Results Of Nonlinear Dynamic Analyses Research Articles

Improved PBPD method for dual steel system considering the global effect of space frames

Performance-based plastic design (PBPD) method has been proposed to design single bay planar frames for twenty years. For a dual steel system, such as an eccentrically braced frame (EBF) structure, there will be both EBF bays and moment resisting frame (MRF) bays. So, the global effect between different frame bays cannot be considered when designing the global structure using the traditional PBPD method. In this paper, a ten-story high-strength steel composite K-shaped eccentrically braced frame (HSS-K-EBF) structure was firstly used for performance design and analysis based on a single bay EBF. The results show that the global structural model obtained by direct performance design of the single bay model cannot achieve the desired performance objectives. To this end, an improved PBPD method for the dual steel system was proposed considering the global effects of space frames. The elastic and elastic–plastic shear distribution relations were calculated for different bays of the frames including EBFs and MRFs. The performance objectives of the global structure were designed and evaluated more accurately by considering the over-strength contribution of shear links and the plastic development rate index ξ of energy dissipation members. The improved PBPD method was used to design the ten-story global HSS-K-EBF structure. The results of nonlinear dynamic time history analysis show that the improved PBPD method can ensure that the plastic damage distribution of energy dissipation members of different bays is more uniform and the plastic damage degree is more consistent with expectations.

Assessment of a Force Method for the Resilient Seismic Design of Special Moment-Resisting Steel Frames with Hysteretic Energy Dissipation Devices

In this paper, the authors present the results of nonlinear dynamic analyses of twelve building models designed according to a methodology based upon the force method, capacity design principles and the concept of structural fuses to achieve resilient seismic designs for special moment-resisting steel frames with hysteretic energy dissipation devices mounted on chevron steel bracing. It is demonstrated that the resilient design mechanism previously checked with pushover analyses is also attained for most studied models with nonlinear dynamic analyses using an acceleration record which is compatible with the elastic design spectrum. Also, it is corroborated that the planned second line of inelastic defense is activated if the seismic action surpasses the considered design spectrum. Based upon the obtained results, it is confirmed that it is possible to perform a resilient seismic design for the studied system under the proposed methodology, even for tall and slender buildings. Therefore, the proposed initial stiffness ratio parameters and the global design parameters previously proposed by the authors to use in a code-oriented force method can be used with confidence for the resilient seismic design of this structural system.

Theoretical and experimental research on the rocking truss system with post-tensioned rocking connection

The weak story failure often occurs in steel frame structures and the collapse risk of the frames will increase because of concentrated plastic deformation in the soft story. The work presented in this paper aims to avoid the soft story mechanisms and the improve self-centering capacity of steel frames by employing the innovative rocking truss. Compared with the previous rocking system, it is more flexible in application and suitable for retrofit of existing buildings. The theoretical approach to quantifying the stiffness demand of the rocking truss was proposed and presented two critical parameters (equivalent bending stiffness ratio η and the rotation stiffness ratio λ) for the design of the rocking truss. The 1/3 scaled steel frame with rocking truss (SFRT) was tested and theoretical analysis results were validated by test results. The finite element model of SFRT was built following the boundary conditions of the test specimen. The numerical results are consistent with the experimental observations. The nonlinear static and dynamic analysis results of the SFRT were compared with those of the same steel frame (SF) with a bracing system. It was found that the rocking truss can reduce the maximum and residual drifts of the main frame as expected, and the plastic development of the RBS at the beam end in SFRT is less than that in SF with a bracing system. The parametric analysis of the rocking connections with different values of prestressing force was carried out. The results confirm that the rotational stiffness and load-bearing capacity of the rocking connection can be accurately evaluated by the theoretical force-displacement curve. The effect of the equivalent bending stiffness ratio η and the rotation stiffness ratio λ on the lateral deformation pattern of structures was discussed by theoretical analysis, and the design procedure of the rocking truss is recommended to satisfy the demand of uniform inter-story drift and self-centering capacity.

Influence of Staggered Truss on Progressive Collapse-Resistant Behavior of Steel Frame Structures

In order to study the effect of the support mode of a staggered truss system on the continuous collapse resistance performance of a steel structure, four finite element models were established based on the bracing arrangement of a five-story steel frame structure. The situations of different columns on the first floor removed were classified into eight scenarios, and five models of each scenario were analyzed with nonlinear dynamic analyses. Finally, a computational metric based on energy robustness was proposed to evaluate the robustness of the structure. The results of nonlinear dynamic analyses indicated that the staggered truss system significantly improved the resistance to progressive collapse of steel frame structures and effectively increased the redundancy of steel frame structures. All four bracing methods effectively reduced the vertical displacement at the point of failure, with the peak displacement at the point of failure reduced by a maximum of 84 percent and a minimum of 41 percent compared to a pure frame structure. Moreover, the staggered truss system can reduce some axial force peaks in the adjacent columns adjacent to the failed columns. The structural robustness coefficients of Model A, Scheme 1, Scheme 2, Scheme 3, and Scheme 4 are 1.144, 1.339, 1.306, 1.584, and 1.176, respectively, according to the proposed robustness calculation method, which shows that the braced steel frame structure has improved robustness over the original structure. The staggered truss system improves the robustness of the steel frame structure so that the steel frame structure has better resistance to progressive collapse.

Optimized machine learning models for prediction of effective stiffness of rectangular reinforced concrete column sections

To evaluate the response of a reinforce concrete (RC) building subjected to nonlinear dynamic loading, it is recommended to use effective stiffness of the members. Currently, design codes and practices provide an empirical fraction of un-cracked stiffness to consider the effect of reduced stiffness in cracked sections. However, it is imperative to conduct an accurate assessment of effective stiffness as it directly affects the distribution of forces and various demands in nonlinear dynamic analyses. Manual calculation of effective stiffness based on strength is a time-consuming process. Therefore, the present study attempts to estimate the effective stiffness ratio of rectangular column sections using machine learning algorithms with ensemble learners namely, Adaptive Boosting (AdaBoost), Random Forest (RF), Extreme Gradient Boosting (XGBoost), Decision Tree (DT) and Categorical Gradient Boosting (CatBoost) using a database of 226 samples of nonlinear dynamic analysis results, obtained from previous work of the author. Additionally, Bayesian Optimization has been used for optimal hyperparameter selection. The results of the present study exhibit that the CatBoost model outperforms other considered machine learning models with R2 value of 0.9921 and 0.9966. A sensitivity analysis based on SHAP has also been implemented to establish the correlation between input parameters and output parameters.

Procedure for evaluation of LNG CCS with reference vessel using nonlinear dynamic analysis

This paper presents a procedure for evaluating the structural safety of Liquefied Natural Gas (LNG) Cargo Containment System (CCS) against sloshing load by comparing the results of linear and nonlinear dynamic structural strength analysis with those of verified reference vessels. This comparative procedure indirectly considers (1) limitation of implementing real physical phenomena in model experiments including the Froude scaling method, density ratio, etc., (2) assumptions in statistical analysis for calculating design loads, and (3) complicated effects not implemented in nonlinear dynamic analysis such as phase transition between liquid and gas, hull deflection, and the detailed geometry of the CCS, among others. The uncertainties in sloshing model experiments and statistical analysis can be addressed by introducing the pressure correction factors, which make the linear design loads of the reference vessel satisfy the CCS’s capacity. Finally, the structural nonlinearity, which was not accounted for in the nonlinear dynamic analysis, can be taken into consideration through a comparison of the usage factors from nonlinear dynamic analysis. To apply the proposed structural assessment procedure, the GTT NO96 series were selected and applied to two failure modes. In the application of this procedure, the Triangular Impulse Response Function (TIRF) method was adopted, to efficiently calculate numerous linear dynamic structural strength analyses required for Dynamic Amplification Factor (DAF). Through this application applying larger sloshing loads to the reinforced NO96 CCS of the target vessel compared to the reference vessel, the feasibility of this procedure was shown.

Seismic performance factors of quarter-elliptic-braced steel moment frames (QEB-MFs) using FEMA P695 methodology

One of the newest lateral load-resisting systems is quarter-elliptic-braced steel moment frames (QEB-MFs). The elliptical geometry of this bracing system not only resolves the shortcomings of conventional concentrically braced frame systems but also leads to greater energy absorption. The QEB-MF system's seismic performance factors (SPFs) are specified in this paper using the FEMA P695 approach. To this end, a three-dimensional group of 2-, 4-, 6-, and 8-story archetypes in two distinct seismic design categories (SDC Cmax and Cmin) were designed according to presumed SPFs. The adjusted collapse margin ratio (ACMR) for each archetype was calculated utilizing the results of non-linear static (pushover) analysis and incremental dynamic analysis (IDA) under far-field ground motion (FFGM) records. In order to confirm presumed SPFs, ACMRs were compared to FEMA P695's acceptable values. The results indicate that the ACMR values for the QEB-MF systems that were designed with a response modification factor of 6.5 are acceptable. In addition, the deflection amplification factor and the over-strength factor have been acquired to be equal to 6.5 and 2.5, respectively.

Seismic fragility analysis of rocking buckling-resistant braced structures subjected to far-field and near-field ground motions

To address the inadequate seismic performance of traditional buckling-restrained braced frame structures (BRBFS), this study introduces a novel structure, the rocking buckling-restrained braced frame structure (RBRBFS). The RBRBFS achieves effective control of main structure damage and enhances structural energy dissipation and seismic resilience by disconnecting the column feet from the foundation in the BRBFS and using friction energy dissipation devices as rocking column feet. This research aims to quantitatively assess the seismic performance and collapse safety margin of the new RBRBFS under different types of ground motions. To achieve this goal, two eight-story structures, one is traditional BRBFS and the other is RBRBFS, were designed. Incremental Dynamic Analysis (IDA) was employed, accounting for ground motion uncertainty, to conduct a comparative study of the seismic fragility of both structures subjected to near-fault pulse-like and far-field earthquake ground motions. Nonlinear dynamic analysis results indicate that under high-intensity ground motions, the RBRBFS significantly improves structural ductility and effectively controls structural damage. Compared to BRBF structures, the BRBFS exhibit a reduction of 26.5% and 18.3% in damage probability deviation under the two seismic excitations, highlighting their more stable structural response under varying seismic conditions. Furthermore, this novel RBRBFS increases the collapse margin ratio by 25% to 30%, demonstrating its higher seismic collapse resistance capacity

Seismic design parameters (R, Cd, and Ω0) for uncoupled composite plate shear walls−concrete filled (C‐PSW/CF)

AbstractComposite Plate Shear Walls−Concrete Filled (C‐PSW/CF) are an innovative seismic force resisting system recently adapted for building applications. The walls consist of parallel steel faceplates connected with tie bars and filled with concrete. This paper summarizes the results of a recent FEMA P695 study completed to verify seismic design parameters for uncoupled C‐PSW/CFs with rectangular flange plate boundary elements. Seven archetype structures were: (i) designed, (ii) modeled using a benchmarked fiber‐based finite element analysis approach, (iii) subjected to nonlinear pushover analysis, (iv) and to incremental nonlinear dynamic analysis to failure for 22‐sets of scaled ground motions, and (v) the results were statistically analyzed to assess performance. These structures ranged from three (3) to twenty‐two (22) stories and included both planar and C‐shaped configurations. As part of this design process, recommendations for stiffness approximations for linear analysis of C‐PSW/CFs were developed. Additionally, these nonlinear incremental dynamic analysis results were post‐processed to determine the rotation and strain demands at the base of these structures at the design basis, maximum considered, and failure level earthquakes. These results showed that the rotation and strain demand at failure level earthquakes were comparable regardless of the ground motion. Ultimately, this FEMA P695 approach verified the R factor of 6.5, Cd factor of 5.5, and Ω0 of 2.5 for C‐PSW/CFs with boundary elements.

Comparison of the effects of traditional and innovative tie-rods in reducing the seismic vulnerability of church façades: the case of San Francesco in Mirandola (Italy)

This contribution discusses the effect of steel tie-rods installed in a church façade subjected to 60 recorded earthquakes. The church façade is firstly analysed as a two-sided and a one-sided rocking SDOF system. For the one-sided rocking, sidewalls are modelled through either elastic or rigid contact to compare the two modelling techniques. Secondly, two configurations of tie-rods are investigated: (i) traditional tie-rods with a specific elasto-plastic constitutive law and (ii) innovative tie-rods with a dissipative component. The chosen case study is the San Francesco Church located in Mirandola, hit by the 2012 Emilia Romagna earthquake. The results of nonlinear dynamic analyses are presented in terms of median and standard deviation of maximum normalised displacements for each of the 60 seismic inputs. The results show the great benefit introduced by both traditional and dissipative tie-rods, with remarkable reductions of maximum rotations up to an order of magnitude with respect to the unrestrained façade. Moreover, the increment of damping coefficient is associated to a reduction of the standard deviation of the amplitude peaks, which is a positive aspect for the reliability of the response of the damped wall. Finally, the two models, rigid and elastic contact, of sidewalls provide results in excellent agreement in terms of median and standard deviation of the maximum normalised rotations.

Hybrid self-centering rocking core system with fiction spring and viscous dampers for seismic resilience

This research presents a novel aseismic system, the hybrid self-centering rocking core (HSRC) system, for obtaining better seismic resilience in steel buildings. Two hybrid self-centering dampers are introduced in the HSRC system to control structural and nonstructural damage. A rocking core, i.e., a steel braced frame with pinned base is included in the HSRC system to facilitate uniform inter-story drift responses under earthquakes. The steel braces in the rocking core can also work as a reserve energy-absorbing mechanism against structural collapse subjected to extreme seismic events whose intensities are more significant than those of the maximum considered earthquakes in design codes. The desired nonlinear responses of the HSRC system were analyzed. Direct displacement-based design steps were developed for the HSRC system. Three-story and six-story HSRC systems were designed following the proposed design method. Nonlinear dynamic analysis results indicate that the designed HSRC systems can show desired nonlinear responses and achieve the expected performance objective under earthquakes. Moreover, seismic fragility analyses were also conducted based on the incremental dynamic analysis results to assess the performance in controlling structural and nonstructural damages of the HSRC system under earthquakes of different intensities. The results confirm that the proposed HSRC system has excellent capacity in resisting structural collapse, achieving reliable post-earthquake recoverability, and controlling structural and nonstructural damage under rare seismic events.

Seismic design and performance of a steel frame-shear plate shear wall with self-centering energy dissipation braces structure

The steel plate shear wall with self-centering energy dissipation braces (SPSW-SCEDB) is a new seismic lateral resistant component. This paper outlines the performance requirements of the steel frame-shear plate shear wall with self-centering energy dissipation braces (SF-SCSPSW) structure and presents a direct displacement-based seismic design method for the structure. A combined strip model of the SPSW-SCEDB that considers the effect of the bolted connection on the wall plate is established. The comparison of the simulated and experimental results shows that the model can accurately predict the strength and hysteretic behavior under cyclic loading. The 8- and 15-story prototype buildings were designed using the presented method. The results of nonlinear dynamic analysis showed that larger inter-story deformations occurred on the lower floors, and the inter-story ratios gradually decreased with an increase in the number of floors. The maximum inter-story drift ratio (1.73%) of the 8-story structure under mega earthquakes and the maximum residual drift ratio (0.018%) of the 15-story structure under large earthquakes were less than the limit values (2% and 0.5%). Local yielding occurred between the brace connection and the column under mega earthquakes, but the columns remained in an elastic state. The seismic responses of the SPSW-SCEDBs in the two structures met the performance requirements of being elastic and suffering light and moderate and serious damage under frequent, medium, large, and mega earthquakes, respectively. The effectiveness of the proposed design method was verified.

In-plane-out-of-plane single and mutual interaction of masonry infills in the nonlinear seismic analysis of RC framed structures

In the aftermath of earthquakes poor seismic response was evidenced by non-structural elements such as enclosure masonry infills (MIs), characterized by a combination of in-plane (IP) and out-of-plane (OOP) damage mechanisms. The present work is aimed at identifying the effects of this mutual interaction on the nonlinear seismic behaviour of reinforced concrete (RC) framed structures. To this end, an extensive parametric study is carried out considering a spatial one-bay multi-storey shear-type model with MIs constituted of two leaves of clay hollow bricks, which is assumed as equivalent to infilled RC framed buildings. An extensive GIS aided structural mapping of the town of Rende (Italy) is adopted in order to obtain benchmark models as close to real structures as possible, focusing on total height, in plan dimensions and maximum and minimum bay lengths of the buildings. The dependence of the results on the variation of the following design parameters is considered for the i-th cluster of buildings characterized by the same number of storeys: i.e. fundamental vibration period; behaviour factor of the bare structure; aspect ratio of MIs, defined as the ratio between the panel length and height. A five-element macro-model comprising four (diagonal) nonlinear beams and one (horizontal) central nonlinear truss for the prediction of the OOP and IP behaviour of MIs, respectively, is first implemented in a homemade computer code. The proposed algorithm addresses the issue of the nonlinear mutual interaction of MIs by modifying stiffness and strength in the OOP direction on the basis of simultaneous or prior IP damage and vice-versa. A lumped plasticity model describes the inelastic behaviour of the RC frame members. Finally, a review of the current Italian, European and American seismic code provisions is performed by means of comparison with results of nonlinear dynamic analyses. To this end, bidirectional spectrum-compatible accelerograms are considered at ultimate limit states.

Canonical Variate Nonlinear Principal Component Analysis for Monitoring Nonlinear Dynamic Processes

Conventional multivariate statistical process monitoring methods constrained by the assumptions of linear and normal distributions for the measurements, such as principal component analysis and canonical variate analysis, demonstrate significantly higher fault alarm rates and lower fault detection rates in nonlinear dynamic industrial process monitoring. Kernel principal component analysis (KPCA) based on the radial basis function, has already been applied in numerous nonlinear industrial processes. However, an infinite-dimensional nonlinear mapping might be inefficient and redundant. To improve the efficiency of traditional methods, this study proposes the implementation of canonical variate nonlinear principal component analysis for monitoring nonlinear dynamic processes. The training data are first preprocessed by performing canonical variate analysis to reduce the effects of the dynamic characteristics of the data. Then, the state vectors are projected into a high dimension feature space by an explicit second-order polynomial mapping. The first k principal components and the remaining residual vectors are obtained in the feature space via conventional principal component analysis for fault detection. The combined statistic Qc is proposed for monitoring the variations in the linear and nonlinear residual spaces; its upper control limits can be estimated by the kernel density function. In comparison to the results of KPCA and nonlinear dynamic principal component analysis, the proposed method yielded significantly higher fault detection rates and relatively lower fault alarm rates in a simulated nonlinear dynamic process and the benchmark Tennessee Eastman process.

Probabilistic Seismic Assessment of Moment Resisting Steel Buildings Considering Soft-story and Torsional Irregularities

In this study, the fragility curves were developed for three-, five-, and eight-story moment resisting steel frame structures with considering soft story and torsional irregularities during the earthquake mainshock to assess the probabilistic effects of irregularities in plan and height of steel structures. These models were designed according to Iranian seismic codes. 3D analytical models of steel structures were created in the OpenSees software platform and Incremental Dynamic Analysis (IDA) was conducted to plot the IDA curves. The maximum value of inter-story drift was selected as the demand parameter and the capacity is determined according to the HAZUS-MH limit states; and finally, the corresponding fragility curves were developed. The results of the 3D nonlinear dynamic analysis indicated that the damage state of the structure due to soft story irregularity was decreased with increasing stories. On the other hand, the damage caused by torsional irregularity in plan was increased by increasing the height of the structure. For example, in the 3-story structure, soft-story effect on damage probability was more dominant than torsional irregularity.

OpenVFIFE: An Object-Oriented Structure Analysis Platform Based on Vector Form Intrinsic Finite Element Method

The vector form intrinsic finite (VFIFE) method is a new and promising structural analysis technique that has many advantages as compared with the conventional finite element method (FEM) in analyzing the complex behaviors of a structure. However, despite the popularization of its application in civil and infrastructure engineering, there is no available unified general analysis framework for it, which limits the applications and developments of VFIFE. This work develops and implements a platform (termed openVFIFE) based on a new proposed object-oriented framework to facilitate the development and application of the vector form intrinsic finite method as well as the efficient and accurate analyses of complex behaviors for civil structures. To validate the platform, a series of numerical examples are conducted. Furthermore, to extend the applications of VFIFE, the nonlinear dynamic and collapse processes of a transmission tower under earthquake load are studied using openVFIFE. The results of these numerical examples simulated by the developed truss or beam elements are consistent with theoretical solutions, previous research or conventional finite element models. The failure modes of the transmission tower under earthquake load simulated by the platform is consistent with those observed in real cases. In addition, the results of nonlinear dynamic analyses of the transmission tower show that the computational efficiency of the proposed platform is 6-10 times higher than that of the conventional finite element method. The results provide sufficient evidence to prove the accuracy and efficiency of the proposed platform in the static, dynamic and elastoplastic analyses of truss and frame structures, especially in the structure analysis characterized by strong geometry nonlinearity. It is noteworthy that in addition to the link and beam elements, further work is undergoing on implementing more elements, such as shell and solid elements. The openVFIFE also allows researchers who are interested in this topic to put their creative ideas into this platform and continuously improve the completeness and applicability of the VFIFE method.

A simplified approach to modeling vertically irregular structures for dynamic assessment

ABSTRACT The nonlinear dynamic analysis is the most sophisticated evaluation method for vertically irregular structures under the effect of the earthquake because the higher mode effects are significant. In particular, vertically irregular structure has a complex geometry, so errors can occur when inputting members as coordinates or when defining the properties of members. Therefore, a simplified modeling method is proposed in this paper. The proposed method was developed by converting vertically irregular structures to geometrically regular structures using a story stiffness equation. The results of modal analyses and nonlinear dynamic analyses obtained by both simplified and typical exact modeling methods were compared. As a result, the difference of fundamental period was about 11%, and the higher mode effects which were evaluated by ASCE 41 criterion governed in both models. In addition, the differences of story shear and story drift were about 15% and 24%, respectively. Therefore, the proposed simplified modeling method can be applied to initial structural design stages to save the project time by predicting approximate nonlinear dynamic results such as story shear, and story drift of vertically irregular structures.

General Substitute Frame Model (GSF) for efficient estimation of seismic demands of steel and RC moment frames

This paper proposes an approach to simplify 2D moment-resisting frames (with equal or non-equal bay lengths) to an equivalent single-bay framed MDOF model. This model, named the General Substitute Frame (GSF), is a promising development of the recently introduced Substitute Frame (SF) model by the authors that was restricted to equal-bay moment frames. The proposed GSF model which resolves the limitation of the SF model is applicable for both the steel and RC moment frames from low-rise to high-rise buildings. In order to evaluate the accuracy of the GSF model rigorously, a combination of 24 full-frame 2D moment frames including 4-, 12-, and 20-story buildings was designed and the results of nonlinear dynamic analyses were compared with their corresponding GSF models in terms of engineering demand parameters. In addition, modal and pushover analyses were also performed. Earthquake ground motions employed in this study include mild far-fault, moderate far-fault, and severe near-fault records selected by the Conditional Spectrum method. To accurately perform the required analyses, OpenSEES software was used, and 3600 runs of nonlinear time history analysis have been carried out. Based on the results of the analyses, it was demonstrated that the GSF model could predict the seismic response of moment frames well enough into both the linear and nonlinear ranges with high accuracy and can be a reliably practical substitution for moment-resisting frames. Moreover, the GSF model can be easily extracted from the primary full-frame based on the proposed equations.

Inelastic Dynamic Eccentricities in Pushover Analysis Procedure of Multi-Story RC Buildings

A documented pushover procedure on asymmetric, single-story, reinforced concrete (RC) buildings using inelastic dynamic eccentricities is extending in this paper on asymmetric multi-story RC buildings, aiming at the Near Collapse state. The floor lateral static forces of the pushover procedure are applied eccentric to the Mass Centers using appropriate inelastic dynamic or design eccentricities (dynamic plus accidental ones) to safely estimate the ductility demands of both the flexible and stiff sides of the building due to the coupled torsional/translational response. All eccentricities are applied with respect to the “Capable Near Collapse Principal System” of multi-story buildings, which is defined appropriately using the well-known methodology of the torsional optimum axis. Moreover, two patterns of lateral forces are used for performing the analysis, where in the second one an additional top-force is applied to consider the higher-mode effects. A six-story, asymmetric, torsionally-sensitive RC building is examined to verify the proposed pushover procedure relative to the results of non-linear dynamic analysis. The outcomes indicate that the proposed pushover procedure can safely predict the seismic ductility demands at the flexible and stiff sides, providing reliable estimates for the peak inter-story drift-ratios throughout the building as well as a good prediction of the plastic mechanism.

Seismic Performance of Two-story RC Frame Retrofitted Using External Steel Frame Equipped with Length-adjustment Device by Pseudodynamic Test

ABSTRACT Seismic retrofitting of exiting building structures is a technical and social issue aimed as earthquake risk mitigation. In this study, a new technique for seismic retrofitting via the attachment of an external steel frame with length-adjustment control box (ESFLC) was developed to strengthen medium-to-low-rise reinforced concrete (RC) buildings. The developed method, categorized as a strength design approach, can be used to perform seismic strengthening construction while residents continue to live within the building, exhibiting excellent constructability because a control box is applied as a length-adjustment device to cope with errors in the field associated with assembly works between the existing structure and reinforcing frame. Two full-size two-story RC frame specimens were designed based on an existing Korean RC building without seismic details; one control specimen and one specimen strengthened with the ESFLC system were used. Pseudodynamic tests were carried out to verify the effects of seismic retrofitting in terms of the maximum response strength, response displacement, and degree of earthquake damage compared with a control RC frame. Nonlinear dynamic analysis was also conducted based on the material properties of the test specimens, including mathematical models that represent the nonlinear hysteresis of the used structural members, to compare the results of the pseudodynamic tests. Test results revealed that the proposed ESFLC strengthening method, externally attached to the existing RC frame, effectively increased the lateral ultimate strength, resulting in reduced response displacement of RC structures under large-scale earthquake conditions. The nonlinear dynamic analysis and test results were in reasonable agreement.