Seismic Design Standards Research Articles

Methods for conceptual and preliminary seismic design of buildings with steel structure

Throughout the last two decades, seismic design standards evolved to ever more comprehensive and detailed prescriptions, stressing out the need for design methods that deal with earthquake effects not as actions, but as a design philosophy. The Eurocode 8 adoption as national law throughout the European Union countries and informally in many parts of Africa, Asia and Latin America is the pretext for the current study. It aims to provide some guidance to the seismic design of steel structures as well as to the Eurocode 8 implementation by the designers.Some lines on the preliminary design of structural systems were written based on several real cases of structures designed taking into account the seismic action. Such a content is, usually, relevant in any design guide, given its value in enhancing the design technical and economical content. However, it is now of utter significance at the current context as an essential tool to facilitate the safety checking of several code requirements.Some of the Eurocode 8 prescriptions are then decoded, explained and justified based on the supportive bibliography. The information is subsequently ordered as a design guide, where some procedures are proposed to cope with the code interrelated prescriptions and one structural solution is proposed in order to overcome a design challenge while complying with the code.One last but not less relevant addressed issue is the fact that some Eurocode 8 prescriptions may be reviewed, in the eyes of a designer, given its practical outcome. Such issues are identified, explained and some slight code adjustments are suggested.

Characteristics of the vertical and horizontal response spectra of the Gyeongju earthquake (12 September 2016, ML = 5.8) series

ABSTRACTThe response spectra of the 20 Gyeongju earthquake series, including the main earthquake (12 September 2016; ML = 5.8), were compared with the design response spectra (Regulatory Guide 1.60, 1973; United States Nuclear Regulatory Commission) for Korean nuclear power plants and the Korean Building Code (KBC) of 2016 for general structures and buildings. A total of 720 horizontal and vertical accelerations were used to derive the response spectra after normalisation by reference to peak ground acceleration. The horizontal and vertical response spectra were strongly dependent on the epicentral distance and the resonance frequency. When developing design response spectra, it is necessary to consider distances >200 km from the epicenter, given the strong dependence of the response on distance. The vertical responses were consistently lower than the horizontal responses, in good agreement with the various existing seismic design standards and empirical rules. It is essential to develop site-specific seismic design standards, reflecting local seismotectonic environments. Such efforts require large amounts of data covering earthquakes of various magnitudes in the Korean Peninsula and surrounding areas, and such standards should replace Regulatory Guide 1.60. In terms of the KBC 2016, it is necessary to make the criteria more conservative in the short periods, and then to create comprehensive design response spectra by referencing large amounts of qualitative data from the region around the Korean Peninsula on earthquakes of various magnitudes and their effects at different distances from the epicenter.

A Cyclic Backbone Curve for Shear-Critical Reinforced Concrete Walls

AbstractBackbone curves are used in seismic design standards as the basis for developing component models for nonlinear static and dynamic analysis. Herein, data from 240 tests of rectangular, barb...

On Setting the Level of Seismic Effect in Seismic Intensity Scales and Design Standards

It is noted in the article that the increase in peak ground acceleration (PGA) by a factor of about 1.4 proposed by seismologists in a project of seismic intensity scale clearly reflects the lessons learned from earthquakes of the past. However, the use of suggested PGA values in the design codes and standards requires modification of the codes and standards themselves, as well as differentiated approach to defining the design level of PGA. Engineers should consider the dependence of the design PGA on the oscillation periods of structures, whereas seismologists should differentiate the PGA value depending on the prevailing period of the seismic effect. Transition to the new seismic scale affects the design and maximum design earthquakes differently. The intensity of a design earthquake for objects of massive structure does not exceed VII on the MSK scale, and in this aspect the new seismic scale does not differ considerably from the existing one. For maximum design earthquakes, PGA increases significantly, but the criterion of seismic resistance changes from acceleration of the structure to the work of plastic deformation forces. In this case, possible destruction depends little on PGA, but rather on such energy seismic effect characteristics as the Arias intensity, absolute cumulative velocity, and seismic energy density. A correct approach to calculation when carrying out the performance-based design and transition to the new intensity scale would not lead to higher costs for most buildings and structures. Moreover, if one does not use the new scale, transition to modern methods of performance-based design will be impossible.

Surface Level Synthetic Ground Motions for M7.6 2001 Gujarat Earthquake

The 2001 Gujarat earthquake was one of the most destructive intraplate earthquakes ever recorded. It had a moment magnitude of M w 7.6 and had a maximum felt intensity of X on the Modified Mercalli Intensity scale. No strong ground motion records are available for this earthquake, barring PGA values recorded on structural response recorders at thirteen sites. In this paper, synthetic ground motions are generated at surface level using the stochastic finite-fault method. Available PGA data from thirteen stations are used to validate the synthetic ground motions. The validated methodology is extended to various sites in Gujarat. Response spectra of synthetic ground motions are compared with the prescribed spectra based on the seismic zonation given in the Indian seismic code of practice. Ground motion characteristics such as peak ground acceleration, peak ground velocity, frequency content, significant duration, and energy content of the ground motions are analyzed. Response spectra of ground motions for towns situated in the highest zone, seismic zone 5, exceeded the prescribed spectral acceleration of 0.9 g for the maximum considered earthquake. The response spectra for towns in seismic zone 5 exhibit peaks in the low period ranges, indicating high vulnerability of low rise structures designed as per the provisions of the Indian seismic code of practice. The response spectra for towns situated in seismic zone 3 were considerably lower than the prescribed maximum spectral acceleration of 0.4 g. The substantial damage reported in towns situated in seismic zone 3 is due to poor construction practices and non-compliance with provisions of seismic design standards.

Direct measurement of building transient and residual drift using an optical sensor system

Interstory drift (ID) is a key response parameter for buildings subjected to lateral loads and is used to define performance-based limit states, allowable deformations and damage states in a number of seismic design codes and standards. An ability to rapidly and accurately measure both transient and residual ID during an earthquake would provide important observables for understanding the seismic demands and post-earthquake condition of a building. Accurate retrieval of ID from accelerometer-based instrumentation systems can be very challenging, if not impossible, as a result ofinstrumentation limitations and the post-processing associated with strong motion accelerometer data. This is particularly true for the case in which residual drifts occur during inelastic building response. In the study presented herein, a newly developed optical sensor system, designed specifically for directly measuring both transient and residual ID, was experimentally evaluated through shake table testing and computational simulations. The ability of the sensor to accurately measure ID is demonstrated and key operational considerations for sensor system deployment are examined through a model-based investigation.

Performance-based assessment of response reduction factor of RC-elevated water tank considering soil flexibility: a case study

The seismic design codes/standards of most countries include the nonlinear response of a structure implicitly through a response reduction/modification factor (R). It is the factor by which the actual base shear should be reduced to find the design base shear during design basic earthquake considering nonlinear behavior and deformation limits of structures. In the present study, attempts are made to determine the ‘R’ factors of four existing RC staging elevated water tanks, which are designed as per draft Indian standards for seismic design of liquid and RC designs and having a ductile detailing considering the effects of soil flexibility. The elevated RC water tanks are analyzed using displacement controlled non-linear static pushover analysis to evaluate the base shear capacity and ductility of tank considering soil flexibility. The ‘R’ factor is obtained for four realistic designs of elevated RC water tanks having different capacities at two performance levels. The evaluated values of ‘R’ factor are compared with the values suggested in the design code. The results of the study show that the flexibility of supporting soil has considerable effect on response reduction factor, period and overall performance of water tank, indicating that idealization of fixity at base may be seriously mistaken for soft soils. All the studied water tanks were designed with higher safety margin than that of specified in Indian Standards.

Evaluation of Seismic Analysis Procedures for Concrete Moment-Resistant Frames with Horizontal Re-entrant Corners Irregularity

Seismic design codes and standards such as the IBC 2012 and ASCE/SEI 7-10 allow using different seismic analysis procedures for buildings having horizontal re-entrant corner irregularity. However, such codes allow using Equivalent Lateral Force (ELF) procedure for buildings having re-entrant corner irregularity but not exceeding 50 m in height. The aim of this study is to quantify the limits on building height and on the percentage of re-entrant corner of building, where ELF procedure may not produce a reasonable results when compared to Response Spectrum (RS) and Response Time History (TH) procedures. Usually, these limits in seismic design standards are based on judgments and experience rather than quantification studies. Based on the results of this study, it is observed that using ELF method mostly overestimates maximum displacements and drift ratio. However, this method can be used safely up to 12-storey buildings, because the maximum underestimation of column shear forces for buildings with higher stories gives 30% less compared to other procedures. Moreover, it has been found that the maximum underestimation of column shear forces for buildings without re-entrant corner is 0% less than those with re-entrant corners. Furthermore, buildings analysed by ELF method are also exposed to have a higher percentage value of underestimation of column shear forces as the case of 12-story buildings with 40% less when compared to TH Procedure. In addition, the column at the re-entrant corner is not effectively affected until a re-entrant corner of 25% exists in buildings. Thus the ASCE/SEI 7-10’s limit for using ELF procedure for buildings with re-entrant corner irregularity may be increased from 15% to 25% with less conservative results.

1-g shaking table tests on seismic enhancement of existing box culvert with partial ground-improvement method and its 2D dynamic simulation

An underground structure buried in a soft ground located in a seismic-active region may experience intolerable deformation due to earthquake loading. The collapse of Daikai Station of the Kobe subway line during the 1995 Hyogoken-Nambu Earthquake demonstrated that underground structures may also sometimes be at high risk for failure in a huge earthquake. In particular, box culverts constructed in a soft ground with a thin overburden are vulnerable to earthquakes. Some previously constructed box culverts do not meet the present requirements of seismic design standards. In this paper, numerical analyses and 1-g shaking table tests are conducted to evaluate the effect of partial ground improvement (PGI) as a seismic countermeasure for the above-mentioned existing box culverts. Particular attention is paid to the optimum pattern of PGI that can most efficiently reduce the impact of an earthquake on a box culvert. The underground structure of Daikai Station is taken as an example and its physical and geometric conditions are used to model the box culvert in the analyses and the tests. In order to accurately consider the influence of the soil-structure interaction (SSI) on the underground structures, both the soil and the box culvert are considered in the analyses and the shaking table tests. Four different patterns of PGI are considered. Based on the analyses and the tests, an optimum pattern for the PGI of existing box culverts is proposed.

Performance of Medium-to-High Rise Reinforced Concrete Frame Buildings with Masonry Infill in the 2015 Gorkha, Nepal, Earthquake

Following the 25 April 2015 Mw 7.8 Gorkha, Nepal, earthquake and subsequent aftershocks, field surveys were conducted on medium-to-high rise reinforced concrete (RC) frame buildings with masonry infill located in the Kathmandu Valley. Rapid visual assessment, ambient vibration testing, and ground-based lidar (GBL) showed that these buildings suffered damage ranging from light to severe, where damage occurred in both structural and nonstructural elements, but was most prevalent in nonstructural masonry infills. Finite-element structural analyses of selected buildings corroborate field observations of only modest structural damage. The lack of severe structural damage in this relatively limited class of engineered medium-to-high rise RC infill frame buildings illustrates the impact of modern seismic design standards and stands in stark contrast to the severe damage and collapse observed in low-rise nonengineered RC infill frame buildings. Nonetheless, the nonstructural damage hindered many of these buildings from being occupied for many months following the earthquake and subsequent aftershocks.

Exterior RC wide beam-column connections: Effect of beam width ratio on seismic behaviour

Abstract Design recommendations stipulated in international standards for seismic design of reinforced concrete (RC) wide beam-column connections are based on limited experimental studies. To supplement the existing information, an experimental study was conducted that focused on the effect of beam width to column width ratio (or beam width ratio) on the seismic behaviour of exterior beam-column connections. Four specimens were designed, constructed and tested under reversed cyclic loading conditions. The primary test variables were the beam width ratio and the joint shear stress ratio ( γ d ). The specimens were designed in conformance with ACI 318-14 and ACI 352R-02. They had beam width ratios of 1, 1.5, 2 and 2.5 and γ d , of 0.74, 1.12, 1.63, and 2.03. According to ACI 352R-02, the γ d value should be lower than γ n = 1.25 for joints confined on three faces. The results indicated that specimens with beam width ratios of 1 and 1.5 and γ d of 0.74 and 1.12 were capable of supporting the complete formation of beam plastic hinges with no major cracks in the joint region. In contrast, specimens with beam width ratios of 2 and 2.5 and γ d of 1.63 and 2.03 exhibited significant damage at the joint core. Torsional failure of the spandrel beam was also observed in specimen with beam width ratio of 2.5.

Pseudo-static Analysis of Fabricated Steel Cage Concrete Frame Structure

In this paper, the stress bearing behavior of three different frame structure groups (allcast- in-place RC, all-cast-in-place steel cage concrete and fabricated steel cage concrete) which under horizontal low cyclic reciprocating force will be analyzed theoretically. Simulation results show that, in these three structures, all-cast-in-place steel cage concrete structure has the maximum bearing capacity, and fabricated steel cage concrete structure is next to it. However, fabricated structure will produce stress concentration phenomenon in its nodes. So, strengthening the connection parts has to be considered. Meanwhile, in these three structures, beam end is where maximum stress can be produced, which illustrates that the damage of concrete is first occurred at beam end and meets the needs of “strong column and weak beam” seismic design standards.

Research on Method of Performance-Based Seismic Design for Electric Apparatuses

基于性能的抗震设计已成为国内外建筑抗震研究的热点问题。高压电气设备的抗震主要依据现行的抗震设计规范设计而成，但在地震作用下仍然会遭受巨大破坏,特别是灾后重建需要巨大投入。因此，提出了电气设备基于性能的抗震设计方法。阐述电气设备进行性能化抗震设计的必要性，给出了基于性能的电气设备抗震设计具体步骤及注意事项。根据抗震设计标准及电气设备的特点，在电气设备中提出变压器、电瓷型电气设备适于基于性能的抗震设计；同时还提出电气设备支架、减隔震装置也适用于基于性能抗震设计；最后提出将电气设备、支架及减隔震装置考虑为一个整体，进行一体化基于性能的抗震设计。 Performance-based seismic design has been the hot issue of seismic design at home and abroad. The high-voltage electrical apparatuses are mainly based on the existing seismic design codes, but they are always subjected to huge damage under the strong earthquake. And this will lead to huge investments in the post disaster reconstruction. The performance-based seismic design for electrical equipment is proposed. The necessity of the electric equipment of performance-based seismic design is elaborated. Then the detailed procedure and matters needing attention of the performance-based seismic design for electrical equipments are provided. According to the seismic design standards and the characteristics of electrical equipments, electrical equipments including transformer and electric porcelain type electric equipments are suitable for performance-based seismic design; at the same time, electrical equipment brackets and isolation devices are also suitable for performance-based seismic design, and finally it is proposed that the bracket and isolation devices of the electrical equipment can be considered as a whole for the integration of performance-based seismic design.

From a GIS-based hybrid site condition map to an earthquake damage assessment in Iran: Methods and trends

From several decades ago, the average shear wave velocity for the top 30m (Vs30) has been proposed as one of the important factors that reflects the amplification behavior of a site. Most of seismic design standards such as National Earthquake Hazards Reduction Program in the United States and Standard No. 2800 in Iran emphasize on the use of Vs30 measurements for site classification according to the soil type. As an important step in profound seismic risk reduction to earthquakes, a site effect study was conducted at a nationwide scale. We followed an indirect method to produce Vs30 map of Iran from geological and topographical data. The outputs indicate that hybrid Vs30 map has better performance than single topography-based Vs30 map. The amplitude map deduced from Vs30 and geology maps then is used for seismic microzonation of Tabriz city and extent of geographical distribution of damage for a possible deterministic scenario (M=7) is investigated through considering different fragility curves to describe damaging behavior of ordinary building types in the city.

Seismic Performance Evaluation for Reinforced Concrete Buildings and Masonry Buildings

Performance-based seismic design is the basis of most new seismic design standards and specifications worldwide. In a performance-based seismic design, a performance objective consists of the specification of a performance level and a corresponding probability that this performance level may be exceeded. This study explored some probability information for seismic performance for reinforced concrete buildings and masonry buildings. The exceeding probabilities of various performance levels for reinforced concrete buildings and masonry buildings during their 50-year useful lives were investigated. Then, a probabilistic evaluation was performed for these buildings to examine the achievement of desired performance design objectives.

Seismic Performance Evaluation of Buildings in Taiwan

Integrating the available research results from fragility analysis of building structures and seismic hazard analysis, this study explored some probability information for current earthquake resistant design for general buildings and examined structural performance of buildings under the action of earthquake motions. The results of this study show that performance objectives suggested by FEMA are not realized for the buildings of light steel, pre-cast concrete, reinforced masonry, and un-reinforced masonry, designed according to the Taiwan seismic design standards. The results may provide some valuable information for future code calibration in Taiwan.

Seismic performance comparison between direct displacement-based and force-based design of a multi-span continuous reinforced concrete bridge with irregular column heights

North American bridge design codes, e.g., Canadian Highway Bridge Design Code and AASHTO 2007, follow force-based design (FBD) method, which is focused at the target force resistance capacity of the structure. Displacement-based design (DBD) method, on the other hand, aims to ensure a target maximum displacement of the bridge during earthquakes in a specific zone. In this study, bridges with irregular column heights have been designed according to DBD and FBD (as per Canadian standards and AASHTO 2007) considering seismic loading. Subsequently, seismic performances of the bridges designed with the two different methods have been compared by conducting nonlinear dynamic analyses in the longitudinal direction. Maximum and residual displacements and energy dissipation capacity are used as performance indicators. This study outlines the necessity of possible modification in the current Canadian seismic design standards as well as DBD for bridges with irregular column heights.

Free and Forced Vibration Analysis of an Infilled Steel Frame: Experimental, Numerical, and Analytical Methods

Structural frames with masonry infill panels make up a significant portion of the buildings constructed in earthquake-prone areas prior to the developing of the seismic design standards. In this paper, the effects of masonry panels on the vibration response of an infilled steel-frame building are investigated. Various ambient and steady state forced vibration tests are carried out to realize the dynamic characteristics of the system. 3D finite element models of the building with and without infill panels are provided based on marcomodeling theorem. A set of analytical approximate formulas are also derived to estimate the vibrational period. The natural frequencies of the building are computed using numerical, analytical, and experimental methods. The results show that neglecting the effect of infill panels leads to considerable error. Moreover, it is shown that there is good agreement among the results obtained by the three methods considering the effect of infill panels.

Comparative Study of Codes for Seismic Design of Structures

Abstract This paper presents a comparative evaluation among some international, European and American, seismic design standards. The study considers the criteria for the analysis of conventional (residential and commercial) buildings. The study is focused on some critical topics: definition of the recurrence periods for establishing the seismic input; definition of the seismic zonation and shape of the design response spectra; consideration of local soil conditions; definition of the seismic force-resisting systems and respective response modification coefficients; definition of the allowable procedures for the seismic analysis. A model for a standard reinforced concrete building (“Model Building”) has been developed to permit the comparison among codes. This building has been modelled with two different computer programs, SAP2000 and SOFiSTiK and subjected to seismic input according to the several seismic codes. The obtained results compared are leading to some important conclusions.

Comparative study of codes for the seismic design of structures

A general evaluation of some points of the South American seismic codes is presented herein, comparing them among themselves and with the American Standard ASCE/SEI 7/10 and with the European Standard Eurocode 8. The study is focused in design criteria for buildings. The Western border of South America is one of the most seismically active regions of the World. It corresponds to the confluence of the South American and Nazca plates. This region corresponds roughly to the vicinity of the Andes Mountains. This seismicity diminishes in the direction of the comparatively seismically quieter Eastern South American areas. The South American countries located in its Western Border possess standards for seismic design since some decades ago, being the Brazilian Standard for seismic design only recently published. This study is focused in some critical topics: definition of the recurrence periods for establishing the seismic input; definition of the seismic zonation and design ground motion values; definition of the shape of the design response spectra; consideration of soil amplification, soil liquefaction and soil-structure interaction; classification of the structures in different importance levels; definition of the seismic force-resisting systems and respective response modification coefficients; consideration of structural irregularities and definition of the allowable procedures for the seismic analyses. A simple building structure is analyzed considering the criteria of the several standards and obtained results are compared.