Footing size is a crucial factor in structural engineering, as it affects the stability and safety of a building or structure. Footing is the part of the foundation that transfers the load from the structure to the soil. How do you determine the optimal footing size for your project? Here are some steps to guide you.
The first step is to understand the load that the structure will impose on the footing. This includes the dead load, which is the weight of the structure itself, and the live load, which is the weight of the occupants, furniture, equipment, and other dynamic forces. You also need to consider the wind load, seismic load, and any other environmental factors that may affect the structure. You can use codes, standards, and software tools to calculate the load for your project.
Footing size is governed by the following parameters 1-Subgrade reaction, Bearing capacity, Ground water table 2- footing type from soil report 3- Soil type ,seismic and wind load data 4-Creating analysis model & add loads 5- Using the code appropriate to the nature of the building &load combination 6- Getting reaction on footing 7-Check stresses 8-Check serviceability & crack width 9-Ultimate design for footing 10-Chek shear & punching 11-Check stability against bouncy it is 1.1 for worst case & 1.25 for high ground water table according Aci 350.4R 12-Check sliding & overturning especially steel structure foundations because vertical load from steel is very light & there is found a big horizontal load from wind
Put simply, A footing needs to withstand > Short and long-term downward forces > Uplift from wind - many times when the footing is submerged and the concrete is not as heavy underwater (often forgotten) > Leaning over - resistance to what’s called ‘moment’ typically caused by high winds or other lateral forces > Twisting - torsional ‘spinning’ forces (less common). Soil has various types of load resistance - direct bearing pressure, frictional resistance (skin friction), amongst others. Loads must always be resisted from the worst case combination of loads against the lowest soil resistance conditions with an established factor of safety.
1- structural analysis of the building 2- determine column load , column cross section area and column Perimeter 3- soil excavations to determine soil profile 4- determine soil bearing capacity 5- determine surface area of plane concrete footing 6- determine surface area of reinforced concrete footing 7- determine depth of reinforced concrete footing based on stress analysis and bunch check
Footing size is governed by the following parameters :- a) Load on the footing supporting the column/columns of the structure - Vertical & Lateral loads b) Spacing between columns - Too closely spaced columns may have combined footings to avoid overlapping between isolated footings for each if the load to bearing capacity ratio is high. c) Bearing capacity of soil - The ratio of the resultant of all loads on each column or a group of columns supported on the footing to that of the bearing capacity of the soil gives the tentative area of the footing assuming the mat to be rigid. d) Modulus of subgrade reaction - Required to find out exact bearing capacity at each point below the footing mat taking care of the rigidity of the foundation
Foundation sizes are finalised based on availability of SBC at founding level from shear and settlement criteria, spacing between adjacent footing, site constraints,if any If spacing foundation is too close then isolated foundations are converted to Raft foundation. In case overall settlements values are found to be more then tolerable settlement, one has to recommend deep foundation that is well ,pile or by doing ground improvement by stone columns .stone columns are preferred if structure is located in seismic zone. For heavier loaded structures located in seismic zone Well are preferred
The next step is to choose the type of footing that suits your project. There are different types of footings, such as isolated, combined, strip, raft, pile, and caisson. Each type has its own advantages and disadvantages, depending on the soil conditions, the shape and size of the structure, the budget, and the design preferences. You should consult with a geotechnical engineer to determine the soil bearing capacity and the best footing type for your project.
In Structural Engineering, footing selection is crucial. Isolated footings are economical for light loads and stable soil. Combined footings are used when columns are close, preventing separate footings. Strip footings are ideal for row houses or light-load walls. Raft footings distribute loads across a large area, suitable for weak soils or heavy loads. Pile footings transfer loads to deeper, stronger soil layers, useful in poor soil conditions. Caisson footings are similar to pile footings but larger, often used in water-based structures. Each type’s suitability depends on soil conditions, structure size and shape, budget, and design preferences. The chosen footing must ensure safety, stability, and cost-effectiveness.
The first priority is to get the geotechnical analysis, right. Everything depends on that and then the selection of the footing. Design considerations for different types of footings are different. So selecting the type of footing is primarily important, aligning it with the functionality of the structure.
In addition to my above note, if you have a basement, make sure to assess the maximum groundwater table level and its fluctuations during the design life (normally not less than 1 m for buildings). All areas that could be flooded based on this rule must have a tanking system (raft and basement walls). On the other side, you need to consider the foundation options agreed upon in the risk mitigation plan. If there are more than one option listed there , then go with the option that leads to value engineering the design to reduce costs and contribute to sustainability.
First thoroughly study the soil report. Understand the type of soil strata. Check water table level. Check the chemical test report of the soil sample etc are also important.
Load Analysis: Identify and calculate all loads acting on the structure: Dead loads: Permanent weight of the structure Live loads: Variable loads due to occupants Other applicable loads: Snow, wind, earthquake, depending on the location and specifics. 2. Soil Investigation: Conduct a geotechnical investigation to determine the soil properties: Type of soil, Maximum pressure the soil can safely support without excessive settlement, water table depth and frost depth 3. Footing Type Selection: Shallow footings, Deep foundation 4. Footing Size Calculation: Divide the total load by the allowable bearing capacity of the soil to get the required footing area. Ensure compliance with local building codes and regulations
The third step is to design the geometry of the footing, such as the length, width, depth, and shape. The geometry of the footing affects the pressure distribution, the settlement, and the reinforcement requirements. You should follow the code provisions and the design criteria to ensure that the footing can support the load safely and efficiently. You should also check the clearance, the cover, and the drainage of the footing.
Before designing, first we need to assess what type of loads are going to bear by footing along with the self weight, wind and earthquake loads. We need to consider soil properties and its bearing capacity to know what type of foundation will be suitable. We need to calculate required size and shape of footing based on some mathematical formulas and Engineering principles to safely distribute loads into the soil.
I would go for understanding and checking the soil bearing capacity and knowing the loads been exerted on the columns and lastly the size of the column.
In determining the size of a footing , typically, you'd follow these steps: Determine Loads. Soil Analysis: Conduct a geotechnical investigation. Calculate Bearing Capacity: Ensure a factor of safety is incorporated to account for uncertainties. Select Footing Type: Common types include spread footings, mat foundations, and pile foundations. Size Calculation: This involves considering factors like soil pressure, settlement, and structural integrity. Consider Local Codes: Comply with local building codes and regulations. Professional Input: It's advisable to consult with a structural engineer and/or geotechnical engineer. Construction Monitoring: During construction, monitor the works to ensure compliance with the design specifications.
When designing it is always imperative to choose the best load combination factor. This may include dead load, wind load and live load. Load from column to footing can be considered as point load while from raft to pile would be considered as uniform distributed load (udl). Hence you use the right formula for your moment, shear force and torsional force.
Numbers one to 5 are normal considering way, but 6&7 related to equitation all used footings as well as soil stresses betwenced all, to achieve an balanced settlements.
The fourth step is to calculate the reinforcement for the footing, such as the steel bars, stirrups, and mesh. The reinforcement provides strength, ductility, and crack control for the footing. You should use the appropriate formulas and tables to determine the reinforcement size, spacing, and layout. You should also consider the bond, anchorage, and development length of the reinforcement.
Es importante recordar que el dise?o de zapatas es un proceso complejo que requiere conocimientos específicos en ingeniería estructural, para calcular la armadura se debe chequear la flexión y cortante, compresión oblicua, y un diámetro mínimo, así como separación mínima de las barras de refuerzo, también se debe comprobar la longitud mínima de anclajes y ganchos, así como parámetros iniciales que la sección sea capaz de soportar las tensiones sobre el terreno y el vuelvo de la zapata.
Getting the reinforcement can be an easy job when you have meticulously designed your structure in respect to moment, shear force and torsional force. Getting the area of steel and spacing is the basic, however I have noticed alot of professional tends to ignore Anchorage bar. This is crucial especially in raft foundation with apron, stirrups are mostly used in raft, pile and caisson foundation, which is highly important to prevent shearing.
Perform structural analysis to calculate the required reinforcement for the footing. Consider factors such as bending moments, shear forces, and torsional effects. Determine the size and spacing of reinforcing bars.
La armadura a flexión en la zapata se determina en base al momento que se genera en el elemento, esto para cada dirección de la zapata. En este punto también interviene directamente el peralte de la zapata. En algunos casos se puede incluir grapas como parte del dise?o a cortante en 1 y en 2 direcciones para reducir el peralte de la zapata. También en algunos casos se suele dise?ar una zapata en forma trapezoidal para hacerla más eficiente.
The fifth step is to check the serviceability of the footing, which means the performance and durability of the footing under normal use. You should verify that the footing meets the requirements for deflection, cracking, vibration, and corrosion. You should also consider the effects of temperature, moisture, and shrinkage on the footing.
Elaborar un estudio de suelos previo será importante para determinar la capacidad portante del suelo, una vez conociendo la capacidad que tiene el suelo para resistir cargas, debemos comprobar que la zapata tendrá una relación de tama?o que ayude a que no falle por punzonamiento por las cargas que llegarán de la columna.
First thing is to understand about the soil strata and characteristics. Next to know about the weight of the proposed structure. Then an experienced structural engineer can choose the type of foundation.
Ensure that the footing satisfies serviceability criteria, including deflection limits and settlement considerations. Evaluate whether the structure will perform adequately under normal service loads.
The final step is to review and revise your footing design, based on the feedback, testing, and inspection. You should compare your design with the actual site conditions, the construction methods, and the quality control. You should also make any necessary adjustments or corrections to improve the footing performance and safety.
Conduct a thorough review of the initial design, taking into account factors like constructability, material availability, and cost. Revise the design as needed to optimize for efficiency and practicality.
1) Safe Bearing Capacity. 2) Wind Load. 3) Seismic Load. 4) Depth of Foundations. 5) Height of Building. 6) Shape of Footing.
1. Check the dead loads based on matrtial weight and density, live loads, wind or Earthquake loads. 2. Check safe bearing capacity. 3. Check the bearing capacity factors. 4. Check reduction of loads could be possible by using lighter materials with enough strength.
Something else to consider, is the impact the surrounding soil will have on the concrete due to underground water/chemical seepage. If the footing is for a mine where the refinery takes place it is best to treat the concrete footing with a protective layer to prevent deteriorating of the concrete due to contact with chemicals underground.
1)entender si es un equipo o una estructura, no basta los estados de carga. Que otras estructuras hay aleda?as a la zona. 2) tipologia de cargas: cíclicas, vibraciones, viento, sismo, etc 3) tipo de suelo 4) Disponibilidad de espacio
Determining footing size in structural engineering is a critical aspect of ensuring the stability and safety of a building or structure. The process involves several steps that account for various factors influencing foundation design, including structural loads, soil characteristics and construction logistics 1. Load Calculation 2. Soil Investigation 3. Foundation Type Selection 4. Bearing Capacity Check 5. Footings Sizing 6. Analysis and Design 7. Construction Considerations 8. Review and Approval 9. Construction Inspection By carefully considering these factors and following established engineering practices, engineers can design safe, reliable, and cost-effective foundations that provide necessary support for buildings and structures.
To simplify a complex set of criteria to determine a footing size, I offer the following questions we ask. What is the bearing capacity of the base to which the footing will be installed? Is the footing founded in natural substrate, modified substrate, or over other building elements? Will the footing be reinforced or unreinforced? What is the dead load to be imposed on the footing? What are the live loads to be imposed on the footing? Is the footing isolated from other building elements or connected? Will the footing be servicing all the potential loads imposed in its own right or a shared load combined with other building elements. Are there any other special considerations such as natural occurrences? Weather, geological, water.
To size a footing, all you need are simply the load it is expected to support under serviceability criteria and the bearing strength of the soil. The initial sizing is however just the beginning of footing design. It may change as calculations progress.
Don't forget uplift if there is a potential for it. Most foundations serve primarily to hold a structure up. In cases where there are buoyant forces (such as in a pump station with high groundwater) or uplift from seismic vertical load, the footing must be sufficient to resist these forces. Both footing size, resultant weight and connections to columns or other substructure elements are important design considerations.