Experimental study on axial compressive behavior of welded built-up CFT stub columns made by cold-formed sections with different welding lines

Morteza Naghipour,Ghazaleh Yousofizinsaz,Mahdi Shariati 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.34 No.3

The objective of this study is to experimentally scrutinize the axial performance of built-up concrete filled steel tube (CFT) columns composed of steel plates. In this case, the main parameters cross section types, compressive strength of filled concrete, and the effect of welding lines. Welded built-up steel box columns are fabricated by connecting two pieces of cold-formed U-shaped or four pieces of L-shaped thin steel plates with continuous penetration groove welding line located at mid-depth of stub column section. Furthermore, traditional square steel box sections with no welding lines are investigated for the comparison of axial behavior between the generic and build-up cross sections. Accordingly, 20 stub columns with thickness and height of 2 and 300 mm have been manufactured. As a result, welding lines in built-up specimens act as stiffeners because have higher strength and thickness in comparison to the plates. Subsequently, by increasing the welding lines, the load bearing capacity of stub columns has been increased in comparison to the traditional series. Furthermore, for specimens with the same confinement steel tubes and concrete core, increment of B/t ratio has reduced the ductility and axial strength.

Experimental investigation of natural bond behavior in circular CFTs

Morteza Naghipour,Aidin Khalili,Seyed Mohammad Reza Hasani,Mahdi Nematzadeh 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.42 No.2

Undoubtedly, the employment of direct bond interaction between steel and concrete is preceding the other mechanisms because of its ease of construction. However, the large scatter in the experimental data about the issue has hindered the efforts to characterize bond strength. In the following research, the direct bond interaction and bond-slip behavior of CFTs with circular cross-section were examined through repeated load-reversed push-out tests until four cycles of loading. The influence of different parameters including the diameter of the tube and the use of shear tabs were assessed. Moreover, the utilization of expansive concrete and external spirals was proposed and tested as ways of improving bond strength. According to the results section dimensions, tube slenderness, shrinkage potential of concrete, interface roughness and confinement are key factors in a natural bond. Larger diameters will lead to a considerable drop in bond strength. The use of shear tabs by their associated bending moments increases the bond stress up to eight times. Furthermore, employment of external spirals and expansive concrete have a sensible effect on enhancing bonds. Macro-locking was also found to be the main component in achieving bond strength.

Effect of progressive shear punch of a foundation on a reinforced concrete building behavior

Morteza Naghipour,Kia Moghaddas Niak,Mahdi Shariati,Ali Toghroli 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.35 No.2

Foundation of a building is damaged under service loads during construction. First visit shows that the foundation has been punched at the 6 column’s foot region led to building rotation. Foundation shear punching occurring has made some stresses and deflections in construction. In this study, progressing of damage caused by foundation shear punching and inverse loading in order to resolve the building rotation has been evaluated in the foundation and frame of building by finite element modeling in ABAQUS software. The stress values of bars in punched regions of foundation has been deeply exceeded from steel yielding strength and experienced large displacement based on software’s results. On the other hand, the values of created stresses in the frame are not too big to make serious damage. In the beams and columns of ground floor, some partial cracks has been occurred and in other floors, the values of stresses are in the elastic zone of materials. Finally, by inverse loading to the frame, the horizontal displacement of floors has been resolved and the values of stresses in frame has been significantly reduced.

Numerical study on the axial compressive behavior of built-up CFT columns considering different welding lines

Mahdi Shariati,Morteza Naghipour,Ghazaleh Yousofizinsaz,Ali Toghroli,Nima Pahlavannejad Tabarestani 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.34 No.3

A concrete filled steel tube (CFT) column with stiffeners has preferable behavior subjected to axial loading condition due to delay local buckling of the steel wall than traditional CFT columns without stiffeners. Welding lines in welded built-up steel box columns is expected to behave as longitudinal stiffeners. This study has presented a numerical investigation into the behavior of built-up concrete filled steel tube columns under axial pressure. At first stage, a finite element model (FE) has been built to simulate the behavior of built-up CFT columns. Comparing the results of FE and test has shown that numerical model passes the desired conditions and could accurately predict the axial performance of CFT column. Also, by the raise of steel tube thickness, the load bearing capacity of columns has been increased due to higher confinement effect. Also, the raise of concrete strength with greater cross section is led to a higher load bearing capacity compared to the steel tube thickness increment. In CFT columns with greater cross section, concrete strength has a higher influence on load bearing capacity which is noticeable in columns with more welding lines.

Experimental study of the behavior of composite timber columns confined with hollow rectangular steel sections under compression

Leila Razavian,Morteza Naghipour,Mahdi Shariati,Maryam Safa 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.74 No.1

There are separate merits and demerits to wood and steel. The combination of wood and steel as a compound section is able to improve the properties of both and ultimately increase their final bearing capacity. The composite cross-section made of steel and wood has higher hardness while showing more ductility and the local buckling of steel is delayed or completely prevented. The purpose of this study is to investigate the behavior of composite columns enclosed in wooden logs and the hollow sections of steel that will be examined in a laboratory environment under the axial load to determine the final bearing capacity and sample deformation. In terms of methodology, steel sheet and carbon fiber reinforced polymer sheet (FRP) are tested to construct hollow rectangular sections and reinforce timber. Besides, the method of connecting hollow sections and timber including glue and screw has been also investigated. As a result, timber lumber enclosed with carbon fiber-reinforced polymer sheets in which fibers are horizontally located at 90 ° are more resistant with better ductility.

Experimental Evaluation of Steel Plate Shear Walls Stiffened with Folded Sheets

Hamed Zamenian,Morteza Naghipour,Mahdi Nematzadeh,Hamed Zamenian 한국강구조학회 2017 International Journal of Steel Structures Vol.17 No.1

This study evaluated a special type of stiffened plate that eliminates the weaknesses of previous stiffened systems, such as early out-of-plane buckling, low ultimate shear capacity, lack of symmetry and stability in the hysteresis curves of shear forcedisplacement. Consequently, folded sheet trapezoidal stiffeners connected to the basic plate by screws were used in order to obtain the values of the ultimate capacity and failure modes under quasi-static cyclic loads. An experimental analysis was performed on three types of steel plate shear walls including unstiffened by two different dimension stiffeners. The results indicated that the appropriate behavior in the stiffened wall using folded-shape specimens significantly amplified the ultimate capacity of the system and enhanced the symmetry and stability of the hysteresis curves of the force-displacement. Energy absorption also increased substantially.

Presentation of Critical Buckling Load Correction Factor of AISC Code on L-Shaped Composite Columns by Numerical and Experimental Analysis

Seyed Ali Mousavi Davoudi,Morteza Naghipour 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.5

Concrete-fi lled steel tubular (CFT) columns have been widely used as structural members in buildings and bridges in recent years, because of their properties, such as high strength and stiff ness, good ductility, and convenience for construction. In CFT columns, the bearing capacity of columns is inversely related to buckling, therefore, buckling is of particular importance at these sections, the AISC Code uses eff ective bending rigidity ( EI eff ective ) to calculate the critical buckling load in concrete fi lled steel columns, to apply the eff ect of reducing concrete confi nement, the AISC code provides a maximum value of 0.9 of the reduced concrete confi nement coeffi cient for the equation. Eff ective bending rigidity ( EI eff ective ), this relationship is provided in AISC code for circular and square sections, therefore, the eff ect of the column shape geometry on the core concrete confi nement is very infl uential and changes the eff ective bending rigidity ( EI eff ective ) of the section. The AISC code does not provide a coeffi cient to consider the type of cross-sectional geometry in CFT columns, therefore, in this study, three groups experimental, numerical (FEM) and theoretical were used to provide critical buckling load correction, fi nally, it was concluded that the critical buckling load for the cross-section (L) shape due to the lower confi nement of the concrete core is 20.07% lower than the AISC code equation, also with a 67% increase in slenderness ratio, the critical buckling load decreased by 14.52%.

The effect of RBS connection on energy absorption in tall buildings with braced tube frame system

Mahdi Shariati,Mostafa Ghorbani,Morteza Naghipour,Nasrollah Alinejad,Ali Toghroli 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.34 No.3

The braced tube frame system, a combination of perimeter frame and bracing frame, is one of the systems used in tall buildings. Due to the implementation of this system in tall buildings and the high rigidity resulting from the use of general bracing, providing proper ductility while maintaining the strength of the structure when exposing to lateral forces is essential. Also, the high stress at the connection of the beam to the column may cause a sudden failure in the region before reaching the required ductility. The use of Reduced Beam Section connection (RBS connection) by focusing stress in a region away from beam to column connection is a suitable solution to the problem. Because of the fact that RBS connections are usually used in moment frames and not tested in tall buildings with braced tube frames, they should be investigated. Therefore, in this research, three tall buildings in height ranges of 20, 25 and 30 floors were modeled and designed by SAP2000 software, and then a frame in each building was modeled in PERFORM-3D software under two RBS-free system and RBS-based system. Nonlinear time history dynamic analysis is used for each frame under Manjil, Tabas and Northridge excitations. The results of the Comparison between RBS-free and RBS-based systems show that the RBS connections increased the absorbed energy level by reducing the stiffness and increasing the ductility in the beams and structural system. Also, by increasing the involvement of the beams in absorbing energy, the columns and braces absorb less energy.

Performance of composite frame consisting of steel beams and concrete filled tubes under fire loading

Mahdi Shariati,Mohammad Grayeli,Ali Shariati,Morteza Naghipour 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.36 No.5

In recent years, the composite columns have been widely used in the structures. These columns are mainly used to construct the structures with a large span and high floor height. Concrete filled tubes (CFTs) are a type of composite column, which are popular nowadays due to their numerous benefits. The purpose of this study is to investigate such frames at elevated temperatures. The method used in this research is based on section 2.2 of Eurocode 4. First, for the verification purpose, a comparison was made between the experimental results and the numerical model of the concrete filled tube. Then a composite frame was analyzed under fire temperature with different parameters. The results showed that the failure time decreased with increasing the friction of different models. Moreover, investigation of the concrete moisture content revealed that an increase in the concrete moisture content from 3% to 10% led to extended failure time for different models. For instance, in the second frame model, the failure time has increased up to 8%.

Compressive behaviour of circular steel tube-confined concrete stub columns with active and passive confinement

Mahdi Nematzadeh,Iman Hajirasouliha,Akbar Haghinejad,Morteza Naghipour 국제구조공학회 2017 Steel and Composite Structures, An International J Vol.24 No.3

This paper presents the results of a comprehensive experimental investigation on the compressive behaviour of steel tube-confined concrete (STCC) stub columns with active and passive confinement. To create active confinement in STCC columns, an innovative technique is used in which steel tube is laterally pre-tensioned while the concrete core is simultaneously pre-compressed by applying pressure on fresh concrete. A total of 135 STCC specimens with active and passive confinement are tested under axial compression load and their compressive strength, ultimate strain capacity, axial and lateral stress.strain curves and failure mode are evaluated. The test variables include concrete compressive strength, outer diameter to wall thickness ratio of steel tube and prestressing level. It is shown that applying active confinement on STCC specimens can considerably improve their mechanical properties. However, applying higher prestressing levels and keeping the applied pressure for a long time do not considerably affect the mechanical properties of actively confined specimens. Based on the results of this study, new empirical equations are proposed to estimate the axial strength and ultimate strain capacity of STCC stub columns with active and passive confinement.