scholarly journals Analysis of concrete-filled steel tubular columns after fire exposure

2018 ◽  
Author(s):  
Carmen Ibáñez ◽  
Luke Bisby ◽  
David Rush ◽  
Manuel L. Romero ◽  
Antonio Hospitaler
Keyword(s):  
Residual Strength ◽  
Steel Structures ◽  
Steel Tube ◽  
Load Level ◽  
Complete Analysis ◽  
Maximum Temperature ◽  
Sustained Load ◽  
Beam Model ◽  
Fire Response ◽  
Cfst Columns

Concrete filled steel tubular (CFST) columns have a high probability to resist high temperatures compared to steel structures, whose evaluation after a fire is limited by the resulting deformation. A better understanding of the behaviour of CFST columns after a fire, affected by the maximum temperature achieved by the concrete infill, is required to properly estimate their residual strength and stiffness in order to adopt a reasonable strategy with minimum post-fire repair. In this paper, a fiber beam model for the simulation of the post-fire response of slender concrete-filled steel tubular (CFST) columns is presented. First, the model is validated against experimental results and subsequently it is employed to analyse the post-fire response of circular CFST columns. The variation of the residual strength with the load level for realistic fire resistance times is numerically studied. Actually, in a building, the columns support load even while a fire is being extinguished, so it is important to take into account this loading condition when predicting the post-fire behaviour. Therefore, in this research, the complete analysis comprises three stages: heating, cooling and post-fire under sustained load conditions. The model considers realistic features typical from the fire response of CFST columns, such as the existence of a gap conductance at the steel-concrete interface or the sliding and separation between the steel tube and the concrete.

Dynamic behavior of concrete filled steel tubular columns

2019 ◽  
Vol 10 (2) ◽  
pp. 244-264 ◽  
Author(s):  
Said Hicham Boukhalkhal ◽  
Abd Nacer Touati Ihaddoudène ◽  
Luis Filipe Da Costa Neves ◽  
Wafa Madi
Keyword(s):  
High Performance ◽  
Research Work ◽  
Steel Frames ◽  
Steel Structures ◽  
Steel Tube ◽  
Absorption Capacity ◽  
Resistant Steel ◽  
Content Type ◽  
Open Section ◽  
Cfst Columns

Purpose The purpose of this paper is to investigate the static and dynamic inelastic response of rigid and semi-rigid connections of steel structures with concrete-filled steel tube (CFST) columns built in high seismic areas, and to compare it with those with open section columns. Design/methodology/approach CFST columns are frequently used in moment resistant steel frames located in seismic areas due to their inherent advantages, including their ductility, energy absorption capacity as well as their high bearing capacity. The smart combination of steel and concrete makes it possible to benefit from the advantages of both components to the maximum. This research work presents the nonlinear dynamic response of moment resistant steel frames with CFST columns, with rigid or semi-rigid connections, built in high seismic areas, according to the Algerian seismic code RPA 99/2003, European EC8 and American FEMA 356 to show the nonlinear characteristics of this type of structures, and their advantages over steel frames with open section columns. Findings The paper presents the advantages of using CFST columns with rigid and semi-rigid connections on the seismic response of portal steel frames. A high performance level in terms of ductility, plastic hinges distribution and their order of appearance has been obtained. It also shows the low effect of seismic loading on the structural elements with CFST columns compared to structures with open section columns. Originality/value The investigation of the numerical results has shown the possibility of their use in the seismic areas for their adequate performance, and also with respect to the design limits specified in the seismic guidelines. In addition, this study represents a first step to develop seismic performance factors for steel structures with CFST columns in Algeria, where the Algerian code do not include a comprehensive specification for the composite steel structures.

scholarly journals Numerical analysis of seismic behavior of square concrete filled steel tubular columns

2021 ◽  
Vol 15 (2) ◽  
pp. 127-140
Author(s):  
Hao Dinh Phan
Keyword(s):  
Numerical Analysis ◽  
Axial Load ◽  
Seismic Behavior ◽  
Concrete Strength ◽  
Steel Tube ◽  
Load Level ◽  
Deformation Capacity ◽  
Element Analysis ◽  
Fea Model ◽  
Cfst Columns

This paper presents a numerical analysis of the seismic behavior of square concrete filled steel tubular (CFST) columns. Finite element analysis (FEA) models in ABAQUS software were used to simulate a series of columns subjected to axial compression and cyclic lateral loading. The CFST columns were simulated using nonlinear tri-dimensional (3-D) finite elements for the infilled concrete, and nonlinear two-dimensional (2-D) finite elements for the steel tube. The feasibility of the FEA model has been validated by published experimental results. The validated FEA model was further extended to conduct parametric studies with various parameters including axial load level (n), width-to-thickness ratio of steel tube (B/t), and concrete strength. The numerical analysis results reveal that with the same B/t and constitute materials, the higher the axial compression, the lower the shear strength and deformation capacity were. The thicker steel wall (B/t = 21) resulted in higher strength and larger deformation capacity of the column. Increasing concrete strength helped to significantly develop the column’s shear strength in all cases. Meanwhile, it just led to an increase in deformation capacity in some cases depending on n and B/t. This study also reveals that the square CFST columns with B/t of 21 satisfy the seismic performance demand in high seismic zones (ultimate interstory drift ratio (IDRu) not less than 3% radian) under the two axial load levels, 0.35 and 0.45, but the columns with B/t of 28 satisfy the above demand under just one axial load level of 0.35. Keywords: square concrete filled steel tubular (CFST) columns; finite element analysis (FEA) model; width-to-thickness ratio (B/t); high axial load level; seismic behavior.

Effects of Sustained Pre-Load on Residual Strength and Stiffness of Concrete-Filled Steel Tube after Exposure to High Temperatures

2008 ◽  
Vol 400-402 ◽  
pp. 769-774
Author(s):  
Jing Si Huo ◽  
Guo Wang Huang ◽  
Yan Xiao
Keyword(s):  
High Temperatures ◽  
Residual Strength ◽  
Axial Load ◽  
Room Temperature ◽  
Steel Tube ◽  
Load Level ◽  
Stiffness Index ◽  
Test Results ◽  
Strength And Stiffness ◽  
Stub Columns

This paper experimentally investigated the effects of axial load level on the residual strength and stiffness of concrete-filled steel tubular (CFT) stub columns which were heated and cooled down to room temperature under sustained axial load. Eight stub columns were axially loaded and heated to specified high temperatures in a purpose-built electric furnace. After the specimens cooled down to room temperature while the axial load was kept constant, the stub columns were loaded to failure. The test results show that not only the axial load level and the high temperature exposure have significant effects on the residual strength and stiffness of stub column, but the residual strength index and stiffness index of the fire-damaged CFT stub columns with pre-load are remarkably different from those without pre-load. From the test results, it is recommended that the sustained axial load effects and the fire cooling phase should be taken into consideration in assessing the fire-damaged CFT columns.

scholarly journals Axial Behaviour of Slender RC Circular Columns Strengthened with Circular CFST Jackets

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Yiyan Lu ◽  
Tao Zhu ◽  
Shan Li ◽  
Weijie Li ◽  
Na Li
Keyword(s):  
Bearing Capacity ◽  
Ductile Failure ◽  
Steel Tube ◽  
Experimental Results ◽  
Strengthening Effect ◽  
Load Bearing Capacity ◽  
Rc Columns ◽  
Load Bearing ◽  
Cfst Columns ◽  
Material Utilization

This paper investigates the axial behavior of slender reinforced concrete (RC) columns strengthened with concrete filled steel tube (CFST) jacketing technique. It is realized by pouring self-compacting concrete (SCC) into the gap between inner original slender RC columns and outer steel tubes. Nine specimens were prepared and tested to failure under axial compression: a control specimen without strengthening and eight specimens with heights ranging between 1240 and 2140 mm strengthened with CFST jacketing. Experimental variables included four different length-to-diameter (L/D) ratios, three different diameter-to-thickness (D/t) ratios, and three different SCC strengths. The experimental results showed that the outer steel tube provided confinement to the SCC and original slender RC columns and thus effectively improved the behavior of slender RC columns. The failure mode of slender RC columns was changed from brittle failure (concrete peel-off) into ductile failure (global bending) after strengthening. And, the load-bearing capacity, material utilization, and ductility of slender RC columns were significantly enhanced. The strengthening effect of CFST jacketing decreased with the increase of L/D ratio and D/t ratio but showed little variation with higher SCC strength. An existing expression of load-bearing capacity for traditional CFST columns was extended to propose a formula for the load-bearing capacity of CFST jacketed columns, and the predictions showed good agreement with the experimental results.

scholarly journals Research on Compression Behavior of Square Thin-Walled CFST Columns with Steel-Bar Stiffeners

2018 ◽  
Vol 8 (9) ◽  
pp. 1602 ◽  
Author(s):  
Zhao Yang ◽  
Chengxiang Xu
Keyword(s):  
Bearing Capacity ◽  
Local Buckling ◽  
Steel Tube ◽  
Steel Tubes ◽  
Compression Behavior ◽  
Steel Bar ◽  
Steel Bars ◽  
Thin Walled ◽  
Structural Measure ◽  
Cfst Columns

Local buckling in steel tubes was observed to be capable of reducing the ultimate loads of thin-walled concrete-filled steel-tube (CFST) columns under axial compression. To strengthen the steel tubes, steel bars were proposed in this paper to be used as stiffeners fixed onto the tubes. Static-loading tests were conducted to study the compression behavior of square thin-walled CFST columns with steel bar stiffeners placed inside or outside the tube. The effect and feasibility of steel bar stiffeners were studied through the analysis of failure mode, load–displacement relationship, ultimate load, ductility, and local buckling. Different setting methods of steel bars were compared as well. The results showed that steel-bar stiffeners proposed in this paper can be effective in delaying local buckling as well as increasing the bearing capacity of the columns, but will decrease the ductility of the columns. In order to obtain a higher bearing capacity of columns, steel bars with low stiffness should be placed inside and steel bars with high stiffness should be placed outside of the steel tubes. The study is helpful in providing reference to the popularization and application of this new structural measure to avoid or delay the local buckling of thin-walled CFST columns.

Residual Strength of Steel Structures After Fire Events Considering Material Damages

2019 ◽  
Vol 44 (5) ◽  
pp. 5075-5088
Author(s):  
Zhanzhan Tang ◽  
Tao Wei ◽  
Yao Ma ◽  
Lingkun Chen
Keyword(s):  
Residual Strength ◽  
Steel Structures

scholarly journals Buckling Analysis and Section Optimum for Square Thin-Wall CFST Columns Sealed by Self-Tapping Screws

2019 ◽  
Vol 2019 ◽  
pp. 1-14
Author(s):  
He Zhang ◽  
Kai Wu ◽  
Chao Xu ◽  
Lijian Ren ◽  
Feng Chen
Keyword(s):  
Bearing Capacity ◽  
Failure Modes ◽  
Steel Plate ◽  
Local Buckling ◽  
Steel Tube ◽  
Thin Wall ◽  
Type Section ◽  
Plate Buckling ◽  
Thin Walled ◽  
Cfst Columns

Two columns of thin-walled concrete-filled steel tubes (CFSTs), in which tube seams are connected by self-tapping screws, are axial compression tested and FEM simulated; the influence of local buckling on the column compression bearing capacity is discussed. Failure modes of square thin-wall CFST columns are, first, steel tube plate buckling and then the collapse of steel and concrete in some corner edge areas. Interaction between concrete and steel makes the column continue to withstand higher forces after buckling appears. A large deflection analysis for tube elastic buckling reflects that equivalent uniform stress of the steel plate in the buckling area can reach yield stress and that steel can supply enough designing stress. Aiming at failure modes of square thin-walled CFST columns, a B-type section is proposed as an improvement scheme. Comparing the analysis results, the B-type section can address both the problems of corner collapse and steel plate buckling. This new type section can better make full use of the stress of the concrete material and the steel material; this type section can also increase the compression bearing capacity of the column.

scholarly journals Influence of Cooling Methods on the Residual Mechanical Behavior of Fire-Exposed Concrete: An Experimental Study

Materials ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 3512 ◽  
Author(s):  
Espedito Felipe Teixeira de Carvalho ◽  
João Trajano da Silva Neto ◽  
Paulo Roberto Ribeiro Soares Junior ◽  
Priscila de Souza Maciel ◽  
Helder Luis Fransozo ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Ambient Temperature ◽  
Mechanical Behavior ◽  
Residual Strength ◽  
Maximum Temperature ◽  
Experimental Program ◽  
Lower Strength ◽  
Cooling Method ◽  
Temperature Levels ◽  
Cooling Methods

This work reports the main conclusions of a study on the mechanical behavior of concrete under ISO 834 fire with different cooling methods. The aim of this research was to provide reliable data for the analysis of structures damaged by fire. The experimental program used cylindrical concrete test specimens subjected to ISO 834 heating in a furnace up to maximum gas temperatures of 400, 500, 600, 700, and 800 °C. The compressive strength was measured in three situations: (a) at the different temperature levels reached in the furnace; (b) after a natural cooling process; and (c) after aspersion with water at ambient temperature. The results indicate that the concrete residual compressive strength is fairly dependent on the maximum temperature reached in the furnace and revealed that concrete of a lower strength preserved relatively higher levels of strength. The cooling method significantly influenced the strength, albeit at a lower intensity. In all cases, the residual strength remained in the range of 38% to 67% of the strength at ambient temperature. The statistical analysis showed that the data obtained by the experimental program are significant and confirmed the influence of the conditions imposed on the residual strength.

On Deformation Charting for Concrete Filled Steel Tube Columns Concrete Core and Steel Shell

2018 ◽  
Vol 878 ◽  
pp. 126-131 ◽  
Author(s):  
Anatoly L. Krishan ◽  
Elvira P. Chernyshova ◽  
Rustam R. Sabirov
Keyword(s):  
Steel Tube ◽  
Steel Shell ◽  
Concrete Core ◽  
New Approach ◽  
Concrete Filled Steel Tube ◽  
The Real ◽  
Side Pressure ◽  
Core Function ◽  
Cfst Columns ◽  
Major Factors

New approach to creating deformation charts for concrete core and steel shell of round CFST columns is offered. For creating such charts the power resistance of short central the compressed concrete filled steel tube element is considered. At the same time two major factors are considered. First, the steel shell and the concrete core function under conditions of complex tension. Secondly, at step-by-step strengthening of axial deformations the side pressure upon concrete core and steel shell constantly changes. As a result coordinates of parametrical points of deformation charts for concrete and steel change. Such approach allows describing the real intense deformed condition of concrete filled steel tube columns more precisely.

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