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From a tectonic perspective, Türkiye is a geographical region known for its high seismic activity, with some of the most active faults in the world. On February 6, 2023, two consecutive earthquakes with magnitudes of Mw 7.7 and Mw 7.6 struck Kahramanmaraş within a remarkably short time span of 9 h. This event stands out as a rare and unprecedented tectonic occurrence in terms of seismicity and tectonic activity over the past 100 years. The impact of these two major earthquakes on the region's reinforced concrete structures was significant, resulting in severe damage and the collapse of numerous buildings. It is of utmost importance to investigate and examine the design flaws and underlying factors that contributed to the damage observed in the reinforced concrete structures affected by these earthquakes. Such research will not only contribute to the improvement of structural design, seismic regulations, and quality control measures during construction but also enhance our understanding of earthquake engineering. In this study, an in-depth field investigation was conducted on reinforced concrete structures in Hatay, one of the regions most affected by the Kahramanmaraş earthquakes. The damages occurring in the buildings were documented through a detailed field survey and analyzed. A total of 540 reinforced concrete structures in the Hatay region were extensively examined, and the damages that occurred in these structures were photographed and interpreted to understand their underlying causes. Subsequently, based on the findings from the field investigation, a structural model was designed that incorporated the most significant design and construction errors responsible for the damages observed in the 540 examined structures. The devised model was subjected to static push-over analysis and nonlinear dynamic analysis using the SAP2000 finite element software, and the results obtained were interpreted. [ABSTRACT FROM AUTHOR]

Concrete is a widely used building material known for its cost-effectiveness and high resistance compared to alternative materials. However, uncertainties in the casting process due to variations in the environment and human error can compromise its strength, increasing the risk of collapse when subjected to seismic excitations. Previous studies have demonstrated the detrimental effects of earthquake vibrations on buildings and infrastructure. This study aims to fill the research gap by investigating the seismic behavior of reinforced concrete (RC) structures constructed with lower-quality concrete under near-fault pulse-like ground motions. The main objective of this research is to assess the impact of diminished concrete strength on structural rigidity and susceptibility to ground disturbances. Specifically, the study aims to quantify the extent of performance changes in defective structures, particularly those constructed with poor-quality concrete, in response to seismic activities. To achieve this, the research involves developing multiple finite element models and conducting nonlinear analysis to scrutinize their behavior. A key focus of the study is to compare the performance of various RC buildings with concrete defects to that of a benchmark model. This comparative analysis highlights the influence of suboptimal quality control on the nonlinear behavior of RC structures. Furthermore, the study examines the correlation between changes in building response and earthquake characteristics to provide comprehensive insights into the potential risks associated with substandard construction practices. Based on the results of this study, it was found that inadequate quality control of concrete significantly impacts the performance of RC frames subjected to pulse-like ground motions. The decrease in compressive strength of the concrete led to noticeable increases in various structural parameters, including story shear, overturning moments, story displacement, drifts, accelerations, and hysteretic energy. These findings highlight the detrimental effects of compromised concrete quality on the overall structural response. [ABSTRACT FROM AUTHOR]

In this study, the sensitivity of the seismic response of irregular bridges to the abutment modeling assumptions has been investigated using inelastic time history analyses and recommendations are provided in this regard. The bridges were modeled using different abutment modeling assumptions, including fixed, roller, simplified, and spring abutment models. In the spring abutment model, the effects of all of the important abutment components, including the gap, bearing pads, shear keys, and backfill soil were considered. Including the abutment modeling for some cases increased the maximum seismic demands in the short columns and made their condition even more critical. The results also showed that using the simplified models in some irregular bridges could lead to an underprediction of the maximum seismic response in the critical columns by up to 30% that could result in an unsafe design. It was shown that the accuracy of the predictions from different models also depends on the bridge configuration and the location of the critical columns in the irregular bridges. A study of the influence of different abutment parameters such as gap length, abutment stiffness and strength, and bearing pad dimensions indicated that the variation of these parameters can change the predictions by up to around 15%, 30%, and 50%, respectively. The assumption of the fixed abutment condition resulted in up to 70% error in some bridges. A simple abutment modeling strategy was proposed to predict the maximum seismic demands in bridges with medium to high column stiffness using the fixed and roller abutment conditions. [ABSTRACT FROM AUTHOR]

An accurate estimation of displacement demand is essential to predict structural performance. However, the calculated displacements will vary depending on the analysis procedure. This paper shows the differences between the seismic demands of reinforced concrete (RC) columns calculated by using three analysis procedures: (1) AASHTO Seismic Guide Specifications (SGS); (2) direct displacement–based assessment (DDBA); and (3) nonlinear time history analysis (NLTHA). The demands were evaluated using two different response spectra definitions (3-period and 22-period representations) of the 2018 USGS seismic hazard model for structures located in shallow crustal and subduction tectonic regimes. Nonlinear time history analyses were performed using spectrally matched records for five design spectra from both tectonic regimes. This paper shows that the AASHTO-SGS significantly underpredicts the demands (compared with NLTHA) as the displacement ductility increases. In contrast, the predictions of the DDBA agree well with those of NLTHA, with mean differences of 10% for ductility higher than μΔ = 3. Lastly, equations are proposed to improve the accuracy of displacement demands for the AASHTO-SGS and the DDBA methodologies. [ABSTRACT FROM AUTHOR]

This paper presents a new hybrid passive control device, consisting of a viscoelastic and a friction damper connected in parallel, to mitigate the effects of wind and seismic events. The two components are synergized with the aid of a novel locking mechanism, which enables the action of one or both the components depending upon the device deformation. This provides an innovative two-phase energy dissipation capacity, and exploiting the individual strengths of the two dampers together. The response of a single degree of freedom (SDOF) hybrid damped system is represented in terms of a linear system using equivalent linearization technique, which includes all associated parameters such as the added stiffness, the added damping and the locking mechanism. In order to ascertain the influence of various parameters of the hybrid device, normalized force and normalized displacement are defined in terms of linear SDOF hybrid damped system and further used to obtain force reduction factor for multi degree freedom (MDOF) system with hybrid device. The proposed design methodology of controlling the structural response using the hybrid device is then applied on a six-story reinforced concrete (RC) building. The response of the conventional moment resisting frame (MRF) system and moment resisting frame system with hybrid device (MRHDF) are compared using the nonlinear time history analysis. The performance of the MRHDF system is found to be superior than the MRF system. The hybrid device can effectively reduce the dynamic response of the building, especially in terms of inter story drift, residual drift, base shear and floor acceleration. In addition the proposed design methodology is very simple as compared to the response modification factor approach. This configuration of hybrid device shows improved performance for meeting multiple objectives under wind/seismic events of real-life structures. [ABSTRACT FROM AUTHOR]

A novel assessment method for rapid structural safety state assessment is developed based on state-of-the-art machine learning technology. In this paper, a deep neural network (DNN), which originated in computer science, is first introduced, including its concept, structure and related training algorithms. Then the evaluation procedure to determine the structural safety state based on the DNN is developed. In the procedure, the pseudo-acceleration spectra and the structural safety states are selected as the input and output of the DNN model, respectively. Finally, the procedure of the novel assessment method is illustrated using a five-story reinforced concrete (RC) frame as an example. The effectiveness and accuracy are validated, and the influence of the number of hidden layers and size of the training data on the performance of the DDN is also investigated. The results demonstrate that the proposed method can evaluate the structural safety state rapidly based on the DNN. The most appropriate number of hidden layers is two considering both training accuracy and test accuracy. The training accuracy and test accuracy were 93.45% and 93.14%, respectively, using the two-hidden-layer DNN model trained on a training dataset of size 66,612. [ABSTRACT FROM AUTHOR]

In this study, the effects of pounding on seismic behavior of mid-rise reinforced concrete (RC) adjacent buildings with insufficient separation distance were investigated. 5, 8, 10, 13 and 15-storey RC building models were created to represent mid-rise buildings. The nonlinear behavior properties of these models are reflected by plastic hinges defined at the column and beam ends. The buildings are modeled as a three dimensional (3D) column-beam frame system. Adjacent building models are derived, which are connected from floor to floor level using Kelvin contact elements. Total of 30 different adjacent building models were created with the use of buildings having different number of floors. The "0" m gaps reflect inadequate separation distance between adjacent buildings while the "5" m gap is used for the reference building without collision. In order to investigate the pounding effects between adjacent buildings, 22 real acceleration records compatible with TBEC-2018 were selected and scaled. Total of 660 3D nonlinear time history analyses were carried out and the roof displacement demands obtained from these analyses were compared for collision and without collision cases The outcomes of this study show that significant changes may occur in the building displacement demands due to the collision of the mid-rise RC neighboring buildings with insufficient seismic gap. Based on the findings obtained on significant number of adjacent building pairs with different period ratios, the displacement amplification factors (β) are proposed for the mid-rise RC buildings. [ABSTRACT FROM AUTHOR]

Determination of structural damage index (DI) is tedious and time consuming process using the available conventional methods. Traditional multivariable regression (MVR) model had been fitted by researchers to find out global damage index (GDI) of buildings although the outcome was not up to the mark. In this paper, the GDI of 18 samples of 8-storey and 12-storey reinforced concrete (RC) buildings with nine irregular plans in each height category have been predicted using artificial neural network (ANN). The results show that maximum damage occurs at the ground storey and minimum damage occurs at the top storey for all cases considered. From the MVR model, it has been found that, inter-storey drift (IDR) and stiffness are not significant input parameters whereas, joint rotation, dissipated hysteretic energy, ductility, and peak roof displacement are the significant input parameters. Based on the numerical results derived, an ANN based GDI prediction model has been derived. In comparison to MVR model, the performance of ANN model is found to be satisfactory. [ABSTRACT FROM AUTHOR]

Today, many strategies have been proposed to improve the behavior of tall buildings under seismic load. Drifts, torsion, and structure period are essential parameters affecting high-rise building behavior. In addition, the stress concentration at the end wing of shear walls is another critical subject in high-rise buildings, which was resolved using end shear walls. The end shear wall connects the end of two shear walls in high-rise buildings without opening. In this study, a new end shear wall connects the end of shear walls in a high-rise building with regular openings (ESWO). Therefore, two 30-story RC buildings with and without end shear walls with opening were modeled by a nonlinear time history analysis under seismic load. The drift was decreased by 49% in a 30-story building with a new end shear wall. Moreover, the residual displacement of 30-story buildings with end shear walls with opening was decreased by 67%. The time history nonlinear analysis investigation indicated that the end shear walls with opening declined the maximum displacement by 62% in tall buildings by OpenSEES software. The reduction of the standard deviation of data increased the confinement in 30-story drifts in the X and Y directions by end shear walls with opening. Based on the results, the performance of the end shear walls with the opening was appropriate in the seismic behavior of high-rise buildings. [ABSTRACT FROM AUTHOR]

This study aims to investigate the determination of seismic separation distance of adjacent low and mid-rise reinforced concrete (RC) buildings using nonlinear time history analysis. The low and mid-rise RC buildings were reflected using 3, 4, 5, 6, 7, 8, 9 and 10-story buildings designed per 2018 Turkish Building Earthquake Code (TBEC). Beam and column elements are modeled as nonlinear frame elements with lumped plasticity by defining plastic hinges at both ends of beams and columns. The adjacent three-dimensional (3D) building models are connected to each other by linear link elements at the floor levels. 28 different adjacent building models were created by using the RC buildings with different building heights. In order to determine the minimum separation distance between these buildings, an earthquake set compatible with TBEC-2018 was selected. The earthquake set consists of 11 different record pair. Nonlinear time history analyses were carried out for each binary model using 22 acceleration records. The distances necessary to avoid pounding obtained from the result of 616 dynamic analyses were compared with the separation distances defined in the TBEC-2018. As a result of the study, it is seen that the required seismic separation distance per the current code was not enough to prevent pounding. A new simplified equation is proposed based on the period ratios of neighboring buildings for the coefficient (α) used in the estimation of gap distances under seismic loads. [ABSTRACT FROM AUTHOR]

Featured Application: Results from this study indicate that in a 3D time history analysis, without considering the directionality of the records, the actual maximum displacements occur in a random direction and they are around 20% larger than those predicted in the principal axes of the structure, based on the current design practice. When the directivity effects are also considered in the analysis, the difference can increase up to 70% compared to the displacements predicted in the principal X and Y directions. This difference may be more significant for different types of structures, particularly irregular structures. These issues need to be considered in the seismic design and analysis of bridges. Inelastic dynamic analyses were carried out using 3D and 2D models to predict the mean seismic response of four-span reinforced concrete (RC) bridges considering directionality effects. Two averaging methods, including an advanced method considering displacement direction, were used for the prediction of the mean responses to account for different incident angles of ground motion records. A method was developed to predict the variability of the mean displacement predictions due to variability in the incident angles of the records for different averaging methods. When the concepts of averaging in different directions were used, significantly different predictions were obtained for the directionality effects. The accuracy of the results obtained using 2D and 3D analyses with and without the application of the combination rules for the prediction of the mean seismic demands considering the incident angle of the records was investigated. The predictions from different methods to account for the records incident angles were evaluated probabilistically. Recommendations were made for the use of the combination rules to account for the directivity effects of the records and to predict the actual maximum displacement, referred to as the maximum radial displacement. [ABSTRACT FROM AUTHOR]

Structural damage index (SDI) is determined to implement damage-based design (DBD) which is a useful design philosophy in terms of safety and reliability nowadays. Literature is available to determine DI using different methods. Park-Ang damage assessment method is popular among them. In this method, first member damage is calculated then storey damage index is determined. From the calculated SDI, global damage index (GDI) is estimated. Park-Ang method requires three steps to estimate DI of structure which is tedious and time-consuming procedure for a multi-storied building. To avoid this complexity, a simplified DI model has been proposed which can estimate global DI directly. In the proposed model, three most influential engineering demand parameters (EDPs) have been combined to estimate GDI directly. For this purpose, 27 typical samples of 4-, 8-, and 12-storey reinforced concrete (RC) buildings with rectangular-shape, L-shape, and U-shape planner geometry were considered to account the effect of planner irregularities. It has been found that the proposed model established a good agreement with Park-Ang DI. The proposed model effectively estimates reliable GDI and can be used as a powerful tool for estimating seismic damage of buildings especially for massive structures. [ABSTRACT FROM AUTHOR]

Masonry buildings are primarily constructed out of bricks and mortar which become discrete pieces and cannot sustain horizontal forces created by a strong earthquake. The collapse of masonry walls may cause significant human casualties and economic losses. To maintain their integrity, several methods have been developed to retrofit existing masonry buildings, such as the constructional RC frame which has been extensively used in China. In this study, a new method using precast steel reinforced concrete (PSRC) panels is developed. To demonstrate its effectiveness, numerical studies are conducted to investigate and compare the collapse behavior of a structure without retrofitting, retrofitted with a constructional RC frame, and retrofitted with external PSRC walls (PSRCW). Sophisticated finite element models (FEM) were developed and nonlinear time history analyses were carried out. The results show that the existing masonry building is severely damaged under occasional earthquakes, and totally collapsed under rare earthquakes. Both retrofitting techniques improve the seismic performance of existing masonry buildings. However, it is found that several occasional earthquakes caused collapse or partial collapse of the building retrofitted with the constructional RC frame, while the one retrofitted by the proposed PSRC wall system survives even under rare earthquakes. The effectiveness of the proposed retrofitting method on existing masonry buildings is thus fully demonstrated. [ABSTRACT FROM AUTHOR]

The equivalent viscous damping is a key parameter in the prediction of the maximum nonlinear response. Damping constitutes a major source of uncertainty in dynamic analysis. This paper studies the effect of using viscous damping, on the reduction of the seismic responses of reinforced concrete RC frame buildings modeled as three-dimensional multi degree of freedom (MDOF) systems, and the use of nonlinear time history analysis as a method of visualized behavior of buildings in the elastic and inelastic range. This study focuses on the implications of the available modeling options on analysis. This article illustrates the effect of using the initial or tangent stiffness in Rayleigh damping in analysis of structures. Correspondingly, this work is also concerned with the estimation of Rayleigh, mass-proportional or stiffness-proportional damping on engineering demand parameters (EDPs). As a result of a series of considerations, a damping modeling solution for nonlinear time history analysis (NLTHA) was carried out to compute the damage index. The application example is a building designed according to reinforced concrete code BAEL 91 and Algerian seismic code RPA 99/Version 2003 under seven earthquake excitations. The simulations demonstrated the accuracy and effectiveness of the proposed method to account for all of the above effects. [ABSTRACT FROM AUTHOR]

Optimum length of glass fiber-reinforced polymers (GFRP), as an advantageous type of composites, on the retrofitted columns of RC frames is obtained in this study by conducting seismic reliability analyses. To achieve this goal, maximum reliability index with different FRP lengths of columns of a six-story RC frame was calculated to find the optimal length for FRP-retrofitted columns. The seismic behavior of structure after verification was assessed by nonlinear time history analysis with OpenSees finite element software. Three scaled far-field earthquake records were selected for nonlinear time history analysis. The reliability analysis was performed by first-order reliability method and Monte Carlo simulation in RT software. The optimal length of FRP was obtained on the results of reliability analysis. The findings of the study showed that increased FRP material quantities do not affect the retrofitted reliability index. The findings of the study showed that increased FRP material quantities do not affect the retrofitted reliability index. The convergence of Monte Carlo simulation occurred after a variety of iterations and, consequently, was alternated with the first-order reliability analysis which has very short run time and is lower error methodology. Moreover, in all cases of reinforcement and analyses, the compressive strength of the concrete is extremely important. [ABSTRACT FROM AUTHOR]

Abstract Buildings can have heavy damages or collapse because of severe earthquakes. Previous studies showed that structural damage due to earthquake is the cause of large displacement. Shear walls in the buildings ensure safety against lateral loads. Thus, using shear walls in buildings can be prevent large displacement and herewith damages due to displacement. The last devastating earthquake is Van 2011 earthquake in Turkey and many buildings were damaged because of Van 2011 earthquake. There were buildings which have shear walls among those damaged buildings. However, it is clear not only shear walls but also whole building should be designed according to a modern seismic code. In this study, two RC buildings with shear walls which had damages because of Van 2011 earthquake were considered and it is tried to determine the existing damages via nonlinear time history analysis using Van 2011 earthquake acceleration data. Time history analyses were conducted with SAP 2000. In addition to this, material qualities were increased and shear walls were designed according to Turkish Seismic Code 2007 requirements for both buildings. Nonlinear time history analyses were conducted for the upgraded buildings and damage distributions were determined. Thus, damage distributions of existing and upgraded buildings were compared and an evaluation was drawn for damage distribution even if only proper concrete and reinforced material and shear walls were used in design of the buildings except beams and columns. According to results of the study, using proper materials and shear walls can prevent heavy damages even seismic response of beams and columns elements is poor. Highlights • Two existing damaged RC buildings due to Van 2011 earthquake were considered in this study. • Nonlinear time history analyses were performed using Van 2011 earthquake ground motion record. • Seismic performance of the buildings were estimated. • Existing damages and analytically estimated damages were compared to verify the analytical model. • Effects of shear wall on seismic behavior of a building were estimated. [ABSTRACT FROM AUTHOR]

The definition of performance limit states for progressive collapse design and assessment of civil structures is an open issue and deserves special attention in view of future building codes and standards. In this study, the main findings of a multilevel sensitivity analysis are presented to characterize the progressive collapse capacity of a selected class of modern European buildings having a reinforced concrete framed structure. After that a group of capacity model properties are assumed as random variables on the basis of earlier studies, the sensitivity of both ultimate load capacity and corresponding maximum and residual drifts to the ultimate steel strain and location of column‐removal scenario is assessed. Then, the influence of the capacity model properties on maximum drift demand corresponding to a code‐compliant design gravity load is evaluated. Finally, five performance limit states associated with increasing levels of damage are introduced and the corresponding load capacity is quantified under varying capacity model properties. Analysis results indicate a high sensitivity to the ultimate steel strain, column location in plan, beam span and yield steel strength. [ABSTRACT FROM AUTHOR]

Nepal Himalayas is one of the most seismic vulnerable zones. The active tectonic action impels the assessment of structures in possible seismic hazards including the bridge structures. This paper presents the impact of the 2015 Gorkha earthquake on the existing reinforced concrete arch bridge at Chobhar, Nepal. A three-dimensional model of the bridge is constructed using OpenSees platform. Nonlinear pushover analysis was performed to find the displacement capacity of the bridge. Ground motion from the main shock of the 2015 Gorkha earthquake is used in this study. Nonlinear time history analysis is performed with three orthogonal ground motions applied in the transverse, longitudinal and vertical direction of the bridge. The study investigates the safety of the bridge scaling up the ground motion to potential PGA in Nepal Himalayas; the result demonstrated the necessity of retrofit to ensure the safety level. Moreover, the horizontal seismic force obtained from the time history analysis is compared with the force obtained from the design code of the bridge. Also, the design force as per the present code (revised code) is presented. [ABSTRACT FROM AUTHOR]

This paper intends to contribute to the validation of the extended N2 nonlinear static method of seismic analysis through the study of two existing reinforced concrete frames. The scope is to further investigate the limitations of the original N2 method in predicting the seismic response of plan asymmetric buildings and to assess the higher accuracy of the extended N2 method. The two case study buildings are representative of the Italian construction between the '70s and '90s. One is designed for gravity loads only, the other is designed according to an old seismic code. Two modelling strategies are used, one with distributed and the other with lumped plastic hinges. Three eccentricities e CM between centre of mass and plan geometric centre are considered (e CM = 0%, 5% and 15%). The pushover analyses are carried out following the N2 method, the N2 method plus the 100:30 directional combination rule and the extended N2 method. The results are compared with those obtained from nonlinear history analyses. For each building the seismic demand is assessed for three hazard levels. The results indicate that the application of the extended N2 method significantly enhances the shape of the demand prediction, particularly for buildings with higher plan eccentricities. On the other hand, the directional combination does not significantly change the results and should be neglected. • This paper investigates the limitations of the N2 nonlinear static method in predicting the seismic response. • Seismic demands obtained from nonlinear static (with N2, extended N2, and 100:30 rule) and nonlinear response history analyses are compared. • Two modelling strategies are used: 1) Beam with Hinges with fibre-section discretization, 2) lumped plastic hinges with phenomenological lows. • The extended N2 method significantly enhances the shape of the demand prediction. • The application of the directional combination to the nonlinear static analysis does not significantly change the seismic demand. [ABSTRACT FROM AUTHOR]

A modified energy-balance equation accounting for P-delta effects and hysteretic behavior of reinforced concrete members is derived. Reduced hysteretic properties of structural components due to combined stiffness and strength degradation and pinching effects, and hysteretic damping are taken into account in a simple manner by utilizing plastic energy and seismic input energy modification factors. Having a pre-selected yield mechanism, energy balance of structure in inelastic range is considered. P-delta effects are included in derived equation by adding the external work of gravity loads to the work of equivalent inertia forces and equating the total external work to the modified plastic energy. Earthquake energy input to multi degree of freedom (MDOF) system is approximated by using the modal energy-decomposition. Energy-based base shear coefficients are verified by means of both pushover analysis and nonlinear time history (NLTH) analysis of several RC frames having different number of stories. NLTH analyses of frames are performed by using the time histories of ten scaled ground motions compatible with elastic design acceleration spectrum and fulfilling duration/amplitude related requirements of Turkish Seismic Design Code. The observed correlation between energy-based base shear force coefficients and the average base shear force coefficients of NLTH analyses provides a reasonable confidence in estimation of nonlinear base shear force capacity of frames by using the derived equation. [ABSTRACT FROM AUTHOR]

Reconnaissance studies on the recent Tohoku earthquake have reported collapse of structures due to multiple earthquake excitations in the earthquake-affected region. Strength and stiffness degradation is shown to be the primary reason for the observed damage. The present study aims to investigate the degrading behavior of irregularly built reinforced concrete structures subjected to the Tohoku ground motion sequences. Three-dimensional numerical models of three irregular reinforced concrete structures are developed. The structural characteristics of these buildings are then altered to achieve a regular case. The models contain appropriate damage features that can capture both the irregularity and material deterioration effects. The capacities of both cases are evaluated using the N2 and extended N2 procedures. The degrading models are then used for ground motion sequences measured at 23 selected stations. The results indicate that multiple earthquake effects are significant, and irregularity effects increase the dispersed damage under these excitation sequences. [ABSTRACT FROM AUTHOR]

Determination of capacities of structural members, both in terms of strength and deformation, and estimation of seismic demand are essential issues in earthquake-resistant design. In energy-based design and evaluation, both the structural capacity and the demand imposed by earthquake are considered in terms of energy and accordingly energy dissipation capacity of the structure is associated with seismic energy demand. Plastic energy dissipation of structures under monotonic lateral loading may be obtained by using the resultant pushover curves of nonlinear static analyses. However, the time variation of individual contribution of structural members to the dissipated plastic energy cannot be determined. In this study, the contribution of beam and column deformations to the plastic energy dissipated in multistory reinforced concrete (RC) frames is determined by using nonlinear time history (NLTH) analysis. It is found that rotational deformations of beams are dominant in plastic energy dissipation. Accordingly, some linear relations considering the contribution of dissipated plastic energy in beam plastic hinges to the total plastic energy dissipation of RC frames are derived. Pushover analysis of frames in conducted and the area under the resultant pushover curve is determined to satisfy the mean value of the maximum plastic energy dissipated in frames during the selected earthquakes. The interstory drift ratios are calculated and compared with the interstory drift ratios directly obtained from NLTH analyses. The results are evaluated and presented by graphs and tables. [ABSTRACT FROM AUTHOR]

This paper presents a simple method based on modal response spectrum analysis to compute internal forces in structural elements belonging to gravity framing not part of the seismic force resisting system (SFRS). It is required that demands on these gravity load resisting system (GLRS) be determined according to the design displacement profile of the SFRS. The proposed new method uses the fact that if the linear stiffness properties of the GLRS not part of the SFRS have negligible values compared to those of the SFRS, only the latter will provide lateral resistance. Displacements of the GLRS then correspond to those of the SFRS alone. The new method is illustrated by computing the seismic responses of a symmetric and an asymmetric multi-storey reinforced concrete building. These results are compared to those obtained from the application of the simplified analysis method proposed in the Canadian standard for the design of concrete structures. Nonlinear time history analyses are also performed to provide a benchmark for comparison. Results show that the new method can predict shear and bending moment in all members at once with ease. Therefore, this new simplified method can effectively be used to predict seismic forces in elements not considered part of the SFRS. [ABSTRACT FROM AUTHOR]

This paper attempts to explore potential benefits of form in a deck-type reinforced concrete (RC) arch bridge in connection with its overall seismic behavior and performance. Through a detailed three-dimensional finite element modeling and analysis of an actual existing deck-type RC arch bridge, some useful quantitative information have been derived that may serve for a better understanding of the seismic behavior of such arch bridges. A series of the nonlinear dynamic analyses has been carried out under the action of seven different time histories of ground motion scaled to the AASHTO 2012 response spectrum. The concept of demand to capacity ratios has been employed to provide an initial estimation of the seismic performance of the bridge members. As a consequence of the structural form, a particular type of irregularity is introduced due to variable heights of columns transferring the deck loads to the main arch. Hence, a particular attention has been paid to the internal force/moment distributions within the short, medium, and long columns as well as along the main arch. A study of the effects of the vertical component of ground motion has demonstrated the need for the inclusion of these effects in the analysis of such bridges. [ABSTRACT FROM AUTHOR]

Several seismic optimization methods have been proposed to improve the performance of reinforced concrete framed (RCF) buildings; however, they have not been widely adopted among practising engineers because they require complex nonlinear models and are computationally expensive. This article presents a procedure to improve the seismic performance of RCF buildings based on eigenfrequency optimization, which is effective, simple to implement and efficient. The method is used to optimize a 10-storey regular building, and its effectiveness is demonstrated by nonlinear time history analyses, which show important reductions in storey drifts and lateral displacements compared to a non-optimized building. A second example for an irregular six-storey building demonstrates that the method provides benefits to a wide range of RCF structures and supports the applicability of the proposed method. [ABSTRACT FROM AUTHOR]

An energy-based approach for determining earthquake safety of reinforced concrete frame structures is presented. The developed approach is based on comparison of plastic energy capacities of the structures with plastic energy demands obtained for selected earthquake records. Plastic energy capacities of the selected reinforced concrete frames are determined graphically by analyzing plastic hinge regions with the developed equations. Seven earthquake records are chosen to perform the nonlinear time history analyses. Earthquake plastic energy demands are determined from nonlinear time history analyses and hysteretic behavior of earthquakes is converted to monotonic behavior by using nonlinear moment-rotation relations of plastic hinges and plastic axial deformations in columns. Earthquake safety of selected reinforced concrete frames is assessed by using plastic energy capacity graphs and earthquake plastic energy demands. The plastic energy dissipation capacities of the frame structures are examined whether these capacities can withstand the plastic energy demands for selected earthquakes or not. The displacements correspond to the mean plastic energy demands are obtained quite close to the displacements determined by using the procedures given in different seismic design codes. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the effect of hysteretic models on displacement demands of reinforced concrete (RC) structures having various irregularities and determine more proper hysteretic models for different types of RC structures. The RC structures having irregularities such as soft story and overhang were analyzed with nonlinear pushover and nonlinear time-history methods. Concrete compressive strength, stirrup amount, and the number of stories for the structures were variable parameters. Totally, 25,664 analyses were carried out. Displacement capacities and performance levels of structures were determined using nonlinear pushover analysis. Exceedance ratios of performance levels and displacements demanded from the structures of 100 severe ground motions that occurred worldwide were obtained using nonlinear time-history analysis (NTHA). In NTHA, various hysteretic models were used to define inelastic behavior of RC structures. The analyses show that the hysteretic models have a significant effect on displacement demands of RC structures. Finally, proper hysteretic models are suggested according to the type of structure and purpose of occupancy. [ABSTRACT FROM AUTHOR]

This article proposes a new approach to predict the plastic drifts and damage states of reinforced concrete frame type structures subjected to monotonic loading. The approach uses plastic energy demand graphs which are determined from nonlinear time history analyses. Plastic energy graphs are obtained by converting the hysteretic moment rotation relations of the structural members to the monotonic behavior. In the study, interstory drift ratio limits are determined from the seismic design codes and used to evaluate the structural damage states of the structures subjected to monotonic loading. The work done by the monotonic type external design loads are expressed by an equation. This plastic energy equation is solved by using the maximum plastic energy values obtained from the plastic energy demand graphs. Plastic design base rotations of the frames are obtained from the plastic energy equalities. Then the total drifts of the stories are determined and assessed by considering the interstory drift ratio limits in Vision 2000 document. Performance levels of the frame type structures may be predicted by comparison of the interstory drifts from the approach in the study with the code-based drift limits. Finally, the accuracy of the approach is evaluated by using the results of nonlinear time history analyses. The total drifts of the structures obtained from energy equalities within the study are checked by the drift results of the nonlinear time history analyses. [ABSTRACT FROM AUTHOR]

In this study, dynamic responses of the multistory base-isolated and base-fixed buildings are investigated under near- and far-fault ground motions. Lead-rubber isolation bearing (LRB) is used in the examination. First, the mechanical properties for LRB isolation system are calculated. The seismic analysis of the buildings is executed by nonlinear time history analysis method for reinforced-concrete two-dimensional building frames. For the purpose of analysis, three records of far-field and three records of near-fault ground motions from the same components are selected in different stations and conducted on building frames. The results of the analysis for isolated-base and fixed-base frames are compared with each other under far- and near-fault ground motions. Story drift, acceleration of the each story, base shear and base displacement are examined as results of the analysis. These results show that the isolators absorb the seismic energy well enough such that there is a considerable reduction in the majority of the dynamic responses. Reduction in the floor acceleration of the middle floors is observed more than in the base and top floor. Base displacement is more considerable in isolated buildings subjected to near-fault than far-fault ground motions. [ABSTRACT FROM AUTHOR]

Highlights: [•] Simplified models for masonry-infilled RC frames with damping systems were studied. [•] Conventional damping correction factors have significant errors for ductility demand. [•] The errors are more severe for intermediate deformations rather than extensive ones. [•] Equations estimating response reduced by supplemental viscous damping are proposed. [•] Proposed equations are useful for preliminary retrofit design of existing buildings. [Copyright &y& Elsevier]

Abstract: In Latin America there is an urgent need for housing; thus, during the last few years a relevant number of mid-height buildings (usually, up to five stories) with thin RC shear–walls have been constructed for low-cost dwellings in Bolivia, Colombia, Ecuador, Mexico, Peru, Venezuela, and other countries located in seismic-prone regions. These walls are 10cm thick and their reinforcement consists mainly of a single layer of welded wire mesh. This construction technology offers two main advantages: economy and rapidity of construction. These buildings do not fulfill the international seismic codes but some national regulations are less demanding, not preventing the use of thin bearing walls. These buildings might be vulnerable to earthquakes because of their low ductility, the insufficiency of the experimental information, the absence of observed damages and, in some cases, poor construction quality. This work describes the initial steps of a wider research aiming at providing reliable seismic design guidelines for thin-wall buildings; the initial objectives are analyzing the seismic performance of these buildings, proposing preliminary design criteria and identifying further research needs. This research focuses on buildings located in Peru, being representative of the situations in the other countries. The vulnerability is numerically evaluated by push-over and nonlinear time history analyses; the structural parameters are obtained from available testing information. The obtained results show that the seismic strength of the analyzed buildings is insufficient; however, minor changes in the structural design might improve significantly their seismic performance. Cheap and easy-to-implement design recommendations are issued. [Copyright &y& Elsevier]

• 1232 nonlinear dynamic (time history) analyses are performed using 56 different building pairs. • Minimum required separation distances of adjacent buildings are investigated. • The distances are compared with minimum requirements of codes, provisions and proposed methods. • Two different simple approaches are proposed to estimate the seismic gap distances. • The first approach requires linear static analysis of the buildings while the second simplified approach does not need any analysis. This study aims to investigate the determination of seismic separation gap of adjacent low and mid-rise reinforced concrete (RC) buildings with no structural irregularity using nonlinear time history analysis. The low and mid-rise RC buildings were reflected using 3, 4, 5, 6, 7, 8, 9 and 10-story buildings designed per 2018 Turkish Building Earthquake Code (TBEC-2018). Beam and column elements are modeled as nonlinear frame elements with lumped plasticity by defining plastic hinges at both ends of beams and columns. The adjacent three-dimensional (3D) building models are connected to each other by link elements at the floor levels. 1232 nonlinear dynamic (time history) analyses were performed using 56 different building pairs and 11 different earthquake record pairs (22 records) compatible with TBEC-2018 to obtain the required seismic gap distances. The distances necessary to avoid pounding obtained from the analyses were compared with the minimum seismic gap requirements of the current earthquake codes, provisions (Eurocode-8, ASCE 7-16 and TBEC-2018) and several proposed methods (ABS, SRSS and DDC) in the literature. The outcomes indicate that the ASCE 7-16 and EC-8 significantly overestimate the required seismic gap distances for the buildings with similar dynamic characteristics while they provide reasonable estimates for the buildings with significantly different dynamic characteristics. However, the TBEC-2018 requirements are insufficient for the neighboring building period ratios greater than 1.25. Although both the ASCE 7-16 and EC-8 requirements are acceptable for the design of new buildings as being on safe side, they are not useful for the evaluation of existing buildings. Two different simple approaches were proposed to estimate the required seismic gap distances between neighboring buildings. The first approach requires linear static analysis of the buildings subjected to the reduced seismic design forces while the second simplified approach does not need any analysis. The proposed equations in this study are simple and useful for the evaluation of existing low and mid-rise RC buildings with no structural irregularity. Besides, their estimates are acceptable for the design purposes. [ABSTRACT FROM AUTHOR]

Normally, Laminated Rubber Bearing Pads (LRBPs) are directly placed between girders and piers and their role is to provide the bridge span with horizontal movement, and to transmit the gravity loads from the deck to the piers. Although not designed for seismic loads, they can act as a fuse, partially isolating the substructure from the superstructure and keeping the piers intact during earthquakes. However, recent investigations show that large relative displacement of superstructure against substructure caused by sliding at bearing (sliding between girders and LRBPs) can cause expansion joint failure or even bridge span collapse. Accordingly, proper restrainers should be selected to prevent large displacement. Among all types of restrainers, viscous dampers as passive energy dissipation devices have shown a great capacity in damping earthquake energy. This study investigates the effectiveness of a VD-LRBP system, a viscous damper in conjunction with LRBPs, in dissipating energy and reducing the displacement of the superstructure with reference to the substructure caused by sliding at bearing during a seismic event. A Finite Element (FE) model was first developed and validated using available experimental and numerical results. With the validated model, a 3D Nonlinear Time History Analysis (NTHA) was conducted on a reinforced concrete bridge model under various records of earthquakes using OpenSees, an open-source finite element software. The relative displacement histories were recorded for the bridge in two cases: 1- with only LRBPs and 2- with viscous dampers and LRBPs (VD-LRBP system). The results of this study show that applying viscous dampers can reduce the relative displacement of the superstructure with reference to the substructure for up to 60 percent. As importantly, it can also reduce the residual displacement after the earthquake to near zero. [ABSTRACT FROM AUTHOR]

Uncertainty quantification is an important issue in the seismic fragility analysis of bridge type structures. However, the influence of different sources of uncertainty on the seismic fragility of the system is commonly overlooked due to the costly re-evaluation of numerical model simulations. This paper aims to present a framework for the seismic fragility analysis of reinforced concrete highway bridges, where a data-driven metamodel is developed to approximate the structural response to structural and ground motion uncertainties. The proposed framework to generate fragility curves shows its efficiency while using a few finite element simulations and accounting for various modeling uncertainties influencing the bridge seismic fragility. In this respect, a class of single-bent bridges available in the literature is taken as a case study, whose three-dimensional finite element model is established by the OpenSees software framework. Twenty near-source records from different sources are selected and the Latin hypercube method is applied for generating the random samples of modeling and ground motion parameters. The Kriging metamodel is then driven on the structural response obtained from nonlinear time history analyses. Component fragility curves of the reinforced concrete pier column are derived for different damage states using the Kriging metamodel whose parameters are established considering different modeling parameters generated by Monte Carlo simulations. The results demonstrate the efficiency of the proposed framework in interpolating the structural response and deriving the fragility curve of the case study with any input conditions of the random variables. [ABSTRACT FROM AUTHOR]

A new method for predicting inelastic displacements of reinforced concrete moment resisting frames under seismic motions is presented. The method uses modal behavior (or strength reduction) factors for the first few significant modes, which are functions of period, interstorey drift ratio, plastic rotation, performance level and soil type. Explicit empirical expressions for these factors have been derived by the first author in the past for design purposes. These factors are used here for inelastic displacement prediction. Thus, these factors are multiplied by the corresponding elastic modal displacements to produce the inelastic modal displacements, which can provide the inelastic displacements via a combination rule like the SRSS rule. The proposed method is compared against the equal displacement rule and three other well-known methods on the basis of nonlinear time history analyses and its merits are demonstrated. • A method for predicting inelastic displacements of reinforced concrete MRFs under seismic motions. • The method uses modal behavior factors q ‾ j for the first few significant modes. • The q ‾ j are functions of period, target deformation, performance level and soil type. • The q ‾ j are multiplied by the corresponding elastic modal displacements to produce the inelastic ones. • The inelastic displacements are obtained via a combination rule like the SRSS rule. [ABSTRACT FROM AUTHOR]

• A method for computing seismic demands in gravity load resisting system is presented. • Foundation movements need to be explicitly considered for soil class D and softer. • Adding a single rotational spring under each core is efficient to do so. • Cracked underground structure properties lead to larger demands in some elements. • Gravity load frame behavior is not captured by linear analysis for soil class E. This paper presents a complete and simple linear method, with a suitable force modification factor, to compute seismic demands in the gravity load resisting system (GLRS) of shear wall buildings including foundation movement. Based on the method first proposed by Beauchamp, Paultre and Léger in 2017, this paper compares two approaches to consider foundation movement on linear soil media such as (a) a simple rotational spring under each core and (b) a complete set of springs and dashpots. A fixed-base model using code foundation factors is also used for comparison. Springs and dashpots are assessed by modelling soil-structure interaction (SSI) with solid finite elements. Then, these approaches are evaluated for a typical 12-storey concrete shear wall building considering several nonlinear time history analyses (NLTHAs). SSI is modelled with a set of springs and dashpots, and ground motions are selected from the conditional spectrum method. NLTHAs are performed for soil classes ranging from stiff to soft, and the effect of the underground structure cracking is analysed. Analysis results show that the proposed methods are accurate in computing seismic demands in the GLRS compared to NLTHA. Foundation movements should be explicitly modelled for soil class D or softer, and underground structure cracking should be considered. For the very soft soil class E, the behaviour of the building is poorly captured in linear analysis methods; thus, nonlinear analyses are required. [ABSTRACT FROM AUTHOR]