Search Results (52)

Prefabricated components inevitably generate numerous assembly joints during installation, with each 1 mm increase in joint width correlating to a 15–20% elevation in the annual occurrence frequency of the frost formation risk. In the Inner Mongolia Region, the water migration at wall connection interfaces during winter significantly exacerbates freeze–thaw damage due to persistent thermal gradients. A coupled heat–moisture transfer model incorporating gas–liquid–solid phase transitions was developed, with the liquid moisture content and temperature gradient as dual driving forces. A validation against internationally recognized BS EN 15026:2007 benchmark cases confirmed the model robustness. The prefabricated sandwich insulation walls reconstructed with region-specific volcanic ash materials underwent a comparative evaluation of temperature and relative humidity distributions under varied winter conditions. Furthermore, we analyze and assess the potential for freezing at connection points and identify the specific areas at risk. Synergistic effects between assembly gaps and indoor–outdoor environmental interactions on wall performance degradation were systematically assessed. The results indicated that, across all working conditions, both the temperature and relative humidity at each wall measurement point underwent periodic variations influenced by the outdoor environment. These fluctuations decreased in amplitude from the exterior to the interior, accompanied by a noticeable delay effect. Specifically, at Section 2, the wall temperatures at points B2–B8 were higher compared to those at A2–A8 of Section 1. The relative humidity gradient remained relatively stable at each measurement point, while the temperature fluctuation amplitude was smaller by 2.58 ± 0.3 °C compared to Section 1. Under subfreezing conditions, Section 1 demonstrates a marked reduction in relative humidity (Cases 1-3 and 2-3) compared to reference cases, which is indicative of internal ice crystallization. Conversely, Section 2 maintains higher relative humidity values under identical therma. These findings suggest that prefabricated building joints significantly impact indoor and outdoor wall temperatures, potentially increasing the indoor heat loss and accelerating temperature transfer during winter. Full article

Due to moisture migration effects, thermal and moisture bridges tend to form at building joints, thereby increasing the thermal conductivity coefficient of construction materials. To examine the influence of moisture transfer on the thermal performance of ‘one-line’ vertical joint walls, this study establishes a thermal–humidity coupling numerical model at the vertical joint of sandwich insulation composite walls. This model is employed to analyze the effects of various joint filling materials (aerated blocks, glass wool, concrete), insulation layer thicknesses, and environmental conditions on the thermal transfer properties of the wall joint. The results indicate that when filled with aerated blocks, the joint is most significantly affected by moisture transfer, exhibiting a heat flow loss rate of 8.08%. In high-temperature environments, the thermal transfer performance at the connection of the composite wall is particularly susceptible to humidity, with heat flow loss rates ranging from 6.17% to 8.74%. Furthermore, an increase in the thickness of the insulation layer leads to a reduction in the “heterogeneity” of the sandwich insulation wall, which reduces the wall’s effects to moisture transfer; however, this is accompanied by a rise in the heat loss rate at the connection. After accounting for the effects of hygrothermal bridging, the mean heat transfer corrected coefficient of the wall in areas with hot summers and cold winters ranges from 1.10 to 1.18 during the summer and from 1.12 to 1.16 during the winter. This finding holds significant relevance for aiding researchers in predicting thermal transfer analysis in scenarios involving wall moisture transfer. Full article

Traditional monolithic precast and precast prestressed concrete joints often face challenges such as complex steel reinforcement details and low construction efficiency. Grouting sleeve connections may also suffer from quality issues. To address these problems, a new precast prestressed concrete frame beam-column exterior joint using ultra-high-performance concrete (UHPC) for connection (PPCFEJ-UHPC) is proposed. This innovative joint lessens the amount of stirrups in the core area, decreases the anchorage length of beam longitudinal reinforcement, and enables efficient lap splicing of column longitudinal reinforcement, thereby enhancing construction convenience. Cyclic loading tests were conducted on three new exterior joint specimens (PE1, PE2, PE3) and one cast-in-place joint specimen (RE1) to evaluate their seismic performance. The study concentrated on failure modes, energy dissipation capacity, displacement ductility, strength and stiffness degradation, shear stress, and deformation’s influence on the longitudinal reinforcement anchoring length and axial compression ratio. The results indicate that the new joint exhibits beam flexural failure with minimal damage to the core area, unlike the cast-in-place joint, which suffers severe core area damage. The novel joint exhibits at least 21.7% and 6.1% improvement in cumulative energy consumption and ductility coefficient, respectively, while matching the cast-in-place joint’s bearing capacity. These characteristics are further improved by 5.5% and 10.7% when the axial compression ratio is increased. The new joints’ seismic performance indices all satisfy the ACI 374.1-05 requirements. Additionally, UHPC significantly improves the anchoring performance of steel bars in the core area, allowing the anchorage length of beam longitudinal bars to be reduced from 16 times of the diameter of reinforcement to 12 times. Full article

Steel traditional Chinese buildings (STCBs) are constructed using modern materials, replicating the esthetics of ancient Chinese buildings, but their irregular joints differ significantly from those in conventional steel structures. To investigate the influence of beam section shape and axial compression ratio on the failure mode and shear resistance of all-welded irregular joints (WIJs) in STCBs, the size proportion relationships in the traditional Chinese modular construction system for such joints in existing practical projects are analyzed. Four exterior joint specimens were designed and fabricated for pseudo-static loading tests. The failure mode, hysteresis curve, and skeleton curve of the specimens were obtained. The test results indicate that the failure mode of the specimens involves shear deformation in the lower core area, with final failure due to crack formation in the weld at the junction between the column wall and the beam flange. As the axial compression ratio increases, the bearing capacity of the joint decreases. Based on the test results, the numerical model was established by using finite element software Abaqus2016, and parameter analysis was performed by varying the axial compression ratio of the column. After analyzing the force transfer mechanism of the core area in the WIJs of STCBs, a simplified calculation formula for the shear bearing capacity of the core area was derived based on the proportional relationship outlined in the construction manual from the Song Dynasty. The calculated results show good agreement with the experimental results, providing a basis for the structural design of WIJs in STCBs. Full article

Adhesion-based space climbing robots, with their flexibility and multi-functional capabilities, are seen as a promising candidate for in-orbit maintenance. However, challenges such as uncertain adhesion establishment, unexpected detachment, and body motion unsteadiness in microgravity environments persist. To address these issues, this paper proposes a coordinated force–position compliance control method that integrates novel adhesion establishment and rotational detachment strategies, integrated into the gait schedule for a space climbing robot. By monitoring the foot-end reaction forces in real time, the proposed method establishes adhesion without risking damaging the spacecraft exterior, and smooth detachment is achieved by rotating the foot joint instead of direct pulling. These strategies are dedicated to reducing unnecessary control actions and, accordingly, the required adhesion forces in all feet, reducing the possibility of unexpected detachment. Climbing experiments have been conducted in a suspension-based gravity compensation system to examine the merits of the proposed method. The experimental results demonstrate that the proposed rotational detaching method decreases the required pulling force by 65.5% compared to direct pulling, thus greatly reducing the disturbance introduced to the robot body and other supporting legs. When stepping on an obstacle, the compliant control method is shown to reduce unnecessarily aggressive control actions and result in a reduction in relevant normal and shear adhesion forces in the supporting legs by 44.8% and 35.1%, respectively, compared to a PID controller. Full article

Background: medical teams continue to face challenges with infections following hip replacement surgery, whether they occur shortly after the procedure or months or years later. Certain medical conditions like diabetes, rheumatoid arthritis, and obesity are risk factors that make patients more susceptible to infections. Traditional intervention methods such as DAIR, one-step, or two-step procedures are being enhanced and refined to ensure quicker and more effective treatment. Some cases present particularly difficult challenges, featuring persistent fistulas and unpredictable responses to treatment. Methods: in our article, we share two unique cases, detailing their histories, progressions, and treatment decisions. We explore the use of antibiotic-impregnated calcium biocomposite as a local adjuvant therapy and the application of negative pressure therapy to expedite healing. The system of NWPT has seen widespread uptake and is now implemented routinely for open wounds, such as open fractures, fasciotomies, ulcers, and infected wounds. Results: our findings demonstrate that surgical debridement and calcium sulfate bead insertion successfully treat bone and joint infections without causing any side effects or complications. As a particularity, in the first case, we encountered the exteriorization of Stimulan pearls after surgery, without other complications related to the biocomposite. Conclusions: we have found that NPWT is a beneficial tool in managing complex wounds in both acute and chronic stages, after the infection is cured, reducing the need for frequent dressing changes, shortening hospital stays, and enhancing patient comfort. Full article

In airborne surveying, light detection and ranging (LiDAR) strip adjustment and image bundle adjustment are customarily performed as separate processes. The bundle adjustment is usually conducted from frame images, while using linear pushbroom (LP) images in the bundle adjustment has been historically challenging due to the limited number of observations available to estimate the exterior image orientations. However, data from these three sensors conceptually provide information to estimate the same trajectory corrections, which is favorable for solving the problems of image depth estimation or the planimetric correction of LiDAR point clouds. Thus, our purpose with the presented study is to jointly estimate corrections to the trajectory and interior sensor states in a scalable hybrid adjustment between 3D LiDAR point clouds, 2D frame images, and 1D LP images. Trajectory preprocessing is performed before the low-frequency corrections are estimated for certain time steps in the following adjustment using cubic spline interpolation. Furthermore, the voxelization of the LiDAR data is used to robustly and efficiently form LiDAR observations and hybrid observations between the image tie-points and the LiDAR point cloud to be used in the adjustment. The method is successfully demonstrated with an experiment, showing the joint adjustment of data from the three different sensors using the same trajectory correction model with spline interpolation of the trajectory corrections. The results show that the choice of the trajectory segmentation time step is not critical. Furthermore, photogrammetric sub-pixel planimetric accuracy is achieved, and height accuracy on the order of mm is achieved for the LiDAR point cloud. This is the first time these three types of sensors with fundamentally different acquisition techniques have been integrated. The suggested methodology presents a joint adjustment of all sensor observations and lays the foundation for including additional sensors for kinematic mapping in the future. Full article

Steel fiber reinforced high-strength concrete (SFRHSC) is a composite material composed of cement, coarse aggregate, and randomly distributed short steel fibers. The excellent tensile strength of steel fiber can significantly improve the crack resistance and ductility of high-strength concrete (HSC). In this study, experimental and numerical investigations were performed to study the cyclic behavior of the HSC beam-column joint. Three SFRHSC and one HSC beam-column joint were prepared and tested under cyclic load. Two different volume ratios of steel fibers and three stirrups ratios in the joint core area were experimentally studied. After verification of the experimental results, numerical simulations were further carried out to investigate the influence of steel fibers volume ratio and stirrups ratio in the joint core area on the seismic performance. Evaluation of the hysteretic response, ductility, energy dissipation, stiffness, and strength degradation were the main aims of this study. Results indicate that the optimal volume fraction of steel fibers is 1.5%, and the optimal stirrups ratio in the joint core area is 0.9% in terms of the enhancement of the seismic performance of the SFRHSC beam-column joint. Full article

This study presents a solution for push-out failure for the staged bond-slip constitutive relationship between the structural steel and high strength concrete, taking into account the concrete strength grade, anchoring length, and stirrup ratio. The critical point coordinates for different stages are determined by the tests of 14 steel-reinforced high strength concrete (SRHSC) specimens. It is observed that with the increase in the concrete strength grade and anchorage length, the ultimate load of the specimens increased significantly, but the influence on the residual bond strength was not significant. The effect of the stirring ratio was mainly manifested in a slight increase in the initial bond strength. The formula for calculating SRHSC characteristic bond strength and characteristic slip value is established, and the bond-slip constitutive relation of SRHSC is proposed based on the tests. The material constitutive model considering the effect of bond-slip is implanted into the software in the case of the ABAQUS finite element platform. The material is applied to the numerical simulation analysis of the SRHSC exterior joints. The rationality and accuracy of the new material are verified by comparing the simulation results with the test results. Full article

Four exterior reinforced concrete beam–column joint subassemblages with poor reinforcement details and low-quality materials were constructed and subjected to cyclic lateral deformations under constant axial loading of the columns. The longitudinal rebars at the top of the beams were well-anchored in the joint region with a 90° hook and transversely welded to prevent premature slippage. The same was true for the longitudinal rebars at the bottom of the beam of the first specimen. Contrarily, the anchorage of the rebars at the bottom of the beam of the other three subassemblages was straight and of insufficient length. One of these specimens (the second) also had deficient lap splices of the column reinforcement, while the other three specimens had continuous column rebars. The third and the fourth subassemblage were designed with different joint aspect ratio and beam shear span/depth ratio values. The overall seismic performance of the specimens was evaluated and compared. The failure mode of the subassemblages was accurately predicted by the proposed analytical model. It was clearly demonstrated that the anchorage of the rebars, the length of the lap splices, the joint aspect ratio and the shear span/depth of the beam ratio value crucially affect the cyclic response of beam–column joints and, hence, may cause a severe detrimental impact to the overall structural integrity. Full article

To study the mechanical performance of bolted connections with different structural forms of reinforced rings, based on the results of monotonic loading tests on two bolted connections between a concrete-filled steel tubular column and a steel beam with an outer reinforcing ring, this article uses ABAQUS v.2020 software to establish a three-dimensional refined finite element analysis model of such connections using appropriate constitutive models for concrete and steel. Subsequently, the effect of the dimensions of the steel beam, reinforcing ring, and cover plate on the load-bearing properties and the failure mechanism of the connections is investigated, and the numerical model is consistent with the verification test results. Then, the numerical simulations comparing bolted exterior reinforced rings under seven different construction measures (i.e., number of bolts, stiffeners) based on a conventional welded exterior reinforced rings with rigid connections (i.e., CGJ) are standardized. The research results indicate that when four rows of bolts are introduced on exterior reinforced rings, the web of steel beam is welded with stiffeners, and the top and bottom reinforced rings are also added with stiffeners; this bolted connection with an external reinforcing ring (i.e., GZ-7) can achieve the rigidity and load-bearing capacity of a fully welded external reinforcing ring rigid connection. At the same time, the reinforcing ring plate is bolted to the flange of the steel beam, and the force transmission path at the connection is changed to avoid the brittle fracture easily caused by the welded flange joints. It is also in line with the development trend of sustainable construction of “assembly” and “disassembly”. Full article

(1) The Hoop Head Tenon-mortise Joint (HHTMJ) in the Tusi Manor in Tibetan areas in Yunnan, China, has a serious decay phenomenon. To understand the effect of decay on the seismic performance of HHTMJ, (2) the five groups of HHTMJ and small-size Pinus kesiya var. langbianensis wood mechanical property testing specimens were placed in an artificially set decay environment and cultivated together with wood decay fungi for 0, 6, 12, 18, and 24 weeks, respectively. Low-cycle repeated loading tests were conducted to compare the failure mode, hysteresis curve, skeleton curve, and cumulative energy consumption of the HHTMJ under different decay cycles. (3) The results indicate that the failure mode of the HHTMJ is fractured at the tenon shoulder, and the deformation and failure of the tenon increase with the increase in decay. Compared with the non-decayed specimens, the ultimate bearing performance of the specimens after 6, 12, 18, and 24 weeks of decay decreased by 8.83%, 16.97%, 19.69%, and 30.22%, respectively. The cumulative energy consumption decreased by 21.6%, 27.4%, 33.2%, and 41.3%, respectively. (4) Decay primarily occurs on the exterior of the tenon, with minimal decay on the interior. The degradation of seismic performance in HHTMJ is relatively close to the degradation observed in small-size wood specimens during mechanical property testing. Full article

This study introduces precast concrete beam–column connections comprised of composite beams, precast columns, and a monolithic joint core. The composite beams consist of U-shaped beams and floor slabs, leveraging the U-shaped beams for their lightweight nature, acceptable stiffness, and reduced demand for on-site support systems. To mitigate reinforcement congestion in the joint core, the precast connections incorporate large-diameter rebars (greater than 25 mm). This study conducted cyclic loading tests on four full-scale beam–column connections under 0.3 normalized compression, encompassing precast interior and exterior connections, along with two monolithic reference specimens, to investigate their behavior under seismic actions. The results revealed that all specimens exhibited bending failure at the beam ends, with minimal concrete deterioration observed in the joint core areas and columns. The hysteresis curves of the precast specimens and the monolithic connections exhibited a slight pinching effect. The strengths of the interior and exterior precast specimens were 13.3% and 7.8% lower than those of the reference monolithic connections, respectively. The ductility of interior precast connections and monolithic specimens stood at 2.36 and 2.23, respectively, indicating a negligible difference of less than 5%. Meanwhile, the positive and negative ductility of exterior precast connections were 3.06 and 2.34, which was approximately 8% lower than that of the reference connections. Furthermore, the stiffness degradation and energy dissipation capacity of the precast specimens aligned closely with the performance of the reference monolithic ones. Full article

This study emphasizes the significance of beam–column joints (BCJs) within reinforced concrete (RC) structures and investigates their performance when subjected to seismic forces. Accurately predicting the load-carrying capacity of exterior BCJs under seismic loading poses a significant challenge. The development of a reliable and user-friendly predictive model is of paramount importance for facilitating cost-effective and safe design practices for RC structures. To address this requirement, we propose an artificial intelligence (AI)-based model that utilizes gene expression programming (GEP) to accurately predict the load-carrying capacity of exterior BCJs under monotonic loading conditions. The model is developed using GEP and utilizes a database of 128 joint load-carrying capacity results of exterior BCJs obtained from a validated finite element (FE) model using ABAQUS, which considers the effects of material and geometric factors, which have often been overlooked in prior studies. These factors encompass multiple aspects, including the beam and column dimensions, concrete material properties, longitudinal reinforcements in beams and columns, and axial loads applied to the columns. This study also compared the results of the proposed GEP model with the numerical data obtained from the validated FE model, demonstrating good accuracy and reliability. The proposed model has the potential to improve the accuracy and reliability of joint load-carrying capacity predictions, thereby aiding the design of safe and cost-effective RC structures. Full article

This paper introduces a new type of hybrid precast MUT, consisting of precast composite top slab and double-skin sidewalls with reserved rebar. The seismic behavior of the top joints was examined through pseudo-static tests. Four full-scale specimens, including both exterior and interior precast joints, in addition to two corresponding cast-in-place (CIP) joints, were fabricated and subjected to reversed cyclic loading. The results showed that both the precast and CIP joints exhibited flexure failure, characterized by the formation of a plastic hinge at the end of the sidewall. The hysteresis curves of both precast and CIP joints exhibited comparable shapes and quantities of hysteresis loops. The load-carrying capacities for exterior precast joints and corresponding CIP joints were 141.25 kN and 143.5 kN, exhibiting a difference of less than 1.6%. The load-carrying capacities for interior precast and corresponding CIP joints were 60.5 kN and 62.75 kN, displaying a variance of less than 3.6%. The precast specimens demonstrated comparable levels of ductility, energy dissipation, and structural integrity as the CIP specimens. These findings provide validation for designing and analyzing the hybrid precast utility tunnel using identical principles and models as applied CIP structures. Full article