Site-specific Design Spectra Research Articles

Nonlinear time domain seismic response and performance evaluation of A-frame jumbo-size container cranes

Seismic responses of A-frame jumbo-size container cranes are comprehensively studied by exciting them as realistically as practical to evaluate the adequacy of the conventional static approach routinely used for their design. Multiple design earthquake time histories corresponding to the structure and site-specific earthquake design spectra corresponding to specific return periods are selected for the nonlinear time domain dynamic analyses. Cranes are considered to be in service (i.e., boom down), (2) at rest (i.e., boom up or stowed) with a friction contact support condition, and (3) at rest with tie-downs installed conditions. They are represented by finite elements, and appropriate dynamic properties are used following the practices commonly used in the profession. The seismic responses, in terms of base shear force, vertical wheel load, main member stress, portal drift ratio, and uplift, are estimated to define several performance objectives and their corresponding limits. Two container cranes with different dynamic properties and their responses are used to make the final recommendations. The in-service operating condition appears to be the most critical. The variation in the stress responses between the cranes in the at-rest and in-service conditions is about 17 %. However, the uplift in the stowed crane can be about 82 % higher than that in the in-service crane. The commonly used lateral load method using the static concept may not always be conservative, especially for the base shear force and vertical wheel load. For example, the method significantly underestimates the base shear force by about 52 % for the slender crane and 26 % for the relatively stiffer crane. Thus, the nonlinear time domain approach proposed here should always be used. It will satisfy the performance-based seismic design concept under development at present.

Dynamic Modal Analyses of Building Structures Employing Site-Specific Response Spectra Versus Code Response Spectrum Models

This paper is aimed at giving structural designers guidance on how to make use of elastic site-specific response spectra for the dynamic modal analysis of a structure in support of its structural design. The use of response spectra in support of the pushover analysis of an RC building forming part of the non-linear static analysis procedure (that can be used to predict seismic demand without relying on the code-stipulated default R factor) is also presented. Seismic analysis of structures based on the use of site-specific response spectra can help to achieve a more optimised, and cost-effective, structural design compared to the conventional approach employing a response spectrum model stipulated by the code for different site classes. Currently, the methodology is only adopted in major projects in which enough resources are available to engage experts who are skilled in operating the procedure; thus, the use of site-specific response spectra in structural engineering practice is still limited despite the merits of the procedure. Deriving a site-specific response spectrum requires a database of representative ground motion records to be developed. Extra analytical tasks to be undertaken include the processing of bore log data, site response analyses, and selection/scaling of bedrock accelerograms for input into site response analyses. Guidelines for implementing this design methodology are currently lacking. To promote the wide adoption of site-specific seismic design, this article presents the procedure for developing the required site-specific design spectra, as well as guidelines for applying these spectra for seismic design based on analyses of linear, or nonlinear, models of the building. Non-linear analysis can be accomplished by dealing with macroscopic models as illustrated in a case study.

Hazard consistent vertical design spectra for active regions of India

According to the current Indian Standard earthquake-resistant design code (IS 1893, 2016), the vertical design spectrum is assumed as two-thirds of the horizontal spectrum. However, a previous investigation of the Indian ground motion records suggests that the vertical spectra exceeded the horizontal in many instances, which would render the previous consideration inadequate. Therefore, the current study aims at developing an appropriate recommendation for obtaining vertical design spectra, through development of hazard consistent vertical design spectra for the active regions of India. The vertical design spectrum is generated through scaling of a weighted average vertical-to-horizontal ratio (V/H) ground motion prediction equation (GMPE) to the horizontal component of the uniform hazard spectrum. The uniform hazard spectrum is obtained for the two active regions of India– the Western Himalayas and the North East India through probabilistic seismic hazard analysis and the weighted average V/H model is obtained by combining the V/H GMPE developed for India with several global models. Based on the proposed relations, a structural engineer can obtain site-specific vertical design spectra with ease and accuracy.

The effect of input ground motion location on design spectrum in a seismic ground response analysis performed for an alluvial site

Site response analyses are performed to estimate the change in the characteristics of the input rock motion occurred during the vertical propagation of seismic waves and to obtain the local variation in intensity and spectral characteristics of surface ground motion. The rock outcrop motions which are selected by considering the source mechanism, fault distance and earthquake characteristics that are compatible with the standard design ground motion level. It is generally agreed that time domain simulated or spectral matched ground motions may be applied as input ground motions at seismic bedrock in the dynamic response analysis of soil layers under earthquake excitation and thus shear stresses and deformations, acceleration-time histories and site-specific design spectrum can be obtained for surface layers. In “Turkish Building Earthquake Code (TBEC), 2018” it is being stated that the input ground motion can be exerted at the base of a soil layer lying at a shallower depth in comparison with seismic bedrock depth by using the method of spectral matching the accelerograms to the target spectrum of corresponding soil layer where the input motion is applied. In this study, by evaluating and combining the findings of the geotechnical borings and microtremor array measurements, the shear wave velocity profiles extending to seismic bedrock (VS≥760 m/s) were obtained for the investigation sites. The results of the site response analyses that were conducted by using the two different methods proposed in TBEC (2018) were interpreted. At the first method, in deeper 1D dynamic analyses, the input ground motions were applied at seismic bedrock defined as site class ZB where the shear wave velocity (VS30) is higher than 760 m/s2. Whilst at the second method, the inputs were applied at the base of the shallower 1D soil column having site class either ZC or ZD where VS30 is in the range of 360 m/s2 < VS30 < 760 m/s2 and 180 m/s2 < VS30 < 360 m/s2 respectively. As a result, the acceleration spectra obtained on the surface of deep and shallow models were compared for 31 strong ground motion records, selected in accordance with the design spectra corresponding to seismic code depending on the location of the investigation area and local site classes.

Acceleration Displacement Response Spectra for Design of Seismic Isolation Systems in Turkey

In this study, base shear and inelastic displacement limits of seismic isolation systems are presented through acceleration-displacement response spectra considering the ground motion and design provisions of the Turkish Building Seismic Design Code. A series of nonlinear response history analyses are performed using a combination of eight site-specific design spectra, six isolation systems having six different periods and five yield levels. As a result, eight spectra presented herein can be used for the preliminary design stage of seismic isolation systems in Turkey.

Force-based seismic design of steel haunch retrofit for RC frames

The paper presents a simplified force-based seismic design procedure for the preliminary design of steel haunch retrofitting for the seismic upgrade of deficient RC frames. The procedure involved constructing a site-specific seismic design spectrum for the site, which is transformed into seismic base shear coefficient demand, using an applicable response modification factor, that defines base shear force for seismic analysis of the structure. Recent experimental campaign; involving shake table testing of ten (10), and quasi-static cyclic testing of two (02), 1:3 reduced scale RC frame models, carried out for the seismic performance assessment of both deficient and retrofitted structures has provided the basis to calculate retrofit-specific response modification factor Rretrofitted. The haunch retrofitting technique enhanced the structural stiffness, strength, and ductility, hence, increased the structural response modification factor, which is mainly dependent on the applied retrofit scheme. An additional retrofit effectiveness factor (ΩR) is proposed for the deficient structure's response modification factor Rdeficient, representing the retrofit effectiveness (ΩR=Rretrofitted /Rdeficient), to calculate components' moment and shear demands for the retrofitted structure. The experimental campaign revealed that regardless of the deficient structures' characteristics, the ΩR factor remains fairly the unchanged, which is encouraging to generalize the design procedure. Haunch configuration is finalized that avoid brittle hinging of beam-column joints and ensure ductile beam yielding. Example case study for the seismic retrofit designs of RC frames are presented, which were validated through equivalent lateral load analysis using elastic model and response history analysis of finite-element based inelastic model, showing reasonable performance of the proposed design procedure. The proposed design has the advantage to provide a seismic zone-specific design solution, and also, to suggest if any additional measure is required to enhance the strength/deformability of beams and columns.

The effect of material strength and discontinuity in RC structures according to different site-specific design spectra

The effect of material strength and discontinuity in RC structures according to different site-specific design spectra

The Effect of Site-Specific Design Spectrum on Earthquake-Building Parameters: A Case Study from the Marmara Region (NW Turkey)

The Marmara Region (NW Turkey) has experienced significant earthquakes (M &gt; 7.0) to date. A destructive earthquake is also expected in the region. To determine the effect of the specific design spectrum, eleven provinces located in the region were chosen according to the Turkey Earthquake Building Code updated in 2019. Additionally, the differences between the previous and updated regulations of the country were investigated. Peak Ground Acceleration (PGA) and Peak Ground Velocity (PGV) were obtained for each province by using earthquake ground motion levels with 2%, 10%, 50%, and 68% probability of exceedance in 50-year periods. The PGA values in the region range from 0.16 to 0.7 g for earthquakes with a return period of 475 years. For each province, a sample of a reinforced-concrete building having two different numbers of stories with the same ground and structural characteristics was chosen. Static adaptive pushover analyses were performed for the sample reinforced-concrete building using each province’s design spectrum. The variations in the earthquake and structural parameters were investigated according to different geographical locations. It was determined that the site-specific design spectrum significantly influences target displacements for performance-based assessments of buildings due to seismicity characteristics of the studied geographic location.

Effect of URM infills on inelastic floor response of RC frame buildings

The effect of unreinforced masonry infills on the floor acceleration response of inelastically responding mid-rise RC frame buildings is studied using incremental dynamic analyses. Two structural building configurations, uniformly infilled, and with open ground storey are analyzed by using the FEMA P695 far-field ground-motion suite. It is observed that the effect of structural nonlinearity is much more pronounced in case of infilled RC frame buildings than bare RC frame buildings. Sequential failure of infills results in a significant elongation of period of vibration resulting in the shifting of peaks in floor spectrum towards longer periods. Modified floor spectral amplification functions are presented for both uniformly infilled and open ground storey RC frame buildings. The proposed spectral amplification functions are validated using nonlinear analysis of typical buildings for recorded as well as spectrum-compatible ground-motions and can be used to estimate the floor response spectra directly from the code-based or site-specific design spectra.

Development of site-specific elastic design spectra for future building codes, Part 1: an updated classification of empirical amplification functions

Development of site-specific elastic design spectra for future building codes, Part 1: an updated classification of empirical amplification functions

Development of site-specific elastic design spectra for future building codes, Part 2: statistical analysis of earthquake ground motions

Development of site-specific elastic design spectra for future building codes, Part 2: statistical analysis of earthquake ground motions

Site-specific probabilistic seismic hazard analysis for northern part of the Qeshm Island, Iran

This paper presents results of a site-specific probabilistic seismic hazard analysis for northern part of the Qeshm Island, one the most seismic prone areas of Iran. Seismotectonic and seismicity properties of seismic sources in the study area were characterized and used for evaluation of various strong ground motion parameters implementing the classical Cornell’s PSHA approach. The results show that peak rock accelerations for 475-year return period are 0.4 and 0.27 g, respectively, for 84th and 50th percentiles while being about 0.37 and 0.61 g for 2475-year return period. These values are slightly smaller than those read from national seismic zonation maps which can be attributed to the considered conservatism for development of such design maps. In order to incorporate local site conditions, a series of dynamic site response analyses based on the equivalent linear approach were also employed. The results indicate that the presence of soft subsurface deposits at the site significantly alters the fundamental characteristics of the response spectra. The obtained median (50th percentile) peak ground accelerations for 975-year return period range between 0.49 and 0.54 g at different locations in the study site showing minor amplifications relative to their corresponding bedrock acceleration of 0.48 g. Finally, the obtained site-specific spectrum was compared with the standard spectrum mandated by the design codes. In this regard, the agreement was found to be reasonable at period ranges shorter than about 0.5 s, while the differences were more obvious at longer periods. This reveals the need for implementation of site-specific design spectrum to avoid underestimation or overestimation of seismic forces for designing critically important structures especially when softer deposits are encountered.

Region-specific deterministic and probabilistic seismic hazard analysis of Kanpur city

A seismic hazard map of Kanpur city has been developed considering the region-specific seismotectonic parameters within a 500-km radius by deterministic and probabilistic approaches. The maximum probable earthquake magnitude (M max) for each seismic source has been estimated by considering the regional rupture characteristics method and has been compared with the maximum magnitude observed \(\left ({M_{\max }^{\text {obs}}}\right )\), \(M_{\max }^{\text {obs}} +0.5\) and Kijko method. The best suitable ground motion prediction equations (GMPE) were selected from 27 applicable GMPEs based on the ‘efficacy test’. Furthermore, different weight factors were assigned to different M max values and the selected GMPE to calculate the final hazard value. Peak ground acceleration and spectral acceleration at 0.2 and 1 s were estimated and mapped for worst-case scenario and 2 and 10% probability of exceedance for 50 years. Peak ground acceleration (PGA) showed a variation from 0.04 to 0.36 g for DSHA, from 0.02 to 0.32 g and 0.092 to 0.1525 g for 2 and 10% probability in 50 years, respectively. A normalised site-specific design spectrum has been developed considering three vulnerable sources based on deaggregation at the city center and the results are compared with the recent 2011 Sikkim and 2015 Nepal earthquakes, and the Indian seismic code IS 1893.

Displacement of the Buildings According to Site-Specific Earthquake Spectra

The probabilistic seismic hazard curves were based on appropriate attenuation relationships at rock sites with a probability of exceedance of 10% in 50 years in this study. Results from the model were compared to the response spectra proposed in Section 7 of TEC ‘07 and were found to dier in both amplitude and frequency content. The impact of these dierences has been investigated with respect to building performance evaluation. Specifically, modal capacity diagrams and response spectra have been obtained for five buildings. Based on the diagrams and spectra, peak displacements have been calculated as well, revealing significant dierences in the demand displacement curves of the buildings. As a result, damage estimates and predicted building performance will deviate from site specific performance to a greater degree. Using site-specific spectra and field data will be important for future earthquake-resistant design. One of the conclusions of the study is that the Code spectra do not oer a sucient or comprehensive enough set of seismic demands and would lead to an under estimation of seismic hazard in the region of study. Therefore, site-specific design spectra for the region should be developed which reflect the characteristics of local sites.

Seismic response analysis of Ganga sand deposits using shake table tests

An accurate estimation of seismic behavior of a soil deposit is important from various aspects, namely, predicting the influence of the deposit in altering the earthquake waves propagating through that medium, quantifying the amplification or attenuation of the seismic shaking intensities, development of site-specific design spectra for seismic design of infrastructure to be built on that deposit, evaluating the possibility of ground failure and so on. The present study focuses on dynamic response analysis of local Ganga sand through performing a number of shake table experiments using a flexible laminar container. Uniform, dry Ganga sand of 30 % relative density exhibited acceleration amplification of 20, 40 and 68 % for input motions with 1, 2 and 5 Hz frequencies with amplitudes 0.2, 0.36 and 0.56 g, respectively. Further, analytical investigation on seismic response of the same soil deposit has been carried by assuming the behavior of the soil deposit as: (1) linear and (2) equivalent linear. The acceleration amplifications are estimated as 1, 4 and 28 % using the linear analysis and 3, 30 and 72 % using the equivalent linear analysis for the 1, 2 and 5 Hz motion, respectively. Compared to the linear analysis, the equivalent linear analysis predicts the surface amplification of the experiment with better accuracy (a maximum deviation being less than 6.7 %). This may due to the strain dependent behavior of the soil bed during strong shakings, which is compatible with the assumptions of the equivalent linear analysis procedure.

Effect of local soil conditions on dynamic ground response in the southern coast of Izmir Bay, Turkey

The city of Izmir, located at the western end of Turkey, has experienced many strong earthquakes throughout its history. The southern coast of Izmir Bay, one of the most densely populated areas of Izmir, is located on deep alluvial sediments. It is important to determine the effect of local soil conditions on dynamic ground response in the study area, where thick loose water-saturated alluvial sediments exist. A database including geotechnical and geological information on the study area is constructed. Majority of the site is classified as D and E according to NEHRP provisions. Dynamic site response analyses are performed with EERA by utilizing the field and laboratory test results and earthquake time histories of moderate-scale earthquakes such as 1977 Izmir (ML=5.3), 2003 Urla (Md=5.6), and 2005 Uzunkuyu-Urla (ML=5.9), which occurred in and nearby Izmir. In addition, a scenario ground motion generated by the Izmir Fault with a magnitude of 6.5, having an average distance of 10km to the study area, is also considered. The output data obtained from the dynamic site response analyses are evaluated, and maps displaying variation in dynamic parameters on ground surface are prepared for the southern coast of Izmir Bay, Turkey. Consequently, the dynamic analyses performed with the soil models constituted for the study area verified the damage occurred in a close distance event of 1977 Izmir earthquake. The scenario earthquake resulted in peak ground accelerations more than 0.6g at the eastern and western ends of the study area. However, long distance events resulted in spectral amplifications by up to 5 times. With this study, it is emphasized that local soil conditions should be evaluated individually in the area of interest. Generation of a site-specific design spectrum is recommended for the areas located on deep alluvial sediments.

Seismic hazard maps and spectrum for Patna considering region-specific seismotectonic parameters

The objective of this paper was to develop the seismic hazard maps of Patna district considering the region-specific maximum magnitude and ground motion prediction equation (GMPEs) by worst-case deterministic and classical probabilistic approaches. Patna, located near Himalayan active seismic region has been subjected to destructive earthquakes such as 1803 and 1934 Bihar-Nepal earthquakes. Based on the past seismicity and earthquake damage distribution, linear sources and seismic events have been considered at radius of about 500 km around Patna district center. Maximum magnitude (M (max)) has been estimated based on the conventional approaches such as maximum observed magnitude (M (max) (obs) ) and/or increment of 0.5, Kijko method and regional rupture characteristics. Maximum of these three is taken as maximum probable magnitude for each source. Twenty-seven ground motion prediction equations (GMPEs) are found applicable for Patna region. Of these, suitable region-specific GMPEs are selected by performing the `efficacy test,' which makes use of log-likelihood. Maximum magnitude and selected GMPEs are used to estimate PGA and spectral acceleration at 0.2 and 1 s and mapped for worst-case deterministic approach and 2 and 10 % period of exceedance in 50 years. Furthermore, seismic hazard results are used to develop the deaggregation plot to quantify the contribution of seismic sources in terms of magnitude and distance. In this study, normalized site-specific design spectrum has been developed by dividing the hazard map into four zones based on the peak ground acceleration values. This site-specific response spectrum has been compared with recent Sikkim 2011 earthquake and Indian seismic code IS1893.

DETERMINISTIC SEISMIC HAZARD ANALYSIS OF ANDAMAN AND NICOBAR ISLANDS

An important component of hazard mitigation is to estimate the future hazard for design calculations. In the present study, a deterministic seismic hazard assessment of Andaman and Nicobar region is carried out, which is one of the most seismically active regions of India. The study area is divided into seven seismogenic source zones based on seismicity and tectonic setting. For ground motion estimation at Andaman and Nicobar, for each seismogenic zone different attenuation relationship is used as per tectonic setting of that seismogenic zone. In order to generate the site specific design spectrum, final results are calculated in the form of peak ground acceleration (PGA) and 5%-damped pseudo-spectral acceleration (PSA) for 0.2 s and 1 s. Calculated results are compared with some earlier works for the studied area and the probable reasons for variations are discussed.

Seismic design spectra for different soil classes

This paper investigates the validity of the soil class dependent spectral shape factors used to calculate seismic design actions in the New Zealand seismic design standard NZS1170.5, which currently specifies seismic design spectra corresponding to five different soil classes. According to the current provisions stipulated in NZS1170.5, for all natural periods, the seismic demand for structures on soft soil is either equal to or greater than that for structures on hard soil. This is opposite to the basic structural dynamics theory which suggests that an increase in stiffness of a system results in an increase in the acceleration response. In this pretext, a numerical parametric study is undertaken using a nonlinear site response analysis tool in order to capture the effect of soil characteristics on structural seismic demand and to scrutinize the validity of the current site specific seismic design spectra. It is identified that the level of input ground motion intensity and shear stiffness of the soil deposit (represented by its shear wave velocity Vs) greatly affect the maximum acceleration and frequency content of the surface motion. The study found some shortfalls in the way the current code defines seismic design demand, in particular the hierarchy of soil stiffness at low structural periods. It was found that stiff soils generally tend to have a higher spectral acceleration response in comparison to soft soils although this trend is less prominent for high intensity bed rock motions. It was also found that for medium to hard soils the spectral acceleration response at short period is grossly underestimated by the current NZS1170.5 provisions. Based on the outcomes of the parametric numerical analyses, a revised strategy to determine structural seismic demand for different soil classes is proposed and its application is demonstrated through an example.

Probabilistic seismic hazard assessment of Eastern Marmara Region

The objective of this study is to evaluate the seismic hazard in Eastern Marmara Region using an improved probabilistic seismic hazard assessment methodology. Two significant improvements over the previous seismic hazard assessment practices are accomplished in this study: advanced seismic source characterization models in terms of source geometry and recurrence relationships are developed, and improved global ground motion models (NGA-W1 models) are employed to represent the ground motion variability. Planar fault segments are defined and a composite magnitude distribution model is used for all seismic sources in the region to properly represent the characteristic behavior of the North Anatolian Fault without the need for an additional background zone. Multi-segment ruptures are considered using the rupture model proposed by the Working Group on California Earthquake Probabilities (2003). Events in the earthquake catalogue are attributed to the fault zones and scenario weights are determined by releasing the accumulated seismic energy. The uniform hazard spectra at 10 % probability of exceedance in 50 years hazard level for different soil conditions (soil and rock) are revealed for specific locations in the region (Adapazari, Duzce, Gemlik, Izmit, Iznik and Sapanca). Hazard maps of the region for rock site conditions at the selected hazard levels are provided to allow the readers perform site-specific hazard assessment and develop site-specific design spectrum for local site conditions.