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In this paper, an efficient and reliable method is developed for assessing the seismic performance of reinforced concrete (RC) frame structures by using the dynamic concentrated plastic beam–column element. Firstly, the beam–column element considering the dynamic effect caused by strain rate sensitivity of RC materials and the epistemic uncertainties in structural parameters is proposed, in which the mechanical behavior of plastic hinge is described by the damage index-based hysteretic model. Moreover, a simplified approach is employed to consider the strain rate-sensitivity of RC materials. Then the computation procedure for probabilistic seismic analysis of RC frame structures is illustrated based on the proposed element. The change in strain rate at each time step is considered by modifying the hysteretic model, which is further used in updating the matrices in dynamic equations. Finally, the probabilistic seismic response and damage analyses of a shaking table test RC frame structure are performed and the proposed method is validated with the experimental data. Furthermore, the influences of structural uncertainties on the analytical results of maximum drift ratio and collapse probability are discussed. It is indicated that both the dynamic effect and structural uncertainties need to be seriously taken into account for obtaining a more reliable seismic response and collapse assessment of RC frame structures. [ABSTRACT FROM AUTHOR]

This paper studies the impact of half-height infilled walls on the failure modes of frame columns through quasi-static tests of both frame models and half-height infilled wall frame models. Based on the experimental results, a seismic analysis model of reinforced concrete (RC) frame structures is established, and parametric studies are carried out to analyze the effects of masonry materials and masonry heights on the seismic performance of structures. The results show that the load-bearing capacity and stiffness of the structure are improved, while the ductility of the structure is reduced because of the existence of infilled walls. As the height of infilled walls increases, there is a notable decrease in the free height of frame columns. At a wall-to-column height ratio of 0.2, the masonry walls exert a negligible effect on the frame structure's seismic performance. In contrast, at a ratio of 0.6, there is a transition in column failure modes from bending to shearing. When evaluated at consistent masonry heights, aerated concrete block-infilled walls demonstrate the least impact on the seismic performance of RC frame structures. Thus, in the absence of additional structural enhancements, the use of aerated concrete blocks is recommended to mitigate the negative implications of infilled walls on the seismic integrity of RC frames. [ABSTRACT FROM AUTHOR]

The chloride ions in the offshore atmospheric environment will erode the RC frame structure, resulting in the continuous deterioration of material properties, which ultimately reduces the seismic performance of the RC frame structure. In order to study the change rule of seismic damage risk of RC frame structure under offshore atmospheric environment, this paper proposes an improved probabilistic model of rebar corrosion rate and constructs a material performance deterioration model based on the uniform corrosion model of rebar and the change rule of rebar corrosion rate before and after concrete cracking. On this basis, according to the theory of analytical susceptibility analysis, a time-varying susceptibility analysis method is established for RC frame structures in offshore atmospheric environments considering chloride ion erosion, and a typical structure is constructed to analyze the time-varying susceptibility curves under different damage states and evaluate its time-varying susceptibility and damage state. The results of the study show that when the values of the ground vibration intensity index are the same, the seismic susceptibility of the structure in each damage state shows a nonlinear increasing trend in the service age, and the seismic performance is degraded continuously. When the susceptibility index is used as the structural damage index, the RC framed structure designed in accordance with China's specifications is able to satisfy China's three-performance seismic defenses in the 30 years of service age. [ABSTRACT FROM AUTHOR]

This paper studies the impact of half-height infilled walls on the failure modes of frame columns through quasi-static tests of both frame models and half-height infilled wall frame models. Based on the experimental results, a seismic analysis model of reinforced concrete (RC) frame structures is established, and parametric studies are carried out to analyze the effects of masonry materials and masonry heights on the seismic performance of structures. The results show that the load-bearing capacity and stiffness of the structure are improved, while the ductility of the structure is reduced because of the existence of infilled walls. As the height of infilled walls increases, there is a notable decrease in the free height of frame columns. At a wall-to-column height ratio of 0.2, the masonry walls exert a negligible effect on the frame structure’s seismic performance. In contrast, at a ratio of 0.6, there is a transition in column failure modes from bending to shearing. When evaluated at consistent masonry heights, aerated concrete block-infilled walls demonstrate the least impact on the seismic performance of RC frame structures. Thus, in the absence of additional structural enhancements, the use of aerated concrete blocks is recommended to mitigate the negative implications of infilled walls on the seismic integrity of RC frames.

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The Reinforced Concrete (RC) systems are composed of different structural RC members such as beams, columns, shear walls, etc. Damage in RC members is found in the form of cracks, compression failure, reduction in effective area etc. Due to the presence of damages, there is a change in the dynamic behaviour. In the present work, the dynamic behaviour of undamaged and damaged RC multi-storey structures is studied with different damage locations in beams and columns at different stories. The damage is introduced by reducing Young’s modulus of concrete by 25%. The critical damage level is identified by using modal analysis. The damage severity in the columns and beams varied from 25% to 75%. The modal analysis and lateral load analysis are carried out to understand the dynamic behaviour of damaged structures. The Equivalent Static Method (ESM) is considered for earthquake analysis as per IS 1893 (Part −1): 2016. Analysis is done by using ETABS software. The natural frequency and time periods are considered as dynamic parameters. From the results, it has been observed that, there is a change in the natural frequency of the structural system with the introduction of damage of certain severity and at a particular location. [ABSTRACT FROM AUTHOR]

An earthquake of magnitude 6.4 occurred in Yangbi County, Yunnan Province on 21 May 2021, with a focal depth of 8 km, and strong ground motion with vertical components was monitored by Yangbi station (53YBX). A total of 14,122 houses were damaged in Yangbi in the earthquake, and 232 of them collapsed. Vertical components of ground motions have been gained more attention for its effect on structure's seismic response in epicenter or near-fault regions at present. Taking the three earthquake ground motions of Yangbi, Chi-Chi, and Loma Prieta as inputs, and modeling based on Perform-3D, this research carried out the seismic dynamic time history analysis of an RC (reinforced concrete) frame structure and a brick-concrete structure under both horizontal and vertical working conditions. The results showed that vertical components of the three ground motions had no evident impact on the top horizontal displacement and acceleration of the two types of structures. Among the three ground motions, the vertical component of Yangbi ground motion has largely influenced the top vertical displacement, acceleration, and axial force of the frame column bottom (or masonry wall bottom). The vertical component had different amplification effects on the axial pressure and the bending moment of a single column at the bottom of the RC frame structure, thus causing resonance amplification effect of the brick-concrete structure floors and amplifying the vertical acceleration of the top floor. In addition, it considerably increase the maximum axial tensile strain of masonry walls and the possibility of faster tensile failure of the brick-concrete structure. Influence of vertical ground motion on the bearing capacity of RC frame structure's columns and the brick-concrete structure's masonry walls should not be ignored. The results of the research may provide a reference for the earthquake-resistant design of building structures, especially the earthquake-resistant design considering the vertical seismic effect. [ABSTRACT FROM AUTHOR]

The uncertainty in structural mechanical properties, termed inter-building variability, should be considered in regional seismic risk assessments. However, existing methodologies require an enormous amount of computing effort, especially when it comes to nonlinear time-history analysis (NTHA) of urban building clusters. This paper presents a regional-scale stochastic NTHA scheme for RC frame structures, which integrates a multi-degree-of-freedom nonlinear lumped parameter (LP) model with the probability density evolution method (PDEM). The nonlinear LP model adopts an inter-story Bouc–Wen hysteretic model, a smooth one that can avoid convergence issues and thus significantly improve computational robustness. A database containing 674 records of existing RC frame structures is constructed through extensive literature searching and stringent data filtering. On this basis, the inter-building variability of the LP model parameters is statistically analyzed and quantified with a random period function model. The stochastic NTHA is then applied to a building cluster containing 771 RC frames, and the computation result interprets the full-process probability density of the responses and the rationality of the proposed random period function model. In addition, it is observed that neglecting the inter-building variability of the natural period will underestimate the probabilistic seismic damage of the same building class. [ABSTRACT FROM AUTHOR]

Base isolation of buildings is the most efficient way of designing seismically resistant structures. Application of seismic isolators allows mutually independent movements of the ground and the structure during earthquakes. The application of seismic isolators increases the natural period of vibrations, which reduces the seismic forces in the structure. The paper analyzes the influence of the application of lead rubber bearings on the response of the structure to the action of an earthquake. A reinforced concrete frame structure was analyzed both for the case of base isolation and rigid foundation. Based on the comparative analysis of the natural period of vibrations, base shear seismic forces, displacement of the top level of the structure and relative inter-storey drift, conclusions were drawn about the efficiency of application of this type of seismic isolator. The required amount of ductility of a structure, as well as damage to structural and non-structural elements, is greatly reduced by base isolation.

Seismic risk assessment of new and existing structures has a long history, which is based on the development of specific methods for seismic hazard and vulnerability analyses. Performance‐based earthquake engineering is the natural evolution and integration of all these aspects that is nowadays implemented in several precodes. However, some critical aspects are not yet completely clarified. As a matter of fact, the vulnerability analysis suffers the so‐called record‐to‐record variability, which is usually controlled through different parameters used as seismic intensity measures (IMs), whose significance is still under discussion. Moreover, this variability represents an additional source of uncertainty, which is added to the dispersion derived from the ground motion prediction equation (GMPE), leading to an overconservatism. For these reasons, the present paper aims to propose a novel framework for the seismic risk assessment of structures, which is found on the idea to control the response variability in evaluating seismic hazard curves without taking into account the randomness (ε) of the GMPE, which instead is transferred to fragility curves. These latter are built by using groups of accelerograms, whose median and 84% fractile spectra fit well, for different return periods, the uniform hazard spectra for ε= 0 and 1, respectively. For this purpose, a new search algorithm for selecting natural records is formulated. The proposed method offers considerable advantages as it is no longer necessary to refer to a specific IM, and allows to select pairs of spectrum‐compatible natural records, which is enable to solve the problem of the seismic assessment of three‐dimensional structures. The procedure is then applied to assess seismic risk of a typical reinforced concrete frame, whose results demonstrate the robustness of the method and the practical independence from the record set used. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The results of an experimental study of four infilled frames with brick masonry walls subject to reversal cyclic lateral load are presented. The variables studied were the height to length aspect ratio of the wall and the use of joint reinforcement. The investigation was motivated by the fact that the Mexican code establishes the same specifications about the use of joint reinforcement for infill walls as for confined walls, because there is not enough experimental evidence on joint reinforced infill walls. To investigate the possible interaction of the study variables in the seismic performance of the walls, two pairs of specimens, scaled 1:2, with different aspect ratios (H/L = 0.75, 0.41) were tested. The specimens in each pair were identical except that one of them included steel bars into the bed-joints as reinforcement leading to amount   p h f y h = 0.6   MPa . The infill walls with H/L = 0.41 were included from a previous study. The behavior of the specimens was defined in terms of lateral strength, ductility, displacement capacity, deformation of the joint reinforcement and crack pattern. The results indicate that joint reinforcement increases the strength of the system; however, the increase was more pronounced in longer walls. Ductility was reduced with horizontal reinforcement and this behavior was more important for longer walls. As occurred in confined walls, the joint reinforcement generates a more distributed cracking and reduces the width of the cracks. The experiments are described and this and other results are discussed in detail. [ABSTRACT FROM AUTHOR]

Based on the first-order second-moment method, a comparative study on seismic fragility analysis with consideration of modeling uncertainty is carried out for a 12-story reinforced concrete frame structure under excitation with far-field and pulse-like near-field ground motions by using the multiple stripes analysis method. The sensitivity of the median fragility capacity of the building to fourteen parameters in the cases of three limit states (i.e., immediate occupancy, life safety, and collapse prevention) is analysed, and the effect of the selection of ground motion intensity measures on the determination of modeling uncertainty is investigated. Finally, the annual probabilities of exceeding each limit state with different confidence levels are calculated, and two methods, the mean estimates approach and the confidence interval method, are used to incorporate uncertainties. The results show that the characteristics of ground motions affect the sensitivity of the median capacity to the disturbance of structural parameters. The modeling uncertainty estimated in the near-field records is meaningfully less than that in the far-field records. Judging from this limited case study, the modeling uncertainty estimated may be underestimated by using an inefficient IM. The influence of the modeling uncertainty in the fragility analysis for each limit state cannot be ignored when using the confidence interval method. [ABSTRACT FROM AUTHOR]

An earthquake of magnitude 6.4 occurred in Yangbi County, Yunnan Province on 21 May 2021, with a focal depth of 8 km, and strong ground motion with vertical components was monitored by Yangbi station (53YBX). A total of 14,122 houses were damaged in Yangbi in the earthquake, and 232 of them collapsed. Vertical components of ground motions have been gained more attention for its effect on structure’s seismic response in epicenter or near-fault regions at present. Taking the three earthquake ground motions of Yangbi, Chi-Chi, and Loma Prieta as inputs, and modeling based on Perform-3D, this research carried out the seismic dynamic time history analysis of an RC (reinforced concrete) frame structure and a brick-concrete structure under both horizontal and vertical working conditions. The results showed that vertical components of the three ground motions had no evident impact on the top horizontal displacement and acceleration of the two types of structures. Among the three ground motions, the vertical component of Yangbi ground motion has largely influenced the top vertical displacement, acceleration, and axial force of the frame column bottom (or masonry wall bottom). The vertical component had different amplification effects on the axial pressure and the bending moment of a single column at the bottom of the RC frame structure, thus causing resonance amplification effect of the brick-concrete structure floors and amplifying the vertical acceleration of the top floor. In addition, it considerably increase the maximum axial tensile strain of masonry walls and the possibility of faster tensile failure of the brick-concrete structure. Influence of vertical ground motion on the bearing capacity of RC frame structure’s columns and the brick-concrete structure’s masonry walls should not be ignored. The results of the research may provide a reference for the earthquake-resistant design of building structures, especially the earthquake-resistant design considering the vertical seismic effect.

Summary: Resilience‐based seismic design of buildings using seismic isolation has become a critical issue. Currently, there are two design codes for isolated structures in China, exhibiting significant differences. It is critical to investigate the resilience‐based design of isolated buildings using these codes. Hence, using reinforced concrete (RC) frame buildings as an example, two groups of buildings with different heights were designed to achieve the lower limit of seismic performance given in two codes. Although different requirements for acceptable isolation efficiency control this design, the seismic resilience levels were assessed to be Level 2 for all cases. The controlling index is the total repair time, which is dominated by the maximum inter‐story drift ratio (MIDR). Meanwhile, significant differences in design results and resilience performance between two codes were identified. Subsequently, the highest resilience performance (i.e., Level 3) oriented optimization was conducted, and the correspondingly designed schemes using two codes were compared; it was identified that the MIDR of the superstructure requires controlling to approximately 0.23% for such a design using both codes, and the differences between two codes became negligible. The research outcome will assist in providing a useful reference for the seismic‐resilient design of base‐isolated RC frame structures. [ABSTRACT FROM AUTHOR]

Buckling restrained braces (BRBs) are a somewhat ongoing improvement in the field of seismic-safe steel structures. Their unmistakable component is the non-clasping conduct regularly accomplished by encasing a steel center in a substantially filled cylinder. However, choices have been proposed. Controlling the support from clasping improves malleability essentially and permits symmetric reaction under pressure or pressure powers. The plan of BRB outlines should consider various explicit issues that are not covered by Indian norms and guidelines. This specific task looks at utilizing BRB inside fortifying of built-up substantial casing developments to meet seismic details dependent on the Indian seismic plan and style code. Flexible reaction range examination just as nonlinear period verifiable past assessment is finished by taking a real designing model which experiences feeble first-floor inconsistency because of extra expansion and heaps of only one story. With all the way to deal with comparable solidness just as removal-based plan technique, clasping limited support factors are reasoned and accordingly are familiar with model BRB in ETABS using plastic wen form. 3 arrangements of clasping limited sections are breaking down alongside normal supports. The relationship in the middle of the fundamental cross piece of customary supports and BRB is concluded because of the definition of computing versatile bearing ability precisely where it’s shown that the spot of the run of the mill supports must be 1.25 events that of BRB for guaranteeing the very same by and large execution. The outcome uncovers that Inverted V support design shown much better usefulness over single support just as V support setups just as X support arrangement, however not exhorted by Indian code, is mimicked just as applied to this undertaking and contains exhibited preferred execution moreover some different arrangements. The extra exploration about the practical use of this support is generally suggested. Moreover, under the movement of significant seismic tremors, by nonlinear time chronicled past assessment, clasping controlled supports showed much better usefulness of reinforcing the construction just as success runs over the need for code. Under this specific condition, conventional supports misfortunes their bearing limit because of unnecessary buckling.

Structures composed of different substructures and materials are a subject of great research and expert interest. It is the purpose of this research to develop an engineering approach for evaluation of seismic demands and to apply the methodology to reinforced concrete frames with or without masonry infill. This paper deals with combination of reinforced concrete frame and masonry infill wall. It is known that the combined structure resists well to severe earthquakes. In this paper, the influence of masonry infill on the seismic demands of a reinforced concrete frame structure is estimated using nonlinear analysis. A strut model was used to model the masonry infill resistance; the strut model is statically equivalent to the masonry infill wall. Therefore, material properties of the strut element are determined based on material properties of continuous masonry wall and geometry data. The seismic analysis is performed including material nonlinearity of the model. Determination of seismic displacement demands is carried out using an approximate procedure of the nonlinear analysis in N2- method. To make evaluation of masonry contribution two varieties of the models have been studied - 'with masonry infill' and 'without masonry infill'.

Copyright of Journal of Zhengzhou University: Engineering Science is the property of Editorial Office of Journal of Zhengzhou University: Engineering Science and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The effect of pulse characteristic of near-fault ground motions on multistory reinforced concrete frame structures is investigated by means of a synthetic broadband ground motion model (SBGM). A simplified analytical pulse model is used to describe the low-frequency components of ground motions, while a stochastic simulation method based on wavelet packet is adopted to simulate the high-frequency components of ground motions. First, the time histories, response spectrum, and structural response of synthetic ground motions are compared with those corresponding to recorded near-fault ground motions. The good agreement indicates that the SBGM model used in this article is a suitable and efficient tool for evaluating the structural response. Sensitivity analysis on structural response of 2-, 4-, 8-, and 12-story building models to the SBGM model input parameters is then performed to identify the key ground-motion parameters which control the main structural response indicators, that is, interstory drift ratio and maximum interstory drift ratio. Final results indicate that the amplitude of velocity pulse in the SBGM model has a significant influence on structural drift demands. Nevertheless, for low-rise buildings, the maximum drift demands would effectively decrease with increasing proportion of high-frequency components. Moreover, the ratio of pulse period to structural fundamental period and number of oscillations impose a large drift demands to the structure under near-fault pulse-like ground motions. [ABSTRACT FROM AUTHOR]

To research the seismic damage characteristics, mechanism and vulnerability of multistorey reinforced concrete (RC) frame structures, statistics and analysis, were made on 930 RC frame structures in Dujiangyan during Wenchuan earthquake, China. Firstly, seismic damage of RC frame structure in Dujiangyan is investigated comprehensively. According to the investigation results, easily damaged locations of this kind of structural system are: infilled wall, frame column, beam-column, joints and stairs. However, a large number of RC frame structures are basically intact or slightly damaged. By using the method of numerical statistical analysis, the non-linear relationship model and the fitting curve of seismic damage investigation samples under multiple seismic damage grades are given. Considering the number of stories, multiple ages and seismic fortification influencing factors, the empirical seismic damage situation of structures under each factor is analyzed, and the non-linear regression curve is developed. The empirical seismic vulnerability matrix and continuous regression function model and curve of RC frame structure in multi-intensity region are established. A calculation model of mean seismic damage index (MSDI) is proposed, and the vulnerability matrix and regression curve based on this parameter are given in combination with the empirical seismic damage investigation data. The above research results can provide a basic reference for vulnerability analysis and intensity scale revision of RC structures. [ABSTRACT FROM AUTHOR]

The results of an experimental study of four infilled frames with brick masonry walls subject to reversal cyclic lateral load are presented. The variables studied were the height to length aspect ratio of the wall and the use of joint reinforcement. The investigation was motivated by the fact that the Mexican code establishes the same specifications about the use of joint reinforcement for infill walls as for confined walls, because there is not enough experimental evidence on joint reinforced infill walls. To investigate the possible interaction of the study variables in the seismic performance of the walls, two pairs of specimens, scaled 1:2, with different aspect ratios (H/L = 0.75, 0.41) were tested. The specimens in each pair were identical except that one of them included steel bars into the bed-joints as reinforcement leading to amount phfyh=0.6 MPa. The infill walls with H/L = 0.41 were included from a previous study. The behavior of the specimens was defined in terms of lateral strength, ductility, displacement capacity, deformation of the joint reinforcement and crack pattern. The results indicate that joint reinforcement increases the strength of the system; however, the increase was more pronounced in longer walls. Ductility was reduced with horizontal reinforcement and this behavior was more important for longer walls. As occurred in confined walls, the joint reinforcement generates a more distributed cracking and reduces the width of the cracks. The experiments are described and this and other results are discussed in detail.

Copyright of Journal of Dalian University of Technology / Dalian Ligong Daxue Xuebao is the property of Journal of Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of South China University of Technology (Natural Science Edition) is the property of South China University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A strong earthquake commonly triggers the occurrence of multiple aftershocks. Since the time interval between mainshock and aftershock is very short, the mainshock-damaged structure cannot be repaired in time and could suffer further damage during aftershocks. A five-story RC frame structure was designed according to the current codes is used as a case study. The cumulative damages of structures subjected to earthquake sequences and the aftershock-induced incremental damages were investigated. A suite of 75 actual mainshock-aftershock sequences was formulated as earthquake inputs. Concurrently，the actual mainshock records were used as seeds to generate two sets of artificial mainshock-aftershock sequences using repeated method and randomized method. The modified Park-Ang damage index was used as the measures of structural damages caused by the actual and artificial mainshock-aftershock sequences. The aftershock-induced incremental damage in terms of the modified Park-Ang damage index was also assessed. The intensity measures of peak ground acceleration, spectral acceleration and Arias intensity, were further used as the indicators of mainshock and aftershock intensities. Then the correlation between the aftershock-tomainshock intensity ratio ami the aftershock-induced incremental damages was investigated. The results show that the artificial mainshock-aftershock sequences using the randomized method can cause the most significant incremental damages in comparison with the actual ones and those generated by the repeated method. The aftershock-to-mainshock intensity ratio can predict the significance of the aftershock-induced incremental damage with considerable confidence. [ABSTRACT FROM AUTHOR]

Summary: To investigate the behavior of a reinforced concrete (RC) frame structure across earth fissure under strong earthquake, a series of shaking table tests on a scaled model were designed and conducted. Three earthquake motion records were selected as input excitations, and the Jiangyou motion has a dramatically greater dynamic effect on the structure mainly due to its inherent rich low‐frequency component. The structural acceleration amplification factor gradually decreased as the peak ground acceleration of input motions increased, implying the progressive degradation of the structure stiffness. The results indicated that the earth fissure site has amplification effect on acceleration of the soil, and the displacement response of frame across the earth fissure was different to that of a typical RC frame structure. The ground floor was the most vulnerable story of the RC frame across the earth fissure. [ABSTRACT FROM AUTHOR]

A nonlinear damage model based on the combination of deformation and hysteretic energy and its validation with experiments are presented. Also, a combination parameter is defined to consider the mutual effect of deformation and hysteretic energy for different types of components in different loading stages. Four reinforced concrete (RC) columns are simulated and analyzed using the nonlinear damage model. The results indicate that the damage evolution evaluated by the model agrees well with the experimental phenomenon. Furthermore, the seismic damage evolution of a six-story RC frame was analyzed, revealing four typical failure modes according to the interstory drift distribution of the structure; the damage values calculated using the nonlinear damage model agree well with the four typical failure modes. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of strain rate effect on the seismic performance of Reinforced concrete (RC) frame structures subjected to far-field and near-field ground motions. An approach for the nonlinear dynamic analysis of RC frame structures considering the strain-rate sensitivity of concrete and reinforcing steel materials is proposed and its effectiveness is validated by the experimental data of RC columns under dynamic loadings. A non-dimensional index is put forward to reveal the regularities of strain rate under different types of ground motions with various intensity levels. The influences of strain rate effect and input ground motion on the seismic performance of the exemplar RC frame are studied by comparing the seismic responses and fragilities of rate-dependent structural models with those of rate-independent ones. Numerical results indicate that the strain rates in structural members increase with the ground motion intensity and the strain rates induced by the near-field pulse-like earthquakes are higher than those by the far-field and near-field non-pulse-like earthquakes. The global response, critical member response, local damage and seismic fragility are all influenced by the strain rate effect, especially under the near-field pulse-like ground motions. Neglecting the influences of strain rate effect, variations in strain rates of different structural members and inputs of pulse-like ground motions may lead to erroneous seismic performance assessments of RC frame structures. [ABSTRACT FROM AUTHOR]

The latest edition of national building standard collective drawings 16G101-2 increased a new type of cast-in-place concrete sliding bearing staircase with upper-end slab, which supported at the cantilever slab. In order to test the seismic performance of this new type of sliding bearing staircase and the reliability of its upper-end slab and lower-end supporting cantilever slab, a 1/2 scaled RC frame model with this new type of staircase was designed, constructed and tested under quasi-static loading. The seismic response of the specimen at cracking state, yield state, peak load state and failure state were analyzed to study the failure mechanism of the sliding bearing staircase structure and determine if the bottom support will slide effectively. Experimental results show that sliding bearing stair with upper-end slabs and lower-end cantilever slab has good seismic performance. The boards of the ladder (including the staircase and upper-end slabs) do not resist lateral force and cracks do not occur before the failure of frame beams and columns. After loading into the failure state, upper-end slab and lower-end supporting cantilever slab has no obvious damage. The design of construction practice can satisfy the seismic requirements. The sliding bearing has good seismic effect. Horizontal sliding occurs on the bottom board of the ladder with vertical tilt phenomenon. [ABSTRACT FROM AUTHOR]

Numerical approach using finite element method has been used to evaluate the behaviour of reinforced concrete frame structure subjected to fire. The structure is previously designed in accordance with Eurocode standards for the design of structures for earthquake resistance, for the ductility class M. Thermal and structural response are obtained using a commercially available software ANSYS. Temperature-dependent nonlinear thermal and mechanical properties are adopted according to Eurocode standards, with the application of constitutive model for the triaxial behaviour of concrete with a smeared crack approach. Discrete modelling of concrete and reinforcement has enabled monitoring of the behaviour at a global, as well as at a local level, providing information on the level of damage occurring during fire. Critical regions in frame structures are identified and assessed, based on temperatures, displacements, variations of internal forces magnitudes and achieved plastic deformations of main reinforcement bars. Parametric analyses are conducted for different fire scenarios and different types of concrete aggregate to determine their effect on global deformations of frame structures. According to analyses results, the threedimensional finite element model can be used to evaluate the insulation and mechanical resistance criteria of reinforced concrete frame structures subjected to nominal fire curves. [ABSTRACT FROM AUTHOR]

The influence of velocity pulse characteristics of near-fault ground motions on the seismic response of base-isolated structures was investigated in this paper. The analysis models of traditional seismic frame structures and corresponding base-isolated structures with different height-to-width ratios were established by using finite element software. Six ground motion records with forward directivity velocity pulse and fling step velocity pulse were selected as the seismic input at foundation of structures, and eight structures were analyzed by nonlinear dynamic time-history analysis. The comparative analysis is carried out on parameters of the structure responses such as the inter-story drifts, bearing displacement and base shear force. Under the velocity pulse-like ground motions, the inter-story drifts and the base shear of base-isolated structures gradually increase when the height-to-width ratio increases but the displacements tend to increase first and then decrease, and the displacement of isolation layer increases with the ratio of peak velocity to peak acceleration of the input ground motions. The base-isolated structures with the height-to-width ratio less than 3 have better vibration reduction capacity under velocity pulse-like ground motions. The smaller the height-to-width, the better the vibration reducing effect, and conversely, the seismic capacity of base-isolated structures is poor if the height-to-width ratio of the structure is 4.The adverse effect of velocity pulse of near-fault ground motion on the response of lower part of the base-isolated structure may even lead to collapse damage on the structure. [ABSTRACT FROM AUTHOR]

A specimen constructed at one-five scale, whose prototype structure is a RC frame destroyed seriously at the first floor under Yushu earthquake, is used to research the complete process of the typical lateral increment collapse modes like domino and failure mechanism of RC frame structures located at high seismic intensity region induced by Wenchuan and Yushu earthquakes. Through the shaking table test, the experimental findings indicate that the complete collapse process can be divided into two parts, that is, horizontal increment collapse and vertically progressive collapse. The specimen is in a boundary collapse state when the inter-story drift at the first floor reaches 1/19. In process of collapse, the corner column named C3 loses its vertical load carrying capacity at first where the progressively vertical collapse begins to occur. The lateral displacements of columns at the first floor are constantly increased under the combination of gravity load and ground motion, causing columns named B2, B3 and C2 next to C1 to fail subsequently. After these, the damaged specimen has a deficient redundancy, and thus a wide range of vertical collapse occurs which finally results in laterally progressive story-by-story collapse. Through the investigation of collapsed ruins, the damaged state of "strong beam weak column" for the specimen is in accordance with the earthquake damage investigation results. In the end, the living space for people to survive is discussed, and the suggestions to resist this typical collapse are also recommended. [ABSTRACT FROM AUTHOR]

• Shaking table tests of a scaled three-story indoor substation were conducted. • Two different isolation techniques were applied and corresponding isolation effect were discussed. • Influence of the far-field earthquake and near-fault earthquake was investigated. • Scaled electrical equipment was also prepared and the influence of the equipment-structure interaction were discussed. In order to investigate the seismic performance of indoor RC substations with combined base isolation technique under far-field earthquakes and near-fault earthquakes, a 1/4 scaled three-story RC frame model was prepared for shaking table tests. Three different model configurations were considered, namely the non-isolated model (control model), the mono-isolated model (model with lead rubber bearings), and the combined isolated model (model with lead rubber bearings and viscous dampers). Scaled transformers and GISs were also installed on the model floors to consider the influence of the electrical equipment. Typical far field and near fault seismic waves, in this study the El Centro wave and the ChiChi wave, respectively, up to a PGA of 0.44 g were used as excitations. It was found that LRBs worked desirably for the RC model under the El Centro wave while less effective under the ChiChi wave. The acceleration responses (roof), the inter-story shear force (1F) and the inter-story drift (2F) were reduced by use of the LRBs at most by 21%, 51% and 26%, respectively, with respect to the non-isolated model under the El Centro wave. However, under the ChiChi wave irregular torsional behavior was observed and the isolation layer displacement reached 88% of the limit value. Combined use of LRBs and VDs effectively reduced the seismic responses of the RC model under the ChiChi wave. In particular, the isolation layer displacement was reduced by 15% and the torsional displacement ratio was reduced to less than 1.15, with respect to the model with LRBs only. Considerable equipment-structure interaction was found in the RC indoor substations and increased the acceleration and the displacement responses by up to 21% and 22%, respectively, given the position and mass of the equipment in this study. Besides, the LRBs and VDs were found to be effective to reduce the equipment-structure interaction. [ABSTRACT FROM AUTHOR]

Consecutive strong motion excitations have high damage capacity and they were found to cause the massive collapse of large amount of building structures in 2008 Wenchuan earthquake. To investigate the seismic behavior of the RC frame under consecutive strong earthquake excitations, the scaled model of a 12-story RC frame was built with a scaling ratio of 1/10. Three series of shaking table tests were performed using four selected ground motions. The results show that the sensitivity of the RC frame to the same input motions reduces in the 2nd and 3rd series of tests, and the structural responses are almost the same. However, the responses increase faster once using different series of input motions. Based on these observations, a new concept namely the seismic toughness was defined and the corresponding conceptual calculation method was provided. The relevant fundamental mechanism such as the ductility and damage, and the main research tasks, application method were conceptually elaborated. It is suggested to conduct related analytical and experimental studies so that the seismic performance especially the collapse prevention capacity of the structures can be improved under the consecutive strong earthquake excitations. [ABSTRACT FROM AUTHOR]

The bond failure between steel bars and concrete under the catenary action was studied, whether steel bars or bond is the earliest failure was investigated in the progressive collapse process of RC frame structures. The effects of changing anchorage length and the arrangement of reinforcement on the bond-anchorage performance were also studied. The steel bars were anchored in reinforced concrete column, and the steel bars formed the mechanical mechanism of catenary which occurred when the end of beam in RC frame structure was damaged but the steel bars was not broken. The process of adding load to the steel bars was achieved by the self-balancing reaction frame. The test results show that the splitting failure of bond has been seen, while the stress of steel bars doesn’t reach the ultimate tensile strength. It is suggested that according to the experimental results, the direct-anchorage form should not be used in the collapse-resistant design of RC frame structures, and other more effective anchorage form should be adopted in the future. It trends to improve the average bond stress under the single row reinforcement arrangement. Compared with the average bond stress under the double reinforcement arrangement, the average bond stress can be increased by 15%. [ABSTRACT FROM AUTHOR]

The effects of catenary action on reinforced concrete (RC) frame structures to resist progressive collapse were investigated. An OpenSees-based macro-model considering the catenary action was developed. The macro-model was validated by comparing the simulated results with the test results of two RC beam-column substructures，which were subjected to the loss of a middle column scenario. Moreover, the effects of catenary action on the response of a ten-story RC frame structure to resist progressive coLapse were examined by both nonlinear static and nonlinear dynamic analyses from the alternative path method. The results show that if ignoring the catenary action, the progressive collapse capacity of RC frame structures will be underestimated. When the catenary action is not considered，the calculated maximum load increase factor for the frame subjected to the loss of the middle column of the first story is less than 2. 0，while it is beyond 2. 0 with considering the catenary action. [ABSTRACT FROM AUTHOR]

A random Pushdown method, which combined the deterministic pushdown analysis with the correlationreduced Latin hypercube sampling (LHS) method, was proposed to evaluate the effects of structural uncertainties on resisting capacity of reinforced concrete (R C) frames to mitigate progressive collapse. To illustrate the development and application of the proposed method, an 8-story and 4-bay RC frame structure was used as a case. A total of 17 structural uncertain parameters covering the types of loading, material strength，and structural geometric dimension， were taken as random variables. The peak vertical load of Pushdown analysis was defined as the structural capacity to resist progressive collapse. The probabilistic results，namely，progressive collapse fragility function，were obtained by statistical analysis. The sensitivities of the uncertain parameters under consideration were illustrated by the tornado diagram method. The results indicate that the influences of structural uncertainties on resisting capacity of the structure to resist progressive collapse are significant. The coefficient of variation of the structural capacity to resist progressive collapse could be up to 20%. Among these uncertain parameters, live load, dead load on the floor, ultimate stress of the steel and the reinforcement areas of the beam are the dominantly significant ones. [ABSTRACT FROM AUTHOR]

To improve the resilience performance of precast concrete frame structure, a novel self-centering prefabricated concrete beam-column joint with controllable plastic hinge (PJ-CPH) is proposed in this manuscript. Controllable plastic hinge is an innovative connection configuration composed by pin shaft, rotational friction damper and disc spring self-centering devices. The rotational friction damper is used for withstanding bending moment and dissipating seismic energy. The disc spring self-centering device is used for withstanding bending moment and providing restoring force, while the pin shaft is merely used for withstanding shear force. A detailed design procedure was presented by introducing self-centering ratio α and moment amplification factor β. A flag-shaped hysteretic model of PJ-CPH was proposed, simultaneously, a numerical model was developed based on the OpenSees computational platforms. The numerical simulation analysis was carried out for four PJ-CPH models with different parameters and one cast-in-situ beam-column joint model under low cyclic loading. Analysis results indicate that the hysteretic curve obtained by theoretical calculation are in good agreement with the numerical simulation results. Consequently, the effectiveness of the established hysteretic model was verified. Compared with the cast-in-situ beam-column joint, PJ-CPH achieves the damage-free connection and exhibits the superior resilience performance. The simulation results suggest that self-centering ratio α values should be assumed approximately in the range 1.00–1.30, moment amplification factor β values in 1.30–1.40, which can induce damage to concentrate in controllable plastic hinge, protect the main structure from damage and reduce repair costs. • A design procedure of PJ-CPH is proposed. • A hysteretic model of PJ-CPH is presented. • A numerical model of PJ-CPH is developed. [ABSTRACT FROM AUTHOR]

• Methods to define the sub-structure range and its boundary conditions are proposed. • A damage index for damage assessment of RC frame structure subjected to blast loads is defined based on energy conservation and could be derived through progressive collapse analysis of RC frames under close-in explosions. • The substructure-based method for damage assessment of RC frame structure is proposed and proved to be accurate, reliable and more efficient as compared to conventional method. Few studies are available in the literature on damage assessment of frame structures under blast loads although local damage of the structural components and even progressive collapse of building structures have been observed in terrorist or accidental explosions. In this paper, considering the initial damage of adjacent structural components under blast loading, a substructure based method for damage assessment of RC frame structures is proposed, including the proposal of the damage criterion, the principles for substructures selection and the calculation of the boundary conditions of the substructures. The accuracy and reliability of the proposed method are verified by comparing the results for damage assessment of a typical 5-story frame structure under different blast scenarios with the conventional method and the proposed method. The results indicated that the proposed method could rapidly and accurately predict the damage levels of the RC frame structure under a given blast load, especially when the building structures are damaged under close-in explosion. [ABSTRACT FROM AUTHOR]

Performance margin ratio (PMR) was presented to assess structural performance under earthquake. The PMR was calculated by the ratio of the median of fragility function to the earthquake intensities corresponding to frequent earthquake (FE), design based earthquake (DBE) and rare earthquake (RE). Four kinds of 5-stoiy and 4-bay RC plane frames were selected as study cases, which were designed for different seismic fortification levels. Then the PMRs of the reference structures were calculated by fragility analysis. The results show that increasing seismic fortification levels leads to the increase of both fragility medians and the seismic actions with respect to FE, DBE and RE. Nevertheless, the resultant increment of fragility medians is less than that of seismic actions, thus a decreasing trend of PMR is found according to the increased seismic fortification levels. Under DBE and RE, the structures show sufficient performance margins to satisfy the performance requirements of 4 no unrepairable damages under DBE' and 'no collapse under RE', respectively. The increase of seismic fortification level may probably cause the structure cannot satisfy the performance requirement of 'no damage under FE'. [ABSTRACT FROM AUTHOR]

In this paper, a nine-story reinforced concrete frame structure was adopted as example, and modeled by using a program named SAP2000. A series of ground motions were selected, and further scaled to the levels corresponding to frequent and rare earthquakes so that the seismic response of the frame structure could be simulated reasonably. After that, buckling restrained braces and viscous dampers were added respectively to the frame. The parameter of dampers were trial calculated until displacement reduction ratios were controlled at around 40% for frequent earthquake. In this way, the seismic responses, including inter-story drift ratio, floor acceleration, base shear, axial compression force of frame columns, distribution of plastic hinges and damper performance were compared. It is concluded that under frequent earthquakes, buckling restrained braces amplify floor acceleration, whereas viscous dampers can effectively reduce floor acceleration. Both buckling restrained braces and viscous dampers can effectively reduce floor acceleration under rare earthquakes, while buckling restrained braces are more effective in reducing displacement, but less powerful in controlling column axial force. [ABSTRACT FROM AUTHOR]

A modified seismic fragility analysis method was presented to examine the effect of collapse probability on non-collapse limit states. This method, based on the total-probability theory, divided structural limit states into two categories as collapse limit states and non-collapse limit states. When the structure occurring collapse, the exceeding probability of non-collapse limit states were taken as 100%. Both a direct method and an indirect method were included in the presented method, where the direct one modified the parameters of fragility functions directly, while the indirect one only modified probabilistic seismic demand parameters. Four reinforced concrete frame structures designed for different heights and different earthquake fortification levels were taken as the study cases. A suite of 100 real ground motion records were selected as the earthquake inputs, and the modified seismic fragility analysis using the direct method and the indirect method was conducted. The results show that the collapse probability has ignorable effect on the limit states of slight damage and moderate damage, where it has a significant effect on the limit state of server damage. The two methods for modifying seismic fragility values result in similar results under small earthquake intensities. With increasing earthquake intensities, the seismic fragility values modified by different strategies are becoming significantly different. [ABSTRACT FROM AUTHOR]

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This study explores the collapse process of a reinforced concrete (RC) frame structure subjected to earthquake shakings, by applying the shaking table test on a three-story, one-bay, 1/5-scaled RC structural model. The frame specimen transformed from an elastic state to a highly nonlinear state, then experienced dynamic instability, and finally collapsed to the ground. The structural responses that have been monitored in the presented test include the specimen’s dynamic properties, displacements, and accelerations. The data collected from this benchmark test program can be used for the verification of existing analytical and numerical simulation methods, especially for cases involving the large displacement and rotation or collapse process simulation of RC frame structures. It is observed from the test that: (1) the frame survived when the maximum story drift ratio and the residual drift ratio reached 12.51% and 9.60% respectively, indicating that the RC frame structure may have a much high ductility capacity; (2) the collapse of the 1 st , 2 nd , and 3 rd stories was due to failure of the plastic hinges at columns; and (3) during the collapse process, the collisions and the damage-induced local oscillation can generate very large horizontal and vertical acceleration responses. More specifically, the collapse of the 1 st story was the result of the failure of plastic hinges, caused by seismic excitation, while collapse of the 2 nd and 3 rd stories resulted from the combined results of plastic hinge failures and punching shear failures in the slab due to impact effects. [ABSTRACT FROM AUTHOR]

Calculating the joint core shear force accurately is an important basis for the shear design of the joint core. Different design formulas for calculating the horizontal shear force of the joint core are proposed by the GB 50010-- 2010 'Code for design of concrete structures ' and GB 50011一2010 ' Code for seismic design of buildings'. According to the basic mechanical equilibrium condition, this paper discusses the available design formulas in both design codes, and the recommendation for improving these design formulas is also given. It is found that the GB 50010--2010 suggests that the joints at different positions should be designed using different equations. However, the formula for the top-story joint provided in the GB 50010--2010 cannot consider the contribution of the single-sided column-end shear force to the horizontal shear force of the joint core, while the formula provided by GB 50011--2010 can consider this contribution. Both the formulas in the GB 50010--2010 and the GB 50011--2010 use the assumption that the summation of the beam-end flexural moments equals the summation of the column-end flexural moments，and therefore they are suitable for the case that the joint core dimension is much smaller than the beam span length or the column height. The proposed formula in this paper can consider the contribution of the single-sided column-end shear force to the horizontal shear force of the joint core, and has broader applicability. [ABSTRACT FROM AUTHOR]

The design method directly based on the internal force under rare earthquake by using equivalent linearization method was studied to realize the design of RC frame structure. First, this paper summarizes existing equivalent linearization methods. Then, through comparing the linear response of the reinforced concrete frame structures obtained by equivalent linearization method with the nonlinear response obtained by nonlinear time history analysis，the effectiveness of different equivalent linearization methods was verified，and the value of equivalent linearization parameters was proposed. Finally, RC frame structures with different heights were designed using equivalent linearization method in accordance with the Chinese seismic code. The nonlinear dynamic time history analysis was performed to investigate the effectiveness of the proposed method in achieving the expected earthquake failure mode. The result indicates that the structural response under rare earthquake could be better simulated by the secand stiffness method in which stiffness reduction and additional damping ratio are considered at the same time. It is a better way to guide the RC frame structure to the preset failure mode using the internal force under rare earthquake obtained by equivalent linearization method. [ABSTRACT FROM AUTHOR]

Most reinforced concrete(RC)frame structures did not achieve the 'strong column-weak beam' failure mode in recent big earthquakes, resulting in a large number of casualties and significant property loss. To deal with this serious problem, a new column-beam relative factor was proposed to characterize the relative yield situation of column ends and beam ends. By limiting the column-beam relative factor, RC frame structures could achieve the 'strong column-weak beam' failure mode under the excitation of strong ground motions. The limit values of column- beam relative factor were calculated, analyzed and verified by using structural simulation models for corner columns in the bottom story of structures, which are destroyed most seriously in earthquakes. The results show that the limit values should be analyzed under bi-directional ground motion and with different axial compression ratios of columns. The peak ground acceleration(PGA)of ground motions has no significant effect on the limit values, while the type of strong ground motions has a significant effect on the limit values. [ABSTRACT FROM AUTHOR]