Search Results (19)

This study applied precast engineered cementitious composite (ECC) shells to replace conventional concrete in precast assembled monolithic composite beams to enhance mechanical performance. A new type of precast monolithic ECC composite beam was proposed. Five ECC composite beams and one reinforced concrete (RC) composite beam were designed and fabricated for the experimental study. The failure pattern, failure mechanism, load-bearing capacity, deformability, and stiffness degradation were quantitatively analyzed through the tests. The main findings were as follows: ECC composite beams developed finer and more densely distributed cracks compared to RC composite beams, without significant concrete spalling. The peak load of ECC composite beams was 8.2% higher than that of RC composite beams, while the corresponding displacement at peak load increased by 29.3%. The ECC precast shell delayed crack propagation through the fiber bridging effect. The average load degradation coefficient of the ECC composite beams was 8.2% lower than that of the RC beam. The stiffness degradation curve of ECC composite beams was more gradual than that of RC composite beams, providing an optimization basis for the design of precast beams in structures with high seismic demands. As the shear span ratio increased from 1.5 to 3, the load-bearing capacity decreased by 32.0%. When the stirrup ratio increased from 0.25% to 0.75%, the ultimate load-bearing capacity improved by 28.8%. Furthermore, specimens with higher stirrup ratios showed a 40–50% reduction in stiffness degradation rate, demonstrating that increased stirrup ratio effectively mitigated brittle failure. Full article

To address the research gap in gas blast resistance of composite precast assembled utility tunnels, this study investigates structural damage evolution and the mechanisms influencing parameters through validated numerical simulations. A three-dimensional numerical model, incorporating the Karagozian & Case (K&C) concrete damage model and tie-break contact algorithm, was developed using LS-DYNA. The first validation against composite precast concrete slab explosion tests confirmed the model’s reliability, with displacement peak errors below 10%. The second validation focuses on the blast resistance test conducted on an underground utility tunnel, revealing an error margin of less than 10%. Results indicate that the utility tunnel exhibits a progressive failure mode of “joint cracking-interface damage-midspan cracking” under explosive loads, with stiffness degradation observed in joint regions at a loading pressure of 700 kPa. Increasing the normal strength of the interface to 5 MPa suppresses 90% of interface delamination, whereas completely neglecting interface strength results in a 9.0% increase in midspan displacement. Concrete strength shows minimal impact (<2.5%) on displacement under high loading conditions (≥0.9 MPa), and increasing the reinforcement ratio from 0.44% to 0.56% reduces displacement of the roof slab by 10.5%. These findings of address the research gap in the gas explosion response of composite precast assembled utility tunnels and could have significant implications for enhancing the disaster resistance of urban underground spaces. Full article

Precast concrete structures have become increasingly popular in the construction industry due to their ability to enhance efficiency, structural soundness, quality, and sustainability. Among these, modular construction has emerged as a transformative approach that fully leverages precast technology by manufacturing 3D modules off-site and assembling them on-site using inter-module connections. This study reviewed current literature trends on precast concrete structures and modular construction, analysing how modular construction distinguishes itself from other precast systems. This review further emphasises the role of composite connections—grouted, bolted, and hybrid systems—critical in ensuring structural integrity, efficiency in load transfer, and seismic resilience in modular construction. Advancements in composite connections have demonstrated significant promise, particularly in seismic performance, with reported energy dissipation improvements of up to 30% in hybrid connection systems. Yet limitations still exist, necessitating improvements in load transfer efficiency, ductility, and reliability under dynamic loads. Additionally, design considerations for modular construction, such as modular configurations, handling stresses, and transportation challenges, are explored to highlight their influence on system performance. This review underscores the feasibility and potential of modular construction in fostering sustainable and resilient infrastructure, as studies indicate that modular construction can reduce project timelines by up to 50% while minimising material waste by approximately 30%. The role of Non-Destructive Evaluation (NDE) techniques and intelligent monitoring systems in assessing and enhancing the lifecycle performance of composite connections is also emphasised. This review further advocates for continued research to refine composite connections and support the broader adoption of modular construction in modern building practices. Full article

The static performances of an assembled integral two-way multi-ribbed composite floor system have been studied experimentally and numerically, while the dynamic characteristics and comfort analysis under a human load have not been investigated. In this article, a 9.2 m × 9.2 m floor system, composed of 16 precast panels and integrated into a whole structure through six wet joints, was designed and tested under pedestrian loads. Dynamic performances related to its natural frequencies, vibration mode shapes, and maximum acceleration were analyzed. Theoretical formulas were proposed to predict its natural frequency and maximum acceleration under a single-person load. It was found that the dynamic behavior of this innovative floor system meets the requirements of GB50010-2010 and ISO 2631. Elastic plate theory could be applied to predict the natural frequency and acceleration, with the bending stiffness obtained from the experiment. Some design and dynamic test suggestions for this floor system and similar structures are proposed based on a parametric analysis. Full article

Prestressed, precast composite panels are a type of building component that combines prestressing technology with composite materials; but, for most of them, it is difficult to balance structural stress performance and assembly efficiency. This paper proposes a series of novel bidirectional, prestressed, prefabricated, composite slabs, aiming to enhance their bidirectional force characteristics and assembly efficiency. By implanting a kind of specially designed concrete movable core rib with the same geometry as the cavity in the hollow-core slab at medium spacing, the transverse stressing performance of the structure is enhanced without affecting the unidirectional structural performance. Then, in the pre-set transverse apertures, several pieces of unidirectional, prestressed, precast hollow-core slabs that are implanted in the core mold are connected in series with high-strength strands and prestressed; finally, we obtain a bidirectional, prestressed, prefabricated composite slab. Two types of slabs (i.e., 3.3 m × 4.5 m and 4.5 m × 4.5 m) are selected and their mechanical behavior is investigated experimentally and by the finite element method, and the results are in good agreement. The proposed bidirectional, prestressed, precast composite slab not only has better overall bearing performance but also improves the structural stiffness and assembly rate, which can greatly improve the economic benefits and is of great significance for the popularization and application of assembled concrete structures. Full article

This paper proposed an innovative precast steel-reinforced concrete (PPSRC) squat wall to simplify on-site construction. In PPSRC squat shear walls, the hollowly precast RC wall panel can be assembled on-site through the pre-erected steel shapes, and the boundary cores will be filled using fresh concrete together with the slab system. The seismic performance of PPSRC squat walls, influenced by different construction techniques (cast-in-place vs. precast) and steel ratios, was examined through pseudo-static experiments on three specimens. Some key performance indicators, including hysteretic behavior, skeleton curves, stiffness degradation, energy dissipation, and load-carrying capacity, were analyzed in detail. The test results indicated that all the PPSRC squat walls failed in typical shear failure, and no significant slippage between the precast and fresh concrete sections was observed during the loading process, indicating that the composite action could be fully achieved via the novel throat connectors. In addition, the PPSRC squat walls could achieve comparable seismic performance compared with that of cast-in-place SRC shear walls (the peak load of the PPSRC squat wall only increased by 0.26% compared with the control specimen), and the load-carrying capacity and deformability could be enhanced by increasing the steel ratio in the boundary elements. Finally, an elaborate finite element model was developed and validated using ABAQUS software. The parametric analysis of the concrete strengths of precast and cast-in-place parts and the axial load was conducted further to investigate the seismic performance of PPSRC squat walls. Full article

The application of reinforced concrete modular integrated construction (MiC) has gained popularity in Hong Kong, but challenges still exist in the temporary tying of side walls during composite wall construction. This paper presents an innovative inner tie system for composite walls, applied in a MiC project in Hong Kong. The system’s components are installed on the side walls of precast modules in the factory without the need to penetrate through the walls. After transport to the site, by rotating the loop on-site to engage the hook, the tying effect is achieved during on-site concrete pouring between the interstitial space of two modules. This system eliminates the use of tie bolts that penetrate precast side walls, allowing for comprehensive interior fitting-out in the factory and minimizing disruptions to internal decoration during on-site construction. The paper presents the system’s mechanism, nonlinear Finite Element Analysis (FEA) simulation, section size optimization, and validation through tensile and punching shear tests. Furthermore, an instrumented mockup module assembly was carried out, and the system was eventually applied in a real MiC project. The system can effectively control the horizontal deformation of MiC module side walls within a limit. Compared to current existing tying methods, this system offers easy installation, load-bearing reliability, adaptability to certain construction errors, savings on manpower and construction time, and also a decrease in construction waste and carbon emission. It will provide a valuable reference for future MiC projects. Full article

Modern bridge construction towards a higher degree of low carbonization and assembly has been the general trend, while developing and broadening the low-carbon and assembled-oriented Accelerated Bridge Construction (ABC) technology can better realize the trade-offs between construction quality, efficiency, cost and sustainability. In the current mainstream ABC technologies such as precast-assembled concrete bridge and assembled steel bridge schemes, it is difficult to achieve an excellent balance between the above multicriterion trade-offs. To this end, this paper proposes a novel low-carbon and assembled composite bridge scheme as an innovative case of ABC technology based on a 26.7 km-length urban viaduct project in China with urgent environmental protection and assembly demands. Construction sustainability, the comprehensive economy and low-carbon performance are well balanced by the collaborative application of new steel–concrete composite structures, the rapid assembly interface design and low-carbon material technologies. The proposed scheme has been applied to a completed real-scale bridge, and the whole construction process only experienced 105 days of effective time, accompanied with slight environmental interference and construction noise and a small amount of labor and equipment input. In addition, the safety of the bridge, the rationality of the design concept and the calculation method have been verified by the static and dynamic loading tests of the real-scale bridge. Full article

In open-cut assembled subway tunnels, foundation pit enclosure piles are typically cast in place. However, this conventional approach limits the functionality of the piles to serving as retaining structures during excavation, resulting in resource inefficiency and the underutilization of prefabrication techniques. To address this issue, a fully prefabricated pile-wall composite scheme is proposed for cut-and-cover tunnels to optimize the retaining effect of the piles and leverage the benefits of prefabricated technology. In this scheme, the retaining pile and lining are both prefabricated. The pile is the temporary retaining structure during pit excavation and a part of the sidewall. This scheme was researched and applied in Jinan, China. Field monitoring and numerical simulation were used to investigate the load transfer within the fully prefabricated pile-wall composite structure (PPWS) and its mechanical response, respectively. The results show: (1) The development of lateral earth pressures on the PPWS experienced three stages. The lateral earth pressure distribution indicates that the PPWS can fully activate the retaining effect of precast piles. (2) Following the backfilling of the joints, the horizontal displacement at the bottom of the precast pile reduced by 0.39 mm. Numerical simulation results indicate the effectiveness of precast pile restraint in PPWS. (3) The PPWS exhibited uniform deformation transition at the joints. The joints play a crucial role in coordinating deformation between the precast piles and sidewalls, utilizing the restraining effect of the precast piles. Full article

A new type of assembled integral multi-ribbed composite floor system with novel wet joint and steel sleeve connections, which exhibits satisfactory strength and stiffness, was proposed in the previous study. To further study the flexural performances of the joints, six groups of specimens, including two cast in situ concrete slabs and four composite slabs sized 4700 mm × 1200 mm × 300 mm and 2450 mm × 1200 mm × 300 mm, were investigated under four-point flexural tests. Four main influence factors were experimentally studied, i.e., casting methods, joint amounts, shear span lengths, and steel sleeve layout directions, on the failure modes, crack distributions, and deflection–load carrying capacity relationship. Test results indicated that the proposed composite slab system could provide the ultimate bearing capacity lower by 7% than that of the cast in situ concrete slabs, largely exceeding the code-predicted strength. No strain difference between the steel sleeve connections and steel rebars indicated good wet joint connection behavior. More hollow-core sections and long shear spans increased the potential of interfacial splitting cracks, leading to a shorter elastic stage and lower elastic stiffness. A finite element model was further parametrically conducted to explore the structural performances. Finite element results also indicate that the precast concrete slab had a more significant influence on the failure loads than the influences of concrete compressive strength and lap-splice steel rebar strength. These findings indicate that the proposed composite slab systems possess a satisfactory performance in the ultimate bearing capacity and deformability. Thus, such an assembled integral multi-ribbed composite floor system can be widely applied in construction. Full article

A novel concrete beam–column connection utilizing L-shaped steel bars is proposed to address the growing demand for prefabricated buildings and to ensure good seismic performance in such beam–column structures. After positioning two prefabricated beams with L-shaped tendons into the designated connection points at the top and bottom of the columns, concrete is poured into the post-cast section of the joint and the composite beam area, realizing a connection between the beams and columns. Quasi-static tests were performed on four combined backbone curves and one cast-in-place joint to investigate their failure modes and stress mechanisms. Through low-cycle repeated loading tests, it is found that measures such as increasing the area of the post-cast concrete in the joint area, the length of the L-shape, and the concrete strength in the composite beam area can effectively improve the bonding ability between the post-cast area of the joint specimens and the precast members, to improve the ductility performance, energy dissipation capacity, and bearing capacity of the joint specimens. The initial stiffness of the joint can be effectively improved by presetting the steel pipe in the column. Concurrently, the finite element method (FEM) was employed for parameter analysis. By integrating the test and FEM results, an equation for calculating the shear capacity of the connection was derived. The findings demonstrate that the hysteresis curve of the newly assembled joints is full, and its overall performance index is roughly the same as that of the cast-in-place joints. Additionally, enhancing the post-casting area of concrete, the length of the L-shaped bars, the concrete strength in the composite beam region, the axial compression ratio, or the steel tube dimensions can effectively improve the overall performance. The derived equation for the shear-bearing capacity of the connection satisfies design and application requirements. Full article

In this paper, a novel precast concrete composite wall connected by tooth groove and grouted sleeve was introduced, which is produced in factories by means of structure-insulation integrated prefabrication, and the prefabrication and assembly process were presented minutely. To verify the feasibility and reliability of this novel tooth groove and grouted sleeve connection method and explore the joint connection performance and the seismic performance of the precast concrete composite wall connected by tooth groove and grouted sleeve, low-cyclic reversed loading tests with an axial compressive ratio of 0.1 were performed on two full-scale precast concrete composite walls. Moreover, the failure mode, hysteretic curve, skeleton curve, stiffness degradation, displacement ductility, energy dissipation capacity, and reinforcement strain were comprehensively discussed. The research results showed that under the vertical axial load and low-cyclic reversed load, the distributed reinforcements in the wall panel only played a structural role, while the connecting reinforcements at horizontal joints can always effectively transfer stress without bond failure, and the tooth groove and grouted sleeve connection performance was reliable. In addition, the hysteretic curves of the precast concrete composite wall connected by tooth groove and grouted sleeve were full, showing good ductile deformation capacity and energy dissipation capacity. In general, the precast concrete composite wall connected by tooth groove and grouted sleeve not only possessed favorable seismic performance but also showed obvious advantages such as green energy saving, high assembly rate, and less on-site wet operation, which can be applied to practical engineering under reasonable design. Full article

An assembled floor system is a main step in the industrialization of construction in civil engineering, where the stiffness and anti-crack properties under designed loads and its self-weight are the main concerns. This paper presents a new type of assembled integral composite floor system, which is composed of precast ribbed bottom slab, lightweight infills, cast-in-situ upper slab and joints. Through the couplers for squeezing and splicing of longitudinal bars, shear keys and cast-in-situ joints between the precast panels and cast-in-situ upper part, the whole hollow floor system could not only exhibit satisfactory mechanical performance, but also lower the self-weight and shorten the construction time. To study its flexural behaviors, a full-scale specimen sized 9.2 m × 9.2 m was designed and tested under static area load. With the load increased to the designed loads of Chinese design code GB50010-2010, mechanical performance (i.e., crack distribution, deformation and stress distribution) were analyzed. To further study its load-carrying capacity and working mechanism, an effective finite element model was established in ABAQUS and compared with experimental and simulation results. It was found that the deflection of the floor under the normal service load and the crack width met the needs of normal use, and the finite element model could serve as a reliable method for the load-carrying capacity calculation. Full article

The joint form plays a vital role in the rapid assembly of precast bridge decks for steel–concrete composite bridges. Existing research primarily focuses on studying the shear performance of joints through direct shear tests, which is insufficient to fully reflect the mechanical behavior of joints under the constraint of prefabricated bridge deck panels during actual vehicular traffic. Considering situations such as vehicle loads and external forces acting on precast bridge decks, this study investigates the shear performance of epoxy joints under constraint through an improved shear test. The influence of constraint force, shear key details and interface defects on the shear performance of epoxy joints is investigated. The results reveal that the shear test method employed in this study can realistically reflect the shear performance of epoxy joints in precast bridge decks. Both active and passive constrained epoxy joint specimens exhibited no interface cracks, and their failure modes were identified as shear failure between mid-span supports. Compared with passive constraint, the shear-bearing capacity of epoxy joint specimens under active constraint was increased by 86.1~130.6%. Among the epoxy joint specimens with depth–height ratios of 15/110, 25/110, 35/110 and 45/110, the joint with a depth of 35 mm demonstrated the highest shear strength. Furthermore, the shear performance of epoxy joints significantly deteriorated when the interface defects exceeded 30%, resulting in the failure mode transforming from shear failure to interface failure. Full article

Assembled steel-composite bridges generally use stud connectors to achieve the connection between the deck slab and the steel main girders. However, the commonly-used cluster studs weaken the integrity of the precast deck slabs and are not conducive to reducing the size of the precast deck slabs. Based on the excellent mechanical performance of UHPC, a precast steel-concrete composite bridge system consisting of precast bridge deck slabs, bonding cavities, and steel girders was proposed in this study. The system was named PSCC (Precast Steel-Concrete Connectors). To verify the applicability of PSCC connectors in engineering, push-out tests and finite element analysis were carried out in this paper to investigate the shear performance and influence parameters of PSCC connectors. The results showed that compared with the full bonding at the steel-UHPC interface, the shear bearing capacity of the specimens with 30% debonded area rate (the ratio of defect area to total interface area) and the shear bearing capacity of the specimens with 60% debonded area rate decreased by 0.35% and 9.74%, the elastic stiffness decreased by 14.86% and 21.72%, and the elastic-plastic stiffness decreased by 1.6% and 12.8%, respectively. When the steel-UHPC percentage of debonded area is less than 30%, the shear resistance of PSCC connectors is affected very little. However, when the steel-UHPC percentage of debonded area is 60%, the shear resistance of PSCC connectors is greatly affected. Therefore, adequate filling of the UHPC connection layer should be ensured in the project. In addition, the PSCC connectors have excellent ductility, their characteristic slip value $S_u$ is much higher than the EC4 specification of 6 mm, and they have better shear performance than conventionally installed stud connectors. According to the results of the parametric analysis, it was found that the failure mode of the PSCC connectors was shear reinforcement fracture when the area ratio of shear reinforcement to stud was less than 1.55, under the premise of the same material strength. On the contrary, the failure mode of PSCC connections was stud fracture. When the transverse spacing of both studs and shear reinforcement is 4d, the PSCC connectors can maintain a high ultimate load capacity while reducing the amount of UHPC in the bonding cavity. Therefore, 4d was chosen as the best spacing for both studs and shear reinforcement. Full article