Large-scale test of symmetric cold-formed steel (CFS)-concrete composite beams with BTTST enhancement

A new connection device, based on bent-up tab shear transfer enhancement called bent-up triangular tab shear transfer (BTTST), has been studied through a symmetric cold-formed steel (CFS)-concrete composite beam subjected to a static bending test. BTTST provides an alternative connector system unique to CFS where CFS sections are usually thinner than hot-rolled sections and welding of headed-stud shear connectors is inapplicable. Coupled with the back-to-back arrangement of two CFS channels where symmetricity of the built-up section is restored, the resulting composite floor system has been proven to possess adequate strength and stiffness properties under static loads. The work has shown that the predicted values of the flexural capacities calculated using a new equation of shear capacity of BTTST agrees reasonably well with the experimental values.     

Performance of shear connection in composite beams with profiled steel sheeting

This paper describes the structural performance of shear connection in composite beams with profiled steel sheeting. An accurate and efficient nonlinear finite element model was developed to study the behaviour of headed stud shear connectors welded through-deck. The profiled steel sheeting had transverse ribs perpendicular to the steel beam. The material nonlinearities of concrete, headed stud, profiled steel sheeting, reinforcement and steel beam were included in the finite element model. The capacity of shear connection, load-slip behaviour of the headed stud, and failure modes were predicted. The results obtained from the finite element analysis were verified against experimental results. An extensive parametric study was conducted to study the effects on the capacity and behaviour of shear connection by changing the profiled steel sheeting geometries, the diameter and height of the headed stud, as well as the strength of concrete. The capacities of shear connection obtained from the finite element analysis were compared with the design strengths calculated using the American Specification, British Standard and European Code for headed stud shear connectors in composite slabs with profiled steel sheeting perpendicular to the steel beam. It is found that the design rules specified in the American and British specifications overestimated the capacity of shear connection, but the design rules specified in the European Code were generally conservative.     

Mechanics of shear deformable thin-walled beams made of composite materials

In this paper, a new theoretical model is developed for the generalized linear analysis of composite thin-walled beams with open or closed cross-sections. The present model incorporates, in a full form the shear deformability by means of two features. The first one may be addressed as a mechanical aspect where the effect of shear deformability due to both bending and non-uniform warping is considered. The second feature is connected with the constitutive aspects, and it contemplates the use of different hypotheses adopted in the formulation. These topics are treated in a straightforward way by means of the Linearized Principle of Virtual Works. The model is developed by employing a non-linear displacement field, whose rotations are formulated by means of the rule of semitangential transformation. This model allows studying many problems of static's, free vibrations with or without arbitrary initial stresses and linear stability of composite thin-walled beams with general cross-sections. A discussion about the constitutive equations is performed, in order to explain distinctive aspects of the effects included in the theory. This paper presents the theoretical formulation together with finite element procedures that are developed with the aim to obtain solutions to the general equations of thin-walled shear deformable composite beams. A non-locking fourteen-degree-of-freedom finite element is introduced. Numerical examples are carried out in several topics of static's, dynamics and buckling problems, focusing attention in the validation of the theory with respect to experimental data and with 2D and 3D computational approaches. Also, new parametrical studies are performed in order to show the influence of shear flexibility in the mechanics of the thin-walled composite beams as well as to illustrate the usefulness of the model.     

Monotonic shear tests of cold-formed steel wall frames with sheathing

This research is focused on the experimental study of the structural strength of cold-formed steel wall frames with sheathing under monotonic shear loading. Two aspect ratios, 1.0 and 2.0 were utilized in the design of wall specimens. Three different kinds of sheathing material, gypsum board, calcium silicate board, and oriented-strand board, with two different thicknesses (9 and 12 mm) were adopted in the test specimens. The ultimate strength, stiffness, energy absorption, and ductility ratio were studied for each test specimen. In final, the ductility ratios of the cold-formed steel wall frames similar to the wall configuration conducted in this study are proposed.     

考虑滑移效应的简支钢-混凝土组合梁挠度计算

采用栓钉等柔性抗剪连接件的钢-混凝土组合梁交界面上存在相对滑移变形,增大了组合梁的挠度。论文研究了冷弯薄壁U型钢-混凝土组合梁的滑移性能,推导了滑移量的计算公式,建立了考虑滑移效应的钢-混凝土组合梁在均布荷载作用下的挠度计算公式。分析表明：滑移效应对组合梁挠度影响不能忽略。     

Detailing recommendations for 1.83 m wide cold-formed steel shear walls with steel sheathing

The paper presents an experimental investigation on 1.83 m wide, 2.44 m high cold-formed steel (CFS) stud framed shear walls using steel sheet sheathing. Four wall configurations were studied through monotonic and cyclic tests. The test results indicated that besides the sheet buckling and screw pull out, the buckling of interior studs might occur for the 1.83 m CFS walls. To prevent the failure in the studs, special detailing was developed in this research. It was discovered that the special detailing could increase both the shear strength and the ductility of the shear walls. The research also found that the codified nominal shear strengths can be conservatively used for walls with an aspect ratio of 3:2. Based on the test results, the nominal seismic shear strength for 1.83 m wide CFS shear walls was established for design purposes.     

Behaviour of headed stud shear connectors for composite steel-concrete beams at elevated temperatures

The behaviour of composite steel-concrete beams at elevated temperatures is an important problem. A three-dimensional push test model is developed herein with a two-dimensional temperature distribution field based on the finite element method (FEM) and which may be applied to steel-concrete composite beams. The motivation for this paper is to increase the awareness of the structural engineering community to the concepts behind composite steel-concrete structural design for fire exposure. The behaviour of reinforced concrete slabs under fire conditions strongly depends on the interaction of the slabs with the surrounding elements which include the structural steel beam, steel reinforcing and shear connectors. This study was carried out to consider the effects of elevated temperatures on the behaviour of composite steel-concrete beams for both solid and profiled steel sheeting slabs. This investigation considers the load-slip relationship and ultimate load behaviour for push tests with a three-dimensional non-linear finite element program ABAQUS. As a result of elevated temperatures, the material properties change with temperature. The studies were compared with experimental tests under both ambient and elevated temperatures. Furthermore, for the elevated temperature study, the models were loaded progressively up to the ultimate load to illustrate the capability of the structure to withstand load during a fire. It is concluded that finite element analysis showed that the shear connector strength under fire exposure was very sensitive. It is also shown that profiled steel sheeting slabs exhibit greater fire resistance when compared with that of a solid slab as a function of their ambient temperature strength.     

Experimental study of composite cold-formed steel C-section floor joists

Twelve large-scale slab specimens and twenty-two companion push-out specimens were tested to study the behavior and capacity of composite slab joists consisting of cold-formed steel C-sections and concrete. Four shear transfer mechanisms, including surface bond, pre-fabricated bent-up tabs, pre-drilled holes, and self-drilling screws, were employed on the surface of the flange embedded in the concrete to provide shear transfer capacity. Results indicated that specimens employed with shear transfer enhancements showed a marked increase in strength and reduced deflection compared with those relying only on a natural bond between steel and concrete to resist shear. Of the three shear transfer enhancements investigated, bent-up tabs provided the best performance at both the strength and serviceability limit states, followed by drilled holes in the embedded flanges. The use of self-drilling screws resulted in the lowest strength increase. The correlation of shear transfer capacity of push-out specimens with the ultimate capacity of large-scale specimens indicated that the average experimental flexural capacity of the slab specimens was approximately 1.16 times the average predicted value based on push-out test results.     

Experimental studies of the shear behaviour and strength of lipped channel beams with web openings

Cold-formed steel members are increasingly used as primary structural elements in the building industries around the world due to the availability of thin and high strength steels and advanced cold-forming technologies. Cold-formed lipped channel beams (LCB) are commonly used as flexural members such as floor joists and bearers. However, their shear capacities are determined based on conservative design rules. Current practice in flooring systems is to include openings in the web element of floor joists or bearers so that building services can be located within them. Shear behaviour of LCBs with web openings is more complicated while their shear strengths are considerably reduced by the presence of web openings. However, limited research has been undertaken on the shear behaviour and strength of LCBs with web openings. Hence a detailed experimental study involving 40 shear tests was undertaken to investigate the shear behaviour and strength of LCBs with web openings. Simply supported test specimens of LCBs with aspect ratios of 1.0 and 1.5 were loaded at mid-span until failure. This paper presents the details of this experimental study and the results of their shear capacities and behavioural characteristics. Experimental results showed that the current design rules in cold-formed steel structures design codes are very conservative for the shear design of LCBs with web openings. Improved design equations have been proposed for the shear strength of LCBs with web openings based on the experimental results from this study.     

Experimental study on shear connection in unfilled composite steel grid bridge deck

This paper describes the results of experimental tests on the shear connection of the unfilled composite steel grid deck. To investigate the slip behavior and the shear strength of the connection, a total of 14 push-out specimens with variables for the number of holes, the area of reinforcements through holes, and the reinforcement diameter, were fabricated and push-out tests were performed. From the test results, each contribution affecting the shear resistance of the connection such as the friction force between the steel beam and the concrete, the concrete dowels, and the shear force due to reinforcement bars, was evaluated experimentally. An analytical expression was developed based on an existing formula used to predict the shear resistance of the connection. The equation predicts the shear strength to within 10% of the experimental results for the connection with reinforcing bars.     

Non-linear model for stability of thin-walled composite beams with shear deformation

A geometrically non-linear theory for thin-walled composite beams is developed for both open and closed cross-sections and taking into account shear flexibility (bending and warping shear). This non-linear formulation is used for analyzing the static stability of beams made of composite materials subjected to concentrated end moments, concentrated forces, or uniformly distributed loads. Composite is assumed to be made of symmetric balanced laminates or especially orthotropic laminates. In order to solve the non-linear differential system, Ritz's method is first applied. Then, the resulting algebraic equilibrium equations are solved by means of an incremental Newton–Rapshon method. This paper investigates numerically the flexural–torsional and lateral buckling and post-buckling behavior of simply supported beams, pointing out the influence of shear–deformation for different laminate stacking sequence and the pre-buckling deflections effect on buckling loads. The numerical results show that the classical predictions of lateral buckling are conservative when the pre-buckling displacements are not negligible, and a non-linear buckling analysis may be required for reliable solutions.     

Global optimum design of cold-formed steel hat-shape beams

Using the computational neural network model developed recently by the authors, a comprehensive parametric study is performed for global optimization of cold-formed steel hat-shape beams based on the AISI Specifications. Design curves are presented for global optimum values of the thickness, the web-depth-to-thickness ratio, and the flange width-to-thickness ratio for unbraced beams having steel yield strengths of 250 and 345 N/mm². The computational neural network model guarantees a local optimum solution. The global optimum is found by an exhaustive search that is guided by a heuristic approach to reduce the search effort. An extensive parametric study yielded insights into the behavior of cold-formed steel beams that are then used as rules to reduce the search space and guide the exhaustive search. The procedure for finding the global optimum design of cold-formed steel beams is presented in a few recursive steps. The optimum design curves presented in this article can be of great value to structural design engineers.     

Assessment of effective slab widths in composite beams

This paper deals with the behaviour of composite beams with particular focus on the effective slab width, which is required for simplified structural analysis and design. Current design codes propose values for the effective width which are mostly a function of the beam span ignoring in this way the influence of other important parameters. Several 3D numerical simulations are conducted in this paper in order to illustrate these parameters and accordingly a new methodology is suggested for evaluating the effective width. The proposed approach is easier to apply in comparison with other existing methods based on stress integration, and provides effective width values which result in a more reliable representation of the actual beam state when simplified analysis is carried out. The application of the new method indicates that the effective width is mostly related to the actual slab width and, in many cases, the values obtained can significantly differ from those proposed in design codes. Validation of the new approach is carried out through comparison of simplified 2D models with the results obtained from a recent experimental investigation as well as from more complex 3D numerical simulations.     

Design of steel sheathed cold-formed steel framed shear walls

A method for the design of steel sheathed cold-formed steel framed shear walls has been developed for inclusion in the American Iron and Steel Institute's North American standards for lateral design using a comprehensive database of single-storey shear wall tests carried out in Canada and in the United States. The wall configurations differed in terms of wall aspect ratio, framing and sheathing thickness, screw fastener schedule and framing reinforcement. The Equivalent Energy Elastic–Plastic (EEEP) analysis approach was used to derive key design information from the test data, including: nominal shear resistance, a resistance factor, an over-strength factor for capacity based seismic design and ‘test-based’ seismic force modification factors for ductility and over-strength.     

Design of semi-continuous composite steel-concrete beams at the fire limit state

A two-dimensional temperature analysis procedure based on the finite element method (FEM) is described and applied to steel-concrete composite beams. A computer program developed for the analysis is detailed. A strategy is also proposed for incorporating the influence of the partial resistance of the composite connections in reducing the sagging moment at central regions of the beam spans when the beam is calculated as semi-continuous. Finally, an example problem is discussed, comparing the design uniformly distributed loads that can be supported by a composite beam calculated as semi-continuous and with simply supported spans. The temperature distribution due to fire at the central region of the spans is taken as in the simplified procedure proposed in European Prestandard ENV 1994-1-2 [ENV 1994-1-2. Eurocode 4, Design of composite steel and concrete structures — Structural fire design. Brussels: European Committee for Standardization (CEN); 1994] and then obtained with the more rigorous calculation using the described numerical algorithm. It will be assumed that no ultimate limit state will occur due to shear force (web buckling) or due to bending moment at the hogging moment regions of the beam (web and bottom flange buckling or distortional lateral buckling).     

Strength and stiffness determination of shear wall panels in cold-formed steel framing

Shear wall panels, as the one of the primary lateral load resisting elements, have been extensively used in lightweight framing of low- and mid-rise residential construction, particularly in seismic applications. In current practice, lateral strengths of shear wall panels with cold-formed steel framing are primarily determined by tests, owing to the lack of applicable analytical methods. Meanwhile, the use of numerical methods such as the finite element method has rarely been employed in the design practice to determine the lateral strength of shear wall panels due to the extensive amount of computational effort associated with the modelling. Presented in this paper is an analytical method to determine the ultimate lateral strength of the shear wall panel and its associated displacement. The method takes into account the factors that primarily affect the behaviour and the strength of the shear wall panel, such as material properties, geometrical dimensions and construction details. Lateral strengths obtained from the proposed method for shear wall panels with different sheathing materials and steel stud thicknesses, sizes and spacing of sheathing-to-stud fasteners were compared with those of recent experimental investigations. The comparison demonstrates that the predicted results are in good agreement with those of the tests. Therefore, it is recommended that the proposed method be used in engineering practice.     

Efficiency reduction due to shear lag on bolted cold-formed steel angles

This work presents 66 new experimental tests carried out on cold-formed steel angles fastened with bolts and under tension. In order to calculate tension-members’ ultimate capacity, net-section failure is considered. The shear-lag phenomenon reduces net-section capacity. This reduction is computed through the reduction coefficient which is a function of two parameters: length of the connection and distance of the shear plane to the centroid of the cross-section. This article examines the reduction coefficient performance based upon the new tests and data available in the literature, comprising a total of 108 lab tests. A new expression for the net-section reduction coefficient is suggested.     

Optimization of mono- and anti-symmetrical I-sections of cold-formed thin-walled beams

Subject of the study includes mono- and anti-symmetrical open I-sections of cold-formed thin-walled beams with double flanges. The beams under uniformly distributed vertical load are simply supported at both ends. Geometric properties of each of the I-sections are separately described by dimensionless parameters. Strength, global and local buckling conditions are defined for these beams. A dimensionless objective function is assumed and formulated on the grounds of the optimization criterion. Numerical study of a family of thin-walled beams is carried out. Results of the study are presented graphically.     

采用剪切弯曲三角杆的对称冷弯型钢-混凝土组合梁的大比例试验

对对称冷弯型钢-混凝土组合梁进行静力受弯试验,介绍了基于剪切弯曲杆改进的剪切弯曲三角杆。冷弯型钢构件比热轧构件更薄,不允许焊接栓钉剪力连接件,剪切弯曲三角杆能解决这一问题。将两个冷弯型钢槽的背靠背连接成对称构件,它在静力作用下具有足够的强度和刚度。通过剪切弯曲三角杆的抗剪方程计算的抗弯承载值与试验数据很吻合。     

Finite element modelling of composite beams with full and partial shear connection

The present investigation focuses on the evaluation of full and partial shear connection in composite beams using the commercial finite element (FE) software ANSYS. The proposed three-dimensional FE model is able to simulate the overall flexural behaviour of simply supported composite beams subjected to either concentrated or uniformly distributed loads. This covers: load deflection behaviour, longitudinal slip at the steel-concrete interface, distribution of stud shear force and failure modes. The reliability of the model is demonstrated by comparisons with experiments and with alternative numerical analyses. This is followed by an extensive parametric study using the calibrated FE model. The paper also discusses in detail several numerical modelling issues related to potential convergence problems, loading strategies and computer efficiency. The accuracy and simplicity of the proposed model make it suitable to predict and/or complement experimental investigations.