## 1 Introduction  
In the last decades, the construction industry has become increasingly focused on strengthening and repairing rapidly deteriorating concrete columns, specifically those in harsh environments, such as seawater and acidic areas, where the structure is subjected to severe chemicals leading to corrosion in concrete or steel reinforcement in constructions with this kind of reinforcement [1, 2]. Furthermore, lacking lateral confinement and low capacity regarding energy absorption are considered the most significant drawbacks of columns [3, 4]. Consequently, researchers have conducted many studies to increase durability and protect the concrete columns during construction [5, 6, 7, 8, 9].  
In this regard, a concrete fill tube (CFT) is considered one of the most effective strategies to overcome the above issues. The CFT term involves a tube (confining tube) filled with plain or reinforced concrete, creating a hybrid system (composite material) with considerable ductility, high bearing capacity, and better energy absorption [10, 11, 12]. Steel tubes and fiber-reinforced polymer (FRP) tubes are considered the most commonly used materials to improve the compressive strength of concrete [8]. The process of confining concrete columns with steel tubes has led to remarkable strides in improving the compressive strength, stiffness, and ductility of concrete columns due to the high mechanical propertiesof steel tubes [13; 14]. However, the steel tubes serve as an outside layer, making them susceptible to corrosion and limiting their applications. On the other hand, concrete-filled FRP tubes showed a remarkable resistance against corrosion, making them a suitable material in critical construction sites, such as bridges and ocean constructions [15; 16; 17]. Furthermore, the confinement of FRP tubes enhances the compressive strength, ductility, and stiffness of concrete columns [18; 19; 20; 21; 22; 23]. However, their practical use is limited due to their high price [24], low fire resistance [25], and not being applicable on wet or dumped surfaces [26].  
Meanwhile, another confining material known as Polyvinyl chloride (PVC) has drawn the attention of many researchers due to several attributes, such as high resistance to corrosion, light weight, which allows easy handling, impermeability to fluids or gases, low price, and durability (life cycle is more than 50 years in civil constructions) [27; 28; 29]. [PERSON] [30] studied the performance of concrete columns with different compressive strengths confined with different diameters of unplasticized polyvinyl chloride (UPVC) tubes. Their results showed a good enhancement in load-bearing capacity, ductility, and energy absorption of concrete columns. [PERSON] et al. [31] showed a significant increase in the compressive strength of concrete columns confined with UPVC tubes compared to unconfined ones. [PERSON] et al. [32] investigated the performance of reinforced concrete columns with polypropylene fibers confined with UPVC tubes. The results showed that the confinement of UPVC tubes improved the loading-bearing capacity and ductility of the concrete columns.  
Given these facts, this study investigates the performance of confining short columns with different diameters with PVC tubes experimentally. Furthermore, this study investigates the influence of different confining strategies on the compressive strength of short columns. Finally, after developing a robust numerical simulation based on the finite element (FE) approach to reproduce the experimental results, obtain a well-calibrated nonlinear FE model and study the behavior of short columns with different confining strategies under uniaxial loads.