Seismic Design Of Such Structures Research Articles

A numerical approach for coupled analysis of the seismic response of a cable-moored submerged floating tunnel

A submerged floating tunnel (SFT) is propounded as an efficacious alternative to conventional bridges and underground/submerged tunnels for crossing deep waterways. SFT designers must ensure safe margins and develop approaches to prevail a wide range of plausible situations related to transport, wave, natural vibrations etc. to evaluate the structural stability. To date, only limited researches on this field have been performed to illustrate the significance of seaquake analyses and their effects have been underlined. The present paper intends at numerically simulating a two-dimensional (2D) fluid-structure interaction (FSI) problem in order to scrutinize the dynamic response of an SFT system under bidirectional earthquake actions. Hydrodynamic Pressure due to seismic base excitation is considered as independent nodal variables to represent the gravity influenced inviscid, compressible and irrotational fluid flow effects and the tunnel shell is considered as flexible. This work exposes the importance of the input seismic excitation characteristics that governs the distribution of the induced internal acceleration/force around the lining of the tunnel. Numerical results indicate that the increment rate of the internal acceleration in high SFT caused by vertical ground motion is nearly by 200% when compared to the low-laying tunnel. It is confirmed that long-period record may amplify the overall response of the SFT (up to 80%) when the tunnel approaches the ocean surface, as well as the mooring tensile force to a lesser extent. Finally the proposed coupled numerical procedure suggests that earthquake response spectrum in various intensity levels has an influential role in the response of long-span SFTs and special attention should be paid to the seismic design of such structures.

Upgrading the seismic performance of underground structures by introducing lead-filled steel tube dampers

Central-column failure can cause large underground structures to collapse during strong earthquakes. The use of lead-filled steel-tube dampers (LFSTDs) in the seismic design of such structures is proposed to mitigate or prevent such an eventuality. Three-dimensional nonlinear dynamic analyses of the Daikai subway station with and without LFSTDs under the action of the Hyogoken–Nambu earthquake has been performed, considering soil-structure interaction. The feasibility of the proposed method was verified from four aspects—force, deformation, damage, and energy dissipation. The effects of variability in seismic inputs, strength ratio, and arrangement mode of dampers on the structural dynamic response characteristics have been discussed. Results reveal that the application of LFSTDs to large underground structures remarkably reduces the force, deformation, and damage associated with the central column under seismic loading. Additionally, a strength ratio of 0.4 is recommended when using LFSTDs, whereas in cases without LFTSTDs, the strength of the central column must be appropriately enhanced.

A computational platform for considering the effects of aerodynamic and seismic load combination for utility scale horizontal axis wind turbines

The wide deployment of wind turbines in locations with high seismic hazard has led engineers to take into account a more comprehensive seismic design of such structures. Turbine specific guidelines usually use simplified methods and consider many assumptions to combine seismic demand with the other operational loads effecting the design of these structures. As the turbines increase in size and capacity, the interaction between seismic loads and aerodynamic loads becomes even more important. In response to the need for a computational tool that can perform coupled simulations of wind and seismic loads, a seismic module is developed for the FAST code and described in this research. This platform allows engineers working in this industry to directly consider interaction between seismic and other environmental loads for turbines. This paper details the practical application and theory of this platform and provides examples for the use of different capabilities. The platform is then used to show the suitable earthquake and operational load combination with the implicit consideration of aerodynamic damping by estimating appropriate load factors.

Parametric study on equivalent damping ratio of different composite structural building systems

Structures consisting of concrete and steel parts, which are irregular in damping ratios are investigated. This investigation is a code-based seismic design of such structures. Several practical difficulties encountered, due to inherent differences in the nature of dynamic response of each part, and the different damping ratios of the two parts. These structures are irregular in damping ratios and have complex modes of vibration so that their analysis cannot be handled with the readily available commercial software. Therefore, this work aims to provide simple yet sufficiently accurate constant values of equivalent damping ratios applied to the whole structure for handling the damping irregularity of such structures. The results show that the equivalent damping ratio changes with the height of the building and the kind of the structural system, but it is constant for all accelerations values. Thus, available software SAP2000 applied for seismic analysis, design and the provisions of existing seismic codes. Finally, evaluation of different kinds of structural system used in this research to find the most energy dissipating one found by finding the best value of quality coefficient.

Seismic response of Cfs strap-braced stud walls: Theoretical study

The use of cold-formed steel (CFS) profiles in low-rise residential buildings has increased in European construction sector. The reason of this interest is related to potentialities offered by this constructive system, which are the high structural performance, lightness, short construction time, durability and eco-efficiency. Nevertheless, the current structural codes, such as Eurocodes, do not provide enough information about the seismic design of this structural typology. In an effort to investigate the seismic response of CFS structures, a theoretical and experimental research has been carried out at University of Naples Federico II, with the main aim to support the spreading of these systems in seismic areas. This study focuses on an “all-steel design” solution in which strap-braced stud walls are the main lateral resisting system. In the present paper the outcomes of theoretical phase are shown with the aim of defining the criteria for the seismic design of such structures. In particular, a critical analysis of the requirements for CFS systems provided by the American code AISI S213 has been carried out by comparing it with those given by Eurocodes for traditional braced steel frames.

Parametric study on equivalent damping ratio of different composite structural building systems

Structures consisting of concrete and steel parts, which are irregular in damping ratios are investigated. This investigation is a code-based seismic design of such structures. Several practical difficulties encountered, due to inherent differences in the nature of dynamic response of each part, and the different damping ratios of the two parts. These structures are irregular in damping ratios and have complex modes of vibration so that their analysis cannot be handled with the readily available commercial software. Therefore, this work aims to provide simple yet sufficiently accurate constant values of equivalent damping ratios applied to the whole structure for handling the damping irregularity of such structures. The results show that the equivalent damping ratio changes with the height of the building and the kind of the structural system, but it is constant for all accelerations values. Thus, available software SAP2000 applied for seismic analysis, design and the provisions of existing seismic codes. Finally, evaluation of different kinds of structural system used in this research to find the most energy dissipating one found by finding the best value of quality coefficient.

Seismic Analysis of a Masonry Structure Retrofitting

According to the current seismic code, we model one project in PKPM, analysis the seismic resistance of the masonry structure with rigidity and flexibility floor, and study the earthquake shear and seismic capacity compared before and after such structural load changes and retrofitting. And the analysis conclusion can provide the reference of seismic design of such structures.

The Analysis of Cantilever on Catastrophe to Irregular High-Rise Structure in Earthquake

Anomalistic architecture especially overhanging structure has become a trend of architectural development, Based on the characteristics of a large vertical eccentric, more prominent facade and strong reverse effect,overhanging structure is often serious super-norm and extremely detrimental to the seismic design[1], Now it has become an important part of seismic review. By the analysis and comparison on the coupling of the translational and torsional seismic response from ANSYS program[2]. The behavior of seismic catastrophe of cantilever building structure is studied under bi-directional earthquake action and the change law of cantilever member with the length is obtained, the suggestions on engineering design are put forward for future seismic design of such structures.

Optimum Design of Gravity Retaining Walls Using Charged System Search Algorithm

This study focuses on the optimum design retaining walls, as one of the familiar types of the retaining walls which may be constructed of stone masonry, unreinforced concrete, or reinforced concrete. The material cost is one of the major factors in the construction of gravity retaining walls therefore, minimizing the weight or volume of these systems can reduce the cost. To obtain an optimal seismic design of such structures, this paper proposes a method based on a novel meta‐heuristic algorithm. The algorithm is inspired by the Coulomb′s and Gauss’s laws of electrostatics in physics, and it is called charged system search (CSS). In order to evaluate the efficiency of this algorithm, an example is utilized. Comparing the results of the retaining wall designs obtained by the other methods illustrates a good performance of the CSS. In this paper, we used the Mononobe‐Okabe method which is one of the pseudostatic approaches to determine the dynamic earth pressure.

Seismic design of special moment‐resisting steel frame with prevention of soft‐storey mechanism failure

SUMMARYMost structures with masonry infills that are continuous along their height, which are interrupted in the lowest storey, are damaged by earthquakes. These structures are anticipated to collapse due to the undesirable soft‐storey mechanism formed by lateral stiffness of masonry infills in other storeys. The seismic design criteria of UBC97 code for special moment‐resisting steel frame (SMRSF) are reviewed. In this paper, a new criterion for seismic design of such structures is presented. The proposed criteria are used to design three SMRSFs: 5, 8 and 15 storeys. Nonlinear time‐history dynamic analyses are applied for the designed SMRSFs based on the proposed criteria. Displacements and storey drifts, which are obtained by the proposed method, are compared with nonlinear time‐history dynamic analysis results, finally. Copyright © 2011 John Wiley & Sons, Ltd.

Global seismic damage assessment of high-rise hybrid structures

Nowadays, many engineers believe that hybrid structures with reinforced concrete central core walls and perimeter steel frames offer an economical method to develop the strength and stiffness required for seismic design. As a result, a variety of such structures have recently been applied in actual construction. However, the performance-based seismic design of such structures has not been investigated systematically. In the performance-based seismic design, quantifying the seismic damage of complete structures by damage indices is one of the fundamental issues. Four damage states and the final softening index at each state for high-rise hybrid structures are suggested firstly in this paper. Based on nonlinear dynamic analysis, the relation of the maximum inter-story drift, the main structural characteristics, and the final softening index is obtained. At the same time, the relation between the maximum inter-story drift and the maximum roof displacement over the height is also acquired. A double-variable index accounting for maximum deformation and cumulative energy is put forward based on the pushover analysis. Finally, a case study is conducted on a high-rise hybrid structure model tested on shaking table before to verify the suggested quantities of damage indices.

Equivalent modal damping ratios for concrete/steel mixed structures

The present work deals with the dynamic response of elastic multi-degree of freedom structures that are irregular in height, consisting of two parts, a lower part made of concrete and an upper part, made of steel. Irregularity is due to different dynamic response characteristics of the two parts, here expressed by their different damping ratios. The two different damping ratios make the seismic design of such structures a troublesome procedure since current codes do not provide analysis solutions for such structural systems. This work aims at concluding at a simple yet efficient method in order to evaluate the equivalent modal damping ratios of such structures.

Decoupling Criteria for Inelastic Irregular Primary/Secondary Structural Systems Subject to Seismic Excitation

The present work deals with the dynamic response of structures that are irregular in height, consisting of two parts, a lower part made of concrete and an upper part made of steel. Irregularity is due to different dynamic responses of the two parts, here expressed by their different damping ratios and inelastic material laws. The seismic design of such structures is not satisfactorily covered by current design codes, especially if a decoupled procedure is chosen for the analysis, where the lower part is excited first and its response is used as excitation for the upper part. The present paper aims at contributing toward better understanding of the interaction between the two parts and at proposing improved decoupling criteria for the seismic analysis of inelastic primary-secondary systems. Toward that goal, each part is modeled as a one-degree-of-freedom system, and the maximum responses of coupled and decoupled inelastic time history analyses are compared over a wide range of dynamic characteristics and strength levels of the two parts. The results are presented in the form of error levels between the two alternative analysis procedures.

Seismic design for steel trussed arch to multi-support excitations

The behavior of steel trussed arch to multi-support excitations is studied. The spatial variation of ground motion is modeled by an empirical coherency loss function. Numerical results indicate that horizontal multi-support excitations have a quite large amplification effect on the seismic responses of the trussed arch. This amplification effect cannot be ignored in the seismic design of such structures. Vertical multi-support excitations reduce the seismic responses of the trussed arch. Therefore the assumption that vertical free-field ground motions are spatially uniform is available to assure the degree of seismic safety reliability of the trussed arch. An average response spectrum method is subsequently introduced to calculate the arch response to multi-support excitations. The advantage of the method is that the linear peak seismic response of the arch to multi-support excitations can be obtained as conveniently as the conventional response spectrum method does. The good agreement of results between the time-history method and the average response spectrum method shows the validity of the latter method.

Earthquake ductility and overstrength in residential structures

This paper reviews aspects of current design procedures for seismic design of structures, and specifically examines their relevance to the design of light framed residential buildings under earthquake loading. The significance of the various structural contributions made by the components of cold formed steel framed residential structures subjected to earthquake induced loadings has been investigated. This is a common form of residential construction worldwide. Particular attention is given to aspects related to ductility and overstrength, the latter arising principally from the contributions of the designated "non-structural" components. Based on both analytical and experimental data obtained from research investigations on steel framed residential structures, typical ranges of the ductility reduction factor and overstrength ratios are determined. It is concluded that the latter parameter has a very significant influence on the seismic design of such structures. Although the numerical ranges for the inelastic seismic parameters given in this paper were obtained for Australian houses, the concepts and the highlighted aspects of seismic design methodology are more widely applicable.

Stability of elevated liquid-filled conical tanks under seismic loading, Part I—theory

Conical steel shells are widely used as water containments for elevated tanks. However, the current codes for design of water structures do not specify any procedure for handling the seismic design of such structures. In this paper, a numerical model is developed for studying the stability of liquid-filled conical tanks subjected to seismic loading. The model involves a previously formulated consistent shell element with geometric and material non-linearities included. A boundary element formulation is derived to obtain the hydrodynamic pressure resulting from both the horizontal and the vertical components of seismic motion acting on a conical tank which is prevented from rocking. The boundary element formulation leads to a fluid added-mass matrix which is incorporated with the shell element formulation to perform non-linear dynamic stability analysis of such tanks subjected to both horizontal and vertical components of ground motion. Although, the formulation was developed for conical vessels, it is general and can be easily modified to study the stability of any liquid-filled shell of revolution subjected to seismic loading. The accuracy of fluid added-mass formulation was verified by performing the free vibration analysis of liquid-filled cylindrical tanks and comparing the results to those available in the literature. © 1997 John Wiley & Sons, Ltd.

Development of seismic design criteria for category I cofferdams

Gravity-type cellular cofferdams are widely used as waterfront retaining structures. Static design of these structures is generally performed by considering several modes of static failure. The experience gained from post-construction observation of cofferdam behavior has greatly enhanced the postulation of admissible failure mechanisms that should be considered in design. In nuclear power plant operation, assuring the safety and stability of waterfront embankments is important in providing an undisturbed supply of cooling water under all seismic and flood conditions. In moderate to highly seismic areas, the protection of the waterfront with an economic class I embankment may be quite difficult or impractical as the area required to develop the relatively flat slope construction that is required for seismic stability is often unavailable. Therefore, more attention should be directed toward the design and construction of cellular cofferdams as waterfront earth retaining structures. However, in the absence of data on dynamic behavior of cofferdams under seismic conditions, the methods for design and construction of structures which meet the current regulatory requirements are not well documented. Because static methods of cofferdam design have become somewhat standardized and have been verified through observations of performance, a promising approach to the seismic design of such structures is centered about the development of consistent pseudo-static failure mechanisms. This paper illustrates such extensions of the static design techniques, and compares the factors of safety obtained from static and pseudo-static (seismic) analyses. Certain design criteria, which have been modified to account for dynamic action, are explained. Local soil, rock and hydrostatic conditions, liquefaction and hydrodynamic forces are considered. Design/analysis parameters are suggested for evaluating extreme condition seismic loading, i.e., the Safe Shutdown Earthquake (SSE). Included among the parameters are; active and passive dynamic earth pressure coefficients; location of groundwater and free water surfaces to be used in conjunction with the SSE; the coefficient of friction acting at the interface between the fill material within the cell and the material on which the cell is founded; dynamic pressure distributions due to groundwater and free-standing water adjacent to the structure; vertical and horizontal coefficients of seismic acceleration. In addition, the consequences of postulated liquefaction of adjacent materials are investigated, and measures are suggested to adjust the analysis to accommodate such an occurrence. Among the postulated failure conditions which are considered under seismic loading are the following: • sliding, • overturning, • slippage between the sheeting and the cell fill, • shear failure along the centerline of the cell, • Cummings method of horizontal shear, and • interlock strength. The method of analysis admits various assumptions that are based on the static failure modes of the analytical models; for example, the postulated sliding failure condition assumes an inflexible rigid body type of behavior while the Cummings method of horizontal shear considers the structure to be flexible and the soil to be capable of developing failure planes. By extending these postulated failure modes for the dynamic analysis, the same modeling assumptions are admitted for the pseudo-static case. The methodology proposed is suggested as a means of conservatively performing design checks, using simplified procedures, and not as a replacement for a dynamic, state-of-stress response analysis.