Design Seismic Action Research Articles

Updating of the seismic fragility curves for RC buildings subjected to slow-moving settlements

The seismic assessment of reinforced concrete (RC) structures is commonly carried out neglecting potential previous damage induced by other phenomena, for example, those related to the actions of slow-moving settlements. Many efforts are dedicated by the research community in properly considering multi-hazard actions and their inter-relations on the structure, instead of a reductionist approach, to be included in the numerical models adopted for the assessment of the seismic vulnerability. Such consequences are increasingly becoming an important issue in the structural assessment, since several structures have an age close to, or higher than, their design life. In this work, a typological 3D case study RC building, chosen to represent gravity loads designed buildings constructed in Italy from the 1950s to the 1970s, is used. The seismic assessment of the building structural elements, caused by the design seismic action, is initially shown. Then, the seismic assessment is repeated, considering as point zero of the analysis the “damaged” building as consequence of slow-moving settlements, acting in different configurations, potentially due to different causes (e.g., landslides, subsidence). A novel comparison in terms of fragility curves is proposed between the safety condition of the building expected in both cases, with or without the consideration of the precedent induced displacements. The effect of the configuration of the previous slow-moving settlements on the seismic response is investigated, by showing that the application of the horizontal settlements has a stronger effect on the penalization of the seismic response of the building, but also the application of the vertical settlements produces a decreasing of the median seismic capacity.

Shallow three-dimensional shear wave velocity model for the Mexico City Basin

In this study, a simplified shallow three-dimensional shear wave velocity (Vs) model is presented for the Mexico City Basin. To this end, previous studies were carefully reviewed to assemble a database of Vs and site period measurements for the region. The new site period measurements obtained at the western edge of the Basin were compared to the existing 2004 Complementary Technical Standards of Mexico site period nominal map, (NTC, 2004) the Lermo et al. (2020) site period map, and Design Seismic Actions System (SASID), 2020 site period predictions. Each site period prediction method was shown to have differences with respect to the new measurements along the western edge of the Basin. However, there was no bias for the prediction methods with the Lermo et al. (2020) and SASID predictions, demonstrating less error between the measured values than the NTC (2004) predictions. To develop the three-dimensional Vs model, the shallow (top 60 m) subsurface was divided into five generalized soil layers. The site period was used as the only input for the three-dimensional Vs model to simplify and maximize the model’s applicability. The performance of the model was assessed by comparing the measured and predicted Vs profiles. Overall, the three-dimensional Vs model developed in this study is a valuable tool that can be used along with geophysical estimates of deeper structure for ground motion modeling and preliminary site response studies along with other benefits to the seismic resiliency of the region.

ПРОБЛЕМЫ ИСПОЛЬЗОВАНИЯ ДИНАМИЧЕСКИХ МЕТОДОВ РАСЧЕТА СЕЙСМОСТОЙКОСТИ СООРУЖЕНИЙ ПО АКСЕЛЕРОГРАММАМ ЗЕМЛЕТРЯСЕНИЙ.

The main problems of structures dynamic calculation using earthquake accelerograms are analyzed. The problems of setting design accelerograms, modeling rigidity and damping structure properties, as well as substantiating the seismic resistance criteria of structures are considered. The design seismic action generated for the structure and for the construction site is considered. Requirements are formulated for the accelerogram digitization and for the number of design accelerograms for a construction site, sufficient for assessing the structure seismic resistance. The difficulties of constructing design accelerograms and taking into account in calculations the accumulation of damage in a structure during seismic vibrations are indicated. It is noted, that calculations using accelerograms of strong earthquakes can be easily made only for structures with given parameters of limit states. For linear calculations, the problem of taking the system damping into account is analyzed. The criteria for limit states limiting the work of plastic deformation forces and the damageability of a structure are considered.

Biaxial capacity envelopes for the capacity design of biaxially loaded shallow foundations

Earthquakes cause bi-directional horizontal actions on structures. While Eurocode 8 recognizes this fact and mandates that the horizontal components of the design seismic action shall be taken as acting simultaneously, neither Eurocode 8 nor the existing literature provide the interaction behaviour of biaxially loaded shallow foundations. Further, it is to be noted that, in a real structure, the horizontal force and moment acting on a foundation, are inter-related through the effective height of the supported column. The present study considers the inter-relation between horizontal force and moment to generate the normalised vertical load-biaxial horizontal load (V-Hx-Hy) capacity envelopes, which can also be used to directly obtain the V-H-M and V-Mx-My capacity envelopes, considering the effective height of the structure. To develop the V-Hx-Hy capacity envelopes, three-dimensional (3D) finite element limit analyses are performed on surface as well as embedded square and rectangular footings, resting on dry sand. The main factors affecting the capacity of a biaxially loaded shallow foundation are discussed. The effect of ground acceleration on the capacity envelope is highlighted. Limitations of the current design procedures for the design of biaxially loaded foundations are demonstrated, through a case study. Finally, a procedure for the capacity design of biaxially loaded shallow foundations, using capacity envelopes, is proposed.

Seismic reliability of Italian code‐conforming bridges

AbstractSeismic reliability assessment of selected bridge structures code‐conforming with respect to the current Italian practice is carried out. Two viaducts, tall and shallow, and two highway overpasses, with traditional seat‐type or integral abutments, are considered. Each structure is ideally placed at three reference sites, that is, Milan, Naples and L'Aquila, characterised by low, moderate and high seismic hazard, respectively. At each site, a soil profile representative of typical local conditions is defined for foundation design, site response analysis and soil‐structure interaction modelling. Probabilistic seismic hazard is used in conjunction with multiple‐stripe non‐linear dynamic analysis, featuring conditional‐spectrum compatible ground motions, to establish the failure rate with respect to two purposely defined and functionality‐related performance levels. It is confirmed the decreasing seismic reliability with increasing design seismic action, already observed for other structural types, and it is shown that integral abutment overpasses tend to be more reliable than traditional ones, even seismically isolated ones. The results are of larger interest given the closeness of the Italian code to the Eurocode.

Exceedance of design seismic actions during the 2016-2017 central Italy seismic sequence: sensitivity to two seismic hazard models

In Italy, seismic ground motion intensity for structural design relies on probabilistic seismic hazard analysis (PSHA). Research has shown that, even in the case of a moderate magnitude earthquake, it is expected that ground motion intensities larger than the design counterparts are observed at some sites in the epicentral region. The area where such an exceedance has possibly occurred can be assessed via ShakeMap. In the case of seismic sequences, ShakeMap envelopes allow to identify the fraction of the region of interest subjected to at least one exceedance of design seismic actions. For the 2016-2017 central Italy sequence, ShakeMap envelopes reveal that exceedance of the design intensity enforced by the current building code occurred in an area covering thousands of square kilometers, depending on the spectral and exceedance return period of the design intensity. This study quantifies the exceedance area of ground motion intensity according to the PSHA results based on two alternative PSHA models for Italy. One is that at the basis of the official PSHA for Italy adopted by the current building code, known as MPS04; the other relies on a grid-seismicity source model deriving from a set of source models recently developed for a new PSHA study for the country (MPS19). Looking at ShakeMap envelopes, it is found that the estimated exceedance area is of the same order of magnitude for the two hazard models, at least for the spectral and exceedance return periods considered herein.

Shear wave velocity and site period measurements for the western portion of the Mexico City Basin following the Mw7.1 2017 Puebla–Morelos, Mexico, earthquake

Dynamic site characterization was performed at 25 sites located on the western portion of the Mexico City Basin that were severely damaged during the Mw7.1 2017 Puebla–Morelos, Mexico, earthquake. Testing was conducted using active and passive seismic surface wave methods and the microtremor horizontal-to-vertical spectral ratio method to determine site periods and develop one-dimensional (1D) shear wave velocity ( Vs) profiles for the first 60 m of the subsoil. The measured site periods were compared to site period maps developed in 2004 and 2020 along with values computed using the Design Seismic Actions System (SASID) software following the 2020 version of the Complementary Technical Norms for Seismic Design (NTC-DS). The most noticeable biases in the predictions from the 2004 site period map were observed between the boundary of Zone II and Zone IIIa, at which site periods are overestimated. These estimates were improved upon in the 2020 site period map and showed a close similarity with SASID computed site period values. The Vs, depth, and thickness of the lacustrine clay layer were also determined to be quite variable within the basin. The softest sites are located between the lakebeds with a Vs between 45 and 57 m/s. Sites located toward the outer rim of the North lakebed have a higher Vs between 80 and 100 m/s. The thickness of the clay layer varies significantly in the western side of the Basin with values ranging between approximately 3 and 34 m. Overall, the results of this study indicate good agreement with the model embedded in the SASID software. The results (1) emphasize the need to regularly monitor changes that occur over time in the lacustrine clay layer, (2) complement the development of models that improve our understanding of wave propagation within the Basin, and (3) update and improve Mexico City’s Norms.

Sequence-Based Hazard Maps for the United Kingdom

ABSTRACT The current practice of probabilistic seismic hazard analysis (PSHA) does not take into account that earthquakes actually occur in time–space clusters. The input for PSHA is based on declustered seismic catalogs, used to characterize only the mainshocks, that is, the largest magnitude events within each cluster. However, the so-called sequence-based PSHA (SPSHA; Iervolino et al., 2014) allows us including the effect of aftershocks in hazard analysis, that is, the events following the mainshock, still conveniently resourcing from declustered catalogs. In the United Kingdom (UK), the seismic source model developed for the national seismic hazard assessment has been recently updated by the British Geological Survey (BGS, 2020). In this study, the source model developed by the BGS (one directly derived from it, in fact) is used to implement SPSHA in the UK. The calibration of the model for the occurrence of aftershocks, that is, the modified Omori’s law, is fitted on a few sequences and under some simplifying assumptions. The results, represented by hazard maps for selected spectral ordinates and exceedance return periods of interest for structural engineering, are compared to the PSHA counterparts to discuss the increase in the design seismic actions when the effects of aftershocks are considered. The maps show that, based on the modeling of aftershock sequences considered in the study, in the UK this increase can be up to 14%, at least for the spectral ordinates and exceedance return periods herein investigated. The discussed maps are provided as supplemental material to this article.

Evaluation of seismic collapse resistance of reinforced concrete frames designed with nonlinear viscous dampers

In earthquake engineering, damping devices are commonly used to enhance the energy dissipation capacity of structures and help control the structural dynamic response under seismic excitation. In the design of building structures with integration of seismic dampers, the section sizes of structural components and the amount of reinforcement may be reduced so that the seismic performance of the structure remains comparable to a conventional design without dampers under design seismic actions. Understandably such changes in the design scheme can lead to some different structural behavior under different levels of seismic actions; however there is little information in the literature on this subject, particularly with regard to the capacities of the structures in resisting collapse in the event of worst case scenario earthquakes. This paper presents an evaluation of the collapse resistance capacities of structures designed with integration of seismic dampers. A numerical model for the collapse resistance analysis of reinforced concrete (RC) frame structures is firstly explored. To ensure that the model is capable of capturing the collapse resistance capacity, a material state based elemental failure criterion is adopted and the adequacy of this is verified against relevant experimental data. The numerical model is then employed to evaluate the collapse resistance performances of RC frames designed for different earthquake intensities with and without nonlinear viscous dampers via collapse fragility analysis. The results show that when designed for low to moderate seismic intensities, the frame structures designed with integrated dampers (DDF structures) exhibit slightly higher collapse resistance capacity as compared with the conventional design without damper (CDF structures). However, when designed for high seismic hazard levels, the DDF structures tend to have a markedly lower collapse resistance capacity than their conventional counterparts. A remedial scheme is proposed to improve the collapse resistance performances of frames designed with consideration of dampers in high seismic hazard applications, and the effectiveness of such a scheme is further evaluated through the fragility analysis.

Macroseismic intensity hazard maps for Italy based on a recent grid source model

Seismic hazard maps from probabilistic seismic hazard analysis or PSHA collect, at different sites, the values of the (site-specific) ground motion intensity measures of interest that, taken individually, have the same exceedance return period. For large-scale analyses, a widely used intensity measure is the macroseismic (MS) intensity, that provides an assessment of the earthquake effect based on the observed consequences in the hit area. Hazard maps can be developed in terms of MS intensity, and some examples exist in this respect. In the case of Italy, the last MS hazard map is based on the same seismic source model (known as MPS04) adopted to derive the design seismic actions of the current building code, a study dating more than ten years ago. It provides results in terms of countrywide Mercalli–Cancani–Sieberg (MCS) intensity level with 475 years return period. This short paper presents and discusses MCS probabilistic seismic hazard maps for Italy based on a recent grid-seismicity source model, herein named MPS19, synthetizing the large effort of a wide scientific community. The results, which are obtained by means of classical PSHA, are given in the form of maps referring to the 475 years return period, and also others of earthquake engineering interest. Moreover, it is discussed that the return period does not univocally identifies the MS intensity because, although MS is, by definition, a discrete random variable, it is modelled, in a given earthquake, by means of a normal distribution, that is, treated as continuous. Thus, the maps of the minimum return period causing the occurrence or exceedance of different MCS intensities are also provided. Finally, the comparison between the 475 years return period hazard map presented and the one which is currently the point of reference in Italy, that is, computed using MPS04, is briefly discussed. All the computed maps are made available to the reader as supplemental material.

Exceedance of design actions in epicentral areas: insights from the ShakeMap envelopes for the 2016\u20132017 central Italy sequence

ShakeMap is the tool to evaluate the ground motion effect of earthquakes in vast areas. It is useful to delimit the zones where the shaking is expected to have been most significant, for civil defense rapid response. From the earthquake engineering point of view, it can be used to infer the seismic actions on the built environment to calibrate vulnerability models or to define the reconstruction policies based on observed damage vs shaking. In the case of long-lasting seismic sequences, it can be useful to develop ShakeMap envelopes, that is, maps of the largest ground intensity among those from the ShakeMap of (selected) events of a seismic sequence, to delimit areas where the effects of the whole sequence have been of structural engineering relevance. This study introduces ShakeMap envelopes and discusses them for the central Italy 2016–2017 seismic sequence. The specific goals of the study are: (i) to compare the envelopes and the ShakeMap of the main events of the sequence to make the case for sequence-based maps; (ii) to quantify the exceedance of design seismic actions based on the envelopes; (iii) to make envelopes available for further studies and the reconstruction planning; (iv) to gather insights on the (repeated) exceedance of design seismic actions at some sites. Results, which include considerations of uncertainty in ShakeMap, show that the sequence caused exceedance of design hazard in thousands of square kilometers. The most relevant effects of the sequence are, as expected, due to the mainshock, yet seismic actions larger than those enforced by the code for structural design are found also around the epicenters of the smaller magnitude events. At some locations, the succession of ground-shaking that has excited structures, provides insights on structural damage accumulation that has likely taken place; something that is not accounted for explicitly in modern seismic design. The envelopes developed are available as supplemental material.

Seismic Vulnerability Assessment of Existing Italian Hospitals: The Case Study of the National Cancer Institute “G. Pascale Foundation” of Naples

Introduction: A large portion of the Italian built heritage is characterized by a significant seismic vulnerability since many structures were designed with outdated criteria, i.e., without accounting for seismic actions. This aspect is particularly relevant for strategic structures and infrastructures, whose functionalities are crucial in case of seismic events. Objective: The main aim of the present paper is to share the key findings related to the seismic vulnerability assessment of the National Institute for the Study and Treatment of Cancer (IRCCS) “Giovanni Pascale Foundation” in Naples. In particular, the main evidences could be easily extended to existing hospitals realized in the last century, with the main reference to: construction techniques, quality of constructional material, overt and convert seismic vulnerabilities and possible intervention strategies for risk mitigation. Methods: In the present paper, the assessment methodologies adopted for such a strategic hospital complex are provided, focusing in particular on: i. preliminary research of original design documents and on-site investigation for determining constructional details; ii. material tests on structural elements; iii. vulnerability seismic assessment by means of non-linear FE analyses (push-over and capacity spectrum method); iv. recommendations on retrofitting measures and cost estimations. Results: The conducted study puts into clear evidence the inadequacy of the investigated buildings to face the design seismic actions provided by the current Italian code and thus showed the significant seismic vulnerabilities affecting the Institute “G. Pascale Foundation” of Naples. Among these, particular attention has also been focused on the so-called intrinsic vulnerabilities, namely the ones not measurable explicitly and interesting non-structural elements (e.g., connection of shelves, stained glass windows, facilities, etc.). Conclusion: The presented case study highlights the strong seismic vulnerability affecting structures realized in the past century, despite their strategic functions. On the whole, the examined structures can be considered as representative of this building typology, and the adopted calculation criteria, as well as the assumptions of the assessment process, could be easily extended to similar case studies.

Probability assessment of structural response modification factor of RC frames by the demand-capacity-factor method

The values of structural response modification factor R are fundamentally critical in the specification of design seismic action for buildings. However, there are significant differences in the values of R in the codes or standards in different countries. In this paper, 15 reinforced concrete (RC) frames with 3-story, 5- story, 8-story, 10- story, and 12-story for design basic earthquake acceleration 0.05 g, 0.10 g, and 0.20 g are designed using the R≈3 implicit in the current Chinese codes. The accuracy of finite element models is verified via data from the shaking table test. A Demand-Capacity-Factor Method (DCFM) is used to evaluate R. The results show that the RC frames designed using the R≈3 and redesigned using the R≈6 can all meet the expected safety goals-against collapse under major earthquakes. The R≈3 implicit in the current Chinese codes are relatively conservative and the seismic influence coefficient curves under minor earthquakes should be improved.

Seismic performance assessment of non-code-conforming and code-conforming supporting structures of elevated tanks using conventional and risk-based decision models

The seismic performance of the supporting structure of the replica of an elevated tank that collapsed during the Kocaeli earthquake and its variant designed according to Eurocode 8 provisions was investigated. First, the performance of the tank was verified for the Kocaeli ground motion. Results of non-linear seismic response history analysis using simplified models accounting for different tank filling levels showed that the simplified model could provide qualitatively the same damage as were observed during the earthquake, while the seismic performance of the code-conforming tank was satisfactory. Then, the seismic performance assessment of the non-code- and code-conforming tanks was further investigated using the conventional decision model, which accounts for the demand-to-capacity ratio given the seismic design action, the conditional risk-based decision model and the risk-based decision model which utilise, respectively, the probability of exceeding a designated limit state for a given design seismic action and for a given period. The seismic performance of the non-code-conforming elevated tank was found insufficient by any of the three decision models, which indicated the need for action towards risk reduction for such structures. The opposite was realised for the code-conforming tank. However, the conventional decision model may be misleading because it indicated that the structure might be considered overdesigned, while risk-based decision model showed that the seismic performance of the code-conforming tank was close to the target value, set to 1% in 50 years. In the future, risk-targeted design approaches can improve decision-making in the design of critical components of industrial facilities.

Mathematical modeling of the transmission pipeline under the influence of earthquake seismic waves

The stress-strain state of an underground transmission pipeline under the action of earthquake seismic waves is considered. The main objective of this study is the construction of a mathematical model with the analytical solution for lower estimation of the influence of earthquake seismic waves on the transmission pipeline. The spectra of the design seismic actions of the earthquake are determined on the basis of parameters of real seismograms of past earthquakes. The generalized functions of seismic impulses are constructed. The transmission pipeline is modeled by a thin bar. Equations of pipeline motion using the Laplace transformation in time are solved, stresses are determined. The numerical example is considered. The results of calculations on the theories of Kirchhoff and Timoshenko are compared. Graphs of stress changes depending on the earthquake’s strength in points are given. The limiting value of the earthquake magnitude resulting in large stresses and deformations is determined. As a result, the transmission pipeline is destroyed.

A Resilience and Robustness Oriented Design of Base-Isolated Structures: The New Camerino University Research Center

This paper analyses the new Research Centre designed for the University of Camerino and entirely financed by the national Civil Protection Department (DPC), following the seismic events in Central Italy in 2016. The building has been designed to guarantee speed of execution as well as a high level of safety, especially regarding seismic actions. The structural solution was to create an isolated system with a steel braced super-structure with pinned joints and r.c. sub-structures able to adapt to the complex morphology of the area. As described in the first part of the paper, design choices have been made to achieve a high level of resilience and robustness, i.e. to limit damage to structural and non-structural components and equipment under moderate and design seismic actions and to avoid disproportionate consequences in the event of extreme actions, larger than the design ones. In the second part of the paper, specific risk analyses have been carried out to evaluate the real performance of the building under increasing intensity levels, with reference to both serviceability and ultimate conditions. To this purpose a site-specific hazard study was first conducted, then nonlinear analyses were performed using a hazard-consistent set of records with return periods ranging from TR=60 years to TR=10000 years. The main demand parameters of both the isolation system and the super-structure were recorded and capacity values corresponding to different ultimate and damage limit conditions were defined. The results obtained in terms of demand hazard curves show that the building performances in terms of rustiness and resilience are very high, confirming the efficacy of the strategies adopted in the design.

Loss impact factors for lifetime seismic loss assessment of steel concentrically braced frames designed to EC8

ABSTRACTThis study employs multiple earthquake time-history response simulations, and the FEMA P-58 performance assessment methodology to evaluate the influence of key design parameters on the lifetime seismic repair costs incurred by case study concentrically braced frames (CBFs) designed to Eurocode 8. The parameters considered include structural mass, stiffness (natural period) and ductility (behaviour factor). A new factor termed the Loss Impact Factor (LIF), is used to quantify the influence of each of these parameters on lifetime costs. Under dissipative seismic design principles, bracing members in CBFs may behave inelastically under infrequent, high-intensity earthquakes. Larger values of the design behaviour factor, q, selected by the structural engineer result in higher ductility demands during these earthquakes, but also reduce the design seismic action, leading to smaller, lighter and more flexible structural members. Hence, variations in one parameter necessarily influence the others, as well as initial construction cost. The variation in expected lifetime seismic repair costs with respect to each of these parameters, which is less clear, is the subject of this paper. Costs are shown to reduce with increased structural mass, stiffness and initial cost, with the impact of the latter two parameters generally increasing with both seismic hazard and frame height.

11.44: An integrated experimental and numerical assessment of force‐based design for concentrically braced steel frames

ABSTRACTThis study uses an integrated experimental and numerical approach to assess the use of the force‐based design (FBD) methodology presented in Eurocode 8 (EC8) for multi‐storey steel concentrically‐braced frames (CBFs).In the EC8 approach, the design seismic action is defined by first generating an elastic response spectrum. This spectrum is reduced to create the design spectrum by applying an appropriate behavioural factor (q) to account for energy dissipation. The value of q chosen depends on the form of the lateral‐load resisting structure, the structural material(s) to be used, the ductility class and the degree of irregularity in the structural layout. The design base shear force calculated from the design spectrum is used to estimate the seismic forces on the structure and hence determine the final member cross‐section sizes.In this study, the FBD approach to the design of structures presented in Eurocode 8 is described and applied to 4‐ and 8‐storey CBF structures. Both dissipative (Ductility Class High – DCH) and non‐dissipative (Ductility Class Low – DCL) design is considered for each structure.A numerical modelling approach developed using the OpenSees seismic analysis software and validated from a series of full‐scale experimental tests of single‐storey CBFs is outlined. The two‐dimensional reference model assigns appropriate out‐of‐plane rotational stiffnesses to the ends of the bracing members based on the strength and geometry of gusset plates specified.The experimental work used to validate the model, carried out as part of the BRACED transnational research project funded by the European Commission's Seventh Framework Programme (FP7) is briefly described. The experimental observations support model validation at different levels of earthquake ground motion including elastic, inelastic and ultimate response conditions.The validated numerical modelling approach is used to perform a series of non‐linear time history analyses (NLTHA) of the designed 4‐ and 8‐storey frames by subjecting them to appropriately scaled simulated ground motion accelerations. The key recorded responses of the NLTHA of the modelled frames (displacements, drift, brace forces and ductility demands) are compared, and the implications of the assumed energy dissipations are discussed.

IM‐based and EDP‐based decision models for the verification of the seismic collapse safety of buildings

SummaryDecision models for the verification of seismic collapse safety of buildings are introduced. The derivations are based on the concept of the acceptable (target) annual probability of collapse, whereas the decision making involves comparisons between seismic demand and capacity, which is familiar to engineering practitioners. Seismic demand, which corresponds to the design seismic action associated with a selected return period, can be expressed either in terms of an intensity measure (IM) or an engineering demand parameter (EDP). Seismic capacity, on the other hand, is defined by dividing the near‐collapse limit‐state IM or EDP by an appropriate risk‐targeted safety factor (γim or γedp), which is the only safety factor used in the proposed decision model. Consequently, the seismic performance assessment of a building should be based on the best possible estimate. For a case study, it is shown that if the target collapse risk is set to 10−4 (0.5% over a period of 50 years), and if the seismic demand corresponds to a return period of 475 years (10% over a period of 50 years), then it can be demonstrated that γim is approximately equal to 2.5 for very stiff buildings, whereas for buildings with long periods the value of γim can increase up to a value of approximately 5. The model using γedp is equal to that using γim only if it can be assumed that displacements, with consideration of nonlinear behavior, are equal to displacements from linear elastic analysis.

An evaluation of the GSA Nonlinear Static Progressive Collapse Methodology applied to EC 8 Seismically Designed RC Moment Frames

This study aims at evaluating the progressive collapse potential of RC framed structures designed to Eurocode 8 with varying design ground accelerations and ductility classes. Four typical 11-storey RC framed structures were designed with ground accelerations of 0.10g and 0.25g at low, moderate and high ductility classes. Analysis of the performance levels and progressive collapse vulnerability of these structures was carried out considering the four column loss scenarios and acceptance criteria specified by the General Service Administration (GSA) document. It was observed that high design ground acceleration and low design ductility classes increase the progressive collapse resistance of EC 8 designed RC framed structures. This observation is counter-intuitive to the principles underpinning the EC 8 design code as higher design ductility class is expected to enhance the energy absorption capacity or ductility of buildings with same design seismic action but varying ductility classes. It is concluded that the use of GSA to assess buildings designed to EC 8 must be modified to include the effects of both design action and design ductility class of a structure. The location of the lost column was also found to be very influential on the progressive collapse resistance of the structure.