In-plane Cyclic Loading Test Research Articles

Testing novel hybrid inter-module joints for steel modular buildings under cyclic load

To bridge the gap between the unrealised disassembly and reuse potential of volumetric modular buildings and the lack for seismic resilience, a hybrid inter-module connection employing a high-damping rubber bearing was proposed to reduce the inelastic deformation in the members of the volumetric module. The cyclic behaviour of the proposed connection was previously investigated at connection level through validated proof-of-concept FEA, reflecting promising damping and re-centring capabilities. In this study, six in-plane cyclic loading tests on inter-module joints with the novel, hybrid inter-module connection were carried out to investigate the connection’s influence on the cyclic behaviour of steel modular buildings under lateral load at joint level. The tests focused on the contribution of the laminated elastomeric bearing to the joint’s lateral behaviour and the effect of different bolting assemblies on the working mechanism of the hybrid connection system. The standard FEMA/SAC loading sequence was employed on single-span, meso-scale joint prototypes with axial and in-plane lateral loading applied to the top post. The results showed that the hybrid IMJs exhibited nonlinear, multi-stage hysteretic responses, governed by the bending resistance of the bolting assembly and the stiffness of the intra-module connection. The aseismic performance of the joints was characterised by residual drifts below the permissible limit of 0.5 % up to 2 % drift ratio and high equivalent viscous damping during the low-amplitude cycles. Overall, the tests demonstrated the feasibility of the proposed connection with respect to the mitigation of damage in the structural elements of the volumetric modules after an earthquake, as proved by the low inelastic deformation recorded up to 4 % drift ratios.

Experimental investigation of seismic response of precast concrete panels with castellated keys support pillar connections under in-plane cyclic loading

The reliable joint connection between precast members is vital to resisting earthquake loads in precast concrete structures. To further improve the convenience of precast construction, this paper presents a new horizontal joint of precast concrete panels with castellated keys supports pillar connections based on the stable mechanical properties of the wet concrete joint. To examine the seismic response of this connection type, a series of in-plane cyclic loading tests were carried out using six full-size precast specimens and one cast-in-place specimen for comparison. The influences of axial compression ratio, joint width, and joint concrete strength on the seismic indicators of the precast concrete panel were considered in the design of specimens. The test results showed all specimens had the same damage process, and the ultimate failure modes combined compression and bending. The precast specimens exhibited similar seismic performance to the cast-in-place specimen, especially whose joint concrete strength is higher than the precast concrete panel. Based on the load–displacement test curve, a hysteretic curve model that included both the envelope curve and the stiffness degradation law was proposed. The predictions from the model showed good compatibility with the experimental results, and the model can be used as a reference for analyzing the elastic–plastic response of the precast concrete panels with castellated keys supporting pillar connections.

In-plane behavior of Chuan-Dou style wooden frames with infill under cyclic loading

Chuan-Dou style wooden frames (CDWFs) with different infill are used widely for residential buildings in Southwest China due to their cost-effectiveness and ease of construction. Four full-scale samples of CDWF were laboratory tested to study the contribution of different infills on its seismic behavior. They are two bare wooden frames, a frame with wooden panel infills and a frame with brick masonry infills. One bare wooden frame was subjected to monotonic load to determine the reference displacement for the in-plane Cyclic loading test in the other frame samples. The damage characteristics, ultimate lateral load carrying capacity, hysteretic behavior, stiffness degradation, strength degradation and energy dissipation were investigated. Test results indicated that the CDWF has exceptional ductility to lateral movement and good energy dissipation capacity. Both the wooden panel infill and brick masonry infill increase the lateral load resistance, lateral stiffness and energy dissipation of the CDWF system. The contribution of masonry infills to the improvement of lateral resistance capacity of wooden frames is much greater than that of wooden panel infills.

Evaluation of the Limit State of a Six-Inch Carbon Steel Pipe Elbow in Base-Isolated Nuclear Power Plants

The installation of base isolation systems in nuclear power plants can improve their safety from seismic loads. However, nuclear power plants with base isolation systems experience greater displacement as they handle seismic loads. The increase in relative displacement is caused by the installed base isolation systems, which increase the seismic risk of the interface piping system. It was found that the failure mode of the interface piping system was low-cycle fatigue failure accompanied by ratcheting, and the fittings (elbows and tees) failed due to the concentration of nonlinear behavior. Therefore, in this study, the limit state was defined as leakage, and an in-plane cyclic loading test was conducted in order to quantitatively express the failure criteria for the SCH40 6-inch carbon steel pipe elbow due to low-cycle fatigue failure. The leakage line and low-cycle fatigue curves of the SCH40 6-inch carbon steel pipe elbow were presented based on the test results. In addition, the limit state was quantitatively expressed using the damage index, based on the combination of ductility and energy dissipation. The average values of the damage index for the 6-inch pipe elbow calculated using the force−displacement (P–D) and moment−relative deformation angle (M–R) relationships were found to be 10.91 and 11.27, respectively.

Development of In-plane Biaxial Compression Test Method for Thin Sheet and Investigation of SD Effect under Biaxial Stress Condition

The accuracy of the finite element simulation (FE simulation) of press forming has improved as a result of sophisticated material modelling using data of the various experiments such as uniaxial compression, biaxial tension, and in-plane cyclic loading tests. However, the biaxial compression test of sheet material has never been reported lowing to the difficulty in buckling suppression, and differences between material behavior under biaxial tension and that under biaxial compression have not yet been discussed. In this paper, the biaxial compression test of sheet material using special tools to suppress buckling and a specimen shape that leads to uniform deformation in the measurement area is proposed mainly on the basis of FE simulation. The special tool has a urethane plate where the tool come into contact with the measurement area of the specimen to prevent damage of the strain gauges. Absolute values of compressive stresses during plastic work measured by the biaxial compression test were larger than tensile stresses during the same plastic work measured by the biaxial tension test. Similar results observed in uniaxial tension and compression tests are known as the strength differential (SD) effect.

Quantitative Limit State Assessment of a 3-Inch Carbon Steel Pipe Tee in a Nuclear Power Plant Using a Damage Index

Seismic motions are likely to cause large displacements in nuclear power plants because the main mode of their piping systems is dominated by the low-frequency region. Additionally, large relative displacement may occur in the piping systems because their supports are installed in several places, and each support is subjected to different seismic motions. Therefore, to assess the seismic performance of a piping system, the relative displacement repeated by seismic motions must be considered. In this study, in-plane cyclic loading tests were conducted under various constant amplitudes using test specimens composed of SCH 40 3-inch pipes and a tee in the piping system of a nuclear power plant. Additionally, an attempt was made to quantitatively express the failure criteria using a damage index based on the dissipated energy that used the force–displacement and moment–deformation angle relationships. The failure mode was defined as the leakage caused by a through-wall crack, and the failure criteria were compared and analyzed using the damage index of Park and Ang and that of Banon. Additionally, the method of defining the yield point required to calculate the damage index was examined. It was confirmed that the failure criteria of the SCH 40 3-inch carbon steel pipe tee can be effectively expressed using the damage index.

Seismic behavior of riser pipes with pressure and groove joints using an in-plane cyclic loading test

In the event of an earthquake, structures are shaken in various ways, and side sway occurs between floors. The equipment installed inside these structures is affected by this side sway, and the effect thereof can be significantly large on the riser pipes that are connected from lower to upper floors of high-rise buildings. In this study, steel jigs that were implemented on the first floor of a structure were fabricated, and riser pipe systems were installed in accordance with the National Fire Protection Association 13 standards. The seismic performance of the riser pipes was analyzed through an in-plane cyclic loading test for the allowable side sway as per the American Society of Civil Engineers 7–16 standard. The pipe systems included elbows and tee joints, which are vulnerable to earthquakes. The pipes were connected using pressure joints and groove joints, and the results obtained using both types of connections were compared. The strain, stress, and deformation angle, which are required to evaluate the seismic performance of the fittings and connectors of riser pipes in the event of an earthquake, were analyzed for the allowable side sway.

Failure criteria of a carbon steel pipe elbow for low-cycle fatigue using the damage index

Abstract A seismic isolation system installed in a nuclear power plant will respond to the load caused by an earthquake. As a result, a larger displacement may occur in the presence of the system, compared to its absence. This increased displacement may involve higher seismic risks for some facilities. Probabilistic seismic fragility analysis is conducted to assess the seismic safety of the major elements and systems of a nuclear power plant that may be at increased seismic risk. The installation of piping systems that connect seismic-isolated and general structures may involve increased seismic risks because they are expected to have a large displacement. For the reliable analysis of the seismic fragility of piping systems, the failure modes and criteria that can represent actual failure must be defined. Therefore, in this study, the ultimate state of the elbow, the vulnerable part of piping systems, was defined as leakage, and an in-plane cyclic loading test was conducted. Moreover, an attempt was made to quantify the failure criteria for a 3-inch carbon steel pipe elbow using a damage index, which was based on the dissipated energy that used the moment-deformation angle relationship.

Ratcheting fatigue failure of a carbon steel pipe tee in a nuclear power plant using the deformation angle

Among the many facilities constituting nuclear power plants, piping is a significant facility that handles the transport of fluids, such as steam and cooling water. These pipes can be exposed to external forces, such as fluid, mechanical vibrations, pressure, wind, and earthquakes. In particular, damage to major piping can cause a loss-of-coolant accident (LOCA), which is a serious accident in nuclear power plants, along with radioactivity leakage. Among the components of piping, elbows and tees are elements vulnerable to earthquakes because the nonlinear behavior caused by earthquakes can be concentrated at these points, and the major failure mode is leakage due to ratcheting fatigue. In this study, for the 3-in. carbon steel pipe system used in nuclear power plants, the limit state of a tee was defined as the leakage caused by a through-wall crack, and an in-plane cyclic loading test was conducted. A leakage line and low-cycle fatigue curves were presented using the relationship between the moment and deformation angle of the tee. Moreover, this paper reports the low-cycle fatigue curve of the ratcheting deformation angle capable of expressing the leakage caused by ratcheting fatigue, which is the major failure mode of the tee. As it is difficult to measure the moment and deformation angle using conventional sensors, the nonlinear behavior of the tee deformed by external forces was measured using an image measurement system.

Fatigue behaviors of the steel pipe tee in a nuclear power plant piping system under in-plane cyclic loading

The safety of a nuclear power plant against earthquakes can be improved by installing seismic isolation devices. As such seismic isolation devices handle seismic loads, however, displacements larger than those generated before the application of such devices may occur. Therefore, the seismic risks are likely to increase for some facilities. In particular, pipes that connect structures with seismic isolation devices to ordinary structures are likely to have higher seismic risks. The piping is affected by the behavior of the two supports, and damage may occur due to the displacement-dominant repeated behavior. In addition, to assess the low-cycle fatigue behavior of the piping system under seismic loads, it is essential to identify the relationships among the number of cycles, moment, and deformation angle until leakage occurs, through an in-plane cyclic loading test. In this study, an in-plane cyclic loading test was conducted to assess the fatigue behavior of a steel pipe tee against seismic loads from the correlation between the moment and the deformation angle.

In-plane Biaxial Compression Test on 780MPa Cold Rolled Sheet Steel

Accuracy in finite element simulation (FE-simulation) of press-forming has improved through sophisticated material modelling partly by using data of various experiments such as uniaxial compression test, biaxial tension test, and in-plane cyclic loading test. However, biaxial compression test on sheet material has never been reported due to difficulty in buckling suppression, and difference between material behavior under biaxial tension and that under compression has not been discussed yet. In this paper, biaxial compression test on sheet material with special tools suppressing buckling and a specimen shape to achieve uniform deformation in measurement area is proposed mainly based on FE-simulation. The special tool has a urethane plate at the place where the tool contact with the measurement area of a specimen to prevent damage of strain gauges. Absolute values of compressive stress at a plastic work measured by the biaxial compression test were larger than tensile stresses at the same plastic work measured by biaxial tension test: the similar results observed in uniaxial tension and compression tests known as stress differential (SD) effect.

In-plane cyclic loading tests of concrete hollow block masonry walls retrofitted with high ductile fiber-reinforced concrete

When subjected to horizontal loading induced by an earthquake, concrete block masonry walls generally exhibit vulnerability, particularly under high shear force. To improve the failure mode and lateral resistance of these walls, and to promote the application of concrete block units in multi-story masonry buildings, this study proposes techniques for retrofitting concrete hollow block masonry walls by installing coated high ductile fiber-reinforced concrete (HDC) layers. Six half-scale testing specimens, including three unreinforced concrete block masonry walls (URM) and three confined walls, were tested under in-plane cyclic loading to investigate their seismic performance before and after the upgrade. The test results indicate that these configurations significantly increased the lateral shear strength, stiffness, and energy dissipation capacity of the URM walls, and changed the brittle failure mode into a ductile mode. For the confined masonry walls, the lateral shear resistance and the stiffness were obviously enhanced, whereas the energy dissipation showed negligible improvement. The retrofitted walls showed higher residual strength and less damage, making them favorable for post-earthquake restoration. To estimate the ultimate shear strength of the tested specimens, relevant formulas developed in this study are presented.

Experimental study of the Seismic Performance of Different Earth Walls and Their Seismic Retrofitting with Externally Bonded Fibers

ABSTRACT This study investigates the seismic performance of various earth walls and their applicability to a seismic retrofitting method that utilizes externally bonded fibers. The failure modes, hysteresis characteristics and load–displacement response of in-plane cyclic loading tests were recorded and analyzed. The experimental results show that the soil property significantly influences the seismic performance of earth walls as well as the effectiveness of the proposed retrofitting technique. The more clayey the soil is, the higher the seismic performance and the better reinforcement effect. However, for sandy clayey wall, the applicability of the proposed retrofitting technique for sandy clayey wall is not promising.

Failure Strain Measurement of the Piping System of a Nuclear Power Plant Using Image Signals

When seismic isolation devices are installed in piping systems, it is expected that such devices will be subjected to larger displacement than before their installation because they handle seismic loads, and it is likely that the seismic risks of some facilities will be increased by such displacement increase. In particular, it is highly likely that the seismic risks of piping systems, which connect seismic-isolated structures with conventional ones, will be increased. Previous studies have revealed that the vulnerable part of piping systems is the elbow, and that failures occur due to the low-cycle ratcheting fatigue in the hoop direction. Therefore, in this study, the ultimate state of the elbow was defined as a leakage, and an in-plane cyclic loading test was conducted. In addition, the hoop-direction strain of the steel pipe elbow was measured using an image measurement system, and the failure strain, which cannot be measured using the conventional sensors, was also measured.

Low-cycle fatigue behaviors of the elbow in a nuclear power plant piping system using the moment and deformation angle

Abstract Maintaining the structural integrity of the major devices of a nuclear power plant is perceived as a particularly important issue in relation to the stability of the structure, and the structural integrity of the piping system is especially important for the safety of the nuclear power plant. In this study, the limit state of a steel pipe elbow, which is a fragile part of the nuclear power plant piping system, was defined as leakage, and an in-plane cyclic loading test was conducted. As it is difficult to measure the moment and deformation angle of the steel pipe elbow using conventional sensors, an image measurement system was used. A deformation angle measurement algorithm that uses an image measurement system applied an improved deformation angle measurement algorithm that uses image filter processing to facilitate noise reduction in images as well as the boundary line of the piping system. This study proposed a leakage line and low-cycle fatigue curves using the relationship between the moment and the deformation angle of a 3-in steel pipe elbow.

Seismic fragility evaluation of the base-isolated nuclear power plant piping system using the failure criterion based on stress-strain

Abstract In the design criterion for the nuclear power plant piping system, the limit state of the piping against an earthquake is assumed to be plastic collapse. The failure of a common piping system, however, means the leakage caused by the cracks. Therefore, for the seismic fragility analysis of a nuclear power plant, a method capable of quantitatively expressing the failure of an actual piping system is required. In this study, it was conducted to propose a quantitative failure criterion for piping system, which is required for the seismic fragility analysis of nuclear power plants against critical accidents. The in-plane cyclic loading test was conducted to propose a quantitative failure criterion for steel pipe elbows in the nuclear power plant piping system. Nonlinear analysis was conducted using a finite element model, and the results were compared with the test results to verify the effectiveness of the finite element model. The collapse load point derived from the experiment and analysis results and the damage index based on the stress-strain relationship were defined as failure criteria, and seismic fragility analysis was conducted for the piping system of the BNL (Brookhaven National Laboratory) - NRC (Nuclear Regulatory Commission) benchmark model.

A Failure Estimation Method of Steel Pipe Elbows under In-plane Cyclic Loading

The relative displacement of a piping system installed between isolated and nonisolated structures in a severe earthquake might be larger when without a seismic isolation system. As a result of the relative displacement, the seismic risks of some components in the building could increase. The possibility of an increase in seismic risks is especially high in the crossover piping system in the buildings. Previous studies found that an elbow which could be ruptured by low-cycle ratcheting fatigue is one of the weakest elements. Fatigue curves for elbows were suggested based on component tests. However, it is hard to find a quantitative evaluation of the ultimate state of piping elbows. Generally, the energy dissipation of a solid structure can be calculated from the relation between displacement and force. Therefore, in this study, the ultimate state of the pipe elbow, normally considered as failure of the pipe elbow, is defined as leakage under in-plane cyclic loading tests, and a failure estimation method is proposed using a damage index based on energy dissipation.

Structural performance of confined masonry walls retrofitted using ferrocement and GFRP under in-plane cyclic loading

This paper presents the results of in-plane cyclic loading tests conducted on confined masonry walls retrofitted using low-cost ferrocement and GFRP systems. Ten wall assemblies with a 0.80-scale were built, consisting of a clay masonry panel, two confining columns and a tie beam. The assemblies were tested under a combination of a vertical load and lateral reversed cyclic loading with a displacement controlled loading protocol up to failure. Wall panels had various configurations, namely, solid walls, perforated walls with window and door openings. Two composite materials (ferrocement and GFRP) and three retrofitting configurations (diagonal “X”, corner, and full coverage) were investigated. Key experimental results showed that the proposed upgrading techniques improved the lateral resistance of the confined walls by a factor ranging from 25% to 32%with a significant increase in the ductility and energy absorption of the panel ranging from 33% to 85%; however, the improvement in lateral drifts was less significant. Regarding the upgrading configurations, the diagonal “X” and full coverage can help prevent diagonal shear failure especially in tie columns and convert the failure mode to a panel-rocking mode. Additionally, in all retrofitting cases, collapse was significantly delayed by maintaining the wall integrity under large lateral deformations. A good agreement was found by comparing deformed shapes, crack patterns and capacity curves of finite element models included in this study.

A practical constitutive model for AZ31B Mg alloy sheets with unusual stress–strain response

Magnesium (Mg) and its alloys have been increasingly used in the automotive industry owning to their superior mechanical compared to other metals. Sheet forming of Mg alloys requires not only a good understanding of the materials but also an appropriate material model. The hardening behavior of Mg alloy sheets during plastic deformation is the main concern in tool design and product manufacturing processes. A simple but computationally effective constitutive model is suggested to predict the mechanical behavior of Mg alloy sheets. The proposed material model is implemented as a user-defined material subroutine in the commercial finite element code PAM-STAMP®, then calibrated and validated using in-plane cyclic loading tests with different values of prestrain. The continuous tension–compression–tension and compression–tension–compression tests are conducted on a newly developed testing system. After calibration, the model can accurately predict the yielding asymmetry behavior and the stress–strain curve featured by the unusual sigmoidal shape which is the result of the activation of twinning and untwinning deformation mechanisms.

OS2006 マグネシウム合金板の繰り返し変形における加工硬化挙動(OS20-2 マグネシウムの変形挙動,OS-20 HCP金属の実験力学と計算力学)

We conducted an in-plane cyclic loading test for an AZ31B magnesium alloy sheet with various strain amplitudes. Metallographic observation was also carried out to investigate the effect of twinning on the work-hardening behavior. The work-hardening rate in later stage of compression rose with the number of cycles, whereas two-stage work-hardenings arose during tension and the beginning of the second work-hardening became later as the cycle number increased. The metallographic observation showed that the area where the twinning was activated increased wholly as the cycle number increased because some areas did not untwin and remained in twinning orientations after tension. This result showed that the work-hardening rate in later stage of compression rose because the activity of twinning tended to saturate and at the same time the slip systems started being activated as the cycle number increased. Similarly the strain range necessary to complete untwining, i.e. the first work-hardening, would expand as the cycle number increased because the area where the twinning was activated increased, thus the beginning of the second work-hardening became later with the number of cycles.