Plastic Hinge Rotations Research Articles

Numerical investigation on plastic hinge behavior of hybrid steel-FRP reinforced concrete columns

This paper presents a numerical study on the plastic hinge behavior and rotation capacity of concrete columns reinforced with a combination of steel bars and fiber-reinforced polymer (FRP) bars. A meso-scale numerical model, which considers the internal heterogeneity of concrete and bond behavior between concrete and longitudinal reinforcements, was developed and validated. The failure modes, lateral load-displacement responses, and the physical plastic hinge lengths of hybrid steel-FRP reinforced concrete (SFRC) columns were investigated and compared with those of conventional steel-reinforced concrete columns. The results indicated that the steel yielding zone and curvature localization zone of SFRC columns with FRP longitudinal bars were enlarged, due to the relatively low modulus of FRP bars. After that, a parametric analysis was performed to study the plastic hinge length of SFRC columns with respect to the nominal area ratio of FRP longitudinal bars, shear span-to-depth ratio, axial load ratio, and longitudinal reinforcement ratio. A new empirical model was proposed to predict the equivalent plastic hinge length, which was subsequently integrated into an analytical method for predicting the ultimate rotation. The comparison of predictions with simulation and test results demonstrated the accuracy of both the proposed empirical model and analytical method.

Inelastic behavior of diagonally reinforced coupling beams confined with steel fibers

Experimental studies were conducted to analyze the plastic rotation capacity and the effect of replacing transverse reinforcements with steel fibers in diagonal reinforced concrete coupling beams. Six specimens were planned, and the steel fiber reinforcing index and total area of transverse reinforcements were the main variables. Reverse cyclic loading tests were conducted to confirm the seismic performance of the coupling beam. The results showed that the plastic hinge rotation capacity increased and the buckling point of the diagonal reinforcing bars was delayed as the steel fiber reinforcing index increased. An analysis of 78 specimens and the results of previous studies confirmed that ductility improved when the confinement effect of the steel fiber was considered. Application of an equation for ductility requirements reflecting the confining stress of steel fiber reinforced concrete confirmed that the amount of transverse reinforcement could be reduced.

Cyclic behavior of high-strength steel beam-to-column welded flange-bolted web connections

Four Q690 high-strength steel beam-to-column moment connections, which use welded joints between beam and column flanges as well as a bolted beam web to the column flange, were tested under cyclic loading. The effects of beam-to-column welding details and panel zone strength were studied. Two pairs of welded flange details were incorporated, including the Chinese code-specified complete-joint-penetration (CJP) welded connections with backing plates where the bottom backing plate is reinforced by a fillet weld, and enhanced CJP welded connections with backing plates removed, weld roots backgouged, and further reinforced by fillet welds. Three panel zone thicknesses were designed to characterize strong, intermediate and weak panel zones, respectively. The test results show that backing plates should be removed in these moment connections to prevent brittle weld fracture, but still rendering only limited plastic hinge rotations in the order of 0.01–0.02 rad in the beam end before ductile fracture of the beam flange. The panel zone, however, survived even after a plastic shear rotation of 0.03 rad, demonstrating much higher plastic deformation capacity than the beam plastic hinge. This suggests that ductility can be exploited in 690 MPa high-strength steel panel zones, but not reliably in 690 MPa steel beams.

Experimental study and numerical analysis on the failure mode of staggered truss framing system

To investigate the seismic performance of staggered truss framing system under different failure modes, two trusses were designed according to the capacity design method. Then, two models with a scale of 1/2.5 were made and subjected to quasi-static tests. The hysteresis curve, stiffness, energy dissipation, and ductility coefficient of the two models were analyzed. The test results show that the specimen designed for chord failure has better seismic performance than that designed for diagonal web failure. The ultimate drift ratios of the two specimens are both less than 1.5%, indicating that the deformation ability of the staggered truss is insufficient. By analyzing the relationship between the plastic hinge rotation and the drift ratio of the truss, it is suggested that the limit value of the drift ratio of the staggered truss framing system should not exceed 1.5%. The yield-bearing capacity calculated by considering the composite effect of the chord and floor slab is closer to the test results than that calculated without considering the composite effect, indicating that the composite effect of the chord and floor slab should be considered when designing the trusses. Through the numerical analysis, it is recommended to take a minimum amplification factor of 1.3 for the internal force of web members to realize the purpose of chord failure.

Probabilistic Assessment of Global Damage Index for Steel Moment-Resisting Frames Based on Local Responses

ABSTRACT A new scenario-based method is proposed to determine the performance range of structural systems. The advantage of this method is using inter-storey drift as a damage index, while exploiting local damage indices of the main structural members without the need for detailed analytical models and computationally expensive non-linear dynamic analyses. A new damage function is proposed by linking the local (plastic hinge rotations) and global (inter-storey drifts) damage levels. The accuracy of the proposed function is evaluated and compared with the indices in ASCE41–06, ATC-13, and HAZUS for a set of steel moment-resisting frames subjected to earthquakes of varying intensities.

Dynamic plastic hinge rotation measurement for RC columns under seismic loads using MEMS inclinometers

Plastic hinge rotation is an efficient and essential response parameter for post-disaster damage assessment on RC structures. In this paper, a micro-electronic mechanical system (MEMS) inclinometer-based approach is developed to dynamically measure the plastic hinge rotation of RC columns under earthquake loads. The plastic hinge rotation is regarded as the relative angle of rotation, measured by inclinometers, between cross-sections such that influence from the absolute rotation of floors can be eliminated. Meanwhile, since the inclinometers are densely installed near the bottom, translational acceleration-induced error can be compensated by subtracting the lowest sensor’s output from others’. However, issues caused by rotational and translational vibration are considered as the major challenges in real applications. The contribution of external vibration to the sensor’s overall output is revealed via analysis on a simplified inclinometer model. A numerical study utilizing typical RC column’s deformation characteristics and dimensions is conducted to analyze the influence of major factors: vibrational frequency, sensor position and damage extent. A method for static and dynamic inclinometer calibration is presented. The related calibration experiments are carried out to quantify the sensor’s sensitivity as well as the relationship between rotational frequency and error. The calibration method is validated with a set of vibration tests that use three seismic waves as input. Finally, performance of the proposed approach in full scale structures is investigated through a shake table test.

Uniform deformation distribution of structures at different seismic hazard levels using endurance time method

This paper evaluates the application of the endurance time method in the optimum performance design of structures using the uniform deformation theory. The structures used in this study include shear-building systems with 5, 10, and 15 stories, and steel moment-resisting frames with 3, 7, and 12 stories. Initially, shear-building systems are optimized to have uniform story ductility ratios at low, moderate and high seismic hazard levels separately using three sets of ground motion records and a compatible series of endurance time acceleration functions. The effectiveness and accuracy of the endurance time method are assessed by comparing lateral force distribution obtained from this method with its corresponding attained from ground motion records. Moreover, as the number of stories and target ductility increases, the compatibility of these two methods improves. However, it is found that the optimum structure at one seismic hazard level does not necessarily lead to the optimum structure at other seismic hazard levels. Next, by adding dampers with gap to the systems, a procedure is suggested to optimize these structures at different seismic hazard levels simultaneously. These dampers are activated at moderate and high seismic hazard levels. Finally, similar optimization algorithm is used for steel moment-resisting frames to make their story drift ratios or plastic hinge rotations uniform along the height at different seismic hazard levels. Results show that combining endurance time method and uniform deformation theory leads to a promising optimization procedure that can significantly reduce computational costs with reasonable error.

Damage inference and residual capacity assessment for an E-Defense 2018 ten-story RC test structure

This paper presents an enhanced vision-based, post-earthquake performance assessment framework for RC building structures. This framework incorporates a damage inference method that can estimate the stiffness and strength reduction factors of components in stories without damage inspection based on the inter-story drift. The framework was validated by the application to the full-scale shaking table test of an E-Defense 2018 ten-story RC structure. The vision-based damage detection method effectively detected multicategory seismic damage on the component surfaces, and the damage states estimated by the vision-based method were consistent with the results estimated by the measured plastic hinge rotation. The proposed inter-story drift-based damage inference method reasonably estimated the reduction factors of components in the stories without damage photos. The numerical model updated by the reduction factors of damaged components provided accurate estimates of the fundamental vibrational frequencies after different levels of seismic shaking, and the drift-based inference method significantly improved the results compared with the trivial linear interpolation method. The residual capacity curves provided by pushover analysis of the updated model using the reduction factors as per FEMA 306 & Chiu et al. reasonably captured the hysteretic responses of the structure.

Quantification of variability in simulated seismic performance of RC wall buildings

This paper quantifies the variability in the seismic performance of slender reinforced concrete (RC) wall buildings simulated using different fiber based nonlinear models. The models use the same material constitutive relationships and other analysis inputs (e.g., damping) so that the quantified variability in the building performance is caused by the numerical modeling approach rather than user-selected parameters. These models were first validated against the measured shake-table test behavior of a 7-story RC wall building. Then, nonlinear dynamic analyses of the 7-story wall test specimen and three RC wall archetype buildings of 4-, 8-, and 12-stories were conducted to quantify the variability in the resulting seismic performance assessment parameters and damage fragility curves. The variability in the numerical model responses was evaluated using ground motion suites corresponding to three hazard levels with 50%, 10%, and 2% probability of exceedance in 50 years, while the damage fragility curves were obtained following the FEMA P695 methodology. The variability was quantified based on global response parameters (interstory drift ratio and roof drift ratio) and local response parameters (plastic hinge rotation and curvature at the critical length), since these parameters are commonly used in seismic performance assessment of RC buildings. Based on the results, it is strongly recommended that the performance assessment of slender RC wall buildings be done using global response parameters rather than local response parameters, since the variability of the predicted response among the nonlinear models was significantly smaller for global response parameters.

Compressive Behaviors of Steel Braces with Different Sectional Shapes

AbstractSteel braces are an essential structural element to resist lateral seismic forces and widely utilized in various types of buildings. The primary source of load carrying capacity in steel braced frames is through buckling and yielding of diagonal braces. Hysteretic behaviors of steel braces exhibit unsymmetric properties in tension and compression. Especially, they show significant strength degradation when loaded into the inelastic range in compression. Therefore, the governing failure modes of steel braces shall be global buckling in compression and this phenomenon shall occur prior to brittle limit states such as net section rupture or local buckling of elements. Except for effects of material properties, most of influential parameters is strongly related to the configuration and sectional shape of steel braces. Of them, the objective of this study is to investigate effects of sectional shapes on compressive behaviors of steel braces. Especially, this study focuses on the variation in the plastic hinge rotation and residual deformation of steel braces with representative sectional shapes which are typically applied on the construction field.

Lateral Load Behavior of C-PSW/CFs Using Steel Members as Boundary Elements

Composite plate shear walls/concrete-filled (C-PSW/CFs), also known as SpeedCore systems, are a relatively new structural member in American codes and standards. Prior research has focused primarily on C-PSW/CF walls with either flange/closure plates or filled composite members as boundary elements. Walls without boundary elements have also been studied, but they are no longer permitted by the American Institute of Steel Construction (AISC 341-22). The reason is that composite walls without boundary elements do not provide adequate ductility for seismic design. This paper presents the results of experimental and numerical studies conducted to evaluate the cyclic lateral load behavior of C-PSW/CFs using hot-rolled structural steel members as boundary elements. The steel web plates of the C-PSW/CF specimens were connected to each other using threaded tie bars with double nut connections. Composite interaction between the steel and concrete infill was achieved using the tie bars and additional shear studs welded to the boundary elements. The composite walls were embedded and anchored to reinforced concrete foundation blocks using welded deformed bar anchors. The experimental investigations focused on the cyclic lateral load-drift responses including test observations and limit states, moment-rotation response of the plastic hinge and the section moment-curvature relationship, overall lateral stiffness, strength, and displacement ductility. The experimental results show that the specimens exceeded their nominal flexural capacities calculated using the plastic stress distribution method or fiber-based section modeling using measured material properties. The specimens had plastic hinge rotation capacity greater than 0.028 rad. and displacement ductility ratio greater than 5.2. Detailed 3D nonlinear inelastic finite element models and simpler fiber-based macro models of the tested specimens were developed and benchmarked using experimental results. The detailed 3D finite element models can reasonably simulate the global and local behavior of the specimens, and are recommended for conducting further parametric studies of composite wall design details. Simpler fiber-based macro models can efficiently simulate the cyclic lateral load behavior of the specimens, and are recommended for modeling C-PSW/CFs while simulating the behavior of multi-story building structures.

Fatigue Experiment Study on Internal Force Redistribution in the Negative Moment Zone of Steel–Concrete Continuous Composite Box Beams

Due to the accumulated fatigue damage in steel-concrete continuous composite box beams, a plastic hinge forms in the negative moment zone, leading to significant internal force redistribution. To investigate the internal force redistribution in the negative moment zone and confirm structural safety under fatigue loading, experimental tests were conducted on nine steel-concrete continuous composite box beams: eight of them under fatigue testing, one of them under static testing. The test results showed that the moment modification coefficient at the middle support increases during the fatigue process. When approaching fatigue failure, an increase of 1.0% in the reinforcement ratio or 0.27% in the stirrup ratio results in a reduction of 13% in the moment modification coefficient. Furthermore, a quadratic function model was proposed to calculate the moment modification coefficient of a steel-concrete continuous composite box beam during the fatigue process, which exhibited good agreement with the experimental results. Finally, we verified the applicability of the plastic hinge rotation theory for steel-concrete continuous composite box beams under fatigue loading.

Seismic evaluation of vertically irregular RC frames subjected to mainshock-aftershock sequences of near-fault and far-fault ground motions

Sequential ground motions can significantly affect the seismic demands of reinforced concrete (RC) frames with irregularity along the height. In this paper, the effect of sequential near-fault and far-fault ground motion records with strong and weak aftershocks on the seismic demands of vertically irregular 10-story RC building frames is investigated. The vertically irregular frames with stiffness and mass irregularities were created by applying a modification factor of MF = 2 in three different locations along the height of the reference regular frame. Eigenvalue analysis was performed to evaluate the dynamic characteristics of the structures (i.e. the period and the effective modal participating mass ratio for different modes of vibration). In order to study the seismic demands of these structures, the non-linear response history analysis (NL-RHA), which is the most accurate method of seismic evaluation of structures, was carried out. The floor displacements, story drifts, plastic hinge rotations and residual story drifts obtained from the NL-RHAs were exhaustively studied, and the effect of seismic sequences on the seismic responses was investigated. Furthermore, the enhanced pushover analyses, including the modal pushover analysis (MPA), consecutive modal pushover (CMP) procedure, extended N2 (EN2) method, single-run multi-mode pushover (SMP) method and non-adaptive displacement-based pushover (NADP) procedure were implemented to consider the effect of higher modes in computing the seismic demands of the structures subjected to sequential near-fault and far-fault records as well as mainshocks. The results accentuate that the maximum seismic demands and damage of the structure for sequential near-fault and far-fault records with strong aftershocks are much greater than those for the corresponding mainshocks. Moreover, the enhanced pushover analyses in the case of sequential records have usually less accuracy in estimating the seismic demands in comparison with mainshocks only.

Plastic hinge rotations of steel braces estimated using improved physical theory models

The cyclic response of a typical steel brace cannot be easily captured due to its asymmetric force-deformation relation due to buckling resulting in substantially strength deterioration. Regardless of experimental and analytical efforts on the behavior of steel braces, current physical theory models overestimate their compression strengths after buckling. This study first reviewed the formulations employed in the current physical theory model and then carried out full scale cyclic tests of W-shaped steel braces to find out and to expose problems of the current physical theory model. The tests show that plastic hinge rotations from the maximum tensile strength to the maximum compressive strength are not maintained, which does not agree with the underlying assumption of the current physical theory model. This paper suggests the improved model that can employ a new finding on the behavior of plastic hinges at buckled steel braces. It was confirmed from the validation that the improved model with a nonlinear assumption can properly capture the changes of hinge rotations during the excursion between the maximum tensile and compressive loads and can be the best candidate for addressing the shortcoming of the existing physical theory model.

Seismic performance of reinforced concrete beam‐column joint made of post‐filling coarse aggregate concrete

AbstractPost‐filling coarse aggregate concrete is a new type of green concrete that not only saves the cost of cementitious material, improves the strength, cracking resistance and durability of concrete, but also reduces the carbon footprint. In view of the lack of research on the seismic performance of post‐filling coarse aggregate concrete, this study designs eight interior beam‐column joint specimens made of post‐filling coarse aggregate concrete and three beam‐column joint specimens made of conventional concrete. It studies the influence of post‐filling coarse aggregate ratio, axial compression ratio and stirrup volume ratio of node area on the seismic performance of joint specimens. Through low cyclic reversed loading test, the failure process and the failure pattern, hysteresis curves, skeleton curves, ductility, stiffness degeneration, residual strength and residual displacement, and plastic hinge rotation of interior joints with post‐filling coarse aggregate concrete are analyzed. Test results show that the failure mode of post‐filling coarse aggregate concrete joints is similar to that of the conventional concrete joints. As the axial compression ratio increases, the seismic performance of the joints shows a trend of increasing first and then decreasing, and it reaches the peak when the axial compression ratio is 0.2. It also demonstrates that the seismic performance of the joints is increased by increasing the stirrup volume ratio of node area. Ultimately, under the same axial compression ratio, the seismic performance of the post‐filling coarse aggregate concrete is not significantly different from that of the conventional concrete. It proves that the reinforced beam‐column joint made of post‐filling coarse aggregate concrete could fulfill the comparable seismic performance as that of conventional concrete.

Confinement detailing of concrete encased steel concrete composite columns

Steel concrete composite construction is now gaining popularity in our country. Concrete-encased steel columns have several advantages, but like RC columns, there is a need to ensure adequate concrete confinement so that it has sufficient ductility under seismic loads. This study investigates the confinement of the concrete based on the detailing of the transverse reinforcement. The ductilities of a typical encased section that satisfies the minimum reinforcement criteria and a highly confined section with special detailing are compared. A nonlinear 3D finite element model is developed in ABAQUS for this purpose. The confined stress-strain curve for M30 grade of concrete is carefully incorporated in the special confined section. The interaction between structural steel and concrete is modelled with an 'embedded region' interaction tool available in the ABAQUS library. Based on the eigen mode of the section, the initial geometric imperfection was given. The significant increment in displacement ductility factor, plastic hinge rotation and drift ratio are observed for a special confined encased column. A parametric study has been carried out by varying the parameters; the axial load ratio, steel contribution ratio, steel width to depth ratio and transverse reinforcement spacing. It was observed that structural section aspect ratio (steel width to depth) and transverse reinforcement spacing significantly affect the ductility of the section. The plastic hinge rotation and drift ratios were also calculated for different sections.

Performance Assessment of Hybrid Steel Frames under Near-field Seismic Excitations

Assessment of the seismic performance of steel structures is topical research for a variety of earthquakes. Moment-resisting rigid steel frames are generally designed and used for high seismic zones. However, the famous Northridge in 1994 and Kobe in 1995 earthquakes exposed the shortcomings of moment frames. During these events, the beam-column connections of rigid moment frames were severely damaged. Since then, an alternative of welded connections called bolted or semi-rigid connections is considered for designing or retrofitting of steel moment frames. From the last few years, the semi-rigid connections combined with rigid connections, termed as hybrid or dual frames have become widely popular for earthquake designers and engineers due to enhanced ductility and reduced cost of construction. Earlier research work was focused on far-field (FF) earthquakes, whereas, the near-field (NF) earthquakes are crucial for civil engineering structures. In this paper, an extensive numerical study is carried on rigid and hybrid steel moment frames for NF and FF earthquakes. For this purpose, a ten-story rigid steel frame is analyzed and designed for seismic requirements as per Indian Standards. The rigid connections of frames are replaced by semi-rigid connections with a moderate degree of semi-rigidity. The six different patterns (locations of semi-rigid connections) of hybrid frames are considered here to compare the seismic performance of hybrid frames under near field earthquakes. The nonlinear response-history analyses are executed using the SAP2000 software at two scaled PGAs defined as low (i.e., 0.2g) and high (0.5g) level. An ensemble of three time-histories, each for both types of earthquakes are considered for the numerical simulation. Response quantities of interest, namely, the maximum value of base shear, story displacement, inter-story drift ratio, the total number of plastic hinges, and the square root of the sum of squares of maximum plastic hinge rotations are considered for the decision of a most appropriate pattern for hybrid frames. The results of the numerical study indicate that the response behavior for the NF earthquakes is distinctly different both in nature and magnitude. It is observed that the seismic demands under the NF earthquakes are substantially more as compared to those obtained for FF earthquakes for all cases of hybrid frames. Further, it is also found that the pattern and number of semi-rigid connections in the hybrid frame have a vital role in seismic performance.

Vision‐based seismic damage detection and residual capacity assessment for an RC shaking table test structure

AbstractIn this paper, the existing postearthquake performance assessment framework for reinforced concrete (RC) building structures is improved by adding a new feature of the computer vision‐based damage detection. In this framework, visible seismic damage is classified and quantified from photographs of damaged RC components using the developed deep convolutional network (CNN) Damage‐Net of semantic segmentation, and then the mechanical property degradation factors of components determined from the detected damage states are used to update the numerical model. Pushover analysis of the updated model assesses the residual capacity of the damaged structure. Large‐scale shaking table tests of a three‐story RC building structure, which was heavily instrumented with sensors and recorded with a large volume of photographs, were used as a case study to demonstrate the improved postearthquake performance assessment framework. The vision‐based approach accurately detected multicategory seismic damage of the test structure and effectively estimated the residual crack widths and angles under various lighting, image acquisition, and surface conditions. The updated model, which incorporated the mechanical property degradation of the damaged components, provided accurate estimate on the fundamental vibrational frequencies of the damaged structure after various levels of seismic motion shaking, which matched well with the system identification results. Using the mechanical property reduction factor values recommended by FEMA 306 & Chiu et al., pushover analysis of the updated models provided residual capacity curves that reasonably captured the measured hysteretic responses of the structure. In addition, the damage states of components as estimated by the vision‐based methods were also compared with the measured plastic hinge rotation data. The successful implementation of the vision‐based assessment in this test case indicates its potential for application in the postearthquake evaluation of buildings.

Influence of vertical seismic component on the response of reinforced concrete regular planar frames

The objective of the present paper is to investigate the influence of the vertical seismic component on the response of reinforced concrete regular planar frames. For this purpose, 20 reinforced concrete single- and multi-storey frames with various span lengths are designed according to Eurocodes 2 and 8 and analyzed by means of inelastic dynamic analysis for 20 recorded near-fault ground motions. In particular, two series of time-history analyses are conducted: one taking into account the horizontal seismic component only and a second considering concurrent action of horizontal and vertical components. For each analysis, the values of representative response quantities (axial forces, displacements, plastic hinge rotations) are calculated. The differences of the response quantities resulting from the two series of analyses provide a measure of the vertical seismic component impact on the response of regular planar frames. The whole study demonstrates that the role of the vertical ground motion is quite underestimated by modern seismic codes.

Column Base Flexibility Effects on the Seismic Performance of Single-bay Single-story Steel Moment Frames

ABSTRACT This paper investigates the seismic performance of one-story one-bay steel moment-resisting frames with flexible column bases from theoretical and numerical perspectives. It is shown that increasing the base flexibility decreased the column top moment for medium to long period elastic structures, thereby reducing the possibility of a soft-story mechanism. For inelastic systems, column top plastic hinge rotation tended to increase for short/medium periods. The top plastic hinge rotation ratio was insensitive to moderate variation in plastic hinge post-elastic stiffness but decreased as the hysteresis behavior changed to self-centering. In almost all cases, increasing the base flexibility increased the lateral deformation.