Column-foundation Connections Research Articles

Experimental hysteretic behavior of CFST column-foundation connections with novel detailing in embedded region

This paper presents a novel CFST column-foundation connection detail to improve stress transfer and damage control. To achieve this aim, seven specimens were created in the lab in three different configurations: exposed connection (base plate), embedded connection without reinforcement, and embedded connection with reinforcement. These specimens were subjected to cyclic lateral load and constant axial load tests. The effect of using internal reinforcement (including reinforcing anchor bar and internal tube) and external reinforcement (including shear studs, external diaphragm, and through diaphragm) in the embedded region on the reduction of the embedded depth was assessed. Performance indices of the tested connections, including the stiffness, lateral loading capacity, energy-dissipation capacity, ductility, and strain distribution of steel tubes, were analyzed based on hysteresis and pushover graphs. The test data demonstrated that all the specimens experienced flexural failure, and consequently, the local buckling of the steel tube was observed in all experiments with the exception of the specimen that had an exposed connection. The specimens with reinforcement in the embedded region had acceptable behavior with ductility coefficients higher than 4.8. The seismic response of the connection with the novel detail showed that the performance indices of the connection with reinforcing anchor rebars and reinforcing internal steel tube in the embedded region were considerably higher than those of the connection without reinforcement in the embedded region and the one in the exposed form. Moreover, the depth at which the connection is embedded was reduced by up to 0.7 times the diameter of the column due to the utilization of reinforcement in the embedded region.

Seismic behavior of embedded rubberized concrete-filled corrugated steel tube column-to-foundation connections: Experimental, numerical modelling, and design

A rubberized-concrete-filled corrugated steel tube composite column-foundation connection is proposed as a solution to mitigate local buckling, bulging, or tearing damage of concrete-filled steel tube columns during seismic load. This proposal aims to improve the ductility and energy dissipation capacity of the column. Experimental studies have been conducted to investigate the axial compressive strength of this novel column and the side shear performance of its connection to the foundation. A quasi-static experiment was carried out on three specimens to facilitate the application of the proposed connection. The influence of embedded depth on the seismic strength of such composite column-foundation connection was studied, and the cast-in-place specimen was used as a reference. The failure modes of the specimens were observed, and the evaluation indicators such as strength, stiffness, and ductility were analyzed. The results show that the connection of the composite column foundation can provide sufficient connection strength under seismic load. Furthermore, seismic design methods are explored and proposed, combined with the side shear database. These investigations aim to inform the design and application of such column-foundation connections.

An innovative connection proposal for the precast prestressed column-foundation connection

An innovative connection proposal for the precast prestressed column-foundation connection

Evaluation of Ductility of Precast Column Foundation Connections

Objectives: To investigate and compare the ductility performance of precast column foundation connection using the method proposed by Park and ASCE 31-03. Methods: Strength and ductility are the most important parameters to resist earthquake forces for the overall safety of a structure. Evaluating ductility from experiments is a cumbersome process. From the experimentally obtained load-displacement envelope, the ductility was evaluated for four specimens of precast column foundation connection by the method proposed by Park and Paulay (1989) and ASCE 31-03. The results were also compared with monolithic specimen. Each of the specimen was subjected to displacement-controlled lateral cyclic loading. The maximum displacement was maintained at 40 mm due to laboratory constraints. Findings: From the evaluated results, ASCE 31- 03 gives better values of ductility than the method proposed by Park. The calculated ductility by ASCE 31-03 were 31.5 %, 41.07 %, 72.7%, 68.3% and 48.9 % higher for monolithic specimen, PCBJ, PC I, PC II and GS specimen respectively. Novelty: The present study reveals the best-suited method that can be applied to evaluate ductility for specimen subjected to lateral cyclic loading that has not been reported in earlier studies. Keywords: Ductility Ratio; Yield Displacement; Ultimate Displacement; Precast Connection; Load Displacement Envelope

Shear-reinforced concrete breakout design methodology for moment transfer at column-foundation connections

Recent studies have shown that the strength of column-foundation connections carrying moment can be limited by the concrete breakout failure mode. Distributed shear reinforcement in the concrete breakout cone region has been observed to increase the strength and displacement capacity of structural connections governed by breakout. However, the ACI 318–19 building code does not allow designers to consider this strength increase. Rather, the code allows the use of anchor reinforcement provided that the concrete contribution to strength is ignored. This paper proposes a design methodology to calculate the breakout strength considering the additive effect of concrete and reinforcement. Physical test data and finite element simulations from previous studies were used to calibrate the proposed strength equations. Detailing requirements are discussed.

Moment Transfer at Column-Foundation Connections: Analytical Studies

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Experimental study of CFST embedded precast concrete bridge column-foundation connection with studs

Accelerated bridge construction (ABC) is increasingly gained attention worldwide based on its advantage of high-quality precast elements, less environmental effect, quick construction speed, and minimum traffic block. The seismic performance of prefabricated bridge structures is mainly dependent on the feasibility of connections. To efficiently bear the load from the gravity of other elements and deformation ability in high seismic areas, in this study, an innovative contrete-filled steel tube (CFST) embedded precast concrete bridge column-foundation connection with studs was put forwards. Two 1:2 scale specimens were designed to verify the seismic performance of the proposed connection type. One is a precast specimen with the bridge column-foundation connection, the other is the conventional cast-in-place (CIP) specimen as a reference. The experimental observations and seismic properties were analyzed and compared with those of the CIP specimen, such as failure mode, load-displacement curves, energy dissipation, etc. The finite element model of the precast specimen with bridge column-foundation connection was established and the validated model was used to conduct the parametric study. The precast specimen with bridge column-foundation connection has a larger capacity, ductility, energy dissipation, and equivalent viscous damping ratio than the CIP specimen. Axial compression ratio, embedded depth, and concrete strength affect the seismic performance of the precast specimen with the bridge column-foundation connection. The proposed CFST embedded precast concrete bridge column-foundation connection can be applied to ABC technology in high seismic areas.

Moment Transfer at Column-Foundation Connections: Physical Tests

Moment Transfer at Column-Foundation Connections: Physical Tests

Side shear strength and load-transfer mechanism of corrugated steel column–foundation socket connection

Accelerated bridge construction has received widespread attention globally owing to its cost-effectiveness. The integrity of the connections between precast bridge piers and other members of the structure is crucial for developing assembly substructures. This issue was examined in the present study. A novel corrugated steel tube socket connection (CSSC) was developed for column–foundation connections. The CSSC method is a rapid bridge construction method in which a prefabricated corrugated steel tubular concrete column and a corrugated steel pipe in the foundation are connected using concrete or ultra-high-performance concrete. A vertical monotonic static load experiment was performed on six CSSC specimens and one cast-in-place (CIP) specimen to investigate the slip performance, failure modes, and load-transfer mechanism. The side shear performances was compared among specimens with different parameters (connection method, embedment depth, presence of studs, and presence of concrete under the columns). The experimental results indicated that the CSSC specimens had better ductility values and higher axial bearing capacities than the CIP specimen. Increasing the embedment depth, adding studs, and adding concrete under the columns increased the ultimate bearing capacity. To accurately estimate the side shear performance of the CSSC, a reliable finite-element model was developed. An additional parametric analysis was performed to investigate the effects of different parameters on the vertical performance. The CSSC is effective connection type in the prefabricated column-foundation connection and is suitable for bridge high-gravity superstructures. Finally, design recommendations regarding the construction details of the CSSC were presented.

Experimental investigation of a new precast column-foundation connection under cyclic loading

In the prefabricated industry, socket connection is generally preferred to be used in column-foundation connection. In this connection type, the foundations and columns produced in the factory are assembled at the construction site. During the assembly, a wet connection is formed by filling the space between the socket and the column with concrete. Socket connections increase the labor costs by extending the installation time. In addition, adjusting the column balance during installation becomes very important for the superstructure. On the other hand, the use of the wet type of connection complicates installation as to be an active earthquake region of Turkey. An earthquake load that may affect the structure during the installation may cause a total collapse in the structure.Studies are carried out on new connection types for the prefabricated industry all over the world. New connection types are being developed. In this study, a new type of connection in mind that disruptions in the production and assembly processes in Turkey were developed. The proposed connection type was produced by enlarged part of the column cross section from the bottom of the column to a certain height. Anchorage bars on the foundation passed through the holes formed in the enlarged part of the column. The proposed connection type, socket connection, and monolithic connection were tested under cyclic lateral loading. The behavior of the connections was interpreted with the data obtained from the experiments. With the proposed connection, while the lateral load carrying capacity increased slightly, a significant increase was obtained in the energy dissipation capacity. Significant mechanical improvements have been achieved under the effect of lateral load compared to the conventional socket connection.

Seismic behavior of carbon fiber reinforced polymer confined concrete filled thin-walled steel tube column-foundation connection

To alleviate the complex construction process of traditional concrete filled steel tube (CFST) column-foundation connections, the anchor rebar column-foundation connection (ARCFC) has been conceived and investigated. To date, the thin-walled steel tube is recommended to be used considering it economic benefits. However, the confinement provided by the thin-walled steel tube is found to be insufficient as bulges of steel tube and concrete are observed. In this paper, carbon fiber reinforced polymer (CFRP) is adopted in the potential plastic hinge region to prevent the local buckling of steel tube. Nine specimens were designed and tested to failure under combined constant axial load and reversed cyclic lateral load. The investigated parameters are the number of CFRP layers and the diameter-to-thickness of steel tube. Experimental results revealed that bulges of steel tube and concrete were observed for ARCFCs with a diameter-to-thickness ratio of steel tube over 120. CFRP could effectively prevent the bulges of steel tube and concrete. All the ARCFCs have excellent energy dissipation capacity and the ductility coefficient is larger than 4.55. A finite element model (FEM) is developed to conduct a parametric study, based on which the sectional strength model is suggested.

Experimental and numerical investigation of a proposed monolithic-like precast concrete column-foundation connection

Precast structures are increasingly used in modern construction since they offer advantages such as cost-efficiency, better material quality, and fast construction due to their mass production compared to cast-in-situ structures. However, development of monolithic-like precast connections to ensure adequate seismic performance is still a challenging task. This study aims to introduce a monolithic-like column-foundation precast connection, which is easy to assemble and disassemble and therefore is replaceable in case of excessive damage. To investigate the efficiency of the proposed system, four full-scale precast and monolithic column-foundation connection specimens are tested under constant axial load and lateral reversed cyclic loading. Experimental results are then used to obtain seismic performance parameters such as failure mode, flexural capacity, initial stiffness, ductility, energy dissipation and curvature distribution. The results indicate that, in general, the proposed precast connections exhibit similar structural performance as their monolithic counterparts. Subsequently, experimentally validated finite element (FE) models are developed to provide practical tools for seismic design and performance assessment of the proposed precast connection system. It is shown that the developed models can accurately estimate the load-bearing capacity, initial stiffness and post-peak behaviour of both precast and monolithic column-foundation connections.

Design method of concrete filled thin-walled steel tube column-foundation connections

The anchor rebar column-foundation connection (SAC) has been proposed for the concrete filled steel tube (CFST) column. To enhance the load transfer between the steel tube and concrete, shear hoop rings or perfobond strips (PBLs) could be used, forming the SAC-H and SAC-P, respectively. Anchor rebars could be directly welded onto the surface of steel tube (SAC-W) to transfer the axial load. To date, experimental studies have been conducted to investigate the seismic performance of the four novel types of column-foundation connections. To facilitate the application of the proposed connections, design methods are explored and proposed in this paper. A test database is assembled first, followed by the development of the finite element model (FEM). On the basis of a parametric study, design methods for the sectional strength and elastic stiffness are proposed.

Behaviour of Precast Column Foundation Connection under Reverse Cyclic Loading

Precast column foundation connection is one of the critical connections under reverse cyclic loading, and the present study focuses on this connection. Three types of connections were considered, such as (i) base plate connection, (ii) pocket connection, and (iii) grouted sleeve connection. All the above connections were designed, and experimental investigation was carried out on 1 : 2 scaled models by subjecting the column to lateral reverse cyclic loading. Displacement-controlled loading pattern has been adopted for the testing of the specimens. The structural response of the connection was studied for their (i) load-displacement hysteresis behaviour, (ii) stiffness degradation, (iii) energy dissipation, and (iv) ductility. The results were then compared with that of the monolithic connection. The precast connection was more ductile, and the energy dissipated by the pocket connection was high compared to the base plate and grouted sleeve connection. The ductility and the load-carrying of grouted sleeve connection were small compared to other connections. The results of the study showed the precast column foundation can be used in seismic prone areas.

EXPERIMENTAL AND NUMERICAL STUDY ON COLUMN-FOUNDATION CONNECTION THROUGH EXTERNAL SOCKET

In practice, bridge foundations and pier columns are usually constructed with cast-in-place concrete. Precast columns are currently widely used in highway bridges in China, which can save construction time and improve concrete quality. The connection between precast bridge columns and the foundation can affect how forces transfer from one to the other. This paper investigates using external sockets to form a connection between the bridge column and foundation. This method can accelerate the bridge construction time with the additional advantages of improving the orientation and creating a large erection tolerance. Two types of connections are presented and tested to investigate the behavior of the column-foundation connections and find a more suitable way to use external socket connections. The experimental results show that the column-foundation connection design satisfies the design requirements. The results also show that roughening the column surface within the external socket is more effective at connecting the column to the foundation when using an external socket compared to attaching a steel plate on the column. The experimental results are validated with a finite element analysis, resulting in a proposal regarding the column-foundation connection behavior as well as design recommendations for the external socket connection.

Seismic behavior of self-centering prestressed precast concrete frame subassembly using steel top and seat angles

In order to improve the seismic resilience of the precast concrete structures, a novel prestressed self-centering concrete frame structure is proposed in this study. The beam-column and the column-foundation connections are all assembled using the post-tensioning (PT) tendons and steel angles. Both the experimental and numerical studies were conducted on a 1/2-scaled frame subassembly to investigate the seismic behavior of the specimen. The test results showed that the precast beam/column members and the PT tendons behaved almost elastically during the course of tests. The steel angles provided energy dissipation capacity for the subassembly through significant plastic deformation. The use of PT tendons ensured a good self-centering capacity of the specimen. The seismic performance of the repaired specimen was also evaluated through experiments and showed comparable load-carrying and energy dissipation capacities that were comparable to the original specimen. The good repairability of the specimen was due to the low damage and residual deformation that was induced to the precast concrete members. Based upon the finite element platform OpenSees, numerical modeling was performed to investigate the effects of various design parameters, including initial PT force, area of the PT tendons, geometry of the steel angles, on the cyclic response of the subassembly. The numerical results indicated that an increase in the initial PT force and the area of PT tendons improved the stiffness and the load-carrying capacity of the specimen. A decrease in the thickness, or an increase in the column gage length of the steel angle may result in a reduction in the energy dissipation capacity of the subassembly.

Experimental investigation of seismic behavior of UHPC-filled socket precast bridge column-foundation connection with shear keys

Accelerated bridge construction (ABC) has been paid great attention in China for the significant advantages compared with cast-in-place (CIP), such as higher construction speed, less environmental impact and structural members of higher quality. However, the reliability, durability and seismic behavior of the connection between prefabricated bridge column and the rest of the structure are primary factors that limit the application of the ABC in the moderate and high seismic zones. In this study, quasi-static experimental investigation of seismic performance of three 1:3-scale ultra-high performance concrete (UHPC)-filled socket reinforced concrete (RC) column-foundation connection specimens were conducted. A fiber-based finite element model is developed considering the rotation effect of the column embedded in the footing. The seismic behavior of the precast column specimens with UHPC-filled socket connection type was compared with that of CIP specimen. The experimental and numerical results show that the damage evolution, failure modes and hysteretic responses of the precast bridge column are equivalent with those of the CIP bridge column. Numerical analysis also validated that the finite element model(FEM) in this paper is adequate to predict seismic response of the precast column with UHPC-filled socket connection. The UHPC-filled socket connection is a reliable connection type in prefabricated column-foundation connection joint which is suitable for moderate and high seismic regions.

The cyclic response of circular reinforced concrete column to foundation connections strengthened with shape memory alloy bars

This study presents a new method for strengthening the circular reinforced concrete (RC) column to foundation connections with shape memory alloy (SMA) bars and carbon fiber reinforced polymer (CFRP) sheets. In the experimental part of the study, three specimens of RC column-foundation connections were cast and tested. One specimen was used as the reference specimen without strengthening. Two other specimens were strengthened with longitudinal SMA bars and CFRP sheets. These specimens were under a constant axial compressive load and cyclic lateral displacements, simultaneously. Next, initial stiffness, energy dissipation capacity, lateral load capacity, ductility, and residual displacement of the specimens were investigated. Due to the superelastic behavior of SMA bars, the residual displacement of column-foundation connections was considerably less than that of the reference specimen. Compared to the reference specimen, the SMA-strengthened and SMA-CFRP-strengthened connections recovered 71.59% and 76.57% of the residual displacement. Therefore, SMA bars were able to recover residual displacements under cyclic loading. Also, the combination of the SMA bars with CFRP sheet was a promising solution for enhancing the amount of the energy dissipation, lateral load capacity, initial stiffness, and ductility parameters. Compared to the reference specimen, the energy dissipation, lateral load capacity, initial stiffness, and ductility ratio parameters of SMA-CFRP-strengthened connection increased about 43.45%, 76.20%, 81.69%, and 242.45%, respectively. In the numerical part of the study, a subroutine was applied for modeling the SMA materials. For the analysis, this subroutine was linked with ABAQUS software. The numerical results showed a close correlation with the experimental results.

Seismic performance of high-strength anchor rebar column-foundation connection for CFST

The anchor rebar column-foundation connection (ARCFC) is proposed for concrete filled steel tube (CFST) column to simplify the construction process of column-foundation connection. In this paper, a total of eight specimens were tested to failure under constant axial load and cyclic lateral load. The influences of reinforcement ratio, configuration of shear hoop rings, and axial load ratio on the seismic performance of ARCFCs are experimentally investigated. The failure mode of all the specimens is characterized by bending, and no tube local buckling was observed in the tested specimens except for the embedded connection. Experimental results show that all the specimens have good ductility with ductility coefficients larger than 4.5. Analysis is conducted to investigate the influence of test parameters on the load-displacement skeleton curves, stiffness degradation, energy dissipation capacity, and strain development of steel tube and anchor rebars. Analysis results reveal that the seismic performance of the proposed connection is similar to the embedded connection when it is designed according to both the “compression equivalence” and “bending equivalence” principles. Based on the test results, a calculation method for the sectional strength of the bottom section is suggested and verified.

Fragility-based methodology for evaluating the time-dependent seismic performance of post-tensioned timber frames

Since 2010, the construction of post-tensioned wooden buildings (Pres-Lam) has been growing rapidly worldwide. Pres-Lam technology combines unbonded post-tensioning tendons and supplemental damping devices to provide moment capacity to beam–column, wall–foundation, or column–foundation connections. In low seismic areas, designers may choose not to provide additional damping, relying only on the post-tensioning contribution. However, post-tensioning decreases over time due to creep phenomena arising in compressed timber members. As a consequence, there is a reduction of the clamping forces between the elements. This reduction affects the seismic response of Pres-Lam buildings in the case of low- and high-intensity earthquakes. Therefore, understanding and accounting for the post-tensioning losses and their uncertainty are paramount for a robust assessment of the safety of Pres-Lam constructions. So far, however, there have been no comprehensive studies which tackle the overall seismic performance of such systems in the presence of time-varying post-tension losses and the associated uncertainty. This study tackles this research gap by introducing a comprehensive seismic evaluation of Pres-Lam systems based on time-dependent fragility curves. The proposed fragility analysis is specifically designed to account systematically for time-varying post-tension losses and the related uncertainty. The method is applied to two case studies, designed, respectively, with and without supplemental damping devices. In terms of structural performance, results show that the use of additional dissipaters mitigates the effect of post-tensioning loss for earthquakes of high intensity. Conversely, performance under low-intensity earthquakes is strongly dependent on the post-tensioning value, as the reduction of stiffness due to the anticipated rocking motion activation would lead to damage to non-structural elements.