The stirrups commonly found in column design

The design of stirrups for column is created on the basis of different factors like changeable cross-sections, the number of longitudinal reinforcement bars and the load bearing strength. Stirrups in column construction are generally called as vertical ties or transverse reinforcement.

The following types of stirrups or ties are found in column construction:

1. Helical Reinforcement: The helical reinforcement is different from the lateral ties since the lateral ties contain spacing among individual ties. In helical reinforcement, the quantified value is pitch, rather than spacing.

The helical reinforcement offers more ductility and flexibility to the built up column with regard to lateral ties. They can effectively support the longitudinal reinforcement. With the insertion of helical reinforcement, the resistance capacity of the column structure against buckling become superior.

a) Ambient temperature of 27 °C (80°F) or greater; and
b) Evaporation rate that surpasses 1 kg/m2/h

The helical reinforcement is also applied as spiral reinforcement. Helical bars are suitable for seismic design. By the influence of seismic loads, the concrete affixed to the helical reinforcement is stripped off preliminary. It facilitates to give a warning sign concerning the structural condition of the column.

The helical reinforcement is a perfect example in respect of uniformly distributing loads as compared to the normal rings (lateral ties).

2. Lateral Ties: The lateral ties stand for transverse reinforcement to develop a separate ring with a fixed spacing among each link. Based on the column cross-section and the number of vertical or longitudinal reinforcement bars applied, the lateral stirrups vary from two-legged stirrups, four-legged stirrups or six-legged stirrups etc.

Given below, the detail information on various lateral tie configurations for several number of vertical reinforcement bars. The configurations are dependent on the ACI 315-99 recommendations.

1. Lateral Tie Configuration for 4- Bars: The tie is configured for 4 numbers of vertical column bars. It is a standard type of configuration applied for simple column design. This configuration is known as 2 legged stirrups column type.

2. Lateral Tie Configuration for 6- Bars: The first arrangement is observed when the spacing of vertical bars are under 150mm ( below 6”). If the spacing is in excess of 150mm, the second arrangement is observed where crossties are used.

3. Lateral Tie Configuration for 8- Bars: The first arrangement is done with the standard 8 number vertical reinforcement arrangement. Here the spacing is under 6”. If the spacing is in excess of 150mm, two crossties are utilized.

The third arrangement is known as bundled bars arrangement. Under this arrangement, two bars are combined at the corners. So, no cross ties are required. Highest 4 numbers of bars are combined.

4. Lateral Tie Configuration for 10- Bars: In this case, it is required to provide cross-ties apart from the square ties. It is also organized in bundled bars. Here bundle of 2 bars is arranged at four corners and two remaining bars are supported with the help of cross ties.

5. Lateral Ties for different column cross sections: The arrangement for 16 bars employ diamond ties. The process is very complicated to fabricate diamond ties perfectly and as a result it is ignored. The process is also complicated to arrange them properly. This tie arrangement is not suggested by ACI 315 because of the complications related to it. But, in some countries, standards utilize this arrangement for simple column design.

In A 16 bars column arrangement according to ACI 315 4 bundled bars can be arranged at each corner.



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Why reinforcement is provided in a column

Concrete is strong at bearing compressive stress. Plain concrete can sustain compressive loads capably. But it is always recommended to utilize the R.С.С. columns in place of plain concrete columns in modern day structures for the following reasons :-

Temperature stresses are formed in Concrete because of differences in weather. Cracks may happen for this stress. To get rid of the issue and reduce cracks, some steel is provided at the face of the concrete.

Columns specifically slender columns are prone to lateral loads and moments. Sometimes, tensile stress may also build up particularly in columns at exterior boundary of the building. Steel can deal with this tensile stress.

While making the design of RCC structures, the reinforcement is provided in beams to tie them securely with beams.

Reinforcement is provided so that the size of the columns is not increased.

Reinforcement steel improves the ductility of the member so that the structure gets the ability to withstand earthquake in a superior way.

In R.C.C. columns, less area is required with regards to a plain concrete column It is found that steel can bear load m-times that of concrete of the similar area. To deal with a specific load, the section of an R.C.C. column will be much finer as compared to that of plain concrete. By applying R.С.С. columns, huge space is saved since the size of the column will be less.

A minimum area of steel should be arranged in the column if any case it is necessary for bearing load or not. It is performed to withstand tensile stresses which occur because of eccentricity of loads.

Two types of reinforcements are arranged in a R.C.C. column.

a. Longitudinal reinforcement.
b. Transverse reinforcement.

Longitudinal Reinforcement: The longitudinal reinforcement comprises of steel bars which are arranged longitudinally in a column. It is also known as main steel. The properties of longitudinal reinforcement are given below:

i. To distribute the compressive loads along with concrete, consequently minimizing the size of the column on the whole and parting more usable area.
ii. To withstand tensile stresses which are formed because of any moment or accidental eccentricity.
iii. To yield ductility to the column.
iv. To lessen the impact of creep and shrinkage because of continuous constant loading applied for a long time.

Transverse Reinforcement: The transverse reinforcement is arranged along the lateral direction of the column in the shape of ties spirals which cover the main steel. The function of transverse steel are as following -

i. To retain the longitudinal bars in exact place.
ii. To resist buckling of the main longitudinal bars.
iii. To avoid diagonal tension that happens because of transverse shear formed due to any moment or load.
iv. To yield ductility to the column.
v. To resist longitudinal splitting or bulging from concrete by enclosing it in the core.



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Steel Beam Connections

Steel beam connections are used to join different members of structural steel frame work; Steel Structure Collections attach various members to make them a unit.

Steel connections

Connections are like the structural elements which are used to connect various members of structural steel frame work and Steel Structure is a collection of different member like Beams, Columns which are joined with one another at member ends fasteners to show a single composite unit.

Types

Generally steel beam connections are used in structures and all beam connections are categorized into two groups like framed and seated connections. The framed steel beam is connected to the supportive steel element by fittings and the seated steel beam is placed on seat like to the case where beam is located on masonry walls.

This article mainly focuses on the different types of steel beam connections with their working process, steel beam connections are divided into following types:

• Bolted Seated Steel Beam Connection

When a beam is joined with a support, a column or a girder with web connection angles, then the joint is names as ‘framed’. Here every the connections must be plotted for the end reaction of the beam, its type, size and toughness of the fasteners and the capacity of bearing strength of core materials should be done. In these connections, the steel beams are connected in a way as supporting elements whether it is steel columns with the web connection angles and the minimum length of connection angle must be at least half of the beam clear web depth. The proportion is specified for right stiffness and solidity; there are different sizes of bolted framed connections besides their capability given by codes. This connection is required to enhance the rapidity of the design and minimum connection is enough to resist the applied load for making the design more economical.

• Bolted Framed steel connections

In seated connection beams right sizes, capabilities and other data are filed in the AISC Manual, there are mainly two main types of bolted seated connections one of them is the soft bolted seat connections and hard bolted seat connection. When the reactions at the end of the beam are big then it is approved as hard or stiffened seat connections for their satisfactory capacity to oppose large forces. But the capability of soft or unstiffened seat connection is blocked for limited bending capacity of seat angle leg. The most helpful thing is that the beam in this connection can be invented economically and seat would give immediate support in the erection period.

• Welded framed steel beam connection

This beam connection can be found in different sizes with their capabilities are available and supplied by codes. The weld of connection is bound to direct shave stress which caused by loads on the beam which beam affect weld pattern so the stresses are needed to be considered. The part of the welding is executed in a field where it seems difficult to get high quality weld for the movements of steel members caused by winds or other factors.

• Welded seat steel beam connection

It is same as to bolt seat connection but used for bonding than bolts and the pressure on the beams affect the weld pattern curiously and create stress which need to be planned. The welded seat connections are of two types: unstiffened and stiffened, unstiffened is used for small loads and the stiffened is used to bear large loads. Use bolts to connect beam bottom border to the seat and the blots can be removed at their position after the end of their welded process. This connection is not requested from environmental point of view and worker as the connection can’t be erected easily.

• End plate steel beam connection

This kind of connection is made through using the welding art and the end plate is joined to the beam by weld for its capability and size which are controlled by shear capacity of the beam web connected with the weld. The applied load on the connection at last of the member doesn’t have irregularities and the plate connections are of various types like flexible, semi-rigid and rigid. The fabrications and cuttings must be connected with the extreme care to stop errors but the end plate connections are not applicable to tall steel structures.

• Special steel beam connections

These connections are used for the case where the preparations of the structural element are placed in a way that standard connections can’t be used. The connections can transfer moments into the columns as per degree of fixity of the connections and the higher degree of fixity of the beam connection is the greater ability to transfer the moments into the columns.

• Simple, rigid and semi-rigid connections

Moment connections can transfer the forces in the beam sides to the column and this transfer moment must be provided for more and usually free of the shear connection needed to support the beam reaction. Simple, rigid and semi-rigid connections are designated simply to support beams and columns for shear only and leave the ends free to move under load. Besides carrying shear they provide enough rigidity to hold virtually unchanged angles between connected members.

Source: www.civilengineeringx.co

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Resist construction issues at site by making cost-effective foundation design

In order to create the design of foundations in a cost-effective manner as well as resolve practical construction issues, some factors should be taken into consideration.

Tips to create the design of the foundations in a cost-effective manner and avoid construction issues at job site.

a. Formation of the foundation should be shallow
b. Curtail construction cost of the foundation
c. Awareness of structural designer
d. Resist the application of costly and complicated formworks
e. Consistency of site investigation
f. Take decision to build up rapid or slow foundation
g. Impact of foundation construction on the ground and structures at area of the foundation
h. Disparities in foundation geometry and requisite of diverse joints
i. Effect of objectionable elements on constructed foundation

Build up the Foundation as Shallow for saving

It is recommended to make the foundation shallow as much as possible. Make the best use of the size to sufficiently support loads and resist ecological impacts. Proper care should be taken to keep the depth and width of the foundation within limit.

This measure should be mostly suitable where the foundation is built up in completely saturated soil in which issues may arise because of existence of water. The cost is increased significantly with regards to the foundation developed in dry soil condition.

Decrease Cost of Foundation Construction: This can happen with a constant modification of construction methods and costs as the frugality of design differs significantly and usable standard might be obsolete.

To get more information, go through the following article theconstructor.org

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Some useful construction tips to provide clear cover for reinforced concrete structure

This construction video tutorial will provide detailed guidelines on how to provide perfect clear cover in reinforcement concrete structure.

With the intension of safeguarding the reinforcement from corrosion as well as arranging fire resistance to bars implanted in concrete, clear cover is set for Reinforced Concrete Structures.

Clear cover stands for the distance among C.G of reinforcement bars and bottom most point of concrete.

The thickness of cover is dependent on ecological conditions and nature of structural member.

The depth of concrete cover is calculated by applying a cover meter.

The clear cover that should be provided is determined by Indian Standards. IS 456:2000.

Watch following youtube video to learn the complete process :-

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Placement of lap in column as per IS Code 13920

This construction video tutorial sheds light on reinforcement lapping zone in column. By going through this video, one can learn how to place lap in exact position in column by adhering to IS code 13920.

A lap is required when two pieces of reinforcing bar (rebar) are overlapped to produce a constant line of rebar. The length of the lap fluctuates according to the concrete strength, the rebar grade, size, and spacing.

The objective of lap is to transmit load from one bar to another bar as well as retain continuity. The positioning of lap is dependent on the bending moment of the column.

Lap length refers to the length of the overlap of bar necessary to securely transmit stress from one bar to another. Lap length varies on the basis of tension and compression zones and mostly relies on grade of concrete and steel. Development length refers to the length of the bar necessary to transmit stress from steel to concrete.

Rebars in column should have been lapped at around 5 feet from the story.

As stated by I.S. 13920 Vertical bars of Columns should be lapped in regular zone (Mid-height ) only and it should be spread out i.e. not surpassing 50% of bar is lapped at one section. Besides, lowest clear vertical distance among lapped bars should be 0.25 times lap length.

To get more details, watch the following video tutorial.

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Details of Foundation in Construction?

A foundation alias ground sill is the low part or sub-structure of an architectural structure that is artificially constructed on the soil to transmit loads from the structure to the ground securely. Foundation of a structure is built up underneath the ground level with the purpose of making the lateral strength of the structure better. The solid ground on which the foundation is supported is known as the Foundation Bed.

On the basis of the condition and bearing ability of soil and nomenclature of structure, the foundation is categorized as shallow foundation and deep foundation.

If the depth of the foundation is under or similar to its width or if the foundation is built up at proper shallow depth, it is called shallow foundation. A shallow foundation delivers the load to a stratum found in a shallow depth. Shallow foundations are generally found in building up low rise structures.

If the depth of the foundation surpasses its width or if the foundation is developed at considerably large depth, it is call deep foundation. The deep foundation transmits the load to a wider depth under the ground surface. Deep foundation is intended for high rise or multi-storey structures.

1) Shallow Foundations
i. Spread footing or open trench foundations
ii. Grillage foundations
iii. Mat or Raft foundations
iv. Stepped foundations
v. Inverted arch foundations
vi. a) Wall Footing
vii. b) Reinforced cement concrete footing
viii. c) Combined footing
ix. d) Eccentrically loaded footing

Deep Foundations - i. Pile foundations, ii. Well foundations, iii. Caisson foundations

To erect a foundation, trenches are excavated thicker into the soil unless a solid stratum is attained. To make the base foundation, concrete is poured into this trench. These trenches are combined with reinforcement cage to raise the foundation stability.

The estimated steel rods which are provided outwards perform as the bones and should be attached with the substructure above. Once the foundation work is completed successfully, the structure of the building is started.

The construction of the foundation can be done with concrete, steel, stones, bricks etc. The material and the type of foundation selected for the desired structure depends on the design loads and the type of underlying soil.

The design of the foundation must incorporate different effects of construction on the environment. For example, the digging and piling works done for deep foundation may result in adverse disturbance to the nearby soil and structural foundation. These can sometimes cause the settlement issues of the nearby structure. The objective of developing of a foundation is to withstand the attack of injurious substances from outside.

The foundation for each structure is made by adhering to the following guidelines:-

1. The underlying soil beneath the foundation structure does not experience shear failure
2. The settlement should be occurred throughout the first service load or should have been within the limit
3. Acceptable bearing pressure should be described as the pressure the soil can resist devoid of any failure.

Objects of Foundation:

1. To allocate the load of structure on wider area to maintain the intensity of load under the safe bearing capacity of the underlying soil.
2. To allocate the load uniformly on the underlying soil to avoid any unequal settlement of foundation.
3. To arrange leveled and hard surface for the super-structure to be constructed over it.
4. To raise the strength of the structure completely against sliding, overturning or other distressing forces like wind, rain, earthquake etc.

For more information, go through the following article theconstructor.org

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Cross Section Analysis & Design is a powerful construction program for analysis & design of structural cross section

Cross Section Analysis & Design (most recognized software for structural uses in America, Europe, Asia and Australia) refers to a robust application that can be applied for computing an extensive range of cross section, along with the formation of design for reinforced concrete sections (rebar calculator).

The resultant cross sections are simple or composite and can comprise of one or more geometric entities (rectangles, polygons, circles, arcs etc.). With the multipurpose featured user interface, it is possible to draw the geometry of the cross section easily.

The user will be able to import standard steel sections out of a complete shape library in relation to all significant codes (AISC, Australian-New Zealand, BS, Chinese, European, Indian, Aluminum etc.)

The shape, materials or loads of a section are free from any restriction, because the program can deal with any random cross section under biaxial bending and axial loads (Mx,My,P). The program has the ability to work out all sectional properties, plot Moment – Curvature and Interaction diagrams as well as calculate the location of the neutral axis under specified sets of biaxial loads and outline the equivalent strain diagrams along with the consequential stress contours. Based on the position of the neutral axis plane on the section, these items can also be calculated.

Besides, the program is adhered to the following codes regarding reinforced concrete sections: AASHTO, UBC, AS 3600, IS 456, ACI 318, BS 8110, CSA A233, EC2, NZS 3101, CP 65.

The user will be able to produce a reinforcement design on the basis of the codes given above, outline the equivalent interaction diagrams etc., or examine a specified reinforcement pattern under the given load cases with some simple mouse clicks.

With Analysis Parameters Sets, the stress – strain curves of concrete, reinforcement and other materials are indicated parametrically. Every load case is allotted with an Analysis Parameters Set, so that estimations can be made for various design situations, like Ultimate/Serviceability or custom defined Limit States, with an automatic adjustment of the material properties, safety factors etc. As for example, while going to select the default ULS Parameters Set, the concrete curve should have been rectangular and its tensile strength should not be taken into account. Alternatively, the default SLS Parameters Set, applies a hyperbolic stress-strain curve for concrete considering its tensile strength. Here, the safety factors are automatically settled as 1.0. The user has the ability to directly modify these parameters.

An extensive material library exists along with almost all concrete/reinforcement material specifications. Besides, concrete and reinforcement materials, the user can also state custom linear, bilinear, trilinear parabolic or completely general materials.

The program supports Windows XP/Vista/7/8/8.1/10.

For more information, click on the following link engissol.com

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Details of Machine Foundation

The design of machine foundation is carried out for evaluating vibration characteristics of the foundation system cautiously. The machine manufacturer supplies the appropriate data essential for the design and development of the machine foundation of machine before creating the design. All parts of machine foundation are created for extreme stresses because of the poorest combination of vertical loads, torque, longitudinal and transverse forces, stresses because of dissimilarity in temperature and the foundation dead load. In case, the machine foundation layout is partially constructed with beam and column construction, straight bars are placed both at top and bottom of the beams and the gaping of the stirrups should be nearby. The primary foundation block must contain the calculated thickness and should be reinforced both at top and bottom, although the reinforcements are not compulsory from design considerations.

General standards of machine foundation design are provided below :-

There should be adequate mass of the foundation block to absorb vibrations and as well as withstand resonance among the machine and the adjoining soil. This is possible with the increased weight of foundation block according to the power of the engines. It is recommended that for every break horse power of multicylinder engines, a lowest 725 kg. weight of foundation should be arranged for gas engines, 565 kg. for diesel engines and 225 kg. for steam engines. This value is raised by 40 to 60% for the single cylinder engines. As a thumb rule, the weight of the foundation must be minimum 2½ times the weight of the entire machine.

To get rid of the variation in settlement, the dimension of the machinefoundation should be perfect so that the subsequent force move through the centre of gravity of the base contact area as a result of the weight of the machine and the weight of the foundation.

The foundation should have been solid enough to maintain required strength as the smallest deflection of foundation can lead to significant bearing troubles.

There should be a gap around the machine foundation so that the vibration is not delivered from the machine to the adjacent parts of the building to separate it from the adjoining parts of the building.

Overhanging cantilevers should not be used in most cases. If it is not possible, they should have been designed for stability and hardness against vibrations.(6) All units of machine foundation are arranged with reinforcement passing both ways along the surface of the concrete block. The concrete cover to the reinforcement must not be below than 75 mm at the bottom, 50 mm on sides and 40 mm at the top. For foundation developed with steam turbo-generators, cover for the reinforcement at bottom, side and top of base slab must not be below 100 mm.

The amount of reinforcement in foundation units should not be below 2 kg per cu. m of concrete toward impact type or reciprocating type of machines, 50 kg per cu. m of concrete for rotary type of machines and 100 kg per cu. m of concrete for steam turbo generators.

M 150 to M 200 grade of concrete should be applied in the foundations and mostly the-entire block should be concreted in one process devoid of construction joints.

Ref.: www.theconstructioncivil.org

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