Precast Concrete Specimens Research Articles

Experimental investigation of seismic performance of precast concrete shear walls with overlapping U-bar loop connections

This paper discusses the seismic performance of five reduced-scale shear walls, including one cast-in-place (CIP) concrete shear wall, two precast concrete (PC) shear walls with overlapping U-bar loop connections, and two PC shear walls with modified form-overlapping U-bar loop connections combined with extruded sleeve connections. A quasi-static test was conducted to evaluate the reliability of the overlapping U-bar loop connections and the modified form by comparing the corresponding mechanical parameters of PC specimens with those of the CIP specimen. Moreover, the differences in seismic performance between the CIP specimen and PC specimens with different connection methods were also analyzed in terms of damage process, hysteretic loops and skeleton curves, load carrying capacity, ductility, equivalent stiffness, and energy dissipation. The experimental findings indicated that the mechanical performances of PC specimens with the modified connection form outperformed those of PC specimens with pure overlapping U-bar loop connections, closely resembling the properties of cast-in-place specimens; the failure mode of PC specimens was consistent with that of the CIP specimen; the generation, distribution and development of cracks in PC specimens were also similar to those in the CIP specimen. Furthermore, although the load-bearing capacity and peak displacement of PC specimens were lower than those of the CIP specimen due to the failure of the post-casted concrete strength to meet the requirements, the ductility, equivalent stiffness, and energy dissipation of PC specimens with the modified connection form closely matched that of the CIP specimen.

Effect of synthetic C-S-H seeds on hydration process, mechanical properties and microstructure of seashell powder calcined sludge cement

Seashell powder calcined sludge cement (SCSC) is a new type of green low-carbon ternary cement prepared by using waste sludge and waste seashells. It reduces carbon emissions in the cement production industry and solves environmental problems such as serious soil-water-air pollution caused by long-term stockpiling of waste sludge and waste seashells, which are difficult to be utilized in a resourceful manner. However, the reduced clinker content results in lower early strength of SCSC, which limits the application of SCSC in applications requiring high early strength such as precast concrete specimens. In this paper, the effects of different dosage of C-S-H seeds on the hydration process, mechanical properties and microstructure of SCSC slurries were investigated. The results showed that C-S-H seeds significantly increased the 12-hour compressive strength of SCSC, and the 2 % addition of C-S-H seeds increased its compressive strength by 271 %, but had less effect on its later strength. The proportion of large pores in the sample with a 1 % addition of C-S-H seeds decreased by 1 %. At 12 hours, 2 % addition of C-S-H seeds increased its total hydration exotherm by 141 %. The addition of C-S-H seeds decreased the fluidity of the slurry but did not change the flow pattern of the slurry. The relationship between the rheological parameters of the slurry and the addition of C-S-H seeds was well fitted with a primary function, and the rheological equations of SCSC slurries with different additions of C-S-H seeds were obtained. The results of this paper can further broaden the application scenarios of SCSC and lay the foundation for the large-scale application of SCSC.

Impact resistance and performance of precast shear walls with various connections under axial and lateral loads

This study conducted pendulum impact tests on three precast concrete (PC) shear wall specimens with various connection types and one cast-in-situ reinforced concrete (RC) shear wall specimen to investigate their behavior under out-of-plane impact loads at a consistent axial compression ratio. The study reported observations on failure patterns, the progression of cracks, the dynamics of impact force over time, relationships between axial force and vertical displacement, deformation behavior, and the strains in concrete and rebars. Through comparative analysis with similar PC columns, the influence of various connections on the impact resistance is analyzed for both shear walls and column specimens. It was found that all PC specimens showed flexural failure modes akin to those of the RC specimen, yet with more extensive cracking and lower stiffness. PC specimens with grouted sleeve connections demonstrated satisfying impact resistance that emulates the performance of cast-in-situ walls. Specimens with grouted corrugated metallic duct connections demonstrated obvious localized damage. Eventually, the study proposes a novel method for rapidly evaluation of the impact resistance of concrete shear walls.

Simplified test method for evaluating progressive collapse resistance of precast concrete frame structures

To evaluate the progressive collapse resistance of precast concrete (PC) structures, various test methods have been used in existing experimental studies. However, verification of whether the progressive collapse resistance can be evaluated equivalently by different test methods has been limitedly investigated. In this study, three simplified and three half-frame test specimens were tested under monotonic vertical loading to investigate the effects of the test method on their progressive collapse resistance. As the test parameters, types of test specimens (i.e., sub-frame, simplified, and half-frame specimens), and joint details (i.e., reinforced concrete (RC) continuous joint, PC with continuous joint, and PC with pinned joint) were directly compared. The test results showed that the progressive collapse resistance was primarily affected by the overall lateral stiffness of the exterior columns (Kh) rather than the test setup. When Kh increased in the simplified specimens, the axial force transferred by the beams increased, resulting in an increase in the peak strength (PCAA). Further, the effect of Kh on the peak strength was greater in PC specimens with pinned joints than in RC and PC specimens with continuous joints. To investigate the effect of Kh on the PCAA, a parametric study was conducted using the existing CAA strength model. The parametric study results also indicated that the relationship between the increase in Kh and PCAA was not significantly governed by the test setup for the same joint details. These results indicated that various simplified test methods can be used to evaluate the progressive collapse resistance of PC structures when an adequate range of Kh is provided. Based on the test and parametric study results, recommendations for progressive collapse tests were discussed.

Experimental study on the progressive collapse resistance of emulative precast concrete beam-column subassemblies with various anchorage details

In this study, seven emulative precast concrete (PC) beam-column subassemblies with or without connecting bars and one concrete (RC) were fabricated and tested to investigate the effect of various types of anchorage detailing for reinforcing and connecting bars on the progressive collapse resistances. Two anchorage detailing formats for steel bars with bending and straight ends were used in the PC specimens for both the reinforcing and connecting bars. Test results show that, as found in the RC specimen, resisting mechanisms including pure flexure, compressive arch action (CAA) and tensile catenary action (TCA) were sequentially activated in all PC specimens. It is demonstrated that the connecting bars improved the progressive collapse resistance in both the CAA and TCA stages. The effect of the anchorage detailing was found to be negligible in CAA stage. However, in the TCA stage, the proper usage of the straight end for steel bars was helpful to improve the deformation capacity and thereafter enhanced the progressive collapse resistance. When the loading resistance, the deformation capacity as well as the construction flexibility are taken into account, the configuration consisting of both reinforcing and connecting bars with straight end as anchorage detailing is recommended for the design of precast beam-column connections in case a central column removal scenario is assumed.

Experimental study on exterior precast concrete beam-to-CECFST column joints with wet connections under cyclic loading

Concrete-encased concrete-filled steel tube (CECFST) structural system has gained popularity in recent years due to its several advantages over conventional structures. Additionally, precast technology has become an effective way of improving construction efficiency and environmental performance. Therefore, it is essential to investigate the structural behaviour of precast concrete (PC) beam-to-CECFST column joints to ensure their optimal performance in applications. In this regard, this paper presents an experimental study of 4 precast exterior joints subjected to lateral cyclic loading. The study investigated the effect of replacing normal concrete with steel fibre-reinforced concrete at the joint region and the presence of axial load on PC composite joints. Based on the test results, cyclic load-carrying resistance, failure modes and crack patterns of the PC specimens were recorded and analysed. In addition, a Digital Image Correlation (DIC) system was adopted to show the crack evolution of joint specimens and calculate shear strains of concrete encasement at the joint region. Further comparisons were conducted in terms of ductility, energy dissipation, stiffness and strength degradation to investigate the joint performance. Finally, existing American and European design code provisions were modified and used to predict joint shear strength. Their predictions were reasonably close to the test results.

Experimental and analytical investigation on the progressive collapse resistance of precast concrete beam-column subassemblies with connecting steel bars

The resisting mechanism of precast concrete (PC) structures against progressive collapse varies from different types of beam-column connection details. In this context, the progressive collapse resistances and the corresponding resisting capacity models for the widely adopted PC structures with additional connecting rebars is significant when extreme events frequently occurred from time to time. In this study, progressive collapse resistance of one emulative PC beam-column subassembly and two PC specimens with connecting rebars were experimentally and analytically investigated. It is found that flexural action, compressive arch action (CAA) and tensile catenary action (TCA) were sequentially developed. Compared with the emulative specimen, the specimens with connecting rebars exhibited higher CAA and TCA capacities and dissimilar failure modes by dispersing the concentrated deformations at the beam ends to other locations. To elucidate such differences, a modified CAA model considering the real stress state of reinforcements and a TCA model accounting for the tensile steel force’s direction and the difference in failure mode were proposed. Experimental validation shows that the proposed models is effective to predict the CAA and TCA capacities with good accuracy. The findings in this study are beneficial to the understanding and formulation of the progressive collapse resistance of PC structures for practical engineering design.

Emulation Evaluation of Interior Beam-Column Connections in PC and RC Moment-Resisting Frames.

Precast concrete (PC) structures have many advantages, but their use in the construction of middle- to high-rise buildings is limited. The construction of PC structures requires skills in various operations such as transportation, assembly, lifting, and structural soundness. In particular, regarding the seismic design of PC structures, it is necessary to clearly evaluate whether they have the same structural performance and usability as integral RC (cast-in-place) structures. In this paper, an experimental study was conducted to investigate whether PC members can achieve a seismic performance equivalent to that of RC members in beam-column joints, which are representative moment-resisting frames. The main variables are the two types of structural systems (intermediate and special moment-resisting frames) and the design flexural strength ratio of the columns and beams. The experimental and analytical results showed that the seismic performance of the PC specimens was equivalent to that of the RC specimens in terms of strength, stiffness, energy dissipation, and strain distribution, except for the specimen with splice sleeve bond failure of the column reinforcement (poor filling of the internal mortar). In addition, the I series satisfied the present emulation evaluation criteria for special moment-resisting frames of PC structures, confirming the possibility of applying intermediate moment-resisting frames.

Seismic performance of precast concrete shear wall using grouted sleeve connections for section steels reinforced at wall ends

A novel precast concrete (PC) shear wall was proposed by disconnecting the vertical rebars in the middle zone of the wall and using grouted sleeve connections for section steels at wall ends. The advantage of this method is to alleviate constructional difficulties when assembling traditional PC shear walls. As an extended study, this paper investigates the seismic performance of the PC shear walls. Four wall specimens of 1:2 scale were tested under pseudo-static loading, including two cast-in-place (CIP) specimens and two PC specimens with different axial compression ratios. Afterwards, parametric studies were performed using the finite element method, considering the axial compression ratio and yield strength of section steel. Test results indicated that the PC and CIP specimens had comparable ultimate resistances, and exhibited similar ductilities and stiffness degradations. The energy dissipation capacities corresponding to ultimate resistances of the PC specimens were 41% and 19% smaller compared to those of the CIP specimens under axial compression ratios of 0.3 and 0.5, respectively. Numerical results found that the ultimate resistances of the PC shear walls increased by 59% when the axial compression ratios increasing from 0.1 to 0.6. Increasing the yield strengths of section steels from 235 MPa to 460 MPa, the ultimate resistances of the PC shear walls slightly increased by 11%, and the energy dissipation capacities improved by 26%.

Experimental Investigation of Seismic Performance of Precast Concrete Wall-Beam-Slab Joints with Overlapping U-Bar Loop Connections.

In the era of energy conservation and environmental protection, as well as the industrialization of buildings, precast concrete (PC) structures have been developed and increasingly applied in construction industries due to their advantages of outstanding workability and ecofriendliness. In order to verify the reliability of overlapping U-bar loop connections and a modified form of these connections, and study the seismic performance of PC wall-beam-slab joints with these connection methods, three full-scale wall-beam-slab joints were designed and tested under low reversed cyclic loading, including one cast-in-place (CIP) specimen and two PC specimens. Based on the test results, the seismic performance of the PC joints was studied by comparing their damage process, hysteretic loops and skeleton curves, load-carrying capacity, ductility, equivalent stiffness, and energy dissipation with those of the CIP joint. After analyzing the experimental results, the following conclusions can be drawn: the overlapping U-bar loop connection and its modified form are effective and reasonable; the specimen with the modified connection form showed slightly better mechanical properties; the failure mode of the PC joints was consistent with that of the CIP joint; and the generation, distribution, and development of cracks in the PC specimens were similar to those in the CIP specimen. In addition, the stiffness of the PC joints was similar to that of the CIP joint, and the load-carrying capacity, ductility, and energy dissipation of the PC joints were better than those of the CIP joint. Moreover, the research in this paper can also provide some guidance for assembling wall-beam-slab joints in PC shear wall structures.

Seismic performance of precast concrete walls with grouted sleeve connections using large-diameter bars

This paper proposes an innovative assembly technique using large-diameter bars anchored in several single-row, widely spaced grouted sleeves at the keyway-type horizontal joint to realize an indirect vertical connection between adjacent precast concrete (PC) walls, which has the advantages of high efficiency and ease of construction. To examine the effect of vertical connection strength (rebars' diameter at horizontal joints) on the seismic performance of PC shear walls, quasi-static cyclic loading tests on five full-size wall specimens, including one cast-in-place specimen and four PC specimens with grouted sleeve connections, are carried out. Seismic performance indicators in terms of failure modes, hysteresis characteristics, energy dissipation, ductility, and stiffness degradation of PC walls are investigated and compared with those of the cast-in-situ wall. Meanwhile, the method for predicting the bearing capacity of PC walls with large-diameter rebars is developed. The results show that the failure modes of cast-in-situ and precast walls are controlled by bending instead of shear, but there is an obvious difference in the crack propagation between the two types of walls. Carrying capacity, ductility factor, stiffness, and energy dissipation of PC walls are significantly enhanced by increasing the connection strength, by 44.1%, 23.9%, 72.1%, and 24.0%, respectively, when the connection strength reaches around 90%. Particularly, the PC wall's seismic performance is comparable to that of the cast-in-situ wall when the connection strength is 90%. The calculated results are well-matched with the experimental results, the proposed calculation method reliably predicts the bearing capacity of PC walls with large-diameter rebars. The assembly technique can be safely applied to multi-story PC wall panel structures in seismic zones.

Effect of joint details on progressive collapse resistance of precast concrete structures

Recently, precast concrete (PC) structures are vulnerable to progressive collapse, because during construction, the structural integrity of the beam–column joint is poor. Even after construction, the interface between PC beam and column is a critical section, due to the discontinuity of concrete and reinforcement. In this study, to investigate the progressive collapse resistance of PC structures with various joint details, three moment sub-frames were tested under monotonic vertical loading. Addressing the actual joint details used in industrial PC buildings, such as warehouses and factories, prestressing was applied to the PC beam, and wet connection was used for beam–column joints. As a test parameter, the joint details were compared (i.e., monolithic reinforced concrete (RC) joint, PC with pinned joint, and PC with continuous joint). The test results showed that the PC specimen with continuous joint exhibited structural behavior equivalent to the RC specimen in terms of failure modes, peak strength, deformation, lateral support reaction, and strain. However, the PC specimen with pinned joint showed significantly less strength than that of the PC specimen with continuous joint, due to the discontinuous top and bottom rebars in the beam–column joint. Further, the deformation and failure modes of PC specimens with pinned joint differed from those of the other specimens (i.e., rigid rotation of PC beams without flexural yielding, and concrete breakout around dowel bar). Using a finite element (FE) model, a parametric study was conducted. According to the analysis results, the progressive collapse resistance was significantly affected by the continuous rebars of the PC beam in the beam–column joint. Based on the test and analysis results, the maximum allowable uniformly distributed floor loads sustained by PC system was estimated. Further, design recommendations to improve the progressive collapse resistance were discussed, such as use of continuous top bars, strength limitation of dower bars, and effect of prestressing force.

Seismic performance of a ductile rod exterior connection system for precast concrete industrial buildings

The seismic performance of a ductile rod system for exterior precast concrete beam-to-column connections was experimentally evaluated. Five full-scale precast concrete beam-to-column subassemblies connected with ductile rods were fabricated, considering various aspects (ductile rod size, prestressing, and flexural/shear capacities). Lateral cyclic loading tests were conducted for the precast concrete connections along with two monolithic reinforced concrete connections. Despite their relatively lower lateral stiffness, most precast concrete connections showed sufficient moment capacities with peak moments at approximately 3% to 4% interstory drifts. The prestressing tendons were effective at enhancing moment and shear strengths of the precast concrete connections, as well as in reducing slip of the ductile rods. The precast concrete specimens generally showed satisfactory seismic performance, fulfilling acceptance criteria specified by the American Concrete Institute. The test results demonstrated that careful considerations are required in the design of ductile rods and high-strength threaded bars to induce stable flexural responses of the precast concrete connections.

MVGCN: Multi-View Graph Convolutional Neural Network for Surface Defect Identification Using Three-Dimensional Point Cloud

Abstract Surface defect identification is a crucial task in many manufacturing systems, including automotive, aircraft, steel rolling, and precast concrete. Although image-based surface defect identification methods have been proposed, these methods usually have two limitations: images may lose partial information, such as depths of surface defects, and their precision is vulnerable to many factors, such as the inspection angle, light, color, noise, etc. Given that a three-dimensional (3D) point cloud can precisely represent the multidimensional structure of surface defects, we aim to detect and classify surface defects using a 3D point cloud. This has two major challenges: (i) the defects are often sparsely distributed over the surface, which makes their features prone to be hidden by the normal surface and (ii) different permutations and transformations of 3D point cloud may represent the same surface, so the proposed model needs to be permutation and transformation invariant. In this paper, a two-step surface defect identification approach is developed to investigate the defects’ patterns in 3D point cloud data. The proposed approach consists of an unsupervised method for defect detection and a multi-view deep learning model for defect classification, which can keep track of the features from both defective and non-defective regions. We prove that the proposed approach is invariant to different permutations and transformations. Two case studies are conducted for defect identification on the surfaces of synthetic aircraft fuselage and the real precast concrete specimen, respectively. The results show that our approach receives the best defect detection and classification accuracy compared with other benchmark methods.

Seismic performance of precast wide beam-column connections with asymmetrical anchorage reinforcement details

This study aims to investigate the seismic performances of precast concrete (PC) wide beam-column connections under reversed cyclic loading, in which the precast beam width is 1.5 times larger than that of column. Experimental program consists of a monolithic reinforced concrete (RC) specimen and two PC specimens with unique connection details. To avoid reinforcement congestions and also to secure emulative connecting performances, the PC specimens were integrated by asymmetrically placed connecting bars anchored into the column panel zone, and their anchorage end details were chosen as a key testing variable. Detailed numerical models were developed to identify the failure mechanisms and key influencing factors of the cyclic responses of PC wide beam-column connections. It appeared that the precast wide beam-column connections with asymmetrical anchorage details can also provide the so-called emulative seismic performance as a monolithic connection. Significant effects of bond-slip behaviors of the anchorage connecting reinforcements in the joint and axial compression level of the column on the seismic performance of PC wide beam-column connections were also identified by the nonlinear numerical simulations.

Numerical investigation of precast reinforced concrete beam–to–column joints by replaceable damper

This study aimed to investigate the precast reinforced concrete beam-to-column joints behaviors through the replaceable damper under cyclic loading. The precast concrete specimens have been embedded with steel reinforcement and specially shaped connectors. After the application of the replaceable damper under cyclic loading, the energy dissipation part has acted very well and increased the bearing capacity of precast specimens. The precast concrete beam–to–column joints were designed and analyzed to compare with the reinforced concrete (RC) specimen. The analysis result of the loading based on the controlled displacement method has illustrated that the precast specimen model with damper has shown a greater hysteric behavior than the RC frame. the PS-1 is passed the 2.8% chord rotation approximately, which showed better performance, and higher resistance than the RC specimen. The efficiency of the PS–1 specimen with a special connection has been elaborated with the finite element method (FEM) and simulated by ABAQUS software.

Experimental investigation of CIP and PC beam-to-CECFST column joints with simple connection details under lateral cyclic loading

Due to the excellent structural performance of Concrete-encased concrete-filled steel tube (CECFST) columns, they have been applied in real practice for several years. In addition, precast technology can be utilised in the construction of CECFST composite structures to further improve productivity. To investigate the behaviour of precast concrete (PC) and cast-in-place (CIP) beam-to-CECFST column joints, a total of 6 joint specimens, including 4 PC and 2 CIP specimens, were thus experimentally studied under lateral cyclic loading. In this paper, the main studied parameters included connection details, construction methods and existence of column axial load. The ultimate strength, failure mode, crack patterns and hysteretic performance of each specimen were analysed in detail. According to the test results, the performance of CIP and PC joint specimens were discussed in the aspect of energy dissipation, ductility and damping coefficients, strength and rigidity degradations. It was found that the PC specimens exhibited comparable cyclic behaviour to the CIP specimens in regards to the maximum strength, hysteretic performance and failure mode. Moreover, based on the measured shear strains, contributions of joint shear resistance from steel tube, inner and outer concrete were quantitatively investigated. Thereafter, the development of shear stress in the outer concrete was compared with the nominal concrete shear strengths from American and European design provisions.

Structural Performance of a Precast Concrete Modular Beam Using Bolted Connecting Plates

In modular structures, prefabricated modular units are joined at the construction site. Modular structures must ensure splicing performance by connecting modular units sufficiently. The bolted connection using steel plates may suffer from alignment issues and corrosion problems. In a precast concrete (PC) modular system, there is difficulty grouting the sleeves when splicing reinforcing bars. This study proposed a PC modular beam using a bolted connecting plate to deal with issues in typical steel modules and PC modules. The structural performance was evaluated by flexural and shear tests on two monolithic beams and two proposed PC specimens. The test results showed that the structural performance of the PC modular specimen was 88% of that of the monolithic reinforced concrete (RC) beam specimen and 102% of the strength calculated by ACI 318-19. Therefore, the proposed PC modular system using bolted connecting plates can solve the problems observed in typical steel and PC modules and improve the structural performance.

Experimental investigation on the effect of local debonding of longitudinal reinforcement on seismic performance of precast concrete columns

The influence of the local debonding of longitudinal reinforcement on the seismic performance of prefabricated column with the grouted longitudinal reinforcement in corrugated sleeves is investigated. A total of 10 precast concrete specimens and 1 cast-in-place concrete specimen were designed and tested. Important factors such as anchorage length, local debonding position, debonding length and axial compression ratio were considered. The seismic performance was evaluated under low cycle reversed loading tests, and the failure mode, hysteretic curve, skeleton curve, ductility performance, energy dissipation capacity and stiffness degradation of the specimens were obtained and analyzed. It is found that the hysteretic curve of the precast column with local debonded longitudinal reinforcement is fuller than that of the bonded precast column, and the ductility and energy dissipation capacity of the precast column with local debonded longitudinal reinforcements are significantly improved. The effects of the debonding length and position of the longitudinal reinforcements on the ductility, energy consumption and bending deformation of the precast columns are also discussed. This study is of great significance to improve the bearing capacity and seismic performance of prefabricated columns on the top of the independent foundation in practical engineering.

Influence of new‐to‐old concrete interface on the damping behavior of recycled aggregate concrete

AbstractThe interface transition zone (ITZ) is a critical component of concrete, as it has a significant effect on the material's mechanical properties. This paper using specimens of bonded new and old concrete analyzes the effect of the interface in recycled concrete on damping performance using semi precast concrete specimens with old and new concrete. To determine the effect of the bonding zone between new and old concrete on the damping ratio of recycled concrete, the free vibration attenuation test method was used. When the acceleration signal from the specimen's transverse vibration is transformed to the frequency domain, the study observes two prominent peaks. The damping ratio is between 0.005 and 0.007 at the high‐frequency position and 0.06–0.08 at the low‐frequency position. When the excitation position is not in the bonding zone, the damping ratio measured in the bonding zone has a smaller average value. Under different recycled aggregate replacement rates, there is a significant difference in the damping ratio and frequency of old and new concrete bonded specimens, as well as complete recycled concrete specimens. The bonding zone's damping ratio data is more discrete than that of other locations. The damping ratio and the acceleration amplitude exhibit an excellent linear relationship, with the damping ratio increasing as the amplitude increases. The damping ratio varies significantly more in the longitudinal direction, with no apparent relationship to the acceleration amplitude.