In the hydraulic hoist design for a water conservancy hub project in western China, the vertically positioned, high-speed, heavy-load hydraulic cylinder is required to achieve closing speeds of up to 16 m/min, which is 4-5 times faster than conventional hydraulic hoists. Traditional buffer structures in hydraulic cylinders are insufficient to meet these performance demands. To address this challenge, a labyrinth buffer sleeve with multi-stage labyrinth buffer channels was designed and manufactured using additive manufacturing technology. The feasibility and effectiveness of the labyrinth buffer sleeve were evaluated through numerical simulations and experimental testing. Results demonstrate that the sleeve offers superior flow capacity, speed control, and pressure reduction capabilities. The maximum flow velocity within the labyrinth flow field reaches 111.7-166.5 m/s at the narrowest section of the flow path. The pressure ranges from 9.95 MPa at the inlet to 0.5 MPa at the outlet. Upon entering the buffer stage, the cylinder's velocity smoothly decreases from 8 to 9 m/min to 2 m/min. Compared to traditional spiral groove buffer sleeves, the 3D-printed labyrinth design enables staged buffering, reducing peak pressures by 80%, with peak values only 1/16 to 1/5 of those seen in conventional sleeves. This results in an 80% reduction in pressure impacts, eliminating the need for frequent on-site disassembly and reassembly for fit clearance adjustments.

The interface between new and old concrete is often considered a weak link of the strengthened structural members. A steel tube working as a casing jacket provides the constraint effect to the interface and will strengthen the weak link. This paper conducts splitting tensile tests to investigate the bonding strength of new-toold concrete confined by a steel tube. A total of 54 cube specimens and 54 cylinder specimens, which vary in casting date, interface roughness and jacket thickness are designed for the splitting tensile test. The observations regarding damages indicate that specimens without a jacket tend to exhibit splitting failure; those with a thin jacket display debonding-controlled failure; and those with a thick jacket demonstrate crushing-controlled failure. Particularly, the splitting tensile strength is significantly affected by the constraint effect, for the thickness of the steel jacket increases from 2 mm to 3.5 mm the strength increases from 4 MPa to 16 MPa. Meanwhile, the strength is mildly affected by the roughness of the bonding surface, for most comparison groups, the strength of roughened specimens is a little higher than that of unroughened specimens. Moreover, the strength is slightly affected by the pouring time interval of old concrete and new concrete, for there is no monotonous relation between strength and pouring time interval. Additionally, a correction formula for splitting tensile strength, which takes the constraint effect into account, is proposed to address the challenge of the newto-old concrete interface in structural reinforcement.

The behavior of bolted connectors with double embedded nuts (BCDENs) in steel-fiber reinforced concrete (SFRC) remains uncertain, restricting their application in steel-SFRC composite beams. This study explored the shear performance of four push-off test specimens, varying bolt diameters, bolt grades, and concrete strength. The analysis covered failure modes, load-slip response, load-strain behavior, shear resistance, initial slip load, stiffness, peak slip, and ductility of BCDENs. Bolt shearing off was the prevalent failure mode observed in all specimens, occasionally accompanied by concrete crushing beneath the nuts. The incorporation of steel fibers in normal-weight concrete (NC) effectively mitigated the formation and propagation concrete cracks. The horizontal slip of the concrete slab ranged between 10.8% and 26.0% of the vertical steel-concrete slip. Shear resistance and post-slip stiffness escalated with increased concrete strength, bolt diameter, and bolt grade. Validated FE models were employed for parametric studies involving concrete strength, bolt pretension, diameter, and tensile strength. Based on experimental and FE findings, practical design recommendations were proposed for predicting shear resistance and force-displacement response of BCDENs in steel-SFRC composite beams.

The current understanding of the shear behavior of double embedded nuts bolted connectors (DENBCs) in steel- fiber reinforced concrete (SFRC) remains unclear, particularly when DENBCs are embedded in the negative moment region (NMR). Two types of push-off test specimens were designed to investigate the differences in shear performance of DENBCs in the positive and negative moment regions of steel-SFRC composite beams. The experimental parameters primarily included bolt diameter, bolt grade, steel fiber volume content, and concrete type and strength. Compared to the failure mode of push-off specimens in the positive moment region (PMR), the concrete slabs in the NMR exhibited more pronounced crack development due to the influence of the tensile stress field. Adding steel fibers in normal-weight concrete (NC) and increasing fiber volume content effectively suppressed the initiation and propagation of cracks. The uplift of DENBCs was more noticeable in the NMR compared to the PMR. The steel fiber volume content had a marginal impact on bolt shear capacity but significantly enhanced ductility. Bolt shear capacity saw augmentation with higher concrete strength, bolt diameter, and grade. The shear resistance of DENBCs in the NMR exhibited lower values than in the PMR. Finite element (FE) models, validated through test data, were utilized to perform parametric studies encompassing concrete strength, bolt pretension, diameter, and bolt tensile strength. Based on the experimental and FE findings, practical design recommendations were formulated to predict the shear capacity and the load-slip response of DENBCs in the PMR and NMR of steel-SFRC composite beams.

The ever-increasing demand for accelerated construction of urban bridges or viaducts calls for more prefabrication with various joint schemes, while satisfying the need for seismic resilience. On the other hand, segmentation into components of various shapes and morphologies is common for multifunctional structures found in living organisms and ancient Chinese timber structures, which also inspires the development of resilient segmental bridge column design. To provide further insights into the cost-effective resilient design of precast bridge columns, this paper suggests the use of resettable sliding joints (RSJ) comprising lubricated gentlyinclined joint interface with partially debonded tendon arrangement, essentially forming a hybrid sliding and rocking seismic isolation system of precast segmental structures. The deformability of the proposed design is high. Similitude analysis was conducted considering the rigid body behavior of individual segments under seismic input. It presents the conceptual shaking table testing of four 1:12 prestressed segmental column models fabricated with special three-dimensional (3D) printed plastic molds and interface treatment. A motion capture system was installed for accurate 3D displacement data acquisition and five typical major near-fault earthquake records were selected. Among all specimens, the RSJ segmental column could reach a high damping ratio of about 20 % during the tests, and it outperformed the others in many aspects: (i) a tolerable maximum top drift of about 1 %; (ii) a moderate percentage of transient rocking of about 20 %; (iii) an evenly distributed sliding displacement among all sliding joints; and (iv) negligible residual sliding drift at sliding joints. These superior attributes of RSJ segmental column are consistent under excitation of consecutive rounds of different major earthquake records, indicating high robustness as well as high seismic resilience in the design of RSJ segmental columns.

To improve the bond durability of fiber-reinforced polymer (FRP) bars with coral aggregate concrete (CAC), this study employed alkali-activated materials (AAMs) as an alternative to ordinary Portland cement for preparing alkali-activated slag CAC (AACAC) and investigated their bond behavior with FRP bars under seawater corrosion environments. The influences of various exposure times (0, 6, 9, and 12 months) and seawater environments (seawater immersion and drying-wetting cycles) on bond performance were considered. Scanning electron mi-croscopy (SEM) and X-ray diffraction (XRD) were adopted to characterize the microstructural changes and mineralogical characteristics at the cross-section of BFRP bars and at paste matrix-aggregates interfaces of the concrete after seawater environment exposure. The tested results manifested that with the increase in exposure age, the bond strength for AACAC and CAC specimens gradually degraded, but their slope at the ascending stage of bond-stress curves (i.e., bond stiffness) tended to be enhanced. Compared with CAC specimens, AACAC specimens achieved a slightly lower rate of performance degradation. After being suffered from seawater con-ditions for 12 months, the compressive strength and bond strength of CAC specimens decreased by approximately 6.5% and 2.3%, respectively, while those of AACAC specimens only degraded by 2.5% and 1.5%, respectively.

Compliant mechanisms (CMs) are a novel type of mechanical systems which depend on the deformation of the built-in flexible members to transfer motion, force and energy. In the current literature, straight beams and circularly pre-curved beams are commonly used in current CMs as the basic flexible members. In this paper, we propose a comprehensive modeling framework to design pre-curved beams as well as analyze their large deflections where we design the beam axis in Cartesian coordinate system and polar coordinate system, and transform the mentioned coordinates into body frame for large-deflection analysis. We first introduce the three mentioned coordinate systems, and the insights of designing beam shapes in these respective coordinate systems. Then, we present the detailed deduction of the coordinate transformation from Cartesian coordinate system and polar coordinate system to body frame. In the following, several numerical examples of modeling a single beam are provided to verify the transformation strategy. In the end, the feasibility of modeling CMs where the defined beams in the mentioned coordinate systems are involved, has also been proved by FEM and experimental testing.

Currently, the repetitive behavior of the advanced bolted shear connector embedded in non-shrink self -com-pacting high strength pouring material (HPG) is unclear, restricting its application in steel-concrete composite beams (SCCBs). This study examined the repetitive performance of 21 push-off test specimens using different bolt diameters, bolt loads, loading paths, and loading programs. The failure models, load-slip response, shear bearing resistance, initial slip load, shear stiffness, peak slip, and ductility of this advanced bolted shear connection were evaluated. Bolt shearing off is the typical failure mode for all specimens, along with some concrete crushing underneath the bolts. Under repetitive loading, bolt shear capacity and load-slip response are similar to those under monotonous loading. Peak slip grows with the increase of bolt diameter under repetitive loading compared to monotonic loading. The shear stiffness under repetitive loading is lower than that under monotonic loading and improves with the bolt diameter and the bolt pretension increase. The ductility ratio under repetitive loading is smaller than that under monotonic loading and enlarges with the increase of the bolt diameter. Some design recommendations are proposed based on the existing formulae for predicting this advanced bolted shear connection.

This paper presented a three-dimensional (3D) numerical model to explore the shear behavior of bolt connections embedded in steel-lightweight aggregate concrete composite beams (SLACCBs) by utilizing the ABAQUS software. Nonlinear geometric effects and material nonlinearities were considered in the finite element (FE) modelling. The accuracy and reliability of the FE modelling were validated against the push-off tests initially. Subsequently, the basic shear properties of the bolted connection embedded in SLACCBs were studied and compared with that of the bolted connection embedded in the normal concrete (NC) slab by applying the verified FE modelling. Meanwhile, the effects of the concrete strength, concrete density, bolt diameter, and bolt tensile strength on the shear behaviour of bolt connection embedded in SLACCBs were also investigated by extensive parametric studies.

Steel lightweight aggregate–concrete composite beams (SLACCBs) with bolted shear connections provide several advantages, such as reducing the overall self-weight, shortening the construction period, and improving the structural seismic performance. However, current research on the mechanical behavior of bolted connections is primarily concentrated on composite structures with normal concrete (NC), and there is no investigation focused on the shear performance of bolt connections embedded in lightweight aggregate concrete (LAC) slabs. Therefore, this paper developed a three-dimensional (3D) numerical model to study the shear properties of the bolt connections embedded in SLACCBs by utilizing ABAQUS software. Nonlinear geometric effects and material nonlinearities were considered in the finite element (FE) modelling. The accuracy and reliability of the FE modelling were initially calibrated and validated against the push-off tests described in the literature. Subsequently, the basic shear properties of the bolted connection embedded in SLACCBs were studied and compared with those of the bolted connection embedded in the NC slab by applying the verified FE modelling. Meanwhile, the effects of the concrete strength, concrete density, bolt diameter, and bolt tensile strength on the shear behavior of the bolt connections embedded in SLACCBs were also investigated using extensive parametric studies. Finally, some design formulae were proposed to predict the bolt connection shear strength.

To reduce the disturbance of train vibration to adjacent tunnels during the operation of near-distance twin tunnels, three reduction methods are proposed. In this paper, the vibration mitigation effects of steel plate (SP), concrete zone (CZ), and double liner (DL) on their tunnels and adjacent tunnels during train vibration are compared by scale model and discrete element method (DEM). The distance between twin tunnels is 0.25 D, where D (6.2 m) is the diameter of the tunnel. The results show that CZ can produce a good vibration isolation effect on the first tunnel (T1) and second tunnel (T2). At the same time, SP has a good vibration isolation effect on the liner and surroundings of T2 but has the potential to increase the dynamic characteristics of T1 surroundings. The vibration mitigation effect of the DL on T1 and T2 is the same, and the ratio of weakening effect is about 30%-50%. In summary, the most recommended vibration isolation method in practical engineering is CZ. This study provides a reference for studying the vibration mitigation effect on adjacent tunnels during operation.

Abstract To adequately develop the application of marine resources for island construction and sustainability in the construction industry, this paper explores the feasibility of using alkali-activated materials (AAMs) as alternatives to ordinary Portland cements (OPCs) for the application in seawater coral aggregate concrete (CAC) structures. Artificial seawater, coral aggregates, and slag-based AAMs containing 5 wt.% silica fume and 15 wt.% fly ash, were mixed to develop the alkali-activated seawater coral aggregate concrete (AACAC), with the workability (slump), compressive and splitting tensile strengths being studied. The influence parameters, such as the total cementitious material content, water-to-binder ratio, and sand rate, were considered through Taguchi orthogonal experimental design method. The experimental results indicated that the most important factor herein for the compressive and splitting tensile strengths of the AACAC was the total cementitious material content. The analysis of range and variance demonstrated that an optimal mixture for AACAC was determined to be a total cementitious material content of 500 kg·m−3, a water-to-binder ratio of 0.60, and a sand rate of 55%. Then, this optimal mixture was adopted to analyze the effect of the replacement ratio of sea sand for coral sand (R s) on the workability, compressive and splitting tensile strengths of AACAC, and the cement-based CAC was selected as the reference. Finally, the microstructures of the paste-aggregate interface for the CAC and AACAC sliced specimens were detected by scanning electron microscopy (SEM). It can be concluded that increasing R s improved the workability of the AACAC, but exhibited a very slight effect on its mechanical properties. Additionally, the utilization of AAMs can effectively reduce the broken of the coral aggregate inside the concrete due to improved interfacial transition zone (ITZ) between the aggregates and the pastes, thereby exhibiting a higher splitting tensile strength than that of the cement-based CAC.

Compared to traditional shear keys, bolted shear connections adopted in steel-concrete composite beams or bridges provide the advantages of improved construction efficiency and rapid replacement of the deteriorated elements. However, current investigations on the shear performance of bolted shear connectors are quite limited. This paper explores the mechanical behavior of the advanced bolted shear connections embedded in steel and concrete composite beams. A total of 10 push-off test specimens were fabricated and carried out to determine the bolt diameter and the bolt pretension on the failure models, shear strength, initial slip load, shear stiffness, and peak slip of this advanced bolted shear connection. The experimental results demonstrate that bolt sheared off is the primary failure mode in all specimens with a small amount of concrete crushing underneath the bolts. Bolt pretension displays a negligible effect on the shear keys' failure models and the shear capacity, while the concrete spalling area increases as the bolt diameter improves. The initial slip load and the shear stiffness of the advanced bolted shear connections grow as the bolt pretension and bolt diameter increase. Based upon the existing formulae, some design recommendations are proposed for predicting this advanced bolted shear connection.

Train vibration from closely aligned adjacent tunnels could cause safety concerns, especially given the soaring size of the tunnel diameter. This paper established a two-dimensional discrete element model (DEM) of small (d = 6.2 m) and super-large (D = 15.2 m) diameter cross-river twin tunnels and discussed the dynamic characteristics of adjacent tunnels during the vibration of a train that runs through the tunnel at a speed of 120 km/h. Results in the D tunnel showed that the horizontal walls have the same horizontal displacement (DH) and the vertical walls have the same vertical displacement (DV). The stress state of the surroundings of the D tunnel is the decisive factor for DH, and the distance from the vibration point to the measurement point is the decisive factor for DV. Results in the comparison of the d and D tunnels showed that the D tunnel is more stable than the d tunnel with respect to two aspects: the time the tunnel reaches the equilibrium state and the vibration amplitude of the structure’s dynamic and static responses. The dynamic characteristic of the d and D tunnel is significantly different. This research is expected to guide the design and construction of large diameter twin tunnels.

Multi-bolt shear connectors (MBSCs), arranging bolts as a group in several rows, can be applied in prefabricated steel–concrete composite beams or bridges (SCCBs) to reduce the construction time and meet the requirements of sustainable development. The mechanical behavior of bolt shear connectors has been broadly investigated in recent years, but they were mainly focused on the normal arrangement. The shear performance of MBSCs is not consistent with that of the same number of single bolts. In this study, a three-dimensional (3D) finite element model (FEM) was developed to investigate the multiple bolts effect and its mechanical performance. Material non-linearities and the interactions among all components were included in the FEM. The accuracy and reliability of the proposed FEM were initially verified against the available push-out test results. The validated FEM further studied the load–slip relationship, shear capacity, and shear stiffness of the MBSCs. A parametric study was carried out to determine the effect of the bolt spacing, bolt row numbers, the concrete strength, and the bolt diameter on the shear performance of MBSCs. Based on the extensive parametric analyses, design recommendations considering the multiple bolts effect for predicting the shear resistance per bolt in multi-bolt connectors were proposed and verified.

High-strength bolted shear connectors (HSBSCs), which can be demounted easily and efficiently during deconstruction, are recommended to replace the conventional steel studs in steel–concrete composite beams (SCCBs) to meet the requirements of sustainable development. The existing investigations on the behavior of HSBSCs mainly focus on the positive moment area of composite beams, in which the concrete slab is in compress condition. In this paper, a three-dimensional finite element model (FEM) was developed to investigate the performance of HSBSCs subjected to inverse push-off loading. Material nonlinearities and the interactions among all components were included in the FEM. The accuracy and reliability of the proposed FEM were initially validated against the available push-off test results. Load-carrying capacity and load–slip response of the HSBSCs under inverse push-off loading were further studied by the verified FEM. A parametric study was carried out to determine the influence of the concrete strength, the diameter and tensile strength of bolt and the clearance between the concrete slab and the bolt as well as the bolt pretension on the shear performance of HSBSCs. Based on the extensive parametric analyses, design recommendations for estimating the shear load at the first slip and load-bearing resistance of HSBSCs were proposed and verified.

采用ABAQUS有限元软件对钢-混凝土组合梁高强螺栓抗剪连接件的受剪性能进行三维实体有限无非线性分析,模型考虑钢梁、混凝土板和高强螺栓等材料非线性以及各部件之间的接触关系,在试验验证的基础上探讨混凝土强度以及高强螺栓直径、屈服强度、长径比和预紧力等参数对抗剪承载力的影响,分析结果表明:高强螺栓连接件的抗剪承载力随混凝土强度、螺栓直径与屈服强度的增大而提高.通过拟合建立考虑混凝土强度、高强螺栓直径和屈服强度影响的单个连接件抗剪承载力计算式,并对现行规范中栓钉受剪计算公式和国外学者及本文提出的高强螺栓受剪计算公式的计算值进行比较,结果表明本文提出的计算式具有较高的精度.

The high-strength bolt shear connector in prefabricated concrete slab has advantages in applications as it reduces time during the construction of steel-concrete composite building structures and bridges. In this research, an innovative and advanced bolt shear connector in steel-concrete composite structures is proposed. To investigate the fundamental mechanical behavior and the damage form, 22 static push-off tests were conducted with consideration of different bolt dimensions, the reserved hole constraint condition, and the dimension of slab holes. A finite element (FE) model was established and verified by using test results, and then the model was utilized to investigate the influence of concrete strength, bolt dimension, yield strength, bolt pretension, as well as length-to-diameter ratio of high strength bolts on the performances of shear connectors. On the basis of FE simulation and test results, new design formulas for the calculation of shear resistance behavior were proposed, and comparisons were made with current standards, including AISC, EN 1994-1-1, GB 50017-2017, and relevant references, to check the calculation efficiency. It is confirmed that the proposed equation is in better agreement with the experimental results.

Abstract:To study the shear behavior of the bolt connection of prefabricated concrete wallboard, through one-way repeated loading test of the four specimens with concrete prefabricated bolt joint, the hysteresis curves, skeleton curves, the characteristic load and displacement of the specimens were obtained. Furthermore,stiffness degradation and ductility index of the specimen were calculated and analyzed. The results showed that the fabricated bolt connection with good bearing capacity, stiffness and energy dissipation capacity, is a reliable way of dry connection; Through adopting stirrup densification to the weak part and increasing the number of bolts, the shear behavior of prefabricated bolt connection can be significantly improved.