Feasibility of developing composite action between concrete and cold-formed steel beam

Cold-formed steel structures are steel structure products constructed from sheets or coils using cold rolling, press brake or bending brake method. These structures are extensively employed in building construction industry due to their light mass, ductility by economic cold forming operations, favorable strength-to-mass ratio and other factors. The utilization of cold formed steel sections with concrete as composite can hugely reduce the construction cost. However, the use of cold formed steel members in composite concrete beams has been very limited. A comprehensive review of developments in composite beam with cold formed steel sections was introduced. It was revealed that employing cold-formed steel channel section to replace reinforcement bars in conventional reinforced concrete beam results in a significant cost reduction without reducing strength capacity. The use of composite beam consisting of cold-formed steel open or close box and filled concrete could also reduce construction cost. Lighter composite girder for bridges with cold-formed steel of U section was introduced. Moreover, types of shear connectors to provide composite action between cold-formed steel beam and concrete slab were presented. However, further studies to investigate the effects of metal decking on the behavior of composite beam with cold-formed steel section and introduction of ductile shear connectors were recommended.

Double⁃Shear Experiments of Cold⁃Formed Steel Stud⁃to⁃Sheathing Connections at Elevated Temperatures

The behavior of cold⁃formed steel(CFS)stud⁃to⁃sheathing connections at elevated temperatures is an important parameter for the fire resistance design and modeling of mid⁃rise CFS structures.In this paper,three kinds of sheathings,namely,medium⁃and low⁃density calcium⁃silicate boards and oriented strand board,were selected for double⁃shear experiments on the mechanical properties of 253 screw connections at ambient and elevated temperatures.The effects of the shear direction,screw edge distance and the number of screws on the behavior of the connections were studied.The results showed that the shear direction and the screw edge distance more significantly influenced the peak deformation,while their impacts on the peak load varied with the type of sheathings.Compared with the single⁃screw connections,the peak loads of the specimens with double⁃screw connections obviously increased but did not double.Finally,a simplified load⁃displacement curve model of stud⁃to⁃sheathing connections at elevated temperature was generated first by establishing the prediction formula for characteristic parameters,such as the peak load,the peak deformation and the elastic stiffness,and then by considering whether the curves corresponded to stiffness increase phenomena.The present investigation provides basic data for future studies on the numerical modeling of CFS structures under fire conditions.

Oxidation Resistance of the Aluminide Coating Formed on Carbon Steels

Low and medium carbon steels were aluminized by the pack aluminizing technique using halideactivated pure-Al and Fe-Al packs. The effect of mixture composition, aluminizing temperatureand time and C content of the steel substrate on the structure and thickness of the aluminidelayer, and on the oxidation resistance was investigated. The optimum oxidation resistance canbe achieved with a low carbon steel substrate when the intermetallic phases Fe3Al and FeAlform the surface of the aluminide layer. In this case, the Al concentration at the surface of thealuminide coating is at least ≥15 wt pct. Formation of high Al concentration phases (FeAl3 andFe2Al5) during aluminizing should be avoided as they tend to embrittle the aluminide layer andreduce its oxidation resistance.

Experimental Investigation of the Effect of the Material Damage Induced in Sheet Metal Forming Process on the Service Performance of 22MnB5 Steel

The use of ultra-high strength steels through sheet metal forming process offers a practical solution to the lightweight design of vehicles.However,sheet metal forming process not only produces desirable changes in material properties but also causes material damage that may adversely influence the service performance of the material formed.Thus,an investigation is conducted to experimentally quantify such influence for a commonly used steel（the 22MnB5 steel） based on the hot and cold forming processes.For each process,a number of samples are used to conduct a uniaxial tensile test to simulate the forming process.After that,some of the samples are trimmed into a standard shape and then uniaxially extended until fracture to simulate the service stage.Finally,a microstructure test is conducted to analyze the microdefects of the remaining samples.Based on the results of the first two tests,the effect of material damage on the service performance of 22MnB5 steel is analyzed.It is found that the material damages of both the hot and cold forming processes cause reductions in the service performance,such as the failure strain,the ultimate stress,the capacity of energy absorption and the ratio of residual strain.The reductions are generally lower and non-linear in the former process but higher and linear in the latter process.Additionally,it is found from the microstructure analysis that the difference in the reductions of the service performance of 22MnB5 by the two forming processes is driven by the difference in the micro damage mechanisms of the two processes.The findings of this research provide a useful reference in terms of the selection of sheet metal forming processes and the determination of forming parameters for 22MnB5.

Plasma Surface Cu Alloyed Layer as a Lubricant on Stainless Steel Sheet:Wear Characteristics and On-job Performance in Incremental Forming

To solve the problems of poor forming and easy adhesion of the stainless steel,Cu alloyed layer on the stainless steels was prepared by the double glow plasma surface alloying technique.The experimentalresults indicated that the supersaturated copper dispersedly precipitated in grain interior and crystalboundaries and formed the vermicular structure.The tribologicaltests indicated that the friction coefficient of the Cu alloyed layer was lower than that of the stainless steels.The wear rate of stainless steelin the presence of Cu alloyed layer was approximately 2-fold lower than that in the absence of the alloyed layer.The results of the incrementalforming indicated that the ploughing phenomenon was not observed on the stainless steelin the presence of Cu alloyed layer during the incrementalforming,while the stainless steelpresented the deep ploughing.Therefore,Cu alloyed layer on stainless steelexhibited excellent self-lubrication and forming properties.

Numerical Simulation and Experimental Study on Interlock Deformation for Roll Formed U-Section Steel Piling

The interlock of a roll formed U-section sheet steel piling under loading was analyzed by means of numeri- cal simulation, and meanwhile the tensile failure experiment was conducted. The results indicated that under the same load, the interlock corners of roll formed steel piling are not only the regions with the lowest safety factor, but also the regions with the highest stress; there are two slippages in the tensile instability process of interlock, Each slippage can be regarded as a failure, and different types of failure mode should be used to evaluate the performance of steel pilings according to different applications. Due to the work hardening effect during the roll forming process, the hardness of the interlock material increases by 16% compared with that of the original sheet steel. It was also found that the instability strength obtained in tensile failure test is only 15.6 % of the tensile strength of the original sheet steel.

Hot Deformation Behavior and Processing Map of Spray Formed M3∶ 2 High Speed Steel

Hot deformation behavior of a new type of M3∶ 2 high speed steel with niobium addition made by spray forming was investigated based on compression tests in the temperature range of 950-1 150 ℃ and strain rate of 0. 001-10 s^（-1）. A comprehensive constitutive equation was obtained,which could be used to predict the flow stress at different strains. Processing map was developed on the basis of the flow stress data using the principles of dynamic material model. The results showed that the flow curves were in fair agreement with the dynamic recrystallization model. The flow stresses,which were calculated by the comprehensive constitutive equation,agreed well with the test data at low strain rates（ ≤1 s^（-1））. The material constant（ α）,stress exponent（ n） and the hot deformation activation energy（ Q_（HW）） of the new steel were 0. 006 15 MPa^（-1）,4. 81 and 546 kJ·mol^（-1）,respectively. Analysis of the processing map with an observation of microstructures revealed that hot working processes of the steel could be carried out safely in the domain（ T = 1 050-1 150 ℃,ε = 0. 01- 0. 1 s^（-1））with about 33% peak efficiency of power dissipation（ η）. Cracks was expected in two domains at either lower temperatures（ 〈 1 000 ℃） or low strain rates（ 0. 001 s^（-1）） with different cracking mechanisms. Flow localization occurred when the strain rates exceeded 1 s^（-1） at all testing temperatures.

Quality Control for Continuously Cast Slab of High Strength Weathering Steel Q450NQR1

In order to reduce the transverse corner cracks of high strength weathering steel Q450NQR1,the factors influencing transverse corner cracks on continuously cast slab,such as level fluctuation of molten steel in mold,mold taper,primary cooling,mold powder,secondary cooling,nitrogen content in steel,spray nozzle structure,processing parameters and equipment of CC,etc.,were analyzed.Based on this,a series of comprehensive countermeasures have been proposed.The operation shows by the use of key technologies,including stabilizing steel level,optimizing the mold taper,weakening the primary cooling and the secondary cooling,reforming the mold powder,and adjusting spray nozzle structure,the transverse corner cracks on continuously cast slab have been significantly reduced,and the edge cracks on hot rolled sheet have been eliminated due to the transverse corner cracks.The qualified slabs are delivered to produce weathering cold forming sectional steel,whose yield strength is greater than 450MPa.

Innovative manufacturing technology enabling light weighting with steel in commercial vehicles

Improved manufacturing technology is often needed when working with high strength steel. In this re- spect manufacturing technology has to adapt to the altered （and typically reduced） formability and weldability of modern high strength steel. However, this is a rather passive approach from a manufacturing point of view. An indeed much more powerful approach is to generate synergies between innovative manufacturing technology, design and material enabling additional weight savings and efficiency gains. Laser-based material processing, in particular laser welding, offers a wide range of opportunities in this sense. Furthermore, hot stamping and roll forming open up new possibilities for advanced manufacturing of commercial vehicle components. Applications and examples of these technologies will be given in terms of producing innovative semi-products as well as final components.

Manufacturing of Long Products Made of Innovative Lightweight Materials

The processing of innovative lightweight materials to sheet metal components and assemblies with globally or locally defined properties is the object of this work. It takes a load-dependent design of components and assemblies, for example, based on the composition of different construction materials or a targeted setting of component areas with specified characteristics to fully exploit the lightweight potential when substituting conventionally used materials. Different process chains for the manufacturing of roll-formed long products made of magnesium alloys and high-strength steels with locally defined properties will be presented in this paper. Depending on the kind of material to be formed and the desired product characteristics, different temperature managements are needed for capable processes. Due to limited formability at room temperature, magnesium alloys require a heating of the forming zones above 200–225 °C throughout the bending process in order to activate additional gliding planes and to avoid any failures in the radii. The realization of local hardening effects requires at least one process-integrated heat treatment when roll forming manganese–boron steels. For both processes, it is imperative to realize a heating and cooling down or quenching appropriate for the manufacturing of long products with the required quality. Additionally, proper line speeds that allow a continuously operated economical production have to be considered. Research results including design, FEA, realization and experimentation of the mentioned process chains and strategies will be described in detail.