The premature end failure of the traditional hollow steel pipe damper (HSPD) greatly affects its energy dissipation performance. This paper proposes a novel hollow steel pipe damper (i.e. ...end-reinforced steel pipe damper, ESPD), which consists of an energy dissipation steel pipe, two inner short steel pipes for strengthening the end of ESPD, and two connecting plates. To study the effectiveness of end-reinforced structure and investigate the mechanical performance of ESPD, one HSPD and three ESPDs specimens with different lengths of inner short pipe are fabricated and subjected to low-frequency cyclic loading. To investigate the influence of the reinforced steel pipe on the mechanical properties of ESPD, numerical analyses are conducted. Results indicate that end-reinforced with short inner pipe is a simple and feasible measure to avoid premature end failure of HSPD. Compared to HSPD, ESPDs own a superior energy dissipation ability and ductility. The reinforcement thickness ratio of 1.67 to 2, and the reinforcement length ratio larger than 0.47 are suggested in designing ESPD.
•A novel hollow steel pipe damper (i.e. end-reinforced steel pipe damper, ESPD) is proposed.•Low-frequency cyclic loading tests are conducted to study the effectiveness of end-reinforced structure and investigate the mechanical performance of ESPD.•Numerical analyses are conducted to investigate the influence of the reinforced steel pipe on the mechanical properties of ESPD.•The reinforcement thickness ratio of 1.67 to 2, and the reinforcement length ratio larger than 0.47 are suggested in designing ESPD.
Segmental tunnel lining is a tunnel lining that is adopted when the Tunnel Boring Machine (TBM) is used as excavation machine. It is a concrete lining that is assembled with segments, connected to ...each other through various devices, including connecting bolts. In order to correctly analyze the behavior of the segmental lining in the longitudinal direction of the tunnel, when actions and loads stress and deform it, it is necessary to know an important mechanical parameter: the shear stiffness of the circular joint. In turn, this fundamental mechanical parameter depends on the behavior of the connecting bolts inside their housing hole. In this work, the behavior of the connecting bolts inside the housing holes was analyzed in detail, through three-dimensional numerical modeling, considering the characteristics of the interaction between the bolt itself and the hole wall, when a relative movement of the lining rings at the circular joint deform the bolt. Thanks to back analysis procedures of experimental laboratory measurements, it was possible to determine the values of some interaction parameters on the bolt-sleeve/concrete interfaces, which are necessary for a correct three-dimensional numerical modeling. The developed numerical model was able to fully describe the behavior of the connecting bolts inside their housing holes and, therefore, also of the circular joint when it is subjected to shear forces that produce the dislocation of the lining rings. The calculation results were compared with experimental measurements obtained from a real-scale tests giving positive results. Thanks to the carried out studies and the developed calculation tool, it is now possible to identify the shear stiffness values of the circular joint with a great detail, in order to evaluate then the mechanical behavior of the segmental lining when subjected to actions and loads (like buoyancy forces due to a liquid filling material around the lining) acting in the longitudinal section of the tunnel.
•Tunnel segmental lining is assembled in segments, connected to each other through various devices, including connecting bolts. The shear stiffness of the circular joint is a fundamental parameter to be able to understand the lining stress-strain condition; it depends on the behavior of the connecting bolts inside their housing hole.•The behavior of the connecting bolts inside the housing holes is analyzed in detail, through three-dimensional numerical modeling, considering the characteristics of the interaction between the bolt itself and the hole wall, when a relative movement of the lining rings at the circular joint deform the bolt.•Thanks to back analysis procedures of experimental laboratory measurements, it was possible to determine the values of some interaction parameters on the bolt-sleeve/concrete interfaces, which are necessary for a correct three-dimensional numerical modeling.•The developed numerical model is able to fully describe the behavior of the connecting bolts inside their housing holes and, therefore, also of the circular joint when it is subjected to shear forces that produce the dislocation of the lining rings.•Thanks to the carried out studies and the developed calculation tool, it is now possible to identify the shear stiffness values of the circular joint with a great detail, in order to evaluate then the mechanical behavior of the segmental lining when subjected to actions and loads acting in the longitudinal direction of the tunnel.
Bridge foundations located in a water flow environment commonly experience scour, which can lead to significant drops in the soil elevation immediately surrounding the foundation. This has ...significant ramifications for lateral bearing capacity as well as the integrity of the supported superstructure. While pile groups are one of the most foundation systems for bridges, current research on scouring effects has been largely limited to single piles. This paper fills this gap through the use of 3D finite element (FE) analysis, validated using centrifuge tests reported elsewhere in the literature. Results from a parametric analysis is described exploring the effects of the scour hole geometry, defined by the depth and slope angle, on the lateral behavior of pile groups. In particular, the influences on the load–displacement and bending moment and soil resistance distributions with depth for each pile within the group are considered. The results show that scour can have a significant detrimental influence on the lateral response of a pile group. An increase in the length of the pile group is also shown to significantly reduce the sensitivity of the lateral bearing capacity of the group to scour.
Due to the difficulties of applying torsional loads to introduce mode III effects, there are few studies for investigating mixed mode I/III fracture in brittle materials. In this paper using three ...novel single or double edge‐cracked diametral compression disc shape specimens, complete ranges of mixed mode I/III are introduced. Fracture factors of the compressed disc specimens with different pre‐notch shapes are determined numerically for a wide range of notch depth and notch inclination angles. The ability of specimens was studied using mixed mode I/III fracture experiments on gypsum. Different fracture envelopes were obtained for the gypsum demonstrating the influence of disc geometry and notch type on mixed mode I/III behavior. For all samples, mode III fracture toughness (KIIIc) was approximately 1.2 to 1.8 times the corresponding value of KIc. Depending on the crack front type, ligament shape and mode mixity, different fracture surfaces were observed. While the mode I fracture surface was smooth and flat in all samples, for mixed mode I/III and mode III, rotation and partially segmentation saw tooth shape wrinkles were observed.
Constant developments in manufacturing technology have made it possible to introduce integrally stiffened elements into load-bearing, thin-walled structures. The application of thin-walled elements ...with integral stiffeners potentially increases buckling and critical loads to maintain the mass of the structure and lower production costs. This paper presents the results of experimental investigations and numerical Finite Element Modelling (FEM) analyses of low-profile, isosceles grid stiffened, aluminium alloy plates subjected to pure shear load. Conducted research included analysing buckling and post-buckling states of deformation, taking into account both geometrical and physical nonlinear effects. Use of the Digital Image Correlation (DIC) system during the experimental tests created representative equilibrium pathways and recorded displacement field distributions over the plate surface. The model was initially validated against the experimental results. The results for the stiffened plate were compared to the reference structure in the form of a smooth plate with equivalent mass. Comparative analyses included examining the displacement fields and stress efforts over the plates. The stiffening configuration under examination increased the critical buckling load by 300% in comparison to the unstiffened structure with the same mass. Obtained results also indicate potential problems with areas of concentrated stress in the case of an incorrect geometry design near to the boundary conditions.
Nowadays Fiber Reinforced Cementitious Matrix (FRCM) systems play a relevant role in the context of innovative interventions for the seismic rehabilitation of masonry structures. Their capacity in ...improving the strength of masonry components is comparable with the one observed in case of Fiber Reinforce Polymer (FRP) systems, but with additional advantages (lower costs, environmental compatibility, removability, etc.). Nevertheless, although a relevant number of applications concerns curved structures (arches, vaults, domes, etc.), the majority of studies available in literature provide a contribution mainly concerning the specific case of applications on flat masonry substrates. The present paper is part of a research activity carried out by the Authors with the main goal to provide a contribution toward the study of the bond behavior of FRCM systems externally applied to curved masonry elements. In particular, the results of numerical analyses carried out by means of a simple modeling approach proposed by the Authors are here carried out by considering as case studies specimens object of a recent experimental investigation. Specific aspects influencing the local bond behavior of FRCM systems applied on curved masonry substrates are then analyzed by opportunely introducing them into the numerical model. The obtained results allow for understanding the effect of important features, experimentally observed in terms of global response, and here assessed in terms of local bond behavior, by particularly emphasizing the role of the curvature and the strengthening position.
Cold-formed steel C- and Z-section beams are widely used in light gauge steel building systems as flexural members. In their applications as flexural members, mono-symmetric C-sections and ...point-symmetric Z-sections are often subjected to transverse loads eccentric to the shear centre, leading to combined bending and torsion actions. However, research and design methods for cold-formed steel beams subjected to combined bending and torsion are limited. Hence this research has investigated the structural behaviour, strength and design of cold-formed steel C- and Z-section beams under the action of combined bending and torsion. Twenty-four tests were conducted on simply-supported beams subjected to a mid-span eccentric load. Two C-sections and two Z-sections were used in the tests with two different spans, each with three loading-eccentricities. A special test set-up was developed and used to simulate the different loading-eccentricities and to provide accurate boundary conditions. Numerical models of tested beams were then developed using ANSYS and nonlinear finite element analyses including the effects of large deformation and material yielding were performed. The numerical results agreed well with the test results in terms of ultimate strengths, failures modes and load-displacement curves. Finally the results from tests were compared with predictions from the current design equation for bending and torsion. This paper presents this investigation of cold-formed steel beams subjected to combined bending and torsion, and the results.
•Cold-formed steel beams were tested to failure under varying levels of combined bending and torsion actions.•Numerical models of tested beams were developed to simulate their behaviour.•The results from tests were compared with predictions from the current design equation for bending and torsion.
This study presents the results of experimental research and numerical calculations regarding models of a typical torsion box fragment, which is a common thin-walled load-bearing structure used in ...aviation technology. A fragment of this structure corresponding to the spar wall was made using 3D printing. The examined system was subjected to twisting and underwent post-critical deformation. The research was aimed at determining the influence of the printing direction of the structure’s individual layers on the system stiffness. The experimental phase was supplemented by nonlinear numerical analyses of the models of the studied systems, taking into account the details of the structure mapping using the laminate concept. The purpose of the calculations was to determine the usefulness of the adopted method for modeling the examined structures by assessing the compliance of numerical solutions with the results of the experiment.
•A multi-physical model of CaO/Ca(OH)2 hydration process is simulated.•Thermal conductivity of solid-phase has a significant effect on hydration process.•Relationships between fins and reaction are ...explored.•Axial fins shorten the exothermic time to 83.4%.
Thermochemical heat storage technology is an important component in energy system, and plays a key role in the balance of energy supply and demand. A multi-physics model is constructed to study the hydration process in a tubular reactor, including fluid flow, heat transfer and reaction. Variations of temperature and conversion of CaO are discussed in detailed to reveal exothermic reaction characteristics. Besides, effects of different reaction conditions during hydration are studied, such as porosity, temperature, pressure, flow rate and thermal conductivity. It is found that the low thermal conductivity of solid-phase is the most important factor which limits the reaction. The heat transfer process can be greatly promoted by adding fins, due to the high heat conductivity. However, the relationship between the reactor structure and the performance of the thermochemical heat storage is not quantitatively clear. The present study aims to investigate the impact of the arrangement of fins on the hydration process. Finally, different types of fins with high thermal conductivity are employed in the reactor. Attributing to the fact that the equilibrium temperature is affected by the vapor pressure, thermochemical reactors with different fin configurations have different flow characteristics and pressure drops, leading to different reaction characteristics. It is shown that the exothermic time was reduced to 84.32% (axial fins), 89.97% (radial fins), and 88.71% (spiral fins) of the original, respectively. This study can reveal the coupling relations of multi-physics fields in thermochemical heat storage, and provide theoretical basis for the design of thermochemical heat storage reactors.
Vibrations are an issue of increasing importance in current footbridge design practice. More sophisticated footbridges with increasing spans and more effective construction materials result in ...lightweight structures and a high ratio of live load to dead load. As a result of this trend, many footbridges have become more susceptible to vibrations when subjected to dynamic loads. The most common dynamic loads on footbridges, other than wind loading, are pedestrian-induced footfall forces due to the movement of people. This paper concerns the experimental and numerical dynamic characterization of a newly built steel and wooden cable-stayed footbridge. The footbridge was dynamically tested in situ under ambient vibration, and the results allowed the real dynamic behavior of the footbridge to be captured. The dynamic response under pedestrian dynamic loads was also investigated and compared with the limitations provided by the main international codes and guidelines for footbridge serviceability assessment. A numerical model of the footbridge was also developed and updated based on the experimental outcomes. Then, the calibrated model was used to numerically assess the footbridge’s serviceability following the guideline prescriptions for pedestrian load simulation, and the design accuracy was also validated. This paper aims to increase the state-of-the-art knowledge about footbridge dynamic testing so as to support the design of new and futuristic structures as well as prove the effectiveness of using the requirements of codes and guidelines for footbridge serviceability assessment by adopting a calibrated numerical model.
PDF
