Seismic Qualification Testing Research Articles

Seismic Performance of Drop-In Anchors in Concrete under Shear and Tension

This paper presents an experimental study conducted on the behavior of drop-in anchors in uncracked concrete slabs. Both seismic (cyclic) load tests and static load tests to collapse are performed on drop-in anchors subjected to tension or shear forces. Three different anchor sizes are subjected to seismic qualification testing, followed by a static load test to collapse. The test results confirm the capability of the tested anchors to sustain simulated pulsating seismic tension and shear loading with frequency ranges between 0.1 and 2.0 Hz. It was observed that no tension failure occurred at the end of the cyclic load tests for all the tested anchors, and their residual inelastic maximum displacement at the end of the cyclic tension test was relatively small. Moreover, the experimental results show that the anchors’ ultimate capacities are higher than those specified by the anchor manufacturer. Finally, the anchors’ experimental pullout shear capacities are compared with the failure prediction equations in the literature and design codes. It is found that the theoretical models provide a conservative prediction of the concrete breakout of anchors in tension compared to the experimental ultimate loads. The coefficient for pry-out strength (kcp) equal to 2 or slightly smaller than 2 is likely to predict a better pry-out capacity with the experimental results compared to the application of the high conservative value of kcp equal to 1, as given in the code.

An analytical model for seismic response analysis of electrical equipment-steel support structure

Electrical equipment mounted on supporting structures is typical in a substation but vulnerable to earthquakes from previous field investigations. To evaluate the seismic performance of such an electrical equipment-support coupling system, a modal space analytical model was developed using the vibration partial differential equation (PDE) with distributed parameters and joint nodes. In the analytical model, resonant frequencies and mode shapes were obtained through numerical algorithms based on the boundary condition of each segmented beam. Then seismic responses of the coupling system can be attained by the modal decomposition method and superposition principle. A full-scale shaking table test was conducted on a 550 kV bushing-support coupling structure, and the accuracy of the analytical model was verified by the experimental results. Furthermore, a ceramic breakage inside the connecting flange at the base cross-section of the bushing specimen was observed after the seismic qualification test, which means its seismic performance can not meet the demand in the IEC seismic design specifications. To figure out this problem, parametric analysis was carried out using the analytical model to study the influence of parameters of the supporting structure and flange connection on the seismic responses of the equipment. In light of the analytical results, halving the original flange's flexural rigidity can reduce the bottom stress of the bushing by about 20% without over-magnifying its top displacement for this bushing-support coupling system. Application of the presented analytical modelling method can assist in the seismic optimization design of other equipment-support coupling systems in substations.

Shake Table Response of Unreinforced Masonry and Reinforced Concrete Elements of Special Moment Resisting Frame

Half‐scaled reinforced concrete frame of two storeys and two bays with unreinforced masonry (URM) infill walls was subjected to base excitation on a shake table for seismic performance evaluation. Considering the high seismic hazard Zone IV of Pakistan, reinforcement detailing in the RC frame is provided according to special moment resisting frames (SMFRs) requirement of Building Code of Pakistan Seismic‐Provisions (BCP SP‐2007). The reinforced concrete frame was infilled with in‐plane solid masonry walls in its interior frame, in‐plane masonry walls with door and window openings in the exterior frame, out‐of‐plane solid masonry wall, and masonry wall with door and window openings in its interior frame. For seismic capacity qualification test, the structure was subjected to three runs of unidirectional base excitation with increasing intensity. For system identification, ambient‐free vibration tests were performed at different stages of experiment. Seismic performance of brick masonry infill walls in reinforced concrete frame structures was evaluated. During the shake table test, performance of URM infill walls was satisfactory until design ground acceleration was 0.40g with a global drift of 0.23%. The test was continued till 1.24g of base acceleration. This paper presents key findings from the shake table tests, including the qualitative damage observations and quantitative force‐displacement, and hysteretic response of the test specimen at different levels of excitation. Experimental results of this test will serve as a benchmark for validation of numerical and analytical models.

Effect of cyclic loading protocols on the experimental seismic performance evaluation of suspended piping restraint installations

Suspended non-structural elements, such as water and sprinkler piping systems, are key to the functionality of important facilities, such as hospitals and schools. Recent earthquakes have demonstrated the vulnerability of these systems, particularly for those that were inadequately restrained. Seismic qualification requirements of non-structural elements contained in recent building codes and industry standards rely on experimental procedures, such as quasi-static cyclic testing of components and sub-assemblies. When conducting such quasi-static testing, the question arises as to what proper loading protocol to use. The first part of this paper reviews and compare existing cyclic loading protocols for testing various types of components and sub-assembles and developed according to scientific methods, including two specifically developed for testing non-structural elements. These two non-structural loading protocols are then used for conducting quasi-static cyclic testing of common components part of piping restraint installations. Characteristic response parameters resulting from test results with each cyclic loading protocol are extracted and compared. Observations and recommendations are provided on the effects of using different cyclic loading protocols for the performance evaluation and seismic qualification testing of suspended piping restraint installations.

스터럽 보강 선설치 앵커의 지진모의실험에 의한 동적 전단 저항강도 평가

스터럽 보강 선설치 앵커의 동적 전단하중 하의 파열파괴강도를 평가하기 위한 실험 연구를 수행하였다. 전단 하중은 ACI 355.2 및 ETAG 001에 제시된 지진모의실험 방식으로 재하하였다. 시험체는 M36 앵커(연단거리 180mm)를 D10 스터럽(간격 100mm)으로 보강하였다. 이들 시험체는 거의 극한 파열파괴 강도에 도달한 후 앵커의 파단이 발생하였다. 이에 M42 앵커(연단거리 160mm)를 D6 스터럽(간격 100mm)으로 보강한 시험체에 대한 실험을 추가로 수행하였다. 실험 결과, 동적 전단강도는 정적 강도에 비해 낮은 값을 보이지 않았다. 또한, ACI 318 및 ETAG 001 기준은 스터럽 보강이 많을수록 파열파괴강도를 안전측으로 평가하는 것으로 나타났다. An experimental study was conducted to evaluate the breakout strength of stirrup-reinforced cast-in anchors under dynamic shear loadings. The shear loadings were applied in the manner specified in the ACI 355.2 and ETAG 001 for the seismic qualification tests. Test specimens were fabricated with M36 anchor (edge distance, 180mm) reinforced with D10 stirrups (spacing, 100mm). The specimens reached almost the breakout strength and thereafter fracture of anchor occurred. Additional tests with M42 anchor (edge distance, 160mm) reinforced with D6 bars (spacing, 100mm) were also conducted. The experimental results showed that the dynamic shear strength was not less than the static resistance. Based on the test results, it was shown that ACI 318 and ETAG 001 specifications estimate the breakout strength of stirrup-reinforced anchors conservatively as more reinforcement is provided.

Substructured Dynamic Testing of Substation Disconnect Switches

The paper demonstrates the substructuring concept in seismic qualification testing of 550 kV electrical substation disconnect switches. In this study, the full and substructured (i.e., without support structure) switches are tested on a six degrees of freedom (DOFs) shaking table. Different combinations of translational and rotational excitations are obtained from full switch tests and used in the substructured ones. The behavior of the post insulators of the switches are compared to demonstrate validity and identify limitations of the substructuring concept applied to electrical substation equipment. From this comparison, critical DOFs for the response of post insulators in switches supported on flexible structures are identified. It is concluded that the in-plane and out-of-plane behavior of the investigated post insulators are uncoupled. The substructured tests driven by combined translational and rotational signals showed the best match with the full switch tests because the out-of-plane rotations contribute significantly to the response of the post insulators.

Real-time hybrid simulation in a shaking table configuration for parametric studies of high-voltage equipment and IEEE693 development

This paper presents extensive discussion on seismic qualification of substation equipment in conventional shake table tests and its comparison to real-time hybrid simulation (RTHS). The hybrid simulation technique is based on a sub-structuring idea where a portion of a test specimen with well-predicted performance can be replaced by its finite element model. The rest of the test specimen is experimentally studied as part of the coupled system, where the test object and the mathematical model are interacting with each other in real time. The real-time hybrid simulation technique has a strong potential of complementing and in some cases replacing seismic qualification testing. In addition to that, it has a strong potential as a comprehensive and reliable tool for IEEE693 development, where code provisions can be developed from parametric hybrid simulation studies of actual pieces of substation equipment which are otherwise difficult to model. As a typical example of successful application of hybrid simulation, a comprehensive study related to RTHS of electrical disconnect switches is discussed in the paper. First, the RTHS system developed for this purpose is described and the results of a RTHS test are compared with a benchmark conventional shaking table test as a validation of the system. Second, effect of the support structures of the disconnect switches on the global and local responses of different insulator types is evaluated using the results of a series of RTHS tests. Third, the paper investigates the advantages of using a sophisticated control approach for RTHS conducted on a long-stroke high-velocity shaking table. Finally, results of an application that uses the sophisticated control approach on a fully assembled phase of a disconnect switch are presented.

지진모의실험에 의한 비균열 및 균열콘크리트에 매입된 비보강 선설치앵커의 전단 저항강도 평가

In this study, an experimental study was performed to evaluate the concrete breakout strength of unreinforced cast-in-place anchors by seismic qualification test under shear loading. The CIP anchors tested herein were 30mm in diameter with an edge distance of 150mm and an embedment depth of 240mm in uncracked and cracked concrete. The cracked specimen consisted of orthogonal and parallel crack to the loading direction, respectively. The dynamic loading sequence during the seismic qualification test was determined based on CSA N287.2, ACI 355.2 and ETAG 001 codes. After the dynamic loading, the static loading was applied until failure occurs. The shear resistance by seismic qualification tests showed almost the same strength as that obtained from the static tests in uncrcaked and cracked concrete, respectively. Meanwhile, the breakout depth did not reach , therefore the modified strength equation of ACI 318-11 could estimate properly the concrete breakout strength, which does not consider effective bearing length.

헤어핀 보강 선설치앵커의 정적 및 지진모의실험에 의한 전단 저항강도 평가

This study evaluated the static and dynamic shear strength of cast-in-place anchors reinforced with hairpin bars in uncracked and cracked concrete. The anchors 30mm in diameter reinforced with D10 hairpin bar were designed with an edge distance of 150mm and an embedment depth of 240mm. The cracked specimens consisted of the orthogonal and parallel cracks to the direction of shear loads, respectively. The dynamic strength was evaluated using seismic qualification tests based on the ACI 355.2 standard. The shear strength of the hairpin reinforced anchor was hardly correlated to the concrete cracks and the dynamic strength was similar to its static shear strength. Finally, a consideration on the design strength of hairpin reinforced anchors was presented.

Seismic Qualification of the Unconventional Valve by Shake Table Testing

To make Nuclear Power Plants (NPP) more acceptable by the public, there is a need to conform to the stringent safety criteria evolved continuously. Among the several safety aspects, the seismically induced effects call more attention at the present scenario. But the adequate full scale testing of the critical components can render a more realistic simulation. Extensively shake table testing is used for the seismic qualification and research purposes. It provides the means to excite structures in such a way that they are subjected to conditions representative of true earthquake ground motions. The seismic qualification tests were conducted as per the test procedure given in IEEE STD 344-1987 standards: IEEE recommended practice for seismic qualification of class 1E equipment for Nuclear Power Generating Station. Valves are one of the active components in the SFR system. The seismic operability of active components can be established only by shake table testing. Shake table testing includes fixing of the equipment into the shake table, exiting the table with a seismic excitation equal to or larger than the design earthquake, resonance search test in all the three directions for 1 to 50 Hz to identify the system frequencies and assessment of the functionality and structural integrity of the valve during and at the end of the test. The valve that has been experimentally qualified completed type test for OBE & SSE cycles, the same will not be utilized in the reactor application. The methodology involved in the seismic qualification of the unconventional valve presented in this paper. Among the various shake table experiments carried out for the seismic qualification unconventional valves, the experiment carried out for the Inclined Fuel Transfer Machine (IFTM) Gate valve is referred in this paper for the above purpose. It is one of the unconventional type large in size and heavy gate valve available in the SFR system

고전압 장비 지그의 동특성에 대한 위상, 형상 및 치수 최적화

In the electric power supplying industry, outdoor sealing end (pothead) is used and sometimes it is necessary to check the seismic qualification analysis or test which is intended to demonstrate that the equipment have adequate integrity to withstand stress of the specified seismic event and still performs their function. And since the pothead is mounted on the supporting jig, the avoidance of resonance between the pothead and jig is required. In order to design jig, three types of optimization are performed to get the minimum weight while satisfying the natural frequency constraint using ANSYS. Optimal array, position and thickness of truss members of the jig are obtained through topology, shape and sizing optimization process, respectively. And seismic analysis of the pothead on the jig for given RRS acceleration computes the displacement and stress of the pothead which shows the safety of the pothead. The obtained natural frequency, mass, and member thickness of the jig are compared with those of the reference jig which was used for seismic experimental test. The numerical results of the jig in the research is more optimized than the jig used in the experimental test.

Important technologies applied for UHV AC substations in Japan

SUMMARYThe Tokyo Electric Power Company, Inc (TEPCO) plans 1100 kV power network system in Japan in order to meet the steady increasing demand for electricity. Four‐hundred kilometer 1100‐kV‐designed double‐circuit transmission lines have already been constructed and are now operated at 550 kV. 1100‐kV substation equipment has also been developed.To realize the best design technically and economically throughout the transmission line and the substation, important technical solutions for network problems peculiar to the ultra high voltage (UHV) system have been introduced. They include insulation coordination, overvoltage countermeasures, and fast multi‐phase reclosing systems with high speed earthing switches (HSESs). The overvoltage countermeasures are realized by high performance metal oxide surge arresters (MOSAs), gas circuit breakers (GCBs) with closing/opening resistor, and disconnectors (DSs) with resistor. These sophisticated technologies realize highly reliable and economical UHV substations and transmission lines.This paper describes important, fundamental, and specific requirements for UHV substations such as their compactness, economical view, and environmental harmony. There are many technical/economical aspects to be considered on UHV substation and based on those considerations: (a) compactness, (b) less impacts to the environment, (c) optimizing cost, could be fulfilled.This paper also describes the technologies addressed to UHV class components such as the introduction of new concept “on‐site assembly transformer,” VFTO reduction countermeasure and the necessity of full‐scale seismic qualification test. Copyright © 2011 John Wiley & Sons, Ltd.

Numerical aspects of a real‐time sub‐structuring technique in structural dynamics

AbstractA time domain coupling technique, involving combined computational and experimental modelling, for vibration analysis of structures built‐up of linear/non‐linear substructures is developed. The study permits, in principle, one or more of the substructures to be modelled experimentally with measurements being made only on the interfacial degrees of freedom. The numerical and experimental substructures are allowed to communicate in real time within the present framework. The proposed strategy involves a two‐stage scheme: the first is iterative in nature and is implemented at the initial stages of the solution in a non‐real‐time format; the second is non‐iterative, employs an extrapolation scheme and proceeds in real time. Issues on time delays during communications between different substructures are discussed. An explicit integration procedure is shown to lead to solutions with high accuracy while retaining path sensitivity to initial conditions. The stability of the integration scheme is also discussed and a method for numerically dissipating the temporal growth of high‐frequency errors is presented. For systems with non‐linear substructures, the integration procedure is based on a multi‐step transversal linearization method; and, to account for time delays, we employ a multi‐step extrapolation scheme based on the reproducing kernel particle method. Numerical illustrations on a few low‐dimensional vibrating structures are presented and these examples are fashioned after problems of seismic qualification testing of engineering structures using real‐time substructure testing techniques. Copyright © 2007 John Wiley & Sons, Ltd.

Modal Testing and Finite Element Analysis of a Battery Rack for Seismic Applications

One of the most challenging aspects of reliability testing in the telecommunication industry is earthquake resistance testing. Cabinet systems, battery racks, equipment racks, and distribution frames are considered compliant with Network Equipment-Building System (NEBSTM) criteria for surviving earthquake conditions if test results indicate (1) the maximum deflection of the top of the structure does not exceed 7.6 cm (3 in.), (2) there are no permanent deformations or structural damage, and (3) the equipment or batteries remain functional (as defined in NEBS Requirements: Physical Protection, Specification GR-73 Issue 2). Based on seismic test results of a large population of telecom enclosures, it is accepted that a system always passes the seismic test if its fundamental natural frequency is at least 6 Hz. It is costly to produce and configure enclosures and conduct seismic qualification testing. To minimize the risk of telecom system failure, a modal finite element analysis (FEA) of the system should first be performed. Numerical results of the FEA should then be verified with experimental resonance search data generated by modal testing or sine sweep testing, combined with static pull testing where applicable. The resonance search results will determine the need for seismic testing (seismic analysis) prior to seismic qualification testing. This paper elaborates on key aspects of the static pull test method supported by the test results for a cabinet framework and a configured cabinet relative to the seismic test results. The paper also discusses sine sweep testing of a battery cabinet and results of two modal test methods used on the corresponding battery rack. Finally, this paper describes modal FEA of the same battery rack anchored to a concrete pad supported by a polystyrene plastic foam sheet and explains the correlation of the numerical results with the experimental modal analysis results. The correlated model serves as the baseline model for analyzing other battery racks and equipment cabinets configured with batteries.

Seismic qualification of expansion anchors to Canadian nuclear standards

A large number of unique seismic qualification tests were performed on different types of expansion anchors to determine their seismic capabilities. These tests followed the requirements of the Canadian CSA N287.2 as well as the ASTM E 488 Standards. Expansion anchors ranging in diameter from 1/4 to 1 1 4 in. were subjected to this seismic qualification testing. Strategically designed and standardised concrete blocks were manufactured to receive each expansion anchor. The anchors were installed according to the anchor manufacturer instructions and the installation was consistent with construction practice. Each anchor type and size was subjected to four different types of tests covering static, dynamic, tension and shear loading. The dynamic cyclic loads applied represented a strong earthquake whose spectrum envelops that of the Design Basis Earthquake (DBE). The seismic testing qualification program involved 300 tests. Results of the testing program are obtained for each type of anchor. Results from these tests confirm that these types of expansion anchors have maintained their tension (pull-out) and shear capabilities following a severe seismic shaking.

Achieving cost savings through collaborative seismic testing

Seismic qualification of nuclear power plant equipment through testing has been perceived by utility personnel as a costly and complicated process. Certainly, some equipment types may only be qualified by test due to the complexity of the item and/or the inability to represent the item in a quantitative analysis. Other factors also influence the reluctance by some to resort to seismic testing. These include cost, dealing with test failures, lack of understanding of the testing process, and greater reliance on new analytical techniques. A group of utilities have allied themselves to address these issues and have formed the Seismic Qualification Reporting and Testing Standardization (SQURTS) group. SQURTS has implemented a program whereby testing is performed at a low cost, often lower than a comparable analytical solution. Testing is conducted at generic seismic levels using generic test procedures, which broadens the applicability of results. Test reports are published in a standard format which shortens the process of review and approval. Testing is no longer just a requirement, but a cost-effective option.

Existing seismic test data and its use

This paper summarizes the results of a current program sponsored by the Electric Power Research Institute (EPRI) with the overall objective of demonstrating the generic seismic adequacy of as much nuclear power plant equipment as possible by means of collating and evaluating existing seismic qualification test data. Concern over the seismic adequacy of equipment in older operating nuclear plants not qualified to today's rigorous standards has motivated recent studies which utilize new approaches to demonstrate the seismic “ruggedness” of mechanical/electrical equipment. The first characteristic of these new approaches is the use of “experience” data. The second characteristic is the demonstration of adequacy on a “generic” basis. The approach, of the study discussed in this paper, is to consider the large amount of information collected during seismic qualification testing of nuclear power plant equipment as an experience data base. These data are then used to construct “ruggedness” spectra below which equipment in operating plants designed to earlier earthquake criteria would be generically qualified.

A Method for Correlating Severity of Different Seismic Qualification Tests

A general methodology has been developed for correlating the severity of various seismic qualification motions that can have very different dynamic characteristics. The approach is based on a vibrational equivalence concept which allows a severity comparison between two different waveforms. The comparison is in terms of a fragility ratio, DFR, which is a ratio of vibrational input level to that which the specific equipment is capable of sustaining at its fragility level. Measurement of the severity at both levels can be characterized in terms of response spectrum, power spectrum, or other parameters which may be used, or have been used, in typical equipment qualification procedures. Relationships among the various parameters are defined so that transformations from one to another are possible. The inherent use of the fragility function for the methodology causes some problem in that such data are not generally included in previous qualification information. This problem is overcome by defining a lower-bound, or acceptable approximate fragility function, which is based on the previous qualification levels. A method of measuring relative severity of two motions is also developed in terms of a relative severity ratio, DSR. This ratio is proportional to several other relative severity factors that have been established by other researchers.

A Dynamic-Test Procedure for Improving Seismic Qualification Guidelines

Several shortcomings of available standards, regulatory guides, and review plans for seismic qualification testing are identified. A rational test nomenclature is proposed. A standard test is developed by optimizing an appropriate test severity measure function. The standard test is a rectilinear test that is equivalent to the three-degree-of-freedom test with uncorrelated excitations, recommended in IEEE-Std. 344. In terms of eigenvectors of a resulting test matrix, a dynamic interpretation is given for principal axes of a test object. The proposed approach to dynamic testing has two main advantages in comparison to the conventional approach of black-box testing. Firstly, knowledge pertaining to test-object dynamics is directly employed in its development. Secondly available information on possible modes of failure in the overall system can be conveniently incorporated into the formulation.

Selection of shaker specifications in seismic qualification tests

A procedure that can be employed to determine suitable exciter specifications for seismic qualification tests is developed. Estimates for force, power, and stroke ratings of exciter are obtained by this procedure, the mass and the damping ratio of test package and the response spectrum of the excitation signal being used. Either an acceleration required response spectrum (RRS) or a velocity RRS may be used in this procedure to specify the dynamic environment for the test. Two numerical examples are given to demonstrate the procedure.