17-12-2012, 01:27 PM
ANALYSIS AND DESIGN OF PROPOSED MATERNITY BLOCK
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INTRODUCTION
GENERAL
Modern reinforced concrete structures how ever complex they may appear to a novice are usually designed as an assembly of structural elements such as beams, columns, walls, slabs, and footing. Each of these may be subjected to various combinations of forces with the material itself undergoing effect of creep, shrinkage, temperature variation as well as environmental influences that effect of the durability of the structure.
Design of a reinforced concrete structure is carried in many stages, for instance, the empirical appointment of economical sizes to the various elements, the detailed calculation of the strength and stability of the structure as a whole, and each of the elements under the various forces it is subjected to, the estimation of the economical amount of reinforcements to be provided for safety, as also the detailing of the in steel in various parts for integrated action. in addition, serviceability aspects and durability aspects should also be given due consideration in the design.
ANALYSIS METHOD
Analysis of large framed structure becomes too cumbersome with the classical method of structural analysis such as claperyron’s theorem of three moments, casiglino’s theorem of least work, poison’s method of virtual work and the slope deflection methods.
Hence if has becomes imperative to evaluate simple and quicker methods. Some of these methods are detailed below:
• Hardy cross method of moment distribution.
• Two cycle method of moment distribution.
• Kani’s method of iteration.
• Kocek’s method of distribution deformation.
Of these methods, the first method in familiar due to its simplicity.
However, this method also becomes tedious in the case of multi bay frames, where there are many joints. Hence, with certain assumptions, the frames can be analyzed, using the second method from which the results can be obtained quite satisfactorily. 1.2.4 ABOUT STAAD PRO
STAAD PRO is a suite for inter related structural software, offering a complete solution for the professional structural engineer. STAAD PRO consists of a core package and several optional.
EXTENSION COMPONENTS
STAAD PRO offers general purpose structural analysis and design along with extensive model generation and post processing facilities. All these features are integrated in one common graphical user interface (GUI). This manual describes the STAAD PRO, GUI in detail.
STAAD PRO introduces the concept of page control. When the page control is switched on (using the page control option from the mode-menu), a gabbed menu appears long the left side of the screen as a guide to the process of creating a structure. every “ page” serves a specific purpose. For example, the general\load page offers facilities to define different types of loads.
STAAD PRO refers two analysis engines - the STAAD analysis/design engine and the STARDYNE advanced analysis engine. The user communicates with STAAD through an input file. The input file is a text file consisting of a series of commands, which are executed sequentially. The commands contain either instruction or date pertaining to analysis and design. The STAAD input file can be created through a text editor or the modeling facility. In general, any text editor may be utilized to create the input file.
TYPES OF STRUCTURES
The STRUCTURE can be designed as an assemblage of elements. STAAD is capable of analyzing and designing structures consisting of both frames and plate/shell elements. Almost any type of structure can be analyzed by STAAD. Most general is the SPACE structure which is a three-dimensional framed structure with loads applied in any plane. A PLANE structure is bound by a global X-Y co-ordinate system with loads in the same plane.
A TRUSS structure consists of truss members, which can have only axial member force and no bending in the member. A FLOOR structure is a two or three dimensional structures having no horizontal (global X or Y or Z) applied loads are any load, which may cause any horizontal movement of he structure. The floor framing (in global X-Y plane) of a building is and ideal example of a FLOOR structure has no horizontal loading. If there is any horizontal load, it must be analyzed as a SPACE structure.
WORKING STRESS METHOD OF DESIGN:
In this method, the structures are analyzed by the classical elastic theory. The stresses in the members are considered for normal working load condition, and no attention is given do the conditions that arise at the time of structural collapse. The working loads are fixed by limiting the stresses in concrete and steel to a fraction of the stresses at which the material fails when tested as cubes and cylinders for concrete and bars of steel. The ratio which the yield stress of the steel or the cube strength of the concrete bears to the corresponding permissible or working stress in usually called factor of safety.
ULTIMATE LOAD METHOD OF DESIGN:
An alternative method of design that was developed was the ultimate load is some known multiple of the maximum working load which the structure is likely to carry. The ratio of the collapse load to the working load is known as “load factor”. The load factor gives exact margin of safety against collapse.
`Since the method utilizes a large reserve of strength in plastic region (inelastic region) and of ultimate strength of member, the resulting section is very slender or thin. This gives rise to excessive deformations and cracking. Also, the method does not take into consideration the effects of creep and shrinkage. The method thus does not take into consideration serviceability requirements of avoidance of excessive deflection and cracking.
LIMIT STATE METHOD DESIGN:
We have seen that while the working stress method gives satisfactory performance of the structure at working loads, it is unrealistic at ultimate state of collapse. Similarly, while the ultimate load method provides realistic assessment of safety, it does not guarantee the satisfactory serviceability requirements at service loads. An ideal method is the one which takes into account not only the ultimate strength of the structure but also the serviceability requirements.
The newly emerging “Limit state method” of design is oriented towards the simultaneous satisfaction o fall these requirements. This new method makes a judicious combination of the working stress philosophy as well as the ultimate load philosophy, thus avoiding the demerits of both. The acceptable limit of safety and serviceability requirements, before failure occurs is called a “limit state”.