Many advantages of concrete-filled steel tube columns have led to their use in a variety of distinctive and important structures in recent years, including high-rise buildings, piers, stairs and other structures. The exterior steel wall of these columns is uncoated, which is the main disadvantage. When these columns are subjected to external pressure on the external steel wall, such as collision, explosion, fire or other accidents, the confinement of concrete will be lost owing to the weakness generated in the steel wall, resulting in an abrupt loss in column strength. In this study, a new upgraded section using internal steel mesh is designed and introduced, with this steel mesh and the external steel wall acting as a double-skin steel tube to protect the concrete core from being destroyed if the external steel wall is destroyed and the column's strength drops suddenly. Under axial and cyclic loads, a comparison of the behavior of this innovative section (with internal steel mesh) with the most commonly used sections of concrete-filled steel columns was conducted. Following the verification of the finite element modeling, various other studies were carried out. The results of the analyses clearly show that the suggested CFT section has increased strength, improved resistance to progressive collapse, and energy absorption capacity under axial and cyclic loading, particularly abrupt loads such as fire or explosion, and thus its use in construction is recommended.

This study aims to determine the dimensions of customer satisfaction. For this purpose, researchers developed a model by taking an experiential view. In this article, a standard questionnaire was used for collecting the data and, the authors report a comparative study that was conducted on two samples of real customers at apartment industry (low income and high income) in Iran. The results from a low income sample revealed that the customer satisfaction is influenced more by customer cost and product quality than other constructs. Moreover, the role of customer satisfaction as a mediating factor in the intention of word of mouth is supported. In contrary, in high income sample customer satisfaction influenced more by product quality and service quality than other constructs. In addition, the role of customer satisfaction as a mediating factor in the intention of word of mouth is rejected. A notable advantage of the model developed in this study is that, it covers essentially all the quality issues an apartment customer may encounter (that is, physical or product, service, and environment).

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This study has been investigated the effect of admixtures on the strength of concrete under water with high aggressive ions, for example under Urmia-lake water in West Azerbaijan, Iran. We made different types of concretes with the ratio of w/c and replaced different percentages of micro-silica, air-entraining, super plasticizer, corrosion-inhibiting and caulk with two types of cement I and II as well as investigating in both ordinary water and Urmia-lake water. The strength of pressure, tension, abrasion and freezing and melting was investigated on these samples. The results indicate that admixtures improved strength of concrete under water with high aggressive ions. Finally, the most proper mixture was presented using both types of cement (I and II) and optimal value for microsilica, caulk and super plasticizer.

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