Column Base Plate Connections Research Articles

Effects of stiffeners on anchor rod flexural strength in column base-plate connections

The present paper reports results of a numerical investigation of the mechanical behavior of a column base plate connection subjected to an axial compression force and a bending moment. A three-dimensional nonlinear model was developed, using the Cast3M software, and validated against experimental data. In addition, the material nonlinearity as well as contact conditions between the different components of the connection were thoughtfully considered. Based on the validated model, an extensive parametric analysis was conducted to investigate the effect of stiffeners on the forces in the anchor rods. The results clearly indicate that the design approaches that consider only the tensile strength of anchor rods while neglecting the bending moments can lead to a poor estimation of the forces applied to these rods. They also suggest that adding stiffeners provides additional strength and reduces the anchor rod bending in one direction. However, it is important to note that the stiffeners also induce an additional moment in the opposite direction. This could make the anchor rod more susceptible to biaxial bending with tension. Furthermore, this study proposes a new specific shape of stiffener is suggested (cbp5). It was concluded that the proposed shape of stiffeners allows a more uniform distribution of forces and avoids excessive stress concentrations, effectively prevents the biaxial bending in the anchor rod.

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.

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.

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.

Modelling of column base plate connections with plate stiffeners and non‐proportional loading

AbstractColumn base plate connections are used widely. Their design is currently codified by Eurocode 3, though with explicit consideration of only base plates without stiffeners and subjected to a proportional loading path. However, both new and existing steel structures might have stiffened base plates. Besides, there might be the need for analyzing the connection response for a non‐proportional loading path (e.g., increasing seismic loads and constant gravity loads). Therefore, the paper provides a contribution into the development of an analytical model for predicting the response of stiffened base plate connections subjected to a non‐proportional loading path. The paper deals with calculation of the connection rotational stiffness and moment resistance. The objective is pursued through finite element modelling and analysis. Then, the application of a proposed analytical model is shown and a comparison with the finite element analysis results is illustrated and discussed.

Numerical and analytical study of pinned column base plate connections

Gravity system column base plate connections are generally classified as pinned connections with no to minimal moment capacities. A low rotational stiffness value is recommended by the New Zealand Steel Structures Standard, NZS 3404, to represent pinned connections. However, numerous past research studies have shown that these so-call pinned connections possess significant rotational stiffness which could attract large moment demand and potentially lead to yielding of the column base. Furthermore, the constant axial load on the gravity column in conjunction with column base yielding could result in axial shortening of the column, which would significantly increase the cost and difficulty of post-earthquake rehabilitation. With the aim to minimize column base yielding and column axial shortening, a numerical parametric study was conducted to examine the influences of various parameters, including base plate thickness, anchor rod diameter, axial load magnitude, foundation depth and anchor rod pitch distance, on the connection behaviour. It was found that the applied axial load greatly affected the moment resistance as well as the rotational stiffness of the connection. Results also showed that the rotational stiffness of pinned column base plate connections was significantly higher than the value suggested in NZS 3404. An analytical model was developed and validated against numerical and experimental studies to predict moment-rotation response of pinned column base plate connections. Satisfactory results were observed.

Seismic Performance of Exposed Column–Base Plate Connections with Ductile Anchor Rods

Seismic Performance of Exposed Column–Base Plate Connections with Ductile Anchor Rods

Investigation of Mechanical Behavior of Steel Column Base Plates

Major earthquakes in the world led engineers and scientists to work on the connections of steel structures. Since the capacities of the connections, which are one of the important components of a steel structure, significantly affect the capacity of the entire structure, scientists are trying to design new connections and determine the limit states of these connections. At this point, column-base plate connections, which are an interface between reinforced concrete foundation and column, are of great importance in steel structures. In this study, the connections designed using base plates with different thicknesses, different numbers of anchor rods and different column types are analyzed under static loads, and comparative results are introduced in terms of stress and deformations occurred on the connection components. Analyzes were performed using ANSYS, a finite element software that is frequently used in engineering disciplines. The results obtained are interpreted and the advantages and disadvantages of the different types of column base plate connections are revealed. The results of the research show that the thickness of the baseplate used in the connection has a significant effect on the total deformation and stresses on the connection and its components. In addition, it has been determined that the number of anchor rods used in the base-plate connections affects the deformation and stresses. It has been observed that the total rigidity of the connections has a dominant role in the mechanical behavior of the joints.

Column base-plates under biaxial bending moment

This paper investigates the behaviour of exposed column base-plates with four outer anchor bolts subjected to monotonic loading. The results of six full-scale tests on steel column base-plate connections subjected to uni/biaxial bending moment are presented. The influence of the base-plate thickness and the bending moment axis orientation on the connection response is thoroughly investigated. In addition to standard measurements, Digital Image Correlation has been used to closely monitor the evolution of the contact area that develops in the tensile and compressive zones. Furthermore, a detailed finite element model has been developed using the software Abaqus and used to explore additional orientations of the bending moment axis. This numerical model allows to investigate the evolution of the anchor bolt forces, the contact pressure distribution and the lever arm, that strongly influence the bending resistance and rotational stiffness. An Analytical model is suggested for the calculation of the bending resistance of a column base-plate connection whatever the orientation of the bending moment axis. The position of the centre of compression directly depends on the base-plate thickness. A plastic redistribution is also considered between the anchor bolt rows when biaxial bending moment is applied to the column base-plate.

Reliability Analysis and Design Considerations for Exposed Column Base Plate Connections Subjected to Flexure and Axial Compression

AbstractExposed column base plate (ECBP) connections are commonly used in steel moment resisting frames. Current approaches for their design are well-established from a mechanistic standpoint. Howe...

An Investigation of Base Plate Connections of a Steel Industrial Building Having Different Column Cross-Sections

In this study, steel column base plate connections of a steel industrial building that are one of the most important connection regions were studied. Two dimensional static analysis of a steel industrial building was performed and exposed column base plate dimensions were determined according to American Institute of Steel Construction Code-LRFD (Load and Resistance Factor Design) method. The effects of selected steel column cross section types on the behaviour of column base plate connections were investigated by using RFEM finite element analysis program. For this purpose, finite element analysis of three types of column base plate connection models were performed and evaluated comparatively. From results, the best value for top column lateral displacement was obtained in W column section-base plate connection and the best behaviour for Von Mises stresses values was obtained in square hollow section column. The undesired behaviour was determined in circular hollow section column-base plate connection type.

Evaluation of existing provisions for design of “pinned” column base-plate connections

Low-rise metal buildings are used in all geographic locations, including high seismicity regions. In the design of low-rise metal building systems, column base connections are commonly modeled as pinned supports with no rotational stiffness or moment capacity. However, past studies have indicated that base connections, which are designed as pinned supports, exhibit a non-negligible level of rotational stiffness and strength. Neglecting the rotational stiffness of the base connection may result in a significant overestimation of the lateral displacement of the frames. This additional displacement is addressed by increasing the flexural stiffness of the frame members thereby increasing the cost of low-rise metal buildings. The moment capacity may similarly be exploited for strength design. However, there is a lack of design guidelines to support the use of rotational stiffness or moment capacity at the pinned column bases. This study evaluates the applicability of existing code-formulations to pinned colum base-plate connections. Both the rotational stiffness and the moment capacity from past experiments are compared with those calculated based on the provisions of the European and American design codes. It was found that the Eurocodes do not accurately estimate the rotational stiffness of the connections. A modification to the Eurocodes is recommended to capture the characteristics of pinned connections. It was also observed that the moment capacity of the connections was conservatively estimated by the existing codes.

Parametric Finite-Element Modeling for Exposed Steel Moment Frame Column Baseplate Connections Subjected to Lateral Loads

AbstractThe behavior of steel column baseplate connections in moment frames subjected to lateral loads has been the subject of numerous experimental investigations, giving rise to a variety of meth...

Investigation of Steel Column–Baseplate Connection Details Incorporating Ductile Anchors

It is widely accepted that the behavior of steel column–baseplate connections will profoundly impact the seismic response of steel buildings and other structures. Previous investigations into moment-frame steel column–baseplate connections have focused on the relationship between global metrics such as connection strength and stiffness to basic design parameters such as anchor arrangement and size, baseplate thickness, and column size. However, there is growing recognition that other details, such as the column setting method, baseplate hole size, anchor material selection, and anchor stretch length may significantly affect connection performance. This paper describes nine full-scale connection tests exploring the effects of such details on strength, rotation capacity, and postyield behavior. A comparison of the present with a prior test program on the basis of physical damage evolution and moment-rotation behavior is undertaken. The baseplate setting arrangement and anchor stretch length were found to have the most pronounced impact on the connection cyclic moment-rotation response. Suggestions for connection details that promote connection robustness, ductility, and strength are presented.

Analysis and design of demountable steel column-baseplate connections

This paper aims to investigate the demountability of steel column-baseplate connections subjected to monotonic and cyclic loading. This paper presents the finite element analysis of steel column-baseplate connections under monotonic and cyclic loading. The finite element model takes into account the effects of material and geometric nonlinearities. Bauschinger and pinching effects were also included in the developed model, through which degradation of steel yield strength in cyclic loading can be well simulated. The results obtained from the finite element model are compared with the existing experimental results. It is demonstrated that the finite element model accurately predicts the initial stiffness, ultimate bending moment strength of steel column-baseplate connections. The finite element model is utilised to examine the effects of axial load, baseplate thickness, anchor bolt diameter and position on the behaviour of steel column-baseplate connections. The effects of various parameters on the demountability of steel column-baseplate connections are investigated. To achieve a demountable and reusable structure, various design parameters need to be considered. Initial stiffness and moment capacity of steel columnbaseplate connections are compared with design strengths from Eurocode 3. The comparison between finite element analysis and Eurocode 3 indicates that predictions of initial stiffness for semi-rigid connections should be developed and improved design of the connections needs to be used in engineering practice.

Analytical approach of anchor rod stiffness and steel base plate calculation under tension

The analysis of column base plate connections under biaxial moment or when large numbers of anchor rods are utilised is complicated. Such complex connections are regularly found in engineering practice, in spite of proposed, up-to-date finite element modelling techniques and analytical formulations being unsuitable. The lack of suitability arises from their development for non-practical column base plate idealised configurations. In the present paper, the results of a finite element study of single-headed anchors under tension are discussed, leading to the derivation of a simple equation that describes the stiffness of the headed anchor rod embedded in concrete. Furthermore, this paper suggests a simple and suitable approach to analyse base plate connections independent of loading scenarios, the number of anchor rods and their arrangement, taking into account the actual rigidity of the connection. In this study, a three-dimensional, nonlinear finite element model is developed through the use of the general-purpose finite element software package ABAQUS. The respective numerical results were verified against experimental ones.

Influence of base-plate connection stiffness on the design of low-rise metal buildings

The objective of this research is to evaluate the influence of column base-plate connection rotational stiffness on the design of low-rise metal building systems. Currently, low-rise metal buildings are designed based on a zero rotational stiffness (pinned connection) assumption at the column-bases. Although prior research indicates that the assumption of zero rotational stiffness of the column base-plate connection could result in a significant underestimation of the overall lateral stiffness of horizontally loaded moment frames (leading to less economical designs), there has been no systematic study to investigate this issue. This paper first presents the details of an experimental research program that was conducted to quantify the rotational stiffness of “pinned” column base-plate connections that are commonly used in the low-rise metal building industry. Eight full-scale column base-plate connections with varying base-plate dimensions, numbers of anchor rods, anchor rod diameters, and gage distances were tested. Then, the data obtained were used to investigate the reduction in the total weight of gabled frames used in metal building construction. Finally, a piecewise nonlinear spring model was fitted to the test data to represent the rotational stiffness of the joints beyond the elastic range. Analyses of example frames indicate that consideration of the rotational stiffness of the pinned connections reduces frame deflections between 11 and 67% and has the potential to make metal building systems more economical by decreasing the frame weight between 0 and 12%, which is considered a substantial cost saving for the metal building industry where profit margins are relatively low.

Effects of Detailing on the Cyclic Behavior of Steel Baseplate Connections Designed to Promote Anchor Yielding

AbstractThis paper presents the results from an experimental investigation into the role that anchor selection, setting arrangement, and stretch length have on the post-yield behavior, rotation capacity, and ultimate strength of column baseplate connections. Eight full-scale column baseplate connections were designed to promote anchor yielding and tested under quasi-static, reversed cyclic loading. The connections utilized cast-in headed bolts, adhesive anchors, undercut anchors, two different types of setting arrangements, and a range of stretch lengths. The performance of the connections was evaluated by comparing their cyclic moment-rotation behavior, kinematics, and physical damage to the connection components. Anchor type, material selection, and the method used to level the column were found to have pronounced impact on the strength and rotation capacity of the connection. Increased stretch length was associated with only moderate increases in connection rotation capacity. In addition, a numerical m...

Rotational behaviour of column base plate connections: Experimental analysis and modelling

A research program aimed at the development of a mechanical model to predict the rotational behaviour of base plate connections under cyclic loads has been recently undertaken at Salerno University. The evaluation of the accuracy of the component approach for predicting the rotational behaviour of base plate connections up to failure under monotonic loads has been carried out as first step of the planned research activity. The accuracy in predicting the rotational stiffness, the flexural resistance and the overall moment–rotation curve of base plate connections by the component method given in Eurocode 3 is evaluated with reference to the experimental tests recently carried out at Salerno University. In particular, the specimens have been preliminarily tested in elastic range under different values of the column axial load and, successively, loaded up to collapse.Such experimental tests are presented and discussed in this paper. In order to widen the investigated range of the geometrical and mechanical parameters affecting the behaviour of base plate connections, the comparison between the predictions coming from component method and experimental tests has been extended not only to the authors’ own tests, but also to a significant number of tests collected from the technical literature.

Exposed column base plate connections in moment frames — Simulations and behavioral insights

The response of exposed column base connections under axial and flexural loadings is controlled by complex interactions of various components within them, i.e. the column, base plate, anchor rods, and footing. Current approaches for strength characterization of these connections show good overall agreement with test data from specimens that are smaller relative to the prototype scale. However, internal stress distributions that underpin these approaches have not been independently verified, presenting challenges for the generalization of these approaches to full scale connections. A finite element (FE) simulation study is presented to offer insights into connection response with a focus on internal stress distributions. The 3-d FE simulations incorporate important aspects of behavior including contact, gapping and nonlinear multiaxial constitutive response of the various components. The simulations are rigorously validated based on multiple data streams obtained from a series of six experiments on exposed base plate connections. The results of the simulations indicate that current strength characterization and design approaches (that assume a rectangular bearing stress block) may grossly misrepresent the stress distribution under the plate. Thicker base plates tend to concentrate the stresses at the compression toe of the base plate. This significantly amplifies the bending moment in the base plate on the compression side of the connection, indicating that current approaches that do not consider this effect may be non-conservative. A simplified approach to address this issue is discussed. Similar issues are not observed for axial force estimates in anchor rods. Limitations of the work are outlined.