Published Test Data Research Articles

Analysis of the Load-Deformation Behaviour and Debonding for FRP-Strengthened Concrete Structures

Results from nonlinear finite element analyses of fibre reinforced polymer (FRP)-strengthened concrete beams and slabs are presented. The direct shear test, a basic application that provides insight into FRP-concrete interfacial behaviour, is also considered. The motivation for this work is the fact that, although there is a large amount of experimental data available on the FRP strengthening of concrete structures, a full understanding of the various load–deformation behaviours and debonding phenomenon is still lacking. The numerical models presented in this paper adopt a displacement-controlled solution and are capable of simulating FRP-strengthened beams either in shear or in flexure, as well as slabs strengthened using either passive or prestressed FRP laminates. Results of the different applications are presented and compared with published test data, and a very good agreement in terms of the ultimate load carrying capacities, load–deflection behaviour and modes of failure, is obtained.

A micromechanical constitutive model for the behavior of concrete

A two-dimensional constitutive law for the behavior of concrete under load has been developed in this paper. Concrete is considered to be a composite material made up of two components: cement mortar and aggregate. The cement mortar is defined as the cement paste (cement and water) plus the fine aggregate. The interaction between these two components, at the local level, governs the macroscopic behavior of concrete. The model proposed herein describes the microstructure of concrete by fabric of a representative sample using the notion of a class of contacts, each class having a common orientation of the contact normal to the aggregate-cement mortar interface. Each class is further broken down into cracked and bonded contacts. Cracked contacts allow slip along the interface and are modeled as granular material. Bonded contacts do not allow slip along the plane of contact. In developing the model, first the overall stresses are related to the interface forces at the microlevel. Simple constitutive relations are used to relate the rate of change of the local interface forces, for both cracked and bonded contacts, to the local velocity gradient. Finally, macroscopic constitutive equations are postulated using a Taylor-averaging method. An incremental procedure for numerical integration of the rate equations is described. Qualitative validation of the model is achieved through comparison with published test data. A limited parametric study is followed by a study of the microstructural changes as depicted by a numerical simulation of monotonic axial compression. The results of these simulations seem to be qualitatively consistent with the observed behavior of concrete.

A Robust Structural Stress Parameter for Evaluation of Multiaxial Fatigue of Weldments

Abstract In this paper, the applicability of a new mesh-insensitive structural stress method is examined for the evaluation of multiaxial fatigue behaviors in welded joints. The mesh-insensitive structural stress method proves to be effective in characterizing stress concentration effects in multi-axial fatigue of welded components. In seeking an effective structural stress based fatigue parameter, some well-known published test data were analyzed. These include those published by researchers, e.g., from the Electric Power Research Intitute (EPRI), the Fraunhofer-Institute for Structural Durability (LBF), the University of Illinois at Urbana-Champaign (UIUC), and the Welding Institute (TWI) under bending, torsion, and in-phase and out-of-phase loading combinations. An effective structural stress parameter has then been formulated in a form of a proposed modified Gough's ellipse for considering both in-phase and out-of-phase multiaxial loading conditions. The aforementioned multiaxial fatigue data from a total of five independent sources can be effectively correlated with a structural stress based parameter presented in this paper, without introducing any other material-related empirical parameters. The present method is rather simple to use for day-to-day finite element based fatigue evaluation of welded joints in actual structures subjected to multiaxial loading conditions.

Mechanical behavior of δ-phase Pu–Ga alloys. Part I: Constitutive model

We developed a constitutive model, based on the mechanical threshold strength (MTS) model reported by Follansbee and Kocks [P.S. Follansbee, U.F. Kocks, Acta Metall. 36 (1988) 81], to predict the stress/strain behavior of face-centered cubic (fcc) δ-stabilized plutonium–gallium (Pu–Ga) alloys. Input to the model is derived from our previous work on other fcc metals and published test data for Pu–Ga alloys. The model accounts for the effects of temperature, strain rate, grain size, and alloy content on the constitutive behavior. In Part I, we describe the development of the model and present all the pertinent equations and parameters. In Part II, we validate the model against existing literature data and demonstrate how the model is used to quantify the effects of test condition, grain size, alloy content, and impurity levels.

Virtual rollover tests

A simulation of an FMVSS 208 rollover dolly test of a generic pickup truck model was performed using PAM-CRASH. Data from published real-world rollover dolly tests of large passenger cars were used to validate the simulations. The pickup truck model used in the simulation had properties similar to that of the cars used by other researchers in their rollover tests. The initial conditions input into the simulation were similar to actual vehicles subjected to FMVSS 208 rollover dolly tests. The vehicle dynamic responses during the rollovers and the simulation were analysed; the results were compared with published test data, namely rotational velocity, energy loss, vertical and horizontal acceleration, velocity and displacement of vehicle centre of gravity.

Simple design formulae for predicting the residual damage of unstiffened and stiffened plates under explosion loadings

In this paper, practical yet accurate formulae are proposed to predict the structural damage of rectangular unstiffened and stiffened plates under explosion loads. The numerical computation method adopted in this study was validated using published test data and then, rigorous parametric studies were conducted for various plate models. Regression analyses of the parametric study results were performed to derive design formulae, which produced linear relationships between the residual damages of plates and an impact parameter. These formulae have been compared with existing ones and it is confirmed that the proposed ones are more accurate and simpler than others.

Best practice for the assessment of defects in pipelines – gouges and dents

Oil and gas transmission pipelines have a good safety record and are a demonstrably safe means of transporting hydrocarbons. This is due to a combination of good design, materials and operating practices. However, like any engineering structure, pipelines do occasionally fail. The major causes of pipeline failures around the world are external interference and corrosion; therefore, assessment methods are needed to determine the severity of such defects when they are detected in pipelines. Defects occurring during the fabrication of a pipeline are usually assessed against recognised and proven quality control (workmanship) limits. These workmanship limits are somewhat arbitrary, but they have been proven over time. However, a pipeline will invariably contain larger defects at some stage during its life, and these will require a ‘fitness-for-purpose’ assessment to determine whether or not to repair the pipeline. Consequently, the past 40 years have seen a large number of full scale tests of defects in pipelines, and the development of a number of methods for assessing the significance of defects. Some of these methods have been incorporated into industry guidance, others are to be found in the published literature. However, there is no definitive guidance that draws together all of the assessment techniques, or assesses each method against the published test data, or recommends best practice in their application. To address this industry need, a Joint Industry Project has developed a pipeline defect assessment manual (PDAM). PDAM documents the best available techniques currently available for the assessment of pipeline defects (such as corrosion, dents, gouges, welding defects, etc.) in a simple and easy-to-use manual, and gives guidance in their use. PDAM is based on an extensive critical review of pipeline fitness-for-purpose methods and published test data. It is intended to be another tool to help pipeline engineers maintain the high level of pipeline safety. In addition to identifying the best methods, PDAM has served to identify a number of limitations in the current understanding of the behaviour of defects in pipelines, and the empirical limits in the application of existing methods. This paper discusses the PDAM project, in the context of both the current best practice available for defect assessment and the limitations of current knowledge.

Considerations of the dilatancy angle in rocks and rock masses

Abstract The present study responds to the poor treatment given to dilatancy in classical rock mechanics post-failure problems such as tunnel or mine pillar design. A comprehensive review of the literature and observations in regard to published test results would indicate that dilatancy is highly dependent both on the plasticity already experienced by the material and confining stress; moreover, it also appears that scale may play a non-negligible role. In our article, we provide a detailed analysis of published test data with a view to proposing a sufficiently significant but conveniently simple formulation of the dilatancy angle that reflects these dependencies and that can be readily implemented in numerical codes. The model is then tested, demonstrating that it is capable of representing rock sample strain behaviour in compressive tests. Finally, the model is applied to the resolution of ground reaction curves for tunnels in poor-to-average-quality rock masses, showing a good correlation with results obtained using practical rock engineering techniques.

Evaluation of FEMA-350 Seismic Provisions for Steel Panel Zones

Steel panel zone design provisions have undergone large changes in the past four decades. The recently introduced FEMA-350 (2000) guidelines are substantially different from previous provisions, and are no longer a function of the plastic strengths of the panel zone and adjoining beams. Rather, they are based on the premise that the framing beams and the panel zone both yield simultaneously to promote controlled inelastic participation of both components. This paper evaluates and discusses the new provisions based on an examination of published test data and the results of transient analyses of buildings with four-, eight-, and sixteen-story moment resisting steel frames. The limited test results reviewed do not confirm the adequacy of the new panel zone provisions and furthermore suggest that panel zone deformation demands could be affected by connection detailing. The frame analysis results show that the FEMA-350 provisions lead to a rather low level of panel zone participation. A discussion of design implications and research needs is provided.

Effectiveness of the head and neck support (HANS1) device in frontal impacts of CART cars: a CAE analysis

Results of a CAE (Madymo) analysis probing effectiveness of the HANS device in reducing injuries to open-wheel racecar drivers in frontal impacts are presented. The model utilised a typical impact pulse used in sled tests. Results show that the HANS device significantly reduces upper-neck shear, tension, and extension moment. These results agree with published test data. Upper-neck loads remain lower than the no-HANS case for a wide range of tether stiffness. The same is true for upper-neck shear and tension for increasing tether slack. Results are more sensitive to changes in slack than stiffness. The predicted head injury criterion is higher for drivers with the HANS device. This is attributable to tether forces at the time of engagement, the magnitude and duration of which depend on contact-interaction between head and helmet-inside. Further tests are needed to better estimate this interaction. Results also show that lowering friction on HANS surfaces reduces head-neck injury potential.

Constitutive Model for High Density Polyethylene Material: Systematic Approach

A constitutive model was developed for high density polyethylene (HDPE) pipe material using published data considering the strain rate effect. A hyperbolic model was used and a conventional approach was employed to estimate the constants of this model from published test data. The observed form of HDPE material behavior as the strain rate changes suggested that a more systematic approach might yield a more robust predictive model. This paper presents a newly developed constitutive model for HDPE material using both the conventional approach and a more systematic “focus point” method.

Reference Stress Based Approach to Predict Failure Strength of Pipes With Local Wall Thinning Under Single Loading

This paper proposes a new method to estimate failure strength of a pipe with local wall thinning. The method is based on the equivalent stress averaged over the minimum ligament in the locally wall thinned region. The highlight of the proposed method is to propose a simple scheme to estimate the equivalent stress in the minimum ligament. Inspired by the reference stress method for approximate creep stress analysis, approximate estimation equations are proposed for the equivalent stress in the minimum ligament, which are then calibrated using detailed elastic-plastic three-dimensional FE analysis. Remarkably the resulting estimation equations are found to be insensitive not only to pipe and defect geometries but also to material. Comparison of failure loads, predicted according to the proposed method, with published test data for corroded pipes shows excellent agreement, which provides confidence in the use of the proposed method to assess local wall thinning in pipes. Furthermore, the proposed method is conceptually simple and thus easy to be extended to more complex situations.

Hypervelocity Impact On Spacecraft Honeycomb: Hydrocode Simulation And Damage Laws

Spacecraft honeycomb structures provide the primary shielding against meteoroid and debris impact for unmanned spacecraft in orbit around the Earth. Hypervelocity impact velocities for spacecraft in Low Earth Orbit can reach speeds of 15-16 km/s yet, for the particle diameters of interest, experimental test facilities are limited to maximum velocities in the range 7-8 km/s. Previous tests onto aluminium and cadmium facesheets with honeycomb core (or cylindrical equivalent) and composite facesheets with aluminium honeycomb core have identified that the honeycomb core influences the impact process (typically called channelling). Tests also identified that the shielding performance was altered under oblique incidence impact. Hydrocode computer simulations can be used to explore the velocity regime beyond the capabilities of existing experimental test facilities. In order to investigate the impact processes on honeycomb and to evaluate damage equation methodologies at velocities beyond the experimental test regime, a simulation programme was defined using the hydrocodes AUTODYN-2D and 3D. First 2D axisymmetric, simulations of normal impact on single and double honeycomb were carried out and compared with published test data. Good agreement was obtained. To model the required geometry, Lagrange, Shell and Smooth Particle Hydrodynamics (SPH) solvers were coupled together. Further 2D simulations were then carried out at velocities of 7, 11 and 14 km/s on two spacecraft honeycomb structures representative of those used in unmanned spacecraft. The ballistic limit was identified and, for impacts above this limit, the post-perforation debris cloud characteristics were calculated by evaluating the momentum recorded on a witness plate or by calculating a momentum pressure function of the post-perforation debris cloud. A honeycomb damage equation, based on the semi-infinite penetration equation, was compared with the simulation results. It shows better agreement with both experimental test results and 2D simulations than the Whipple bumper shield (Christiansen-Cour-Palais) formulation previously applied to honeycomb data, and therefore provides a means to characterise single honeycomb shielding performance as part of spacecraft design and verification activities. The simulation methodology was extended and two 3D oblique incidence simulations were carried out at 11 km/s. These simulation results were also consistent with the equation predictions. (C) 2003 Published by Elsevier Ltd.

A compressible flow theory for regenerative compressors with aerofoil blades

Regenerative flow compressors (RFCs) are rotodynamic machines capable of producing high heads at very low flowrates. They have very low specific speed and share some of the characteristics of positive displacement machines such as a roots blower, but without the problems of lubrication and wear. They can produce heads equivalent to that of several centrifugal stages from a single rotor with comparable tip speed. The compression process is usually not regarded as efficient. Typically they produce efficiency of less than 50 per cent but still they have found many applications because they allow the use of fluid dynamic compressors in place of positive displacement compressors for duties requiring high heads at low flowrates. There are very few mathematical models in the literature that explain the behaviour of regenerative turbomachines and predict the performance. Most of these models assumed incompressible flow, thus limiting their use to only pumps and blowers. Moreover, they needed extensive experimental support for performance prediction. Hence, it is very interesting from an industrial point of view to find efficient theoretical means that are able to forecast regenerative compressor performances, using easy to find geometric and fluid dynamic parameters. A compressible flow theory is thus presented for the first time in this paper to describe complex three-dimensional corkscrew flow patterns in regenerative compressors. Conventional RFC were designed with radial, non-radial or semicircular impeller blades. In the present investigation, the authors have discussed RFCs with aerofoil blades and an annular flow channel containing a core to direct circulating flow to the blades with a minimum amount of losses. The effects of various geometric elements on the performance of RFCs are studied. All the major sources of losses in blade and channel region are identified. Governing equations for the flow in the compressor are derived and a performance prediction code based on governing equations and loss models is developed. Theoretical performance results are compared with published test data on aerofoil blade RFCs. Based on sensitivity analysis from the code, design changes are suggested for performance improvement.

A simple engineering approach in the prediction of the effect of stress ratio on fatigue threshold

In situ SEM observations [1] have revealed that fatigue crack propagation is caused by the shear band decohesion around the crack tip and the formation and cracking of the shear band is mainly caused by the plasticity generated in the loading part of a load cycle. Based on the crack tip plasticity a theoretical analysis has been performed and a model has been set up to consider the effect of the applied stress ratio on fatigue threshold. The obtained results have been compared with a wide range of published test data and good agreement has been achieved. This method is very easy to use and no fatigue crack closure measurement is needed, therefore this model is significant in engineering application.

Parameter C lifetime calculation for the high cycle regime

ABSTRACTAn analytical fatigue lifetime prediction using the nominal stress concept and the Palmgren‐Miner‐Rule is performed. A comparison of prediction and experiment shows a large uncertainty. Miner‐Rule modifications have been developed to improve the fatigue lifetime prediction. Stress amplitudes below the fatigue limit are assumed to contribute to the damage at different ratings.The modifications have a significant influence on the predicted fatigue lifetime especially in the high cycle regime. When the maximum stress value is just above the fatigue limit, this influence is most significant. Because there are not many test results of variable amplitude loads available for the high cycle regime, a verification is difficult.In the present paper a new modification for the lifetime prediction is applied. The modification was introduced in 1988 by Hück and suggests a variable slope of a reference S–N‐curve for the damage accumulation. A parameter C and the relation between the maximum stress value of the load spectrum distribution and the fatigue limit determine the slope of the reference S–N curve.The aim is to characterize the influence factors of the parameter C using test results for the high cycle regime achieved on a new test facility and from published test data. This would lead to an improvement of the lifetime prediction in the high cycle regime.

Seismic Damage and Collapse Assessment of Composite Moment Frames

Damage and stability assessment techniques are developed for evaluating the seismic performance of composite steel-concrete moment frames. The approach features a new seismic damage index based on cumulative member ductility that employs the concept of primary and follower load cycles to distinguish loading history effects. Equations are presented to determine the limiting rotation capacity for RC columns, steel and composite beams, and composite steel-concrete connection subassemblages, and the resulting damage model is validated by comparisons with published test data. The damage index is incorporated in a methodology that combines nonlinear time history and gravity load stability analyses to evaluate collapse prevention performance as a function of earthquake ground motion intensity. In contrast to existing seismic assessment procedures, the proposed methodology integrates the destabilizing effects of local damage indices to evaluate overall system response. The assessment technique is illustrated through a trial design study of a six-story frame conducted under Phase 5 of the U.S.-Japan Cooperative Research Program on composite and hybrid structures.

Membrane action of unrestrained lightly reinforced concrete slabs at large displacements

Following full-scale fire tests on a steel-framed building, together with observations from real fires, it has been shown that membrane action, at large displacements, of composite floors comprising steel deck, concrete, and anti-crack mesh, is extremely beneficial to the survival of the building. It was therefore decided to review previous research conducted on unrestrained concrete slabs, under large displacements, at normal temperatures. It was found that the assumptions used to develop previous theoretical predictions for the load-carrying capacity, for a given vertical displacement, are only valid for square slabs and do not conform to test observations for rectangular slabs. A new theoretical approach is therefore presented which is valid for both square and rectangular slabs and conforms to the mode of behaviour observed in tests. The design method is shown to give excellent correlation with published test data. A prediction for ultimate collapse of the slab due to fracture of the reinforcement is also presented, which limits the allowable mechanical strain in the reinforcement. Comparison with available test data shows that this prediction is always conservative.

Crack opening analysis of complex cracked pipes

Based on the reference stress approach, two sets of the crack opening displacement (COD) estimation equations are proposed for a complex cracked pipe. One set of equations can be used for the case when full stress-strain data are known, and the other for the case when only yield and tensile strengths are available. To define the reference stress, a simple plastic limit analysis for the complex cracked pipe subject to combined bending and tension is performed, considering the crack closure effect in the compressive-stressed region. Comparison with ten published test data and the results from the existing method shows that the present method not only reduces non-conservatism associated with the existing method, but also provides consistent and overall satisfactory results. These results provide sufficient confidence in the use of the present method to estimate the COD (and thus the leak rate) for the Leak-before-Break (LBB) analysis of complex cracked pipes. Finally, the J-estimation equations are also provided for complex cracked pipes, for the LBB analysis of complex cracked pipes.

New engineering approach for estimating crack opening displacement of complex cracked pipes

An engineering estimation equation for the crack opening displacement(COD) is proposed for a complex cracked pipe, based on the reference stress approach. To define the reference stress, a simple plastic limit load analysis for the complex cracked pipe subjected to combined bending and tension is performed considering the crack closure effect in the compressive-stressed region. Comparison with ten published test data and the results from existing method shows that the present method not only reduces non-conservatism associated with the existing method, but also provides consistent and overall satisfactory results.