Regular detection and repair for lining cracks are necessary to guarantee the safety and stability of tunnels. The development of computer vision has greatly promoted structural health monitoring. This study proposes a novel encoder–decoder structure, CrackRecNet, for semantic segmentation of lining segment cracks by integrating improved VGG-19 into the U-Net architecture. An image acquisition equipment is designed based on a camera, 3-dimensional printing (3DP) bracket and two laser rangefinders. A tunnel concrete structure crack (TCSC) image data set, containing images collected from a double-shield tunnel boring machines (TBM) tunnel in China, was established. Through data preprocessing operations, such as brightness adjustment, pixel resolution adjustment, flipping, splitting and annotation, 2880 image samples with pixel resolution of 448 × 448 were prepared. The model was implemented by Pytorch in PyCharm processed with 4 NVIDIA TITAN V GPUs. In the experiments, the proposed CrackRecNet showed better prediction performance than U-Net, TernausNet, and ResU-Net. This paper also discusses GPU parallel acceleration effect and the crack maximum width quantification.
Three-dimensional concrete printing (3DCP) technology begins to be adopted into construction application worldwide. Recent studies have focused on producing a higher concrete quality and offering a user-friendly construction process. Still, the 3DCP construction cost is unlikely to be lower than that of conventional construction, which is especially important for projects where the cost is sensitive. To broaden the 3DCP construction applications, reduction of the quantity of 3DCP material usage is needed. This work aims to perform structural analysis of several patterns of geometric textured 3DCP shell wall structures. 21 different cantilevered textured patterns of 3DCP shell wall structures were architecturally designed and then subjected to structural analysis by a finite element method (FEM). The results indicated that by designing appropriate patterns, the structural performance to weight ratio could be improved up to 300%. The study therefore offers an innovative design process for constructing 3DCP housing and suggests pre-construction analysis methods for 3DCP shell wall structures.
To completely solve the problem of fatigue cracking issue of orthotropic steel bridge decks (OSDs), the authors proposed a steel–ultra-high performance concrete (UHPC) lightweight composite deck (LWCD) with closed ribs in 2010. Based on the successful application of that LWCD, an adaptation incorporating an innovative composite deck structure, i.e., the hot-rolled section steel–UHPC composite deck with open ribs (SSD) is proposed in this paper, aiming to simplify the fabrication process as well as to reduce the cost of LWCD. Based on a long-span cable-stayed bridge, a design scheme is proposed and is compared with the conventional OSD scheme. Further, a finite element (FE) calculation is conducted to reflect both the global and local behavior of the SSD scheme, and it is found that the peaked stresses in the SSD components are less than the corresponding allowable values. A static test is performed for an SSD strip specimen to understand the anti-cracking behavior of the UHPC layer under negative bending moments. The static test results indicate that the UHPC layer exhibited a satisfactory tensile toughness, the UHPC tensile strength obtained from the test is 1.8 times the calculated stress by the FE model of the real bridge. In addition, the fatigue stresses of typical fatigue-prone details in the SSD are calculated and evaluated, and the influences of key design parameters on the fatigue performance of the SSD are analyzed. According to the fatigue results, the peaked stress ranges for all of the 10 fatigue-prone details are within the corresponding constant amplitude fatigue limits. Then a fatigue test is carried out for another SSD strip specimen to explore the fatigue behavior of the fillet weld between the longitudinal and transverse ribs. The specimen failed at the fillet weld after equivalent 47.5 million cycles of loading under the design fatigue stress range, indicating that the fatigue performance of the SSD could meet the fatigue design requirement. Theoretical calculations and experiments provide a basis for the promotion and application of this structure in bridge engineering.
Quality assurance and maintenance play a crucial role in engineering construction, as they have a significant impact on project safety. One common issue in concrete structures is the presence of defects. To enhance the automation level of concrete defect repairs, this study proposes a computer vision-based robotic system, which is based on three-dimensional (3D) printing technology to repair defects. This system integrates multiple sensors such as light detection and ranging (LiDAR) and camera. LiDAR is utilized to model concrete pipelines and obtain geometric parameters regarding their appearance. Additionally, a convolutional neural network (CNN) is employed with a depth camera to locate defects in concrete structures. Furthermore, a method for coordinate transformation is presented to convert the obtained coordinates into executable ones for a robotic arm. Finally, the feasibility of this concrete defect repair method is validated through simulation and experiments.
It is known that clay-based building materials such as bricks and tiles accumulate in landfills at the end of their useful lives. As an alternative, recycling clay-based building material can reduce the negative environmental impacts. Recycled brick powder (RBP) is obtained by grinding waste brick and tile collected from end-of-life landfills. Within the scope of the study, the use of self-compacting fiber reinforced mortars (SCFRMs) produced with RBP using CEM-I 42.5R and 52.5R class cements for two different cement classes was investigated. In accordance with EFNARC, a water binding ratio of 0.42 was used to control the workability and strength of the SCFRM. In the produced SCFRM, 1%, 2%, and 3% by weight binder Polypropylene (PP) fiber was added to the blends with 10%, 20%, and 30% RBP substitutes. A total of 32 SCFRM mixes were produced and tested. The flexural and compressive strengths at 7, 28, 56, and 90 d were evaluated on the produced samples. In addition, porosity and water absorbency values were examined since these are significant for durability properties. It was observed that the use of RBP increases durability, and the use of fiber can have positive effects in terms of both durability and strength.
Intensive construction methods offer benefits for metro station development, yet they present challenges for seismic design due to the spatially asymmetric configuration of passageway-shaft structures. In this study, a detailed numerical model of a station-passageway-shaft structure system built using intensive construction methods was developed and the deformation and damage modes under seismic loadings were analyzed. The results indicate that inconsistent deformation between the shaft and the station generates interaction through the connecting passageway, leading to damage near the opening of the station structure and both ends of the connecting passageway Damage is more severe under longitudinal excitation. Compared with the opening plan that spans four segments, the opening plan that spans five segments exacerbates the overall degree of damage to the structure system. Under transverse excitation, the presence of interior structures intensifies the damage to the station and connecting passageway, while with such internal structure in place the impact is relatively minor under longitudinal excitation. Reinforcement with steel segments near the station opening can appreciably attenuate the damage. In contrast, introducing flexible joints at both ends of the connecting passageway intensifies the damage. Hence, reinforcement using steel segments emerges as an optimal seismic mitigation strategy.
To improve the deficiencies of prefabricated autoclaved lightweight aerated concrete (ALC) panel such as susceptibility to cracking and low load-bearing capacity, a textile-reinforced mortar-autoclaved lightweight aerated concrete (TRM-ALC) composite panel was developed in this study. One group of reference ALC panels and five groups of TRM-ALC panels were fabricated and subjected to four-point flexural tests. TRM was applied on the tensile side of the ALC panels to create TRM-ALC. The variable parameters were the plies of textile (one or two), type of textile (basalt or carbon), and whether the matrix (without textile) was applied on the compression side of panel. The results showed that a bonding only 8-mm-thick TRM layer on the surface of the ALC panel could increase the cracking load by 180%−520%. The flexural capacity of the TRM-ALC panel increased as the number of textile layers increased. Additional reinforcement of the matrix on the compressive side could further enhance the stiffness and ultimate load-bearing capacity of the TRM-ALC panel. Such panels with basalt textile failed in flexural mode, with the rupture of fabric mesh. Those with carbon textile failed in shear mode due to the ultra-high tensile strength of carbon. In addition, analytical models related to the different failure modes were presented to estimate the ultimate load-carrying capacity of the TRM-ALC panels.
The high-speed maglev vehicle/guideway coupled model is an essential simulation tool for investigating vehicle dynamics and mitigating coupled vibration. To improve its accuracy efficiently, this study investigated a hierarchical model updating method integrated with field measurements. First, a high-speed maglev vehicle/guideway coupled model, taking into account the real effect of guideway material properties and elastic restraint of bearings, was developed by integrating the finite element method, multi-body dynamics, and electromagnetic levitation control. Subsequently, simultaneous in-site measurements of the vehicle/guideway were conducted on a high-speed maglev test line to analyze the system response and structural modal parameters. During the hierarchical updating, an Elman neural network with the optimal Latin hypercube sampling method was used to substitute the FE guideway model, thus improving the computational efficiency. The multi-objective particle swarm optimization algorithm with the gray relational projection method was applied to hierarchically update the parameters of the guideway layer and magnetic force layer based on the measured modal parameters and the electromagnet vibration, respectively. Finally, the updated coupled model was compared with the field measurements, and the results demonstrated the model’s accuracy in simulating the actual dynamic response, validating the effectiveness of the updating method.
China’s architecture, engineering, and construction (AEC) industry needs a clear and sustainable development roadmap. Drawing inspiration from speeches delivered at a seminar hosted by the Chinese Academy of Engineering and extensive literature research on Chinese policies, this article presents a summary of the current trends in the AEC industry in four dimensions: industrialization as the foundation, intelligence as the enabler, lean management as the strategy, and green development as the goal. These four dimensions are intricately interconnected and rooted in multiple disciplines. The article provides a detailed review of the current practices, challenges, and future directions associated with each dimension. Additionally, ten grand challenges were proposed to stimulate discussions on the future of the AEC industry. This article offers an overarching understanding of the AEC industry and presents a four-dimension framework for sustainable development, which can be valuable for AEC practitioners.
