Three-Dimensional Numerical Model for Seismic Analysis of Structures

Critical building separation distance in reducing pounding risk under earthquake excitation

In the realm of structural design, Seismic Analysis is crucial. Many structures have collapsed because of earthquakes; as a result of numerous studies, different methods for analysing and determining vibration modes of a structure have been created. Seismic analysis can be done in two ways: static analysis and dynamic analysis. The basic mode of vibration dominates the response in the static technique of seismic analysis, and the mass and stiffness of the structures are evenly distributed, resulting in a regular shape, however this assumption fails for irregular buildings. As a result, dynamic methods are used to solve this issue. Response spectrum is one such dynamic method that is relatively simple to utilize compared to others. The benefit of employing the seismic response spectrum method is that it aids in the prediction of displacement and member forces in structural systems. As a result, this method aids in determining peak structural responses within a linear range, which can then be used to calculate lateral forces created in structures due to earthquakes, allowing for more earthquake-resistant building design. Although this method is approximate, it is a cost-effective and beneficial method for preliminary design research. The response spectrum method is used on STAAD.PRO V8i software to design a G+4 residential structure in our study. The building’s measurements are 16 meters long, 12 meters wide and 15 meters tall. The foundation was built to a depth of 1.5 meters. The structure was built to withstand earthquakes in seismic zone III on medium-density soil. Dead load (IS 875 Part I), Live load (IS 875 Part II), Seismic Load (IS 1893 Part I), and Wind Load are some of the load instances that were presented based on Indian Standard code (IS 875 Part III). To acquire the best response, the response spectrum modal combination Complete Quadratic Combination (CQC) is used. Various parameters like wind intensity, seismic parameters, dynamic weight, modal participation factors, base shear and peak storey shear are calculated. Base shear and peak storey shear are found to maximum in Mode 2 and between 5th and 6th respectively.

Seismic fragility assessment of a super tall building with hybrid control strategy using IDA method

This paper proposes a new procedure for predicting the maximum seismic response based on the capacity spectrum method (CSM) for the passively controlled suspended ceiling structures named “Pulley Damper Ceiling System (PDCS)”. The structural system has a supplemental nonlinear viscous damper and a bilinear hysteretic damper in parallel with displacement amplification mechanisms of block and tackle pulley system. The single degree-of-freedom model of the PDCS is initially discussed. The accuracy of a simplified calculation method for obtaining the structural equivalent damping coefficient, determined by the sum of the inherent damping and the square root of sum of squares (SRSS) of each damping provided by the nonlinear viscous damper and the bilinear hysteretic damper, is verified by comparing with the full-scale shake table test results of the PDCS. Then, the pseudo capacity curve of the structure is generated by continuously plotting the transition of maximum force and displacement values under different amplitudes of sinusoidal waves. Finally, the availability of the response prediction based on proposed CSM procedure considering floor response spectrum (FRS) is examined by the comparison of time history analysis results, and the sufficient accuracy to evaluate the seismic response is confirmed.

The peak dynamic responses of two mathematical models of a fifteen‐storey steel moment resisting frame building subjected to three earthquake excitations are computed by the response spectrum and time history methods. The models examined are: a ‘regular’ building in which the centres of stiffness and mass are coincident resulting in uncoupled modes with well‐separated periods in each component direction of response; and an ‘irregular’ building with the mass offset from the stiffness centre of the building causing coupled modes with the translational modes having closely spaced periods. Four response spectrum modal combination rules are discussed and are used to predict the peak responses: (1) the square root of the sum of the squares (SRSS) method; (2) the double sum combination (DSC) method; (3) the complete quadratic combination (CQC) method; and (4) the absolute sum (ABS) method. The response spectrum results are compared to the corresponding peak time history values to evaluate the accuracy of the different combination rules. The DSC and the CQC methods provide good peak response estimates for both the regular and irregular building models. The SRSS method provides good peak response estimates for the regular building, but yields significant errors in the irregular building response estimates. The poor accuracy in the irregular building results is attributable to the effects of coupled modes with closely spaced periods. It is concluded that the DSC and CQC methods produce response estimates of equivalent accuracy. Both methods are recommended for general use. In addition to the DSC and CQC rules, the SRSS method is recommended for systems where coupled modes with closely spaced periods do not dominate the response.

Base isolation is an effective seismic design strategy that has received considerable attention in recent decades. This research is dedicated to developing a response spectrum method (RSM) for analysis of base-isolated structures under seismic excitation. A novel analytical model consisting of a linear superstructure under equivalent base excitations is proposed in the present study. To determine the response spectra corresponding to the base excitations, termed as the base response spectra, a sufficient number of samples of base excitations comprising base responses need to be obtained through time-history analysis of the nonlinear base-isolated structure in conjunction with the Monte Carlo simulation (MCS). To improve the efficiency for each sample analysis, the recently proposed explicit time-domain method (ETDM) is utilized for fast analysis of the base acceleration and velocity responses with a dimension-reduced iteration scheme. Once the base response spectra are obtained, the mean peak values (MPVs) of structural responses of the linear superstructure can be conveniently evaluated through the complete quadratic combination (CQC) rule. A 4-story nonlinear base-isolated frame structure was analyzed to validate the effectiveness of the proposed analytical model and the feasibility of the present approach for seismic response analysis of nonlinear base-isolated structures.

The research investigates the validity of the complete quadratic combination (CQC) method. A new approach is proposed in order to consider the effect of modal correlation more accurately than the CQC method. Statistical analysis indicates that the error in the estimation of modal correlation could be reduced compared to the CQC method. This method is especially more accurate in higher frequency ratios where the role of interaction between modes in the seismic response is noticeable. Statistical analysis reveals that the proposed method is more precise, especially for far-field records. Meanwhile, the proposed method is not sensitive to different site classes.

Two-stage deep learning for accelerated 3D time-of-flight MRA without matched training data

The independent support motion (ISM) response spectrum method is currently used in seismic analysis to calculate the response of piping systems subjected to independent excitations at several points of a supporting structure. This approach leads to considerable over estimation when the maximum responses by multiple excitations are combined by the absolute sum rule, while this may result in underestimation when the maximum responses by the multiple excitations are combined by the square root of sum of squares rule. Then authors have developed an advanced method of the ISM approach named SATH (spectrum method assisted by time history analysis), which was presented in PVP2020. In the SATH method, both floor response spectra and time histories of floor acceleration are used as independent inputs of support excitations. The maximum responses by multiple excitations are combined using correlation coefficients calculated by taking into account each time history of modal response due to independent inputs of support excitations. When the SATH method is applied to actual design using broadened FRS, the structural frequency uncertainty corresponding to broadened FRS should be considered in the calculation of correlation coefficients. The applicability of the SATH method to the structural frequency uncertainty was presented in ICONE2020. Furthermore, when piping systems are subjected independent excitations at several points of a supporting structure, the response of piping systems can be considered to have two different components. One is due solely to the inertia of the mass (the dynamic component) and the other is due to the time-varying differential motion of the support point (the pseudo-static component). Here, the dynamic component consists of two parts: the damped-periodic response (dynamic response) and the residual rigid response (high frequency response). Then authors have improved the SATH method to cope with above three responses (dynamic response, high frequency response and pseudo-static response), which was presented in ASME PVP 2023. Thus, since its presentation at ASME PVP 2020, the SATH method has been evaluated and improved several times and is now an appropriate method to use in design. In this paper, the entire procedure of the SATH method, which combines the dynamic response using broadened FRS, with the high-frequency response and the pseudo-static response, is described as an actual design method. In addition, the advantages of the SATH method in design are clarified by comparing the response by the SATH method with that by the conventional method (the uniform response spectrum analysis method and the independent support motion response spectrum analysis method) for a three-dimensional piping system model subjected to independent excitations at several points of a supporting structure.

A hybrid structure is one that combines more than two different types of materials to compensate for weak places while also maximizing strength. Hybrid steel and concrete frameworks, as well as other modern materials, are unified at the member or framework unit. Hybrid structures are frequent in high-rise and super-high-rise building projects, and they provide the benefit of cost savings. Shear walls are built to withstand lateral loadings like earthquakes and winds loads. The response spectrum analysis approach is frequently used to measure design stresses for earthquake-prone structures. The modelling and analysis of the regular plan structures are done by CSI ETABS 2019 in IV seismic zones, on type II (medium soil) of India According to IS 1893 (Part-1) 2016. The aims of this study Response spectrum analysis of 41 storey RCC and hybrid structures with shear walls and without shear walls are compared. RCC and hybrid structures with shear walls showed lower storey displacement, storey drift, and story shear values than RCC and hybrid structures without shear walls, according to the results of this study. The research results will be helpful as a reference and a tool for seismic analysis of hybrid structures.

Evaluation of equivalent linearization methods of MDOF isolated structures in response spectrum analysis

Presented is a detailed case study on structural Finite Element (FE) modeling and Modal Pushover Analysis (MPA) of a 14-story office building instrumented for seismic response investigation. The system identification tool was used to identify the structural dynamic properties, including the natural periods of vibration of the structure and level of critical damping based on seismic data recorded during small seismic ground motions. A series of FE models were created to improve the modeling technique. The final corrected FE model was refined and calibrated to match the identified structural natural periods. It was found that a FE model can be calibrated to give a good prediction of earthquake response. Using the calibrated FE model, the structural seismic behavior has been examined using the MPA procedure. In the MPA procedure, an improved analysis based on structural dynamic theory with invariant force distributions was used to generate the push loads. Four recorded ground acceleration time histories were used as input data for the MPA procedure. Five sets of push forces, corresponding to the effective earthquake forces from the first five modal expansions, were applied to the FE model. The final MPA results were combined from these five push-over cases using the Square-Root-of-Sum-of-Squares (SRSS) rule and the Complete Quadratic Combination (CQC) rule to get the total response. The MPA results were also compared with the Incremental Dynamic Analysis (IDA). It is found that the MPA and IDA results are reasonably matched. The MPA procedure is an improved tool for estimating seismic demands on buildings. Using the MPA procedure, the structural behavior can be examined during seismic loading and future performance of the building during damaging earthquakes can be predicted.

Tri-axial Seismic Simulation of Solar Inverter – Productivity Improvement

This paper presents a comparison of the seismic forces generated from a Modal Response Spectrum Analysis (MRSA) by applying the provisions of two building codes, the 1997 Uniform Building Code (UBC) and the 2000–2009 International Building Code (IBC), to the most common ordinary residential buildings of standard occupancy. Considering IBC as the state of the art benchmark code, the primary concern is the safety of buildings designed using the UBC as compared to those designed using the IBC. A sample of four buildings with different layouts and heights was used for this comparison. Each of these buildings was assumed to be located at four different geographical sample locations arbitrarily selected to represent various earthquake zones on a seismic map of the USA, and was subjected to code-compliant response spectrum analyses for all sample locations and for five different soil types at each location. Response spectrum analysis was performed using the ETABS software package. For all the cases investigated, the UBC was found to be significantly more conservative than the IBC. The UBC design response spectra have higher spectral accelerations, and as a result, the response spectrum analysis provided a much higher base shear and moment in the structural members as compared to the IBC. The conclusion is that ordinary office and residential buildings designed using UBC 1997 are considered to be overdesigned, and therefore they are quite safe even according to the IBC provisions.

최근 감쇠장치 등을 가진 초고층 건축물의 지진해석에 시간이력해석법이 자주 사용되고 있다. 지진기록은 구조물의 기본 진동주기를 T라 할 때 설계기준에서 요구하는 바와 같이 0.2T에서 1.5T 사이의 스펙트럼 값을 설계응답스펙트럼에 부합하게 조정되어 사용되고 있다. 설계기준에서 제시한 방법으로 조정할 경우 주기가 길어질수록 두 해석법 사이의 응답차이는 커지는 현상이 발생한다. 즉 설계기준에 의하여 조정된 지진기록을 사용하여 시간이력해석을 수행하면 밑면전단력 등은 비슷하지만 변위, 층간변위, 부재력 등은 적게 평가되는 현상이 발생하였다. 이들 결과에 밑면전단력 조정계수를 적용하면 응답이 더욱 작아지는 것을 확인하였다. 이에 본 연구에서는 인공지진을 만드는 데 어려움이 있는 엔지니어들을 위하여 기존 설계기준에 부합하는 지진기록 조정방법을 제시하였다. In recent years, time history analysis has been the method generally used for the seismic analysis of tall buildings with damping devices. When T is the natural period of the first vibration mode of the structure, the sum of the spectral acceleration of the earthquake ground motion is usually adjusted to that of the design response spectrum in the period ranging from 0.2T to 1.5T to meet the requirements of design code. However, when the ground motion is scaled according to the design code, the differences in the responses obtained by response spectrum analysis (RSA) and time history analysis (THA) of the structures increase as the natural period of the structure becomes longer. When time history analysis is performed by using ground accelerations that are scaled according to the design code, base shear is similar to that obtained from RSA, but other responses, such as displacements, drifts and member forces, are underestimated compared to RSA. If these results are adjusted by multiplying with the scale-up factor, the scaled responses become much smaller. Therefore, a scaling method of ground motions corresponding with the design code is proposed in this study, as a way of assisting structural engineers in generating artificial ground motions.