Severe Earthquake Loading Research Articles

Seismic performance evaluation of fiber-reinforced prestressed concrete containments subject to earthquake ground motions

Given the unpredictability of the occurrence of the earthquake and other potential disasters into consideration, the nuclear power plant may be confronted with beyond design-basis earthquake load in the future. The containment structure may be severely damaged under such severe earthquake loading, increasing the risk of containment concrete cracking and potential radioactive materials leaking. Moreover, initial damage caused by the earthquake may significantly alter the pressure performance of the containment under follow-up internal pressure. To compromise the dangers of beyond design-basis earthquake to the containment, an alternative of replacing the conventional concrete with fiber-reinforced concrete (FRC) to upgrade the seismic resistance capacity of the containment is attempted and thoroughly researched. In this study, the influence of various fiber types such as rigid fiber and mixed fiber is regarded to constitute fiber-reinforced PCCVs. The physical properties of traditional and fiber-reinforced PCCVs under earthquake ground motions are scientifically compared and identified by using traditional and proposed evaluation indices. The results indicate that both the traditional evaluation index (i.e. top displacement, stress, strain) and the proposed damage index are greatly reduced by the practice of fiber strengthening under earthquake ground motions.

Local Buckling Behavior of Buckling-Restrained Braces with Longitudinally Profiled Steel Core

One of the most important requirements for a well-designed buckling restrained brace (BRB) under severe earthquake loading is to ensure its stability until the brace achieves sufficient elasto-plastic deformation. This study presents the finite element analysis results of the proposed buckling restrained brace with a longitudinally profiled steel core (LPBRB). The objective of the analyses is to conduct a performance evaluation of the proposed LPBRBs, and to perform a parameter study with different clearance, width:thickness ratio, mortar strength, and friction coefficient for investigating the local buckling behavior of the LPBRBs. Numerical analyses results demonstrate that the LPBRBs exhibited good ductile performance and stable hysteretic behavior. The local buckling failure can be predicted by the demand:capacity ratio formula. The friction coefficient has little influence on the hysteretic behavior of LPBRBs. The local stability can be improved by adopting the mortar with higher compression strength or the LP core with lower width:thickness ratio. The proposed LPBRBs have a similar hysteretic response to the conventional BRBs.

INFLUENCE OF BOND AND FRICTION ON TENSILE STRENGTH OF PERFORATED STEEL PLATE CONNECTOR UNDER CONFINEMENT

Concrete-filled steel tube (CFST) columns are commonly used in Japan, which utilize onsite full-strength welded splices between columns. However, onsite welding requires high technical skill and a controlled environment. Further, this type of splice is expensive and, in most cases, is not necessary for dependable building performance under severe earthquake loading conditions. Recently, new types of CFST column splices have been developed that enhance constructability and avoid the need for onsite welding. In the proposed column splice method, perforated steel plates are placed on each column half and are welded into place. To evaluate the performance of this splice, it is important to determine the pull-out strength and behavior modes of the perforated steel plates embedded into the CFSTs. In this paper, a pull-out experiment with perforated steel plates embedded into a square CFST stub is conducted. The experimental parameters are the bond between the steel plate and the concrete, the embedded length of the perforation, and the extra length of the steel plate. The effect of the bond and friction strength between the steel and concrete are discussed, and a design formula for the pull-out strength of the perforated steel plate is examined.

Damage capacity on RC structures using performance based analysis

Performance based analysis is conducted on a structure to know the performance of building under severe earthquake loads with limited and well-distributed damage. To do this analysis a non-linear static analysis called pushover analysis had conducted on the structure. In this paper, an RC building with both 5 storey and 10 storey is designed for both gravity loads and earthquake resistant loads using SAP2000 software. Analysis is done in both X and Y direction to get a damage curve (pushover curve). By studying the damage curve, the results that obtained are earthquake resistant designed building had more strength when compared to gravity load designed building and it is better to consider earthquake in building design , because gravity loads alone cannot give the adequate results.

Parameter Identification for Modeling Steel Fiber Reinforced Concrete under Compression to Prevent Concrete Cover Spalling under Severe Earthquake Loading Condition

The use of steel fiber in concrete material can improves both the strength and the ductility of concrete. The fibers can postpone or mitigate the concrete cover spalling under severe loading conditions such as during an earthquake. In this paper, the behavior of Steel Fiber Reinforced Concrete (SFRC) under compression is modeled using the Attard and Setunge’s stress-strain model. The parameter identification consisted of the elastic modulus (Ec), the peak strength (/cc), the residual strength (fes), and the peak strain of concrete under compression (ecc). From the investigation, it is found that the models proposed for active confined concrete can be applied for steel fiber reinforced concrete. It was also shown that the axial strain at peak stress increases as the fiber volumetric ratio and fiber aspect ratio increased. A simple formula to predict the approximate value of confining pressure to account for the steel fiber presence is proposed. The verification of the proposed model with the experimental results is presented in detail. Furthermore, insight into the performance of the reinforced concrete column made of SFRC using the fiber-based cross-sectional analysis is sighted.

Numerical Evaluation of Earthquake Effect on Cisumdawu Tunnel Stability

Cisumdawu Tunnel is located approximately 3.95 km southeast of the activeLembang Fault. Earthquakes induced by movement of the the active the strike-slip fault may influence stability of the twin tunnel. This paper presents results of numerical analyses carried out to demonstrate effect of a worst-case scenario of earthquake load potentially induced by the Lembang Fault on the stability of the Cisumdawu Tunnel. Static and pseudo-static tunnel stability analyses were carried out at 11 observation stations of tunnel face mapping using RS2 finite element package (Rocscience, Inc.). In the pseudo-static analyses, a 0.48 horizontal seismic load coefficient, which was obtained from a deterministic seismic hazard analysis (DSHA) based on a 6.8 maximum magnitude of estimated earthquake sourced from the Lembang Fault using Campbell-Bozorgnia (2014) attenuation relationship, was applied to the finite element models. The numerical analysis results showed that strength factors of the rock masses around the twin tunnel were greater than unity, both under the static and earthquake loads. The forepolling zones, however, appeared to be under an overstressed condition. Reduction of rock strength factor around the tunnel roof due to application of the earthquake load occurred at all observation stations. Total displacement contours of rock masses around the twin tunnel indicated an increased rock mass displacement due to the earthquake load, as compared to that due to the static load. Under the static load, the largest displacement occurred at the tunnel inverts. The predicted roof displacements obtained from this study were in a reasonably good agreement with those obtained from the field measurements. Number of yielded elements and extend of shear and tension failure zones in the rock masses around the twin tunnel also appeared to increase due to the earthquake load. Despite slight tunnel displacement as predicted in the numerical analyses, the worst-case scenario of earthquake load potentially induced by the Lembang Fault may only cause failures of the rock masses around the Cisumdawu Tunnel. To prevent the twin tunnel displacement caused by such relatively severe earthquake loads, however, stabilizing surrounding the relatively poor ground condition may be necessary.

Monitoring physical and dynamic properties of reinforced concrete structures during seismic excitations

This study investigates the feasibility of tracking the structural/dynamic properties of reinforced concrete (RC) structures while subjected to damaging earthquake loads. The methodology proposed implements an unscented Kalman filter scheme that updates the properties of a simplified non-parametric model of the structure. Calibration and validation of the methodology is accomplished using experimental and simulated data from a full-scale RC column test performed at the NEES Large High Performance Outdoor Shake Table. The results obtained show that peak displacement, stiffness, frequency, shear force and damping ratio are well monitored by the proposed approach at all performance levels. However, residual displacements are not captured due to the non-hysteretic nature of the model. Despite its simplicity, the proposed approach seems suitable for identification and damage assessment of highly nonlinear structures exhibiting nonstationary responses, as is the case of RC structures subjected to severe earthquake loads.

Progressive Collapse Analysis of Reticulated Shell Structure under Severe Earthquake Loading Considering the Damage Accumulation Effect

A reticulated shell is one of the conventional long span space structures, prone to progressive collapse under a severe earthquake due to its unique single layer feature. This is. However, the collapse mechanism of this type of structure is not well studied. In this paper, a numerical modelling technique using the fiber beam elements is developed. The correspondent material model based on the inclusion of damage accumulation was also developed in order to determine the failure criteria of structural members. An effective way to simulate the buckling behavior of the structural members is also used in the numerical simulation. The relevant numerical method is developed and validated against experimental tests: good agreement is achieved. Based on this numerical method, a parametric study of the reticulated shell under severe earthquake loading is performed and the responses of the structure is investigatedand a three-stages collapse mechanism of this type of structure was observed.

Investigation on seismic performance and functionality of self-centring post-tensioned segmental columns

The precast post-tensioned segmental columns react against lateral seismic loading with low residual displacement, predominantly because of the self-centring capability of post-tensioning strands. However, their application is still limited in high seismic zones due to their unknown behaviour during and following severe earthquake loading. In this work, experimental study is conducted to inspect the functionality of post-tensioned segmental columns after suffering severe damages. In earlier work by the authors, partial yield of central strands had been occurred during the unloading stage in the last cycle at 4% drift level. In current study, the experimental work is extended and the specimen retested under loading and unloading up to 4.0% drift. The results indicate that the first segment shows approximately 10 mm horizontal movement on the surface of foundation. However, the specimen showed identical strength at 4.0% drift level. In addition, using finite element method (FEM), a numerical study was conducted in order to investigate the influence of various parameters such as mild steel ratio, concrete strength, number of segments, post-tensioning force and axial loading. Finally, design recommendations were proposed for the yield displacement, ductility and correlation of residual displacement and displacement ductility of post-tensioned segmental columns with various aspect ratios.

Design of Buildings with Seismic Isolation Using Linear Quadratic Algorithm

Seismic isolation is a widely accepted control strategy to protect building against earthquakes. The seismic isolation control is a technique that employs a flexible element at the base of a building and allows the resonant frequency of this building being shifted away from the dominant frequency in earthquake excitations. However, large base displacements resulting from the increased flexibility of the seismic isolation system can potentially exceed the design limit of the building subjected to severe earthquake loading. Thus, design codes recommend equipping additive damping devices along with the seismic isolation bearings to lower the base displacements. In this study, a new design method of seismic isolation is developed using the linear quadratic algorithm that concurrently provides the terms of stiffness and damping coefficient. This design method facilitates the linear quadratic regulator control algorithm with output feedback. For a multiple-degree-of-freedom structure, the shear force provided by seismic isolation can be separated from the superstructure and formed as a control input. This control input is a function of the relative displacement and velocity at the isolation layer with a constant stiffness quantity and damping coefficient. This control algorithm provides the opportunity of deriving these two constants. Moreover, the derivation of isolation stiffness and damping coefficient depends on the user-defined weightings that allow adjusting performance of the isolated building in this control algorithm. One example is provided with eight-story buildings as the superstructures. As seen in the result, the root-mean-square responses are quite compatible between isolated buildings with linearly and nonlinearly isolated bearings. Therefore, the proposed method is useful for designing seismic isolation based on a multiple-degree-of-freedom building.

Theoretical Investigation of Bridge Seismic Responses with Pounding under Near-Fault Vertical Ground Motions

Vertical earthquake loading is normally regarded not as important as its horizontal components and are not explicitly considered in many seismic design codes. However, some previous severe near-fault earthquakes reveal that the vertical ground motion component can be much larger than the horizontal components and may cause serious damage to the bridge structures. This paper theoretically investigates the vertical pounding responses of a two-span continuous bridge subjected to the severe near-fault vertical ground motions. The bridge is simplified as a continuous beam-spring-rod model. The structural wave effect and the vertical pounding between the bridge girder and the supporting bearing are considered, and the theoretical solutions of bridge seismic responses are derived from the expansion of transient wave functions as a series of eigenfunctions. The effects of vertical earthquake and vertical pounding on the bridge bearing, girder and pier are investigated. The numerical results show that the severe vertical earthquake loading may cause the bridge girder to separate from the supporting bearing and hence result in vertical poundings between them when they are in contact again. These vertical poundings can significantly alter the seismic responses of the bridge structure and may cause severe damage to the bridge components such as bridge girder, supporting bearing and bridge pier. Neglecting the influence of vertical earthquake loading may lead to inaccurate estimation of seismic responses of bridge structures, especially when they are subjected to near-fault earthquake with relatively large vertical motion.

Efficiently Implementing Genetic Optimization with Nonlinear Response History Analysis of Taller Buildings

AbstractNonlinear response history analysis is an important tool for accurately determining the performance of tall buildings under severe earthquake loading. When a standard genetic algorithm is used in conjunction with nonlinear response history analysis, it is desirable to use smaller generation sizes because of the computational effort to analyze individual designs. A study was conducted to evaluate how different genetic algorithm techniques influence the reliability and efficiency of the algorithm when used with nonlinear response history analysis and small generation sizes. The system used in the study was a nine-story buckling restrained braced frame that was optimized to minimize brace areas under individual earthquake records. A baseline study showed that a typical genetic algorithm did not converge to the same best design for different random number sequences (seed numbers). Forced diversity improved the reliability of the algorithm such that it converged to the same optimum, regardless of initi...

Overall buckling behavior of all-steel buckling restrained braces

One of the key requirements for the desirable mechanical behavior of buckling restrained braces (BRBs) under severe earthquake loading is to prevent global buckling until the brace member reaches sufficient plastic deformation and ductility. This paper presents finite element analysis results of the proposed all-steel buckling restrained braces. The proposed BRBs have identical core sections but different buckling restraining mechanisms (BRMs). The objective of the analysis is to conduct a parametric study of BRBs with different amounts of gap (between the core and the BRM) and initial imperfections to investigate the global buckling behavior of the brace. The results of the analysis showed that BRM flexural stiffness could significantly affect the global buckling behavior of a brace, regardless of the size of the gap. In addition, a minimum ratio of the Euler buckling load of the restraining member to the yield strength of the core, Pe/Py is suggested for design purposes. This ratio is the principal parameter that controls the global buckling of BRBs.

Strain Life Analysis at Low-Cycle Fatigue on Concentrically Braced Steel Structures with RHS Shape Braces

The seismic performance of concentrically braced frame systems, with braces designed in order to buckle inelastically under a severe earthquake loading, mainly depends on the hysteretic response of the steel braces. As observed in past earthquakes and in experimental programs available in the literature, rectangular hollow section shape braces are more susceptible to early fatigue failures compared to other section shapes. This research, in particular, is focused on the evaluation of the hysteretic response of rectangular hollow section shape braces through appropriate low-cycle fatigue model implemented in a fiber-based element computer program. Firstly, the main influence regarding the number of integration points, number of subdivisions for single brace members, and initial camber on the local response of fiber-based inelastic beam-column element models based on force formulation is investigated. Secondly, the peak strain distribution is used to calibrate the input parameters of the low-cycle fatigue material model. Several data obtained from past experimental programs developed at the Universities of Montreal, Washington, and Calgary are also considered. Finally, an eight-story steel building is designed in order to evaluate the performance levels through incremental time history analyses.

Structural Steel Performance Following Severe Earthquake Loading

The second Christchurch earthquake on February 22, 2011, Magnitude 6.35, generated more intense shaking in the Central Business District than the September 4, 2010 Darfield earthquake, Magnitude 7.1. The second earthquake was closer to the CBD and at shallow depth, resulting in peak ground accelerations 3 times higher. There was significant failure of unreinforced masonry buildings and collapse of a few reinforced concrete buildings, leading to loss of life. Steel structures on the whole performed well during the earthquake and the plastic, inelastic deformation was less than expected given the strength of the recorded ground accelerations. For steel buildings designed to withstand earthquake loading, a design philosophy is to have some structural elements deform plastically, absorbing energy in the process. Typically elements of beams are designed to plastically deform while the columns remain elastic. In the earthquake some of these elements deformed plastically and the buildings were structurally undamaged. The question which then arises is; the building may be safe, but will it withstand a further severe earthquake? In other words how much further plastic work damage can be absorbed without failure of the structural element? Previous research at Auckland on modern structural steel, where the steel was prestrained various levels, to represent earthquake loading, the toughness was determined, as a function of prestrain for the naturally strain-aged steel. Further research, on the same steel, investigated life to failure for cyclic plastic straining in tension and compression loading at various plastic strain amplitudes. This work has shown that provided the plastic strain in the structural element is in the range 2 – 5% the steel will still meet the relevant NZ Standards. To determine the remaining life the plastic strain must be determ ined then the decision made; to use the building as is, replace the structural element or demolish.

Numerical study of a full‐scale six‐story reinforced concrete wall‐frame structure tested at E‐Defense

SUMMARYA full‐scale shake table test on a six‐story reinforced concrete wall frame structure was carried out at E‐Defense, the world's largest three‐dimensional earthquake simulation facility, in January 2006. Story collapse induced from shear failure of shear critical members (e.g., short columns and shear walls) was successfully produced in the test. Insights gained into the seismic behavior of a full‐scale specimen subjected to severe earthquake loads are presented in this paper. To reproduce the collapse process of the specimen and evaluate the ability of analytical tools to predict post‐peak behavior, numerical simulation was also conducted, modeling the seismic behavior of each member with different kinds of models, which differ primarily in their ability to simulate strength decay. Simulated results showed good agreement with the strength‐degrading features observed in post‐peak regions where shear failure of members and concentrated deformation occurred in the first story. The simulated results tended to underestimate observed values such as maximum base shear and maximum displacement. The effects of member model characteristics, torsional response, and earthquake load dimensions (i.e., three‐dimensional effects) on the collapse process of the specimen were also investigated through comprehensive dynamic analyses, which highlighted the following seismic characteristics of the full‐scale specimen: (i) a model that is incapable of simulating a specimen's strength deterioration is inadequate to simulate the post‐peak behavior of the specimen; (ii) the torsional response generated from uniaxial eccentricity in the longitudinal direction was more significant in the elastic range than in the inelastic range; and (iii) three‐dimensional earthquake loads (X–Y–Z axes) generated larger maximum displacement than any other loading cases such as two‐dimensional (X–Y or Y–Z axes) or one‐dimensional (Y axis only) excitation. Copyright © 2011 John Wiley & Sons, Ltd.

Tests on impact effect of partial fracture at steel frame connections

Impact effect of sudden fracture at steel frame connections under severe earthquake or other extreme loads is presented in this paper. The relation of impulse caused by structural fracture to the release of inner force at the cracked location, the magnitude of the response to impact on the basis of one degree of freedom model, and the ratio of the peak value of response to natural period of the system are investigated. Two types of fracture tests were designed and carried out both on uniaxial steel bar tensioned and moment resistant steel frame model. It is proven that the response during the fracture process can be measured quite well using high-frequency data processing system. It is also revealed that the instant fracture of structural connection is characterized by progressive and partial fracture. Numerical evaluation of the impact effect of connection fracture is carried out.

Critical excitation of sdof elasto-plastic systems

The critical excitation of a dynamical system is defined as the input excitation with the lowest energy that drives the system from one specified state to another within a given time span. Critical excitations play an important role in first passage problems because they are the most probable point in the first passage failure region of the standard Normal stochastic load space. They may also be used to provide efficient solution of other stochastic analysis problems by means of asymptotic approximations. Although the solution of critical excitation for linear systems can be obtained through unit impulse response functions, the case of nonlinear hysteretic systems is still under research. The latter has important relevance in the study of nonlinear response of structures under severe earthquake loads, where the characteristics of critical excitations may aid understanding the collapse potential of earthquakes. This paper investigates the critical excitation of single-degree-of-freedom (sdof) elasto-plastic systems. Through observations on dynamic characteristics, the critical excitation is parameterized in the time domain that allows for its efficient numerical solution. It is found that, in addition to resonance phenomenon that is observed in linear systems, a mechanism called ‘boundary criticality’ is responsible for driving elasto-plastic systems to its target by maximizing the capability of gaining momentum during elastic loading while avoiding opposing plastic deformations.

Study of the Dynamic Strength of Reticulated Domes under Severe Earthquake Loading

The behaviour of selected steel domes subject to severe earthquake loading has been investigated and reported. Particular attention has been given to assess the development and spread of plasticity throughout these structures. Several dome configurations have been considered, both perfect and imperfect, together with a range of varying rise to span ratios. Finite element analysis of these structures has been undertaken to determine the rate of spread of plasticity and the rate of increase in node displacement under seismic loading. The dynamic strength failure acceleration (DSFA) has been defined as the acceleration at which the rate of spread of plasticity and node displacement reaches a runaway level and the structure becomes dynamically unstable. For the dome structures under consideration DSFA occurred at an acceleration of approximately 8 m/s2. In addition, the DSFA decreased by 15%–50% for the imperfect structures when compared with the perfect domes and was lower for the multi-directional seismic input. Also, the DSFA decreased gradually with a corresponding increase in the rise to span ratio.

Experimental Study on Embedded Steel Plate Composite Coupling Beams

A research study has been conducted on a newly proposed design of embedded steel plate composite coupling beams with shear studs in order to improve the performance of reinforced concrete (RC) coupling beams under severe wind or earthquake loading. The experimental results on three coupling beams tested under reversed cyclic loading are discussed in this paper. One of the coupling beams was conventionally reinforced, while each of the other two contained a vertically embedded steel plate along the whole span either with or without shear studs. It was found that embedded steel plates could improve the strength and the stiffness of coupling beams, while shear studs are required to enhance the plate/RC interaction in order to achieve good inelastic performance under large imposed shear deformations. Equations for calculating the required shear connection strength in the beam span to ensure the plate/RC composite action and for estimating the available plate/RC interface slips to mobilize shear studs have been proposed.