Nonlinear Incremental Dynamic Analysis Research Articles

Modelling and evaluation of brittle shear effects on the seismic performance and loss assessment of RC buildings

This paper focuses on the seismic vulnerability assessment of old RC buildings prone to brittle shear effects, i.e., with extremely low transversal reinforcement ratios in columns. Within this context, two limitations are identified: 1) the inadequacy of the available analytical shear models in literature since most of them are based on experimental results performed on specimens with transversal reinforcement ratios higher than those found in old buildings and 2) the lack of simplified numerical modelling approaches to simulate shear failure prior to flexural yielding of the element’s longitudinal reinforcement. To overcome these limitations, a simple modelling approach is proposed, and its impact is evaluated through seismic and loss assessment of a RC structure typical of the Lisbon building stock. For comparison purposes, the building is modelled using two different numerical models: one that only captures the nonlinear flexural behaviour of the structural elements, and another that considers both flexural non-linear behaviour and brittle shear failure through the incorporation of uncoupled shear springs that limit the maximum strength that the RC columns can withstand. The seismic performance evaluation is carried out through nonlinear static and Incremental Dynamic Analysis (IDA). Collapse assessment is evaluated considering two different collapse criteria, namely global failure (GF) based on the identification of flattening of the IDA curves and first component failure (FCF) which is conducted based on post-processing analysis of shear forces and inter-storey drifts. The results show that the proposed modelling approach combined with the GF collapse criterion leads to estimates of expected annual losses (EAL) compatible with those reported in other studies found in the literature. Additionally, it is observed that the adoption of a first component failure criterion based on shear force control conducts to consistent estimates of EAL.

Seismic design and assessment for midrise buildings equipped with damped‐outrigger system

SummaryThe damped‐outrigger system has been proposed to improve the performance of conventional outrigger systems in controlling the structural seismic response by increasing the damping and stiffness. The purpose of this study is to demonstrate the effectiveness of using damped‐outrigger systems in midrise buildings and provide engineers with a comparison between conventional structural systems such as moment resisting frame (MRF) and buckling‐restrained braced frame (BRBF) in proposing the most suitable structural system. In this study, the buckling‐restrained brace and viscous damper are adopted as the energy dissipation devices in the damped‐outrigger system. A total of 48 midrise numerical models with various building heights and structural systems are analyzed using nonlinear response history analysis and incremental dynamic analyses. The analysis results show that the midrise buildings equipped with a damped‐outrigger system with either viscous damper or buckling‐restrained brace (BRB) can reach similar and even better seismic performance when compared with the BRBF; it also reduces the structural responses by around 30% for the maximum roof drift and acceleration responses when compared with MRF. The analysis results could provide a reference for structural engineers when selecting suitable lateral force resisting systems for midrise buildings.

Fragility curves for steel moment frame with welded flange plate connection

The importance of evaluating the performance of structures against earthquakes is not hidden from anyone. It is important to have an overview of the resistance level of the structure to achieve a safe and economical design against the potential input forces. Therefore, a lot of research is always done in this area in different ways. This article contains the method and results of the study of seismic vulnerability for WFP connection which is widely used and pre-approved connection for steel moment frames that Has been introduced in the tenth section of the Iranian building code. The purpose is to draw the fragility curve using numerical methods. Due to the fact that this connection is pre-approved just for medium moment frames, it is necessary to check its reliability if want to use it in a special moment frame. The probability of structural damage caused by seismic force can be presented as a function of ground motion characteristics and various design parameters Using fragility curves. In this study, seven records of earthquake accelerograms were used for incremental nonlinear dynamic analysis (IDA) those most consistent with the site intended for this structure

Numerical investigation of the contribution of the soil-structure interaction effects to the seismic performance and the losses of RC buildings

Seismic vulnerability and loss analyses of buildings are usually estimated under the fixed-based condition, omitting the soil-structure interaction (SSI) effects. However, according to the literature and the seismic damage due to past events, mid-to high-rise buildings located on soft soils can present a worse seismic performance. This manuscript aims to investigate whether the SSI effects affect the seismic performance and the losses of reinforced concrete (RC) buildings. To do so, a real 5-storey RC building has been selected as the case study. It was built prior to restrictive Spanish seismic codes. The building was constructed over soft alluvial strata and it has a shallow foundation. The area is characterised by a moderate seismic hazard. Nonlinear static analysis (NLSA) and incremental dynamic analysis (IDA) have been performed to assess the seismic behaviour and the losses expected of the case study building. The calculations have been done in the OpenSees finite-element framework. The direct method has been used to model the SSI. The results have been obtained for the fixed-base and for the SSI models. The numerical outcomes have shown the remarkable effect of the SSI on the fragility and on the performance of these structures. It has been observed that the severe damage expected can be worsened by up to 38% if SSI is taken into account. Additionally, the soft-storey mechanism at the ground floor concentrates all the damage expected, showing that this is the most seismic vulnerable part of the building (owing to higher interstorey-drift ratios and peak floor acceleration values). The losses expected derived for structural and non-structural components have been 140% higher if the SSI is considered.

Multi-level simulation studies on seismic performance evaluation of steel-sheathed cold-formed steel framing shear walls

Cold-formed steel (CFS) framing shear walls has been widely used as the lateral force resisting system of light-weight steel structures. While the behaviors of walls have been numerically studied, there is a need to develop more convenient and efficient modeling strategies. In this paper, a simulation framework consisting of component-level to system-level analysis for the seismic evaluation of steel-sheathed CFS walls was proposed by using OpenSees software. Based on the improved fastener-based method, refined numerical models were developed and validated against tests of steel sheathed CFS shear walls. Self-drilling screw connection tests were conducted to characterize the nonlinear properties of the member-to-sheathing connections as inputs in the models. Then, a set of structural archetypes were systematically analyzed by nonlinear static and incremental dynamic analysis in accordance with FEMA P695. The results showed that the proposed simulation framework could well capture the response of CFS walls and evaluate the seismic performance of structural system. The post-peak behavior of wall had a significant impact on the collapse resistance of the structure. The seismic response modification coefficient value was suggested (R = 4.25) for the high-performance steel-sheathed CFS framing shear walls studied in this paper.

Determination of Seismic Performance Factors for Buildings with Concentrically Braced Frame Systems under the Excitation of Near- and Far-fault Records

Performance coefficients are widely used in seismic design codes to achieve performance objectives. The values of these coefficients have significant importance in achieving pre-specified performance goals. Studies have shown that near-fault earthquakes decrease the ductility and increase the risk of failure in the structures; however, the current codes use the same performance coefficients to design structures against near- and far-fault records. In the present study, 1-, 5-, 10- and 15-story special concentrically braced frame (SCBF) structures designed in the region with high seismic hazard have been evaluated. Non-linear static, linear dynamic, and incremental non-linear dynamic analyses under the influence of two sets of near- and far-fault records extracted from FEMA-P695 have been used to calculate the performance coefficients. Furthermore, the fragility curves are calculated for three performance levels (IO, LS, CP) using a probabilistic assessment of the results derived from incremental dynamic analysis to investigate the relationship between obtained factors with the probability of exceedance from a specified level. According to the mean results of all records, the behavior factor for the steel special concentrically braced frame is 5.92. The mean behavior factor obtained for the near-fault records is 35% less than the far-fault records. Differences in the obtained behavior factor for structures under excitation of two types of earthquake records (near- and far-fault) are observed in the fragility curves related to the probability of exceedance from CP level. However, there is no significant correlation between the resulted behavior factors and the probability of exceeding IO and LS levels.

Seismic fragility investigation of hybrid structures BRBF with eccentric-configuration and self-centering frame

In this study, the incremental nonlinear dynamic analysis (IDA) is used to assess the seismic fragility investigation of hybrid structures with buckling-restrained braced frames with eccentric configuration (BRBFE) and self-centering frames. For this purpose, three systems BRBFE, BRBFE with the moment-resistant frame, and BRBFE with the self-centering frame, are designed and developed by numerical method for static pushover and IDAs. To prove the accuracy of the results of numerical studies, performed validation with experimental results. In this numerical study, 24 ground motions to perform IDAs are used, and IDA curves and fractile IDA curves are used to compare the seismic capacity of structures. Eventually, seismic fragility curves are plotted for structures in three performance levels of immediate occupancy (IO), repairability (RP), and collapse prevention (CP). The results showed that the BRBFE with moment-resistant frame was the most effective way to reduce the failure probability at IO performance level among the three systems. In contrast, the BRBFE with the self-centering frame was the most effective way to reduce the failure probability at two performance levels of RP and CP.

Seismic performance evaluation of base-isolated nuclear power plant reactor building considering aging effect of isolation device

ABSTRACT The base isolation (BI) device is widely used for reducing seismic energy transmitted to the upper part of the structures. The rubber property of lead rubber bearing (LRB) BI devices degrades with time and environmental conditions, affecting the controlling performance of BI devices. This study investigates the degradation of capacity of base-isolated nuclear power plant (BI-NPP) considering the aging of rubber material used in the LRB BI device. An NPP reactor building with BI devices is numerically modeled. To capture the nonlinear behavior of the BI device, a bilinear hysteretic model is considered. Assuming different ages, the nonlinear incremental dynamic analysis is conducted using a set of 25 earthquakes and the seismic outcomes are evaluated through fragility analysis. The seismic capacity is extracted from the fragility parameters in terms of High Confidence of Low Probability of Failure (HCLPF) capacity. The outcome shows that the capacity degraded remarkably up to 21% for 100 years of service life. Finally, the seismic capacity degradation model is proposed through the investigation, which will be helpful to evaluate the capacity of the BI-NPP structure for any instant of time.

Development, seismic performance and collapse evaluation of steel moment-resisting knee braced frame

This paper introduces and assesses the seismic and collapse behavior of a new lateral load-resisting system referred to as steel Moment-Resisting Knee Braced Frame (MKF). A design method following the Performance Based Plastic Design (PBPD) procedure is proposed to analyze the structure and size the structural members. A prototype frame part of an office building located in Vancouver, British Columbia, Canada is then selected to demonstrate the design method and evaluate the performance of the proposed system. The prototype MKF is also designed using the conventional elastic approach in accordance with the National Building Code (NBC) of Canada. The seismic performance and collapse response of the proposed system are examined using the nonlinear static analysis, nonlinear response history analysis (NLRHA) and incremental dynamic analysis (IDA) performed on the prototype five-story MKF under potential sources of seismicity in the west coast of Canada including shallow crustal, subduction interface and subduction intraslab events. Fragility curves are finally developed using results of the IDA to obtain the collapse probability of the system. The results of the analyses are compared to those obtained from a steel Moment-Resisting Frame (MRF) counterpart designed in accordance with the PBPD and elastic approaches. Findings of the study show that the proposed steel MKF can efficiently satisfy the code-specified story drift limit and manifest the yielding mechanism assumed in design. The MKF designed according to the PBPD approach offers the lightest structure among all frames studied and yields a collapse probability lower than that of the MKF designed as per the elastic design method. The proposed system can be used in seismic design of steel multi-story buildings as an alternative to conventional steel MRFs.

Lateral Reliability Assessment of Eccentrically Braced Frames Including Horizontal and Vertical Links Under Seismic Loading

Eccentrically Braced Frames (EBFs) have been widely used in the last decades and proved their efficiency to resist strong earthquake intensities by providing suitable ductility and lateral stiffness. Using the PBPD method for the design, EBFs can fulfill the target performance objectives under major earthquakes. The most commonly used configurations are the K-shaped and the recent Y-shaped EBFs, which have the advantage that the links are independent of the beam and can be easily replaced after an earthquake without serious damage to the beam and slab. This study focused on the lateral reliability of both systems under seismic loading. Nonlinear static pushover and Incremental Dynamic Analysis (IDA) were performed on 5-story and 10-story K- and Y-shaped EBFs. A series of 14 near- and 7 far-field seismic records were considered to analyze and compare the inter-story drifts of both systems using the Seismostruct software. Moreover, Peak Ground Accelerations (PGA) and the different performance levels were also examined.

Seismic-resilient diagrid structures with hybrid buckling restrained braces

Typical diagrid systems inherently possess significant structural strength and stiffness, yet buckling of diagonal members is highly probable under seismic loadings which sequentially leads to a brittle behavior. Thus, in this study, the seismic resilience of typical diagrid structures is improved by proposing an innovative type of buckling restrained braces called “Hybrid Buckling Restrained Brace” (HBRB). Unlike the standard buckling restrained braces, HBRB is erected by at least two different steel materials, low yield point (LYP) steel and high-performance steel (HPS) in a single core. To this end, a set of 32 diagrid models with different configurations are designed and simulated numerically. Nonlinear static analysis and incremental dynamic analysis are conducted based on the FEMA P695 methodology to assess the ductility factor, over-strength factor, collapse safety and self-centering capacity of diagrid archetypes. Results indicate that the application of HBRBs significantly improve the seismic response of the diagrid structures. This is due to the early yielding of low yield point (LYP) steel material lead to improving the ductility of hybrid diagrid structures; and application of high performance steel (HPS) material lead to enhancing the post-yield stiffness of diagrid structures. Moreover, employing the HBRB increases the response modification factor (R), collapse margin ratio (CMR) and re-centering characteristic of diagrid structures. The findings of this study can assist structural designers to decide an appropriate form of HBRB in the height of diagrid structures.

Lightweight steel systems: Proposal and validation of seismic design rules for second generation of Eurocode 8

The current edition of Eurocode 8 (EN 1998 (CEN (2004))) does not explicitly cover the earthquake-resistant design of the Lightweight steel (LWS) buildings made with cold-formed steel (CFS) frame. Extensive research has been carried out in the past decade on this topic that provides a solid background for an update of the current provisions and the development of a new edition of the code. As part of the revision process of Eurocode 8, several activities are currently under development. Within this framework, this paper presents a set of design rules for the seismic design of LWS buildings based on background studies carried out at the University of Naples “Federico II”. A critical review of the provisions given by international design standards for the seismic design of LWS systems is also presented. The proposed design rules include a set of provisions for achieving the dissipative behaviour of Lateral Force Resisting System (LFRS) and predicting their design strength, together with behaviour factor values and geometrical and mechanical limitations. Different types of LFRS are analysed, namely CFS strap-braced walls and CFS shear walls with steel sheets, wood, or gypsum sheathing. Worked examples are also presented to show the applicability of the proposed design rules on a set of building archetypes. Validation numerical study is performed using both nonlinear static and incremental dynamic analysis approaches. Finally, the collapse performance of the archetypes is assessed following the seismic performance evaluation protocol of FEMA P695.

A study of the dynamic seismic performance index of building in Indonesia

ABSTRACT Recent earthquakes have exposed the vulnerability of buildings in Indonesia. An evaluation is needed to confirm the seismic performance of the structures. A seismic index is a method to determine building performance. This research aims to evaluate the performance using a dynamic seismic performance index dIs by considering Indonesia’s seismic hazard. The nonlinear incremental dynamic analysis with a bilinear hysteretic model was used in the analysis. The estimation method using the equivalent linearization and using the characteristic displacement response is proposed to estimate a dynamic ductility index dF. The dynamic seismic performance index tends to increase with an increase in the critical ductility factor. The dynamic ductility index dF represents a modification factor (R) that also increases with an increase in the critical ductility. The accuracy of the equivalent linearization is more accurate in the lower period, but the characteristic displacement method gives the closest estimate in the higher period.

Seismic response of nonlinear soil-structure interaction systems through the Preisach formalism: the Messina Bell Tower case study

In this paper the seismic response of linear behaving structures resting on compliant soil is addressed through the application of the Preisach formalism to capture the soil nonlinearities. The novel application of the Preisach model of hysteresis for nonlinear soil-structure interaction problems is explored through the study of the seismic response of a real structure. Through a harmonic balance procedure, furthermore, simplified nonlinear springs and dashpots are derived in closed form for a ready and accurate evaluation of the nonlinear soil-structure interaction response. The selected case study is the bell tower of the Messina Cathedral in Italy. The Bell Tower hosts the largest and most complex mechanical and astronomical clock in the world and it has been recently equipped by a permanent seismic monitoring system. A pertinent finite element (FE) model including the superstructure and the soil underneath, has been defined using authentic drawings and engineering design reports. The modal properties of the FE model have been compared with the experimental ones, identified from environmental noise recorded through the seismic monitoring system. Furthermore, the FE model has been validated by means of acceleration time histories recorded at different floors during two independent seismic events. A nonlinear incremental dynamic analysis of the Bell Tower has been also performed. The seismic response obtained by the complete FE analysis, has been compared with the proposed Preisach lumped parameter model, assembled with nonlinear springs and nonlinear dashpots. The results are well in agreement, offering an alternative promising strategy for the nonlinear soil-structure interaction studies.

Optimizing Seismic Capacity of Existing Masonry Buildings by Retrofitting Timber Floors: Wood-Based Solutions as a Dissipative Alternative to Rigid Concrete Diaphragms

The inadequate seismic performance of existing masonry buildings is often linked to the excessively low in-plane stiffness of timber diaphragms and the poor quality of their connections to the walls. However, relevant past studies and seismic events have also shown that rigid diaphragms could be detrimental for existing buildings and do not necessarily lead to an increase in their seismic performance. Therefore, this work explores the opportunity of optimizing the retrofitting of existing timber floors by means of a dissipative strengthening option, consisting of a plywood panel overlay. On the basis of past experimental tests and previously formulated analytical and numerical models for simulating the in-plane response of these retrofitted diaphragms, in this work nonlinear incremental dynamic analyses were performed on three case–study buildings. For each structure three configurations were analyzed: an as-built one, one having floors retrofitted with concrete slabs and one having dissipative diaphragms strengthened with plywood panels. The results showed that the additional beneficial hysteretic energy dissipation of the optimized diaphragms is relevant and can largely increase the seismic performance of the analyzed buildings, while rigid floors only localize the dissipation in the walls. These outcomes can contribute to an efficient seismic retrofitting of existing masonry buildings, demonstrating once more the great potential of wood-based techniques in comparison to the use of reinforced concrete for creating rigid diaphragms.

Quantification of seismic performance factors of beam-through steel frames with self-centering modular panel and replaceable hysteretic dampers

In recent years, self-centering modular panels (SCMPs) are proposed as a prefabricated portable lateral-load resisting member for potential application to new structure installation or seismic retrofit of existing structures. Several types of seismic fuse devices have been studied for implementation in the SCMPs, including tension-only braces, slit steel plate shear walls and replaceable hysteretic dampers (RHDs). Previous experimental testing and numerical simulation study results have demonstrated that these SCMPs show flag-shaped hysteretic response with anticipated seismic behavior. This study is focused on quantifying the seismic performance factors, including the response modification coefficient (R), the system overstrength factor (Ω0), and the deflection amplification factor (Cd), to enable seismic design of future SCMP structural systems in compliance with FEMA P695 procedure. The beam-through steel frames (BTSFs) with SCMPs installed into are used as an example to showcase the procedure. Numerous BTSF-SCMP-RHDs buildings, arranged in four performance groups (PGs), were designed as prototype structures based on assumed performance factor values. Next, these structures are investigated through nonlinear static analysis and incremental dynamic analysis. From this study, the response modification coefficient, the overstrength factor and deflection amplification factor are concluded to be 6.0, 3.0 and 6.0, respectively for the BTSF-SCMP-RHD structures. The results also indicate that the initial pre-stress level of post-tension (PT) cables has a major influence on the overstrength factor and collapse resistance capacity of BTSF-SCMP-RHDs system.

Seismic fragility assessment of Chilean skewed highway bridges

The 2010 Maule, Chile earthquake demonstrated that many bridges were highly vulnerable to seismic demands. Among these bridges, skewed multi-span prestressed concrete girder bridges supported on non-anchored elastomeric bearings were the most vulnerable ones. After the 2010 Maule earthquake, several damaged skewed bridges were repaired and retrofitted using an updated seismic design criterion. Therefore, this study aims to compare the seismic performance of typical Chilean skewed highway bridges in their original design (prior to 2010) and in their repaired condition (post 2010). With this aim, three-dimensional (3D) nonlinear finite element models of four skewed bridges, which were damaged during the 2010 Maule earthquake, are developed and analyzed. Nonlinear static and incremental dynamic analyses (IDAs) are conducted, and fragility curves are obtained to evaluate the short-term evolution of the Chilean design practices. Additionally, the influence of the skew angle, vertical seismic bars, modelling assumptions and anchorage of elastomeric bearings, on the seismic performance of Chilean skewed highway bridges is analyzed through IDAs and fragility curves. The results of this study show that repair measures considered after the 2010 Maule earthquake improve the seismic performance of skewed bridges and effectively prevent span unseating. However, the adopted measures do not significantly improve the performance at slight to moderate damage states. It is also demonstrated that the skew angle and deck-abutment pounding have significant influence on the seismic performance. Finally, the results show that an adequate modelling of vertical elements, such as elastomeric bearings, must be considered to avoid underestimating displacement demands.

Seismic performance and fragility analysis of infilled steel frame structures using a new multi-strut model

Whether UnReinforced Masonry (URM) infills should be employed as structural members in frame structures is a debatable subject in performance-based earthquake engineering. This paper presents a detailed assessment of the seismic response of infilled moment-resisting steel frames. A recently proposed multi-strut model is applied here to consider both the local and global effects of URM infills. The capability of the employed model in predicting the local and global effects of URM panels has previously been verified by the authors of this study. Two structures, a four-story building and a two-story building, were designed using seismic design codes, and one of the outer frames of each structure was selected for the numerical models. Based on the conventional layouts of URM panels in buildings, three different configurations are considered: the bare frame (model in which the URM panels are isolated from the surrounding frame), the infilled frame, and the soft-first story frame. Fifteen ground motion records have been used to perform nonlinear Incremental Dynamic Analyses (IDA), which were then employed to derive the fragility curves of the studied structures for the Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP) limit states. The results show that in lower limit states, the masonry infill leads to some beneficial effects. However, at more severe limit states, these beneficial effects diminish and at some point, revert to adverse effects. This is evident in the CP limit state, wherein the masonry infill weakens the seismic performance of the structure.

Seismic Vulnerability Assessment of a Stone Arch Using Discrete Elements

ABSTRACT Conservation of the European-built heritage is nowadays closely related to interventions in masonry construction. Since a significant part of these structures are located in earthquake prone zones, designing protective measures that ensure their preservation requires the assessment of the associated seismic vulnerability and the understanding of their degradation mechanisms. However, due to the presence of discontinuities between its constituent elements, the numerical simulation of the non-linear response of masonry structures subjected to strong earthquakes is a cumbersome task, especially when performed using the traditional finite element method. As an alternative, the discrete element method is particularly suitable for the numerical analysis of such structures under large, damaging loads. By allowing discrete displacements/rotations of individual bodies, and by automatically recognising new contacts between bodies, while eliminating obsolete ones, this numerical approach can simulate the complete detachment of discrete bodies initially in contact. The present paper illustrates the use of the discrete element method to assess the seismic vulnerability of stone arches. A probabilistic approach allows to consider the variability of the seismic action and the uncertainties in the definition of the material properties. First, an un-reinforced masonry arch is considered. Based on non-linear multi-directional incremental dynamic analyses, five damage states are proposed and the respective fragility curves are elaborated. To improve the arch’s seismic performance, two reinforcing solutions using steel elements are considered and analysed comparatively.

Seismic fragility assessment of self-centering hybrid precast walls subjected to mainshock-aftershock sequences

This study primarily investigates the seismic fragility of mainshock damaged self-centering (SC) hybrid precast walls in aftershocks, and the results are compared with equivalent conventional reinforced concrete (RC) walls. A 5-story case-study structure is selected and designed comparatively using SC walls and RC walls to resist all the lateral seismic forces for design requirements. Thereafter, nonlinear time history incremental dynamic analyses (IDA) are conducted for the two analytical wall models using 44 artificially constructed seismic sequences. In the first step, mainshock IDA analyses are performed followed by aftershock IDA analyses considering different mainshock damages on the considered wall models. Three mainshock damage levels relating to three distinct post-mainshock inter-story drift ratios are induced in both wall models. The IDA curves in terms of maximum inter-story drift and residual drift are produced and comparatively studied for both wall models at predefined mainshock damage levels. The results are investigated and compared regarding seismic collapse capacity, residual drift, and effects of the polarity of aftershocks. It indicates from the study that in a general sense, the SC walls and RC walls exhibit similar collapse capacities for both undamaged conditions (i.e., subjected to mainshock only) and damaged conditions (with distinct mainshock damage levels). However, SC walls are intrinsically designed with significantly reduced residual drifts (proved again in this study), which results in much less influence from the aftershock polarity as compared to RC walls.