Results Of Nonlinear Dynamic Analyses Research Articles

Performance-Based Seismic Design and Evaluation of Fused Steel Diagrid Frame

A fused steel diagrid frame (FSDF) is an innovative earthquake resilient structural system. FSDF combines the steel diagrid structural system with shear links (SLs) and moment connections (MCs) to dissipate earthquake energy. SLs are placed between diamond-shaped grid units and serve as the primary seismic force-resisting system (SFRS). MCs provide the additional resistance as the secondary SFRS. To facilitate the design of the proposed FSDF system, a performance-based equivalent energy design procedure (EEDP) is utilized to design a prototype building. EEDP allows designers to select multiple performance objectives under different earthquake hazard intensities. A detailed finite element model is developed to simulate the nonlinear dynamic response of the structure under earthquake shaking intensities. The results of nonlinear dynamic analyses show that the FSDF has superior seismic performance and can be efficiently designed using EEDP. Lastly, detailed collapse risk assessment of the prototype building utilizing the FSDF is conducted using the Federal Emergency Management Agency FEMA P695 (2009) methodology. The result shows that the EEDP-designed FSDF has superior margin against collapse.

Pulse‐like versus non‐pulse‐like ground motion records: Spectral shape comparisons and record selection strategies

SummaryPulse‐like records are well recognized for their potential to impose higher demands on structures when compared with ordinary records. The increased severity of the structural response usually caused by pulse‐like records is commonly attributed to the spectral increment around the pulse period. By comparing the building response to sets of spectrally equivalent pulse‐like and ordinary records, we show that there are characteristics of pulse‐like records beyond the shape of the acceleration response spectrum that affect the results of nonlinear dynamic analysis. Nevertheless, spectral shape together with the ratio of pulse period to the first‐mode structural period, Tp/T1, are confirmed as “sufficient” predictors for deformation and acceleration response metrics in a building, conditioned on the seismic intensity. Furthermore, the average spectral acceleration over a period range, AvgSA, is shown to incorporate to a good proxy for spectral shape, and together with Tp/T1, form an efficient and sufficient intensity measure for response prediction to pulse‐like ground motions. Following this latter route, we propose a record selection scheme that maintains the consistency of Tp with the hazard of the site but uses AvgSA to account for the response sensitivity to spectral shape.

SSI effects on seismic demand of reinforced concrete moment resisting frames

We present the results of nonlinear dynamic analyses performed on reinforced concrete (RC) moment resisting frames (MRFs). The analyses were performed considering SSI by means of both a plane-strain soil-structure finite element model approach and a structure-on-springs approach. The results show that the complete FE model approach may produce significant differences in the evaluation of the seismic demand, in terms of maximum inter-storey drift, with respect to the fixed-base structure and to the structure-on-springs approach, mainly because of the different incorporation of the damping in the two modeling approaches.Differences in the soil properties, the seismic design level of the structures and the modeling technique of SSI effects are reflected as reduction in the seismic demand with respect to a fixed-base model, up to 50% in maximum inter-story drift ratio and up to 20% in maximum base shear for the complete FE model and up to 20% in both maximum base shear and maximum inter-story drift ratio for the simplified BNWF model.

EVALUACIÓN DEL DISEÑO SÍSMICO RESILIENTE CONFORME AL MÉTODO DE LAS FUERZAS DE MARCOS DÚCTILES DE ACERO CON DISIPADORES DE ENERGÍA HISTERÉTICOS

Se presentan los resultados de análisis dinámicos no lineales realizados a doce modelos de edificios que se diseñaron conforme a una metodología que emplea el método de las fuerzas y principios de diseño por capacidad y de fusible estructural, la cual permite obtener diseños sísmicos resilientes de estructuras con base en marcos contraventeados de acero estructural dúctiles con disipadores de energía histeréticos. Se demuestra que los mecanismos de diseño sísmico resiliente corroborados previamente mediante análisis pushover se cumplen para la enorme mayoría de los modelos ante la acción de un registro de aceleración compatible con el espectro elástico considerado en el diseño de los modelos, y si la excitación dinámica rebasa los parámetros de resistencia o demanda supuestos en el diseño de los modelos, se activa exclusivamente la segunda línea de defensa inelástica planeada para el sistema. Con base en los resultados presentados, se confirma que es muy factible diseñar resilientemente al sistema en estudio, incluyendo a edificios altos y esbeltos. Por lo tanto, se pueden emplear con confianza los parámetros globales de diseño sísmico y balances óptimos de rigideces derivados en estudios previos.

Force-based seismic design of mixed CLT/Light-Frame buildings

This paper presents the results of a numerical study aimed to investigate the seismic behaviour of mixed multi-storey wood buildings made of CLT and Light-Frame shear walls acting at the same level. Eurocode 8 provides little information on the seismic design of buildings with different lateral load resisting systems working at the same level. A suggestion is given to perform non-linear static or non-linear dynamic analysis to design the structure. The application of linear analysis methods using the force-based procedure is not possible since the value of the behaviour factor q of the mixed system is unknown. The aim of this investigation is to propose a simple analytical formulation to estimate the value of the q-factor of the mixed system, so as to enable the use of the force-based philosophy of Eurocode 8 for the seismic design of mixed CLT/Light-Frame buildings. This was achieved by analysing the results of non-linear dynamic (time-history) analyses performed on a four-storey case-study building with different combinations of CLT and Light-Frame shear walls. Finally, the validity of the proposed formulation is checked by means of non-linear dynamic (time-history) analyses performed on the same four storey case-study building in one of the hybrid combinations of CLT and Light-Frame shear walls.

Investigating modeling approaches of buckling-restrained braces under cyclic loads

The Main purpose of this paper is to present a practical method for accurate modeling and provide a simple model of buckling restrained braces (BRBs). The components of a BRB were introduced. Furthermore, two complete experimental specimens of BRBs were modeled using the ABAQUS finite element method program. The validity of these models was confirmed after comparing the results of nonlinear dynamic analysis with the experimental specimen results. An intended simple model such as steel core and springs was proposed. It was evaluated and analyzed after modeling, then a method was presented to find the spring stiffness. In this study, a comparison was made between the experimental and analytical hysteresis curves (the complete model and the simplified model) and a good agreement was observed between the two results with 5% difference. Moreover, the two-story moment frame with a BRB in both the complete details and simple states was modeled to verify the simple method of core-spring. The results showed a high accuracy of the simple model of core-spring. In addition, the use of the simplified spring-core model may significantly reduce the time of the analysis compared to the complete model.

Acceleration amplification due to rotational components of near-fault earthquakes in triple concave friction pendulum base-isolated structures

Recent studies show that rotational components of earthquakes can amplify the floor acceleration in a base-isolated structure. As a result, the seismic force of nonstructural components could be significantly increased. In this paper, a simple rectangular deck with various geometrical properties mounted on triple concave friction pendulum (TCFP) bearings is examined. At first a set of three translational components from 25 near-fault ground motion records are considered. Then, three rotational components, i.e., torsional and two rocking motions are computed for each earthquake. The results of nonlinear dynamic analysis in a rectangular structure with an aspect ratio in plan equal to 3, demonstrate that the acceleration approximately intensifies 3.4 times in presence of all six ground motion components compared to three translational ones. Finally, a new formula is proposed to determine the maximum acceleration of base-isolated structure without performing the dynamic analysis due to rotational components of ground motions.

A lateral load pattern based on energy evaluation for eccentrically braced frames

Performance-Based Plastic Design (PBPD) method has been recently developed to evaluate the behavior of structures in different performance levels. The PBPD method utilizes a base shear force and a lateral load pattern that are estimated based on energy and yielding mechanism concepts. Using of current lateral force pattern results in weak structural members in upper stories of a structure so that the values of the story drift in these stories are larger than the target drift, particularly in high-rise buildings. Therefore, such distribution requires modifications to overcome this drawback. This paper proposes a modified lateral load pattern for steel Eccentrically Braced Frames (EBFs) based on parametric study. In order toachieve the modified load pattern, a group of 26 EBFs has been analyzed under a set of 20 earthquake ground motions. Additionally, results of nonlinear dynamic analyses of EBFs have been post-processed by nonlinear regression analysis in order to derive the new load pattern. To prove the efficiency of present study, three EBFs as examples were designed by modified pattern and current PBPD distribution. Inelastic dynamic analyses results showed that the story drifts using modified lateral load pattern were well within the target values in comparison with current pattern in PBPD, particularly where the effect of the height is significant. The modified load pattern reduces the possibility of underdesigning in upper levels and overdesigning in lower levels of the frames.

Evaluation of Performance Levels of Zipper-Braced Frames Using Structural Damage Index

The determination of structural and nonstructural damage under earthquake excitations is usually considered as a key factor in performance-based seismic design (PBSD) methods is In this regard, various damage indices have been developed in recent years to quantitatively estimate structural damage. The aim of this study is to develop a simple method to evaluate performance levels of zipper-braced frame (ZBF) structures by using damage indices based on the results of nonlinear static and dynamic analyses. To this end, 5, 7, 10, 12 and 15 story zipper-braced frames (ZBF) are modeled and undergone to twenty different synthetic ground motion records and their damage values have been computed. In dynamic damage analysis procedure, the performance levels of the ZBF models have been computed based on the FEMA-356 standard. Considering the results of the nonlinear dynamic analyses, the correlation between FEMA-356 performance levels and damage indices has been investigated and some simplified formula is presented. On the other side, in static damage analysis approach, by using pushover analysis the performance points of ZBF models have been estimated based on capacity spectrum method (CSM) provided by ATC-40 standard. Then, the correlation between ATC-40 performance levels and some static damage indices has been investigated and some simple equations have been proposed. These relations can be utilized to estimate the performance levels of structures from damage indices. Finally, tables are represented for determination of the structural damage index values for assumed performance levels of the ZBF structures based on static and dynamic damage analysis.

Seismic performance evaluation of a structure retrofitted using steel slit dampers with shape memory alloy bars

In this paper, a hybrid slit- shape memory alloy (SMA) energy dissipation device is devised by attaching a SMA bar to each face of a steel slit plate. An analysis model of a SMA bar with super elastic capability is developed using various link elements, and the accuracy of the analysis model is verified by comparing with finite element analysis results. The seismic performance of the hybrid slit damper is verified by incorporating them in seven-story steel structure. The nonlinear dynamic analysis results of the model structure subjected to seven earthquake ground motions show that the addition of SMA bars in slit damper results in significant reduction both in the maximum and the residual deformation compared to those of the structure installed with typical steel slit dampers.

Improved evaluation of inelastic displacement demands for short‐period masonry structures

SummaryThis work discusses the simplified estimation of earthquake‐induced nonlinear displacement demands as required by nonlinear static procedures, with particular attention on short‐period masonry structures. The study focuses on systems with fundamental periods between 0.1 and 0.5 s, for which inelastic amplification of the elastic displacement demand is more pronounced; hysteretic force‐displacement relationships characteristic of masonry structures are adopted, because these structures are more commonly found within the considered period range. Referring to the results of nonlinear dynamic analyses of single‐degree‐of‐freedom oscillators, some limitations of the Eurocode 8 and Italian Building Code formulations are first discussed, then an improved equation is calibrated that relates inelastic and elastic displacement demands. Numerical values of the equation parameters are obtained, considering the amount of hysteretic energy dissipation associated with various damage mechanisms observed in masonry structures. Safety factors are also calculated to determine several percentiles of the displacement demand. It is shown that the proposed equation can be extended to more dissipative systems. Finally, the same formulation is adapted to the estimation of seismic displacements when elastic analysis procedures are employed. Copyright © 2017 John Wiley & Sons, Ltd.

Analytical investigation on cyclic response of buckling-restrained braces with short yielding core segments

Buckling-restrained braced frames (BRBFs) are considered to be one of the efficient lateral force-resisting systems used in buildings located in the seismically active regions. Nearly symmetric hysteretic response of buckling-restrained braces (BRBs) in tension and compression due to the yielding of steel core plates helps the BRBFs to withstand the seismic excitations without causing any extensive damage to the primary frame members. However, BRBFs may exhibit the excessive post-earthquake residual drift response due to the low axial stiffness of BRBs under the strong ground motions. A reduction in the yielding core segments of BRBs results in the improved elastic and post-elastic axial stiffness of BRBs which may help in controlling the excessive residual drift response. This study is focussed on the analytical evaluation of hysteretic response of BRBs of varying lengths using finite element (FE) software. The results of FE study are further used to evaluate the inter-story and residual drift response of a 3-story braced frame fitted with BRBs of short core lengths (referred as SBRBF). Nonlinear dynamic analysis results of SBRBF are compared with the conventional BRBF and concentrically braced frame (CBF). It is concluded that the optimum reduction in yielding core lengths of BRBs can improve the overall seismic response of BRBFs with a reduction in the residual drift response.

Progressive Collapse Analysis of Concrete-filled Steel Tubular Column to Steel Beam Connections Using Multi-scale Model

The multi-scale model which combined the fiber beam element with the fine element was used to investigate the progressive collapse performance of steel beam to concrete-filled steel tubular (CFST) column connections. By using the nonlinear static analysis method and taking into account the influence of the adjacent framework of joints, the resistance of progressive collapse, the failure modes and the stress distribution revealed the resistance mechanism of these joints during the process of progressive collapse. And the vertical displacement time history curves of joints which displayed the progressive collapse resistance demands of these joints were obtained by using the nonlinear dynamic analysis method. The relationship between resistance capacity and resistance demand of these joints were obtained by analyzing the nonlinear static analysis results and the nonlinear dynamic analysis results. These analysis results showed that the frame structure with these joints which enabled to form the resistance mechanism and new alternate path of unbalanced loads can prevent the occurrence of progressive collapse after the failure of column connected to joints. And the adjacent framework can improve the ability of anti-progressive collapse of these joints.

New Design Detail to Enhance the Seismic Performance of Ordinary Reinforced Partially Grouted Masonry Structures

AbstractRecent studies have shown that in the event of a strong earthquake, partially grouted (PG) masonry walls would most likely not perform according to code expectations. The research reported herein is focused on introducing an economically competitive design detail to enhance the seismic performance and safety index of PG reinforced masonry shear walls. Besides the conventional design details of single grouted vertical cells with single bond beams, two other details called double grouted vertical cells with double bond beams, and double grouted vertical cells with single bond beams plus joint reinforcement, were constructed and tested in this study. Test results demonstrated that the single grouted wall failed in a low ductility shear-dominated mode, while the modified design details resulted in a change to the high ductility shear failure mode. Results of nonlinear static and incremental dynamic analyses showed that using the proposed enhanced detail can significantly improve the seismic performanc...

Investigation of Nonlinear Behavior of Concrete on Seismic Performance of an Arch Dam Using Finite Element Method

In this paper the effect of nonlinear behaviour of concrete is investigated on seismic performance of a double curvature concrete dam. The Morrow Point concrete dam has been selected as the case study and dam-reservoir-foundation interaction considered in the model. Finite element method has been used for modelling and analysis of case study by applying the El Centro earthquake components considering nonlinear behaviour of concrete. The obtained results of nonlinear dynamic analysis illustrate the increasing of displacement of dam crest along the river and decreasing of maximum principle stresses in critical points. The results demonstrate the importance of consideration of nonlinear behaviour of material in seismic performance of arch dams to achieve the optimal design of models.

Simplified methods for seismic assessment of existing buildings

Besides the complex instructions of guidance documents for seismic rehabilitation of existing buildings, some institutions have provided simple criteria in terms of simplified rehabilitations. ASCE 41-06 is one of documents that introduced a simple method for assessment of certain buildings that do not require advanced analytical procedures. Furthermore the New Zealand guideline has presented a simple lateral mechanism analysis that is a hand static analysis for determining the probable collapse mechanism, lateral strength and displacement capacity of the structure. The present study is focused on verifying the results of the simplified methods which is used by NZSEE and ASCE 41-06 in assessment of existing buildings. For this, three different special steel moment and braced frames are assessed under these two guidelines and the accuracy of the results is checked with the results of nonlinear static and dynamic analysis. After comparison of obtained results, suggestions are presented to improve seismic retrofit criteria.

외부접합형 카고메 감쇠시스템을 사용한 철근콘크리트 라멘조 공동주택 비탄성 지진 응답 제어

이 논문은 지진응답을 감소시키기 위해 외부설치형 카고메 감쇠시스템의 유효성을 비선형 동적 해석 결과를 통해 나타내었다. 이전의 연구에 의해 제안된 카고메 감쇠시스템을 활용하여 본 연구에서는 등방성, 이선형 이력특성 및 설치구성이 새롭게 제안하였다. 또한, 외부접합형 카고메 감쇠시스템의 여러 가지 효과를 15층 및 20층 철근콘크리트 라멘조 아파트를 대상으로 검증하였다. 원구조물에 대한 감쇠장치 지지구조물의 강성비, 감쇠장치의 수량 및 설치 층수는 설계변수로 고려하였다. 수치해석결과, EKDS는 기존의 한 방향 층간에 설치되는 감쇠시스템과 비교할 때 더 작은 수를 적용하여도 두 방향의 지진하중을 감소시키는데 매우 효과적임을 입증되었다. Various passive energy dissipation systems have been proposed and widely applied to real building structures under seismic load due to their high energy-dissipation potential and low cost for installation and maintenance. This paper presents nonlinear dynamic analysis results of the effectiveness of exterior-installed Kagome damping system(EKDS) in passively reducing seismic response. Kagome damping system proposed by previous studies has isotropic and bi-linear hysteretic characteristics and the installation configuration is newly presented in this study. The 15 and 20 story RC framed apartment buildings are used for verifying the effectiveness of the EKDS. The stiffness ratio of the damper supporting column to the original building, the number of the dampers, and the installed stories were considered as design parameters. Numerical results demonstrated that the EKDS were very effective in reducing both the two horizontal directional seismic responses by just using smaller number of exterior-installed damping system when compared to the traditional one-directional inter-story installed damping systems.

A Procedure for the Displacement-Based Seismic Assessment of Infilled RC Frames

The aim of this study was to propose an extension of the displacement-based assessment procedure for infilled reinforced concrete (RC) frames. Two fundamental steps of the displacement-based approach were studied: the determination of the equivalent viscous damping and the definition of the limit-state displacement profile. The proposed criteria were derived by examining the results of two different numerical investigations regarding the nonlinear seismic response of single- and multi-story infilled RC frames. Lastly, the effectiveness of the method was verified through comparisons, in terms of displacement demand, with the results of nonlinear dynamic analyses.

On the relevance of nonlinear static procedures for buildings with vertically asymmetric setbacks

Basic pushover methods, which are in practice today, are considered not to be reliable for structures having significant higher mode participation. Efforts are being continued worldwide for modifying conventional nonlinear static procedures (pushover methods), to make them applicable for the seismic assessment of irregular building structures. This study aims at developing a load pattern to be used with the basic nonlinear static procedures for the analysis of two-dimensional reinforced concrete frames with vertically asymmetric setbacks. The accuracy of the basic nonlinear static procedures when applied to such buildings is also verified against the results of nonlinear dynamic analyses. The results are not conclusive in identifying any single pushover method absolutely suitable for such buildings. However, the load pattern proposed in this article can be used with all the basic nonlinear static procedures considered in this study, to obtain the displacement demands of bare frames with vertically asymmetric setbacks. Another load pattern is identified to predict their base shear demands. It is also understood that masonry in-filled frames cannot be analysed with a single load pattern throughout the analysis. A suitable method for analysing reinforced concrete frames with asymmetric setbacks using the basic nonlinear static procedures is evolved at the end.

Seismic retrofit of asymmetric structures using steel plate slit dampers

A seismic design and retrofit procedure were developed for estimating the proper amount of steel plate slit dampers required to keep the seismic response of low-rise asymmetric structures within a given target performance level. Parametric studies for displacement response of a single story plan-wise asymmetric structure were conducted with varying eccentricities between center of mass and center of stiffness. Then a procedure was developed to distribute the damper based on the ductility demand of the structure. The procedure was applied to install slit dampers at proper locations of low-rise structures with horizontal and/or vertical irregularities subjected to an earthquake load. According to the nonlinear static and dynamic analysis results, the structure with hysteretic dampers installed in accordance with the proposed procedure showed satisfactory inter-story drifts in both the stiff and the flexible edges when they were subjected to the design level seismic load.