End Of Beam Research Articles

Identification of the tip mass parameters in a beam-tip mass system using response surface methodology

Abstract In this study, a response surface based approach is introduced to determine the physical parameters of the tip mass of a beam – tip mass system, such as mass, mass moment of inertia and coordinates of the centre of gravity with respect to the beam end point. To this end, first, a difference function was formulated based on the differences between the peak frequencies and peak amplitudes of the experimental and analytical frequency response functions. Later, observation points were established in the design space using orthogonal arrays, and a response surface was developed using the difference function values at these points. Next, the tip mass parameters were determined by minimizing the response surface with genetic algorithm and particle swarm optimization as well as fmincon, a gradient-based solver of the Matlab program. For comparison purposes, those parameters were obtained by also direct minimization of the difference function with the same algorithms. It was concluded that the tip mass parameters were successfully determined within reasonable error limits by the response surface method with less computational burden. Finally, the effect of design space width on the response surface quality is demonstrated numerically.

Seismic behaviour of the non-straight steel beams in the structural plans

Purpose This research study focuses on investigating the seismic performance of non-straight beams in steel structures and exploring the mechanism by which plastic hinges are formed within these beams. The findings contribute to the understanding of their behaviour under seismic loads and offer insights into their potential for enhancing the lateral resistance of the structure. The abstract of the study highlights the significance of corners in structural plans, where non-coaxial columns, diagonal elements or beams deviating from a straight path are commonly observed. Typically, these non-straight beams are connected to the columns using pinned connections, despite their unknown seismic behaviour. Recognizing the importance of generating plastic hinges in special moment resisting frames and the lack of previous research on the involvement of these non-straight beams, this study aims to address this knowledge gap.Design/methodology/approachThis study examines the seismic behaviour and plastic hinge formation of non-straight beams in steel structures. Non-straight beams are beams that connect non-coaxial columns and diagonal elements, or deviate from a linear path. They are usually pinned to the columns, and their seismic contribution is unknown. A critical case with a 12-m non-straight beam is analysed using Abaqus software. Different models are created with varying cross-section shapes and connection types between the non-straight beams. The models are subjected to lateral monotonic and cyclic loads in one direction. The results show that non-straight beams increase the lateral stiffness, strength and energy dissipation of the models compared to disconnected beams that act as two cantilevers.FindingsThe analysis results reveal several key findings. The inclusion of non-straight beams in the models leads to increased lateral stiffness, strength and energy dissipation compared to the scenario where the beams are disconnected and act as two cantilever beams. Plastic hinges are formed at both ends of the non-straight beam when a 3% drift is reached, contributing to energy damping and introducing plasticity into the structure. These results strongly suggest that non-straight beams play a significant role in enhancing the lateral resistance of the system. Based on the seismic analysis results, this study recommends the utilization of non-straight beams in special moment frames due to the formation of plastic hinges within these beams and their effective participation in resisting lateral seismic loads. This research fills a critical gap in understanding the behaviour of non-straight beams and provides valuable insights for structural engineers involved in the design and analysis of steel structures.Originality/valueThe authors believe that this research will greatly contribute to the knowledge and understanding of the seismic performance of non-straight beams in steel structures.

Single-component Multi-rate Real Time Hybrid Simulation Pilot Test on a Composite Structure

This paper represents a single component multi-rate Real-Time Hybrid Simulation (mrRTHS) strategy for structural assessment of a cantilever Glass Fiber Reinforced Polymer (GFRP) beam loaded at the tip by a sinusoidal point load. This emulated structure is implemented as a simplified wind turbine blade in terms of geometry, scale and load – here with special attention paid to the root and max-chord section. Thus, the experimental substructure comprises the clamped end of the GFRP beam while the free end makes up the numerical substructure. The partitioning between the numerical and experimental substructure – referred to here as the shared boundary – Includes a discrete point with 3 degrees-of-freedom (dof). The numerical substructure generates a displacement signal through a Taylor basis with a coarse time step to optimize computational resources. Using the previous displacement data points, a finer control signal is generated to ensure accurate actuator control in the transfer system. A DIC and inertia compensator is implemented to account for the compliance and dynamics imposed by the load train in the transfer system. The structural response is investigated by mrRTHS for an execution frequency in the range: 0.074Hz – 2.96Hz for the sinusoidal point load. The system performance is evaluated against an experimental test setup of the emulated structure – referred to here as the experimental reference. With a root-mean-square (RMS) error in the order of 8-20% between the mrRTHS and reference, the system proved successful in terms of stability and overall correlation at the shared boundary, which is considered an important milestone towards single component mrRTHS on a structure like e.g. a wind turbine blade, aircraft wing or similar cantilever-shaped large load carrying structure.

Hysteretic Behavior of Full-Scale Precast U-Shaped Composite Beam–Column Connections with Large-Diameter Reinforcements under High Axial Compression

This study introduces precast concrete beam–column connections comprised of composite beams, precast columns, and a monolithic joint core. The composite beams consist of U-shaped beams and floor slabs, leveraging the U-shaped beams for their lightweight nature, acceptable stiffness, and reduced demand for on-site support systems. To mitigate reinforcement congestion in the joint core, the precast connections incorporate large-diameter rebars (greater than 25 mm). This study conducted cyclic loading tests on four full-scale beam–column connections under 0.3 normalized compression, encompassing precast interior and exterior connections, along with two monolithic reference specimens, to investigate their behavior under seismic actions. The results revealed that all specimens exhibited bending failure at the beam ends, with minimal concrete deterioration observed in the joint core areas and columns. The hysteresis curves of the precast specimens and the monolithic connections exhibited a slight pinching effect. The strengths of the interior and exterior precast specimens were 13.3% and 7.8% lower than those of the reference monolithic connections, respectively. The ductility of interior precast connections and monolithic specimens stood at 2.36 and 2.23, respectively, indicating a negligible difference of less than 5%. Meanwhile, the positive and negative ductility of exterior precast connections were 3.06 and 2.34, which was approximately 8% lower than that of the reference connections. Furthermore, the stiffness degradation and energy dissipation capacity of the precast specimens aligned closely with the performance of the reference monolithic ones.

Impact of Variable Parameters of Expansion Joints and Bearing Supports on the Vehicle-Induced Vibration of Curved Girder Bridges

To study how varying the parameters of expansion joints and bearing supports (E-B parameters) affects the dynamic response of a coupled vehicle–bridge system for curved girder bridges, a dynamic response analysis method for the coupled vehicle–joint (bearing)–bridge system, which takes into account centrifugal forces, was proposed and verified. Subsequently, taking a continuous curved box girder bridge as the prototype, the influence of the E-B parameters on the vehicle-induced dynamic response of the curved girder bridge was explored. The results showed that the dynamic amplification factor (DAF) of the middle beam of the expansion joint (DAF-EJ) and the main girder of the curved bridge (DAF-MG) were both significantly influenced by the E-B parameters. When there were height differences between the middle beam and side beam in the EJ, the DAF-EJ obviously varied, and the DAF-MG increased. When the EJ was damaged, the impact effect of the vehicle on the bearing support increased. The DAF-EJ and DAF-MG both increased with the decrease of the vertical support stiffness of the bearing support. The DAF-EJ was greatly affected by the single-support void at the near-slit end of the lane. The DAF-MGs at the beam end, the 1/4 point and 1/2 point of the first span, and the 1/2 point of the second span, were significantly affected by the single-support void near the measuring point. Compared with the single-support void, the DAF-EJ and DAF-MG more significantly increased under the double-support void. Variation in the height difference of the EJ had a more significant effect on the DAF-EJ and DAF-MG at the beam end, while a vertical stiffness reduction in the bearing support had a more significant effect on the DAF-MG.

Improvement effects of knee-bracing friction dampers on cyclic behavior of steel joints in antique buildings

To inherit the unique characteristics of historical timber architecture, the steel antique building (SAB) imitating ancient Chinese timber structures has been constructed using contemporary steel materials and fabrication techniques. These buildings typically exhibit premature yielding cracks and weak energy dissipation at the beam ends under seismic loads. To improve the seismic performance of SABs, two different types of friction dampers were deployed at the knee-bracing region around beam-column joints in SABs. First, cyclic loading tests on dampers indicate that both shear friction dampers and rotational friction dampers exhibit full hysteretic behavior, demonstrating an excellent and stable energy dissipation capacity. The friction coefficient of dampers with brass pads was theoretically calculated to be 0.35. Second, the quasi-static test showed that failure of steel joint specimens with knee-bracing dampers primarily occurred at replaceable angles in the beam-column connection region, which demonstrates that the repairability of steel joints in SABs can be greatly improved without overcomplicated labor. Adding knee-bracing dampers effectively postpones damage to the replaceable angles, which improves the strength, stiffness, and energy dissipation capacity of the steel joints significantly. The shear damper exhibits a more pronounced improvement in the overall structural seismic performance compared to the rotational damper with the same frictional sliding force. Moreover, numerical simulations showed that the strength of the proposed joints with knee-bracing friction dampers decreases with an increase in the axial compression ratio, while increasing the thickness of angles or the sliding force of dampers can effectively improve the seismic performance of the steel joints in SABs.

Influence of joint forms on the seismic behavior of concrete-filled PVC-CFRP tubular column-RC beam joints connected with core steel tubes

To examine the effects of joint forms on the failure mode, hysteretic behavior, ductility and energy dissipation capacity of concrete-filled PVC-CFRP tubular column-RC beam connected with core steel tubes (“RC beam” for short), low-cycle reversed loading tests on 13 cross-joints and 11 T-joints were designed and conducted. The findings demonstrate that the core regions of both joint types experience normal shear failure. Less flexural cracking is present in the RC beams of T-joints, but the concrete crush failure is severer in the joint core area and mostly occurs on the ends of the cantilever beams. The seismic behaviors of both joint forms alter in the same pattern with an increase in the radius-thickness ratio of the core steel tube, the joint area stirrup ratio and the steel ratio. With a rise in the axial compression ratio, the ductility of the cross joints improves but the energy dissipation capacity shows no evident change, while both decrease for the T-joints. The cross joints show better energy dissipation capacity in the whole test. As the reinforcement ratio of the beam longitudinal reinforcement rises, the cross joints show a decrease in ductility and energy dissipation capacity, while T-joints have the exact opposite effect. The seismic behavior of core steel tube joints throughout the whole test is unaffected by CFRP strip spacing.

Effects of boundary conditions on RC beams subjected to accidental thermal load in nuclear power plants

Reinforced concrete (RC) beams in nuclear safety related structures should be designed for accidental thermal gradient combined with mechanical loads. Design capacity and structural behavior of those beams are affected by constraint boundary conditions at beam ends. In design approaches widely used in nuclear power plants (NPPs), it is commonly assumed that the thermal curvature of a RC member is fully constrained while axial constraint condition is often not specified. In this paper, RC beams with various constraint boundary conditions that are subjected to accidental thermal gradient combined with mechanical loads are studied using both experimental tests and nonlinear finite element (NLFE) models. Both rotational and axial stiffness ratios at boundary and their effects on thermal moments and ultimate flexural capacity of RC beam are evaluated. Results shows that the assumption of a fully constrained rotational boundary condition is practically accurate for most RC beams in NPPs subjected to thermal gradient. On the other hand, results also show that axial constraint boundary condition has considerable influence on both thermal moment and usable design flexural strength thus neglecting its effect may lead to insufficient design of RC beam. In addition, this study established relationship between axial constrain stiffness ratio and thermal moment, as well as relationship between axial constrain stiffness ratio and usable design flexural strength for different accidental temperature gradients and reinforcement ratios. That information can be used for correction of thermal moment and usable design flexural strength in design practice.

Nonreciprocal propagation of bending waves in spatiotemporally modulated prestressed beam

Breaking time or/and spatial symmetry can lead to unprecedent mechanical responses of a structure, the design of which is usually very intricate. This paper proposes a simple design of a beam structure with spatiotemporal modulation. In fact, a time-varying axial load applied to the ends of an elastic beam will induce space-time dependent axial force propagating in the form of longitudinal wave in the beam, which can modulate spatiotemporally the propagation of transverse bending waves. The governing equation is derived, of which the Floquet solution leads to a quadratic eigenvalue problem that can be solved for the frequency as a function of the wavenumber. Theoretical results show the existence of asymmetric wavenumber bandgaps and the unique dispersion diagram which is not periodic with respect to time or space. The breaking of temporal symmetry enables nonreciprocal propagation of transverse bending waves, which is confirmed by the finite element simulations. This modulation method offers promise for applications in the fields of elastic wave filter, frequency converter and magnitude amplifier.

Seismic Performance at Beam Ends of Unbonded Prestressed Precast Concrete Frames

Numerical modelling was conducted to investigate the seismic performance at beam ends of unbonded prestressed precast concrete frames. The established finite element model was verified by the test results. Through numerical simulation, the influence of such factors as the presence or absence of energy-dissipating reinforcement, the length of the unbonded section of energy-dissipating bars, the amount of prestressed or non-prestressed reinforcement on the seismic performance at beam ends of unbonded prestressed precast concrete frames were further analyzed. The results show that all prestressed precast beam-end models have similar initial stiffness. The bearing capacity and energy-dissipating performance of beam-end models without energy-dissipating bars are the lowest. The length of the unbonded section of energy-dissipating bars has no significant effect on the bearing capacity and energy-dissipating capacity of beam-end models, though the yield displacement increases obviously with the increase of the length of the unbonded section, as the local stress of energy-dissipating bars is reduced by setting the unbonded section. The bearing capacity of beam-end models can be improved by increasing the amount of prestressed or non-prestressed reinforcement. In the case of the same amount of prestressed reinforcement, increasing the amount of energy-dissipating bars can significantly improve the energy-dissipating capacity.

Multilayered Inhomogeneous Beams under Torsion and Bending: An Analytical Study of Energy Dissipation

The present theoretical paper is devoted to the problem of energy dissipation in multilayered inhomogeneous beam structures of visoelastic behaviour. In particular, our attention is concentrated on studying the energy dissipation for the case of a beam that is loaded simultaneously in torsion and bending. Both torsion and bending moments which are applied on the beam change with time so that the angles of twist and rotation of the beam end vary continuously with time. The viscoelastic mechanical behaviour of the beam under torsion is treated by a viscoelastic model that has two linear springs and a linear dashpot. The model is under time-dependent shear stress. The viscoelastic behaviour of the beam under bending is modelled in a similar way. An analytical approach of deriving the energy dissipation is applied. The approach treats a multilayered beam that has an arbitrary number of layers of different thicknesses and material properties. The layers are longitudinally inhomogeneous. An investigation of the energy dissipation is carried-out to clarify the effect of the parameters of the time-dependent bending and torsion moments, the material inhomogeneity and the beam size on the energy dissipation.

Research on time-varying degradation of RC buildings coupled environmental effects and corrosion-induced damage from multi-scale

Corrosion of steel reinforcement in reinforced concrete (RC) buildings is influenced by several factors, including oxygen content, chloride ion diffusion, concrete damage, and humidity. A numerical method is presented to evaluate the long-term structural performance of RC buildings under environmental conditions, which takes into account the impact of steel corrosion-induced damage from multi-scale. The macro-index used for calculation is the level of reinforcement corrosion-induced damage, which considers the inter-connected effects of oxygen content, chloride ion, moisture transport, mechanical stresses, and corrosion uncertainties. In the case of RC beams, corrosion tends to occur more severely on the outer edge near concrete surface. When the corrosion factor is taken as 1.0, the calculated compression side corrosion rate of RC beam agrees well with experimental results. Due to the influence of multiple factors, the corrosion of tension-side reinforcement exhibits some degree of variability. Furthermore, the corrosion of tension-side longitudinal reinforcement in RC beams gradually intensifies from beam ends towards mid-span, with corrosion at mid-span being particularly significant. The relationship between corrosion rate and corrosion time obtained from tests falls within the range of calculation results, and the calculated results from micro-scale align favorably with tests conducted to measure crack width.

Indeterminate Continuously Inhomogeneous Beam under End Rotation: A Longitudinal Fracture Study

The present paper describes a theoretical analysis of the effect of the end rotation of a statically indeterminate beam structure on the behaviour of a longitudinal crack. The beam is made of a material that is continuously inhomogeneous along the beam thickness. Besides, the material has non-linear elastic behaviour. The left end of the beam is supported with an axial double rod, while the right end is rigidly fixed. There is no external mechanical loading on the beam. Thus, the only influence on the beam is the rotation of the beam left end. Equations for determination the curvatures and the coordinates of the neutral axes are worked out and solved together with equations for resolving the static indeterminacy. The response of the longitudinal crack to the rotation of the beam left end is studied by deriving the strain energy release rate. For this purpose the balance of the energy in the beam is analyzed. The strain energy release rate is verified by applying the integral, J. A parametric analysis is performed to evaluate the influence of the beam end rotation and other factors on the longitudinal fracture.

Effect of infill walls on progressive collapse behavior of self-centering precast concrete frame

To study the effect of infill walls on the progressive collapse resisting-performance of self-centering precast concrete (PC) frame structures, three 1/2 scaled, two-span and two-story self-centering PC frame specimens with and without infill walls were tested under quasi-static pushdown loading regime. The test results showed that the failure modes of self-centering PC frames were governed by concrete cracking and local spalling at the beam ends under progressive collapse scenario. Compared with self-centering bare frame, the presence of infill walls provided additional load path, thereby reducing the concrete damage at the beam ends to some extent. The full infill walls with lower strength could still increase the initial stiffness and peak resistance of self-centering bare frame to 2.47 times and 1.33 times, while the infill walls with 20% opening ratio could increase to 2.21 times and 1.19 times, respectively. Nevertheless, the infill walls also reduced the self-centering capacity of the structures. Numerical analyses further indicated that the magnitude of prestress force of steel strands between beams and columns, the strength of bed joints as well as the width of infill walls had a great effect on the progressive collapse of self-centering infilled frames. Finally, based on numerical results, a reduction factor formula was proposed to quickly estimate the structural resistance of self-centering infilled frames with different opening ratios.

Seismic Behavior of Demountable Reinforced Concrete (RC) Beam-to-Column Joints with Damage-Control Fuses

In this paper, a new type of assembled RC beam–column joint with a beam-end steel cover-plate connection is proposed to achieve seismic toughness and damage control of the joint. Energy-dissipation plates with different structural forms are proposed, and a series of seismic performance indexes of the joints are calculated and analyzed by using the finite element method. The energy-dissipation plate with an arc notch can reach the yield condition faster, and the ultimate bearing capacity of the joint reaches the maximum. The bending design of energy-dissipation plates is carried out by calculating the demand bending moment, and energy-dissipation plates of different structural forms are simulated and verified. The results show that the proposed design formula can ensure that the bending moment at the beam end still maintains elastic deformation when the energy-dissipation plate yields. The important parameters affecting the bending moment of the weakened part in the middle of the energy-dissipation plate are analyzed. Finally, this paper also analyzes the important parameters affecting the seismic performance of the joints. The results show that the seismic performance of the newly assembled RC beam–column joints proposed in this paper is better than that of cast-in-place joints. Increasing the longitudinal reinforcement ratio appropriately can greatly improve the ultimate bearing capacity and ductility of the joints. Increasing the thickness of the energy-dissipation plate, increasing the strength of the energy-dissipation plate, increasing the axial compression ratio of the column, increasing the strength of the concrete, and increasing the strength of the shear web can improve the ultimate bearing capacity of the joints but also reduce their ductility. Under different axial compression ratios, the strain in the core area of the joints is low, and the compressive damage of the concrete is zero, which verifies the effectiveness of the damage-control design of the proposed model.

Analysis of the mechanical behavior of bolted joints with slotted-in steel plate considering the move path of rotation center for single-layer timber reticulated shell

The mechanical behavior of the bolted joints with slotted-in steel plate plays an important role in maintaining the stability of single-layer timber reticulated shell, yet methods to estimate the mechanical behavior of the bolted joints still remains to be improved. Assuming that the ductile failure of the bolted joints and the compressive failure of the glulam beam end occurred, the move path of the rotation center was obtained through theoretical derivation and used to determine the ultimate moment and rotational stiffness of the bolted joints. The equations for calculating the ultimate moment of the bolted joints were derived based on the European Yield Modes, t. Moreover, employing the beam on elastic foundation theory, a simplified equation of slipping stiffness was obtained and used to calculate the rotational stiffness. Experimental investigations on bolted joints for single-layer timber reticulated shell were conducted to verify the accuracy of the proposed theoretical methods. The results showed the rotational stiffness and ultimate moment obtained from theoretical calculation were consistent with the results of experimental tests. Furthermore, by calculating the move path of the rotation center, it was found that the rotation center started from the geometrical center of bolts at earlier loading stage and moved towards the compressive region of the glulam beam end with the increase of the external force. And the moment-rotation curves predicted by the linear model was in good agreement with the moment-rotation curves obtained from experimental tests, showing a convenient and reliable way to the design of bolted joints for single-layer timber reticulated shell.

Test on seismic behaviors of stainless steel bolted extended end-plate beam-column joints

This study conducted tests on the seismic behavior of austenitic stainless steel bolted extended end-plate beam-column joints, which have been few reported. Considering the influence of material type, end-plate thickness, bolt diameter, panel zone thickness, and loading scheme, 11 stainless steel joints and two carbon steel joints were designed and tested. Material properties, joint failure modes, moment-rotation curves, bolt load distributions, and joint component yield sequences were reported in detail. Experimental research showed that the beam-column joints in austenitic stainless steel experienced four failure modes, i.e. plastic hinge at the beam end, fracture failure of weld between the beam flange and end-plate, bolt rupture failure, and composite failure. All the tested joints had good seismic behavior, with rotation capacity greater than 0.03 rad. The influence of joint configurations on the seismic behavior were analyzed. The results indicated that the end-plate thickness, end-plate stiffener, and bolt diameter had a substantial impact on the joint seismic behavior, while the thickness of column web in panel zone, material properties, and loading scheme had a comparatively small effect. The initial rotational stiffness and moment resistance(yield moment) of joint obtained from the experiment were compared with the predictions of the EN1993-1-8, Design Guide 16, and JGJ 82-2011. Comparisons indicated that the EN1993-1-8 overestimated the initial rotational stiffness; Both the EN1993-1-8 and JGJ 82-2011 underestimated the moment resistance, while the predictions from the Design Guide 16 were significantly higher than the moment resistance and closer to the ultimate moment.

An Experimental Study on Flexural-Shear Behavior of Composite Beams in Precast Frame Structures with Post-Cast Epoxy Resin Concrete

Epoxy resin concrete has superior mechanical properties compared to ordinary concrete, and will play an increasingly important role in urban construction. In this paper, the application effect and prospect of epoxy resin concrete in precast composite frame structures are discussed. Taking the joint surface of the old and new concrete at the end of the composite beam as the research object, three specimens were devised and fabricated. Subsequently, a horizontal cyclic load test was conducted, and the seismic performance indices were analyzed. Multiple finite element models were established to assess the influence of precast concrete strength, the diameter of the longitudinal bar of the beam, the shear span ratio, and the epoxy resin concrete post-cast area, among other factors, on the seismic performance of the beam end. Four findings indicate the following: Firstly, epoxy resin concrete, characterized by its high performance attributes, can be used as a post-cast material in precast concrete structures. Secondly, when the strength of the post-cast epoxy concrete approximates or slightly exceeds that of the precast concrete, and the ratio of longitudinal reinforcement and shear span ratio are appropriately balanced, the operational performance of the composite beam frame structure is enhanced. In addition, when post-cast epoxy resin concrete is employed in the beam-column joint area, the mechanical performance of the composite beam end in the joint area matches or even surpasses that of the structure that was cast in situ. And subsequently, the expansion of post-cast area resulted in better mechanical performance. Finally, when the area of post-cast epoxy resin concrete is a non-node area, the mechanical properties of the composite beam end are worse than the former. However, the amount of epoxy resin concrete used will be greatly reduced, and as the precast node area expands, the bearing capacity of the beam end will increase and gradually approach the cast-in situ structure, indicating that this construction scheme also has advantages.

Experimental and numerical study on seismic performance of steel semi-rigid joints equipped with SMA bars and friction dampers

To reflect and inherit the characteristics of ancient Chinese architecture and regional culture, the Chinese antique building (CAB) imitating ancient Chinese timber building has been constructed using contemporary steel materials. These buildings mostly deploy steel rectangular-shaped beams and circular cross-sectional columns, which normally exhibit typical premature yielding fractures at the beam ends under seismic actions, as well as weak energy dissipation capacity and significant residual deformation. A steel semi-rigid joint equipped with SMA bars and friction dampers was proposed to improve the seismic performance and recoverability of CABs. The proposed joint aims to achieve the purpose of "self-centering during minor to moderate earthquakes" and "high energy-dissipating capacity under severe earthquakes" for CABs. Compared to simple semi-rigid joints, the energy dissipation of joints with friction dampers improved, while the joints equipped with the shape memory alloy (SMA) bar-friction damper coupling devices exhibited significant increases in yield displacement, strength, and overall stiffness, along with remarkable reduction in residual deformation. Based on the test observations, a numerical model was constructed to parametrically optimize the structural design of the damage-controllable steel semi-rigid joints equipped with SMA bars and friction dampers. The research results shall provide a theoretical basis for the proposed joint in engineering applications of steel antique buildings.

Failure mechanism and dynamic response of reinforced concrete joints under impact load acting on beam ends

Beam-column joints are crucial to guarantee the integrity and ductility of reinforced concrete (RC) frame structures. Considering the strain rate effect, the failure mechanism of RC beam-column joints under impact load acting on the beam near the core area of joints was numerically investigated. Based on the verified numerical model, the differences between failure modes of joints under static and dynamic loads were compared. The deformation and damage of joints were analyzed. In addition, the effects of impact location and impact velocity were discussed. The results show that the joints that meet the shear demand under static load have shear failure under impact load. The impact load causes greater deformation and damage to the joints. The transfer of the shear force and the development of the bending moment is different as the impact location changes, resulting in various dynamic responses. As the impact location approaches the core area, the joint evolves from bending failure to shear failure. The maximum shear force only appears at the impact location when the distance between the impact location and the core area is more than 3.5 times the width of the core area (b). However, the rotation of the joint causes the yield of the stirrup in the core area. It is worth noting that when the distance is less than or equal to 2b, the maximum shear force is transmitted to the core area. With the decrease of the distance, the time history curves of impact force have multiple peaks with increased peak values while the displacement and duration decrease. The damage range of the joint is expanded when impacted with higher velocities. Meanwhile, the magnitude and duration of impact force, as well as displacement are increased. With the decrease of distance or impact velocity, more energy is consumed by concrete rather than rebars due to the smaller rotational deformation of the joint.