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The pressed sleeve connection is a new type of connection technique reported in China recently. To explore the possibility of combining the advantages of pressed sleeve connections and recycled aggregate concrete (RAC) in precast concrete, the seismic performance of precast shear walls with pressed sleeves and recycled fine aggregate (RFA) concrete was investigated through a thorough experimental programme. A total of seven precast shear wall specimens and one cast‐in‐situ specimen were fabricated and tested under lateral cyclic loading, considering the effects of the aspect ratio, the axial compression ratio, and the RFA content. The failure modes, hysteretic behavior, bearing capacity, energy dissipation, stiffness and shear distortion of the specimens, as well as the strains of the steels, were reported and discussed. The test results demonstrated that the pressed sleeve connections were capable of transmitting both tensile and compressive forces between reinforcements, and the precast shear walls with pressed sleeve connections exhibited the same hysteresis behavior, strengths, ductility coefficient and energy dissipation capacity as the cast‐in‐situ counterpart. Moreover, the seismic behavior of the precast specimens with the RFA content of 30% was almost the same as those with natural aggregate concrete (NAC). The increase in the axial compression ratio and aspect ratio led to higher peak loads of the precast shear walls. Finally, existing design methods of ordinary reinforced concrete shear walls were evaluated for their application to the design of precast RFA concrete shear walls with pressed sleeves. Overall, the evaluation results revealed that the examined design methods offer generally accurate strength predictions for the proposed shear walls. [ABSTRACT FROM AUTHOR]

With the rapid development of underground rail transportation in China, the demand for precast concrete pipe sheets in metro construction continues to increase, and the quality and safety of precast concrete pipe sheets profoundly affect the safety of tunnels. The quality and safety of precast concrete pipe sheets have a profound impact on the safety of tunnels. The maintenance of pipe sheets plays an important role in ensuring the strength and durability of concrete pipe sheets. Therefore, it is important to study the maintenance methods of concrete pipe sheets. The method of substituting immersion curing with spray curing is proposed in this paper. It has been shown that spray curing can overcome the challenges of high pollution and high cost caused by the immersion curing of precast concrete pipe (PCP) sheets. Experimental tests investigate the influence of macro-mechanical properties and microstructure of pipe sheet materials under various ages of the two curing conditions. The results highlighted that the conventional methods of water immersion for PCP have minimal effect on concrete's macro-mechanical characteristics or microstructure after a certain curing age. The comparative studies on both curing processes showed that after seven days of curing, the degree of moisture attained by the spray-cured samples was relatively lower than that of the water immersion approach. In addition, samples with the water spray curing process had larger pore sizes (which could degrade faster) with lower mechanical strength. Interestingly, after 28 days of curing age, both approaches attained complete hydration levels, resulting in a dense pore structure with reduced median pore size and higher mechanical performance. Investigations on two distinct methods indicated that the early strength properties (after seven days of curing) acquired with water immersion curing were higher than the mechanical properties obtained with spray curing. This difference in mechanical properties, in addition, was not significant after 28 days of curing age. As a result, the suggested technique of water spray curing is an appropriate method with minimum water use to some extent. [ABSTRACT FROM AUTHOR]

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The traditional precast concrete column-to-column connections are widely used in the prefabricated concrete frame structures in China. However, many studies on the column-to-column joints have demonstrated their complex forms and poor construction efficiency. To overcome these shortcomings, a new type column–column connection with steel plate hoop and bolts was designed and proposed. In order to reveal the seismic performance of this new type connection, four precast concrete columns and two cast-in-situ columns were tested by cyclic lateral loading. They were compared and analyzed from the aspects of test phenomenon, failure mode, load–displacement relationship, strength, and stiffness degradation. The results showed that the prefabricated columns with this new type connection had the same seismic performance as the cast-in-place columns. Additionally, the strain curves of longitudinal reinforcement, stirrups, and steel plate hoops were presented, and the force transmission mode of this novel connection was analyzed. The results indicated that the innovative connection had reliable force transmission mode, which can provide reference for the application of prefabricated frame structure in the earthquake area. [ABSTRACT FROM AUTHOR]

A concrete‐cored gravel (CCG) column is composed of a precast concrete pile inserted at the center of sand or gravel materials. This technique has been experimentally adopted to support the soft soils in China. However, there has been limited investigation on the consolidation characteristics of a CCG column improved foundation under embankment loading. This study develops analytical solutions for the consolidation of a composite foundation partially penetrated by the CCG columns. The rigid pile's upward and downward piercing effects were considered to improve CCG column‐soil equal strain relationship. The partially penetrated consolidation problem was addressed by assuming the seepages in the unpenetrated layers to be vertical or horizontal and vertical combined. A simplified approximate method was also provided, enabling the users to quickly evaluate the consolidation process of a foundation partially penetrated by the CCG columns. The proposed solution was applied to a case history of an anti‐flood embankment on soft soil with partially‐penetrated CCG columns, and a good agreement was found between predictions and the field measurements. [ABSTRACT FROM AUTHOR]

The mechanical performance of precast RC structures relies on the connections, especially the connections of steel bars, between precast RC members. Grouted sleeve splices and grouted spiral-confined overlap connections are widely used in engineering practice in China. Both of these two connection splices require on-site grouting. The process is concealed and invisible, leading to difficult on-site inspection. The unseen defects cause a challenge for detection and repair, which may impair the reliability of precast RC members' behavior. This paper presents an RC member assembly connection with visible on-site construction quality-monitoring. The proposed confined headed-bar connection (CHBC) consists of two overlapping headed bars and confinement stirrup. With CHBC, the potential construction defects are diminished, and subsequently the construction quality as well as the reliability is upgraded. Experimental investigation on 18 CHBC specimens was carried out; the main parameters considered were overlap length and bar-head size. The failure modes, bearing capacity, stirrup strain development and bond versus slip response are studied. Working mechanism of CHBC is investigated in terms of bond behavior force and concrete compression force at head experimentally and numerically; distributive relationship of these two forces is revealed. The results show that for Φ12 reinforcement, a 90 mm overlap length under test parameters is adequate to reach headed bar ultimate strength in CHBC. Finally, a CHBC-bearing capacity prediction method is suggested based on the superposition method and strut-and-tie model theory. [ABSTRACT FROM AUTHOR]

In this paper, the fatigue performance of six steel–concrete composite beam specimens was tested following subjection to chloride-induced corrosion and cyclic freeze–thaw conditions. The specimens included cast-in-place concrete slab composite beams with uniformly distributed studs and precast concrete slab composite beams with a cluster distribution of studs. According to the climatic characteristics of large temperature differences between day and night in alpine and high-altitude areas of Qinghai Province of China, together with the working conditions of bridges under deicing salt after snow, corrosion tests and freeze–thaw tests of composite beam specimens were performed prior to fatigue testing. The test results show that the freeze–thaw cycle causes obvious frost heave damage to the concrete, which affects its strength and stiffness. When the composite beam specimens were subjected to fatigue loads, tearing failure of the steel plates at the welds and interface failure at the studs were observed. Furthermore, with the influence of stress amplitude, fatigue life was found to be related to the initial crack defect within the specimen itself. Reduction in the initial stiffness of composite beams was found to be affected by the freeze–thaw cycle, stud arrangement type (uniformly distributed or cluster distributed), and steel type (ordinary steel or weathering steel). However, the stiffness degradation rate of all specimens against loading times was essentially identical before fatigue failure. [ABSTRACT FROM AUTHOR]

The rapid development towards automated construction has been witnessed in recent years mainly due to the growing shortage of skilled labor. Against that backdrop, an accelerated method, with the aid of robotic cranes, is emerging in China to speed up the construction of industrial facilities such as warehouse structures. This method requires that the steel bars in the precast beams do not extend beyond the beam ends to facilitate the temporary fixation of the robotic crane at the top of cast-in-place columns. This, nonetheless, brings a series of new problems, one of which is how to choose a suitable anchoring type for the beam bottom bars. To address this issue, three large-scale exterior beam-to-column connections were fabricated and tested under lateral load reversals. Two anchorage forms, namely, mechanical splices and grouted sleeves, were adopted and compared with the monolithically cast specimen. The test results showed that the specimen using the grouted sleeves had similar seismic performance to that of the cast-in-place specimen, whereas the specimen using the mechanical splices presented significant post-peak deterioration under positive beam bending moments. This happened because the congestion of steel bars within the joint core made it difficult to fully tighten the beam bottom bars into the threaded couplers; consequently, a "slop" was formed which could substantially impair the cyclic behavior of the specimen. As such, it is suggested that grouted sleeves should be more applicable and reliable for the new construction method. This counter-intuitive finding also indicates that, for intelligent construction, no detail should be taken for granted, but rather needs due consideration. [ABSTRACT FROM AUTHOR]

Summary: Nowadays, the grouted splice sleeve and grouting‐anchoring overlap‐joint of steel bars are widely used as a connection method between precast concrete elements. However, the further development of these connection methods in the engineering is limited because of the high construction cost and complex construction technology in China. Hence, a precast concrete reinforcement connector, that is, double‐pipe connector (D‐P connector) based on strong lapping concept, was proposed, and the feasibility of the D‐P connector was validated by tensile tests, and the failure pattern and mechanical properties of the specimens were observed. Then, the wall panel specimens that connectors were surrounded by concrete were tested to prove the constraint effect of surrounding concrete on the connecting members. Finally, the influences of the parameters, including grout strength, grout height, and connector length, on the failure pattern and mechanical properties of the specimens were investigated. The results show that the influence of the parameters on the performance of the specimens is insignificant, demonstrating that the infill material was mainly used to fix the relative positions of the bar and the D‐P connector. To save cost effectively, high‐strength grout could be replaced by common cement slurry, and the length of D‐P connector could be properly reduced. [ABSTRACT FROM AUTHOR]

The fatigue life of the cement asphalt (CA) mortar in the slab track of the China Railway Track System (CRTS) II is crucial to the smooth and safe operation of high-speed railways. To investigate the fatigue life of the CA mortar under the combined thermal action and vehicle loads, this paper develops a new coupled thermal-mechanical finite element (FE) model for the concrete slab track at the mesoscale. First, the meteorology and heat transfer principle are adopted to simulate the temperature distribution of the concrete slab track. The heterogeneous characteristics of the concrete of the precast slab are modelled by the three-phase composite material at the mesoscale using the new developed random aggregate algorithm. Then, the energy-based exponential cohesive zone model is adopted to simulate the interface between the CA mortar and the precast concrete slab. The proposed mesoscale numerical model can provide reliable predictions for the temperature distribution and the deformation of the precast concrete slab under thermal action, which are confirmed by the relevant field measurements. Finally, the fatigue life of the CA mortar is estimated by the nonlinear damage cumulative method associated with the stress time history under the combined thermal action and vehicle load. From the obtained results for the numerical example, the thermal action can decrease severely the fatigue life of the CA mortar, and the fatigue life varies significantly at different positions, with the most vulnerable zone located near but not directly below the rails. • Proposing the coupled thermal-mechanical FE numerical modelling for railway concrete slab tracks. • Developing new random aggregate algorithm for modelling heterogeneous concrete at the mesoscale. • Predicting reliably CA mortar fatigue life using nonlinear damage cumulative method under combined action. [ABSTRACT FROM AUTHOR]

In China, with the expansion of the prefabricated construction market, the demand for precast concrete (PC) components is increasing and the construction of production plants to meet this need is expanding. To address the problem of siting PC component plants in China's construction industry, a combination of qualitative and quantitative analysis using principal component analysis (PCA) and geographic information system (GIS) is proposed for their siting. Taking the site selection process of a PC component plant in Wuhan, Hubei Province, China as an example, the diamond model is combined with six dimensions of environmental factors, requirements, regional competition, related and supporting industries, technological innovation and policies and regulations to construct an indicator system for PC component plant site selection. In the preliminary selection stage, PCA was applied to analyze the site selection indexes to obtain the overall score and ranking of each district for the selection of PC component plants in Wuhan, and it was concluded that three districts, namely, Xinzhou, Hannan, and Huangpi, were more suitable for the construction of component plants. In the precise selection stage, based on the availability of data, Hannan was selected among the three areas suitable for site selection for GIS analysis, using the visual-spatial analysis function of GIS to quantify the four geographical information indicators of environmental factors, and the results showed that Area C in Hannan was the most suitable area. The results show that the method has high accuracy and good applicability. [ABSTRACT FROM AUTHOR]

For emulating cast‐in‐place (CIP) precast concrete (PC) shear wall structures in China, the adjacent PC shear wall components are joined by vertical post‐cast concrete. Shear behavior of concrete‐to‐concrete interfaces is critical for structural integrity. A novel preparation method, as cast using bubble film (BF) form, is proposed. Shear performance experiments are conducted to obtain the shear capacity and deformation characteristic of the specimens by the preparation methods of hydro‐demolition (HD), as‐cast by patterned steel plate (PSP) form and BF. Concrete strength and shear reinforcement are also considered. By comparison with reference CIP specimens, HD specimens performs best, followed by BF specimens, and the worst are PSP specimens. The collected shear loads for HD and BF specimens are larger than calculated results under diagonal shear failure, assuring structural integrity. Concrete strength and shear reinforcements have effective influence on interface shear capacity. Shear reinforcements with small diameter and small spacing are recommended. [ABSTRACT FROM AUTHOR]

• Solar energy and PCM are used to augment the indoor steam curing process. • Mathematical model of the curing process is developed. • Comparison with experiments confirms the accuracy of the mathematical modelling. • Benefits of the proposed technology are quantitively demonstrated. Steam is used to provide heating and moisture in the curing process for the production of precast concrete (PC) construction elements. The generation of steam requires large amounts of fossil fuels. This study considers the incorporation of solar thermal energy into the steam curing of PC construction elements for reducing the need for fossil fuels and associated CO 2 emissions. For this purpose, the board made of composite phase change material covers the inner surface of the main sun-facing wall in the heating & curing building. The PCM board is heated by sun rays and accumulates thermal energy during the PCM's phase transition, and this energy then is released to the indoor environment of the building, reducing the amount of steam required to maintain a certain level of temperature during the curing process. The energy consumption simulation software, EnergyPlus, and two physical models (built on the scale of 1:3) were used to study the effects of two different PCMs on the thermal performance of such new type of heating & curing buildings. Composite PCMs considered were GH-33 and GH-37 with 33 and 37 °C melting temperatures developed by the research team. The theoretical and experimental results are in good agreement and demonstrate that, compared to the GH-33, GH-37 PCM increases the temperature of the inner surface of the main sun-facing wall and the upper surface temperature of the PC construction element by 3.4 and 1.4 °C, respectively. The heat accumulation and discharge rates also were greater by 62%. For the investigated design of the building and given location in China, the deployment of studied PCM wall panels results in a reduction in the annual energy consumption and CO2 emissions by 58.6 GJ and 5 tons, respectively. The method developed for applying solar energy and selecting PCMs for augmenting steam curing of PC construction elements can be deployed in different geographical regions. [ABSTRACT FROM AUTHOR]

Joints are always the key issue of the precast bridge structures for accelerated construction. In this paper, the transverse joint of a fully precast steel–UHPC lightweight composite bridge was proposed. Based on the first small–medium-span fully precast steel–UHPC lightweight composite bridge in China, the flexural test of the proposed T-shaped joint was conducted. The test result showed that no apparent crack can be seen in the middle of the specimen, and the successively poured joint interface was the weak link of the design. The equations of the joint interface maximum crack width and the ultimate bearing capacity were presented through theoretical analysis, and the prediction and the experimental results were generally consistent. The length of the proposed T-shaped joint upper part was discussed with the spans of 20–50 m, and the value of 0.1L was finally determined. [ABSTRACT FROM AUTHOR]

As the development of building industrialization and housing industrialization is speeding up in China, the application of precast concrete structure has been the research focus. The connection of prefabricated components is one of the key technologies in prefabricated concrete structure. So, a new type of column–column connection with steel plate hoop and bolts is proposed in this paper to promote the application of precast concrete structure. In order to reveal the flexural behavior and force transfer mechanism about this new type connection, six precast concrete beams and one integral casting beam were tested by the three-point bending under loading and unloading cycle. The comparative analysis is made between the new type connection and traditional integral cast-in-place member from the aspects of test phenomenon, failure mode, and load-deflection relationship. The analysis results show that the new type connection has the same bending bearing capacity as the integral casting member. Based on the analysis of the load-strain relationship of longitudinal reinforcement, bolts, and steel plate hoop, the moment transmission mechanism and theoretical calculation formula of the new type connection are proposed, and the theoretical calculation results are consistent with the experimental results. [ABSTRACT FROM AUTHOR]

In practice, bridge foundations and pier columns are usually constructed with cast-in-place concrete. Precast columns are currently widely used in highway bridges in China, which can save construction time and improve concrete quality. The connection between precast bridge columns and the foundation can affect how forces transfer from one to the other. This paper investigates using external sockets to form a connection between the bridge column and foundation. This method can accelerate the bridge construction time with the additional advantages of improving the orientation and creating a large erection tolerance. Two types of connections are presented and tested to investigate the behavior of the column-foundation connections and find a more suitable way to use external socket connections. The experimental results show that the column-foundation connection design satisfies the design requirements. The results also show that roughening the column surface within the external socket is more effective at connecting the column to the foundation when using an external socket compared to attaching a steel plate on the column. The experimental results are validated with a finite element analysis, resulting in a proposal regarding the column-foundation connection behavior as well as design recommendations for the external socket connection. [ABSTRACT FROM AUTHOR]

To overcome poor construction conditions, shorten construction time and improve project quality, the construction of Yushan Bridge in China is a fully industrialised, based on prefabrication of key components, site installation. The navigation span of the Yushan Bridge has a main span of 260 m and is the world's first segmented precast steel–concrete composite continuous-beam bridge. A new type of steel–concrete composite segment (a girder that connects the concrete box girders and the steel box girders) is used to ensure the bearing capacity and precision of closure. Thickened-edge U-shaped ribs and ultra-high-toughness concrete pavings are employed together to improve the durability of the orthotropic deck. A single-pile and single-column foundation is fully employed, with a maximum diameter of the steel composite pile (a pile that is outside is steel pipe, and the interior is filled with concrete) of 5 m. It is found that the construction time is reduced by 40%, the wave flow force is decreased by 80%, the scouring depth is decreased by 20% and the cost is reduced by 30% compared with group pilings. In addition, this method avoids durability problems of the pile cap due to group pilings. The use of a prefabricated exterior shell with cast-on-site concrete for the interior pier-top blocks of the 50 m non-navigation span solves the problems associated with the bearing force, durability, construction availability and quality control of the pier-top block. [ABSTRACT FROM AUTHOR]

Accelerated bridge construction (ABC) is becoming progressively popular in China due to its advantages in sustainable development. However, some challenges still prevent it from being further widespread, especially in some harsh environments. As one of the greatest advances in material science, ultra-high-performance concrete (UHPC) is regarded as a competitive option for addressing the challenges of ABC due to its excellent material properties. A new cost-effective UHPC was developed with some modifications to weaken some adverse factors influencing the applications of UHPC in ABC, that is, high initial cost of material and steam/extreme heating curing requirements. Cost-effective UHPC is deemed to have the potential to build the critical zones of precast bridges, such as stress concentration zone, fatigue stress zone, inelastic deformation zone, harsh environment exposure zone, and late-cast joint zone, considering its material properties. In recent years, a series of tests have been done to investigate the cost-effective UHPC's material properties and its structural elements' mechanical behaviors. This paper systematically reports the cost-effective UHPC alternative for ABC from the laboratory tests on material properties and structural elements to real bridge implementations. Some challenges and future opportunities are presented for reference. The experimental results show that the cost-effective UHPC can have superior material properties and its structural elements can have satisfactory mechanical behaviors. Real engineering examples demonstrated that the cost-effective UHPC enables precast bridges to be lighter in weight, have higher strength, and support longer spans. The biggest challenge may be that more research and engineering examples are required to validate the feasibility of UHPC codes for cost-effective UHPC when it is applied in ABC. [ABSTRACT FROM AUTHOR]

A new structure named reinforced concrete grid moment‐resisting frame (RC‐GMRF) have been adopted in high‐rise buildings in China. However, complex construction due to numerous beam‐column joints restricts the application of this structure. A novel precast reinforced concrete GMRF (PC‐GMRF) is proposed in this paper to solve this problem. Three specimens, including one traditional reinforced concrete moment‐resisting frame (RC‐MRF) as reference, were tested under reverse cyclic loading to evaluate the seismic performance. All three specimens were designed using the same amount of construction material. The experimental results showed that PC‐GMRF exhibited comparable seismic performance with that of RC‐GMRF. The load‐carrying capacity, initial stiffness and energy dissipation capacity were improved by an average of 43%, 29%, and 21%, respectively, compared with those of RC‐MRF. This study indicated that the performance of PC‐GMRF was acceptable and could be used in the moment‐resisting frame as a novel structure. [ABSTRACT FROM AUTHOR]

Most of the foundation structures of high-piled wharfs in North China are precast pre-stressed concrete square piles, and the main reinforcement is pre-tensioned pre-stressed steel bar. In order to deeply study whether there is stress loss in the process of pretensioning method and the influencing factors of stress loss, through the detection of reinforcement stress in reinforced frame of concrete square pile in tension under different working conditions, the influencing factors and magnitude of the stress are analyzed, the construction technology is improved, and the electro-hydraulic servo control system for DGS-16 channel prestressed tension are developed and introduced, which provides strong technical support for the reinforcement tensioning of the subsequent pretensioning construction and provide reference for similar projects in the future. [ABSTRACT FROM AUTHOR]

Based on the first successful application of new prefabricated technology in underground metro stations on line 2 of the Changchun Metro in China, a comprehensive analysis and discussion on research strategies for new prefabricated technology for large underground structures is provided. This paper introduces the application status of prefabricated technology in underground engineering worldwide, illustrates the different characteristics of prefabricated technology applied to ground buildings and underground structures, puts forward the key technologies, and compares the major technical, economic, and social benefits achieved. The successful application of prefabricated technology for underground structures in Changchun Metro demonstrates the feasibility and great advantages of the new prefabricated technology for underground engineering. [ABSTRACT FROM AUTHOR]

Precast concrete structure has been increasingly used all over the world. Its seismic performance has always been the key factor of its application in earthquake‐affected zones, especially in China. A new precast concrete shear wall structure using grouted lap splice connection and cast‐in‐place concrete was proposed in this paper. Low‐cyclic reversed load testing was conducted on a one‐half scale spatial specimen of the bottom four stories of the new precast concrete shear wall structure. The test results were compared with the push‐over analysis results to evaluate the seismic performance of the specimen. The specimen showed good integrity and satisfies the current demands for Chinese seismic fortification. Moreover, due to the effect of infill walls strengthening the shear walls, and the effect of local cast‐in‐situ concrete regions constraining the precast components and connecting transverse walls to longitudinal walls, the specimen performed as tube structure and possessed excessive strength and stiffness. [ABSTRACT FROM AUTHOR]

The quality of precast concrete (PC) component connections is one of the main factors that affect the seismic reliability of PC structures. China is developing PC structures in high seismic regions, and it is important to assess the effect of connection deficiency on seismic performance of PC structures. This paper presents a comprehensive method to assess the seismic reliability of PC shear wall-frame structure whose wall panels are assembled through grouted sleeve connections which are susceptible to insufficient grouting. Considering the uncertainties associated with the number, locations and loading behavior of defected sleeve connections, the probabilistic behavior of PC shear wall with defected connections is estimated through point estimate method using simulation results of the experiment-validated finite element model. Then, a simple shear wall-frame building, designed for the seismic intensity of 8 according to China's seismic design code, is modeled on platform of OpenSees. Static pushover analyses and seismic fragility analyses are performed on the structure with different degrees of connection deficiency, to investigate the effect of deficiency occurrence rate on seismic performance. The seismic performance is significantly affected by connection deficiencies; it no longer meets the requirement of seismic design as the deficiency occurrence rate exceeds 25%, so the occurrence rate of defected connections should be controlled carefully in construction site. [ABSTRACT FROM AUTHOR]

Highlights • The static and dynamic mechanical properties of steam-cured concrete under frozen state were investigated. • The influence of subfreezing temperature on mechanical properties was analyzed quantificationally. • The mechanism of ice influencing concrete was discussed by proposing a physical model. Abstract The precast structures prepared by steam-cured concrete have been increasingly used in order to speed up the construction of China's High-Speed Rail and passenger dedicated lines in recent years. In the high-cold regions, such as Harbin, the precast concrete structures are exposed to continuous subfreezing temperature for several months every year. However, the influence of continuous subfreezing condition on mechanical properties of concrete has not been systematically investigated yet. According to the Laplace Equation and Gibbs-Duhem Equation, the theoretical size of minimal frozen pores and ice content in water-saturation concrete at −20 °C can be calculated. It is discovered that the change ratios of mechanical properties are related to the theoretical ice content in concrete. Phenomenological models between change ratios and ice content are established based on hyperbolic equations. Finally, the mechanism of phase transition of free water on mechanical properties is explained by means of classical fracture theory of concrete. In this research, a contrastive research was carried out under two temperature conditions of 20 °C and −20 °C on mechanical properties of steam cured concrete at 28 days, including compressive strength, flexural strength, dynamic modulus of elasticity and damping ratio. Experimental results obtained at −20 °C indicate that compressive strength, flexural strength and dynamic modulus of elasticity increase to some extent and damping ratio decreases. And the application of supplementary cementitious materials (fly ash and GGBS) on concrete has a significant impact on the variation ratio of mechanical properties under freezing temperatures. The results of micro structure by quantitative test reveal that the pore distribution was greatly optimized and the percent of harmful pore were substantially reduced by the supplementary materials of fly ash or GGBS. [ABSTRACT FROM AUTHOR]

China’s rapid urbanization along with the development of the modern economy is certain to result in a long-standing and substantial energy demand in the entire society. Therefore, industrialization in building construction is a vital strategy for alleviating adverse environmental burdens and accelerating urbanization with the current construction practice. An integrated method was employed to evaluate the life cycle energy performance of prefabricated buildings, using the process-based hybrid life cycle assessment and scenario-based energy simulation as the underlying methods. Results revealed the less obvious energy reduction potential of prefabricated buildings during the embodied phase. During the building operation phase, the scenario and comparative analyses from a life-cycle perspective indicate that prefabrication generates environmental gains by providing enhanced thermal performance. A regional level policy analysis reveals the backwards status quo of the precast construction in Northern and Western China. Given the significance of using prefabrication in building energy conservation, it is quite urgent and necessary to establish a mature construction market with highly evolved industrialization in these “backward” regions. [ABSTRACT FROM AUTHOR]

The development of prefabricated buildings is a long-term industrial policy in China. In the prefabricated frame structure, the slab is one of the critical components. However, two kinds of famous prefabricated slabs in China need the template system and sometimes need a particular fabrication site. The paper proposed a novel prefabricated concrete composite slab, which adopts the high-strength bolt as the shear connector. Compared with the traditional precast concrete composite slab, the novel prefabricated concrete composite slab does not need a template and temporary support. Compared with the conventional composite slab, it has analogous rigidity. Still, it does not require a fireproof coating. It has fast construction speed and a low comprehensive cost. The paper conducted 13 slab specimen bending tests on the novel composite used recycled aggregate concrete (RAC) and normal weight concrete (NWC) to reveal the slab's flexural behavior. The test data and analysis show that the three-inch-high profiled steel sheeting as a shear connection can have an excellent composite effect. The neutral axis of the whole section always locates within profiled steel sheeting. And the profiled steel sheeting has been participating in the load-bearing work of the composite slab. The composite slabs showed good bending bearing capacity and ductility. The RAC with a replacement ratio of 50% recycled aggregate has the same material performance and member performance. The composite slab proposed can meet most civil buildings' design requirements. The standard push test revealed that the bolt shear connectors' ultimate bearing capacity meets the Chinese design code with the floor's considerable slippage. [ABSTRACT FROM AUTHOR]

Prefabrication techniques have been adopted for the last two decades in public housing projects in Hong Kong, but the use of prefabrication in the private sector was encouraged only after the implementation of the Joint Practices Notes which promote its use. Although previous studies acknowledge the environmental benefits of using prefabrication, only a few studies have addressed sustainable design concepts (closed-loop) in the adoption of precast construction. A questionnaire survey was administered to experienced Hong Kong construction professionals, and case studies of recently completed building projects were compiled to ascertain the use of prefabrication with reference to life cycle approach. The findings revealed that prefabrication, combined with modular design and standard components, saved time and construction/design costs, as buildings systems were used across projects. However, in some projects, specific site conditions restricted the use of similar prefabricated building systems across projects. Surprisingly only a few participants addressed life cycle design concepts such as design for deconstruction when adopting precast construction. Also, although it is common knowledge that flexible and demountable prefabricated building systems would result in efficient use of resources, their use is seldom practised in Hong Kong. [ABSTRACT FROM AUTHOR]

• A novel connecting approach for precast members with notches is proposed. • A total of 54 specimens with and without new-to-old concrete interfaces are tested. • Critical influence factors on bond performance are discussed in depth. • Feasibility of proposed connection and its failure mechanism are studied. • Design method and calculation formulas for notched connection are developed. In monolithic precast concrete structures, the connection between precast components with extended reinforcing bars usually encounters problems regarding conflicts in reinforcement placement. In particular, the problem of reinforcement conflicts is more prominent for precast slabs in China. In order to solve reinforcement conflicts encountered during practical construction, a novel connecting approach for precast members is proposed. This new approach involves setting notches at the end of precast components and anchoring reinforcing bars at the specially designed notches. This new approach ensures that the structural performance of the joints for precast members is similar to that of cast-in-place structures while minimizing the protrusion of reinforcement at the end of the member. In order to investigate the force transfer mechanism of the proposed method and its applicability to precast slabs, a total of 54 specimens with and without notches are designed and tested using pull-out experiments. Based on the experimental analysis, it is found that the existence of the new-to-old concrete interface changes the anchorage strength of steel bars in the notches. The effect of new-to-old concrete interface on the bond strength of steel bars and the desirable anchorage length of steel bars at the concrete interface are analyzed. The influences of steel bar diameter, anchorage length, concrete strength and reinforcement ratio of the concrete cover on the structural performance are discussed and compared in depth. Through the experimental results, the main factors affecting the bond strength of steel bar anchorage in the notched connection are identified. The physical mechanism of force transfer of the proposed method is developed and described. Preliminary calculation and design methods are presented to guide the practical application of the proposed method and to further facilitate the construction process of the precast structures. [ABSTRACT FROM AUTHOR]

• A 3-D nonlinear finite element model of the CRTS II slab track was developed. • The influences of the lateral differential subgrade settlement were discussed. • The concrete damaged plasticity model was used to simulate concrete damage. • The cohesive zone model was used to model interface damage. The differential subgrade settlement is a key issue in the operation of the high-speed railway, which affects the mechanical properties and service status of the track structure. To estimate the effects of the lateral differential settlement of the subgrade on the China Railway Track System (CRTS) II slab track, a 3-D finite element model was developed considering the damage behaviors of the concrete material and the interface cohesion of the slab track. The track deformation, the concrete damage, the interface damage were analyzed, respectively. The results indicate that the track structure has an obvious lateral tilt in the subgrade settlement section. The track structure on the side with the larger settlement is in a more unfavorable state. The concrete base and the precast slab are successively damaged when the settlement amplitudes of the subgrade are 20 mm and 40 mm respectively under the subgrade settlement condition with a settlement wavelength of 20 m. There exists a particular wavelength that maximizes the interface damage variable. The track structure is in a suspended state under the settlement condition with a large settlement amplitude and a short settlement wavelength. [ABSTRACT FROM AUTHOR]

The construction industry in Hong Kong heavily relies on conventional cast in-situ construction involving extensive use of timber formworks and wet trades. In 2001, the Construction Industry Review Committee (CIRC) report described the construction activities in Hong Kong as 'labour intensive, dangerous and polluting', in which 'built products are rarely defect-free'. Globally, however, the recent trend is prefabrication, which is being increasingly used in the building industry, alleviating some of the environmental burdens associated with conventional construction. The sustainable construction aspects of adopting prefabrication in high-rise buildings are examined, and the economic, environmental and social aspects of using prefabrication are assessed. A questionnaire survey was administered to experienced professionals and case studies of seven recent residential and non-residential buildings in Hong Kong were conducted. The findings revealed that environmental, economic and social benefits of using prefabrication were significant when compared to conventional construction methods. This implies that a wider use of prefabrication techniques could contribute to sustainable construction in a dense urban environment like Hong Kong. [ABSTRACT FROM AUTHOR]

• Bilinear CZM was introduced and utilized to simulate the interface damage. • A 3-D finite element model of the CRTS II slab track was established. • The effects of high temperature on the arching of the track slab were studied. • Mechanical performance of the slab track with joint concrete damage was analyzed. To study the interface damage and the arching deformation of China railway track system (CRTS) II slab track under high-temperature conditions, a three-dimensional (3D) finite element model of the CRTS II slab track was developed. A cohesive zone model (CZM) with a non-linear constitutive law was utilized to simulate the interface damage between the precast slab and the cement asphalt (CA) mortar layer. The model was verified by comparing the simulation results with the experimental results. The effects of the overall temperature rise and positive temperature gradient on the interface damage and deformation of the track structure under the different damage levels of the joint concrete were studied. The analysis indicates that when the joint concrete is intact, the interface between the precast and the CA mortar layer does not appear damage under the effect of the overall temperature rise or the positive temperature gradient. The damage of the joint concrete is an inducement for the interface damage and the arching of the slab track under the action of high temperature. The interface damage area and the height of the interface gap increase with the increase of the damage degree of the joint concrete. Especially under the action of the overall temperature rise, the interface gap can reach more than 30 mm. More attention needs to be paid to the construction quality and maintenance of joint concrete. [ABSTRACT FROM AUTHOR]

Hybrid concrete (HC) structures are being promoted in China, as well as in other countries. The construction process of HC structures differs from that of traditional cast-in-situ (CiS) structures in two aspects: 1) the construction unit for HC structures is no longer a floor or a construction zone, but a single component, 2) both PC components and CiS components exist in HC structures, and are usually being constructed in parallel. Thus, the optimization of component-level construction schedule considering the construction sequence of different PC and CiS components is necessary for HC structures. However, existing studies about construction sequence optimization or schedule optimization have not taken such aspects into account. To fill the research gaps, this study proposes an approach to optimize the component-level construction schedule for HC structures. An optimization model for the component-level resource-constrained project scheduling problem for HC structures (C-RCPSP-HC) is formulated, involving the precedence relationships and resource constraints, with the objectives of the minimization of the construction makespan and the construction cost. To solve the C-RCPSP-HC model, a multi-objective discrete symbiotic organisms search (MODSOS) is developed to obtain the non-dominated solutions. A case study originated from a real project is conducted to verify the proposed approach. The result shows: 1) the component-level construction schedule optimized by the proposed approach is superior to the traditional construction zone-level construction schedule in eliminating construction conflicts, and contributes to shortening the makespan, decreasing the cost, and enhancing the resource utilization efficiency, 2) the proposed MODSOS has better comprehensive performance than other competitive multi-objective optimization algorithms in solving the C-RCPSP-HC model, as far as convergence, spread, and spacing are concerned. For future improvement, the estimation of the construction durations of activities from historical data will be done by using artificial intelligence methods. Besides, Building Information Modeling will be integrated to automate the data extraction. • A model for component-level resource-constrained project scheduling problem for hybrid concrete structures is proposed. • A multi-objective discrete symbiotic organisms search is developed to solve the proposed model. • A case study is carried out on the construction of a hybrid concrete shearing wall structure. • The component-level schedule contributes to improving the makespan, cost, and resource utilization. [ABSTRACT FROM AUTHOR]

• Cyclic tests of ten corroded beam-column joints of SCOPE system were conducted. • Corrosion of steel bars significantly affected seismic behaviors of the structure. • Key slot length affects the seismic performance and should be carefully determined. A frame Structure Comprised of Precast Prestressed Concrete Components (SCOPE) has been widely used in China. According to previous research, the length of non-contact lapped splice between U-shape bars and the steel strands plays an important role in seismic performance of the beam column joint. However, the splice may deteriorate due to corrosion when the frame is used in coastal region. This paper presents an experimental investigation on seismic behaviors of the corroded beam-column joints of the SCOPE system. Ten specimens with different key slot lengths and different corrosion levels were tested under cyclic loading, and their hysteretic loops, envelop curves, bearing capacity, and energy dissipation were compared and analyzed. It is observed that the corrosion of steel bars would significantly affect seismic behaviors of the structure, and most specimens showed flexural failure, while for the seriously corroded specimens with long key slots, failure might occur at the interface between the precast beam and the key slot due to severe corrosion and bond failure of the lapped splice. In general, the energy dissipation of specimens with shorter slot length was greater than that of specimens with the longer key slot under the same corrosion level. However, as the corrosion level increases, the difference became smaller. [ABSTRACT FROM AUTHOR]