CHAPTER 1 INTRODUCTION
2.6 Research on Composite Beams and its Components
Many experimental, analytical and numerical research works were carried out on Composite beams to understand their behavior. Some of the investigations performed by previous researchers are briefly discussed below.
2.6.1 Experimental Investigations
Experimental researches were carried out on Composite beams by several research teams (Baran and Topkaya 2014, Pavlović et al. 2013, Aida Mazoz et al. 2013) to investigate the behavior of beams and shear studs. Several tests were performed on Composite beams with various types of beams and shear studs. Their behavior was recorded. Summary of these experiments are described below:
Baran and Topkaya (2014)
An experiment was performed to investigate the flexural behavior of partially composite beams. Channel type shear connectors were used for composite action. Four full scale steel concrete composite beams were compared with a simple steel beam. Objective of the study was to identify the variation of strength and stiffness properties for various degrees of composite actions. AISC recommendations were followed for assessment of the influence of partial composite actions on flexural behavior. The experiment revealed that the stiffness and strength of composite beams with channel type shear connectors are acceptably close with calculated values. It also revealed that steel beams had significantly lower stiffness and strength compared to the fully composite beams.
Pavlović et al. (2013)
Pavlovic et al. performed an investigation to compare between the use of high strength bolts and shear studs as shear connectors. Bolted and welded shear connectors are tested.
Basic shear connector properties i.e. shear resistance, stiffness, ductility and failure modes was compared. The research was done in order to improve competiveness of prefabricated composite structures. To understand the difference between the headed shear studs and the bolted shear connectors, push out tests were performed according to EN1994-1-1, using 4 M16-grade 8.8 bolts with embedded nuts. Same layout was followed for the bolted and headed shear studs. Finite element models were also prepared to compare the results with experimental findings. The tests revealed that the bolted shear connectors with single embedded nuts achieved approximately 95% of shear resistance
16
against static loads. Stiffness of the bolted shear connectors we less due to the slip in hole.
Also bolted shear connectors with single embedded nut in full depth concrete showed brittle behavior.
Mazoz et al. (2013)
This paper presents the results of 24 push out test specimens with a new type of shear connector. The connector was called I shape connector. The experiment was done the investigate the effect of four parameters on the ultimate load capacity. They are a) height of the I shape connector, b) length of the I shape connector, c) compressive strength of concrete and d) the number of transverse reinforcing bars. Failure modes and the load slip behavior were mainly focused. The experimental results were compared with the design equations to predict the ultimate load capacity of I shape shear connectors. From the push out tests, two basic types of failure modes were observed; i.e. shearing of the connector and crushing-cracking of the concrete slab. Shear failure of connector was observed when lower steel grade, and smaller length connectors were used with higher strength concrete.
On the other hand, concrete crushing-cracking occurred when higher steel grade and lower strength concrete slab was used. The slip values obtained from the push out tests were greater than 6mm, so the I shape connectors can be considered as ductile as per Eurocode.
2.6.2 Numerical Investigations
Several numerical investigations have been done to analyze the performance of composite beams and its components. Some of them are briefly discussed below:
Jeyarajan et al. (2015)
This paper investigates the progressive collapse behavior of steel concrete composite buildings subject to ground blast explosion using nonlinear dynamic analysis and conventional alternative path approach. The analysis model was prepared in ABAQUS.
Steel beams were modelled as a two-node linear beam element. Interaction between beam and slab was defined by tie constraint to represent the composite action between the concrete slab and steel beam. Partial composite action was not considered. Local buckling of beam was not considered. A simplified composite slab model was used to avoid geometrical complication and to reduce the computational time required for analysis the 3-D large scale framework. The profile metal deck was represented by rebars in a longitudinal direction based on equivalent area of the respective web and flange plates of
17
the metal deck. Profile concrete is converted into an equivalent uniform concrete section.
The concrete section was modelled using a four-node homogeneous shell element. Rebar of deck concrete was defined using rebar definition through the ABAQUS library. A slab model with an equivalent second moment area was compared against the proposed slab, which was based on an equivalent area of steel and concrete. It was observed that the effect on global response of frame is not significant since the slab is being modelled with a steel beam.
Katwal et al. (2015)
This paper has presented a simplified numerical model for composite beams with trapezoidal steel decking. The model has been implemented in ABAQUS. Detailed finite element modelling using shell and solid elements can predict the behavior of composite beams precisely. But this method is time consuming. Katwal et al. (2015) used shell elements to simulate concrete slab, rebar elements to represent steel sheeting and connector elements to simulate the shear studs. The behavior of shear stud was incorporated in the model by defining shear force versus slip relationship. The predicted results were compared with test results from other experiments and from results from detailed FE models using solid elements. From the comparisons it was concluded that simplified model can predict the behavior of composite with reasonable accuracy. The predictions for both deflection and beam end slip have excellent correlation with the test results of composite beams.
Begum et al. (2013)
This paper presents a comparison between the costs involved for composite construction and pure concrete construction in Bangladeshi context. One of the aims was to provide a brief description to various components of steel concrete framing system for buildings.
Also a cost effectiveness of steel-concrete composite frames over traditional reinforced concrete frames for buildings structures was to be investigated. A typical commercial building with a floor area of 7720 sft was selected for the study. Design and estimation was done for similar floor patterns and for variable storey heights like 6 storey, 12 storey, 18 storey and 24 storey. Costing was estimated for two type of framing systems based on Bangladesh standard. A cost versus number of storey curve was developed. It was found that RCC framing system is cheaper for low-rise buildings. For buildings with number of stories greater than 15, composite construction becomes economic than RCC construction.
18