Experimental Test Program Research Articles

Shear Behavior of Sand–Silt Mixtures: A Laboratory Investigation of Coastal Silty Sand Soils of Mostaganem

In recent years, interest in understanding the mechanisms of mechanical instability of porous media, leading to catastrophic failure has been continuously revised to include, new porous media parameters generating the phenomenon of liquefaction under static or dynamic loadings. Results from experimental test programs have concluded too many physical concepts based on material intrinsic properties, initial states, and other characteristics. Despite the great progress on the subject, these concepts do not allow a unified treatment of such porous media. The assessment of critical shear strength of sandy soils as porous media under undrained conditions is a major challenge in stability analysis. Such strength serves to evaluate the occurrence of flow deformation under liquefaction phenomena. The determination of the critical undrained strength is essentially fundamental for the design of soil structures such as earth dams, bridge supports, building foundations as well as soil densification process to avoid catastrophic failure due to soil instability manifested by failure or large displacement such as settlement. In this work, experimental program on reconstituted loose and medium dense specimens of terrigenous silica sands with different specified fine contents was carried out to analyze its mechanical behavior under undrained conditions. The present article is an attempt to experimentally describe mechanical behavior and theoretically justify such response of loose and medium dense sand by means of critical state soil parameters.

Elastic Stiffness of Volcanic Sand through Resonant Column Tests

The resonant column method is established as a standard laboratory method for the study of the elastic properties of soils. The study presents low-amplitude resonant column test results on volcanic sands with intra-particle voids. The experiments were performed on dry samples prepared at variable relative densities and tested in torsional mode of vibration. In the first part of the article, the important factors that control the elastic stiffness of uncemented sands are described shortly and recent findings on granular soils dynamic properties are presented briefly. The second part describes the basic features of the resonant column used in the investigation and the materials of the study and in the third part representative results of an extensive experimental testing program on volcanic granular soils are presented and discussed with a focus on comparisons between the elastic stiffness of volcanic and quartz granular soils. The importance of the effect of the presence of intra-particle voids within the particle mass of the volcanic soils is emphasized, which in turn affects markedly the global void ratio of the samples.

Shaking table tests of a base isolated structure with Double Concave Friction Pendulum bearings

An extensive experimental testing programme named JETBIS project (Joint Experimental Testing of Base Isolation Systems) was developed within the RELUIS II project (Task 2.3.2) and RELUIS III project (Line 6) involving partners from different Italian universities. This paper describes the seismic tests performed by the research unit of University of Basilicata (UNIBAS) on an isolation system based on Double Concave Friction Pendulum (DCFP) bearings. The DCFP bearing contains two separate concave sliding surfaces and exhibits different hysteretic properties at different stages of displacement response. The main objective of this work is to evaluate the horizontal response of the DCFP isolators by means of controlled-displacement tests and shaking table tests. The experimental model was a 1/3 scaled steel framed structure with one storey and one bay in both directions. Four DCFP bearings with equal properties of the sliding surfaces were considered. In this work, three different sliding surface conditions (with and without lubrication) have been studied. The isolated base model was subjected to 8 natural earthquakes of increasing seismic intensities and considering two mass configurations (with both symmetrical and eccentric masses). The reliability of the design procedure considered for the isolation system was verified also when relevant residual displacements occurred due to previous earthquakes. In this paper, the comparisons between the experimental outcomes and the numerical results of nonlinear time-history analyses using SAP2000 are shown.

A Laboratory Study on the Shear Behavior of Mixtures of Coal Wash and Steel Furnace Slag as Potential Structural Fill

The accumulation of industrial waste materials (e.g., coal wash and steel furnace slag) has become a critical environmental problem in Australia in recent years. The possible re-use of these types of materials as structural fill for transport embankments and land reclamation is one of the preferred options from a waste management perspective. Consequently, an experimental testing program was undertaken using the triaxial apparatus to evaluate the shear behavior of compacted mixtures of coal wash (CW) and steel furnace slag (SFS). The effect of varying the confining pressure and the percentage of coal wash on the isotropic compression line, the stress-strain behavior, and particle degradation during drained shearing was evaluated. The percentage of coal wash was found to influence the shearing behavior of the CW-SFS mixtures. When the content of coal wash increased, the shear strength of the CW-SFS mixtures decreased and the axial strain corresponding to the peak stress ratio increased. Moreover, the incidence of particle breakage increased for those mixtures with a higher CW content due to the low particle strength of CW. This paper also provided a non-linear strength envelope and a corresponding empirical equation to capture the shear strength of CW-SFS mixtures.

Load-carrying behavior of tranmission-tower connected foundations subjected to different load directions

Connected foundations comprise an effective option for improving the mechanical performance of transmission tower foundations. In this study, the load-carrying behavior of connected foundations for transmission tower structures was investigated focusing on the effect of the load direction based on the field experimental testing program. Improved performances of connected foundations were observed for load directions of both θ=0° and 45° considered in this study. The downward settlements at the compressive side for θ=45° were larger than those for θ=0°, while the upward displacements were similar. For both vertical and lateral displacements, the use of connected foundations was more effective for θ=45°, and the effectiveness became more pronounced as the connection-beam stiffness increased. However, the lateral load-carrying capacities for θ=0° and 45° were not significantly different for all connection-beam conditions. From the prototype-scaled model load tests, it was confirmed that the use of connected foundations for transmission tower structures is similarly effective for different load directions. Based on the test results, it was suggested that a unified design methodology is applicable for the stability analysis of transmission tower structures subjected to different load directions.

The effect of temperature on the performance of glass-fiber-reinforced high-density polyethylene composite railroad crossties

The effect of temperature on structural materials is a major concern in engineering applications. Thermoplastic composites are highly sensitive to temperature changes and recycled high-density polyethylene (HDPE) is no different in that respect. Temperature variations may alter the mechanical properties for even the best designed HDPE compositions. Thermoplastic materials usually experience a lower modulus of elasticity and higher ductility at elevated temperatures and a higher modulus of elasticity and lower ductility at low temperatures. Therefore, it is of vital importance to study and fully understand the nature and extent of this effect. This knowledge will enable the safe implementation of these materials in structural applications where low or elevated temperature exposure is expected. In this paper, an experimental testing program that aims to assess the effect of temperature variation on the performance of HDPE composite railroad crosstie is presented. It employs an AREMA-recommended flexural testing method for crossties; center bending, to investigate a practical operating temperature range; from 10 °F (−12.22 ℃) to 125 °F (51.67 ℃). The effect of the temperature variation has been studied for several vital performance criteria: initial modulus; modulus of elasticity; secant modulus; ultimate strain; and modulus of rupture. Finally, the development and calibration of temperature-scaling models capable of predicting these vital parameters at an arbitrary exposure temperature within the investigated range is also presented. The HDPE composite crossties exhibited favorable qualities and predictable performance variation due to temperature changes. Moreover, optimization strategies are recommended to limit and control the effect of temperature on the HDPE crossties.

Program of experimental atmospheric corrosion tests of weathering steels

Abstract This article presents the program of experimental atmospheric corrosion test of weathering steels. This program is designed as a long-term project. Attention is paid to study of corrosion processes at different structural elements of supporting structures of bridges. Measurements of corrosion losses and average thicknesses of corrosion products are carried out within this experimental program. Protective ability of corrosion products is evaluated using X-ray diffraction analysis. The article presents results of corrosion tests after one year of exposure of corrosion specimens. It results from the tests that corrosion losses of weathering steels are signifi cantly conditioned by position and location of exposed surface within the structure.

A novel hybrid technique for leak detection and location in straight pipelines

Underground gas pipeline leaks can lead to tremendous economic loss and human injury. Therefore, it is vital to detect and locate the pipeline leaks in time to maintain the normal operation. However, continuous leak-detection methods of require a lot of manpower, marterial resources and financial supports, while other detecting activities break the normal operation of the pipeline. Hybrid techniques consisting of two or more different technologies appear to be the most probable future trend in pipeline leak detection and location field. In this paper, a novel hybrid technique based on real-time transient modeling method and negative pressure wave method is proposed. An experimental bench for straight pipelines is set up to evaluate the performance of the proposed hybrid technique, and corresponding experimental test programs for gas leak detection and location are designed and conducted. A mathematical model for the transient flow in pipelines has been established and solved under different boundary conditions. The occurrence of a leak can be preliminarily judged by the difference between the measured data and the predicted value from the model; and the changing patterns of parameters under the leak condition, the valve-opening adjusting condition and the compressor-speed regulating condition are investigated to identify the leak condition out of the operational changes. Finally, the leak point is located using the stimulus-response method. Results show that the hybrid technique is successful in detecting and locating gas pipeline leaks. It is expected that the research outcomes can serve as a technical base for the safe operation of gas supply networks.

Hydrodynamic Experiment of the Wave Force Acting on the Superstructures of Coastal Bridges

AbstractThis paper presents a hydrodynamic experiment that examines the wave forces acting on the superstructure of coastal highway bridges to gain insight into the mechanical characteristics of the wave forces caused by the combination of storm surges and huge waves. The experiment is unique in that the specimen is a full bridge model, including its superstructure, substructure, and neighboring segments. After introducing the experimental setup and test program, this study analyzes the quasi-static and slamming components of the vertical wave force, the horizontal wave force of the superstructure in different clearances, wave heights, and wave periods. The test results are subsequently compared with two theoretical models suggested by Douglass and AASHTO guidelines to provide the experimental validation of those models. By comparing the test results and the existing models, a number of observations and discussions are produced to improve the accuracy of those theoretical models further.

Post-installed concrete anchors in nuclear power plants: Performance and qualification

In nuclear power plants (NPPs), post-installed anchors are widely used for structural and non-structural connections to concrete. In many countries, anchor products employed for safety relevant applications have to be approved by the authorities. For the high safety standards in force for NPPs, special requirements have to be met to allow for extreme design situations. This paper presents an experimental test program conducted to evaluate the performance of anchors according to the German Guideline for Anchorages in Nuclear Power Plants and Nuclear Technology Installations (DIBt KKW Leitfaden, 2010). After a brief introduction to anchor behavior and the regulative context, the results of tension and shear tests carried out on undercut anchors are discussed. Robust load capacities and relatively small displacements determined for demanding load and crack cycling tests demonstrated the suitability of anchors qualified according to a state-of-the-art qualification guideline.

Two dimensional numerical and experimental models for the study of structure–soil–structure interaction involving three buildings

This paper explores the adverse and beneficial effects of structure–soil–structure interaction (SSSI) under seismic excitation on a group of three buildings. A simple discrete formulation of the problem is employed that uses rotational interaction springs between buildings. A physical experimental shake-table test program is used to qualitatively validate the discrete theoretical model. Subsequently, a numerical study is performed which demonstrates that the central building in a three building case can act as a tuned mass damper for its adjacent buildings. Results indicated that this adverse effect can be more pronounced than the case where there are just two buildings interacting.

Flexural behavior of high-density polyethylene railroad crossties

Hardwood timber has been the predominant material of choice for crossties since the establishment of the railroad industry in the US. Recently, several concerns, including higher speeds, heavier loads, durability and negative environmental effects associated with deforestation and wood-treating chemicals, have invoked the railroad industry's interest in alternative materials for crossties. Currently, several manufacturers offer alternative and sustainable solutions using different recycled plastic composite materials. Thousands of plastic crossties are currently in service in a wide variety of railroad applications. Several researchers have been studying and testing these new materials, specifically high-density polyethylene, however, their behavior when subjected to rail loading is not yet fully understood. Uncertainties in mechanical properties, failure modes and fracture render their performance and safety questionable. More research is required to properly characterize, describe and model the behavior of these materials as well as to assess the feasibility of implementing these materials in railway applications in terms of performance, safety, practicality and economy. Therefore, this study aimed to investigate the performance of plastic composite crossties through experimental testing and analytical modeling. A flexural testing program addressing two AREMA recommended tests for crossties; center and rail seat bending, was conducted. The behavior of the crosstie with the rail and fastening system installed was also investigated. An analytical finite element model, capable of simulating the flexural behavior of plastic crossties, was constructed using a material model that was calibrated using the experimental data. The plastic composite crossties demonstrated adequate performance throughout the experimental testing program. This paper also highlights the potential structural, social and economic benefits of implementing high-density polyethylene crossties in railroad applications.

Basalt FRP rods for reinforcement and repair of timber

Limited research has been undertaken into the use of basalt fibre reinforced polymer (FRP) materials for the strengthening and repair of structural timber elements. This paper describes an experimental test programme in which the flexural performance of low-grade glued laminated timber was reinforced using bonded-in basalt FRP rods. Tension test results show that basalt FRP rods compare extremely well to the mechanical characteristics of glass FRP rods. Strengthened and repaired beams exhibited considerable ductility in contrast to brittle tension behaviour of the unreinforced sections. With the use of a modest reinforcement percentage of 1.4% strategically located in circular routed out grooves at the soffit of the beam, mean stiffness enhancements of 8.4% and 10.3% for the global and local measurements were achieved respectively and a mean improvement in the ultimate moment capacity of 23% was achieved in comparison to the unreinforced glulam beams. The distance of the reinforcement to the neutral axis was shown to be highly influential on the mechanical enhancements. The use of basalt FRP rods is seen to be highly effective as a repair technology for damaged timber elements. Strain profile readings from the beams which included the reinforcement demonstrated improved utilisation of the compression characteristics of the timber. In all testing, a good quality bond is reported between the basalt FRP and wood. There exists significant potential for the development of environmentally friendly engineered structural elements by combining timber based products with other natural materials such as basalt fibre reinforced polymers.

Experimental Investigation on the Coefficient of Lateral Earth Pressure at Rest of Silty Sands: Effect of Fines

Abstract The coefficient of lateral earth pressure at rest (K0) is an important state variable of soils and is often estimated using Jaky's K0 equation, which is based on the internal friction angle (φ′). When fines are contained in sand, the effect of the fines content needs to be properly taken into account for the φ′-based estimation of K0, as the strength characteristics change because of changes in particle interlocking and contact conditions. In this study, an experimental testing program was established to measure and analyze K0 and its correlation to shear strength characteristics of sand–silt mixtures focusing on the effect of silt content. Thin-wall oedometer tests, triaxial tests, and other property tests were conducted to obtain K0 values and characterize the test materials. The values of K0 became higher as the relative density and silt content decreased, which was found because of decreasing particle interlocking and friction angle. Jaky's K0 equation using the peak strength tended to underestimate K0 at lower relative densities, whereas the K0 matched closely to measured values for higher relative densities. The K0 correlation based on the mobilized inter-particle strength was proposed and was applicable to various sand conditions. The calculated results using the proposed K0 correlation matched the measured results well, confirming the effectiveness of the proposed method.

NUMERICAL MODELING OF DEBRIS IMPACTS USING THE SPH METHOD

The significance of coastal forests as a protection barrier against tsunami waves has been of particular interest following recent tsunami events. Coastal forests have been shown to attenuate tsunami–induced inundation and are believed to be capable of reducing the propagation of tsunami-borne debris onshore. The current paper aims to examine the suitability of using a Smoothed Particle Hydrodynamics (SPH) model to (1) simulate debris impact forces acting on a structure and (2) to determine if it is possible for a small coastal forest to attenuate tsunami-borne debris. The results of this study indicate that the SPH model utilized was able to reasonably replicate the hydrodynamic forces acting on structures and the water surface elevation, but was not able to reproduce the large debris impact forces observed in an experimental test program. However, the authors concluded that coastal forests can potentially provide protection against floating debris.

Stochastic fracture‐mechanical parameters for the performance‐based design of concrete structures

AbstractThe experimental results for quasi‐brittle materials such as concrete and fibre‐reinforced concrete exhibit high variability due to the heterogeneity of their aggregates, additives and general composition. An accurate assessment of the fracture‐mechanical parameters of such materials (e.g. compressive strength fc and specific fracture energy Gf) turns out to be much more difficult and problematic than for other engineering materials. The practical design of quasi‐brittle material‐based structures requires virtual statistical approaches, simulations and probabilistic assessment procedures in order to be able to characterize the variability of these materials. A key parameter of non‐linear fracture mechanics modelling is the specific fracture energy Gf and its variability, which has been a research subject for numerous authors although we will mention only [1, 2] at this point. The aim of this contribution is the characterization of stochastic fracture‐mechanical properties of four specific, frequently used classes of concrete on the basis of a comprehensive experimental testing programme.

Riveted patch repairs for helicopter tail drive shafts with battle damage

AbstractThe ability to repair battle damage in a helicopter tail drive shaft (TDS) caused by small arms fire is a very important capability. A successful repair will enable the helicopter to continue its mission or at least allow it to return safely to base. This paper describes assessment of conventional and novel repair techniques using riveted metallic patches to restore the balance and strength of a damaged TDS. Analytical approaches are provided for the design of the repair. Modal analyses indicated that the effect of repair on change of the natural frequency of the TDS was negligible. An experimental testing program was conducted to validate the proposed repair methods. It has been demonstrated that the proposed repair methods achieved sufficient balance restoration by a defined repair procedure, assuming the unbalance could not be measured during a repair in the field. The conventional thin, single aluminium sheet, riveted repair significantly restored static strength. However, it only gave a fatigue life of 15hrs, and thus the repaired shaft may only be used for limited time for a military mission. The improved thick, two-half aluminium shell, riveted repair had sufficient static strength and met the 100-hour fatigue requirement.

Effect of Panel Joints on the Performance of Cold-Formed-Steel Light-Frame Shear Walls

AbstractSome existing qualification/validation data for alternatives to code-compliant light-frame cold-formed steel (CFS) shear wall construction were developed before requirements for test specimens with 1∶1 aspect ratios and the inclusion of a vertical panel joint. These requirements were introduced on the notion/assumption that walls with an included panel joint and 1∶1 aspect ratio provide a lower bound estimate of wall performance (strength, displacement, and toughness). In this technical note, data from three independent experimental test programs were analyzed to shed light on panel joint and aspect ratio effects on cold-formed steel frame shear wall performance. The analysis showed that the performance of walls without a panel joint and with aspect ratios as high as 214∶1 provide reasonable lower bound measures of performance.

The dynamic response of pressure relief valves in vapor or gas service. Part II: Experimental investigation

An experimental testing program designed to evaluate the opening stability characteristics of direct acting pressure relief valves (PRV) in gas/vapor service is described. Three different valve sizes from each of three different manufacturers were tested at two different set pressures to determine their opening characteristics (disk lift vs. time). The valves were tested with several different lengths of inlet piping as well as with and without discharge piping to determine the conditions under which unstable operation (chatter) would occur. Part I of this program described a mathematical model for predicting the dynamic response of PRV's, and the data described in this test program were used to evaluate the accuracy of the model, as described in Part III of this study to follow.

Got Steam? Understanding ESP Steam-Handling Capabilities in the Centrifugal Pump

Summary The successful development and implementation of high-temperature electrical-submersible-pump (ESP) technology for steam-assisted-gravity-drainage (SAGD) applications have enabled operators to reduce their flowing bottomhole pressures and achieve higher production rates. However, operating under these conditions brings the pump-intake pressure (PIP) closer to the saturation pressure of steam, which can result in live-steam production through the pump. The effect that live-steam has on pump performance is not well-understood, and has been a key challenge for operators when designing and optimizing ESP systems for SAGD applications. In early 2011, ConocoPhillips, Baker Hughes, and C-FER Technologies (herein referred to as the operator, manufacturer, and independent laboratory, respectively) embarked on an experimental test program to determine the consequences of producing live steam through a centrifugal pump. This new program was meant to build on multiphase work that had begun more than a decade ago at the University of Tulsa, where researchers had focused on experimentally measuring the two-phase-flow performance of ESP stages with air at moderate temperatures (Pessoa and Prado 2003). The University of Tulsa work ultimately resulted in a wave of new technology aimed at increasing ESP gas-handling capabilities. Following a similar testing and ESP-instrumentation philosophy, this new collaboration looked to build upon the University of Tulsa experiments and expand the test fluids to include live steam, water, and air at higher temperatures. This ultimately involved the design and construction of a unique high-temperature-steam flow loop that enables live-steam injection into a centrifugal pump, while monitoring both head and performance degradation. This paper will reveal some of the unique test results collected with the first pumping system, including snapshots of the stage-by-stage pressure contributions captured in real time as air or air and steam migrated through the ESP being tested. These results also demonstrate the impact that other gases can have on steam flashing and the importance of considering gas- and steam-vapor effects in SAGD-ESP designs.