Unfavorable Load Research Articles

An Indirect Measurement Methodology to Identify Load Fluctuations on Axial Turbine Runner Blades.

Smooth integration of intermittent energy sources, such as solar and wind power, into the electrical grid induces new operating conditions of the hydraulic turbine by increasing the off-design operations, start/stops, and load variations. Therefore, hydraulic turbines are subject to unstable flow conditions and unfavorable load fluctuations. Predicting load fluctuations on the runner using indirect measurements can allow for optimized operations of the turbine units, increase turbine refurbishment time intervals, and avoid structural failures in extreme cases. This paper investigates an experimental methodology to assess and predict the flow condition and load fluctuations on a Kaplan turbine runner at several steady-state operations by performing measurements on the shaft in the rotating and stationary frame of references. This unit is instrumented with several transducers such as miniature pressure transducers, strain gages, and proximity probes. The results show that for any propeller curve of a Kaplan turbine, the guide vane opening corresponding to the minimum pressure and strain fluctuations on the runner blade can be obtained by axial, torsion, and bending measurements on the shaft. Torsion measurements on the shaft could support index-testing in Kaplan turbines particularly for updating the cam-curve during the unit operation. Furthermore, a signature of every phenomenon observed on the runner blade signals, e.g., runner frequency, rotating vortex rope components, and rotor-stator interaction, is found in the data obtained from the shaft.

Design and Calculation of PC Composite Rigid Frame Bridge with Variable Section Steel Truss Webs

Steel truss web prestressed concrete composite bridge has many advantages, such as light weight, clear stress, beautiful structure, convenient construction, etc., but it is still in its infancy in China. Taking Shuinianbao bridge of Yanchong high speed as an example, this paper introduces the design method of PC composite rigid frame bridge with variable cross-section continuous steel truss web, and analyzes the static calculation of the whole bridge in combination with the code, so as to provide design reference for the construction and development of PC composite bridge with variable cross-section steel truss web. The analysis results show that: the calculation results obtained after modeling according to the design size meet the design requirements. Under the condition of ultimate bearing capacity, the top plate obtains a more uniform maximum resistance, and the arch curve makes the internal force of the bottom plate relatively small. Under the combination of short-term load effect, the main tensile stress of the inclined section appears at the position close to the support and the middle span section of the top plate. The main tensile stress of the steel truss web member is the most different under the unfavorable load combination, the maximum tensile stress is greater than the compressive stress, and the maximum tensile stress occurs at 1/4 of the mid-span.

Study on Model Structure and Mechanical Anisotropy of Columnar Jointed Rock Mass Based on Three-Dimensional Printing Method

The natural structure of columnar jointed rock mass (CJRM) is complex because it was formed during the cooling process of volcanic rock. In CJRM, both the structures of columns and columnar joints are oriented, and the exact mechanical properties are difficult to obtain due to the lack of testing samples that correspond to natural rock masses. Therefore, this brings challenges for underground engineering construction related to CJRM. The reconstruction of CJRM is an effective method that can be used to resolve this problem. However, using an artificial method means that it is difficult to consider the detail of structures, such as irregular columns, columnar joints, and microcracks in columns. With the development of 3D printing (3DP) technology, a useful method for the accurate reconstruction of CJRM has been provided. In this paper, based on laboratory and in situ tests, the structural characteristics and mechanical properties of CJRM in Baihetan Hydropower Station will be investigated. Then, based on the accurate structural reconstruction of CJRM that considers the similarity constant between in situ and laboratory tests, the mechanical anisotropy and failure modes of 3DP CJRM specimens will be investigated. The results show that 3DP is an effective method for reconstructing the structures of CJRM and that it is necessary to consider the detail of the structures, such as the irregularity of columns, columnar joints, and microcracks. In addition, the unfavorable loading angles between the axis of the column and loading direction were obtained. The 3DP results presented in this paper could provide a reference to help understand the structural characteristics of CJRM.

Analysis of piston applications due to fuel burning

The paper aims to analyze the demands of four-stroke naval pistons. To begin with, a brief analysis of the evolution of shipbuilding was made. Mechanical requests are produced by the gas pressure force and inertial force of the alternate moving masses. Under its action, the piston suffers an axial deformation. The thermal demands appearing in the engine are all the more important as the engine power is higher. The possibility of calculating them is more difficult due to the complexity of the thermogazodinamic phenomena in the engine cylinder. Thus, in the piston head, which comes in contact with both the hot gases and the fresh (much cooler) load, a non-stationary heat flow is installed which leads to a certain thermal regime of the engine. Considering the demands outlined in the last chapter, they lead to the conclusion that although the most unfavourable loading situation was considered as the maximum pressure during the processes and even exaggerated in establishing the working conditions, the piston is still close to the elastic limit. This demonstrates that the way of calculating the dimensions of the piston is correct and safe, as long as its constructive dimensions are not oversized.

Analytical solutions for geosynthetic-reinforced cohesive subgrade spanning trench voids

Geosynthetic-reinforced structures are required for constructing roads in the presence of trench voids. In this study, we propose a novel method with respect to the geosynthetic-reinforced cohesive subgrade spanning trench or column voids. Using this method, we can estimate the geosynthetics deformation w and strain ε by considering various load patterns, the upper interface friction of geosynthetics, the subgrade subsidence, and further investigate the effect of the soil cohesion and the filling in voids on the geosynthetics. Moreover, the node tension bar model was employed with respect to the geosynthetics in the subsided area and the settlement area. The present results were in good agreement with the previous experimental and numerical results. Extensive parametric studies have also been conducted. Thus, the invert parabolic load pattern is the most unfavourable load pattern. Affected by the soil-geosynthetic relative displacement and subgrade soils, w and ε are off by at least 10%. With the loss of fillings in void, w and ε are increased up to 590% and 300%. Reducing the stiffness of geosynthetics leads to increasing w and ε by up to 55% and 250%. In addition, the larger void width results in maximum 260% and 150% increases in w and ε.

Equivalent uniform live loads under transit vehicles for floor slab of long-span urban transportation hubs

ABSTRACT Rapid development of long-span urban transportation hubs arouses higher requirements of structural design methods. However, the current design codes do not give effective provisions of the equivalent uniform live load for long-span transportation hubs. A revised equivalent uniform live load is developed by considering the aspect (length-to-width) ratio of the one-way slab system for the urban transportation hubs. The most unfavorable loading positions of the bus tires are determined, and the equivalent uniform live load is computed by using the Chinese Load Code. The structural response under equivalent uniform live load is further compared to that under actual load, then the original equation of the equivalent uniform live load with the Chinese Load Code is revised by considering the aspect ratio of one-way slab. An actual engineering computation of equivalent uniform live load is carried out. The results reveal that the calculation methods of the Chinese Load Code cannot reflect the force transmission characteristics of the small-area tire load on the one-way slab. The structural responses under the revised equivalent uniform load are in good agreement with that under the actual load. The revised calculation method is suitable for most areas in this urban transportation hub and similar structures.

Multi-scale load identification system based on distributed optical fiber and local FBG-based vibration sensors

Deformation and stress are the most important parameters for structural damage identification, but the sensors used for structural deformation or stress monitoring cannot be effectively installed on the pipeline with insulation layer, highway, railway and other service structures. In this case, the unfavorable load identification is of great significance for the damage assessment of large-scale structures. The distributed optical fiber vibration sensor (DOFVS) can realize continuous vibration monitoring for tens of kilometers, but the identification accuracy of vibration load is vulnerable to environmental vibration interference and the local position accuracy is not high. In this paper, one multi-scale load identification system based on distributed optical fiber and local FBG (fiber Bragg grating)-based vibration sensors are developed for solving this problem. In this system, the local FBG-based acceleration sensors (also known as FBG-based vibration sensors) are arranged in the area prone to adverse vibration loads for high precision measurement. The distributed optical fiber vibration sensors are continuously deployed in the structure for full scale measurement. In order to verify the feasibility of the load identification system, a field load identification test is carried out, and the distributed optical fiber vibration sensor and the FBG-based acceleration sensor are compared for use to monitor the vibration signals caused by different types of vibration loads. Test results show that the FBG-based acceleration sensor belongs to fixed-point positioning, the distributed optical fiber vibration senor belongs to large-scale positioning, and the vibration responses of the two sensors have good consistency.

Stress distribution in column-plate foundations of Monument of Christ The King erected in Świebodzin

The paper presents results of numerical simulations of the stress distribution and deformations within of foundations of huge monument of Christ The King erected in Świebodzin (Poland) in 2010. It is 3 meters taller than the better known statue of Christ the Redeemer in Rio de Janeiro, standing at 30.1 meters tall without its pedestal. Foundations were built as a system of reinforced concrete columns and slabs which can be classified as a spatial column-slab system. Actual mechanical parameters of the substrate and of the artificial mound made of field stones, sand, gravel and clay were adopted in calculations. The numerical simulations of structural members of foundation and determination of the stress distribution are presented in the article. Monument itself was not included into the model. Instead of it the rigid cantilever was introduced to which resultant forces were applied. Three different stages were distinguished: the initial state after foundation and mound accomplishment, the initial state plus the dead load and the initial state plus the dead load and the wind load. It was assumed that the wind load was taken into account in a quasi-static formulation by applying the equivalent horizontal force and the torque. Stresses and displacements for these three stages were determined by Finite Element Method using Simulia ABAQUS system. It was disclosed what was a contribution of particular parts of foundations in sustaining loads in considered load cases. The state of exertion of structural members of foundations and the soil itself was assessed. It was showed that the column-slab foundations and soils of the mound play important role in taking loads of the statue, spreading them and safe transferring to the undisturbed level of natural soils. According to the numerical simulations results the columns of foundation take as much as 64% of the vertical load (in the most unfavourable load conditions). At the same time soils of the mound take through the side surface of piles about 20 % of the vertical load.

Mechanical performance test and finite element analysis of prefabricated utility tunnel L‐shaped joint

SummaryIn order to promote the industrial production of utility tunnel, based on the actual prefabricated utility tunnel engineering background, two types of precast L‐shaped joint with end boundary elements are experimentally studied. In this paper, two precast L‐shaped top plates with the haunch zone and two precast L‐shaped bottom plates without haunch zone were designed. These two types of specimen were tested to investigate the mechanical performance of precast L‐shaped joint under different load combination effects. There were no obvious phenomenon in the whole opening test, and the most unfavorable load combination was in the elastic stage. In the closed test, the average ultimate bearing capacity of the prefabricated top and bottom plant specimens decreased by 2% and 1%, respectively, compared with the cast‐in‐place specimens, and the average ductility coefficients of the top and bottom plates are 5.78 and 2.73, respectively. It is also found that the setting of the haunch zone can improve the bearing capacity. The bending capacity of prefabricated L‐shaped joints calculated by the Chinese code's recommended formula is conservative, and the ratio of the test value to the calculated value is about 1.5. Finally, the reinforcement arrangement of the prefabricated specimens in the closed test was optimized by finite element software. It can be considered that changing the diameter of the reinforcements in the concrete compression zone to 16 mm will not affect the mechanical properties of precast joints.

Optimal structural design searching algorithm for cooling towers based on typical adverse wind load patterns

This investigation aims at typical adverse wind load patterns under tower group interference and overall structure optimization of large cooling towers considering multiple geometric parameters, focusing on potential unfavorable load patterns. Wind tunnel tests were performed on typical six-tower groups with various central distances, incoming flow directions and arrangement types, and external wind pressures were measured under interference conditions. Adverse wind load patterns are summarized with the help of interference criteria for three parameters: aerodynamic load, structure response and weighted internal force combination. Furthermore, overall structure optimization is achieved through the hybrid of grid search and gradient descent method, taking into account various possible wind loading distributions. Total 13 geometric parameters are adjusted to seek an optimized design that satisfy the requirement of structure strength, stability and economy under a particular wind load pattern. Crossover checks are then introduced to select a final optimized design scheme that is universally applicable to different adverse wind load patterns. The optimization procedure proposed in this study shows that adverse wind load patterns of grouped towers has distinct features comparing with wind load codes. It is necessary to consider the influence of multiple typical adverse wind load patterns for structural design, and the final optimization scheme should be determined through crossover checks to guarantee structure safety, stability and economy of cooling towers. • Typical adverse wind load patterns under complex six-tower group are proposed. • A hybrid optimization algorithm of the grid search and gradient descent is proposed. • Multi-parameters for cooling tower structure design are optimized. • Crossover check is used to ensure structural safety for multiple wind load patterns.

Experimental Research of Mechanical Behaviour of GFRP Cross Arm of 500kV Transmission Tower

Glass fibre reinforced polymer (GFRP) material is used in the field of transmission tower structure because of its excellent electrical and structural performance. In this paper, a full scale GFRP composite cross arm of 500kV transmission tower is designed and a triaxial load-unload experiment is conducted to study the mechanical properties of it. Three kinds of the most unfavourable load cases of GFRP cross arm are loaded, and the strain changes of the upper, middle and lower parts of the cross arm are obtained. It is verified that the bearing capacity of GFRP cross arm meet the design requirements and GFRP cross arm can be used safely in the transmission tower engineering.

The influence of excavation of the dredged foundation of transmission towers on the stability of Yanzi landslide

With the construction of the national network project, transmission towers are inevitably erected on the landslide body. Excavation of transmission tower foundation often causes disturbance to the soil of the slope and reduces the stability of the slope. At the same time, the unfavorable stacking of construction spoil is also an unfavorable load to the slope. Under the combination of various unfavorable factors, slope instability accidents are prone to occur, causing losses to the grid operation. In order to reduce the amount of excavation and to minimize the impact of foundation excavation on the landslide, generally, dredged foundation is the selected excavation method of the transmission tower foundation. Therefore, this article takes the Yanzi landslide and 500kV transmission tower as the research object. Firstly, the mechanical parameters of the soil of the Yanzi landslide were analyzed, and then the influence of the excavation of dredged foundation and the spoil pile loading on the stability of the landslide was studied by 2D finite element method. Finally, 3D finite element method was used for verification and supplementation. The results show that the foundation excavation of transmission tower has negligible effect on total landslide stability, but local potential landslides need to be considered.

Snow Load Modeling on Different Surfaces

The snow load distribution model on the buildings and structures coatings is considered. The main factors affecting the snow load formation on the coatings of random shape are revealed. The dependence of the snow thickness on the coating on the angle of the roof inclination, the coating curvature radius, and the snow friction coefficient on the surface of the roof is determined. The level of individual factors influence on the snow load distribution is revealed. Recommendations on the coating structures calculation are given. These allow taking into account possible unfavorable loading options during the highest snowfall period.

Experimental study on bearing capacity of glass bridge deck under different boundary conditions

In order to study the bearing capacity of the vehicle glass bridge deck structure, the displacement sensor is used to measure the deformation of the glass panel, and the strain gauge is used to measure the change rule of the strain on the outer surface of the glass panel, and the failure mode, the load-displacement curve, safety performance and stiffness requirements of the glass plate under different boundary conditions and the most unfavorable load position are analyzed. The results show that the ultimate bearing capacity of a single glass plate supported on both sides is about 53.7% of that of a simple glass plate supported on four sides, and that of laminated glass plate supported on both sides is about 66.7% of that of a simple glass plate supported on four sides. The deformation of the glass plate is the largest when the load acts on the center of the plate, and the stress of the glass plate is the largest when the load acts on the corner of the plate. From the perspective of meeting the structural strength requirements, the load acting on the corner of the plate is the most unfavorable working condition, and from the perspective of meeting the structural stiffness requirements, the load acting on the center of the plate is the most unfavorable working condition. Under the two most unfavorable conditions of plate angle and plate center position, applied 0.8, 1.0, 1.2, 1.5, 1.8 and 2.0 times of wheel load, the maximum strain and deformation of laminated glass plate can meet the requirements of the code. The test results can provide a reference for the practical engineering of vehicle glass bridge plate.

Influence Surfaces for Slab Bridges Using Finite Element Analysis

Influence surfaces have proven to be very useful in analysis and design practices, particularly in situations where the design of plate-like elements is required. It is because these surfaces have proved themselves useful in the most unfavorable load positions on plate elements like slabs. Many researchers worked in this area established different ways to plot these surfaces. In this paper, finite element analysis is used for developing influence surfaces. The influence surfaces prepared using finite element analysis are found to match with Pucher charts which were prepared using deflection equations. Further, some example problems are solved using the influence surfaces thus developed and are compared with the results obtained using existing methods like the effective width method and the finite element analysis to understand the accuracy of the results.

Analysis of Ultimate Bearing Capacity of Large Span Continuous Rigid Frame Curved Bridge

In order to study the ultimate bearing capacity of the large span continuous rigid frame curved bridge, a three-dimensional solid finite element model of a curved bridge was established based on ANSYS software. Different load cases were considered in analysing the ultimate bearing capacity. The results show that the loading process of the selected background curved bridge can be divided into elastic, elastoplastic and failure stages. Besides, under the most unfavourable load case, the living load coefficient and the safety factor is are 20.40 and 2.94, respectively. This indicates that the calculation formula of ultimate bearing capacity provided by the current standard has enough safety degree. In addition, because of the coupling effect of bending and torsion, the tensile stress and compressive stress on the outside of girder are larger than those on the inner part. Moreover, the ultimate bearing capacity of vehicle eccentric loading is lower than that of medium load, which should be considered in the design.

Mechanical and numerical characterization of ceramic femoral components for hip resurfacing arthroplasty.

Hip resurfacing arthroplasty may have distinct advantages for young and active patients, but large metal-on-metal bearings can be associated with increased wear, adverse tissue reactions and higher rate of implant loosening. Ceramic wear couples are a commonly used alternative to metals and therefore might be an alternative for hip resurfacing arthroplastys. The aim of this study was to evaluate the mechanical strength of femoral components made of an alumina-toughened zirconia composite by means of experimental testing and finite element analysis. For the mechanical characterization, ceramic femoral components (Ø: 48 mm) were tested under compression loading experimentally until fracture occurred or a maximum load of 85 kN was obtained. The femoral components were either loaded against a ceramic cup or a copper ring (outer diameter Ø: 7.0 mm). In addition, the complex geometry of the ceramic femoral component was simplified, and only the stem was loaded in a cantilever test until fracture. In addition, the fracture tests were numerically simulated to investigate the influence of additional loading conditions and geometric parameters, which were not experimentally tested. The experimental data were used for validation of the finite element analysis. None of the tested ceramic femoral components fractured at a compression load of 85 kN when they were loaded against a ceramic cup at an inclination angle of 45°. When the femoral components were loaded against a copper ring, the femoral components fractured at 29.9 kN at a testing angle of 45°. The fracture load was reduced when an angle of 30° and increased when an angle of 60° was simulated. Using an experimental cantilever test, the stem of the femoral component fractured at 1124.0 N. When the stem length was increased or the diameter was reduced by 10% in the finite element analysis, the fracture load was reduced. Decreasing the length or increasing the diameter led to an increase of the fracture load. The strongest influence was found for the reduction of the transition radius of the stem, with a decrease of the fracture load up to 27.2%. The analyzed femoral components made of alumina-toughened zirconia (ATZ) showed sufficient mechanical capability to withstand high loadings during unfavorable loading conditions. However, further biomechanical and tribological investigations are required before clinical application.

STUDY ON THE INTERACTION BETWEEN FORMWORK SHORING SYSTEMS AND RC STRUCTURES IN A HIGH-RISE BUILDING DURING CONSTRUCTION 2

In the construction process of high-rise building structure, the formwork temporary supports and the concrete structure are considered as a whole. Quantifying the load under the template supports can provide a better reference for the design of the template supports. In order to study the load transfer law between formwork support scaffolds and multi-storey structure, through the installation of sensors at the bottom of formwork supports and the floor slab, the load transfer law of the 3 adjacent formwork supports were monitored for a long time during the construction of high-rise buildings via the high-frequency wireless transmission systems. The main conclusions are as follows: (1) The monitoring data shows that the most unfavourable load occurs when concrete is poured into the upper story, about 1.9 times the axial force generated when concrete is poured into the test floor. (2) The monitoring data has a similar shape which is summed up as an ideal curve of change, 3 times of peak value, 3 times of decline and 1 time of sudden drop. (3)The transfer ratio of load accounts for about 57% ~ 69% of a total load of fresh concrete. (4) Considering the fluid-plastic state of concrete, a correction factor of 1.22 for vertical pole axial force is proposed, and the deviation between the modified simulated value and the measured value is less than 3%.

Numerical analysis of steel-concrete joint section shear transfer behavior

The location, structural form, thickness and geometric dimensions of steel-concrete joint section and its shear connector form, shear connector layout are not the same, the mechanical properties of the joint section are not uniform. It is necessary to calculate and analyze the mechanical properties of the joint section. the part finite element simulation model joint section is established, considering most unfavorable load combination condition, mainly analyzed the steel section, the steel transition section, the concrete section and the concrete transition section. It is obtained that stress distribution, deformation trend, and larger stress value position, the stress horizontal, vertical and vertical distribution quantitatively in each maximum inner force working condition so as to offer reference for design and construction departments.

Experimental study on asynchronous construction for composite bridges with corrugated steel webs

Asynchronous construction is a new construction method for composite girder bridges with corrugated steel webs. This new construction technology has multiple advantages over conventional cantilever construction technology, including a simple basket structure, low steel consumption, high material utilization, short construction period and superior stability. Herein, a 1:1 full-scale corrugated steel web model test is designed based on the Fenghua River Bridge, which is the longest span composite girder bridge with corrugated steel webs in China. This test analyzes the shear stress distribution of corrugated steel webs under the most unfavorable stress conditions and the ultimate bearing capacity of single corrugated steel webs under the most unfavorable load conditions during asynchronous construction. The deformation and stress conditions are measured to identify critical stress areas during construction. Additionally, the safety of each area during construction is verified to provide guidance for asynchronous construction plans for the same type of bridge structures.