Search Results (4)

Wastewater accumulates debris as it moves through sewage systems and must undergo purification at treatment plants, where insoluble debris is screened at the inlet. Previous studies have focused on screening mechanisms using rotating or ascendible sub-screens with vertical bars, and the effects of horizontal bars on structural integrity and fluid flow have not yet been explored. The present study addresses this gap by proposing a novel screening mechanism with horizontal bars and providing insights into flow behaviour and structural performance. The proposed mechanism consists of a main screen, an ascendible sub-screen and a rake system, and its effects on the flow distribution inside the channel and the resulting deformations and stress affecting the mechanism are computationally analysed. The problem is modelled as a fluid–structure interaction and solved using the arbitrary Lagrangian–Eulerian approach. Velocity distribution, structural deformation and stress are analysed for the various inlet flow velocities and critical configurations of the screening mechanism. The sub-screen in the proposed mechanism exhibited reduced deformation (0.9 mm for vertical bars and 0.2 mm for horizontal bars versus 2.2 mm in previous vertical-only designs). The maximum von Mises stress values were well below the 250 MPa yield strength, with peak stresses of 3.8 MPa in the sub-screen and 0.23 MPa in the main screen. Key operating conditions causing flow separation and velocity fluctuations are identified, and design improvements are suggested. The study provides guidelines for manufacturing and operating wastewater-screening mechanisms whilst mitigating undesirable performance and minimising deformation and stress in the mechanism. Full article

Transverse joints are introduced in jointed plain concrete pavement systems to mitigate the risk of cracks that can develop due to shrinkage and temperature variations. However, the structural behaviour of jointed plain concrete pavement (JPCP) is significantly affected by the transverse joint, as it creates a discontinuity between adjacent slabs. The performance of JPCP at the transverse joints is enhanced by providing steel dowel bars in the traffic direction. The dowel bar provides reliable transfer of traffic loads from the loaded side of the joint to the unloaded side, known as load transfer efficiency (LTE) or joint efficiency (JE). Furthermore, dowel bars contribute to the slab’s alignment in the JPCP. Joints are the critical component of concrete pavements that can lead to various distresses, necessitating rehabilitation. The Swedish Transport Administration (Trafikverket) is concerned with the repair of concrete pavement. Precast concrete slabs are efficient for repairing concrete pavement, but their performance relies on well-functioning dowel bars. In this study, a three-dimensional finite element model (3D-FEM) was developed using the ABAQUS software to evaluate the structural response of JPCP and analyse the flexural stress concentration in the concrete slab by considering the dowel bar at three different locations (i.e., at the concrete slabs’ top, bottom, and mid-height). Furthermore, the structural response of JPCP was also investigated for several important parameters, such as the joint opening between adjacent slabs, mispositioning of dowel bars (horizontal, vertical, and longitudinal translations), size (diameter) of the dowel bar, and bond between the slab and the dowel bar. The study found that the maximum LTE occurred when the dowel bar was positioned at the mid-depth of the concrete slab. An increase in the dowel bar diameter yielded a 3% increase in LTE. Conversely, the increase in the joint opening between slabs led to a 2.1% decrease in LTE. Additionally, the mispositioning of dowel bars in the horizontal and longitudinal directions showed a 2.1% difference in the LTE. However, a 0.5% reduction in the LTE was observed for a vertical translation. Moreover, an approximately 0.5% increase in LTE was observed when there was improved bonding between the concrete slab and dowel bar. These findings can be valuable in designing and evaluating dowel-jointed plain concrete pavements. Full article

The calculation method of steel pipe support in current specifications is not uniform, and it is unsafe to directly apply the stability coefficient of the vertical bar in the current code, which leads to frequent safety accidents of fastener steel pipe supports. Through the field statistics of the initial defects of the steel pipe, it is found that the initial bending values of the 3 m and 6 m steel pipes with the largest size are larger in L/400. The stability coefficient table is obtained by taking the initial bending of L/400 as the initial defect, which is 43.15% smaller than the stability coefficient given by the specification. Through the comparative analysis of the actual engineering monitoring results, the calculation results of the original specification and the calculation results after the correction of the stability coefficient, it is concluded that the stress calculated by the stability coefficient proposed in this paper is similar to the actual monitoring results of the project and is greater than the stress of the vertical rod calculated by the stability coefficient of the original specification. It is suggested that the corrected stability coefficient should be applied to the actual project. Full article

In this study, uniaxial tension tests and high-stress repeated tension and compression tests were conducted on 32 APC (all vertical members precast in concrete structures) connectors. After high-stress repeated tension and compression, the bearing capacities of the connector specimens improved due to the strengthening of the steel bars, and the ductility of the specimens was reduced due to the further development of cracks between the steel bars and the grout. The residual deformation values of the specimens, namely u₀ (uniaxial tension) and u₂₀ (repeated tension and compression), were reduced with the increase in the lapping length of the specimens. The longitudinal compressive strain and hoop tensile strain of the middle section of the sleeve near the steel bar side were reduced under the ultimate load state when the specimens were stretched under uniaxial tension and in the last tension process after repeated loading with the increase in the lapping length. The distribution and development of the longitudinal compression stress of the sleeve were analysed based on the bonding stress of the steel bar and concrete. Finally, the ultimate bonding strength and critical lapping length formulas were proposed, which involved the introduction of a grouting defect coefficient ω. Full article