A staged constraint construction method of a CFST box composite column

Abstract

The application discloses a CFST box-shaped composite column staged constraint construction method and belongs to the technical field of building structure member construction. Four steel plates enclose a column cavity, anchor seats are arranged in the column cavity along the column height, continuous isolated protection transverse pull rods and detection pieces are arranged, the pre-tightening is controlled by the actually measured force of the anchoring end, the concrete is graded and strengthened after reaching the selected strength and being qualified, the locking is rechecked, and then the upper adjacent bin construction is entered, the constraint of the lower bin is maintained and monitored during the construction, and after all the bins reach the design strength and are stable, the graded slow release is performed from the middle part to both ends, the current bin and the adjacent bin are rechecked at each stage, the advance is controlled by the fixed target reserved pulling force and the single unloading upper limit, and the convergence is performed according to the remaining difference when the target is approached. The method is used for the transverse constraint connection and residual constraint maintenance of different age bin sections in the bin construction.

Description

Technical Field

[0001] This invention relates to the field of construction technology for composite structures in building engineering, specifically to a construction method that corresponds the lateral constraint state of each casting compartment within a box-shaped steel component with the construction continuity of adjacent compartments and the graded slow release after molding. CFST represents concrete-steel tube; the construction object in this article is limited to a composite column formed by four steel plates connected to form a box-shaped steel tube, with the concrete compartments inside the tube sharing the load. The box-shaped composite columns mentioned below are all understood according to this specific structure. Background Technology

[0002] The cross-sectional composition of steel-concrete composite members is related to their force transmission path. The prototype described in the project application, "Research on Seismic Damage Mechanism and Seismic Calculation Method of CFST Box-Shaped Composite Columns under Combined Compression, Bending, Shear, and Torsion," consists of steel-concrete composite column segments, reinforced concrete outer casings for the column segments, and reinforced concrete webs connecting the column segments, forming a box-shaped cross-section with an internal cavity. The data from this project is used to illustrate the research background of the collaborative force-bearing of composite members. For members where four steel plates enclose the column cavity and concrete is poured within the cavity, construction constraints should be determined separately based on the steel plates, concrete, and connection configurations; the structural and load-bearing parameters of the two types of members are not equivalent.

[0003] Existing technologies improve the constraint relationship between the concrete within a column and surrounding components through tie rod construction. For example, patent application CN115717454A describes a precast concrete square tube, connecting reinforcement, core-filled concrete, and constraint tie rods located in the plastic hinge zone; patent application CN109707104A describes a steel-tube concrete casting with tie rods and its construction method. The precast concrete square tube in the former differs from the four-plate box-shaped steel component in this method. The two documents respectively illustrate the background of tie rod construction and concrete construction within the steel tube. For segmented construction, it is also necessary to correlate the pouring, strength gain, and temperature changes of each segment with tie rod adjustments and their verification conditions; the construction instructions for each stage cannot be determined solely by the presence of tie rods.

[0004] When the column cavity is poured in sections along its height, the age, temperature history, and lateral pressure of the concrete in each section are not entirely consistent. The lower sections are poured first, and the upper sections are poured after the lower sections are ready for subsequent construction. The load changes caused by continued upward construction must be shared by the existing steel plates, concrete, and connecting structures. If the entire column is tensioned uniformly or the pre-tensioning is released simultaneously, it may cause premature unloading of sections that require continued restraint, or sections that have already stabilized may still be subjected to unsuitable external forces. Therefore, the section boundaries should correspond to the construction joint treatment, anchor bolt configuration, and section number of the test data, and strength and restraint checks should be performed separately for each section.

[0005] Simply arranging construction based on fixed tension parameters or pouring intervals cannot directly determine the required lateral constraint state for sections at different ages. The issues to be addressed include not only whether each section reaches a certain strength value, but also when the reinforced constraint of the lower section allows the upper adjacent section to begin pouring, how the lower section is maintained and verified during the construction of the upper adjacent section, and whether the state changes caused by a single unloading after the entire column is formed allow for continued progress. Therefore, the pre-tensioning conversion within the same section, the sequential construction of upper and lower sections, and the gradual release should be organized as an interconnected construction process, ensuring that the operational sequence is simultaneously constrained by the corresponding section's monitoring status and actual constraint conditions. Summary of the Invention

[0006] This invention provides a staged constraint construction method for CFST box-shaped composite columns. The technical problem to be solved is: in a component where four steel plates enclose the column cavity and are constrained by transverse tie rods, how to continuously connect the transverse constraint of different casting age sections with the segment-by-segment construction and the unloading process after the entire column is formed. This method is based on the conversion between initial pre-tightening and reinforced pre-tightening in the same segment, uses the completed reinforced state of the lower segment as the entry condition for construction of the upper adjacent segment, and uses the full column slow release permit and the step-by-step verification results of the current segment and adjacent segments as conditions for the continued slow release.

[0007] To achieve the above objectives, a box-shaped steel component is formed by four steel plates, with adjacent splicing edges connected by welding, bolting, or a combination of both to create a continuous connection. The steel plates and the concrete within the column cavity serve as retained load-bearing components. Anchors are installed on the outer sides of the steel plates, with transverse tie rods connecting the anchors at both ends. The rods are continuously isolated within the column cavity to prevent direct bonding between the concrete and the rods after solidification. The anchoring reaction force is transmitted to the steel plates via the rod-end locking components and bearing members, forming a cross-cavity pressure support without the use of isolation sleeves. The tensioning mechanism applies and adjusts the force, while the mechanical locking mechanism maintains the anchoring position. The actual force values ​​at both ends, along with the contact state between the steel plates and concrete, are used for feedback verification.

[0008] The column cavity is divided into at least two sequentially poured sections along its height. Each section is equipped with at least one set of adjustable pre-tensioning rods, with the design construction joint elevation serving as the boundary between adjacent sections. Each section is equipped with pressure and temperature sensors, and strain gauges are installed on the outer surface of the steel plate. Strength development data is obtained from specimens cured under the same conditions, or from maturity-strength relationships calibrated using the same mix proportions. The monitoring unit associates the monitoring data according to the section number, rod position, and range of action, and the construction control unit outputs commands to the corresponding tensioning adjustment parts accordingly. The construction status of each section is determined separately. At any given time, the upper adjacent section may be in the initial pre-tensioning and pouring stage, while the lower section remains in a locked and constrained state that has already been strengthened and verified.

[0009] Record the first preload before each section is poured; the initial loading causes controlled inward elastic pre-deformation relative to the steel plate, and the column cavity that has not yet been poured cannot be described as being subjected to concrete contact pressure. The second preload is the actual force at the anchor end after the same section has been strengthened, adjusted, locked, and verified, and should be higher than the first preload recorded in the same section. When comparing, keep the tie rod number, anchor end, and calibration diameter consistent, and do not mix readings from different sections or different ends.

[0010] After initial pre-tightening is completed, valid test data is obtained as the concrete is poured into the formwork. If the test data is within the calibration range for the corresponding construction stage, the following formula is used to form the first... The target preload force for a single tie rod corresponding to each pouring chamber:

[0011]

[0012] In the formula, For the first The target preload of the corresponding single tie rod; The reference tension is predetermined and recorded for this stage; This is the correction for the target tensile force calculated based on the steel plate strain, lateral pressure, and temperature condition. All three are expressed in Newtons. Number the pouring chamber; establish separate records for multiple tie rods within the same chamber, and the following relationship applies to the same force value channel for one tie rod each time. Within the stage Keep the values ​​constant and do not repeatedly accumulate corrections after replacing the baseline with the values ​​from the previous step. Determine the first preload based on the initial state of the steel plate before pouring, without substituting in measured values ​​of concrete that do not yet exist. The stage target, current actual force, actual force before release, and retained force all correspond to the same measurement location and calibration caliber.

[0013] Each tension symbol corresponds to the same force measurement channel at the anchorage end specified in the record; the other end of the same rod is measured simultaneously and used for consistency and friction anomaly verification, but the readings at both ends are not added together. The support reaction force of the tensioning mechanism must not bypass the corresponding force measurement path; the force measurement reading after locking is used to update the actual force for the next step, and the jack hydraulic pressure and nut rotation angle are only used as auxiliary information.

[0014] Once the concrete strength of the current pouring section reaches or exceeds the selected strengthening threshold, and the pressure, steel plate strain, and anchorage condition have been verified, a second preload higher than the first preload in the same section is applied in stages; the second preload must also be within the allowable tensile force range for this stage. Only after the strengthening loading, condition verification, and locking of this section are completed can the first preload be applied to the adjacent section to be poured and poured. During the construction of the adjacent section, the lower section maintains locking constraints and its steel plate strain and lateral pressure are continuously monitored. The above process is repeated when there is an adjacent section to be poured, and after the uppermost section completes strengthening, it switches to full column constraint maintenance. When there is numerical overlap between the initial window and the strengthening window, the second preload in the same section must still be higher than the first preload.

[0015] After all cast sections have completed reinforcement and pre-tightening, anchoring and curing continue. Full column release is only permitted when each section reaches its design strength and the residual pressure, steel plate strain, and temperature meet the preset stability conditions. Release proceeds step-by-step from the middle of the column upwards and downwards. After unloading at each level, the pressure, steel plate strain, and anchorage condition of the current section and its adjacent cast sections are checked. Unloading continues or the process moves to adjacent sections only after the preset stability conditions and permissible component conditions are met. Each rod retains its corresponding target tensile force as the final value. After completion, the rods and anchorages are permanently retained and protected. The spatial operation sequence cannot replace the verification of adjacent sections.

[0016] The target preload should first be checked against the allowable tension range for the corresponding stage, and then compared with the current actual tension. For a single adjustment that passes the condition verification, the following variation constraints are applied:

[0017]

[0018] In the formula, This refers to the actual tensile force to be verified after this adjustment; This refers to the current actual tension confirmed before adjustment; The maximum allowable change per cycle is expressed in Newtons, and is a positive value. First, verify the data and component status, then check if the target is within the allowable range for this stage. Finally, determine the adjustment direction based on the difference between the target and the current value; the commanded change amount should not exceed the remaining difference and the maximum allowable change per cycle. The absolute value in the formula simultaneously limits loading and unloading. After each step, lock and resample, verifying the actual force change and component status; stop subsequent actions if the actual change or execution deviation exceeds the allowable range. The new current value uses actual feedback, not commanded values ​​to replace measurements. Stop new automatic adjustments if the target exceeds the limit or if the data or anchor status is abnormal; for slow release, execute according to the target retained tension and unloading ratio.

[0019] The allowable tensile force range for each stage is jointly defined by the out-of-plane deformation and local bearing pressure of the steel plate, the effective cross-section of the tie rod, the bearing capacity of the anchor and connection, and the allowable state of the concrete at the corresponding age. The initial, strengthening, slow-release, and permanent retention stages each form a usable range; the design tensile force is only the denominator in the preload ratio conversion and does not replace these ranges. No new orders are issued if the candidate target falls outside the range; if the actual component exceeds the limit, the anchor slips, the isolation protection fails, or the measurement is invalid, new orders and affected subsequent procedures are stopped, and the on-site handling plan is reviewed. The conventional unloading ratio is only used to propose candidate step lengths and does not cover the upper limit of a single force value, the target endpoint, or the actual measurement capability.

[0020] The box-shaped steel components, splicing connectors, outer anchors, adjustable preload tie rods, in-cell testing devices, and construction control units constitute a coordinated construction constraint system. Testing devices reflect the status of each compartment, the construction control unit determines the stage and generates adjustment commands, and the tie rods apply lateral force to the corresponding steel plates through the anchors, creating a shared stress relationship between the steel plates and the concrete within the corresponding compartment. Pressure and strain measurements are used to verify the actual effect, and readings at individual measuring points are not directly equated to the uniform constraint pressure across the entire cross-section.

[0021] This method integrates the pre-tensioning, state verification, and locking of the lower section with the initial pre-tensioning and pouring of the adjacent upper section, ensuring that sections of different ages maintain lateral constraints corresponding to their construction stages, rather than simply advancing the entire column construction according to a uniform tension value or time interval. The release mechanism uses the design strength and stable state of all sections as the starting condition, and the step-by-step verification of the current and adjacent sections as the condition for continued advancement, constrained by the target retained tension and single unloading boundary, ensuring that the operational sequence from the middle to both ends corresponds to the detection feedback. The target calculation for the fixed stage benchmark and the release calculation for the fixed final value of this round respectively limit the reference quantity and the actual execution quantity, reducing control ambiguities caused by repeated accumulation of corrections or rolling changes in the unloading endpoint. Within the verified applicable range of structural and control parameters, the above coordination is used to improve the controllability of the section construction connection and constraint conversion process. Attached Figure Description

[0022] Figure 1 This is the overall technical roadmap for initial pre-tightening of compartments, enhanced continuity, and graded slow release across the entire column.

[0023] Figure 2 This is a framework diagram showing the relationship between the box-shaped steel plate, the casting compartments, the anchor bolts, the construction joint connections, the monitoring, and the construction control unit.

[0024] Figure 3 This is a comparison chart of normalized flexural bearing capacity and its decrease rate under different torsion ratios in the project research background.

[0025] Figure 4 This is a boundary diagram showing the range of values ​​for steel plate thickness and single compartment height, as well as the net distance from the anchor to the edge of the steel plate.

[0026] Figure 5 A comparison chart showing the calculated tensile force ratio under initial and enhanced pre-tightening windows and different release coefficients.

[0027] Figure 6 This is a diagram showing the nominal cross-sectional area density and initial-strengthened preload increment analysis of the tie rod size combination. Detailed Implementation

[0028] This embodiment focuses on a box-shaped composite member where four steel plates enclose the column cavity, and the steel plates and the concrete inside the cavity share the load. It employs anchorages, continuously isolated and protected transverse tie rods, and double-end force feedback for constraint adjustment. The following isolation, force measurement, and tensioning configuration provides a specific implementation design; the steel plates, rods, and anchorages are retained after the load is released. The column limbs, external reinforced concrete casing, and web structure mentioned in the project application are identified separately for research background purposes only.

[0029] like Figure 1 As shown, the construction route is formed by assembling compartments, monitoring pre-tightening of the compartment, reinforcing locking, connecting adjacent compartments, slow release of the entire column, and residual retention. "Strength and condition are qualified" and "all compartments reach design strength and meet stability conditions" are prerequisites for transitioning to the next stage; if these conditions are not met, the next process cannot proceed. During the construction of adjacent compartments, the lower compartment is maintained and monitored; each slow release stage verifies both the current and adjacent compartments. Figure 1 The attached diagram is selected as the summary. For detailed interlocking and abnormal handling procedures, please refer to Table 1 and the following implementation process.

[0030] Table 1 Construction Stages and Conversion Conditions

[0031] Construction phase Entry and review conditions Execution and Conversion Initial preload Steel components, tie rods, anchors, and force measuring devices are in place; initial condition is acceptable. Initial pre-tightening and verification were performed at each stage; after passing the verification, the main section was poured. Pouring and curing monitoring Concrete delivered to the formwork; testing results are valid and within the specified range. Obtain pressure, temperature, strain, and strength data for this chamber; monitor the lower chamber during construction of the adjacent upper chamber. Strengthen pre-tightening The strength of this warehouse has reached the threshold, the target is higher than the initial value, and the status is satisfactory. Tiered reinforcement and locking verification; then proceed to the adjacent position, and maintain the entire column after the top position is completed. Full column retention All warehouses have been reinforced; release permits are being continuously verified. Maintain anchoring and maintenance; slow release should only be implemented after all chamber strength and continuous stability conditions are met. Graded sustained release The target is fixed, and the current step size and measurement capabilities are compatible. The verification process proceeds step by step from the middle towards both ends; small-step convergence is performed near the target, and anchoring is maintained upon completion.

[0032] Box-shaped steel components consist of four steel plates enclosing a rectangular or near-rectangular column cavity. The steel plates can be Q355, Q390, or structural steel plates of equivalent strength. The plate thickness can be selected based on the column cross-section dimensions, design axial compression ratio, and expected lateral restraint requirements, and is preferably 8mm to 30mm. When the column cross-section side length is large or the concrete pouring height is high, a steel plate thickness of 12mm to 24mm is recommended, combined with external stiffening structures to improve the out-of-plane stability of the plates. The spliced ​​edges of the four steel plates are connected by full penetration welds, fillet welds, bolted connecting plates, or a combination of welding and bolting to form a closed box. When using welded connections, a visual inspection of the welds and necessary non-destructive testing should be completed before pouring to prevent cracking, local yielding, or deformation instability at the connection edges during the loading of the pre-tensioned tie rods.

[0033] The column cavity adopts a square, rectangular, or partially corner-treated cross-section formed by four steel plates; the corner treatment does not change the enclosure of the four steel plates or the tie relationship between the relative steel plates. The side length of the cross-section can be selected in the range of 400mm to 1200mm in combination with the design. Stiffening ribs, transverse stiffening plates, or locally thickened plates are used to control the out-of-plane deformation of the steel plates. The stiffening structure can be densified at the boundary of the casting chamber, anchorage, and connection area. Its dimensions, connections, and spatial relationship with the tie rods are checked according to the configuration of the same component, and the stiffening measures do not replace the adjustable tie rod constraints.

[0034] Anchors are installed on the outer sides of the steel plate, with high-strength bolts or precision-rolled threaded steel tie rods passing through each set of anchors. The rod ends are equipped with bearing components and locking nuts. Threaded adjustment or hydraulic tensioning devices with force feedback can be used. The rod axis should preferably be perpendicular to the constrained steel plate, and the anchors diffuse force through locally thickened pads or force-transmitting ribs. The nominal diameter can be selected from 20mm to 50mm, and the design tensile force can be selected within the range of 20% to 65% of the yield bearing capacity of the effective section used, serving as the common denominator for the initial and reinforced preload rates. The actual allowable force is still taken as the intersection of the allowable conditions for each component and the corresponding concrete age.

[0035] Implementation configuration of isolation tie rods, force measurement, and tensioning.

[0036] The tie rod segment located between two opposing steel plates is isolated using a continuous sleeve. The sleeve contains a non-consolidating, corrosion-resistant medium compatible with the rod and its seal. A flexible grout-stop seal, allowing for relative axial displacement, is used at the plate penetration point of the sleeve. Sufficient space is left between the sleeve end and the bearing member to accommodate planned adjustment strokes, preventing the sleeve from being rigidly pressed between the opposing steel plates. The outer side of the sleeve can contact concrete, but the interior is not filled with cement grout that would lock the rod to the concrete. Before pouring, continuity, unobstructed flow, and sealing are checked. After hardening, small adjustments are made to check the axial expansion and contraction of the rod and the stress response at both ends.

[0037] Each anchoring end is equipped with a through-type force measuring element and a matching bearing component on the rod axis; the reaction force of the locking nut and the support reaction force during tensioning are transmitted to the anchor seat through the designated force measuring element, without any contact branch that allows the reaction force to bypass the force measuring element. Both ends are numbered and calibrated separately, and the zero point, bearing surface flatness, and eccentricity sensitivity of the force measuring element are verified after assembly. The force path is as follows: the axial tensile force of the rod acts on the steel plate through the locking element, bearing component, and anchor seat, and then the lateral force is transmitted through the contact between the steel plate and the concrete in the slab; the local stiffening element undertakes the diffusion effect, and the isolation sleeve does not undertake the supporting effect between the two steel plates.

[0038] When using a hydraulic system, the tensioner is supported on the anchor bearing member by a matching reaction support, with the tensioning end connected to the exposed rod end, leaving space for clamping and return. Only the locking element at the controlled operating end is loosened at a time, while the other end remains anchored. When increasing the preload, the tensioner first smoothly takes over the existing load at that end, adjusting it to the allowable value under force feedback. After tightening the lock nut, it slowly returns to the starting position, transferring the force to the locking element. After locking, the force values ​​at both ends are read again, and the steel plate strain, pressure, and anchor displacement are checked. Deviations caused by installation or load transfer are still included in the allowable changes, and there is no need to compensate for locking losses by applying excessive force.

[0039] During the gradual release, the tensioner first takes over the original anchorage load under controlled conditions. After confirming that the locking nut has relieved its pressure, the nut is retracted within the stroke and anti-disengagement conditions. Then, the force borne by the tensioner is slowly reduced to the target value. The locking parts are then re-engaged and the load is transferred. Finally, the actual force after locking is read. Reliable anchorage is maintained throughout the process. It is forbidden to directly remove the nut under load or unload by sudden disengagement. If the force difference between the two ends exceeds the allowable deviation specified by the device, or if the force change does not produce a corresponding steel plate and contact pressure response, check the friction, grout jamming, and anchorage force transmission. Do not continue to blindly apply force.

[0040] One or more layers of tie rods may be installed between the relative steel plates in each pouring section; when the column cross-section side length exceeds 800mm, tie rods should preferably be installed in two orthogonal directions. The rods, connecting reinforcements, and shear connectors in the orthogonal directions should avoid each other and should not intersect in the same spatial location. The spacing of tie rods along the same direction of the column height can be 300mm to 900mm, with increased spacing at the section boundary, anchorage, and key control locations based on the structural conditions. The clear distance from the edge of the anchorage to the edge of the steel plate should preferably be no less than six times the steel plate thickness and no less than 80mm; the dimension should be recorded according to the same measurement start and end boundaries. This lower geometric limit is used in conjunction with the verification of local bearing pressure at the anchorage, the clear cross-section of the steel plate, and splice connections.

[0041] The column cavity should be divided into at least two casting sections based on its height. Components with a floor height of 3m to 6m can be divided into two to four sections, while taller components can be divided into three to six sections; the height of a single section should preferably be between 0.8m and 2.5m. The number of sections, the height of each section, and the elevation of the construction joint should be matched with the total casting height of the same column, and selected in conjunction with supply capacity, temperature conditions, and construction loads. The relationship between the total height and the number of sections cannot be ignored by arbitrarily selecting the number of sections and the height of each section.

[0042] Adjacent pouring sections are separated by the construction joint elevation. The cross-joint connecting reinforcement is positioned before the lower section is poured, and the upper anchorage section is retained. After the lower section meets the corresponding process conditions, the top surface is roughened or treated to remove laitance and loose particles before pouring the adjacent upper section. Connecting reinforcement, shear keys, or local shear-resistant components are configured according to the same connection design; the inner wall of the steel plate and connecting components are cleaned before sealing and pouring. When using full-height steel components, the construction design must clearly define the operating tools, material handling, and inspection passages extending from the upper opening; it cannot be assumed that personnel can still enter the column cavity after tie rods and reinforcement have blocked the passage. The flexible sealing of the isolation sleeve at the through-slab, the clear spacing of the reinforcement, and the concrete passage conditions are checked simultaneously.

[0043] Pressure and temperature sensors are installed in each casting chamber. Pressure sensors should ideally be located in the middle of the inner side of the box-shaped steel plate, at locations where deformation is most pronounced across the span. If necessary, pairs of sensors can be installed on adjacent sidewalls to identify non-uniform lateral pressure distribution. Temperature sensors should be embedded in the central area of ​​the concrete cross-section within the chamber and near the inner wall of the steel plate to acquire hydration temperature rise, peak temperature, internal and external temperature difference, and subsequent temperature drop and shrinkage. Resistance strain gauges, fiber optic strain gauges, or other strain monitoring devices suitable for steel structure construction can be attached to the outer surface of the steel plate to obtain strain changes during pre-loading, concrete pouring, and hardening.

[0044] The sensing element should avoid direct impact from material feeding, strong vibration disturbances, and areas with dense studs. For pressure sensors, select a non-zero range based on the expected lateral pressure with a margin; the selection range can be determined within 0MPa to 5MPa, while verifying resolution and zero-point stability in low-pressure areas. The maximum permissible absolute value of temperature detection error should not exceed 0.5℃. Before construction, standardize strain direction, sign, zero point, and temperature compensation. A 1-15 minute interval is used for routine state recording; feedback readings during pouring and pre-tightening adjustments are encrypted according to actual actions and state changes, and outdated timed records are not used to replace current control inputs. The measuring point number is associated with the compartment number, lever range of action, and sampling time; new automatic adjustments are stopped if there are missing, drifting, or mismatched numbers.

[0045] Before each pour, an initial preload is applied to the steel plate, causing it to be subjected to a force towards the column cavity and forming a controlled elastic pre-deformation. This is used to limit outward bulging caused by the lateral pressure of subsequent concrete. At this point, when there is no concrete in the section, this preload is not considered pressure already applied to the concrete. The initial preload force is determined based on the steel plate thickness, cross-sectional dimensions, tie rod configuration, concrete workability, and expected pouring speed. It can be selected within the range of 15% to 35% of the single-strand design tension, and the first preload force of the same section is recorded. Values ​​under conditions of higher fluidity or higher temperature must still be verified through the permissible conditions of the steel plate, anchorage, and tie rods.

[0046] Pre-tightening employs a symmetrical, graded, and cyclical verification method, with orthogonal directions and relative steel plates alternating in a predetermined sequence. Each round verifies the actual force at both ends, steel plate strain, anchor displacement, rod expansion and contraction, and splicing status; actual expansion and contraction, along with the force values ​​at both ends, are used to identify and isolate damage or abnormal friction. The unbonded force transmission path is continuously confirmed during installation verification and subsequent small-scale operations; a single end reading does not directly prove uniform force distribution across the entire rod and plate surface. If significant eccentricity, jamming, anchor slippage, or continuous increase in local strain is detected, subsequent operations are stopped and the cause addressed.

[0047] Concrete is selected according to design strength, workability, and durability requirements. For ordinary pumped concrete, strength grades from C40 to C80 can be used, selected based on a slump range of 160mm to 220mm combined with the actual mix proportions. When using self-compacting concrete, the corresponding spread, cohesiveness, and segregation resistance indices are used; the ordinary slump window is not used directly to replace its workability assessment. The placement location, placement rate, and vibration method are matched with the actual reinforcement, tie rods, sensors, and concrete properties. During pouring, the lateral pressure and deformation of the steel plate are continuously checked. If workability or conveying conditions change beyond the original control range, the corresponding automatic adjustments are paused and rechecked.

[0048] After fresh concrete enters the formwork, the monitoring unit records the lateral pressure on the inner wall, hydration temperature, and steel plate strain. Within the defined measurement direction and operating range, the target correction is calculated based on the difference between the current state and the reference state for this stage, and then combined with the fixed stage reference tension to form the target preload. The target is executed after verification against the allowable tension and single-amplitude limit. The next sampling recalculates the target relative to the same reference, without repeatedly accumulating the corrections corresponding to temperature differences or strain differences cycle by cycle.

[0049] To enable the above-mentioned target correction amount to be recalculated, for the first... The container uses the following formula; the force unit is Newton, the area is square millimeter, the stress and elastic modulus are megapascals, and the temperature difference is degrees Celsius:

[0050]

[0051] In the formula, This is the target correction amount for the rod relative to the reference tension in this stage; , and For the dimensionless correction factors of strain, pressure and temperature terms; The elastic modulus of the tie rod material; This represents the actual effective cross-sectional area under stress. This represents the effective compression area of ​​the constrained steel plate on one side corresponding to this rod; and For targets within the same monitoring range and in the same direction, and the measured average strain; and The target and measured average lateral pressure within the corresponding range; This is the coefficient of linear expansion of concrete, expressed in degrees Celsius. and This serves as the temperature baseline and corresponding measured average temperature for this stage. Force values ​​are expressed in Newtons, areas in square millimeters, elastic modulus and pressure in megapascals, and strain is substituted as dimensionless decimals. The overline indicates the average value formed by a predetermined set of measurement points; for a single valid measurement point, that point's value is used. Local extreme values ​​and data failures are checked separately; the average value is not used to mask out-of-limit conditions.

[0052] The statistical area of ​​the same steel plate under pressure is divided by the midline of adjacent anchors and the plate boundary. The area and set of measuring points are determined according to the single-sided area corresponding to the tie rod. This is the zoning scope for control calculation and does not imply that the pressure within the area is necessarily uniform. Edge areas are cut off according to the actual boundary. Areas with multiple tie rods are not measured repeatedly, and opposite sides are not added to the same rod. During calibration, adjacent areas and local extreme values ​​are measured simultaneously. If the mutual influence cannot be described by the zoning and parameters, the zoning is adjusted or the joint response of the component is used for calibration before it is used again. Orthogonal directions are recorded separately, and the coefficients and allowable conditions are updated synchronously when the area changes.

[0053] The strain, pressure, and temperature terms are written in the order of reference value minus the current measured value. The signs, values, and applicable ranges of each coefficient are determined by the calibration of the corresponding structure or verified construction analysis. The same symbol is not directly used when the steel plate measuring points are in different directions. The temperature reference, target strain, target pressure, and reference tensile force for the same stage use the same version, updated after stage switching or recalibration. The target strain can be selected according to the control direction within the range of 10% to 35% of the design yield strain; local strain still meets elasticity and connection allowable conditions. The temperature difference term only represents the shrinkage demand correction in the control relationship. The three inputs may respond to the same regulation simultaneously; the combined target value and the actual response should be verified. The combined control cannot be considered verified simply because the dimensions of each individual term are correct.

[0054] Parameter determination, joint calibration and transition acceptance

[0055] The calibration process begins by fixing the component geometry, rod and sleeve configuration, anchor force measurement setup, concrete mix proportions, age or strength range, and construction load boundaries, and recording the complete version. The allowable force range for each stage is determined by the effective cross-section of the rod, local bearing pressure of the anchor, plate deformation, and corresponding age concrete calculations. The intersection of the initial or strengthening window with this range is taken as the candidate range. Then, benchmark tensile force, strain target, pressure target, and temperature benchmark, all of which have undergone stability checks, are selected. Both the target and the benchmark are fixed within a single stage.

[0056] On a representative configuration matching this stage, apply small-scale loading and unloading within permissible limits. After stabilization, record the force value at the same anchorage end, the check value at the other end, pressure, strain, temperature, and anchorage displacement. Cover the pressure changes on the casting side, the selected strength range, and the temperature drop condition. For conditions that cannot be independently changed on-site, a calibration sample can be formed using a construction model verified by the response of a representative component. The pressure and strain changes caused simultaneously by the same tensioning should not be mistakenly treated as two independent tests.

[0057] For each sample, the tensile force that meets the corresponding plate pressure and strain control zone and is within the allowable range is used as the reference output for that working condition. The difference between this output and the fixed-stage baseline is listed as the correction value. The strain, pressure, and temperature terms (which do not contain coefficients) in the original correction formula are listed as three input columns, and joint least squares are used to determine the three coefficients. The input columns are checked for sufficient independent variation; if insufficient rank or severe collinearity occurs, unique coefficients are not reported, and independent working conditions should be added or the application range narrowed before recalibration. The coefficient signs are determined by the measurement point direction recorded and the joint fitting.

[0058] Examine the target error, direction of change, and response after a single adjustment using unfitted operating conditions, and verify continuous operation in the sequence of actual locking—sampling—readjustment. Only activate the corresponding parameter version when the target, local strain, pressure, and end force values ​​are all within allowable ranges, and the operation does not exhibit sustained oscillations or error amplification; otherwise, reduce the permissible step size, adjust parameters, or stop automatic adjustment for that configuration. The parameter version generated according to the above process is only used within the scope of the verified construction and building phases.

[0059] Stability conditions are determined through representative maintenance tests: for pressure, plate strain, end force, and anchor displacement, the static fluctuations and uncertainties of the sensing system are first measured, and then the stability zone is determined based on the acceptable changes in the component. The observation period should at least cover the stabilization process after locking of the tensioning device used, and the peak-to-valley differences and trends of each quantity are checked with continuous and valid data. During the temperature drop phase, the temperature change during the observation period is also checked; if any local value exceeds the limit, a persistent trend exists, or the effective sampling is discontinuous, the observation period is not extended. The stability zone must not be less than the resolvable measurable fluctuation, nor greater than the corresponding allowable change in the component.

[0060] The strength development value is obtained from the maturity-strength relationship calibrated under the same conditions, or with the same mix proportion and applicable curing conditions. First, determine the specimen type, strength definition, and statistical caliber, then calculate the strength development ratio using the following formula:

[0061]

[0062] In the formula, For the first The intensity of warehouse development ratio; To determine the concrete compressive strength obtained using the selected method at the specified time; To ensure the design reference strength uses the same test definition and statistical caliber, both tests employ the same stress units. The strengthening trigger threshold is pre-selected from 0.45 to 0.70. The strengthening stage only begins when the selected value is reached or exceeded, and the pressure, plate strain, and anchorage condition are all verified. Different defined cubic strength and axial compressive strength design values ​​are not directly divided; the ratio threshold used for strengthening does not replace the allowable release conditions after the design strength. The design reference strength must be positive, and the ratio is only calculated after the strength data and conversion basis are valid; if the reference strength is missing, zero, or the test caliber is inconsistent, the stage transition is not triggered.

[0063] The second preload in the reinforcement stage should be higher than the first preload in the same compartment. It can be selected within a window of 30% to 60% of the single-strand design tensile force, and must meet the actual allowable range for this stage. If the window does not overlap with the allowable conditions, or if there is no available value higher than the first preload in the same compartment, reinforcement execution should not proceed. Multiple small adjustments should be made, and the actual force, steel plate strain, pressure, and anchor displacement should be checked after each tightening step. If the detected change is inconsistent with the verified response direction, or if local strain continues to increase, the force transmission, anchoring, and sensing status should be checked first; the target value itself is not proof that the constraint effect has been achieved.

[0064] Before constructing the upper adjacent compartment, first confirm that the lower compartment has reached the selected strength threshold and completed reinforcement loading, condition verification, and locking. Then, apply initial pre-tightening to the upper adjacent compartment and pour the concrete. If the strength threshold is reached but reinforcement verification and locking are not completed, the construction step for that upper adjacent compartment will not proceed. During the pouring of the upper adjacent compartment, the lower compartment maintains the confirmed locking constraints, and continues to verify the steel plate strain, lateral pressure, and actual force values. Subsequent maintenance adjustments are still implemented according to the calculation basis and allowable conditions of the same stage of that compartment. The upper adjacent compartment enters reinforcement based on its own strength and condition, without using the age or already reached strength of the lower compartment as a substitute for judgment. After the uppermost compartment completes reinforcement, it enters full column retention and will no longer trigger the pouring of the upper adjacent compartment.

[0065] After all sections have been reinforced, they must remain anchored and maintained. The full column slow-release permit requires each section to reach the design reference strength confirmed using the same strength caliber, and that residual pressure, steel plate strain, end force, anchor displacement, and temperature change meet the stability zone and local allowable values ​​within the calibrated observation period. Residual pressure refers to the contact pressure between the locking element and the current construction load, not the retaining force of the tie rod. Each verification uses the corresponding section, corresponding strength range, and the same parameter version; a passing grade for one section does not guarantee passing grades for all sections, and a single stable reading does not replace continuous stable observation.

[0066] The release process identifies the geometric center of the column and its corresponding starting compartment based on the actual upper and lower elevations of each compartment. The process proceeds incrementally from the center upwards to both ends, without mechanically equating the middle compartment number with the geometric center. When the center corresponds to two compartments or when the entire column has only two compartments, a symmetrical, small-level alternating operation is employed. After each unloading stage, the pressure, steel plate strain, and anchorage status of the current compartment and adjacent compartments are checked; here, adjacent compartments refer to the casting compartments adjacent to the current compartment along the column height. Unloading continues or progresses to adjacent compartments only after the pre-set stability conditions and component allowable conditions are met. The process does not wait until all compartments in the center are unloaded to their final values ​​before starting the inspection of adjacent compartments. The starting point and spatial order of the operation are prioritized for the center, while the conditions for continued progress are specified for the adjacent compartment checks; both are executed concurrently. This method does not presuppose that the center is necessarily the area of ​​maximum stress.

[0067] During the slow-release phase, a conventional unloading ratio is selected from 5% to 20% of the current actual force to form a candidate step size. The actual unloading amount is also constrained by the upper limit of a single change and the remaining difference from the target, and can be less than this conventional ratio. After each operation, the actual forces at both ends, steel plate strain, residual pressure value, and anchor displacement are checked, and the operation is only carried out after the state is stable. Before the start of this round, the fixed starting force is recorded, and the target retained tension is determined by the following formula; this target is not the final rolling value recalculated based on the current force at each stage:

[0068]

[0069] In the formula, For the first The target retains tension for a single tie rod in the compartment; Minimum retainable tension as required by design; This refers to the actual tension recorded before the start of this round of slow release; The release coefficient, ranging from 0.2 to 0.8, represents the planned release percentage of the tension exceeding the minimum retainable tension before release. All tension values ​​are in Newtons and are non-negative. When... Greater than When the coefficient increases, the target retains less tension; when the two are equal, the current value is maintained and unloading is not performed. Below The release is paused and reviewed periodically; automatic tension replenishment is not utilized. Same round of freezing. , , The final value is determined and is not repeatedly updated based on the current tension after each level.

[0070] Each stage uses the difference between the current actual force and the fixed target as the remaining amount, and proposes candidate unloading amounts according to a selected conventional ratio. The positive command is selected if it does not exceed the minimum of the candidate amount, the single-change upper limit, and the remaining amount. The conventional 5% ratio is not used as a mandatory lower limit: when the single-change upper limit is small or close to the target, smaller convergence steps are executed to avoid crossing the target to reach the required ratio. Invalid commands are not repeatedly issued when the available step size is less than the device's reliable resolution capability; first, it checks whether the pre-set target confirmation zone is met. If it is met, the process ends after stabilization verification; otherwise, it is recorded as incomplete and the automatic operation stops.

[0071] The target confirmation zone is determined before construction based on force measurement uncertainty, repeatability after locking, and permissible component deviation, and is simultaneously constrained by the allowable range of permanent retention force. The minimum design retention force is checked using a conservative lower bound after subtracting the uncertainty from the measured value; readings potentially below this lower limit are not accepted as completion. Before the first stage of execution, the compatibility of the starting force, target, allowable range, minimum resolvable step size, and confirmation zone is confirmed. Slow release is not initiated if the target exceeds the limit or the starting force is below the lower limit. The rod is considered complete only when the target confirmation zone, the current compartment, and adjacent compartments are stable, the force values ​​at both ends are verified, and the anchoring is effective.

[0072] The slow-release mechanism proceeds according to a "one-round inspection from the middle to both ends - next-round inspection" approach: each round begins with the corresponding bin in the actual geometric middle, and each selected pole position executes only one allowed small increment, checking the current bin and adjacent bins before moving outwards; pole positions that are not yet completed enter the next round, while completed pole positions are only monitored. When the middle corresponds to two bins, operations are alternated; if any bin is abnormal, the affected progress is stopped to avoid unloading the middle bin to its final value first while the outer bins are not involved in the step-by-step coordination for a long time.

[0073] In this embodiment, the tie rod is permanently retained. After the release is completed, the nut, locking part, and anchor remain anchored, and the actual retained tension and the corresponding steel plate, pressure, and anchor condition are recorded at the same measurement location. Tensile force changes during service life are continuously reviewed according to component maintenance requirements, and the locking state is not equated with a constant tension at any given time. Exposed connection areas are equipped with anti-corrosion and necessary fire protection. The outer protective cover should be easy to inspect, and the removal and installation of the protective cover should not involve the removal of the rod.

[0074] In areas prone to plastic deformation, additional tie rods and monitoring components can be incorporated into the design. When the spacing is reduced by 20% to 40% compared to ordinary areas, compatibility with the established spacing range, concrete passage, anchorage distance, and connection structure should still be verified. Shear-resistant connectors or local stiffening ribs should be configured on the inner side of the steel plate according to the design. This arrangement is used to strengthen the constraint and condition monitoring of the corresponding areas; the specific load-bearing capacity, ductility, and energy dissipation performance should correspond to the actual component conditions and should not be directly inferred from the spacing reduction ratio.

[0075] For industrial buildings in marine, humid, or highly corrosive environments, corrosion-resistant materials, reliable sealing structures, or reinforced anti-corrosion systems should be used for the outer anchorages and tie rod connection areas of box-shaped steel components. The cementitious material system, protective layer conditions, and steel plate inner wall protection measures of the column cavity concrete should be adapted to the environmental rating. For low-temperature construction environments, the reinforcement restraint adjustment or slow-release operation can be delayed based on the concrete temperature development to avoid excessive lateral restraint due to insufficient early-age strength of the concrete; for high-temperature construction environments, the peak temperature rise and subsequent temperature drop should be closely monitored to prevent the restraint requirements during the temperature shrinkage stage from being underestimated.

[0076] While maintaining the relationship of four steel plates enclosing the column cavity, the outer anchorage, and the staged application of lateral constraints by the tie rods, the steel plates can be locally thickened, ribbed, or have corner reinforcement structures; the tie rods can be mechanically threaded or hydraulically tensioned; and the sensors can be wired or wirelessly collected. All implementation configurations must clearly correspond to the loading direction, effective pressure area, corresponding compartment number, and construction stage, and the tie rods must be controlled and permanently retained after reaching the design strength.

[0077] Through the above process, initial pre-tightening, enhanced pre-tightening, constraint retention, and graded slow release form a continuous construction path. Figure 1 , Figure 2 This reflects the path and the relationships between units; Figures 4 to 6 Used to illustrate parameter ranges, preload windows, and corresponding calculation relationships; Figure 3 This data is retained separately as background data for project research. Construction records are saved by compartment number, including test inputs, reference values ​​used, coefficient versions, target tension, actual execution values, locking status, and verification results, corresponding to each stage of the operation.

[0078] like Figure 2 As shown, the steel plates and compartment units correspond to the construction objects, the construction joint units are responsible for force transmission between compartments, and the anchor bolt units include the isolation protection, force measurement, and tension locking configurations described in this document. The monitoring unit collects the status inside the compartment and at the bolt end and transmits it to the construction control unit, which outputs commands to the tension adjustment parts; solid lines represent component configurations or functional relationships, and dashed lines represent detection and control signals. In the figure, "Abnormal Hold" means stopping new commands and retaining mechanical anchoring, and does not replace on-site handling after exceeding limits. Figure 1 This document only summarizes the main points; the transitions, convergence steps, interlocking of adjacent warehouses, and abnormal exits at each node are specifically defined by this implementation method and Table 1.

[0079] Figure 3This data is compiled based on the preliminary OpenSees results listed on pages 5 and 21 of the project application. The project model consists of concrete-filled steel tubular columns and reinforced concrete webs. Using the zero-torsion-to-bending ratio condition as a baseline, the corresponding reduction rates for torsion-to-bending ratios of 0, 0.1, 0.2, and 0.3 are 0%, 19%, 27%, and 35%, respectively, yielding normalized values ​​of 1.00, 0.81, 0.73, and 0.65. This figure uses the aforementioned textual records and does not reverse the coordinates or legends of the project images. This set of values ​​is only for the research background of the project prototype and does not constitute experimental, computational verification, or performance improvement comparison results for this phased constrained construction method.

[0080] Figure 4 The left image shows the thickness of the steel plate. and single-warehouse height Using coordinates, the parameter selection ranges are shown for 8mm to 30mm and 0.8m to 2.5m; the 12mm to 24mm color band corresponds to the aforementioned thickness selection suggestions, and the specific configuration within each range should still be verified according to the component conditions. The right figure shows the net distance from the anchor to the edge of the steel plate. Represented as ,in , All measurements are in millimeters; the two lower limits intersect at approximately 13.33 mm thickness, and the lower limit of the clear distance is 180 mm when the thickness is 30 mm. The lower limit of the clear distance does not replace the load-bearing verification of the anchorage and splice. The 12 mm to 24 mm range in the figure is the thickness range given in the text, and does not mean that a plate thickness of 24 mm to 30 mm is excluded in high-bay conditions; the actual selection is still subject to the constraints of component verification.

[0081] Figure 5 The initial and reinforced preload rates in the left figure are both calculated using the design tensile force of the same tie rod as the denominator, ranging from 15% to 35% and 30% to 60% respectively; the horizontal axis represents the proportion of this design tensile force to the yield strength of the member, ranging from 20% to 65%. Although the two windows overlap, the second preload in the same compartment should still be greater than the first preload. The right figure uses... and set The value is 0.20, obtained by preserving the tensile relationship. The release coefficients are taken from 0.2 to 0.8 in increments of 0.1, corresponding to retention ratios of 0.84, 0.76, 0.68, 0.60, 0.52, 0.44, and 0.36, respectively. Blue bars represent calculated values ​​for each release coefficient, and the orange horizontal dashed line represents the minimum retention ratio of 0.20. Each bar represents a comparison of parameter values ​​under fixed pre-release tension and fixed lower limit conditions; these are not measured data or fitting results. The horizontal axis does not represent construction time or the order of step-by-step unloading. The retention ratios in this figure are obtained by normalizing from a positive pre-release tension; when the pre-release tension is zero, this ratio is not used, and the actual force and design lower limit are directly used for verification.

[0082] Figure 6 The left figure shows the nominal cross-sectional area density per unit column height calculated based on a solid circular nominal section. .in Nominal diameter, The spacing along the column height is in millimeters. Measured in square millimeters per meter; length conversion factor 1000 corresponds to one meter. Diameters from 20mm to 50mm and spacing from 300mm to 900mm are shown in the diagram for comparing nominal geometric configurations. The control formula... This refers to the actual effective cross-sectional area of ​​the tie rod under stress, and should be used separately from the nominal area in this drawing. This density is calculated using one tie rod of the same specification per floor in the same direction as the geometric unit, and is not based on steel content, reinforcement ratio, or full-section confinement strength. The total number of multiple or orthogonally arranged tie rods should be itemized according to the actual quantity.

[0083] Figure 6 The right figure uses initial preload rates of 15%, 20%, 25%, 30%, and 35% as columns, and reinforced preload rates of 30% to 60%, in 5-percentage-point increments, as rows. The values ​​within each cell represent the difference between two preload rates, expressed as percentage points. Of the 35 combinations, the three groups with a reinforced rate no higher than the initial rate are indicated by slashes and crosses; the remaining 32 groups only meet the stage size relationship and still require verification of the component's allowable conditions. The slow-release variable and target retained tensile force are determined by... Figure 5 And the corresponding sustained-release formula explanation.

[0084] To verify the dimensions and execution sequence, the following explicitly set calculation inputs are retained: design tension of the tie rod 100kN, first preload of the same compartment 25kN, allowable range of 30kN to 60kN during the reinforcement stage. It is 40kN. It is 41kN. The value is 2kN. Let... For 200,000 MPa, For 500mm², It is 160,000 mm²; , , The values ​​are 0.50, 0.05, and 0.20 respectively. The value is 0.00001 per degree Celsius. The target and input strains are 0.00025 and 0.00020, respectively; the target and input pressures are 0.020 MPa and 0.015 MPa, respectively; and the temperature reference and input are 30℃ and 25℃, respectively. All kilonewtons are converted to newtons before calculation. These parameters are for arithmetic verification and are not actual measured values ​​of the component or approved construction allowable values.

[0085] Substituting the target correction terms, the strain, pressure, and temperature terms are 2500N, 40N, and 1000N respectively. It is 3540N. The target value is 43540N. This target is within the reinforcement allowable range set in the example and is higher than the first preload force in the same compartment. The current 41000N differs from the target by 2540N. Constrained by the single-use upper limit of 2000N, it is first adjusted to 43000N. After this step of locking and verification, if the actual feedback is 43000N and the detection input remains unchanged, the next step is to adjust only the remaining 540N. If the actual feedback differs from the command value, the next step uses the actual feedback to recalculate the remaining difference.

[0086] Sustained release is set up separately It is 50kN. It is 10kN. If it is 0.50, then The initial tension is 30kN, and 20kN is planned to be released from the 40kN minimum retention force. The upper limit for a single change is set at 5kN. A general example step difference is used, with 10% of the current tension as the threshold. When approaching the target, the final stage is selected based on the remaining difference. The results are shown in Table 2. All inputs are assumed to be the actual tension that has been verified after the previous step. This round... Maintain a constant load of 50 kN, with a target of 30 kN.

[0087] Table 2. Step-by-step unloading calculations for the sustained-release example.

[0088] Level Adjust the tension (kN) before adjustment. Unloading volume (kN) Percentage of current tension (%) Adjusted tension (kN) 1 50.000 5.000 10.0000 45.000 2 45.000 4.500 10.0000 40.500 3 40.500 4.050 10.0000 36.450 4 36.450 3.645 10.0000 32.805 5 32.805 2.805 8.5505 30.000

[0089] Table 2 shows the final stage unloading of 2.805 kN, approximately 8.5505% of the actual tension before adjustment for that stage; each step does not exceed the 5 kN single-pass upper limit used in the example. This set of inputs keeps all stage differences within the normal range of 5% to 20%, but the restricted small steps and final stage under general inputs are allowed to be below 5%, so the proportional distribution in this table should not be interpreted as a forced lower limit. Each stage continues operation based on actual feedback and status verification.

[0090] To illustrate the boundary actions after removing the mandatory lower limit, an additional arithmetic check is performed: With the current actual force at 31 kN, the fixed target at 30 kN, the selected normal proportion at 10%, and a single-step upper limit of 5 kN, comparing the candidate quantity of 3.1 kN with the remaining quantity of 1 kN, a 1 kN convergence step is allowed, which is approximately 3.2258% of the current force, preventing a situation where there are no usable steps due to less than 5%. After execution, confirmation based on actual feedback and stability conditions is still required; the measured value cannot be assumed to be exactly 30 kN simply by subtracting 1 kN from the instruction of 31 kN. This boundary example and Table 2 are used for arithmetic and program sequence checks and do not represent results already measured on-site.

Claims

1. A staged constraint construction method of a CFST box composite column, characterized in that, include: Assemble a box-shaped steel component consisting of four steel plates forming a column cavity. Connectors are installed at the joints of adjacent steel plates to divide the column cavity into at least two sequentially poured sections along its height. Each section is equipped with a transversely adjustable pre-tightening tie rod spaced along the column height. The two ends of the tie rod are connected to anchors on the outer side of the steel plates. Continuous isolation protection is provided between the rod section inside the column cavity and the concrete, so that the rod can still expand and contract axially after the concrete hardens. Force detection devices are installed at the anchoring ends. Pressure and temperature sensors are installed in each section, and strain detection devices are installed on the outer surface of the corresponding steel plates. Construction proceeds from bottom to top, compartment by compartment. Before pouring the current compartment, the initial preload is determined and applied based on the initial strain of the steel plate and the design lateral constraint requirements of the compartment. This causes controlled elastic pre-deformation of the relative steel plate. During pouring and curing, lateral pressure, temperature, steel plate strain, and actual tensile force are collected to obtain strength development data. Once the concrete strength of the current compartment reaches or exceeds the selected strengthening threshold, and the pressure, steel plate strain, and anchorage condition are qualified, the corresponding tie rods are adjusted in stages to a second preload higher than the first preload of the same compartment. After verification and locking, initial preload is applied to the adjacent compartment to be poured above, and then the compartment is poured. During the construction of the adjacent compartment, the lower compartment is kept anchored and construction continues. The lower compartment constraint is monitored until the uppermost compartment is reinforced. After all compartments reach the design strength and the residual pressure, steel plate strain, and temperature meet the preset stability conditions, the tension is gradually released from the middle of the column to both ends under the target retention tension constraint. At each stage, the pressure, steel plate strain, and anchorage status of the current compartment and adjacent compartments are checked. Only after passing the check can unloading continue or the process be advanced to the outer adjacent compartment. After the target is reached and the check is passed, the tie rod is retained for anchorage. Among them, the target preload force during the pouring and curing stages is determined based on the steel plate strain, concrete lateral pressure, and temperature changes. The actual adjustment is simultaneously constrained by the allowable tension of the corresponding stage, the upper limit of a single change, and the target residual difference. 2.The CFST box column method according to claim 1, wherein, The connectors include connecting plates, bolted connectors, or welded connectors located at the splicing edges of adjacent steel plates. The adjacent steel plates are connected by welding, bolting, or a combination of welding and bolting to form a closed box, and the box-shaped cross-sectional dimensions are maintained during concrete pouring and pre-tightening. 3.The CFST box column method according to claim 1, wherein, The continuous isolation protection includes a continuous sleeve covering the rod segment inside the column cavity and a flexible seal at the end of the sleeve. The sleeve contains a non-consolidated anti-corrosion medium, and the rod does not form a direct bond with the concrete inside the silo. The sleeve does not act as a pressure-bearing support between the relative steel plates. The anchoring end is equipped with a pressure-bearing component, a locking nut, and a force detection device. The pressure-bearing component transmits the anchoring reaction force to the anchor seat and the steel plate. The tension rod force is adjusted by the threaded adjustment part or the hydraulic tensioning part, and the locking part maintains the anchoring state. The adjustment part is located outside the steel plate and maintains the operating space.

4. The CFST box column method according to claim 1, wherein, A construction joint control zone is set between adjacent pouring sections. When the next pouring section is being constructed, the connecting steel bars extend out of the top surface of the concrete. Before pouring the next pouring section, the top surface is roughened or roughened so that the connecting steel bars cross the construction joint control zone and are anchored into the concrete of the two adjacent pouring sections to form a continuous force transmission path between the sections. 5.The CFST box column method according to claim 1, wherein, The pressure sensor is installed in the contact area between the concrete and the steel plate in the pouring chamber, and the temperature sensor is installed in the internal area of ​​the concrete in the pouring chamber, so as to obtain data on the lateral pressure of the concrete on the steel plate and the temperature change data inside the concrete, respectively.

6. The CFST box-shaped composite column staged constraint construction method according to claim 1, characterized in that, The strength development data is obtained from the strength of specimens cured under the same conditions as the corresponding pouring chamber, or from the maturity-strength relationship calibrated based on the temperature history of the chamber and the same concrete mix proportion. The strength values ​​used to determine the strength threshold adopt the same test and statistical methods as the reference strength.

7. The CFST box-shaped composite column staged constraint construction method according to claim 1, characterized in that, The first preload is determined based on the initial strain of the steel plate before pouring and the lateral constraint requirements of the silo design. It is applied in a symmetrical, graded loading manner. After each round of loading, the strain of the steel plate, the displacement of the anchor seat, and the elongation of the tie rod are checked to keep the steel plate in an elastic working state.

8. The CFST box-shaped composite column staged constraint construction method according to claim 1, characterized in that, Based on the calibration records of the corresponding structural and construction stages, determine the benchmark tensile force, strain target, pressure target, temperature benchmark, and correction coefficient. Add the target tensile force correction amount formed by steel plate strain, concrete lateral pressure, and temperature state to the benchmark tensile force to obtain the target preload. Keep the benchmark and parameter versions unchanged within the same stage. After the target preload is checked within the allowable range of the corresponding stage, perform a single amplitude limit adjustment based on the difference between it and the actual feedback tensile force at the same anchorage end. After each adjustment, verify the actual force, pressure, steel plate strain, and anchorage status at both ends. Stop the new adjustment command when the data is invalid or the component status is unqualified.

9. The CFST box-shaped composite column staged constraint construction method according to claim 1, characterized in that, Identify the starting pouring chamber corresponding to the geometric center of the column based on the actual upper and lower elevations of each pouring chamber. The pouring chamber is gradually expanded upwards from the starting pouring chamber to both the upper and lower ends. When the geometric center corresponds to two pouring chambers or when the entire column has only two pouring chambers, the two pouring chambers are operated symmetrically with small differentials. After each operation, the pressure, steel plate strain, and anchor condition of the current chamber and adjacent chambers are checked. The subsequent unloading and advancement are then determined based on the check results.

10. The CFST box-shaped composite column staged constraint construction method according to claim 8, characterized in that, Before the corresponding tie rod begins to release, record the actual tension at the same measurement position, and determine the target retention tension by combining the designed minimum retention tension and the release coefficient. During unloading at each stage of the same round, keep the recorded actual tension before release, the designed minimum retention tension, the release coefficient, and the target retention tension unchanged. Candidate unloading amounts are generated based on the selected conventional unloading ratio according to the current actual tension. The difference between the current actual tension and the target retained tension is determined as the remaining difference. The unloading amount of the actual command is a positive value that does not exceed the minimum of the candidate unloading amount, the pre-determined single change upper limit of the slow release stage, and the remaining difference. When limited by the single change upper limit of the slow release stage or close to the target retained tension, a convergence step lower than the conventional unloading ratio is allowed. The conventional unloading ratio is not used as the lower limit of forced unloading. The actual force value is reread at each stage and the current compartment and adjacent compartments are checked. The allowable confirmation deviation of the target retained tension is determined before construction based on measurement uncertainty, execution repeatability, and component allowable conditions. Automatic action stops when there is no indistinguishable positive adjustment and the termination condition is not met. The completion judgment is not replaced by exceeding the target retained tension or reducing the design minimum retained tension.

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