Formation Of Plastic Hinges Research Articles

Tube-in-tube rigid beam to CFT column connection in moment-resisting frames: An experimental study

Using concrete-filled steel tube (CFT) columns in high-rise buildings has attracted considerable attention in recent years. Aside from its advantages, rigid beam to CFT column connections are followed by some challenges. Difficult construction and implementation, sophisticated details of connection, and most importantly, placing and welding internal stiffeners (continuity plates) are among the common challenges. In the present study, a novel connection called “Tube-in-Tube (TIT) connection” has been proposed. In TIT connection, an inner tube and a pair of vertical straps are utilized in the panel zone area. To investigate the proposed connection, two full-scale specimens were tested using cyclic reversal loading. The two specimens were identical in dimensions and detailing, except for their strap width and the diameter of inner tube. Specimen 1 and Specimen 2 were detailed with inner tube diameter equal to half and one-third of the column dimension, respectively. The inter-story drift ratio, joint's shear deformation, plastic hinge formation, and energy dissipation capacity were analyzed. Moreover, mechanical parameters such as yield and ultimate strengths, and ductility of the specimens were calculated. Specimen 2 showed 3% and 8% increase in the peak flexural strength and cumulative energy dissipation in comparison with Specimen 1. The results showed that the panel zone remain elastic during the test. In order to further investigate the proposed connection, finite element (FE) analysis was conducted on the specimen. The results of FE analysis confirmed the elastic behavior of the tube and straps.

Seismic performance and shear capacity of modular steel frames infilled with cold-formed steel walls with openings

Door and window openings, which universally exist in the external load bearing walls of module units, significantly impact the seismic performance and shear capacity of cold-formed steel walls (CFSWs). In this study, we conducted cyclic loading tests on three full-scale specimens to investigate the seismic performance of a single frame of modular steel structures infilled with cold-formed steel walls (MSS-CFSWs). The CFSW of two specimens had window and door openings, while that of the remaining specimen did not have any openings. Test results indicated that the failure mode of the specimens had two stages; the self-drilling screw connection of the CFSW failed first, followed by plastic hinges formation at the beam end of the steel frame. We observed 45° inclined cracks on the wallboards on both sides of the CFSW with openings. The window and door openings reduced the initial lateral stiffness by 24.4% and 28.7% and shear capacity by 3.8% and 15.5%, respectively, compared with those of the specimen without openings. Both the CFSW and steel frame contributed to the shear capacity of the MSS-CFSW. Furthermore, the irregular wallboard units were divided into rectangular wallboard units. Based on the modified global analysis method and the failure mode of the plastic hinges formed at the beam end, we developed a calculation method for the shear capacity of the specimen. We verified the accuracy of the proposed method by comparing the theoretical and test values. The results of this study are expected to serve as a reference for engineering design.

A novel data-driven analysis for sequentially formulated plastic hinges of steel frames

Although many different nonlinear analysis techniques for steel frame structures, they causes the increase in total computational cost. A data-driven approach can then be used to substitute the classic finite element nonlinear analysis including second order methods and inelastic modelling. In this paper, a novel data-driven method using ensemble learning models for geometric and material nonlinear analyses of frame structures is proposed. For this approach, the data acquisition process and machine learning-based models are needed to train a large amount of dataset, which is collected from the nonlinear analysis and a yield surface equation. Ensemble learning algorithms are then used to build the data-driven models. After training, the sequence of plastic hinge formation in steel frame structures can be predicted without any nonlinear analysis process. In that situation, the data-driven model is more effective, especially in practical cases with the lack of experimental information due to limited sensors. The validity of the proposed method has been demonstrated by several numerical examples.

Mechanical performance of an improved aluminium alloy gusset joint under simplex and complex load states

An improved aluminium alloy gusset joint (I-AAGJ) with two types of shear connectors (SCs) and a peripheral bending system (PBS) is proposed to address traditional aluminium alloy gusset joint (T-AAGJ) imperfections. The mechanical performance of the I-AAGJ, including axial stiffness, in-plane and out-of-plane flexural stiffness, and ultimate bearing capacity, is investigated by full-scale testing under simplex and complex load states. Numerical simulation results of I-AAGJ behaviour are presented via nonlinear finite element analysis (FEA). Three-phase models are determined to explain the I-AAGJ deformation process. In the linear phase, PBS is proven to provide significant assistance for the joint bearing axial force and bending moment. By comparing with the T-AAGJ, an at least 30% improvement of joint stiffness along three directions can be observed respectively. In the nonlinear phase, SCs strengthen the joint by delaying plastic hinge formation and preventing gusset plates from being folded. The complex load state of lower level has a negligible impact on the I-AAGJ mechanical performance, while that of higher level still has to break through the protection of PBS and SCs before it destructs the joint.

Mechanical Behavior of Special-Shaped Double-Web Steel-Reinforced Concrete Column Joints

In this paper, five new joints of special-shaped double-web steel-reinforced concrete (SDSRC) columns connected with steel beams are designed. The load-displacement curves, joint yield states and damage forms of the beam ends of the five joints under monotonic loading with the same axial pressure ratio are investigated. Additionally, the hysteresis performance, strength and stiffness degradation under cyclic loading are studied. The results show that the bearing capacity of joints with studs can increase by approximately 10%. Since the arrangement of multiple rows of studs at the connection between the beam web and the column has better force transfer performance and concrete synergy behavior, the failure modes of these joints are plastic hinge formation at the end of the beam, satisfying strong column-weak beam requirements. Moreover, these joints exhibit good ductility and energy dissipation capacity under cyclic loading, and their strength and stiffness gradually decrease. In contrast, joints with single-row studs or without studs at the connection between beam web and column exhibit beam flange buckling rather than full-section plastic hinge formation at the beam end, and tensile deformation of column web is larger. Although these joints exhibit good ductility performance, their energy dissipation capacity is weaker than that of joints with multiple rows of studs at the beam web-column connection.

Moment redistribution capacity of continuous RC beams with High-Strength steel reinforcement

Moment redistribution (MR), a nonlinear behavior occurring in continuous reinforced concrete (RC) beams, is related to the redistributed section's ductility and the stiffness distribution along the whole beam. The use of high-strength steel (HSS) reinforcement could affect the redistributed section’s ductility and can delay or even prevent the formation of plastic hinge after another. The lack of research regarding the influence of those phenomena on MR is one of the reasons that hinder design engineers from using HSS. This paper conducts a broad-range parametric study through finite element (FE) method to check if the design provisions on MR are still applicable to beams with HSS reinforcement of yield strength of more than 600 MPa. The critical sections' yield state (whether the plastic hinge is formed) at the ultimate limit state (ULS) and its influences on MR are investigated. The study demonstrations that the MR capacity decreases with the increase in yield strength of reinforcement, especially when the midspan section cannot yield at ULS due to the use of HSS reinforcement. Besides, the yield state is influenced by the coupling effect of multi-parameters and significantly affects the influence degree of each parameter on MR. A new method considering the yield state is proposed to estimate the MR capacity of the continuous beams. This method's reasonable accuracy is proved. It is recommended to reduce the specified MR by about 6% for every 100 MPa increase in yield strength of reinforcement.

SIMPLE ANALYSIS METHOD USING RIGID ZONE FOR A BEAM AND COLUMN WITH GUSSET PLATE

In a steel structure building, it is easy to theoretically elucidate the behavior of each member, but it is difficult to evaluate the stiffness and strength at joints. Above all, in the joint where a gusset plate is attached diagonally to the frame and the dampers are connected, beams, columns, and gusset plates influence each other and show complicated behavior. In this study, a bare steel beam with gusset plate is reproduced with a simple model consisting of a rigid zone and a beam element. Furthermore, the rigid zone length and the plastic hinge formation position are shown.

Thermal and seismic performance evaluation of the innovative cylindrical RBS connection using numerical modelling

Ductile connections have remarkably influenced the structural response during a fire or earthquake and prevented brittle failure. In this paper, an RBS connection with a robust cylindrical assembly is proposed and simulated by using the finite element program ABAQUS. The cylindrical RBS connection is made by cutting the continuous web and flange of the beam and replacing these parts with horizontal and vertical cylinders at the reduced region. Models with variable thickness and inner radius are subjected to thermal and seismic loading separately to assess failure mechanisms and plastic hinge formation. Based on the numerical results, the cylindrical RBS connection not only provides suitable ductility to overcome the fire-induced axial force but also exhibits a larger hysteretic enclosed area without lateral-torsional buckling under cyclic loading.

Seismic behavior of reinforced concrete beam-column joints with unstressed steel strands fully or partially used for beam longitudinal reinforcement

Five beam-column joint specimens: three exterior and two interior specimens were subjected to cyclic loading to investigate the effectiveness of using unstressed Grade 1860 MPa steel strands as full/partial replacement for the conventional Grade 420 MPa deformed bars as beam longitudinal reinforcement. The study also developed a special hooked anchorage detail to anchor the steel strands in the joint region. The test specimens failed by beam plastic hinge formation near the column face as intended in design, with drift capacities between 5.12% and 7.57%. However, the full (100%) and partial (50%) replacement of deformed bars by strands led to a 58% and 28% decrease in average relative energy dissipation. Despite this, the full/partial replacement of deformed bars by strands as beam longitudinal reinforcement resulted in enhanced reentering capabilities. Fracture of longitudinal steel strands observed in the beam plastic hinge region at the end of the test indicated the effectiveness of the special hooked anchorage detail in allowing steel strands to develop their capacity. Further, the flexural strength of the beams of test specimens was evaluated through a detailed moment-curvature analysis, which predicted the beam flexural strength with high accuracy and less variation (mean = 1.01, standard deviation = 0.02). After that, beam flexural strengths were evaluated following the ACI 318–19 procedure modified to include the proposed bilinear strand model, which produced conservative estimates of beam flexural strength (mean = 1.15) suitable for design. Also, the procedure to estimate the beam's probable flexural strength is presented. Finally, required modifications to the conventional seismic design procedure were proposed to incorporate the use of strands as beam longitudinal reinforcement.

Nonlinear Time History Analysis for Seismic Effects on Reinforced Concrete Building

A typical Reinforced Concrete (RC) building frame comprising of RC columns and connecting beams that participates in resisting the earthquake forces. Due to earthquake, reversal tension generates at both faces of a beam and column; and hence damage occur in the frame for the disability of tension carrying capacity of concrete. Therefore, the structural performance of RC building for seismic load has been analyzed by nonlinear time history analysis method for this study. A residential building located in Dhaka, Bangladesh subjected to various types of gravity load and seismic load was considered to analyze using ETABS software as per the guideline of BNBC (2020). According to the guideline of ATC 40 (1996), the seismic performances like maximum displacement and story drift for RC building were evaluated both at structural and element levels by applying El Centro (1940) ground motion at the base of the structure. Formation of plastic hinges is used as the basis to evaluate the local performance and story drift is used to evaluate the global performance. At first, the considered building was designed only for gravity load, and then for both gravity and seismic load according to BNBC (2020). Further studies have been performed on that building considering double height column at a story level. It was observed that the maximum displacement and story drift exceeds the allowable limit for all the considered cases if seismic load is applied on the structure.

Effectiveness of the Seesaw System as a Means of Seismic Upgrading in Older, Non-Ductile Reinforced Concrete Buildings

This work investigates and discusses the effectiveness of the seesaw system when installed in an older, non-ductile reinforced concrete (RC) building for seismic upgrading purposes. In particular, two different configurations of the seesaw system are assumed in a two-storey 3D RC framed building which was designed according to older seismic provisions and, thus, is susceptible to flexural and shear failures. To check if there is any merit in employing the seesaw system in this RC building, non-linear time-history (NLTH) analyses are conducting using 11 seismic motions. Peak values for inter-story drift ratios (IDR), residual inter-story drift ratios (RIDR) and floor accelerations (FA) are computed, and the sequence and cause (i.e., due to surpass of flexural or shear strength) of plastic hinge formations are monitored. Leaving aside any issues related to fabrication and cost, interpretation of the results obtained by the aforementioned seismic response indices for the RC building under study leads to the conclusion that the seesaw system can be a retrofitting scheme for the seismic upgrading of older, non-ductile RC framed buildings.

Disregarding the Effect of Openings in Infill Walls in Indian Seismic Code: A Scrutiny

This study attempts to scrutinize the provision of IS 1893(Part–I): 2016 in neglecting the effect of openings in infill walls in the context of earthquake performance of the same. It evaluates the effect of openings as per FEMA-273 and ATC-40 and compares the result with the provisions of Indian code. The comparative seismic performance, in terms of base shear and top displacement, using the response spectrum of IS 1893(Part–I): 2016, is done on an irregular block of the Jorhat Engineering College old building situated in Seismic Zone-V. Two models of the frame structure are made in SAP 2000®. Modelling of infill is done as Equivalent-Strut, pin-jointed to the RC frame, the width of the strut taking care of effect of openings as per FEMA-273 and ATC-40. The width of the infill wall with openings is found to be 61.465mm whereas, without opening it is 503.80mm. In contrast, as per IS provision the width of infill is 486.27mm. Nonlinear Static Pushover Analysis is performed in SAP 2000®. The building base shear capacity for pushover analysis according to FEMA-273andATC-40 with infill is 10626.107kN and Maximum displacement is 0.042m. In contrast, provisions of IS 1893(part-I):2016 yield the base shear capacity with infill as 20231.365kN and Maximum displacement was 0.063m. An increase in base shear in the latter case may be attributed to the bigger strut width as per IS provision. The formation of plastic hinges is also more in the latter case. It is concluded that IS codal provisions resulted in a doubly stiffer structure.

Nonlinear Static Analysis of Core Wall RCC Framed Buildings

RCC framed buildings mainly consists of shear walls and columns for resisting lateral force due to earthquakes. In most of the framed buildings shear walls are provided in the outer frames. In addition to shear walls provided in the outer frames, RCC lift -well (core wall) is also provided in the inner core of the buildings to accommodate lift. Core wall also acts as shear wall contributing to the lateral resistance to the buildings. In the present study, nonlinear static analysis is performed to study the behaviour of high rise RCC buildings, the buildings have a centralised lift core wall with a door opening and shear walls in outer frames. The flange of core wall is joined together at regular interval by floor and slabs and connecting beams to provide proper connection in between flange. This Residential G+14 RCC framed building is lying in seismic zone 4 and analysed as per guidelines of is 1893 (part 1) 2016 and ETABS 17.0.1. Responses namely lateral loads, story drift, base shear, story displacement and the formation of plastic hinges compared for two types of buildings, namely with core wall and without core wall to understand the effect of core wall against the lateral loads.

Evaluation of Seismic Response of Irregular Buildings Subjected to Near-Field Earthquakes

This study deals with the evaluation of the seismic performance of irregular buildings by comparing various seismic responses of six types of building, namely regular building, setback building, stepped building, mass irregular building, stiffness irregular building, and building with floating columns which are constructed of Reinforced Cement Concrete (RCC) subjected to extreme earthquake loads. The nonlinear time history analysis (NTHA) method is carried out to obtain different seismic response parameters for all considered irregular and regular buildings. The structural response results are compared by applying real earthquake records of different near-field and Far-field earthquakes and were compared for four different seismic response parameters which include top storey displacement, inter-storey drift, top base shear, and pattern of plastic hinges formation. This research concludes that the storey displacement, storey drift, and top base shear is significantly less for stepped and setback buildings, and significantly high for mass irregular, stiffness irregular, and floating columns buildings as compared to a regular building. Stepped buildings yield less responses and high responses are yielded in the building with floating columns.

Seismic Performance of Special Truss Moment Frames With X-Bracing Type: Influence of Building Height

Abstract This study investigated the implementation of Special Truss Moment Frames (STMF) X-braced type in accordance with the recommendations of the National Earthquake Hazards Reduction Program (NEHRP), 1997:2000 and Indonesian National Standards (SNI) 1726 where it is stated that the STMF may only be used up to a maximum building height of 48 m (160 feet) for Seismic Design Category of D. The analyses compared the seismic response of apartment buildings using STMF system with different height: 44 m (11 stories), 48 m (12 stories), and 52 m (13 stories). The nonlinear behaviors were investigated through a series of nonlinear time history and pushover analyses, including the inelastic response of the structural components, top-roof displacement, drift ratio, and ductility. The structural modeling and the selection of steel sections were performed in SAP 2000 based on SNI 1726 code, considering that the structure was built on medium soil in Aceh region. Seismic performance was examined through a series of pushover and nonlinear time history analysis (NLTHA) using three scaled accelerogram: Elcentro 1940, Northridge 1994 and Kobe 1995 records. The results of the study show that in case of STMF structure with the height of 52 m (higher than the maximum height of STMF structure stated in the codes), the seismic performance of the structure was excellent and met the requirements. Axial plasticization occurred only in X-braces, not followed by the formation of plastic hinges at the ends of the ductile segments. Meanwhile, the other structural components remained elastic. This indicates that the structure can still be used after the earthquake, by replacing only the X-braced components. The drift ratio met the requirements and the roof displacements behavior was asymptotic, indicating that there is no residual horizontal displacement of the building after the seismic loads occurred.

Response of perforated H-pile subjected to coupled lateral displacement history and axial loading

ABSTRACT The substructure of an integral abutment bridge is designed to accommodate the lateral demand induced by the expansion and contraction of the bridge deck. The assembly of H-piles oriented about their weak axis of bending and aligned in a single row with a rigid connection to the abutment is most preferred for supporting the integral abutment bridges. The weak axis orientation of H-pile allows for higher displacement capacity, thus accommodating the cyclic thermal demand induced by a superstructure. The hysteretic response of H-piles is suggestive of the early onset of the plastic hinge formation, which helps in accommodating the cyclic demand. The H-piles in the integral abutment bridge experience low cycle fatigue induced by cyclic thermal variations, resulting in the buckling of flanges at the critical zone. This study assesses the impact of perforation made on H-pile flanges at the critical buckling zone. In this study, six unique geometries of perforations are modelled and analysed using combined nonlinear kinematic and isotropic hardening formulation. The hysteretic response of the perforated H-pile models has been compared with an unperforated model to assess the proposed perforation geometry's impact on the H-pile's hysteretic response.

Monitoring the behaviour of seven storeyed RC frame subjected to reversed cyclic loading by nonlinear NDT

Large-scale structures are more prone to risk than small-scale structures due to their increased weight, stiffness and ductility parameters. The main focus of this investigative study is on the structural monitoring of a building using the non-destructive method of non-linear ultrasonic pulse velocity. A single-bay seven-storeyed frame model subjected to reverse cyclic loading of varying amplitudes is monitored by non-linear ultrasonic technique based on third harmonic wave generation. The critical nodes are identified in two different ways: the points of possible plastic hinge formation (PPPHF) through the theoretical background of plastic hinge analysis and the highly sensitive regions in structures (HSR) through numerical analysis. The common nodes of PPPHF and HSR are considered to monitor the structure. The invisible primary structural damage in the initial stage and the visible structural damage up to ultimate load are observed using non-linear ultrasonic waves. The fundamental frequency value and the third harmonic frequency value are observed and processed in MATLAB in the form of a Fast Fourier Transform (FFT) algorithm. The relationship between the condition of the structure and the ratio of third harmonic parameter, load and displacement is compared. In the initial stage of loading, only slight change or no variation in third harmonic ratio is observed at the observation points indicating material disintegration. This varies consistently up to the development of visible cracks and the same varies inconsistently on further loading after the appearance of visual cracks.

Simplified analytical procedure to calculate the impact behaviour of steel parking-structure columns

The steel supporting frame of automatic mechanical garages is called a parking structure. Presently, for these novel structures, the design codes are without giving detailed guidelines to predict the response of their impacted column. Thus, this paper presents a simplified analytical procedure to calculate the impact behaviour of the column. The proposed method is based on the co-rotational rigid body model and follows the energy-balance principle. Compared with the previous analytical method, it specially targets the parking-structure column and can be used to conveniently and quickly calculate the column transverse displacement with considering the effects of the surrounding structural members and axial loads on the column. The research covers the situation where the column is subjected to the impacts at a low velocity, critical velocity, and overcritical velocity. Primarily, an approach is developed to simplify the overall parking structures. On that basis, the calculation formula for the critical impact velocity, i.e. the velocity that results in the formation of plastic hinges in the column, is derived. To predict the behaviour of the column under the impact beyond the critical impact velocity, the simplified analytical procedure is provided and then its accuracy is examined by validated numerical models. Eventually, according to the procedure, some suggestions are given to improve the design of the column after parametric analyses. It is recommended that control the axial-load levels of the column, particularly the column with a small section area, as well as set stiffeners on the column within the height of 1000 – 1500 mm.

Seismic design and performance evaluation of typical lightweight and heavyweight RC girder bridges with friction pendulum bearing in Indonesia

Seismically isolated bridges have shown better seismic performance than bridges with conventional bearings during large earthquakes. While elastomeric type of isolation has been introduced in various new highway bridges in the country, the use of friction pendulum system for bridge bearing is not yet common in Indonesia, a highly seismically active country. In this paper, design and seismic performance evaluation of two typical reinforced concrete bridges seismically isolated by single concave friction pendulum (SCFP) bearings system and designed according to Indonesian seismic code is described. The reference bridges are selected from typical light rapid transit (LRT) bridge and highway reinforced concrete (RC) bridge in Indonesia. Seismic performances of SCFP-isolated bridges with different bearing configurations and the conventional non-isolated bridges under 1000-year design earthquake were investigated and compared using nonlinear finite element analyses. The results show that SCFP-isolated bridges performed better than non-isolated bridges under design earthquake as shown by reductions in the base shear force, absolute deck acceleration, and deck acceleration amplification ratio. Effects of SCFP on the seismic performance of isolated bridge was evaluated by comparing the moment and rotation values of each pier and the possible formation of plastic hinges. Performance comparisons of SCFP-isolated bridges with various friction types and arrangements revealed that the LRT bridge with all higher friction and the highway bridge with lower friction have the best seismic performance among all isolated bridge models analyzed.

Investigation of the performance of grouted couplers in vehicle impacted reinforced concrete ABC bridge piers

Increased dynamic impact on bridge piers caused by seismic events, blasts, and vehicular impact have become increasingly common. Recent research efforts indicate that code provisions for designing reinforced concrete members to withstand such dynamic loads are inadequate and need additional insights for this purpose. Numerous works have been undertaken to investigate reinforced concrete (RC) traditional bridge pier performance on high strain rate loading. However, little attention has been given to evaluate the performance of connections used in present day bridges including accelerated bridge constructions (ABC) to withstand vehicle impacts, and hence, is relatively unknown. In this study, the use of grouted couplers to contain the unbalanced moments resulting from vehicular impact forces exceeding the moment capacity of the reinforced concrete piers and avoiding extensive damage to the piers is investigated. A representative column, typical of those specified by state departments of transportation, is studied to determine the performance. The performance of the coupler is investigated for both dynamic and static combined stresses. Quasi-static to dynamic strain rates of steel reinforcement connected to the couplers is also evaluated. Quantifying the stresses and strains developed at coupler region from dynamic impact can help coupler manufacturers to optimize the strength properties, thus improving serviceability. This study investigated utilizing splice sleeves in mitigating the formation of plastic hinges, as well as addressing the essential properties of coupler sections required to adequately carry out this function, and will provide a useful design tool for the manufacturers, forensic structural engineers, and practitioners.