Search Results (7)

Prefabricated structures are widely used because of their advantages of energy savings, environmental protection, standardization, and universality. However, due to the complex structure of the joints, it is easy to make the joint installation difficult and the prefabricated column connection unreliable, and further lead to the poor seismic performance of the structure. Therefore, a new type of dry sleeve joint with double screw sleeve without support is proposed, and the seismic performance and influencing factors of the new dry-sleeve-joint prefabricated column are studied. This study encompasses seven reinforced concrete columns characterized by cross-sectional dimensions of $600 \mathrm{mm} \times 600 \mathrm{mm}$. Among these, five specimens feature a novel dry sleeve connection, while the remaining two specimens were entirely cast-in-place. Low-cycle reversed loading experiments were conducted on all specimens to analyze and compare the damage patterns, hysteresis curves, skeleton curves, displacement ductility, energy dissipation capacity, and ultimate bearing capacity between precast and cast-in-place columns. Several parameters, including fabrication method, axial compression ratio, longitudinal reinforcement diameter, and hoop spacing, were examined. The findings demonstrated that the calculated-to-tested ratio of the ultimate bearing capacity for the prefabricated specimens was determined to be 0.62, indicating a high level of safety. The displacement ductility coefficient for each specimen ranged from 2.43 to 3.31, while the ultimate drift ratio was within the range of 1/41 to 1/33, satisfying the specified requirements for seismic performance. However, the hysteresis curve of the prefabricated specimens exhibited a pinching effect, which may be related to the existence of a weak layer on the joint surface of the post-cast section. In general, the shape of the new dry sleeve is maintained in the test, the connection form can effectively transfer the force, and the longitudinal bars can be strained and yield when the prefabricated column reaches the peak load. The new type of dry sleeve connection can be used for longitudinal reinforcement connection of reinforced concrete columns with seismic design. Full article

This study aims to reveal the buckling behavior of filament-wound composite cylindrical shells subjected to external pressure. The boundary conditions of the cylindrical shells were one end fixed and the other free. The carbon fiber stacking sequences were [±90]₂/([±20]/[±90]/[±40]/[±90]/[±60]/[±90])₂/[±90]. Finite element software ANSYS 16.2 was used for the numerical simulation to predict the critical buckling pressure and buckling behavior of composite cylindrical shell. External hydrostatic pressure tests were conducted, where the buckling behavior and strain response were observed. Numerical simulation accurately predicted the critical buckling pressure of carbon fiber/epoxy filament composite cylindrical shells under external pressure with 3.5% deviation from the experimental results. The buckling modes simulated by the finite element method agreed well with the deformed shape observed in the experiment, which was characterized by the uniform distribution of the three hoop waves. Comparing the axial compressive strain and hoop compressive strain of the composite shell, it was found that the circumferential stiffness of the shell was weaker than the axial stiffness. In addition, a comparative study of the strains of the fixed-end and free-end metal control sleeves was carried out. The results show that the boundary conditions have a significant influence on the strain response of control sleeves. 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

The aim of this article is to quantify the loads exerted by heavy-duty vehicles when crossing over buried pipeline. This problem arises in connection to the question pertaining to the use of protective sleeves (casings) applied to gas pipelines in regions with increased demands on pipeline operation safety. An experiment was conducted on a test pipe section made from L360NE pipeline steel equipped with strain gauges along the pipe perimeter, measuring strains in the axial and circumferential directions. Strain measurements were taken after back-filling the pipe trench, then during vehicle crossings over the empty pipe, and again after pressurizing the test pipe with air. Strain-based hoop stresses at the surface of the empty test pipe were found to exceed 30 MPa after back-filling the trench and increased to more than 40 MPa during the vehicle crossings. Similarly, axial stresses reached extremes of around 17 MPa in compression and 12 MPa in tension. Applying internal air pressure to the test pipe resulted in a reduced net effect on both the hoop and axial stresses. Full article

The ratcheting behavior of a steel pipe with assembly parts was examined under internal pressure and a cyclic bending load, which has not been seen in previous research. An experimentally validated and three dimensional (3D) elastic-plastic finite element model (FEM)—with a nonlinear isotropic/kinematic hardening model—was used for the pipe’s ratcheting simulation and considered the assembly contact effects outlined in this paper. A comparison of the ratcheting response of pipes with and without assembly parts showed that assembly contact between the sleeve and pipe suppressed the ratcheting response by changing its trend. In this work, the assembly contact effect on the ratcheting response of the pipe with assembly parts is discussed. Both the assembly contact and bending moment were found to control the ratcheting response, and the valley and peak values of the hoop ratcheting strain were the transition points of the two control modes. Finally, while the clearance between the sleeve and the pipe had an effect on the ratcheting response when it was not large, it had no effect when it reached a certain value. Full article

Compared to grouted splice connectors that have been widely used in constructing precast concrete structures, grouted sleeve lapping connectors have the advantages of a large sleeve interior diameter and low manufacturing cost. In this study, 16 grouted sleeve lapping connectors and three grouted splice connectors were tested under an incremental tensile load. The differences in their tensile capacities and failure modes, especially the mechanical properties of the grouted sleeve lapping connectors, were investigated. It was found that the tensile capacities of the grouted sleeve lapping connectors were up to 2.45 times that of the grouted splice connectors when the sleeve inner surfaces were smooth. All of the grouted sleeve lapping connectors failed by a bar tensile fracture or bar-grout slip, whereas the only failure mode of the grouted splice connectors was grout-sleeve failure. The bond stress distribution around the inserted bar in the grouted sleeve lapping connector was similar to the bond stress distribution around a single bar anchored in concrete. The ultimate hoop compressive strain of the sleeve and the corresponding load increase with greater lap length. In addition, an approximate mechanical model with high reliability was put forward to describe the mechanical properties of the grouted sleeve lapping connector. Full article

The rolled joint of a pressure tube, consisting of three axial symmetric parts, modified SUS403 stainless steel as an inner extension, Zr–2.5Nb as the pressure tube and an Inconel-718 outer sleeve has been examined by neutron diffraction for residual stresses. It was heat treated to 350 °C for 30, 130 and 635 h to simulate thermal aging over the lifetime of an advanced thermal reactor respectively for 1, 5 and 30 years at an operating temperature of 288 °C. The crystallographic texture has been investigated from cylindric disks cut from the heat treated Zr–2.5Nb pressure tube to determine the proper sample-orientation-dependent hkl reflections for reliable residual strain measurements. Corresponding in situ tensile deformation was carried out to obtain the necessary diffraction elastic constants for the residual stress evaluation. Three-dimensional crystal lattice strains at various locations in the rolled joint before and after the aging treatments for various times were non-destructively measured by neutron diffraction and the residual stress distribution in the rolled joint was evaluated by using the Kröner elastic model and the generalized Hooke’s law. In the crimp region of the rolled joint, it was found that the aging treatment had a much weaker effect on the residual stresses in the Inconel outer sleeve and the modified SUS403 stainless steel extension. In the non-aged Zr–2.5Nb pressure tube, the highest residual stresses were found near its interface with the modified SUS430 stainless steel extension. In the crimp region of the Zr–2.5Nb pressure tube near its interface with the modified SUS430 stainless steel, the average compressive axial stress was −440 MPa, having no evident change during the long-time aging. In the Zr–2.5Nb pressure tube outside closest to the crimp region, the tensile axial and hoop stresses were relieved during the 30 h of aging. The hoop stresses in the crimp region evolved from an average tensile stress of 80 MPa to an average compressive stress of 230 MPa after the 635 h of aging, suggesting that the rolled joint had a good long-term sealing ability against leakage of high temperature water. In the Zr–2.5Nb pressure tube close to the reactor core and far away from the modified SUS403 stainless steel extension, the residual stresses near the inside surface of the pressure tube were almost zero, helping to keep a good neutron irradiation resistance. Full article