Large-scale Test Facilities Research Articles

Stress Build-Up during Multilayer Welding with Novel Martensitic Filler Materials*

Abstract Controlling the level of mostly detrimental residual stresses already during the welding process would be highly attractive as time and cost consuming post processing may be prevented. Innovative Low Transformation Temperature (LTT-) filler materials are specially designed for controlling weld residual stresses by means of adjusted martensite formation already during welding. Numerous publications can be found on this issue, but they provide only little insight into the interaction between martensite formation and resulting welding residual stresses. Within this study a component weld test was performed in a special large-scale testing facility. In-situ load analysis revealed that the amount of stress reduction during deposition of the individual weld runs is dependent on the weld volume undergoing phase transformation related to the shrinking volume. The residual stresses found after welding show that the desired residual stress control by using LTT alloys is sensitive to welding boundary conditions (i. e. weld geometry, plate thickness) and to be evaluated separately for varying weld scenarios.

Large-scale testing on wind uplift of roof pavers

This paper presents a large-scale experimental study to investigate the wind loading on concrete roof pavers on the flat roof of a low rise building. The experiments were performed in Wall of Wind, a large-scale hurricane testing facility at Florida International University. Experiments included both wind blow-off tests and pressure measurements on the top and bottom surfaces of the pavers. The effects of the pavers׳ edge-gap to spacer height ratio and the relative parapet height on the wind performance of roof pavers were also investigated. The results showed that increasing the edge-gap to spacer height ratio parameter decreases the net pressures by enhancing pressure equalization between top and bottom surfaces. Also, increasing the relative parapet height reduces the worst suctions for the parapet heights considered in this study. The resolution of the pressure taps was found to have significant influence on the test results. Too few taps can result in underestimation of the net uplift and overturning moments that can cause failure under strong winds. Guidelines on the resolution and location of pressure taps were provided for better capturing the effects of conical vortices on wind loads on pavers. Results of the wind blow-off tests are compared with those obtained from pressure measurements and a typical practice based on ASCE 7-10 exterior pressures.

「マリンエンジニアリングを支える大型試験設備（３）」の特集号に寄せて

「マリンエンジニアリングを支える大型試験設備（３）」の特集号に寄せて

Effect of Martensitic Phase Transformation on Stress Build-up during Multilayer Welding

Innovative low transformation temperature (LTT) welding filler materials are featuring a characteristic chemical composition which favors the formation of martensite at comparatively low temperatures. This permits deliberate adjustment of welding residual stresses. Even though numerous investigations can be found in the literature on this issue, they provide only little insight into the interaction between phase transformation and resulting welding residual stresses. For this purpose, a component weld test was performed in a special large-scale testing facility. The results illustrate that the desired residual stress control by using LTT alloys is actually feasible. With increasing shrinkage restraint, however, higher tensile residual stresses are formed in transverse direction of the weld. By contrast, the residual stress level in longitudinal weld direction is nearly independent of the restraint conditions. On-line stress analysis revealed that the amount of stress reduction during cooling of the individual weld runs is dependent on the weld volume undergoing phase transformation. Overall, evidence was furnished that the approach of residual stress engineering by LTT alloys is suitable even in the case of large-scale multilayer welding.

Compression-Fatigue, Elastic Modulus, and Thermal Contraction of Insulated Conduit Arrays of ITER CS Modules

Compression-fatigue tests at ~ 77 K were conducted to compare two insulation systems (epoxy resin impregnated glass/Kapton) for use in the ITER central solenoid modules. Test samples consisted of insulated conduits that were stacked in 4 × 4 arrays. The thermal contraction (295-77 K) prior to fatigue, elastic modulus during fatigue, and the structural integrity of the insulation were measured and assessed at the National Institute of Standards and Technology large-scale test facilities. The maximum cyclic stress of 72 MPa, minimum stress of 25 MPa, and 1.2 × 106 cycles were used to comply with ITER design objectives. Thermal contraction between 295 and 77 K and the elastic modulus were measured using strain gages and strain-gage extensometers. Calibration of the strain was obtained through the use of an equivalent-size block of 6061-T6 aluminum alloy with known thermal contraction and elastic moduli. Following fatigue, the arrays were cross-sectioned and optically examined for resin-impregnation quality and fatigue cracking tendencies of the insulation systems. The thermal contraction and elastic modulus of cross-sectioned samples were remeasured at the National High Magnetic Field Laboratory for property confirmation, using different techniques.

「運輸技術を支える大型試験設備」特集号に寄せて

「運輸技術を支える大型試験設備」特集号に寄せて

Aerodynamic Mitigation of Roof and Wall Corner Suctions Using Simple Architectural Elements

This paper presents the use of simple architectural elements such as aerodynamic mitigation devices for reducing high wind-induced suctions occurring at roof and wall corners of low-rise buildings where wind-induced building envelope failures usually initiate. The architectural elements considered in the current study include trellises (pergolas), roof extensions of gable ends (gable end ribs), ridgeline extensions (ridge rib), and sideways extensions of walls (wall ribs). A small-scale model of residential villa was tested in a boundary layer wind tunnel for two different roof geometries (gable and hip). Moreover, selected cases were investigated at the Wall of Wind, a large-scale testing facility, to investigate scale effects. The effectiveness of these architectural elements in reducing high suction (negative pressure) was assessed by comparing the wind-induced pressure measurements obtained before and after introducing the elements. Based on the results obtained for the worst wind angle of attacks, the peak suction was reduced after introducing the architectural elements by 65% at gable-end corners, 60% close to roof ridges, 45% at soffits, 35% at wall corners, and 25% at eaves. These simple architectural elements, which can be retrofitted to the stock of existing homes or incorporated into the design of new buildings, can be used as aerodynamic mitigation devices for reducing peak suction at critical locations of the building envelope.

Full-scale aerodynamic testing of a loose concrete roof paver system

The paper presents an experimental study to assess wind induced pressure on full-scale loose concrete roof pavers by using Wall of Wind, a large-scale hurricane testing facility at Florida International University. Experimental tests were conducted on full-scale concrete pavers mounted on a test building to evaluate wind-induced external and underneath pressures acting on the pavers. The study shows that roof pavers could be subjected to significant uplifting wind forces due to negative pressures. In corner and edge areas of the roof, pressure differences produced net uplift on the pavers, at design wind speed, that was greater than the individual weight of the pavers. The study provides new insights by testing the actual roofing material at high wind speeds in a controlled environment and also showed that locking the pavers together can mitigate the issues at corners and edges by increasing the weight of the pavers that acts together to counterbalance the net uplift pressure.

Numerical calculation of residual stress development of multi-pass gas metal arc welding under high restraint conditions

During welding, residual stresses build-up created by the steep thermal gradient that occurs in the weld zone from localized heating and cooling, and phase transformations appearing in low-alloyed structural steel is inevitable. Welding of rather simple test plates do not cover the actual structural effects, which have to be considered during real component welding. However, the resulting welding-induced residual stress state is highly influenced by the structural characteristics, i.e. restraint conditions, of the welded construction. Therefore, a unique large-scale testing facility providing a specific shrinkage restraint while welding and subsequent cooling was used for the present investigations. Hereby, a six bead multi-pass gas metal arc weld of 20mm thick structural steel S355J2+N was welded under shrinkage restraint. The residual stresses were experimentally and numerically investigated, and compared to an analysis of plates welded under force-free support and free shrinkage conditions.The experimentally determined and calculated residual stresses using both 2D and 3D numerical models are in a good agreement. Furthermore, the influence of a shrinkage restraint on the residual stress distribution is both experimentally and numerically shown for the present test set-up.

Circular precast concrete manholes: experimental investigation

Circular precast concrete manholes are widely used in sanitary sewer and storm water systems. The lack of detailed technical information on them and the conservatism of their governing codes and standards call for a detailed investigation on them. The main objectives of this paper are to evaluate the state of strains in the precast concrete manhole and state of stresses in the soil beneath the base to be used in developing enhanced guidelines for the design of their bases. Three full-scale circular precast concrete manholes, two 1200 mm in diameter and one 1500 mm in diameter, were tested in the large-scale geotechnical testing facility (LSGTF) at the University of Western Ontario. Only one 1200 mm manhole base was reinforced. Twenty seven load tests were performed on the manholes, which involved loads representing the Ontario truck loads incorporated in the Canadian Highway Bridge Code. None of the manhole sections tested in the experimental program experienced any cracks. The test results showed that traffic loading had a small effect on the pressure under the manhole base. All three specimens could withstand the critical Ontario truck loads, even the non-reinforced ones.

Dynamic Load-Displacement Behavior of Rc Shear Walls under Different Loading Rates: Tests and Simulations

As a typical structural member, the dynamic behavior of RC shear walls under seismic dynamic loads and/or strong winds is a critical topic. In recent years, with the development of test facilities and numeric techniques, efforts have been made to study the dynamic behavior of RC shear walls under dynamic loadings experimentally and numerically. But available test results on the dynamic behavior of RC shear walls are limited because of the limitation of the large-scale test facilities for dynamic tests. In this paper, test on four RC shear walls under rapid loads are conducted and a finite element model of RC shear walls through introducing the strain rate effect to the concrete damaged plasticity model in ABAQUS is established to simulate the dynamic behavior of the four specimens tested. Through comparing the simulation result with the test result, it is clear that the developed dynamic damage plastic constitutive model of concrete can be employed to simulate the nonlinear behavior of RC walls with acceptable accuracy under dynamic load.

特集号「マリンエンジニアリングを支える大型試験設備(2)」によせて

特集号「マリンエンジニアリングを支える大型試験設備(2)」によせて

Boiling water reactor with innovative safety concept: The Generation III+ SWR-1000

AREVA NP has developed an innovative boiling water reactor (BWR) SWR-1000 in close cooperation with German nuclear utilities and with support from various European partners. This Generation III+ reactor design marks a new era in the successful tradition of BWR and, with a net electrical output of approximately 1250 MWe, is aimed at ensuring competitive power generating costs compared to gas and coal fired stations. It is particularly suitable for countries whose power networks cannot facilitate large power plants. At the same time, the SWR-1000 meets the highest safety standards, including control of core melt accidents. These objectives are met by supplementing active safety systems with passive safety equipment of various designs for accident detection and control and by simplifying systems needed for normal plant operation on the basis of past operating experience. The plant is also protected against airplane crash loads. The functional capabilities and capacities of all new systems and components were successfully tested under realistic and conservative boundary conditions in large-scale test facilities in Finland, Switzerland and Germany. In general, the SWR-1000 design is based on well-proven analytical codes and design tools validated for BWR applications through recalculation of relevant experiments and independent licensing activities performed by authorities or their experts. The overview of used analytical codes and design tools as well as performed experimental validation programs is presented. Effective implementation of passive safety systems is demonstrated through the numerical simulation of transients and loss of coolant accidents (LOCAs) as well as through analytical simulation of a severe accident associated with the core melt. In the LOCA simulation presented the existing active core flooding systems were not used for emergency control: only passive systems were relevant for the analyses. Despite this – no core heat-up occurred. In the case of reactor core melting numerically is demonstrated that the molten core debris would be retained inside the reactor vessel due to the effective passive external water cooling of the vessel, keeping it completely intact. A short construction period of just 48 months from first concrete to provisional take over, flexible fuel cycle lengths of between 12 and 24 months and a high fuel discharge burn-up all contribute towards meeting economic goals. Realistic average availability for a plant lifetime of 60 years and 12 months cycle is 94.5%. Systems and plant design were reviewed by expert groups of European utilities. With the SWR-1000, AREVA NP has developed a design concept for a BWR plant that is now ready for commercial deployment and which fully meets the most stringent international requirements in terms of nuclear safety and nuclear regulatory.

低温工学に関わる真空の物理と技術 核融合炉用超伝導コイル試験装置の真空漏れ探索技術の開発

Japan Atomic Energy Agency (JAEA) has developed leak detection technology for liquid helium temperature experiments in large-scale superconducting magnet test facilities. In JAEA, a cryosorption pump that uses an absorbent cooled by liquid nitrogen with a conventional helium leak detector, is used to detect helium gas that is leaking from pressurized welded joints of pipes and valves in a vacuum chamber. The cryosorption pump plays the role of decreasing aerial components, such as water, nitrogen and oxygen, to increase the sensitivity of helium leak detection. The established detection sensitivity for helium leak testing is 10-10 to 10-9 Pam3/s. A total of 850 welded and mechanical joints inside the cryogenic test facility for the ITER Central Solenoid Model Coil (CSMC) experiments have been tested. In the test facility, 73 units of glass fiber-reinforced plastic (GFRP) insulation break are used. The amount of helium permeation through the GFRP was recorded during helium leak testing. To distinguish helium leaks from insulation-break permeation, the helium permeation characteristic of the GFRP part was measured as a function of the time of helium charging. Helium permeation was absorbed at 6 h after helium charging, and the detected permeation is around 10-7 Pam3/s. Using the helium leak test method developed, CSMC experiments have been successfully completed.

Uplift performance of FRP tapered piles in dense sand

The influence of taper angle on the uplift performance of FRP tapered piles in dense sand at various embedment ratios is investigated using a large-scale testing facility (pressure chamber). The current study evaluates the uplift performance of tapered piles relative to the uplift performance of straight-sided wall piles. Thirteen pile installations were performed in a pressure chamber using conventional head driving and a novel toe driving technique. Twenty­six uplift load tests were performed at different radial and vertical confining pressures in order to simulate pile segments at different depths. The results of uplift loading tests are presented and discussed. The results showed that the uplift capacity of tapered piles is slightly higher than that of cylindrical piles with similar average diameter and length. The taper effect on the pile uplift performance is evaluated using the uplift taper coefficient. A hyberbolic relationship is established between the uplift load and displacement that can be used to determine the soil stiffness for use in non­linear analysis. A simplified design approach for uplift capacity of tapered piles is discussed and evaluated.

GPR performances for thickness calibration on road test sites

This paper presents ground penetrating radar (GPR) experiments conducted on a number of road test sites. In its capacity as a State civil engineering research organization, the Laboratoire Central des Ponts et Chaussées (LCPC) possesses large-scale testing facilities, such as a circular pavement fatigue test track, ideal for road-related research. This particular facility is composed of several sections of different known structures especially well-adapted for GPR investigations. Our study of GPR techniques made use of a commercial system for measuring asphalt layer thickness. Various road structures have been examined with a GSSI system. Cores have been drilled and permittivity measurements performed in the laboratory. The initial study reveals a comparison between thickness measured by coring and that calculated from both measured permittivities and GPR-selected times. A second study has consisted of avoiding calibration with core drilling, by means of recording GPR signals with a non-destructive testing technique on the multi-layer structures (i.e. common middle point). A numerical reconstruction has then been developed in order to calculate the thickness and velocity of each layer from experimental data. When compared with the cored samples, results show a sufficient level of accuracy in the first two or three layer thickness measurements to satisfy the needs of road facility managers.

Particle image velocimetry in aerodynamics: Technology and applications in wind tunnels

Particle image velocimetry (PIV) is increasingly used for aerodynamic research and development. The PIV technique allows the recording of a complete flow velocity field in a plane of the flow within a few microseconds. Thus, it provides information about unsteady flow fields, which is difficult to obtain with other experimental techniques. The short acquisition time and fast availability of data reduce the operational time, and hence cost, in large scale test facilities. Technical progress made in the last years allowed DLR to develop a reliable, modular PIV system for use in industrial wind tunnels. The features of this system are summarized and results of recent PIV applications are presented.

Axial response of piles in electrically treated clay

Improvement of the shear strength of soft clayey soils around steel pipe piles using high-voltage electrokinetics is investigated in the present study. The experimental setup of a large-scale testing facility is described. Four model piles were installed in two identical cylinders filled with simulated marine sediment. Five electrically insulated electrodes were installed close to the piles to apply a high-voltage electric field in the test cylinder. Negative direct current voltages of -20, -30, and -10 kV were applied in three phases, respectively, for 33 days in the treatment cylinder. Axial compression and pullout pile load tests were performed and the results were compared for both cylinders after each phase of treatment. The pile response is presented in terms of the experimental load deflection curves. It is observed that the axial capacity was increased 30, 29, and 8% after the first, second, and third treatment phases, respectively. The pullout capacity was increased due to the treatment by 11, 23, and 12% after the first, second, and third treatment phases, respectively. Further development of this technique may provide potential solutions for the improvement of soft marine clays, and ultimately it could be applied in the field to rehabilitate existing offshore foundations.Key words: electrokinetics, piles, marine clays, soil improvement, bearing capacity, axial loading.

Lateral and cyclic responses of model piles in electrically treated clay

An innovative technique to improve the capacity of piles installed in soft clayey soils using high-voltage electrokinetics was investigated in the present study. A largescale testing facility was established to execute the treatment and perform loading tests on the model piles. Eight steel pipe piles were installed in two identical cylinders filled with simulated marine sediment. Five electrically insulated electrodes were installed close to the piles to develop a non-uniform electric field in the test cylinder. Negative DC voltages of −20, −30 and −10 kV were applied in three phases for 33 days in the treatment cylinder. Lateral and cyclic lateral loading tests were performed, and the results were compared for both cylinders after each phase of treatment. The pile response was presented in terms of the experimental load–deflection curves. It was observed that the lateral capacity increased 81, 60 and 12% after the first, second and third treatment phases, respectively. The pile stiffnesses increased, and the displacements at the peak amplitude of the cyclic load decreased, due to the treatment. The improvement in the cyclic performance of the piles was evaluated in terms of the change of the soil degradation factors. The soil degradation factor increased 4·6, 14·6 and 2% after the first, second and third treatment phases, respectively.

Recent applications of particle image velocimetry in aerodynamic research

Particle image velocimetry (PIV) is increasingly used to investigate unsteady velocity fields instantaneously. For the first time the PIV technique allows the recording of a complete velocity field in a plane of the flow within a few microseconds. The PIV technique thereby provides information about unsteady flow fields which is difficult to obtain with other experimental techniques. The short acquisition times and fast availability of data reduce the operational time, and hence cost, in large scale wind tunnels and test facilities. At DLR a variety of PIV systems for use in industrial wind tunnels has been developed in the past decade. The flexibility of these portable systems is illustrated by presenting several results of recent PIV applications. More recently the original photographic means of PIV image recording has been partially replaced by high resolution electronic imaging which can provide PIV data nearly on-line. Images recorded by either system use the same multiple-pass, cross-correlation analysis software, whose algorithms are briefly described. Several examples of actual applications are given: the flow issuing from a jet nozzle was imaged by a specially developed high-speed video camera at close proximity. A high resolution dual-frame digital camera was applied in the study of helicopter rotor aerodynamics and wake vortex measurements of an airplane model. Further, large image sequences exceeding 100 PIV recordings provided detailed information on the structure of a turbulent boundary layer.