Nonlinear Dynamic Procedure Research Articles

Seismic analysis of RC building with plan irregularity in Baghdad/Iraq to obtain the optimal behavior

Abstract A study was conducted for four-story reinforced concrete (RC) structure existing in Baghdad-Iraq (residential building) to evaluate the accuracy and reliability of the equivalent lateral force procedure (ELFP) analysis and the response spectrum model (RSA) according to Iraqi seismic code (ISC 2016) for designing and analyzing irregular buildings. The building was classified as an irregular in plan according to American Society of Civil Engineers (ASCE 7-16). The seismic behavior of the building was investigated by verifying many parameters: the ratio of shear demand to shear strength on the columns ( V V / V n {V}_{n} ), internal force (bending moment, shear force, and axial force) for beams and columns, and the inter-story drift ratio (IDR) obtained from the (ELFP and RSA); then, the results were compared with the nonlinear static procedure (NSP) and the nonlinear dynamic procedure (NDP) according to ASCE 7-16. Also, this study investigated the effects of the higher modes in the plan (roof plan displacement). From the results, it can be concluded that ELFP and RSA are not a suitable analysis for asymmetric structures and should use appropriate methods such as the NSP and NDP.

Discussion of “ASCE/SEI 41 assessment of reinforced concrete buildings: Benchmarking nonlinear dynamic procedures with empirical damage observations”

This is a Discussion of the following article: Cook D., et al. (2023). ASCE/SEI 41 assessment of reinforced concrete buildings: Benchmarking nonlinear dynamic procedures with empirical damage observations, Earthquake Spectra, August 2023, Vol. 39, No. 3, pp. 1721–1754.

Simplified Nonlinear Dynamic Analysis by Hexagonal Collapse Surface Model of Steel Frame Structure

AbstractBased on the need for effective evaluation of multistorey structures response to seismic loading, this research includes the study of simplified nonlinear dynamic analysis (SNDA) by hexagonal collapse surface model. Existing conventional analysis methods such as FEMA440, restrict the extended use of Nonlinear Static Procedure (NSP) and Nonlinear Dynamic Procedure (NDP) by using the equivalent one‐degree‐of‐freedom (SDOF) model on multi‐degree‐of‐freedom (MDOF) structure. A large error known as Multiple‐Degree‐of Freedom Effects occurs in the elastoplastic behavior. To overcome the limitations of this analysis technique, the understanding of it in the entire structural system due to the influence of the higher‐order vibration modes are investigated, in addition to distinguish the elastoplastic behavior of a structure more precisely. Based on the important collapse mechanisms that are probable to occur during earthquake response, the development of a simplified dynamic analysis technique in which higher‐order vibration mode components were extracted to construct the plastic collapse safety region of a structure. Simplified nonlinear dynamic analysis (SNDA) aims to develop such method whereby multiple vibration mode components are properly considered. Primary and secondary mode of vibrations are generally examined with multiple load patterns corresponding to the condition whereby several independent variables reach maximum concurrently. The formation of hexagonal plastic collapse surface from the probability limit analysis based on proportional load results was discussed. The target for this study is to investigate the competency of this simplified analysis approach in seismic response of structure evaluating techniques.

Assessing seismic performance of code-compliant steel special moment frames using ASCE 41-17

ASCE 41 standard, increasingly used by practitioners, is a desirable tool to evaluate the seismic performance of different types of structures according to the Performance-Based Earthquake Engineering framework. The latest edition of this standard (ASCE 41-17) has undergone significant changes with respect to its previous versions, which could substantially affect the results of structural performance evaluation. Within this context, the present study performs a comprehensive quantitative investigation of the seismic performance of steel structures based on the component-level Tier 3 systematic evaluation procedure of ASCE 41-17, using both nonlinear static (conventional and enhanced pushover analyses) and dynamic analyses. The evaluation is conducted on six ASCE 7 code-compliant steel special moment frames considering different heights (i.e., 6, 12, and 18 stories) and two versions of the seismic design code (i.e., ASCE 7-10 and -16). The results of the nonlinear dynamic procedure demonstrate that both the ASCE 7-10 and -16 designed buildings satisfy the acceptance criteria of ASCE 41-17. It is also shown that the linear dynamic procedure recommended by ASCE 41-17 to supplement the results of the nonlinear static procedure for buildings with significant higher modes effect cannot provide an accurate estimation of the structural performance compared to enhanced pushover procedures. Additionally, the comparison of the structural performance evaluation between the ASCE 41-13 and -17 indicated that the previous edition of this code (ASCE 41-13) is overly conservative for columns compared to ASCE 41-17. Finally, the applicability of using the modeling parameters recommended by ASCE 41 for simulating the elements’ behavior in case of the lack of sufficient available experimental data is demonstrated.

ASCE/SEI 41 assessment of reinforced concrete buildings: Benchmarking linear procedures and FEMA P-2018 with empirical damage observations

The US consensus standard for seismic evaluation and retrofit of existing buildings, ASCE/SEI 41, establishes provisions for seismic analysis procedures that vary in complexity and fidelity. Although ASCE/SEI 41 provides detailed nonlinear dynamic procedures, most engineers rely on simpler methods to evaluate building seismic performance and retrofit, particularly the ASCE/SEI 41 linear procedures and, more recently, the FEMA P-2018 methodology for evaluating collapse potential. Under ideal conditions, these procedures identify similar structural deficiencies. However, evaluation outcomes in practice may differ due to the complexity of real building response, approximations used in modeling and analysis, and level of intentional conservativism that reflects the limitations of the procedures. To quantify these differences, this study considers six reinforced concrete buildings that sustained damage in real earthquakes or in shake table tests and compares the performance assessed by the ASCE/SEI 41 linear and nonlinear dynamic procedures, as well as the FEMA P-2018 seismic evaluation methodology. The results show that for these highly damaged buildings, the overall performance level estimated from the ASCE/SEI 41 linear procedures is consistent with observed damage. In general, the procedures also correctly identify the story with the most damage and the component failure mode. However, the ASCE/SEI 41 linear procedure generally underpredicts drift response and greatly overpredicts peak floor accelerations. Though these are not directly used to evaluate structural performance, they are related to component deformation and force demands, respectively. Moreover, the linear procedures predict damage in components that would be precluded by yielding or failure of other components in the load path. Results from the FEMA P-2018 methodology for the six buildings provide more distinction between buildings than the ASCE/SEI 41 Collapse Prevention performance level. The results also suggest the FEMA P-2018 limit-state mechanism analysis can provide supplemental information to support and improve the ASCE/SEI 41 linear procedures.

ASCE/SEI 41 assessment of reinforced concrete buildings: Benchmarking nonlinear dynamic procedures with empirical damage observations

ASCE/SEI 41 is the consensus US standard for the seismic evaluation and retrofit of existing buildings. Although the performance-based engineering standard is based on decades of research and has been significantly vetted by ASCE and other committees, it is unclear how well the evaluations capture the seismic response of real building systems. This article examines six, primarily nonductile, reinforced concrete buildings, including four damaged in earthquakes and two experimental structures tested and damaged on shake tables, to compare the measured response and observed damage to simulated outcomes produced following ASCE/SEI 41 nonlinear dynamic procedure. The results show that the simulations are generally able to capture the story mechanism and peak transient story drift demands at the critical story (predicted values are typically within ±20% of the measured values). However, drifts at non-critical stories and floor accelerations at all stories show greater error relative to the measured responses. At the component level, the simulations, in most cases, correctly identify the location(s) of the critical component(s) and the failure mode (e.g. flexure vs shear). However, the extent of the damage is overestimated in some cases. These results form the basis for recommendations for column, beam, and wall modeling procedures that can be used to improve ASCE/SEI 41.

Soil–Structure Interaction Effect on the Resistance of a Steel Frame against Progressive Collapse Using Linear Static and Nonlinear Dynamic Procedures

In recent years, increases in terrorist attacks or other unexpected explosions have shown that their effects can cause critical damages to buildings and cause partial or total collapse of buildings. This chain collapse mechanism is named a progressive collapse. Subsoil effects on a building are often ignored in studies on progressive collapse. In this study, the effect of soil–structure interaction on the risk of progressive collapse of a steel frame is investigated by using the modified Vlasov model, which has not been used in the studies on progressive collapse before. For this purpose, a steel building model was investigated. A linear static procedure (LSP) and nonlinear dynamic procedure (NDP) with alternative path method were used for the analysis of the frame. SAP2000 software was used to model subsoil effect on the frame via an interface coded in MATLAB interactively. The results from the analyses showed that the soil–structure interaction effect can significantly affect the progressive collapse resistance of the building.

Behavior assessment of asymmetrical building with concrete damage plasticity (CDP) under seismic load

According to the research conducted, the asymmetric multi-storey buildings are complex and suffer from severe damage caused by increased torsional response. This paper addresses the behavior assessment of setback building with irregularity in the plan under severe seismic event such as Kobe earthquake. Using three-dimensional model, the structure is subjected to seismic waves in the three directions through ground accelerations. Nonlinear dynamic procedures have been used by means time-history analysis method. The mechanical model describes physical nonlinear behavior with damage and plasticity showing the regions of cracking propagation, mainly the columns-beams connections and the whole column as well, corroborating the weak column and strong beam concept. The slabs did not present significant failures despite indicating damage regions on the borders of the first floors.

On the Applicability of Conventional Seismic Design Methodologies to Hybrid RC‐Steel Systems

AbstractThis paper analyses the adequacy of the q‐factor approach when applied to hybrid RC‐steel systems. This approach is prescribed by EC8‐1 as the basic design method, and usually referred to as the most conservative. However, due to its simplicity and popularity for the design of new structures, practitioners are more likely to resort to it, than to the more complex nonlinear static and dynamic procedures, when dealing with the seismic assessment and strengthening of existing RC buildings. A case‐study application is thus presented to analyse and discuss the difficulties a practitioner will face when assessing the efficiency of a steel‐brace retrofitting system designed within the framework of EC8‐1.

Modified Partial Capacity Design (M-PCD): achieving partial sidesway mechanism by using two steps design approach

Partial Capacity Design (PCD) has been developed by using magnification factor to keep some columns undamaged during major earthquake. By doing so, the structures will experience the partial side sway mechanism which is also stable, instead of the beam sidesway mechanism. However, in some cases, structures designed by PCD method failed to show the partial side sway mechanism since unexpected damages were still occurred at some columns. In this research, modification of PCD method is proposed by using two structural models in the design process. The first model is used to design beams and columns which are allowed to experience plastic damages, while the second model is used to design columns which are intended to remain elastic when the structure is subjected to a target earthquake. Two nominal earthquakes corresponding to Elastic Design Response Spectrum (EDRS) level with seismic modification factors (R) of 8.0 and 1.6 are used in the first and second structural models, respectively. It should be noted that the second model is identical to the first model except that the stiffnesses are reduced for elements to simulate potential plastic damages. This proposed method is applied to symmetrical 6 and 10 storey buildings with seismic load according SNI 1726:2012 and with soil classification of SE in Surabaya city. A Non-linear Static Procedure (NSP) or pushover analysis and Non-linear Dynamic Procedure (NDP) or time history analysis are employed to evaluate the performance of the structure. The evaluation is conducted at three earthquake levels which are nominal earthquake that is used in second model, earthquake corresponding to EDRS level, and maximum considered earthquake (MCER) specified by the code (50% higher than EDRS level). The building performances satisfy the drift criteria in accordance with FEMA 273. However, the partial side sway mechanism was not achieved at NDP analysis at maximum seismic load, MCER.

Performance of Six- and Ten-story Reinforced Concrete Buildings Designed by using Modified Partial Capacity Design (M-PCD) Method with 70% Shear Force Ratio

One design alternative of earthquake resistant building is Partial Capacity Design (PCD) method. Unlike the commonly used capacity design method, PCD allows a safe failure mechanism which is called partial sidesway mechanism. In this mechanism, all beams and some columns are allowed to experience plastic damages while some selected columns are designed to remain elastic (called elastic columns). A new approach to predict the required strengths needed to design each structural member, called modified-PCD (M-PCD) is proposed. In this research six- and ten-story reinforced concrete buildings were designed using M-PCD, and their seismic performances are investigated. The base shear force resisted by the elastic columns was set to approximately 70% of the total base shear. Both nonlinear static procedure (NSP) and nonlinear dynamic procedure (NDP) are used to analyze the structures. The results show that the expected partial side sway mechanism is observed, and the drifts of the buildings are acceptable.

Comparison of Different Procedures for Progressive Collapse Analysis of RC Flat Slab Structures under Corner Column Loss Scenario

Progressive collapse is the failure of the whole structure caused by local damage, which leads to significant economic and human losses. Therefore, structures should be designed to sustain local failures and resist subsequent nonproportional damage. This paper compared four procedures for a progressive collapse analysis of two RC structures subjected to a corner column loss scenario. The study is mainly based on the methods outlined in the current Russian standard (linear static (LS) pulldown, nonlinear static (ND) pulldown, and nonlinear dynamic), but also includes LS and NS pushdown procedures suggested by the American guidelines and linear dynamic procedure. We developed detailed finite element models for ANSYS Mechanical and ANSYS/LS-DYNA simulations, explicitly including concrete and reinforcement elements. We applied the Continuous Surface Cap Model (MAT_CSCM) to account for the physical nonlinearity of concrete. We also validated results obtained following these procedures against known experimental data. Simulations using linear static pulldown and linear dynamic procedures lead to 50–70% lower results than the experimental because they do not account for the nonlinear behavior of concrete and reinforcement. Displacements obtained from the NS pulldown method exceed the test data by 10–400%. It is found that correct results for both RC structures can only be found using a nonlinear dynamic procedure, and the mismatch with the test data do not exceed 7%. Compared to static pulldown methods, LS and NS pushdown methods are more accurate and differ from the experiment by 28% and 14%, respectively. This relative accuracy is provided by more correct load multipliers depending on the structure type.

Assessment of the Seismic Behavior of a Precast Reinforced Concrete Industrial Building with the Presence of Horizontal Cladding Panels

The latest earthquakes in Europe exposed some critical problems in the connections of cladding panels in industrial precast reinforced concrete (PRC) structures. These connections did not perform as desired, causing the panels to fall, leading to significant nonstructural damage that resulted in the loss of human life and significant socio-economic impacts due to the interruption of business. Furthermore, in addition to the behavior of the cladding system itself, it is still not clear to what extent it can influence the overall seismic performance of the main structure. Making use of a simplified macroelement, the present study assesses the seismic performance of commonly employed cladding-to-structure connections, as well as the interaction of cladding panels with industrial PRC buildings. The analyses were carried out considering a PRC building representative of a Portuguese industrial park, studied with and without cladding panels. The seismic behavior of the structure was assessed considering both nonlinear static and dynamic procedures.

Cloud Capacity Spectrum Method: Accounting for record-to-record variability in fragility analysis using nonlinear static procedures

This paper investigates a number of computational issues related to the use of nonlinear static procedures in fragility analysis of structures. Such approaches can be used to complement nonlinear dynamic procedures, reducing the computational and modelling effort. Specifically, this study assesses the performance of the Capacity Spectrum Method (CSM) with real (i.e. recorded) ground motions (as opposed to code-based conventional spectra) to explicitly account for record-to-record variability in fragility analysis. The study focuses on single-degree-of-freedom systems, providing a basis for future multi-degree-of-freedom system applications. A case-study database of 2160 inelastic oscillators is defined through parametric backbones with different elastic periods, (yield) base shear coefficients, values of the ductility capacity, hardening ratios, residual strength values and hysteresis rules. These case studies are analysed using 100 real ground motions. An efficient algorithm to perform the CSM with real spectra is proposed, combined with a cloud-based approach (Cloud-CSM) to derive fragility relationships. Simple criteria to solve the issue of multiple CSM solutions (i.e. two or more points on the backbone satisfying the CSM procedure) are proposed and tested. It is demonstrated that the performance point selection can be carried out based on a particularly efficient intensity measure detected via optimal intensity measure analysis. The effectiveness of the proposed Cloud-CSM in fragility analysis is discussed through extensive comparisons with nonlinear time-history analyses, the code-based N2 method, and a simple method involving an intensity measure as a direct proxy for the performance displacement. The Cloud-CSM provides errors lower than ±20% in predicting the median of the fragility curves in most of the analysed cases and outperforms the other considered methodologies in calculating the fragility dispersion.

High Rise Buildings: Design, Analysis, and Safety

High-rise buildings have been rapidly increasing worldwide due to insufficient land availability in populated areas and their primary role as essential buildings in modern cities and capitals. However, high-rise buildings are very complicated due to the huge number of structural components and elements unlike low-rise buildings, as well as these high-rise buildings demand high structural stability for safety and design requirements. This paper aims to provide brief information about high-rise buildings regarding the basic definition, safety features, structural stability, and design challenges. A brief description of existing structural systems that are available in the literature is presented to articulate a technical issue that has been widely reported, named, adopting an effective structural system for resisting lateral loads resulting from wind and seismic activities. Consequently, a general overview is presented that covers the behavior of various structural systems for different heights of high-rise buildings by implementing a number of nonlinear static procedure analyses (pushover) and nonlinear dynamic procedure analyses (for wind and earthquake loading). Finally, a critical review of the available simplified model and seismic energy base design are also presented. This paper is intended to help in the development and application of construction systems for high-rise buildings in the future.

BEHAVIOR OF INDUSTRIAL BUILDING UNDER SEISMIC LOADING

Every year, earthquakes cause injuries, deaths, severe structural damage to buildings anddestruction of property in many countries. In developing countries, economic growth depends on industrialdevelopment. Therefore, if an earthquake occurs, it may cause severe damage to large industrial factories. Thispresent study aims to examine the structural behavior of industrial buildings under the earthquake force whichis a reinforced concrete building. The structure of an industrial building is different from a general building. Inthis study, the factory is a four-story building with the dimensions of 34.4 meters in width, 59.2 meters inlength and 16.2 meters in height. In the analysis, the nonlinear dynamic procedure is applied to analyze thebuilding behaviors. The 20 seismic waves are selected and adjusted with the ASCE41-13. LMSR wave areconsidered in x-direction and y-direction. From the results, the responses and damage of the industrial structureare analyzed. The building has performed the soft story irregularity. The performance level for the acceptancecriteria, according to ASCE41-13 and FEMA365 is life safety performance level. Therefore, the industrialfactory building is needed to enhance the seismic capacity for damage prevention.

Are the nonlinear static procedures feasible for the seismic assessment of irregular existing masonry buildings?

The nonlinear static procedure (NSP) is commonly adopted by practitioners for the seismic assessment of unreinforced masonry (URM) buildings, although a systematic validation of the procedure when applied to this type of buildings still lacks in the literature. The aim of this paper is to contribute to the validation and the improvement of the NSP when used for the seismic assessment of irregular URM buildings.The effectiveness of the NSP is tested on numerical models representative of URM buildings that present both in plan and in elevation irregularities. The concept of irregularity is also extended to that consequent to the presence of flexible/stiff diaphragms, so frequent in existing URM buildings. To this aim a total of 13 numerical models representative of 3 and 4 stories URM buildings were developed. The results derived by the application of the NSP are compared with the nonlinear dynamic procedure, considered as the reference solution.Based on the findings of the present research, original contributions are provided to: (1) the load patterns to apply for the pushover analysis; (2) the identification of damage levels; (3) the evaluation of the target displacement and the corresponding intensity measure that causes its attainment.

Effect of Common U.S. Ground Motion Selection Methods on the Structural Response of Steel Moment Frame Buildings

This study quantifies the impact of two common ground motion (GM) selection methods, included in U.S. standards, on the seismic performance evaluation of steel special moment frames. The methods investigated are a “traditional” approach, herein referred to as the target maximum considered earthquake (TMCE) method, and a newer approach known as the conditional mean spectrum (CMS) method. The TMCE method selects GMs using the risk-based maximum considered earthquake (MCER) spectrum as the target spectrum, while the CMS method uses the CMS that anchors the MCER at multiple conditioning periods. Three special steel moment frames of 4, 8, and 16 stories are designed in accordance with ASCE/SEI 7-10, and their seismic performance is assessed with the nonlinear dynamic procedure prescribed in ASCE/SEI 41-13 using GMs selected and scaled in accordance with the aforementioned methods. A comparison of statistical parameters for the reduced beam sections and column hinges is conducted using the normalized demand-to-capacity ratio ( DCR), as the output parameter. The buildings are evaluated at the collapse prevention performance level for a far-field site located in Los Angeles, CA. In general, the CMS method results in lower DCRs of the frame components and smaller output parameter dispersion. In addition to the spectral shape, the demands are largely influenced by the spectral accelerations prescribed for each evaluated method. The consideration of collapse realizations is also documented as well as the existing and proposed statistical methods to account for these realizations. The study shows that the GM selection process can cause significant differences in structural response that may lead to different retrofitting decisions.

Statistical evaluation of maximum displacement demands of SDOF systems by code-compatible nonlinear time history analysis

By the developments in structural and earthquake engineering, modern seismic codes have begun to recommend nonlinear static and dynamic procedures to approximate the maximum displacement demands which have uttermost importance for seismic assessment of buildings. Dynamic procedure is the most accurate and reliable among them and requires the selection of real/artificial ground motion records compatible to considered elastic design spectra. In this study, maximum displacement demands of SDOF systems with various lateral strength ratios and vibration periods are determined via nonlinear time history analyses using the code-compatible different records sets constructed by real accelerograms. For this purpose, 30 ground motion record sets compatible with elastic design spectra defined for each local soil class in Turkish Earthquake Code are used separately. Evaluations have highlighted that i) variation of maximum displacement demands in the sets are high; ii) Distinct ground motion record sets may result in different displacement demands even though they are compatible with the same design spectra; iii) maximum displacement demands of different ground motion record sets can be simply accepted as random samples of the same population at 95% confidence level. In addition to dynamic analysis results, maximum displacement demands of static procedure are determined for the same target spectra and results of both methods are compared. Comparisons showed that special attention should be made to static procedure estimations for the buildings with long periods on stiff soils. Finally, linear regression models, depending on the fundamental periods for each lateral strength ratio and soil type, are proposed for rapid prediction of displacement demands in reliability based manner.

Infill Walls Contribution on the Progressive Collapse Resistance of a Typical Mid-rise RC Framed Building

This study investigates the effect of the autoclaved aerated concrete infill walls on the progressive collapse resistance of a typical RC framed structure. The 13-storey building located in Brăila (a zone with high seismic risk in Romania) was designed according to the former Romanian seismic code P13-70 (1970). Two models of the structure are generated in the Extreme Loading® for Structures computer software: a model with infill walls and a model without infill walls. Following GSA (2003) Guidelines, a nonlinear dynamic procedure is used to determine the progressive collapse risk of the building when a first-storey corner column is suddenly removed. It was found that, the structure is not expected to fail under the standard GSA loading: DL+0.25LL. Moreover, if the infill walls are introduced in the model, the maximum vertical displacement of the node above the removed column is reduced by about 48%.