Dimensions of Foundation

Guidelines for minimum dimensions are given below:

(a) Depth of Foundation: For all types of foundations minimum depth required is calculated
using Rankine’s Formula:

However in any case it is not less than 0.9 m. Finding safe bearing of the soil is an expert’s job,
and it is found after conducting tests in field or in Laboratories. However general values for common
soils are listed in Table 1.



(b) Width of Foundation: Width of wall foundations or size of column footing is determined by
first calculating the expected load and then dividing that with SBC. Thus,

Manufactured Foundation Drainage System Installation.

Material is generally supplied in rolls that is simply applied to the waterproofed walls by using double-sided masking tape, sealant, or other adhesives recommended by the waterproofing membrane manufacturer; see installation photograph, Fig. 2.10. The material is installed like roofing shingles, overlapping in the direction of water flow, starting with the lower portion first, lapping higher elevation goods over the already installed piece to match the manufacturer-supplied flange edges (Fig. 2.11). Drainage systems can also be applied directly to lagging prior to concrete placement (Fig. 2.12).

FIGURE 2.10 Application of drainage system system using termination bar directly over
terminating edge of waterproofing membrane.

FIGURE 2.11 Application of drainage system.

FIGURE 2.12 Drainage system being applied directly to founda-
tion lagging.

The filter fabric material is always  applied facing out, and manufacturers provide additional fabric at ends to overlap all seams. The terminated ends of the material are covered with the fabric by tucking it behind the plastic core sheet. Side edges of the sheet are typically attached together by overlapping and applying an adhesive. Figure  2.13 shows a partially completed drainage system installed with appropriate drain field gravel backfill.

FIGURE 2.13 Installation of drainage field adjacent to foundation for completion of prefabricated
drainage system.

Figure 2.14 details the use of drainage systems for under-slab drainage. Figure 2.15 details the use of these systems for horizontal transitioning to vertical drainage at a below-grade tunnel installation.

Backfilling should take place as soon as possible after installation; using the available site soil is acceptable. Backfill should be compacted as required by specifications using plate vibratory compactors. Caution should be taken during compaction not to damage the fabric material.

FIGURE 2.14 Manufactured drainage system used for below-slab drainage.

FIGURE 2.15 Below-grade tunnel waterproofing using both horizontal
and vertical drainage application.

MANUFACTURED FOUNDATION DRAINAGE SYSTEMS

In addition to the premanufactured foundation and soil drainage systems, there are also available drainage systems used in conjunction with both vertical and horizontal belowgrade waterproofing systems. These drainage systems provide additional protection against water infiltration and effectively reduce hydrostatic pressure against below-grade envelope components.

The products aid in the drainage of groundwater by collecting and conveying the water to appropriate collection points for drainage away from the structure. A simplified typical design is shown in Fig. 2.7.

FIGURE 2.7 Simplified design detailing for premanufactured drainage system.

 The products provide low-cost insurance against water infiltration and should be used with every below-grade waterproofing application (with the possible exception of hydrous-clay materials). More often than not, the drainage systems can be used in lieu of protection board for most membrane applications, effectively negating any additional costs for the system’s superb protection.


Besides the additional drainage protection for occupied spaces, the systems are also used alone for protecting various civil structures such as landfills and retaining walls or abutments. Among the many uses for manufactured drainage systems:

● Below-grade walls and slabs
● Retaining walls and abutments
● Tunnels and culverts
● Lagging
● Embankments
● Landfills
● French and trench drains (described in the previous section)
● Drainage fields for golf courses and other park and play field structures
● Specialized drainage requirements
● Above-grade plaza decks and similar installations

The system is similar to the prefabricated soil drainage systems only available in larger sheets and drainage cores to facilitate drainage.

The material consists of a formed plastic three-dimensional core that acts as the collector and drainage transporter of the water, as shown in Fig. 2.8. The plastic drainage product is also covered with a geotextile fabric to prevent the silt, soil, clay, and sand from clogging the drainage system. The systems usually have some type of plastic sheeting adhered to one side to protect from indenting waterproofing membranes as well as acting as an initial water-proofing system.

FIGURE 2.8 Typical manufactured drainage systems.

The systems not only eliminate the need for protection board, but also eliminate the requirement for special backfill material consisting of sand or gravel materials to promote drainage. Typically, the existing soil is used as backfill material, reducing the overall costs of new construction. A typical below-grade wall detailing, using the drainage as protection for the waterproofing membrane, is detailed in Fig. 2.9.

FIGURE 2.9 Below-grade waterproofing application with drainage board used as
protection.

The systems also provide a drainage flow rate (depending on the size of plastic core structure, which varies from 1 4 in to 1 2 in) 3–5 times the capacity of commonly used drainage back-fill materials such as sand or small aggregate fill. The material is obviously lightweight, with one person capable of carrying the average roll of material that covers as much as 200 ft 2 of substrate, the equivalent of a small dump truck of aggregate backfill.

Materials selected should have a high compressive strength to protect waterproofing applications (a minimum of 10,000 psf). Also, the system should be resistant to any chemicals it might be exposed to, such as hydrocarbon materials at airports.

Among the many advantages of manufactured drainage systems over conventional aggregate backfill:

● Cost effectiveness.
● Attached filter fabric or geotextile eliminates the usual clogging of traditional systems.
● High-strength material can be used in lieu of protection board for membranes.
● Provides belt and suspender protection for below-grade spaces by quickly channeling ground and surface water away from the structure.
● Permits backfilling with the excavated soils.
● Lightweight and idiot-proof installations.

Prefabricated Foundation Drainage System Installation

The product can be laid into preexisting trenches available from foundation construction or trenches constructed specifically for the drainage field. The width of the trench is typically 2–6 in wide. The depth of the trench is determined upon the actual site conditions and soil permeability. Figure 2.6 represents a typical drainage detail.

The prefabricated plastic drains usually permit the excavated soil to be used as back-fill, eliminating the requirement for special backfill material. The backfill must be mechanically compacted in layers.
Geotextile covering is selected based on the soil conditions. Here are the basic geotextiles required for typical soil conditions:

● High clay content—nonwoven needle-punched geotextile
● Sandy soils—woven materials with high permeability
● High silt content—small-opening geotextiles

Soils of any combinations of the above types generally require testing to be performed and specific recommendation by the drainage system manufacturer.

Manufacturer-provided tees, splicing connectors and outlet connectors should be used as designed. The system is designed to collect and drain water in a variety of ways that meet specific site requirements. Drainage can be as simple as outflow to bare soil away from the structure as surface drainage, or it can be designed to outflow into municipal storm drains.

FIGURE 2.6 Typical detailing for foundation drainage system.
(Courtesy of TC Mira DRI)

PREFABRICATED FOUNDATION AND SOIL DRAINAGE SYSTEMS

These field-constructed foundation drainage systems are obviously very difficult to build properly and often perform poorly over time due to infiltration into the drainage piping by silt, sand, and soil that will eventually clog the entire system. Manufacturers have responded by developing “idiot-proof” systems to replace these now-antiquated field constructed systems. These prefabricated systems are relatively inexpensive and make them completely reasonable for use as additional water control for practically any construction project including residential, multifamily, commercial, and civil structures. These systems add superior protection for minor costs to any project. For example, concrete slabs without reinforcing can withstand hydrostatic pressure equal to approximately 2.5 times the slab’s thickness. In practically every structural design, it becomes much more economical to add under-slab drainage than to increase the thickness of the slab.

Prefabricated plastic soil drainage systems are available from a number of manufacturers. These products are manufactured in a variety of plastic composite formulations including polypropylene, polystyrene, and polyethylene. Figure 2.2 pictures a typical manufactured drainage product. The systems combine specially designed drainage cores covered with geotextile fabric in prepackaged form that eliminates all field construction activities except trenching and backfilling operations.

FIGURE 2.2 Typical foundation premanufac-
tured drainage system with geotextile attached.

The systems are idiot-proof in that the product is merely laid into the area designated for a drainage field. Only appropriate sloping of the trench to collection points is required. Figure 2.3 presents a simplified isometric detail of a drainage system installation. The product is puncture- resistive to protect its performance during backfill. Manufacturers also provide ample accessories (including termination and transition detailing) to complete the installation. Figures 2.4 and 2.5 show available accessories including a tee connection to join one branch of a drainage to another, and an outlet connection for collection of water that terminates at a drain box or culvert.

FIGURE 2.3 Isometric detail of drainage system.
(Courtesy of American Wick Drain Corporation)

FIGURE 2.4 “T” connector for drainage system.
(Courtesy of American Wick Drain Corporation)

FIGURE 2.5 Outlet connection for drainage sys-
tem. (Courtesy of American Wick Drain
Corporation)

Materials are available in a variety of widths (up to 36 in) and lengths provided in rolls of up to 500 ft long. The product should be puncture-resistant with some elongation capability for movement after installation, and be resistant to the natural or human-made elements to be found within the intended service area.

Prefabricated Foundation Drainage System Installation The product can be laid into preexisting trenches available from foundation construction or trenches constructed specifically for the drainage field. The width of the trench is typically 2–6 in wide. The depth of the trench is determined...

Design Example: Holed balanced foundation.

This example again makes use of the same building as in the previous examples. The trapezoidal shape will be squared off to give a 3.0 m × 8.325 m rectangular outline, as shown in Fig. 12.12.

To minimize differential settlements – both within the base and between adjacent bases – the combined base will be designed as a balanced foundation, with a bearing pressure equal to the allowable bearing pressure na = 150 kN/m2.

A balanced holed  foundation will be investigated for this example. By inserting a hole off-centre to the centroid of  the 3 m × 8.325 m base, it is possible to cause the centre  of gravity of the base to shift until it coincides with that of the applied loads.

Fig. 12.12 Holed balanced foundation design
example – loads.

The superstructure total load coming onto the base is given by

Area of hole
The area of the holed base is given by

A = (area of unholed base) − (area of hole)
= Au − Ah

From Fig. 12.12, the area of the unholed base is given by

Au = 3.0 × 8.325
= 24.5 m2

The size of the hole would optimally be chosen to give a bearing pressure equal to the allowable bearing pressure, i.e.

Thus the required area of the hole is

Ah = Au − A
= 25.0 − 20.0
= 5.0 m2

Condition for a balanced holed foundation
For a balanced foundation, the centre of gravity of the holed base is required to coincide with the centroid of applied loads. Let Y be the distance from the centre of the unholed base to the centroid of applied loads, and Yh the distance to the centre of the hole. From Figs 12.12 and 12.13, taking moments of area about x–x, Y is given by

YA = 0(Au) + Yh(Ah)

Thus

This is the condition for a balanced foundation.

From Fig. 12.12, Y = 0.34 m. Thus

Fig. 12.13 Holed balanced foundation design
example – hole size.

Dimensions of base
To achieve a balanced foundation, the centre of the hole must be at a distance of Yh = 1.36 m from the centre of the unholed  base. Provided this condition is met, the actual shape of the hole, e.g. square or rectangular, is not critical.

The area of the hole was calculated earlier in this example as Ah = 5.0 m2. A rectangular hole will be adopted in this instance, having dimensions of 1.6 m × 3.125 m = 5.0 m2 (see Fig. 12.13).
 
Ultimate design pressure
The holed base has been sized to give a bearing pressure at working loads of 150 kN/m2 . The ultimate design pressure for reinforcement design, pu, is calculated as follows, with γP = 1.51 as in the previous example,

Design Example: Trapezoidal balanced foundation.

This example deals with the same building considered in the previous two examples, and designs the foundations for the perimeter columns where these occur along a site boundary, as shown in Fig. 12.11. As in the previous examples, the close proximity of the perimeter columns to the site boundary means that isolated pad foundations are not suitable, and that the foundations of the perimeter columns must be combined with those of the adjacent  internal columns.

Since the ratio of internal to perimeter loads is 2 : 1, i.e. the same as in Design Example 2 (section 12.3.4), the centroid  of loads will again be 2.0 m from grid line B. A 9.0 m long base, as in Design Example 2, would therefore again be required to achieve a balanced rectangular foundation.

This relatively long base would however be associated with comparatively large bending moments and reinforcement areas. A more economic foundation is likely to be achieved using a shorter trapezoidal balanced foundation.

Fig. 12.11 Trapezoidal balanced foundation design
example.

Condition for a balanced trapezoidal foundation
Again the condition for a balanced foundation is for the centre of gravity of the base to coincide with the centroid of the applied loads.

With reference to Fig. 12.11, and taking moments of area about x–x, the location of the centre of gravity of the base of area A is given by

Area of base
The values of B1 and B2 would normally be chosen to minimize the size of the base. This would result in a bearing  pressure equal to the allowable bearing pressure, na, giving a base area

Dimensions of base
The end of the base furthest from the site boundary will,  in this instance, be chosen to extend beyond grid line B  by the same amount as a standard 3.65 m × 3.65 m internal pad foundation (see section 12.3.4), i.e. extending by 3.65/2 = 1.825 m.

Thus, from Fig. 12.11,

These values will give a balanced trapezoidal foundation, with a bearing pressure of p = 150 kN/m2.

Ultimate design pressure
The combined dead and imposed partial load factor is  γP = 1.51, as in the previous examples. The ultimate design pressure for reinforcement design, pu, is given by

Design Example: Cantilever Balanced Foundation.

An existing live service run requiring a 1.5 m wide zone is required to pass along one edge of the combined base in the previous example, as indicated in Fig. 12.10. The design is required to be adjusted accordingly.

Before redesigning the foundation, the designer should explore the possibilities, and relative costs, of either persuading the services engineer to relocate these services,  or setting back the two columns on grid line 1, and cantilevering the building out to the site boundary at each floor level. Either solution may well prove more economic than changing the foundation.

If these options fail to bear fruit, the designer will need to design the combined base to cantilever over the service zone without loading it. As in the previous example, the base will be designed as a balanced foundation.

Fig. 12.10 Cantilever balanced foundation design example.

Size of base
The column loads and positions are unchanged, and therefore the centroid of the superstructure loads remains in  the same place as in the last example. Again a balanced

foundation will be achieved by making the centre of gravity of the effective base (i.e. the centroid of the uniform stress block below the base) coincide with that of the applied loads.

The service zone does not affect the centre of gravity of the base in the Y direction, and the overall dimension in this direction for a balanced foundation therefore remains at  9 m. In the x direction, the 1.5 m width of the service zone is discounted in considering the effective base area.

The weight of the cantilever section of the slab acts as a  net applied load in this direction and must be taken into account in calculating the centroid of all applied loads.

It will therefore be included as part of the superstructure load, P.

The weight of this strip of foundation is

With reference to Fig. 12.10, the distance from the centroid to the effective left-hand edge of the base is 5.0 − 2.25 = 2.75 m. Thus, in order to align the centre of gravity with the  centroid of applied loads, the right-hand edge of the  base must also be located at 2.75 m from the centroid of  the applied loads. This gives an effective horizontal base  width of 2 × 2.75 m = 5.5 m, and a total horizontal base width of 5.5 + 1.5 = 7.0 m. The effective area of the base is given by

Bearing pressure
The actual bearing pressure will be

Ultimate design pressure
From design example 2, the imposed load Q is 55% of the 4500 kN column loads, i.e.

Design Example: Rectangular Balanced Foundation.

A five-storey concrete-framed office building has columns located on a regular 6 m × 6 m grid. The soil is a sandy clay with a net allowable bearing pressure, na = 150 kN/m2.
 
Loadings
The column loads are as follows:
Internal column: 2000 kN
Perimeter column: 1000 kN
Corner column: 500 kN

The imposed load may be taken to be 55% of the total load for all columns. Thus, from Fig. 10.20, the combined partial load factor γP = 1.51.

Fig. 10.20 Combined partial safety factors for dead +
imposed loads.

Size of isolated pad bases
Normal internal column foundations have been chosen to be isolated pad foundations, with an area given by

which for a square base gives plan dimensions of 3.65 m × 3.65 m. This size will be used for internal columns,  with proportionally smaller sizes for perimeter and corner columns.

The building is however built tight to the site boundary along two sides, as shown in Fig. 12.9. To keep foundations within the site boundary, the four columns adjacent  to the corner will share a combined base.
The base  will be designed as a rectangular balanced foundation  in order to minimize bearing pressures and differential  settlements.

Fig. 12.9 Rectangular balanced foundation design example.

Size of combined base
Superstructure total load, ∑ P = 2000 + 1000 + 1000 + 500 = 4500 kN

Taking moments about grid line 2 to calculate the distance of the centroid of the column loads from this grid line,

Similarly, by symmetry, Y = 2.0 m.

To achieve a balanced foundation, it is necessary to provide a base whose centre of gravity coincides with the centroid of the applied loads. The distance, in either direction, from the centroid of loads to the site boundary edge of the base  is 6.5  − X = 4.5 m: therefore if the opposite edge is like- wise located 4.5 m from the centroid of loads, the two will coincide. Thus a 9 m × 9 m base will provide a balanced foundation in this situation.

The base will only remain exactly balanced if all four columns have the same level of imposed loading. From a foundation point of view this is unlikely to be critical unless extreme variations in the distribution of imposed loads occur. Where such variations are expected, these should be designed for as a separate load case.

Bearing pressure 
The actual bearing pressure will be equal to

The value of p (= 56 kN/m2) indicates that, although the  balanced foundation would limit differential settlement between the four columns sharing the base, it would not, for this particular building example, reduce differential  settlements between columns on this base and those on adjacent bases. Adjacent bases would be sized to give bearing pressures close to the allowable value of na = 150 kN/m2.

The superstructure would therefore be required to accom- modate the differential settlement between the combined corner base and the adjacent isolated bases. If it is unable  to accommodate these differential settlements, the bearing pressure on the balanced foundation could be increased, within limits, by turning the foundation into a holed balanced foundation. In this particular example this would involve cutting a hole out of the centre of the base, thus reducing the area of the base. Provided the centre of gravity of the base remains in line with the centroid of applied loads, the bearing pressure would remain uniform, but its magnitude would increase.

Ultimate design pressure
The ultimate design pressure for reinforcement design  is given by pu =γPp, where  γP is the combined dead and imposed partial load factor.

Balanced foundations (rectangular, cantilever, trapezoidal and holed) Design.

Design decisions
The decision to use a combination of column loads to produce a combined balanced foundation would depend upon a number of factors, for example:

(1) The spacing of the point loads.
(2) The combination of loads being considered.
(3) The restrictions of projections due to site boundaries.
(4) The overall eccentricities produced from the resultant of the loads.
(5) The bearing area available.
(6) The need to produce a uniform pressure.
(7) The economics compared to other possible alternatives, if any. For example, in some situations a combination of column loads can be used to balance out eccentric loads which would otherwise extend isolated foundations beyond the boundaries of the site. Balancing out these column loads means that the boundaries can be maintained within a base giving uniform pressure and this may prove more economic than say a piled solution.

In other situations an attempt to balance out the loads may produce cantilevers which would extend beyond the site boundaries therefore making it necessary to look at alternative column combinations or alternative means of support such as piling.

In most cases where these foundations are adopted they relate to: boundaries which are restrictive; foundations which would otherwise overlap; or situations where, by introducing a load from other columns onto the same  foundation, bending moments are reduced and pressures become more uniform.

Sizing up the design

(1) Rectangular balanced foundations
The foundation base is designed by calculating the position of the resultant applied load and making the centre of gravity of the base coincide with that of the downward load.

This is done by first calculating the area of the base required to resist the resultant load and then finding the most  economic rectangular pad to achieve this. The pad is then located so that its centre of gravity is in the same position as the resultant load (see Fig. 12.6).

Fig. 12.6 Rectangular balanced pad base.

The base is then designed to resist the bending moments and shear forces produced by the solution, and the depth and reinforcement are determined and detailed accordingly.

(2) Cantilever balanced foundations
The design of the cantilever balanced foundation is carried out by assuming locations for the pad supports based upon the physical considerations and calculating the reactions from the cantilever beam. The reactions are then accommodated by calculating the required size of rectangular pads for each reaction based upon a uniform bearing pressure.

The beam is then designed to support the loads from the superstructure taking account of the induced bending and shear forces, etc. (see Fig. 12.7 for a typical example).

Fig. 12.7 Bending and shear diagram for typical
cantilever base.

(3) Trapezoidal balanced foundations
The design is carried out by first of all calculating the area of the base required for a uniform pressure to resist the total applied load. The resultant load and its point of application is then calculated. By fixing the dimensions for the length of the base, the dimensions A and B (see Fig. 12.8 (a)) can be calculated to give a centre of gravity which coincides with the location of the resultant load.

Fig. 12.8 Trapezoidal and holed balanced foundation.

The applied bending moments and shear forces are then calculated and the reinforced foundation designed to suit.

(4) Holed balanced foundations
The design is carried out by first calculating the resultant load and its location. The area required for the base is then determined by dividing the resultant load by the allowable bearing pressure. By fixing the length of the base an average width can hence be determined, and by inspection  of the eccentricity of the resultant load, an allowance can  be made for an approximate size of hole and a trial width determined (see Fig. 12.8 (b)).

From this trial width a size and location for the hole can  be calculated to give a centre of gravity for the base which will coincide with that of the applied loads and result in a uniform pressure.

Having determined the base dimensions the bending moments and shear forces can be calculated and the foundation design completed.

(5) General sizing considerations
The size of the sections involved is based upon bending moments, shear forces and bond stresses in a similar manner to any other reinforced concrete section. With foundations, however, due to the slightly reduced shuttering cost for concrete below ground compared to elevated sections,  it is often more economic to go for slightly larger concrete sections to avoid the use of excessive shear reinforcement or large-diameter bars.
Each condition will demand dif- ferent sizes and therefore the engineer will need to deter- mine the initial size from a feel of engineering, which will develop with experience. The design may then be finalized by trial and error.

Design Example: Tied Portal Frame Base.

The pad bases for a single-bay portal frame are to be joined by a horizontal tie to take out the horizontal thrusts from the portal legs. The portal is similar to the one which was designed as an untied portal in section 11.3.4. Loads and dimensions are shown in Fig. 12.4.

Loadings
From section 11.3.4,

vertical superstructure load, P = (dead load)
                                                + (imposed load)
                                               = G + Q
                                               = 175 + 225
                                               = 400 kN

Q as a percentage of P is 100 Q/P = (100 × 225)/400 = 56%.

From Fig. 10.20, the combined partial factor for dead and imposed loads is γP = 1.51.

Horizontal thrust, H = 50 kN

The horizontal thrust H arises from vertical loads G and Q, and will therefore have the same combined partial load  factor γP = 1.51.
 
Size of base
From section 11.3.4, the net allowable bearing pressure, na = 300 kN/m2.

On the basis that the horizontal thrust will be taken out by the tie joining the portal feet, the minimum area of foundation required is

A base 1.2 m × 1.2 m will therefore be chosen. Comparison with the example in section 11.3.4 shows that the introduction of the horizontal tie has reduced the base size.

Design of horizontal tie
The tie will be a mild steel bar, as shown in Fig. 12.5, encased in concrete for durability.

Ultimate tensile force in bar, Hu =γPH
                                               = 1.51 × 50
                                                = 76 kN

From BS 8110, the characteristic tensile stress fy = 250 N/mm2 for hot rolled mild steel. The partial material factor γs = 1.05.

The required cross-sectional area of bar is

Provide one number 25 mm diameter mild steel bar (area  = 491 mm2 ) to act as the tie. This will need to be  adequately anchored into the pad base as shown in Fig. 12.5.

To prevent possible foundation spread from lack of fit, the tie will incorporate a turn-buckle, to take up any slack prior to steel erection.

Fig. 12.5 Tied base design example – tie rod detail.

Tied foundations - Design.

Introduction
Tied foundations are often adopted as a means of exploiting to advantage opposing forces. This is achieved by linking them together via a tie or tie beam. The effect this has on  the design is to reduce the horizontal force requiring to be resisted by the ground (see Fig. 12.1 (a)).

The use of a tie can reduce the amount of movement likely to occur in developing the reaction and reduce the cost of the foundation.

Fig. 12.1 Tied foundation.

Design decisions
In any situations where horizontal forces, such as thrusts from portal frames, etc., act in opposite directions, consideration should be given to connecting the forces via a tie in order to reduce or totally react a horizontal force. For example, if the forces are equal and opposite then the total force can be reacted. On the other hand, if the forces are opposite and not equal, the smaller of the two forces can be tied and the remainder left to be reacted by foundation 1 or, if a higher tie force is used, foundation 2 can also be utilized, thereby reducing the force to be taken in passive pressure (see Fig. 12.1 (b)).

Sizing the foundations
The main pad foundations are designed in the same way as those previously discussed in Chapter 11 but taking into account the tie force reaction in accordance with the above considerations. The tie itself must be designed to resist the force H1 or H2, as the case may be, and must be detailed to
transfer this force without excessive slip or failure between the bases of the stanchions.

This is usually achieved by designing a tie rod for the total force using appropriate permissible tensile stresses for the steel and ensuring that suitable mechanical anchorage or bond anchorage is achieved in the details between the  stanchion and tie (see Fig. 12.2).

In detailing these ties, the detailer should ensure that the  tie acts on the centreline of the horizontal thrust force or that any eccentricity produced is designed into the foundation by the designer. The tie rod itself could contain a turn-buckle for tensioning in order to reduce lateral movement due to possible slackness in the rod, alternatively, if adjustment is not required, a reinforced concrete tie beam as shown in Fig. 12.3 could be used. Care should be taken  to ensure axial tension across any connections which may  be required in the tie by the use of turn-buckle or male/ female-type plate connectors. In the case of portal framed factories it is often desirable to construct the floor slab after
erection and cladding of the building. In this case the engineer must ensure that all tie members are constructed and covered prior to the erection of the steelwork, in order that the presence of the tie members does not impede the construction process.

Fig. 12.2 Tie anchorage.

Fig. 12.3 Reinforced concrete tie beam.