Full-scale Shake Table Tests Research Articles

Adaptive numerical method algorithms for nonlinear viscous and bilinear oil damper models subjected to dynamic loading

Adaptive numerical method algorithms are presented for the numerical simulation of the hysteretic behaviour of nonlinear viscous and bilinear oil dampers within a finite element program for nonlinear dynamic analysis of frame structures under earthquake excitations. The adaptive algorithms are applicable for computing high-precision solutions for nonlinear viscous and bilinear oil dampers with valve relief that are typically represented mathematically with a nonlinear Maxwell model. The algorithms presented possess excellent convergence characteristics for viscous dampers with a wide range of velocity exponents and axial stiffness properties. The algorithms are implemented in an open source finite element software, and their applicability and computational efficiency is demonstrated through a number of validation examples with data that involve component experimentation as well as the utilization of full-scale shake table tests of a 5-story steel building equipped with nonlinear viscous and bilinear oil dampers.

Quantitative investigation on collapse margin of steel high-rise buildings subjected to extremely severe earthquakes

Reponses of structures subjected to severe earthquakes sometimes significantly surpass what was considered in the design. It is important to investigate the failure mechanism and collapse margin of structures beyond design, especially for high-rise buildings. In this study, steel high-rise buildings using either square concrete-filled-tube (CFT) columns or steel tube columns are designed. A detailed three-dimensional (3D) structural model is developed to analyze the seismic behavior of a steel high-rise towards a complete collapse. The effectiveness is verified by both component tests and a full-scale shaking table test. The collapse margin, which is defined as the ratio of PGA between the collapse level to the design major earthquake level (Level 2), is quantified by a series of numerical simulations using incremental dynamic analyses (IDA). The baseline building using CFT columns collapsed with a weak first story mechanism and presented a collapse margin ranging from 10 to 20. The significant variation in the collapse margin was caused by the different characteristics of the input ground motions. The building using equivalent steel columns collapsed earlier due to the significant shortening of the locally buckled columns, exhibiting only 57% of the collapse margin of the baseline building. The influence of reducing the height of the first story was quite significant. The shortened first story not only enlarged the collapse margin by 20%, but also changed the collapse mode.

Full-scale shake table tests of the tension-only concentrically braced steel beam-through frame

The tension-only concentrically braced steel beam-through frame (TCBBF) has the potential to enhance the seismic and post-earthquake performance for low-rise buildings in low to moderate seismic regions. To a better understanding of the dynamic response of TCBBFs, full-scale shake table tests under different seismic hazard levels and aftershocks were conducted on a three-story structural model. From the test results, the damage-control and low-residual-displacement behaviors were verified firstly. Under maximum considered earthquake (MCE), the main frame nearly remained elastic while all the braces yielded and there was almost no residual displacement. Under stronger earthquakes exceeding the MCE, yielding occurred at the beam-column connections, and the main frame demonstrated pinching behavior. Meanwhile, the residual displacement of the structure was still at a very low level. The tension-only braces played a key role in the seismic behavior. The existence of prestress made the braces able to sustain a little compression and thus increased the initial lateral stiffness of the structure. The slackness of the brace would enlarge story drift response and also induce dynamic impact due to the sudden tensioning. This impact effect was effectively controlled because of the high ductility of the braces. Tightening the slack braces was a convenient way to restore the structural behavior if the main frame was not damaged.

Seismic performance of small earth dams with sloping core zones and geosynthetic clay liners using full-scale shaking table tests

In Japan, a large number of old small earth dams are in critical need of repair due to leakage and poor earthquake resistance. In addition to cohesive soils, geosynthetic clay liners (GCLs) are used as impervious materials to repair such dams. This paper discusses the seismic performance of small earth dams, with reservoirs on their upstream side, repaired with a sloping core zone and a GCL on the basis of the results of full-scale shaking table tests performed at the E-Defense facility. The main focus is on the differences in mechanical behavior between the upstream and downstream sides of the dam. The results elucidate that the effective stress of the upstream embankment materials increased because of the undrained shear behavior of the compacted soils, although the deformation on the upstream side was larger than that on the downstream side. A large phase difference in the measured accelerations between the upstream slope and the downstream slope was also observed. Therefore, it is concluded that significant differences occurred in the dynamic behavior of the upstream side and the downstream side.

Full-Scale Shaking Table Test and Analysis of Seismic Ceiling Systems

Full-Scale Shaking Table Test and Analysis of Seismic Ceiling Systems

Seismic testing and modeling of cylindrical electrical equipment with GFRP composite insulators

Glass fiber reinforced polymer (GFRP) composite is a desirable alternative to porcelain for insulators of cylindrical electrical equipment in electrical substation. However, mechanical properties of composite insulator in an event of earthquake are not fully known yet. This study aimed to investigate both the static and dynamic properties of GFRP composite insulators and electrical equipment through impact hammer test, quasi-static flexural tests and full scale shaking table tests. The flexural properties, in terms of flexural stiffness, damping and hysteretic behavior, were investigated, based upon which a mechanical model was proposed. Moreover, the possible failure modes were identified in order that a design and qualification procedure was recommended for engineering application. The procedure has been further validated by a full scale shaking table test of 1000 kV cylindrical composite electrical equipment.

Optimal design of isolation devices for mid-rise steel moment frames using performance based methodology

This paper develops and applies the performance-based analysis and design methodology to assess the seismic vulnerability of mid-rise steel moment frame structures and to optimally design the isolation devices to reduce the direct losses due to earthquake damages. An isolated steel moment frame, originally tested in the 2011 E-Defense blind prediction contest, is selected and modeled in detail. The numerical model and the predicted seismic responses of the structure are validated against the full-scale shaking table test results. Subsequently, the fragility functions are derived for the structure when subject to near-fault ground motions exhibiting distinctive acceleration or velocity pulses and far-field motions with less impulsive characteristics. To quantify the system level damage states of the building, the concept of total loss ratio (TLR) is applied as the performance index to account for the direct loss due to structural, non-structural and isolation components in relation to the total repair cost of the original structure. The TLR considers the failure probability (as defined by fragility functions), the damage percentage and related cost for each damage state. Finally, among various isolation designs, the optimal configuration is derived for cases with the minimum TLR. It is shown that the optimal design can reduce the TLR up to 90% of that of the un-isolated structure and it also outperforms the adopted design in the test program. The study demonstrates a systematic way of achieving the optimal isolation design with considerations of uncertainties in earthquake inputs and the combined structural and non-structural damages.

Shake table test of a full-scale four-story reinforced concrete structure and numerical representation of overall response with modified IMK model

This paper mainly addresses the validity and verification of our current code-based knowledge through the utilization of test data of benchmark structure in Japan. A full-scale, four-story reinforced concrete building within the 2010 E-Defense test program is revisited to assess the capability of the current state of practice for the prediction of the actual seismic response of reinforced concrete structures by taking advantage of invaluable data and high-quality measurement techniques applied during the tests. The detailing of the structural elements was in compliant with the Japanese seismic design code whereas minor modifications were applied to the final design of the structure to bring it closer to the selectively well-known US design practice. A series of full-scale shake table tests were performed by gradually increasing the two ground motions of the 1995 Hyogo-Ken Nanbu earthquake for reaching to the near collapse limit state. Global dynamic response characteristics of the structure due to damage accumulation were derived from the test data to trace the strength and stiffness deterioration in the force–deformation hysteresis. Even though the story drift angles were exceeded the critical 0.04 level beyond the limitations of code-provisions, the structure has preserved dynamic stability and its intact form. Based on the surveys and measurements performed at the end of each test, shear walls and beam–column joints were sustained the severe damage while the beams and columns were maintained their structural integrity during the entire test program. Parameters of advanced hysteretic models in the moment-resisting and shear wall frames were calibrated using test data for developing analytical models that can represent all modes of the cyclic deterioration under pinching action as an alternative to the customarily used Takeda model in Japan. For the transformation of MDOF system to equivalent SDOF system, a straightforward procedure is applied to adopt the global response characteristics to the versatile hysteretic model. Moreover, the capability of capturing the seismic response of RC system through advanced hysteretic models is justified. The test results and numerical analyses implied the necessity of further improvements on MLIT and US design provisions for the reduction of observed damages on structural elements particularly in shear walls and beam–column joints to achieve reparability goals.

Fully Floating Suspended Ceiling System: Experimental Evaluation of Structural Feasibility and Challenges

Full scale shake table testing is conducted on a novel type of suspended ceiling called fully floating ceiling system, which is freely hung from the floor above lacking any lateral bracing and connections with the perimeters. A gap is provided on all sides of the ceiling. Throughout different tests, a satisfactory agreement between the fully floating ceiling response and simple pendulum theory was demonstrated. When subjected to input motions with significant energy in the floating ceiling's resonant frequency, the horizontal displacement of the ceiling exceeded the gap width resulting in pounding induced large acceleration pulses. To mitigate such effects, the perimeter gap fillers of a compressible material are proposed. The addition of perimeter isolation was found effective in inducing extra damping and protecting the ceiling from pounding impact; resulting in much reduced ceiling displacements and accelerations. Throughout the tests a single panel dislodgement was observed as the only instance of damage.

Experimental Study of Large Area Suspended Ceilings

ABSTRACTDamage of nonstructural components during past seismic events was shown to be not only a critical threat to life safety in extreme cases but also led to substantial reduction of functionality of buildings and other facilities. Because of the complex construction of nonstructural and architectural components, current standards provide only limited guidance for the seismic design. Suspended ceiling systems are among the less understood important nonstructural/architectural components in buildings for which design standards provide limited guidance. To understand the dynamic behavior of suspended ceiling systems, a series of full scale shake table tests of 20 ft × 53 ft and 20 ft × 20 ft ceiling systems were conducted at the Structural Engineering and Earthquake Simulation laboratory (SEESL) at University at Buffalo (UB). For the full scale dynamic testing, a new test frame providing a continuous suspended ceiling area of 1,060 ft2 was constructed on the tandem shake tables and was equipped with an open-loop shake table compensation procedure. The combined designs of the physical frame and of the shake table motion controllers allowed simulating the required floor/roof motion according to ICC-ES AC156 standard at the roof of the test structure. Various test configurations were selected in order to determine the influence of different system conditions and the effects or efficiency of various protective systems required by the current standard ASTM E580 for seismic design. Based on the test data and the failure mechanisms observed, damage states are defined, and fragility curves are developed. The results of the fragility analysis show that a ceiling system becomes more vulnerable as (a) it is subjected to multi-directional input motions, (b) heavier tiles are installed, (c) the size of a ceiling area increases, and (d) lateral restraints are not installed. In addition, simplified numerical models that can capture the special behavior of ceiling systems are developed and presented in a companion paper. This paper presents the experimental study of large area suspended ceiling systems involving test setup and configurations, test motions generated by a unique control system, and basic lessons gained from the experiments.

Shake table assessment of gusset plate connection behaviour in concentrically braced frames

Diagonal bracing members and their connections to beams and columns are the key lateral resisting components in concentrically braced frames (CBFs). Although gusset plate connections are widely used to connect bracing and frame members in such systems, their design often involves significant simplifications and idealisations due to the complexity of their behaviour under seismic loading. A conventional approach, which utilises a standard linear clearance zone that permits out-of-plane brace deformation, is typically used in the design of gusset plates. This approach can result in overly large connections with cumbersome details. The desire to achieve an improved balance between the gusset over-strength, on the one hand, and a favourable overall frame performance coupled with practical connection detailing, on the other, has prompted proposals for an improved design approach. However, before new recommendations on the design of gusset plate connections can be provided for use in codified guidance, there is a need to assess the performance of such detailing alternatives under realistic earthquake loading conditions. Accordingly, in this study, the performance of different brace connection configurations and gusset plate designs are examined using shake table testing. The paper describes twelve single-storey full scale shake table tests, which were performed on the AZALEE seismic testing facility at CEA Saclay. In seven of these tests, the gusset plates at the end of the brace members were connected to both beam and column flanges, while in the other five tests these were connected to the beam flange only. Conventional gusset plate design with a standard linear clearance was used for six tests, whereas a more balanced design with a nonlinear elliptical clearance detail was used for the others. The experimental set-up, specimen details, and loading procedures are presented, together with a detailed account of the results and observations. The main findings and their implication on the performance at the local component, as well as the overall frame levels, are highlighted. In particular, it is shown that, provided a number of recommendations are followed, the balanced design approach using a nonlinear clearance can enhance the overall drift capacity, while maintaining control of the failure mode within the bracing member.

Mass Timber Rocking Panel Retrofit of a Four-Story Soft-Story Building with Full-Scale Shake Table Validation

Soft-story wood-frame buildings have been recognized as a disaster preparedness problem for decades. There are tens of thousands of these multi-family three- and four-story structures throughout California and other cities in the United States. The majority were constructed between 1920 and 1970, with many being prevalent in the San Francisco Bay Area in California. The NEES-Soft project was a five-university multi-industry effort that culminated in a series of full-scale soft-story wood-frame building tests to validate retrofit philosophies proposed by (1) the Federal Emergency Management Agency (FEMA) P-807 guidelines and (2) a performance-based seismic retrofit (PBSR) approach developed within the project. Four different retrofit designs were developed and validated at full-scale, each with specified performance objectives, which were typically not the same. This paper focuses on the retrofit design using cross laminated timber (CLT) rocking panels and presents the experimental results of the full-scale shake table test of a four-story 370 m2 (4000 ft2) soft-story test building with that FEMA P-807 focused retrofit in place. The building was subjected to the 1989 Loma Prieta and 1992 Cape Mendocino ground motions scaled to 5% damped spectral accelerations ranging from 0.2 to 0.9 g.

Considering seismic interaction effects in designing steel supporting structure for surge arrester

Porcelain surge arrester is common in electrical substation and is vulnerable in earthquakes. In most cases, surge arrester needs to be mounted on the top of a steel supporting structure. The seismic response behaviors and failure modes of a steel supporting structure – surge arrester system are critical for the safety and reliability of substations. This paper aims at investigating such interaction effects on the seismic responses of surge arrester. Porcelain surge arresters in 220kV, 500kV, 750kV and 1000kV are considered in this study. Earthquake induced flexural stress and displacement are identified as key response parameters of a steel supporting structure – surge arrester system based on a full-scale test of 1000kV porcelain surge arrester. Analytical model of the system was then developed and verified by full-scale shaking table test. The effects of supporting structure on the bending moment and displacement responses are then investigated through time history analysis, modal analysis and a parametric study. Finally, a structural design procedure is proposed for selecting suitable value of flexural rigidity of the steel supporting structure.

全尺寸钢筋混凝土桥墩柱ABAQUS动力分析

本文提出两个纤维梁单元混凝土模型。模型由拉压骨架曲线和加载卸载路径组成，其中，受拉骨架曲线由弹性和线性软化两段组成；受压骨架曲线由线性弹性和随后EN 1992版欧盟混凝土规范建议公式结合KENT-PARK模型组成，其混凝土峰值压应力，对于非约束混凝土采用圆柱体抗压强度，对于约束混凝土采用KENT-PARK模型计算。加载卸载路径分别采用OpenSees的CONCRETE01和CONCRETE02模型路径。依据ABAQUS平台的用户材料接口UMAT，开发了两个适用于纤维梁单元的混凝土模型用户子程序，F1-CON和F2-CON。通过对比全尺寸振动台试验各项结果，本文开发用户子程序与模拟方法的可靠性得到验证，结果表明用户子程序能很好地反映受地震荷载作用的钢筋混凝土柱强度与刚度的退化，模型可以广泛用于精细化模拟钢筋混凝土柱及其它弯曲构件。 Two fiber-beam-element concrete models are presented. The models are comprised of a tension/compression envelope and unload/reload path. The tension envelope contains an elastic range and a linear soft zone. The compression envelope also includes a linear elastic range followed by the formulation of Eurocode No. EN 1992 and KENT-PARK model, whose peak stress is the concrete cylinder compressive strength for the unconfined concrete and is calculated by the KENT-PARK model for the confined concrete. The unload/reload paths of OpenSees CONCRETE01 and CONCRETE02 are used. According to UMAT interface provided by ABAQUS platform, two user subroutines of concrete, F1-CON and F2-CON, are developed for fiber beam element. By means of comparison with the results of a full scale shaking table test, reliabilities of the user subroutines and modeling methods were validated. The results show that the subroutines can well reflect strength and stiffness degradation of reinforced concrete columns produced by earthquake loading. The subroutines are widely applicable to refined simulation of concrete columns or other flexural members widely.

Direct displacement based seismic design for single storey steel concentrically braced frames

The direct displacement based design (DDBD) approach is spreading in the field of seismic design for many types of structures. This paper is carried out to present a robust approach for the DDBD procedure for single degree of freedom (SDOF) concentrically braced frames (CBFs). Special attention is paid to the choice of an equivalent viscous damping (EVD) model that represents the behaviour of a series of full scale shake table tests. The performance of the DDBD methodology of the CBFs is verified by two ways. Firstly, by comparing the DDBD results with a series of full-scale shake table tests. Secondly, by comparing the DDBD results with a quantified nonlinear time history analysis (NLTHA). It is found that the DDBD works relatively well and could predict the base shear forces (<TEX>$F_b$</TEX>) and the required brace cross sectional sizes of the actual values obtained from shake table tests and NLTHA. In other words, when comparing the ratio of <TEX>$F_b$</TEX> estimated from the DDBD to the measured values in shake table tests, the mean and coefficient of variation (<TEX>$C_V$</TEX>) are found to be 1.09 and 0.12, respectively. Moreover, the mean and <TEX>$C_V$</TEX> of the ratios of <TEX>$F_b$</TEX> estimated from the DDBD to the values obtained from NLTHA are found to be 1.03 and 0.12, respectively. Thus, the DDBD methodology presented in this paper has been shown to give accurate and reliable results.

Special Issue on Seismic Resistant Timber Structures

In the last decade, there has been a renewed interest in timber buildings around the world, owed in part to the naturally optimal structural properties of timber and to the environmental advantages of building with timber. Several midrise buildings have been constructed, including a nine-story building in London, a ninestory building in Milan, and a 10-story building in Melbourne. A 14-story building is being constructed in Norway, and even taller timber buildings have been designed in Sweden, Austria, and Canada. Timber is a lightweight material and, as such, performs particularly well in moderate to intense earthquakes. However wood itself is not ductile and can have brittle failure modes, such as splitting, if not addressed properly within the seismic design procedure. A large body of research has been completed, and a number of projects are under way worldwide on the seismic behavior of timber structures and buildings. Full-scale shake table tests have been conducted in Japan, the United States, and Europe on an array of designs. Extensive component and joint testing has also been completed, and advanced numerical models developed. An effort has been made to implement this new knowledge in codes of practice, such as the Eurocode and the New Zealand and the Canadian standards. This special issue brings together papers from the key researchers all over the world working on the seismic resistance of timber structures. It includes a forum paper and 17 technical papers presenting research carried out in the United States, Canada, Italy, Germany, Slovenia, China, Japan, and New Zealand. Five topics are addressed: (1) light-frame timber buildings, (2) retrofit of existing light-frame timber buildings, (3) cross-laminated timber buildings, (4) innovative rocking and hybrid heavy timber walls, and (5) alternative bracing systems.

Evaluation of Simplified and State-of-the-Art Analysis Procedures for Steel Frame Buildings Equipped with Supplemental Damping Devices Based on E-Defense Full-Scale Shake Table Tests

This paper summarizes a number of key findings that affect the use of linear and nonlinear analysis procedures for the seismic evaluation of steel frame buildings with supplemental damping devices and in particular, buckling-restrained braces (BRBs) and nonlinear viscous dampers (NVDs). The assessment is based on a comparison of various engineering demand parameters (EDPs) with experimental data obtained from a series of full-scale shaking table tests of a five-story steel building equipped with BRBs and NVDs. It is shown that: (1) there is no clear advantage between three-dimensional (3D) and two-dimensional (2D) analyses in the prediction of the dynamic behavior of regular plan view steel frame buildings regardless of the damper type; (2) incorporating the brace and nonlinear viscous damper axial flexibility in the analytical model of the test structure with NVDs significantly improves the overall numerical predictions; and (3) the current effective damping ratio recommended by ASCE 41-13 as part of linear static procedures for the evaluation of frame buildings with BRBs or NVDs may not be conservative enough. A new performance-based design tool called performance-spectra (P-Spectra) is able to reliably predict the EDPs of interest. The P-Spectra tool is also able to validate the efficiency of various damper solutions on the dynamic performance of the test structure. It is demonstrated that P-Spectra can be employed to predict estimates of potential residual deformations that traditional linear and nonlinear static procedures cannot.

Seismic Proofing Capability of the Accumulated Semiactive Hydraulic Damper as an Active Interaction Control Device with Predictive Control

The intensity of natural disasters has increased recently, causing buildings’ damages which need to be reinforced to prevent their destruction. To improve the seismic proofing capability of Accumulated Semiactive Hydraulic Damper, it is converted to an Active Interaction Control device and synchronous control and predictive control methods are proposed. The full-scale shaking table test is used to test and verify the seismic proofing capability of the proposed AIC with these control methods. This study examines the shock absorption of test structure under excitation by external forces, influences of prediction time, stiffness of the auxiliary structure, synchronous switching, and asynchronous switching on the control effects, and the influence of control locations of test structure on the control effects of the proposed AIC. Test results show that, for the proposed AIC with synchronous control and predictive control of 0.10~0.13 seconds, the displacement reduction ratios are greater than 71%, the average acceleration reduction ratios are, respectively, 36.2% and 36.9%, at the 1st and 2nd floors, and the average base shear reduction ratio is 29.6%. The proposed AIC with suitable stiffeners for the auxiliary structure at each floor with synchronous control and predictive control provide high reliability and practicability for seismic proofing of buildings.

Seismic stability of interconnected glove boxes

Glove boxes are extensively used in a nuclear industry to handle hazardous materials. They are generally interconnected with each other through a flexible link and stand freely on the floor. To check the seismic stability of the interconnected glove boxes and evaluate safety margins in design, extensive full scale shake table testing of two interconnected glove boxes had been carried out. Objective was to observe effects of rigid body and elastic motions, arising due to base excitation, on stability and integrity of the system. It was observed that sliding was predominant mode of motion with associated low amplitude rocking motion. Elastic deformations were very limited to affect the integrity of the system. It was observed that to increase seismic stability of the interconnected glove box system, relative sliding displacement between the two should be controlled.Further to shake table testing, nonlinear time history finite element analysis was also carried out. Analysis results were found to be coherent with the corresponding test results. In addition to that, to determine a safe upper bound on sliding displacement, a numerical method is proposed. This paper discuss the test results to enhance understanding of seismic behavior of two interconnected glove boxes. Important interpretations are accentuated to give a clear understanding to the designers.

Dynamic properties of typical consultation room medical components

The dynamic response of typical components of a consultation room in hospital buildings is investigated through full-scale shake table tests. Low-intensity random vibration tests were carried out on two freestanding medical cabinets and a desk. The natural frequency and the damping ratio of the components are evaluated via standardized methods.Simplified finite element models of the tested components are implemented in order to assess whether simplified models can adequately describe the dynamic behavior of medical components. The outcomes of the numerical analyses fairly match the results obtained from the experimental tests. It is demonstrated that simple models are able to adequately simulate the dynamic properties of sample medical components and can be employed in the earthquake response analysis of healthcare facilities.