Drift Ratio Research Articles

Seismic Damage and Behavior Assessment of Drift-Hardening Concrete Walls Reinforced by LBUHS Bars.

This paper experimentally and analytically investigated the damage and seismic behavior of concrete walls reinforced by low-bond ultra-high-strength (LBUHS) bars. To this end, four half-scale rectangular concrete walls were fabricated and tested under reversed cyclic loading and constant axial compression. The test variables were the shear span ratio and the axial load ratio. Based on the test results, the propagation of cracks on the wall surface, the maximum strain capacity of concrete, the hysteresis loops and envelope curves, the residual drifts, and the strain distributions of LBUHS rebars were presented and discussed. The experimental results showed that all the test walls could exhibit drift-hardening capability until at least a 2.0% drift ratio if LBUHS rebars were anchored by nuts at their ends. The test results also indicated that the maximum strain capacity of concrete was above 0.86%, much larger than the currently recommended 0.4%. After unloading from the transient drift ratios of 2.0% and 2.5% for the walls with shear span ratios of 1.5 and 2.0, respectively, the measured residual drift ratios were controlled below 0.4%, which is less than the critical drift ratio (0.5%) having 98% repairable probability recommended in the FEMA document (P-58) for general concrete structures. Furthermore, a numerical method was presented to evaluate the cyclic response of the test walls, and a comparison between the experimental and the calculated results verified the reliability and accuracy of the proposed numerical method.

Seismic behavior of precast segmental bridge columns confined by grouted glass fiber reinforced plastic tubes

The application of precast segmental bridge columns (PSBCs) is still restricted in seismicity areas due to concerns such as lower lateral stiffness and column base bearing capacity. To enhance the applicability of PSBCs, this study proposed a novel approach of confining them with grouted GFRP tubes. Four novel and one reference specimens were tested under low cyclic loading to evaluate the effects of energy dissipation (ED) bars ratios, concrete interlayer strength, type of segment concrete, and concrete pouring methods within the outer GFRP tube (OGT) on the seismic behavior. Experimental results reveal that the failure modes of all specimens were triggered by the yielding of ED bars and the break of OGT at the top of ED bars. No crushed concrete at column bases or cracks at the segment joint were observed during the test due to the good confinement of GFRP tubes. All the specimens exhibited stable hysteretic behavior with small residual drift ratios and low strength degradation. Furthermore, finite element models (FEMs) were generated to predict the hysteretic behavior of novel specimens. The effects of some parameters such as OGT thickness, ED bars diameter, and concrete strength were further studied.

Investigating seismic performance of SMRF buildings under subshear and supershear rupture conditions: Assessment of storey-level internal damage

The source effect of earthquake ruptures causes spatial-temporal variability in ground motion characteristics in the vicinity of a fault. This research employs a dynamic rupture-based method with SPECFEM3D to simulate two rupture types: subshear and supershear. While the former depends on the rupture length of the fault, the latter depends on the rupture velocity. Synthetic earthquake ground motion data are generated across the entire domain, encompassing both near-fault and far-fault locations. Ground motions exhibit multidimensionality, with subshear effects evident in the fault normal component and supershear effects distinctly reflected in the fault parallel component. These ground motions have been employed to excite low (S1L), mid (S1M), and high-rise (S1H) steel special moment resisting frame (SMRF) buildings modelled using the modified Ibarra-Medina-Krawinkler (IMK) analogy. Understanding the far-field effects of supershear earthquakes and the near-field effects of directivity in subshear earthquakes on the structural response of SMRF buildings has been aided by several engineering demand parameters (EDPs), including floor acceleration, interstorey-drift ratio, and roof drift ratio.

Numerical investigation of nonlinear soil-structure interaction effects on response of irregular RC buildings

Kathmandu, located in a high seismic zone, predominantly features irregular structures among its building stock. These structures are particularly susceptible to severe damage during seismic events, primarily due to torsional effects. Traditional seismic designs rely particularly on fixed-base conditions that underestimate forces and displacement primarily on soft soil conditions leading to irrational design practices. This study aims to quantify the seismic performance of buildings on various base conditions through fully nonlinear Soil-structure Interaction (SSI). The soil nonlinear behaviour was modelled using the Pressure-Independ-Multi-Yield (PIMY) material with an octahedral shear stress-strain backbone curve. Three distinct soil types were considered, and structures with irregular plan configurations were modelled using finite elements in both Opensees and STKO platforms. Structural performance was analyzed through nonlinear dynamic analysis, and outputs were evaluated based on seismic parameters. Comparing nonlinear SSI with linear SSI and fixed-base conditions revealed a significant increase in structural response, expressed in terms of displacement, drift ratio, and base shear. The magnitude of diaphragm rotation was found to be influenced by a combination of building torsional irregularity and SSI effects. It is suggested that the conventional practice of using the torsional irregularity ratio as a measure of torsional irregularity be revised and enhanced to better account for these influences. It has been quantified that torsional irregularity has a relatively lesser impact on displacements, drifts, and base shear compared to SSI. In all cases, fixed-base conditions consistently exhibited the minimum response. The study explored that linear SSI and fixed-base conditions tend to underestimate structural responses, while nonlinear SSI coupled with dynamic analysis provides a more accurate representation of realistic structural behaviour for seismic design particularly in soft soil cases.

Structural behavior of steel tube reinforced resilient RAC shear walls under static cyclic loading

This paper proposed a method to enhance the energy dissipation capacity of recycled aggregate concrete (RAC) shear walls reinforced with ultra-high strength bars (UHSB). The proposed method encases circular steel tubes within the boundary elements of walls. With the presence of steel tubes, steel fibers and axial load level as primary research variables, five RAC shear walls were fabricated and tested under reversed cyclic lateral force and constant axial compression to verify the effectiveness of the proposed method. The test results showed that the presence of steel tubes upgraded lateral resistance and enhanced energy dissipation capacity, while causing some subtle splitting cracks. Due to the yielding of the steel tubes, the encasement of the steel tube increased residual drift ratio at large drift, but the measured residual drift ratios of test walls still were kept less than 0.5 % until 2.5 % drift ratio. The addition of steel fibers delayed cracking, constrained the cover concrete and reduced damage to the specimens. Test results also indicated that increasing concrete strength and axial compression level could enhance the lateral resistance of the proposed wall. In addition, a numerical analytical method is presented to analyze the cyclic behavior of the proposed shear walls. Good agreement was observed between the measured and calculated hysteretic loops.

Comparative seismic performance evaluation of friction, self-centering and hybrid self-centering dampers

This study explores comparative seismic performance of a shape memory alloy (SMA)-only device, a friction damper, and a hybrid self-centering device. The self-centering device considered in this study, named as superelastic friction dampers (SFDs), is a hybrid damper operating on a mechanism where SMA cables and frictional components are arranged in parallel. A detailed description of the device and an experimental characterization of mechanical behavior are presented first. Then, an 8-story archetype steel frame building is designed and modeled with each seismic protection device (SMA-only, hybrid self-centering, and friction only). To enable comparative performance assessment, each device is designed to have similar initial stiffness and the same maximum force at design displacement. Nonlinear time history analyses are conducted using a total of 44 ground motion records. The results are evaluated to compare performance of each frame design at design-basis and maximum considered earthquake hazard levels. Next, a risk-based seismic hazard demand analysis framework that involves comprehensive incremental dynamic analyses is employed for further assessing the performance of each system. The experimental results validate the parallel working mechanism of SMA cables and frictional components in the SFD, with 90% of the damper deformations recovered. Comparative analysis of seismic responses demonstrates the excellent performance of the SFDs in reducing interstory drift ratio, residual interstory drift ratio, and absolute acceleration responses. Furthermore, fragility analysis and risk-based seismic hazard assessment further reveal that the SFDs provide a well-balanced combination of energy dissipation capability and self-centering ability, thereby enhancing the seismic resilience of structures.

Strain energy-based uniformity spectrum for elastic deformation control of super high-rise buildings under near-fault pulse-like earthquake excitations

To reasonably control the elastic lateral deformation of super high-rise buildings under near-fault pulse-like ground motions, inspired by a potentially close link between material utilization and normalized strain energy, a novel generalized uniformity spectrum of normalized strain energy (GUSNSE) is proposed via the nonuniform flexural-shear coupled model. With a full understanding of the characteristics of spectral shapes and the influence of shear-flexural stiffness ratios and mass-stiffness nonuniformity, the GUSNSE is fitted by artificial pulses. Utilizing the GUSNSE, a lateral stiffness estimation strategy is developed with the requirement of peak interstory drift ratios (IDRs). The feasibility and effectiveness of the proposed strategy are systematically demonstrated by comparison with not only the original lateral stiffness schemes of three significantly distinct buildings but also those designed for uniform IDRs. The accuracy of the fitted GUSNSE is also validated via the data estimated by four sets of ground motions. The GUSNSE-based strategy is promising as an efficient, reliable, and practical tool for providing lateral stiffness of super high-rise buildings in the preliminary design.

Model updating of a shear‐wall tall building using various vibration monitoring data: Accuracy and robustness

SummaryAcceleration measurements are often used for model updating of civil engineering structures, especially in the case of seismic monitoring. It is yet unclear if accelerations alone would generate an accurate and robust finite‐element (FE) model. This study examines this notion and analyzes the possibility of using other vibration monitoring data for model updating of shear‐wall tall buildings. This study compares the accuracy and robustness of the FE models being optimized via accelerations, roof displacement, wall rotations, interstory drift ratios, and the linear combination of these measurements. A numerical case study is analyzed using Timoshenko beams for modeling the lateral vibration of a benchmark 42‐story building under seismic excitations. Results show that the acceleration response of the examined building is mostly governed by its higher vibration modes. Depending on the characteristics of ground motions, using accelerations alone may generate an FE model biased towards higher‐order modes without effectively capturing the lower‐order modes. For instance, the first modal frequency of the updated FE model could be 12.0% lower than the true value, and the reconstructed displacement and rotation responses are noticeably inaccurate. Employing multi‐source monitoring data for model updating, for example, the combinations of roof displacement and acceleration measurements, could reduce the normalized root‐mean‐square errors in displacements by more than 70%. This study also quantifies the robustness of the FE model under various measurement noise levels and 50 pairs of earthquake records. Finally, the effects of multi‐source data on FE model updating are validated via experiments on a 7‐story shear wall building. Analysis reveals that a more accurate and robust FE model can be determined via a combination of accelerations and top displacement than via acceleration alone.

Average spectral acceleration (AvgSa) for high-confidence probabilistic seismic demand modeling of urban highway bridge portfolios: What period range and damping ratio shall we use?

The average spectral acceleration (AvgSa), i.e., the geometric mean of spectral accelerations over a period range, has attracted widespread recognition as one of the most promising intensity measures (IMs) for probabilistic seismic demand modeling of structures. As AvgSa is a structure-related spectral IM, a pivotal step in calculating AvgSa is to determine an appropriate period range and damping ratio. Whilst optimal AvgSa has been well documented for buildings, consensus on the period range and damping ratio of AvgSa for urban highway bridges is yet to be reached. To this end, a pool of AvgSa candidates with different combinations of lower and upper period bounds and damping ratios are assessed to identify the optimum combination(s) for straight and curved urban highway bridge portfolios against bidirectional seismic excitations, in terms of peak pier drift ratio, peak bearing displacement, and residual pier drift ratio. Results indicate that for the peak demand parameters, optimal AvgSa is characterized by a damping ratio of 0.2 and a period range of [Tf, 1.5Tf], where Tf is the structural fundamental period, for bridges with relatively short piers; and the optimal period range becomes [Tf, 2Tf] for medium to tall-pier bridges. Besides, the optimal period range for the conventional 5%-damped AvgSa is also detected, where [0.5Tf, 1.5Tf] is the optimal range for bridges with relatively short piers, while [0.5Tf, 2Tf] is recommended for medium to tall-pier bridges. Regarding the residual pier drift ratio, averaging spectral accelerations over any examined period ranges does not outperform traditional spectral accelerations at specific periods.

Inerter-based tuned mass dampers for response control of multi-degree-of-freedom structures subjected to wind and earthquake excitations

The present work explores the utilization of the tuned mass damper-inerter (TMDI) in controlling the structural response subjected to wind and earthquake excitations. An example of a 25-storey reinforced concrete building is taken up. The equations of motion of the structure-TMDI combined system are established by assuming the building behaves as a shear-building with multiple degrees of freedom. These equations are solved using Newmark’s time integration method. The objective functions are the wind- and earthquake-induced structural response quantities, such as the maximum inter-storey drift ratio (MIDR) and peak floor acceleration (PFA). The prime contribution of this study is the inclusion of statistical measures such as the mean, 85th, and 95th percentiles for these quantities. A genetic algorithm-based multi-objective optimization is performed to estimate the optimum TMDI parameters. Based on the outcomes of this study, it can be recommended that the TMDI be optimized to perform well under the 95th percentile for MIDR and PFA in effectively reducing the peak structural responses. Frequency domain analysis results demonstrate TMDI’s multiple-mode controlling capability. The energy comparison plots of the uncontrolled and controlled structures prove the effectiveness of the optimum TMDI in providing enough damping and ensuring structural stability.

Optimal seismic design for self-centering concrete wall structures equipped with U-shaped flexural plate dissipaters

In self-centering wall (SCW) structural system, additional energy dissipation devices are crucial members that are expected to provide both partial lateral force resistance and energy dissipation capacity aiming at mitigating structural response. This research aims to develop a seismic design framework based on particle swarm optimization algorithm for SCW structures equipped with U-Shaped Flexural Plates (UFPs), which can be used to seek out the optimal configuration of UFPs of each floor to reduce seismic response, while maintaining a constant total lateral force resistance provided by all UFPs. For validation, a 10-story SCW structure is chosen as the design case. Specifically, two configurations are considered: a 10-story SCW structure equipped with identical UFPs following conventional design (SCF10-Original) and one equipped with UFPs from optimized configuration (SCF10-Optimized). Their drift and acceleration response are calculated and compared under different seismic intensities through nonlinear time history analysis (NATH). The results demonstrate that the optimized configuration of UFPs can significantly mitigate the drift response in SCW structure. For instance, the maximum inter-story drift ratios of SCF10-Optimized are 0.2 % smaller than those of SCF10-Original under maximum considered earthquake, while the maximum residual inter-story drift ratios of SCF10-Optimized are only half those of SCF10-Original under Extremely Rare Earthquake. Furthermore, the optimized UFPs can effectively reduce the maximum floor acceleration response under various seismic intensities. Therefore, the optimized configuration of UFPs is more effective in reducing both structural and non-structural damage for SCW structural systems compared to conventional configuration. It is also found that greater energy dissipation levels in SCW structure equipped with UFPs may not always result in smaller seismic response, while the configuration of UFPs may play a major influencing factor due to different inter-story lateral force resistance and inter-story energy dissipation demands of SCW structure.

Seismic behavior of drift-hardening precast concrete walls reinforced with SBPDN rebars

Six precast concrete walls reinforced with weakly bonded ultra-high strength (WBUHS) rebars were fabricated and tested under reserved cyclic lateral loading and constant axial compression to investigate the seismic behavior of the precast drift-hardening concrete walls. The emphasis was placed on clarifying the proper embedded length for WBUHS rebars and verifying the influence of the shear span ratio. The experimental variables were the embedded length of the WBUHS rebar, the shear span ratio of the walls, and the axial load ratio. Test results indicated that if the embedded length of the WBUHS rebar, whose ends were anchored by nuts and a washer, was 20d (d is the nominal diameter of rebar) and/or longer, the precast walls could exhibit identical seismic performance to the cast-in-site walls and had sufficient drift-hardening capability up to at least 2.0 % drift ratio. Test results also showed that the larger the shear span ratio, the less the residual drift. The residual drifts after unloading from the 2.0 % transient drift were less than 0.4 % regardless of the axial load level and the shear span ratio. Furthermore, an analytical method was presented to evaluate the seismic behavior of the precast walls reinforced by WBUHS rebars. The analytical method can consider the effect of bond slippage of WBUHS rebars and the confinement effect by transverse steels placed in the boundary elements on the cyclic response of the walls. Comparison between the measured cyclic loops and the predicted ones has indicated that the proposed analytical method can predict the cyclic behavior of the precast walls very well in important aspects such as overall performance, the ultimate lateral resistance, and the deformation capacity.

Cyclic response of innovative modular joints for modular buildings under bidirectional loading

Based on their dual functions of loading-bearing and energy-dissipating, modular loading-bearing and energy-dissipating joints (MVJ) was used to vertically connect modules, particularly high-rise modular building applications. Fully bolted MVJs can be assembly and disassembly rapidly, and the modules can be recycled after disassembly. Quasi-static tests were conducted on two full-scale space specimens to evaluate seismic resistance properties of the MVJs. Owing to the critical function of MVJs in the buildings, the constant axial loading on the modular column and the vertical displacement on both double beams were implemented simultaneously to simulate the worst loading condition. Owing to the characteristics of double beams under vertical forces, and the requirements of simulation of boundary conditions, a double-beam hinged loading device was proposed. The experimental results demonstrate that the proposed MVJs exhibited great moment capacity. Accordingly, the ratios of the tested average ultimate moment capacity Mu to the designed ultimate moment capacity of double beams MP,beam were 0.828 for S1 and 0.995 for S2. Diagonal cracks occurred on the ends of MVC web for both S1 and S2, indicating that the proposed MVJs were crucial in both loading-bearing and energy-dissipating; the MVC web was used to dissipate energy. Because of the insufficient weld strength between the column and the ceiling beam, as well as the bidirectional cyclic displacement observed at both ends of double beams, the error in the average ultimate moment capacity between the tested and the predicted result is 17.08 %. Analysis conducted on the ductility factor and inter-storey drift ratio demonstrated the feasibility of implementing MVJs in seismic regions.

Experimental investigation of the mechanical performance of novel rigid connections in prestressed circular composite precast concrete columns under cyclic lateral loading

The present study introduces an advanced design of Prestressed Circular Composite Precast Concrete Columns (PCCPCCs), which have been applied in real-world structures, equipped with two novel rigid connection types (i.e., the reinforcing-cage connection and the welded-plate connection) to address existing challenges in the design, construction, and quality control of traditional precast concrete (PC) columns. Five full-scale specimens were experimented individually to assess the mechanical performance of PCCPCCs subjected to cyclic lateral loading and constant axial loading. The results indicate that the specimens exhibited no signs of collapse or loss in axial load capacity during the tests. Furthermore, all specimens met or exceeded the performance criteria set by relevant standards, such as GB50011-2010 and ACI 374.1-05, regarding drift ratio, moment capacity, energy dissipation, and ductility. It demonstrates that the novel design of PCCPCCs proposed in this study can be integrated into practical construction projects designed as lateral-force-resisting systems, such as moment-resisting frames and bridges, to accommodate diverse construction project requirements.

Seismic analysis of RC building with plan irregularity in Baghdad/Iraq to obtain the optimal behavior

Abstract A study was conducted for four-story reinforced concrete (RC) structure existing in Baghdad-Iraq (residential building) to evaluate the accuracy and reliability of the equivalent lateral force procedure (ELFP) analysis and the response spectrum model (RSA) according to Iraqi seismic code (ISC 2016) for designing and analyzing irregular buildings. The building was classified as an irregular in plan according to American Society of Civil Engineers (ASCE 7-16). The seismic behavior of the building was investigated by verifying many parameters: the ratio of shear demand to shear strength on the columns ( V V / V n {V}_{n} ), internal force (bending moment, shear force, and axial force) for beams and columns, and the inter-story drift ratio (IDR) obtained from the (ELFP and RSA); then, the results were compared with the nonlinear static procedure (NSP) and the nonlinear dynamic procedure (NDP) according to ASCE 7-16. Also, this study investigated the effects of the higher modes in the plan (roof plan displacement). From the results, it can be concluded that ELFP and RSA are not a suitable analysis for asymmetric structures and should use appropriate methods such as the NSP and NDP.

Experimental study on seismic performance of stainless steel full-scale frames: Global response

This paper presents an experimental study of the seismic performance of austenitic stainless steel full-scale frames using the pseudo-static test method. The bottom single-span, two-storey substructure of the designed prototype frame was chosen as the test frame. Two full-scale frames were tested, one with a bolt-welded joint and the other with an extended end-plate joint. This paper is the first of two accompanying papers to this experimental study and focuses on the specimen design, testing details and global response of the stainless steel frame under cyclic loading. The test results were utilized to analyse the global response of the frames, encompassing failure mode, bearing capacity, deformation capacity, energy dissipation capacity, the overstrength factor, ductility factor and seismic response modification factor. The experimental findings suggest that the stainless steel frames with two joint types demonstrate consistent ability to dissipate energy during cyclic loading. The structure also performs well in terms of deformation, with uniform inter-storey deformation and no soft-storey detected. The maximum storey drift ratio of the frame is 7%. Prior to reaching a storey drift ratio of 2%, the frames with both joint types exhibit similar cumulative plastic deformation, stiffness degradation, and cumulative energy dissipation.

Behaviour of Grouted Sleeve Wall Connection under Lateral Load

A grouted sleeve’s efficiency in splicing steel bars makes it a potential choice for connecting precast elements. While most studies have focused on the feasibility of grouted sleeves under tension, only a few have investigated the real response of precast concrete members connected using grouted sleeves. In this study, Tapered Head Sleeves (THS) were utilized as connections for precast walls. The objectives were to examine their behavior under incremental lateral loads and assess the feasibility of THS as a wall connection. Five test specimens and one control specimen were fabricated, each comprising two walls joined by THS. The load was applied 1.8 m above the joint until specimen failure. Specimens that experienced bar fracture failure exhibited a relatively large drift upon failure, while those failing due to bar bond slip showed smaller drift. Factors contributing to wall drift included horizontal slip, rocking displacement, cantilever bending deformation, and compressive settlement. The ultimate load increased by 71% as the embedded length increased from 75 mm to 175 mm, and it increased by 50% as the sleeve diameter decreased from 75 mm to 50 mm. The sleeves' performance was evaluated for feasibility based on the strength ratio, drift ratio, ductility ratio, failure mode, performance ratio, serviceability ratio, and length ratio. Only THS-8 met all the criteria, suggesting that the bar's embedded length should be at least 11 times the bar diameter.

Seismic Response of Vertical Hybrid Concrete/Steel Frames Considering Soil–Structure Interaction

The aim of this study is to investigate the seismic behavior of concrete/steel mixed structures. In engineering praxis, many buildings consist of two parts: one made of reinforced concrete and the other made of steel. There are several difficulties in the code-based seismic design of these structures due to the different dynamic responses of each discrete part. Seismic design codes, such as the IBC and Eurocode 8, do not provide instructions for structures consisting of two parts. In addition, they use a single-loading scenario, but there are many locations that are affected by more than one earthquake in a short period. Another drawback is that recent provisions do not consider soil–structure interaction effects. The specific issue addressed here is the seismic response of mixed structures, which is evaluated through inelastic time–history analysis. More specifically, the response indices involve height-wise distributions for peak interstory drift ratios, maximum floor horizontal displacements, maximum floor accelerations, and plastic hinge formations in the frame elements when they are subjected to seismic sequences of earthquakes, as well as in far fault ground motions for different soil types. The results reveal that sequential ground motions lead to increased displacement demands, and they affect the permanent displacements. This phenomenon appears in both cases of stiff and flexible soil, as well as for both regular and irregular frames. It is found that soil–structure interaction generally leads to lower values of IDR, and maximum horizontal displacement and acceleration in comparison with the case of rigid soil assumptions.

Plastic hinge behavior of rectangular CFRP-confined RC columns: Meso-scale modelling and formulation

The ultimate rotation capacity, depending on the plastic hinge length, is a vital factor in the seismic design of flexural members. This paper focuses on the investigation of the plastic hinge length and size effect of rectangular carbon fiber-reinforced polymer (CFRP)-confined reinforced concrete (RC) columns. Firstly, considerable scatter and evident bias of the calculation results were found after evaluating existing models for calculating the plastic hinge length of FRP-confined RC columns. Accordingly, a meso-scale numerical approach was developed, with concrete heterogeneity considered, to investigate the influences of the confinement ratio and corner radius on the plastic hinge length and size effect of rectangular CFRP-confined RC columns. Results show that columns having different cross-sectional sizes exhibit similar failure patterns, and the region of lateral crack propagation for columns with lower confinement ratios is larger than that for columns with higher confinement ratios. The actual plastic hinge length is determined based on the yielding zone of reinforcement, the crushing zone of concrete, and the localization zone of curvature, while the localization zone of curvature is employed to determine the real plastic hinge zone. The size effect is found to exist in the plastic hinge length ratio, and it is weakened with the increase of the corner radius, which can be attributed to the fact that columns with higher corner ratios have more effective confinement. Taking into account the size effect, a new model for calculating the ultimate drift ratio of CFRP-confined RC columns was proposed based on an assumption of curvature distribution and presented accurate predictions.

Experimental investigation of retrofitting seismically damaged reinforced-concrete frames using steel jacketing

Retrofitting seismically damaged structures provides significant economic and social benefits. To investigate the rationality of using steel jacketing to retrofit seismically damaged reinforced concrete (RC) structures, we initially tested a half-scale single-span two-story frame structure under pseudo-static loads to achieve a severe damage state. Subsequently, the structure was retrofitted using steel jacketing and tested under another round of pseudo-static loads. The seismic performances of the original and retrofitted structures were compared. The test results indicated that both the original and retrofitted specimens sequentially developed plastic hinges at the beam ends and the bottom of the columns, indicating a generally similar damage evolution mode. Comparing to the original structure, the retrofitted specimen exhibited an increase of 33% and 78.5% in initial stiffness and strength, respectively. Although the ductility ratio of the retrofitted specimen was reduced by about 14%, the ultimate drift ratios of both specimens exceeded the threshold value (1/50), indicating an adequate deformation capacity. The retrofitted specimen exhibited a certain degree of pinching behavior on the hysteretic curve because of the presence of extensive inclined shear cracks at the mid span of the beams and the progressive failure of the anchoring of the strengthening steel angle at the beam ends and column base. Consequently, the energy-dissipation coefficients of the retrofitted specimen were lower than those of the original specimen. Based on the test, the finite element analysis modeling method for RC frame structures retrofitted using steel jacketing was also studied. By comparing the numerical simulation analysis results with the experimental ones, the reliability of the proposed numerical simulation method was verified. This study can serve as a foundation for the practical application of steel jacketing to retrofit seismically damaged RC structures.