Story Drift Ratio Research Articles

Effects of Lead Core Heating on the Response of Isolated-Base and Fixed-Base Regular and Irregular Reinforced Concrete Structures

In this study, the seismic behavior of isolated- and fixed-base regular and irregular reinforced concrete structures was investigated. For this purpose, a three-dimensional, eight-story reference building model without any irregularity was designed in accordance with the Turkish Building Earthquake Code (TBEC-2018). Later, the building models with irregularities were created using the reference building model. In the building models with seismic isolators and fixed supports, fiber hinges were used for columns and beams to model nonlinear behavior. Moreover, nonlinear behavior at the isolation level was taken into account in building models with seismic isolators. Eleven different earthquake records were scaled using the geometric scaling method. Bi-directional nonlinear response history analysis (NRHA) was performed simultaneously for both horizontal components of the earthquake records in all building models. In addition to boundary analyses (Lower Bound and Upper Bound), which do not take into account the strength loss defined by the codes, analyses considering the strength loss as a result of heating in the lead core due to cyclical motion (Temperature Including) were carried out for building models with seismic isolators. In the analyses, displacement, acceleration, story drift ratio, base shear ratio, and damage mechanisms in the columns and beams obtained from the fixed-base and isolated-base structures were compared. In addition, the results of the analysis, in which the loss of strength due to temperature increase due to cyclical motion in the lead core is taken into account, were compared with the results obtained from the boundary analysis. As a result of the study, it was deduced that significant improvements were observed in the structural behavior of all regular and irregular models with seismic isolators under earthquake effects.

Soil-structure interaction effects on the seismic performance of steel moment-resisting frames equipped with optimal rotational friction dampers

This study investigate the soil-structure interaction (SSI) effects on the seismic performance of steel moment-resisting frames (SMRF) equipped with optimal rotational friction dampers (RFDs). Firstly, a simultaneous optimal design based on the energy concepts is expanded to find the optimal placement and the corresponding optimal parameters of the RFDs for the seismic protection of a nonlinear six-story SMRF. Then, the direct method is adopted to simulate the nonlinear SSI effects on the optimal RFDs-equipped SMRF. The input, hysteretic, dissipated energies and the drift of stories of the controlled SMRF subjected to four real earthquake excitations indicate that SSI can considerably influence the seismic performance of the controlled SMRF. Nevertheless, the significant amount of the seismic input energy is dissipated by optimal RFDs and therefore its limited amount is dissipated by the structural. Moreover, the optimal RFDs can maintain the story drift ratios within the acceptable drift limits.

Seismic Response Study of L-Shaped Frame Structure with Magnetorheological Dampers

To analyze the multi-dimensional seismic mitigation performance and the torsional vibration characteristic of an L-shaped frame structure with a magnetorheological damper (MRD). Firstly, the mechanical property of the MRD is experimentally studied. Then, the calculation models of the L-shaped frame structure without and with MRDs are found through theoretical analysis, and the programs of the calculation models are compiled. Finally, the time history responses of the calculation models are calculated during the excitation of bi-directional seismic wave; the responses of displacement, acceleration, story drift ratio, shear force and bending moment and torsional vibration are then compared and analyzed. The results show that by adjusting the current, the damping force provided by the MRD can be adjusted continuously in the range of 3.1 to 120 kN. The compiled calculation model programs of the L-shaped frame structure without and with MRDs can effectively simulate the multi-dimensional seismic response of the structure. Reasonable arrangement of MR dampers can effectively reduce the displacement, acceleration, shear force, bending moment, multi-dimensional vibration, and torsional vibration response of L-shaped frame structures.

Investigation of cyclic behavior of full-scale tree-like hollow structural section columns with infilled concrete

The cyclic behavior of tree-like hollow structural section (HSS) columns with infilled concrete was experimentally and numerically investigated. A full-scale column, with the height of 3.7 m and the treetop plan dimension of 4 m × 3 m, was designed and manufactured according to a practical engineering prototype. The column was composed of a petal-shaped trunk using a concrete-filled steel tubular (CFST) section, four primary branches using a circular CFST section, and twelve secondary branches using a circular HSS. The column with a capacity protected reinforced concrete foundation was tested under combined constant axial compression and cyclic lateral loading through a specifically designed setup. The cracking and spalling of the reinforced concrete foundation were observed initially, followed by yielding of the bottom end of the primary branches when the story drift ratio reached 1.00%. The specimen failed by fracture of the full penetration groove welded splices in the petal-shaped trunk embedded in the foundation when the story drift ratio reached 3.00%. A detailed finite element analysis model for the tree-like column was then established and verified. Parametric studies were conducted to investigate the influence of the axial load level (0.016–0.3), filling range of concrete (including no filling, partial filling, and overall filling), steel yield strength (235–460 MPa), and the height to width ratio of the petal-shaped trunk (0.75–3.14). The results showed that the higher the filling height of concrete was, the greater the lateral load-carrying capacity and stiffness of the specimen were, but the filling height after reaching the secondary branches hardly affected the mechanical properties of the specimen. With the increase of the axial load level, the load-carrying capacity and deformation capacity decreased. Both the filling range and the height to width ratio of the petal-shaped trunk could change the failure mode of the tree-like column. Finally, some design considerations were proposed.

Development of fragility curves in adjacent steel moment-resisting frames considering pounding effects through improved wavelet-based refined damage-sensitive feature

Fragility curves present useful information related to earthquake-induced probability assessment of steel moment-resisting frames (MRFs) and determine the probability of the damage exceedance at different floor levels of MRFs. The review of the literature shows that most of the previous studies dealing with the fragility curves were based on conventional measures, such as spectral acceleration at the first mode period, peak ground acceleration, and/or engineering demand parameters (e.g. maximum story drift ratio (max SDR)) to estimate the structure's damage state. In this article, a new approach is developed to map the fragility curves in adjacent MRFs including effects of pounding through improved wavelet-based refined damage-sensitive feature (WB-rDSF) which considers contributions of the upper modes. Morlet and complex Morlet (cmorfb-fc) wavelets, which is known as extremely precise rDSF, were extended to map the fragility curves. The correlation coefficient between rDSF and max SDR is evaluated as a criterion to determine the efficiency of wavelets-based damage index (WB-DI). The steel MRFs with six and nine stories are selected to implement the proposed approach concerning adjacent MRFs prone to structural pounding during earthquakes. Acceleration responses recorded at the roof of both colliding and non-colliding MRFs were determined using incremental dynamic analysis (IDA) including different seismic ground motion records to formulate the damage index. Moreover, the first mode structural period, used in assembling the WB-rDSF, is estimated via auto-regressive moving-average with exogenous input method along with a stabilization diagram. The results show that the fragility curves, derived from cmorfb-fc WB-rDSF for both colliding and non-colliding MRFs due to higher correlation coefficient, have lower damage probabilities and are more efficient than the estimated fragility curves based on Morlet WB-rDSF which consider only the structural period of the first mode. Furthermore, due to the pounding phenomenon, the lower MRF experiences more damages with a larger probability.

Experimental study of U-shaped steel-concrete composite beam to square CFST column joints

Concrete-filled steel tubular (CFST) columns and U-shaped steel-concrete composite (USCC) beams have received extensive attention because of superior mechanical performance over steel and reinforced concrete members. In this study, an innovative cost-effective and construction-effective USCC beam to CFST column joint configuration with T-shaped internal diaphragms is proposed. Four beam-column joint specimens were designed according to the proposed design provisions, and were tested under combined constant axial compression and cyclic lateral loading, including one specimen with T-shaped diaphragms in strong direction, two specimens with T-shaped diaphragms in weak direction, and one control specimen with conventional internal diaphragms. Test results revealed that the specimens with T-shaped diaphragms exhibited similar cyclic behavior, moment-bearing capacity, ductility, stiffness, and energy dissipation capacity to the specimen with conventional internal diaphragms. The primary failure modes were fracture and buckling of bottom flange of the U-shaped steel in the connection vicinity, leading to a remarkable pinching effect in the cyclic behavior. All specimens were tested up to a story drift ratio of 4%, showing good elasto-plastic deformation capacity. The specimens have a superior bearing capacity under negative moment and a lower one under positive moment due to premature fracture of bottom flange. All specimens were classified as the semi-rigid and partial strength joint under positive moment, semi-rigid and full strength joint under negative moment. Additionally, the contributions to story drift were analyzed theoretically and the results via the proposed calculation formulas were found to be in good agreement with the measured story drift.

Seismic demands of steel moment resisting frames with inelastic beam‐to‐column web panel zones

AbstractThis paper intends to provide quantitative seismic response characteristics of steel moment resisting frames (MRFs) with inelastic beam‐to‐column panel zone joints. Two modeling approaches are proposed for this purpose along with a methodology to consider the fracture potential at the bottom beam flange in steel MRFs due to panel zone kinking. Both approaches, which are validated with available experiments, preserve the behavioral insights of inelastic panel zones. Nonlinear static and dynamic analyses are then conducted to quantify the seismic demands of 32 prototype steel MRFs while their panel zones exhibit various levels of inelastic deformations. Engineering demand parameter hazard curves are developed to interpret the results for a risk‐targeted seismic performance. The results demonstrate that steel MRFs with panel zone shear distortions of 10 to 15 times the shear distortion at yield, , have a mean annual frequency of collapse ranging from to , which is up to two times lower than corresponding results with code‐compliant steel MRFs (i.e., It is shown that steel MRFs with inelastic deformations of 10 in their panel zones, (a) enjoy up to 50% reduction in residual story drift ratios at a design basis earthquake; (b) their beam‐to‐column connections do not experience fractures due to panel zone kinking; and (c) local buckling in steel beams is very limited even at low probability of occurrence earthquakes. The above hold true when the current detailing and fabrication practice is employed. The findings have implications on seismic design and the post‐seismic repairability of steel MRFs.

Experimental study on seismic behaviour of eccentrically braced composite frame with vertical LYP steel shear link

An experimental investigation is conducted to study the seismic behaviour of eccentrically braced composite frame (EBCF) with vertical shear links, which has a better repairability and replaceability compared with traditional EBCFs with horizontal shear links. Particularly, the low-yield-point (LYP) steel is applied in the shear links to verified its influence on the seismic performance of the EBCFs. Cyclic loads are applied to two composite frames respectively with a bare moment resisting frame system and with a dual system composed of the moment resisting frame and the eccentric bracing system, the comparison of results indicates that the eccentric bracing system can effectively increase the stiffness, strength and energy dissipation capacity of the composite frame, but has few effects on the force conditions on the ends of the primary beams and columns, both two specimens failed by the fracture and buckling of the bottom flanges of the primary beams at a story drift ratio of 1/38. Due to the low-yield-point property and high ductility of the LYP steel, the shear link starts to efficiently dissipate energy when the story drift ratio is only 1/300, and the shear link has reached an inelastic rotation capacity of 0.16 before failure. However, due to the strain hardening of the LYP steel, the shear link achieved an over-strength factor up to 2.78, and the over-strength property of the shear link has resulted an unignorable bending moment of the middle segment of the primary beam, the concrete slab in this area is severely damaged with a maximum crack width of 0.16 mm. Finally, the analysis of working mechanism and test data indicates that, the added stiffness, added strength, and added energy dissipation capacity by the eccentric bracing system are directly in proportional to the contribution of the vertical shear link, and formulas to evaluate the added damage of concrete slab are also given.

Shear design equation and updated fragility functions for partially grouted reinforced masonry shear walls

This paper proposes specific ultimate shear strength expressions for partially-grouted reinforced masonry (PG-RM) shear walls that are bed-joint reinforced (BJR) and made with either multi-perforated clay bricks (MPCLBs) or hollow concrete blocks (HCBs). For each unit type, a set of constant coefficients of an arbitrary mathematical expression is optimized to minimize the error against experimental databases of walls made with the same unit types. Additionally, the assembled databases are employed to calculate lognormal empirical fragility functions, following performance-based earthquake engineering (PBEE) methodologies. For this, two different engineering demand parameters (EDPs) (story drift ratio, SDR, and normalized diagonal shear demand, NDSD) are proposed, and two damage states (DS) (named DS4 for moderate damage and DS5 for severe damage) are investigated. The proposed shear formulae are used in the normalization of calculated NDSD values. Moreover, databases are sorted by a selected design parameter (aspect ratio) to calculate design parameter-sensitive fragility functions.Overall, the results indicate that the proposed expressions are more accurate than the corresponding expressions proposed by the American and Canadian codes when assessing BJR-PG-RM shear walls in terms of the average error and dispersion of relative prediction error. All the fragility curves adjusted to the whole database pass the Lilliefors goodness of fit test (α=5%). Comparing SDR-based curves of walls of a different unit type, DS4 curves present a smaller difference in the median value (θ) than DS5 curves. Additionally, the variations in the θ of NDSD-based curves of walls of different units are smaller than those observed in SDR-based fragility functions, indicating that NDSD represents a less variant EDP to describe the probability of shear damage at DS5 when a proper expression is employed for the normalization. Regarding design parameter-sensitive fragility functions, sorting databases reduces the number of data points used to calculate the functions, which produced two SDR-based and one NDSD-based function to fail the Lilliefors test (α=5%). In general, the θ value of SDR-based curves increases in proportion to the aspect ratio. Additionally, classifying the databases by a design parameter (aspect ratio) corroborated that the proposed expression has acceptable accuracy based on the adjusted NDSD-based DS5 fragility functions. It is highlighted that calculating design parameter-sensitive functions might increase the accuracy of PBEE assessments (e.g., loss estimations) when an EDP insensitive to design parameters normalization (e.g., SDR) is employed.

Dinamička analiza posmičnih stijena s čeličnom ispunom

In this paper, the Timoshenko beam model (continuous system model) is originally adapted for dynamic analysis of steel plate shear wall (SPSW) systems. Dynamic characteristics for the first three modes are found by solving differential equation of the equivalent Timoshenko beam model using the differential transformation method. Dynamic characteristics are tabulated for quick and practical calculation. With the help of the dynamic characteristics, the response spectrum analysis of such buildings is performed. The continuous system calculation model has been used in the literature for free vibration analysis of such systems. Using the approach developed in this study, it is possible to calculate not only natural periods, but also the base shear force, maximum storey displacement, and maximum storey drift ratio. The differential transformation method is used in this study for solving the differential equation written according to the continuous system calculation model. To investigate the suitability of the method presented in the study, an example taken from the literature is solved and the results are evaluated. The results show that the method presented can be used in the preliminary design stage.

Experimental study on L-shaped precast concrete superposed shear walls under quasi-static cyclic loading with different axial compressive load ratios

This study experimentally investigates the seismic behavior of L-shaped precast superposed shear walls with cast-in-place boundary elements. Five full-scale L-shaped specimens were constructed and quasi-static cyclic loading applied to them. A new vertical joint connecting the superposed wall panels and a boundary element was designed. The influence of different vertical joints, boundary elements, and axial compressive load ratios on the seismic behavior of the L-shaped superposed shear wall were analyzed. The failure mode, strength, hysteresis feature, ductility, energy dissipation capacity, and stiffness degradation of each specimen were compared. The test results showed that the specimens with boundary columns exhibited a flexural failure characterized by concentrated crushing of the bottom of the free end of the webs, whereas the specimens with special boundary elements exhibited shear compression failure characterized by a principal inclined crack in the center of the webs. The vertical connecting longitudinal steel bars were effective in resisting load under the action of an earthquake, and the force transfer performance of the connecting reinforcement was reliable and stable. The transverse confinement at the free end of the specimens with special boundary elements ensured a stable bond stiffness to prevent the crack from opening at the horizontal joint. The increase in the axial compressive load ratio may lead to an increase in positive shear deformation. The story drift ratios of the L-shaped superposed shear walls with cast-in-place boundary columns and special boundary elements met the limit value requirements of the story drift ratio in Chinese code JGJ/ 3-2010. The seismic performance of L-shaped superposed shear walls with boundary columns was slightly lower than that of L-shaped cast-in-place shear walls. The seismic performance of L-shaped superposed shear walls with special boundary elements was significantly better than that of the reference cast-in-place shear walls. Furthermore, based on the characteristics of shear compression failure, a calculation formula for the shear bearing capacity of an L-shape precast concrete superposed shear wall was established, and the proposed equations were validated.

Seismic Strengthening of RC Structures Using Wall-Type Kagome Damping System

In this study, the Kagome truss damper, a metallic wire structures, was introduced and its mechanical properties were investigated through theoretical analyses and experimental tests. The yield strength of the Kagome damper is dependent on the geometric shape and diameter of the metallic wire. The Kagome damper has higher resistance to plastic buckling as well as lower anisotropy. Cyclic shear loading tests were conducted to investigate the energy dissipation capacity and stiffness/strength degradation by repeated loadings. The hysteretic properties obtained from the tests suggest that a modification of the ideal truss model with a hinged connection could be used to predict the yield strength and stiffness of the damper. For seismic retrofitting of a low-rise RC moment frame system, a wall-type Kagome damping system (WKDS) was proposed. The effectiveness of the proposed system was verified by conducting cyclic loading tests using a RC frame with/without the WKDS (story drift ratio limit 1.0%). The test results indicated that both the strength and stiffness of the RC frame increased to the target level and that its energy dissipation capacity was significantly enhanced. Nonlinear static and dynamic analyses were carried out to validate that the existing building structure can be effectively retrofitted using the proposed WKDS.

Teaching-Learning Based Optimization of Nonlinear Isolation Systems under Far Fault Earthquakes

Seismic isolation systems exposed to far-fault earthquakes can reduce floor accelerations and story drift ratios to acceptable levels. However, they exhibit different structural performances in each earthquake due to different excitation frequency contents. By optimizing the isolation system parameters, their performance may be maintained at the best level under different far-fault earthquakes. In this study, the optimization of the parameters of the nonlinear isolation system of a 5-story benchmark building is performed by Teaching-Learning Based Optimization (TLBO) algorithm to minimize peak floor accelerations under historical far-fault earthquakes with and without exceeding a specified base displacement limit. According to the results of the analyses, it can be said that TLBO algorithm is a robust algorithm with low standard deviations for determining optimum nonlinear isolation system parameters.

Experimental Study of Earthquake Simulator for 3D Cold-Formed Steel Frame Structure

This paper aims to perform the experimental test and numerical FE analysis of the cold-formed steel frame structure to provide new proposals to improve the strength, rotation capacity, and seismic energy dissipation in these structures. A 3D full-scale three-story CFS frame structure is experimentally investigated under four sets of input data for 100% and 50% scales of Northridge and Kocaeli earthquake acceleration records using the shaking table test. In each test, the frame acceleration and displacement are observed. A FE model is employed to assert the validity of the experimental test. The results indicated that the maximum story drift ratio of the frame ranges from 1.14% to 3.70%. It is observed that the average similarity ratio of the maximum displacement results between FE analysis and shaking table test is 92%. It is shown that the translational stiffness for the system decrease as the earthquake acceleration records decrease. It is also shown that using the image processing technique in the shaking table test can offer much more acceptable and economical solutions in determining the displacement parameters.

Effects of demand parameters in the performance-based multi-objective optimum design of steel moment frame buildings

This paper investigates the effects of various demand parameters involved in the optimal performance-based design of steel moment frame buildings. These parameters include the peak values of story drift ratio, floor velocity, floor acceleration, and residual drift ratio. The performance-based design is performed to minimize two conflicting objectives, including the initial construction cost and the expected annual repair cost of the building under the design constraints. FEMA P-58 is utilized as a comprehensive and popular methodology for seismic risk assessment and building loss estimation in this paper. It evaluates the building performance in a probabilistic manner in terms of several metrics such as repair cost, repair time, carbon emissions, embodied energy, injuries, and fatalities. The Monte Carlo analysis is used to consider various uncertainties affecting seismic performance. A set of three steel moment-resisting frame (MRF) buildings representative of low-to mid-rise frames are selected as a case study in this research. The results of this study indicate that the story drift ratio has a major role in the performance-based optimal design of steel MRFs. Accordingly, despite increasing the two parameters of floor acceleration and floor velocity due to increasing the initial cost of structural moment frames, the annual repair cost of the building decreases when the story drift ratio decreases.

Study on the Development of Seismic Fragility of Steel SMRF

Abstract: Vulnerability assessment of the structure is the most important and wide area of research which requires more input from the engineers and seismologist. The seismic vulnerability assessment of the structure can be evaluated by developing Fragility curves. Fragility curves shows the conditional probability of the structure exceeding the particular performance limit of the given damage state during strong ground motions. Fragility curves can be developed for different parameters like spectral displacement (Sd), spectral acceleration (Sa) Peak ground acceleration (PGA) , Inter storey drift ratio (IDR) etc. This paper describes about the different methods used in deriving the Fragility curves like conventional methods, Nonlinear Dynamic analysis methods and Nonlinear Static analysis methods. Also the fragility analysis of 5 Storied Steel Moment Resisting Frame (SMRF) has been carried out based on the parameters suggested by HAZUS M.H 2.1. Nonlinear static pushover analysis of the frame has been carried out in ETABS2016. Fragility curves are developed based on the pushover analysis results. The damage states defined as per HAZUS are Slight damage (SD), Moderate damage (MD) Extensive damage (ED) and Complete damage (CD). After carrying out the fragility analysis for the steel SMRF, it has been found out that, as the spectral displacement increases probability of failure for the slight damage of the structure is very high and the probability of failure for the complete damage is very low. Hence the probability of failure of the structure reduces from slight damage to complete damage. Keywords: Fragility curves, vulnerability assessment, Nonlinear static pushover analysis, HAZUS M.H 2.1.

Seismic evaluation of a renovated wooden hypostyle structure: A case study on a mosque designed with the combination of Asian and Byzantine styles in the Seljuk era (14th century AD)

Wooden hypostyle structures are primarily built using timber-framed construction types, surrounded by masonry walls on two or three facades. This construction technique is a combination of Asian (wooden frame) and Byzantine (masonry wall) techniques. The primary load-bearing system in these structures consists of multiple rows of wooden pillars. This paper focuses on the restoration of a historical wooden hypostyle mosque constructed in 1366. The mosque is a crucial example of wooden hypostyle tradition in the Anatolia region of Turkey. The study consists of four steps: field survey, lab tests, restoration practices, and seismic performance analyses for the examined structure. The on-site examination includes the visual inspection of material deterioration and the analyses of obtained samples from different places of the structure. Moreover, a building survey was carried out using three-dimensional laser scanning. Secondly, a laboratory study was performed using the samples gathered from the structure. The physical tests revealed that while the stone sample taken from the minaret had the highest porosity, the stone sample represents the west facade displayed the lowest porosity. Accordingly, the water absorption capacity of the stone sample taken from the west facade was the lowest. On the other hand, among samples, this stone sample had the highest wet and dry density. In the third step, the renovation process of the mosque considering its originality is presented. Lastly, the seismic performance level of the renovated structure is obtained using three analyses: linear, pushover, and kinematic approaches. Story drift ratios of the structure at the performance points for three earthquake ground motion levels meet the target performance requirements. Considering the realistic behavior of the material, the vulnerability of the main structure against the maximum credible earthquake is revealed in terms of tensile and shear stresses. The seismic vulnerability of the minaret is also determined in terms of both tensile and shear stresses and the story drifts ratios in both analysis types. We believe that the structural restoration processes presented in this paper to bring back a deteriorated historical mosque to its original form will provide a comprehensive approach to the literature.

Evaluation of pounding effects between reinforced concrete frames subjected to far-field earthquakes in terms of damage index

In this paper, three different damage indexes were used to detect nonlinear damages in two adjacent Reinforced Concrete (RC) structures considering pounding effects. 2-, 4- and 8-story benchmark RC Moment Resisting Frames (MRFs) were selected for this purpose with 60%, 75%, and 100% of minimum separation distance and also without any in-between separation gap. These structures were analyzed using the incremental dynamic analysis method under 44 far-field ground motion records. Comparison of the results between the MRFs with and without considering pounding effects show that collisions lead to a decrease in the values of coefficient of determination and the nonlinear damage occurs in lower seismic intensity. As a result, using the damage indexes, nonlinear damages can be detected during a specific seismic intensity. Moreover, considering a minimum separation distance leads to an increase in the coefficient of determination between the damage index and the maximum story drift ratio. Furthermore, due to pounding, shorter MRFs are damaged more significantly than the taller structures.

Hysteretic behavior of circular tubed reinforced concrete column to steel beam frames

Tubed reinforced concrete (TRC) columns have good deformability and energy dissipation capacity under horizontal cyclic loads; and even with plastic hinges formed at the column ends, the corresponding frame structure may still have sufficient inter-story deformation capacity. Extensive research has been conducted on the static and seismic performances of TRC columns. However, little attention has been paid to the structural system containing TRC columns. To overcome this shortcoming, an experimental study on the seismic behavior of circular tubed reinforced concrete (CTRC) column to steel beam frames (referred as “CTRC frames”) is described first in this study. Based on the previous studies on CTRC columns and joints, two double-bay two-story CTRC frames of 1/2 scale were designed and tested under quasi-static loading: one frame with stronger flexural strength in columns than the beams and the other frame is the opposite. The test results indicated that although the frame failed in column plastic hinge mode had the ductility coefficient of 3.56, a weak story with the maximum story drift ratio of 1/18 formed in this frame, which increased the collapse risk of the overall structure. Therefore, considering the unfavorable deformation mode, the column plastic hinge mode should be avoided in practical designs; and the control of frame deformation modes should be considered when proposing a suitable column-beam strength ratio for CTRC frames. A fiber-based element model using OpenSees software was developed, which showed a good agreement with the test results. Utilizing the numerical model, the affecting parameters to the hysteretic behavior of CTRC frames, such as the axial load ratio, concrete compressive strength, and column-beam strength ratio, were further investigated.

Cyclic loading test of reinforced concrete frames protected with brace-type friction dampers

In this study, cyclic loading tests were conducted on reinforced concrete (RC) portal frames with brace-type friction dampers. The boundary conditions that could reproduce the axial forces exerted on the beams were adopted. To resist the axial force acting on the RC member, a damper connection method was employed by using steel inserted through the center of the RC member. The purpose of this study was to a) understand the behavior of the damper connection and the RC frame with brace-type friction dampers based on experimental tests and b) to confirm the effectiveness of the new connection method. According to the test results, the proposed connection method achieved effective damper connections in the RC frames. For the RC frame specimens with dampers, it was confirmed that the damper reached its sliding force and started to dissipate energy at an early stage with story drift ratios smaller than those at RC beam yielding. The welded part of the gusset plate and the steel inserted through the center of the RC beam were broken. When the welded part inside the beam broke and the axial deformation of the beam increased, the sliding displacement of the damper decreased. Therefore, a reliable jointing method of this part needs to be established.