Single Foundation and Tie Beams


In cases where the column loads are large, the columns are close to each other or the regional ground is weak, a single footing is manufactured under the two columns. This single bolt takes the loads from the two columns and transmits them to the ground uniformly. These types of foundations are called “compound foundations”. On the side of the column with high axial strength, the footing is made wider, so that the soil stress is uniform under the footing.

Unified Basics


It is used in cases where the ground is weaker, the column distances are closer or the building loads are higher. Foundations that transfer loads from bearing elements to the ground with sufficient rigidity by arranging plates with or without beams under vertical bearing elements in one or more directions are called “continuous foundation”. The risk of differential settlement is less on continuous foundations than on individual foundations. Different seating can be prevented in multi-storey buildings, but still this risk is high in high buildings.

Continuous foundations in one direction are called “strip foundation”. Since it is obligatory to connect the foundations to each other in both directions, a continuous foundation, i.e. a strip foundation, is made in one direction, but the foundations are connected to each other with tie beams in the other direction.

Continuous foundation in one direction (strip foundation)

Foundations in more than one (double) direction are called “field foundation”.

Continuous foundation in two directions (field foundation)
Strip Foundation (One Direction) -Field Foundation (Two Directional)


The foundation types in which the ground is very weak or varies from place to place, the building loads are high, and all vertical bearing elements of the building are placed on a single foundation are called “raft foundation”. However, today it is the most used foundation type not only on weak grounds but also on solid grounds. Raft is also called general foundation. It can be preferred in high-rise buildings. Basically, the risk of differential sitting is low. Since it has more foundation area than other foundation types, the stresses that will occur on the ground due to the building load are reduced by spreading the load of the structure. Therefore it is also called a spread foundation. This is the reason why it is preferred on floors with small ground safety stress.

Beamless (Flat) Raft Foundation

It is a type of raft foundation that covers the sitting area (as long as the conditions allow, the building is made as a wider-console-in every direction than the sitting area), in which all vertical bearing elements sit directly on a thick slab, working as an inverted plate (floor).

The most important problem in beamless flat raft foundations is the stapling effect that may occur in the column areas. For this reason, the thickness of the plate should be determined by taking the stapling effect into consideration and by checking the punching, and it should be ensured that the stapling effect is prevented. In some cases, for example; By making a column head against the punching effect in a few columns, the plate thickness can be increased in the punching areas of those columns.

You can get more detailed information by examining our article titled “Raft Basic Equipment Manufacturing without Beams”.

Kirişsiz Radye Temel Kesiti
Kirişsiz Radye Temel Uygulama Örnekleri

Beam Radies

It is divided into 2 as top beam and bottom beam radii. Although it is more demanding in terms of formwork workmanship, it is safer than beamless radii. As we mentioned in raftless raft foundations, cantilever can be made to slabs and / or beams. In general, raft foundations without beams (flat) and with top beams are preferred.

Top Girder (Flat Beam) Raft Foundation

It is a type of raft foundation formed by placing the vertical bearing elements of the building on the beams and the beams on a plate covering the entire building area.

Top Girder Raft Foundation

Bottom Beam (Reverse Beam) Raft Foundations

In raft foundations with bottom beams, the load from the vertical bearing elements is transferred to the plate and from the plate to the beams.

In raft foundations with bottom beams, a flat surface is obtained at the basement floor and less excavation is done. For example; Suppose the regions between the beams in our base area are hard rock. With this basic application, you can save money from excavation, thus time etc. we gain. Still, it is not a preferred type of foundation.

Compared to the top beam raft foundation, it is generally less healthy in terms of static. Since the foundation slab area does not cover the entire floor, the ground stresses do not spread uniformly for the entire foundation area and the stresses are higher than the raft foundation with or without beams under the same conditions. If there is variation in the ground, the probability of different settlements is higher than the raft foundations without beams and top beams. If the foundation soil has a feature that can cause slippage in the foundation (which should be a very weak soil), soil improvement, pile etc. methods should be applied. (Applicable for all types of superficial foundations)

We can think of bottom beam raft foundations as follows;
Consider a beamed continuous foundation (in two directions). It makes filling between beams after foundation construction and then lean concrete etc. We try to obtain a flat surface on the basement floor with the material. When manufacturing a continuous foundation with beams, imagine that you do not dig these gaps and manufacture a plate that covers the entire foundation area so that there is no gap between the beams. The only difference is that there is no plate under the beam as in continuous foundations. This means that the structural load will be spread over a smaller area of ​​the ground and the ground stresses will be high. Of course, although the plates on the beam take some of the load, it is difficult to obtain a uniform distribution. However, it would be wrong to talk only on concrete values. If necessary, a plate can be made under the beam, the beam dimensions can change. Soil values, building load etc. Necessary measures can be provided by considering conditions such as. For example, if there is a swelling problem in the ground, it can be evaluated together with other conditions and the bottom beam raft foundation system can be applied to prevent damage to the building due to swelling in the ground.

Bottom Beam Raft Foundation Section

Mushroom Shaped Raft Foundations

In our article titled “Beamless Raft Foundation Reinforcement Manufacturing”, we mentioned that the most important problem in raftless raft foundations is stapling and when controlled with staples, some columns with insufficient plate thickness can be capped or trayed. In this way, it enables us to spread the load transferred by the column to the slab over a wider area due to the punching effect occurring in the column regions of the beamless (flat) raft foundations and thus take measures against the punching force. This means that from time to time, this application can be made for several columns on raft-free (flat) raft foundations (This is optional. Measures can be taken in this way in order not to increase the thickness of the slab for a few columns and to avoid excessive cost).

In short, raft foundations without beams, which have heads with or without inclination (based on certain calculations) under the column against the punching effect, are called mushroom raft foundations. These titles are usually made on the plate. However, a flat surface will not be obtained on the basement floor. Sometimes they are applied under the plate. In such an application, raft excavation work should be done very properly. There should be no gaps or disturbed ground under the raft foundation plate.

Cork raft Foundation

Inverted Arch Shaped Raft Foundation

It is the application of a non-beam (flat) raft foundation plate in the form of a reverse vault. We can call it slab foundations in the form of reverse vaults.

Although the vaults and domes are thin, they are systems with high carrying capacity compared to flat plates. The load in the shells is generally evenly distributed and the moment values ​​are very low compared to the flat plate.

There are implementation difficulties. The foundation floor should be prepared to fit the shell form. It requires proper, painstaking workmanship and therefore cost. The shell should sit on the ground at every point, that is, there should be no gaps under the reverse vault plates and the damaged ground should not be created. It should be ensured that the soil stress is uniform. For these reasons, it is difficult to implement, has a high margin of error and is risky. In today’s method and technology, there are no situations where its application is mandatory. It is a type of foundation that is not preferred. (We are grateful to them for the information provided by Prof. Dr. Ahmet Topçu on the subject.)

Inverted Arch Shaped Raft Foundation – Cross Section

Rigid Shear Wall (Cellular) Raft Foundations

In buildings with a basement floor, curtains are made that can carry lateral floor loads due to the basement floor being inside the ground. These curtains work together by connecting the reinforced concrete with the beam and floor (basement floor ceiling). Such foundations are called rigid raft foundations. Non-beam (flat) raft basis is manufactured. The only difference is that this foundation is deeper than the natural ground level and because it is within the ground, curtain, beam and deck are manufactured. As the building loads are transferred from the columns and curtains on the upper floors to a curtain system that sits on the foundation and from there to the foundation, the loads will be distributed more uniformly to the foundation and reduce the ground tension, thus increasing the bearing force of the ground, that is, the safe bearing capacity of the foundation, and minimizing the settlements that may occur. In this way, we can get a rigid foundation. These curtains are formed as curtains, beams and slab cellular (along all axes) due to the insufficiency of the beams in the raft foundations with upper beams, depending on the situation.

Rigid Foundation
In fact, we can name these structures with the basement (remaining in the ground) as a kind of rigid foundation.

In cases where beam heights are insufficient in top beam raft foundations or when we need to make the beams high, curtains are made instead of making these beams high, and torsion is prevented to form beams and plates on the upper parts to prevent twisting.

In other words, rigid foundations are not made only for structures where basement floors will be used. For example; If we need to make a rigid foundation according to static calculations and ground parameters, and if this rigid foundation is deeper than the ground but cannot be used as a basement because the basement height will be insufficient, the cellular rigid foundation is applied in the same way and these walls are filled with suitable material. (Like basement curtains)


In weak soils that cannot bear the load of the structure, the ground stresses cannot meet the stresses that will occur due to the building loads (ie, the stresses on the ground caused by the loads from the structure, therefore from the foundation, are greater than the ground safety stress); If the solid ground that can carry the load of the building is too deep for a healthy ground improvement, deep foundations are created in order to ensure that the solid ground carries the building loads.


The solid ground is not deep enough to require piling; If the solid ground is too deep, which is valid for all deep foundations, that the ground improvement will not be healthy, or if the risk continues despite the ground improvement to be made, the necessary calculations are made and the foot foundations are placed on a solid ground. Foot foundations should be connected to each other with reinforced concrete beams at the top.

Foot Basics

Cost and labor, safety stresses of the floor, etc. Considering the factors, foundation shoes are formed in suitable dimensions in a flat, curved or ampattered way as in single foundations. Although it is connected with reinforced concrete beams from the top if necessary, it can also be connected from the bottom with tie beams. If necessary, foot foundations can even be placed on a plate. These and similar situations should be applied if deemed necessary, taking into account the ground and building parameters.


In very weak grounds, because the solid ground is too deep, the pile foundation system is applied with various methods to transfer the load of the structure to the solid ground. Structure loads are transmitted to the ground either by end piles or by friction of the side surfaces of the pile (lateral friction). These piles are connected to each other by reinforced concrete beams or slabs at the top. Available in reinforced concrete, steel and wooden pile types.

According to the way the loads are transferred to the ground:
End Post
Friction Post
Combined Pile

According to the way of carrying the load:
Pressure Peg
Tensile Post

According to the material from which they are made:
Reinforced Concrete Piles (In-situ or pre-cast)
Steel Pegs
Wooden Pegs

According to the production method, which varies according to the soil type and structure characteristics:
Driven Piles
Bored Piles (Bored)
– Piles without Coating Pipes
– Compressed Piles
– Kornart Pegs
– Express Pegs
– Piles Remaining on the Ground of the Coating Pipe
– Raymond Pegs
– Mansard Piles
– Stren Piles
– Jansen Pegs
– Alborenz Piles
– Benoto Pegs
– Piles with Lining Pipe Removed
– Siplex Piles
– Wolfholz Pegs
– Straus Piles
– Franki Pegs
– Pedestal Pegs
– Combined Piles

The most commonly used pile foundation is bored piles. Bored piles are in the class of cast-in-situ reinforced concrete piles.

Bored piles are manufactured as follows:

It is made in 3 ways: the coating pipe is not used, the coating pipe is left on the ground, and the coating pipe is removed from the ground. In cases where the use of pipes is insufficient, application is made with the help of bentonite.

Bored pile holes are drilled up to the solid ground and concrete is poured by placing iron reinforcements inside. It is connected to each other by reinforced concrete elements (beams or raft foundation) in the upper layer, leaving shoots at the top.

Drilling (Bored) Pile Application Stages

There are many methods for pile foundations. Earthquake in Turkey Buildings Ordinance (Draft was published), this has been referred to the basic system must necessarily be examined.

For detailed information, you can review the resources mentioned at the bottom.

Bored Pile – Screenings
Bored Pile Application Pictures

Caisson Foundations

Caissons, which are literally crate, are used in very weak, loose or watery grounds and foundations to be formed in water. In cases where pile foundations are not suitable or insufficient, caisson foundations are used. Large diameter circular and hollow caissons, which can be made of reinforced concrete, steel or wood, are submerged into the ground or into the solid ground by various methods in water. It is placed on top of each other. The soil inside etc. concrete or stone – concrete, etc. filled with materials. Reinforced concrete caisson foundations can be manufactured by casting on-site or by pre-casting. Its cost is quite high. They are generally used in bridge and port constructions.
There are basic types of caissons such as open (well) caissons, pneumatic (pneumatic) caissons and floating (crate) caissons.

On-site reinforced caisson foundations
Caisson Basic Application Methods

For detailed information about caisson foundations, you can examine the resources mentioned at the bottom.

Note: If the ground is solid, a single foundation should be used, if it is weak, a raft foundation should be used, or if it is a low-rise structure, it should not be inferred that the raft foundation is not used. For example; There is no base as piled foundation will not be applied in a region with rock ground. Considering the soil – foundation – structure interaction, the decision should be made by making the necessary analysis.

Earthquake Insulated (With Isolator) Foundations

It is made by placing an earthquake isolator under, in the middle or above the lowest columns of the building connected to the foundation. These systems, also called seismic isolators, have various application techniques. These insulators reflect the earthquake movements that occur on the ground during the earthquake to the superstructure as little as possible, thus reducing the earthquake forces acting on the carrier elements. They absorb the energy caused by the earthquake. They are not used to prevent collisions in adjacent structures.

The aim in all buildings is to ensure that the energy generated by the earthquake does not cause as little damage to the building or the structure collapses suddenly, but that the possible collapse occurs within a time period that will save the lives of the living creatures in the building and allow them to escape. in other words, to provide enough time for living things to escape and save their lives. For this reason, a civil engineer should take the responsibility of human and other living lives by thinking and calculating the worst situation in every job they do, and act as an engineer accordingly.

For this reason, our designs should be created with various principles (ductile structure, strong column, weak beam, foundation design, ground properties) and principles, taking into account the interaction of structure – foundation – ground, and the first and greatest aim in all our structures should be to prevent loss of life as we mentioned above. .

The foundation systems with isolators, on the other hand, absorb the earthquake energy very well compared to other systems, minimizing the different displacements in the upper floors and between the floors, reducing the earthquake loads and effects on the building. Therefore, such structures can be designed according to limited ductility level.

Foundations with isolators behave flexible against horizontal forces, but they are rigid against vertical forces. There should be no pulling force in earthquake isolation systems.

Earthquake isolator methods; Although there are various types and methods such as lead rubber based insulators, sliding layer rubber insulators, steel ball insulators, friction pendulum type or flat surface insulators, they are divided into 2 main elements:

  1. Rubber Based Earthquake Insulators
    1. Friction Based Earthquake Isolators

Earthquake in Turkey Buildings Ordinance (Draft was published), this has been referred to the basic system must necessarily be examined.

For more detailed information on the subject, you can review the resources at the bottom of the article.

1- Rubber Based Earthquake Insulators
2- Friction Based Earthquake Isolators

Earthquake in Turkey Buildings Ordinance (Draft was published), this has been referred to the basic system must necessarily be examined.

For more detailed information on the subject, you can review the resources at the bottom of the article.

Earthquake Behavior of Structures with Earthquake-Insulated Foundation
Earthquake Isolators – Application

Additionally damping devices;

Damper devices (damper systems or seismic dampers), which can be applied to the superstructure as well as the foundations apart from the earthquake isolated foundations, are also used as horizontal earthquake, wind etc. It is a system used to dampen the energy that occurs in situations. However, the way these damper systems work in the superstructure is not flexible like the insulators applied, but rather rigid, and unlike earthquake isolators, they have the function of preventing the collision of adjacent order structures.

You can find more detailed information on the subject from the resources we mentioned at the bottom of the article.

Seismic Damper Systems

We would like to mention that;

Professor of Engineering Sciences at METU. Dr. Murat Dicleli made an invention known as “Seismic Damper”. These damper systems (seismic dampers), called MRSD, have a much better performance compared to foreign origin products marketed for similar purposes. The tests were carried out at the Munich War Academy in Germany under the responsibility of Maurer Söhne. While the durability of similar products in the current technology varies between 25 and 50 years, the durability of these products is 125 years.

You can find more detailed information on the subject from the resources we mentioned at the bottom of the article.

Special Foundations

Created by the design of various foundation types, using various methods; They are the foundations applied in rare structures in large span structures, structures exposed to vibrating loads, areas with high risk of earthquakes or landslides, built on the basis of ground and structure characteristics or in a sense that go beyond the borders by using special designs and methods.

Helmet Basics in connection with this topic:

The construction of hard hat foundations is similar to bored piles in general; “Drill, insert reinforcement, concrete.”

However, there are features that distinguish helmet foundations from bored piles. These are the excavation (drilling) method and its application in different geometric ways.

They have more friction area compared to bored piles with the same cross-sectional area and they have the capacity to meet larger vertical and horizontal loads according to their application. Its application is increasing in our country.

Hard Hat Basics Application Stages and Various Shapes



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