National Center For Research On Earthquake Engineering Research Articles

CRACK OBSERVATION OF RC-WALL EXPERIMENTS USING IMAGE MEASUREMENT

This paper presents the image-based measurement for a set of reinforced concrete (RC) wall experiments. The experiments were carried out at the multi-axial testing system (MATS) in National Center for Research on Earthquake Engineering (NCREE) in Taipei, Taiwan. Four specimens of RC walls with different aspect ratios, tie spacing, axial forces were subjected to displacement controlled cyclic loadings. Image measurement were employed to estimate the major displacements, deformations, and crack distributions. The measurement verifies the crack development and the failure mechanisms at different specimens. In addition to the measurement results of the experiments, this paper introduces the procedures of the image-based measurement, as well as the software tools developed in this work. The measurement procedures include camera calibration, image tracking of major points on the specimens, three-dimensional triangulation, image projection and rectification, deformation analysis, and crack analysis. The crack pattern and their opening widths of several selected time points during the experiment are briefly displayed.

Rapid damage assessment of 1/3 scaled-down two-story reinforced concrete school building models

ABSTRACT This study presents a damage assessment scheme for seismically excited torsion-coupled nonlinear buildings based on the normalized relative displacement vibration shape (NRDVS). In order to investigate the applicability of the proposed NRDVS, the relative displacements are obtained from a real-time structural response integrator (RTSRI) by integrating the relative accelerations simulated from multiple-degree-of-freedom nonlinear models. As a result, the normalized inter-story drift ratio (NIDR) calculated by differencing the normalized displacements of the two successive floors of NRDVS and dividing by the story height can reveal the damaged floors as well as the location of damaged building members. Furthermore, the proposed damage assessment scheme is validated by observing the experimental measurements of shaking table tests of three 1/3 scaled-down two-story reinforced concrete school building models conducted at the National Center for Research on Earthquake Engineering (NCREE), Taipei, Taiwan.

Shake table tests of seven-story reinforced concrete structures with torsional irregularities: Test program and datasets

The shake table tests presented in this article aims to explore seismic displacement demands for existing reinforced concrete buildings resulting from inelastic torsion associated with different sources of irregularities. Two half-scale seven-story reinforced concrete structures were subjected to unidirectional earthquake excitations on the shake table at the National Center for Research on Earthquake Engineering (NCREE) Tainan laboratory. The specimens reflected structural weaknesses of buildings which collapsed during the Meinong earthquake in Taiwan. This data paper presents an overview of the project as well as the organization of obtained test datasets. The data are available for public use under the Designsafe-CI project “Shake table tests of seven-story reinforced concrete structures with torsional irregularities.”

3D modeling of the ground deformation along the fault rupture and its impact on engineering structures: Insights from the 1999 Chi-Chi earthquake, Shigang District, Taiwan

The reactivation of the Chelungpu Fault triggered the 1999 Chi-Chi Mw 7.6 earthquake, resulting in substantial ground surface ruptures and severe damage. After the earthquake, the surveys organized by the Central Geology Survey (CGS) of Taiwan and the National Center for Research on Earthquake Engineering (NCREE) immediately investigated a variety of cases related to engineering structures damaged by substantial ground deformation. The investigations gathered valuable in-situ data before human activities disturbed the local setting and altered co-seismic features of interest, providing opportunities for studying the interaction between surface rupture and engineering structures. This study outlines the reconnaissance of damaged engineering structures in Shigang District that cover three typical types of foundations and analyzes the fault geometry and fault slip at the local scale to construct a geomechanical model for numerical simulation. In addition, 3-dimensional (3D) modeling was performed for each case study to investigate the damage mechanisms of the structures subjected to the substantial ground deformations by using PFC3D (Particle Flow Code 3D), which is based on the discrete element method (DEM). The results of the DEM analyses, which have been calibrated with the in-situ data, showed the ability to evaluate the overall ground deformation, the detection of structural movement, and the critical elements of progressive collapse during faulting. This study demonstrates that the 3D DEM simulation is a reliable analysis tool for studying earthquake fault rupture-overburden layer-engineering structure interactions and can produce useful information for hazard assessment with an acceptable computation time. The 3D DEM analysis is therefore suggested to be applied to assess the potential damage scenarios for the engineering structures located in active fault zones.

Inelastic behavior and seismic design of multistory chevron-braced frames with yielding beams

Chevron or inverted V-braced frames offer numerous architectural and structural advantages, but the current special concentrically braced frame (SCBF) seismic-design requirements in the American Institute of Steel Construction (AISC) Seismic Provisions for Structural Steel Buildings lead to deep, heavy chevron beams; as a result, few chevron SCBFs are built today. Recent research on single-story chevron SCBFs demonstrated that beam yielding can be advantageous at higher demand levels, and design for large, inelastic unbalanced brace-force demands may still result in acceptable seismic performance. However, this prior research did not consider the response of multistory frames. In particular, questions remain as to the potential for concentration of damage, the impacts of composite slabs, and the effects of different beam-to-column connections; these issues can only be investigated using multistory frames. A companion research program was conducted to investigate multistory systems with chevron SCBFs using experimental and computational simulation methods. In the first phase of the research, a three-story chevron SCBF designed to permit beam yielding was tested at the National Center for Research on Earthquake Engineering (NCREE) Laboratory in Taipei, Taiwan. The test results were then used to validate a nonlinear, continuum finite-element model. A limited parametric study was conducted to build upon and further the experiments, specifically to evaluate different beam strengths and stiffnesses. These results were combined to develop design recommendations for chevron SCBFs with yielding beams.

Developing base domain ontology from a reference collection to aid information retrieval

Abstract Information Retrieval (IR) is a common technique used to manage a growing technical document collection. Owing to the complexity of technical documents, the direct application of IR often leads to unsatisfactory results. Therefore, many semantic approaches, such as ontology, are applied to enhance IR performance. However, ontology development is often a labor-intensive process and the availability of ontologies significantly influences the applicability of IR. Consequently, many efforts are dedicated to the automation of the ontology development process for reducing the human labors. In addition, reference collections, which are developed as the golden standards to evaluate IR performance in many IR research, can be regarded as an available resource for ontology development. To ease domain ontology development for supporting IR, this research proposes a semi-automated approach to develop a base domain ontology from a reference collection. This research also validates the base ontology on an Earthquake Engineering reference collection, called the NCREE (National Center for Research on Earthquake Engineering) collection. The results reveal that the human workload of the proposed approach is affordable. Furthermore, the base domain ontology can help achieve a satisfactory IR performance.

Steel Structures Research Update:Seismic Performance and Design of Steel Panel Dampers for Steel Moment Frames

Ongoing work on the seismic performance and design of steel panel dampers for steel moment frames is highlighted. Dr. Keh-Chyuan Tsai, professor in the Department of Civil Engineering at National Taiwan University, leads the team from National Taiwan University and the National Center for Research on Earthquake Engineering (NCREE) in Taipei. In 2018, At NCREE, one recent collaboration with the University of Washington included cyclic tests of a three-story chevron special concentrically braced frame (SCBF). Current seismic design provisions require large beam sizes to resist the unbalanced forces from the chevron braces after brace buckling. The research has explored options for alternative ductile mechanisms and reduced beam sizes. Steel research at NCREE has also included studies on steel beam-to-box-column moment connections and electro-slag-welded (ESW) joints in those connections. Meanwhile, research into premature fracture of ESW diaphragm-to-column joints in beam-to-box-column connections has revealed sensitivity to eccentricity in loading between the beam flange and the diaphragm. Further, a micromechanical-based stress-modified critical stress (SMCS) model has been developed and shown to be capable of predicting the crack initiation of the diaphragm-to-column ESW joint (Li et al., 2018).

FE simulation of cylindrical RC containment structures under reserved cyclic loading

The nuclear containment structure is one of the most important infrastructure systems ensuring the safety of a nuclear power plant. The structural behavior of a cylindrical containment structure made of reinforced concrete (RC) with large dimensions and numerous rebars is complex and difficult to predict. The complex behavior of the RC containment structure has been investigated in an international collaboration project between the National Center for Research on Earthquake Engineering (NCREE) in Taipei, Taiwan and the University of Houston (UH), Houston, Texas. At NCREE two 1/13 scaled cylindrical RC containment specimens were tested under reversed cyclic loads [1]. At UH, a finite element simulation of the two tested specimens was developed using a finite element analysis (FEA) program SCS [2]. In the program, a new shell element, the so-called CSMM-based shell element, was developed based on the Cyclic Softened Membrane Model [3] and the formulation of an 8-node Serendipity curved shell element [4] with a multi-layer approach [5]. The UH simulated seismic behavior was close to the NCREE experimental results. This paper presents the theoretical development of the FEA program SCS and the comparisons of its predictions with the experimental structural behavior of the two RC containment specimens. This simulation model and the FEA program are excellent tools to develop effective performance-based design provisions.

A structural health monitoring system based on multifractal detrended cross-correlation analysis

In recent years, multifractal-based analysis methods have been widely applied in engineering. Among these methods, multifractal detrended cross-correlation analysis (MFDXA), a branch of fractal analysis, has been successfully applied in the fields of finance and biomedicine. For its great potential in reflecting the subtle characteristic among signals, a structural health monitoring (SHM) system based on MFDXA is proposed. In this system, damage assessment is conducted by exploiting the concept of multifractal theory to quantify the complexity of the vibration signal measured from a structure. According to the proposed algorithm, the damage condition is first distinguished by multifractal detrended fluctuation analysis. Subsequently, the relationship between the q-order, q-order detrended covariance, and length of segment is further explored. The dissimilarity between damaged and undamaged cases is visualized on contour diagrams, and the damage location can thus be detected using signals measured from different floors. Moreover, a damage index is proposed to efficiently enhance the SHM process. A sevenstory benchmark structure, located at the National Center for Research on Earthquake Engineering (NCREE), was employed for an experimental verification to demonstrate the performance of the proposed SHM algorithm. According to the results, the damage condition and orientation could be correctly identified using the MFDXA algorithm and the proposed damage index. Since only the ambient vibration signal is required along with a set of initial reference measurements, the proposed SHM system can provide a lower cost, efficient, and reliable monitoring process.

The multi-axial testing system for earthquake engineering researches

Multi-Axial Testing System (MATS) is a 6-DOF loading system located at National Center for Research on Earthquake Engineering (NCREE) in Taiwan for advanced seismic testing of structural components or sub-assemblages. MATS was designed and constructed for a large variety of structural testing, especially for the specimens that require to be subjected to vertical and longitudinal loading simultaneously, such as reinforced concrete columns and lead rubber bearings. Functionally, MATS consists of a high strength self-reacting frame, a rigid platen, and a large number of servo-hydraulic actuators. The high strength self-reacting frame is composed of two post-tensioned A-shape reinforced concrete frames interconnected by a steel-and-concrete composite cross beam and a reinforced concrete reacting base. The specimen can be anchored between the top cross beam and the bottom rigid platen within a 5-meter high and 3.25-meter wide clear space. In addition to the longitudinal horizontal actuators that can be installed for various configurations, a total number of 13 servo-hydraulic actuators are connected to the rigid platen. Degree-of-freedom control of the rigid platen can be achieved by driving these actuators commanded by a digital controller. The specification and information of MATS in detail are described in this paper, providing the users with a technical point of view on the design, application, and limitation of MATS. Finally, future potential application employing advanced experimental technology is also presented in this paper.

Seismic performance of a two-story unsymmetrical reinforced concrete building under reversed cyclic bi-directional loading

Abstract Reinforced Concrete (RC) buildings are often subjected to multi-directional loadings under earthquake ground motions due to the structural configuration and inherent multi-dimensional earthquake motions. Previous researches have been focused on individual components with a few bi-directional tests. Essentially no research data, including experiment and simulation, exists for an entire unsymmetrical building under reserved cyclic bi-directional loading conditions. To provide a context for this complex problem, a test on a two-story reinforced concrete building subjected to bi-directional reversed cyclic loadings was performed at the National Center for Research on Earthquake Engineering (NCREE) in Taiwan to examine the torsional effect caused by the eccentricity of the building plan layout. The study was undertaken as part of an international collaboration project between the National Center for Research on Earthquake Engineering (NCREE), Taipei, Taiwan and the University of Houston (UH), Houston, Texas, USA. This paper presents the experiment and simulation of the building specimen. First, the test program is summarized including the descriptions of the test specimens, the test setup, the loading method and the experimental results. Then the numerical analyses conducted using a finite element analysis (FEA) program Simulation of Concrete Structure (SCS) developed at UH are presented. The predicted results turned out to agree very well with the experimental data. The results obtained from this research can be used to correlate analytical tools, new design methodologies and the capacity of design codes of such complex structures.

Critical limit states in seismic buckling‐restrained brace and connection designs

SummaryA welded end‐slot buckling‐restrained brace (WES‐BRB) has been developed at the Taiwan National Center for Research on Earthquake Engineering (NCREE). A steel frame equipped with a WES‐BRB can offer a cost‐effective solution to meet interstory drift and earthquake‐resistant design requirements for seismic steel buildings. According to the WES‐BRB and connection design procedure proposed by NCREE, there are seven key elements of a buckling‐restrained braced frame (BRBF) design that require design checking. In order to assist an engineer with the design of the WES‐BRB members and connections, an innovative cloud service named Brace on Demand has been constructed at NCREE. In this study, using 581 BRBF design examples, the effectiveness of the proposed design procedures to meet all design checks is demonstrated. It is found that the most critical limit states for an initial design are joint region buckling, gusset plate buckling, and gusset‐to‐beam and gusset‐to‐column interface strength. Accordingly, the causes of improper designs and associated strategies for improving the initial designs are discussed in this paper. Recommendations on initial selections including the BRB joint size and gusset plate thickness are given. The paper provides the detailed road map for engineers to develop the spreadsheet for BRB and connection designs. Copyright © 2014 John Wiley & Sons, Ltd.

Damage Detection of Hysteretic Structures with a Pinching Effect

Some civil engineering structures, such as RC frames, exhibit hysteretic behavior when subject to dynamic loads, such as earthquakes. The identification of hysteretic systems with stiffness and strength degradations is a practical but challenging problem encountered in the engineering field. A recently developed technique, referred to as the adaptive quadratic sum-square error with unknown inputs (AQSSE-UI), is capable of identifying time-dependent parameters of hysteretic structures. In this paper, the AQSSE-UI technique is applied to the parametric identification of hysteretic RC frames with stiffness and strength degradations and with the pinching effect. The performance of the AQSSE-UI technique will be demonstrated by the experimental data. A 1/3-scaled 2-story RC frame has been tested experimentally on the shake table at the National Center for Research on Earthquake Engineering (NCREE), Taiwan. This 2-story RC frame was subject to different levels of ground excitations back to back. The structure is first considered as an equivalent linear model with time-varying stiffness parameters, and the tracking of the degradation of the stiffness parameters is carried out using the AQSSE-UI technique. The same RC frame is then considered as a hysteretic model with plastic hinges following the generalized Bouc-Wen model, and the time-varying nonlinear parameters are identified. The equations of motion of the 2-story RC frame have been formulated based on the finite-element model, and the reduced-order system has been constructed to be used for the damage detection. Experimental results demonstrate that the AQSSE-UI technique is quite effective for the tracking of (1) the stiffness degradation of linear structures, and (2) the hysteretic parameters with stiffness and strength degradations and with the pinching effect.

Damage Localization of Structures Identified with a Deterministic-Stochastic Model

In this study, a scheme integrated with deterministic stochastic subspace system identification and the method of damage localization vector (DLV) is proposed for damage detection of structures based on seismic response data. A series of shaking table tests has been conducted in National Center for Research on Earthquake Engineering (NCREE), Taiwan. Damage condition is simulated by reducing the cross-sectional area of some of the columns at the bottom ends. Both single and multiple damage conditions at various locations have been considered. Full or partial observation conditions have been taken into account in the system identification analysis. It has been shown that local damages (stories) can be identified from global responses of the structure to earthquakes if sufficiently observed.

Seismic Upgrading Strategy for Near-Fault School Buildings in Taiwan

All types of school buildings were seriously damaged in Taiwans 921 Chi-Chi earthquake. Seismic evaluation and retrofit of these numerous vulnerable school buildings has become an important issue to be resolved. The National Center for Research on Earthquake Engineering (NCREE), Taiwan assisted the Ministry of Education on the arrangement of programs to accelerate retrofit and rebuilding works of elementary school, junior high school, senior high school and vocational school buildings, as part of the project called, Economic Recovery Act. Based on the database for seismic assessments and retrofits of school buildings, this study recommends a seismic upgrading procedure of near-fault school buildings. The proposed procedure can control effectively the seismic upgrading progress of near-fault school buildings. It also provides suggestions on the seismic retrofitting and reconstruction plans of near-fault school buildings to reduce damages and losses in a possible seismic event.

Investigation of the seismic response of three-story special concentrically braced frames

Special concentrically braced frames (SCBF) are stiff, strong and economical lateral-load resisting systems, which can sustain large inelastic deformation if properly detailed. Historically, experimental research on the seismic response of braced frame research has focused on the cyclic and monotonic responses of isolated components, such as braces or gusset plate connections. However, these components do not work in isolation, and recent research shows that accurate evaluation of their seismic performance requires consideration of the complete system. A collaborative research program with investigators from National Center for Research on Earthquake Engineering (NCREE) in Taiwan, and the Universities of Washington (UW), California, and Minnesota was undertaken to investigate the full system response of SCBFs. The research results presented herein focus on two three-story SCBFs that were tested at the NCREE laboratory. The specimens evaluated a new design approach for midspan gusset plate connections. The two specimens had HSS or wide-flange braces in combination with framing members and connections typical of those used in a three-story building in regions of high seismicity. Composite, concrete slabs were placed on each story. The tests were designed using a recently proposed design method to balance the desired yield mechanisms and form yield hierarchy. The results demonstrate that multi-story SCBFs exhibit good inelastic seismic performance with proper design detailing. Together with prior test results, the test specimens advanced design recommendations for SCBFs, which result in thinner, more compact corner gusset plate connections, a rational method of dimensioning mid-span gusset plates, and a balanced-design procedure for enhanced ductility.

A Case Study of Earthquake Resistant Retrofit Design with Economical Braced Steel Frame System for a Primary School

This paper makes a case study of an elementary school in Feng-shan District, Kaohsiung City. According to “The handbook of seismic resistant evaluation standard for school buildings” issued by National Center for Research on Earthquake Engineering (NCREE) in 2009, this study analyzes elementary school building adopting braced steel frame retrofit system, conducts seismic evaluation, as well as compares its seismic performance with shear-wall retrofit structure and RC strengthening of columns . If space permits, braced steel frame retrofit system can be applied into school building retrofit scheme; its seismic performance is compared with shear wall and RC strengthening of columns proposals. Adopting shear wall or RC strengthening of columns retrofit would affect main structure system of school building. These constructions will make existing reinforced concrete school building crack, especially old school building whose structure strength is greatly influenced. Therefore, an economic braced portal frame systems are proposed as new way of retrofitting. This paper uses ETABS program to make a seismic evaluation for structural system of the study object. It also compares the research object with commonly-used shear wall retrofit and RC strengthening of columns retrofit, thus to judge whether it meets requirements stipulated in seismic standards issued by NCREE and provide an another alternative scheme for the primary school retrofit construction.

Full-scale fatigue tests of a cable-to-orthotropic bridge deck connection

Using a specially designed lever arm, full-scale fatigue tests of a cable-to-steel orthotropic bridge deck connection were conducted in the National Center for Research on Earthquake Engineering (NCREE). A 9.59 m long, 2.7 m high and 2.55 m wide full-scale bridge deck was constructed in the steel fabricator's shop. The specimen was then shipped and anchored on the strong floor in NCREE's laboratory. Four actuators were mounted horizontally on the reaction wall and connected to the top end of a steel lever arm. The lever arm was pin-anchored at the bottom end to the strong floor while its one-quarter point was attached to the rear end of the stay-cable anchor box. Two-million cycles of fatigue loads ranging between 3836 and 6759 kN were applied at the rear end of the stay-cable anchor box, and the forces of the fatigue test correspond to design dead load plus the maximum and minimum design live loads in the cable. Tests results confirmed that the full-scale welded cable-to-orthotropic bridge deck connection sustained two-million cycles of the stated loading without any sign of failure. Test results indicate that the strains observed in the test specimen can not be satisfactorily predicted by the FEM analysis with the model used in this study.

Implementation of a bio-inspired two-mode structural health monitoring system

A bio-inspired two-mode structural health monitoring (SHM) system based on the Naive Bayes(NB) classification method is discussed in this paper. To implement the molecular biology based Deoxyribonucleic acid (DNA) array concept in structural health monitoring, which has been demonstrated to be superior in disease detection, two types of array expression data have been proposed for the development of the SHM algorithm. For the micro-vibration mode, a two-tier auto-regression with exogenous (AR-ARX) process is used to extract the expression array from the recorded structural time history while an ARX process is applied for the analysis of the earthquake mode. The health condition of the structure is then determined using the NB classification method. In addition, the union concept in probability is used to improve the accuracy of the system. To verify the performance and reliability of the SHM algorithm, a downscaled eight-storey steel building located at the shaking table of the National Center for Research on Earthquake Engineering (NCREE) was used as the benchmark structure. The structural response from different damage levels and locations was collected and incorporated in the database to aid the structural health monitoring process. Preliminary verification has demonstrated that the structure health condition can be precisely detected by the proposed algorithm. To implement the developed SHM system in a practical application, a SHM prototype consisting of the input sensing module, the transmission module, and the SHM platform was developed. The vibration data were first measured by the deployed sensor, and subsequently the SHM mode corresponding to the desired excitation is chosen automatically to quickly evaluate the health condition of the structure. Test results from the ambient vibration and shaking table test showed that the condition and location of the benchmark structure damage can be successfully detected by the proposed SHM prototype system, and the information is instantaneously transmitted to a remote server to facilitate real-time monitoring. Implementing the bio-inspired two-mode SHM practically has been successfully demonstrated.

Development of PISA4SB for Applications in the Taiwan School Building Seismic Retrofit Program

The National Center for Research on Earthquake Engineering (NCREE) in Taiwan has implemented the static pushover procedures for the detailed seismic evaluation of school buildings. In the pushover analysis, the hinge properties of columns, beams, brick walls and RC walls are carefully calibrated based on the full scale experiments conducted in NCREE in the past ten years. Additionally, auxiliary modules for calculating the hinge properties have been developed by NCREE researchers to enhance user friendliness. This could allow engineers to more accurately apply available commercial software. However, when the auxiliary modules are applied to commercial software, the user must first define then assign the sections to the corresponding columns, beams, brick and RC walls in the text-based files. Without the graphic user interface, errors have commonly been found in cross-platform operations. The Platform of Inelastic Structural Analysis for 3D systems (PISA3D) has been developed since 2002 in NCREE. PISA3D provides a friendly user interface and high computational efficiency for engineers and researchers to simulate the nonlinear systems under various kinds of load effects. In order to resolve these issues noted above in the application to commercial software, NCREE has customized the nonlinear structural analysis program, PISA4SB (Platform for Inelastic Structural Analysis of School Buildings) specifically for the school building structures. PISA4SB allows the user to conveniently construct the analytical models for typical low-rise school buildings. After the gravity load analysis is conducted, PISA4SB automatically incorporates the column axial loads in calculating the parameters for the multilinear fracture material properties of any plastic hinge. PISA4SB evaluates the capacity curve and computes the seismic performance point based on the given design response spectrum provided by the user for the school building site. Engineers can conveniently apply PISA4SB to complete the seismic evaluation of a school building without cross-platform operations. The detailed development and example applications of PISA4SB are illustrated in this paper.