Precast Concrete Segments Research Articles

Experimental and numerical investigation of flexural behavior of precast tunnel segments with hybrid reinforcement

Precast concrete segments reinforced with a combination of steel fibers and conventional rebar (RC-SFRC) have gained prominence in the mechanized construction of tunnels in recent years due to the advantages offered by this hybrid reinforcement solution in enhancing the mechanical behavior of these structural members. This research aims to understand better the flexural behavior of RC-SFRC tunnel segments proposed to replace conventional reinforcement in São Paulo Metro Line 5. An experimental program and numerical analyses using a multiscale model were conducted to predict the post-cracking parameters of SFRC through three-point bending tests according to EN14651 and assess the flexural behavior of full-scale tunnel segments. In both scenarios, 2D multiscale numerical models with discrete and explicit representations of the reinforcements were applied. The comparison of numerical and experimental results in terms of crack width, mean crack spacing, deflection, and the ultimate and service loads derived from design predictions demonstrate that the proposed RC-SFRC reinforcement represents an advantageous alternative, significantly enhancing the performance of the segments for both serviceability and ultimate limit states. Furthermore, the responses show that the adopted numerical strategy is promising and can be consolidated as a tool for optimizing the design process.

Lok-Test and Capo-Test pullout for in-situ concrete strength

Among the test systems for in-place concrete strength available today, two measure the in-place physical strength, pullout, and cores. Both systems are dealt with in detail in this paper, the pullout systems named LOK-TEST/CAPO-TEST (ASTM C900-19) and coring (ASTM C42/42M-18). Testing in-situ with accurate test systems will reveal effects on the final strength from a potential mix’s over transportation, pumping, consolidation, compaction, and curing. With the LOK-TEST system testing of the pre-installed inserts takes 4–5 minutes each, easily and with only one small suitcase brought along. The CAPO-TEST, originally designed to supplement the LOK-TEST, takes 15–20 minutes for each test to be performed anywhere on a structure without pre-installed inserts. No large holes are left in the structure from coring and thinner elements may be tested without weakening them structurally. The pullout test provides accurately the In-Place Strength without testing cores and the duration is about 15 minutes compared to 3–4 days for coring correctly cured. General robust correlations to strength of standard specimens exist no matter what parameter is considered for normal concrete, even for carbonation of the surface layer. With the systems the cover layer protecting the reinforcement may be checked efficiently and quickly, not at least in areas with dense reinforcement or on slim structures. Bad curing conditions are revealed and the consequences in terms of reduced service life for presence of chlorides or carbonation may be estimated swiftly. This paper is benchmarking 50 years of successful in-situ concrete strength measurements, from studies of the failure mechanism and laboratory/on-site correlations to full scale testing of structures in Europe, Scandinavia, and Canada. Six testing cases with emphasis on pullout and cores are illustrating different applications: Case 1. Production testing at the Great Belt Link, Denmark. Case 2. Service life of bridge pier, Great Belt Link, Denmark. Case 3. Curing of the cover layer evaluated by pullout and conductivity, Denmark. Case 4. Strength testing with CAPO-TEST for further loading of old bridges, Poland. Case 5. In-Situ compressive strength testing of quarantined precast concrete tunnel lining segments using CAPO-TEST, UK. Case 6. Safe and early loading with LOK-TEST, Canada. Other cases are given on www.NDTitans.com

Detecting wire breaks in post-tensioned tendons of wind turbines: A signal energy spectrum analysis approach

In the wind industry, recent advancements have led to the research and development of wind turbines featuring hybrid towers, a novel combination of steel tube and precast concrete segments. These concrete modules, which absorb the high stresses caused at the intersection between the tower and its foundation, are commonly joined with post-tensioned tendons. This study focuses on the identification of wire breaks in post-tensioned tendons through the application of acoustic emission testing. Measurements involve the evaluation of wire breaks under controlled laboratory conditions and the analysis of the dynamic operational environment of a functioning wind turbine. The investigation encompasses the development and assessment of a methodology based on principles of discrete Fourier transformation and Parseval’s theorem for analyzing the frequency-dependent energy distribution of acoustic signals. This analytical approach extends to the examination of wire breaks generated under varying stress levels as well as the operational noise within the actual wind turbine. The findings demonstrate a notable concentration of energy within the frequency range of 5-20 kHz in the wire break signals. In contrast, the operational noise signals show a distinct pattern, presenting an extreme value distribution within the 0-2 kHz range. The developed methodology exhibits robustness, even in the presence of high background noise levels, establishing itself as a valuable tool for wire break detection. Additionally, its potential for integration with machine learning algorithms offers the prospect of automated wire break detection, enabling further advancements in structural health monitoring for wind turbines.

Study via the finite element method of the behavior of deck joints in a bridge composed of precast concrete segments

AbstractThere is a demand for research to better understand the structural performance of segmental bridge joints. In this context, the main objective of this work is to present a 3D numerical modeling using the Finite Element Method (FEM) to physically simulate the behavior of concrete joints in a segmental concrete bridge. The analysis was conducted using the design of a real bridge, and the structure studied was the main span of the New Guaíba Bridge, located in Porto Alegre, RS, Brazil. The modeling was implemented using ANSYS software, version 21.2. The simulation considers a complete model of the span to provide a more realistic determination of the joint openings and the stress distributions in the elements. It is crucial to emphasize that the results obtained from the model do not reproduce the observed behavior of the studied bridge. The analysis considered only one span with simplified boundary conditions and higher loads than those typically adopted in usual design procedures.

Numerical Analysis of Ground Surcharge Effects on Deformation Characteristics in Shield Tunnel Linings

To investigate the deformation characteristics of shield tunnel linings under ground surcharge, finite element software was employed to create a detailed three-dimensional model of the staggered assembly of the shield tunnel lining. This model includes components such as precast concrete segments, reinforcements, and joints (comprising bent bolts, washers, and bolt sleeves). Additionally, the model accounts for interface frictions between segments and the interactions between different rings. The reliability of the numerical model was verified based on the results of a full-scale model test. Additionally, the model accounts for interface frictions between segments and the interactions between different rings. Changes in tunnel convergence, joint tensioning, bolt stresses, reinforcement stresses, and concrete crack development were systematically analyzed. The results indicate the following: (1) the deformation mode of the lining structure under ground surcharge resembles a “transverse ellipse”. Joints located near the haunch opened along the outer arc, while those near the vault and bottom opened along the inner arc. The restraining effect of the bolts on joints opening in the inner arc was greater than that on the outer arc. Notably, when the opening of the inner arc reached 4.9 mm, the bolt stress escalated to the yield strength of 640 Mpa. (2) Under larger loads, the lining structure’s joints are susceptible to greater deformation, resulting in the tensile yielding of local reinforcement within these joints. (3) Cracks predominantly occur near the haunch, vault, and bottom of the lining structure, with the central angle of crack distribution ranging between 70° and 85°.

Experimental Studies on the Seismic Performance of Underwater Concrete Piers Strengthened by Self-Stressed Anti-Washout Concrete and Segments

Given that the existing drainage strengthening methods for underwater damaged piers are expensive, inefficient, and cause shipping traffic disruptions, an urgent need exists to explore undrained strengthening methods, such as the precast concrete segment assembly method (PCSAM). However, the PCSAM has certain limitations, including a considerable strength loss of filled concrete, poor accuracy, poor connection performance of the segment sleeves, etc. Hence, this study developed an improved PCSAM (IPCSAM) by adopting self-stressed anti-washout concrete (SSAWC) as the filling material and developing a lining concrete segment sleeve (LCSS) based on the design principle of shield tunnel lining segments. Subsequently, the seismic performance of the strengthened piers was investigated. First, nine 1/5-scale pier column specimens were designed by considering different influencing factors: the self-stress of the SSAWC, LCSS reinforcement ratio, and initial damage and length–diameter ratio of the pier column. These specimens were tested under low reversed cyclic loading. Second, an extended parameter analysis was performed based on the established numerical models consistent with the quasi-static test’s parameter settings. Finally, a restoring force model of the strengthened piers, including the trilinear skeleton curve model and hysteresis curve model, was established based on the results of the quasi-static test and parameter analysis. The results indicated that the bearing capacity, ductility, and initial stiffness of the specimens strengthened using the IPCSAM increased by approximately 83.5–106.4%, 16.3–50.2%, and 83.9–177.3%, respectively, with the energy dissipation capacity also significantly improved. The self-stress of the SSAWC should not exceed 2.2 MPa, and the recommended ratio of the LCSS thickness to pier column diameter is 1/10. Additionally, the proposed restoring force model is highly accurate and applicable, able to provide a reference for the practical seismic strengthening design of piers.

Effect of test parameters on the punching-shear strength of precast tunnel segments reinforced with GFRP bars

While assessing the load cases is crucial for designing the precast concrete tunnel lining (PCTL) segments, none of the tunnel-specific standards or codes explicitly consider punching-shear loads. This study aimed at determining the structural performance of full-scale precast concrete tunnel segments reinforced with glass fiber-reinforced polymer (GFRP) bars. The segments were constructed with a rhomboidal shape measuring 2100 × 1500 × 250 mm and subjected to point loading on their extrados surfaces until failure. Such loading simulates the geotechnical exposure conditions surrounding tunnels, such as rock expansion. The effects of concrete strength and GFRP flexural reinforcement ratio on the punching behavior were analyzed and are discussed herein. The load–deflection response, failure mode, punching strength, cracking behavior, reinforcement and concrete strain, deformability, and energy absorption were all evaluated in the experiments. The results reveal that increasing both the flexural reinforcement ratio and concrete strength enhanced the punching response and decreased crack width. In addition, using HSC in tunnel segments yielded higher pre-cracking stiffness, punching-shear capacity, and energy absorption. A theoretical investigation involving a comparison between predictions of the FRP-reinforced concrete slab design provisions and experimental results was performed to assess the applicability of the current punching equations for PCTL segments. The equations in the FRP-reinforced concrete codes predicted the punching capacities conservatively, while the researchers’ proposed equations overestimated. Moreover, CAN/CSA S806-12 showed the most accurate prediction of the punching capacity even if the concrete compressive strength exceeded 60 MPa.

Casting and installation of segmental precast quadratic concrete driven geothermal energy piles

Geothermal energy pile foundations are used both for structural purposes and to provide sustainable, clean, and cost-effective ground energy for heating and cooling buildings [1]. The majority of energy piles are cast-in-place concrete piles, which require extensive and expensive drilling during construction. A better alternative is to use precast concrete segmental driven energy piles, which can be cast in large quantities with high-quality assurance at a concrete factory, after which they are transported and installed into the ground [2]. This study aims to present a novel method of casting and installing segmental energy piles that utilize an innovative steel joint [3] for connecting the precast concrete segments on-site. In addition to structural integrity, the steel joint provides the possibility of a leak-proof coupling and continuity for heat-exchanging pipes embedded in concrete segments. The precast-driven pile foundations are made of high-strength concrete with a 14-day compressive strength of almost 80 MPa and have a quadratic shape with a maximum length of 12 m and a square width of 270 mm or 350 mm. In the 270-mm piles, a single U-loop can be used, while in the 350-mm piles, two U-loops can be used as presented in Figure 1. The heat-exchanging pipes are coupled inside the sidewall channels of the steel joint which are shielded using a steel cover plate, riveted to the joint. At the tip of the bottom segment of the piles, there is a strong steel rock shoe with a hardened steel point that allows the piles to penetrate the bedrock [4]. At a construction site, the joint and pipes can be connected quickly without any welding or electric equipment that expedites the installation work and obsoletes the health and safety risk associated with electricity. Utilizing the precast energy piles presented in this study increases the quality, and speed of installation while decreasing the overall cost of the project compared to cast-in-place energy piles. To prove the proper performance of the piles under real construction conditions, structural integrity tests and hydraulic pressure tests were performed according to BS EN 12794:2005 [5] and ASTM F2164–21 [6], and the results are briefly presented and discussed in the present study. Structural integrity tests consisted of impact tests in which 1000 blows imposing a minimum stress level of 28 MPa were applied on the pile segments connected using the new driven energy pile joint. During the impact tests, the pile structure and the joints remained undamaged. After the impact tests, the pipes were pressurized up to 100 psi (690 kPa) and no leakage or pressure drop was observed. Then the pile segments were cut according to the standard into shorter segments and subsequent bending tests were performed to measure the bending capacity. The bending tests show that the driven energy pile joints have a similar bending capacity as conventional normal joints. The results of this study show that segmental precast concrete energy piles using the new steel driven energy pile joints, are a perfect alternative for cast-in-place energy piles, which can provide sufficient structural and bearing capacity and can be used both for heating and cooling buildings.

Preparation and performance of ultra-early strength polycarboxylate superplasticizer

The rapid development of subway and prefabricated building industry, along with the adoption of the “dual carbon” strategy, have put forward higher demands on early strength, environmental protection and high efficiency for precast concrete products and concrete segments. In this study, a ultra-early strength type polycarboxylate superplasticizer (ES) was synthesized successfully by a design molecule structure such as introducting ultra long polyoxyethlene side chains, functional monomer (2-acrylamide-2-methylpropanesulfonic acid), and cationic monomer (Methacrylatoethyl trimethyl ammonium chloride) composition. Discovered through performance testing, the dispersion capacity of ES firstly are increased and then decreased with increasing the acid-ether ratio, and the same trend as the compressive strength harden concrete with ES at the age of 1, 3, and 7 days. The sulfonate groups and cationic monomers into molecular structure, they have little effect on the dispersion capacity, but the compressive strength of concrete at the age of 1, 3, and 7 days get improved. Through camparative study in the setting time of concrete and compressive strength of concrete between ES and an engineering application product SX. The results show that addition of ES does not retard cement hydration, and accelerates the coagulation of cement. Moreover, the compressive strength of concrete is better than SX at all ages, its further verified with X-ray diffraction and Scanning electron microscopy. This study indicates that rational design of molecular structure through the introduction of ultra-long side chains and functional monomers can maximize the early strength performance of polycarboxylate superplasticizer without affecting later strength development.

Quasi-static cyclic behavior of precast high-strength concrete tunnel segments reinforced with GFRP bars

The cyclic behavior of fiber-reinforced polymers (FRP) reinforced precast concrete tunnel lining (PCTL) segments under quasi-static cyclic flexural loading has not yet been experimentally tested and reported on in the literature. This study investigated the cyclic behavior of glass-FRP (GFPR) reinforced precast high-strength concrete (HSC) tunnel lining segments. Full-scale segments measuring 3100 × 1500 × 250 mm were tested under quasi-static cyclic flexural loading. Two cycles of loading and unloading were applied at 1.25%, 2.5%, 5%, 10%, 25%, 50%, and 75% of the maximum displacement obtained from the static testing results, followed by a single cycle up to failure. The test parameters included concrete compressive strength, longitudinal reinforcement ratio and transverse reinforcement configuration (closed ties versus double U-shaped ties). The experimental findings of this study revealed that the GFRP-reinforced HSC PCTL segments exhibited stable hysteretic response until failure. In addition, the test results show that the GFRP-reinforced HSC PCTL segments were able to achieve adequate ductility indexes as well as deformability limits. A theoretical prediction according to the North American codes and design guidelines, including flexural capacities, cracking moment, and crack width, was made and the results compared to the experimental results. This research illustrates the advantages of using HSC for PCTL segments internally reinforced with GFRP bars under quasi-static cyclic flexural conditions.

Development of strength interaction diagrams for designing precast concrete tunnel lining segments reinforced with GFRP bars

Replacing conventional steel reinforcement with noncorroding glass fiber-reinforced polymer (GFRP) reinforcement can be an effective solution to mitigate the corrosion problem in precast concrete tunnel lining (PCTL) segments. PCTL segments should be effectively designed to withstand the applied load during production, transportation, construction, and service stages. The literature, however, offers limited design recommendations or guidelines for designing GFRP-reinforced PCTL segments. In this study, an experimental program was conducted to investigate the effect of reinforcement ratio and tie configuration on the behavior of GFRP-reinforced PCTL segments at the service and ultimate stages. Novel procedures and equations were developed to obtain axial load–bending moment interaction diagrams at the ultimate and service stages. In addition, interaction diagrams were developed to consider the creep-rupture stress limits in GFRP bars. Furthermore, axial load–shear-strength interaction diagrams were developed for GFRP-reinforced PCTL segments, as well as a simplified procedure to control cracking. Afterward, a parametric study was performed to evaluate the effect of concrete compressive strength, reinforcement ratio, and cross-sectional thickness on the axial load–bending moment interaction diagrams of GFRP-reinforced PCTL segments. The analytical results were compared to the experimental results from the current study and the literature. The comparison revealed that the proposed analytical procedure was suitable for designing GFRP-reinforced PCTL segments.

Rehabilitation of defective connections between two precast concrete segments (experimental and analytical study)

Connections in precast concrete elements are essential for improving the structures' utilization, cost, and quality control. Moment connection in beams was one of the easiest ways to achieve good performance of the structures by eliminating the plastic hinges zone. Due to constructing precast elements, some of them can be defective. This paper presents an experimental and analytical study to rehabilitate defective connections between two precast concrete segments. Six simply supported beams with beam-to-beam connections and one simply supported beam without connections, each with dimensions of 200 × 400 × 1600 mm, were fabricated and loaded to failure with a four-point load. The main variables parameters were a) the type of concrete mix in the splice region, two types of concrete were employed: Normal Strength Concrete (NSC) and High Strength Concrete (HSC) b) effect of rehabilitation techniques with using NSC in the connection zone such as; using warped fiber sheets around splice region or Carbon Fiber Reinforcement Polymer CFRP laminates at the tension surface of the tested beams c) effect of rehabilitation techniques with using HSC in the connection zone. Also, a new model was proposed based on some codes and guidelines of beams strengthened with Externally Bonded FRP Systems to calculate the flexure capacity for rehabilitating the beam-to-beam connections. The results indicate that neither casting NSC nor the HSC at the connection region has any effect on increasing the beam's capacity and cannot be used only as a rehabilitation technique in beam-to-beam connection. The fiber sheet warped around the splice region constructed from either NSC or HSC did not significantly increase the beam's capacity compared to rehabilitated beams with casting concrete only in the connection region. The load capacity of the rehabilitated beam with CFRP laminates and warped fiber sheets is increased significantly by about 122 % and 209 % compared to rehabilitated beams with splice regions constructed from NSC and HSC, respectively. The proposed model based on CNR-DT 200 R1/2013 equation gave a good prediction of the capacity of the rehabilitation connection for rehabilitated beams with CFRP laminates and warped fiber sheets.

Influence of structural form on hydration-heat-induced temperature rise of precast concrete lining segments for a metro transit station

This paper describes research on the effect of structural form on hydration-heat-related changes in large-scale precast concrete lining segments. These segments of mass concrete were used in the construction of an underground metro transit station in Changchun, China, a location where conventional cast-in-place construction is interrupted for months by cold winter weather. Heat of hydration analysis of closed-cavity and solid lining segments was conducted using the finite element method (FEM). Two ambient temperatures of 25°C and 10°C (77°F and 50°F) were selected to simulate segment manufacturing conditions in summer and winter, respectively. The FEM and selected parameters were found to be reasonable because the numerical predictions and experimental observations from the closed-cavity segment were consistent. At both of the ambient temperatures, the maximum internal concrete temperature of the closed-cavity segment was much lower than that in the solid one and the temperature distribution in the closed-cavity segment was more uniform. As a result, thermal stress was lower in the closed-cavity segment than in the solid segment, which reduced the risk for cracking. The closed-cavity form of the lining segments enhanced the structural integrity and durability, and the ability to prefabricate these segments in cold ambient temperatures effectively accelerated construction on this project.

EXPERIMENTAL INVESTIGATION OF STEEL FIBERS’ EFFECT ON THE IMPROVEMENT OF MECHANICAL PROPERTIES OF CONCRETE SEGMENTAL LINING IN MECHANIZED TUNNELING

The lining system, used in tunnel boring machines, is made of precast concrete segments. The use of steel fibers in this kind of support system can not only decrease production time and costs but also can improve compressive, tensile as well as flexural behaviors. A study has been carried out to examine the mechanical properties of segments in the Tabriz metro line-2 project using three types of steel fibers: 3D, 4D, and 5D. Various experiments were investigated to monitor the workability of Steel Fiber Reinforced Concrete (SFRC) under various loads. The results confirmed an improvement in the specimens’ mechanical properties because of these types of steel fibers. 5D, 4D, and 3D fibers provided the greatest effect on the tensile and flexural strength of steel fiber-reinforced concrete, respectively. The 28-day compressive, tensile, and flexural strengths of the specimens are incremented by 13%, 68%, and 154%, respectively. In addition, by conducting tests on the orientation of steel fibers, placing the fibers perpendicular to the load can improve the compressive strength of concrete by almost 18%.

Experimental study of the mechanical properties of two-component backfilling grout

In mechanised tunnelling, the filling of the annular gap behind the precast concrete segments is one of the essential operations. The main goal of filling this space is to reduce surface settlements and limit movements due to tunnel excavation in the soil mass. To achieve this aim, a two-component grout is often used to fill the annular gap. Determination of the amounts of ingredients in the two-component grout should be carried out in such a way that the injection materials will be able to fulfil the required performance and technical properties. In this study, laboratory tests were carried out to investigate two-component grout properties, such as flowability, bleeding, gelling time and uniaxial compressive strength. The effect of lateral pressure on grout resistance was studied according to real excavation situations. The influences of the grout ingredients and effective parameters such as bentonite and cement contents, water–cement ratio and the dosage of accelerator (sodium silicate) and accelerator ratio were also investigated.

Influence of different curing conditions on water absorption of cement-based materials under dry and wet cycles

As the main structural material of a subway, the precast concrete segment is produced under the steam-curing condition, and frequently experienced dry–wet cycles environment. In this study, steam-curing and dry–wet cycling methods were used to simulate the water absorption process of cement-based materials under special circumstances. The results showed that the water absorption in cement-based materials decreased with an increase in the number of dry–wet cycles. Based on a micro-analysis, the proportion of large capillary pores (dimension >0.1 μm) in the steam-cured mortar increased during the water absorption process with the increase in the number of dry–wet cycles compared with the standard cured mortar. Through thermodynamic and kinetics analysis, the mechanism and model were calculated to explain the component transformation mechanism of cement-based materials under dry and wet cycles.

Brief Analysis of Safety Management of Precast Concrete Segment Production in TBM Tunnel

Brief Analysis of Safety Management of Precast Concrete Segment Production in TBM Tunnel

Numerical and analytical studies of flexural behaviour of prestressed UHPC joints

This study numerically and analytically investigates flexural behaviour of precast ultrahigh performance concrete (UHPC) segments connected by post-tensioned prestressing strands with or without epoxy on keyed joint surfaces. The analytical formulas are proposed for calculation of joint opening load and ultimate flexural capacity, and a numerical model is established to investigate flexural behaviour of the jointed beam. The joint surfaces without epoxy are simulated by a pair of contact elements with a friction coefficient of 0.6. For the joint surfaces with epoxy, besides the contact elements, a spring element is defined for consideration of the epoxy and an optimized force–displacement relationship is first proposed and input for the spring property. The previous test data and data from one intact beam with low reinforcement ratio tested in the present study are used for validation of the analytical and numerical calculations. The numerical results agree well with the test results in terms of load-midspan deflection, load-joint opening displacement as well as failure modes. Based on the validated numerical model, the effect of number of prestressing strands and beam depth on the flexural behaviour of the prestressed jointed beam is investigated. This study will promote prestressed UHPC joints’ application in practical engineering.

Rehabilitation of Defective Connections between Two Precast Concrete Segments (Experimental and Analytical Study)

Rehabilitation of Defective Connections between Two Precast Concrete Segments (Experimental and Analytical Study)

Experimental Study on the Axial Compression Performance of an Underwater Concrete Pier Strengthened by Self-Stressed Anti-Washout Concrete and Segments.

Compared with the conventional drainage strengthening techniques, the precast concrete segment assembly strengthening method (PCSAM) is regarded as a fast, more economical, and traffic-friendly underwater strengthening method for damaged bridge piers and piles, as the drainage procedure can be omitted. However, this method still has some disadvantages, such as strength loss of the filling material, debonding of the interface due to shrinkage of the filling material, poor connection effects, and poor durability of the segment sleeves. To solve these problems, the PCSAM is improved in this study by using self-stressed anti-washout concrete (SSAWC) as the filling material and by developing a lining concrete segment sleeve (LCSS) by referring to the design theory for shield lining segments. Six specimens are designed and prepared with consideration of the influential factors, such as the self-stress, thickness of the filled concrete, and concrete strength of the LCSS, then the monotonic axial compression test is carried out to investigate the improvements in the axial compression properties of the specimens. Accordingly, extended parametric analyses are performed based on the established numerical models. Finally, the calculation formula for the bearing capacity is proposed based on the analysis results. The results indicate that the SSAWC can provide initial confining compressive stress in the core region of the piers, in addition to increasing the bearing capacity and ductility of the specimens. The improved LCSS segment connection is more reliable and increases the strengthening efficiency. The influence of self-stress on the bearing capacity of the specimens is cubic and the influence of the filled concrete strength on the bearing capacity of the specimens is nonlinear. The calculation formula for predicting the bearing capacity of axially compressed columns possesses good applicability and can be used as a reference for practical engineering.