A hybrid analysis method for displacement-monitored segmented circular tunnel rings

Investigations of in-plane nonlinear elastic buckling and postbuckling of parabolic shallow arches have been reported in some literature, where a basic assumption that curve arc differential being equaled to horizontal line differential was used to facilitate the derivation. However, this assumption can be accepted only when the rise-to-span ratio of an arch is quite small, and when the rise-to-span ratio of an arch is greater than 1/12.5, the analytical predictions for buckling and postbuckling responses of the arch based on the assumption have significant deviations from the corresponding finite element results. It is known that parabolic arches having a rise-to-span ratio from 1/8–1/4 are often used in the engineering practice, especially in the arch bridges. This paper aims to improve accuracy of nonlinear analyses for parabolic arches with different rise-to-span ratios. A more precise strain expression that includes an approximate curve arc differential item in the Cartesian coordinate system is derived in this paper. Based on the strain expressions and principle of virtual work, nonlinear differential equilibrium equations are derived and more accurate analytical solutions for the buckling and postbuckling behavior are derived. Parabolic arches with the rise-to-span ratio ranging from 1/12.5–1/3 are taken as examples to investigate the effectiveness of the proposed method for prediction of the buckling and postbuckling behavior by comparisons with the predictions of a finite element method. The comparisons show that the solutions are in good agreements with the finite element results and that the new strain expression can lead to more accurate closed-form analytical solutions for the buckling and postbuckling behavior of parabolic arches with different rise-to-span ratios. It is found that the rise-to-span ratio has a significant influence on the in-plane nonlinear buckling behavior of parabolic arches.

In-plane non-linear elastic stability of parabolic arches with different rise-to-span ratios

In the engineering practice, arches, such as arch bridges, are often subjected to localized loading. It is known that the nonlinear in-plane instability of shallow arches is caused by the significant in-plane bending action. The different localized loading produces very different in-plane bending distributions and so the instability of arches under localized loading would be quite different from that under a central point load or under a radial load uniformly distributed over the entire arch. However, there are no studies about the nonlinear instability and post-instability of arches under localized loading reported in the literature. This paper presents nonlinear in-plane analyses for fixed shallow circular arches under a localized uniform radial load. Novel theoretical solutions for nonlinear equilibrium, limit point instability, and bifurcation instability for arches under a localized uniform load are obtained, and new theoretical solutions of the certain modified slenderness switching the instability patterns of an arch under localized uniform loading are also obtained. It is found that the length of localized loading segment significantly influences the in-plane instability and post-instability responses of an arch. The limit point and bifurcation instability loads decrease with a decrease of the length of the localized loading segment. However, the modified slenderness switching instability patterns is found to increase with a decrease of the length of the localized loading segment. Comparisons against the finite element results show the theoretical solutions derived in this paper are accurate. These theoretical solutions provide comprehensive solutions for nonlinear instability and post-instability of fixed arches and they can reduce to those under a central point load or to extend to those under a uniform load over the entire arch.

Localized loading and nonlinear instability and post-instability of fixed arches

The aim of the paper is to analyse an exemplary bolted connection under the conditions of loss of bearing capacity of some fasteners in the connection. The presented tests are numerical and concern an asymmetric bolted connection. The joined elements in the connection were modelled as 3D finite elements, and the fasteners were treated as hybrid models consisting of rigid heads and nuts, and flexible beams between them. The bolted connection was first preloaded according to six different tensioning orders using a standardised force. After all bolts were tensioned, the selected bolts were removed, simulating bolt damage. The connection was then tested for external loads with temperatures ranging from 20 to 600°C. The influence of loosening the connection on the load in the remaining bolts at the operational stage of the connection was investigated. The calculation results were compared with the test results for a healthy bolted connection. It was shown that the bearing capacity of the connection in the damaged state decreased by 13%.

https://ein.org.pl/pdf-158448-84742?filename=Thermal strength analysis.pdf

Thermal strength analysis of a steel bolted connection under bolt loss conditions

Shear Behavior of Lapped Connections Bolted by thread-fixed one-side bolts at elevated temperatures

Effect of preloading in high-strength bolts on bolted-connections exposed to fire

Because of their geometrical shape, two-pinned steel arches (TPSAs) have special internal force distributions and deformations compared with conventional straight beams. However, the present studies on TPSAs exposed to fire are still quite limited with regard to their fire-induced deflection modes or deflection limits and ultimate temperatures. This paper employs several numerical models to analyse the high-temperature performance of TPSAs at elevated temperatures in terms of the effects of the load ratios, horizontal restraints, rise-to-span ratios, fire fields and geometrical sizes of the cross-section. The results show that TPSAs exposed to high temperatures are more sensitive to the load ratios than the horizontal restraint stiffness and geometrical size of the cross-section. The TPSAs could not develop catenary actions such as those of straight beams in fire; previous investigations have not predicted the behaviour of TPSAs in fire. The in-plane buckling and excessive mid-span sagging of TPSAs are the final failure modes regardless of the location of the fire actions. To date, the acceptable rise-to-span ratio is approximately 0.25–0.35 for TPSAs in fire. Finally, this paper presents a prediction formula for the limit state of TPSAs at elevated temperatures by using trigonometric functions and logarithmic regression.

Behaviour of a two-pinned steel arch at elevated temperatures

The utility model discloses a metal section heating deformation test device. The metal section heating deformation test device is provided with a square framework, wherein the top part of the framework is provided with a transverse beam; two sides of the framework are provided with side beams which are provided with supporting frames; a rectangular heater is arranged at the lower end of the middle part of the transverse beam in a hanging way; two symmetric sides of the heater are provided with jacks in the hanging way; a tested I-shaped beam penetrates through the heater; two ends of the I-shaped beam are arranged on the supporting frames at the two sides; an instrument box is arranged on the supporting frames; a thermocouple is arranged in the heater; an elastic spring is arranged under an electromagnetic heating plate of the bottom part of the heater and is used for supporting the electromagnetic heating plate. According to the metal section heating deformation test device disclosed by the utility model, by changing a heating way, local heating analysis is carried out by adopting an electromagnetic heating way, so that the operation is convenient and easy, the cost is low, and the metal section heating deformation test device is favorable for use in a lab; the deformation of section steel under different temperatures can be measured, the temperature distribution can be obtained by measuring the temperature on the surface of a component by the thermocouple, and the analysis on a relationship among the deformation characteristics of a section material under high temperature of fire disaster, the heating and the stress can be conveniently carried out.

Metal section heating deformation test device

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Effect of preloading in high-strength bolts on bolted-connections exposed to fire

Behaviour of a two-pinned steel arch at elevated temperatures

Metal section heating deformation test device