Seismic Force Distribution Research Articles

Seismic Analysis of Irregular Multistorey Building

Abstract: The seismic analysis of buildings is crucial for ensuring structural safety and resilience against earthquake forces. Irregularities in building configurations pose unique challenges, influencing the distribution of seismic forces throughout the structure. This study focuses on the seismic analysis of a G+12 building characterized by irregularities in plan and elevation using STAAD.Pro software. Here we have taken four models consisting of bare bay frame , bay frame with shear wall on one corner, , bay frame with shear wall on two opposite corners, , bay frame with shear wall on all corners for the further analysis. This research contributes to enhancing understanding and design practices for irregular high-rise buildings, emphasizing the importance of advanced analytical tools in seismic engineering. From this analysis we can conclude that within all four models ,building having shear wall on all four sides shows minimal deflection attributed to its maximum stiffness characteristics, hence considered most stable

Seismic force distribution in members of confined masonry buildings

Seismic design codes for confined masonry (CM) buildings are few; therefore, in many places these buildings are generally designed and constructed using simplified guidelines or handbooks. For brevity, it is assumed that masonry walls resist all possible loads imparted on CM buildings, while the only role of reinforced concrete (RC) confining members, also known as tie-members, is to provide the confinement and stability (both in-plane as well as out-of-plane) to the masonry walls. Though such an assumption simplifies the design process, it results in missing out on significant material strength that the tie-members can potentially add up to the structural strength. On the other extreme, such a simplification can also result in construction of weaker tie-members, especially the tie-columns, because the seismic design forces are generally not distributed to different members of the CM buildings. In the present study, a methodology was developed to distribute the seismic design forces to different members of CM buildings such that the tie-columns can be formally designed to not only provide confinement and stability to the masonry walls, but also provide reserved strength that may be utilized in case of failure of masonry walls. Empirical and numerical approaches were followed in developing the methodology. The approaches utilized all the available empirical methods for lateral strength estimation of CM walls and results reported in large number of past experimental studies, including three tests carried out by the authors. An extensive parametric finite element study was carried out considering the influence of several important parameters, and a methodology was developed for relative distribution of shear forces in tie-columns and masonry walls of CM walls.

Static Equivalent Modeling of Dynamic Seismic Forces for Realizing Earthquake-Resistant Spatial Truss Structures

This study deals with spatial truss structures composed of a double layer spatial truss dome and two truss plate-type wall substructures subjected to horizontal earthquake motion. Comparative investigations of the structures are also carried out by considering the structural eccentricity varying the wall height. The equivalent static seismic force, which is hereinafter referred to as the static seismic force, is calculated by the response spectrum method, and the seismic force distribution and response deformation applied on the structure are analyzed and investigated. The elastic seismic response analysis using static seismic force and the influence of eccentricity on seismic response characteristics is carried out. In addition, a method to calculate the static seismic force of medium and medium-sized large-span double-layer truss dome is also proposed by considering the shape, height, span and support conditions of the structure. The purpose of this study is to investigate the effect of the substructure on the seismic static force because the roof truss structure with curved surface has higher stiffness. In addition, the seismic response characteristics of long-span structures are different from those of multi-story structures, which have the structural characteristics of its vertical response as well as horizontal response to horizontal earthquake motion. Based on the elastic seismic response analysis and the static analysis of the static seismic force calculated by the response spectrum method, the seismic force distribution and deformation characteristics of the analysis model with or without eccentricity are analyzed and discussed. It is seen that the static equivalent modeling with the maximum effective mass ratio can be used to obtain the seismic force distribution in this kind of long-span structure.

STUDY ON THE ISOLATION EFFECT OF SUBWAY COVER STRUCTURES

In order to study the seismic isolation effect of the subway superstructure comprehensively, a simplified two-degree-of-freedom model of the large base with multiple towers was presented, and the influences of mass ratio and period ratio on dynamic characteristics and seismic response of structures were investigated. In addition, a precise model of the subway superstructure was established by ETABS to study the effect of tower height, tower number, isolation floor stiffness, and viscous dampers on the structural dynamic characteristics, seismic isolation coefficient. The analysis results of the simplified two-degree-of-freedom model show that in the general period ratio range, the shear-weight ratio of the tower has almost no change with its mass variation, while the shear-weight ratio of the large base decreases when the tower mass increases. The analysis results of the precise model of the large base with multi-tower show that the seismic inertial force is evenly distributed along the height of the tower, and the building height has little effect on the earthquake action, and the seismic effect of the large base increases slightly as the height of the tower increases. As the number of towers increases, the seismic isolation effect of the tower decreases slightly, the seismic effect of the large base is less than that of non-seismic isolation structures. As the stiffness of the seismic isolation floor increases, the seismic effect of the tower increases and the seismic effect of the large base decreases. After viscous dampers are installed, the distribution of seismic force along the height of the tower changes significantly, the seismic action decreases at the bottom of the tower and the seismic action is significantly amplified at the top. Setting viscous dampers can effectively reduce the seismic action of the large base.

Effects of shear keys and track system on the behavior of simply-supported bridges for high-speed trains subjected to transverse earthquake excitations

China railway track system II (CRTS-II) slab ballastless track is usually constructed on high-speed railway (HSR) bridges to ensure the rail smoothness and the running safety of high-speed trains, but the use of the longitudinal continuous track system would significantly alter the dynamic characteristics of the bridges and therefore influence the bridge seismic responses. The pounding at shear keys has also been identified as one of the critical factors affecting the seismic behavior of bridges. To investigate the effects of shear keys and CRTS-II track system on the seismic behavior of HSR simply-supported bridges subjected to transverse earthquake excitations, detailed 3D finite element models are developed by using ABAQUS. The seismic responses calculated from the bridges with and without considering shear keys are firstly compared. The result shows that the shear keys can effectively limit the development of pier-girder relative displacement and thus decrease the potential of girder dislocation. However, large pounding forces would be generated between the shear keys and bearing pads and transferred to bridge piers, which will amplify the seismic responses of the bridge piers. The result of seismic analyses of multiple-span simply-supported bridges with and without considering the track system shows that the track system will significantly influence the distribution of seismic forces among the bridge spans. For a bridge with equal pier heights, considering the track system will reduce the seismic responses of side spans (close to subgrade) but will increase those of the middle spans. Whereas an opposite trend is found for bridges with high middle piers and short side piers.

TORSION EFFECTS IN BUILDING SEISMIC PERFORMANCE

The paper considers torsion effects that occur during the building response to seismic action. Computation and parametric analysis are conducted for various values of building eccentricity induced by mass and stiffness variation. Such a model accounts for the actual dynamic effect of accidental eccentricity, usually considered in building design by quasi-static value of the torsion moment. Two types of models are employed to explore dynamic parameters of the building. The models are formed using Wolfram Mathematica software in which the mass and stiffness properties are parametrically related to the basic dynamic characteristics of the building. The commercial software package CSI ETABS ver.17 is used for validation of the model. Seismic performance of the building is evaluated, and the results of the parametric analysis are presented using the shear forces and torsion moment. The analysis showed that the nature of eccentricity has a major influence on distribution of seismic forces due to the torsion.

Effect of seismic resistance capacity of moment frames on progressive collapse response of concentrically braced dual systems

In this study, the effect of seismic force resistance capacity of moment-resisting frames on progressive collapse response of dual systems was discussed to find the most appropriate and cost-effective way to distribute seismic forces to moment frames and braced frames of dual systems. In this way, it is possible to make a proper design that simultaneously leads to a robust structure under both progressive collapse loads and seismic loads. Thus, the progressive collapse resistance of concentrically braced dual systems with three different seismic force resistance shares of the steel moment frames, namely 25, 50 and 75% was investigated. Two different bracing types, including X and inverted V braces, were considered in different seismic hazard sites. The nonlinear static alternate path method recommended in the Unified Facilities Criteria guideline is used to assess the progressive collapse performance of model structures. These studies showed that an increase in the seismic force resistance share of moment frames in dual systems resulted in a more robust structure against progressive collapse when the moment frame subjected to column loss. However, this was reduced when a braced column was removed. Using greater seismic force resistance share for moment frames led to an increase in cross-section of structural elements of moment frames, and it led to higher progressive collapse resistance of moment frames. As a result, an increase in the seismic force resistance of the moment-resisting frame up to 50% is recommended as a proper and economic seismic force distribution for dual systems that are prone to progressive collapse in moment frame column loss scenarios.

ОБ ОСОБЕННОСТЯХ МЕТОДОЛОГИИ НЕЛИНЕЙНОГО СТАТИЧЕСКОГО АНАЛИЗА И ЕГО СОГЛАСОВАННОСТИ С БАЗОВОЙ НОРМАТИВНОЙ МЕТОДИКОЙ РАСЧЁТА ЗДАНИЙ И СООРУЖЕНИЙ НА ДЕЙСТВИЕ СЕЙСМИЧЕСКИХ СИЛ

The nonlinear static analysis should be clear for engineers in case of its integration into building design in seismic regions of Russia. Basic assumptions and advantages of the analysis, as well as its coordiantion with the linear spectral calculation method are considered by the author. The examples of structures calculated according to NSA, in particular in SAP2000 software are given. Keywords: earthquake-resistant structures; diagram method of calculation; patterns of seismic force distribution; performance-based plastic design (PBD) method.

Effect of nonlinearity of restrainer and supports on the elasto-plastic seismic response of continuous girder bridge

During an earthquake, the nonlinearity of the bridge structure mainly occurs at the supports, bridge piers and restrainers. When entering nonlinear stage, members of the bridge structure affect the elasto-plastic seismic response of the whole structure to a certain extent; for multi-span continuous bridges, longitudinal restrainers can be installed on the movable piers to optimise the distribution of seismic force and enable the movable piers to bear a certain amount of seismic effect. In order to evaluate the effect of nonlinearity of restrainer and supports on the elasto-plastic seismic response of continuous girder bridge, analytical models of continuous girder bridge structure considering the nonlinearity of movable supports, restrainers and bridge piers were built and the nonlinear time history analysis was conducted to evaluate the effect of nonlinearity of restraining devices and supports on the elasto-plastic seismic response of continuous girder bridge. Relevant structural measures and recommendation were made to reduce the seismic response of the fixed piers of the continuous girder bridge.

Lateral force distribution on base-isolated structures under near-field earthquakes

In the current paper the accuracy of the International Building Code equivalent static method for base-shear distribution is evaluated to determine the response of seismically isolated structures under near-field earthquakes. For this purpose two-, three-, four- and six-storey building models are designed according to the equivalent lateral-response procedure for different elastomeric isolation systems of 2 s, 2·5 s and 3 s for periods of isolated structures and 6%, 8% and 11% for their damping ratio. Different lateral-force resisting systems such as ordinary steel moment frame, ordinary steel concentrically braced frame and ordinary reinforced concrete shear wall are employed as a superstructure and the effects of 13 near-field ground motions on vertical seismic force distribution, and the linear and non-linear properties of isolation systems are investigated. The results of the equivalent static procedure in vertical distribution of base shear are compared with results obtained from dynamic linear and non-linear analysis and the efficiency of their application is studied. Based on linear and non-linear dynamic analysis results of isolated structures, two new formulae are proposed for vertical distribution of base shear for the isolated structures under near field earthquakes. The proposed linear formula is based on the first mode shape of an isolated structure and the non-linear formula follows three first mode shapes which implies contribution of higher modes in more realistic non-linear analyses.

Effect of Seismic Joint in the Performance of Multi-Storeyed L-Shaped Building

The choices of building shapes and structural systems have significant effect on their seismic performance. While symmetrical buildings result in a fairly uniform distribution of seismic forces throughout its components. Unsymmetrical buildings result in highly indeterminate distribution of forces making the analysis and prediction more complicated. L-shaped buildings are among those unsymmetrical structures which are most commonly found in practice in the form of school, office, commercial buildings. In this work three dimensional models of L-shaped buildings are investigated for their seismic performance, varying bay length and storey height. These models were analysed for three conditions viz with gap, with seismic joint and with neither of these. The modeling of structures analysis is carried out using STAAD Pro V8i, also the performance is analysed providing brick infill and compared with, without infill condition. Performances is measured in terms of displacements, axial forces, bending moments, shear forces and compared for those conditions mentioned in the identified column viz., corner, intermediate and interior.

Calculating Method of Active Earth Pressure behind Rigid Retaining Wall Based on Pseudo-Dynamic Theory

By means of pseudo-dynamic theory, a new calculating method is presented to calculate the pseudo-dynamic seismic active earth pressure behind rigid retaining wall. Considering time and phase difference within the backfills, the horizontal slices is used to analyze the distribution of seismic active force behind retaining wall in more realistic manner. Under the assumption that the soil backfills are rigid body, the equations derived in this paper can be degenerated to Mononobe-Okabe equations. Through numerical analysis, it is shown that the values of seismic active force obtained from present study are smaller than those obtained from Mononobe-Okabe theory and the distribution of seismic force along the depth of the wall is nonlinear. It is also found that the action point of the total seismic active earth pressure is higher than one third of the wall height, which is corresponding to previous experimental results.

Seismic Response Analysis of Frame Structure on a Slope

Frame structure on a slope is a common kind of structure in a mountainous area. It can diminish the impact on environment, by avoiding to dug or fill the slope, using an opening platform, supported by beams and columns. Because the frame structure on a slope connects with the ground on different elevation level, it is evidently different from general frame structure in seismic design. Four sets of frame structure example on a slope sample are designed, with three opening floors connected with the ground on different elevation level, and three, six, nine, twelve upper floors correspondingly. The seismic responses characteristics of frames on a slope are studied in the paper from period, lateral deformation, seismic shear and so on, based on the analysis of the characteristics of frame structure on a slope. The main conclusions are as follows: the slope can enhance structural lateral stiffness to a certain extent; the opening floors connected with the ground on different elevation level, are not necessarily frail stories; the distribution of seismic force is uneven between the columns in the same floors which connect with the ground on different elevation level, and fixed columns undertake more than others, making them more fragile; the torsional effect is noticeable in the frame structure on a slope.

Procedure to predict the storey where plastic drift dominates in two‐storey building under strong ground motion

AbstractA procedure is presented to predict the storey where plastic drift dominates in two‐storey buildings under strong ground motion. The procedure utilizes the yield strength and the mass of each storey as well as the peak ground acceleration. The procedure is based on two different assumptions: (1) the seismic force distribution is of inverted triangular form and (2) the rigid‐plastic model represents the system. The first and the second assumptions, respectively, lead to lower and upper estimates of the base shear coefficient under which the drift of the first storey exceeds that of the second storey. The efficiency of the procedure is verified by dynamic response analyses using elasto‐plastic model. Copyright © 2008 John Wiley & Sons, Ltd.

Seismic Design of Lifeline Bridge using Hybrid Seismic Isolation

This paper presents the merits of a hybrid seismic isolation system used for the seismic design of a major bridge. The bridge is analyzed for two different arrangements of seismic isolation systems. The first arrangement consists of friction pendulum bearings at all substructure locations; the other incorporates a hybrid system where laminated elastomeric bearings are used at the abutments and friction pendulum bearings at the piers. Analysis results have demonstrated that the hybrid seismic isolation system provided a structure with a fundamental period long enough to attract smaller seismic forces, while controlling the magnitude of isolation bearings displacements. It also provided a more uniform distribution of seismic forces among substructure elements. As a result, higher seismic forces on the piers were reduced, allowing for a more economical design of substructures. The hybrid seismic isolation system helped to control the wind-induced vibrations and reduced the sizes of the isolation bearings.

Shear and Overturning Moment for Earthquake-resistant Building Design

The provisions of the present Canadian and U.S. seismic codes are examined with respect to their requirements on the distribution of seismic forces and overturning moments throughout the heights of building structures. Assuming the code design base shears to be correct, it is shown that the prescribed distribution of lateral forces may underestimate the shear forces in the upper stories of the building. It is further shown that the contribution of the higher modes is not directly related to the height-to-width ratio of the building, but rather to its fundamental period of vibration. By idealizing the building as an average uniform cantilever deflecting partly in a shear mode and partly in a bending mode and by taking a root-sum-square combination of the modal responses to a standard seismic acceleration spectrum, the envelope of the resultant maximum shears throughout the building height is obtained; the maximum overturning moments throughout the building height are obtained in a similar manner. By comparing these with the cantilever overturning moments computed from the shear envelope referred to above, the moment reduction factors applicable to the various levels of a building are calculated. New empirical relationships are then developed to approximate the shape of the maximum shear and overturning moment envelopes.

7) 建築物の震度分布に就いて

7) 建築物の震度分布に就いて