Linear Response Spectrum Research Articles

Impact of irregular masonry infill walls on the seismic response of reinforced concrete frame buildings using linear dynamic analysis

This paper aimed to investigate the seismic response of reinforced concrete (RC) frame buildings using linear dynamic analysis. The study focused on the effects of irregular distributions of masonry infill walls both in elevation (soft story at different levels) and in horizontal (plan) distribution on seismic behavior. Seventeen models were analyzed, including infill frame models with soft stories, models with infill panels only in certain bays, and bare frame models. All models were analyzed using the linear response spectrum (RS) dynamic analysis method. Structural design typically focuses on peak response values, and response spectrum analysis examines the structure's behavior and performance through these peak values. The analysis results indicate that masonry infill walls significantly affect the building's fundamental time period, base shear, story shear, and inter-story drift.

Seismic Analysis of High Rise Building with Transfer Floor

A transfer floor is the floor system which supports a vertical as well as lateral load resisting system and transfer its loading to different underneath system. Transfer floor distribute the load from closely spaced columns to the columns with long span. This study presented, a seismic analysis of high rise building with transfer floor. A number of proto type models of high rise building were analyzed using linear response spectrum analysis. The models were analyzed using structural software for building analysis ETABS 2016 software. The analyzed models has transfer slab system at different floor levels in high rise building. In this paper, five different models of 10 storey building had studied by providing a transfer slab at different floor levels such as first floor, second floor, third floor, fourth floor and fifth floor of the building. And the vertical position of transfer slab with respect to building height was investigated. The seismic response of high rise building such as storey shear, storey moment, storey displacement, inter-storey were numerically evaluated. Key Words: Transfer slab, Response spectrum analysis, Storey shear, Storey moment, ETABS 2016.

Comparison of Bracings and Fluid Viscous Dampers in 15-Storey Buildings across All Seismic Zones of India under Bi-Directional Excitation

Abstract: An earthquake is a natural phenomenon i:e, sudden horizontal movement of earth’s crust that causes sudden collapse of buildings and other structures such as large monuments, bridges etc. The damage of the building is based on the amount of magnitude and intensity of the earthquake. A building can withstand in lower intensity of earthquake. But higher intensity causes lots of damages on building or a building can suddenly collapse and causes increase in number of deaths. To mitigate these effects a control system is to be provided such as base isolations, dampers, bracings etc. The current topic is based on the behavior of linear and non linear fluid viscous damper provided at center and both side corners of 15 Storey RC building in diagonally bracing system. The building is modeled and analyzed by using ETABS software. Here IS 1983(part1): 2002 and medium soil type are to be considered for analysis with respect to all seismic zones (zone II - zone V) of India. Here linear static and response spectrum analysis are applied in each model. Results are to be drawn based on base shear, storey displacement and storey drift to understand how fluid viscous dampers helps to reduce the effects of earthquake.

Modal-based fragility analysis of high-rise tubular structures: A methodology for vulnerability assessment

This study addresses the limitations of current vulnerability assessment processes for tall buildings, which fail to incorporate the effects of higher modes and the resulting structural vulnerability to seismic hazards. Additionally, the extensive computational resources required for assessing tubular high-rise buildings make vulnerability assessments almost impossible. This study proposes a new methodology for assessing the modal-based structural vulnerability of high-rise reinforced concrete (RC) tubular buildings by incorporating nonlinear response and reducing computational effort. The proposed methodology discreetly develops the vulnerability information of each structural vibrational mode separately using nonlinear time history analysis rather than the linear Modal Response Spectrum Analysis (MRSA). The methodology includes steps for establishing vulnerability information for high-rise tubular buildings, and a case study of a 55-story RC building with core wall is presented to demonstrate the methodology. The vibrational modes of the building were decoupled and analyzed separately using single degree of freedom (SDOF) systems, and fragility curves were developed for three different limit states using various intensity measures. The obtained fragility relationships were compared with the curves of another structure of similar class. The results indicated good compatibility and significance of incorporating higher vibrational modes in assessment of structural vulnerability, thus, proposed methodology can be extended to any structural configuration of tubular buildings.

Comparison of Linear and Nonlinear Procedures for the Analysis of the Seismic Performance of Straight Multi-Span RC Bridges

The assessment of the seismic performance of transportation infrastructures is of primary importance for the management of the aftermath of an earthquake. To perform such an assessment, various modeling approaches characterized by different levels of accuracy are available and modern seismic design codes provide recommendations about their use. Non-linear time-history analysis (NLTHA) is acknowledged as the most reliable method, but is difficult to implement and is computationally expensive. This paper aims to investigate the viability of less complex methods, but with low computational cost, for the assessment of straight, multi-span bridges and compare their performance against the results of NLTHA in order to quantify the expected accuracy. The study is developed considering three bridge archetypes with either simply-supported or continuous-deck layouts, representative of typical features of the Italian bridge stock. The bridges are analyzed first through nonlinear dynamic analyses, to define the benchmark solution; then linear dynamic analyses, such as Linear Time-History and Response Spectrum Analysis, nonlinear static analyses, such as MPA (Modal Pushover Analysis), and Equivalent Static Analysis are considered. A comparison among the examined procedures is eventually proposed, highlighting the strengths and weaknesses of each approach.

A framework for nonlinear peak response evaluation from linear response spectra of base-isolated structures using the bilinear hysteretic model

This paper proposes a simple computational framework that can account for both properties of the base-isolated structure using the bilinear hysteretic model and reliably evaluate the nonlinear peak response without nonlinear response history analysis. The proposed computational framework requires the construction of new non-proportional damping models that match the base-isolated structure to accurately decompose the nonlinear multi-degree-of-freedom structure into multiple single-degree oscillators with intrinsic frequencies and damping ratios by equivalent linearization and complex-mode superposition methods. Each oscillator is excited by a response spectrum matching its own damping ratio, and this procedure is iteratively computed until the displacement error of the isolation layer achieves a preset value. Simultaneously, the peak nonlinear response of interest is calculated using the complex-mode-superposition complete square combination rule. The effect of peak response on nonlinear parameters is analyzed using a typical numerical example, and the relative error values for the applicable range are presented. Parametric research demonstrates that the new non-proportional damping matrix accurately reflects the modal characteristics of the base-isolated structure and prevents Rayleigh damping from suppressing the first-order modal characteristics. The particular example evaluation shows that the computational framework can effectively evaluate the nonlinear peak response of the BIS, with the isolation layer displacement error controlled within +5 %, the bottom shear force error within +20 %, and the top acceleration error between −10 % and +25 %.

Development of practical downsampling methods for nonlinear time history analysis of complex structures

One of the main problems of nonlinear time history analysis is its high computational effort, especially in structures with large number of structural components, high-rise buildings and complex structural systems. The ground motions recorded in recent years also include more recorded points than in the past, which has also increased the required volume of calculations. In this paper, three downsampling methods for reducing calculation costs of nonlinear time history analysis are presented and their applicability is investigated through practical examples of complex structures. These methods include the discrete wavelet transform, the time step correction, and the wavelet time step correction which is introduced in this paper. The efficiency of these downsampling methods is investigated for near-fault and far-fault earthquake records, as well as for records on different soil types. A comprehensive study is performed on five sets of ground motions consisting of 20 records. Each record is filtered up to three stages using one half, one quarter, and one eighth of the number of the main record points. First the linear and nonlinear response spectra based on the original records and the approximate waves are investigated. Subsequently, to evaluate the performance of the methods on more complex structural systems, two three-dimensional structures of 6-story and 15-story are analyzed. The 6-story structure is equipped with viscous dampers, while the 15-story structure has seismic isolators. The results indicate that the wavelet time step correction method has better performance in most cases, compared to the other two methods. It is shown that careful consideration is needed when dealing with earthquake records with high frequency contents. In such situations, one filtering step for the discrete wavelet transform method and two filtering steps for the other two methods are recommended. Also, in practical applications, it is advisable to choose earthquake records exhibiting the least error based on the results of SDOF systems analyses. Employing this technique can significantly cut down computational effort (up to 90%), while maintaining an average error ranging from 1% to 2% for the wavelet time step correction method.

Comparative Study of Analysis, Design and Total Cost Differences between Monolithic Structure and Conventional Structure

The primary objective of this research is to investigate the behavior of conventional buildings featuring non-structural walls as AAC blocks and all the remaining things same, with monolithic structure buildings constructed using tunnel formwork. To compare the design steel and total cost between these two types of structures subjected to seismic loads, as defined by the IS codes. To achieve this, a comprehensive seismic analysis was conducted using the Linear Dynamic Response Spectrum Method in ETABS 2020 software.

Seismic Performance Assessment of the 18th Century Jesuit College in Dubrovnik’s Old City

The seismic performance assessment of heritage architecture presents many challenges due to the restrictions set forth by the conservation principles to protect the associated social and cultural values. These buildings are typically characterized by unreinforced masonry walls connected by tie-rods, vaults, and wooden floors. The era of construction dates to the time when seismic design regulations were largely unknown, making heritage structures potentially vulnerable to earthquake damage. This study presents the seismic performance assessment of the Jesuit College located in the southern part of the Old City of Dubrovnik. A series of field surveys were conducted to qualitatively examine the material composition and obtain geometrical details in part of the Croatian Science Foundation research project IP-2020-02-3531 entitled “Seismic Risk Assessment of Cultural Heritage in Croatia—SeisRICHerCRO”. The structural response is thoroughly investigated by means of a complex finite element model calibrated using the frequencies determined from ambient vibration measurements and material characteristics obtained from the literature review of representative cultural heritage buildings. The seismic performance is evaluated using linear static and response spectrum analysis in accordance with Eurocode 8 guidelines for the demand seismic action level. The numerical analysis indicates several structural components in the building exhibiting high shear stress concentration and exceeding the elastic tensile limit under the demand ground acceleration level. The assessment further reveals substantial out-of-plane bending of vulnerable wall components (identified by local mode shapes) at low peak ground acceleration levels. The stress concentration in numerous structural components leads to the identification of vulnerable zones where retrofitting measures are essentially required.

Seismic Assessment of RC Frame Building using Gross and Cracked Section as per IS 1893: 2016 and IS 16700: 2017

The primary objective of this research is to investigate the behaviour of tall concrete buildings featuring structural walls combined with Special Moment Resisting Frames (SMRF) when subjected to seismic loads, as defined by the IS 1893:2016 and IS 16700:2017 codes. To achieve this, a comprehensive seismic analysis was conducted using the Linear Dynamic Response Spectrum Method in ETABS 2020 software.

Design Demand of RC Building as per Soil Type

The RC-framed building is one of the most common construction techniques for seismic-resistant structures due to its ductile nature. But the seismic performance of the RC structure is affected by various factors among which site soil condition is vital. The sub-soil condition affects the time period of the structure which eventually impacts the earthquake force in the structure, thus making variations in seismic loadings. Although several studies have been performed and design elastic spectra have been defined as per soil types in the design codes, there are no studies quantifying the effect of design demand in the buildings due to variation of soil type in the context of Nepal and NBC 105:2020. Therefore, this study aims to present the variation in design demand for moderately high-rise RC buildings in different soil types. A representative sample building has been taken and analyzed in the Finite Element platform SAP 2000. Numerical analysis is performed using linear static and response spectrum methods. Based on the study, variation in the base shear, story displacement, inter-story drift, and section size to meet the limit state of strength are compared for soil types A, B, C, and D.

Next generation ground-motion prediction equations for Indo-Gangetic Plains, India

Seismic hazard analysis (SHA) of Indo-Gangetic Plains (IGP), India, and its proximity to the Himalayas requires reliable ground motion prediction equations (GMPEs). This study attempts to derive the GMPEs for IGP using strong-motion accelerometer data recorded from 2005 to 2015 on IGP. For regression, peak ground acceleration (PGA) and pseudo-spectral acceleration (PSA) of 5% damped linear pseudo-absolute acceleration response spectra at 27 periods ranging from 0.01–10 s were used. Two-stage nonlinear regression trains the functional form of nonlinear magnitude scaling, distance scaling, and site conditions. The model includes a regionally independent geometric attenuation finite fault distance metric, style of faulting, shallow site response, basin response, hanging wall effect, hypocentre depth, regionally dependent anelastic attenuation, site conditions, and magnitude-dependent aleatory variability. Developed GMPEs are validated for active crustal continental earthquakes for epicentral distances REPI ranging from 10–1500 km, magnitude ranging from 3.3–7.9, and focal depths 1–70 km. The GMPEs developed are compared with the Campbell and Bozorgnia 2008, 2013 and 2014, and North Indian GMPEs, which are agreed upon consistently. The model can predict the horizontal ground motion for SHA on IGP, considering possible maximum magnitude earthquakes from the seismic gaps of the Himalayas.

Evaluating the performance of different mother wavelet functions for down-sampling of earthquake records

Application of discrete wavelet transform for down-sampling earthquake records has been started since 2002. Although the mother wavelet function plays an important role in the accuracy of wavelet transform, there is no study to investigate the effect of this function on dynamic analysis error. In addition, most studies have used a limited number of earthquake records for down-sampling application of wavelet transform. Therefore, in this paper, a comprehensive study is performed on 36 different mother wavelet functions and 100 earthquake records. The linear and nonlinear response spectra of the main records and their down-sampled ones have been used to evaluate the performance of different mother wavelet functions. Approximate waves are obtained for three levels using wavelet transform. Also, dynamic analyses are done for 101 single-degree-of-freedom systems (with a period between 0 and 5 s) and 5 behavior coefficients consisting of more than 7 million analyses. Results show that the Daubechies family of wavelet functions used in previous studies for down-sampling earthquake records often cause errors greater than 15%. But the Biorthogonal wavelet functions which have not been used for down-sampling before, have an error of less than 2.5% and are the best wavelet functions for down-sampling earthquake records. In addition, a method called wavelet functions combination is presented to ensure minimum errors at different levels of down-sampling. In the next step, to evaluate the effect of the wavelet function on the accuracy of dynamic analysis of real structures, 3, 9, and 20 story structures are analyzed using the IDA method and finally, an irregular structure is also analyzed. The results obtained from the nonlinear analysis of these structures show that Biorthogonal wavelet functions can reduce the wavelet error from 27% to 6%.

Seismic demand estimation of isolated buildings with nonlinear bearings subjected to linear response spectra

Response spectrum analysis is a commonly used method for the seismic design of linear structures with fixed bases since the seismic input is normally provided in terms of the response spectrum in many codes. This study proposes a more generalized response spectrum method for the seismic design of three-dimensional isolated structures. Firstly, the theory basis of this method is derived in the framework of the random vibration theory. The equivalent parameters of each bearing are expressed in terms of the statistics of the displacement amplitude. Then, the complex mode theory is introduced into this method to consider the effect of the nonclassical damping resulting from the isolation layer. Finally, an iterative analysis procedure is presented, which combines the equivalent linearization with the complex mode theory. Moreover, the convergence and applicability of this method are discussed in detail. The parameter analyses show that the relative error of the base shear of the superstructure estimated by using this method is within 10% compared with that of the nonlinear time history analysis. In addition, a benchmark base-isolated structure is used as a numerical example to examine the effectiveness of the proposed method. The results show that the iteration is convergent and computationally efficient. The results also show that the maximum relative errors of the predicted isolation layer displacement, the inter-story drift of the bottom floor and the absolute acceleration of the top floor are 9.5%, 3.9% and 18.9%, respectively, by comparing them with the nonlinear time history analysis, while these responses are underestimated by 9.8%, 25.9% and 40.2%, respectively, when using the classical complete quadratic combination (CQC) method that neglects the nonclassical damping effect. Although in this study the proposed approach mainly focuses on isolated structures, in essence, this approach can also be applied to inelastic structures or structures with nonlinear dampers.

Critical issues in existing RC deck stiffened arch bridges under seismic actions

Existing Reinforced Concrete arch bridges represent still today an important part of transportation network. The peculiarities of such bridges make particularly complex the assessment of their behaviour under both static and dynamic actions and, therefore, their safety. This work concentrates on a specific arch bridge typology known as the “Maillart –Type Arch Bridges” or “Deck-Stiffened Arch Bridges”, characterized by a very stiff deck beam and a slender and wide vault. As well as for the RC structures designed during 50s of the last century, where some important details for concrete elements were not considered, RC Deck-Stiffened Arch Bridges could be subjected to similar structural deficiencies. Moreover, the current loading conditions provide actions that were not considered in the original design or have changed over the time, such as the seismic actions or the moving loads due to the vehicular traffic.For the evaluation of the main critical issues related to the current performance of the “Maillart–Type Arch Bridges”, this study, starting from a “simulated design” according to the design rules and the mandatory codes in force at the construction time, defines a large building inventory of simulated bridges (3000 samples) characterized by different values of the most significant geometrical parameters. Firstly, each bridge of the inventory is modelled and studied by means of a linear Response Spectrum Analysis (RSA) implemented in the software SAP2000. The large number of structural analyses allowed to investigate the seismic behaviour of such a bridge typology, assess and localize the most frequent failure modes. The results of the RSA allowed developing preliminary fragility functions at the Ultimate Limit State, based on shear or flexural failure of single elements of the bridges. Lastly, Non-Linear Time History Analyses (NLTHA) were carried out on two representative case studies extracted from the simulated inventory and the results were examined in terms of fragility curves obtained according to the Cloud methodology for four Damage States. Despite the different approaches (RSA on large scale and NLTHA on two prototypes), a comparison of the fragility curves for equivalent Damage States was also proposed and a good agreement was found. These fragility curves are a first step for the assessment of the seismic vulnerability of “Maillart–Type Arch Bridges” and can be useful for planning seismic risk mitigation interventions for such a bridge typology.

Study on Dynamic Behaviour of Irregular R.C Framed Structures with Different Location of Shear Walls

In the recent researches it was found to be the most appropriate loads resisting system in recent and present years is shear walls system. In the high rise building shear walls are of the most achievable and hence commonly used lateral load resisting components. It is supplied in building from foundation level to through the height of the building. The scope of the present work is to find the optimum location of the shear walls in plan irregular structures with shear walls such as in I frame, L frame, T frame for different zones in G+17 stories each storey height of 3.2 m, Shear walls are given at corners and at periphery of the building. And also, the outcome of results in seismic zones as per IS CODE 1893(Part1): 2016 has been presented. The seismic analysis performed is linear dynamic response spectrum analysis utilizing the well-known analysis and design software ETABS 18.1.0. Seismic performance of the building has been examined based on specification such as storey displacement, Storey drift, Storey Shear, Base shear, Time period of modes.

Linear dynamic analysis of high-rise irregular structures with or without LFRS & frictional damper

This study categorically assists in describing the behavior of Irregular structures consist of G + 20 Storey through linear dynamic analysis for seismic assessment of structures. Linear dynamic analysis or response spectrum analysis helps us to evaluate the several parameters in respect of severe responses in irregular structures. At the time of design, A well analyzed structure shows which fragile part of structure needs to give an attention at the time of design to resist and dissipate the energy of seismic force occur on a structur3e during the earthquake. Response spectrum analysis is a seismic analysis method, which shows the response of structure when a seismic load taken into an account. In this study series of sequential response spectrum analysis of High-rise irregular structures have compared with the similar structures after assigning shear walls, Steel bracings and Frictional dampers respectively, and simultaneously all the purposed structure responses have compared with a regular structure accordingly with same consideration of lateral force resisting system. The complete modelling and analysis have done by the prominent analytical FEM integrated software “ETABS” in the seismic zone IV by considering relevant data for the particular seismic zone by IS 1893 (Part-1) 2016. All the reinforcement criteria for the components of structure has been taken into consideration as per suggested by IS 13920 for the ductile design. The response parameter aims for structures due to seismic loading are in terms of Max. displacement, Storey shear. Ultimately, it was concluded that the shear wall is more desirable than the other for reducing the max. displacement with the average reduction percentage of 61.33%.

Ground motion of the Ms7.0 Jiuzhaigou earthquake

Abstract Eighty-eight free-field strong ground motion observation datasets obtained by the National Strong Motion Observation Network System of China for the Jiuzhaigou Ms7.0 earthquake were used to study the characteristics of the strong ground motion and the site response. In this study, we calculated the VS30 of the near field station and compared the observed values of the horizontal peak acceleration and peak velocity with the CB2014 ground motion prediction models developed by Campbell et al. (2014). The results indicate that the observed values of the horizontal peak acceleration and peak velocity of the Jiuzhaigou earthquake are both smaller than the predicted values obtained from the ground motion prediction equations. By regressing the spatial variation curves of the D SR (5–95%) and D SR (5–75%) ground motion durations, and comparing them with Bommer’s (2009) ground motion duration prediction curve, it was found that the duration of the Jiuzhaigou earthquake was greater than that obtained from the global empirical prediction equation. The scope of the source duration corresponding to the D SR (5–75%) duration is 2.76–4.28 s, and the scope of the source duration corresponding to the D SR (5–95%) duration is 8.88–10.36 s, which are close to the peak time and completion time of the seismic moment release during the source rupture process. The linear elastic acceleration response spectra of 11 stations within 100 km of the fault were calculated for comparison with the design spectrum. It was concluded that the range of the predominant period of the response spectrum was 0.05–0.26 s, which is less than the natural vibration period of the local multistory building. However, the response spectrum value recorded by station 51JZZ is greater than the design spectrum of the 8° rare earthquake and the observation values of the nearby strong ground motion stations. Through analysis of the H/V spectrum ratio and the case of station 51JZZ, which is closest to the epicenter, this phenomenon was concluded to be related to the magnification effect of the near-surface soil layer and the nonlinear response of the site under the action of strong earthquakes.

Dynamic performance of soft-storey structures with gap elements at beam-column joints

Soft-storey structures are more susceptible to failure for seismic vibrations, which is well-known to the world. But, in multi-storey apartments, it is a practice to provide a parking place at the ground storey, inducing soft-storey effects. In the present study, an effort is made to reduce the soft-storey effect on the structure's dynamic performance by introducing an arrangement of gap elements at beam-column joints. To that context, a numerical assessment is carried out to check the performance of the RC structure. The gap element is modelled as a spring either in a beam or in a column or both.The research has been performed in two parts; the first part of the analysis is focused on optimizing the gap element pattern. Diagonal compressive struts replace the infill walls, and the ground storey is modelled as an open ground storey without infill walls, which is considered a soft-storey. From the first part, an optimal gap element pattern from five different arbitrary patterns is obtained from the results of linear dynamic response spectrum analysis, depending upon the comparison of various seismic parameters. The second part of the analysis involves checking the effect of the gap element's optimized pattern for four levels of structures with vertically varied aspect ratios. Response spectrum analysis is performed, and a study is conducted to compare the seismic parameters for the four levels. The models with gap elements have shown an apparent reduction in storey displacements, inter-storey drift ratios, over-turning moments, and increment in storey stiffness when compared to the conventional models, thus exhibiting constructive outcomes.

Magnetic-field tuning of the intraexcitonic absorption and gain in transition metal dichalcogenides

A systematic microscopic approach combining ab-initio density functional theory with the Dirac-Bloch equations is applied to investigate the intra-excitonic transitions of magneto-excitons in transition metal dichalcogenide monolayers. For the example of hBN-encapsulated $\mathrm{Mo}{\mathrm{S}}_{2}$, the linear optical response and mid-infrared spectra of the pre-excited system are numerically evaluated. It is shown that the transition probability between a subset of the magneto-excitons can be inverted under suitable conditions to display negative absorption, i.e., gain. With the help of an applied magnetic field, the absorption and gain spectra can be tuned over a wide spectral range. Evaluating the Zeeman shift of the excitonic states, effective $g$ factors are deduced that depend on the dielectric environment of the sample under consideration.