DEVELOPMENT OF NOVEL SHEAR CONNECTORS FOR COLD FORMED STEEL  CONCRETE COMPOSITE BEAMS:-

Shear connectors are key components to ensure the efficient composite action and satisfactory transfer of shear forces at the steel–concrete interface in composite beams. Under hazardous circumstances, such as fire in a building, the performance of a composite beam significantly relies on the performance of shear connectors. Studies on the behavior of shear connectors subjected to elevated temperatures performed in the last decade are reviewed in this paper. The experimental testing of push-out specimens, the design approaches provided by researchers and different codes, the major failure modes, and the finite element modeling of shear connectors are highlighted. The critical research review showed that the strength of a shear connector decreases proportionally with the increase in temperature. Compared with the volume of work published on shear connectors at ambient temperatures, a few studies on the behavior of shear connectors under fire have been conducted. Several areas where additional research is needed are also identified in this paper.

Two shear connectors named trapezoidal and hexagonal respectively have been proposed.  In order to determine the load slip curve of the proposed shear connectors  push out specimens were prepared as per eurocode 1994-1-1 (2004) to test under monotonic loading. Total four specimens are prepared out of that 2 are hexagonal Connectors and and 2 are trapezoidal connectors. The test specimens are placed in position using crane. The test was conducted using hydraulic jack of 20 tonne capacity.

Belts were put around the specimen to prevent parts from falling apart. During test force in hydraulic jack and displacements are continuously monitored using proving ring and dial gauge.The load was applied using two hydraulic jacks on a horizontal beam onto the proving ring, which measures the load applied on tthe specimen. The arrangement is made in such a way that load is applied concentrically on the I beam so that load is distributed on both sides of the specimen equally. The vertical displacement is measured using a digital dial gauge .

CONCLUSION:-

Hexagonal Connector failed by connection failure . In trapezoidal connector failure occurred by the crushing of concrete followed by slip of the connector. For cold formed steel composite beams and situations where welding should be avoided the proposed trapezoidal and hexagonal shear connectors can be used as alternative.

COLD FORMED STEEL CONCRETE COMPOSITE SHEAR WALL:-

Introduction:

Constructions with cold-formed steel sections have become very successful in Scandinavia and North America during the last couple of years. The construction differs from timber frame structures. Floor panels and shear walls are made of bearing cold-formed steel sections, which are arranged in a pattern of 400–800 mm. In addition, the construction includes sheathing on both sides. As a rule, the plate thickness of the sections varies between 1.0 and 2.0 mm. An elastic composite construction is made by the connection of the sections and the sheathing. Analogue to timber frame construction the stiffening of a building can be carried out with help of these floor panels or shear walls. A shear wall is then stressed by both vertical and horizontal loads from the floor panels. The assembly of a shear wall is identical to that of a light separating wall. The studs are made of C-sections which are placed into the floor- and ceiling-U-sections.

The sheathing is attached to the steel substructure by self-drilling screws. To examine the structural behaviour of the shear walls an analysis with several test runs has been carried out at the Institute for Steel Construction and Material Mechanics. The maximum horizontal load of shear walls with 1.25 m width and 2.60 m height and different types of sheathing was established during the first test run. The structural behaviour with additional vertical loads was examined in the following test run. The most important parameter in the analysis of the structural behaviour of shear walls is the connection with self-drilling screws between the cold-formed steel section and the sheathing. Therefore, a third test run was carried out on detail specimens of screwed connections. The maximum load as well as the load–displacement curves were determined in this test run.

Experimental investigation to find the lateral load carrying capacity of cold formed steel concrete composite shear wall under static shear load:

The parameters varied were the cross-sectional shape (flat, trapezoidal and square) of the shear wall and the number of intermediate fasteners (4 and 20 no’s). The experimental set-up consists of a reaction frame resting on a base frame on which specimens are attached through the foundation. Foundation of the shear wall is designed in such a way that the failure load for foundation will be approximately twice of the failure load for shear wall, other components like connections between shear wall and foundation and connection between the base frame and foundation. The composite shear wall has a RCC foundation of 1250x500x260mm constructed monolithically with shear wall. Composite wall specimens were tested to failure by applying lateral shear load through hydraulic jack. The hydraulic jack of 200 kN capacity is used to apply the load to the cold-formed steel-concrete composite wall panel. This jack is attached to the reaction frame of through bolting. Proving ring of 500KN capacity is placed in between the jack and the wall panel and the load is calibrated from the proving ring readings. A computer aided data acquisition system was utilized to record the data from LVDTs. LVDT-1 was placed on the top edge of the wall to measure the lateral displacement. LVDT-2 was placed on the bottom edge of foundation to measure any possible slips and LVDT-3 was placed perpendicular to the wall to measure any possible out of plane displacements

CONCLUSION:

 Specimens having a greater number of intermediate fasteners showed higher load carrying capacity because of the enhanced composite action between the steel and concrete. Square shaped composite shear wall showed the maximum lateral load carrying capacity as it had more area of steel cross section.

COLD-FORMED STEEL-CONCRETE COMPOSITE COLUMNS:-

A new system of composite columns is developed using lipped cold-formed steel channels with embossments and cast-in-place concrete. The combined action of the embossments and the channel’s lips leads to very good bond between the steel and the concrete. It has been found that by replacing the standard longitudinal reinforcing bars by cold-formed steel sections of equal area, the structural performance of the columns remains almost unchanged, while considerable savings are achieved in time and material of construction. Hence in this study, an attempt is made to experimentally investigate the effect of stiffeners in the behaviour of cold-formed steel-concrete composite columns

ROLE OF STIFFENERS:-

The steel-concrete composite columns exhibit improved strength and ductility characteristics owing to the ability of the concrete infill to prevent the local buckling of the steel tube. Though concrete infill prevents inward local buckling, outward buckling still limits the sections from yielding. The provision of stiffeners is known to effectively delay the local buckling effects in the case of hollow cold-formed steel columns.

EXPERIMENT TO INVESTIGATE EFFECT OF STIFFENERS IN THE BEHAVIOUR OF COLD-FORMED STEEL-CONCRETE COMPOSITE COLUMNS:-

Incorporating cold-formed steel sections in composite columns creates further complications in connection as welding of very thin sections pose practical difficulties. Hence connection using self-tapping screws replaces the conventional connections in this work.

A series of 12 specimens were tested to determine the cross-sectional strength and the failure patterns. A scaled down cross section of 100 mm x 100 mm was chosen. Cold rolled steel of 1.6 mm was adopted. Columns belonging to different slenderness category namely short, intermediate and long column were selected. Sections with and without intermediate stiffeners in the form of bends were investigated. A 1000 kN hydraulic jack mounted on a column testing frame was used to apply the load. The support condition assumed was simply supported and it was achieved by the provision of two hinged plates on both sides of the column. The behavioural responses of the specimens were recorded by DAQ system with the help of linear variable displacement transducers (LVDT) for axial displacement and 300 kN load cell for the loads imposed.

CONCLUSION:-

The stiffener provided is found to be effective for all hollow sections, but their effectiveness is not pronounced in the composite sections. Self-tapping screws are found to provide a good mode of connection