Combined Action Of Compression Research Articles

Performance of round-ended CFST columns under combined actions of eccentric compression and impact loads

Round-ended concrete-filled steel tubular (RECFST) columns are gaining increasing usage in bridge structures. During their service life, RECFST columns under eccentric compression may suffer from impact loading. This study conducted test and numerical investigations to assess the performance of RECFST columns under the coupled actions of compression, bending and lateral impact loads. Fourteen columns were fabricated and tested, considering the influences of axial-load ratio, bending moment and impact energy. The damage mode and the time histories of impact force and displacement were accessed and analyzed. The experimental findings revealed that the initial bending moment negatively affected the impact resistance of RECFSTs. In addition, finite element model was established in ABAQUS and calibrated against the test results. The calibrated model was then employed to conduct the failure mechanism analysis and parametric study. Finally, a single-degree-of-freedom (SDOF) analysis was conducted to predict the mid-height deflection of RECFST columns under combined action of compression, bending and lateral impact loads, by incorporating the influences of pre-axial load and initial bending moment.

Mechanical properties and damage model of coral seawater sea sand concrete under compression-shear composite action

The present study investigates the mechanical properties of coral seawater sea sand concrete (CSSC) under compression-shear composite action. A total of 54 concrete specimens were designed for the shear test with varying parameters such as normal stress ratio, curing age and different aggregate types considered. The CSSC shear stress-displacement curve was obtained by observing the damage morphology of the specimen under a combination of compressive and shear stresses. The effects of different normal stress ratios on the shear strength, peak shear displacement, and damage evolution pattern of the CSSC specimen are analyzed. The results show that the width of the main cracks on the surface of the specimen gradually increases with the normal stress ratio, and the tiny oblique cracks gradually become denser. The peak shear displacement and shear strength also increase with normal stress, and the damage evolution of the concrete gradually slows down. When the curing age was increased from 7d to 14d and 28d, the shear strength of the CSSC specimens increased by 5.9% and 11.3%, respectively. In this paper, we propose two failure models that better reflect the shear strength of CSSC under the combined action of compression and shear. Finally, a compressive-shear damage constitutive model for CSSC at different normal stress ratios has been developed and the results are in good agreement with the experimental results.

Damage detection of concrete segment in steel-concrete hybrid wind turbine tower

The steel–concrete hybrid tower (SCHT) has been applied as an alternative supporting structure for wind turbines due to its advantages of higher hub height and loading bearing capacity. To improve the construction efficiency of such a tower on site, the lower concrete section was divided into several prefabricated segments and the connection between different segments was achieved by grouting joints, which may become the weakest part of the tower under the combined action of compression, bending, shear and torsion, leading to progressive collapse or other undesirable failures of the SCHT. However, up to now, there were limited studies focused on the monitoring system detecting the damage of the concrete segment and most of them required inspection at downtime. To fill up the research gap, this paper developed a real-time monitoring system for detecting the possible failure of the concrete segment effectively and accurately. To start with, the formulation of the damage index based on the dynamic acceleration responses is firstly presented based on the mechanical characteristics of the wind turbine towers. Then, an experimental investigation and parametric analysis based on numerical simulation are arranged to validate the reliability of the proposed method. The analysis results indicate the proposed method can provide a reference for the damage monitoring of the SCHT.

Bending restoring force model of angle-steel reinforced concrete columns under combined torsion

To explore the restoring force model of an angle steel truss reinforced concrete column (ASRC) under the combined action of compression, bending, shear, and torsion, nine ASRC columns under a combined torsion environment were tested and analyzed. This study observed and summarized the failure mode characteristics of different component columns, distinguished different failure modes, and analyzed the hysteresis curve and energy dissipation capacity of component columns. Then, a trilinear skeleton curve model suitable for ASRC columns is adopted, and the calculation method of skeleton curves in different stages under the combined action of compression, bending, shear, and torsion is given. Finally, the ASRC hysteresis rule is simplified, and fitting produces the formulae for positive and negative hysteresis curve unloading stiffness. The restoring force model of the ASRC column under coupled torsion is established, and the test results validate the restoring force model. The results show that the established restoring force model can predict the hysteretic behavior of ASRC under combined torsion. This research can be used as a theoretical foundation as well as an experimental reference for the technical use of ASRC.

Seismic behavior of RC cross-shaped column under combined torsion loading: Experiment and simulation finite element

The seismic behavior of the reinforced concrete (RC) cross-shaped columns under the combined action of compression, bending, shear, and torsion were studied by experiment and numerical simulation. The effects of torsion-bending ratio (T/M) and axial compression ratio (n) on the seismic indexes, i.e., failure modes, skeleton curves, hysteretic curves, strength, ductility and stiffness were studied. Experimental results suggested that the T/M ratio determines the failure modes of RC cross-shaped section columns. Both the damage length and crack angle increase with the raise of the T/M ratio. The displacement ductility factor and elastic–plastic drift ratio are higher than 3.0 and 0.02, respectively, indicating that the RC cross-shaped columns exhibit good ductility and deformation capacity under combined torsion loading conditions. The normalized shear-displacement hysteretic model and the torque-twist angle hysteretic model were established. Based on the experimental results, as well as the finite element model for RC cross-shaped columns under combined torsion, was proposed. The results derived from the hysteretic models and finite element simulation are in good agreement with the experimental results.

Spatial Deformation of Osteosynthesis Systems. Message 1. Criteria of Functional Reliability.

Based on experimental studies, an analytical method is proposed for assessing the functional reliability of osteosynthesis systems. As criteria for the rigidity of osteosynthesis systems, displacements and mutual rotations of parts of bone fractures with fixation tools were used. The characteristics of the “bone with a fracture - fixation system”, necessary for calculations, determined experimentally from individual loads by compression, bending, and torsion of bone samples with simulated fractures and fixation tools.The characteristics of the plates for fixation of tibial fractures are determined, the level of allowable loads is calculated according to the combined action of compression, bending and torsion, and the areas of valid loads are determined.The proposed criteria for functional reliability make it possible, using simple tests and analytical calculations, to determine permissible load levels that do not lead to the occurrence of dangerous movements in the fracture area.

Seismic behavior of steel reinforced concrete cross-shaped column under combined torsion

Experiments were performed to explore the hysteretic performance of steel reinforced concrete (SRC) cross-shaped columns. Nine specimens were designed and tested under the combined action of compression, flexure, shear and torsion. Torsion-bending ratio (i.e., 0, 0.14, 0.21) and steel forms (i.e., Solid - web steel, T - shaped steel, Channel steel) were considered in the test. Both failure processes and modes were obtained during the whole loading procedure. Based on experimental data, seismic indexes, such as bearing capacity, ductility and energy dissipation were investigated in detail. Experimental results suggest that depending on the torsion-bending ratio, failure modes of SRC cross-shaped columns are bending failure, flexure-torsion failure and torsion-shear failure. Shear - displacement hysteretic loops are fuller than torque - twist angle hysteretic curves. SRC cross-shaped columns exhibit good ductility and deformation capacity. In the range of test parameters, the existence of torque does not reduce the shear force but it reduces the displacement and bending energy dissipation capacity.What is more, the bending energy dissipation capacity increases with the rising of displacement level, while the torsion energy dissipation capacity decreases.

Development of multiple ordered fracture in an elastic homogeneous, structured and layered medium

ABSTRACTMechanical models of a series of fracture processes accompanied by formation of structures of fracture (ordered systems of cracks (violations)) are presented. The models are based on the fracture mechanics concepts and account for an influence of an initial structure and texture of material (medium) and loading conditions. Attention is paid to the model of linear structures of fracture formation in a porous material (medium) under the combined action of compression and tension. An influence of various mechanisms of local brittle fracture in the vicinities of pores and microcracks on the material bearing capacity at complex stress state is considered. Possibilities of a hierarchy of echelon‐like crack systems formation near a macroconcentrator of stresses are illustrated by experiments on fracture near a macrocut (notch) of longitudinal shear. A model of the process is also discussed.

Design of two crushing devices for release of the fluid inclusion volatiles

Abstract Two crushing cells have been described for the release of volatiles from fluid inclusions in minerals in vacuum, static gas, and gas-flow applications. To minimize the adsorption of released volatiles on the freshly created mineral surfaces, both devices employed heated crushing. In the MTSN (Museo Tridentine di Scienze Naturali) crusher, samples were disintegrated by a piston driven by an induction coil. For efficient crushing, the electromagnet operated in dynamic impulse mode. In the LFU (Leopold-Franzens-Universität) crusher, the sample was disintegrated through the combined action of compression (manually operated hydraulic ram) and attrition. Crushers are able to be used in off-line and on-line modes, in gas chromatographic and mass spectrometric analyses.

Mechanism Analysis and Experiment Study on RC Composite Core Walls

Two 1/6 scale core walls specimens were designed，including a normal reinforced concrete core wall and a reinforced concrete composite core wall with steel truss. The experimental study on two core walls subjected to combined action of compression, bending moment, shear and torque, was carried out. Based on the rotating-angle softened truss model theory, this paper presents a three-dimensional model for analysis of reinforced concrete composite core walls with steel truss subjected to complex loading. Through the results of calculation coincided with the test well, this model can predict the ultimate strength of the load-carrying capacity of reinforced concrete composite core walls with steel truss, and provide a tool to obtain the entire load-deformation history.

Study on behaviour and strength of SFRC under combined action of compression and shear

Steel fibre reinforced concrete (SFRC) has been gaining popularity in load-carrying members because of its positive contribution to both concrete strength and energy absorption capacity. This paper presents both experimental and theoretical study of the fibre reinforcing effect on the concrete failure mechanism. The compression/shear tests of cubic steel fibre reinforced concrete specimens with fibre volume fractions of 0%, 1·5% and 3% are conducted in the wedge shear apparatus. Their failure patterns are analysed at macro- and meso-scale levels. Subsequently, these experimental data are analysed by a twin-shear strength theory. One concise compression/shear failure criterion is then developed for SFRC. It is found that the predicted results by this criterion agree well with those by experiments. Finally, the changes of concrete twin-shear strength parameters with the fibre volume fraction are explored.

Design of Slender Angle Section Beam-Columns by the Direct Strength Method

This paper is concerned with the application of the direct strength method to equal angle section beam-columns with locally unstable legs. In contrast to existing design methods, which independently determine the compression and bending capacities and use an interaction equation to combine these, the direct strength method determines the elastic local buckling stress for the actual stress distribution resulting from the combined action of compression and bending, and incorporates the elastic buckling stress into a direct strength equation for beam-columns. In applying the method to equal leg angles, the torsional buckling mode is ignored when determining the overall buckling capacities, since it is accounted for through the local buckling mode, and the shift of the effective centroid is incorporated as an additional loading eccentricity. The shift in the effective centroid resulting from local buckling is determined from the actual stress distribution, as obtained using Stowell’s classical solution, in place of an effective cross section. The predicted strengths are conservative compared to tests on slender equal angle columns, and are shown to accurately predict the variation in load with applied loading eccentricity.

Recent research developments in stability and ductility of steel bridge structures: General Report

Some ductility and strength researches of thin-walled steel bridge structures recently conducted at Nagoya University are summarized in this paper. The first part is on the investigations of the behavior of component plates, which are subjected to compression or shear. Both the monotonic and cyclic loading conditions have been considered. Then the studies of stub-columns under combined action of compression and bending are presented. The considered stub-columns are composed of stiffened and unstiffened box sections or pipe sections. For both the plates and stub-columns, empirical equations of strength and ductility have been developed. Based on the equations, a simple ductility evaluation method for thin-walled steel structures which involves a nonlinear pushover analysis and a definition of failure criterion is finally proposed. Moreover, some recent results of thin-walled structures through cyclic experimental and numerical studies are also included in this paper and are compared with the ductility estimations through the proposed simple method.

Ultimate Strength Analysis of Thin Plated Structures Using Eigen-functions

In order to increase the safety of plates structures such as ships, ultimate strength analysis should be performed taking into account of local failures of buckling and yielding of component plate elements. Direct application of the finite element method still needs enormous computation time and is not economical to use at the design stage, even most advanced computers are provided. In order to achieve this purpose, one of the authors proposed the “Idealized Structural Unit Method (ISUM)” and proved its usefulness by many applications. The previous rectangular plate element was developed based on the numerical results on buckling and post-buckling and formulation of its stiffness equation was complicated. In this paper, a new rectangular plate element has been developed. The formulation of its stiffness equation has been performed completely analytically for buckling and post-buckling behaviors by introducing eigen-functions, being paid attention to use only one or two parameters to reduce computation time. For partial yielding of the element, the plastic node method is introduced. This new element can be applied to the complete range of the behavior incluing buckling, post-buckling, ultimate strength and post-ultimate strength. The numerical results indicate that necessary computation time is very short for any aspect ratios and the accuracy is very high in comparison with FEM. There is some improvement is expected to reduce higher shear force at the ultimate strength under a combined action of compression and shear.