Inter-story Drift Distribution Research Articles

Self-centering rocking steel frame with column mid-height uplift: Experimental and numerical investigation

This paper proposes a self-centering rocking steel frame with column mid-height uplift (SCRSF-CMU) that exhibits high post-yield stiffness and energy dissipation capacity. The hysteretic performance of the SCRSF-CMU was investigated through cyclic loading tests. A numerical model of the SCRSF-CMU was established and validated against experimental results. Subsequently, the seismic performance of the SCRSF-CMU was compared with that of the self-centering rocking steel frame with column base uplift (SCRSF-CBU) using nonlinear time history analysis. Finally, the seismic responses of the SCRSF-CMU and SCRSF-CBU under varying earthquake intensities were analyzed using the endurance time analysis. The results indicate that the designed SCRSF-CMU demonstrates excellent lateral force resistance, energy dissipation, and self-centering capabilities. The rocking effect and the restoring force of the post-tensioned steel strands effectively controlled the residual lateral displacement of the specimens. The multi-scale numerical model of the SCRSF-CMU accurately captured its hysteretic behavior and deformation patterns. Compared to the SCRSF-CBU, the SCRSF-CMU exhibited superior rocking deformation capacity, post-yield stiffness, and hysteretic energy dissipation. Under MCE excitation, both SCRSF-CMU and SCRSF-CBU showed uniform inter-story drift distribution with minimal residual deformation, creating a satisfactory condition for the post-earthquake repair work if necessary. The high post-yield stiffness of the SCRSF-CMU was more effective in reducing both maximum and residual displacements. Endurance time analysis revealed that SCRSF-CMU and SCRSF-CBU exhibited relatively uniform inter-story drift distribution under SLE, DBE, and MCE earthquakes. Under FE excitation, the inter-story drift ratio of both structures were nearly identical; however, under DBE and MCE excitations, the maximum roof drift ratio and inter-story drift ratio of the SCRSF-CBU were larger, indicating that the SCRSF-CBU had higher deformation demands than the SCRSF-CMU.

Mitigating inter-story drift concentration in seismic-resistant self-centering braced frames by using strong backup systems

Seismic-resistant self-centering concentrically braced frames (SC-CBFs) are susceptible to the concentration of inter-story drifts during earthquakes owing to the relatively low energy dissipation ability of braces. To address this limitation, this study proposed a novel solution by designing a strong backup (SB) system to mitigate inter-story deformation concentration in “weak” stories. The proposed SB system consisting of truss members can be attached to the existing SC-CBF through pin connections, forming a system, termed strong backup SC-CBF (SC-CBF-SB), to promote a more uniform distribution of inter-story drifts along the height of the frame and mitigate the weak story behavior. A six-story chevron-braced frame is adopted to investigate the seismic performance of SC-CBF and SC-CBF-SB. Finite element models of SC-CBF and SC-CBF-SB are built. The mechanical characteristics and dynamic responses of the SC-CBF-SB are examined. To comprehensively evaluate the performance of both SC-CBF and SC-CBF-SB, static pushover analyses and nonlinear time-history analyses are conducted. Additionally, incremental dynamic analysis (IDA) is performed to evaluate the responses (particularly drift concentration) of both frame types subjected to increasing seismic intensity levels. Numerical results show that the maximum value of the drift concentration factor (DCF) is around 1.3 and 1.8 for SC-CBF-SB and SC-CBF, respectively, indicating that SC-CBF-SB can effectively mitigate inter-story drift concentration of SC-CBF. Meanwhile, the proposed SB system has a minimal negative impact on the favorable SC ability of the frame.

Effects of pulse like ground motion records with and without acceleration pulses on the earthquake responses of structures with varying dynamic properties

This study is focused on the effects of acceleration pulses on the damaging potentials of velocity pulse-like ground motion (GM) records. In the study, previously identified pulse-like GM records with and without acceleration pulses are used together with far fault (FF) GM records. The selected GM records are used in the nonlinear time history analyses of structural systems with different dynamic properties. The structural systems used in the analyses were designed to represent commonly used short and medium height structures. The damaging potentials of GM records are compared in terms of commonly used engineering demand parameters (EDPs); (i) doof drift ratio, (ii) residual displacement, (iii) interstory drift distribution, and (iv) shear force distribution throughout the height of the building. The results of the analyses revealed that the velocity pulse-like GM records with acceleration pulses significantly increase the earthquake demands on short to medium height structures. On contrary to that the velocity pulse-like GM records without significant acceleration pulses don't have any additional damage potential for short to medium height structures. Furthermore, in terms of considered EDPs, the structural demands due to FF GM records are even higher than those caused by velocity pulse-like GM records without acceleration pulses. These results showed that the studies focusing on the damaging effects of pulse-like GM records on short to medium height structures should eliminate the velocity pulse-like GM records without acceleration pulses from their GM pools. Such an elimination may reduce the scatter observed in the results of such studies.

Hybrid self-centering companion spines for structural and nonstructural damage control

This paper intends to develop a new lateral force-resisting system – the hybrid self-centering companion spines system (denoted as the HSCS system) – for obtaining better seismic resilience by controlling both structural and nonstructural damage. The HSCS system consists of two rigid spines pinned to the ground and several hybrid dampers. The two rigid spines can facilitate the structure to avoid soft-story mechanisms and control higher mode responses by promoting uniform inter-story drift distribution under strong earthquakes. The hybrid damper is made of a friction spring damper and a viscous damper in parallel and provides the self-centering feature, energy-absorbing capacity, and acceleration- and velocity-control capacity for reducing structural and nonstructural damage. A performance-based design (PBD) procedure was developed for the HSCS system based on the concept of the direct displacement-based design method. The three-story and six-story demonstration buildings were considered in this study to investigate the seismic performance of steel buildings equipped with the proposed HSCS systems. Four designs with different design parameters were performed for the demonstration buildings based on the proposed PBD procedure. The three- and six-story self-centering companion spines systems (denoted as SCS systems) were considered for highlighting the benefits of adopting HSCS systems. Nonlinear dynamic analyses were conducted to evaluate the structural and nonstructural damage of the designed buildings under earthquakes. The analysis results indicate that the designed HSCS systems can achieve the desired performance objective and nonlinear behavior under dynamic excitations. The HSCS systems can show excellent structural damage control performance and post-earthquake recoverability by controlling the residual inter-story drift much smaller than 0.2% even under MCE excitations. The excellent nonstructural damage control capacity can be also observed in the designed HSCS systems, while most of the nonstructural components are only slightly damaged even under MCE excitations. Moreover, the HSCS systems can achieve smaller absolute floor acceleration and floor velocity responses than SCS systems under both DBE and MCE although they are designed to achieve similar maximum inter-story drift responses under DBE.

Performance-based seismic design method for retrofitting steel moment-resisting frames with self-centering energy-absorbing dual rocking core system

This research intends to propose an upgraded strategy for steel moment-resisting frames (SMRFs) by implementing Self-Centering Energy-absorbing Dual Rocking Core (SEDRC) systems to achieve enhanced seismic performance, improved seismic resilience, and avoid inter-story drift concentration. A performance-based method is developed to design the SEDRC system for upgrading the existing SMRF. The maximum inter-story drift and drift concentration factor are adopted as the design performance objectives. Two prototype SMRFs with three and nine stories are introduced to validate the proposed performance-based design procedure. Nonlinear static analyses were first performed for the original SMRFs and the updated ones (denoted as SEDRC-MRFs) to investigate the efficiency of the proposed retrofit strategy. The pushover curves of the analytical structures confirm that the SEDRC systems can increase the stiffness and strength of SMRFs, and SEDRC-MRFs upgraded through the proposed design procedure show no strength deterioration before the fracture of the brace in the SEDRC system. A set of 18 ground motions were chosen to study the seismic performance of the designed SEDRC-MRFs. The analysis results indicate that SEDRC-MRFs can obtain the desired performance objectives. The SEDRC system could reduce the maximum and residual inter-story drifts of SMRFs and promote uniform inter-story drift distribution. Moreover, the designed SEDRC-MRFs can be used immediately without the need for repairing structural members after the design basis earthquakes and can be repaired economically after the maximum considered earthquakes.

Interstory drift based scaling of earthquake ground motions

AbstractA novel amplitude scaling procedure is proposed in this study where the ground motion scaling factors are defined as the ratio of interstory drift distributions under target spectrum versus under the associated ground motion spectrum. The advantage of employing interstory drift ratio in ground motion scaling, compared to employing spectral intensity directly, is that it provides a strong theoretical link between the target spectrum intensity and the fundamental dynamic characteristics of the structure. Hence, scaling is conditioned on structural response, which is in turn a function of seismic intensity. The interstory drift‐based scaling procedure (IDS) is presented herein for planar frames for brevity. Accuracy and efficiency of the IDS procedure is assessed under a set of near fault strong motions from large magnitude events. The results revealed that the proposed procedure is accurate since the resulting bias in estimating linear elastic interstory drifts is negligibly small. Further, it is noticeably more effective as compared to the conventional procedures suggested in recent seismic codes, yet it is simpler.

Design concepts and seismic behavior of ductile linked rocking steel frames

This paper proposes a novel ductile linked rocking steel frame (DLRF) that relying on gravity load and rocking column base components rather than post-tensioning elements to provide the self-centering capacity. In the DLRF, rocking steel braced frames remain elastic by being permitted to uplift and rock at the rocking column bases, coupled with ductile links that act as structural fuses to dissipate energy through accommodating vertical movement between the two-rocking steel braced frames. Rocking column bases can dissipate energy through fuses that can be repaired easily by being bolted to the column. The design equations to govern the corresponding resistance mechanism of the DLRF for each limit state are presented and applied to a four-story prototype structure. Nonlinear dynamic analyses were performed to examine the behavior of the DLRF. The seismic performance of the DLRF is contrasted with a corresponding fixed-base structure, in which the column base is designed as a rigid connection. The comparison indicated that the DLRF exhibited uniformed interstory drift distribution as well as negligible residual drift subjected to DBE and MCE intensities, and thus the soft-story failure can be effectively avoided. Dynamic analyses also confirmed that the proposed design equations can predict the mechanical behavior of the DLRF with expected drift capacity and flag-shaped hysteretic response. Therefore, the proposed DLRF is a viable alternative to a seismic load-resisting system which could avoid severe and expensive damage to the structure, enhancing resilience capacity.

Self-centering companion spines with friction spring dampers: Validation test and direct displacement-based design

This paper aims to propose self-centering companion spines with friction spring dampers (denoted as SCS) for obtaining better post-earthquake resilience in steel building structures. Two typical configurations of SCSs in buildings were first introduced. The SCS mainly consists of two rigid spines (RSs) and many friction spring dampers (FSDs). The two RSs have adequate strength and stiffness to create uniform inter-story drift distribution in SCS. The FSDs are the lateral force-resistant and energy-absorbing components and provide self-centering capacity for SCS. Some validation tests were further performed to investigate the hysteretic behavior of the developed SCS. Two different loading protocols were adopted in the experiments to test the stability of SCS subjected to different loading histories. 6% was set as the maximum loading roof drift to indicate the superior deformability of SCS. Moreover, three repeated loadings were performed for each loading protocol to study the behavior of SCS under aftershocks or multiple earthquakes. The experimental results show that the developed SCS can obtain stable and convincing self-centering hysteretic responses under repeated loading with different loading protocols, and no strength or stiffness deterioration can be found. These observations confirm that SCS is fully recoverable after earthquakes and has the potential to be used as a resilient seismic-resistant system in the building located in seismic regions. Lastly, the direct displacement-based design (DDBD) method was developed for SCS. A three-story SCS was designed on the basis of the proposed DDBD method. Nonlinear static and dynamic analyses were performed to validate the efficiency of the proposed DDBD procedure. The numerical results show that the designed SCS can show the anticipated nonlinear behavior and obtain the expected performance target.

Seismic design and performance evaluation of low-rise steel buildings with self-centering energy-absorbing dual rocking core systems under far-field and near-fault ground motions

This research focuses on seismic design and performance evaluation of low-rise steel buildings with self-centering energy-absorbing dual rocking core systems (denoted as SEDRC systems) under far-field and near-fault ground motions. The SEDRC system consists of two rocking cores (RCs) and several shear friction spring dampers (SFSDs). These SFSDs are located between the two RCs and arranged over the height of the SEDRC system to absorb energy and provide a self-centering feature. The two RCs are considered as two buckling restrained braced frames in this paper, which are utilized to obtain uniform inter-story drift distribution in buildings. The two RCs can also act as a backup lateral force-resisting and energy-dissipation system if necessary. A direct displacement-based design (DDBD) procedure is introduced for the SEDRC system. A physical test was conducted to investigate the stability of the SEDRC system under repeated loading with near-fault loading protocol. The test results show that the SEDRC specimen can get stable self-centering behavior under repeated rounds of tests, indicating that the SEDRC system can be fully recoverable against multiple earthquakes before the development of the bearing action in SFSDs. The computational model of the SEDRC system was created and verified with the test results. A three-story representative building was designed through the proposed DDBD method, and the numerical models of the building were generated using the verified modeling method. Forty far-field ground motions and twenty near-fault ground motions were selected to perform Nonlinear Dynamic Analyses (NDA) on the designed building. The NDA results show that the designed three-story SEDRC system can satisfy the drift limit under DBE far-field excitations. And the designed SEDRC system can also survive and achieve small residual drifts subjected to the fault-normal components of the selected near-fault excitations and MCE far-field excitations.

Drift-based seismic design procedure for Buckling Restrained Braced Frames

In this paper, a drift-based seismic design (Dr.BSD) procedure is proposed by which a multi-story frame can be proportioned for a predetermined maximum inter-story drift uniformly distributed along all stories. While conceptually the proposed step-by-step design procedure is applicable for any lateral load resisting system, this study mainly focuses on Buckling-Restrained Braced Frames (BRBFs). Dr.BSD has a coupled theoretical-empirical basis developed for medium to high-rise multistory frames. It accounts for higher mode effects, flexural-shear behavior of the frame, and material and geometrical nonlinearities. From nonlinear dynamic analyses, it is shown that regular or moderately irregular BRBFs designed according to Dr.BSD would experience a rather uniform inter-story drift distribution close to the predefined target inter-story drift. In addition to the maximum inter-story drift, residual inter-story drift would be rather uniform in all stories. Sensitivity studies show that Dr.BSD is applicable for different target ductility demands, different target inter-story drifts, frames with different aspect ratios, and different design spectra with different soil types.

Seismic collapse risk of RC frames with irregular distributed masonry infills

Masonry infills are normally considered as non-structural elements in design practice, therefore, the interaction between the bounding frame and the strength contribution of masonry infills is commonly ignored in the seismic analysis work of the RC frames. However, a number of typical RC frames with irregular distributed masonry infills have suffered from undesirable weak-story failure in major earthquakes, which indicates that ignoring the influence of masonry infills may cause great seismic collapse risk of RC frames. This paper presented the investigation on the risk of seismic collapse of RC frames with irregularly distributed masonry infills through a large number of nonlinear time history analyses (NTHAs). Based on the results of NTHAs, seismic fragility curves were developed for RC frames with various distribution patterns of masonry infills. It was found that the existence of masonry infills generally reduces the collapse risk of the RC frames under both frequent happened and very strong earthquakes, however, the severe irregular distribution of masonry infills, such as open ground story scenario, results in great risk of forming a weak story failure. The strong-column weak-beam (SCWB) ratio has been widely adopted in major seismic design codes to control the potential of weak story failures, where a SCWB ratio value about 1.2 is generally accepted as the lower limit. In this study, the effect of SCWB ratio on inter-story drift distribution was also parametrically investigated. It showed that improving the SCWB ratio of the RC frames with irregularly distributed masonry infills can reduce inter-story drift concentration index under earthquakes, therefore, prevent weak story failures. To achieve the same drift concentration index limit of the bare RC frame with SCWB ratio of about 1.2, which is specified in ACI318-14, the SCWB ratio of masonry-infilled RC frames should be no less than 1.5. For the open ground story scenario, this value can be as high as 1.8.

Development and validation test of a novel Self-centering Energy-absorbing Dual Rocking Core (SEDRC) system for seismic resilience

This research focuses on the development and validation tests of a novel seismic force-resisting system named as the Self-centering Energy-absorbing Dual Rocking Core (SEDRC) system for improving seismic resilience in steel building frames. An innovative Shear Friction Spring Damper (SFSD) was developed to provide seismic energy dissipation capacity and self-centering characteristic to the SEDRC system. Two Rocking Cores (RCs), pinned to the ground, are introduced in the SEDRC system for obtaining uniform energy absorption and evenly uniform distribution of the inter-story drift. The components, working principle, and mechanical performance of the proposed SEDRC system are first described, where its notable perceived advantages compared to the existing rocking system are highlighted. A physical test on the hysteretic behavior of individual friction ring springs used in SFSDs is subsequently introduced. Then, the validation test of the SEDRC system is presented, where the key properties including the strength, stiffness, deformability, re-centering capability and energy-absorption capacity are discussed in detail. The experimental test results of the SEDRC specimen show positive and stable flag-shaped hysteretic behavior. Nearly no residual drift was observed after removing the applied lateral forces up to 6% roof drift, indicating that the SEDRC system has excellent deformability and self-centering capability. The two RCs could remain elastic during the entire cyclic loading process and promote uniform distribution of inter-story drift in the SEDRC specimen. Moreover, the computational model of the SEDRC specimen was developed and verified. Twenty-one ground motions were utilized to investigate the dynamic behavior of the SEDRC system. Numerical results further confirm the expected seismic behavior of the SEDRC system.

Evaluation of Seismic Response of Concrete Structures Reinforced by Shape Memory Alloys (Technical Note)

Shape memory alloys (SMAs) are unique smart materials that have many advantages, such as ability to resist large strains without leaving residual strains and ability to recover original form. However, the high costs of SMAs have limited their usage. This paper evaluates the behavior of concrete structures equipped with SMAs in an optimal manner as they are being used along the plastic hinge of the beams. For this purpose, a reinforced concrete (RC) beam, a 2D RC frame and a 3D RC building are considered, which were tested in previous studies under cyclic loading and on a shaking table. After verifying RC beam in the Seismostruct software, the steel rebars are replaced by SMAs in all connections of models and time history analysis is performed. The seismic response of concrete structures equipped with SMAs is compared with the conventional RC structures. The maximum base shear and roof displacement, amount of residual displacement and distribution of interstory drift at the structure height are among the factors to be evaluated. The results show that, due to the use of SMAs in concrete structures, the maximum base shear does not significantly change compared with the conventional RC structures, and the residual displacements in the structure roof have been reduced. On the other hand, the maximum displacement of the roof was increased in the structures with SMAs. The concrete structures equipped with SMAs experience a slight residual deformation, and the distribution of interstory drift is even more uniform at the height of such structures.

Mitigating Inter-Story Drift Concentration of Concentrically Braced Steel Frames Using Energy-Dissipative Columns

ABSTRACT Concentrically braced steel frames (CBSF) always suffer from weak-story failure with a large inter-story drift concentrated on the weakest story. A novel system of Energy-Dissipative Column (EDC) is proposed in this paper to improve the seismic behavior of low and mid-rise CBSFs. The EDC system consists of dual hinge supported steel boundary branches and replaceable steel strip dampers between them. Nonlinear dynamic analyses are conducted on 3-story and 6-story benchmark CBSF buildings with and without EDCs. The effectiveness of EDCs with different stiffness ratios on mitigating the seismic responses of CBSFs under design based and maximum considered earthquakes are investigated. The results show that the presence of EDCs in an existing multi-story CBSF can not only dissipate seismic energy to reduce the maximum inter-story drift, but facilitate more uniform inter-story drift distribution by redistributing the seismic forces along the structural height. It is found that the maximum inter-story drift and drift concentration can be reduced by half when the lateral stiffness ratio of EDC to CBSF reaches 0.2.

Developing Nonlinear Behavior of Reinforced Concrete Elements Using an Intelligent Approach

ABSTRACT In this paper, attempts are made to present an intelligent procedure, namely, least square supported vector machine (LSSVM) to provide the reinforced concrete (RC) elements’ nonlinear model. For this purpose, an existing database developed from several experiments is taken from PEER reports and a simple mathematical procedure is presented to estimate parameters of the expected model. This idealized model is capable of predicting the monotonic as well as cyclic characteristics of RC beams and columns. In order to investigate the accuracy of the proposed procedure, a RC structure with six stories is designed and the intelligent method is used to find the inelastic characteristics of the frames’ elements. Afterward, different comparisons are made between the results of the suggested procedure and the outputs of an introduced method usually used for modeling the nonlinear behavior of concrete structures. This comparison shows the good agreement between the results of the intelligent method with existing procedure. In addition, nonlinear static analysis, as well as statistics analysis, is performed to obtain median inter-story drift distribution along the height of the structure, structural members’ ductility and dissipated energy under design basis earthquake (DBE). It is revealed that the outputs of the new method have less deviation with the utilized experimental database in comparison with the other ones. Furthermore, the plastic hinges constructed by the new approach indicate more ductility and energy dissipation than the results of existing method.

Experimental study on seismic performance of RC frames with Energy-Dissipative Rocking Column system

The conventional reinforced concrete Moment Resisting Frames (MRFs) have suffered from soft story failure during major earthquake events. A novel system of steel Energy-Dissipative Rocking Column (EDRC) is proposed to mitigate seismic responses of MRFs. Pseudo-dynamic tests are conducted on large-scale two-story and two-bay reinforced concrete frames, with and without EDRC, respectively. The post-earthquake behavior of these two systems is also compared through quasi-static cyclic tests. The experimental results show that the presence of EDRC can effectively mitigate the maximum value, residual value and inhomogeneous distribution of inter-story drifts, and thus prevent the soft story failure of MRFs. It is found that the maximum and residual inter-story drift of combined MRF and EDRC systems is reduced by 26.0% and 82.0%, respectively, compared to pure MRFs. The inhomogeneous degree of inter-story drifts can be reduced by 25.0% and 11.0%, respectively, in the pseudo-dynamic and quasi-static tests.

Self-similar interstory drift spectrum and response distribution of flexural-shear beam with nonuniform lateral stiffness

This paper proposes the concept of self-similar interstory drift spectrum based on the dimensional analysis of flexural-shear beam with nonuniform lateral stiffness, and scrutinizes the effects of lateral stiffness reduction on the seismic responses and response distribution. Firstly, the finite element formulation for the combined beam is established, which is convenient for parametric analysis. Subsequently, the intrinsic length scale and time scale are proposed to conduct correctly the dimensional analysis for seismic responses of flexural-shear beam, indicating that the normalized maximum interstory drift ratio and normalized maximum floor acceleration present a complete similarity in the normalized building height and the beauty of order. Hence, the concept of self-similar interstory drift spectrum is suggested to avoid the use of empirical relationship between fundamental period and building height. Moreover, the effects of lateral stiffness reduction on the normalized responses and response distribution of flexural-shear beam are examined under the idealized pulses and near-fault ground motions. With the exception of significant stiffness reduction, the effect of lateral stiffness reduction is generally small. In particular, the vertical distribution of interstory drift mainly depends on the structural type, whereas the floor acceleration generally increases along the building height. Finally, the established regression model can sufficiently fit the mean self-similar interstory drift spectrum and mean self-similar floor acceleration spectrum, and the normalized seismic responses can be well predicted by the fitted curves.

Parametric Study on the Seismic Response of Steel‐Framed Buildings with Self‐Centering Tension‐Only Braces

Self‐centering bracing systems, by which residual deformations of structures after earthquakes can be minimized, are considered effective solutions to achieve seismic resilience. In this paper, a parametric study on the seismic response of intermediate and high‐rise steel‐framed buildings with novel self‐centering tension‐only braces (SC‐TOBs) is numerically conducted. Three key parameters, the stiffness degradation factor, the activation strain, and the initial axial stiffness of the SC‐TOBs, are investigated to explore the design space for the SC‐TOB frames (SC‐TOBFs) because of their unique tunability compared with traditional bracing systems. Identical steel frames equipped with buckling restrained braces (BRBs) are also designed and examined for comparison purposes. The results indicate that increasing the stiffness degradation factor can improve the second stiffness of SC‐TOBFs and successfully make the distribution of interstory drifts more uniform; an increase in the activation strain leads to a larger activation deformation of SC‐TOBFs, but it has a very limited effect on the interstory drifts; increasing the initial axial stiffness appropriately is beneficial to reduce the interstory drifts of the low stories. The lateral behavior of SC‐TOBFs is comparable to that of BRB frames when a lower activation strain and a higher initial axial stiffness are selected. Furthermore, when a higher stiffness degradation factor and a lower initial axial stiffness are selected simultaneously, the seismic action on SC‐TOBFs can be effectively reduced, and a relatively uniform distribution over the building height can be obtained. The SC‐TOBFs are considered to be a type of performance‐tunable structure, and tuning can be achieved by varying a frame’s adjustable parameters.

Probabilistic seismic assessment of non-ductile RC buildings retrofitted using pre-tensioned aramid fiber reinforced polymer belts

The current manuscript presents a probabilistic seismic assessment of non-ductile RC structures retrofitted by pre-tensioned aramid fiber reinforced polymers (AFRP). Three RC buildings with different heights (4-, 6- and 8-stories) are designed according to older construction practice and the poorly detailed columns of each model are then retrofitted using pre-tensioned AFRP belts. The numerical finite element models are developed in OpenSees using concentrated plastic hinge models that can capture shear weakness of original columns and deterioration of beams’ stiffness and strength. Incremental dynamic and nonlinear static analyses are performed to quantify structures’ performance in terms of both global- and component-level metrics. The structures’ global response is evaluated using fragility curves, mean annual frequency of collapse, and collapse margin ratios. Furthermore, statistical analyses are performed to obtain median inter-story drift distribution along the height of the structure, structural members’ ductility and dissipated energy under three different seismic hazard levels. The results indicate that retrofitting by pre-tensioned AFRP improves the structure’s global-level ductility and reduces the collapse probability significantly. Moreover, it can prevent weak story formation by engaging a larger number of stories in collapse mechanism. From a component-level perspective, pre-tensioned AFRP increases columns’ ductility and dissipated energy and enhances their performance, particularly at near-collapse-limit states.

Nonlinear damage model for seismic damage assessment of reinforced concrete frame members and structures

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.