Pseudo-dynamic Tests Research Articles

Seismic design and pseudo-dynamic tests of blind-bolted CFT frames with buckling-restrained braces

A novel dual system composed of blind bolted end plate concrete filled steel tube (BECFT) composite frames and buckling-restrained braces (BRBs) was proposed and presented in this paper. The direct displacement-based design (DDBD) method was modified and used to design the BECFT composite frames with BRBs (BRB-BECFT) at a certain seismic hazard level. Meanwhile, a series of pseudo-dynamic tests (PDTs) were conducted on two specimens of 2/3-scaled two-story, one-bay BRB-BECFT composite frames. The test observations at different seismic hazard levels were recorded. It was indicated that the BRB-BECFT frame system exhibited reasonable failure mode, good hysteretic behavior, high ductility and sufficient energy-dissipating capacity. The installation of BRBs effectively enhanced the lateral stiffness and resistance of the dual system in comparison with their bare counterparts. Moreover, the inter-story drift responses of both specimens at the frequent occurrence earthquake (FOE) and the maximum considered earthquake (MCE) levels were less than the pre-defined values, and the experimental base shears were also close to the analytical results at the MCE level, suggesting the modified DDBD method could provide good control of drifts for the dual system at a target loading level. These research results presented a good alternative for application in earthquake resistant design of braced frame structures.

Numerical and experimental investigations on the Park-Ang damage index for high-speed railway bridge piers with flexure failures

The traditional Park–Ang damage index (DI) has been devised for damage assessment of highway bridge piers and building columns, but is inappropriate for high-speed railway (HSR) bridge piers, which have much larger cross sections, much less longitudinal bar ratios and much less axial compression ratios under earthquakes. In order to obtain the appropriate DI for HSR bridge piers, numerical analysis of 144 HSR bridge piers and quasi-static test of 7 HSR bridge piers was done to study the combined parameter β in DI. The new DI was subsequently validated by pseudo-dynamic testing of 2 HSR bridge piers. The results show that the new combined parameter β in the reformulated DI for HSR bridge piers is mainly affected by the longitudinal bar ratio and the axial compression ratio; however, the traditional β and DI are significantly affected by the stirrup reinforcement ratio. It is suggested that 0.06, 0.19, 0.49 and 1.0 should be taken as the critical values for the new DI among the basically intact, slightly damaged, moderately damaged, severely damaged and collapsed states of HSR bridge piers with axial compression ratio being less than 0.09, while values 0.11, 0.33, 0.49 and 1.0 are recommended for HSR piers with an axial compression ratio from 0.09 to 0.15. As for the collapse state of HSR bridge piers, the cumulative damage contribution of energy to the full DI (of value 1.0) is 0.64. It is a large value and indicates that HSR bridge piers are vulnerable to cumulative damage from earthquakes.

Pseudo-Dynamic Tests of Cold-Formed Thin-Walled Steel Wall

This paper presents the dynamic response and failure mechanism for the cold-formed thin-walled steel wall. Based on current seismic provisions and previous research, Full-scale pseudo-dynamic tests (PDTs) were conducted on a 3m high cold-formed thin-walled steel wall. The time-history response, hysteretic behaviour, failure mode, stiffness degradation and ductility were investigated to analyse the dynamic response of the cold-formed thin-walled steel wall structure under a series of ground motion records. The results showed that the structural deformation position was concentrated at the intersection of the cross bar and the diagonal bar in the middle of the wall, and other joints had no obvious plastic deformation; The structure was still elastic under the frequently occurred earthquake of 7 degree and 8 degree. Under the rare earthquake, the stiffness degradation was developed rapidly and the bearing capacity was still higher, and also had better ductility. Cold-formed thin-Walled steel structure which exhibits excellent seismic behaviour and ductility, can be used as a reliable and effective assembly structure in seismic regions.

Pseudo-dynamic and cyclic loading tests on a steel-concrete vertical hybrid structure

This paper presents the experimental investigations on the seismic performance of a peculiar steel-concrete vertical hybrid structural system referred to as steel truss-RC tubular column hybrid structure. It is typically applied as the supporting structural system to house air-cooled condensers in thermal power plants (TPPs). Firstly, pseudo-dynamic tests (PDTs) are performed on a scaled substructure to investigate the seismic performance of this hybrid structure under different hazard levels. The deformation performance, deterioration behavior and energy dissipation characteristics are analyzed. Then, a cyclic loading test is conducted after the final loading case of PDTs to verify the ultimate seismic resistant capacity of this hybrid structure. Finally, the failure mechanism is discussed through mechanical analysis based on the test results. The research results indicate that the steel truss-RC tubular column hybrid structure is an anti-seismic structural system with single-fortification line. RC tubular columns are the main energy dissipated components. The truss-to-column connections are the structural weak parts. In general, it has good ductile performance to satisfy the seismic design requirements in high-intensity earthquake regions.

Pseudodynamic Test of a Deficient RC Frame Strengthened with Buckling Restrained Braces

Three story–three bay reinforced concrete (RC) frames with and without chevron braces were tested using the continuous pseudodynamic test method. New steel–concrete composite lateral load–carrying members called Buckling Restrained Braces (BRBs) were used as chevron brace members while retrofitting the RC frame. The BRBs were fitted to the interior span of the RC frame by using anchorage rods. The chevron braced frame was observed to be effective in controlling interstory drift. The test results indicated that retrofitting with BRBs was beneficial in resisting deformation without significant damage under simulated ground motions. Furthermore, significant yielding that occurred on the core plate of the BRBs enabled the braced frame to dissipate energy induced by dynamic loading. The test results were compared with the results of the nonlinear time-history analysis. The analysis results were capable of estimating the base shear capacity and displacement demands with reasonable accuracy.

Seismic Response Investigation and Analyses of End Plate Moment-Resisting CFST Frames Under Pseudo-Dynamic Loads

This paper reported an innovative semi-rigid composite frame comprised of concrete-filled steel tubular (CFST) columns and H-shaped steel beams assembled using flush or extended end plates with blind fasteners. Two specimens of two-story single-bay end plate moment-resisting square or circular CFST frames were investigated by a series of pseudo-dynamic tests. To analyze dynamic response of this type of structure under the earthquake action, time history response and story drift were investigated. The influence of the column section type and the end plate type on seismic performance of semi-rigid moment-resisting CFST frames under different earthquake loading levels were also discussed according to hysteretic behavior, rigidity degradation and energy dissipation capacity. The experimental and analytical results indicated that at the same section width and steel ratio of the column, the rigidity of end plate moment-resisting square CFST frame was greater than that of circular CFST frame, while the story drift of square CFST frame was smaller than that of circular CFST frame. The type of end plate moment-resisting CFST frames with blind fasteners, which can provide good seismic behavior and energy dissipation ability, can be well used in a seismic region.

Numerical simulation of bridge piers with spread footings under earthquake excitation

This study simulates the responses of large-scale bridge piers under pseudo-dynamic tests to investigate the performance of four types of numerical models that consider the nonlinear behavior of the pier and the rocking behavior of the footing. In the models, beam-column elements with plastic hinges are used for the pier, two types of foundation models (rotational spring and distributed spring models) are adopted for the footing behavior, and two types of viscous damping models (Rayleigh and dashpot models) are applied for energy dissipation. Results show that the nonlinear pier model combined with the distributed spring-dashpot foundation model can reasonably capture the behavior of the piers in the tests. Although the commonly used rotational spring foundation model adopts a nonlinear moment-rotation property that reflects the effect of footing uplift, it cannot suitably simulate the hysteretic moment-rotation response of the footing in the dynamic analysis once the footing uplifts. In addition, the piers are susceptible to cracking damage under strong seismic loading and the induced plastic response can provide contribution to earthquake energy dissipation.

Influence Mechanism of Steel Diagonal Braces on Mechanical Behavior of Steel Truss-RC Tubular Column Hybrid Structure

ABSTRACT This paper aims to investigate the influences of steel diagonal braces (SDB) on the deformation performance and seismic behavior of steel truss-RC tubular column hybrid structures. Firstly, the vertical deformation performance of the structures with and without SDB was compared through finite element analysis. Then, pseudo-dynamic tests were carried out to investigate the seismic behavior of a 1/8-scaled substructure with SDB, and hysteretic curves were obtained by applying a subsequent displacement-controlled cyclic loading. The test results indicated that adding SDB is an effective approach to decrease the deflections of steel truss and enables to improve the lateral stiffness and lateral bearing capacity of the steel truss-RC tubular column hybrid structure. In addition, numerical modeling of the specimen with SDB was built on the basis of the refined finite element program. The comparisons between the finite element analysis and test results indicated that the FE modeling approach is reasonable to predict the seismic behavior of this type of hybrid structure.

Experimental study on seismic performance of RC frames with Energy-Dissipative Rocking Column system

The conventional reinforced concrete Moment Resisting Frames (MRFs) have suffered from soft story failure during major earthquake events. A novel system of steel Energy-Dissipative Rocking Column (EDRC) is proposed to mitigate seismic responses of MRFs. Pseudo-dynamic tests are conducted on large-scale two-story and two-bay reinforced concrete frames, with and without EDRC, respectively. The post-earthquake behavior of these two systems is also compared through quasi-static cyclic tests. The experimental results show that the presence of EDRC can effectively mitigate the maximum value, residual value and inhomogeneous distribution of inter-story drifts, and thus prevent the soft story failure of MRFs. It is found that the maximum and residual inter-story drift of combined MRF and EDRC systems is reduced by 26.0% and 82.0%, respectively, compared to pure MRFs. The inhomogeneous degree of inter-story drifts can be reduced by 25.0% and 11.0%, respectively, in the pseudo-dynamic and quasi-static tests.

Multichannel Inductive Sensor Based on Phase Division Multiplexing for Wear Debris Detection.

Inductive wear debris sensor has been widely used in real time machine lubricant oil condition monitoring and fault forecasting. However, the small sensing zone, which is designed for high sensitivity, of the existing sensors leads to low throughput. In order to improve the throughput, a novel multichannel wear debris sensor that is based on phase division multiplexing is presented. By introducing the phase shift circuit into the system, multiple sensing coils could work at different initial phases. Multiple signals of sensing coils could be combined into one output without information loss. Synchronized sampling is used for data recording, and output signals of multiple sensing coils are extracted from the recorded data. A four-channel wear debris sensor system was designed to demonstrate our method. Subsequently, crosstalk analysis, pseudo-dynamic testing and dynamic testing were conducted to check the sensing system. Results show that signals of four sensing coils could be simultaneously detected and the detection limit for ferrous wear debris is 33 μm. Using the presented method, real time wear debris detection in multiple channels could be achieved without increasing the number of excitation source and data acquisition equipment.

Experimental and numerical investigation of material non-linearity in steel elements under different loading protocols

In order to investigate the behaviour of a steel structure and provide effective design, most of the time analyses procedures which can take account the non-linear material behaviour are needed. These non-linear analysis procedures which are widely applied with different levels of accuracy, adopt two major approaches which can be classified as lumped plasticity and distributed plasticity models. This paper aims to analyze the accuracy of two different plasticity approaches such as lumped and distributed plasticity models on providing the non-linear material behaviour of steel elements under different loading protocols by comparing numerical and experimental results. In the first part, monotonic and cyclic quasi static tests and pseudo dynamic tests under instantaneous constant load and seismic load are conducted by using the small scale Load and Boundary Condition Box. Small scale steel specimens are used for the experiments. Results of the experiments are comprehensively reported. In the second part of the study, several numerical models are generated for each test. Monotonic and cyclic loading pushover analyses are carried out with both lumped plasticity models and distributed plasticity models. In these numerical studies, different types of material models are considered and numerical analysis results are validated against the experimental results. Accuracy of lumped plasticity and distributed plasticity models are assessed and a comprehensive comparison of different analysis and material models is reported. It is generally observed that using the fiber based method with bilinear kinematic hardening material model provides more accurate element responses for hot rolled steels.

Investigation on steel-concrete composite frame in Chinese traditional style buildings by pseudo-dynamic test

A series of pseudo-dynamic tests of a 1/2-scale 1-story 3-bay Chinese traditional style frame using steel - concrete composite columns was performed. During the test, the input ground motions were chosen from El Centro wave, Taft wave and Lanzhou wave. And peak ground acceleration (PGA) were 35 gal (minor earthquake of 7 degrees), 100 gal (precautionary earthquake of 7 degrees), 220 gal (major earthquake of 7 degrees) and 400 gal (major earthquake of 8 degrees), respectively. The failure modes, displacement and acceleration time history curves, hysteretic loops of restoring force- displacement, energy dissipation capacity and deformability, inter - story drift ratio of the test model were analyzed. It is shown that the typical failure modes of the model are concrete cracking at the connection between hypostyle column and penetrating tie as well as yield of longitudinal reinforcement of hypostyle column and peristyle column. And also, the model has better plastic deformation capacity. With a larger PGA, natural frequencies and dynamic amplification factors decreased, but its energy dissipation capacity increased. The energy dissipation of the model subjected to El Centro wave was largest with the same PGA. Based on the experimental results, the modal analysis and dynamic elasto-plastic analysis of the test model was performed using finite element software SAP2000. The results showed that under the action of horizontal earthquake, the 1st mode was translation of the model, and the plastic hinges of the model first formed on the ends of penetrating tie and successively developed at the root of hypostyle column, peristyle column, CRST-2 and CRST-3 and CRST-1 and CRST-4. And the inter-story drift ratios of the model subjected to 700 gal El Centro was close to the limited value in Chinese Code for Seismic Design of Buildings (GB50011-2010), indicating that the frame had a higher safety margin.

유사동적실험에 의한 HSWF 외부접합공법으로 내진보강 된 실물 2층 철근콘크리트 골조의 내진성능 평가

본 연구에서는 기존 강도증진형 내진보강법의 단점을 보완 · 개선할 수 있는 새로운 개념의 내진보강법인 HSWF(H-section Steel Window-typed Frame) 외부접합형 내진보강공법을 제안하였다. HSWF 내진보강법은 거주자가 거주가 가능하면서 내진보강 공사를 실시할 수가 있으며, 접합부 시공성이 탁월하며, 특히 필요 내진보강량 산정이 간편한 전형적인 강도증진형으로 전단파괴가 지배적인 비내진상세를 가지는 국내 철근콘크리트 건물에는 내력확보가 용이한 내진보강공법이다. 본 연구에서 제안한 HSWF 외부접합형 공법의 유용성을 검증 할 목적으로 기존 비내진상세를 가지는 철근콘크리트 학교건물을 바탕으로 한 실물 2층 골조 실험체를 대상으로 유사동적실험을 실시하여 검증함과 동시에 내진보강효과를 검토하였다. 그 결과, 국내 내진설계용 지진수준인 200 gal 지진규모에서 무보강 골조는 붕괴를 하였지만, HSWF 외부접합형 내진보강법으로 보강한 골조는 경미한 지진피해가 예상되었으며, 국내에서 발생 가능한 최대 지진규모(300 gal)를 상정한 경우에도 소규모 이하의 지진피해가 예상되어 본 연구에서 개발한 HSWF 내진보강법의 유효성이 검증되었다고 사료된다.

Choices of Structure-Dependent Pseudodynamic Algorithms

AbstractStructure-dependent integration algorithms have been implemented for pseudodynamic testing because they are very promising for this type of test due to the combination of unconditional stab...

Pseudo-Dynamic Test for Soil-Structure Interaction Analysis using Shake Tables

This paper presents an effective pseudo-dynamic (PSD) test method for analyzing the response of a multi degree of freedom structural system. In addition to the physical and numerical substructuring of the structure, the effect of the soil-structure interaction (SSI) is numerically modeled without a large soil box. The governing equation is separated into those for the superstructure and the base. These are coupled equations that can be solved recursively with the prediction of the superstructure acceleration, for which polynomial extrapolation is employed. The input for the structure is then obtained by solving the coupled equilibrium equations for experimental and analytically modeled systems. The restoring force applied underneath the superstructure is measured and used to update the superstructure acceleration. The stability condition for the proposed method is investigated, revealing a longer range of the convergence criterion than the Newmark explicit method. The implicit feature of the proposed method enables PSD tests irrespective of the modal properties, if the sampling frequency condition is satisfied. Additionally, the amplitude decay and period elongation are investigated for accuracy comparison in the structural responses. A series of PSD tests are performed using a two degree of freedom shear-building model to validate the proposed method. The experiment is performed on one part of the physical structure, while a numerical simulation is performed on the other part of the structure and on the SSI. The test results confirm that the proposed PSD algorithm is reliable for simulating the substructure and SSI effect.

Performance study of self-centering steel frame with intermediate columns containing friction dampers

A self-centering steel frame system with intermediate columns containing friction dampers (ICSCF) has been proposed in this study to resolve the problem that the interstory drift of the structure may exceed the specified limit in standards when self-centering steel frames (SCF) are applied in multi-rise and high-rise buildings with larger spans, and ICSCF comprises two kinds of friction dampers, intermediate column containing friction dampers (ICFD) and web friction devices (WFD), thus possesses larger energy dissipation capacities under rare earthquakes. An eight-floor prototype of ICSCF was designed and pseudo-dynamic test was conducted on a two-floor testing substructure. Finite element analysis was performed to validate the reliability of testing results. Seismic performance analysis on the overall structure of ICSCF was carried out, which was then compared that of SCF utilizing only beam web friction dampers. The test and the analyses results indicated that the introduction of ICFD has greatly increased the lateral stiffness of the structure and energy dissipating capacity, further extending the application field of self-centering structural systems, making it possible to be applied to larger-span structures.

Preliminary Finite Element Analyses on the Experimental Mock-Up Frames of FREEDAM Research Project

Recent research ventures focus on structural systems characterized either by low-damage or easily repairable solutions. In this context, moment resisting frames (MRFs) equipped with friction joints represent a viable option. Among the different types of friction beam-to-column connections, the arrangement with symmetric friction devices are very effective to provide stable and ductile friction hysteresis, thus reducing the damage in the structural members (beams and columns) to a minimum or even to zero. Numerical and experimental investigations on the beam-to-column assemblies within the RFCS FREEDAM project testify to the good seismic performance of the friction device when properly designed. However, within this research project full scale pseudo-dynamic tests will be performed for a better understanding of the influence of such joint on the overall structural behaviour of MRFs. In this paper the results of preliminary numerical simulations are presented to give the first insights on the response of the experimental mockup as well as to validate the accuracy of two software with largely different capabilities. Static pushover and nonlinear dynamic analyses were performed and the results for the benchmark structure (frame equipped with reduced beam section joint) and for the structure equipped with the friction devices are presented

Discrete Tangent Stiffness Estimation Method for Pseudo Dynamic Test

In pseudo dynamic (PSD) test, researchers have long recognized the importance and potential benefits of utilizing the tangent stiffness of experimental specimen to correct the restoring force and analyze the energy error. However, improving accuracy and efficiency of the instantaneous stiffness estimation still presents a challenge. Based on the theory of discrete curve parameter recognition and the geometrical analysis approach, this paper proposes a discrete tangent stiffness estimation (DTSE) method to estimate the instantaneous tangent stiffness of a single degree of freedom (SDOF) experimental specimen. For different magnitudes of measurement noise, the proposed method can adaptively select and retain a series of latest valid data and ignore outdated information, of which the advantage is highly improving the accuracy and promptness of instantaneous stiffness estimation. The numerical study shows that the DTSE method has better accuracy and promptness of tangent stiffness estimation when compared with other existing methods. In a PSD test involving a sliding isolator, the DTSE method is utilized to analyze the cumulative energy error, the result of which shows the cumulative energy error is negative and decreases gradually. The analysis of experimental results demonstrates that the undershooting error of actuator added extra energy into the PSD testing system. Thus, the proposed method provides a desirable solution to instantaneous stiffness estimation.

Seismic Analysis of Steel Solid Web Girder-RC Tubular Column Hybrid Structure

This paper aims to investigate the seismic performance of a novel type of steel–concrete hybrid supporting structure consisting of reinforced concrete (RC) tubular columns, steel solid web girder platform, and A-shaped steel frames. It is typically used to house air-cooled condensers (ACC) in thermal power plants (TPPs). First, the finite-element (FE) model was implemented in ABAQUS and the simulation approaches were validated by pseudo-dynamic test results of a scaled steel-concrete hybrid supporting structure. Then, the elasto-plastic time-history analysis of the steel solid web girder-RC tubular column hybrid structure was conducted. The El Centro (NS) record was scaled to peak ground acceleration (PGA) of 0.07, 0.20, 0.40 and 0.62 g to reflect the frequent, basic, rare, and very rare earthquakes. The dynamic characteristics, base shear force, lateral deformation performance, stiffness deterioration, and damage evolution characteristics were analyzed. The numerical results showed that the first vibration mode of this hybrid structure is torsion, due to its small torsional stiffness and the nonuniform distribution characteristics of stiffness and mass in the vertical direction; the lateral deformation shape is shear mode; and the damage mainly occurred on the RC tubular columns, while the steel components did not yield under severe earthquakes. In general, the overall seismic performance of the steel solid web girder-RC tubular column hybrid structural system could meet the seismic design requirements with respect to the high-intensity earthquakes.

Real‐time hybrid aeroelastic simulation of wind turbines with various types of full‐scale tuned liquid dampers

AbstractThe present paper presents the real‐time hybrid simulation (RTHS) technique for multimegawatt wind turbine (WT) with various types of full‐scale tuned liquid dampers (TLDs). As an evolvement of the pseudodynamic testing technique, the RTHS is executed in real time, thus allowing accurate investigation of the interaction between the aeroelastic WT system and the rate‐dependent nonlinear TLD device. As the numerical substructure, the WT is simulated in the computer using a 13‐degree‐of‐freedom (13‐DOF) aeroelastic model. As the physical substructure, the full‐scale TLDs are manufactured and physically tested. They are synchronized with each other by real‐time controllers. Taking advantage of RTHS technique, 2‐ and 3‐MW WTs have both been simulated under various turbulent wind conditions. TLDs with different configurations have been extensively investigated, eg, various tuning ratios by varying the water level, TLD without and with damping screens (various mesh sizes of the screen considered), and TLD with flat and sloped bottoms. It is shown that a well‐designed TLD is very effective in damping lateral tower vibrations of WTs. Furthermore, RTHS results and results from a proposed theoretical model are compared. This study gives comprehensive guidelines for employing various types of TLDs in large WTs and indicates huge potentials of applying RTHS technique in the area of wind energy.