Double Skin Research Articles

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.

Cyclic test evaluation of double skin composite hybrid coupled wall with frictional steel truss coupling beams

The seismic performance of double skin composite shear walls (DSCSWs) has significant superior to conventional reinforce concrete (RC) shear walls. Previous studies have neglected the changes of axial compressive forces and bending moments actting on the top of wall piers. In addition, behaviors hybrid coupled wall (HCW) under real boundary condition have not been fully investigated. Thus, in this study, a novel quasi-static test which incorporates the boundary conditions of substructures in a prototype building was preformed. And a cyclic test was carried out on a 2/3-scaled double skin composite (DSC) HCW with frictional steel truss coupling beams (FSTCBs) using the proposed method. The seismic behavior of specimen under reversed lateral cyclic loads was investigated. The failure modes of the wall piers mainly included local buckling of the steel faceplate, fracture of the side plate, and concrete crushing at the corners of walls. The force-displacement hysteresis curve of FSTCBs was obtainable from the attached instruments as the force transmission path of the steel truss could be clearly observed. DSCSW pier deformation was evaluated based on the deformative relationship between the wall pier and FSTCB. The FSTCB primarily dissipated 80% of the total energy input prior to damage occurring in the DSCSW. Strain distribution curves along the DSCSW showed that the pre-peak-resistance plane section assumption was still valid.

Axial compression behaviour of concrete filled double skin steel tube columns anchored with orbicular rings: Experimental and numerical approach

Double-skin tube column sections have been used extensively in recent years. These sections are composed of two adjacent, coaxially spaced steel casings, and the space in the middle of them is occupied with concrete. These CFDST columns behave similarly to CFST sections but are more rigid and have a lesser self-weight. The behavior of a novel type of CFDST column, the orbicular anchored CFDST column, was assessed under axial compression in the current research. It comprises an inside and an outside steel tube with orbicular rings near the ends of the columns. The orbicular rings were positioned at various spots such as [Formula: see text] and [Formula: see text] and a wide range of tests were accomplished to evaluate the functionality of orbicular anchored CFDST columns in respect of maximum load-bearing capability, load-strain behavior, and load-deformation behavior. A FE model was developed and its accuracy was authenticated by comparing its findings with experimental results. Furthermore, a parametric investigation was carried out employing the authenticated FE model to examine the functioning of the proposed CFDST to variations in orbicular position, cross-sectional dimensions of rings, yield strength of orbicular ring, etc. The outcomes of the study indicated that orbicular anchored CFDST columns had 15% higher ultimate load capacity than unstiffened counterparts. The orbicular anchorage improved the ductile response and increased the axial stiffness of the CFDST column. Further, it was concluded that orbicular rings enhanced the constraining effect of external steel casing on sandwiched concrete and improved the composite action of CFDST specimens. The design formula to ascertain the load-bearing ability of columns was also developed and can be employed amid preliminary designs of proposed column sections.

Naturally ventilated folded double-skin façade (DSF) for PV integration - Geometry evaluation via thermal performance investigation

Studying the thermal performance of Double Skin Facades (DSFs) with vertical layers has dominated the literature, however, there is still a lack of in-depth research on the performance of DSFs with atypical geometries such as folded cases which can be applied to Building Integrated Photovoltaic (BIPV) systems to improve their performance. To this end, the study evaluates the influence of the fold geometry on heat transfer, flow structure, and airflow rate in the Folded DSF cavities under a hot climate in Iran using an efficient method titled “patching”; the method integrates Soltrace3 with a 2D steady-state CFD model by ANSYS-Fluent. The results show that the fold position and its depth can alter the DSFs performance significantly; the higher the fold depth the more distortion of the flow field inside the cavity; from a practical perspective, the fold position in the upper part of the cavity is suitable for BIPVs application since it can capture 250% higher amount of solar radiation compared to a conventional vertical-layer DSF as the Base Case; the net heat gain through outer layer could improve with increase of fold depth and reach at least 33% higher than the Base Case, meanwhile, the total electricity generation potential of folded cases could be up to 169% higher than the Base Case; thus, the study proved that if the architectural design is of interest, it is highly recommended to consider folded DSFs as a design option.

Retrofit strategies to mitigate overheating linking urban climate modeling and urban building simulations with outdoor comfort. An urban sector in Malaga (Spain)

This work evaluates the cooling effect of retrofit strategies on urban buildings and outdoor comfort in an urban sector in Málaga on one of the hottest days. The methodology links urban climate modeling and urban building simulations with outdoor comfort. The solar reflectance (SR) of roofs, urban surfaces and green areas and their forestation increases after the retrofit. Only the SR façade remains the same, be it in the current or the retrofit scenarios: 0.3. Both façade retrofit strategies consist of an opaque double skin façade (ODSF) with ceramic or metal tiles. Energy cooling is reduced by 52.51% with ceramic and by 52.57% with metal ODSF while urban comfort improves after retrofit: Universal Thermal Comfort Index (UTCI) decreases by 0.62 °C and Mean Radiant Temperature (MRT) decreases by 2.58 °C. Simultaneously, seven points at the pedestrian level assess outdoor comfort in different urban canyons. UTCI decreases more with the metal than with the ODSF ceramic. Regardless the canyon height, the width ratio or the orientation, the UTCI decreases between 2.45 °C and 4.86 °C when under a tree and it decreases more as S/N canyons narrow. This methodology and insights help stakeholders, designers, planners, and policy-makers make data-driven decisions to mitigate overheating and UHI in Mediterranean cities with similar urban building and canyon morphology.

Improving aerodynamic response of tall buildings using smart morphing facades

Slender buildings are prone to vortex-induced vibrations and turbulence-induced buffeting. Usually, vortex-induced vibrations govern the strength and serviceability design criteria. The building's shape determines the aerodynamics of it; therefore, optimizing building shape can greatly reduce wind-induced vibrations. With a growing industry in adaptive and double-skin facades—mainly for energy saving purposes—there is an opportunity to innovate and implement smart, morphing facade modules (which we refer as Smorphacades) that actively modify their aerodynamic shape to alleviate flow-induced vibrations during high winds. This paper evaluates the performance of a 44-story tall building with the different configurations of the developed Smorphacade module system in mitigating building vibrations. Dynamic nonlinear time history analysis of the building under varying wind speeds ranging between 35 and 75 m/s are performed to evaluate the performance of building equipped with Smorphacade at low and high wind speeds. The performance measures chosen in the study are displacements and accelerations. Structural responses of building equipped with Smorphacade are compared against the bare building model responses to evaluate improvements in performance. Acceleration response comparisons at lower wind speeds provide insights into Smorphacade contributions to improving occupant comfort. Displacement comparisons at high wind speeds help understand the improvements in overall structural performance by reducing nonlinear response.

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 study and numerical analysis on the dynamic response of steel tube confined concrete with a circular hollow section (STCC-CHS) under transverse impact loading

The dynamic response to lateral impact of steel tube confined concrete with a circular hollow section (STCCCHS) was investigated via pendulum impact tests in the laboratory. Nine STCCCHS columns and two concrete-filled double skin steel tubes (CFDST) were tested under lateral impact. The hollow ratio, the thickness of the outer steel tube, the impact height, and axial load ratio were varied. The failure pattern was observed along with the time histories of the impact force and the mid-span deflection. Strain development in the outer steel tube was quantified. The failure mechanism was integral bending and local buckling under lateral impact. Increasing the outer wall thickness and adopting an appropriate hollow ratio can effectively improve the impact resistance of such columns. Changes in impact energy have a significant influence on the plastic deformation of the members. Modest axial loading has little effect on the impact resistance. The test results were used to tune a finite element simulation of the process. A whole dynamic response investigation of STCCCHS columns under impact loads was carried out, and compared with the impact resistance of CFDST columns.

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.

Experimental investigation on the operation performance of photovoltaic double skin façade in winter

Photovoltaic double skin façade (PV-DSF) offers a versatile solution to address the escalating energy demands of buildings by combining power generation and indoor air temperature adjustment functionalities. Most prior research concentrated on its summer performance, while the winter season receives less attention. This paper concentrates on its operation performance in winter, to provide an experimental framework for its efficient operation. In this regard, the performance of internal circle and thermal buffer mode (both are possible operation modes in winter) were compared via control variable experiments, and the feasibility of mechanical ventilation is also examined regarding the trade-off between the energy consumption of fans and additional energy benefit. These experiments were performed in the full-size experiment rig at Harbin, China, a city with severe cold climate. The experiment results conclusively demonstrate that the internal circle mode can outperform the thermal buffer mode on a cold, sunny day by 10.9%, and the total energy-saving potential can be further increased by 12.6% if fans are activated to enhance cavity airflow. While the experimental data during partly cloudy emphasizes the significance of a suitable operation schedule and shows that PV-DSF can only be switched to internal circle mode when cavity air is fully heated.

Management of complications after skin surgery relevant for melanoma in the trunk and extremities during the COVID-19 pandemic: a case series report

BackgroundPatients with melanoma have been found to be at greater risk of adverse outcomes including mortality after contacting COVID-19. Management of postsurgical complications presented additional challenges by potentially increasing exposure to COVID-19 through repeated inpatient admissions to hospital during the pandemic. We report four cases for which skin flaps, lymph ligation, and split-thickness skin graft (STSG) were successfully used in the treatment of complications in the trunk and extremities after wide local excision (WLE). This study details the operative experience in management of postsurgical complications for melanoma in the trunk and extremities during a 6-month period at the height of the COVID-19 pandemic.Case presentationWe present 4 cases detailing management of complications that occurred after wide local excisions performed for melanoma during Feb. to Oct. 2020. Case 1: A 90-year-old man who experienced wound dehiscence and necrosis on the shoulder after non-radical excision for an aggressive melanoma and underwent the side-to-side closure after ellipse formed WLE with modified tangent-to-circle method. Case 2: An 80-year-old man who had undergone excision for melanoma in his left upper arm and histopathology did not show radically. Two weeks after the excision, he underwent a WLE and direct reconstruction with double rotation skin flap. Case 3: A 55-year-old man that experienced a large wound dehiscence on his back due to WLE. He underwent an advanced double skin flap operation. Case 4: A 36-year-old woman who had a lymphorrhea and graft necrosis after WLE and STSG on the right lower leg. A combination of micro lymph ligation and re-STSG was performed. One month after the operation, all wounds had healed. There was no clinical evidence of tumor recurrence after 8 months post procedure.ConclusionsSevere complications (e.g., large wound dehiscence, necrosis, or lymphorrhea) following wide local excision of melanoma are infrequent but must be swiftly and appropriately managed, especially during the COVID-19 pandemic to decrease the likelihood of COVID-19 infection and impaired oncology outcomes from delaying systemic cancer therapy due to the complications in primary interventions.

Analytical model for axially compressed circular concrete-filled double skin steel tubes (CFDSTs): Insights from concrete non-uniformly confined states

Concrete-filled double skin steel tube (CFDST) is becoming a competitive structural concept in deep-sea and deep-ground engineering structures. However, the passive non-uniform confinement of the sandwiched concrete needs to be further clarified and quantitatively described to achieve better design efficiency of CFDSTs in sophisticated application scenarios. This investigation suggests a development approach for the analytical model of the axially compressed circular CFDSTs considering the non-uniform confinement effect. The strength and deformation characteristics of the concrete subjected to constant lateral stresses have been first systematically analyzed through the extensively collected experimental database, and the corresponding constitutive models have been formulated accordingly. The stress distributions of the sandwiched concrete and the influence of the cross-sectional geometric properties have been discussed, and then the calculation method for the non-uniform confining factor has been developed. An efficient analytical model has been established on the basis of an incremental-iterative procedure, with the steel tube-concrete interaction and bonding behavior appropriately considered. The proposed analytical model has been verified through the widely collected experimental data of axially compressed CFDSTs, and the results show that it could effectively simulate the full-range axial load–strain curves and improve the prediction accuracy of ultimate loads by about 5% to 16% compared with the existing design formulas.

Innovative bio‐based steel envelope systems

AbstractThe INCSEB project is aimed at developing 5 ultra‐low carbon envelope systems made in steel and that incorporate innovative use of wood fiber insulation. The systems under development are: 3 sandwich panels (cladding, pitch & flat roofing), 2 claddings (double skin & façade with plank). INCSEB includes tests to study various behaviors: mechanical, fire, thermal calculation, acoustic insulation, air/water/vapor permeability. Interpretation and classification reports will be done for each type of test. 2 full scale prototypes will allow to estimate the durability in real life conditions. LCA indicators and comparison of carbon footprint (GWP) to conventional systems based on a real office building will be provided. An economic study of the projected price of the 5 systems compared to existing conventional systems is also planned. Besides, as far as the production of innovative panels is concerned, it appears that they can be integrated in current production lines. Finally, actions to facilitate the dissemination of results and industrial application will be organized: drafts of design and installation guides, publications, submission of 3 amendments to relevant EN standardization committees, workshop, BIM objects. Lastly, the manufacturers plan to apply for patents protection.

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.

Optimizing Energy Efficiency in High-Rise Residential Buildings in Abu Dhabi’s Hot Climate: Exploring the Potential of Double Skin Façades

This study investigates energy efficiency in high-rise residential buildings in Abu Dhabi, where the increased use of glass building façades has led to increased air-conditioning costs due to heat gain. The research focuses on evaluating the type of glass and the appropriate cavity between glass façades to minimize energy consumption while incorporating sustainability and innovative design principles. To achieve these objectives, this study employs a Double Skin Façade (DSF), a high-performance façade that adapts to the external climate conditions to fulfill internal cooling load requirements and meet occupants’ needs. Data were collected through an online survey distributed among residents of a selected residential tower, and a combination of qualitative and quantitative approaches was utilized to analyze the gathered information. The selected case study was analyzed using Energy Plus simulation software using the existing data and available details. The analysis aimed to identify the optimal DSF design that significantly enhances energy efficiency. The findings of this study emphasize the substantial impact of the optimum DSF design on energy efficiency in high-rise residential buildings. Through modeling existing data and comparing them with new model results for each variable, this study demonstrates that a DSF with a 35 cm cavity, comprising a double-glazed single skin layer in the interior and a Low-E double-glazed single skin layer as an outer layer, can reduce overall air-conditioning energy consumption by over 25%. These outcomes provide valuable insights into implementing DSF as a solution to address the unique energy challenges presented by high-rise residential buildings in hot climates.

Double Skin Façade Mechanical Systems as Ad-vanced Building Technologies

The double-wall façades (or “double skin façades”) are deter-mined as building mechanical and engineered systems realized by the cavity between the inner curtain and the outer screen, for thermal and acoustic insulation, for ventilation and for the inser-tion of functional devices (such as sunscreens) and, also, plant ducts. The cavity between the two enclosures constitutes a venti-lated cavity that can be used according to certain modes of func-tioning (passive or active type) aimed at controlling external cli-matic and environmental stresses in order to regulate the condi-tions of the interior spaces. The double envelope system is real-ized as an apparatus of mediation and reaction towards envi-ronmental loads, according to the needs of well-being and reduc-tion of energy consumption. In general, the system offers the functioning in the form of a passive solar system, assuming the use and accumulation of solar radiation for the regulation of indoor thermal comfort conditions, and the functioning for the capture and input of air flows. The calibration of solar radiation is integrated with the use of shading devices in order to achieve diffuse lighting conditions in interior spaces. In addition, the application of the double glass surface reduces thermal losses from the interior spaces by reducing the speed of the airflow in contact with the inner curtain, increasing thermal insulation. The system foresees that the ventilated cavity performs various inte-grated functions (for the definition of complex mechanisms of dynamic interaction with the external climatic conditions), both permanent (e.g. for the increase of thermal inertia and acoustic insulation relative to the internal curtain) and temporary (e.g. for the cooling of the same spaces during periods of high tempera-ture).

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.

Numerical study of seismic performance of steel-concrete composite rigid-frame bridge with precast segmental CFDST piers crossing fault-rupture zones

Although seismic performance of bridges crossing fault-rupture zones has been studied in recent two decades, there is still no effective solution to mitigate the hazard of fault-crossing effect. Recently, a new type of post-tensioned precast segmental (PTPS) concrete-filled double skin steel tube (CFDST), known as PTPS-CFDST column, has been proposed and verified to exhibit excellent performance with respect to seismic resilience. Moreover, PTPS-CFDST columns can accommodate torsional deformation through joint slip and are thus considered as a promising structural solution for bridges crossing fault-rupture zones. This study aims to investigate the performance of a steel–concrete composite rigid-frame bridge (SCCRFB) with PTPS-CFDST piers subjected to across-fault ground motions through numerical simulations. Two detailed three-dimensional (3D) finite element (FE) bridge models are developed using the explicit FE code LS-DYNA. In particular, Bridge 1 uses the new PTPS-CFDST pier, while Bridge 2 serves as a reference model with monolithic CFDST piers. Two types of across-fault ground motions with strike- and dip-slip mechanisms are used as seismic inputs, and the influence of fling-step is parametrically investigated. Structural responses, including the global seismic responses, seismic damages, energy absorption, and local joint slip and opening, are systematically discussed. The numerical results indicate that, compared to the monolithic CFDST piers, PTPS-CFDST piers exhibit advantages in terms of seismic resilience, with lower damage and outstanding self-centering performance, which facilitates post-earthquake recovery after experiencing across-fault ground motions. This study provides valuable references for the seismic design of bridges with PTPS-CFDST piers crossing fault-rupture zones.

Axial compressive behavior of circular composite columns with external confinement

With the advance of externally confined composite columns, a generic model that can predict the ultimate axial compressive strength of both circular concrete-filled steel tube (CFST) and concrete-filled double skin steel tubes (CFDST) short columns with external confinement is very attractive. For this purpose, a rich experiment database of composite columns is assembled, guides to build up this database are outlined, and its limitations are also summarized. Based on some fundamental considerations, a simple formula for estimating ultimate axial compression of circular composite short columns is proposed first. The hoop and longitudinal stresses of outer and inner (if any) steel tubes are then determined by the stress analysis, from which the assumption frequently used in previous studies that the sandwiched concrete in a CFDST column is under uniform confinement is demonstrated to be unreasonable. Besides, the additional external confining pressure provided by external confinement in the form of steel spirals, rings, jackets, or tie bars is thoroughly investigated. Further, to comprehend the triaxial strength of infilled concrete in both CFST and CFDST columns, a novel concept of equivalent confining stress that can reflect both uniform and non-uniform confinement effects is defined, with which a modified Power-law failure criterion is established. Model validations illustrate that this generic model can reasonably estimate the strength of externally confined CFST and CFDST columns. Although it currently slightly underestimates the strength of ring-enhanced CFDST columns, this limitation can be easily overcome by recalibrating some coefficients without rebuilding the proposed framework.