Concrete and steel are materials with extensive use in human construction activities. Concrete is a material with high stiffness which is less expensive than other available construction materials, and steel is a material with high strength and ductility. Steel-concrete composite structural systems have been utilized in the construction of high-rise buildings due to their superior structural behavior. Fibrous concrete-encased steel columns are one of the most important composite structural members in which the Axial load is carried by the steel and concrete at the same time. These columns are attracting the interest of many researchers due to their excellent structural performance under both static and seismic loading conditions. The steel-concrete interaction enhances the performance when carrying monotonous and earthquake loading. Reinforcing steel fibers help control crack propagation and prevent brittle failure in concrete through improving aggregate interlocking and thus enhance the properties of concrete including the tensile strength and ductility. This paper aims to investigate the Axial capacity of fibrous concrete-encased steel composite stub columns. A total of 36 specimens with different cross-sectional shapes of steel profiles, including H-shaped and C-shaped, were tested, and Axial parameters and compressive behavior were investigated. The variables of the research included the shape of the steel profile (H-shaped and C-shaped), steel fiber volume ratio (0%, 0. 75%, and 1. 25%), and the stirrup spacing (40, 65, and 130 mm). The results showed that the loading capacity of fibrous concrete-encased steel columns was affected by the shape of the steel profile inside. In this regard, the use of the H-shaped steel profile in the columns led to a higher Axial loading capacity than the use of the C-shaped steel profile, due to greater confinement provided by concrete in columns with this section type (H-shape). Moreover, the addition of fibers significantly increased the ductility of these columns in comparison with those without fibers, and also, the addition of fibers increased the Axial capacity of the steel-concrete composite columns by 6%. On the other hand, given the results, it is found that the stirrup spacing had a considerable effect on the load-carrying capacity of these columns, in that by increasing the stirrup spacing, due to the lower confinement of the column, the Axial load-carrying capacity declined. In this regard, as the stirrup spacing increased, the decline in this parameter reached up to 11% for the columns with the H-shaped profile and 9% for the columns with the C-shaped profiles. Furthermore, the results of this study showed that the specimen with the H-shaped steel sections, 1. 25% fibers, and the stirrup spacing of 40 mm generally were the optimal specimens in terms of the Axial load-carrying capacity and ductility in comparison with the other specimens under study. All the specimens had almost similar damage patterns up to their failure. The difference was that the specimens containing fibers experienced failure mainly in the form of the crushing of concrete cover and its breakage from the middle of the column height, due to greater integrity of the concrete structure in these specimens. However, in the specimens without fibers, a considerable portion of the concrete cover was completely detached from the column.

The Presence of defects in the compressive structural members may reduce their load-carrying capacity to a large extent. These defects may be in the form of cracks, corrosion, perforation, or dents existing on the smooth surface of the member. In most cases, the impact of an external object is the main cause of these damages. For example, tubular sections of offshore platforms which are mostly under Axial loads, may be damaged with the collision of supply vessels. Similarly, the columns of bridges and buildings, may be hit by heavy moving vehicles. The Existence of the mentioned defects in compressive members with circular cross-sections may cause premature failure of these structural elements due to local buckling followed by the member's overall instability. Hence, the effect of these damages on the buckling strength of tubular columns, and the effect of different influencing parameters should be studied in depth. This study presents a parametric investigation on the Axial load-carrying capacity of cylindrical columns damaged by a spherical indenter. For this purpose, the numerical models were generated in general purpose finite element software "Abaqus" and verified against results of two Axial compression tests on intact and damaged thin-walled cylinders. The studied parameters included depth of the damage, shell slenderness ratio, location of the damage, length of the Axial member, and radius of the indenter object. The analysis results showed that, the depth of the damage, shell slenderness ratio, and the damage location were the parameters affecting the buckling capacity of the damaged cylinders under Axial load. The increase in damage depth or shell slenderness ratio decreased the buckling load of the member. On the contrary, the buckled shape of the members with different damage depth values or shell slenderness ratios was almost identical. The post-buckling behavior of the studied specimens was affected by the shell slenderness ratio, the damage location, and the length of the compressive member. As the shell slenderness ratio or length of the member increased, the member strength in the post-buckling range experienced more rapid reduction. Also, as the damage became closer to the one of supporting ends, the buckling ring at the farther support vanished while the buckling ring at the closer support became more critical, resulting in an increased strength reduction. The radius of the indenter object had a negligible effect on the buckling capacity and post-buckling behavior of the specimens. For samples with the same damage depth and different radius of the indenter object, the damage profile difference was very small. This small difference vanished during the buckling process, and the final deformation profile for the samples became almost identical. Finally, a regression analysis was conducted on the results of analyses considering the effect of different parameters, and two predictive equations were proposed to determine the buckling and residual capacity of the studied members as functions of influencing parameters. The evaluations performed to estimate the accuracy of the proposed equations showed that they have good accuracy and provide reliable predictions for design rechecking of damaged cylindrical members subjected to Axial compression.

Determination of ultimate pile capacity is important for proper design and construction of pile foundations. Most of the time, the pile load test is carried out shortly after the installation of pile. The pile capacity obtained from the load test is often assumed to be the ultimate pile capacity in most of design methods. However, during pile installation, the soil around the pile experiences large deformations and changes in excess pore water pressure, which in turn reduces the shear strength and pile bearing capacity. After the completion of pile driving, the pile capacity increases as the strength of the surrounding soil increases mainly by reconsolidation, manifested by the dissipation of excess pore pressure at the soil-pile interface zone. the ultimate pile capacity could be underestimated if pile load test was carried out while excess pore water pressure still remains, which may lead to a conservative pile design. It should be noted that a pile static load test (SLT) and a dynamic load test (DLT) only measure the pile load– displacement relation and ultimate load at the time of testing; they do not provide any information on pile capacity variations over time. Pile load tests must be repeated at different times to evaluate any set-up effects, which can be time-consuming and costly during pile construction. Therefore, it is essential to develop empirical and numerical solutions to enable analyzing and estimating long-term pile set-up effects on the basis of limited numbers of SLT and DLT tests. Accurate estimation of pile setup, rather than measuring directly in the field, may reduce the cost of piling and still provide the required performance for the pile. Prediction of pile capacity gain with time after driving would certainly be advantageous from an economic standpoint. Incorporating the effects of setup into pile design is expected to reduce the general cost of piling project by reducing pile diameter, pile length, size of driving equipment, and subsequently piling duration. The major reasons for set-up can be categorised into the following two groups: (1) the generation of excessive pore water pressure during pile driving and subsequent dissipationover time, leading to soil consolidation, and (2) the aging process. The purpose of this research is to conduct experimental research aimed at developing an understanding of pile capacity in soft clays and to develop relationship between the pile capacity and elapsed time after the end of initial driving for cohesive soils. An experimental program was developed to study the evolution of pile capacity increase with time for piles driven into a type of soft clay in northern Iran. results of a series of pile load tests conducted on small-scale Aluminum pile foundations driven into soft clay. The piles were tested instantly after driving to measure their initial bearing capacities, and were tested repeatedly over different elapsed times to study the evolution of pile capacity over time. Results show pile capacity increases approximately 80% of initial value, 14 days after initial pile driving. A large proportion of this pile capacity increase over time, also known as setup, was generated within the three days due to fast excess pore water pressure dissipation, and afterward, the pile capacity increased at a lower rate.

The load carrying capacity, buckling and post-buckling behavior of cylindrical thin-walled shells exposed to Axial loads are very sensitive to imperfections in the initial geometry. These imperfections are invariably caused by an assortment of manufacturing processes like displacing, installing or welding; one of the most important imperfections caused by welding that has been reported to have an essential detrimental effect on the buckling resistance of these shells under Axial load is circumferential imperfections. Despite many determinations of the effect of imperfections on Axial load carrying capacity of cylindrical thin-walled shells, the major part of these studies are concentrated on the existence of imperfections on the shell wall, and a comprehensive research on circumferential imperfections and their effects on Axial load carrying capacity has not been performed. This is the main subject of this research. Also in this paper, the interaction of two imperfections on each other and on the load carrying capacity of cylindrical shells in various cases are analyzed and determined using a finite element program (ABAQUS).

Concrete-filled steel tube are widely used today in many civil engineering structures. The advantage of steel members is their high tensile strength and ductility and, on the other hand, concrete members have high compressive strength. Composite members combine steel and concrete, which have positive properties of both materials. In members under compressive loading, circular tube columns, for a given cross section area, have the large uniform bending strength in all directions in comparison to other cross-sections. Filling the pipe with concrete will increase the ultimate strength of the member without significantly increasing costs. On the other hand, the concrete in the tube delays the local buckling of the pipe wall. In this type of section, the outward buckling will reduce the amount of confinement, ductility and ultimate strength. Subsea and offshore marine structures are mainly made of hollow steel circular sections, where water pressure reduces their load carrying capacity. By converting these sections to concrete filled tube, external pressure can improve the behavior by increasing the confinement. This paper tries to investigate the effect of external pressure on the ultimate strength of CFT, so that the use of this kind of composite sections in construction and retrofitting of marine structures would be investigated. This paper tried to evaluate the effect of lateral pressure on improving the behavior of concrete-filled steel tubes (CFT) by conducting laboratory studies. For this purpose, tri-Axial testing set up, with capability of 400 bars pressure, was designed and constructed by the authors. Parameters such as lateral pressure, concrete strength and diameter to thickness ratio (D/t) of steel tube were tested. Concrete with strength of 15 to 45 MPa was cast in pipes of 0. 5 to 2 mm thickness and subjected to Axial loading under external pressure between 0 and 150 bars. All specimens have a constant diameter of 100 mm and a height of 250 mm and are filled with ordinary concrete. All specimens have a diameter of 100 mm and a height of 250 mm and are filled with normal concrete. To evaluate effect of lateral pressure on the final strength, the ratio of d Parameters such as ultimate strength and failure mode of specimens along with their displacement load diagrams were investigated. Diameter to thickness in some samples was considered higher than the values proposed in the standards. Experimental tests results were compared with the relationships presented in the Eurocode 4 and AISC standards. According to the calculations, the AISC standard result in conservative numbers compared to the EC4 standard for the ultimate strength of the specimen. External pressure has increased the loading capacity, as well as the ductility of the specimens by preventing the buckling and sudden crushing of the core concrete. Increase in load carrying capacity due to external pressure was up to 91% in some specimen. The effect of increasing on ultimate strength on the lower thickness specimens was significant. In conclusion, results of the experiments showed a significant effect of lateral pressure on the final strength of the CFT with normal concrete.

Due to the increasing demand in construction and use of different types of piles on the one hand and the high cost of conducting large-scale tests on different types of piles, on the other hand, new methods have been proposed to study the behavior of different types of piles. Physical modeling provides the researcher the capability of studying model piles in the scaled environment at low costs. Among the different methods of physical modeling, the use of frustum confining vessels (FCV) has gained attraction in recent years. FCV is a cone-shaped vessel that can produce a stress distribution similar to the idealized linear stress distribution in depth. Helical piles are common types of deep foundations which were first used about 200 years ago. Helical Apiles are driven to the soil by applying a torque to the end of piles in the presence of vertical loads. Their quick and noise-free installation method, the minimal disturbance during the installation, and  environmental compatibility make them popular for working in urban areas. In this research, using the finite element method, the optimal dimensions of FCV apparatus were selected, and the FCV apparatus with optimal dimensions were constructed. A total of 18 compression tests were performed on Anzali sand in different relative densities and moisture contents, using single-helix and three-helices piles. Results indicate that increasing the number of helices and relative density of soil increases the pile and sand contact and causes higher bearing capacity for helical piles. Soil saturation, on the other hand, significantly reduces the ultimate strength.

Plate elements is one of the most important parts of structures specially ships and offshores structures. Pitting corrosion is one of the most important types of deterioration of steel structures. There have been many losses of the merchant vessels due to exposure to large environmentally induced forces. Residual strength assessment of damaged structures subjected to pitting corrosion is essential. Present study investigates the ultimate strength characteristics of plate elements with pit corrosion subjected to axil compressive loads. A series of ABAQUS non-linear FEM analysis of plates with partial depth corrosion pits are carried out, changing geometrical attributes of both pits and plates, i. e., the radius and depth of pits and the slenderness of plates. Simulation results show that the volume of corrosion loss, yielded stress, the loaded dimension have a remarkable influences than the depth and radius of corrosion pits on the ultimate strength of damaged steel plate elements by pitting corrosion.