The columns of frame structures are the key load-bearing components and the exterior columns aresusceptible to attack in terrorist blasts. When subjected to blast loads, the columns would suffer a loss of bearingcapacity to a certain extent due to the damage imparted which may lead to their collapse and even cause theprogressive collapse of the whole structure. The concrete-filled steel columns have been extensively used in theworld due to the existence of all suitable characteristics of concrete and steel, more ductility, increasing concreteconfinement using the steel wall, the large energy-absorption capacity and the appropriate fire behavior. In thepresent study, the concrete-filled steel square columns have been simulated under the influence of the blast loadusing the ABAQUS software. These responses have been compared for scaled distances based on the distance tothe source and the weight of the explosive material. As a result, it can be seen that although concrete deformationhas been restricted using the steel tube, the inner layer of concrete has been seriously damaged and the columndisplacement has been decreased by increasing the scaled distance. We also concluded that the concrete-filled steelcolumns have the high ductility and the blast resistance.

One of the most sensitive decisions a structural designer should consider is choosing the type of consumables in the structure. This decision is in many cases dependent on the type of structure, financial issues also the experience and skill of the designer. The main aim pursued in the design is to obtain highly secure, economical structures. Concrete and steel are materials that are widely used in construction. The benefits of both materials are well known today. The clever combination of these two materials, an effective explosion-proof system, will have the effect of exploding explosions in the Plasco building in Tehran compared to using any of the materials. Lack of efficient performance factors, lack of clear and valid guidelines for the seismic design of such columns, how to model their geometry and material can still be obstacles to using such systems. In this research, according to the objectives of the problem, different parameters should be evaluated, this parameter is the type of column cross-section geometry. The aim is to determine the effect of defined parameters, especially column geometry, on the behavior and seismic capacity of composite columns )CFST(, achieving high resistivity, especially for columns that, incidentally, increase their loading exponentially with increasing classes. It is found that circular sections of composite columns )CFST( show better behavior and performance than columns with square geometry and further show that composite columns )CFST( can be used as a basic solution. Use it to solve challenges between designers and architects.

This paper presents behaviour of normal concrete, ultrahigh-strength concrete, engineered cementitious composite, lightweight concrete, self-consolidating concrete and crumb rubber concrete under confinement. Forty-six circular, square and rectangular concrete-filled steel tube columns with varying slenderness are tested under axial compression. Failure modes, axial load– displacement responses and stress– strain characteristics are analysed as well as concrete confined strengths are determined based on experimental results and existing models. The performance of existing confined strength models is evaluated and modified to accommodate different types of high-performance concretes and column shapes. The modified model improves the prediction of confined concrete strength with a mean predicted-to-experimental ratio of 1. 05 as shape and concrete type factors are introduced.

Predicting the residual load-bearing capacity of damaged concrete-filled steel tube (CFST) columns exposed to fire, based on the effects of eccentricities, is a subject on which relatively little research has been done. This paper aims to present the results of a series of post-fire residual capacity tests for CFST columns with different cross sections (circular and square), under axial load, and different eccentricities in the event of a failure. In this experimental study, the influence of parameters such as cross-sectional shape, load eccentricity, slenderness and fire protective coating on the post-fire residual capacity of CFST sections was investigated. Based on the results of this study, the following conclusions were obtained in the scope of this research work: The results showed that eccentricity could be effective in reducing the residual capacity of the column, but the change in the amount of eccentricity cannot be as effective as reducing the residual capacity of the columns. The studies indicate that the residual capacity is significantly reduced by increasing the slenderness ratio. Therefore, in order to determine the residual capacity of the CFST columns under load eccentricity, a simplified equation for predicting the reduction factor was proposed, a comparison between the predicted and experimental results shows that there is a reasonably good agreement. The tests show that by increasing the temperature over a cross-section of CFST columns, the residual axial load capacity and the axial stiffness of the unprotected columns decreased significantly compared to the unheated columns. Comparison of the axial compressive capacity of CFST columns with square and circular have shown that for columns having the same concrete material, the circular column has slightly better structural post-fire behavior than the square column. To fire-protected sections, the effect of the cross-sectional shape on the residual strength is significant, relative to the unprotected sections is more. In fact, by comparing the temperature distribution on the surface of the circular and square sections, one can find that the maximum temperature distribution at the circular cross sections is less than the square cross sections. Therefore, with less degradation of the properties of the cross-sectional materials, the more residual load-bearing capacity is expected. Finally, based on the experimental results, the ability to predict the residual load-bearing capacity of the concrete-filled hollow tube columns after exposure to the ISO-834 standard fire as per the modified design method in Eurocode 4 for the fire and ambient conditions were evaluated. The investigation’, s results showed that the simplified method of Eurocode 4, in the ambient temperature produced safe results for predicting residual resistance of CFST columns after fire exposure, under both concentric and eccentric loading conditions. This approach was considered as a conservative method, with the MPEs for concentric loads, as well as both concentric and eccentric loads as-5. 51% and-3. 06% lower than the prediction, respectively.