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THE EFFECT OF REINFORCED CONCRETE ON SAFETY OF RESIDENTIAL BUILDINGS

CHAPTER ONE

INTRODUCTION

BACKGROUND TO THE STUDY

Residential building is defined as the building which sleeping accommodation is provided for normal residential purposes. It is provided with or without cooking or dining or both facilities. Residential building includes one or two story or multi-family dwelling, lodging or rooming houses, dormitories, and apartment houses. The residential building can be owned by an individual or co-operative association. Each resident or resident household has membership in the co-operative association. In non-equality co-operative members have occupancy right to a specific suite within the housing co-operative as outlined in their “occupancy agreement” or “proprietary lease” which is essentially a lease. In ownership co-operatives occupancy rights are transferred to the purchaser by way of the title transfer.

The major function of the residential building is for the accommodation, both for private and the public users. Due to th aforementioned reasons, there is need for well construction of the residential structure, with the materials that will be capable of resisting both direct and indirect forces and the weathering effects, not just for a moment but for the long lasting time, hence the use of concrete is being adapted. Concrete can be defined as a hard, strong construction materials consisting of sand, conglomerate gravel, pebbles, broken stones, or slag in a motor or cement mixture. It is also known as the mass formed by the coalescence or particles. Concrete could also be defined as the mixture of gravel, pebbles or broken stone with cement or with tar, etc, used for sidewalks, roadways, foundations, etc and especially for submarine structure. So many issues has led to the construction of different types of building like bungalow and high rise building in order to save money.

According to an economist that says human wants is unlimited and that there are limited resources with which wants can be satisfied. And this has lead to the absolute maximization and utilization of the said available resources to man which include fixed and liquid assets. This is one of the reasons why the conservation of land to safe place was adapted, which led to the construction of high rise building in town and mostly in well developed countries, for the fact that human being resides in, and other valuables are kept in these buildings; safely of the structure under all forces that may be applied must be guaranteed.  Recently, reinforced concrete has proven to be the cheapest retail that can effectively resist these forces like (wind force, direct force and indirect force) and other force that may be applied within the building, which can be found into various shape. The need for the forces stability of this structure under these factors has brought a challenge to the engineer; hence the reinforced concrete design is concern.

AIM AND OBJECTIVES

The reinforced concrete uses extra materials like steel bars, wooden beams or fibers, along with a wire frame to help mold the concrete and ensure the safe construction under the worst condition of the force that may be applied within and outside the building. The reinforcement interacts with the concrete, strengthening it and providing support houses and other structures. The concrete provide shielding for the steel so it doesn’t corrode as quickly and together they are a common component in the modern construction. Therefore, this project is aimed in ensuring the safety of life and property based on the use of limit state design code (BS 8110) in understanding the problem that is involved in design and resolving same appropriately. It also aimed in knowing the members of the structure and its weight and the steps taken in achieving the internal and external forces and proper way of applying the reinforcement for the proper structural stability.  Its objectives includes knowing that concrete tends to be brittle, breaking easily under sudden stress and crumbling under the influence time and weather. This makes it difficult to use traditional concrete structures intended to hold a large amount of weight or last a long time. Reinforced concrete on the other hand can hold much more weight and does not wear as easily. Hence most structure built today use reinforced concrete.

Uses

The reinforced concrete is used in large scale construction such as bridges and skyscrapers. It was first created for building construction in the mid 1800s, and soon spread across both Europe and America. Most major building built by the beginning of the 1900s was created with reinforced concrete. Consideration: Reinforced concrete   is subjected to the same principles as normal concrete, and the quality depends on the mixture of the cement and how well it is set. The extra material used will also cost more, especially if steel bars are used instead of wood or recycled fiber alternatives. However, the glass and fiber alternatives can present difficulties on their own by becoming weaker in a fire.

METHODOLOGY

Reinforced concrete is concrete in which the reinforcement bars (rebels) reinforcement girders, plates or fibers have been incorporate to strengthen the concrete in tension. It was the concrete that is reinforced with steel or iron is called a reinforced concrete only. Other materials used to reinforced concrete can be organic and inorganic fibers as well as composite in different forms. Prior to the invention of reinforcement, concrete was strong in compression, but weak in tension. Adding reinforcement crucially increases the strength in tension. The failure strain of concrete in tension is so low that the reinforcement has to hold the concrete sections together. For a strong ductile and durable construction, the reinforcement needs to have the following properties.

High strength

High tensile strain

Good bond to the concrete

Thermal compatibility

Durability in the concrete environment.

In most cases, reinforced concrete uses steel rebels that have been inserted to add strength. Concrete is reinforced to give it extra tensile strength; without reinforcement, many concrete building would not have been possible. Reinforced concrete can compasses many members or types of structures and components which includes:

Slabs

Walls

Beams

Columns

Foundations

Frames and more

Reinforced concrete can be classified as (1) pre-cast and (2) in-situ concrete. Reinforced concrete is focused mainly on the floor system. Designing   and implementing the most efficient floor system is key to creating optimal building structures, small changes in the design of a floor can have a significant impact on material cost; construction schedule, ultimate strength, operating costs, occupancy levels and end use of building.

REINFORCEMENT AND TERMINOLOGY OF MEMBERS

It is found that the architectural drawing has been thoroughly examined and right systems of design have been chosen. In this modern computer age, the easiest way to carry out design is by computer method, but the system of manual method is still use to arrive at the same point going through all the worst critical members of the structure by using the factors like

Ly/Lx  ≤  2.0 for two-way slab

Ly/Lx  ≥  2.0 for one-way spacing

The load on this slab is being estimated using the appropriate moments data, shears, torsion, the reinforcement are calculated using the appropriate method of provided by design code. The moment coefficients given in the code and moment distribution method were employed in the determination of slabs and beam moments while the analyses of the substitute frame were used for columns. Beams bending in small curvature at the outer face (tensile face) of the curvature the concrete experiences tensile stresses while at the inner face, (compressive face) it experiences the compressive stress. The slab and beam and also the roof structure causes axial load on the column. Reinforcement are been provided to each of the members after deign using the appropriate chart from design codes.  The column transfers loads from slab and beam down to the foundation and distribute same to the soil. The shear reinforcement where also calculated providing the reinforcement with the appropriate table approved by design code in respects of the value gotten. The shear reinforcement is in form of links, stirrup where also provided where necessary.

SCOPE AND LIMITATION

On the process to ensure that a structure is safe and of the standard required, this project have been designed accordingly based on the rules stipulated in limit state design  as provided by the code of practice  BS 8110. Therefore, some instances are referenced to other codes of practice. In this project, the total members of beams which were analyzed representing typical cases of the whole structure and designed.  Three footing wear design together with stairs and its value were provided in details drawing and theory. Artificial engineering materials made form a mixture of Portland cement, water, fine and coarse aggregate and small amount of air. It is the most widely used construction materials in the world and must be properly treated.

Concrete is the only major building material that can be delivered to the site and care must be taken to avoid fake materials. The unique quality of concrete makes concrete desirable as a building material can be molded virtually to any forms of shape. Concrete provide a wide latitude in the surface texture and colours and can be used to construct a wide variety of structures such as highway  and streets, bridges, large buildings, airports runways, irrigation structures, breakwater, pier and docks, sidewalks silos and farm building, homes and even barges and ships.  The two major component of concrete are cement paste and inert materials. Under normal conditions, concrete grows stronger as it grow older. The chemical reactions between cement and water that cause the paste to harden and bind the aggregates together requires time. Therefore proper materials have to be chosen at the time of construction in order to achieve a stable structure.

LIMIT STATE DESIGN BS 8110

BS 8110 is a British standard for the design and construction of reinforced and pre - stressed concrete structure. This theory came into existence as a result of the discrepancies between the behaviour of materials by elastic analysis and that which occur in practice. Although BS 8110 is used for most civil engineering and building structures, bridges and water-retaining structures, this are covered by separate standards of (BS 5400 and BS 8007). Limit sate design requires the structure to satisfies two principal criteria, that is the Ultimate Limit State (ULS)  and the serviceability Limit State (SLS). A limit state is a set of performance criteria (eg. vibration level, deflection, strength, stability, buckling, twisting, collapse) that must be met when the structure is subjected to loads. This later leads to checks for the protection for instance deflection and cracks checks.