Full-scale Shake Table Tests Research Articles

Full-scale shaking table tests of cross-laminated timber structures adopting dissipative angle brackets and hold-downs with soft-steel and rubber

Cross-laminated timber (CLT) has recently attracted significant interest in building timber or hybrid structures owing to the rapidly growing demand for low-carbon construction materials with excellent mechanical properties. To investigate the seismic performance of CLT structures adopting novel dissipative angle brackets and hold-downs with soft-steel and rubber (i.e., SRD-ABs and SRD-HDs), a series of shaking table tests were performed on two full-scale specimens, i.e., a benchmark specimen (Specimen Ⅰ) and a specimen with a multi-doorway at the ground (Specimen Ⅱ). Several representative ground motions, including the Turkey wave, El Centro wave, Wenchuan wave, and Shanghai artificial wave, were selected as excitations, whose peak acceleration increased gradually from 0.035 g to 0.80 g. The damage patterns of the structures were revealed, and the dynamic characteristics and responses were obtained and analyzed. The results show that the fundamental frequencies of Specimen Ⅰ and Specimen Ⅱ were 4.125 Hz and 3.625 Hz, respectively. The mode shapes of each specimen remained similar before tests with peak ground acceleration (PGA) of 0.51 g, with only a slight decrease of approximately 5 % in the fundamental frequency, indicating that the specimens only suffered minor damage because of the great energy-dissipating capacity of the SRD-ABs and SRD-HDs. After experiencing tests with PGA of 0.80 g, the specimen exhibited a maximum inter-story drift of 1/60 with a structural damping ratio of 13 %, and the damage was mainly exhibited at the SRD-ABs and SRD-HDs, which realized the performance objective of replaceability of dissipative connections and repairability of structures under the 9-degree rare earthquakes. Furthermore, non-linear numerical models were developed to duplicate the dynamic characteristics and responses of the test specimen, and the analytical results from the models show satisfactory agreement with the test results. Overall, the outcomes of this paper can provide valuable references for future research and applications of CLT structures with the SRD-ABs and SRD-HDs.

Dynamic identification and seismic capacity of an innovative cleanroom with walkable ceiling system

AbstractPast earthquakes highlighted the vulnerability of cleanrooms, especially in earthquake-prone countries like Italy; the post-earthquake reconnaissance showed that damage to cleanrooms led to immeasurable economic losses. This study investigates the seismic performance of an innovative cleanroom, seismically designed and provided with innovative components. Full-scale shake table tests were performed on the cleanroom according to ICC-ES AC156 protocol; the cleanroom was tested under operating conditions. Both dynamic properties and seismic behavior of the specimen were assessed. The tests showed the excellent seismic behavior of the cleanroom, confirming that simple devices can significantly improve the seismic performance of nonstructural elements.

Seismic behavior of discontinuous suspended ceiling system with boundary constraints

The boundary condition of the discontinuous suspended ceiling (SC) system has significant influence on its seismic performance. This study aims to comprehensively understand the seismic behavior of the discontinuous SC system with boundary constraints. Full-scale shaking table tests were conducted on a discontinuous SC specimen designed according to Chinese code firstly. Test results confirm that the damage to peripheral connections between the grid ends and the boundary could be effectively avoided. The grid connections are most vulnerable to earthquakes, and the main tee-cross tee connections closest to the fixed boundary are firstly damaged. Because of the strong constraints provided by seismic clips at the perimeter, the seismic responses at the middle of the ceiling are significantly larger than those at other locations. Secondly, an improved finite element model for this ceiling system is proposed, which can well predict its responses under the earthquake, such as acceleration and displacement, and damage status. The modeling efficiency is greatly improved by the developed automated modeling technique.

Unmanned Aerial Vehicle-Based Structural Health Monitoring and Computer Vision-Aided Procedure for Seismic Safety Measures of Linear Infrastructures.

Computer vision in the structural health monitoring (SHM) field has become popular, especially for processing unmanned aerial vehicle (UAV) data, but still has limitations both in experimental testing and in practical applications. Prior works have focused on UAV challenges and opportunities for the vibration-based SHM of buildings or bridges, but practical and methodological gaps exist specifically for linear infrastructure systems such as pipelines. Since they are critical for the transportation of products and the transmission of energy, a feasibility study of UAV-based SHM for linear infrastructures is essential to ensuring their service continuity through an advanced SHM system. Thus, this study proposes a single UAV for the seismic monitoring and safety assessment of linear infrastructures along with their computer vision-aided procedures. The proposed procedures were implemented in a full-scale shake-table test of a natural gas pipeline assembly. The objectives were to explore the UAV potential for the seismic vibration monitoring of linear infrastructures with the aid of several computer vision algorithms and to investigate the impact of parameter selection for each algorithm on the matching accuracy. The procedure starts by adopting the Maximally Stable Extremal Region (MSER) method to extract covariant regions that remain similar through a certain threshold of image series. The feature of interest is then detected, extracted, and matched using the Speeded-Up Robust Features (SURF) and K-nearest Neighbor (KNN) algorithms. The Maximum Sample Consensus (MSAC) algorithm is applied for model fitting by maximizing the likelihood of the solution. The output of each algorithm is examined for correctness in matching pairs and accuracy, which is a highlight of this procedure, as no studies have ever investigated these properties. The raw data are corrected and scaled to generate displacement data. Finally, a structural safety assessment was performed using several system identification models. These procedures were first validated using an aluminum bar placed on an actuator and tested in three harmonic tests, and then an implementation case study on the pipeline shake-table tests was analyzed. The validation tests show good agreement between the UAV data and reference data. The shake-table test results also generate reasonable seismic performance and assess the pipeline seismic safety, demonstrating the feasibility of the proposed procedure and the prospect of UAV-based SHM for linear infrastructure monitoring.

Damage inference and residual capacity assessment for an E-Defense 2018 ten-story RC test structure

This paper presents an enhanced vision-based, post-earthquake performance assessment framework for RC building structures. This framework incorporates a damage inference method that can estimate the stiffness and strength reduction factors of components in stories without damage inspection based on the inter-story drift. The framework was validated by the application to the full-scale shaking table test of an E-Defense 2018 ten-story RC structure. The vision-based damage detection method effectively detected multicategory seismic damage on the component surfaces, and the damage states estimated by the vision-based method were consistent with the results estimated by the measured plastic hinge rotation. The proposed inter-story drift-based damage inference method reasonably estimated the reduction factors of components in the stories without damage photos. The numerical model updated by the reduction factors of damaged components provided accurate estimates of the fundamental vibrational frequencies after different levels of seismic shaking, and the drift-based inference method significantly improved the results compared with the trivial linear interpolation method. The residual capacity curves provided by pushover analysis of the updated model using the reduction factors as per FEMA 306 & Chiu et al. reasonably captured the hysteretic responses of the structure.

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.

Full-scale shaking table test on seismic performance of a steel frame with translational-type precast-concrete exterior wall panel

In order to investigate the deformation behavior, mechanical characteristics of connections, and failure mode of translational precast concrete wall-panels under earthquake loading, a full-scale two-story steel frame model was designed. This test model consisted of 12 precast concrete wall-panels connected with fixed connections at the bottom end and translational-type connections at the top end. This model passed the shaking table testing, and the results demonstrate that the translational-type precast concrete exterior wall panel can ensure the sufficient relative displacement between the wall panel and the main structure under large earthquake loads. It has sufficient capacity to adapt the deformation between the main structure and the wall panels. During the test, localized cracking was observed on the wall panel, while all connections remained in elastic state. The connections between precast concrete exterior wall panels exhibited good performance, that indicates it is an effective tool to protect frame building hangings with exterior wall panels under strong earthquake events.

Seismic Response of Reinforced-Concrete One-Storey Precast Industrial Buildings with Horizontal Cladding Panels

An extensive parametric study of the seismic response of one-storey precast buildings with horizontal cladding panels frequently used in Central Europe was conducted to analyse the panels’ influence on the overall response of buildings and to find out if the panels can be considered non-structural elements when they are attached to the main building with the connections typically used in practice in Central Europe. The studied structural system consisted of reinforced concrete columns and beams connected by dowels. Horizontal cladding panels were attached to columns using one of the most frequently used isostatic fastening systems. The top connections provided out-of-plane stability, and the bottom connections supported the panel in the vertical direction. The parametric study was preceded by extensive experimental research, including cyclic tests on connections and full-scale shaking table tests of whole buildings. The results of experiments were used to reveal the basic response mechanisms of panels and connections and to develop, validate and calibrate numerical models employed in the parametric study presented herein. Fifteen generalised structures with different masses and heights were subjected to 30 accelerograms with two peak ground acceleration (PGA) intensities of 0.3 g and 0.5 g, corresponding to significant damage and near-collapse limit states. The effects of the construction imperfections in connections, the silicon sealant panel-to-panel connections and different types of connections of the bottom panel to the foundation were analysed. The crucial parameter influencing the response was the displacement capacity of the connections, which was considerably affected by the construction imperfections and, consequently, difficult to estimate. It has been observed that in some buildings, particularly in shorter structures with smaller mass, cladding panels can have a somewhat more notable influence on the overall response. However, in general, when the considered types of connections are used, the panels can be considered as non-structural elements, which do not importantly influence the response of the main building. Owing to structural imperfections and relatively short available gaps, the failure of the considered top connections and falling of the panels is very likely in the high seismicity regions. In the most adverse cases, it can occur even in the moderate seismicity regions.

Joint state–parameter estimation for structures with seismic isolation and damping systems: Theoretical observability and experimental verification

The objective of this study is to examine the feasibility of estimating the parameters of various devices in seismic control systems and evaluating the maximum responses of the quantities of interest. The observability condition was applied to determine the sensor layout and modeling assumptions of the structure for the joint estimation problem and to eliminate unsuitable layouts. To estimate the parameters of multiple members at the isolation layer, including laminated rubber bearings, oil dampers, and elastic sliding bearings, and to evaluate the maximum response, an adaptive unscented Kalman filter was utilized. Moreover, the study investigated the influence of partially unmeasured inputs on the observability of the established system through a case study involving the base layer of the building model colliding with the retaining walls. Experimental data from a full-scale shaking table test on a seismic isolation building was used as an example for validation purposes. The results demonstrated that even under varying initial estimates, varying sensor layouts, and the occurrence of unmeasured impact forces, the parameters and maximum responses of interest can be estimated with acceptable accuracy when the observability condition is met.

Machine learning and model driven bayesian uncertainty quantification in suspended nonstructural systems

This paper presents a novel framework for the uncertainty quantification of inverse problems often encountered in suspended nonstructural systems. This framework adopts machine learning- and model-driven stochastic Gaussian process model calibration to quantify the uncertainty via a new blackbox variational inference that accounts for geometric complexity through Bayesian inference. The soundness of the proposed framework is validated by examining one of the largest full-scale shaking table tests of suspended nonstructural systems and accompanying simulated (numerical) data. Our findings indicate that the proposed framework is computationally sound and scalable and yields optimal generalizability.

Seismic and collapse behavior of existing high-rise steel buildings under long-period earthquakes

This work presented the experimental and numerical evaluation of the seismic and collapse behavior of Japanese existing high-rise steel buildings subjected to long-period ground motions (LPGMs). Initially, the experiment (E-Defense, 2008) was performed by the full-scale shaking table tests on a typical 21-story steel frame substructure. Accordingly, a nonlinear rotational spring model was used in the numerical modeling. In consideration of the stiffness/strength deterioration and fatigue fracture of beam-column connections, the cyclic pushover analysis was utilized to account for such effect using seismic response data from system-level testing. Subsequently, the numerical model parameters were derived and validated with the initial experiment on the high-rise steel frame substructure. Herein, a well agreement on the seismic failure behavior between simulation and experiment was found in this situation. Furthermore, both field-welded and shop-welded connections on the seismic performance were included for comparison. For the 21-story prototype steel building (built before 1970s), a series of numerical collapse analyses were performed. The above revised model using nonlinear static pushover analysis and time history analysis were conducted to simulate and compare the effects of connection details and composite slabs on the 21-story prototype building. Finally, a cyclic loading protocol for simulating LPGMs was proposed, and the related ultimate failure behavior of the high-rise building was analytically discussed. Critically, this work should provide a viable strategy to numerically simulate the seismic and collapse behavior of high-rise steel buildings in this progressing construction field.

Experimental and numerical investigation of seismic response of access floors based on shake-table tests using 2-story steel moment frame

In this study, a full-scale shake-table test was conducted utilizing a 2-story steel moment frame to evaluate the seismic performance of access floors (or raised floors). A total of four access floor specimens were fabricated that are typically used in offices and computer/server rooms. Based on test results, critical failure modes and nonlinear behavior of access floors were discussed in detail. Specimen utilizing a flexible 600 mm-high access floor (FH600-F) exhibited several cracks in its joint connection plates (or pedestal heads) before the specimen eventually collapsed under the 60% RRS intensity test (PFA = 0.65 g). Due to a partial pull-out of the pedestal heads from their supporting columns, a highly pinched hysteretic response was also observed. A simplified SDOF numerical model was presented that can effectively capture the complex pinching behavior of access floor specimens. Based on the calibrated numerical analysis, it was identified that the partial pull-out of pedestal heads caused about 60% strength loss during the reverse cyclic phase of the specimen, which was the main source of the high pinching. The specimen also exhibited severe stiffness-degradation, which may have resulted from the cracks that developed in a significant number of its joints. The initial stiffness of the specimen was reduced by about 30% before its eventual collapse. Extensive numerical analyses were also conducted to evaluate the effects of pinching and stiffness-degradation on the acceleration response of access floors based on the floor motions obtained from the time history analysis of four multi-story building models.

Full-scale shaking table tests and numerical studies of structural frames with a hybrid isolation system

A typical hybrid isolation system (HIS) incorporating natural-rubber bearings (NRBs) and nonlinear fluid viscous dampers (NFVDs) is proposed for seismic protection of critical equipment in nuclear power industrial buildings (NPIBs) under strong earthquakes. Design procedure with a parametric study towards the HIS considering various stiffness and damping values is first investigated via extensive nonlinear time history analyses. Then a preliminary recommendation for the specific structural demands of the considered system is proposed to direct the seismic design for both member- and system-level tests. Through a suite of full-scale shaking table tests on two typical NPIBs, the efficiency and reliability of the HIS are verified, in comparison to the structure with conventional rubber isolation system (RIS). The shaking table test results exhibit a superior behavior of the HIS in structural dual control strategies, i.e., transient acceleration control in critical equipment and bearing deformation control. Also, the HIS presents stable and resilient performances in both negligible residual bearing deformation and undetectable damage to structural/nonstructural components (containing the seismic isolated devices, i.e., NRBs and NFVDs). Finally, a three-dimensional finite element (FE) structural model and a single-degree-of-freedom (SDOF) system are successively developed to simulate the dynamic responses of the test structures. The well-validated SDOF FE model, serving as a reliable alternative for the isolated NPIBs, can be further utilized to facilitate practical design.

Shaking table test and numerical analyses of a full scale three-leaf masonry wall

This paper discusses the main results of a full-scale shaking table test campaign carried out under the auspices of the EU funded research project SERA, whose objective is to investigate the seismic performance of three-leaf masonry walls with weak lime-mortar joints. These masonry walls are widely found in seismic prone regions in the Mediterranean area, thus assessing their behaviour under dynamic actions is an important pre-requisite for the seismic vulnerability evaluation of a plethora of historical centres. The first part of the paper presents a preliminary study on the mechanical properties of the wall component materials that was carried out through an ad-hoc experimental campaign. The outcomes are of particular interest for the characterization of the mortar and of the infill materials, that were designed to reproduce the low strength that is typically found in old masonry buildings. The design of the masonry wall that was tested and the test set-up are presented next. The applied loading protocol consisted of the horizontal component of a ground motion record that is repeatedly applied to the shaking table with increasing intensity. Finally, the main results of the experimental test are discussed. The damage patterns, drift ratios and base shear are presented for the ground motion sequence. The results are also discussed through a dynamic capacity curve that shows the attainment of different limit states with increasing ground motion intensity. A set of nonlinear numerical simulations, both static and dynamic, using a 3D FE model of the wall verify the experimental study as they report good agreement with the experimental tests and exhibit stable numerical behaviour.

Evaluation of the seismic performance of butt-fusion joint in large diameter polyethylene pipelines by full-scale shaking table test

High-density polyethylene (HDPE) pipelines in nuclear power plants (NPPs) have to meet high requirements for seismic performance. HDPE pipes have been proved to have good seismic performance, but joints are the weak links in the pipelines, and pipeline failures usually initiate from the defects inside the joints. Limited data are available on the seismic performance of butt-fusion joints of HDPE pipelines in NPPs, especially in terms of defects changes inside the joints after earthquakes. In this paper, full-scale shaking table tests were performed on a test section of suspended HDPE pipelines in an NPP, which included straight pipes, elbows, and 10 butt-fusion joints. During the tests, the seismic load-induced strain of the joints was analyzed by strain gauges, and it was much smaller than the internal pressure and self-weight-induced strain. Before and after the shaking table tests, phased array ultrasonic testing (PA-UT) was conducted to detect defects inside the joints. The locations, numbers, and dimensions of the defects were analyzed. It was found that defects were more likely to occur in elbows joints. No new defect was observed after the shaking table tests, and the defects showed no significant growth, indicating the satisfactory seismic performance of the butt-fusion joints.

Seismic fragility analysis of suspended cable trays in civil buildings

The cable tray is a kind of non-structural component used to distribute the electric cable, which plays a vital role in maintaining the function of the building. Post-earthquake investigations proved that the collapse of the cable tray led to the loss of human life and business continuity. This study aims to understand the seismic fragility of typical suspended cable trays in civil buildings through full-scale shaking table tests and numerical simulation. Based on the shaking table test results, the damage states of the cable tray are defined. The finite element model for cable tray is established and verified by test results. The seismic fragility analysis of the cable tray is carried out by the incremental dynamic analysis method. The peak floor acceleration and the spectral acceleration are taken as intensity measures of seismic motions. The calculation results show that the peak floor acceleration is more suitable to be an intensity measure for the seismic fragility analysis of the cable tray. Seismic fragility curves of two typical types of cable trays are generated.

Seismic response mitigation of prefabricated industrial equipment structural frames through a hybrid isolation system

For reducing the excessive acceleration response of the critical equipment in a type of industrial equipment structural frames under strong earthquakes, a hybrid isolation system (HIS), incorporating linear natural rubber (LNR) and lead rubber (LR) bearings, is proposed. The efficiency and reliability of the HIS are verified through a series of full-scale shaking table tests on two prefabricated industrial moment resisting frames (MRFs), with respect to a corresponding fixed-base system (FBS). The structural dynamic characteristic and seismic performance of the two types of MRFs, i.e., reinforced concrete structure (RCS) and composite concrete-filled steel tube structure (CCFSTS), are examined both with the HIS and FBS subjected to a range of seismic intensities. The test results demonstrate the superior performance of the HIS in controlling transient acceleration response under near-fault, far-field and artificial ground motions. The average peak acceleration reduction coefficients (PARCs) of the HIS range between 75.60% and 79.51% in the two considered MRFs along two horizontal directions, with a strict satisfaction on the peak acceleration response for normal operation of the critical equipment. Also, the hysteretic behavior of the HIS is stable and controllable during the earthquake excitations. The peak transient displacement of the HIS is satisfactory, and the residual deformation is negligible even under the maximum considered earthquake (MCE) excitations. Besides, components of the two MRFs are undamaged during the whole test. Thus, with the capacity of protecting the acceleration-sensitive equipment and structural components, the proposed HIS possesses a great prospect in enhancing the structural resilience.

Finite-Element Modeling for Seismic Damage Estimation of Suspended Ceiling Systems

The seismic qualification and seismic performance assessment of suspended ceiling systems have been traditionally conducted through large-scale shake table testing. This experimentally-based approach not only involves significant financial and time resources but is also not flexible to evaluate several configurations of suspended ceiling systems. As an alternate approach, this paper discusses the development of a general finite-element (FE) model of suspended ceiling systems that accurately captures the propagation of damage observed during full-scale shake table testing using the commercial finite-element analysis software, Abaqus/Explicit. The results of the large-scale shake table testing on suspended ceiling systems conducted at the University at Buffalo as part of the NEES nonstructural project were used to validate the FE model. The major components of suspended ceiling systems such as grid runners, ceiling tiles, and hanger wires were modeled and assembled with significant detail in the FE model. The properties of the connections between the grid runners, which are vital for capturing the seismic behavior of suspended ceiling systems were derived numerically. A user-defined subroutine was incorporated in the Abaqus/Explicit software framework to capture the multidirectional pinched hysteretic behavior of the connections between grid runners. An illustrative example of the application of the proposed FE model to develop robust numerically generated fragility curves for suspended ceiling systems is presented.

A Modified Full-Scale Experimental Method on the Seismic Performance of Complex Façade System

ABSTRACT The façade system is one type of building envelope. It is both acceleration sensitive and displacement sensitive under dynamic loads. However, some novel complex façade systems lack comprehensive study, especially under earthquake excitations, and full-scale shaking table test for both façade system with the main structure is expensive. Thus, a test design procedure is proposed, which includes the input excitations into the façade by using the finite element method (FEM) model, and aims for achieving acceleration and drift demands for acceleration-and-displacement sensitive nonstructural components (NCs). According to this procedure, full-scale shaking table tests for the façade system only are designed and conducted under different earthquake intensity levels. The responses (such as acceleration and displacement) are recorded, and critical damages (such as the relative residual displacement between panels and bolt scratch) are observed. Several key factors that affect the seismic performance, such as the component acceleration amplification factor and the required distance to prevent collision between panels, are discussed.

MAXIMUM SEISMIC RESPONSE PREDICTION BASED ON CAPACITY SPECTRUM METHOD FOR VIBRATION-CONTROLLED CEILING STRUCTURE EMPLOYED PULLEY MECHANISM

This paper proposes a new procedure for predicting the maximum seismic response based on the capacity spectrum method (CSM) for the passively controlled suspended ceiling structures named “Pulley Damper Ceiling System (PDCS)”. The structural system has a supplemental nonlinear viscous damper and a bilinear hysteretic damper in parallel with displacement amplification mechanisms of block and tackle pulley system. The single degree-of-freedom model of the PDCS is initially discussed. The accuracy of a simplified calculation method for obtaining the structural equivalent damping coefficient, determined by the sum of the inherent damping and the square root of sum of squares (SRSS) of each damping provided by the nonlinear viscous damper and the bilinear hysteretic damper, is verified by comparing with the full-scale shake table test results of the PDCS. Then, the pseudo capacity curve of the structure is generated by continuously plotting the transition of maximum force and displacement values under different amplitudes of sinusoidal waves. Finally, the availability of the response prediction based on proposed CSM procedure considering floor response spectrum (FRS) is examined by the comparison of time history analysis results, and the sufficient accuracy to evaluate the seismic response is confirmed.