Types of Foundation System
Foundation in structural design building can be defined as the part of the structural structure that bears the weight of the structure coupled with the weights of other direct and indirect weights that are attached to it. The foundation ensures that these direct and indirect loads are transmitted to the underlying rock or improvised soil for a proper support system. Therefore, this process that is used in designing the foundation system is based on the study of soil mechanics, geology, structural engineering, and rock mechanics. The foundation will act as a link that connects the properly built structure with the earth system that it is laid on. Equally, a foundation can be a superficial structure that is built in an artificially laid base to connect other building structures. Therefore, the principal factor in the construction of a foundation for a given building structure is to identify the most suitable type of foundation and whether one will be using a shallow or a deep foundation for the building proposed. Developing a great and strong foundation also depends on the parameters such as the bearing of the shears capacity, the type of soil, and the rock beneath the surface of the earth. This means that a proper foundation must entail the diameter and the reinforcement bar, the steel grade, and all the diameters of the reinforcement bars. All these when put into consideration then a very strong structure can be built as a foundation to support very many buildings at once. Equally, in very many cases the foundation design involves putting together the ideas of a geotechnical engineer and the structural engineer and then materializing the ideas effectively. It means that in the initial stages of the foundation, the geotechnical engineer and the structural engineer must be present to access the area and write appropriate findings of the site. The geotechnical engineer will write all the findings of the soil bearing capacity while the structural engineer will be responsible for performing the actual requisite design of the foundation to be built. Previous studies and research as proposed that the foundation can be divided into two parts. These parts are the deep foundation and the shallow foundation. The two parts can also be further subdivided into other subparts and hence depends on the structural properties and the physical form of the materials to be used and accessed. It, therefore, means that the geotechnical part of the analysis will be based on factors such as the corrosively levels, site history, and other surrounding structural designs.
Shallow foundation
The first steps that must be put in place in designing a foundation require basic knowledge of the site location, landslide systems, geological hazards, faults lines, and areas that are prone to the sand system. The requisite knowledge about the project site and size will be beneficial in the initial planning and budgeting of the full work process. This will then help to avoid errors that may occur or underquoting due to poor or negligence in other important perspectives of the project. During the construction phase of the foundation factors such as laboratory testing helps in detailing the feasibility of the project plus the compaction testing processes. In most cases when working on simple design structures, the construction project should be fully based on the initial design plan and all the building materials entailed. These factors must be optimized in order to achieve the goal of setting up a strong foundation that can help in carrying weights of up to twenty-story buildings. Frost protection has also been a major challenge in the design of the foundation. However, if the bedrock levels can easily be found at shallow depths, then the piling process becomes very easy. This means that building a foundation that is of shallow depth is more cost-effective than a deep foundation building. The materials used in the construction of the deep foundation will also be more than the materials that will be used in the construction of the shallow foundation system. The major idea here is that the foundation built is tested enough to withstand turbulence and earth conditions such as tremors and stand still for a very long time. Previous research has already been done on the best ways in which frost prevention can take place to mitigate the effects of the penetration adequately and effectively. Therefore, if any of this laid down activity is not followed to the latter, then there might exist damages within the foundation system and hence be costly in terms of repair services. This project will therefore look into the two types of .foundation, that /is the shallow and deeper foundation with stress in the deeper foundation. The project also aims in building a foundation with the necessary visualization materials in oasys software.
The shallow foundation design system is said to distribute the load of the structure above the surface of the ground. This means that the depth measurement is meant to vary for different regions and can never be uniform throughout all regions. However, a general loo into the shallow foundation the depth of the field side is seen to be less than about five times the thickness of the requisite foundation. The shallow foundation does not require transferring the load to the subsurface or through different ranges of depth. The shallow foundations range from mat slab foundations, spread footing foundations, pad foundations, slab on grade foundations, earth foundations, and rubble trench foundations. This means that they are constructed where the soil layers at shallow depth will be able to support all the structural loads that will be laid on them. Equally, the length and the width are not the same with that the depth is less in length than the width. A shallow foundation can therefore be used in areas whereby the bearing capacity of the soil on which the construction of the foundation should take place maximum.
Deep foundation
Deep foundations are a different type of foundation that help in the transfer of building loads to the earth from a deep down earth layer to the surface. This means that the foundation is built on different layers within the earth until the surface. This means that the foundation will be strong enough to carry different weights and houses. The deep foundation is always required to carry different loads from the built down structure and hence through the weak soils that are compressible until the surface of the earth. Equally, the foundation can be filled on the les and stronger compressible rocks and soils that are found below the earth’s surface for all the functional reasons. This means that the deep foundations can enter up to lengths of about three to six or even more meters below the earth’s surface.
The construction site for the project has been designed for the building of the slab foundation that will help in carrying residential buildings of up to 3rd flour. The drafting analysis design of the foundation will be carried out in oasys software. The axial load that is brought to the column will be performed through the use of Fleming software system. The software ensures that they give a visualize information on how the foundation will be packed from the first slab until it reaches the last slab on the earth’s surface. Equally, the visualization process ensures that the heights, materials, and different mechanism processes are in place for the building of the residential structure. The site allocation should be environmentally friendly to both human beings and the animals. Once more local authorities should be consulted about the site in order to get the right information on the settling patterns of the site area.
The classification of the piles takes place as per the effects of the pile on the ground that aid in the load transfer mechanisms. The capacity that the ground can bear and very many other specific requirements of the site for the project is far much essential ij choosing the best pick for the pile. The project scope uses the combined end –bearing and friction pile in order to build the slab foundation. The process entails the developing of the bearing capacity through the combination of a end bearing resistance which id found that the bottom tip and the adhesion resistance that exists in the surrounding materials and the pile surfaces. In this case the piles are driven deep down in the soil to help in gaining sufficient frictional force resistance. In other case it is possible for the bearing area which is ground at the bottom of the soil to increase through the enforcement of concrete above the area tip to help in the enlargement of the area in which the whole slab should lie in. therefore, through this process, the total load that is carried by the pile will be equal to the load that is carried by the friction caused and supported by the skin ground system. The design and pile method here is chosen since the soil and bedrock lie very deep and layers above the bedrock supports the skin friction. The equation QU=QS+QP is used to explain the mathematical design of this system. From the equation, the value of QU is said to be the ultimate load capacity of the given pile, QS is the load that is carried by the frictional pile present and the QP is the requisite load that is carried by the end bearing piles to give a strong stack foundation.
Site Details
A large variety of material shave been used in the piling method especially when building the foundation. The usage of these several materials depends on the availability of the materials, project requirements and the requisite costs of the project. Equally, technology has played an important part in the improvement of the materials that are used in the piling process. The use of timber for piling processes has been of benefit especially when building a slab that is above the ground level. Equally, timber usage has been used to raise slabs for housing system especially in areas that are swampy or are prone to flood system. For this to be essential, the quality of the time must be top high to ‘withstand the harsh environment conditions such as rot or rust in cases of using steel. The use of timber piles is known to be economical options especially when one is setting up structures that are light in areas where the soils are saturated with water. The project here however uses concrete piles in building of the slab foundation. The use of concrete is economical and depends on the site location and availability of the building materials. It is seen that the entire allowed concrete load will depend on the capacity bearing of the stratum that is found right below the pile system. This means that for the compressive soils, the cast in place concrete piles will not be suitable in the formation of the foundation process. The concrete piles determination therefore depends on the length, dimensions, and the design loads that the foundation is meant to support. This type of pile is chosen since the fabrication time is very low. Previous research has predicted that the time span for the concrete motor to be ready is about fourteen days as compared to other pile system. In scenarios whereby high head and tensile strength are required, then it is important for the reinforcement services to be carried out on a daily basis. This type of piling can never be effective without carrying out an assessment on the type of the soils that are present in the area. This means that the soil profile assessment must be carried out through the blow counting method and hence helping in the precast pile driving for the foundation slab.
The load test on different piles often takes place after the completion of the casting process of the pile. This time span always varies depending on the type of pile that is being tested at that particular time. Two important steps always talks place that is the initial and the routine test for each and every loading completion that is present. The initial test of the concrete pile is performed to help in the confirmation of the calculations in the load designs and the necessary guidelines in setting acceptable limits within the routine tests. For effective analysis in the test done, the initial test must be carried at different locations with different climatic conditions to check on how best they can withstand the conditions. Carrying out the routine testing on the concrete slab is always carried out as always based on the number of piles that are being used in building the foundation. The test is done ton half of the entire slab within the site area. This means that the test carried out will be around two times the carrying capacity of the set required guideline procedures for the test. The test is always performed to help ensure that there is a safe loading of the load capacity in the piles used and also the test carried out to cut off levels within the site system. The concrete system uses the fatigue tests that are conducted on the plain concrete cylinder systems. The different cylinders are subjected to compressional forces by the use of axial cyclic compression methods. This ensures that the upper part of the cyclic stress is made to range from about sixty to ninety percent of all the strength used in the static compression. Equally, there is also a method that is based on the use of volume strain that can be used in the prediction of the effective static strengths of all the unique samples that are being tested.
Pile Classification based on the Load Transfer
It is evident to recognize that settlement within the pile groups may differ tremendously from a single slab pile to vast amounts of slabs. The method used here in the prediction of pile settlement entails the process from the initial work process to the end work product. The steps followed here starts from the ground investigation and the establishment of all the geotechnical models to be used in the making of the foundation. This is closely followed by the interpretation of the interpretation of the pile load that will be used in the testing process. The process is carried out to attest to the site stratigraphy and the differences in the load test during configuration process. The application of a suitable model is then analyzed to give the following input systems ; the local ground parameters that shows the stiffness process, the global ground stiffness parameters that is used to show the influence of the load pile test data, and lastly the applied loads in the structural and the foundation characteristics in the parameters. The last steps entail the calculations of all the weights within the foundation slab that has been created. The method here used in the calculation is simple and aid in the collection of the correct order consistency. Equally, the process used in the prediction of the pile settlement performance should be done by the use of proper geotechnical assessment tools to ensure that the correct result analyses are achieved.
The process takes place with the assumptions of the ground behavior and the requisite pile analysis. This ensures that the effective parameters must first be interpreted after being achieved from the behavior of the measured settlement of the load. The transfer of the load can then be adopted from the initial slope to ensure that all the subsequent shapes that will be used to derive the load transfer curves are achieved. The process puts assumptions such as the soil types and the nature of the bedrock to give the correct plotting of the graphs.
While designing the project foundation system, a case study in the load test and the interpretation system was studied in East London. The case study is done in one of the building in the United Kingdom to test the loads and the stress factors weight that the slab foundation is capable of supporting. Therefore the foundation system of the tower buildings is meant to be higher than the normal residential buildings.
Factors to consider in designing the Slab Foundation
The perquisite investigation on the conditions of east London revealed that there was a relatively uniform stratigraphy across the whole site. This was considered the adequate level in the characteristics of the site that the slab foundation was to be set in. the geotechnical model is used in the project to test the pile settlement prediction which is the summarized to help in the analysis process. Other computer programs like the Flemings were used to in providing the tensional and the static compression tests and hence the uniaxial compressive strengths achieved.
|
Item |
Slab |
Beam |
Column |
|
Dimension |
160mm |
220X550mm |
220x500mm |
|
Steal grade |
Fe415 |
F500 |
Fe500 |
|
Grade of concrete |
M30 |
M30 |
M30 |
|
Shear wall |
230mm thick |
||
|
Staircase slab |
200mm |
||
|
No. of columns |
25 |
The layout of this design is shown below
The software is used to aid in the calculations of the analyzed foundation design. The beams are therefore assigned
Photo credit; oasys.org
Calculating The Dead Load from the Data given
The main brick wall is given as 166mm, so we assume that the unit wait of the brick, r= 19.2KN/M
The Brick load therefore is (3-0.45) x 19.2 x 0.230= 11.2608
For the partition wall = 19.2 x (3-0.45) x 0.166 = 8.12736
To get the live the volume of the concrete becomes = 0.23 x 3 x 0.166 = 0.11454
The weight of the concrete = 0.11454 x 2400 = 274.896
Weight of steal in concrete = 0.11454 x 0.11 x 8000 = 100.7952
Total live weight of the slab = 100.79 + 274.89 = 375.68
The program in the pile loading test took place in areas such as the tensional, lateral, and compression load tests in the file of varying diameters. This area required a deep attention for the analysis programs. For the compressional loading tests, the use of jacks was vital to load the concreate as the reaction took place in the number of drillers and hence into the calcisilitite that was found beneath. The anchors wreck then one by one connected to the test piles using different unique crowns that were attached above the load cells and the jacks.
Photo credit; oasys.org
To help in the analysis of the pile load test and in driving relevant conclusions and recommendations, the load test was calculated after being fitted as the calculated settlement against the working load at different time spans. This means that the calculated settlement was using different value numbers and adopting the reference layout respectively. From the above data that were computed, the plots below were found to be most relevant
The calculated settlement of the foundation system then took place almost immediately using the corresponding modulus and the reference value points. In this it was realized that the relationship between the relative pile spacing and the computed interaction factors are correlating to each other. The graph below gave a two case scenario of the same
Recommendation and Conclusion
Carrying out a site analysis program before determining the type of foundation to lay for residential purpose houses is very vital. Processes that are economical and does harm the environment should be given a priority when building the foundation. Equally, a recommendation on the use of technology must always be a number one goal for every engineering project. This will ensure that the working processes are cheap, simple, and require very less time for completion purposes. Safety measures should also be put in place while working at the site.
Reference
ACI Committee 209, 1992. Prediction of creep, shrinkage and temperature effects in concrete structures. ACI 209R-92. American Concrete Institute, Michigan, USA.
ACI Committee 209, 2005. Report on factors affecting shrinkage and creep in hardened concrete. ACI 209.1R-05. American Concrete Institute, Michigan, USA.
Building Research Association of New Zealand, 1972. Concrete ground floor slabs, Building information bulletin 152.
BRANZ, Wellington, NZ. Bulleyment, A, 2012. Concrete slabs and basements (second edition). BRANZ Good practice guide. BRANZ, Wellington, NZ. Chisholm,
Derek, 2013. SR0963 Revisit concrete floor slabs: Reference material search. Personal communication. Department of Building and Housing, 2011. Compliance document for New Zealand Building Code, Clause B1 Structure. Amendment 10, May 2011. NZ Government, Wellington New Zealand.
McManus, KJ, Burdon, NRR, 2001. Lateral resistance of shallow foundations. Proceedings of Annual Conference, NZ Society for Earthquake Engineering.
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