Full-scale Static Tests Research Articles

Experimental investigation on structural collapse of a large composite wind turbine blade under combined bending and torsion

This study presents a comprehensive investigation on structural collapse of a 47m composite blade under combined bending and torsion in a full-scale static load test. The primary focus is placed on root causes and failure mechanism of the blade collapse. The investigation consists of three parts. First, video records of the blade collapse are examined on a frame-by-frame basis. Direct evidence is presented on how the blade collapses in progressive chain events. Second, the detailed post-collapse investigation is conducted both in-situ and in laboratory. The critical failure modes and the associated stress/strain state once experienced by the blade are indentified. Third, strain measurements are analyzed to provide quantitative evidence of the process leading to the blade collapse and consequently confirm the findings of this study. It is found that longitudinal compressive crushing failure and the following delamination of the spar cap, which are driven by local buckling, are the root causes of the blade collapse. The constraint of the loading saddle and local reinforcement of the blade section also contributes to the blade collapse. Torsion loads, although exhibiting no significant effect on the blade strength, are found to affect post-collapse characteristics of the blade.

Komputerowe wspomaganie procesu projektowania i obliczeń układów obciążających do prób statycznych statków powietrznych

Komputerowe wspomaganie procesu projektowania i obliczeń układów obciążających do prób statycznych statków powietrznych

T–z curves for piles from pressuremeter test results

Pile design is not only based on the assessment of bearing capacity, but can involve settlement calculations when the structures supported by piles need high service requirements. In this context, the load transfer approach with t–z curve models is one of the calculation methods used. The main issue for this method is the choice and implementation of the t–z curve modelling the behaviour of the soil around the pile and accounting for the progressive shaft friction mobilisation. In this paper, three types of t–z curve models from pressuremeter test results are compared: one proposed previously by R. Frank and S. R. Zhao in 1982 and two others presented here. The stiffness of each model is studied and a comparison is performed by considering 90 full-scale static load tests extracted from the IFSTTAR pile database. Measured and calculated values of the pile head displacement are compared for several loading levels considering different soil and pile types. For the three t–z curve models, the ratio of the measured pile head settlement value to the calculated one is analysed and the scatter of each t–z curve model is studied. Some considerations regarding the safety of the pile settlement calculations are proposed.

A novelin situtest for the design of drilled foundations

This paper describes a novel in situ test concept called the Borehole Plug Test that could improve the design of drilled foundations. The test method involves casting a small-scale grout plug at the bottom of a typical borehole for site investigations and load testing the plug to obtain the load transfer behaviour and the maximum unit side shear resistance (or bond strength). The plug test results can then be used to simulate full-scale load tests for design purposes. A field trial is presented that demonstrated its feasibility and potential benefits. Additional research is needed both to study fundamental behaviour and to collect more field data to compare with full-scale static load test data in a variety of soil and rock types.

Development of a Novel Ablative Composite Tape Layup Technology for Solid Rocket Motor Nozzle and Liquid Engine Liners

Solid rocket motor nozzles and liquid engine throats use ablative composite materials to protect the structures from the extremely severe operating conditions of high temperature, pressure and particle impingement. These ablative nozzle liners are processed from carbon phenolic/silica phenolic prepregs using a complex processing cycle. The process starts from impregnating the fibres with phenolic resin followed by either moulding or wrapping/winding prepreg tapes over metallic mandrels followed by polymerization under pressure. Traditionally, prepreg is cut into straight tapes and wound on mandrels to form the divergents. For throats and convergents, prepreg patterns are cut and stacked for curing. Plies of shape conforming to the development of base cone are cut from the prepreg and wound on the mandrel. After polymerization, the final required configuration is machined from this cylindrical blank after the liners are cured. The new method, described in this paper, replaces the straight-cut prepreg tapes by bias-cut prepreg tapes. These can be used for ablative liners in which the plies are at an angle to the direction of the flow. Bias tapes are cut at 45° to the warp and weft directions of the fabric to the required width and formed to the required frustum of cone. Since the cone is formed from straight cut bias tape, the fibre construction will be uniform around the circumference unlike the pattern cut tape. The efficiency of this process depends on the wrapping ratio which is in turn a function of the diameter, ply angle and tape width. To get the best wrapping ratio, shaped mandrels are used which brings down the material wastage and machining allowances. This paper describes the attempts to develop the Bias wrapping technology for angle wound liners. The details of process trials, challenges faced and how they were overcome, advantages of the process over conventional process etc are explained. Exhaustive material characterization of the material was done. Property comparison and validation of performance in subscale tests and a full scale static test are also discussed. The analysis indicates that this new technology has good potential in replacing the traditional tape-winding technology for rocket motor nozzle liners.

실대형 실험을 통한 아스팔트 노반상 자갈궤도의 거동 특성

아스팔트 노반상 자갈궤도(이하, AC자갈궤도)는 아스팔트 콘크리트 노반(이하, AC노반)에 의한 열차하중의 분산으로 노반 두께 감소 효과, 빗물의 침투방지 효과로 인한 노반부의 강도저하와 연약화 방지 효과, 노반 분니 방지 및 동상방지에 의한 유지보수비 절감 효과를 얻을 수 있다. 이와 같은 장점들에 의해 AC자갈궤도는 유럽 및 일본 등에서 널리 사용되고 있으며 국내에서도 도입을 위한 연구가 진행 중이다. 본 논문에서는 유한요소해석 프로그램인 ABAQUS을 이용하여 현재 철도설계기준에 제시되어 있는 고속철도용 자갈궤도의 성능에 부합하는 AC자갈궤도 단면을 선정하고 선정된 2개의 단면을 대상으로 실물 대형 정 동적 열차하중 재하 시험을 수행하였다. 실대형 실험 결과, AC자갈궤도가 강화노반 상면에 작용하는 토압이 상대적으로 작게 측정되었으며 탄성 및 소성변위도 상대적으로 유사 또는 작은 것을 알 수 있었다. 따라서 AC자갈궤도가 자갈궤도에 비해 열차하중 분산효과에 의한 강화노반 두께 감소효과가 있고 소성변위도 작으므로 궤도의 장기 유지관리 측면에서도 유리한 궤도구조임을 확인하였다. Ballasted track on an asphalt roadbed can be beneficial for its various effects such as (i) decreasing of roadbed thickness by dispersing train load; (ii) prevention of both strength reduction and weakening in roadbed system by preventing rainwater penetration; and (iii) reducing maintenance cost by preventing roadbed mud-pumping and frostbite. With these beneficial effects, ballasted track on asphalt roadbed has been widely used in Europe and Japan, and relevant research for applying such ballasted track on asphalt roadbed systems in Korea is ongoing. In this study, full-scale static and dynamic train load tests were performed to compare the performance of ballasted track on asphalt roadbed and ballasted track. The optimum thickness levels of asphalt and reinforced roadbeds, corresponding to the design criteria for reinforced roadbed of high-speed railway, was estimated using the FEM program ABAQUS. Test results show that the earth pressure on reinforced roadbed of ballasted track on the asphalt roadbed was relatively low compared with that of simple ballasted track. The elastic and plastic displacements of simple ballasted track on the asphalt roadbed were also lower than those of ballasted track. These test results may indicate that the use of ballasted track on asphalt roadbed is an advantageous system in view of long-term maintenance.

Control Algorithm of Static Loading Test for Wind Turbine Blades Based on Fuzzy Theory

In the process of full-scale static loading test of wind turbine blades, the loading forces all had relatively strong coupling effect, which seriously affected the accuracy of the test result. In order to eliminate this effect, firstly, a vertical static loading device for 10MW wind turbine blades was established and the coupling rule of loading force was obtained. Then, a control algorithm was put forward based on fuzzy theory. This algorithm took the error of loading force, error’s change rate as the input variables and the opening degree of proportional valve as the output variable. A control strategy based on this algorithm was constructed. In the end, the static device took the max flapwise of aeroblade5.0-62 wind turbine blade as example to conduct loading test. The result suggested the algorithm in this paper could ensure that the loading forces on five nodes always kept uniform changing and the control errors were respectively less than±2KN, ±2KN,± 2KN,± 2KN and±1KN. When in the 100% phase, the loading force could be finely maintained at the set value. The statistical results showed that the error rates of loading force with control algorithm were smaller than those without control algorithm. The test results verified the feasibility of control strategy applying to full-scale static loading test for wind turbine blades.

Full-scale experimental study on the influence of damages on the static behavior of the single-layer cable net structure

As a novel type of supporting structure of glass buildings, the single-layer cable net will inevitably be subjected to different kinds of damage during service. In order to study the influence of potential damage on its static behavior, a full-scale static test of the single-layer cable net is performed on a 4×4 grid model with the dimensions 4.85m×4.85m. Three types of damage are investigated: failure of the connectors between horizontal and vertical cables, loss of prestress in the cable, and damage and failure of the cable anchorage end. The experimental results show that failure of connectors has little influence on the static behavior of the single-layer cable net. The change of nodal displacements induced by the cable prestress-loss does not exceed 15%. The cable anchorage failure affects significantly the local part of the structure, and the induced change of nodal displacements can be up to 36%. It is found that, the influence of damage is stronger on nodal displacements than on cable tension forces, and the intensity of this influence depends on the extent and location of damage. The influence decreases when the load increases. The research results in this paper provide some qualitative conclusions for safety evaluation of single-layer cable net structures and establish a foundation of the further study.

Research and Application of Beam String Structures

By virtue of their excellent structural performance and attractive shape, beam string structures have been used extensively in large-span public buildings since their first appearance in the 1980s. A large number of beam string structures with spans of more than 80 m have been built in China. This paper presents an overall review of research on beam string structures and their applications. The inverse iteration method is introduced, mainly to carry out the form-finding, as well as other modified methods. For the prestressing process, most typical experimental studies are represented, including both the full-scale tests and the down-scale orthogonal tests. To study the static behavior, the effect of a prestressed cable on structural stability is presented, followed by a typical full-scale static loading test. For the dynamic behavior of beam string structures, noteworthy issues when performing dynamic numerical analysis are discussed, such as the natural vibration characteristics and the seismic response during earthquakes. To demonstrate the progressive collapse resistance, structural sensitivity to the steel cable and other structural components is discussed, and conceptual design concerns regarding resistance to progressive collapse are presented. In addition, a detailed introduction of the latest applications of beam string structures in China is presented.

Research of Weight Deduction in Full-scale Aircraft Static Strength Test

Weight deduction is one of the key steps in full-scale aircraft static strength test. It will keep the experimental craft zero-gravity during the full-scale aircraft static strength test and fatigue strength test to make the test status as real flight condition of the plane more truly. In consideration of the necessary and benefit of weight deduction, a complete scheme of weight deduction in full-scale aircraft static structural test was presented, which including the method for calculating the weight of test piece, method for deducting the weight of test piece and loading device and the design of the weight deduction device. The full-scale static strength test of one type of aircraft was used as research object. The test was successfully completed and valid test result was obtained by deducting the weight of test piece and loading device based on the above-mentioned scheme. The result shows that the method for calculating weight deducted is scientific and logical, and the weight deduction scheme is viable. The proposed scheme could deduct the weight of test piece and loading device effectively, reduce the weight effect on test results and has important reference value to similar test.

Non-Destructive Structural Integrity Assessment of a Decommissioned Rail Wagon System

This paper presents a multi-criteria based approach for non-destructive diagnostic structural integrity assessment of a decommissioned flatbed rail wagon (FBRW) used for road bridge superstructure rehabilitation and replacement applications. First, full-scale vibration and static test data sets are employed in a finite element (FE) model of the FBRW to obtain the best “initial” estimate of the model parameters. Second, the “final” model parameters are predicted using sensitivity-based perturbation analysis without significant difficulties encountered. Consequently, the updated FBRW model is validated using the independent sets of full-scale laboratory static test data. Finally, the updated and validated FE model of the FBRW is used for structural integrity assessment of a single lane FBRW bridge subjected to the Australian bridge design traffic load.

Model factor for the bearing capacity of piles from pressuremeter test results – Eurocode 7 approach

This paper focuses on the establishment of a model factor for the calculation of the ultimate limit state (ULS) bearing capacity of piles in compression from Ménard pressuremeter tests results. First, the requirements of Eurocode 7 are presented: calculation methods used for pile foundations must be validated against the results of static load tests and a model factor can be introduced to reach a target safety. This model factor is meant to take into account the scatter of the calculation model, whereas the spatial variability of the ground properties is dealt with by means of statistical methods. Then an analysis of a database of 174 full-scale static pile load tests carried out by the Laboratoire Central des Ponts et Chausées (LCPC, now called IFSTTAR), over the last 40 years, mainly in France, is performed and a new calculation model is established based on pressuremeter test results. Finally, the calibration procedure for deriving the model factor used in the recent French standard for pile design following Eurocode 7 is explained using two approaches: one compares the dispersions of the former and new calculation models and the other performs statistical analysis combining the scatter of the calculation model and the spatial variability of ground properties. This model factor is introduced into the recent French standard for pile design following Eurocode 7.

Development of cost-effective PL-3 concrete bridge barrier reinforced with sand-coated glass fibre reinforced polymer (GFRP) bars: static load tests

One of the main factors concerning durability and service life of steel-reinforced bridges is corrosion of steel bars especially when exposed to a harsh environment. The use of glass fibre reinforcing polymer (GFRP) bars as non-corrosive material has emerged as an innovative solution to corrosion related problems, reduce the maintenance cost, and increase the service life of bridge structures. A recent cost-effective design of PL-3 bridge barrier was developed at Ryerson University incorporating high-modulus GFRP bars with headed ends. This paper presents results of full-scale static tests to collapse performed on the developed PL-3 bridge barrier at interior and exterior locations to investigate the ultimate load carrying capacity to be compared with Canadian Highway Bridge Design Code (CHBDC). The experimental ultimate load carrying capacity of the barriers was observed to be far greater than CHBDC factored design transverse load. The failure pattern was initiated by a trapezoidal crack pattern at the front face of the barrier, followed by punching shear failure at the transverse load location. Based on the punching shear failure developed in the barrier wall and comparison with available punching shear equations in the literature, an empirical punching shear equation is proposed to determine the transverse load carrying capacity of PL-3 bridge barrier walls reinforced with GFRP bars.

Bolt Static Finite Element Numerical Simulation and Experimental Research

This study investigated the wind turbine blade root bolt static strength using the full scale static test, selected the root bolts of 1/4 bridge strain gauge using the finite element analysis method and the dynamic and static strain instrument. The data of the stress loading combined tension and bending bolt were obtained.

KC-100 전기체 정적 구조시험

A full-scale static test for a composite structure small aircraft (KC-100) was conducted in the KARI. The test includes 15 full-scale test and 7 local test conditions. Test requirements with test schedule, test article with dummy structures, test load generation, test system, and equipment are introduced for the test. Test load data of the 1st test condition(U1) was analyzed to evaluate an accuracy of load control for the test. The analysis results show that load data obtained during test were within tolerance of Static Null Pacing Error(SNPE) and the error value of load control was 8.6N. The error of load controls for the full-scale static test using dozens of actuators was calculated by a method suggested by authors. Test data for all other test conditions is also shown in this paper. Finally, reactions measured from restraint system of the U1 test condition show that the reaction changes as load increment. The factors which may change the change of reactions for a full-scale static test are introduced in this study.

Full-scale static test of small composite aircraft

This paper addresses the accuracy of test load application and reaction prediction of aircraft full-scale static test. Factors which have an effect on the accuracy of load application have been identified. An effective procedure for installing test article and actuators is proposed to achieve accurate loading direction compared to conventional one. A method to define quality of load control for a full-scale static test is suggested by using root mean square deviation (RMSD) of command-feedback (CMF) values. Test result of U1 test condition for the KC-100 full-scale static test has shown 8.7 N of averaged RMSD value. At the end, an approach to make general equation for reaction to load increment has been presented and reaction can be assumed to have relation of linear to load increment for symmetric load condition. The linear behavior has been shown through a test data of the KC-100 aircraft which has high stiffness of composite material structure. The test result presents that the linear behavior of the reaction has been well corresponding to the linear model.

Lightweight Reinforcement Systems for Fatigue-Cracked Orthotropic Bridge Decks

Two systems for reinforcing “in-service” orthotropic bridge decks (OBDs) have been researched: the bonded steel plates system and the sandwich steel plates system. The main idea of these types of reinforcements is to stiffen the existing deck plate, thereby reducing the stress at the fatigue-sensitive details, and thus extending the fatigue life of the OBD. Both reinforcement systems consist of adding a second steel plate to the existing steel deck. The behaviour and the effect of the reinforcement systems on full-scale OBD are investigated. Full-scale static tests and finite element analyses were performed on reinforced deck panels, using realistic wheel loads. The results showed at least 40% of stress reduction close to the fatigue-sensitive details after applying both reinforcements. The two suggested reinforcement systems showed a good performance and proved to be efficient lightweight solutions to refurbish orthotropic bridge decks and extend their life span.

Prediction of ultimate axial load-carrying capacity of piles using a support vector machine based on CPT data

The support vector machine (SVM) is a relatively new artificial intelligence technique which is increasingly being applied to geotechnical problems and is yielding encouraging results. In this paper SVM models are developed for predicting the ultimate axial load-carrying capacity of piles based on cone penetration test (CPT) data. A data set of 108 samples is used to develop the SVM models. These data were obtained from the literature containing pile load tests and each sample contains information regarding pile geometry, full-scale static pile load tests and CPT results. Moreover, a sensitivity analysis is carried out to examine the relative significance of each input variable with respect to ultimate strength prediction. Finally, a statistical analysis is conducted to make comparisons between predictions obtained from the SVM models and three traditional CPT-based methods for determining pile capacity. The comparison confirms that the SVM models developed in this paper outperform the traditional methods.

Flexural Tests and Associated Study of a Full-Scale 65-kW Wind Turbine Tower

Full-scale static test to failure was conducted on a 21.9-m-long 65-kW wind turbine tower to evaluate the flexural strength and failure mode. The test was conducted in a displacement-control mode. The flexural limit state in the form of local buckling near the tower base was developed. The buckling occurred in the elastic range because of a high diameter-thickness ratio of the section. Although local buckling caused slight strength degradation, the reduction was not very significant and the recorded response showed a good amount of post-buckling ductility. The local buckling flexural strengths predicted from established standards correlated very well with the measured buckling strength. A parametric finite-element analysis was also conducted. By properly modeling the boundary condition and a local dent on the tower wall, a good correlation of the structural response and failure mode was also achieved. It was found that the ultimate strength and failure mode were sensitive to the boundary condition considered in the model. The presence of a local dent would affect both the location and type of local buckling, although the failure load is less sensitive to local dent.

Measurement of Strain Distribution along Precast Driven Pile During Pile Load Test

One of the basic parameters required for forecasting pile deformation under loads is the characteristics and profile of the shaft load transfer from the pile to the surrounding soil. This parameter can be obtained by measuring the strain distribution along the pile during full-scale pile load test. For cast-in situ bored pile, the strain measurement can be easily done by fixing the sensors to the reinforcement cage before pouring the concrete. For precast driven / jack-in piles, the application of instrumented full-scale static load tests is far more challenging than their bored pile counterparts due to significant difference in method of pile installation. Due to practical shortcoming of conventional instrumentation method instrumented full-scale static load tests are in fact rarely used in driven pile application in this region. For hollow precast spun concrete piles attempts have been made by geotechnical engineers to measure the strain distribution by installing either an instrumented reinforcement cage or instrumented pipe into the hollow core of spun piles followed by cement grout. However in this method, known as approximate method, the measured characteristics cannot be considered to represent the working piles because the presence of reinforcement/pipe and the grout would alter the stiffness of the test pile. In this paper a method to measure the strain distribution along the installed precast spun concrete pile during full-scale pile load test is described. The method utilizes the hollow core of the spun pile without changing the physical properties e.g. stiffness, of the pile. The main advantages of this method are: the measurement can be done at any location along the pile, the sensors can be retrieved and the measured characteristics are representative of those of the working piles.