Piering

This technical guide to the Pier Masters^SM product line has been prepared to assist architects, engineers and contractors in designing and writing specifications for residential and commercial buildings that have become distressed due to settlement and/or ground deformation and need corrective action by underpinning.

FIGURE 1 FIGURE 2 FIGURE 3

Figures 1, 2 and 3 to the left show three types of Pier MastersSM products in three different installation situations. The versatility of the Pier MastersSM system allows for use on full foundations, crawl spaces, slab on grade, grade beams, etc. The hand-carried portability of Pier MastersSM creates unmatched flexibility of installation with minimal disruption of activity, landscape and structure. WHY Pier MastersSM? The Resistance Pier Solution Many foundations for residential and commercial buildings undergo significant settlement or movement that causes exterior brick walls to crack, gaps to develop in window frames, doors to no longer fit properly, and roofs that leak. This settlement and movement of the foundation is caused by any one of a number of factors: Clay soils that expand shrink with differing amounts of moisture, Foundations placed on compressible soils, Foundations placed on improperly compacted fill soils, or Improper maintenance of the areas around foundations. Pier MastersSM has developed a permanent solution for these foundation problems through its patented and tested system. Pier MastersSM systems are an assembly of structural steel components that include a pier head assembly attached to the foundation which is then mounted on steel piers that are installed to bedrock or firm bearing strata. The pier system is self-locking to insure permanent configuration support, thus offering a permanent solution to foundation problems. All piers have a triple coating to provide enhanced corrosion protection. All materials and installation procedures are of the highest quality standards. Pier MastersSM systems are available in three types of assemblies. Pier MastersSM Standard System (S2PS) - Figure 1 Pier MastersSM Modified System (M2PS) - Figure 2 Pier MastersSM Slab System (ASPS) - Figure 3 Both the Pier MastersSM Standard and Modified Systems can be installed in either an interior or exterior mode. Every Pier MastersSM system provides for a two-stage system of initially driving the manufactured piers to load-bearing support then, using hydraulics, lifting the structure to the desired elevation. Pier MastersSM systems not only stop settlement but actually raise the structure, closing the cracks and correcting other structural flaws caused by the settlement and/or ground movement. Since the corrective actions are permanent, Pier MastersSM systems offer an economical solution and are rapidly becoming the industry standard. SPECIFICATIONS: Pier MastersSM Resistance Piers Composition: Mill-rolled galvanized steel. Minimum gauge .160 wall (3/16"). 50,000 pounds minimum yield strength. Conforms to ASTM A-513. Couplings Minimum wall thickness .180 wall Minimum length 6 inches Conforms to ASTM A-513 Weldment Multiple button weld Welding Welding performed by certified welders Top Pier Assembly 1", 5/8", and 1/2" steel plate thickness 8" support plate - 80 square inches 2 steel concrete anchors - 7200 psi yield Conforms to ASTM A-36 Top Assembly Coating Hi-solids catalyzed epoxy coating Conforms to ASTM D3912

Design Steps

The recommended procedure for designing Pier Masters^SM Systems involves a series of steps leading to the selection of the pier assembly type, spacing and depth of installation.

STEP1: Local Building Codes
City or County agencies may have controlling building codes or design standards for foundation repair procedures by underpinning and for establishing dead and live loads for building structures.  These agencies should be checked with initially to determine if there are any controlling codes or standards.  These codes and standards should then be taken into account in following their design procedure.

TABLE 2

STEP 2: General Geotechnical Conditions
Information should be gathered concerning the general soil type, soil consistency and depth to firm bearing strata. Pier Masters^SM systems, which have a maximum structural installation capacity of 90,000 pounds, have been economically installed to depths of 100 feet.   In certain applications, it may be necessary to take field borings, including Standard Penetration Test Data and laboratory tests on recovered soil samples.    Initial efforts directed at determining the actual soil foundation conditions will aid significantly in the design and installation of the piers.

STEP 3: Define Building Type and Size
In order to calculate the structural loads and determine the required pier spacing, it is necessary to establish the building type and size.  Table 3 can be used  to assist in classifying the building type.  The dimensions required are the exterior length (L) and width (W) of the structure.

STEP 4: Estimate Dead and Live Loads for Structure
Table 3 can also be used, along with the information on building size to obtain an estimate of the structural line load, D in lbs./ft.  This line load is the dead load due to the structure weight.  The values indicated in Table 3 are average for the noted building classification and size.  Certain buildings or project requirements may require more detailed building structure load analysis.  To this dead load must be added the live load due to building occupancy, L, and snow loads, S (in geographic regions where applicable).

The live load, L (lbs./ft.) can be estimated from Table 3.  The required snow load can be determined from the locally approved national building code (e.g. BOCA - Basic National Building Code, 1984, pp. 162 - 168).  This will determine the snow load, S (lbs./ sq. ft.). The total load, P, in lbs/ft. can be determined as: P(lbs./ft.) = D + L + S x [ (W x L) / 2 (W + L) ].

STEP 5: Select Pier Type and Spacing
Two (2) different types of Pier Masters^SM assemblies are available for use in foundation underpinning projects and one (1) assembly is available for use in slab underpinning projects.  Table 2 indicates the features of each type to assist the designer in proper selection. The required pier spacing is given as: X(ft.) = R/P.  Where R = Selected pier design capacity (lbs.) and P = Total structure line load (lbs./ft.).

The selected pier design capacity, R, can range up to the ultimate pier capacity indicated in Table 1 (see also Table 2) but should incorporate a minimum factor of safety of 2.0.  Past experience with the use of Pier Masters^SM systems indicates a preferred pier spacing the 4 to 10 ft. range. If pier spacing in the 6 to 10ft. ranges are used, the designer should verify that the foundation footer has adequate structural strength for that span length.

STEP 6: Selection of Installation Force and Factor of Safety
The final step involves estimating the required drive strength, (DS), that is the maximum installation force imparted on the pier during field installation.  The Pier Masters^SM hydraulic drive assembly cylinder, which operates with a 24" stroke, as a 3 1/2" diameter drive bore.  For most installations, Pier Masters^SM recommends that the hydraulic drive pump be set at 5,000 psi which results in a drive strength: DS = Effective Area of Drive x Hydraulic Pressure (psi), where DS = [ pi x (3 1/2 inches squared) / 4 ] x 5,000 = 41,500 lbs.

For heavier structures, Pier Masters^SM has a high capacity drive assembly that is able to generate a drive strength of approximately 90,000 lbs.   Since the drive assembly procedure uses the dead weight of the structure for reaction, there will be some limitation  on the maximum available drive strength, DS. In many instances, however, Pier Masters^SM field installers have the ability to hang weights on the drive assembly thus further increasing the available drive strength.

Two factors of safety, (FS) can be determined in regard to use of the Pier Masters^SM systems as follows: Ultimate Factor of Safety = FS(mu) = Q(mu)/R.   Where Q(mu) = Ultimate pier assembly strength as determined from field load tests (see Figure 4 and Table 1), and Integrity Factor of Safety = FS(D) = DS/R. Where DS = installed drive strength. 

In the case of most Pier Masters^SM system installations, the Integrity Factor of Safety, FS(d) should be at least 1.2 to 2.0. Except for heavier structures where the drive strength approaches the ultimate pier assembly strength, the Ultimate Factor of Safety, FS(mu) would be 2.0 to 3.0 or higher.

TABLE 3