Concrete-filled Double Skin Steel Tubular Research Articles

Compressive behaviour and design of tapered lightweight concrete-filled double-skin stiffened steel tubular short columns with large hollow ratio

Tapered concrete-filled double-skin steel tubular (CFDST) members, due to their high strength-to-weight ratio and inherent spatial advantages, hold significant prospect in marine structures, such as ocean platforms and wind turbine tower. As the height and span of the column continue to increase, its weight and local buckling problems begin to emerge and become the main concerns of engineering design. To address this issue, lightweight concrete instead of normal concrete and tapered steel tubes with longitudinal stiffeners are adopted. As a result, a novel composite member, called tapered lightweight concrete-filled double-skin stiffened steel tubular short columns with large hollow ratio (LHRTL-CFDSST), is developed by the authors. In order to gain a more comprehensive understanding of the axial compression behavior of LHRTL-CFDSST members and provide an axial strength model, this study conducted axial compression tests on ten LHRTL-CFDSST short columns, investigating key parameters such as hollow ratio, longitudinal stiffeners and diameter-to-thickness ratio. The results indicated that both larger hollow ratio sections and diameter-to-thickness ratios tend to reduce the axial compressive strength and the ductility of such members, while the effect of the longitudinal stiffeners are opposite. Based on the test results, finite element (FE) model was developed and validated, and was then to conduct the mechanical analysis of the studied members, followed by a parametric study. Finally, a novel method for predicting the axial compressive strength of LHRTL-CFDSST short columns, applicable across a wide range of parameters, was proposed.

Research on hexagonal concrete-filled steel tubular transition pieces for wind turbine hybrid towers under axial compression

With the escalating height of wind turbine structures, wind turbine steel-concrete hybrid towers have gradually become a new type of structure to replace pure steel towers. As a component connecting the upper steel tower with the lower concrete tower, the transition piece assumes an indispensable role in the overall structure of the hybrid tower. The traditional reinforced concrete-type transition piece has necessitated enhancements owing to the complicated construction and concrete cracking problems. A hexagonal concrete-filled double skin steel tubular (CFDST) transition piece is proposed to fit the hexagonal steel-concrete hybrid tower. Studies that investigate the hexagonal CFDST structures are currently few. Based on this, three hexagonal CFDST stub columns were tested, with the variables in stiffened measures. The experimental portion included a thorough investigation of local buckling behaviors and failure modes in addition to the analysis of typical mechanical indexes. Further, the validated finite element (FE) model was then utilized for mechanism analysis about the contact stress between different interfaces, the stress distributions, and so on. Besides, a parametric study was done to identify the sensitive parameters affecting this kind of structure's peak loads. Ultimately, the peak load prediction formulas found in published studies and specifications were modified by incorporating the findings from this investigation.

Axial compressive behaviors of multi-cavity concrete-filled double-skin tubular stub columns

The axial compressive behaviors of multi-cavity concrete-filled double-skin steel tubular (MCFDST) stub columns are investigated using experimental and numerical methods in this study. The MCFDST columns comprise two concentric steel tubes (circular hollow section (CHS) inner and square hollow section (SHS) outer), sandwiched concrete filled between them, and four strips connecting outer and inner tubes. Fourteen MCFDST stub columns and two concrete-filled double-skin steel tubular (CFDST) (CHS inner and SHS outer) stub columns are fabricated and tested. Experimental results are used to validate the accuracy of finite element models of MCFDST and CFDST stub columns, and based on which, extensive parameter analyses are conducted. The analysis results show that the strips delay the local buckling and change the buckling mode of outer steel tube, as well as improve the bearing capacity and ductility of stub columns. Observed failure modes are controlled by the local buckling of the outer tube associated with the crushing of filled concrete. In addition, the axial compressive performance of MCFDST stub columns can be improved by reducing the width-to-thickness ratio of outer tube, increasing the steel yield strength of outer tube and concrete strength, and adding strips. The hollow ratio has a negligible effect on the axial compressive behaviors when it ranges from 0.26 to 0.56. Furthermore, the predicted results by European, Japanese, British, and Chinese codes are compared with the experimental and FE results, suggesting that the formula in the European code has the best accuracy when predicting the load-bearing capacity of MCFDST stub columns.

Experimental and theoretical investigation on residual bearing capacity of CFDST-T joints after lateral impact

This study investigates the residual performance of concrete-filled double-skin steel tubular (CFDST) T-joints after lateral impact. One hollow T-joint and five CFDST-T joints with various steel tube thickness and hollow rate were first tested by a pendulum machine. The axial compression test was subsequently performed to explore the residual performance in terms of failure mode, residual bearing capacity, ductility, energy dissipation, and strain evolution. Results indicated that the failure modes of the CFDST-T joint and hollow T-joint were characterized by global bending and severe local indentation, respectively. Besides, the CFDST-T joints exhibited the strongest residual bearing capacity with a hollow rate of 0.52 and the greatest ductility of 0.63. Moreover, increasing the outer tube thickness improved the residual bearing capacity and simultaneously reduced the ductility coefficient while the inner tube exerted little effect on residual performance. Simplified calculation formulas were finally derived to predict the impact residual deflection and residual bearing capacity of the CFDST-T joint based on parametric analysis. This study will provide a reference for future research to contribute to the design of more reasonable CFDST-T joints and promote their application.

Predicting axial compression capacity of CFDST columns and design optimization using advanced machine learning techniques

Concrete-filled double-skin steel tubular (CFDST) columns are fundamental in civil engineering, known for their exceptional mechanical properties. Their load-bearing capacity, influenced by factors such as geometry, material properties, and loading conditions, is a critical aspect of CFDST column design. This study introduces an innovative approach that leverages the synergy between gradient-boosting regression (GBR) and three metaheuristic optimization algorithms: sine-cosine-based swarm optimization (SCSO), grey wolf optimization combined with whale optimization (GWO_WOA), and artificial rabbits optimization (ARO). Its primary aim is to accurately predict the axial compression capacity (ACC) of CFDST columns for optimal design. Using a comprehensive database of 153 empirical results from CFDST columns subjected to axial loads, the proposed model is rigorously compared with eight alternative machine learning models, three established design standards, and two empirical equations to validate its robustness. The results highlight the superiority of the finely tuned GBR model, optimized with the ARO algorithm, over peer models and conventional benchmarks. This framework also serves as the foundation for optimizing the CFDST column design by identifying the optimal dimensions that maximize ACC while meeting the design constraints. Clearly, this model can significantly improve CFDST column design, thereby benefiting structural engineers and designers striving to enhance the safety and efficiency of CFDST structures.

A machine learning based interaction model to predict robustness of concrete-filled double skin steel tubular columns under fire condition

Concrete-filled double skin steel tubular (CFDST) column is a hollow composite structure component, which shows better performance than traditional reinforced concrete and steel columns due to the favorable composite action between steel and concrete. In the current study, a machine learning based interaction model combine with the extended Rankine method is developed to predict fire resistance of eccentrically loaded CFDST cylinder columns. The prediction of the reliable shear bond parameter was conducted by back propagation artificial neural network (BP-ANN) and Extreme Gradient Boosting Tree (XGBoost). To perform a reliable production, the architecture and the parametric setting of both models were constructed. Furthermore, the results of the prediction were verified by experimental results and finite element analysis. The results show that the proposed method can predict the behavior of the eccentrically load CFDST columns under fire attack with reasonable accuracy.

Machine learning models for predicting axial compressive capacity of circular CFDST columns

Machine learning (ML), widely recognized for its advanced predictive capabilities, is progressively being employed in structural design. Concrete-filled double skin steel tubular (CFDST) members are extensively utilized due to their exceptional mechanical behavior. However, existing formulas encounter challenges in accurately calculating the axial compressive capacity of circular CFDST members, particularly when high-strength concrete and steel materials are involved, leading to complexity and low accuracy. This paper presents a data-driven framework that leverages the superior predictive performance of machine learning approaches to predict the axial compressive capacity of circular CFDST columns. Finite element models are developed through secondary development of ABAQUS using custom script, which are then validated against experimental data, confirming their effectiveness and applicability. A general database is established, comprising 226 test results and 550 finite element results obtained from the script, to facilitate the prediction of axial compressive capacity for circular CFDST columns. By incorporating the physical mechanisms of CFDST members and conducting correlation analysis, the input parameters for the machine learning models are determined. Decision Tree, Artificial Neural Network (ANN), K-nearest neighbor (KNN) and two ensemble methods including Random Forest, XGBoost, are trained and optimized using the database to provide accurate predictions. The results demonstrate that the KNN model exhibits superior performance and high accuracy, outperforming the four commonly used calculation formulas in the field, particularly for circular CFDST columns using high-strength materials. The proposed data-driven framework shows promising potential for achieving outstanding predictive performance.

Hysteretic performance of circular high-strength concrete-filled double skin steel tubular columns: Experiment

In marine structures, utilizing high-strength materials in concrete-filled double skin steel tubular (CFDST) members can provide an optimized solution upon the tendency of light self-weight and high performance. The cyclic load in the marine environment usually determines the safety margin for whole offshore structures. Therefore, this paper experimentally investigated the hysteretic performance of circular high-strength concrete-filled double skin steel tubular (HCFDST) columns with out-of-code diameter-to-thickness ratios. The typical failure mode appeared with the infill material crushing, steel fracture and local buckling of outer tubes. Subsequently, the detailed analysis of hysteretic curves, skeleton curves and ductility, energy dissipation, stiffness degradation, and lateral force reduction was conducted to reflect the influences of hollow ratios, axial compression ratios, and infill types, e.g., increasing the hollow ratio from 0.54 to 0.68 and 0.82, respectively reduced the bearing capacity by 6.25% and 11.20%, and the ductility coefficient had an apparent decrease of 19.27% and 26.61%. The out-of-code HCFDST columns with reasonable design could behave with favorable hysteretic performance. A theoretical model considering the tensile strength effect of engineered cementitious composite (ECC) was finally established and verified to predict the moment-resisting capacity of HCFDST columns using ECC. The reported research on HCFDST columns can provide significant references to marine structure applications.

Research on the Concrete-Filled Double Skin steel Tubular (CFDST) columns subjected to axial force after fire

This article investigates the structural performance of Concrete-Filled Double Skin Steel Tubular (CFDST) columns after fire under the axial compress. 13 experiments were conducted on the residual bearing capacity of CFDST columns under axial compression after different fire duration time. The variation parameters included the hollow ratio, fire duration time and strength of concrete. The effect of different parameters on the axial load and displacement changes after fire was revealed. The experimental and finite element simulation results were compared and analyzed, and they were in good agreement. The results indicate that CFDST columns have good fire resistance, and the strength of concrete has little effect on the residual bearing capacity of CFDST columns after the fire. With the increase of hollow ratio from 0 to 0.72, the axial residual bearing capacity of CFDST columns increases first and then decreases after the same fire duration time. Compared with the column without initial load, the residual bearing capacity of CFDST columns will increase with an initial load before fire, but different initial loads have no significant impact on the ultimate bearing capacity after fire.

Experimental and numerical investigation on strengthening mechanism of rib-reinforced round-over-round RCFDST column jointed with steel beam under cyclic loading

This paper involved both experimental and numerical investigations on the behaviour of twelve types of recycled-concrete filled double-skin steel tubular (RCFDST) structures subjected to the cyclic loading with reinforced ribs at the column–steel beam joints, of which the damage pattern and seismic performance were analysed by varying the ratio of beam–column flexural linear stiffness, axial compression ratio, hollow ratio, type and strength of the concrete, and the length of ribs. The results indicate that the specimens primarily exhibited the damage pattern of the plastic hinge at both ends of the beams, and that the horizontal load–displacement hysteresis curves with full loop at the top of the column were observed. Moreover, the structures composed of recycled concrete from 40 MPa to 60 MPa presented no reduction in ultimate load as well as the joint ductility to those of the ones with normal concrete. Regarding the performance of RCFDST, the optimal ratio of beam–column flexural line stiffness (ki) is found in the range of 1.0 to 1.5. This study demonstrated that the recycled concrete made from the industrialized aggregate formed by crushing waste concrete from road bases has potential application prospects in Concrete-filled double skin steel tubular (CFDST) structures due to its low cost and good seismic performance, including high ultimate load capacity and low energy consumption.

Hysteretic energy distribution model of CFDST composite frame with metallic dampers using coupled shear-flexural beam model

Novel steel–concrete composite structures have drawn increasingly attention in recent years especially in high-rise buildings owing to its superior structural performance over conventional concrete and steel structures. Moreover, energy dissipation devices such as metallic dampers and buckling-restrained braces (BRB) were necessarily added in this type of structure to resist seismic loads. However, the existing research regarding to the dual system consisting of composite frame and energy dissipation was limited. In this paper, the dual system consisting of concrete-filled double skin steel tubular (CFDST) composite frame and metallic damper was set as the research subject, especially focusing on the analysis of hysteretic energy distribution along the height. The 10- and 20-story dual systems were designed with different parameters revealing the influence of semi-rigid connection and metallic damper. Nonlinear models of structures established by Opensees software were validated by the test results. Afterwards, the energy distributions of all stories were discussed. It demonstrated that the metallic damper could absorb considerable energy under seismic loads while a semi-rigid connection with relatively high moment strength had a detrimental effect on the column. Moreover, the semi-rigid connection in the span without metallic damper in high story exhibited significantly larger rotation than that in the span with metallic damper. Finally, the method to estimate the energy distribution estimation of the dual system was developed, in which the lateral displacement pattern was observed by the coupled shear-flexural beam model to fully consider the flexural deformation of the dual system. An equivalent distribution of the shear and bending stiffness was also proposed considering the effect of the semi-rigid in the span without metallic damper. The predicted results from the model were validated by the analysis results derived from the nonlinear model. The theoretical and analytical results of the paper could activate the application of the dual system and provide a reasonable method to estimate the hysteretic energy distribution of the dual system.

Influence of anchored orbicular rings on the performance of sandwich concrete‐filled double‐skin steel tube columns

AbstractSince recent years, double‐skin tube column sections formed from two parallel, concentrically spaced steel casings, with the sandwiched area between the casings packed with concrete infill, have been employed extensively. The cross‐sectional shapes of the inner and outer casings might be the same or different, such as round, square, octagonal, etc. These concrete‐filled double‐skin steel tubular (CFDST) columns act similarly to concrete‐filled steel tubular (CFST) sections but have less self‐weight and better stiffness. The present study evaluated the response of CFDST column stiffened with orbicular rings under axial compression. It consists of inner and outer steel tubes stiffened by orbicular rings near both ends of columns. The orbicular rings were provided at different locations as L/3, L/4, and L/5, and a series of tests were conducted to obtain the performance of CFDST columns stiffened with orbicular rings with regard to the maximum load‐carrying capacity, load–strain behavior, and load‐deformation behavior. Furthermore, a parametric study was conducted by varying the diameter to thickness ratio, hollowness ratio, the thickness of orbicular rings, yield strength, and location of orbicular rings. The results showed that CFDST column stiffened with orbicular rings have higher ultimate load capacity than unstiffened CFDST. Stiffened CFDST with orbicular rings showed more ductile response than CFDST column and helps to improve the outer steel tube's restraint on sandwiched concrete. In order to estimate the load‐bearing capacity of CFDST columns stiffened with orbicular rings under axial compression, an empirical equation was proposed. The experimental results and findings of the suggested equations were found to be in good agreement.

Compressive–Flexural Failure Mechanism and Bearing Capacity Calculation of Over-Ranging Tapered CFDST Members for Support Structures of Offshore Wind Turbines

Upon the higher requirement on high-performance structures of large-scale supporting structures of offshore wind turbines, the systematic analysis on the compressive-flexural behavior and ultimate bearing capacity of tapered concrete-filled double skin steel tubular (CFDST) members designed by over-ranging parameters was performed. Investigating the entire-process mechanism, e.g., the moment–deformation response, stress development, interaction stress, and subassembly contribution, was based on the finite element (FE) analysis, where the moment–deformation curve can be distinguished by four characteristic points, and the transverse local buckling of outer tube partly weakens distribution height of interface pressure in compression zone compared to that in tension zone. Influences of material strengths and geometric parameters were examined by the parametric study, e.g., increasing tapered angle (ψ) slightly reduces the bearing capacity; the higher axial compression ratio (n) contributes a noteworthy action on the post-peak behavior and carrying capacity, e.g., the bearing capacities at n = 0.9 and n = 0.5 reduce by 64.14% and 18.44% compared to capacity at n = 0.1, respectively; influence of Do/to ratio is more significant than Di/ti ratio. Subsequently, the modified cross-sectional stress integration (CSI) method was proposed to predict the moment–strain (M-ε) curves of tapered CFDST members; meanwhile, a confined concrete model with transverse confinement stress as an explicit parameter was modified, and influences of different confined concrete models on predicting M-ε curves were compared. Finally, design methods based on the modified CSI method and limit state method were proposed as a simplified calculation method to determine the correlative relationship of axial compressive strength and moment-resisting capacity (N-M curve).

Shaking table test on seismic behavior of posttensioned precast segmental Concrete-Filled double skin steel tubular piers

Posttensioned precast segmental bridge piers have proven to be an attractive solution for accelerated bridge construction and seismic resilience. Although extensive research efforts have been made to understand the seismic performance of such piers under quasi-static loading and unidirectional/bidirectional ground motions, there is limited information available regarding to their dynamic behavior when subjected to tri-directional ground motions. Therefore, this study performed shaking table tests on an innovative posttensioned precast segmental concrete-filled double skin steel tubular (CFDST) pier to explore its seismic behavior under a set of tridirectionally applied far-field ground motions. A total of six 1/5 scaled piers were investigated with different design details, including one monolithic pier as reference, two posttensioned precast segmental piers without internal energy-dissipating (ED) bars but different amounts of prestressing tendons, and three posttensioned precast segmental piers with different amounts of ED bars. It has found that the relative displacement responses decreased with increase in amounts of prestressing tendons or ED bars. The segmental piers without ED bars twisted obviously when PGA reached 0.3 g under tri-directional ground motion excitations, while the segmental piers with ED bars did not due to additional shear resistance across joints provided by ED bars. Moreover, the dynamic responses of segmental piers with and without vertical ground motion excitation were compared in details to investigate the effect of vertical ground motion on their seismic behavior. It has found that the change in vertical acceleration response due to vertical ground motion excitation was a significant importance compared to the change in lateral accelerations, relative displacements and tendon force increment. In consequence, the axial compressive force as well as shear resistance across joint provided by dead load reduced by almost 33% due to appearance of vertical ground motion at the PGA of 0.7 g.

Comparative Study on Behavior of Circular Axially Loaded CFDST Short Columns under Different Loading Arrangements

So far, almost all studies have concentrated on the compressive performance of fully loaded concrete-filled double-skin steel tubular (CFDST) columns, but there have been few studies on partially loaded CFDST columns, and the difference in their behavior remains unclear. Thus, by focusing on the mechanical behavior of circular CFDST columns under different loading arrangements, this paper conducts a comparative study on circular axially loaded CFDST columns based on the author’s previous experimental results. A total of 28 experiments were conducted, in which 14 fully and 14 partially loaded specimens were tested. The influence law of crucial parameters on the compressive behavior of CFDST specimens with two different loading arrangements were compared and the results were discussed. It is shown that when the void ratio is 0 and 0.2, the ultimate strength of partially loaded CFDST columns is greater than that of fully loaded ones, but the results are opposite for the columns with the void ratios of 0.4 and 0.6. Subsequently, based on the experimental data, a finite element analysis (FEA) model was developed and used to ascertain the compressive behavior of CFDST columns with two different loading arrangements. The results suggested that, at the beginning of the loading phase, the outer tube of partially loaded CFDST columns provided a certain lateral confining stress to the concrete, while the lateral confining stress of fully loaded CFDST columns fluctuated around zero. The axial load of the inner tube of fully loaded CFDST columns first increased linearly and then remained almost unchanged. Due to the existence of friction, the inner tube of partially loaded CFDST columns also undertook a certain axial load, which first increased and then decreased to zero.

A REVIEW ON CONCRETE FILLED DOUBLE SKIN STEEL TUBULAR COLUMNS

Concrete-filled double-skin steel tubular (CFDST) Columns considered as a new type of Concrete Filled Steel Tubular (CFST) Columns. It consists of an inner and outer steel tube with the annulus between the skins filled with concrete. The concrete is properly compacted and filled in between the steel surfaces. CFDST are high performance composite columns that are increasingly being used in bridges and high-rise buildings as well as to reinforce CFST columns. CFDST has many advantages over CFST such as improved stability, section modulus, lighter weight and better damping characteristics. The inner tube increases their strength and ductility as compared to CFST. The hollow steel tubes can be chosen with any type of cross section, commonly circular and square tubes are preferred.

Analytical behavior and bearing capacity research on out-of-code tapered CFDST members under pure torsion and compression-torsion combination

Facing the apparent enhancement of rated power of offshore wind turbines, the increasing rotor diameter and blade length gradually pose severe challenges to its support structure for resisting extreme loads. Due to the remarkable composite effect, the recently developed tapered concrete-filled double skin steel tubular (CFDST) members can provide a high-performance structural type and competitive application prospect compared to traditional steel tower barrels. Therefore, this paper conducted the numerical and theoretical research on out-of-code tapered CFDST members under pure torsion and compression-torsion combination. The finite element (FE) model was established to examine the full-range mechanism including torque versus deformation response (T-θ curve), interaction behavior and component contribution, indicating that four characteristic points can distinguish the T-θ curve under pure torsion, and slight contact pressure between the inner tube and sandwich concrete exists along the height direction. The parametric study was performed to investigate the influences of geometric-physical parameters, e.g., by increasing tapered angle (ψ) 0.2°, the torsional capacity obtains a reduction of 5%; hollow ratios (χ), axial compression ratios, and diameter-to-thickness (D/t) ratios of double-skin tubes obviously affect the torsion resistance; altering steel yield grade influences torsional capacity than concrete grade. Subsequently, a theoretical multilayered cylinder model as the simplified design tool was proposed to simulate full-range T-θ curves of tapered CFDST members. Moreover, a modified design method for calculating N-T correlation curve was developed and validated by introducing the refined equations of pure torsion resistance (Tu), where the design methods in current codes displayed a quite conservative prediction for tapered CFDST members with out-of-code parameters (e.g., hollow ratios or D/t ratios). The above research on out-of-code tapered CFDST members can offer valuable design guidelines for its engineering applications.

Experimental study on torsional behavior of tapered high strength thin-walled concrete-filled double-skin steel tubular columns

Comparing with traditional straight concrete-filled double-skin steel tubular (CFDST) members, tapered CFDST members have been increasingly used in the domain of power industry due to esthetics and special spatial experience. In addition, the utilization of high strength materials can reduce cross-sectional area and further lower construction cost. In this paper, the torsional behavior of tapered high-strength thin-walled CFDST (THSTW-CFDST) columns with or without longitudinal stiffeners was investigated and a total of twenty tapered THSTW-CFDST specimens were tested. The failure modes, torque-torsional angle curves and torsional capacity of the THSTW-CFDST columns were investigated. The results demonstrate that the installation of stiffeners can significantly improve the local stability of thin-walled steel tubes, but reduce the torsional capacity of the members. Compared with THSTW-CFDST specimens without stiffeners, the torsional capacities of those with stiffeners have been apparently reduced. Based on the experimental results, the finite element (FE) model was developed and verified, and then utilized to ascertain the force-transfer mechanism and the stress development process of each component of THSTW-CFDST columns. In addition, the effects of the various parameters including hollow ratio, diameter-to-thickness ratio, inner steel tube strength to outer steel tube strength ratio, concrete strength the torsional behavior of THSTW-CFDST members were quantitatively assessed. Finally, the accuracy of the existing methods for predicting the torsional capacity of THSTW-CFDST members was evaluated.

Hybrid simulation test and seismic assessment of CFDST moment resisting frame

Concrete filled double skin steel tubular (CFDST) moment resisting frame is an effective structural system owing to the higher strength to weight ratio and better fire performance compared with traditional concrete filled steel tubular (CFST) structures. This paper aims to analyze the seismic response of assembled CFDST moment resisting frame with blind bolted joints by the hybrid simulation test and numerical approaches. A prototype CFDST moment resisting frame was designed and its numerical model was established by Opensees software. After the validation of the numerical model, typical failure modes and dynamic response of the CFDST moment resisting frame observed from the hybrid simulation test were detected and discussed under maximum-considered earthquake (MCE) and 2MCE levels (2 times MCE level), respectively. Detailed behavior of the columns and joints were analyzed for the prototype building. It verified that a large portion of energy was dissipated by the joints under seismic loads. Subsequently, parametric analyses were performed to study the influence of joint stiffness on the global behavior of CFDST moment resisting frames by the endurance time method. The energy dissipated by the columns and joints were investigated in detail, indicating that the energy dissipated by the joints was more than 70% of the total hysteretic energy of the frame under earthquakes. It indicated that decreasing the joint stiffness was beneficial for the joint to dissipate more energy and for protecting the column from being damaged. It also generalized that decreasing the joint stiffness had a positive contribution to the uniform story drift distribution and would not always increase the maximum story drift. The analysis results verified that the CFDST moment resisting frame exhibited excellent seismic behavior and activated the application of CFDST moment resisting in engineering practice.

Experimental and numerical investigation on hysteretic behavior of posttensioned precast segmental Concrete-filled double skin steel tubular piers

The posttensioned precast segmental concrete-filled double skin steel tubular (CFDST) piers proposed in this study combines the advantages of posttensioned precast segmental piers and composite CFDST piers, in such way to reduce on-site construction burdens, increase section modulus, and reduce self-weight. To investigate the hysteretic behavior of this new type of bridge pier, one posttensioned precast segmental CFDST pier was designed and tested under cyclic lateral loading, with one cast-in-place CFDST pier as reference. Test results show that the proposed posttensioned precast segmental pier performs well with good ductility, satisfactory energy dissipation, and small residual displacement. The damage to precast segments is effectively avoided by using CFDST members. Moreover, a numerical study was also conducted to investigate the influences of different design parameters on the hysteretic behavior of posttensioned precast segmental CFDST piers. The design parameters studied in this paper included the pier aspect ratio, amount of energy-dissipating (ED) bars, axial load ratio due to gravity, axial load ratio due to prestressing force, initial stress level in prestressing strands and CFDST cross-sectional parameters. It has been found that the amount of ED bars, axial load ratio due to gravity and axial load ratio due to prestressing force are the more important factors on energy dissipation and self-centering capacities. The pier aspect ratio being greater than 7 has a negative effect on residual drift ratio of posttensioned precast segmental CFDST piers due to P-Δ effect. The initial stress level in prestressing strands has little effect on energy dissipation and self-centering capacity, but influences the failure mode and deformation capacity.