam. Concentrated loads transmitted from secondary beams to main beams .

9. The design method for a temporary support system in the post-cast strip area of ​​a frame structure according to claim 1, characterized in that, The method, when determining the design support force, corrects for the construction preloading effect, concrete aging effect, or load changes during the construction stage by introducing a correction coefficient.

10. The design method of a temporary support system for the post-cast strip area of ​​a frame structure according to any one of claims 1-9, which provides mechanical reference for the temporary support of the main beam during the process of leaving the post-cast strip at the construction site of a building project.

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