Horizontal Seismic Excitation Research Articles

Study on Hybrid Control Method of Mega-Sub Controlled Structure Subjected to Seismic Action

A new structural configuration that named Mega-sub controlled structure (MSCS) is presented in the process of tall buildings, super tall buildings and super tall tower construction. To further improve the structural control effectiveness of MSCS, new hybrid control method which employs active control and adjusts the stiffness of substructure is proposed. At the same time, the control law and dynamic equation are presented that assembling parameter matrixes for the MSCS subjected to horizontal seismic excitation. Then, the influence of adjusting structure parameter and active control parameter on control effectiveness, dynamic characteristic and control force of the MSCS under hybrid control is discussed. Results indicate that, the new hybrid control method proposed in the paper has the ability to develop a high level of response control effectiveness when subjected to seismic action, and a much better control effectiveness will be obtained after parameters optimization.

The effects of long term uniform corrosion on the buckling of ground based steel tanks under seismic loading

Material degradation due to corrosion significantly alters the seismic response of ground-based cylindrical steel storage tanks. A numerical study is conducted to investigate the effects of internal shell corrosion on the dynamic buckling of three cone roof ground-based, steel cylindrical tanks with height to diameter ratios (H/D) of 0.40, 0.63 and 0.95, subjected to horizontal seismic base excitations. Internal corrosion is considered as a time dependent uniform thinning of the wall at the upper and the lower parts of the tank being in contact with, respectively, atmospheric oxygen and acid gases and residual water. Detailed numerical models of the tank–liquid systems at different stages of corrosion degradation are subjected to two representing accelerograms and for each model the critical peak ground acceleration (PGA) for dynamic buckling of the shell and its associated mode of failure are evaluated. It is found that in all three tanks, the critical PGA is markedly reduced with thinning of the shell, irrespective of the type of ground input. The buckling mode of failure of the tanks also changed from an elastic diamond-shaped failure at the top of the shell to an elasto-plastic elephant foot type failure near the base, after 10 years for the shorter tanks (H/D=0.4 and 0.63) and after 15 years for the tallest tank. The effects of uniform corrosion degradation on the critical buckling load of the tanks were found to be such that after 20 years of thinning due to corrosion, the static loading alone was responsible for the elephant foot buckling of the shell.

Application of 3d Time Domain Method for Seismic Soil-Structure Interaction Analysis of Spatial Grid Structure

This paper proposes a direct three-dimensional (3D) numerical method in time domain for seismic soil-structure interaction (SSI) analysis of spatial grid structure. First, a finite element model including soil, foundation and typical spatial grid structure is developed. Then, the precisions of equivalent viscous-spring artificial boundary element (VSABE) and size effect of site soil region are discussed. Finally, under different site types, time history analyses for models with or without considering SSI effect are implemented respectively under horizontal seismic excitation. The results show that VSABE has the same precision as infinite element boundary and plane size of truncated soil region can be five times of structure plane size for SSI analysis of spatial grid structure. Moreover, except for hard site, it is shown that horizontal acceleration and displacement of spatial grid roof increases substantially when SSI effect is considered. Therefore, it is suggested that SSI influence should be taken into account in engineering design of spatial grid structure.

Theoretical Research on Base Sliding Collapse Performance of Chinese Ancient Timber Buildings

In order to study the collapse behaviors due to base sliding of Chinese ancient timber buildings, a simplified model was constructed. The motion equation of the model subjected to horizontal seismic excitation was established, and the maximum relative sliding displacement was derived on a twice filtered Gaussian white noise with mean zero. A formula was given to judge the collapse of base sliding. By comparison of the diameter of column in Song and Qing dynasty with the critical displacement, it is drawn that the maximum slippage can not surpass the radius of the plinth’s top face even when the input excitation reaches 1000gal. The result shows the base-sliding-induced collapse never occurs even when buildings are subjected to super earthquakes.

Dynamic Stability of Large-Span Suspen-Domessubjected to Seismic Excitations

Dynamic stability of suspen-domes is analyzed in the paper. Theoretical investigation is conducted based on the Lypumov dynamic stability theory. Based on B-R criterion, an improved method to evaluate the dynamic stability of suspen-domes is proposed. According to the method and time-history response curves, the dynamic stability of the suspen-domes is evaluated under horizontal seismic excitations. The dynamic stability characteristics, stability mode and cable mechanical behavior of the suspen-domes with different rise-span ratios are analyzed. The results show that the effect of the rise-span ratios on the dynamic stability is different. When the exciting acceleration approaches the critical point, some cables may relax, but they may be tensed again.

Study on the Effect of Uplift-Restraint on the Seismic Response of Base-Isolated Structures

Under certain conditions isolation bearings can sustain undesirable tensile forces or uplift, the occurrence of which potentially entail detrimental effects on the isolation-system and the superstructure. This study reports on the effect of uplift-restraint, provided by the XY-friction-pendulum (FP) sliding isolation-system, on the seismic response of base-isolated structures. Belonging to the new generation of isolation hardware, the uplift-restraining FP isolator (XY-FP) is capable of providing uplift-restraint to the superstructure by virtue of its inherent property of developing tension. To better understand the phenomena of uplift or tension of isolators and their impact on the performance of structural and isolation-systems, nonlinear response-history analysis of a seismically-isolated real building subjected to bidirectional horizontal seismic excitation is conducted. The analysis was performed with an enhanced version of program 3D-BASIS-ME, which was modified to include an element representative of the mechanical behavior of the tension-capable XY-FP isolator. The results demonstrate that tension in individual XY-FP isolators, and by extension the increase of isolation-system friction force, did not have any appreciable effect on either the total isolation-system response or the superstructure response.

Seismic performance of prestressed concrete stand structure supporting retractable steel roof

The seismic behavior of a structural system composed of pre-stressed concrete stand supporting a retractable steel roof was studied, which is typically based on the prototype of engineering project of Shanghai Qizhong Tennis Center. By elasto-plastic finite element analysis and shaking table test, the following were investigated: the effects of roof configurations in opening and closing, the effect of pre-stress on the structural seismic response, and the failure mechanism of the spatial stand frame systems featured with circularly arranged columns and inverse-cone type stands. It was found that the roof status has great effect on the natural period, vibration modes, and seismic response of the whole structure, the stand response to horizontal seismic excitation is stronger in roof opening configuration than in closing state, and the response mode is dominantly translational rather than rotational, though the stand is characterized by its fundamentally torsional vibration mode. The study indicated that the pre-stressed inverse-cone stands can keep the system from global side-sway collapse under gravity loads, even in the case that most columns loose moment capacity.

Offshore triangular tension leg platform earthquake motion analysis under distinctly high sea waves

TLPs are compliant structures designed to withstand moderate loads without damage and severe loads without seriously endangering the occupants. Dynamic behavior of TLPs under distinctly high sea waves in the presence of both horizontal and vertical seismic excitations is examined and method of analysis is discussed. Seismic forces imposed at tether bottom make tether tension unbalanced when the hull is under offset condition. Tether tension varies nonlinearly under vertical seismic excitations generated using Kanai-Tajimi ground acceleration spectrum. Analytical studies conducted on triangular TLPs show that this tension variation is much higher than the regulation values indicating the necessity for examining them for seismic safety. Clearly, the peaks seen in the response of all active degrees-of-freedom occurring near to the average sum frequencies of waves and input ground motion is a significant influence of seismic excitations on TLP tethers under high sea waves. The numerical results obtained also verify/establish the fact that TLPs built in deeper sea locations show significantly lesser response to the combined wave and earthquake loading.

Response of an open-plane frame to multiple support horizontal seismic excitations with soil–structure interaction

The problem of seismic structural design reduces ultimately to estimating the response of the structure to an assumed forced motion imposed on the ground. For multiple supported structures, in most cases, it is generally sufficient to assume that the arrival time of each component of the base motion is the same for each support point, making the transmission time zero (i.e., uniform or rigid base excitation). The inappropriateness of this assumption has been established for long structures like bridge spans. In the current study, the effect of wave passage on the response of an open-plane frame building structure on isolated column bases has been examined for a few selected horizontal accelerograms. Soil–structure interaction has also been considered. The results indicated that a multiple supported excitation approach yields significantly different peak column shear compared to uniform base excitation. Further, the peak column shear mobilized is affected by soil–structure interaction. The pseudo-static contribution to the peak response was seen to be very significant (>90%) particularly for low wave velocities even though the span was only 6.0 m for the non-interactive structure. When soil–structure interaction was considered, the pseudostatic contribution was found to be (for certain accelerograms depending on the ground displacement record) in excess of 25% for the structure founded on hard soil. These results suggest that is prudent to consider wave passage effects when determining the response to seismic excitations even of open plane frames with short spans.

Non linear seismic response of a low reinforced concrete structure : modeling by multilayered finite shell elements

The main purpose of this paper is the numerical analysis of the non-linear seismic response of a RC building mock-up. The mock-up is subjected to different synthetic horizontal seismic excitations. The numerical approach is based on a 3D-model involving multilayered shell elements. These elements are composed of several single-layer membranes with various eccentricities. Bending effects are included through these eccentricities. Basic equations are first written for a single membrane element with its own eccentricity and then generalised to the multilayered shell element by superposition. The multilayered shell is considered as a classical shell element : all information about non-linear constitutive relations are investigated at the local scale of each layer, whereas balance and kinematics are checked afterwards at global scale. The non-linear dynamic response of the building is computed with Newmark algorithm. The numerical dynamic results (blind simulations) are considered in the linear and non linear cases and compared with experimental results from shaking table tests. Multilayered shell elements are found to be a promising tool for predictive computations of RC structures behaviour under 3D seismic loadings. This study was part of the CAMUS International Benchmark.

Experimental verification of torsional response control of asymmetric buildings using MR dampers

AbstractThis paper proposes a semiactive control system to reduce the coupled lateral and torsional motions in asymmetric buildings subjected to horizontal seismic excitations. Magnetorheological (MR) dampers are applied as semiactive control devices and the control input determination is based on a clipped‐optimal control algorithm which uses absolute acceleration feedback. The performance of this method is studied experimentally using a 2‐story building model with an asymmetric stiffness distribution. An automated system identification methodology is implemented to develop a control‐oriented model which has the natural frequencies observed in the experimental system. The parameters for the MR damper model are identified using experimental data to develop an integrated model of the structure and MR dampers. To demonstrate the performance of this control system on the experimental structure, a shake table is used to reproduce an El Centro 1940 N–S earthquake as well as a random white noise excitation. The responses for the proposed control system are compared to those of passive control cases in which a constant voltage is applied to the MR damper. Copyright © 2003 John Wiley & Sons, Ltd.

Effects of column axial force – bending moment interaction on inelastic seismic response of steel frames

AbstractIt is well known that axial force – bending moment interaction (N–M interaction) affects to a large extent the cyclic inelastic behaviour of structural elements, especially columns in framed structures, with reduction in bending capacity and loss of available ductility. A few studies have also shown that significant inelastic axial shortening affects the response of column elements subjected to medium–high levels of axial loads and cyclic bending.This paper is primarily aimed at evaluating the effects of column N–M interaction on the inelastic seismic response of steel frames. By considering the contemporaneous action of vertical loads, due to gravity, and of horizontal seismic excitation, it is shown that the progressive axial shortening of adjacent columns may differ substantially, thus inducing significant relative settlements at the ends of the connecting beams and, then, remarkable amplifications in beam plastic rotations. An evaluation of additional beam plastic rotations induced by column N–M interaction is carried out for real structures by investigating the inelastic response of steel frames designed according to European standards under horizontal and vertical earthquake excitations. Copyright © 2003 John Wiley & Sons, Ltd.

Hysteretic Modeling of Thin-Walled Circular Steel Columns under Biaxial Bending

To ensure the safety of elevated highway bridges under major earthquakes, it is important to predict the ultimate behavior of columns used as bridge piers. After the Kobe earthquake, many analytical and experimental studies have been conducted to examine the ultimate seismic behavior of thin-walled steel columns. However, these studies are mostly restricted to the in-plane behavior of the columns. As observed in the Kobe earthquake, the damages to the columns are usually influenced by the two-dimensional horizontal seismic excitations. Therefore, it is more desirable to consider the effect of biaxial bending at the ultimate stage of earthquake response in the design of steel columns. Herein, we propose a hysteretic model of thin-walled circular steel columns under biaxial bending to predict the ultimate seismic behavior of cantilever-type thin-walled circular steel columns with constant axial load. The proposed column model consists of a concentrated mass and a rigid column with multiple nonlinear springs located at the column base. As the hysteretic constitutive relation for each spring, we adopt the Dafalias and Popov’s bounding-line model by modifying the original model in order to take into account the local buckling behavior. The material constants of the modified bounding-line model can be determined, based on the in-plane hysteretic behavior of the column obtained either by FEM shell analyses or by experiments. The validity of the proposed model is examined by comparing it with results of the two-dimensional horizontal earthquake-response analyses, using the FEM shell model.

Deterministic Control of Column under Horizontal-Vertical Excitation

A control methodology is presented for a column, modeled as a single-degree-of-freedom system subjected to simultaneous horizontal and vertical support motion. It is assumed that the support motions are uncertain, time varying, and norm bounded, and that the column itself has no uncertainties associated with it. The control signal is based on Lyapunov theory and noise-free state feedback measurements. The states of the resulting closed-loop system (namely displacement and velocity) are uniformly and ultimately bounded within a neighborhood of the zero state. To illustrate the features of the proposed controller, examples of nonhysteretic and hysteretic columns subjected to combined horizontal and vertical nonstationary seismic excitation are considered. Numerical results for the uncontrolled and controlled responses are obtained and analyzed. Several issues involved in the controller design are examined, and results illustrating the control performance and effectiveness are presented and discussed.

Active Vibration Control of Multiple Buildings Connected with Active Control Bridges. (1st Report. Seismic Response Control of Four Model Buildings Arranged in Parallel).

This paper proposes a vibration control method for four high-rise buildings arranged in parallel subjected to horizontal seismic excitation. According to this method, four structures connected by control devices called as active control bridge are controlled actively by controlling each other. This method have a merit to obtain enough control force under the low frequency. By means of this method, it is able to control vibration of the super tall building against the strong wind and a large earthquake. In this paper, the control effect of this method is demonstrated by the vibration control using LQ and suboptimal control theory using earthquake excitation theoretically and experimentally.

Modal Predictive Control of Structures. II: Implementation

This paper is continuation of a companion paper in which a numerical assessment about the efficiency and the robustness of predictive control of structures was performed on single-degree-of-freedom systems. In this paper a formulation for predictive control of multi-degrees-of-freedom systems using a reduced number of sensors and actuators is presented. Control law is formulated, into an independent modal space control approach, for controlling individually some modes and the values of the parameters defining the control algorithm are chosen according to the recommendations derived in the companion paper. The efficiency and the stability of the control action are numerically assessed on a full-size six-story experimental building placed in Tokyo and subject to horizontal unidimensional seismic excitation. Three control cases have been considered using one, two, and three sensors and actuators, respectively. Presented results allow one to conclude that the proposed strategy seems to be able to generate stable and efficient control actions for active aseismic protection of building structures.

Dynamic stability of liquid storage cylindrical tanks subjected to horizontal seismic force excitation

In this study we obtain linear as well as nonlinear analytical solutions for the critical stress that causes dynamic instability in a liquid storage tank following excitation by a seismic horizontal force. It is well-known in the static stability problem that the critical longitudinal load for a cylindrical shell to be unstable in longitudinal compression according to the classic linear theory is thrice the value obtained from experimental results. Satisfactory theoretical results can only be calculated from nonlinear theory, and these results agree well with experimental data. For the dynamic stability problem, only numerical solutions have previously been obtained for nonlinear cases. 1 We will give analytical solutions for the nonlinear dynamic stability problem and compare the result with the analytical result of linear theory.

Parametric Study of Seismic Soil‐Tank Interaction. I: Horizontal Excitation

Dynamic soil‐tank interaction under horizontal seismic excitations has a profound effect on the amplification of hydrodynamic forces and moments exerted on tank structure. Analytical mechanical models for flexible cylindrical tanks, which also account for the effect of rigid‐base rocking motion and lateral translation, are used with a lumped‐parameters idealization of foundation soil. A comprehensive parametric analysis is conducted to study the effects and relative importance of a few factors influencing the seismic response of tank‐liquid‐soil systems. Computer programs are implemented to evaluate the system response to ground earthquake motions. Results are presented in the form of graphs that give engineers a useful tool for understanding the seismic performance of the system and for developing effective design procedures.

A computational tool for evaluation of seismic performance of reinforced concrete buildings

A special-purpose computational tool is developed to evaluate the inelastic seismic response of reinforced concrete buildings. A macromodel approach is used to analyze a discretized building composed of parallel frame-wall systems interconnected by transverse elements. The macro-behavioral models include the essential hysteretic characteristics of reinforced concrete sections and also account for the effects of distributed plasticity. All developments are incorporated into a computer code, IDARC. The program performs a series of tasks to enable a complete evaluation of the structural system: (a) monotonic analysis to establish the collapse mechanism and base shear capacity of the structure; (b) quasi-static cyclic analysis under force or deformation control; (c) transient dynamic analysis under horizontal and vertical seismic excitations; (d) reduction of the response quantities to damage indices so that a physical interpretation of the response is possible. The program is built around two graphical interfaces: one for preprocessing of structural and loading data; and the other for visualization of structural damage following the seismic analysis. The program can serve as an invaluable tool in estimating the seismic performance of existing reinforced concrete buildings and for designing new structures within acceptable levels of damage.

Response of a NPP reactor building under seismic action with regard to different soil properties

The object of this investigation is the response of a reactor building on seismic action with systematic variation of the soil stiffness. A thin-walled orthotropic containment shell on varying heavy and rigid foundations is regarded as calculation model. The soil stiffness is simulated by means of spring elements for horizontal translation and for rocking motions of the building. By the response spectra method the loads of the containment shell are calculated for a horizontal seismic excitation. The investigation is aimed at determining the influence of differentiated soil stiffnesses on the containment action effects and at recognizing the causes for the occurring effects. The results are thoroughly represented by selected quantities of the building's response, the effects from the soil-structure interaction are discussed and the causes of the effects clearly explained. A possibility is provided for determining critical soil stiffnesses which cause a significant intensification effect. The results of the investigations show that both the soil stiffness and structural configuration of the reactor building, particularly in case of the substructure being heavy and rigid, exert a decisive influence on the loading of the superstructure.