Bearing Capacity

The term bearing capacity is very often used without a theoretically correct definition of what is meant. Bearing capacity of a foundation is the maximum load that can be applied on a foundation, leading to failure. Failure is defined as the development of large uncontrolled deformations under a small load increment. 

An example of a bearing capacity calculation method for shallow foimdations is the theory developed by Meyerhof (1951, 1953, 1963) A short overview of this theory can be found in Appendix D Geotechnical Principles. 

It is noted that the maximum depth of the shear planes underneath a footing is limited which means that the fill material below a certain depth does not contribute to the bearing capacity of the foundation. The following formula gives an indication of the maximum depth of the active wedge below the foundation level  

This indicates that in case of a high value for the friction angle 40° of the fill, the shear planes will not reach a depth of much more than 2.0-2.5 times the width of the foundation. Note that this rule of thumb may not apply if a relatively thin layer of fill is covering soft soil strata. Punching through might become the governing failure mechanism (see Section 8.4.3.5) in that case. 

The use of Finite Element Methods (FEM) in order to predict the bearing capacity of a foundation is also commonly accepted and will not be discussed in detail in this Manual. However, it should be realised that bearing capacity is often a 3D problem while most commercial FE software is limited to a 2D analysis only. Although 3D FE analysis methods do exist, they are not commonly used for analysing the bearing capacity of shallow foundations. 

For application to shallow foundation design, it is commonly considered that the general shear case applies to dense granular soil and to firmer saturated cohesive soils subject to undrained loading. The punching shear case is considered appropriate for compressible soil, such as sands having a low to medium relative density, and for cohesive soils subject to slow loading. 

The following definitions are used in bearing capacity analyses. 

Bearing capacity is governed by a number of factors. The following are the some of the more important factors that affect bearing capacity. 

In view of the wide variety of factors that affect the bearing capacity, a systematic study of the factors involved in a logical sequence is necessary for a proper understanding. 

The soil immediately beneath the foundation forms a wedge (zone I) which moves downwards. The movement of the wedge forces the soil aside and produces two zones of shear (zone II and zone III), consisting of a radial shear zone (zone II) and a linear shear zone (zone III). Zone I is considered to be at Rankine active state, zone II under radial shear and zone III at Rankine passive state. At the verge of failure, EF = 0, thus 

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Sihcone oils are good hydrodynamic lubricants but have generally poor frictional lubricating properties (352—354). The latter can be improved by incorporating chlorophenyl groups into the polymer side chains (355). For steel on steel, the coefficient of friction is about 0.3—0.5. The load-bearing capacity of PDMS (Almen-Wieland machine) is only 50—150 kg, compared with - 1000 kg for polychlorophenyLmethylsiloxane and up to 2000 kg for mineral oil. 

Impact and Erosion. Impact involves the rapid appHcation of a substantial load to a relatively small area. Most of the kinetic energy from the impacting object is transformed into strain energy for crack propagation. Impact can produce immediate failure if there is complete penetration of the impacted body or if the impact induces a macrostress in the piece, causing it to deflect and then crack catastrophically. Failure can also occur if erosion reduces the cross section and load-bearing capacity of the component, causes a loss of dimensional tolerance, or causes the loss of a protective coating. Detailed information on impact and erosion is available (49). 

The purpose of these specifications is to produce a mixture where the fines fill the voids in the coarser fractious, thus to increase load-bearing capacity. (See Refractories above.)... 

Stone is the oldest of all construction materials and the most durable. The pyramids are 5000 years old the Parthenon 2200. Stone used in a load-bearing capacity behaves... 

At the risk of oversimplification it might be said that the Vicat test gives a measure of the temperature at which a material loses its form stability whilst the higher stress level heat distortion temperature (1.82 MPa) test provides a measure of the temperature at which a material loses its load-bearing capacity. The lower stress (0.45 MPa) heat distortion temperature test gives some rather intermediate figures and it is perhaps not surprising that it is today less often quoted than the other two tests. 

Abdomen of women of child bearing capacity at work (in any consecutive period of 3 months)... 

The amount of cement used can be varied to produce high-bearing capacities thereby making the waste/concrete material a good subgrade and subfoundation material. 

Investigating a site is to first look at the type of soil and its bearing capacity. This should be done by digging boreholes at several designated locations over the entire landfill design site. There are several parameters which should be evaluated on the soil and they are ... 

Shearing strength of a soil is usually important in determining bearing capacity of the soil. Shearing stress, t (Ib/in. ), of a soil is expressed as... 

Direct shear tests are made in the laboratory to obtain data for determining the bearing capacity of soils and the stability of embankments. 

Spread Foundations. The purpose of the spread foundation is to distribute loads over a large enough area so that soil can support the loads safely and without excessive settlement. Such foundations are made of steel-reinforced concrete. When concrete is used for a foundation, it should be placed on undisturbed soil. All vegetation should be removed from the surface therefore, the upper few inches of soil should be removed before concrete is laid down. The area of the foundation must be large enough to ensure that the bearing capacity of the soil is not exceeded or that maximum settlement is within acceptable limits. If details are known of the subsurface soil conditions, the foundation must be sized so that differential settlement will not be excessive. For... 

Allowable Bearing Capacities of Sedimentary Rock and Soils [37]... 

The initial square foundation dimension that would be needed to meet the allowable bearing capacity of 5,500 Ib/ft is... 

In many instances, adequate existing civil/stmctural or services installation information may not be available. Guessing the likely bearing capacity of floor slabs, foundations, structural steel or sub-slab ground, etc. can prove disastrous. Equally, assuming likely operational conditions for new installations can lead to embarrassing (and quite possibly dangerous) under-performance. The cheapest or quickest installation is not always the best or... 

Where load-bearing capacity is required and in food, pharmaceuticals and cosmetics processing industries. 

Its closed-cell structure makes cellular glass particularly suitable for refrigeration applications on pipes and cold stores. High load-bearing capacity enables it to be used under rooftop car parks. 

The safe weight-bearing capacity of the soil must not be exceeded at any point on the foundation base. 

The specification of these later coatings is covered by the German DIN 30670 standard for steel tubes and DIN 30674 for ductile iron pipes. These standards note that some 1 mm thickness of polyethylene is required for corrosion protection alone, but to improve the mechanical load-bearing capacity of the coating, total thicknesses of 1.8-3.0 mm, depending on pipe diameter, are to be specified. 

The DTUL, also called the heat distortion temperature (HDT) of a plastic is a method to guide or assess its load-bearing capacity at an elevated temperature. Details on the method of testing are given in ASTM D648. Basically a 1.27 cm (V2 in.) deep plastic test bar is mounted on supports 10.16 cm (4 in.) apart and loaded as a beam. A bending stress of either 66 psi or 264 psi (455 gPa or 1,820 gPa) is applied at the center of the span. 

Flexible foams are used in applications where a high degree of resiliency is required with moderate load-bearing capacity. Essentially all foam seating is urethane based, including the furniture and automotive markets. Other examples are packaging, textiles, filters, sports equipment, and recreational items. 

Another family of polyols is the filled polyols.llb There are several types, but die polymer polyols are die most common. These are standard polyether polyols in which have been polymerized styrene, acrylonitrile, or a copolymer thereof. The resultant colloidal dispersions of micrometer-size particles are phase stable and usually contain 20-50% solids by weight. The primary application for these polyols is in dexible foams where the polymer filler serves to increase foam hardness and load-bearing capacity. Other filled polyol types diat have been developed and used commercially (mainly to compete with die preeminent polymer polyols) include the polyurea-based PEID (polyhamstoff dispersion) polyols and the urethane-based PIPA (poly isocyanate polyaddition) polyols. 

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