Construction control method for post-tensioned prestressed beam-slab upper camber

Abstract

The application discloses a post-tensioned prestressed beam slab camber construction control method, comprising the following steps: S1: selecting the first piece or the first batch of the beam slab to be post-tensioned prestressed to carry out a prestressed steel beam tension test, and calculating the camber adjustment coefficient D of the beam slab according to the test data; S2: calculating the concrete standard strength Q of the beam slab under the prestressed steel beam tension based on the camber adjustment coefficient D of the beam slab; and S3: adjusting the measured concrete strength of the beam slab during the prestressed steel beam tension according to the difference between the designed camber of the beam slab and the measured camber within 48 hours after the prestressed steel beam tension is completed, so that the camber of the post-tensioned prestressed beam slab reaches the standard. The application has the advantages that the camber of the beam slab can be effectively controlled, and the application is a technical guarantee measure for preventing and eliminating potential major quality and safety hidden dangers of bridge structures and components.

Description

Technical Field

[0001] This invention belongs to the field of bridge construction technology, specifically relating to a method for controlling the camber of a post-tensioned prestressed beam slab during construction. Background Technology

[0002] After the steel tendons of a prestressed concrete beam / slab are tensioned, the beam / slab structure remains under constant tension (design standard). Therefore, the camber of the prestressed concrete beam / slab after tensioning is also in a relatively fixed stress state, and it is essentially impossible to change the camber value through targeted rectification methods and technical measures (this may be one of the reasons why quantitative standards for construction technical specifications have not yet been established). Beams / slabs with substandard camber must be scrapped, causing irreparable and significant economic losses to the project.

[0003] During the storage period of the prestressed concrete beam during the continuous hydration heat process of the concrete, the camber of the prestressed concrete beam slab changes due to the effects of concrete creep and shrinkage. The camber data also undergoes slight changes, and the data changes will affect the pass rate of the camber of the prestressed concrete beam slab.

[0004] Because the factors affecting the camber of post-tensioned prestressed concrete beams and slabs are numerous and complex, even slight negligence or oversight in the control of details during construction can significantly reduce the camber compliance rate, potentially leading to major quality and safety hazards. The camber of the beams and slabs also severely impacts the quality (inconsistent thickness and exceeding tolerances) and service life of the bridge deck pavement.

[0005] Therefore, using a scientific and reasonable method for setting the pre-camber (lower camber) of the abutment is an important technical guarantee measure to effectively improve the camber compliance rate of concrete beams and slabs; improve the quality (thickness) and service life of bridge deck pavement; and improve the strength, stiffness, durability, safety and service life of bridge structures and components. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the prior art by providing a method for controlling the camber of post-tensioned prestressed beams during construction. This method calculates the camber adjustment coefficient D and the standard concrete strength Q, and adjusts the measured concrete strength of the beam during prestressing by considering the difference between the designed camber of the beam and the measured camber within 48 hours after the prestressing tendons are tensioned, thereby ensuring that the camber of the post-tensioned prestressed beam meets the standard.

[0007] The objective of this invention is achieved through the following technical solutions:

[0008] A method for controlling the camber of a post-tensioned prestressed beam slab during construction, characterized by the following steps:

[0009] S1: Select the first piece or the first batch of beams and slabs to be post-tensioned for prestressing and conduct prestressed steel strand tensioning tests. Calculate the camber adjustment coefficient D of the beams and slabs based on the test data.

[0010] S2: Based on the camber adjustment coefficient D of the beam slab, calculate the standard concrete strength Q of the beam slab under prestressed steel strand tension;

[0011] S3: Based on the difference between the designed camber of the beam and the measured camber within 48 hours after the prestressing tendons are tensioned, adjust the measured concrete strength of the beam during prestressing tendon tensioning so that the camber of the post-tensioned beam meets the standard.

[0012] The formula for calculating the camber adjustment coefficient is as follows:

[0013] D=(K n-1 ―k n ) / (S n-1 -S n );

[0014] In the formula:

[0015] D is the camber adjustment coefficient, with units of MPa / mm;

[0016] K represents the measured concrete strength of the beam when prestressed steel strands are tensioned, in MPa.

[0017] S represents the measured camber of the beam slab within 48 hours after the prestressed steel strand tensioning is completed, in mm.

[0018] n represents the number of tensioning cycles for the beam / slab, increasing from small to large.

[0019] The formula for calculating the standard strength Q of the concrete in the beam under prestressed steel strand tension is as follows:

[0020] Q = K + [(Sa - S) × D];

[0021] In the formula:

[0022] K represents the measured concrete strength of the beam when prestressed steel strands are tensioned, in MPa.

[0023] Sa is the design camber of the beam / slab, in mm;

[0024] S represents the measured camber of the beam slab within 48 hours after the prestressed steel strand tensioning is completed, in mm.

[0025] D is the adjustment coefficient for the upward camber.

[0026] The formula for calculating the measured camber S of the beam slab within 48 hours after the prestressed steel strand tensioning is as follows:

[0027] S = CA;

[0028] In the formula:

[0029] C is the vertical distance between the center point of the bottom arc surface of the beam and the center point of the arc surface of the platform;

[0030] A is the pre-camber setting value of the platform.

[0031] When Sa-S is negative, the concrete strength of the beam slab under prestressed steel tendon tension is reduced to ensure that the camber of the beam slab meets the standard; when Sa-S is positive, the concrete strength of the beam slab under prestressed steel tendon tension is increased to ensure that the camber of the beam slab meets the standard.

[0032] The advantages of this invention are: it enables effective control of the camber on the beam slab, and is a technical guarantee measure to prevent and eliminate potential major quality and safety hazards in bridge structures and components. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the beam plate being mounted on the pedestal in this invention;

[0034] Figure 2 For the present invention Figure 1 The large-scale drawing at point I in the image. Detailed Implementation

[0035] The features and other related features of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments, so as to facilitate understanding by those skilled in the art:

[0036] like Figure 1-2 The markings in the diagram are as follows:

[0037] Beam plate 1, pedestal 2;

[0038] A is the pre-camber setting value for platform 2;

[0039] S represents the measured camber of the beam slab 1 within 48 hours after the prestressed steel strand tensioning is completed.

[0040] Example: Figure 1 , 2 As shown, this embodiment specifically relates to a construction control method for the camber of a post-tensioned prestressed beam slab, which includes the following steps:

[0041] (S1) Select the first or first batch of beams and slabs to be post-tensioned for prestressing to conduct prestressing tendon tensioning tests. Concrete strength is a key factor affecting the camber of prestressed concrete beams and slabs. When post-tensioning prestressed concrete beams and slabs 1, concrete strength and camber are a pair of closely related and mutually restrictive key data. By measuring, collecting, summarizing, and calculating the concrete strength and camber data of the first (batch) post-tensioned concrete beams and slabs 1, strong data support is provided for the control of camber in subsequent batch construction of post-tensioned concrete beams and slabs 1 of the same specifications, ensuring that the camber meets the design technical requirements to the greatest extent.

[0042] Please fill in the summary table of measurement data for the first piece (batch) of beams and slabs in a timely, accurate and truthful manner, as shown in the table below:

[0043]

[0044] Note: The camber of the C50, 25m post-tensioned prestressed concrete T-beam slab in the design and construction drawings is 11.7mm.

[0045] The definitions of each measured data in the table above are as follows:

[0046] Strength K: The concrete strength of beam slab 1 during prestressed steel strand tensioning. Its index value must meet the requirements of 7.8.5.2 of the "Technical Specification for Construction of Highway Bridges and Culverts" JTG / 3650-2020. If there are relevant design requirements, those requirements shall be followed. Strength K should be accurately measured and recorded point by point for the first beam slab 1 of the same specification, model, and design mix ratio during prestressed steel strand tensioning, from the lowest concrete strength point to the highest value point.

[0047] Upper arch S: The vertical distance between the upper and lower arch points, that is, the distance (vertical distance) between the center point of the platform arc surface and the center point of the bottom arc surface of the beam slab.

[0048] Within 48 hours after the prestressed steel strands are tensioned, the upper arch value should be accurately measured using a feeler gauge or vernier caliper (accuracy of 1%), and the value should be filled in corresponding to the strength K node at the time of tensioning, for example, K1 and S1, K2 and S2, etc.

[0049] The purpose of measuring, calculating, and summarizing concrete strength and camber data is to provide timely, accurate, and reliable data foundation and support for calculating the camber adjustment coefficient D of post-tensioned prestressed concrete beams and slabs and the standard data for concrete strength during prestressing of the prestressed steel strands in the beams and slabs. The measurement data of concrete strength and camber for the first piece (batch) of beams and slabs should be determined according to the batch number of beams and slabs of that specification and model. The larger the amount of measurement data, the more effectively the camber compliance rate of the concrete beams and slabs can be improved.

[0050] The camber adjustment coefficient D of beam 1 is calculated based on the measured test data. The calculation formula is as follows:

[0051] D=(K n-1 ―k n ) / (S n-1 -S n );

[0052] In the formula:

[0053] D is the camber adjustment coefficient, with units of MPa / mm;

[0054] K represents the measured concrete strength of beam 1 when prestressed steel strands are tensioned, in MPa.

[0055] S represents the measured camber of the beam slab 1 within 48 hours after the prestressed steel strand tensioning is completed, in mm.

[0056] n represents the number of tensioning cycles for beam slab 1, increasing from small to large.

[0057] It should be noted that the calculation formula for the camber adjustment coefficient D is based entirely on the measurement, calculation, and summary data of the first piece (batch) of beam slab 1.

[0058] The following is a calculation example based on the table above (summary table of measurement data):

[0059] [(K1-K2)+(K2-K3)+(K3-K4)+(K4-K5) / (S1-S2)+(S2-S3)+(S3-S4)+(S4-S5)] / 5-1;

[0060] Based on the summary table of measurement data for beam 1 above, calculate the camber adjustment coefficient D (MPa / mm) for the 25mT beam slab:

[0061] D = [(K n-1 )―k n … / (S n-1 )-S n )...] / n-1;

[0062] D=[(41-43)+(43-45)+(45-47)+(47-50)] / [(11.8-11.5)+(11.5-11.1 )+(11.1-10.4)+(10.4-9.6)]÷(5-1)==(-9 / 2.2)÷(5-1)=-1.02MPa / mm;

[0063] Based on the above calculation results and the camber adjustment coefficient D (MPa / mm), it can be seen that if the camber of the middle slab of a 25m prestressed concrete T-beam increases by 1mm, the concrete strength needs to be reduced by -1.02MPa.

[0064] Explanation of the calculation formula:

[0065] (1) K (MPa): The first piece (batch) produced with the serial numbers K1, K2, K3, K4...K n The concrete strength during the tensioning of prestressed steel strands in post-tensioned concrete beams and slabs.

[0066] S(mm): The camber of a post-tensioned concrete beam slab 1 numbered S1, S2, S3, S4...Sn within 48 hours after the prestressed steel strands are tensioned in the first piece (batch).

[0067] (2) This formula uses the data collected and summarized from the concrete strength and camber measurement of the first piece (batch) of post-tensioned concrete beams and slabs, and uses the weighted balance calculation method to answer the camber adjustment coefficient of the beams and slabs. This provides important data for the calculation of the standard data of concrete strength for subsequent prestressed steel strand tensioning of beams and slabs of the same specification.

[0068] (3) The larger the weight n, the higher the accuracy of the camber adjustment coefficient D. The smaller the weight n, the lower the accuracy of the camber adjustment coefficient D.

[0069] (4) Due to the influence of factors such as tension force error during steel strand tensioning, prestressing shape (bending error), and concrete material properties (particle size, crushing value), the camber data of prestressed concrete beams and slabs with the same concrete strength after tensioning will also have certain errors. The camber adjustment coefficient D will also have certain errors, which may form a reasonable adjustment range.

[0070] (S2) Based on the camber adjustment coefficient D of beam 1, calculate the standard concrete strength Q of beam 1 under prestressed steel strand tension. The calculation formula is as follows:

[0071] Q = K + [(Sa - S) × D];

[0072] In the formula:

[0073] K represents the measured concrete strength of beam 1 when prestressed steel strands are tensioned, in MPa.

[0074] Sa is the design camber of beam 1, in mm;

[0075] S represents the measured camber of beam 1 within 48 hours after the prestressed steel strand tensioning is completed, in mm.

[0076] D is the adjustment coefficient for the upward camber.

[0077] The following example calculations are based on real-world scenarios:

[0078] For the C50, 25m post-tensioned prestressed concrete T-beam slab, the camber of the design and construction drawings is 11.7mm. Based on the summary table of measurement data for the first piece (batch) of the beam slab, the camber adjustment coefficient D (MPa / mm) for the 25m T-beam slab is calculated to be -1.02MPa / mm.

[0079] Calculate the standard concrete strength data for the steel strand tensioning of the middle slab in the batch construction of C50, 25m post-tensioned prestressed concrete T-beams. The concrete strength K (45.2MPa) and camber S (10.9mm) of the first piece (batch) of post-tensioned prestressed concrete beam slab are calculated using the weighted balance method, as detailed in (1). Perform the following calculations.

[0080] Q=45.2MPa+[(11.7mm-10.9mm)×(-1.02MPa / mm)]

[0081] = 45.2MPa - 0.82MPa

[0082] =44.38MPa

[0083] Explanation of the calculation formula:

[0084] (1) K (MPa): The concrete strength of the first piece (batch) of a post-tensioned concrete beam slab 1 numbered K1, K2, K3, K4...Kn when the prestressed steel strands are tensioned. That is, K1+K2+K3+K4+K5 / 5.

[0085] S (mm): The camber of the first piece (batch) of a post-tensioned concrete beam slab 1, numbered S1, S2, S3, S4...Sn, within 48 hours after the prestressed steel strands are tensioned. It is calculated as S1+S2+S3+S4+S5 / 5.

[0086] (2) This formula, based on the concrete strength and camber measurement and calculation data of the first (batch) post-tensioned concrete beams and slabs, studies and analyzes the factors affecting the camber of the beams and slabs and calculates the key values ​​of the interaction point (camber adjustment coefficient D). It provides a precise basis for calculating and determining the standard concrete strength data for steel strand tensioning during normal batch construction of post-tensioned prestressed concrete beams and slabs. The standard concrete strength data for steel strand tensioning can provide accurate concrete strength standard data and construction technology support for improving the camber compliance rate of post-tensioned prestressed concrete beams and slabs.

[0087] (S3) Based on the difference between the design camber of beam 1 and the measured camber within 48 hours after the prestressing tendons are tensioned, adjust the measured concrete strength of the beam 1 during prestressing tendon tensioning so that the camber of the post-tensioned prestressed beam 1 meets the standard.

[0088] The formula for calculating the measured camber S of the beam slab within 48 hours after the prestressed steel strand tensioning is as follows:

[0089] S = CA;

[0090] In the formula:

[0091] C is the vertical distance between the center point of the bottom arc surface of beam 1 and the center point of the arc surface of platform 2;

[0092] A is the pre-camber setting value of the platform.

[0093] When Sa-S is negative, the concrete strength of beam 1 under prestressed steel tendon tension is high, and its bending strength is also high. The camber resistance of the beam body under prestressed concrete beam 1 under prestressed steel tendon tension is high, and the camber is small. It is necessary to reduce the concrete strength of beam 1 under prestressed steel tendon tension in order to make the camber of beam 1 meet the standard.

[0094] When Sa-S is positive, the concrete strength of beam 1 is low when the prestressed steel strands are tensioned, and its bending strength is also low. The upward camber resistance of the beam body is small and the camber is large when the prestressed concrete beam 1 is tensioned. It is necessary to increase the concrete strength of beam 1 when it is tensioned by the prestressed steel strands so that the upward camber of beam 1 meets the standard.

[0095] The beneficial effect of this embodiment is that it can effectively control the camber of the beam slab, which is a technical guarantee measure to prevent and eliminate potential major quality and safety hazards in bridge structures and components.

Claims

1. A post-tensioned beam-slab camber construction control method, characterized by The construction control method comprises the following steps: S1: selecting the first piece or batch of the beam slab to be post-tensioned to perform a tension test on the prestressed steel beam, and calculating an up-camber adjustment coefficient D of the beam slab according to test data; S2: calculating a standard concrete strength Q of the beam slab under tension of the prestressed steel beam based on the up-camber adjustment coefficient D of the beam slab; S3: adjusting the measured concrete strength of the beam slab during tension of the prestressed steel beam according to a difference between a designed up-camber of the beam slab and a measured up-camber of the beam slab within 48 hours after the tension of the prestressed steel beam is completed, so that the up-camber of the post-tensioned beam slab meets the standard; The calculation formula of the up-camber adjustment coefficient is: D = (K n-1 — k n ) / (S n-1 — s n ); In the formula: D is the up-camber adjustment coefficient, with a unit of Mpa / mm; K is the measured concrete strength of the beam slab during tension of the prestressed steel beam, with a unit of Mpa; S is the measured up-camber of the beam slab within 48 hours after the tension of the prestressed steel beam is completed, with a unit of mm; n is the tension times of the beam slab, which increases from small to large; The calculation formula of the standard concrete strength Q of the beam slab under tension of the prestressed steel beam is: Q=K+[(Sa-S)×D]; In the formula: K is the measured concrete strength of the beam slab during tension of the prestressed steel beam, with a unit of Mpa; Sa is the designed up-camber of the beam slab, with a unit of mm; S is the measured up-camber of the beam slab within 48 hours after the tension of the prestressed steel beam is completed, with a unit of mm; D is the up-camber adjustment coefficient.

2. The post-tensioned beam slab camber construction control method according to claim 1, characterized in that The calculation formula of the measured up-camber S of the beam slab within 48 hours after the tension of the prestressed steel beam is completed is: S=C-A; In the formula: C is a vertical distance between a center point of a bottom arc surface of the beam slab and a center point of an arc surface of a pedestal; A is a pre-camber setting value of the pedestal.

3. The post-tensioned beam slab camber construction control method according to claim 1, characterized in that When Sa-S is negative, the concrete strength of the beam slab during tension of the prestressed steel beam is reduced to make the up-camber of the beam slab meet the standard; when Sa-S is positive, the concrete strength of the beam slab during tension of the prestressed steel beam is increased to make the up-camber of the beam slab meet the standard.

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