Effects Of Seismic Actions Research Articles

Assessment of the seismic failure of reinforced concrete structures considering the directional effects of ground motions

Seismic intensity measures at different levels significantly impact the seismic damage of building clusters. Reinforced concrete (RC) structures are a type of building widely used in different regions worldwide. A large amount of field seismic damage observation data indicates that within the same seismic intensity zone, the directional effects of varying ground motions lead to significant differences in damage to RC structures on different floors. However, relatively little research has been conducted on estimating the seismic fragility and vulnerability of RC structures considering the directional effects of seismic action. To further study the directional effect of seismic motion on the damage of different floors, this study conducted dynamic time history and spectral analyses on 1472,379 acceleration records in multiple directions obtained from monitoring at nine actual seismic stations during the 2008 Wenchuan earthquake in China. This paper innovatively reports on the actual damage features of RC structures during the Mw6.2 magnitude Jishishan earthquake in Gansu Province, China, on December 18, 2023 (the most severe destructive earthquake in China in 2023) and analyses the influence of earthquake directionality on the damage to different floors of RC structures. A three-dimensional numerical model of a four-story RC frame structure was established using numerical simulation and the finite element method. Different intensity measures were taken to input seismic excitations of different intensities into the RC structure in the 0°, 30°, 60°, and 90° directions, and damage simulation analysis was conducted. The nonlinear dynamic time history curves of structures under multiple directions of seismic excitation in different intensity zones have been developed. Using the interstory stiffness and interstory displacement angle as engineering demand parameters, damage assessment curves and stress clouds for RC structures with 1–4 floors considering different seismic directional effects were generated. The analysis results and major findings indicate that the seismic sequence in the 0° direction has a relatively heavy impact on the first floor of the RC structure in zone IX, which is consistent with the actual field observation results.

Retrofitting Alternatives for an Existing Maillart-Arch-Type Bridge: A Case Study

This article examines different retrofit approaches for a still-in-use deck-stiffened arch bridge, the Viadotto Olivieri in Salerno (A3 Highway—South Italy). In its current state, the viaduct is characterized by a central Maillart-arch system, separated by 6 cm-deep joints from two lateral girder portions: the whole system works as an isostatic scheme on a global scale. Dating back to the 1960s, it derives from an early design approach, not including the effects of seismic actions. Considering the demands of current codes, also in light of recent bridge collapses and the resulting plan for assessing the structural safety and vulnerability of existing bridges, studies on seismic capacity become necessary to highlight the potentials and deficits of such complex structures. Analysing a still-in-use example of a Maillart-arch-type bridge, the article examines two different retrofit approaches. The first retrofit alternative includes the strengthening and partial modification of the original deck bridge: it exploits the beneficial effects of making the slender vault collaborate with a more rigid single deck, resulting from joint closure. Moving in the opposite direction, the second alternative considers the application of seismic isolation to the original scheme. An intermediate Isolation System (IS) has been postulated, inserting rubber devices—High Damping Rubber Bearings (HDRBs)—below the deck, at the top of the cross-walls. The advantages of an IS are clear, observing a great reduction of base reactions; moreover, the introduction of the IS completely modifies the original static scheme and exacerbates bridge deformability, at the expense of slender cross-walls, suffering for buckling. A comparison between these retrofit alternatives is argued in the article, evaluating the impact of different types of solution on the valuable original structural scheme.

The effect of seismic action on stability of saline soil subgrade in cold region based on isothermal stratification method

With the change of seasons, the shear strength of saline soil subgrade filler will change with the change of external temperature, which will aggravate the adverse effects of seismic on the subgrade. To explore the influence of seismic action on the stability of saline soil subgrade under the influence of temperature on the strength of saline soil subgrade filler, this paper first carried out saline soil shear tests at different temperatures to obtain the influence of temperature on the shear strength of saline soil. Then, the temperature field of the saline soil subgrade was simulated, and then based on the subgrade isothermal stratification model and FLAC3D, the displacement and acceleration amplification effects of seismic action on the shady slope, sunny slope and subgrade of saline soil subgrade in different months were analyzed. The following conclusions were finally drawn: under the action of seismic, In the process of the change of subgrade temperature of Qarhan - Golmud Expressway between −7.7 ​°C and 27 ​°C, the change of saline soil cohesion is the main factor affecting the stability of subgrade slope, and the maximum and minimum values of subgrade surface settlement appear in September and June of each year, respectively. In August, the differences of settlement between the shady slope and the sunny slope shoulder of the subgrade were the largest, and the acceleration of the shady slope and the sunny slope and the inside of the subgrade changed most significantly in the vertical direction. Special attention should be paid to the seismic early warning in the above key months; In the range from both sides of the shoulder to the centerline of the roadbed, the acceleration amplification effect starts to increase significantly from about 3m from the centerline of the roadbed to the centerline, so it is necessary to pay attention to the seismic design of this range.

Multiple reinforcement measures of flysch landslide.

This work is mainly intended to investigate the flysch landslide reinforcement measures used in the Smokovac-Mateševo section of the North-South Expressway project in Montenegro. Bentley's Plaxis software is used for a numerical analysis of sliding surface parameters of flysch strata in the limit equilibrium state. This study analyzes the slope safety factor for rreinforcement measures such as rock bolts, retaining walls, anti-sliding piles, slope unloading and bolt anchoring and obtains an optimal combination of reinforcement application for the flysch landslide. The effects of seismic action on complex stress and the discontinuous stress boundary conditions arising from various reinforcement measures on landslide stability are also examined. The measures applied in this paper can be used as a reference for flysch landslide reinforcement or other similar slope engineering measures.

Verification of seismic enforced-displacement pushover procedure on torsionally flexible, asymmetric, multi-storey r/c buildings

A recently proposed direct Displacement-based procedure of nonlinear static (pushover) analysis on multi-storey reinforced concrete (r/c) buildings is verified here against the results of Nonlinear Response History Analysis. An asymmetric, regular in elevation, torsionally flexible, multi-storey r/c building designed according to Eurocode EN 1998 is investigated. Taking fully into account the inelastic torsion and the higher mode effects, as well as the P-Delta effects, the proposed procedure applies a pattern of seismic floor enforced-displacements along on the “Capable Near Collapse Principal Axes of the building”, aiming at Near Collapse state.  The envelope of the results of sixteen final non-linear static analyses on the investigated building shows that the main aspects of the spatial seismic action effects can be safely captured by the proposed procedure, especially regarding the inelastic interstorey drift ratios, as well as the plastic mechanism of the building.

Provisions for avoiding brittle fracture in steels used in Australasia including effects of seismic action

Provisions for avoiding brittle fracture in steels used in Australasia including effects of seismic action

Seismic Response Analysis of Tunnel through Fault Considering Dynamic Interaction between Rock Mass and Fault

In order to explore the influences of fault dislocations on tunnel stability under seismic action, a nonlinear dynamic simulation method for the rock–fault contact system is proposed. First, considering the deterioration effect of seismic action on the ultimate bearing load of the contact interface between rock mass and fault, a mathematical model is established reflecting the seismic deterioration laws of the contact interface. Then, based on the traditional point-to-point contact type in a geometric mesh, a point-to-surface contact type is also considered, and an improved dynamic contact force method is established, which considers the large sliding characteristics of the contact interface. According to the proposed method, a dynamic finite element calculation for the flow of the rock–fault contact system is designed, and the accuracy of the method is verified by taking a sliding elastic block as an example. Finally, a three-dimensional (3D) calculation model for a deep tunnel through a normal fault is built, and the nonlinear seismic damage characteristics of the tunnel under horizontal seismic action are studied. The results indicate that the relative dislocation between the rock mass and the fault is the main factor that results in lining damage and destruction. The seismic calculation results for the tunnel considering the dynamic interaction between the rock mass and the fault can more objectively reflect the seismic response characteristics of practical engineering. In addition, the influences of different fault thicknesses and dip angles on the seismic response of the tunnel are discussed. This work provides effective technical support for seismic fortification in a tunnel through fault.

Coupling methods and optimal use of modern anti-seismic insulation systems at building and bridge construction structures

The construction industry has recorded an unprecedented advance in recent years, especially in the world recent developed countries and this involves the increasing development of insulation techniques against the effects of seismic actions that can threaten the structure integrity at a certain time. Most recent achievements in terms of structure insulation systems are successfully used within building and bridge structures in order to ensure the optimal stability level during a potential earthquake, which allows ensuring a proper safety level both for operation and in terms of investments protection. the protection methods of the structures are directed in two directions, namely in achieving the insulation at the base of the structure by strategically positioning the systems at the base of the structure while the second direction is directed at seismic energy consumption or energy dissipation by using dissipative systems mounted on frames the resistance structure of the building. By combining the action of the two types of mechanical systems, good results can be obtained regarding the behaviour of the structure isolated by the earthquake. The paper presents constructive aspects of the mechanical systems used for the seismic insulation of both building and bridge structures and their functional role in the whole structure to which they are mounted. Through the experimental tests made are highlighted the better results in terms of acceleration for the structure isolated with the composed system. Are emphasized in this manner the protective system role in ensuring an improved behaviour for the structure where is mounted at seismic dynamic motions that can occur in time.

Seismic response analysis of steel–concrete hybrid wind turbine tower

The steel–concrete hybrid wind turbine tower is characterized by the concrete tubular segment at the lower part and the traditional steel tubular segment at the upper part. Because of the great change of mass and stiffness along the height of the tower at the connection of steel segment and concrete segment, its dynamic responses under seismic ground motions are significantly different from those of the traditional steel tubular wind turbine tower. Two detailed finite element models of a full steel tubular tower and a steel–concrete hybrid tower for 2.0 MW wind turbine built in the same wind farm are, respectively, developed by using the finite element software ABAQUS. The response spectrum method is applied to analyze the seismic action effects of these two towers under three different ground types. Three groups of ground motions corresponding to three ground types are used to analyze the dynamic response of the steel–concrete hybrid tower by the nonlinear time history method. The numerical results show that the seismic action effect by the response spectrum method is lower than those by the nonlinear time history method. And then it can be concluded that the response spectrum method is not suitable for calculating the seismic action effects of the steel–concrete hybrid tower directly and the time history analyses should be a necessary supplement for its seismic design. The first three modes have obvious contributions on the dynamic response of the steel–concrete hybrid tower.

Resetting response of precast segments with gently keyed interface under seismic action

SummaryIn an attempt to promote the use of precast segmental bridge columns in regions of moderate to high seismicity, sliding planar joints have been adopted to relieve the adverse effects of seismic action. However, despite the ability to survive an earthquake, the sliding segments often result in noticeable residual relative movements afterwards, which require costly repairs. To better understand the kinetic and self‐centering performance of sliding segments with W‐shaped gently keyed interface, the concept of sliding hysteresis center curve is put forward. A bidirectional asymmetrical pure sliding model is explored for better control of the self‐centering ability, where the downslope slip caused by the energy at the post‐peak stage of an earthquake may benefit the self‐centering performance of asymmetrical sliding systems. A series of parametric studies using real earthquake records are then conducted to evaluate the effects of inclination θ and coefficient of friction μ at the interface on the dynamic response. It is found that the seismic excitations, especially the post‐peak cycles, have profound influence on the residual displacement of an asymmetrical sliding system. With proper design, a W‐shaped gently keyed sliding system can provide superior self‐centering performance without affecting its seismic isolation ability during the peak stages of earthquakes.

Irregularity Effects of Masonry Infills on Nonlinear Seismic Behaviour of RC Buildings

Despite extensive research studies, the seismic response of infilled reinforced concrete buildings remains an open problem due to both the complexity of the interaction between the infill and the frame and the large number of parameters involved. Thus, guidelines for both modelling and analysis are still lacking and the infill walls are normally treated as nonstructural components in seismic codes. However, it may be not conservative to neglect the influence of infills. In fact, the infill masonry walls may significantly affect the stiffness, strength, and energy dissipation capacity of RC buildings, even when they are regularly distributed. Recognizing this influence and its importance on the vulnerability of infilled frames, Eurocode 8 requires amplifying seismic action effects due to infills. In this paper, the effectiveness of the Eurocode 8 design provisions for infill irregularity in plan and/or elevation was investigated. To this aim, different in-plan layouts of infill walls were selected as marginal cases for which Eurocode 8 does not require amplification of the action effects due to the presence of infills, or the additional measures to counteract these effects are not mandatory. The seismic vulnerability of the infilled RC buildings was evaluated using nonlinear static and nonlinear dynamic analyses. Both cracking and crushing of masonry and stiffness and strength degradation were considered in the analysis. The effect of the layout of the masonry infills on the seismic response in terms of resistance and displacement was evaluated. Results show that in one of the case studies here examined, it is not conservative to neglect the influence of infill panels. In fact, structural failure due to torsion and soft-storey effects may occur even in cases where Eurocode 8 does not require the amplification of the action effects. Finally, the total shear demand on columns may be underestimated, even in cases where the code provisions for infills irregularity are not mandatory, and the additional shear demand in the columns induced by the masonry infill is very low.

Optimal Design of Seismic Resistant RC Columns.

Although the author is well aware that it is nothing special, presented here is the method that he uses to design the columns of a seismic resistant reinforced concrete structure, in hopes that this could be of use to someone. The method, which is directed at satisfying the capacity design requirements without excessively large sections, consists of proportioning the column so that the seismic action effects shall be resisted by the maximum of the bending moment–axial force interaction curve. That design condition is defined by two equations whose solution provides the optimal aspect ratio (or, alternatively, the optimal section side length) and the maximum feasible reinforcement ratio. The method can be used directly to determine the optimal column for given beam spans and vertical loads, or indirectly to determine the optimal beam spans and vertical loads for given cross-sectional dimensions. The paper presents the method, including its proof, and some applications together with the analysis on the optimality of the obtained solutions. The method is intended especially for the practicing structural engineer, though it may also be useful for educators, students, and building officials.

Soft real-time hybrid simulation based on a space steel frame

Soft real-time hybrid simulation (S-RTHS) is a novel seismic test method for structures. It combines pure finite element simulation with laboratory physical component tests, and can lead to a more realistic simulation of real-time effects of seismic action on specimens. Based on the OpenFresco test communication platform and an MTS electro-hydraulic servo loading system, a systematical study on the technological application of S-RTHS is presented in this paper. A single-story, single-span space steel frame was taken as a prototype, a column was taken as an experimental substructure, and the remaining part of the structure was taken as a numerical substructure to be simulated in OpenSEES. S-RTHS with bidirectional loading was performed, and the boundary conditions of the experimental substructure were simulated and analyzed. The results from the pure numerical simulations and S-RTHS were compared along with the responses from these simulations. The command displacement and feedback displacement of the system were discussed to verify the accuracy and stability of the S-RTHS. Finally, a comparison with the slow substructure hybrid simulation test results shows that the S-RTHS can better simulate the dynamic response of the experimental substructure.

A Simplified Model for Investigation on the Effects of Seismic Actions on Masonry Arch Bridges

Masonry bridges are vulnerable structural systems to the ground motion excitation and their survival in case of such incidents has to be studied in detail. In this work, a simplified model for dynamic analysis of masonry bridges based on rocking motion of rigid blocks is proposed. Using this model, nonlinear time integration analysis on these bridges can be done with ease and in a short time. The proposed model was used in evaluation of seismic performances of a monumental masonry bridge subjected to both horizontal and vertical seismic actions. The study shows the importance of vertical component of ground motion in determination of internal forces and shear sliding deformation at bottom of the bridge’s pier. The proposed model has also shown its ability in defining the effectiveness of a seismic retrofit approach for the same bridge system in a comparative study. According to this investigation, seismic performances of the bridge can be significantly improved in case of adding ductility to its deck assembly.

Effects of vertical seismic actions on the responses of single-storey industrial steel building frames

Single-storey industrial steel frames with crances are considered as being vertically irregular in structural configuration and load distribution under strong earthquake excitations. In this paper, various analytical frames with their spans of 20, 26, 32 and 38 m and locations built in Ha Noi and Son La regions were designed to resist dead, roof live, crane and wind loads. The equivalent horizontal and vertical static earthquake loads applied on the frames were determined. Next, by using linear elastic analyses of structures, the effects of vertical seismic actions on the responses of the frames were evaluated in terms of the ratios K1 and K2 at the bottom and top of the columns corresponding to different combinations of dead loads and static earthquake loads, as denoted by CE1, CE2 and CE3. The effects of seismic actions compared with those of wind actions were also evaluated in terms of the ratios K3 and K4. As a result, the effects of vertical seismic actions were significant and increased with the span lengths of the frames. In addition, by using nonlinear inelastic analyses of structures, the levels of the static earthquake loads were determined corresponding to the first yielding and maximum resistances of the frames.
 Keywords: 
 single-storey industrial buildings; steel frames; span lengths; irregularity; vertical seismic actions; earthquake levels; wind loads

Research on the Influence of Bed Joint Reinforcement on Strength and Deformability of Masonry Shear Walls.

The areas of Central and Eastern Europe and, thus, Poland are not exposed to the effects of seismic actions. Any possible tremors can be caused by coal or copper mining. Wind, rheological effects, the impact of other objects, or a nonuniform substrate are the predominant types of loading included in the calculations for stiffening walls. The majority of buildings in Poland, as in most other European countries, are low, medium-high brick buildings. Some traditional materials, like solid brick (>10% of construction materials market) are still used, but autoclaved aerated concrete (AAC) and cement-sand calcium-silicate (Ca-Si) elements with thin joints are prevailing (>70% of the market) on the Polish market. Adding reinforcement only to bed joints in a wall is a satisfactory solution (in addition to confining) for seismic actions occurring in Poland that improves ULS (ultimate limit state) and SLS (serviceability limit state). This paper presents results from our own tests on testing horizontal shear walls without reinforcement and with different types of reinforcement. This discussion includes 51 walls made of solid brick (CB) reinforced with steel bars and steel trusses and results from tests on 15 walls made of calcium-silicate (Ca-Si) and AAC masonry units reinforced with steel trusses and plastic meshes. Taking into account our own tests and those conducted by other authors, empirical relationships were determined on the basis of more than 90 walls. They are applicable to the design and construction phases to determine the likely effect of reinforcements on cracking stress that damage shear deformation and wall stiffness.

Numerical Modeling of Masonry Infilled Reinforced Concrete Building during Construction Stages Using ABAQUS Software

The effects of seismic actions on reinforced concrete (RC) structures are strongly influenced by the dynamic behavior of their materials. It is crucial to find a simple definition of the natural frequencies of reinforced concrete buildings, particularly in relation to both principal and secondary elements constructing the reinforced concrete building type. This paper firstly presents a comparison with the ambient vibration surveys. An analysis model of different stages of construction of the reinforced concrete masonry wall was compared using the finite element software. In the second step, structural responses of the model were investigated by means of static analysis. Three main types were examined: Bare frame for one, two and three storeys; brick-walled; and coated cases. Modal analysis is carried out by ABAQUS software starting from the deformed building, to provide the natural frequencies and mode shapes. For the natural frequencies, a good agreement is obtained between analytical and experimental results. Furthermore, the comparison results between different cases show that the application of the plaster work increases the lateral stiffness and has significant effects on the dynamic response of the buildings.

A new numerical approach for determining optimal thrust curves of masonry arches

In this paper a new numerical approach for determining admissible thrust curves for masonry arches is proposed. Arbitrary loading conditions, including distributed loads applied to the extrados and to the intrados of the arch, but also horizontal inertial forces simulating the effects of seismic actions are considered for arches of any geometry. The admissible solutions, corresponding to equilibrium thrust curves entirely contained in the thickness of the arch, are consistent with the lower bound theorem of Limit Analysis and, thus, are “safe” solutions from a structural point of view. The well-established Milankovitch's theory for the equilibrium of masonry arches is reviewed and generalized. Then, a specific formulation of the theory is presented, allowing the construction of an effective and efficient numerical procedure based on the Point Collocation Method and enriched by a constrained optimization routine. The latter is aimed at determining, among all the admissible equilibrium solutions, the optimal solution matching specific requirements of interest for applications, as the solution corresponding to the maximum or minimum thrust. The proposed procedure is discussed and validated with reference to the cases of circular, parabolic and pointed arches. In particular, maximum and minimum thrust solutions have been determined for all the examined cases.

Seismic behavior of a low-rise horizontal cylindrical tank

Cylindrical storage tanks are widely used for various types of liquids, including hazardous contents, thus requiring suitable and careful design for seismic actions. The study herein presented deals with the dynamic analysis of a ground-based horizontal cylindrical tank containing butane and with its safety verification. The analyses are based on a detailed finite element (FE) model; a simplified one-degree-of-freedom idealization is also set up and used for verification of the FE results. Particular attention is paid to sloshing and asynchronous seismic input effects. Sloshing effects are investigated according to the current literature state of the art. An efficient methodology based on an “impulsive-convective” decomposition of the container-fluid motion is adopted for the calculation of the seismic force. The effects of asynchronous ground motion are studied by suitable pseudo-static analyses. Comparison between seismic action effects, obtained with and without consideration of sloshing and asynchronous seismic input, shows a rather important influence of these conditions on the final results.

Simplified direct loss measure for seismic isolated steel moment-resisting structures

Seismic base isolation provides an effective means for resilient structures, protects structures from the damaging effect of seismic action and reduces structural vibration, casualties and financial losses. The life cycle costs and advantages of using base isolation can be quantitatively supported by using the FEMA P-58 methodology, but damage and loss estimation using such an approach is time consuming and costly. This study presents a new direct loss measure (LM) for seismic isolated steel moment-resisting structures. Three steel moment-resisting frames of 4, 6 and 8 stories were studied with and without isolation system and 3D nonlinear model of the structures was developed in Opensees. Using common incremental dynamic analysis (IDA) under far-field and near-field records, the expected annual loss (EAL) based on FEMA P-58 approach was estimated. In this regard, LM was introduced for rapid modeling of response based on two main sources of structural damage, that is, interstory drift ratio and peak floor acceleration considering structural and non-structural elements. A good correlation was observed between the EAL and proposed LM. The fixed-base structures were subject to extensive damage and complete failure in the maximum considered earthquakes (MCE), while the base-isolated structures were subject to moderate failure rate in the same situation, indicating the resilience of these structures. The proposed LM can be used for prompt and efficient loss estimation of the base-isolated structures and demonstrate the cost-effective seismic risk management of these systems.