Action Of Seismic Load Research Articles

Identifying the effect of low-cycle fatigue of reinforced concrete structures on the properties of the reducing coefficient under the action of a seismic type load

The object of consideration is seismic design, and the subject of the study is the determination of the reduction coefficient. One of the important problems of earthquake-resistant design is to determine the effect of low-cycle fatigue of reinforced concrete on the reduction coefficient and determine its optimal value. This problem is not disclosed and is not specifically taken into account in the standards for earthquake engineering when determining the maximum bearing capacity of types of structures due to the lack of study of the issue. To solve the problem, a series of experimental studies were carried out on low-cycle fatigue of reinforced concrete bending elements and frame units. The range of results of the reduction coefficient values and the degree of influence of monocyclic fatigue on the properties of the reduction coefficient are obtained. A feature and characteristic of the results obtained is that the reduction coefficient Rμ depends on the nature of the hysteresis deformation pattern and the plastic life of structural elements estimated by the plasticity coefficient μ, which is significantly influenced by low-cycle fatigue manifested at peak accelerations of strong seismic impacts. The above test algorithm, the feature and characteristics of the results obtained made it possible to solve the problem under study. The results obtained are accepted for practical use in the action of seismic loads: on the calculation of strength taking into account new low-cycle coefficients, reduction coefficients for determining the spectra of design reactions and seismic loads, taking into account energy absorption. New reduction coefficients are proposed for determining the spectra of calculated reactions and seismic loads

INVESTIGATION OF THE DYNAMIC CHARACTERISTICS OF A MULTI-STORY BUILDING WITH A POLYMER CONCRETE FRAME

Formulation of the problem. An urgent problem in construction is the development and introduction of new types of structural materials with improved characteristics: high strength, resistance to aggressive environments, frost resistance, etc. One of these materials is polymer concrete. Polymer concretes can be effectively used in modern construction in the manufacture of monolithic elements of structures, such as wall panels, slabs, columns of frame buildings. The purpose of the work is to study the dynamic characteristics of a multi-story building with a polymer concrete frame under the action of seismic loads. Method. Dynamic calculations were carried out using the finite element method in the LIRA−CAD software complex. Scientific novelty. New analytical formulas have been obtained, which allow an approximate estimation of the dimensions of structural elements of polymer concrete buildings. It was determined how changes in the properties of the frame material affect the weight of the building, the frequency of natural oscillations and displacement under the action of seismic loading. Practical significance. The results of the work make it possible to perform design calculations related to the dynamic properties of multi-story buildings with a polymer concrete frame. Conclusions. The use of polymer concrete for the construction of frames of multi-story buildings allows to reduce the cross-sectional dimensions of structural elements, reduce the weight and material consumption of buildings.

Proposal for improving the solid clay brick contact surface to increase the initial shear strength of masonry

Under normal service conditions, masonry is mainly subjected to the action of gravity loads, however, under the action of seismic loads, masonry is subjected to the combined action of vertical and lateral forces which develops a biaxial stress state and generates considerable shear stresses at the brick/mortar joint interfaces. The work of masonry under the action of shear forces parallel to bed joints is widely studied and leading researchers in the field of masonry structures have studied the behaviour, constitutive models, failure criteria and numerical models of masonry, however there are almost not studies on the influence of the horizontal contact surface of bricks on the initial shear strength of masonry. This work proposes a slight modification of the horizontal contact surface of solid brick to increase the initial shear strength of the masonry. The experimental proposal consists of drilling superficial blind holes with a depth of 6–8 mm with an overall drilled area of 10–13% of the horizontal surface of the brick. The arrangement of the holes is such that main difference with similar proposals is that the central part of the brick remains unaltered. Experimental results show that this proposed modification of the brick increases the initial shear strength by about 45% and allows the development of the plastic deformation phase, which is an important improvement for the structural behaviour of masonry structures under the action of considerable lateral forces.

METHOD OF ASSESSMENT OF STRESSDEFORMED CONDITION OF STRUCTURAL STRUCTURES ON THE BASIS OF SUBSYSTEMS METHOD

he article considers a method for dynamic analysis of the interaction of the system "ground part  base  soil". The analysis of experimental data of the building, after action of seismic loading is used. The technique allows to solve dynamic problems taking into account physical nonlinearity. The problem of solving a dynamic problem in time by the method of subsystems is smoothed out. A practical example of calculating the reinforced concrete frame of a building in Odessa, taking into account the joint work of the foundationpilebuilding.

Performance of column-to-column mechanical connection in precast concrete building under seismic loading

Precast columns in precast concrete structures with floor heights require connections that need confident, reliable, and cost-effective design and implementation methods that can speed up both processes. At the same time, still ensure adequate strength, stiffness, and ductility to the column behavior. Columns specifically have the main role in structures for transmitting vertical and horizontal loads due to seismic effects to the base to fulfill life safety requirements, but the existence of a connection in the column cannot ensure the required. This work aims to study the performance and efficiency of mechanical bolted column connections under the action of seismic loading. In this regard, a column connection used in the precast structure of the new Karbala Provincial Council (KPC) under seismic loading is used as the case study. This building was analyzed and then designed employing special mechanical bolted connections produced by Peikko’s products (Column-shoe & Anchor bolts). The analysis gave the exact forces at the connection location and the design using Peikko’s column connection performed well under all loading cases including the seismic case. The analysis and design lead to smaller column section selection since it takes into account the interaction of applied loads using special equations.

Seismic Response of a Large LNG Storage Tank Based on a Shaking Table Test

In order to study the dynamic response of the LNG storage tank under the action of seismic load and the seismic isolation effect of the lead-core rubber bearing, this paper establishes the experimental storage tank model with reference to the structural form of the large-scale LNG storage tank, and the seismic response of the test tank is obtained using a shaking table test. Simplified mechanical models of non-isolated and isolated storage tanks are proposed and the seismic responses of the corresponding storage tanks are calculated using the Newmark-beta method. Under the action of seismic waves with different acceleration peaks, the results show that (a) more excitation directions of the seismic wave can lead to the greater acceleration and displacement response of the tank and (b) the isolation bearing has a damping effect on the acceleration response of the storage tank, but it has an amplifying effect on the displacement of the storage tank. Comparing the results of the simplified model and the shaking table test, it is found that the change trend of the acceleration response of the experimental results and simplified mechanical models is the same. The spectral characteristic curve of them is not large, which verifies the effectiveness of the simplified model.

Simulation of the stress-strain state of a cylindrical tank under the action of forced oscillations

The paper considers the classification of steel cylindrical tanks failure from the action of seismic loads. Features of static calculation of tanks were revealed. Physical and mechanical properties of the material and geometric parameters of the vertical tank were determined. A full-size finite element model of a filled vertical steel tank has been developed. The calculation of the filled vertical steel tank was performed. The values of frequencies and periods of natural oscillations were obtained. Finite element method that was implemented in LIRA-multifunctional software package allows to design and calculate the structures for various purposes.

Nonlinear soil-pile-structure interaction for midrise STMD buildings

One of the effective vibration control systems used for structures is the semi active tuned mass damper (STMD), which is popular since it is reliable and simple. STMD characteristics in the design for piled foundations are usually obtained by modelling the foundation raft only to incorporate the soil structure interaction (SSI). However, as it proposed in the recent studies the role of SSI and simulation of piled raft in the analyses proved to be very important in the determination of the STMD parameters. Hence, in this study, efficiency of STMD with respect to the control of seismic response of the structure, is studied by considering the soil-pile-structure interaction (SPSI). Nonlinear time history analysis is applied for a three-layered soil profile including pile foundations by using the well-known substructure (spring) model under two different ground motion records. In order to increase the accuracy of the results, soil profile with piles and building structure with STMD are considered all at once in a single model under the action of seismic loading, named as direct method. P-Y curves which are suggested by American Petroleum Institute (API) are used in the spring method for simulating soil-pile-structure interaction. The results showed that, adjusting the STMD characterizations on piled structures without considering the soil-pile-structure interaction may result to ineffective control of the seismic vibration and in the worst case may lead to amplification of the vibration of buildings.

Behaviour of Floating Column in RC Building at Optimum Location under Action of Seismic Load

Behaviour of Floating Column in RC Building at Optimum Location under Action of Seismic Load

Shaking Table Tests for Seismic Response of Oblique Overlapped Tunnel

To study the dynamic response and spectrum characteristics of the three-dimensional crossing tunnel under the action of seismic load, we established a 1/50 downscale model based on a typical of the oblique overlapped tunnel and conducted a series of shaking table tests. Through examining the recorded dynamic responses (acceleration and dynamic strain measured at different locations in model tunnels), we found that the seismic response of the crown was the largest at the central section, and the invert of the tunnels was exactly opposite to the crown, which presented a “parabolic” distribution, and we inferred that the damage within the model may be mainly concentrated on the crown of the tunnels. Additionally, the dynamic strain showed obvious nonlinear and nonstationary characteristics under the action of different degrees of seismic intensities. Different from a single tunnel, the acceleration superposition effect appears in the cross section of two tunnels because of the spatial effect of overlapping tunnels, resulting in the obvious seismic response in the cross section. Meanwhile, we also found that the 1st dominant frequency (0.1–6.26 Hz) seismic wave played a leading role in the process of tunnel slope failure. Furthermore, the analysis of the acceleration response spectrum also showed that the surrounding rock mass has an amplification effect on low-frequency seismic waves. These results help us better understand the features of the dynamic responses and also provide evidence to reinforce the overlapped tunnels against earthquakes.

Reliability analysis of steel buildings considering the flexibility of the connections of the GFs

A numerical study to evaluate the reliability of 3D steel buildings with moment-resisting frames (MRFs) at the perimeter and gravity frames (GFs) at the interior under the action of seismic loading, is carried out. To this aim, the median values (MV) of the maximum drifts (MD) and fragility curves are obtained. The reliability, expressed as the mean annual rate of exceeding (υ) particular values of MD, is calculated by using the probabilistic seismic hazard analysis format. Three models, representing steel buildings of low-, mid- and high-rise are considered. The interior connections are assumed to be, first perfectly pinned (PP) as considered in practical design, and then as semi-rigid (SR). The Beam-Line Theory together with The Model of Richard are used to represent the SR connections. Results indicate that the MV demands and the seismic fragility can be significantly reduced when the stiffness and dissipation of energy at interior connections are considered; reductions larger than 40% and 60%, respectively, are observed in many of the cases. The structural reliability is also significantly improved; reductions close to 20% in the expected maximum drift are observed in many cases. It is concluded that the effects of the stiffness and energy dissipation of the connections of GFs on the seismic response (in terms of MV), on the fragility curves, and on the mean annual rate of exceedance (υ), are significant so they should not be ignored. Even for shear connections whose contribution in practical design is totally ignored, the effect is considerable.

SPH Simulation of High-Volume Rapid Landslides Triggered by Earthquakes Based on a Unified Constitutive Model. Part I: Initiation Process and Slope Failure

Landslides triggered by seismic loading pose a great threat to human lives, property, and infrastructure. This paper embeds a unified constitutive model in the smoothed particle hydrodynamics (SPH) method and analyzes the initiation process of landslides. A seismic wave is applied to bottom boundary particles by imposing velocities calculated using the seismic wave. The bottom boundary is set as a no-slip boundary and the free field boundary is chosen to reduce seismic wave reflection. The reliability of the developed SPH method is first validated by the simulation of a benchmark problem of thin plate oscillation and stability analysis of a homogenous slope. Initiation of the earthquake-induced Tangjiashan landslide is then simulated as a case study. Formation of a shear zone under the action of seismic loading is followed by the formation of a continuous slip surface at about 15[Formula: see text]s. The sliding surface formed in the SPH simulation agrees well with the speculative sliding surface based on field observations. The velocities of monitored points during the initiation process are also captured by the SPH method.

Verification Analysis of the Degradation of Frequency Parameters Under the Action of Seismic Load

The article discusses the results of a numerical study of the effect of local damage to bearing structures on the degradation of frequency parameters during seismic effects. The studies were carried out in the LS-DYNA software package which implemented the nonlinear concrete model — Continuous Surface Cap Model (CSCM). Design models of a building are modelled both with regard to direct reinforcement using volumetric FE (finite elements) and flat FE. The object of modelling is a 3-storey building of cellular framing. The analysis of the results of the conducted studies suggests that the effect of degradation of natural vibration frequencies cannot be estimated in the building modelled by means of bar FE. The degradation is insignificant; the frequency reduction occurs within the limits of errors. At the moment, it is not possible to identify the effect of degradation in the bar model in this formulation. To do this, it is necessary to conduct additional researches, including those with other models of materials. Taking into account certain assumptions, the LS-DYNA software package allows computational studies of the effect of local damage to bearing structures on dynamic characteristics, including those resulting from an earthquake.

Seismic Performance Analysis of Highway Subgrade Retaining Structure

Subgrade retaining structure is the most common structure of highway, once it is damaged by earthquake, its damage is universal. Under the action of seismic load, whether the subgrade retaining structure cracks or collapses, and the failure mechanism is one of the key problems in the design of retaining structure in earthquake area. Therefore, it is necessary to systematically study the typical failure mode, failure mechanism and seismic earth pressure of highway retaining structures. In this paper, through the investigation and analysis of earthquake damage law and failure mode of highway retaining structure, combined with numerical model test, the seismic damage mode of highway retaining structure is summarized, and effective seismic reinforcement method is put forward, which provides a certain basis for post-disaster reconstruction of highway structure.

Masonry: the brittle or plastic material?

The results of experimental studies of masonry on the action of dynamic and static (short-term and long-term) loads are presented. The possibility of plastic deformations in the masonry is analyzed for different types of force effects. The falsity of the proposed approach to the estimation of the coefficient of plasticity of masonry, taking into account the ratio of elastic and total deformations of the masonry is noted. The study of the works of Soviet scientists revealed that the masonry under the action of seismic loads refers to brittle materials in the complete absence of plastic properties in it in the process of instantaneous application of forces. For the cases of uniaxial and plane stress states of the masonry, data on the coefficient of plasticity obtained from the experiment are presented. On the basis of experimental studies the influence of the strength of the so-called base materials (brick, mortar) on the bearing capacity of the masonry, regardless of the nature of the application of forces and the type of its stress state, is noted. The analysis of works of prof. S. V. Polyakov makes it possible to draw a conclusion that at the long application of the load, characteristic for the masonry are not plastic deformations, but creep deformations. It is shown that the proposals of some authors on the need to reduce the level of adhesion of the mortar to the brick for the masonry erected in earthquake-prone regions in order to improve its plastic properties are erroneous both from the structural point of view and from the point of view of ensuring the seismic resistance of structures. It is noted that the proposal to assess the plasticity of the masonry of ceramic brick walls and large-format ceramic stone with a voidness of more than 20% is incorrect, and does not meet the work of the masonry of hollow material. On the basis of the analysis of a large number of research works it is concluded about the fragile work of masonry.

Effects of Moisture Content on the Dynamic Response and Failure Mode of Unsaturated Soil Slope Subjected to Seismic Load

Understanding the relationship between the moisture content of unsaturated soil and the instability and dynamic response of slope under the action of seismic load can bring convenience to the field of slope safety assessment. The effect of moisture content of the unsaturated soil on the failure mode and dynamic response of slope under seismic loading was investigated using shaking table tests. In this regard, three different moisture contents of 5%, 8.1%, and 12.5% were considered. The experimental results show that the amplification factor of acceleration (AFA) on the slope surface increases with the increase in both relative elevation and excitation amplitude of acceleration (EAA). As the moisture content of unsaturated soil increases, AFA tends to decrease. An empirical correlation describing the relationship among AFA, relative elevation, dimensionless EAA, and moisture content of unsaturated soil was proposed. The excitation frequency of acceleration (EFA) has a significant impact on the AFA at the middle and upper parts of the slope. The deformation of slope surface is able to reflect the failure mode of slope, which can be used in slope monitoring work. The slope with different moisture contents of unsaturated soil has different instability modes. With the increase in soil moisture content, the slope needs more energy to reach the unstable state under seismic loading. There are three typical regions of principal stress field in the slope exposed to seismic loading, which control the evolution of initial slip plane inside the slope.

Failure mode and dynamic response of a double-sided slope with high water content of soil

A double-sided slope with high water content in sandy clay was considered under the action of seismic load. Its failure mode and dynamic response were investigated using a hydraulic servo shaking table test. The typical characteristic of failure mode and dynamic responses of the double-sided slope were analyzed. Experimental results show that slope failure undergoes a process of progressive deformation. The slope failure mode can be explained as creep sliding landslide. AFA (Amplification Factor of Acceleration) at the surface and inner parts of the slope shows an increasing trend with the increase of relative elevation. The relationship between AFA and EAA (Excitation Amplitude of Acceleration) is nonlinear. An empirical formula is proposed to describe preferably the relationship between AFA, relative elevation and dimensionless EAA. The AFA at the middle and upper parts of the slope increases apparently with increasing EFA (Excitation Frequency of Acceleration).

Seismic behavior of geosynthetic encased columns and ordinary stone columns

This study is concerned with evaluating and comparing the behavior of geosynthetic encased stone columns (GECs) and ordinary (conventional) stone columns (OSCs) during and after seismic excitations. For this purpose, well instrumented GECs and OSCs are installed in kaolinite clay beds consolidated in a large steel tank. In order to simulate the seismic behavior of columns supporting an embankment, surcharge loads are applied and the experimental setup is subjected to large-scale shaking table tests. The strains in the encasement are measured by making use of water-proof strain gauges during the course of the experiments. The vertical load capacities of GECs and OSCs after the seismic excitation were measured by a series of stress controlled column load tests. The experimental data at hand suggests that under the action of seismic loads there is a significant strain demand on the encasement confining the GECs. An almost linear relationship between the seismic energy input expressed in terms of IA (Arias Intensity) and reinforcement strain amplitude is observed. GECs in general have exhibited a superior performance both under static and seismic loads when compared to OSCs.

Finite Analysis and Research of Lift-sliding Stereo Garage Structure

The paper took the lift-sliding stereo garage with four floors and six columns as the research object, established steel structure finite model, determined the load type and put forward load conversion methods. On this base, aiming at steel structure finite model, static analysis, model analysis, dynamic analysis and seismic response spectrum analysis were carried out. It calculated and obtained the maximum displacement of the beams, steel structure inherent frequency and vibration mode as well as displacement changes of steel structure under the action of seismic load. The simulation results show the stiffness of steel structure can meet the design requirement for resisting 8 grade wind and M7 earthquake, and has great safety margin.

EFFECT OF CONCENTRIC AND ECCENTRIC TYPE OF BRACINGS ON PERFORMANCE BASED SEISMIC ANALYSIS OF RC BUILDING

When a tall building is subjected to lateral or torsional deflections under the action of seismicloads, the resulting oscillatory movement can induce a wide range of responses in the building’s occupants.[1]As a result, lateral stiffness is a major consideration in the design of tall buildings. Bracing is a highly efficient and economical method of resisting lateral forces in a frame structure. In this present study, the effect of four different types of bracing systems have been studied, for the use in SMRF RC framed building situated in seismic zone IV, in order to provide lateral stiffness and results in terms of storey shears and storey drifts have been presented.