Introduction
The unique requirements of structures have demanded the advancement in construction technology to attain optimal versatility and efficiency. The construction has also metamorphosed from the conventional objective of strength to the need for comfort. The latter has attracted the need for customization of the structures to fit the matchless necessities posited by the structures under construction. Consequently, this has necessitated the debasement of the construction materials from the traditional pure materials to amalgamations. Composite steel is a material comprising at least two different metal alloys combined into one, especially to attain different properties from the constituent components. The fundamental metal element of composites is iron. The composites may consist of materials of significant difference. Essentially, this type of steel is a ferrous alloy profile that works in combination with concrete. The report will describe metal decking with concrete fillers as the first and steel girders with concrete-embedded connectors as the second type of main composite steel. This report has opted for composite steel and it will elucidate the rationale of the selection before summing up through an overall conclusion.
Rationale of the choice of structure
An understanding must prevail that the composite steel structure mainly emphasizes the arrangement, contrary to the product. Essentially, the fundamental composite steel products are bimetallic plates that are developed through the bonding of two dissimilar alloy plates. The outcome of the bonding is a product containing different chemical and mechanical features manifested on both planes, inside and outside. The combination of two different alloy properties targets a different product that can achieve desirable outcomes in building and construction. The use of composite steel is fundamental for harnessing the best properties of the final product that are always better than those of the individual alloy constituents. The output of the combination is hybrid steel that is stronger, can withstand the greater weight, and lighter. Any alloy constitutes a minimum of two materials and at least one metal.
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Figure 1 : Types of Composite Steel Structures
Metal decking with concrete fillers
This is a metal deck consisting of an embossment pattern created into the sides at specified intervals. The embossments permit concrete to contact metal and form a bond with the decking panel as the allowed concrete cure. After the completion of the curing phase, both the metal deck and the concrete become a single component bonded together strongly, becoming a composite metal deck. The strength attained by the bonding is greater than the sum of the two individual components. Composite steel decking can be used for both floor and roof. Decking is essential in enhancing the bonding membrane to ensure additional support for strength.
Figure 2 : Steel Deck
Figure 3 : Profile Steel Deck
Steel girders with concrete-embedded connectors
Steel girders are critical factors in structural engineering and girders developed from composite steel are superior because they have led to revolutionizing of the industry. The girders form a special type of beams. Girders help in the connection of structures especially horizontally by supporting the smaller beams. Consequently, the outlined fact renders all girders to beam though not all beams are girders.
The arrangement of the girders and the embedment offers a larger surface area for contact between the steel and concrete. The contact leads to a greater bonding strength between the composite steel and the concrete.
Figure 4 : Steel-Concrete Composite Column
Members of composite steel structure can be bonded through two main ways, adhesion or bond that occurs at the interface of steel-concrete composite in beams or columns that are encased. The second method is mechanical shear connectors used in uncased composite steel structures, especially slabs and beams.
The mechanical connectors labelled by letters are represented as follows (S) stud, (T) bolt, (U) channel, (V) pinned, (W) bar, (X) angle, (Y) external bolt, and (Z) friction grip bolt.
Welded studs are advantageous because they are regarded as ductile and this implies that without contemplation of any fatigue, structures can be designed applying principles of plastics. These rules apply because there is a presumption that redistribution of force can occur between studs located adjacent to each other. When a beam is crafted and designed, and a full shear connection is incorporated, it implies that adequate connectors are available and one of two possibilities can result. First, can fail the concrete in compression absolutely or fail the concrete in steel section tension fully, and this happens according to the section with a smaller force. Nevertheless, a restricted number of connectors can be applied, and this will lead to partial shear connection. This phenomenon may occur if the loading applied is at the lower level that meets the threshold. For instance, the occurrence is common in the circumstances where the design considered serviceability of the structure or the stage of construction. Since the connection is a critical concern, codes have stipulations targeting the stability and quality of the structures. The codes provide the minimum extent of connection required to avert excessive slip between concrete and steel because such will lead to failure among the connectors.
When designing structures using composite steel it is apt to limit bond stress to a minimum value. The restriction of the bond stress will offer a margin for the incalculable impacts of concrete contraction, cater for poor adhesion to the surfaces under the steel, and stresses attributed to fluctuations in temperatures. Scholars, engineers, and professional researchers have performed studies on the definitive strengths of the encased beams and realized that the calculated bond stresses on the encased beams are insignificant at high loads. The bond stresses have little meaning because cracking and local failures of bonds develop. Shear connectors are mandatory and codes of practice do not permit designs targeting ultimate strength without the connectors in composite steel structures. Evaluations on uncased composite beam structures indicate that most of the longitudinal shear is relayed at the surface by the bonding of materials at low loads. Additionally, the bond disintegrates when subjected to high loads and cannot be restored once broken. The shear connection happens through welding of the dowel into the steel member’s top flange and then enclosed by an in situ concrete when casting of the deck or floor slab in beams that are uncased.
Figure 5 : Steel Concrete Composite Sections
Overall conclusion
This report has succeeded in achieving its objectives as observed in the comprehensive elucidations in every section. Every invention in structural engineering targets the improvement of structures and the introduction of composite steel structures are not exempted. Composite steel has a higher strength to weight ratio and this is their great advantage compared to other structures. This feature allows for the structures to be used in circumstances where weight is a fundamental concern. Composites are more durable and this is commonly observed in their resistance to rust notwithstanding of the environment. The high dimensional stability of the structures makes them maintain the best shape in all conditions. Composite steel structures are flexible and have opened more avenues for new designs. With conventional materials, it is not easy to achieve designs that have been made possible with composite steel. Finally, it is easier to produce composites. Initially, engineers got engaged in tedious processes of generating the composites but the process became easier with the introduction of digital composite manufacturing.
