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CONTENTS:COMPOSITE BEAM:

WHAT IS COMPOSITE CONSTRUCTION?Composite construction is a generic term to describe any building construction involving multiple dissimilar materials. Composite construction is often used in building aircraft ,watercraft, and building construction. There are several reasons to use composite materials including increased strength, aesthetics, and environmental sustainability. It is not to be confused with the Composite order which is a specific order of classical architecture that combines elements of the Ionic and Corinthian orders.

COMPOSITE CONSTRUCTIONS

WHAT IS COMPOSITE ACTION ?

In structural engineering, composite construction exists when two different materials are bound together so strongly that they act together as a single unit from a structural point of view. When this occurs, it is called composite action.

EXAMPLE OF COMPOSITE ACTIONOne common example involves steel beams supporting concrete floor slabs. If the beam is not connected firmly to the slab, then the slab transfers all of its weight to the beam and the slab contributes nothing to the load carrying capability of the beam.EXAMPLE (CONT) However, if the slab is connected positively to the beam with studs, then a portion of the slab can be assumed to act compositely with the beam. In effect, this composite creates a larger and stronger beam than would be provided by the steel beam alone.

COMPOSITE BEAM:

A structural member composed of two or more dissimilar materials joined together to act as a unit in which the resulting system is stronger than the sum of its parts. An example in civil structures is the steel-concrete composite beam in which a steel wide-flange shape (I or W shape) is attached to a concrete floor slab.

COMPOSITE BEAM:

COMPOSITE MATERIALS USED INCONSTRUCTION:

STEEL-CONCRETE COMPOSITE MATERIAL:Combining aggregate, sharp sand and a cement binder produces concrete which is used in the construction of roads, bridges and buildings. Though concrete is weak when under tension, it is a very strong material. Addition of wires, metal rods and cables makes it able to withstand tension. Casting cement around these rods produces reinforced concrete. COMPOSITE MATERIALS USED INCONSTRUCTION:PLASTIC COMPOSITE MATERIAL:Plastic is an engineered composite material composed of a reinforcement fiber and a polymer binder. Plastic is durable and can resist corrosion. It is light-weight and maintenance costs are low. Plastic composites are designed to produce desired characteristics more than the individual ingredient components.

COMPOSITE MATERIALS USED INCONSTRUCTION:WOOD-PLASTIC COMPOSITE MATERIAL:Wood is one of the common materials used in the construction industry. Wood contains cellulose fibers which are strengthened by lignin.Wood-plastic composite can last for a long time due to its resistance to rotting and decay. Because it provides a lower thermal expansion, it is able to withstand harsh climatic conditions.

COMPOSITE MATERIALS USED INCONSTRUCTION:MUD BRICKSA normal mud brick is sturdy and resistant to compression, but can break if bent. Straw is a material that has excellent tensile strength, meaning that it resists stretching. By combining both, early humans were able to create composite mud bricks that could resist weight and compression as well as stretching.

COMPOSITE MATERIALS USED INCONSTRUCTION:CONCRETEConcrete is a composite material made of cement, sand, stones and water. Combined, concrete is stronger than any one of these materials. Concrete is used heavily in building and road construction

COMPOSITE MATERIALS USED INCONSTRUCTION:FIBERGLASSFiberglass is a material made of tiny glass shards held together by resin and other components. Fiberglass can also be a less expensive alternative to other materials.

THE ADVANTAGES OF COMPOSITE MATERIALS

COSTTooling, labor and manufacturing costs are considerably lower for composite materials. Higher performance than steel and aluminum can also mean lower service costs and longer-lasting products or components.

THE ADVANTAGES OF COMPOSITE MATERIALSSTRENGTH AND WEIGHTComposites have a much lower density than metals such as steel and aluminum, and are therefore considerably lighter. While metals tend to be equally strong in all directions, composites can be designed to have much higher strength for any single application, thus providing a much better strength-to-weight ratio.

THE ADVANTAGES OF COMPOSITE MATERIALSSTIFFNESSComposites often contain strong, stiff fibers running through them which provide much added stiffness. Glass and carbon fibers are commonly used as reinforcement.

BAD THINGS ABOUT COMPOSITE MATERIALS FADING AND STAINSComposite decks generally hold up better than wood decks, but they are still prone to weathering over time. In particular, composite decks are prone to fading because they are exposed to sunlight year-round.

BAD THINGS ABOUT COMPOSITE MATERIALS PLASTIC-LIKE APPEARANCEComposite decking materials are usually designed to simulate the look of real wood grain. However, in many cases, composite decking has a shiny, plastic-like appearance that belies the natural look that homeowners are usually trying to achieve.

BAD THINGS ABOUT COMPOSITE MATERIALS ADDITIONAL SUPPORT REQUIREDComposite decking materials are weaker than natural wood, so they cannot support their own weight and may begin to sag if they are not properly supported.

FAILURE

Shock, impact, or repeated cyclic stresses can cause the laminate to separate at the interface between two layers, a condition known as delamination. Individual fibres can separate from the matrix e.g. fibre pull-out

BUCKLING OF COLUMNS.

WHAT IS A COLUMN ?

A compression member is generally considered to be a column when its unsupported length is more than 10 times its least lateral dimension. A column is a compression member that is so slender compared to its lengthTYPES OF COLUMNSLong Column: Long columns fail by buckling or excessive lateral bending. (Slenderness ratio Above 150)Intermediate Column: Intermediate columns fail by a combination of crushing and buckling.Short Column:Short columns fail by crushing. (Slenderness Ratio Below 30)

WHAT IS BUCKLING ? Buckling is characterized by a sudden failure of a structural member subjected to high compressive stress where the actual compressive stress at the point of failure is less than the ultimate compressive stresses that the material is capable of withstanding. For example, during earthquakes, reinforced concrete members may experience lateral deformation of the longitudinal reinforcing bars. Buckling is the sudden instability that occurs in columns or members that support an axial load.WHAT IS BUCKLING ?

TYPES OF BUCKLINGFlexural-torsional bucklingLateral-torsional bucklingPlastic bucklingDynamic buckling

FLEXURAL-TORSIONAL BUCKLING

Occurs in compression members only and it can be described as a combination of bending and twisting of a member. And it must be considered for design purposes, since the shape and cross sections are very critical. This mostly occurs in channels, structural tees, double-angle shapes, and equal-leg single angles.

LATERAL-TORSIONAL BUCKLINGWhen a simple beam is loaded in flexure, the top side is in compression, and the bottom side is in tension. When a slender member is subjected to an axial force, failure takes place due to bending or torsion rather than direct compression of the material. If the beam is not supported in the lateral direction (i.e., perpendicular to the plane of bending), and the flexural load increases to a critical limit, the beam will fail due to lateral buckling of the compression flange. In wide-flange sections, if the compression flange buckles laterally, the cross section will also twist in torsion, resulting in a failure mode known as lateral-torsional buckling.

LATERAL-TORSIONAL BUCKLING

PLASTIC BUCKLING

Buckling will generally occur slightly before the theoretical buckling strength of a structure, due to plasticity of the material. When the compressive load is near buckling, the structure will bow significantly and approach yield. The stress-strain behavior of materials is not strictly linear even below yield, and the modulus of elasticity decreases as stress increases, with more rapid change near yield. This lower rigidity reduces the buckling strength of the structure and causes premature buckling.

DYNAMIC BUCKLING

If the load on the column is applied suddenly and then released, the column can sustain a load much higher than its static (slowly applied) buckling load. This can happen in a long, unsupported column (rod) used as a drop hammer. The duration of compression at the impact end is the time required for a stress wave to travel up the rod to the other (free) end and back down as a relief wave. Maximum buckling occurs near the impact end at a wavelength much shorter than the length of the rod, at a stress many times the buckling stress if the rod were a statically-loaded column. DYNAMIC BUCKLING