How to design Doubly Reinforced Beams

Concrete has quite high compressive strength, but low tensile strength. However, steel has very high tensile strength. That is why we insert steel reinforcements in the tension zones of a structure.

Now, you can provide reinforcements in concrete beams in two ways - single reinforcement (commonly used) and double reinforcement. Today, we will talk about doubly reinforced beams.

In case of doubly reinforced beams, steel reinforcements are inserted into both the tensile and compression zones of a beam. Meaning, at the top and the bottom of the beam. In contrast, the singly reinforced beams have reinforcements only at the bottom, where it needs tensile support.

Further, in singly reinforced beams, there are two steel bars to be provided, but you need not consider the moment of resistance. However, when you do need to consider this, you have to provide additional bars to reduce the tension in the over-reinforced section.

In case of doubly reinforced beams, though, the matter is quite different. In this case you will have to find out the moment of resistance first! Then, you need the area of tension steel (Ast) and area of compression steel (Asc). Combined, they would overcome the Excess Bending Moment (Mu2).

Designing doubly reinforced beams

When we begin designing a doubly reinforced beam, we need to be careful about some factors. For example, the depth of the beam may need to be limited to given values, be it for architectural reasons or otherwise.

If that is the case, you will have to implement the doubly reinforced beam with the requirement to resist more than standard limiting moment in that confined space you have for it. As a general rule of thumb, we design doubly reinforced beams when the go-to design moment of resistance is higher than that of the limiting moment of resistance.

The beam can be defined as a structural member that carries all vertical loads and resists bending. There are several types of materials used for beams, such as steel, wood, fibers, etc. But the most common material is reinforced concrete.



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Published By
Rajib Dey
www.constructioncost.co
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Fixed Cross Section Prestressed Concrete

Prestressed concrete is versatile to a wide assortment of basic frameworks. These incorporate pre-tensioned and post-tensioned structures, both cast set up and precast, and other prestressed elements related to regularly reinforced concrete. While there is no broad arrangement for precast and prestressed concrete, it is valuable to amass certain elements and structures to clarify how prestressed and precast concrete is designed and built.

Prestressed and precast concrete might be considered in four general classes:

1. Standardized Elements
2. Fixed Cross Section Elements
3. Fully Engineered Elements
4. Precast Non-prestressed Elements

While there is some cover, each gathering has its own special attributes. We will discuss the Fixed Cross Section Elements of prestressed concrete today.

Fixed Cross Section Elements

The design engineer is required to decide the prestressing forces and tendon areas in fixed cross section circumstances. Two regular fixed section design conditions are post-tensioned pillars and slabs for building or parking structure development, and girders for bridge development. Different utilizations of fixed section elements incorporate structures, for example, water tanks and post-tensioned slabs on-ground.

Flat plate and flat slab floor frameworks are undeniably appropriate for the utilization of post-tensioning tendons. Another well known framework is single direction slab and pillar floor frameworks that are thrown set up. The design engineer determines a tendon profile geometry and a normal viable post-tensioning force important to fulfill the design necessities.



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www.constructioncost.co
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Guidelines to set up reinforced concrete pipe (RCP)

Reinforced concrete pipes alias RCPs, are suitable for storm sewer systems and water sewer systems. The set up of these pipes is complicated since they are weighty and heavy equipments are required to shift and place them. Given below, the details about RCP handling and installation.

Handling Reinforced Concrete Pipe: Reinforced concrete pipes should be dealt with cautiously so that the bell is not damaged (the wide or flared end of the RCP) and spigot (the narrow end that is inserted into the bell of an adjacent pipe).

RCPs should not be pulled to the site. It is suggested that initially, the pipes should be unloaded with a nylon sling or other certified material to support the weight of the pipe, and make balance properly in the sling.

Excavating Reinforced Concrete Pipe: Prior to start the installation process, make sure to arrange the trench to adapt minimum two pipes so that it becomes possible to check that the installation will retain the necessary slope and the consequent trenching will not affect the pipe being installed as well as endanger the security of workers.

Once each RCP is installed, the line and grade levels should be examined properly. Keep in mind that the trench should be adequately wide to facilitate the workers installing and controlling the pipe securely.

It is recommended not to change the pipe alignment or grade with the pipe in the home position. Keep in mind that all through the installation process the pipes should not be supported on bells since it could damage them. The bedding material should not contain any debris and should retain a consistently level surface.

How to arrange joining surfaces of RCP: Prior to placing the RC pipe, it is required to cleanse all impurities from the joining surfaces of the bell of the pipe cautiously to provide perfect homing of the pipe.

Provide lubricant to the bell portion of the RCP with a brush or gloves. Check with the RCP manufacturer for suggested lubricants that should be used. Lubricant should be sufficient to prevent the gasket from rolling away and damaging the bell end.

Cleanse the spigot or tongue end of the pipe to seal the gasket properly. Lubricate the tongue end of the pipe along with the gasket recess. If the lubricating grease is inadequate, the gasket may twist out of recess. The gasket should be lubricated prior to arrange it on the tongue of the RCP.

How to set up RCP: To set up the RCP, the pipe should be managed with few workers. It is necessary to lubricate pipe bell and gasket not to utilize extra force.

Set up the gasket and apply a round object to level the gasket stretch. Pass the object frequently along the circumference to keep everything in exact location. When the gasket is not expanded, leaks may occur at the joint or the bell may crack. Align bell and spigot, and ensure that the gasket gets in touch with the entry taper.

Ensure the pipe is aligned with surveying or leveling instruments. If the pipe going to be installed contains a small diameter, a wood block should be arranged across the bell end of the pipe and pushed with a wedge bar to shift the pipe gradually into place. Continue pushing unless the pipe is entirely installed. When the pipe diameter remains somewhat bigger and heavier, the pipe pullers should be applied to install the pipe.

Backfilling Reinforced Concrete Pipe: Backfill material should be set cautiously along the pipe and compacted methodically. Backfill material should be arranged consistently in lifts on both sides of the pipe and fill the trench up one foot over the top of the pipe.

The material should not be bulldozed into the trench or provided directly on top of the pipe. The backfill material with large boulders should not be utilized since they will not be consolidated and may damage the pipe.

The material with roots or other organic material should not be used. Backfill should be arranged based on the geotechnical recommendations on particular backfill material.

Lastly, heavy construction equipment should not be operated over the pipe unless sufficient backfill is prepared or the pipe is sufficiently deep in order that it is not damaged.

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Published By
Rajib Dey
www.constructioncost.co
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Detailed guidelines on Bar Bending Schedule of Beam

This construction video is based on Beam Reinforcement Details. By watching this video, one will be familiar with Bar Bending Schedule of Beam with some easy to follow processes.

Reinforcement in beam

The role of reinforcement is to withstand tensile stresses because of bending and shear in beams for singly reinforced sections. But some factors like architectural reasons or basement floors can limit the depth of section. Therefore, the beam section is designed as doubly reinforced to withstand tensile and compressive stresses and delivered with reinforcement in compression face.

Bar Bending Schedule for RCC Beam

Bar bending schedule is used to make the reinforcement calculation toward reinforced concrete beam. It presents the details of reinforcement cutting length, type of bends and bend length.

The following article will provide you more information on Bar Bending Schedule For RCC Beam. theconstructor.org

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Rajib Dey

www.constructioncost.co

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A position is vacant for Assistant Staff Project Manager - Construction Materials Testing

An award-winning consulting firm that provides geotechnical engineering, construction materials testing and environmental and facilities consulting services and has been ranked as one of the top 100 engineering and environmental firms by ENR, is seeking an assistant staff project manager for construction materials testing.

Duties and Responsibilities: 

Mainly perform with management of construction materials testing projects. The candidate has to take liabilities for testing of soils, foundations, reinforced and post-tensioned concrete, masonry, structural steel, fire proofing and asphalt pavement. Besides, there are other project management liabilities which range from application of technical support, day-to-day assessment of field reports, checking progression of project for performance and budgetary conditions, support with collection efforts, planning for proposals and invoicing, participating with project site meetings and providing support with the resolution to technical and administrative problems.

Functionalities:

• Analysis of soils, foundations, reinforced and post-tensioned concrete, masonry, structural steel, fireproofing and asphalt pavement.

• Laboratory tests.

• Day-to-day field reports.

• Project meeting and providing support in project resolutions.

• Scheduling, training and oversight of field technicians.

• Special inspections of structural components.

• Development of proposals.

Qualifications: 

• BSCE from an ABET recommended college/university required; knowledge with MS Geotechnical Engineering will be an added advantage.

• 0-2 years working experience with associated field.

• EIT certification desired. Possibility for acquiring a PE license is essential for career development.

• Outstanding oral and written communication skills.

• Interest in project management and the ability to work effectively in teams, with clients, peers and subordinates, as required.

Notes: Please specify your compensation expectations [$$/hour] while sending application for this post otherwise your application will be disqualified. This position is non-exempt under FSLA. This position is not eligible for visa sponsorship.

Link for application

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www.constructioncost.co

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Benefits of externally bonded reinforcement toward concrete & masonry

If concrete or masonry structures contain inadequate strength, externally bonded reinforcement provides good solution. Externally bonded fiber-reinforced polymer (FRP) composite systems is considered as the greatest substitute to traditional methods for solidification and retrofit. But the epoxy matrix of FRP systems is unstable to failure in high-temperature or aggressive surroundings.

Fabric-reinforced cementitious matrix (FRCM) systems are gaining popularity as a feasible substitute to FRP systems. FRCM systems are originated as a progression of FRP where the epoxy matrix is substituted with a cementitious matrix. With the cementitious matrix, FRCM systems can function efficiently under high temperatures, humidity, and ultraviolet radiation as compared to FRP systems. The cementitious matrix can significantly enhance the stability of the strengthening system in moist and chemically aggressive atmospheres, or in applications where vapor conformity of the strengthening system is necessary.

Properties of FRCM

FRCM systems are externally bonded strengthening systems which contain a fabric mesh implanted in a cementitious matrix. Identical to FRP systems, the fabric in an FRCM system bears the pressures transmitted from the concrete or masonry substrate via the cementitious matrix. The fabric usually includes meshes formed with carbon, alkali-resistant glass, basalt, or polymeric fibers (like polyparaphenylene benzobisoxazole, PBO), or hybrid systems.

The cementitious matrix applied in FRCM is non-shrinkable and executable in order that it can be smoothly shoveled as well as pervade the fabric mesh openings. Both hydraulic and non-hydraulic cements are applied. Sands graded superiorly (grain size less than 0.02 inch) can make the functionality of the fresh mix better as well as the saturation of the fabric mesh. The water-to-mortar ratio by weight generally varies from 15% and 25%. The mortar mix contains chopped fibers to lessen cracking that may occur due to compression in plastic. Organic compounds are also applied to manage the hardening rate and the functionality of the fresh mix, to enhance the bond to the fabric mesh, and to improve the mechanical properties. The fiber content is usually restricted to below 5% by weight of cement to achieve a fireproof matrix.

To read the complete article, click here.

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Reinforcing Of Shear Wall

The boundary elements, whether regular or hidden, are reinforced based on the rules which are assigned to columns.

For reinforcing of the wall body, there are two parallel grates (known as curtains) one at each face. They are retained collectively through an ‘S’-shaped vertical bar. The vertical and horizontal grate rebars should contain a diameter at least identical to Ø8 .The reinforcement with “S” shape must be higher or equivalent to 4Φ8/m2

To avoid cracked surfaces e.g. in pool sides, narrow spaced grates should be applied having the lower possible rebar diameter.

To avoid cracked surfaces e.g. in pool sides, narrow spaced grates should be applied having the lower possible rebar diameter.

The ‘S’- shaped reinforcement

The ‘S’-shaped bar offers anti-buckling restraint to the longitudinal reinforcement. Besides, it makes sure that the vertical and the horizontal rebars will progress work jointly regardless of a potential concrete spalling that may occur due to an strong earthquake.

The ‘S’-shaped link is developed with one closed corner at an angle similar to 180°, or 135° and the other corner bent at an angle equivalent to 90°. This is crucial for positioning it without any difficulty. Once it is applied, the second corner must be also bent at an angle at least equivalent to 135°.

It is acceptable to apply soft steel to have the ability to bent the ‘S’-shaped reinforcement manually.

If the vertical rebars are positoned in an interior layer, then the ‘S’-shaped link must detain the horizontal rebars to the region that they bisect with the vertical ones or get around both horizontal and vertical rebars simultaneously.

On the other hand, in an rectangular shear wall, the reinforcement of the boundary column and the distribution rebars of the wall’s body is carried out as two ‘Γ’ shaped parts. Folded mesh is applied to develop the ‘Γ’ shaped parts.

Ref : debug.pi.gr

Image Courtesy - debug.pi.gr

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Published By

Rajib Dey

www.constructioncost.co

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