Dynamic Test Sequence Research Articles

Comparing seismic performances of pilotis and bare RC frame structures by shaking table tests

This study investigates the role of masonry infill walls in the responses and failure modes of RC frames subjected to earthquake, by applying shaking table tests on two three-story, two-bay, 1/4-scale RC frame structures. Two types of RC frame structures, an infilled RC frame without infill walls in the first story (pilotis frame) and a bare RC frame, are constructed according to the seismic design codes of China. The pilotis and bare frames are simultaneously deployed on a shaking table when I-ELC180 ground motion and Wolong ground motion excitations are used. The two specimens are subjected to a sequence of dynamic tests with increasing intensity. This paper mainly presents and compares the phenomena observed from the shaking table tests of the pilotis and bare frames, including the dynamic properties, acceleration and displacement responses, evolution of damage and final failure mechanisms. The tests indicate that, compared with the bare frame, the infill walls in the pilotis frame can significantly affect the failure mode and damage distribution. Plastic hinges first appear in the 1st story columns for the pilotis frame under seismic loading, while plastic hinges first appear at the beam ends in the 1st story for the bare frame; The damage to the pilotis frame is increasingly concentrated in the 1st story as the earthquake intensity increases, while the damage distribution along the height of the bare frame remains almost the same as the earthquake intensity increases. The maximum interstory drift ratio of the pilotis frame is up to 50% larger than that of the bare frame under the same earthquake intensity.

Pretest Nonlinear Finite-Element Modeling and Response Simulation of a Full-Scale 5-Story Reinforced Concrete Building Tested on the NEES-UCSD Shake Table

A full-scale five-story reinforced concrete building specimen, outfitted with a variety of nonstructural components and systems (NCSs), was built and tested on the Network for Earthquake Engineering Simulation at the University of California, San Diego (NEES–UCSD) large outdoor shake table in the period March 2011–June 2012. The building specimen was subjected to a sequence of dynamic tests including scaled and unscaled earthquake motions. A detailed three-dimensional nonlinear finite-element (FE) model of the structure was developed and used for pretest response simulations to predict the seismic response of the test specimen and for decision support in defining the seismic test protocol and selecting the instrumentation layout for both the structure and NCSs. This paper introduces the building specimen and the shake table test protocol and describes the techniques used for the nonlinear FE modeling and response simulation. Utilized as blind prediction, the pretest simulation results at different scales (global structural level and local member/section/fiber levels) are compared with their experimental counterparts for seismic input (base excitation) of increasing intensity from serviceability to design levels. The predictive capabilities of the used FE modeling techniques are evaluated and possible sources of discrepancies between the FE predictions and experimental measurements are investigated and discussed.

Influence of the construction process and nonstructural components on the modal properties of a five‐story building

SummaryA full‐scale five‐story reinforced concrete building was built and tested on the NEES‐UCSD shake table during the period from May 2011 to May 2012. The purpose of this test program was to study the response of the structure and nonstructural components and systems (NCSs) and their dynamic interaction during seismic base excitation of different intensities. The building specimen was tested first under a base‐isolated condition and then under a fixed‐based condition. As the building was being erected, an accelerometer array was deployed on the specimen to study the evolution of its modal parameters during the construction process and placement of major NCSs. A sequence of dynamic tests, including daily ambient vibration, shock (free vibration) and forced vibration tests (low‐amplitude white noise and seismic base excitations), were performed on the building at different stages of construction. Different state‐of‐the‐art system identification methods, including three output‐only and two input‐output methods, were used to estimate the modal properties of the building. The obtained results allow to investigate in detail the effects of the construction process and NCSs on the dynamic parameters of this building system and to compare the modal properties obtained from different methods, as well as the performance of these methods. Copyright © 2015 John Wiley & Sons, Ltd.

Model based temperature controller development for water cooled PEM fuel cell systems

PEM (proton exchange membrane) fuel cell operation necessitates thermal management to satisfy the requirements of safe and efficient operation by keeping the temperature within a certain range independent of varying load conditions. Heat generation within the fuel cell changes according to the power delivered from the stack, requiring a dynamic control system to remove this excess heat and maintain the desired stack temperature. In this study, a closed loop water circulation strategy is considered and evaluated for cooling a 3 kW PEM fuel cell. The cooling system consists of a water circulation pump and a radiator coupled to a fan, integrated with the fuel cell stack. A first principles based model is developed for the integrated cooling system through an energy balance containing the relevant terms. A sequence of dynamic tests is performed on the cooling system to identify the parameters appearing in the model developed. The resulting semi-empirical model is used to evaluate possible control strategies managing the cooling loop. Three specific strategies are analyzed and the performances of these controllers are evaluated in terms of stack temperature, integral time weighted absolute error (ITAE) and the parasitic energy requirements. Minimizing fan usage with an on/off controller while keeping the pump voltage as a continuously manipulated variable through a feedback PI (proportional–integral) controller delivers the best results. The MATLAB-SIMULINK® platform is used in the development and implementation of the models and controllers. In our strategy, the characterization of the cooling loop is physically de-coupled from the development of the fuel cell stack – allowing for the evaluation of candidate equipment and algorithms prior to the fuel cell stack being available, which is often the case during prototype development.

Experimental modal analysis of an aluminum rectangular plate by use of the slope-assisted BOTDA method

We report an experimental modal analysis of an aluminum rectangular plate (50 cm×30 cm×0.3 cm), carried out by use of a Brillouin optical time-domain analysis (BOTDA) sensor operating in the slope-assisted configuration, i.e. at a fixed pump–probe frequency shift. Strain measurements were acquired along an optical fiber attached to the structure, at a maximum acquisition rate of 250 Hz, a spatial resolution of 30 cm and a sampling distance of 5 cm in both x- and y-directions. A sequence of dynamic tests, aimed to evaluate the resonant frequencies and strain modal shapes of the structure, were performed on the plate for various boundary conditions (plate clamped with four, three or two bolts). Comparison with finite element method (FEM) analysis and dynamic strain measurements with strain gauges shows that Brillouin based distributed sensors can be usefully employed to perform the modal analysis of a vibrating structure, even if the spatial resolution is comparable with the plate dimensions.

Shake‐table tests of a reinforced concrete frame designed following modern codes: seismic performance and damage evaluation

SUMMARYThis paper presents shake‐table tests conducted on a two‐fifths‐scale reinforced concrete frame representing a conventional construction design under current building code provisions in the Mediterranean area. The structure was subjected to a sequence of dynamic tests including free vibrations and four seismic simulations in which a historical ground motion record was scaled to levels of increasing intensity until collapse. Each seismic simulation was associated with a different level of seismic hazard, representing very frequent, frequent, rare and very rare earthquakes. The structure remained basically undamaged and within the inter‐story drift limits of the ‘immediate occupancy’ performance level for the very frequent and frequent earthquakes. For the rare earthquake, the specimen sustained significant damage with chord rotations of up to 28% of its ultimate capacity and approached the upper bound limit of inter‐story drift associated with ‘life safety’. The specimen collapsed at the beginning of the ‘very rare’ seismic simulation. Besides summarizing the experimental program, this paper evaluates the damage quantitatively at the global and local levels in terms of chord rotation and other damage indexes, together with the energy dissipation demands for each level of seismic hazard. Further, the ratios of column‐to‐beam moment capacity recommended by Eurocode 8 and ACI‐318 to guarantee the formation of a strong column‐weak beam mechanism are examined. Copyright © 2013 John Wiley & Sons, Ltd.

Shake‐table tests of a three‐story reinforced concrete frame with masonry infill walls

SUMMARYThis paper presents the shake‐table tests of a 2/3‐scale, three‐story, two‐bay, reinforced concrete frame infilled with unreinforced masonry walls. The specimen is representative of the construction practice in California in the 1920s. The reinforced concrete frame had nonductile reinforcement details and it was infilled with solid masonry walls in one bay and infill walls with window openings in the other bay. The structure was subjected to a sequence of dynamic tests including white‐noise base excitations and 14 scaled historical earthquake ground motion records of increasing intensity. The performance of the structure was satisfactory considering the seismic loads it was subjected to. The paper summarizes the design of the specimen and the major findings from the shake‐table tests, including the dynamic response, the load resistance, the evolution of damage, and the final failure mechanism. Copyright © 2011 John Wiley & Sons, Ltd.

Test sequence compaction methods for acyclic sequential circuits using a time expansion model

AbstractTest sequences for acyclic sequential circuits can be generated by using a time expansion model. In this paper, static and dynamic test sequence compaction techniques are proposed in which the test sequence generated by the time expansion model has two characteristics: (1) The test sequence length is constant, and (2) The location of an undefined value (X) for all primary inputs can be determined independently of test generation faults. First, a static test sequence compaction method is proposed that uses a template which is independent of the value of the test sequence. Then a dynamic test sequence compaction method is presented using reverse transform fault simulation, performing fault simulation for the time expansion model of the test pattern in which the test sequence after compaction is reverse‐transformed. As a result of application of the proposed method to acyclic sequential circuits made by using partial scan design, the test sequence length was reduced by 19 to 34%. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(10): 105–115, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1162

Efficient techniques for dynamic test sequence compaction

Dynamic test sequence compaction is an effective means of reducing test application time and often results in higher fault coverages and reduced test generation time as well. Three simulation-based techniques for dynamic compaction of test sequences are described. The first technique uses a fault simulator to remove test vectors from the test sequence generated by a test generator if the vectors are not needed to detect the target fault, considering that the circuit state may be known. The second technique uses genetic algorithms to fill the unspecified bits in a partially-specified test sequence in order to increase the number of faults detected by the sequence. The third technique uses test sequences provided by the test generator as seeds in a genetic algorithm, and better sequences are evolved that detect more faults. Significant improvements in test set size, fault coverage, and test generation time have been obtained over previous approaches using combinations of the three techniques.

A Simplified Model as the Basis for a Thermal Storage Test Procedure

A generalized thermal storage model is described whose parameters are identified using a test procedure. Provision is made for time and/or temperature dependent parameters. The same model is used for establishing the long term system performance. The equations describing the model are solved numerically with a scheme that yields high accuracy during the identification phase but great speed during the long term system simulation. Examples are given for the use of the model in the identification phase and in a “long term” five day dynamic test sequence. These results indicate that the generalized model is a promising basis for testing and comparing thermal storage devices.