Structural Design – Minimum Standard

Thumb rules for Structural Design of RCC Structures: It is advisable to use superior structural design software like ETabs or Staad Pro for making the design of structures. There exist different types of variables in making the design of a structure and therefore no minimum standards are perfect.

This guide is very helpful for making the design of very small structures, as for instance up to G+1 floors. It is recommended to apply good software for structural designer instead of manual methods. Manual method is only applicable for checks.

Real design is accomplished by applying the computers, through very advanced design concepts like pushover analysis, seismic analysis, wind loads simulation and various advanced processes.

Design of RCC Structural Components: This construction article sheds light on the minimum standards that should be undertaken for making the design of RCC structural components of a structure, like columns, beams, slab and foundation. Besides, the explanation is also provided for the minimum safe standards for the reinforcing bars which should be employed for the design of the above mentioned Structural Components.

Minimum cross-sectional dimension for a Column is 9”x 9” (225MM x 225MM). But to get rid of slenderness issues, a rectangular column with dimension 9″x 12″ (225 MM x 300 MM) should be designed for maintaining safety.

It is recommended to utilize M20 grade concrete for construction as per IS 456:2000 standard. The minimum steel required in a 9″ x 9″ column is 4 bars of 12 MM containing stirrups of 8 MM steel rings at a gapping of 150 MM centre to centre.

In a 9″ x 12″ column, two more bars should be included to easily manage the total to 6 bars having 12 MM diameter. This design is trustworthy for up to G+1 floors.

Minimum RCC beam size should not be under 9″x 9″(225MM X 225MM), with an extra slab thickness of 125 MM. It will be perfect to apply a minimum of 4 bars, with 2 bars having 12 MM thickness in the bottom of the beam, and 2 bars having 10 MM at the top of the beam.

A concrete cover having 40 MM dimension should be used. Besides, M20 grade of concrete (1 part cement : 1.5 parts sand : 3 parts aggregate : 0.5 parts water) should also be used.

Minimum thickness of RCC slab should be 5″ (125MM) as a slab may comprise of electrical pipes which are implanted into them with 0.5″ dimension or more for internal wiring to significantly decreases slab depths at specific places. It leads to cracking, weakening and water leakage throughout rains. Therefore, a minimum thickness of 5″ should have been retained.

Minimum size of foundation for a single storey of G+1 building should be 1m x 1m, where safe bearing strength of soil is 30 tonnes per square meter, and the approaching load on the column does not surpass 30 tonnes. Minimum depth of footing should be 4′underneath ground level. It is suggested to go to depths up to had strata.

To get more information, go through the following link www.civilprojectsonline.com



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Published By
Rajib Dey
www.constructioncost.co
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Common causes of downfalls of Dam Structures

A dam is a block across flowing water that opposes, directs or slows down the flow, often creating a store, lake or captivities. Most dams have a section named a spillway or weir over or through which the water passes and have some hydroelectric power generation systems installed.

Dams are like ‘installations containing dangerous forces’ due to the huge impact of a possible destruction on the normal population and the environment.

Generally dam failures are happen rarely but can do huge damage and loss of life, it happens as the dam structures are constrained to horizontal loading from the water head behind. The pressure comes from the water to the dam materials such as the adjoining geology and size of the reservoir which are very new in the case of dam structures.

Common reasons of downfalls of Dam Structures: The most known reason of the downfall of the dam structures is overtopping which is happen either for exceeding that is something concerned with the design of the spillway.

• Overtopping: It is happen when water slopping over the top of a dam and become a reason of dam failure. The two major factors of the overtopping failure are one id created due to surface elevation exceeds the total structural elevation profile and the other one is the over washes of the waves.
• Foundation defects and Slope instability: Foundation defects with settlement and slope instability causes most of the dam failures.

• Cracking: happens by the movements like the natural setting of a dam.
• Water Violating.
• Piping.
• Subsidence and the movement of the foundation.
• Uplift form the ground and sliding of the structure.
• Variation in temperature.
• Dynamic blasting in the nearby areas.

• Seismic load action.
• Wave action on the structure and weak energy absorption.
• Higher amount of silting.
• Loosing shear capacity of the concrete.

Reasons of downfalls of Earth Dam Structures: In case of earth dam, that unique materials that are used for the structure is made from the earth materials is nearby the side and makes the structure to be mixed in nature showing different properties in different conditions of weather and bring variations in the physical properties. There are other reasons of the earth dam failure are: insufficient spillways, piping, failure of the structure etc. and many more.

Reasons of downfalls of Gravity Dam Structures: Gravity dams are made from concrete and masonry and the major causes of failures of these structures are: soil erosion, failed construction joints, poor material etc.

Reasons of downfalls of Arch Dam Structures: This dam is different as it has plane stresses existing and thrust and these factors are caused for the design of the structure and completely dependent on the conditions of soil and rock. The failure happens for lack of structure, penstock vibration and insufficient grouting action.

Reasons of downfalls of Buttress Dam Structures: They have the horizontal forces transferred to the rock foundation and carried out by water pressure which is analyzed for the sliding and overturning failure of dam structure. The main reasons of failure are: alternate freeze and thraw cycles, masonry etc.

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Published By
Rajib Dey
www.constructioncost.co
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Post Tension Slab and its benefits

Generally, post-tensioned (PT) slabs belong to flat slabs, band beam and slabs or ribbed slabs. PT slabs provide the leaner slab type, as concrete functions to its strengths, mostly being maintained in compression. Longer spans are obtained because of pre-stress, which are also utilized to resist deflections.

Post-tensioned slabs employ high-strength tensioned steel strands to compress the slabs to retain most of the concrete in compression. Reinforcement is arranged to control the compression.

In Post tension slab, the cables/steel tendons are applied to replace the reinforcement. It develops a very well-organized structure to reduce material usages as well as economic span range with regard to reinforced concrete.

Post-tensioning is very useful to defeat the natural weakness of concrete in tension and to optimize its strength in compression. In concrete structures, high-tensile steel tendons/cables are placed in the element prior to casting.

If the concrete attains the preferred strength the special hydraulic jacks are used to drag tendons and retain them in tension with specially designed anchorages fixed at each end of the tendon. It offers compression at the edge of the structural member that enhances the strength of the concrete for withstanding tension stresses.

If tendons are properly curved to a specific profile, they will employ, besides compression at the perimeter, a beneficial upward set of forces (load balancing forces) that will resist applied loads, alleviating the structure from a portion of gravity effects.

In this type of slab, cables are attached in spite of reinforcement. In Steel reinforcement the gapping among bars is 4 inch to 6 inch while in Post tension slab the gapping is over 2m.

Benefits:

• It facilitates slabs and other structural members to be slimmer
• It facilitates us to develop slabs on expansive or soft soils
• The produced Cracks are retained firmly mutually
• Post tension slabs are useful for building up stronger structures economically.
• It minimizes or removes shrinkage cracking. So, no joints, or fewer joints, are essential
• It allows us to design longer spans in elevated members, like floors or beams

Drawbacks:
• Only experienced professionals can construct post tension slabs.
• If precaution is not undertaken at the time of making it, it can cause future mishaps. In various situations, untaught workers become unable fill the gaps of the tendons and wiring entirely. These gaps lead to decay of the wires which become breakable quickly and unexpected collapsing may occur.

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Published By
Rajib Dey
www.constructioncost.co
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Some practical issue prior to start foundation design

In foundation design, there may occur different types of issues associated with construction and costs.

Given below, the details of main issues :-

1. The foundations should be retained as shallow as possible, suitable for coping up with climatic effect, and strength of the surface soil; particularly in waterlogged ground. Excavation in severely waterlogged ground is extravagant and time consuming.

2. Expensive and complicated shuttering details should be bypassed specifically in stiffened rafts. Proper care should be taken with buildability.

3. Curtailment in the costs of piling, betterment in ground treatment, improvements in soil mechanics, etc. have significantly impacted the economics of design, and various standard solutions becomes obsolete. So, it is very much important to evaluate construction costs and methods on a regular basis.

4. Designers should have clear ideas on the assumptions which are provided in design. These range from the inconsistencies of ground conditions, the infrequent unsuitability of refined soil analyses and the feasibility of construction.

5. The authenticity of the soil analysis, through vital evaluation.

6. Impact of construction on ground properties that range from vibration from piling, degradation of ground uncovered with excavation in unfavorable weather conditions, exclusion of overburden, seasonal disparity in the water-table, compaction of the ground by construction plant.

7. Impact of changeable shape, length and inflexibility of the foundation, and the requirement for movement and settlement joints.

8. Consequences on finished foundations of sulfate attack on concrete, ground movements because of frost heave, shrinkable clays, and the impacts of trees; also modifications in local environment due to new construction, re-orientations of heavy traffic, setting up of plant in adjacent factories inducing impact and vibration.

9. Rapid but invaluable construction is more cost-effective as compared to low-cost but slow construction to clients to bring quick return on capital investment.

10. Impact of new foundation loading on obtainable adjacent structures.

For more information, go through the following construction article civilblog.org

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Published By
Rajib Dey
www.constructioncost.co
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How to design the RCC columns inexpensively

This construction article is extracted from https://theconstructor.org. The articles sheds light on how to minimize the cost by creating the design of reinforcement column as well as its construction practices and recommendations inexpensively.

Columns are considered as the most vital components in reinforced concrete structures and they ensure the security and constancy of the structure significantly.

Because of various factors, the cost of a column for each linear meter per MPa of load bearing strength fluctuates considerably. As for instance, the position of the column in the structure (outside column and inside column) and the configuration of the loads enforced on the column and others.

Given below, some other types of recommendations and measure which can reduce the cost of designing and development of reinforced concrete column significantly.

Recommendations for inexpensive design of Reinforced Concrete Columns

1. Potency of concrete used for reinforced concrete column
2. Formwork employed for casting reinforced concrete column
3. Steel reinforcements applied in the reinforced concrete column construction

4. Details of reinforcement of concrete column

Strength of Concrete for Reinforced Concrete Column

An important recommendation given for concrete strength is the utilization of utmost concrete compressive strength required to bear factored loads and least allowable reinforcement ratio. It is due to the lowest price that should be attained when such measure is undertaken as the cost of reinforcement decreases.

It is suggested that, if the least reinforcement ratio is employed for a specified column, it can minimize total column cost considerably (around 32% for concrete strength of 56MPa and 57% for concrete strength of 100MPa) relating to the case where highest reinforcement ratio is applied.

The nominal size of columns in multi storied structures is indicated on the basis of the utmost concrete compressive strength and a constraint on the highest reinforcement ratio.

If the size of column is smaller than the least permissible size at the base of the structure, then reinforcement ratio should be reduced.

Lastly, both reinforcement ratio and concrete compressive strength are reduced as the enforced factored loads decline in the upper stories.

To gather more information on recommendations, go through the following article theconstructor.org

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Published By
Rajib Dey
www.constructioncost.co

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