Cable Roof Research Articles

Numerical study on the dynamic pressure control for self-forming roadways using CHRCT in thin coal seams with thick and hard roofs

Close-hole roof-cutting technology (CHRCT, also called “dense drilling”) has been widely applied in coal mines due to its economic and safety benefits. Inappropriate cutting parameters and support schemes can lead to dynamic pressure disturbances in self-forming roadways with thick and hard roofs. Moreover, fully characterizing the procedure and process of self-forming roadways using CHRCT in the field is difficult, resulting in unconvincing results. Therefore, this study aims to fill the gaps in theoretical knowledge and methodology. First, the dynamic pressure characteristics of the self-forming roadway using CHRCT were investigated, and the dynamic pressure types of the roadway were classified. There are three main types: roof cut off along the coal wall side of, severe deformation, and overhanging roof of a roadway after the second working face mining. The effects of different hole parameters (inclination angle, depth and spacing) on the roof cutting to form a roadway were also investigated. The optimal hole inclination, depth and spacing of 15°, 8 m, and 200 mm were determined through a series of experiments. Then, three support schemes embedded in the roadway were compared in terms of stress evolution, bolt and cable axial forces, roof displacement, and structure. Finally, this study proposes a dynamic pressure mitigation strategy through the optimization of parameters for close-hole roof-cutting and support schemes, monitoring and controlling ground pressure in roadways, and taking auxiliary measures for pressure relief. The results show that this strategy can effectively eliminate the dynamic pressure of the roadway and meet the stability requirements of the full mining cycle. This paper presents a methodology for analysing CHRCT via numerical simulation. Moreover, this approach is of great theoretical and practical importance for dynamic pressure control for self-forming roadways using CHRCT in thin coal seams with thick and hard roofs.

The influence of supports stiffness on the cable nets force distribution and geometry

This paper presents the initial stage of the design process of elastically supported cable net roofs. The form-finding and static analyses with large deformations are performed for two examples of structures. In both cases, the influence of real supports stiffness on the tensile force distribution and geometry of cable nets was compared. It was confirmed that it significantly influences designing of the final cable net configuration

Numerical method used for the simulation of fluid–solid transitions based on the VOF and SAM models and prediction of snow distributions on large-span roofs

During a snowfall, the surfaces of the snow beds on roofs change dynamically with time and wind conditions. The generation of body-fitted computational fluid dynamics grids for simulating dynamic snow surfaces using the moving-grid method remains challenging. Therefore, a numerical method was developed to simulate the fluid–solid transition based on the volume of the fluid model and solidification and melting models. The snowfall process was divided into n stable steps, and a stable state calculation method was adopted to calculate the air and snow phases. The dynamic snow boundary was simulated at each stage by converting the fluid or solid characteristics of the domain in which the grids resided. Based on the results of the (n−1)th stage, the fluid domain grids buried by the snow were filled with liquid and frozen into the solid domain. Instead, the fluid in the frozen grids, where snow was about to be eroded, was evacuated and converted into fluid-domain grids. Thus, a complex and changeable snow boundary could be adapted without re-meshing. A modified wall friction velocity equation was derived to correct the wall friction velocity at the snow boundary owing to the serrated boundary of the solidified grids, thereby improving calculation accuracy. The numerical simulation results were verified via field observations of snow distribution on the stepped flat and gable roof models. The snow variation on a full-scale, three-span, suspended cable roof under snow-fall conditions was predicted using the proposed method.

A novel integrated sleeve-wedge anchorage system for multi-tendon CFRP cable utilized in cable roof structures: Concept and numerical investigation

Carbon fiber-reinforced polymer (CFRP) cables demonstrate exceptional mechanical properties and offer significant potential for utilization in large-span cable roof structures. However, the implementation of efficient CFRP cable anchorage systems specifically designed for cable roofs remains an urgent necessity. In this paper, a novel integrated sleeve-wedge anchorage system (NISWAS) consisting of two components, a multi-channel integrated sleeve-wedge (MCISW) and a barrel, has been proposed to achieve the anchorage of CFRP cable with multiple tendons. Compared to the traditional wedge-type anchorage system (WTAS), which can only clamp a single CFRP tendon, the use of the novel integrated steel wire anchorage system (NISWAS) reduces both the volume and self-weight of the cable anchorage end, significantly improving construction efficiency. The design concept of NISWAS was validated through finite element method (FEM) as an example of a 6-Φ5 CFRP cable, and its anchor performance was systematically evaluated. Three key factors affecting the anchor performance were analyzed: the slope angle of MCISW, the anchor length and the differential angle between barrel and MCISW. The results show that the NISWAS is an effective way of anchoring multiple CFRP tendons, and the design of the MCISW can prevent excessive transverse stress on the CFRP cable at the loaded end of the anchorage. The slope angle of the MCISW exerts the most significant impact on the anchor performance. The optimal choice of angle is 3°, beyond which the effect of the anchorage system on the sliding of CFRP cable becomes less significant, while excessive transverse stress may cause premature failure of the cable. The differential angle between barrel and MCISW has a secondary influence on the anchor performance. A moderate angle difference value (0.1° to 0.2°) can alleviate the transverse stress on the CFRP cable, but a too large value (more than 0.3°) will reduce the force transmission between the MCISW and barrel, resulting in premature cable pullout. Increasing the anchor length can reduce transverse stress and cable slip, but the reduction effect is not significant. After analysis, the anchor length of 90 mm can satisfy the anchoring requirement. According to the influence law of the above three factors, the parameter design scheme of the NISWAS was finally proposed.

Experimental and Numerical Investigation of the Mechanical Properties of a CFRP Tendon-Wedge Assembly Loaded under Transverse Compressive Loading.

Carbon-fiber-reinforced polymer (CFRP) tendons have become a viable alternative to steel cables in cable roof structures owing to their high tensile strength, low weight, and resistance to corrosion. However, the effective anchoring of CFRP tendons is a challenge because of their poor transverse mechanical properties. Therefore, the mechanical properties of CFRP tendons and a tendon-wedge assembly under transverse compression were investigated by simulating the force environment of the CFRP tendon inside an integrated-wedge anchorage. The deformation of and local damage to CFRP tendons under transverse compression were explored using load-strain curves and full-field strain measured using digital image correlation. The experimental and numerical results show that large-diameter CFRP tendons with a length in the range of 90-110 mm had better cross-sectional deformation resistance and more stable transverse mechanical properties. Longer CFRP tendons with larger diameters have lower contact compressive stress and local maximal shear stress under the same transverse compressive load. Based on the analysis of the experimental and numerical results, we propose design suggestions for tendon size selection and integrated-wedge design details, such as the manufacturing materials of the wedge, the radius through the gap of the wedge, and the radial difference of the groove, to improve the anchoring properties and efficiency of the integrated-wedge anchorage.

A Field Study Implementing New Monitoring Technology for Roof Caving and Systematic Monitoring for Gob-Side Entry Retaining via Roof Cutting in Underground Coal Mining

The longwall mining method with gob-side entry retaining via roof cutting is a new underground coal mining method which has the characteristics of a high resource recovery ratio and environmental friendliness. Due to the complexity of this method, the research method of case-based dynamic on-site monitoring, analysis, adjustment, and optimization is usually adopted. Based on a roadway retaining via roof cutting project, in addition to the traditional indirect monitoring method of hydraulic support pressure, this study innovatively establishes a direct monitoring method for roof caving by monitoring the gangue pressure in the goaf, which provides data for the roof cutting effect and offers a new method for studying the overlying strata movement. In the project, a comprehensive monitoring and analysis system was established, including gangue pressure, cable bolt stress, bracket pressure, roadway deformation, and roof separation, which was used to dynamically analyze the effect of roof cutting and optimize the support design. The results show that the pressure of the hydraulic support close to the roof cutting is low, indicating that roof cutting is favorable in the roadway retaining mining method. The roadway deformation in the advanced abutment pressure area of the working face is small. The mining-induced stress caused by the collapse and compaction of the overlying strata in the goaf is the dominant factor affecting the effect of roadway retaining, especially in the 50-100 m range behind the working face, where the dynamic load causes high bearing capacity of the support elements, large roadway convergence, and roof separation. Temporary support and supplementary reinforcement should be added when necessary. The monitoring system presented in this study is highly comprehensive, simple, reliable, and low in cost, providing a reference for roof cutting roadway retaining projects and roof caving-related studies.

Research on dynamic stability of large deformation roadway with application of segmented resistance anchor bolt

The dynamic stability of large deformation roadway can be significantly affected by seismic vibration. In order to improve the support effect, a segmented constant resistance anchor bolt structure is proposed. The preload can be set in segments to effectively reduce the tension deviation. The support stability of this type of bolt is verified by field test and experimental simulation. Based on the bearing and deformation characteristics of surrounding rock, the supporting and installation, grouting process and anchor cable stress monitoring of this type anchor bolt are designed. Through the field measurement of the roadway, the variation laws of the rock swelling coefficient, anchor cable tension and roof subsidence under the condition of bolt support are obtained. A tunnel dynamic deformation test-bed is built to study the dynamic vibration response of the designed anchor bolt to alternating load. Applying orthogonal exciting force, the tension changes in different constant resistance sections are obtained. The results show that this type of bolt has remarkable effect of resisting alternating load, and the maximum tension deviation within ±200 m working face is less than 8 %, which has better support stability than conventional bolt.

Advanced form finding of cable roof structures integral with supporting frames: Numerical methods and case studies

Traditional form-finding methods usually assume that the boundary conditions of cable roofs are fixed constraints without considering the influence of the supporting frame. However, the cable roof interacts with the supporting frame and they work together as a whole. Pre-tensioning for cables will cause the deformation of the supporting frame toward the center, which will lead to the deviation between the actual initial equilibrium state and the target design result, especially the interconnection between the cable roof and the flexible supporting frame. To solve this problem, the interaction mechanism between the cable roof and supporting frame was first analyzed theoretically in this study. A novel form finding method of cable roof structures integral with supporting frames was proposed. The parameters that affect the form-finding result were analyzed, including the prestress, the stiffness of the supporting frame, and the stiffness of the cable. For the convenience of engineering applications, this method was developed using the ABAQUS software and was compiled in the Python language. According to different types of cable roofs, two form-finding schemes and two algorithmic procedures were proposed. The form-finding results of six typical cases were presented. The novel method was confirmed to be feasible and may be valuable for engineering applications.

Three-dimensional laser scanning for large-scale as-built surveying of 2022 Beijing Winter Olympic Speed Skating Stadium: A case study

The latest 3D laser scanning technology is implemented in a practical project—2022 Beijing Winter Olympic Speed Skating Stadium—to investigate its effectiveness on the large-scale as-built surveying of civil infrastructures. The laser scanning was used for measuring the vertical deformation of flexible orthotropic cable net roof structure and for assessing the installation tolerance of curved glass curtain wall system. It was observed that 66% of clamps in the flexible roof structure showed vertical deviations within the range of ±5 mm and 94% of clamps showed deviations within ±10 mm. Additionally, about 60% of the vertical joints in transparent glass curtain wall showed deviations within the range of ±10 mm and the overall median deviation was only 2 mm. Given the complex structural form of the cable net roof structure and the glass curtain wall system, 3D laser scanning demonstrated unparalleled efficiency as compared to the conventional measuring methods.

Research on the failure mechanism and control technology of surrounding rock in gob-side entry driving under unstable overlying strata

The main reason of gob-side entry deformation is surrounding rock movement near the goaf. During underground excavation, it is common that surrounding rock behavior and crack development under unstable overlying strata are substantially different from rock under strong and competent main roof. To study the failure mechanism due to main roof deformation near the edge of goaf, UDEC Trigon model was constructed with strong and thick hanging roof. Laboratory and Rock Quality Designation (RQD) results were used for model calibration. Results show that stress acting on the pillar increased dramatically due to roof subsidence prior to roof caving and breakdown. At the same time, considerable number of fracture developed in the roof and rib. After separation of failed roof, the influence on crack development decreased. Once the separated roof was stabilized, failure zone of surrounding rock stopped expanding. To manage the unsymmetrical deformation due to dynamic loading from hard main roof under gob-side entry driving, a combined strata control method was proposed, including roadway expansion, long cable bolt installation and roof cutting via blasting. Field trials prove that the optimized supporting plan can effectively control the large deformation of 9102 gateroad; and, the implementation of roof cutting can reduce gateroad failure from dynamic loading.

Non-linear normal modes of plane cable trusses

A model for the non-linear dynamic behaviour of pre-stressed cable trusses is presented. The model provides the basis for a simplified description of the (in-plane) non-linear dynamical behaviour of biconcave and bi-convex cable structures (as well as of single cables) subject to different loading (and mass distribution) conditions. The simplicity of the proposed approach is coupled with its ability to schematically represent a wide range of actual structures, including light pedestrian suspended cable bridges and cable roofs with vertical harnesses, under different vertical loading conditions. Although aiming at the needs of the practitioner, in search for a simplified and intuitive understanding of the effects of nonlinearities on the dynamic response of cable structures (to confirm and explain results from more detailed FEM models), the proposed approach also paves the way for the investigation in the extensive taxonomy of the non-linear dynamic behaviour of cable structures. The present paper focuses on non-linear normal modes (NNMs) arising as a continuation of linear vibration modes of the structure when energy is increased. The identification of non-linear normal modes is achieved through harmonic balance; a time-integration analysis is then performed on the same model, with initial conditions derived from the harmonic balance approach, demonstrating consistent results. To further test the model, its behaviour is compared to simulations on a 66-degrees of freedom finite element truss model, with satisfactory results.

Examination of artificial neural networks to predict wind-induced displacements of cable net roofs

This paper discusses the implementation of an Artificial Neural Network (ANN) model for predicting the wind-induced, vertical displacements of cable net roofs with a hyperbolic paraboloid shape. The ANN model was calibrated by training and comparing three preliminary ANN topologies. The first one was trained using both experimental pressure coefficients on similar building geometries and wind-induced vertical displacements estimated by Finite Element Method (FEM). This first set was subsequently used to calibrate a second ANN model, which was based on surrogate modeling of pressure coefficients, calculated by polynomial fitting of the experimental data. Further generalization of the pressure coefficients was obtained through parametrization of the polynomial fitting as a function of geometrical properties. Pressure loads were used to calibrate the third ANN, which was employed to synthetically generate vertical displacements of a varied geometrical sample. The ANN-based models exhibit remarkable results; the coefficient of determination between physically-estimated flexible roof displacements and approximated values was usually above 0.90 for all the tested geometries, suggesting that this type of surrogate model is capable of replicating complex, geometrically nonlinear structural behavior.

Static Analysis of Circular Cable Suspended Roofs.(Dept.C)

The main aim of the present work is to investigate the static analysis of circular cable suspended roofs, which are the most common forms of suspended roofs. minimizing of total potential energy by the conjugate gradient technique. The results are used to investigate the factors that affect the design and the response of cable suspended roofs. Also, these results have been used in making non-dimensional tables and graphs and to infer new relationships. These tables, graphs and relationships form a good technique for the preliminary design of circular cable suspended roofs either nets or grids. This good preliminary technique was examined using several examples and the results are in good agreement with these solved using the computer program based on minimizing the (TPE) using the (CG) technique for the analysis of cable roofs

Investigation of wind-induced dynamics of a cable net roof with aeroelastic wind tunnel tests

This paper examines the results of experiments conducted in a boundary layer wind tunnel on rigid and flexible models of a tensile structure with a hyperbolic paraboloid roof. Pressure tests on the aerodynamic model were used to calculate a numerical finite element model that was used to design the aeroelastic model. The response of the aeroelastic model was then used to calibrate the numerical model. Dynamic identification of the aeroelastic model with and without wind is discussed in terms of natural frequencies and damping ratios. The focus of the experiments was the description of a continuous chain of measurements made of aerodynamic, numerical and aeroelastic models for a structure with several close natural frequencies. The random decrement technique was used to calculate aerodynamic damping of the flexible model. The results indicate that the wind load significantly modifies the natural frequencies of vibration and damping ratios of the structure when compared with the unloaded structure.

Frequency Analysis of Circular Cable Suspended Roofs (Dept.C)

The main aim of the present work is to investigate the dynamic analysis of circular cable suspended roofs which are the most common forms of suspended roofs using the frequency domain method. Although frequency domain analysis is used basically for linear systems, it may be used to analyze cable suspended roofs for which, wind is considered as the fundamental dynamic factor affecting in these structures. This is due to the fact that the fluctuating wind speed, except for sites in mountainous areas, may be neglected comparing with the mean wind speed. Many circular cable roofs have been analyzed using a computer program constructed by the second author based upon the frequency domain analysis. The results WTC used in making non-dimensional graphs. These graphs were used to used to investigate the factors that affect the natural frequencies of circular cable suspended roofs.

Static and Dynamic Analyses of Suspended Cable Roofs for Halls Having A Rectangular Shape to Wind Loads (Dept.C)

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Investigation of wind induced vibration and acoustic performance interactions for a flexible roof through multiphysics approach

This paper analyses structural and acoustic performance interactions of a building covered with a cable net and membrane roof following a multiphysics approach. The problem has three different variables: the roof time-depending deformed shape under wind action (duration 1800 s), the extremely variable position of a singer on the stage (30 s speaker recorded movements were expanded through a 6th order Hermite chaos polynomials to cover all the potential acoustic source positions) and finally, the listeners’ location (assumed according to Beranek for a listener located in the middle of the aisle between two stalls). The Initial Time Delay Gap was assumed as a measure of speech or song diffusion. In addition, reverberation time, clarity and early decay time were estimated for both undeformed and deformed roof shapes to evaluate acoustic performance variations. Roof deformation was calculated using time-history nonlinear structural analyses done by applying wind action measured in wind tunnel.

Improved time-hardening creep model for investigation on behaviour of pre-tensioned steel strands subject to localised fire

Pre-tensioned steel strands as basic elements have been widely used in hybrid string structures, cable suspension roofs and cable-stayed bridges. There is a growing need to evaluate the damage of such structures whenever subjected to fire. The aim of this research is to experimentally and numerically investigate the behaviour of pre-tensioned steel strands considering the effect of creep strains at elevated temperatures. A charge-coupled device camera (CCDC) system is used to capture the high-temperature creep strain of steel strands accurately. A regression analysis is carried out to develop a set of new parameters for Time-Hardening creep model based on the test results of 1860 MPa strands twisted by 7 wires. The test results show that target temperatures influence the high-temperature creep rate more greatly than pre-stressing ratios. The Time-Hardening creep model with new parameters is used in finite element software ANSYS to investigate the mechanical behaviour of pre-tensioned steel strands subject to localised fires. The influencing factors include the pre-tensile force ratio, span length of steel strands, temperature distribution along strand length and fire location. The numerical results indicate that the tensile force in steel strands reduces more greatly as high temperature creep strain is taken into account. Pre-tensioned steel strands will fail when the rupture strain rather than the ultimate tensile stress is achieved at elevated temperatures.

Large Deformation Mechanism and Three-Level Control Technology of Entry Retaining in Three-Soft Thick Coal Seams

Gob-side entry retaining (GER) has been widely used around the world. However, when the technology of gob-side filling and roadway retaining is applied to the mining of three-soft thick coal seam, large deformation of surrounding rock and failure of support structure are still unavoidable, especially the floor heave deformation, even the closure of the roadway section in serious cases. Taking 16,011 working face of Zhaogu No. 1 Coal Mine as the research object, mineral composition analysis showed that there are a lot of clay minerals in the surrounding rock, which shows strong swelling characteristics. The mechanical model of the overlying strata with long cantilever structure was constructed to explain the process of ground pressure transferring from two sides of roadway to the floor after retaining roadway, and then the variation and distribution law of stress on both sides of the floor with the working face promotion was obtained. With the aid of uncoupling support theory, this paper analyzed the floor heave mechanism of GER in three-soft thick coal seam, and pointed out that shear staggered floor heave was the main cause of floor heave deformation. Based on above analysis of large deformation mechanism of GER, the three-level control technology of surrounding rock in entry retaining in three-soft thick coal seam was put forward: directional pre-splitting decompression technology, constant resistance & large deformation anchor cable (CRLDAC) roof support technology and floor deformation control technology. The key parameters of the three-level control technology were determined by field industrial test. Monitoring data proved that the three-level control technology can effectively control the deformation of surrounding rock in retained roadway, in which roof-to-floor convergence had been reduced by 58%, and floor heave had been reduced by 65%, finally, the roadway had been retained successfully.

Approximate static analysis of circular convex cable roof beams in the existence of central and edge rings

Approximate static analysis of circular convex cable roof beams in the existence of central and edge rings