Column-base Joints Research Articles

Seismic response of a steel resilient frame equipped with self‐centering column bases with friction devices

AbstractIn the last two decades many researchers focused on the development of innovative building structures with the aim of achieving seismic resilience. Among others, steel Moment Resisting Frames (MRFs) equipped with friction devices in beam‐to‐column joints have emerged as an effective solution able to dissipate the seismic input energy while also ensuring the damage‐free behaviour of the system. However, to date, little attention has been paid to their column bases, which represent fundamental components in order to achieve resilience. In fact, column bases designed by current conventional approaches lead to significant seismic damage and residual drifts leading to difficult‐to‐repair structures. The present paper evaluates the seismic performance of steel MRFs equipped with an innovative damage‐free, self‐centring, rocking column base joints. The proposed column base consists of a rocking splice joint where the seismic behaviour is controlled by a combination of friction devices, providing energy dissipation capacity, and pre‐loaded threaded bars with disk springs, introducing restoring forces in the joint. The design procedure of the column base is presented, a numerical OpenSees model is developed to simulate the seismic response of a perimeter seismic‐resistant frame, including the hysteretic behaviour of the connection. Non‐linear dynamic analyses have been carried out on a set of ground motions records to investigate the effectiveness of the column base in protecting the first storey columns from yielding and in reducing the residual storey drifts. Incremental Dynamic Analyses are used to investigate the influence of the record‐to‐record variability and to derive fragility curves for the whole structure and for several local engineering demand parameters of the frame and of the column base connection. The results show that the damage‐free behaviour of the column bases is a key requirement when self‐centering of MRFs is a design objective.

PARAMETRIC STUDY ON SEISMIC PERFORMANCE OF COLUMN BASE WITH SHEAR TYPE ENERGY DISSIPATION DEVICES

To study the seismic performance of the steel column base with shear type energy dissipation device, the ABAQUS is used to analyze the parameters of nine column base joint models. The results of finite element calculation are compared with the test results to verify the model accuracy. The influences of the variation of cross-sectional area, width-thickness ratio and the axial compression ratio of the column, on the seismic performance of the column base, such as the resistance capacity, initial stiffness, energy dissipation capacity and self-reset capacity, are studied by using effective column base joint model. The results show that the resistance capacity of the column base is less affected by the width-thickness ratio; when the section area of the weakened section of the energy dissipation device increases to 1.1 times, the resistance capacity can be increased by 36%; when the axial compression ratio of the column base becomes 4 times larger, the resistance capacity can be increased by 58%. The results show that the energy dissipation capacity of column base joint is less affected by the axial compression ratio of steel column; when the section area of the weakened section of energy dissipation device becomes about 2.1 times of the original, the energy consumption of column base joint increases about 79%; when the width-thickness ratio of shear type energy dissipation device increases 3.1 times, the energy consumption of column base joint increases nearly 20%. In addition, the residual deformation of the column base has little influence on the width-thickness ratio of the energy dissipation device. When the weakened section area of the column base increases by one time, the residual displacement angle of the column base node increases by 209%; when the axial compression ratio of the steel column increases by two times, the residual displacement angle of the column base decreases by 54%. In conclusion, when the axial compression ratio is constant, the resistance capacity and energy dissipation capacity of the steel column base can be improved by increasing the cross-sectional area of the shear type energy dissipation device or increasing the width-thickness ratio of the shear type energy dissipation device.

Column base joint made with ultrahigh-strength steel bars and steel tubular: An experimental study

The use of ultrahigh-strength steel in civil, bridge, and offshore engineering is increasing rapidly. In this study, the seismic behavior of a concrete-filled steel tubular (CFST) column base joint with implanted ultrahigh-strength reinforcing bars has been investigated. The steel tubular and the implanted reinforcing bars are made of ultrahigh-strength steel. Four column base joints with square and circular cross-sections and with 0 and 0.25 axial force ratios have been tested to discuss the hysteretic capacity, deformation, ductility, failure modes, and energy dissipation. The axial force is the main parameter to improve the flexural capacity of the column base joints. Owing to the slip between the infilled concrete and the steel tubular columns, the hysteresis loops show an obvious pinch phenomenon. The tested specimens demonstrate good ductility behavior. Finally, the flexural capacity of the CFST column base joint has been determined by analyzing the failure characteristics and stress of the CFST columns. The flexural capacity of the CFST column base joints determined by the calculation formulae matches well with the test results. The ratio of the calculated and tested flexural capacity is between 0.967 and 1.059, and the absolute relative error is between 0.131% and 5.595%.

Effect of column foot tenon on behavior of larch column base joints based on concrete plinth

The wooden columns in timber structures of ancient buildings have column foot tenons of various sizes. The main reason for these differences is their use for different roof loads. Six full-scale specimens with different sizes of column foot tenon were designed and manufactured. The tree species used for the specimens was larch. The quasi-static test was conducted on the specimens that were used in timber structures of ancient buildings. The effects of column foot tenon size on the mechanical properties of larch wooden columns were studied. The moment-rotational angle hysteretic curves, moment-rotational angle skeleton curves, ductility, stiffness degradation, energy dissipation capacity, slippages between the wooden column and the plinth, and the damage of the column foot tenons were examined. The test results showed that the column foot tenon played an important role in the mechanical behavior of the wooden column under low-cycle reversed cyclic loading. The rotation of the column foot tenon improved the energy dissipation capacity of the wooden column. As the rotational angle of the column base increased, the column foot tenon had different degrees of damage. Different sizes of column foot tenon had their own advantages and hysteretic behavior.

Experimental investigation on seismic performance of mechanical joints with bolted flange plate for precast concrete column

The conventional assembled monolithic grouted sleeve connection of column–column joints continues to require in situ grouting, which has certain disadvantages, including the necessity of wet construction. Compared with cast-in-situ columns, its seismic performance is relatively insufficient in terms of deformation and energy dissipation capacity. In this paper, a new type of precast concrete column–column joint and its corresponding column base joint with a steel jacket for confining the concrete core and bolted flange plate is proposed to achieve rapid erection. Six specimens are tested at a high axial compression ratio and cyclic reversed loading, including three precast column–column joints with bolted flange plate, one column base joint with bolted flange plate, one grouted sleeve connection joint, and one cast-in-situ column. This study focuses on the effects of the ratio of longitudinal reinforcement to the gap between the steel jacket and upper concrete on seismic performances. Test results indicate that this new joint is reliable, and all failure modes involve the flexural failure of the precast upper column. The influence of tensile reinforcement on the out-of-plane deformation of the flange plate is minimal. Compared to the cast-in-situ column, the column with a flange plate connection has a more gradual crack development, a slightly higher resistance, an improved ductility, and a better energy dissipation capacity. With the increase in longitudinal reinforcement ratio, the confining effect of the steel jacket on the concrete core becomes more distinct. The gap between the steel jacket and upper concrete could effectively delay the compressive damage on the concrete surface. Finally, considering the confining effect of the steel jacket, the flexural capacity of the proposed precast column is determined using the fiber model. The predicted results approximate the test values and are all within the safe range.

Investigation on Seismic Performance of Bidirectional Self-Centering Reinforced Concrete Frame Structures by Shaking Table Tests

This paper presents an experimental study on the seismic performance of a bidirectional self-centering reinforced concrete (RC) frame structure. In the structure, the column-base joints, which were installed with external mild steel (MS) dampers, could uplift freely and the beam-column joints could open effectively under earthquake excitations. Angle steels and MS dampers were installed at the beam-column joints in the structural X and Y directions, respectively. During the gap opening of the joints, unbonded posttensioned (PT) steel wires, which passed through the plastic ducts inserted in the RC beams and columns, provided the structure with the ability to return to pre-earthquake positions, and the yielding MS dampers and angle steels dissipated the seismic energy. A 1/2-scale two-story model structure was designed and constructed. Shaking table tests were performed on the structure under four different types of earthquake excitations with increasing seismic hazard levels. The test results indicated that the self-centering RC frames installed in both the directions showed satisfactory seismic performance, with only slight damage to the main structure after extreme earthquakes. The natural frequencies of the self-centering frames installed in both the directions degraded progressively, mainly because of the prestress loss of the PT steel wires and the yielding of the MS dampers. The structure showed desirable self-centering ability with very small residual deformation under ground motions of all hazard levels. The structural deformation was mainly concentrated at the column-base and beam-column joints, and hence, damage to the concrete beams and columns was considerably alleviated. In addition, the residual gap opening of the joints was minimal.

Experimental response of a low-yielding, self-centering, rocking column base joint with friction dampers

The sliding hinge joint (SHJ) is a supplemental energy dissipation system for column bases or beam-to-column connections of steel Moment Resisting Frames (MRFs). It is based on the application of symmetric/asymmetric friction dampers to develop a dissipative mechanism alternative to the column/beam yielding. This typology was initially proposed in New Zealand and, more recently, is starting to be tested and applied also in Europe. While on the one hand this technology provides great benefits such as the damage avoidance, on the other hand, due to the high unloading stiffness of the dampers in tension or compression, its cyclic response is typically characterized by a limited self-centering capacity.To address this shortcoming, the objective of the work herein presented is to examine the possibility to add to these connections also a self-centering capacity proposing new layouts based on a combination of friction devices (providing energy dissipation capacity), pre-loaded threaded bars and disk springs (introducing in the joint restoring forces).In this paper, as a part of an ongoing wider experimental activity regarding the behavior of self-centering connections, the attention is focused on the problem of achieving the self-centering of the column bases of MRFs by studying a detail consisting in a column-splice equipped with friction dampers and threaded bars with Belleville disk springs, located above a traditional full-strength column base joint. The main benefits obtained with the proposed layout are that: (i) the self-centering capability is obtained with elements (threaded bars and Belleville springs) which have a size comparable to the overall size of the column-splice cover plates; (ii) all the re-centering elements are moved far from the concrete foundation avoiding any interaction with the footing. The work reports the main results of an experimental investigation and the analysis of a MRF equipped with the proposed column base joints.

The Design on Laminated Prefabricated Column base joint and The Research on its Construction Technics

Based on the loading features and disease characteristics of the existing column base joint, this paper studies a kind of laminated prefabricated column base joint and systematically analyses its structural layout, construction process of technics, quality control, and principles of technics.

Seismic design methodology for self-centering reinforced concrete frames

This paper presents a new design approach for self-centering reinforced concrete frames (SRCFs). SRCF is a seismic resilient structure characterized by minimal structural damage and little residual deformation under seismic excitations. This remarkable seismic performance is achieved by specially designed self-centering beam-column joints and column-base joints. These joints connect beams and columns by clamping force provided by unbonded post-tensioning steel. By this means, when the lateral load exceeds serviceability level (i.e. gravity load, frequent earthquake and wind load), the gaps at self-centering joints are allowed to open and the columns are allowed to uplift at the base. The opening and uplifting behavior significantly mitigates the damage in “plastic hinge area”, where conventional concrete frame intends to sacrifice in exchange for ductility and energy dissipating capacity. After unloading all the gaps between components will close under clamping force, and the components thus restore their original position with negligible residual deformation. This state change of opening and close makes the conventional design methodology no longer applicable for SRCFs. Despite its extraordinary seismic performance, the absence of applicable design method hinders the application of SRCFs. In this paper, key configurations of SRCFs are summarized based on existing research, and load capacities of different limit states are analyzed. A two-phase design approach is presented based on these load capacities. In the first phase, the elastic performance of the structure is designed to accommodate the gravity load and meet the displacement requirement under frequent earthquakes. The detailed design of post-tensioning steel, damping devices and the reinforcement of the components are determined in the second phase to achieve the performance target under strong earthquakes. Design examples are given to illustrate the design approach. Time history analyses of design examples are conducted to verify the validity of this approach. Analysis result indicates that this approach can be used to design structures to achieve predefined performance targets with reasonable conservative.

Seismic performance and fragility functions of a 3D steel-concrete composite structure made of high-strength steel

This paper provides insight into a probabilistic seismic demand analysis of a steel-concrete composite structure made of a novel type of high-strength steel moment resisting frame, to be used either in a seismic risk assessment or a fully probabilistic Performance-Based Earthquake Engineering (PBEE) framework. The application of the PBEE methodology with a full probabilistic character is able to rigorously evaluate the seismic risk to which a structure may be exposed, as well as to quantify economic losses, including both direct -repair, reconstruction costs, etc.- and indirect costs -downtimes, etc.-. In this respect, the knowledge of seismic fragility functions is paramount. Moreover, due to the dynamic complexity of the examined structure caused by irregularity in elevation and different lateral-force resisting systems in the two main directions -moment resisting frames (MRFs) and concrete shear walls- the seismic behaviour is not straightforward to foresee. Therefore, two separate 2D analyses along the building main directions may not suffice to identify the actual dynamic response and, consequently, a 3D comprehensive probabilistic seismic demand analysis was performed by taking into account the earthquake incident angle. In order to exploit the inherent overstrength of non-dissipative members, consistently with the capacity design philosophy, the structure, that is a representative example of a realistic office building, is characterised by a newly-conceived type of moment resisting frame made of high-strength steel circular columns filled of concrete and of mild steel beams. In this respect, a nonlinear 3D FE model was developed and calibrated on experimental tests performed on both beam-to-column and column-base joints that formed MRFs. A multiple incremental dynamic analysis (MIDA) was then performed with two groups of bespoke accelerograms characterised, on one hand, by large magnitude and large distance and, on the other hand, by near-source effects. The earthquake incidence angle was also considered and, to decrease the number of simulations, the accelerogram-incident angle pairs were selected by means of the Latin hypercube sampling (LHS) method. The relevant seismic analyses highlighted the need to include the incident angle to better characterise its dynamic behaviour. Hence, the seismic fragility functions were built both for damage and collapse limit states considering both the maximum interstorey drift ratio as engineering demand parameter and different intensity measures as well as the incident angle randomness. The results showed that peak ground displacement entails a more efficient probabilistic model because the dominant structural dynamic behaviour was governed by MRFs characterised by fairly long periods.

11.30: Experimental behaviour of base plate joints equipped with self‐centering system and friction dampers

ABSTRACTA FREE from DAMage friction connection is a connection where friction dampers are introduced by adding friction pads, sliding on slotted steel plates, pre‐stressed with high strength bolts. Even though such a technology provides great advantages in terms of removal of damage to the structural elements, it has the main drawback to provide a limited re‐centering capability. In fact, during a seismic loading history, FREEDAM joints rotate concentrating the dissipation in the friction interface but, due to their high stiffness, after the end of the ground motion, they remain in a deformed position, leaving also the structure with residual drifts resulting in out‐of‐plumbs.The goal of the work is to propose an approach to provide FREEDAM structures with a self‐centering capacity by studying particular devices, to be installed in beam‐to‐column joints or column base joints. In this paper, the attention is focused on the problem of re‐centering of base plate joints studying a detail consisting in a connection located at the base of the columns of the first storey equipped with friction dampers and threaded bars. The threaded bars work as elastic springs thanks to sets of Belleville washers used to increase the deformability and to allow the opening of a gap in the connection. The main breakthrough of the proposed technology with respect to the existing literature, aside from the methodology employed for the design of the friction connection, is that the self‐centering capability is obtained with re‐centering elements (threaded bars and Belleville springs) which are not conceived to be extended up to the end of the column at the top storey of the building, but they have a size similar to the column splice's cover plates. The work reports the results of a preliminary experimental investigation on this joint detail which has regarded cyclic and pseudo‐dynamic tests. The experimental results presented seems very encouraging towards the possible development of base plate joints with self‐centering capacity combined with friction dampers.

Experimental investigation of tri-axial self-centering reinforced concrete frame structures through shaking table tests

This paper presents an experimental study on the seismic performance of a tri-axial self-centering reinforced concrete (RC) frame structure. In such a structure, the column-base joints were free to uplift, and the beam-column joints were relaxed to open. Post-tensioned (PT) strands passed through the RC beams and columns to provide re-centering capability. In order to accommodate the gap openings in beam-column joints, rubber pads were placed underneath the floor slabs to provide a smooth sliding motion between the RC beams and the slab. A 1/2.5-scale model of a tri-axial three-story self-centering RC frame structure was designed and tested on a shaking table under a series of earthquake excitations with increasing amplitudes. The results showed that the self-centering RC frame structure had desirable seismic performance with little damage even under extreme earthquakes. The reduction in natural frequencies were quite small after the extreme earthquakes, indicating that the structure had remained almost elastic. The test model showed a desirable tri-axial re-centering capability with negligible residual deformation. The sliding of the slabs was also measured throughout the tests, and the data indicated that the slabs re-centered to their original positions after the tests.

Comparison of Displacement Measurements in Exposed Type Column Base Using Piezoelectric Dynamic Sensors and Static Sensors

The Hyogo-ken Nanbu earthquake (Kobe earthquake) of January 17, 1995 caused extensive and severe damage to numerous Kobe city area buildings. After the earthquake, many steel structures were constructed using exposed-type column-base joints. Nevertheless, the capacity of these joints to absorb energy during earthquakes is small. For that reason, in the design of steel structures that use exposed-type column-base joints, it is believed that higher earthquake-resistant characteristics must be provided especially for joints of the first floor of a structure. Therefore, structural health monitoring is recommended. This paper presents the use of piezoelectric limit sensors to evaluate the resistance and displacement characteristics of exposed-type column-base using simple measurements.

Seismic performance of a controlled rocking reinforced concrete frame

A controlled rocking reinforced concrete frame is a new type of vibration control structure system that uses resilient rocking columns and joints. The effects of earthquakes on this type of structure are reduced by weakening the overall stiffness, whereas the lateral displacement is controlled by the energy-dissipation dampers introduced into the structure. Two tests were performed for research: the reversed cyclic loading test and shaking table test. Two single-span single-story controlled rocking reinforced concrete frames were designed for reversed cyclic loading tests. These tests (i.e. a column-base joint stiffness test, beam-column joint stiffness test, and frame stiffness test) were performed under different conditions. The mechanical analysis model of the rocking joints was derived from the test results. With the parameters obtained from the cyclic tests, a numerical simulation method that established the analytical model of the controlled rocking reinforced concrete frame using the program ABAQUS is proposed, and the dynamic time-history analysis results of the controlled rocking reinforced concrete frame and of the conventional approach are compared to investigate the vibration control effect and seismic performance of the controlled rocking reinforced concrete frame. In addition, the inter-story drift could be effectively controlled by adding metallic dampers, and the shaking table test models of the controlled rocking reinforced concrete frame with metallic dampers were designed and constructed. The comparison of the results of the numerical analysis and the shaking table test demonstrates that the model building of the controlled rocking reinforced concrete frame structure is efficient and that the controlled rocking reinforced concrete frame exhibits an excellent seismic performance.

Assessment of the seismic behaviour of braced steel storage racking systems by means of full scale push over tests

Pallet racking systems, made of thin-walled cold formed steel profiles, are commonly used to store valuable goods and products in the logistics industry. In service conditions, longitudinal (down-aisle) stability of the racks is provided by the flexural stiffness of the demountable beam-upright column connections and base joints. Rack designers usually prefer to avoid bracings for a full accessibility of shelves from both aisles. However, under seismic conditions, typical rack connections cannot often provide sufficient flexural performance in terms of stiffness and strength, which deems necessary to introduce spine (longitudinal) bracings in the down-aisle direction. Yet the racks can only be braced at one of their two longitudinal planes to allow pallet loading from the aisle, which results in an asymmetric horizontal bearing configuration. This combined with their perforated upright columns, and non-standard beam-upright and base connections make it even more difficult to estimate their complex global seismic performance. Therefore, full scale experimental investigations are strongly needed in order to understand and quantify the global performance of the braced storage racks, and improve their design for seismic actions.This paper presents the experimental results of the Europe's largest full-scale push-over testing program that has been carried out on racking systems. In particular, experimental global capacity curves of 6 fully-loaded pallet racking specimens with spine bracings, provided by 5 different international rack producers, are presented, discussing the key factors influencing the racks’ response, as well as the failure mechanisms of the different rack typologies. Furthermore, behaviour factor (q) values of each specimen are derived from re-analysis of test results. Vulnerability of braced racks to bracing connection failure is demonstrated, highlighting its causes. Design indications are provided in order to guarantee a globally homogenous ductility under seismic actions.

Shaking table test and numerical simulation of a 1/2‐scale self‐centering reinforced concrete frame

SummarySelf‐centering reinforced concrete frames are developed as an alternative of traditional seismic force‐resisting systems with better seismic performance and re‐centering capability. This paper presents an experimental and computational study on the seismic performance of self‐centering reinforced concrete frames. A 1/2‐scale model of a two‐story self‐centering reinforced concrete frame model was designed and tested on the shaking table in State Key Laboratory of Disaster Reduction in Civil Engineering at Tongji University to evaluate the seismic behavior of the structure. A structural analysis model, including detailed modeling of beam–column joints, column–base joints, and prestressed tendons, was constructed in the nonlinear dynamic modeling software OpenSEES. Agreements between test results and numerical solutions indicate that the designed reinforced concrete frame has satisfactory seismic performance and self‐centering capacity subjected to earthquakes; the self‐centering structures can undergo large rocking with minor residual displacement after the earthquake excitations; the proposed analysis procedure can be applied in simulating the seismic performance of self‐centering reinforced concrete frames. To achieve a more comprehensive evaluation on the performance of self‐centering structures, research on energy dissipation devices in the system is expected. Copyright © 2015 John Wiley & Sons, Ltd.

An experimental study on different socket base connections under cyclic loading

Abstract. This paper presents an experimental study on socket base connections of precast reinforced concrete columns. The main purpose of this study is to determine socket base connection which has the closest behavior to monolithic casted column-base joints. For this purpose, six specimens having different column-socket base connection details were tested under cyclic loading. For each test, strength, stiffness, ductility and drift ratios of the specimens were determined. Test results indicated that a suggested connection type is 10% - 30% stronger than the other type of connections under lateral loading. The welded connection (PC-5) had better lateral load carrying capacity and ductility. On the other hand, performance of standard connection (PC-1) which is commonly used in construction was weaker than other connections. Thus, decision of connection type should be referred not only performance but also applicability. Keywords: precast columns; socket base connection; cyclic loading; energy dissipations; stiffness degradation; displacement ductility

Full strength design of column base connections accounting for random material variability

The seismic design of moment resisting steel frames, classically, is carried out by adopting full strength joints. In this approach, the dissipation of the seismic input energy is obtained relying on the plastic hinges developed at beam ends and at the base of columns preventing from plasticization the elements composing the connections. Currently, the design of full strength joints can be led in the framework of Eurocode 8, which proposes to design joints adequately overstrengthened with respect to the flexural resistance of the connected beam/column. This overstrength depends on two factors: the first one accounting for the strain-hardening of the steel composing the beam/column, the second one depending on the materials’ random variability. In this work, the attention is focused on the evaluation of the accuracy of the code approach for the case of exposed column base plate joints. In order to reach this goal four steps are developed. First, a wide set of full strength column base joints is designed according to the component method codified in last version of EC3. Then, a Monte Carlo simulation accounting for the statistical distribution of the material composing the elements of the base plate (i.e. concrete, steel of plate, steel of anchors, steel of column) is set up and the accuracy of the approach provided by Eurocode 8 is analyzed. Finally, a criterion accounting for both the material random variability and the overstrength of the connected member due to the strain hardening is proposed and its accuracy is evaluated on the base of the collected statistical data.

Simplified Analysis Research on Ancient Chinese Timber Structure

In order to study the inherent characteristics and aseismic characteristics of ancient Chinese structure, according to the reconstruction engineering data of the embrasured watchtower on Yong-Ning Gateway of Xi'an City Wall, two finite element models (local and whole models of large timber frame of the embrasured watchtower are built by applying semi-rigid spring element to simulate the mortise-tenon joint, the bracket set and the plinth (that is column base) joint in the real timber structure. The first 10 natural frequencies as well as corresponding vibration modes of the structure are obtained using the method of Block-Lanczos. With full transient analysis, considering time history analysis of two models under the three earthquake excitations of the El-Centro wave, Taft wave and the Lan-Zhou artificial wave, the model displacement and acceleration time history curves were got. By comparing the two model’s basic modeling parameters as well as, the relative errors of the frequencies, the vibration modes, the excitation effects and, the feasibility of using the local model instead of the whole model in the structural analysis were to be discussed one by one. the results show that the local model can stand for the whole model for structural analyzing. Based on the results, the analysis methods and the relevant conclusions could be referenced to study the preservation and the rehabilitation of the ancient Chinese timber structures.

PRACTICAL MEASUREMENT STUDIES OF “HIKIMUN” FRAME IN AMAMI-OSHIMA

It is investigated about “Hikimun” frame that is building construction of traditional folk dwelling that remains in Amami-Oshima Kagoshima Prefecture.By the measurement survey of the folk dwelling in “Hikimun” frame in two houses of the in existence in Syodon village, we made up the plan and the framing elevation, and clarified details in the Capital joint and the Column base joint.