Modal Response Spectrum Analysis Research Articles

The Application of Artificial Neural Networks in Predicting Structural Response of Multistory Building in The Region of Sumatra Island

Artificial Neural Network (ANN) method is a prediction tool which is widely used in various fields of application. This study utilizes ANN to predict structural response (story drift) of multi-story reinforced concrete building under earthquake load in the region of Sumatera Island. Modal response spectrum analysis is performed to simulate earthquake loading and produce structural response data for further use in the ANN. The ANN architecture comprises of 3 layers: an input layer, a hidden layer, and an output layer. Earthquake load parameters from 11 locations in Sumatra Island, soil condition, and building geometry are selected as input parameters, whereas story drift is selected as output parameter for the ANN. As many as 1080 data sets are used to train the ANN and 405 data sets for testing. The trained ANN is capable of predicting story drift under earthquake loading at 95% rate of prediction and the calculated Mean-Squared Errors (MSE) as low as 1.6.10<sup>-4</sup>. The high accuracy of story drift prediction is more than 90% can greatly assist the engineer to identify the building condition rapidly due to earthquake loads and plan the building maintenance routinely.<strong></strong>

Performance based Seismic Analysis on RCC Framed Elevated Circular Tanks with Flat and Domical Bases

Objectives: This paper replicates the comparative study of RCC staged circular water tanks with flat base and domical base of same capacity of 320m3 under seismic conditions. Method: Analysis is carried out for dynamic responses, with inclusive variables as height of staging, soil condition, damping factor, seismic zones adhering to IS 1893-2002. Layout of staging frame and circular tank is with accordance to IS 11682-1985 and IS 3370 accordingly. Series of analysis has been done using Staad pro v8i as a tool for Modal analysis and Response spectrum analysis adhering to IS 1893-2002, and response is depicted in the form of graphs for each zone. Findings: Graphs sketched for the governing design criteria i.e. Base Shear, for each height and type of tanks considered under the pertaining conditions for each zone perspicuously delivers the basic idea to the structural designer fellows for the ease of selection of water tank's configuration and height for optimum performance under seismic loading prior to designing in order to work out for a better and optimum design. Improvements: Different conditions has been incorporated as variables for precise and discreet graphs for each zone that is additive to the selection process of the structure.

Seismic Assessment of Unreinforced Masonry Buildings

The first case study used in this work is an existing seven-storey unreinforced masonry building (representing a typical residential building located in the district of L ́Example in Barcelona). The accuracy of the non-linear static procedures was evaluated by comparison with non-linear dynamic analyses for seven ground motion records and different levels of seismic intensity. The results obtained from the analyses showed good performance of the static pushover methods on the analysed building. The second case study used in this work is a two-storey unreinforced masonry building which was tested at ELSA in Ispra, Italy. First a modal response spectrum analysis was carried out. Subsequently, non-linear static analysis was performed using two different computer programmes. The results of the present work were compared with experimental results.

Case study of load-bearing precast wall system subject to low seismic intensity by linear and nonlinear analyses

This paper investigates the behaviour of load-bearing precast wall system (namely the HC Precast System − HCPS) subject to seismicity in Malaysia. Recent tremors felt across the country heeded the call for the need of seismic design guidelines to be implemented. For this study, the design ground acceleration for Malaysia has not been finalized. Throughout the years, several schools of thought that occurred among different researchers pertaining to the value of design ground acceleration, ranging from 0.05g to 0.1g. The implications of the selected values can be great especially in designing new buildings or retrofitting existing ones. Thus, linear analysis using Modal Response Spectrum Analysis (MRSA) and nonlinear pushover analysis of representative HCPS were performed for this study. The finite element (FE) model focused particularly on the nonlinear behaviour of the interface between a precast wall and cast in-situ column. Prior to the modal and pushover analyses, the FE model was validated against quasi-static cyclic test results of identical precast system obtained from literature. Differences between the MRSA and pushover approaches are presented and discussed. Performance levels of the structural system were subjected to three levels of design ground acceleration (0.05, 0.075 and 0.1g) have been included.

Vibration Analysis on the Tripod Sliding Universal Joint of Ships

Vibration is a torsional vibration essentially, which will produce additional stresses in the shaft, and when the stress exceeds the allowable limit total the shaft parts will produce fatigue damage. The vibration analysis on the tripod sliding universal joint of ships is analyzed including modal analysis and response spectrum analysis. The analysis result shows that it need to increase the strength of the shell and the tripod in the future design to enhance the reliability, safety and work life of the tripod sliding universal joint.

Structural analysis of ITER multi-purpose deployer

The Multi-Purpose Deployer (MPD) is a general purpose ITER in-vessel remote handling (RH) system. The main handling equipment, known as the MPD Transporter, consists of a series of linked bodies, which provide anchoring to the vacuum vessel port and an articulated multi-degree of freedom motion to perform various in-vessel maintenance tasks. During the in-vessel operations, the structural integrity of the system should be guaranteed against various operational and seismic loads.This paper presents the structural analysis results of the concept design of the MPD Transporter considering the seismic events. Static structural, modal and frequency response spectrum analyses have been performed to verify the structural integrity of the system, and to provide reaction forces to the interfacing systems such as vacuum vessel and cask. Iterative analyses and design updates are carried out based on the reference design of the system to improve the structural behavior of the system. The frequency responses of the system in various kinematics and payloads are assessed.

Uplift of deck or footings in bridges with distributed mass subjected to transverse earthquake

SummaryThe eigenvalue problem is analytically formulated in symmetric bridges with distributed mass and moment of inertia under transverse earthquake. The piers are elastically supported on the ground. The deck is monolithically connected to one or two piers for all degrees of freedom and restrained or transversely free at the abutments. The characteristic equation, symmetric normal modes, modal participation factors, and participating mass ratios are given analytically. The problem is expressed in terms of few dimensionless parameters: (i) the radius of gyration of the deck mass divided by the pier height; (ii) the ratio of the rotational stiffness of a footing to that of the pier at the base; (iii) the ratio of flexural stiffness of the outer spans to those of the pier; (iv) the ratio of torsional stiffness of side spans to the rotational stiffness of the pier top; (v) for two piers, the side‐to‐central‐span ratio. Modal response spectrum analysis gives the moment at the base of the footings and the torque in the deck at its supports on the abutments as ratios to the values at incipient uplifting from the ground or the bearings. The peak ground acceleration of the motion at the onset of either one of these two types of nonlinearity is depicted as a function of the dimensionless parameters and the fundamental period of an elastic deck supported only at the abutments, or of a rigid deck on piers fixed against rotation at top and bottom. Copyright © 2015 John Wiley & Sons, Ltd.

An alternative approach for computing seismic response with accidental eccentricity

Accidental eccentricity is a non-standard assumption for seismic design of tall buildings. Taking it into consideration requires reanalysis of seismic resistance, which requires either time consuming computation of natural vibration of eccentric structures or finding a static displacement solution by applying an approximated equivalent torsional moment for each eccentric case. This study proposes an alternative modal response spectrum analysis (MRSA) approach to calculate seismic responses with accidental eccentricity. The proposed approach, called the Rayleigh Ritz Projection-MRSA (RRP-MRSA), is developed based on MRSA and two strategies: (a) a RRP method to obtain a fast calculation of approximate modes of eccentric structures; and (b) an approach to assemble mass matrices of eccentric structures. The efficiency of RRP-MRSA is tested via engineering examples and compared with the standard MRSA (ST-MRSA) and one approximate method, i.e., the equivalent torsional moment hybrid MRSA (ETM-MRSA). Numerical results show that RRP-MRSA not only achieves almost the same precision as ST-MRSA, and is much better than ETM-MRSA, but is also more economical. Thus, RRP-MRSA can be in place of current accidental eccentricity computations in seismic design.

Application of conditional mean spectra for evaluation of a building’s seismic response in Eastern Canada

An existing eight-storey reinforced concrete shear wall building located in Montreal is studied to evaluate the impact of applying a conditional mean spectrum (CMS) in lieu of the conventional uniform hazard spectrum (UHS) to the seismic evaluation of such structures. The construction of the CMS is reviewed and adapted to take account of seismic hazard in Montreal. The developed CMS and their envelopes were used to conduct modal response spectrum analyses of the building and the results are compared to those obtained from the NBCC 2005 UHS. Justifications of similarities or differences between CMS- and UHS-based results are illustrated throughout the paper.

Inelastic shears in ductile RC walls of mid-rise wall-frame buildings and comparison to Eurocode 8

Nonlinear response-history analyses (NLRHA) are performed for 16 five- or eight-storey prototype regular reinforced concrete wall-frame (“dual”) buildings designed to Eurocode 8 for ductility class (DC) M (Medium) or H (High), in order to evaluate the higher-mode inelastic magnification of shear forces in the walls. The percentage of the total base shear taken by the walls in the 16 buildings covers evenly a range from 37 to 90 %. The NLRHA results show that there is indeed post-elastic amplification of wall shear forces due to higher modes, but that it is overestimated by the current approach for DC H in Eurocode 8. A recently proposed rational modification of that approach, which suits better modal response spectrum analysis (MRSA), is also evaluated; it is found to be in better overall agreement with NLRHA in an analysis context, but, in general, to underestimate inelastic shears above the ground storey in a design context. The design envelope of wall shears in “dual” buildings prescribed in Eurocode 8 is found to cover such shortfalls; it should be extended to wall systems as well, even in case the current approach in Eurocode 8 is modified per the recent, more rational proposals. The current design envelope of wall moments in Eurocode 8 does not safeguard against plastic hinging at upper levels; even if the linear design envelope is anchored to the moment resistance of the base section, instead of the moment from elastic analysis with the design (i.e., reduced) spectrum, it does not preclude flexural plastic hinging in upper storeys. Although for the design of walls safe-sided envelopes and approximations may be appropriate, for the purposes of evaluation of seismic performance and vulnerability of walls, NLRHA seems to be the only means to estimate with certain confidence the post-elastic higher mode effects on wall shears.

Seismic risk assessment of a 50 m high masonry chimney using advanced analysis techniques

The analysis of a brickwork chimney damaged by the 2012 Emilia earthquake is presented. A survey campaign revealed evident diagonal cracks and a significant mortar deterioration in the upper part of the structure. Laboratory tests were carried out to estimate the masonry properties. Lateral force method and pushover analyses using traditional force profiles were shown to be unable to capture the seismic behavior of the chimney. In contrast, the modal pushover analysis (MPA) using force distributions based on six modes of vibration led to crack patterns consistent with the observed damages. The behavior factor to be used in modal response spectrum analyses, estimated from the MPA results, was shown to be slightly higher than unity, indicating a very low dissipative capacity of the structure. Finally, a number of nonlinear response history analyses were carried out using natural accelerograms. In particular, an accurate finite-element model was built using rigid triangular elements connected by means of nonlinear interfaces that incorporate suitable tension, compression, and shear constitutive laws. The results systematically emphasized a shear failure mechanism of the upper part of the chimney. The residual deformations obtained from the analyses were close to those measured after the earthquake.

Comparison of nonlinear static methods for the assessment of asymmetric buildings

Traditional nonlinear static methods, e.g. the original version of the N2 method implemented in Eurocode 8, are not always effective in the assessment of asymmetric structures because of the errors committed in the evaluation of the torsional response. To overcome this shortcoming, two methods have recently been suggested by Kreslin and Fajfar (Bull Earthquake Eng 10(2):695–715, 2012) and Bosco et al. (Earthq Eng Struct Dyn 41:1751–1773, 2012). In particular, the method proposed by Kreslin and Fajfar adjusts the results of the nonlinear static analysis by means of those of a standard modal response spectrum analysis. In the method proposed by Bosco et al., the researchers suggested the use of two nonlinear static analyses characterized by lateral forces applied to different points of the deck. In this paper, the two improved nonlinear static methods and the original N2 method are applied to predict the maximum dynamic response of single- and multi-storey systems subjected to artificial and recorded accelerograms. The results highlight that the improved nonlinear static methods provide estimates which are more accurate than those of the original N2 method. Further, the comparison of the results identifies the range of the structural properties within which the original N2 method is still reliable and the range within which one of the two improved methods should be preferred.

Seismic Performance of Conventional Girder Bridges in Moderate Seismic Regions

AbstractThe majority of continuous girder bridges in regions of moderate seismicity were designed before the introduction of modern seismic codes that prescribe seismic design verification for such structures. The objective of this study is to investigate the seismic performance of typical Hungarian continuous girder bridges through a parametric study. A design space is described by a set of eight parameters. More than 10,000 bridge archetypes are designed without any seismic verification to mimic the design of conventional bridges. The seismic performance of each archetype is then evaluated with modal response spectrum analysis of a detailed finite-element model. The results highlight the vulnerability of piers and bearings and imply that the superstructures are not expected to fail under moderate ground motion intensities. Long bridges with short piers and large spans show the worst performance, especially if the number of fixed bearings in the longitudinal direction is small. This indicates the large i...

Effect of higher modes on the seismic response and design of moment-resisting RC frame structures

Recently, extensive research has been conducted regarding higher-mode effects on the response of multi degree-of-freedom (MDOF) systems. The research has been focused mainly on structures with a lateral force resisting system consisting of slender walls, since these types of buildings are expected to be mostly affected by higher-mode phenomena according to structural dynamics, and simplified expressions have been proposed for slender-wall structures to account for higher-mode response in estimating shear forces. Current seismic design practice assumes the same reduction factor for all modes, even though there is strong evidence that inelasticity affects higher modes of vibration unequally. Additionally, simplified design methods are based only on the fundamental mode of vibration neglecting the effect of higher modes or considering them as elastic. In this paper, higher-mode contributions on the overall response of a nine-storey moment resisting frame (MRF), for which a domination of the first mode is expected, are investigated. The accuracy of a modified Modal Response Spectrum Analysis (mMRSA) method and other available methods is evaluated by comparing the results with the ones of the nonlinear response history analysis. Modal behaviour (reduction) factors are directly calculated for the first three modes and the validity of common assumptions is examined. The assessment of the methods is not restricted to deformations, but is extended to storey inertial forces and shears as well, which have attracted less interest from structural engineers, even though they are considered responsible for numerous structural and non-structural failures during major recent earthquakes and are critical for the design of several structures, such as precast buildings. The results suggest that the storey inertial forces and accelerations at all storeys and shear forces at higher storeys are significantly underestimated by methods neglecting or non-properly accounting for higher modes, even for first-mode dominated structures. The contribution of higher modes depends on the ground motion characteristics, the overstrength associated with each mode and the response quantity examined.

Seismic performance evaluation of an airport traffic control tower through linear and nonlinear analysis

Due to a lack of adequate information about seismic design and the performance of airport traffic control (ATC) towers, structural engineers often rely on building codes. However, seismic performance and the demands of ATC towers differ significantly from common structures. In this paper, the seismic performance of Kuala Lumpur International Airport traffic control tower, with a height of 120 m, was investigated. The results showed that in comparison to modal response spectrum analysis, equivalent static analysis overestimated overturning moments, drifts, maximum displacement and demand/capacity ratio. In addition, linear analysis underestimates base shear, drifts and overturning moments in comparison to the results of nonlinear time history and pushover analysis.

Study on Influence of Infilled Wall of RC Frame Structures

Based on the simulation of a eight-storey reinforced concrete(RC) frame, study has been carried out considering the rigid effect of infilled wall to explore the effect of masonry infilled on the framework by the difference of its quantity . MIDAS structural analysis software is used to make modal analysis and response spectrum analysis for the finite element models. In current chinese specification, infilled wall is often considered as nonstructual components in the buildings regardless load-supporting and shear-resistant action while the impact of rigid effect of infilled wall is not properly considered simply with the method of the reduction of structures’ vibration period. In this paper, a comparison to the current code was also made to get a better understanding of the difference between these two approaches.

Extension of N2 method to plan irregular buildings considering accidental eccentricity

The paper deals with the topic of analyses performed according to modern code provisions, in particular Eurocode 8 (EC8) rules. Non linear static and non linear dynamic analyses of a plan irregular multi-storey r/c frame building designed according to Eurocode 2 (EC2) and EC8 provisions are carried out.The extension of the N2 method to torsionally flexible structures, as applied in previous papers, does not consider the accidental eccentricity, which is prescribed by EC8 also in the case of non linear static analysis. In this paper, three methods combining the accidental eccentricity prescribed by EC8 to the procedure which extends the N2 method to torsionally flexible structures are proposed and discussed. Each of them provides four modal response spectrum analyses (one for each model, corresponding to each position of centre of mass) and eight non linear static analyses (two signs for four models). NLSA(meth. n.2) seems to be the more reliable method of the three proposed, because it better fits absolute displacements obtained by non linear dynamic analysis.In the paper it is also observed that the value of the behaviour factor assigned by EC8 to torsionally flexible systems seems too conservative.

Dynamic behavior of a building structure tested with base and mid-story isolation systems

The discrepancies of dynamic behavior in base-isolated and mid-story isolated buildings are investigated experimentally in this study. In a mid-story isolated building, the isolation system is incorporated into the mid-story rather than the base of the building. The shaking table test results disclose that with the same design of the isolated superstructure and isolation system, a mid-story isolated building has smaller fundamental modal quantities than a base-isolated building. Besides, the seismic response at the superstructure is mainly attributed to the fundamental mode response, while the higher mode responses contribute significantly to the seismic responses at the substructure below the isolation system. Therefore, the modal response spectrum analysis appropriately considering the contribution of higher modes, rather than the equivalent lateral force procedure only considering the fundamental mode, is suggested for the preliminary design of mid-story isolated buildings prior to performing nonlinear responses history analyses.

Seismic Design and Construction Practices for RC Structural Wall Buildings

Reinforced concrete buildings utilizing structural walls for lateral load resistance are the predominant form of construction in Chile for buildings over four stories. Typical buildings include a large number of walls, with ratios of wall cross-sectional area to floor plan area of roughly 3% in each principal direction. Based on the good performance of RC buildings in the March 1985 earthquake, requirements for closely spaced transverse reinforcement at wall boundaries were excluded when Chile adopted a new concrete code in 1996 based on ACI 318-95. In recent years, use of three-dimensional linear models along with modal response spectrum analysis has become common. Since 1985, nearly 10,000 new buildings have been permitted. Although the newer buildings have similar wall area to floor plan areas as older buildings, newer walls are thinner and buildings are taller, leading to significantly higher wall axial load ratios.

Response of tall cantilever wall buildings to strong pulse type seismic excitation

SUMMARYThis paper investigates the seismic response of tall cantilever wall buildings subjected to pulse type ground motion, with special focus on the relation between the characteristics of ground motion and the higher‐modes of response. Buildings 10, 20, and 40 stories high were designed such that inelastic deformation was concentrated at a single flexural plastic hinge at their base. Using nonlinear response history analysis, the buildings were subjected to near‐fault seismic ground motions and simple closed‐form pulses, which represented distinct pulses within the ground motions. Euler–Bernoulli beam models with lumped mass and lumped plasticity were used to model the buildings. The response of the buildings to the closed‐form pulses fairly matched that of the near‐fault records. Subsequently, a parametric study was conducted for the buildings subjected to three types of closed‐form pulses with a broad range of periods and amplitudes. The results of the parametric study demonstrate the importance of the ratio of the fundamental period of the structure to the period of the pulse to the excitation of higher modes. The study shows that if the modal response spectrum analysis approach is used — considering the first four modes with a uniform yield reduction factor for all modes, and with the square root of sum of squares modal combination rule — it significantly underestimates bending moment and shear force responses. A response spectrum analysis method that uses different yield reduction factors for the first and the higher modes is presented. Copyright © 2011 John Wiley & Sons, Ltd.