Case Study of PLC Synchronous Lifting Technology in Concrete Column Reinforcement: Design, Construction, and Monitoring

Abstract

Traditional support methods, such as full-frame scaffolding, often pose significant safety risks during the replacement of defective concrete. In contrast, the application of programmable logic controller (PLC) synchronous jacking technology combined with an encircling beam is an innovative approach to concrete replacement. However, there is currently a lack of effective theoretical guidance for determining its design parameters, and there are also few measured data available to verify its effectiveness. To address this issue, this study investigates a concrete structure in which it was discovered, during the topping-out phase, that the compressive strength of several load-bearing columns did not meet the design specifications. Through structural analysis and load calculations, a reinforcement scheme utilizing the synchronous jacking system in conjunction with an encircling beam was proposed to replace the defective concrete. The monitoring of the settlement and deformation during the replacement process revealed a minimal settlement of 0.45 mm, which is approximately 23% of the predefined warning threshold. The results demonstrate that the integration of the synchronous jacking system with an encircling beam offers a safe and reliable solution, thus providing an effective approach to addressing similar challenges in concrete structural reinforcement.

1. Introduction

The ongoing acceleration of urbanization, coupled with the prolonged service life of many buildings, has raised concerns regarding the structural integrity of aging constructions. Among various structural components, concrete columns are particularly prone to degradation due to their fundamental role as primary load-bearing elements. Over time, this deterioration becomes especially evident in structures that have not received timely maintenance or retrofitting, increasing the risk of compromised safety and performance [1,2,3,4]. Concrete columns not only support routine operational loads but also experience substantial stress from external forces such as earthquakes and wind loads [5,6,7,8]. Any damage or deterioration in these columns can significantly compromise the structural stability of an entire building or result in localized collapse, thereby posing serious risks to occupant safety. Furthermore, the design and construction standards of many older buildings are significantly lower than modern requirements, rendering them inadequate to meet current functional and safety demands [9,10,11]. As a result, aging buildings often fail to provide sufficient structural protection when exposed to new loading conditions and environmental factors. Improving the load-bearing capacity of concrete columns, extending their service life, and ensuring their overall structural safety have thus become pressing challenges in the field of structural reinforcement [12,13,14].

To address these issues, various reinforcement methods have been developed for concrete structures [15,16,17,18]; these include section enlargement, external steel jacketing, surface-bonded fiber-reinforced composites, and replacement reinforcement. Among these, the replacement reinforcement method, which involves removing defective concrete and replacing it with material that meets particular design specifications, has attracted increasing attention. This approach effectively addresses the problems associated with insufficient concrete strength without altering the original cross-sectional dimensions of the columns, thus preserving the architectural and spatial configuration of the building [19,20,21]. Several studies have demonstrated the feasibility and benefits of this method. For example, Liu reported that structural displacement during the replacement process was minimal and had a negligible impact on the superstructure [22]. Other researchers found that, among various reinforcement schemes, the replacement method was the most reliable and cost-effective for strengthening shear walls [23]. Zhang et al. demonstrated that replacing the concrete at both ends of low-strength shear walls can significantly improve their seismic performance, and that with a sufficient replacement length, the reinforced walls can achieve seismic behavior comparable to those constructed using design-strength concrete [20]. Overall, replacement reinforcement has proven effective for structures with low concrete strength or severe localized defects, particularly in newly constructed buildings with poor-quality concrete. However, the method is associated with certain risks, especially during construction. It requires well-designed safety protocols, including the selection of appropriate temporary support systems to ensure structural stability throughout the process. Commonly used systems, such as full-frame scaffolding, often involve complex design and stringent implementation standards, where any oversight may jeopardize construction safety [24,25,26].

To address the limitations of traditional reinforcement methods—such as low precision, high labor intensity, and the risk of structural instability—an innovative approach that combines programmable logic controller (PLC) synchronous jacking technology with the use of an encircling beam has been developed. The encircling beam is a specially designed steel frame that wraps around structural components such as columns to form a closed or semi-closed load-bearing system. During the replacement process, two encircling beams are installed at the top and bottom of the damaged concrete section, with hydraulic jacks positioned in between. When activated, the jacks lift the structure slightly, transferring the axial load originally borne by the defective concrete to adjacent structural elements via the encircling beams. This ensures overall stability throughout the operation. Central to this method is the PLC synchronous jacking system, which integrates electrical, mechanical, and hydraulic control technologies to achieve highly coordinated motion [27]. The system enables the real-time monitoring of displacement, pressure, and velocity at each jacking point. Based on sensor feedback, the PLC automatically adjusts the opening of hydraulic valves to control the speed and position of each jack with millimeter-level precision. This automated, closed-loop system eliminates the differential displacement that is common in manual lifting, thereby improving both the accuracy and on-site safety of construction. Moreover, it reduces reliance on skilled labor and minimizes the risk of human error, making the method particularly suitable for complex retrofitting scenarios that demand high precision and low disturbance.

Despite the clear technical advantages of this combined PLC jacking and encircling beam system, it has rarely been applied in engineering. To bridge this gap, the present study investigates a real-world case of concrete column reinforcement conducted in Xiamen, China. The primary objective of this study is to demonstrate the feasibility, safety, and performance of PLC-controlled synchronous jacking combined with an encircling beam system in the context of column replacement reinforcement. By detailing the design scheme, construction process, and monitoring results, this case study not only validates the system’s millimeter-level deformation control and zero-disturbance performance but also provides valuable insights for similar future projects. The findings highlight the system’s potential to serve as a safe, reliable, and replicable solution to modern structural reinforcement.

2. Project Overview

The reinforcement and renovation project of Building 1# is situated in Jimei District, Xiamen, China. The total building height of this project is 57.85 m (locally 14.05 m), with thirteen floors above ground and one underground floor. Although the main structural frame has been topped out, the infill walls, excluding those for stairwells and elevator shafts, have not yet been installed. Recent strength verification tests revealed that several concrete columns did not meet the original design specifications, necessitating structural reinforcement. Among the available reinforcement techniques, methods such as section enlargement and external steel jacketing were considered. However, these approaches tend to increase the cross-sectional dimensions and interfere with the architectural layout. In contrast, the replacement reinforcement method offers distinct advantages: it restores structural performance without altering the existing spatial configuration, while enabling improvements in accuracy, reduced settlement, and faster construction. Given these benefits, the replacement reinforcement approach was adopted for this project. The method involves removing the defective concrete and recasting the columns using higher-strength concrete to recover their load-bearing capacity.

3. Collaborative Reinforcement Scheme Adopting PLC Synchronous Jacking System and Encircling Beam

3.1. Design Load Review

The service life of the structure in this project needs to satisfy the original design requirements through replacement and reinforcement. The replacement load was calculated according to the standard value of the top load of each column, and required adjustment taking into account the actual situation on site at the same time. During the replacement process, all loads, except for dead loads, within the load transmission range of the replaced columns were systematically removed (e.g., pile loads, live loads). As a result, the live load on the floor was set to 0 kN/m², and the dead load of the floor was its own weight with a value of 0.5 kN/m². By using structural analysis software PKPM2021, the standard load values at the top of each replacement column could be calculated. Taking the sixth floor as an example, there were four concrete defective columns, including 7/D, 10/D, 15/D, and 11/A. The load standard values are shown in

Table 1. Information on the replacement columns.

No.	Location	Load Standard Value of Column (kN)	Seamless Steel Pipe Type Between Encircling Beams	Encircling Beam Type
1	7/D	2159	Φ219 × 16	II
2	10/D	3656	Φ219 × 16	II
3	15/D	1605	Φ180 × 12	I
4	11/A	2002	Φ219 × 16	II

, and the location distribution is shown in Figure 1.

3.2. PLC Synchronous Jacking System and Encircling Beam

Two encircling beams were set up at the upper and lower positions of the defective column, in which the defective concrete needed to be reinforced. Seamless steel pipes and jacks were then installed between the upper and lower encircling beams, as seen in Figure 2. It can be seen that the jacks are located on the seamless steel pipe, in which the upper load can be transferred to the lower concrete column without passing through the defective columns. The reinforcement steel used in this project was primarily HRB400, a common hot-rolled ribbed rebar (China New Steel Group Co., Ltd., Xuzhou, China) in China with a nominal yield strength of 400 MPa that is suitable for load-bearing structural elements. The welding rods employed were E5016, a low-hydrogen electrode with a tensile strength of ≥500 MPa that is known for its good crack resistance and weldability. For the replacement steel supports between the encircling beams, seamless steel pipes with specifications of Φ180 × 12 and Φ219 × 16 were utilized, as shown in Table 1. Additionally, a seamless steel pipe with a diameter of Φ159 × 8 was used to support the beam end of each floor, which can be seen clearly in Figure 2. The choice of these diameters and wall thicknesses ensured a sufficient axial bearing capacity while maintaining a manageable installation weight. Notably, the grouting material used in this project has a strength grade of C30 and all structural adhesives used were A grade unless otherwise specified.

There are several key steps in the construction of the encircling beam, including sequential orientation location and line setting, surface cleaning, interface roughing, drilling and rebar placement, formwork installation, formwork inspection, rebar binding, rebar inspection, the positioning of embedded components, concrete pouring, concrete curing, and formwork removal. According to the CECS 295-2023: Technical Specification for Building and Structure Replacement Technology [28], for the interface between new and old concrete, it should be noted that the original surface should be made into a rough surface with a concave–convex difference of more than 6 mm, and shear steel bars should be used. The vertical bearing capacity P of the interface b is calculated as follows:

$$P\le (0.56f_s{A}_s+0.16f_c{A}_c)/\gamma$$

(1)

where P is the vertical bearing capacity of the interface between the new and old concrete, f_s is the design value of the tensile strength of the rebar planted on the joint surface, A_s is the summary area of the rebar planted on the same section of the joint surface, f_c is the design value of the compressive strength of the beam and column concrete, A_c is the effective area of the interface between the new and old concrete, and γ is the comprehensive reduction influence coefficient of the interface bearing capacity.

Based on the standard values of column top loads provided in Table 1, two types of encircling beams were adopted for the replacement of four defective concrete columns on the sixth floor. The corresponding structural configuration and reinforcement details are provided in Figure 3, using Type I as a representative example. Specifically, Type I and Type II encircling beams differ primarily in their jack capacities and steel pipe dimensions. Type I beams employed 100 t (metric tons) hydraulic jacks and seamless steel pipes with dimensions of Φ108 × 12 mm, while Type II beams adopted 200 t (metric tons) jacks and Φ219 × 16 mm pipes to accommodate higher loading demands. In both configurations, four jacks were positioned above the steel pipe and below the upper encircling beam, following the design principle of maintaining a safety factor greater than 2.0.

The PLC synchronous jacking system consists of a hydraulic jacking control pump station, sensor, oil pipe, distributor, a remote-control system, and hydraulic jacks, As shown in Figure 4. This system enables the precise lifting and positioning of a large-scale, heavy or complex structure by dynamically adjusting it based on feedback from displacement and pressure sensors, which is applicable to structural components with any weight distribution. The synchronous jacking process mitigates bending, twisting, or tilting effects caused by uneven weight distribution or load variations among different jacking points. A single PLC continuously monitors the displacement and load at each jacking point, and adjusts the hydraulic flow accordingly to ensure high-precision position control. This automated control system eliminates the need for manual intervention when load displacement deviations occur; thus, the efficiency and safety of the jacking operation are improved.

3.3. Construction Process

The complete construction process for the replacement and reinforcement of defective concrete columns includes the following steps: construction preparation, encircling beam construction, temporary slab opening at the excavation location, the installation of temporary supports, the removal of defective concrete, the cleaning and supplementation of longitudinal reinforcement and stirrups, formwork installation, the preparation and casting of high-strength non-shrink grout (C60), formwork removal and curing, the removal of temporary supports, and finally, the cutting of the encircling beam and the restoration of slab openings. In particular, the construction of the encircling beam involves the surface roughening of the defective column, the application of a 1–2 mm thick interface bonding agent, the installation of shear-resistant reinforcement and stirrups, formwork installation, and the casting and curing of C60 high-strength non-shrink grout. The grout used features a compressive strength of no less than 60 MPa after 28 days, a shrinkage rate not exceeding 0.02%, and excellent fluidity and bond performance, which together ensure its dimensional stability and structural reliability. The construction sequence is further illustrated in Figure 5, and the completed encircling beam can be seen in Figure 6.

4. Monitoring Plan and Result

4.1. Monitoring Plan

Under the entire replacement and reinforcement process of defective concrete columns, real-time stress and deformation monitoring of the main building and encircling beam are essential to ensure the safety of construction. Therefore, according to the construction plan and relevant specification [29], a monitoring program was conducted; this included the inclination and vertical settlement of the main building and the settlement of the replacement column. For the vertical settlement of the main building, observation points were located at the four corners of the building and on the internal column foundation, 1000 mm above the ground; for the settlement of the replacement column, observation points were set on the concrete column requiring reinforcement. Regarding the inclination of the main building, four sets of monitoring points were used, with each set including two points; these were arranged on the upper and lower parts of the main building, respectively. Notably, each set of points was aligned vertically. A total of 61 vertical displacement monitoring points were strategically installed, including 42 points on the main building and 19 settlement monitoring points on the replacement columns.

The monitoring of the settlement and inclination of the main building spanned ten months, and 24 monitoring sessions were conducted, in which the monitoring frequency was once per week from the first month to the third month, once every 15 days from the fourth month to the seventh month and once a month from the eighth month to the tenth month. As for the 19 replacement columns, the settlement monitoring time for each column lasted three weeks. During the column replacement process, designated personnel were assigned to perform real-time monitoring. After replacement, monitoring was conducted once a day within the first 7 days, and every 3 to 5 days from 7 to 21 days.

This monitoring schedule was planned to cover critical phases of the structural response, especially during and shortly after column replacement. The frequency and duration were sufficient to capture both immediate and delayed deformations, with the results showing no abnormal displacements. Therefore, long-term monitoring is not currently required, though provisions have been made for future tracking if needed.

4.2. Monitoring Results

Safety monitoring is very important in engineering construction, providing feedback on the quality of design and construction so that the stability and safety of the building can be ensured. During the monitoring of this project, it was found that the main building had no tilt displacement, which indicates that it has not tilted.

Table 2. Monitored vertical displacement value distribution of main building (mm).

Point Number	Monitoring Times
	1	2	3	4	5	6	7	8	9	10	11	12	13	14
C1–C5	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C6	0	0	0	0	0	−0.1	0	0	0	0	0	0	0	0
C7–C9	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C10	0	0	0	−0.1	0	0	0	0	0	0	0	0	0	0
C11–C12	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C13	0	0	−0.1	−0.1	0	0	0	0	0	0	0	0	0	0
C14–C15	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C16	0	0	−0.1	0	0	0	0	0	0	0	0	0	0	0
C17–C21	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C22	0	0	0	−0.1	0	0	0	0	0	0	0	0	0	0
C23	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C24	0	0	0	−0.1	0	0	0	0	0	0	0	0	0	0
C25–C26	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C27	0	0	−0.1	0	0	0	0	0	0	0	0	0	0	0
C28–C42	0	0	0	0	0	0	0	0	0	0	0	0	0	0

shows the results of 14 rounds of vertical displacement monitoring at 42 monitoring points in the main building. Most monitoring points exhibited negligible settlement, while a few—such as C6, C10, C13, C16, C22, C24, and C27—recorded minor displacements between −0.1 mm and −0.2 mm.

Table 3. Monitored vertical displacement value distribution of replacement column (mm).

Point Number	Monitoring Times
	1	2	3	4	5	6	7
1	0	−0.10	−0.03	−0.25	−0.04	0	0
2	0	−0.05	−0.03	−0.22	−0.05	0.02	0
3	0	−0.01	−0.03	−0.20	−0.03	0	0
4	0	−0.11	−0.05	−0.19	−0.04	−0.01	0
5	0	−0.12	−0.05	−0.15	−0.02	0	0
6	0	−0.10	−0.03	−0.21	−0.03	0	0
7	0	−0.11	0	−0.24	−0.02	0	0
8	0	−0.08	−0.03	−0.23	−0.03	0	0
9	0	−0.04	−0.03	−0.25	−0.02	0	0
10	0	−0.12	−0.02	−0.21	−0.02	0	0
11	0	−0.02	−0.02	−0.26	−0.01	0	0
12	0	−0.11	−0.01	−0.32	−0.01	0	0
13	0	−0.09	−0.02	−0.20	−0.03	0	0
14	0	−0.03	−0.02	−0.22	−0.01	0	0
15	0	−0.09	−0.02	−0.20	−0.03	0	0
16	0	−0.12	−0.02	−0.24	−0.03	0	0
17	0	−0.13	−0.02	−0.26	−0.01	0	0
18	0	−0.10	−0.02	−0.20	−0.02	0	0
19	0	−0.15	−0.02	−0.22	−0.01	0	0

summarizes the monitoring data for 19 replacement columns, showing that settlement primarily occurred during the first four to five monitoring cycles and gradually stabilized thereafter. Figure 7 visually illustrates the cumulative vertical displacements of both the main building and the replacement columns. The maximum settlement displacement was 0.20 mm for the main building and 0.45 mm for the replacement columns. Both values remained well below their respective warning thresholds—0.2% of the center-to-center distance between adjacent column foundations for the main building, and 2.00 mm for the replacement columns—leaving a 1.55 mm safety margin for the latter. These findings confirm that the structural system remained stable and that the reinforcement process maintained displacement within safe and controlled limits throughout construction.

5. Economic Implications and Practical Advantages

In this project, the use of a PLC synchronous jacking system combined with an encircling beam significantly improved the efficiency and cost-effectiveness of construction. The replacement of four defective columns was completed in approximately 9 working days, compared to the 15–20 days typically required by traditional reinforcement methods. Labor costs were reduced by 25–30% due to automation, and precise deformation control prevented secondary structural damage, potentially saving CNY 30,000–50,000 in repair costs per engineering project. Although the initial equipment cost was 15–20% higher, the overall economic benefits—including reduced labor, a shorter construction period, and improved safety—make this method a time-saving, cost-efficient, and reliable solution for structural retrofitting, especially in complex or space-constrained environments.

6. Conclusions

This study has introduced a novel structural reinforcement method that integrates a PLC synchronous jacking system with encircling beam technology to achieve the precise replacement of defective concrete columns. By combining intelligent control with conventional reinforcement measures, the method demonstrates outstanding deformation control, enhanced construction safety, and strong practical feasibility in real-world applications. The main conclusions are as follows:

(1)

A precise and minimally invasive method was developed, integrating PLC synchronous jacking with encircling beam technology. This system enabled millimeter-level vertical displacement control and ensured operational safety during the replacement of damaged columns.

(2)

The method was validated in a full-scale engineering application. The monitoring data showed that all deformations remained well below safety thresholds, with the maximum settlement not exceeding 0.5 mm, confirming its safety, reliability, and controllability.

(3)

The method enhances efficiency and cost-effectiveness. Column replacement was completed in 9 days, compared to the 15–20 days required by traditional methods. Automation cut labor costs by 25–30%, while precise control prevented the occurrence of secondary damage, saving up to CNY 30,000–50,000 per project. Despite there being a 15–20% higher initial equipment cost, the overall benefits outweigh the investment, especially in complex retrofit scenarios.

Future work will explore the integration of finite element modeling (FEM) and artificial neural networks (ANN) to better simulate structural behavior and enable adaptive control, enhancing the system’s intelligence and robustness.