Reinforced Concrete - Literature review Example

Name Course title Tutor Date Table of Contents Table of Contents 2 Introduction 3 Reinforced concrete slabs 3 Reinforced concrete beams 5 Reinforced concrete column 6 Reinforced concrete foundations 8 Conclusion 9 References 11 Literature review on primary reinforced concrete elements used these days Introduction Reinforced concrete is a composite material used as one of the primary material in building and structural design. It consists of steel reinforcement embedded in a concrete matrix. The concrete has low tensile strength but high compressive strength. However, reinforcement steel bars have high tensile strength, but buckle under compressive stresses. Concrete is less expensive than steel. Thus by providing steel bars within the concrete, an economical structure is produced which has both tensile and compressive strength. In addition, the concrete protect the steel bars reinforcement from heat and corrosion. Reinforced concrete building structures have different elements that include columns, foundation, beams and slabs (Ghambir, 2006). Elements of a building structure Reinforced concrete slabs Reinforced concrete slabs are flexure structural elements that are subjected to loads acting perpendicular to their surface. They are broad, flat and horizontal, with bottom and top parallel surfaces. They form a variety of elements in a structure that include roofs, foundations, floors and staircases. They may be supported by reinforced concrete walls, beams, steel members or columns (Williams, 2004). There are various types of slabs that include the following. a) One way slabs- they are supported on two sides by beams. Therefore, the load on the slab is spanned between the supporting beams. The structural action of the slab is one way; the loads are carried in the direction that is perpendicular to the supporting beams. b) Two way slabs – they are supported by beams on all of the four sides such that two-way flexural action is obtained. The load is carried by the slab by spanning in two orthogonal directions. Thus the high load scan is supported with less deflection. But if the ratio of the short side to the long side exceeds the two, the applied load is mainly supported by flexural action in the direction of the span, and the panel act like one-way slab (Williams, 2004). c) Flat plates are slabs that are supported at the corners by column, with the use of beams. They provide simple, unobstructed and minimum construction depth. d) Flat slabs are flat plates that are thickened at the column with drop panels. The slabs are supported without beams and are resistant to shear and high moment at the column. They support increased loads over long spans (Williams, 2004). e) Waffle slab or Two-way grids are flat slabs that are constructed with voids producing orthogonal grillage with less dead load compared to flat slab. Grid floor is supported at column or walls that are positioned at regular intervals (Williams, 2004). (Williams, 2004) Material properties Strength classes required for slab is determined by the compressive strength characteristics of a concrete. The strength class contains characteristics cylinder strength with characteristic cube strength. For the slab, a concrete class of at least C25/30 with the characteristics cylinder strength of 25Nmm-2 is used (Williams, 2004). Reinforced concrete beams Reinforced concrete beams are structural elements in flexure which transmits the load from the slabs to the vertical supporting walls, columns or girders. They are capable of resisting bending due to external loads, mainly due to vertical gravitational force. Beams are mainly characterized by the shape of the cross section, material and length. Beams are mainly made of reinforced concrete, wood or steel. They may form T-section for interior of the building, L-beam for exterior beams or I-section (Punmia et al., 2009). a) Singly Reinforced Rectangular Beams – they are beams reinforced with tension steel only. They have embedded steel bars or rods which are resistant to tensile forces like. Its section is like as shown below. b) Doubly Reinforced Rectangular Beams – they are beams that are reinforced with compression and tension steel. They are necessary when there is some restriction in the depth of the construction of the section. The tensile and compressive steel at the support section has to be well tied with closed stirrups to stop buckling of the compressive bars at the support. The doubly reinforced beam is shown below. (Punmia et al., 2009; McCormac, 1986)) c) T-section and L-section are produced through monolithic construction between the slab and beam. Therefore, the slabs and beams are tied together such that when the beam deflects under external loads it drags along a portion of slab. The portion of slab assists the beam in resisting the loads act as the flange of L- or T – beam. T-section and L-section are shown below. The concrete slabs have smaller thickness compared to beams (Punmia et al., 2009). Materials Concrete should have sufficient strength to withstand compressive stress, and the compressive strength class for the concrete can be C30/37. Steel reinforcement provides tensional strength, but they are also placed in compression zone to increase compressive force (McCormac, 1986). Reinforced concrete column This is a vertical structure element that transfers the weight of a structure to other structure elements by compression. The column is subjected to bending and axial stresses and they are very significant when considering safety of a structure. A concrete column must always have steel reinforcement to resist bending (Ghambir, 2006). a) A tie column – is a column that has lateral ties that restrain expansion by providing intermediate lateral support for vertical reinforcement. Ties prevent square column from cracking and bulging that lead to failure of the column. Four vertical reinforcing bars caries the axial load, while the four intermediate bars serves as intermediate vertical reinforcement (United States, 1999). b) Spiral column – this is a round column that has been wounded with a continuous spiral lateral enforcement that encircles its core and the vertical reinforcement bars that contain expansion. This type of column is considered to be stronger than tied column, because the spiral reinforcement is much stronger the imperfect anchorages at the end of lateral ties in a tie column. A more effective literal support can be obtained by reducing the pitch of the spiral reinforcement (United States, 1999). c) Combination and composite column – this is a structural cast iron or steel column embedded in concrete, and reinforced vertically and spirally. The cross section area for the metal section is less than 20% of the cross section of the column. Combination column is a steel structure column that is enclosed in a concrete with thickness of at least 2.5 inches and reinforced with welded wire (United States, 1999). The three types of columns are shown below. (United States, 1999) Material properties The following materials are used to produce columns. Concrete with normal weight and strength class of at least C25/30 with characteristics and production that conforms to the required standard. The strength class of C25/30 has characteristics strength of 25Nmm-2 (Pillai & Devadas, 2003). Reinforcement steel with qualities that conforms to the required standard. For example, the steel grades should be between S235 to S460. The steel yielding strength should lie between 235Mpa to 430Mpa (Pillai & Devadas, 2003). Reinforced concrete foundations These are structures that support the building and transmit the load of the building to the soil or rock underneath. The foundation must provide adequate safety against crumpling by supporting structure. In addition, any settlement as a result of differential settlement must not interfere with the function of the building. They can be divided into pad foundations combine foundation as discussed below. a) Pad foundations – they are rectangular or square foundation supporting a single pier or column. They spread the load from the structure on the ground, with the column sitting in the middle. Plain concrete may be economical if the load is relatively lighter; otherwise thick pads may be required which may not be economical (Bangash, 2003). Pad foundations b) Combined foundation is made of a composite of reinforced concrete and may support a number of columns. Reinforced concrete produces wide but shallow foundations, which are normally in square area for easy construction. Rectangular pads are usually constructed on an inclined loading (Bangash, 2003). Reinforced concrete They are used in foundations that are close to a site boundary as it enables balancing of the internal column to be incorporated. Combined foundation (Bangash, 2003; Curtin & Seward, 2006) Material properties Due to the fact that the foundation of the building supports the entire structure, it is necessary to create correct mixture that will ensure durability and strength, which is safe and is capable of carrying the load of the building. The choice of foundation depends on the ground conditions, the site and environment, ground water conditions and the building structure. A relatively high quality concrete of a strength class of up to C50/60 is used. For grounds that are exposed to aggressive chemical environment, the designer should provide the required strength class and the limit of the aggregate size as well as maximum permissible cement/water ratio, and the permitted combinations types suitable for foundation (Pillai & Devadas, 2003). Conclusion The design of concrete structural elements has to take into account the specific requirements for the building, which include functionality, aesthetic, structural and economic. In other words it should not only serve the functionality purpose, but it should be serviceable, attractive and economically cost effective. The properties of steel reinforcement and concrete must be known in construction design. The designer focus on the compressive strength for the concrete, but for steel, tensile strength is important. Basically, a concrete is a mixture of fine and coarse aggregate, water and cement that hardens to become like stone, and it may not be possible to create a homogenous material from the mixture. The concrete strength and other features are dependent on the processes such as curing, transportation and compaction (Ghambir, 2006). References Bangash, M. Y. H. (2003). Structural detailing in concrete: A comparative study of British, European and American codes and practices. London: Thomas Telford Curtin, W. G., & Seward, N. J. (2006). Structural foundation designers' manual. Malden, MA: Blackwell Pub. Ghambir, M. L. (2006). Fundamentals of reinforced concrete design. India: Prentice Hall. McCormac, J. C. (1986). Design of reinforced concrete. New York: Harper & Row. Pillai, S. U., & Devadas, M. (2003). Reinforced concrete design. New Delhi: Tata McGraw Hill. Punmia B.C., Jain P. A. K., & Jain A. K., (2009). Comprehensive Rcc. Designs, Laxmi Publications United States. (1999). Concrete, masonry, and brickwork: A practical handbook for the home owner and small builder. Mineola, N.Y: Dover Publications. Williams, A. (2004). Design of reinforced concrete structures. Chicago, IL: Dearborn Real Estate Education Read More

(Williams, 2004) Material properties Strength classes required for slab is determined by the compressive strength characteristics of a concrete. The strength class contains characteristics cylinder strength with characteristic cube strength. For the slab, a concrete class of at least C25/30 with the characteristics cylinder strength of 25Nmm-2 is used (Williams, 2004). Reinforced concrete beams Reinforced concrete beams are structural elements in flexure which transmits the load from the slabs to the vertical supporting walls, columns or girders.

They are capable of resisting bending due to external loads, mainly due to vertical gravitational force. Beams are mainly characterized by the shape of the cross section, material and length. Beams are mainly made of reinforced concrete, wood or steel. They may form T-section for interior of the building, L-beam for exterior beams or I-section (Punmia et al., 2009). a) Singly Reinforced Rectangular Beams – they are beams reinforced with tension steel only. They have embedded steel bars or rods which are resistant to tensile forces like.

Its section is like as shown below. b) Doubly Reinforced Rectangular Beams – they are beams that are reinforced with compression and tension steel. They are necessary when there is some restriction in the depth of the construction of the section. The tensile and compressive steel at the support section has to be well tied with closed stirrups to stop buckling of the compressive bars at the support. The doubly reinforced beam is shown below. (Punmia et al., 2009; McCormac, 1986)) c) T-section and L-section are produced through monolithic construction between the slab and beam.

Therefore, the slabs and beams are tied together such that when the beam deflects under external loads it drags along a portion of slab. The portion of slab assists the beam in resisting the loads act as the flange of L- or T – beam. T-section and L-section are shown below. The concrete slabs have smaller thickness compared to beams (Punmia et al., 2009). Materials Concrete should have sufficient strength to withstand compressive stress, and the compressive strength class for the concrete can be C30/37.

Steel reinforcement provides tensional strength, but they are also placed in compression zone to increase compressive force (McCormac, 1986). Reinforced concrete column This is a vertical structure element that transfers the weight of a structure to other structure elements by compression. The column is subjected to bending and axial stresses and they are very significant when considering safety of a structure. A concrete column must always have steel reinforcement to resist bending (Ghambir, 2006). a) A tie column – is a column that has lateral ties that restrain expansion by providing intermediate lateral support for vertical reinforcement.

Ties prevent square column from cracking and bulging that lead to failure of the column. Four vertical reinforcing bars caries the axial load, while the four intermediate bars serves as intermediate vertical reinforcement (United States, 1999). b) Spiral column – this is a round column that has been wounded with a continuous spiral lateral enforcement that encircles its core and the vertical reinforcement bars that contain expansion. This type of column is considered to be stronger than tied column, because the spiral reinforcement is much stronger the imperfect anchorages at the end of lateral ties in a tie column.

A more effective literal support can be obtained by reducing the pitch of the spiral reinforcement (United States, 1999). c) Combination and composite column – this is a structural cast iron or steel column embedded in concrete, and reinforced vertically and spirally. The cross section area for the metal section is less than 20% of the cross section of the column. Combination column is a steel structure column that is enclosed in a concrete with thickness of at least 2.5 inches and reinforced with welded wire (United States, 1999).

Read More