Rotation Capacity Research Articles

Enhancing progressive collapse resistance of steel structures using a new bolt sleeve device

In the present study, frame robustness is enhanced by improving the contribution of the bolts to the rotational capacity of connections; the higher the bolts' elongation, the higher the rotational capacity that can be achieved. The proposed method comprises a hollow steel sleeve, with a predetermined wall curvature, that is inserted between the washer and the end plate interrupting the load path in the connection thus enabling a more ductile response. In order to demonstrate the efficacy of the proposed method, end plate connections with varying sleeve parameters are numerically examined using verified FE models. The proposed system significantly increases the ductility and strength of the connection by up to 2.6 and 2.5 times that of the standard connection, respectively. Additionally, different ductile responses can be achieved based on the sleeve parameters without changing the configuration of the connection.

Structural behaviour of improved WUF-B joints with longitudinally profiled plates

In this paper, an improved type of beam-to-column joint was proposed to enhance the material efficiency and structural behaviour of typical welded unstiffened flange-bolted web (WUF–B) joints, where the thickness of the flange on the beam was varied using longitudinally profiled (LP) plates. LP plates are plates manufactured to various thickness along the rolling direction to optimise their design under different loading distributions. Three full-scale beam-to-column WUF-B joints with LP plates were designed and tested under cyclic load. Different thickness change ratios and lengths of the variable thickness were considered in the specimen design. The obtained moment-rotation curves and the failure modes of the specimens were reported. Compared with a conventional WUF-B joint, it was found that the moment capacity of the joints can be significantly improved as a consequence of higher material efficiency. As WUF-B joints tend to fail from brittle weld metal fractures, micromechanical fracture model of cyclic void growth model (CVGM) was incorporated in the numerical models developed herein to predict the joint failure. A subsequent parametric study was carried out, considering a range of LP flange lengths and thickness change ratios as an extension of the tests. It was found that designing the improved WUF-B joints with a short LP flange length and a high thickness change ratio can enhance the plastic rotation capacities and avoid brittle failure.

Rotation Capacity of I-Shaped Beam Failed by Local Buckling in Buckling-Restrained Braced Frames with Rigid Beam-Column Connections

A buckling-restrained braced frame (BRBF) reduces the response of buildings during a strong earthquake, during which the surrounding members such as beams and columns must resist the axial force imposed by the buckling-restrained braces (BRBs). However, the steel beams and columns are subjected to reversed axial force from the horizontal and vertical component of BRB axial force. The steel beams might then buckle under the compressive force or even yield under the subsequent tensile axial force because the beams are not designed primarily to sustain the axial force. Therefore, the rotation capacity becomes inconsistent with the typical loading protocols. Faced with this concern, this study examines a BRBF design with reasonable balance between the steel frame and the BRBs. Pushover analyses and nonlinear response history analyses (NRHAs) are undertaken to quantify the magnitude of the beam axial force. Furthermore, a detailed finite-element analysis (FEA) model is constructed based on results obtained from a previous experiment. The strain distribution and axial force transfer mechanism are identified using an experimentally validated FEA model. Results confirm that BRB axial force is transmitted primarily to the single side of the flange. Furthermore, the parametric study in terms of the beam section, BRB axial force, and loading protocols establishes a database of the structural performance. The results of this research are used to formulate a novel index and equations describing the ultimate strength ratio, rotation capacity, and energy dissipation capacity.

INNOVATIVE NUMERICAL APPROACHES FOR STRAIN LIMITED DESIGN OF COMPOSITE BEAMS

AbstractFor composite cross‐section in steel and concrete plastic bending resistance is often used. However, also for cross‐section of class 1 and 2 rotation capacity may be reduced, then strain‐limited or elastic resistance becomes important. The strain‐limited resistance refers to the design of concrete sections according to EN 1992‐1‐1, considering the material nonlinearity. For the numerical approaches, the conventional “finite fibre method” demands high programming and calculation efforts due to the vast amount of fibres to be computed. In this article, three alternative numerical approaches: the finite cell method, the integral strain method and the direct analytical method are introduced. These approaches reduce the number of elements compared to the fibre method. They take different levels of simplification, varies in application ranges, accuracy and calculation speed. For conventional composite beam and slim‐floor beam cross‐sections, an efficient alternative to the fibre method is presented by the alternates.

Finite Element Analysis of a Semi-Rigid Endplate Beam-to-Column Joint with Stiffeners

This article examines the mechanical behavior of steel endplate beam-to-column joints with different stiffeners under bending moment. This type of connection is commonly used in steel frameworks to transmit loads from beams to columns. In frame design procedures, engineers tend to consider beam-to-column joints either ideally pinned or fully rigid. The present study aims to show their semi-rigid behavior by analyzing the characteristics of the relation between the bending moment and the rotation of the studied connection. The analysis is based on the development of a finite element model considering the material, geometrical and contact nonlinearities between the components. Three types of stiffeners are introduced in different positions to investigate their effect on the global behavior of the joints. The moment rotation curve is defined together with the procedure of determination of the initial rotational stiffness, the elastic and plastic moments of the connection. The numerical model is validated by comparing the moment rotation curves with those of similar studies available in the literature and also with the design approach proposed by Eurocode 3. The obtained results have showed that the use of stiffeners in the column web or on the endplate increases significantly the rigidity of the studied connection. The failure modes have been discussed in detail for each configuration with respect to the rotation capacity and the initial stiffness. Finally, the model has been used to show the influence of three bolts classes on the ultimate load of the joints and the deformation of the endplate and bolts at failure.

Experiments and a tension-bending catenary model for the progressive collapse resistance of concrete beam-column structures

Catenary action (CA) is an extremely vital resistance mechanism for the progressive collapse of concrete beam-column structures. However, the systematically theoretical researches on CA are rather scarce due to the complexity of structural forces in the large deformation stage. To address this dilemma, an evaluation method for distinguishing the types of structural anti-progressive collapse performance was put forward and applied in 75 existing beam-column structures, by which the conditions of potential CA were revealed. Based on our experiments and collected databases, an innovative Tension-Bending Catenary (TBC) model was proposed, which considers the eccentric tension of the beam, the deformation compatibility conditions of the overall structure, and the plastic rotation capacity of the beam. The CA peak capacity, displacement, and horizontal resultant force can be predicted by the proposed model, whose accuracy and feasibility were verified via 16 specimens. Moreover, the main influencing factors on the CA capacity were revealed via a series of parametric analyses, including the beam depth-span ratio (h/ln), the properties of beam top longitudinal reinforcements (area As, ultimate strength fu, and ultimate tensile strain εsu), and the relative axial stiffness (ra). Parametric analysis results indicate that the CA capacities positively correlate with the beam top longitudinal reinforcements (As, fu, and εsu). Nevertheless, the CAcapacity markedly declines for a relative axial stiffness of end supports of less than 1.0. The CA capacity first displays an ascendant trend and then decreases with the beam depth-span ratio. Meanwhile, the bearing capacity of CA is superior to that of compressive arch action (CAA) until a critical depth-span ratio. Furthermore, the ultimate strain of the longitudinal reinforcements εsu is recommended to be as large as possible and not less than about 0.1 because a minor εsu causes the CA capacity to drop significantly. Especially, εsu should exceed 0.05 to make CA greater than CAA. Finally, practical anti-progressive collapse strategies were summarized and proposed.

Experimental tests on composite beam-column joint with WUF-B connection subjected to impact loads

This paper presents a test programme on composite welded unreinforced flange-bolted web (WUF-B) joints subjected to impact loads from a drop-weight test machine. A total of four beam-column joints were designed and tested to investigate the governing parameters including the impact velocity, joint type and slab thickness of composite decking. Structural responses such as impact force, axial force and bending moment developed at the joints were presented. Typical failure modes for the middle and side joints were shown and discussed. Besides, development of strains at different locations of the joints, as well as strain rate effect on material strength was investigated. A comparison of design predictions and measured values of tying resistance, flexural resistance and rotation capacities was conducted. In addition, a comparison with the similar specimens but subjected to quasi-static tests was conducted. It was found that the strain rate effect could enhance flexural resistance and tying resistance but reduce the ultimate rotation capacity. Composite slab effect would enhance flexural resistance but reduce tying resistance.

Numerical investigation on failure modes of bell-spigot jointed ductile iron pipelines subjected to dip-slip faults with different dip angles

Effective identification of failure modes for buried pipes subjected to earthquake-induced fault movements is crucial in the design and assessment of underground water supply networks. For bell-spigot jointed ductile iron (DI) pipes, the relationship between pipe failure mode and dip angle is still unclear. In this study, a three-dimensional finite element model of buried DI pipelines crossing dip-slip faults perpendicularly is established, based on which the joint kinematics and mechanical responses of DI pipes subjected to dip-slip faults with a dip angle between 50° and 130° are systematically evaluated. Four failure modes controlling the joint sealing performance and structural integrity of DI pipes are identified, i.e., joint pull-out failure, joint rotation failure, joint compressive failure, and excessive local buckling in the pipe segment. The results reveal that joint self-locking induced by the action of horizontal compression can reduce the joint rotational capacity greatly, rendering a segmented pipeline to behave like a continuous pipeline. Upon the occurrence of joint self-locking, the pipe mode changes from kinematic-controlled failure (joint pull-out or rotation failure) to mechanical-controlled failure (joint compressive failure or excessive local buckling). Finally, the relationship between failure mode and allowable dip angle is derived for use in design.

Plastic hinge length and inelastic rotational capacity of reinforced concrete shear walls detailed with Self-Centering reinforcement

The application of damage-resisting reinforced concrete (RC) shear walls is a novel topic in structural engineering. In recent years, more studies have been performed on the response of damage-resisting RC shear walls. These studies were mainly conducted on one-story specimens with limited ranges of dimension, reinforcement ratio, and axial load ratio. Furthermore, the studies were mostly aimed at the performance parameters of damage-resisting walls and overlooked the seismic design parameters, such as the plastic hinge length and inelastic rotational capacity, of the walls.This paper presents a parametric finite element analysis study on the plastic hinge length and inelastic rotational capacity of three types of damage-resisting RC shear walls with improved self-centering properties under cylic lateral loads. The studied walls were reinforced with conventional steel bars and a type of self-centering reinforcement consisting of shape memory alloy (SMA) bars, glass fiber reinforced polymer (GFRP) bars, and post-tensioned high-strength steel strands. The study showed that the plastic hinge length was comparable in partially post-tensioned walls and conventional steel-reinforced RC walls, while the plastic hinge was longer in steel-GFRP reinforced walls and shorter in steel-SMA reinforced walls with respect to conventional steel-reinforced RC walls. It was also shown that the inelastic rotational capacity was comparable in partially post-tensioned and conventional RC walls, while the inelastic rotational capacity was larger in steel-GFRP reinforced walls and slightly smaller in steel-SMA reinforced walls with respect to conventional steel-reinforced RC shear walls.This paper also offeres a method to adapt the plastic hinge length and inelastic rotational capacity formulas of CSA and ACI standards for the seismic design of the studied steel-GFRP reinforced, steel-SMA reinforced, and partially post-tensioned RC shear walls.

Experimental study on flexural capacity and fire resistance of high strength Q690 steel flush end-plate connections

High-strength steel is widely used in building structures, but fire-induced damage and collapse of high-strength steel structures cause huge economic losses. As a primary part of the structure, the reliability of beam–column joints is essential for the structure’s fire safety. This paper presents an experimental study on high-strength Q690 steel flush end-plate connections (Q690-FEC) at ambient and elevated temperatures. Ultimate bending capacity tests were conducted at ambient temperature to investigate its structural performance, where initial rotational stiffness, bending capacity, and ultimate rotation were obtained. Numerical models were developed to reproduce the tests, and parametric analyses were performed to investigate the influence of load ratio, end-plate thickness, and bolt diameter. Transient fire-resistance tests were performed on specimens with different end-plate thicknesses, where specimen temperature, furnace temperature, and joint rotation were measured. The test results indicate that increasing end-plate thickness has little influence on the critical temperature and fire resistance. Finally, a rotation-temperature relationship model was proposed to predict the fire behavior of Q690-FEC and validated against the experimental data.

Experimental and numerical investigations into seismic behavior of corroded steel frame beams and columns in offshore atmospheric environment

With the strong promoting of “national carbon peak and carbon neutrality” strategy and the continuous deepening of “performance-based seismic design” concept, the seismic performance evaluation field of Chinese steel structures has developed rapidly. Nevertheless, previous studies are generally aimed at new building structures, ignoring the seismic performance degradation characteristics caused by the durability loss of existing structures under environmental erosion. Thus, in this paper, accelerated offshore atmospheric corrosion and quasi-static cyclic loading tests were carried out on five steel frame beams and four steel frame columns. The effects of corrosion level on the failure mechanism, hysteretic behavior, skeleton curve, bearing capacity, ductility, stiffness degradation and energy dissipation of steel frame members were revealed and analyzed in detail. The test results indicate that with an increase in corrosion level, the appearance of plate local buckling, steel cracking and final failure shows a forward tendency, and all seismic performance indexes significantly decrease. Moreover, the deterioration models of the maximum load, ultimate displacement and cumulative energy dissipation with weight loss rate for corroded steel frame beams and columns were proposed. In addition, a finite element analysis method for corroded steel frame members was established and validated, which considered the corrosion damage and introduced a nonlinear mixed hardening constitutive model and a stress triaxiality dependent ductile damage criterion. On this basis, the parametric analysis was further presented to systematically study the influence of corrosion level, plate width - thickness ratio and its assembly factors, and stress conditions on the mechanical performance of H-shaped steel members, then obtaining the regular expressions of bending capacity and plastic rotation capacity.

Rotational capacity of exposed base plate connections with various configurations of anchor rod sleeves

This paper presents a new approach that can enhance the rotational capacity of exposed base plate connections without degrading the initial stiffness or strength of the standard configuration. By inserting a steel sleeve with a designated geometry between the base plate and the anchor rod washer, the load path between the end plate and the rod can be interrupted, promoting a more ductile response. Exposed base plate connections with various sleeve geometries are numerically investigated using a validated FE model to demonstrate the concept of the proposed method. It was concluded that the proposed sleeve system substantially enhances the rotational capacity of the exposed column bases. An elastic response consistent with standard base plate connections is maintained indicating that the proposed system is compatible with existing codified elastic design approaches without modification.

Cyclic Behavior of Gabled Frames with Web-Tapered Columns and Rafters

Cyclic loading tests were conducted on three 1/2-scale, half-bay steel gabled frames (SGFs) to investigate their seismic performance. The three specimens with reduced joint stiffness were designed based on the prototype drawing shown in China design guideline 02SG518-1: specimen SV1 with a reduced thickness of the joint end-plate and bolt diameter, specimen SV2 with a reduced number of bolts, and specimen SV3 with a reduced bolt diameter. The load capacity, rotational stiffness, rotational capacity, and ultimate failure mode of specimens SV1, SV2, and SV3 were investigated. The experimental results showed that specimen SV1 failed due to the local buckling of the lower flange of the rafter, and specimens SV2 and SV3 due to the local buckling of upper flange of the rafter. The joint zone of all specimens kept well, indicating that the prototype joint had a large margin of safety. The hysteresis curves of all specimens were not full, and the ductility and energy dissipation capacity were limited. The end-plate thickness, bolt diameter, and steel grade affected the hysteresis performance of the SGF little. A refined finite element model was established, and the predicted results compared well with the test results. The test and analysis results demonstrated that there was slight utilization and distribution of post-buckling strength.

Influence of beam/gusset plate thicknesses on the moment–rotation capacity of cold-formed steel screwed back-to-back sections

Influence of beam/gusset plate thicknesses on the moment–rotation capacity of cold-formed steel screwed back-to-back sections

Seismic performance of timber through-tenon joints with shrinkage flaw in tenon

In several Chinese historic timber buildings, widening flaws in tenon of joints are usually a consequence of weathering and shrinkage. To investigate the impact of flaws on the seismic performance of through-tenon joints (TTJ), cyclic loading tests on four specimens were conducted. The hysteresis, skeleton, energy dissipation and stiffness experimental curves were so obtained. A finite element (FE) model to describe the behavior of such experimental specimens has been then established calibrating the mechanical properties by means of coupon tests. By comparing the numerical simulation results with the experimental results, it is concluded that this kind of damage has less impact on the mechanical performance of TTJs under negative load, while it has a greater impact under positive load. The impact was more noticeable as the length of large head of through tenon increased. The rotation capacity, stiffness and energy dissipation capacity of the damaged joints were significantly lower than the intact ones. The bearing capacity of TTJs with the damage decreased by about 32.4%–38.5%, the energy dissipation coefficient decreased by about 17%–38%, and the cumulative energy consumption decreased by 33.3%–60%.

Experimental study on the rotation capacity of bolted and welded beam-column connection using cold-formed steel sections

This paper investigates new bolted and welded beam-to-column connection types on the cold-formed steel sections (CFS) and their behaviors determined using full-scale experiments. This study aimed to analyze the influence of weld/bolt connections based on CFS profile and failure modes to provide the necessary data for improving Eurocode 3. In contrast, the rotation and ductility of a joint of the welded connection are lower than the bolted connection. Thus, the bolted connection exhibits a semi-rigid behavior‒also, the energy dissipation capacity values in the bolted connection are bigger than welded connection. Thus, the bolded connection has a semi-rigid behavior. Also, model failure is determined by the type of connection (bolted and welded). The rotation and ductility of a joint of the welded connection are lower than the bolted connection. Thus, the bolted connection exhibits a semi-rigid behavior‒also, the energy dissipation capacity values in the bolted connection are bigger than welded connection. Furthermore, the specimens of the welded connection have rigid behavior in the failure modes.

Response of steel frame filled by prefabricated RC infill walls with eccentric opening: Experimental study

A steel frame filled by prefabricated RC infill wall (SFRCW) is an effective lateral load-resisting system wherein RC infill walls are embedded inside. The presence of eccentric opening (EO) such as door or window usually significantly reduces the lateral stiffness and strength. In order to accurately evaluate the effect of the EO on the seismic performance of the SFRCW structure, the cyclic quasi-static tests on two, 1/3-scaled, two-story, single-span SFRCW-EO specimens were performed. Both specimens showed the shear-dominated failure mode, moderate ductile behavior, and pinching hysteretic feature. The concrete cracks were induced from the corners of the EO and were attributed to stress concentration phenomena. The initial lateral stiffness was approximately 50 kN/mm, overall ductility ranged from 2.48 to 2.95, and the overstrength factor reached 2.5. The interface slips and separations between RC infill wall and surrounding steel frame in SFRCW-EO specimens were considerably tiny that could be neglected. The flushed end-plate connection, which had the enough rotation capacity and tension-resisting capacity, was an effective partially-restrained (PR) connection used in the SFRCW-EO. The overall seismic behavior of SFRCW-EO was weaker compared to that of the steel frame with solid RC infill walls because it failed by serious concrete crush. In addition, the on-site assembly was more convenient for the SFRCW-EO specimen. Further, strengthening measures such as the use of an embedded beam were essential for ensuring the integrity of infill walls and improving their overall seismic behavior.

The numerical simulation of soil–structure interaction containing sustainable materials

As a result of urban transformation activities, natural disasters, regional and global wars, billions of tonnes of waste concrete occur. Therefore, the remediation process of waste concrete is one of the critical research topics of recent years. The sustainability concept provides a primary bridge between the demand for natural concrete material and the remediation process of waste concrete. Recycled aggregate and recycled concrete aggregate, which may be named sustainable materials, are obtained by the recycling process of waste concrete. Many experimental and numerical studies have been conducted in recent years to show that this sustainable material is an alternative product to natural aggregate. In this study, a comprehensive numerical simulation of foundation beams resting on soils incorporating conventional and sustainable materials has been performed. The foundation beams considered include some with conventional concrete properties and some with sustainable concrete properties. Additionally, the material conditions of soils are assessed, using six different mixed recycled aggregates as filling material. Based on the numerical simulation, the deflection, rotation, bending moment, shear force and spring force capacities of conventional and sustainable foundation beams resting on soils exhibited slightly different behaviour depending on the recycled concrete aggregate and mixed recycled aggregate ratios. Finally, comparing the numerical simulation results of soil–structural interaction members incorporating conventional and sustainable materials indicated that the soil–structure interaction modeling process applied to conventional foundation beams resting on soils is also valid for sustainable members.

Behaviour and design of high strength steel homogeneous and hybrid welded I-section beams

The behaviour and design of high strength steel (HSS) beams are addressed in the present study. Six in-plane three-point bending tests on three different welded I-sections − two homogeneous S690 steel welded I-sections and one hybrid welded I-section with S690 steel flanges and an S355 steel web, were first conducted. The beam tests were carried out in major axis bending and a bespoke restraint system was designed and employed in the test programme to prevent lateral-torsional buckling. Following the experimental investigation, a thorough finite element (FE) modelling programme was performed, which included a validation study confirming the accuracy of the developed FE models in replicating the flexural behaviour of HSS welded I-section beams, and a parametric study generating additional FE data on HSS welded I-section beams over a broader range of cross-sectional slendernesses, steel grades and loading configurations. The test results obtained in the present study and collected from the literature, together with the generated FE data from the parametric study, were used to evaluate the suitability of the current Eurocode 3 cross-section slenderness limits for HSS homogeneous and hybrid welded I-sections in bending. It is shown that the current Eurocode Class 2 and Class 3 slenderness limits are suitable for the classification of the outstand flange (in compression) and internal web (in bending) elements of both HSS homogeneous and hybrid welded I-sections subjected to major axis bending, while stricter Class 1 slenderness limits are considered necessary to achieve sufficient rotation capacity for plastic design. The findings from the present study indicate that plastic design can be used for HSS structures, provided the proposed stricter Class 1 slenderness limits are employed.

Experimental study on high-strength Q460 steel extended end-plate connections at elevated temperatures

This paper presents an experimental study on high-strength Q460 steel extended end-plate connections at ambient and elevated temperatures. Ambient temperature tests were conducted on connections with 8 and 12 mm end-plates to investigate the ambient temperature structural response, including the initial rotational stiffness, plastic flexural resistance and ultimate rotation. The results show that high-strength steel connection with 12 mm end-plates significantly improves mechanical properties compared to that with 8 mm end-plate with an increase of 22% at least while not influencing the failure modes. Then, the experimental results were compared with the theoretical predictions of Eurocode 3. There are reasonable agreements between these two methods on plastic resistance, while the calculation by Eurocode 3 on initial rotational stiffness exhibits much higher results. In addition, the temperature distribution of the connection specimens and furnace air, rotation-temperature characteristics, and failure modes of the connections in transient tests were obtained to study the influence of different end-plate thicknesses. The 12 mm end-plate effectively improves the connection's rotation capacity at elevated temperatures with an increase of 29% compared to 8 mm end-plate while influencing the critical temperature and fire endurance lightly. Besides, the fire performance results were compared and discussed between mild steel and high-strength steel connections. Finally, a rotation-temperature relationship model was proposed to predict the fire behavior of high-strength steel end-plate connections under transient conditions and validated against the experimental data with considerable accuracy.