Nonlinear Seismic Analysis Research Articles

On advantages of the “Substitute Frame” model for incremental dynamic analysis: Integration of speed and accuracy

The “Substitute Frame” (SF) model, which is a simplified MDOF system consisting of a one-bay multistory frame, has recently been introduced by the authors to predict the static and dynamic response of RC building frames, especially in terms of Interstory Drift Ratio (IDR) and plastic hinge rotation. It is known that incremental dynamic analysis (IDA) is one of the most accurate nonlinear seismic analyses that is of course a time-consuming method, having a high computational cost. Hence, this paper aims to focus on the accuracy and speed of the Substitute Frame (SF) as a simplified frame model in performing IDA, fragility analysis, and other probabilistic analyses. If the desired result is achieved, this can be promising to perform extensive probabilistic analysis efficiently. To this end, three 8-, 12-, and 20-story benchmark RC moment frames were selected and the corresponding simplified SF models were generated. To accurately perform the required analyses, the OpenSEES software by implementing modified Ibarra-Medina-Krawinkler springs with deteriorating peak-oriented behavior was used to apply Nonlinear Time-History Analysis (NTHA) using the Hunt-Fill algorithm for IDA analyses. The results showed that the SF model can be reliably applied to perform IDA analyses and developing fragility curves and it is computationally efficient and robust. The selected OpenSEES example files for the present study, are shared through the link “https://web.nit.ac.ir/~h.hamidi/software_data.htm”.

In-plane-out-of-plane single and mutual interaction of masonry infills in the nonlinear seismic analysis of RC framed structures

In the aftermath of earthquakes poor seismic response was evidenced by non-structural elements such as enclosure masonry infills (MIs), characterized by a combination of in-plane (IP) and out-of-plane (OOP) damage mechanisms. The present work is aimed at identifying the effects of this mutual interaction on the nonlinear seismic behaviour of reinforced concrete (RC) framed structures. To this end, an extensive parametric study is carried out considering a spatial one-bay multi-storey shear-type model with MIs constituted of two leaves of clay hollow bricks, which is assumed as equivalent to infilled RC framed buildings. An extensive GIS aided structural mapping of the town of Rende (Italy) is adopted in order to obtain benchmark models as close to real structures as possible, focusing on total height, in plan dimensions and maximum and minimum bay lengths of the buildings. The dependence of the results on the variation of the following design parameters is considered for the i-th cluster of buildings characterized by the same number of storeys: i.e. fundamental vibration period; behaviour factor of the bare structure; aspect ratio of MIs, defined as the ratio between the panel length and height. A five-element macro-model comprising four (diagonal) nonlinear beams and one (horizontal) central nonlinear truss for the prediction of the OOP and IP behaviour of MIs, respectively, is first implemented in a homemade computer code. The proposed algorithm addresses the issue of the nonlinear mutual interaction of MIs by modifying stiffness and strength in the OOP direction on the basis of simultaneous or prior IP damage and vice-versa. A lumped plasticity model describes the inelastic behaviour of the RC frame members. Finally, a review of the current Italian, European and American seismic code provisions is performed by means of comparison with results of nonlinear dynamic analyses. To this end, bidirectional spectrum-compatible accelerograms are considered at ultimate limit states.

Three-Dimensional Seismic Nonlinear Analysis of Topography–Structure–Soil–Structure Interaction for Buildings near Slopes

Three-Dimensional Seismic Nonlinear Analysis of Topography–Structure–Soil–Structure Interaction for Buildings near Slopes

Nonlinear Seismic Ground Response Analysis in Northeastern India Considering the Comprehensive Dynamic Soil Behavior

Nonlinear Seismic Ground Response Analysis in Northeastern India Considering the Comprehensive Dynamic Soil Behavior

Comparative nonlinear seismic analysis of an existing RC bridge designed with obsolete codes

The evolution of seismic design and calculation criteria for highway bridges has a direct influence on their structural behavior. This paper presents a nonlinear dynamic analysis using a detailed 3D finite element model of an existing bridge, with different design criteria for the column transverse reinforcement, according to code requirements of different times. The numerical model is able to simulate both the collapse of the structure and the generation of damage in its elements when subjected to extreme seismic actions. Through the numerical model, it is possible to represent the cyclic behavior of the concrete, and to evaluate the influence of the transverse reinforcement assigned to the column on the overall response of the bridge. The formation of plastic hinges is verified, as well as the identification of different collapse mechanisms.

Nonlinear seismic analysis of composite coupled shear walls strengthened by CFRP sheets

Nonlinear seismic analysis of composite coupled shear walls strengthened by CFRP sheets

Nonlinear Seismic Analysis of Composite Coupled Shear Walls Strengthened by CFRP Sheets

Nonlinear Seismic Analysis of Composite Coupled Shear Walls Strengthened by CFRP Sheets

Performance evaluation of PM4Sand model for simulation of the liquefaction remedial measures for embankment

Non-linear seismic deformation analyses of an earth embankment founded on liquefiable soil were performed using the FLAC 2D and PM4Sand as the constitutive model to simulate the seismic behaviour of loose sand foundation. PM4Sand model was calibrated to the cyclic behaviour of Nevada 120 sand. The untreated embankment-foundation system was subjected to three sinusoidal shaking events. Though the computed deformations are in reasonable agreement with measured results, the excess pore pressures (EPP) in the central foundation region were found to be overpredicted. The temporal variation of sand permeability was considered for the simulation of untreated sand deposit supporting the embankment. The low effective stresses computed to be regained following the dissipation of EPP for the case with variable sand permeability implies that the numerical model is not capable of accounting the shear-induced dilation in the foundation soil underlying the embankment. So, the class-C1 simulations were performed to evaluate the numerical model by adjusting the dilation parameters in the model. Following this, the three different liquefaction mitigation measures such as dense sand columns within the foundation soil, gravel berms along the side slopes of the embankment, and vertical sheet piles below the embankment toes were simulated and comparisons with experimental data are reported.

Seismic analysis of high-speed railway irregular bridge\u2013track system considering V-shaped canyon effect

To explore the effect of canyon topography on the seismic response of railway irregular bridge–track system that crosses a V-shaped canyon, seismic ground motions of the horizontal site and V-shaped canyon site were simulated through theoretical analysis with 12 earthquake records selected from the Pacific Earthquake Engineering Research Center (PEER) Strong Ground Motion Database matching the site condition of the bridge. Nonlinear seismic response analyses of an existing 11-span irregular simply supported railway bridge–track system were performed under the simulated spatially varying ground motions. The effects of the V-shaped canyon topography on the peak ground acceleration at bridge foundations and seismic responses of the bridge–track system were analyzed. Comparisons between the results of horizontal and V-shaped canyon sites show that the top relative displacement between adjacent piers at the junction of the incident side and the back side of the V-shaped site is almost two times that of the horizontal site, which also determines the seismic response of the fastener. The maximum displacement of the fastener occurs in the V-shaped canyon site and is 1.4 times larger than that in the horizontal site. Neglecting the effect of V-shaped canyon leads to the inappropriate assessment of the maximum seismic response of the irregular high-speed railway bridge–track system. Moreover, engineers should focus on the girder end to the left or right of the two fasteners within the distance of track seismic damage.

Macro-modeling approach incorporating fiber plastic hinge for reinforced concrete frames with masonry infill

An indefinite guide from technical codes around the world leads to confusion and repudiation of masonry infill during the structural design and analysis of infilled frames. In recent years, the rising interest in nonlinear seismic analysis has called for a robust yet simple numerical modeling strategy to model the seismic behavior of reinforced concrete frames with masonry infill. This study aims to propose a reliable macro-modeling approach that incorporates fiber plastic hinge to simulate the in-plane hysteresis response of reinforced concrete frames with masonry infill. An existing constitutive law and a simplified pivot hysteretic law were fine-tuned to describe the nonlinear behavior and cyclic response of the equivalent diagonal strut representing solid clay brick masonry. A comparison with experimental observations showed that the proposed numerical modeling strategy can satisfactorily predict the in-plane global response of infilled frames.

Modelling the 2D seismic response of the Kutch basin on the Indian Subcontinent

The Kutch region in India experienced one of the largest intraplate earthquakes on January 26, 2001, with approximately 20,000 fatalities. Although strong motion recordings from the aftershocks in this region indicate basin effects, no detailed numerical studies on the effect of the basin on the ground surface motion in this region have been reported. In the present study, we conduct a 2D non-linear seismic site response analysis of a shallow triangular basin model with various bedrock slopes using the finite difference method to examine the behaviour observed in the Kutch basin. The spatial amplification pattern of the ground motion in the basin with a bedrock slope 10⁰ accords with the recorded ground motion data. The developed basin model is tested with different earthquake motions recorded at various basins across the world. We then develop the amplification factors with respect to the rock outcrop for the peak ground motion parameters and Arias Intensity. Significant amplification is observed at the basin centre and the region between the centre and the edge. The frequency content of the surface motion shifts from a narrow to a broad spectrum from the edge towards the basin centre.

Simple models for simulating shear key arrangement in nonlinear seismic analysis of arch dams

Shear keys are commonly designed on contraction joints to limit joint slipping and improve the overall seismic behavior of arch dams. However, shear keys are usually over-simplified in the current nonlinear seismic analysis. This paper proposes a geometric simplification method for simulating shear key arrangement. Actual shear keys on a contraction joint are simplified into the combination of large oblique-type shear keys along the cantilever direction and horizontal direction. Key geometric features and progressive failure of shear keys can be naturally considered using the contact boundary model and the plastic-damage model. Nonlinear seismic analysis of the Xulong arch dam is implemented with different shear key models for verification and comparison. The proposed method is firstly verified by analyzing seismic responses of the dam with geometrically-simplified shear keys and fine shear keys, respectively. Furthermore, seismic responses of the dam with geometrically-simplified shear keys, free-slipping plane joints (ignoring shear keys but considering surface friction), and non-slipping plane joints (modeling perfect shear keys) are compared to investigate the effects of shear key modeling methods. Ignoring shear keys and modeling perfect shear keys underestimate and overestimate the seismic capacity of the dam, respectively. The nonlinear dynamic behavior of shear keys can be more reasonably represented with the proposed method without much increasing modeling efforts.

Structural analysis of a school building with viscous dampers applied

Viscous damper, as a type of energy-dissipating device, is applied in the 3-story school building. To investigate the function of viscous dampers, seismic nonlinear analysis is performed on the FE model with viscous dampers simulated in. The analysis is done for both minor earthquake and severe earthquake. The analysis results show that the viscous dampers start to dissipate energy in minor earthquake input and dissipate more energy in severe earthquake. Therefore, application of viscous dampers significantly reduce the seismic response of the building and effectively protect the structure building from severe damage or collapse.

Three-dimensional nonlinear seismic response analysis of subway station crossing longitudinally inhomogeneous geology under obliquely incident P waves

With the rapid development of underground space, more adverse site conditions are occurring in the construction of underground structures. For example, a subway station passes through longitudinally inhomogeneous geology. When the subway station crosses the interface of soft soil and hard soil, this may lead to the destruction of underground structures. In this paper, three-dimensional (3D) nonlinear seismic response analysis of subway stations crossing longitudinally inhomogeneous geology subjected to obliquely incident P waves is presented based on actual engineering background. The earthquake input method for the longitudinally inhomogeneous site that transforms the site seismic response into an equivalent nodal load is first developed and verified. The viscous-spring artificial boundary is used to simulate the radiation damping effect of infinite domain media. Subsequently, the topographic and geological effects on seismic response of engineering site are investigated. Finally, the failure mechanism of the subway station structure crossing longitudinally inhomogeneous geology under the obliquely incident P waves is revealed. The investigation demonstrates that the plastic zone of site usually appears along the interface between the hard and soft soil media, and appears on the side of the soft soil. The sidewall and bottom slab of the structure experience obvious tensile damage at the interface location between the hard and soft soil media. The results show that topographic and geological effects should be considered in seismic analysis and design of underground structures when the topography and geology change significantly.

Implementation of Seismic Ground Response Analysis in Estimating Liquefaction Potential in Northern Thailand

DOI:10.17014/ijog.8.3.371-383It has been known that northern Thailand is an active tectonic region in Southeast Asia. Some earthquakes with low to medium magnitudes had occurred in northern Thailand. The Mw6.1 Mae Lao Earthquake occurred on May 5th, 2014 in Chiang Rai Province. The earthquake also resulted in the unique phenomenon of ground failure, which was known as liquefaction. Learning from the event, the liquefaction potential based on seismic ground response analysis was performed. Several site investigations including standard penetration test and seismic down-hole test in Chiang Rai Province were carried out. The next generation attenuation model was conducted to generate the ground motion for nonlinear seismic response analysis. The peak ground acceleration at the ground surface from seismic ground response analysis was used to analyze the empirical analysis of liquefaction potential. The results show that liquefaction could occur at the investigated locations during the earthquake. The results also confirm the liquefaction evidence found in Chiang Rai Province during the Mw 6.1 Mae Lao Earthquake. This research can help the people to consider the earthquake impacts to northern Thailand.

Seismic Performance of CFST Frame-Steel Plate Shear Walls Connected to Beams Only

The safety and cost of structures composed of concrete-filled steel tube (CFST) frame-steel plate shear walls (SPSWs) with two-side connections are governed by the seismic performance. The response modification factor R and displacement amplification factor Cd are important seismic performance factors. In this paper, nonlinear seismic responses of 10-story, 15-story, and 20-story CFST frame-SPSWs (CFST-SPSWs) are studied. A nonlinear finite element model which includes both material and geometric nonlinearities is developed using the finite element software OpenSees for this study. The accuracy of model was validated by comparing with experimental results. Nonlinear seismic analysis shows that CFST-SPSWs, in high seismic region, behave in a stable and ductile manner. Also, R and Cd of CFST-SPSWs were evaluated for the structure models using incremental dynamic analysis (IDA), and the average values of 3.17 and 3.05 are recommended, respectively. The recommended R value is greater than the value (2.8) in the “Chinese Code for seismic design of buildings” for composite structures, indicating the code is conservative. The structural periods provided by current code are generally lower than the periods calculated by finite element analysis. Research results show that R and Cd increase with increasing story number, span number, and structural period. Ductility reduction factor Rμ increases with increasing span number and decreasing story number. Overstrength factor Rs increases with increasing story number and decreasing span number.

Nonlinear random seismic response analysis of the double-trough aqueduct based on fiber beam element model

As an important lifeline project, large reinforced concrete aqueduct structures sometimes pass through areas with high seismic intensity. Therefore, the aqueduct structure is susceptible to earthquake damage or destruction during the water conveyance process, resulting in interruption of water conveyance and major safety accidents. In fact, because concrete is a multiphase composite material, it has obvious nonlinear and random characteristics. At the same time, seismic excitation is also naturally random due to differences in frequency spectrum and duration. Based on this, this paper uses the concrete elastoplastic random damage constitutive relationship and the random seismic excitation model to carry out the random nonlinear seismic response analysis of the double-trough aqueduct structure. The thin-walled characteristics of the girder section of the aqueduct structure is significantly different from that of the general bridge structure, and there is a certain error in the simulation of the seismic response of the aqueduct with traditional beam elements. Therefore, this paper combines the refined fiber beam element model, compiles the TCL language program suitable for the OpenSEES open analysis platform, and establishes the refined fiber beam finite element model of the aqueduct structure based on the random damage constitutive relationship of the concrete. The study of the response law and failure mechanism of aqueduct structures considering the coupling of concrete nonlinearity and seismic excitation randomness provides an important theoretical basis for the seismic optimization design of large-scale aqueduct structures.

Structural performance of a steel tower model under seismic loading

This research represents the dynamic behavior of the steel tower structural model due to applying seismic load. The 3D finite element model is created using ANSYS-software to simulate the real structure used in experiment. The dynamic properties, natural frequencies and mode shapes, are extracted and compared with the experimental model values. The comparison is implemented to verify the FE analysis procedure of the tower model with experimental model results and they are accepted by 83% tuning ratio. The nonlinear seismic analysis is applied to the structural model using observed ground motion in 1999 Turkey Earthquake. The seismic load is applied in two cases; the first is in the x-direction of the structural tower model and the other in the y-direction of the model in a horizontal plane. The maximum response displacements in x and y-axis and load displacement hysteresis for both loading cases are exhibited. The results display that the tower structural model failed with large response displacement in the first few time of ground motion according to IBC-2018 and NBCC-2005. The collapse of the tower structural model occurred after time 18 sec and the applied seismic loading in x-axis has significant effect.

Nonlinear seismic analysis of masonry bridges under multiple geometric and material considerations: Application to an existing seven-span arch bridge

Resilient infrastructure is nowadays attracting attention when designing new infrastructure projects. However, many countries around the world still have a large stock of existing transport infrastructure, such as railways and roads. In particular, masonry bridges are significantly widespread in Europe. These bridges, built a long time ago could suffer structural damage due to earthquakes, as their design in the past did not take this into account. The issue becomes critical because the scientific world still lacks cutting-edge monitoring techniques and calculation tools to accurately assess the integrity of existing bridges. These steps are fundamental before any maintenance activities are developed by infrastructure managers. In this study, the seismic behaviour of a seven-span masonry arch bridge is intensively investigated in order to provide new insights into the seismic vulnerability analysis of existing masonry bridges. In particular, parametric analyses are carried out to assess the effect of haunching, fill, and pier cross-section types on the seismic capacity of multi-span masonry bridges. Interesting observations were made on the change in ductility, capacity, and stiffness of the structure when the studied parameters are modified.

Damage protection of earthquake resistant structures by means of damped braces

Supplementary energy dissipation is an efficient technique for the retrofitting of as built framed buildings as long as the loss of capacity due to previous seismic degradation is evaluated properly. Most of the displacement-based design procedure of damped braces only considers the capacity curve of an initially undamaged structure, while the hysteretic energy is accounted for by an equivalent viscous damping. However, structures may be initially damaged by previous earthquakes, so the proportioning of the damped braces should include the effects of the cumulative damage caused by previous loading cycles. A displacement-damage-based design procedure is proposed and implemented by means of a computer-aided tool named DAMPERS (DAMage Protection of Earthquake Resistant Structures). The residual capacity that a building might experience when subjected to more than one earthquake during its nominal life is taken into account. The loss of capacity of the original structure is evaluated by a combined plastic-damage model, obtained as an in-parallel combination of elastic-perfectly plastic and elastic-softening damage mechanisms, and a damage index, accounting for the cyclic damage of each pair of mechanisms. An archetype six-storey reinforced concrete framed building, representative of the Italian residential housing stock constructed during the 1990s, is retrofitted with hysteretic damped braces designed assuming different damage evolution laws during previous earthquakes. Three configurations of masonry infills (MIs) are considered: bare frame, with nonstructural MIs; infilled frame, with a uniform in-elevation distribution of structural MIs; pilotis frame, with no MIs at the ground floor and structural MIs at the other floors. OpenSees is the computational platform for the nonlinear seismic analysis of the unbraced and damped braced structures, with reference to records scaled in line with the hypotheses adopted and considering failure modes of structural and nonstructural elements.