Concrete Anchors

Table of content: 1. What is concrete anchors.

                              2. Types of concrete anchors.

       

• Masonry and concrete anchors – These are designed to anchor and secure concrete, block and brick. There are multiple types of concrete anchors available, including concrete screws, hammer-in anchors, lag shields, lead screw anchors, plastic wall plugs and more.

• Drywall anchors – Also known as hollow wall anchors, these are best suited for hollow walls to provide a strong base for the hold. Types of drywall anchors include cement board screws, expansion anchors, threaded anchors and toggle bolts.

A Concrete Anchors are Join concrete with other types of objects like metal, wood, plastic, machinery, and even more concrete elements.
The types of concrete are used for different purposes as light duty concrete Anchors are used for hanging towel, doors and other objects under 50lbs means 22.7kg to concrete wall.

Anchors make it easier to insert screws directly into a thicker wall or surface and are designed to hold as much weight as the wall they’re attached to can bear. Use a hammer drill when installing anchors into hard surfaces such as stone, concrete and brick. 

If you want to build a concrete structure more secure and stable in nature then use anchor bolts for concrete, a footing mostly connected with concrete anchors can be a great solution.

Concretes are a great material for any type of foundation. It is very dense, more workable, affordable, weather–resistant, and very strong.

Medium duty concrete anchors are mostly used for holding weights up to 200 lbs means (90.7 kg). These types of anchors are used for securing heavier objects such as hanging T.V.

Heavy Duty Concrete Anchors are designed for construction purposes. These can behold weights of over 200 lbs means (90.7 kg). It is used to secure the foundation with just about other materials.

If you are building a house on top of concrete without anchoring it down then a flood or bad storm could lift it off the foundation.

Types of Concrete Anchors

The several types of Concrete anchors are given below with a brief description.

     1. Wedge Concrete Anchors

     2. Concrete Sleeve Anchors

     3. Split Drive Concrete Anchors

     4. Stud Concrete Anchors

     5. Lag Shield Concrete Anchors

     6. Self Drilling Concrete Anchors

     7. Drop-In Concrete Anchors

     8. Machine Screw Anchors

     9. Strike Anchors

1. Wedge Concrete Anchors: 

A Wedge concrete anchor is named after the wedges that open and expand up to 1/16” at the anchors base .when the bolt is tightened.

This is a male concrete anchor which is used for fastening to the base of concrete by the use of a nut and washer.

Also, the wedge concrete anchors are widely used because it is easy to insert, corrosion-resistant and among the strongest concrete anchors.

It is actually a stud constructed of two adjoined pieces one-piece is threaded at the top end and the other end consists of a process that includes a wedge and clip that is expanded between the stud and the wall of the hole in the concrete.

The wedge concrete anchors are generally a good option for a heavy shear application and for heavy load. Also the heavier duty seismic wedge anchors are used in areas frequented by seismic activities.

A couple of things are to keep in mind regarding wedge anchors:

The holes drilled into the concrete for a wedge anchor should be equal to the diameter of the anchor.

Also, it is used for solid concrete only not for stone, mortar, brick, etc.

2. Concrete Sleeve Anchors:

A Concrete Sleeve Anchors are male fasteners and  It consists of a threaded bolt enveloped by an expander sleeve at the top end and a washer and nut at the other end.

The Sleeves anchors are threaded through the fixture and into the pre-drilled hole in the concrete, stone, brick and mortar.

 The action of turning the bolt on the nut pulls the bolt up through the sleeves causing the sleeve to flare out up to 1/8”.

3. Split Drive Concrete Anchors: 

These split Drive concrete anchor got their holding power from the source of resilient composition of the piece of one anchor itself.

Also this anchor is male fasteners with a split expanded base. Generally, it is suitable for light-duty tasks and suitable for block, concrete, brick, and stones base.

Most important things keep in your mind when you install split drive concrete anchors,

The diameter of the anchor base is similar to the size of the drilled out hole.

4. Stud concrete anchors: 

The sleeve concrete and wedge anchors are used as a tighten nut so that the anchors expand a lot against the hole or sides of the walls. The stud anchor also expands.

But when you expand a stud anchor then you need hammering on the top portion of the anchor.

The expansion anchors are threading on the top end portion and the bottom end at that time drill holes have consisted of a vertical slit.

At the bottom end of the stud anchor, there is a hole that sits on the tapered shaped steel plug.

When you apply a hammer onto the top portion of the stud then the bottom part of the steel stud will e forced to e set over the tapered steel.

This makes the stud expand against the side or wall of the hole.

5. Lag shield concrete anchors:

Lag shield concrete anchors are female type of anchors and they having sleeve that is tapered and ripped in shape and texture. The lag concrete anchor sleeves are made of a zinc alloy material and the sleeves are plain in nature.

These sleeves are placed into the pre-making drill hole base that could be a mortar, concrete, brick, stone, etc.

These lag screws are goes inside and expand that zinc material sleeve, and then cut the threaded portion of the anchor.

That lag concrete anchors are pressed inside the exterior wall of the base materials. Depending upon the diameter of a bolt that is supposed to go inside the screw then the lag concrete anchor is designed according to their embedded length.

Generally, the longer lag anchors are having a stronger and adequate grip that holds the base material.

Another side the lag concrete anchor is short then it is dense and hard.

6. Self drilling concrete anchors:

A self-drilling concrete anchor is a name suggested as the anchor itself has its own teeth which means it is cutting holes into the concrete base by itself.

The top end of this anchor has internal threading and tapered shaped steel plug too. So that bolt can easily be screwed into it.

When you drill the shell on the tapered steel plug with the help of hammering, the bottom end of the shell will end up expanding while bearing the walls or side of the hole.

7. Drop In concrete anchors:

Sometimes confused with widge anchors because they expand similarly, drop in anchors are female anchors that are placed in a pre–drilled hole.

The expander plug at the anchor’s base is set using a setting tool which is essentially a steel rod with one end necked down.

The necked-down portion of the tool is inserted into the drop–in anchor and tapped with a hammer until the lip of the anchor meets the lip of the setting tool.

Like the wedge anchor, drop-in anchors are intended for solid concrete only and can’t be used effectively in brick, block, mortar, or stone.

8. Machine screw concrete anchors:

It's a female anchor this type of fastener consists of a cylindrical base inserted into a pre-drilled hole in brick, mortar, stone and concrete.

These anchor screws are threaded through the fixture and into the base and hole, and the setting tools are used for turning the screw.

As the screw turns down into the base, it is expanding the base for securing the anchor in the hole, thereby fastening the fixture to the surface of concrete.

Each machine screw anchors have specific setting tools these are determined by the diameter of the machine screw anchor being used.

The anchors are properly set when the lip of the setting tools meet the lip of the anchor.

But the main point is a, for machine screw anchors, the hole size required is larger than the anchor size being used.

9. Strike anchors:

Strike anchors are male fasteners and it is used to join lightweight fixtures such as shelf brackets, conduit and electrical boxes to solid concrete.

The strike anchors are an impact expansion fastener consisting of a tabular body capped by a drive pin that is expanded from the tubular casing.

When the strike anchors are inserted into the pre-drilled hole then the head of its pins are driven further into the tube via hammer strikes, expanding the tube and creating the necessary hold within the hole.

The hole diameter to be drilled for the strike anchors are the same diameter as that of the anchor to be used.

Strike anchors enable long runs of fixtures to be quickly installed but once placed then not removable.

  Grillage Foundation

Table of Content:    1.  What is grillage foundation.

                                        2.  Installation of grillage foundation.

                                        3.  Types of grillage foundation.

                                        4.  Construction of grillage foundation.

                                        5.  Advantages and disadvantages of grillage foundation.

A foundation which consists of one, two or more tiers of beams (typically steel) superimposed on a layer of concrete to disperse load over an extensive area is grillage foundation. Grillage foundation is used when heavy structural loads from columns, piers or stanchions are required to be transferred to a soil of low bearing capacity. Grillage foundation is often found to be lighter and more economical. It is used at the base of columns. These tiers are encased in concrete and are at right angles to each other. This type of foundation is generally used for heavy structure columns piers and scaffolds

Installation of Grillage Foundation:

First, for solid monolithic grillage, we have to produce and install the framework. We prefer this grillage because it is more dependable.

Formwork is made from edging boards in the form of rectangular troughs. Its height is 1 ft and width are equal to the minimum wall thickness of the house. It must be set about 6-8 inches gap in between each grillage. 

Inside the formwork, we have to set a framework of reinforcements connections using binding wire. The least distance from the frame to the side of the formwork is required to be same. 

Next, the reinforcement is linked with the same binding wire used before. 

Then, Concrete has to be prepared using the cement mixer. It is poured in the formwork in a continuous cycle. Fittings must be placed on a height about 25-30mm so that it completely immerses in concrete. Concrete should be carefully poured to avoid unwanted cavities. 6. After filling the surface, the surface has to be leveled and left to dry. When it is dried, the formwork can be removed. The foundation is ready now.

Types of Grillage Foundation:

1.  Steel Grillage foundation

2.  Timber Grillage Foundation

1. Steel Grillage Foundation:

The Steel Grillage foundation consists of joints or steel beams supplied in single or double layers. Its name defines its function and structure, as it is composed of steel beams, structurally known as rolled steel beams.

A minimum coverage of 10 cm is maintained on the outer sides of the outer beams, as well as above the upper flanges of the upper layer.

The depth of the concrete must be at least 15 cm. After leveling the base and pouring the concrete, we must check that the compaction is done properly and that an impermeable layer of a thickness of not less than 15 cm is formed.

It protects steel beams from groundwater, which can lead to corrosion. Then, we place the first layer of beams on the concrete bed at a distance of 100 to 300 mm, with the help of tube separators.

The depth of the concrete must be at least 15 cm. After leveling the base and pouring the concrete, we must check that the compaction is done properly and that an impermeable layer of a thickness of not less than 15 cm is formed.

It protects steel beams from groundwater, which can lead to corrosion. Then, we place the first layer of beams on the concrete bed at a distance of 100 to 300 mm, with the help of tube separators.

Then, we pour concrete between and around the beams of the first layer. After that, we place the second beam level at right angles to the first levels with the help of the separator.

Then again, we pour concrete between and around the steel beams. In doing so, we connect the steel supports to the top layer with the help of a base plate, side angles, and a reinforcement plate.

These connecting elements are also embedded in the concrete to make the joint rigid.

2. Timber Grillage Foundation:

The timber-type foundation is provided for masonry walls heavily loaded with Timber columns.

This foundation is especially useful in flooded areas, where the carrying capacity of the soil is very low and where the load on the soil is limited to 50-60 KN/M2.

Timber planks and Timber beams are used instead of steel beams. there is no concrete enclosed between the Timber joints.

However, the lower concrete supplied in the steel grid is replaced by a Timber platform built with Timber planks.

The excavation of the base is level. The bottom layer of Timber boards of size 20 to 30 cm and width of 5 to 7.5 cm thick is placed side by side, with no space between them.

Above this layer, a Timber beam of the same section as that of the Timber post is placed at a right angle.

Then, another layer of planks is placed again at right angles to the direction of the beams. The top layer of boards maybe 7.5-10 cm. Thick, extending the entire width of the base of the wall, on which the masonry wall is built.

Construction of Grillage Foundation:

The steps followed for the construction of the grillage foundation are listed below:

The framework must hold the grillage in place for a solid monolithic grillage foundation.

The formwork is prepared from edging boards in the form of rectangular troughs.

The height of the formwork ranges from 1-1.5 ft, and the width shall be equal to the minimum wall thickness of the building

Concrete is poured into the formwork to form a concrete pad of 450 mm to 600 mm.

The grillage sections (timber or steel) are placed above the concrete pad with sufficient cover on all the sides.

Concrete is poured into the foundation up to the desired depth. 

A minimum cover of 10 mm shall be maintained at the top grillage to avoid corrosion of steel beams.

Advantages of Grillage Foundation:

1.  The time required for the installation and casting of grillage foundation is comparatively less than that of conventional foundation.

2.  Grillage foundation is capable of successfully transforming heavy loads over a larger area.

3.  These foundations are used to construct significant structures such as column piers and scaffolds.

4.  Grillage foundation avoids deep excavations in soft soils, and the depth of the foundation can be limited to 1-1.5 m.

Disadvantages of Grillage Foundation:

1.  Its steel joints require protection from corrosion by concrete.

2.  For greater depth the construction of piles is needed in this foundation.

3.  Space below the grillage needs to be filled and warmed.

4.  Not suitable for multi-story buildings.

Safe Bearing Capacity of Soil

 Safe Bearing Capacity of Soil

 The capacity of the soil to allow the loads coming from the foundation is called the bearing capacity of the soil.

It is essential to know the bearing capacity of the soil before designing the foundation. Different field tests can determine it. However, standard safe bearing capacity values are available for different soil types, and these values can be assumed where test data is limited or speedy construction is required.

S.No	Type of Soil	Safe Bearing Capacity ( kN/m2)
	Cohesive Soils
1.	Soft shale, hard or stiff clay in a deep bed, dry state	440
2.	Medium clay readily indented with a thumbnail	245
3.	Moist clay and Sand clay mixture, which can be indented by thumb pressure	150
4.	Black cotton soil/expansive clay ( 50% saturated) in the dry state	130 to 160
5.	Soft clay indented with moderate thumb pressure	100
6.	Very soft clay which can be penetrated with the thump up to few centimeters	50
	Cohesionless Soil
7.	Compact gravel/sand and gravel mixture with good resistance against penetration of tools	440
8.	Compact and dry coarse sand	440
9.	Compact and dry medium sand	245
10.	Loose gravel or sandy gravel mixture, dry state	245
11.	Fine sand and silt ( consists of dry lumps)	150
12.	Loose and dry fine sand	100
	Rocks
13.	Hard rocks such as granite trap, diorite, etc.	3240
14.	Laminated rocks such as sandstone, limestone, etc.	1620
15.	Residual deposits of shattered and broken bedrock and hard shale cemented material	880
16.	Soft rocks	440

The Ultimate Bearing Capacity: The gross pressure intensity at the base of the foundation which would cause shear failure of the soil.