In steel moment-resisting frames, tubular columns have many structural and architectural advantages over open-section columns. Circular Hollow Sections (CHS) are in fact particularly recommended for structural elements subjected to compression and bending forces in all directions, thanks to their higher radius of gyration and the axial-symmetric distribution of their mechanical properties. Therefore, the use of CHS profiles for the realization of columns can lead to a reduction of the total costs and furthermore to simplifications in the realization process of steel-concrete composite structures. However, the difficulties in realizing tubular column joints adopting open I-section beams, the most commonly used all around the world, severely reduce the use of CHS columns. Nowadays, I-beam-to-CHS-column steel and composite joints are commonly realized in two main ways: i) the connection is made by directly welding the beams or the beam stub to the wall of the steel tube; ii) supplemental plates are used to connect the beams to the circular column. The direct connection is the most convenient solution in terms of rapidity and easiness of fabrication but the performance of the joint is strongly limited by significant local distortions of the tube wall near the girder flanges. Therefore, the joint performance results very far from the ideal mechanical behavior of a rigid full-strength beam-to-column connection. The local buckle of the tube wall, which can lead to brittle failures, often suggests the use of supplemental plates for the realization of the tubular column joints. Additional elements can indeed assure a more effective transfer of the stresses from the beam flanges to the column wall or from the flanges of one beam directly to the beam placed on the opposite side. In general, two types of additional elements are currently used for I-beam-to-CHS-column moment joints: interior diaphragm joints, which imply the discontinuity of the column, and exterior diaphragm joints, which guaranty the total continuity of the column. Although internal diaphragms are very effective in distributing the internal forces and improving the collaboration between the steel elements and the concrete core in the case of composite columns, their use implies a discontinuity in the column and requires extensive welding to reconnect the column pieces. On the contrary, exterior diaphragms guarantee the steel tube continuity through the connection; nevertheless, several welding should be performed also in this case. Moreover, in the case of filled column, the composite behavior is not improved by the presence of steel elements, and the presence of big external stiffeners spoils down the aesthetic of the whole building. To overcome the main issues inherent the direct connections and the use of diaphragms, innovative solutions with continuous passing-through elements inside the column were studied, highlighting several advantages from a mechanical point of view. Indeed, the continuous elements can pass by slots of limited size made on the column wall, without requiring the complete discontinuity of the column itself and the joint requires less cutting and welding operations, resulting in lower overall cost and better mechanical behavior. The use of passing-through elements can lead to obtain the same mechanical benefits highlighted by internal diaphragms joints, without requiring the complete discontinuity of the column wall in the joint. However, despite all these advantages, many problems arise from the fabrication and constructional points of view, limiting the effective performance of the joints. Indeed, the difficulties in implementing high precision cutting processes spoiled the development of this construction technique, favoring more practice solutions. One of these difficulties lies in the production tolerances that affect the effective geometry of the beams. These tolerances shall be considered in the definition of the dimensions of the slots in which the beams need to pass through: dimensions of the slot very close to the nominal ones of the beam can lead to difficulties in the assembly process, whereas big gaps can result in ineffective welding. One of the solutions to overcome the difficulties in the fabrication and constructional processes of this joint typology lies in the application of the modern Laser Cutting Technology (LCT) to steel and composite structures. Laser cutting machines, commonly used in the industrial field, allow performing high precision and completely automated cutting processes on steel tubes and open sections profiles with the typical structural dimensions. To limit the influence of the beam dimensions tolerances, the laser cutting machines have the intrinsic advantage of directly providing measuring instruments that can be used to measure the elements to be passed. Therefore, the whole fabrication process can start with the simultaneous cutting and measuring process of the I-beams and plates. Subsequently, slots can be realized on the tube-wall considering the previously taken and recorded measurements and applying a defined strict tolerance margin. In this way the correct passage of the beam portions or plates through the column is guaranteed without requiring excessive gaps, and the welding processes is performed in the best conditions. Furthermore, thanks to the possibility of cutting with different inclinations with the tube-face, the penetration welding may be realized without performing any additional preparation processes on the worked-pieces. The LCT is also a very competitive solution in terms of time of fabrication and cost, thanks to the high automatization of the process reached by the modern technologies. However, even though the LCT provides the perspective of realizing the I-beam-to-CHS-column connection type that exhibited the best mechanical behavior in the past researches, several issues still need to be faced in order to define an appropriate fabrication process and to better characterize the behavior of the I-beam-to-CHS-column connection. For these purposes, in the presently exposed research, preliminary practical, numerical and theoretical studies are conducted to confirm the mechanical and technological advantages previously reported, and to understand the global and local behavior of the passing-through tubular column connections in case of both vertical and horizontal loadings acting on the structure. Considering the analyzed aspects inherent the practical realization and the mechanical behavior of the I-beam-to-CHS-column with passing elements, new joint solutions are proposed for both steel and composite structures. Afterwards, the proposed joint typologies are experimentally tested in order to have information on their mechanical behavior. On the basis of the behavior exhibited in the tests, mechanical models for steel and composite joints are developed with the aim of drafting practical methods for the definition of design forces acting on the singular components, and global elastic stiffness and strength of the joints.

Passing-through Tubular Column Joints for Steel and Composite Constructions made by Laser Cutting Technology / Andrea Piscini. - (2020).

Passing-through Tubular Column Joints for Steel and Composite Constructions made by Laser Cutting Technology

Andrea Piscini
2020

Abstract

In steel moment-resisting frames, tubular columns have many structural and architectural advantages over open-section columns. Circular Hollow Sections (CHS) are in fact particularly recommended for structural elements subjected to compression and bending forces in all directions, thanks to their higher radius of gyration and the axial-symmetric distribution of their mechanical properties. Therefore, the use of CHS profiles for the realization of columns can lead to a reduction of the total costs and furthermore to simplifications in the realization process of steel-concrete composite structures. However, the difficulties in realizing tubular column joints adopting open I-section beams, the most commonly used all around the world, severely reduce the use of CHS columns. Nowadays, I-beam-to-CHS-column steel and composite joints are commonly realized in two main ways: i) the connection is made by directly welding the beams or the beam stub to the wall of the steel tube; ii) supplemental plates are used to connect the beams to the circular column. The direct connection is the most convenient solution in terms of rapidity and easiness of fabrication but the performance of the joint is strongly limited by significant local distortions of the tube wall near the girder flanges. Therefore, the joint performance results very far from the ideal mechanical behavior of a rigid full-strength beam-to-column connection. The local buckle of the tube wall, which can lead to brittle failures, often suggests the use of supplemental plates for the realization of the tubular column joints. Additional elements can indeed assure a more effective transfer of the stresses from the beam flanges to the column wall or from the flanges of one beam directly to the beam placed on the opposite side. In general, two types of additional elements are currently used for I-beam-to-CHS-column moment joints: interior diaphragm joints, which imply the discontinuity of the column, and exterior diaphragm joints, which guaranty the total continuity of the column. Although internal diaphragms are very effective in distributing the internal forces and improving the collaboration between the steel elements and the concrete core in the case of composite columns, their use implies a discontinuity in the column and requires extensive welding to reconnect the column pieces. On the contrary, exterior diaphragms guarantee the steel tube continuity through the connection; nevertheless, several welding should be performed also in this case. Moreover, in the case of filled column, the composite behavior is not improved by the presence of steel elements, and the presence of big external stiffeners spoils down the aesthetic of the whole building. To overcome the main issues inherent the direct connections and the use of diaphragms, innovative solutions with continuous passing-through elements inside the column were studied, highlighting several advantages from a mechanical point of view. Indeed, the continuous elements can pass by slots of limited size made on the column wall, without requiring the complete discontinuity of the column itself and the joint requires less cutting and welding operations, resulting in lower overall cost and better mechanical behavior. The use of passing-through elements can lead to obtain the same mechanical benefits highlighted by internal diaphragms joints, without requiring the complete discontinuity of the column wall in the joint. However, despite all these advantages, many problems arise from the fabrication and constructional points of view, limiting the effective performance of the joints. Indeed, the difficulties in implementing high precision cutting processes spoiled the development of this construction technique, favoring more practice solutions. One of these difficulties lies in the production tolerances that affect the effective geometry of the beams. These tolerances shall be considered in the definition of the dimensions of the slots in which the beams need to pass through: dimensions of the slot very close to the nominal ones of the beam can lead to difficulties in the assembly process, whereas big gaps can result in ineffective welding. One of the solutions to overcome the difficulties in the fabrication and constructional processes of this joint typology lies in the application of the modern Laser Cutting Technology (LCT) to steel and composite structures. Laser cutting machines, commonly used in the industrial field, allow performing high precision and completely automated cutting processes on steel tubes and open sections profiles with the typical structural dimensions. To limit the influence of the beam dimensions tolerances, the laser cutting machines have the intrinsic advantage of directly providing measuring instruments that can be used to measure the elements to be passed. Therefore, the whole fabrication process can start with the simultaneous cutting and measuring process of the I-beams and plates. Subsequently, slots can be realized on the tube-wall considering the previously taken and recorded measurements and applying a defined strict tolerance margin. In this way the correct passage of the beam portions or plates through the column is guaranteed without requiring excessive gaps, and the welding processes is performed in the best conditions. Furthermore, thanks to the possibility of cutting with different inclinations with the tube-face, the penetration welding may be realized without performing any additional preparation processes on the worked-pieces. The LCT is also a very competitive solution in terms of time of fabrication and cost, thanks to the high automatization of the process reached by the modern technologies. However, even though the LCT provides the perspective of realizing the I-beam-to-CHS-column connection type that exhibited the best mechanical behavior in the past researches, several issues still need to be faced in order to define an appropriate fabrication process and to better characterize the behavior of the I-beam-to-CHS-column connection. For these purposes, in the presently exposed research, preliminary practical, numerical and theoretical studies are conducted to confirm the mechanical and technological advantages previously reported, and to understand the global and local behavior of the passing-through tubular column connections in case of both vertical and horizontal loadings acting on the structure. Considering the analyzed aspects inherent the practical realization and the mechanical behavior of the I-beam-to-CHS-column with passing elements, new joint solutions are proposed for both steel and composite structures. Afterwards, the proposed joint typologies are experimentally tested in order to have information on their mechanical behavior. On the basis of the behavior exhibited in the tests, mechanical models for steel and composite joints are developed with the aim of drafting practical methods for the definition of design forces acting on the singular components, and global elastic stiffness and strength of the joints.
2020
Walter Salvatore, Benno Hoffmeister, Francesco Morelli
ITALIA
Andrea Piscini
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Utilizza questo identificatore per citare o creare un link a questa risorsa: https://hdl.handle.net/2158/1222586
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