Influence Of Seismic Loads Research Articles

A methodological approach to evaluate the dynamic response of internal septa and pillars in soft rock underground cavities

A large amount of underground cavities nowadays exists throughout the Apulian region (south-eastern Italy) as a result of mining processes of soft calcarenite, which frequently followed the “room and pillar” technique. In these cave systems, pillars and septa are critical structures, whose failure can lead to a significant increment of the sinkhole hazard. The behaviour of these rocky structures in the dynamic field is poorly studied in literature, and the present study aims to investigate their dynamic stability, according to regional seismicity data. For this purpose, ideal pillar geometries were considered, for which the evolution of the stress–strain field under dynamic inputs was observed in both 2D and 3- configurations by means of parametrical finite element analysis. For shallow cavities, slender septa were found to be the most affected by the influence of seismic loading. For deep cavities, dynamic instability is observed only for rather squat septa, with the cavity width also influencing the dynamic behaviour. To quantitatively assess the septum stability, a stability index was also proposed in 2D models. Moreover, three-dimensional analyses showed a stabilizing effect in the pillar exerted by the stress component perpendicular to the earthquake.

Effect of Seismic Loading on Porewater Pressure in Clayey Soil under Disconnected Piles-Raft Foundation

The disconnected piled raft foundation (DCPRF) is one of the newly introduced foundations for specialization in geotechnical engineering, which significantly reduces the moment and stress on the pile head. In addition, this type of foundation is an ideal choice in areas with seismic activity due to the presence of cushion material between the raft and the piles. This work aims to present a numerical model in PLAXIS 3D software for connected piled raft and disconnected piled raft foundations under the influence of seismic loads and investigate the effect of pore water pressure on the disconnected foundation compared to the connected foundation. The study will depend on the earthquake that struck Iraq in November 2017 in the Halabja region. Strength was 7.3 on the Richter scale with PGA (0.1g). The results of changing pore water pressure showed the variation of pore water pressure. In the case of a DCPRF, the porewater pressure and excess porewater pressure in the soil are much greater than in the case of a CPRF. The increase in the porewater pressure is due to the weight of the building and the weight of the additional cushion layer on the soil. The mechanism for transferring the load in the case of a DCPRF is carried out by raft, then to the cushion, and then to the soil and piles. The load transferred to the soil in the case of DCPRF is more than that transferred to the soil in the CPRF system.

DEVELOPMENT OF LOADING MODELS AND ANALYSIS OF THE STRESS-STRAIN STATE OF THE MAIN GAS PIPELINE WITH COMPOSITE LININGS

The operation of sections of main gas pipelines that are on the verge of developing a design resource is associated with a number of problems in ensuring industrial safety. One of the most acute problems is the occurrence of local defects. The main material for the manufacture of main gas pipelines is steel. During the operation of the pipeline, local defects occur due to metal corrosion or mechanical damage to the gas pipe. Such concentrators with high internal pressure in the gas pipeline can lead to the destruction of the entire structure. In this case, the situation of destruction is especially critical, since it can cause a man-made disaster. To increase the shelf life of damaged sections of main pipelines in places where defects are located, banding with composite linings is used. The article contains part of a comprehensive study, which consisted in the development of methods for modeling the main gas pipeline for oil and petroleum products under seismic loads, dynamic stress-strain state under the influence of seismic loads and stress-strain state of a damaged gas pipeline reinforced with composite linings under the action of internal pressure. The technology of manufacturing linings from composite material is also described in detail. At the same time, a geometric model of the section of the main gas pipeline with composite linings was developed and an analysis of the loading of the section of the main gas pipeline in ANSYS was carried out, provided that the lining is mounted without tension on the pipeline and provided that the lining is mounted with tension, where a comparative analysis showed that the installation condition of composite linings does not significantly affect the static stress state.

Seismic combined bearing capacity of strip footings on partially saturated soils using lower bound theorem of finite element limit analysis and second-order cone programming

The seismic bearing capacity of strip footings resting on unsaturated soils subjected to combined loading is investigated in this study using a combination of lower bound limit analysis and finite element discretization. Second-order cone programming (SOCP) is used in this instance to simulate the nonlinear form of the universal perfectly-plastic Mohr-Coulomb yield criterion during the stress field optimization process. Under no-flow and steady-state infiltration/evaporation flow conditions, the significant influence of matric suction induced below the surface footing is accounted for using the suction stress concept. The load eccentricity and inclination applied to the footing and pseudo-static forces exerted simultaneously to the footing (superstructure) and underlying soil are all incorporated into the equilibrium equations, resulting in combinations of limit moment (M), and vertical (V), and shear (H) forces, under the influence of seismic loading. The results demonstrate that the matric suction induced within the porous structure of the underlying soil stratum increases the capacity of the surface footing to withstand various combinations of eccentric and inclined loadings under seismic excitation. Moreover, at a given hydraulic condition, the failure envelopes of obliquely/eccentrically loaded shallow foundations shrink significantly with the increase in the seismic intensity; the process which is more highlighted in sand (no-suction and all flow conditions). As the flow state in the unsaturated clay changes from infiltration to evaporation, the failure envelopes are observed to enlarge. In addition, as the load inclination angle reaches the soil-footing interface friction angle, the ultimate horizontal bearing capacity of the foundation resting on sand (no-suction) drops to zero; however, there still exists a residual shear resistance in the underlying clay layer or unsaturated sand, posing non-zero horizontal bearing capacity even at extremely high angles of inclination. Last but not least, the influence of earthquake horizontal loading on the bearing capacity envelopes of a shallow footing resting on a sand deposit was corroborated to be more pronounced than on a cohesive soil deposit. Indeed, the intrinsic (residual) cohesion, normally found in cohesive soils, was realized to contribute significantly to suppress the detrimental effect of earthquake horizontal loading.

Application of mathematical modeling for calculation of dock structures of the spillway construction of the Krasnodar reservoir

The article deals with modern issues of the application of mathematical modeling taking into account the changing parameters of the reliability of the final resource of the dock structures of the spillway construction of the Krasnodar reservoir. Hydraulic structures of the pressure front of the Krasnodar reservoir are designed and built as structures of the II capital class. Analyzing the performed mathematical modeling, we see that the sections in the wall are “dangerous” at the place where it adjoins the bottom. To perform static calculations, we select a strip with a width of 1 linear meter in the longitudinal direction. Authors apply all types of loads acting on the structure of the strip of the cross-section of the structure and determine the forces in the dangerous sections of the wall and bottom. The main one is the calculation of the structure in the transverse direction. To construct diagrams of bending moments and transverse forces in the bottom plate, with the worst-case scenario of the structure, during mathematical modeling, a model of the dock structures of the spillway construction of the Krasnodar reservoir was built and later various emergency situations under the influence of seismic loads were calculated.

Features of interaction of the construction works with a layered base under the influence of seismic loads

The paper considers the problem of dynamic joint work of a structure with a base during seismic actions propagating from the level of a mountain massif through a layered group medium in the direction of the structure. The main attention is focused on the extreme case of vertically propagating transverse seismic waves, their reflections and transitions through the layered medium of the soil. Wave equations of elasticity theory are used to describe dynamic processes.

Reducing Environmental Hazards of Prismatic Storage Tanks under Vibrations

Regular operation, pre-repair and repair work on tanks, as well as outflows of oil products and other flammable liquids under the influence of seismic loads, fires and explosions on tanks are the source of technogenic impact on the environment. Therefore, the influence treatment of the fluctuations and vibrations on the storage tanks for environmentally hazardous liquids and the assessment of reducing the load on nature is a very relevant scientific and practical issue to improve the environmental safety of areas adjacent to the tanks. This paper treats free and forced liquid vibrations in prismatic tanks filled with an incompressible ideal liquid. The developed method allows us to estimate the level of the free surface elevation in prismatic tanks under suddenly enclosed loadings. The proposed method makes it possible to determine a suitable place with a proper height for installation of the baffles in tanks by using numerical simulation and thus shortening the expensive field experiments. The proposed approach could be applied to various environmentally hazardous liquids. This will increase the environmental safety level of the territories adjacent to stationary tanks with environmentally hazardous liquid. It will also be possible to prevent emergencies.

Influence of Seismic Loads Considering Soil Properties and Wave Passage Effect on the Seismic Response of a Multi-Span PSC Girder Bridge

This paper investigates the analytical results of the seismic response of multi-span prestressed concrete (PSC) I-girder bridges under seismic loads. To perform numerical analyses, a three-span PSC I-girder bridge with a width of 12 m, a total length of 100 m, and a maximum span length of 40 m was modeled, and a virtual location was selected to consider the soil properties of the area where the bridge was constructed. The seismic load acting on the PSC I-girder bridge was applied in consideration of the soil properties around the pier and the wave passage effect of the bedrock in the artificial seismic load generated, according to the U.S. Nuclear Regulatory Commission (NRC) standard. The analysis results confirmed that the seismic load, with consideration of the soil properties and wave passage effect, generated the maximum response acceleration and bending moment at the deck of the bridge—152% and 232% greater than without considering them, respectively. Therefore, in order to ensure the earthquake resistance of the bridge, the soil properties of the area where the bridge will be built and the wave passage effect of the bedrock must be considered.

Comparative analysis of the dynamic stability of a multistorey building with different base arrangements

The article presents the results of studies by the numerical method of pile and slab foundation with a reinforced base by the method of deep soil mixing (DSM) under the influence of seismic loads using the LIRA-SAPR software package, which implements the finite element method. The parameters of the computer model are presented, which make it possible to obtain the calculation results. A comparative analysis of the calculation results is carried out. In the course of the study, it was revealed that the use of a slab foundation with a reinforced base by the deep soil mixing method (DSM) is more effective than a pile foundation under seismic loads.

РАСЧЁТ МНОГОЭТАЖНОГО ЗДАНИЯ НА ПРОГРЕССИРУЮЩЕЕ ОБРУШЕНИЕ ПРИ СЕЙСМИЧЕСКОМ ВОЗДЕЙСТВИИ

The article provides an analysis of existing computational practices for solving the problems of survivability of structures of buildings and structures. The issues of progressive collapse of buildings under the influence of seismic loads are considered separately. It is noted that in order to ensure the reliability of the structures of buildings and structures under special impacts, it is necessary to have a clear regulation in the system of regulatory documentation of the Russian Federation. Most calculations for progressive collapse are made for frame buildings. In this paper, one of the approaches to solving the problem of survivability is proposed on the example of calculating a multi-storey building of a wall structural system for progressive collapse with a sequential failure of the most loaded walls of the first floor. The change in the stress-strain state of the building's load-bearing structures with successive failure of the walls of the first floor at each stage of the calculation is shown.

Seismic Bearing Capacity of a Strip Footing Over an Embankment of Anisotropic Clay

The present study adopts lower bound finite element limit analysis technique in association with non-linear optimization to compute the seismic bearing capacity of a strip footing placed over an embankment of anisotropic clay. The influence of seismic loading is incorporated in terms of a horizontal seismic acceleration coefficient. The bearing capacity factor Nc of the strip footing is obtained for various combinations of (i) slope angle, (ii) footing setback distance, (iii) horizontal seismic acceleration coefficient, and (iv) anisotropic strength ratio of clay. The bearing capacity factor of the strip footing increases with the increasing setback distances. However, beyond a certain setback distance, hardly any influence is found. For a particular footing position and constant value of horizontal seismic acceleration coefficient, the magnitude of bearing capacity factor increases with the increase in anisotropic strength ratio. However, the percentage increment in the bearing capacity reduces when the value of anisotropic strength ratio becomes greater than one. In addition, the bearing capacity reduces with the increasing slope angle and horizontal seismic acceleration coefficient. Failure patterns are obtained to understand the failure mechanism.

Investigation of Seismic Stability of High-Rising Buildings Using Grid-Characteristic Method

The purpose of this work was the numerical simulation of dynamic wave processes in heterogeneous media with the subsequent evaluation of their influence on various structures. The effect of earthquakes on ground buildings and underground structures was studied. In the work, we used the grid-characteristic method, which allows taking into account the physics of arising wave processes. The use of hierarchical grid systems allows the calculation of seismic waves directly from the earthquake source to ground-based buildings and underground structures. The work investigated the destruction of high-rise buildings under the influence of seismic loads. The emerging areas of fractures in various structures were studied. The effect of the earthquake on the underground structure was considered. The influence of the depth of the earthquake source was analyzed. Images of wave processes in structures and places of destruction were obtained. Note that we do not calculate the damage caused by falling of some collapsed parts of the building to others, but we calculate only damage caused directly by seismic activity. This type of damage is of the greatest interest, since it is necessary to avoid precisely this primary destruction. Also we investigate the nature of this type of damage, e.g, internal, near the surface, causing collapse, asymmetric. The novelty of the approach used also lies in the fact that we solve a linear elastic wave equation with constant coefficients in various subdomains of the integration domain, between which contact conditions are established. And the size and shape of these subdomains vary over time and depend on the solution. That is, the complete boundary problem of the elastic wave equation is nonlinear.

Influence of seismic loading on axial load variation in reinforced concrete columns

Influence of seismic loading on axial load variation in reinforced concrete columns

Critical setback distance for a footing resting on slopes under seismic loading

A footing located on slopes possess relatively lower bearing capacity as compared to the footing located on the level ground. The bearing capacity further reduces under seismic loading. The adverse effect of slope inclination and seismic loading on bearing capacity can be minimized by proving sufficient setback distance. Though few earlier studies considered setback distance in their analysis, the range of considered setback distance was very narrow. No study has explored the critical setback distance. An attempt has been made in the present study to comprehensively investigate the effect of setback distance on footing under seismic loading conditions. The pseudo-static method has been incorporated to study the influence of seismic loading. The rate of decrease in seismic bearing capacity with slope inclination become more evident with the increase in embedment depth of footing and angle of shearing resistance of soil. The increase in bearing capacity with setback distance relative to level ground reduces with slope inclination, soil density, embedment depth of footing and seismic acceleration. The critical value of setback distance is found to increase with slope inclination, embedment depth of footing and density of soil. The critical setback distance in seismic case is found to be more than those observed in the static case. The failure mechanisms of footing under seismic loading is presented in detail. The statistical analysis was also performed to develop three equations to predict the critical setback distance, seismic bearing capacity factor (Nrqs) and change in seismic bearing capacity (BCR) with slope geometry, footing depth and seismic loading.

GENERAL STATEMENTS OF BUILDINGS ANALYSIS AND PROTECTION BY POSSIBLE COMBINED INFLUENCE OF SEISMIC LOADS AND BASE SUBSTANTIAL DIFFERENTIAL SETTLEMENTS

Common results of cycle of investigations and developments for the reinforced concrete and masonry buildings analysis and protection methods in conditions of possible combined influence of seismic loads and base substantial differential settlements are considered in the article.

Influence of seismic loading on segment opening of a shield tunnel.

The influence of seismic loading on segment opening of a shield tunnel was explored using the dynamic finite element method to analyze the distribution of segment opening under multidirectional seismic loading, combined with a typical engineering installation. The calculation of segment opening was deduced from equivalent continuous theory and segment opening was obtained through calculations. The results show that the scope of influence of the foundation excavation on segment opening is mainly resigned to within 5 segment rings next to the diaphragm wall and 4 joints nearest the working well when the tunnel is first excavated followed by the working well in the excavation order. The effect of seismic loading on segment opening is significant, and the minimum increase of the maximal segment opening owing to seismic loading is 16%, while that of the average opening is 27%. Segment opening under bidirectional coupled seismic loading is significantly greater than that under one-dimensional seismic loading. On the basis of the numerical calculations, the seismic acceleration and segment opening caused by seismic action were normalized, and a new calculation method was proposed for predicting the maximal segment opening of a shield tunnel at different depths under conditions of seismic loading.

SEISMIC EVALUTION OF CRACKED MASONRY BARRAGE PIERS REPAIRED WITH DIFFERENT METHODS

The most common defects observed in masonry structures are cracking due to tensile stresses. Repairing process is needed to restore the structural capacity of the distressed masonry piers. Crack repair methods used in rehabilitation of water structures that have been built using clay bricks may affect the performance of those structures during their resistance to seismic loads. This research deals with evaluating the common methods used to repair major cracks of masonry piers. The evaluation process considered the performance of the repaired piers under the influence of seismic loads. Dynamic tests using shaking table with harmonic excitation were carried out to represent the effect of seismic loads. Therefore, the current paper investigates the dynamic structural performance of cracked masonry barrage piers, which are repaired using different techniques. Three different techniques are used for the purpose of repairing the cracked piers namely; epoxy pasted-repair, stapled using reinforced bars, and tied using pre-stressed technique. Four masonry piers were built on a shaking table and they were exposed to cyclic loads with different frequencies to simulate the earthquake. It was observed that the type of repair technique used affects the load carrying capacity of the piers and leads to a redistribution of the strains and hence stresses in repaired piers. All repair techniques are found to be able to restore or enhance the dynamic structural behavior for all the repaired piers that can stand against lateral loads with efficiency more than the uncracked pier. Guidelines for the assessment of the use of epoxy, reinforced and pre-stressed repair techniques in construction and strengthening of masonry barrages were suggested. For tied technique, some cautions must be considered when applied to overcome the base shear failure.