Column Base Connections Research Articles

Seismic behavior of resilient concrete column-base connection with SMA bolts and RSPs

This paper presented a novel resilient concrete column-base connection with shaped memory alloy (SMA) bolts and rectangular slotted plates (RSPs) to achieve the demountable and recoverable capabilities in precast concrete columns. Quasi-static tests were conducted on one monolithic and three resilient concrete connections to investigate the effects of RSP number and yield strength on seismic behavior. Results showed that the resilient connection with both flange and web RSPs had superior lateral capacity, ultimate drift ratio, and energy dissipation compared to the monolithic connection. The resilient connection also exhibited minimal concrete damage and smaller residual deformation. However, low-yield-strength flange RSPs significantly reduced lateral capacity, initial stiffness, and energy dissipation, which should be considered in engineering design. Additionally, adjustment coefficients for rocking interface rotations were determined from digital image correlation (DIC) data using a fitting method. A formula was proposed to predict the flexural capacity of resilient specimens, assuming a plane section in the compression zone. The predictions closely matched the test data, with differences within 10 %, demonstrating the formula's effectiveness. The length, diameter, and material yield strength of the anti-shear steel bar (ASB) had a significant impact on the shear capacity of the interface.

Biaxial seismic response of base-column connections in sub-standard steel buildings: dataset.

Existing steel frames not complying with modern seismic codes are often vulnerable to earthquakes due to inadequate seismic detailing. These types of framed structures typically feature semi-rigid and partial strength column-base connections; the behaviour of such connections may significantly affect their seismic performance. However, current code provisions offer limited guidance for the assessment and retrofit of column-base connections To fill the knowledge gap, the H2020 EU-funded Earthquake Assessment of Base-Column Connections in Existing Steel Frames (HITBASE) project experimentally investigated, the response of exposed column-base plate connections. Bi-directional Pseudo-Dynamic tests were carried out at the Structures Laboratory (STRULAB) of the University of Patras within the framework of Engineering Research Infrastructures for European Synergies (ERIES). The case-study steel frame featured two types of column-base plate connections, i.e., stiffened and unstiffened, representing respectively the base connections of an external moment-resisting frame and an internal gravity frame. The experimental programme comprised free vibration tests to identify the modal properties of the sample steel frame. A set of quasi-static cyclic tests and Pseudo-Dynamic tests were then carried out to investigate the performance of the steel frame under bi-directional earthquake sequences. The response of each component constituting the column-base plate connections was monitored during the tests to fully capture the behaviour of the connections. Such experimental results allow model calibration and further parametric investigation on column base plate connections.

Rocking Steel Column Base Connections Equipped with a Viscoplastic Damper for Seismic Resilience: Design, Modeling, and Response Assessment

Rocking Steel Column Base Connections Equipped with a Viscoplastic Damper for Seismic Resilience: Design, Modeling, and Response Assessment

Investigating the effectiveness of concentric welded anchor rods in column base plate connections: A numerical and experimental study

This study presents a new strategy for column base plate connections, which involves the utilization of welded anchor rods positioned concentrically beneath the base plate, in alignment with the connected column. The objective was to remove the eccentricity between the anchor rods and the column, thereby excluding the base plate from the load-transferring chain. A numerical study was performed to compare the cyclic behavior and uplift response of the proposed connection with conventional column base connections. Additionally, different weld types were investigated to connect the anchor rods to the base plate, and their efficiency was evaluated based on a comprehensive dataset of nine tests on equivalent base-plate T-stub connections with different base-plate thicknesses, anchor-rod strengths, and anchor-rod diameters. The numerical results showed that using welded anchor rods could remove the pinching from the hysteresis loops, as the anchor rods can effectively resist cyclic loads in both compression and tension. Furthermore, removing the eccentricity between the anchor rods and the column enhanced the uplift stiffness by approximately 31 %. The experimental results indicated that the failure mode was the fracture of anchor rods for all specimens, while the other components remained elastic. The specimens with high-strength anchor rods showed a brittle failure accompanied by a sudden drop in load, which coincided with the fracture of anchor rod in the softened heat-affected zone. All developed weld types successfully withstood the ultimate tensile strength of anchor rods upon fracturing.

Performance Assessment of Base Plate Connections with Anchor Rod Sleeves

This research presents findings from a study focused on evaluating the performance of exposed base plate connections featuring anchor rods under cyclic loading conditions. The study introduces an innovative sleeve system approach designed to enhance the ductility of column base connections. The inclusion of a steel sleeve with defined geometric characteristics between the base plate and the anchor rod washer modifies the load path within the connection, resulting in a more ductile response. The study utilizes a validated finite element (FE) model to analyze exposed base plate connections featuring different sleeve shapes, illustrating the concept behind this novel method. The innovative approach discussed in this research has the potential to significantly increase the rotational capacity of connections without compromising their inherent strength.

Experimental and analytical investigations on reusable column base connection with pinned energy dissipators

This research paper introduces a novel, yet simple, column base connection that is reusable for moment resisting frames (MRFs). The performance of this connection was evaluated through a comprehensive experimental investigation. The proposed design incorporates a pinned energy dissipator (ED) that effectively absorbs seismic energy. Moreover, the connection utilises the weight of the column itself to provide a recentring force. Unlike existing self-centring column base connections, the ED in this innovative design is equipped with pins to prevent resistance to recentring caused by inelastic deformation after earthquakes. This unique feature ensures that the connection possesses self-centring capability, energy dissipation ability, and reusability. The analytical simplified models developed in this study effectively illustrate the monotonic and cyclic behaviours of the proposed connection. To validate the design concepts and simplified models, tests were conducted on specimens of the ED and the complete column base connection.

Experimental and FE analysis of the behavior of steel column base connections under tension and bending moment

Most design procedures represent the steel base connection by assuming either a perfectly hinged or a fully rigid connection. However, these kinds of connections are, in fact, semi-rigid or flexible and their actual behavior is complicated. Most of the previous studies investigated these base connections experimentally under moments and axial compression only, which is completely different in the case of axial tension and moment. Therefore, experimental and numerical investigations with variable base plate thicknesses and diameters and arrangements of the anchor bolts were carried out to verify the behavior of this kind of base connection under axial tension and moment. Full-scale steel columns with hinged base plate connections were tested under the effect of two simultaneous actions, axial tension force and bending moment. Moreover, Finite Element (FE) models were developed and verified against the experimental results to conduct a parametric study. The investigated parameters were the base plate thickness and anchor bolt diameter and arrangement. The base plate connections under the effect of axial tension with moment instead of axial compression caused reductions in the rotational stiffness up to 99%. In addition, using only two bolts in this type of connection concentrated stresses on the base plate that led to big deformations. The small base plate thickness deformed easily under the effect of tension force which induced big initial gaps between the steel base plate and the Base beam and subsequently decreased the moment resistance and rotational stiffness of the base plate connection. The big elongation of the anchor bolts with small diameters increased the gap between the steel plate and the Base beam.

Seismic Performance of Embedded Column Base Connections with Attached Reinforcement: Tests and Strength Models

Embedded column base (ECB) connections used in mid- to high-rise steel moment frames derive moment resistance through bearing of the embedded column and base plate against the concrete footing. Five large-scale tests on ECB connections are presented; these feature cantilever columns subjected to axial compression and cyclic lateral loading. The tests feature reinforcement details including (1) horizontal reinforcement bars attached to the column (either directly welded to the flanges or in the form of U-hairpins wrapped around the column); and (2) vertical reinforcement in the form of stirrups in the footing. These tests complement previous experiments that are nominally identical but without the additional reinforcement. The tests indicate that while the horizontal reinforcement enhances moment strength due to resisting forces in the horizontal direction, it also produces a tension field that decreases the restraint to the rotation of the embedded base plate, ultimately reducing overall moment strength. The addition of vertical reinforcement in the form of stirrups mitigates this issue to an extent. A strength model considering these effects is proposed and shown to predict strength with good accuracy across a range of configurations, encompassing the different configurations of horizontal and vertical reinforcement. Limitations of the approach are discussed.

Experimental investigation of the damage characteristics and seismic response of moment-resisting bolted column base joints for precast concrete frames

Although several studies have been carried out on the development of bolted dry joints for precast concrete structures, damage assessment and seismic performance of bolted dry joints for column base joints under the different axial compression ratios have been rarely studied. In this study, six half-scale reinforced concrete columns, half of them were bolted connected and others were monotonically connected to the foundation, are subjected to combined cyclic lateral load and static axial compression load. The tests were carried out under three axial compression ratios: 0.10, 0.20, and 0.30. The seismic performances, including failure modes, lateral load-displacement responses, displacement ductilities, energy dissipation capacities, stiffness degradation behaviors, and moment-curvature responses, were evaluated and compared. The influence of axial compression ratio and reinforcement details on the seismic performance, plastic hinge characteristics, and damage assessment of specimens was also investigated in detail. The experiment results show that the increase of axial compression ratio from 0.1 to 0.3 increased the lateral load capacity, secant stiffness, and plastic hinge length while reducing the ductility. The efficiency of current formulations to predict plastic hinge length for the determination of plastic hinge length of specimens was also compared. Proposed damage descriptions for different performance levels (or damage states) were summarized and observed damage states correlated with drift ratio demands. Some modifications to the Park and Ang damage index for each damage state were proposed and stiffness reduction factors for the damage states were comparatively investigated. In addition, the displacement-based seismic capacities of this novel RC column base connection are presented in detail.

The cyclic performance of column base plate connections using different types of stiffeners

Column base connections represent the support system of a structure, and they should be strong enough to sustain the transmitted demands between the columns and foundation. This study describes numerically the performance of strengthened column base plate connections under cyclic loading. Four types of stiffeners were considered in the analysis: bracket plates, angles, channels with vertical stiffeners, and built-up stiffeners. The efficiency of used stiffeners, the cyclic performance of the strengthened connections, and along with the failure modes were investigated. The numerical results showed that all the proposed strengthening methods have sufficient flexural strength and stiffness higher than the column. A pinched hysteretic response was observed for all strengthened connections under the applied cyclic loading. The built-up stiffener presented the maximum moment capacity and rotational stiffness among the other configurations. Using strengthened connections with more stiffeners made the anchor rods the fuse elements in the connection.

Seismic performance evaluation of a five-story column-and-beam glulam frame with steel-timber buckling restrained braces

This paper summarizes the results of numerical simulation and fragility analysis of a five-story column-and-beam glulam frame with chevron steel-timber buckling restrained braces (BRBs). Key parameters of the rotational behavior of the bolted beam-to-column connections and column base connections were modeled and calibrated using shaking table test results. Prediction methods of the stiffness and capacity of the steel-timber BRBs were proposed and validated with the test results. An FEM model of the glulam frame with steel-timber BRBs was developed to capture the frame seismic response and validated using shaking table test results. The FEM model which considered damping change and damage accumulation achieved good agreement with shaking table test results, with the modelling errors of displacement amplitude for most conditions less than 15 %. Fragility analysis of the frame was conducted based on the validated FEM model. The probability of exceeding the collapse prevention limit state under the VII-rare earthquake excitations was reduced to close to zero when steel-timber BRBs were used. This study demonstrates the potential for using glulam frames with steel-timber BRBs in Chinese VII seismic regions.

A novel damage evaluation method for exposed column bases (ECBs) affecting the seismic properties of low‐rise steel moment‐resisting frames (MRF)

AbstractExposed column base (ECB) connections are widely used in low‐ and mid‐rise steel moment‐resisting frames (MRFs). In this study, we investigated the impact of ECB damage on the overall seismic properties of low‐rise MRFs. A novel method was proposed to evaluate the post‐earthquake conditions of steel frame structures based on the coupling coefficient (CC). Using only the strain gauge data of the columns in the bottom storey, a method using a modified CC was adopted to classify the degree of damage by estimating the residual capacity of the MRF and predicting the future seismic response under specific intensity levels of hypothetical earthquakes, considering both the structural and non‐structural components. The limit values of CC were obtained by solving the deduced equations. Finite element analyses were conducted to validate the proposed method. The method was applied for calculating the test data of a four‐storey MRF tested at the E‐Defense shaking table facility. Four loading cases comprising six groups of monitored data in the X‐ and Y‐directions were used in this study. A comprehensive and systematic evaluation result was eventually obtained, and the accuracy of the method was validated.

Influence of Column Base Connections on the Cyclic Loading Performance of Double-Jointed Engineered Bamboo Columns

The cyclic loading performance of bamboo double-jointed components of different column base connection types was investigated through reversed cyclic loading tests and finite element analysis. Test results indicated that the types of column base connections played an important role in the failure modes of the engineered bamboo double-jointed columns: for an encased steel plate column base connection, the main failure mode was tensile fracture failure of the bamboo scrimber section at the bottom of the cladding plate; for a slotted-in steel plate column base connection, the main failure mode was splitting failure of the bamboo scrimber cross-grain at the bolt connection line at the bottom of the sheathing plate. The initial stiffness of the encased steel plate column base connection specimen was 41.8% higher than that of the slotted-in steel plate column base connection specimen, with the two specimens having similar average bearing capacities. The ductility ratio of the two specimens was below 3.0 due to the brittle failure nature of the engineered bamboo connections. The finite element model accurately predicted the ultimate bearing capacity of the double-jointed bamboo column members. The modeling error was within 12%, which was sufficient to satisfy the accuracy requirements for engineering purposes.

Directly Reusable Steel Column Base Connection ‐ Concept and Numerical investigation

AbstractConstruction industry as a whole should transform into designs that enable demountability and direct reuse of structural elements to achieve the circularity in construction. Currently, structural connections enabling direct reuse of components in construction are limited. Column base connections are one of the main load transfer units of a steel structure for the magnitude of the forces being transferred from the superstructure. This paper presents an interlocking type of column base connection that enables direct reuse of all associated structural components. The proposed interlocking connection transfers the force through the plate bearing and holding mechanisms and requires minimal number of bolts. In addition to the direct reuse and better load transfer approach, the new interlocking connection enhances and simplifies the mounting procedure that leads to increased productivity in construction. This article discusses the overall concept of the proposed interlocking connection, design philosophy and compares the failure modes with existing conventional bolted column base connections for various loading cases through finite element analyses. Main parameters investigated are the effects of bearing length of connector element and connector element thickness under uniaxial loading. A finite element model of the proposed interlocking connection is built through which the influential parameters are analysed.

Design and Numerical Simulation of a Reusable Steel Column Base Connection with Pinned Energy Dissipators

AbstractThis paper presents a reusable steel column base connection in moment resisting frame (MRF), which involves simple yet effective pinned steel plates to dissipate seismic energy and makes full use of the self‐weight of the column to provide re‐centring force. Permanent deformations of dissipative plates may induce non‐negligible lateral drifts of the column. By virtue of the pinned design, additional rotational degrees of freedom are added to mitigate the resistance to the restoring behaviour. Based on the proposed connection, the column can rock back to its original position after earthquake‐generated deformations while remaining within the elastic range. Moreover, the proposed connection can be conveniently installed and replaced to facilitate adaptability and reusability. The mechanical performances of the proposed column base connection under monotonic and cyclic loadings are described by simplified analytical models. A refined three‐dimensional finite element (FE) model is developed. The results of FE modelling help verify the feasibility of the simplified analytical models. Besides, the self‐centring capacity, energy dissipation capacity and low damage behaviour of the proposed connection are then evaluated by the FE models.

Fully demountable column base connections for reinforced CDW-based geopolymer concrete members

CDW-based concrete requires alkali-activators to generate geopolymerization process. These alkali-activators are difficult to be handled at the construction site and one of the rational ways to built reinforced geopolymer structures is the prefabricated construction. The connection of the precast structures is the most vulnerable component under the effect of seismic actions. Proper detailing and design of connections are crucial for sufficiently-ductile performance under seismic loading. Additionally, to achieve the disassembling and reusing of structural members, a demountable connection, i.e., dry connection, should be used instead of a wet connection. In this study, four novel fully-demountable connections for reinforced construction and demolition waste-based (CDW) geopolymer concrete members are developed. Seismic performances of these different demountable connections and one reference monolithic connections are experimentally investigated. The connections are subjected to reversed cyclic lateral displacements under constant axial loading. Comparisons are made referring to observed damage patterns, connection strengths, moment–curvature relations, initial stiffnesses, plastic hinge lengths, and energy dissipation characteristics of the proposed demountable connections and the monolithic connection. The results of the experimental study indicate that one proposed demountable connection exhibited larger lateral capacity and better seismic performance than its monolithic counterpart, whereas the other three proposals showed less performance than the monolithic counterpart.

Investigation of column-to-base connections of pole-mounted solar panel structures

This study investigated the load-carrying capacity of solar panel structures focusing on the column-to-base connection of pole-mounted structural systems using full-scale testing and numerical simulations considering the connection details as a key variable. The aim was to develop a non-welding connection detail for improved durability. For the connection details, a total of 10 plinths with base plates and supporting plate units were developed. The plinths with supporting plate units included two different bolt layouts at the column and base connections. The experimental results indicated that most specimens had sufficient load-carrying capacity to withstand the calculated yielding force even for the non-welding connections with supporting plate units. The failure modes observed in the experiments included cracking in the welded region, local buckling of the column, and bolt tear-out. The numerical simulations demonstrated that the details of the connection, such as the shape of the side plates, use of rib plates, and bolt layout, affected the structural performance. In addition, it was found that some specimens had strong and weak axes, depending on the orientation and shape of the side plates. Therefore, the details of the column–base connections of pole-mounted solar panel structures should be carefully designed based on proper structural evaluation of the connection details.

3D vision-based bolt loosening assessment using photogrammetry, deep neural networks, and 3D point-cloud processing

Structural bolts are essential structural elements. Detection of structural bolt loosening is of great importance to provide earlier warnings of structural damages and prevent catastrophic system-level collapse. Most existing studies about bolt loosening assessment were built in 2D computer vision, where the assessment may be restricted based on the camera views. In this paper, a novel 3D vision-based methodology is proposed for autonomous bolt loosening assessment. First, a 3D point cloud of bolted connection is created using readily available 2D images. Second, a new convolutional neural network (CNN)-based method is developed to localize structural bolts in the 3D point cloud. Further, a 3D point cloud processing algorithm is developed to recognize and quantify bolt loosening. Parameter studies were conducted to investigate the effectiveness of the proposed pipeline. Finally, a real-world implementation has been conducted to quantify bolt loosening on a steel column base connection with bolts. The results indicate that the proposed bolt loosening assessment methodology can effectively localize and quantify bolt loosening at high accuracy and low cost.

Experimental Study on Seismic Behavior of Steel Column Base Connections with Arc End-Plates Slip-Friction

This paper proposes a new type of steel slip-friction column base connections with arc end-plates. Two arc end-plates of the steel column base, which can slide between each other to some extent, were set at the position where the column base is subject to plastic deformation. Thus, the sliding-friction energy dissipation between the arc end-plates can effectively minimize or eliminate the energy dissipation of the traditional column base connections. Cyclic loading tests were conducted to study the hysteretic performance and energy consumption performance of the proposed connections. Considerations have been given to different axial compression ratios, Belleville springs (Bes), brass plates, and horizontal loading protocols. The test results show no obvious deformation or damage during the radial cyclic loading test. The curve shape of the test measurement approximates a parallelogram, showing good force performance. The proposed connections with the increasing axial compression force can increase the energy dissipation ability and load-carrying capacity. Therefore, the proposed connection has perfect seismic behavior.

Connection of a Steel Column Base Plate: Mechanical Behavior and Stiffening Effects

This paper investigates the behaviour of a steel column base connection subjected to a bending moment and compressive axial force. The behaviour of this connection is quite complex due to the number of components, such as the base plate, anchor rods, and stiffeners, to be considered in the numerical models. Moreover, a nonlinear three-dimensional finite element model was used to simulate the column base connection. This model can be used to analyze the moment-rotation relationship for the connection through the validation of numerical modeling with those given by the experimental test results and compared with the analytical model based on the components method of Eurocode 3. It was shown that in addition to the stiffness and bending resistance of the column base connection, other mechanical parameters, such as moment-rotation shape, stress distribution, and prying actions, can be significantly influenced by changing the properties of the components. It has been demonstrated that the anchor rod is not only affected by the axial force but also by a local moment that is not taken into consideration by the analytical model of Eurocode3. An extensive parametric study on stiffeners showed very interesting effects obtained by adding the welded stiffeners to the column base connections. Doi: 10.28991/CEJ-2022-08-09-02 Full Text: PDF