June 19, 2012 PARTIES INTERESTED IN SCREW FOUNDATION SYSTEMS

Transcription

1 June 19, 2012 TO: PARTIES INTERESTED IN SCREW FOUNDATION SYSTEMS SUBJECT: Acceptance Criteria for Screw Foundation Systems (SFSs), Subject AC R1 (DZ/KS)] Dear Colleague: We are enclosing the new ICC-ES Acceptance Criteria for Screw Foundation Systems (SFSs) (AC443), which was approved by the Evaluation Committee during the June hearings. The new criteria was approved as proposed by the ICC-ES staff, as noted in our April 27, 2012, staff letter and our June 1, 2012, staff memo. Additionally, the committee revised Section of the draft by adding Group R-3 Occupancy for recognition under high seismic use. The criteria provides guidelines for evaluating screw foundation systems (SFSs), which are factory-manufactured steel foundations designed to transfer axial compression, axial tension, and lateral loads from structures to the ground. The screw foundation systems consist of a round hollow structural section (HSS) central shaft (screw shaft) with helical-shaped screw threads and a top connection device to allow for attachment to the supported structures. The screw foundation systems, addressed under this criteria, are different from the code-specified Helical Pile foundation system (HPS) in the following aspects: thread dimensions, shaft geometry, embedment, top support, and the intended end use. Thank you for your interest. If you have any questions, please contact David Zhao, P.E., S.E., at (800) , extension 3722, or by at dzhao@icc-es.org. Yours very truly, GGN/md Enclosure cc: Evaluation Committee Gary G. Nichols, P.E., SECB Vice President

2 (800) (562) A Subsidiary of the International Code Council ACCEPTANCE CRITERIA FOR SCREW FOUNDATION SYSTEMS (SFSs) AC443 Approved June 2012 PREFACE Evaluation reports issued by ICC Evaluation Service, LLC (ICC-ES), are based upon performance features of the International family of codes. (Some reports may also reference older code families such as the BOCA National Codes, the Standard Codes, and the Uniform Codes.) Section of the International Building Code reads as follows: The provisions of this code are not intended to prevent the installation of any materials or to prohibit any design or method of construction not specifically prescribed by this code, provided that any such alternative has been approved. An alternative material, design or method of construction shall be approved where the building official finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, at least the equivalent of that prescribed in this code in quality, strength, effectiveness, fire resistance, durability and safety. This acceptance criteria has been issued to provide interested parties with guidelines for demonstrating compliance with performance features of the codes referenced in the criteria. The criteria was developed through a transparent process involving public hearings of the ICC-ES Evaluation Committee, and/or on-line postings where public comment was solicited. New acceptance criteria will only have an approved date, which is the date the document was approved by the Evaluation Committee. When existing acceptance criteria are revised, the Evaluation Committee will decide whether the revised document should carry only an approved date, or an approved date combined with a compliance date. The compliance date is the date by which relevant evaluation reports must comply with the requirements of the criteria. See the ICC-ES web site for more information on compliance dates. If this criteria is a revised edition, a solid vertical line ( ) in the margin within the criteria indicates a change from the previous edition. A deletion indicator ( ) is provided in the margin where significant wording has been deleted. ICC-ES may consider alternate criteria for report approval, provided the report applicant submits data demonstrating that the alternate criteria are at least equivalent to the criteria set forth in this document, and otherwise demonstrate compliance with the performance features of the codes. ICC-ES retains the right to refuse to issue or renew any evaluation report, if the applicable product, material, or method of construction is such that either unusual care with its installation or use must be exercised for satisfactory performance, or if malfunctioning is apt to cause injury or unreasonable damage. NOTE: The Preface for ICC-ES acceptance criteria was revised in July 2011 to reflect changes in policy. Acceptance criteria are developed for use solely by ICC-ES for purpose of issuing ICC-ES evaluation reports. Copyright 2012

3 ACCEPTANCE CRITERIA FOR SCREW FOUNDATION SYSTEMS (SFSs) 1.0 INTRODUCTION 1.1 Purpose: The purpose of this acceptance criteria is to establish requirements for screw foundation systems (SFSs) to be recognized in ICC Evaluation Service, LLC (ICC-ES), evaluation reports under the 2012 and 2009 International Building Code (IBC). The basis for recognition is IBC Section The reason for the development of this acceptance criteria is to provide guidelines for evaluating screw foundation systems, since the codes do not specify procedures for qualifying such foundation systems. 1.2 Scope: This criteria provides methods to establish the allowable load and deformation capacities of screw foundation systems (where the shafts are round hollow structure sections [HSSs]) used to transfer axial compression, axial tension and lateral loads from the supported structures to the surrounding soil. This criteria applies to screw foundation systems as defined in Section and includes provisions for determining soil embedment and soil capacity. This criteria is limited to screw foundation systems used under the following conditions: a. For structures assigned to Seismic Design Categories (SDCs) A and B and Site Classes A through D, as determined in accordance with 2012 IBC Section (2009 IBC Section ), unless additional requirements prescribed in Section 3.13 of this criteria are satisfied for SDCs C through F and Site Classes E and F. b. In conditions where exposure to soil are not indicative of potential screw foundation deterioration or corrosion, where corrosive conditions are defined as: (1) soil resistivity less than 1,000 ohm-cm; (2) soil ph less than 5.5; (3) soils with high organic content; (4) soil sulfate concentrations greater than 1,000 ppm; (5) soils located in landfills; (6) soil containing mine waste, or (7) other corrosive conditions as defined in a site-specific technical report. c. Screw foundation products are manufactured from carbon steel, with zinc coating by hot dip galvanizing method. d. SFSs are limited to support structures constructed from steel or wood materials. e. SFSs addressed under this criteria are different from code-specified Helical Pile foundation systems (HPSs). HPSs must be evaluated in accordance with the IBC and the ICC-ES Acceptance Criteria for Helical Pile Systems and Devices (AC358). 1.3 Codes and Referenced Standards: Where standards are referenced in this criteria, unless noted otherwise, these standards shall be applied consistently with the code (IBC) upon which compliance is based in accordance with Table and 2009 International Building Code (IBC), International Code Council AASHTO LRFD Bridge Design Specifications, Customary U.S. 4 th edition, American Association of State Highway and Transportation Officials AISC 341, Seismic Provisions for Structural Steel Buildings, American Institute of Steel Construction AISC 360, Specifications for Structural Steel Buildings, American Institute of Steel Construction ANSI/AF&PA NDS, National Design Specification for Wood Construction, American Forest & Paper Association ANSI/AF&PA SDPWS, Special Design Provisions for Wind and Seismic, American Forest & Paper Association ANSI/ASME B , Square and Hex Bolts and Screws, Inch Series, American Society of Mechanical Engineers ANSI/ASME B , Fasteners for Use in Structural Applications, American Society of Mechanical Engineers ANSI/AWS D1.1/D1.1M, Structural Welding Code Steel, American Welding Society ASCE/SEI 7, Minimum Design Loads for Buildings and Other Structures, American Society of Civil Engineers ASTM A123-09, Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products, ASTM International ASTM A153-05, Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware, ASTM International ASTM D e1, Standard Test Methods for Deep Foundations Under Static Axial Compressive Load, ASTM International ASTM D , Standard Test Method for Penetration Test and Split-Barrel Sampling of Soils, ASTM International ASTM D , Standard Test Methods for Deep Foundations Under Static Axial Tensile Load, ASTM International ASTM D , Standard Test Methods for Deep Foundations Under Lateral Load, ASTM International ASTM E6-09 b1, Standard Terminology Relating to Methods of Mechanical Testing, ASTM International. 1.4 Definitions: Terminology herein is based on definitions in the IBC and the Glossary of the AISC and the following definitions: Conventional Design: Methods for determining design capacities of the screw foundation system that are prescribed by and strictly in accordance with standards and codes referenced in Section Empirical Design with Verification Testing: This method is intended to address soil capacity P4, in which, due to complex soil-structural interaction, not all applicable limit states can be clearly identified and reliably predicted. It is expected that a substantial amount of test data exists which can be used to form the basis for empirical design (equations). The purpose of the verification testing is to provide a correlation between the capacities predicted by the empirical equations and the tested results.

4 1.4.3 Engineering Analysis with Validation Testing: Methods to determine design capacities of the screw foundation system that incorporate analysis (special analysis defined in this Section is an example), as described in IBC Section , design provisions (which can be conventional design or the code-prescribed design provisions with modifications), and validation testing. The purpose of the validation testing is to provide a correlation between the capacities predicted by the engineering analysis and the tested results Equivalent Slenderness Ratio: Defined as the slenderness ratio of a non-prismatic member with the chosen governing radius of gyration such that it has the same buckling resistance as that of a prismatic member. The non-prismatic and prismatic members differ only in uniformity of cross sections Lateral Resistance: Capacity of a screw foundation system or device to resist forces acting in a direction that is perpendicular to the longitudinal direction of the screw shaft Screw Foundation Device: For purposes of this criteria, a screw foundation device is any part or component of a screw foundation system Screw Foundation System (SFS): A factorymanufactured steel foundation designed to transfer axial compression, axial tension, and lateral loads from structures to the ground. The system consists of a central shaft (screw shaft) with helical-shaped screw threads and a top connection device to allow for attachment to the supported structures. The screw shafts with screw threads are screwed into the ground by application of torsion and with simultaneously applied downward pressure until a desired depth or a suitable soil or bedrock bearing stratum is reached. From a load resistance perspective, an SFS consists of the following elements: top connection capacity (P1), shaft capacity (P2), thread capacity (P3) and soil capacity (P4), where P1, P2 and P3 are structural capacities of the SFS and P4 is the geotechnical capacity (resistance) Shaft Configuration: A specific combination of shaft material strength and shaft geometries (outside diameter, wall thickness, length of uniform shaft segment, length and number of tapered segments, inclination angle for tapered segments, as applicable) Shaft Flexural Length: The length of shafts, measured from the top of shaft embedment (typically at ground level) to the first point of zero lateral deflection when subjected to the allowable lateral load of the SFS Shaft Seismic Flexural Length: The length of shafts equal to 120 percent of the shaft flexural length, measured downward from top of the shaft embedment (typically at ground level) Slenderness Ratio: Defined as KL/r of compression members, where K is the effective length factor defined in the Glossary section of AISC 360; L is the effective length defined in the Glossary section of AISC 360 (corresponding to the total unbraced length, defined in Section of this criteria); and r is the governing radius of gyration defined in the Symbols section of AISC 360 (which varies along the shaft length for a SFS with non-uniform shaft configuration) Special Analysis: Methods for determining design capacities of the screw foundation system that 3 incorporate finite element modeling, discrete element modeling, strain compatibility, or other analytical/numerical techniques. Computer software developed for the analysis of laterally loaded deep foundations, which incorporate methods of analysis considering the nonlinear interaction of the screw shaft with soil, is an example of special analysis Substantially Different Soil Conditions: For the purpose of this criteria, two soil conditions (either two sites or two locations at the same site) are considered substantially different, if one of the following conditions is satisfied: The weighted average soil property (refer to Section 20.4 of ASCE 7 for guidelines), such as Standard Penetration Resistance, Static Cone Tip Resistance or Undrained Shear Strength, as applicable, of the affected soil strata for the two soil conditions, differ more than 10 percent from each other; or The site variability of either soil condition is medium or high, as defined in AASHTO LRFD Bridge Design Specifications Section C Thread Configuration: A specific combination of thread material strength and thread geometries (projected length from the shaft, thickness, pitch, and edge geometry) Top Connection Devices: Structural components, such as welded steel plate, steel bolt, threaded steel fastener, steel nut or other steel connection devices, that are used to connect the supported structure to the shaft of screw foundations Unbraced Embedment Length: The portion of shaft embedment into soil, from the top of shaft embedment (typically at ground level) to the first shaft section with zero lateral displacement or zero rotation (zero slope), whichever result in a larger embedment length, when the allowable axial compression load (under the given soil condition) is applied at top of the screw foundation. This embedment length corresponds to the pile embedment prescribed in IBC Section , which is 5 feet (1524 mm) into stiff soil or 10 feet (3048 mm) into soft soil, and is modified to account for the specific combination of SFSs, loading and soil conditions. Firm soils shall be defined as any soil with a Standard Penetration Test blow count of five or greater. Soft soils shall be defined as any soil with a Standard Penetration Test blow count greater than zero and less than five. Fluid soils shall be defined as any soil with a Standard Penetration Test blow count of zero [weight of hammer (WOH) or weight of rods (WOR)]. Standard Penetration Test blow count shall be determined in accordance with ASTM D BASIC INFORMATION 2.1 General: The following information shall be submitted with ICC-ES evaluation report applications: Summary Document: A tabulated list of the screw foundation systems, devices, and combinations thereof to be included in the ICC-ES evaluation report, along with proposed structural capacities, design methods and empirical equations, as applicable. All systems and devices shall be clearly identified in the documentation with distinct product names and/or product numbering.

5 2.1.2 Product Description: Screw foundation products shall be manufactured from carbon steel, with hot dip galvanized coatings. Complete information pertaining to the screw foundation systems or devices, including material specifications and drawings showing all dimensions and tolerances, and the manufacturing processes, shall be submitted. All materials, welding processes and manufacturing procedures used in screw foundation systems and devices shall be specified and described in quality documentation complying with Section 5.2. All material specifications shall comply with ASTM, NDS, AISC, or IBC (IBC Section ) requirements, or shall be deemed to be equivalent. Material composition, grade, sizes and performance of bolts and fasteners shall be based on criteria in AISC, ASME, or ASTM requirements, or shall be deemed to be equivalent Installation Instructions: Procedures and details regarding screw foundation system or device installation, including product-specific requirements, exclusions, limitations, and inspection requirements, as applicable Packaging and Identification: A description of the method of packaging and field identification of each screw foundation system device. Identification provisions shall include the manufacturer s name and address, product name and model number, evaluation report number and name or logo of the inspection agency Design Calculations: Clear and comprehensive calculations of ASD or LRFD structural capacities for system or device, based on requirements of the IBC and this criteria. Calculations shall be sealed by a registered design professional Connection Details: Typical connection details, including connections between the supported structures and the top connection devices, the top connection devices, and the connections between the top connection devices and the screw foundation shafts. 2.2 Testing Laboratories: Testing laboratories shall comply with Section 2.0 of the ICC-ES Acceptance Criteria for Test Reports (AC85) and Section 4.2 of the ICC-ES Rules of Procedure for Evaluation Reports. 2.3 Test Reports: Reports of tests required under Section 3.0 of this criteria shall comply with AC85 and reporting requirements in referenced standards. 2.4 Product Sampling: Sampling of devices for tests under this criteria shall comply with Section 3.1 of AC DESIGN, TEST, AND PERFORMANCE REQUIREMENTS 3.1 General: The screw foundation systems and devices shall be evaluated for resistance to axial compression, axial tension, and lateral loads (shear and/or bending moment), or a combination of these loads. The required capacities shall be evaluated by considering four primary structural elements of the screw foundation system as shown in Figures 1 and 2.These elements are described as Top Connection Capacity (P1), Shaft Capacity (P2), Thread Capacity (P3), and Soil Capacity (P4). The allowable capacity of a screw foundation system shall be the lowest value of P1, P2, P3, and P4, from each application. For any screw foundation device and system subject to combined lateral and axial compression or axial 4 tension, the evaluation report shall contain the maximum allowable lateral strength and the maximum allowable axial strength, separately, and shall state that the registered design professional must design the SFSs for the effects of combined axial and lateral loads. For shaft design (P2 capacity), the allowable strength under combined load conditions shall be determined using the interaction equations provided in the AISC referenced standard. 3.2 P1 Top Connection Capacity: The P1 top connection capacity is the maximum load that can be transferred between the supported structure and the top portion of the shaft based on strength in accordance with Section P2 Shaft Capacity: The P2 shaft capacity is the specified load that can be sustained by the screw shaft element of a screw foundation system based on strength in accordance with Section P3 Thread Capacity: The P3 Thread capacity is the specified load that can be sustained by the screw thread element (threads) of a screw foundation system based on strength or deformation in accordance with Section P4 Soil Capacity: The P4 soil capacity is the specified load that can be sustained by the soil or bedrock bearing stratum supporting the foundation system or device based on strength and settlement or pullout of the SFS in accordance with Section Determination of Allowable Design Capacities: In accordance with Section 3.7, the allowable screw foundation capacities (P1, P2 and P3) shall be based on Conventional Design (Section 3.7.1), Engineering Analysis with Validation Testing (Section 3.7.2) or solely on tests (Section 3.7.3). The allowable capacity P4 shall be based solely on tests (Section 3.7.3) or Empirical Design with Verification Testing (Section 3.7.4). Soil capacities that are not addressed by tests or Empirical Design with Verification Testing shall be determined by a registered design professional. All load tests shall be conducted in accordance with Section Design Methods: Conventional Design: For conventional design of the SFS component used to support steel and wood structures, either Allowable Stress Design (ASD) or Load and Resistance Factor Design (LRFD) methods referenced in the IBC may be used to calculate the allowable design capacity. The allowable stresses for materials of screw foundation elements shall not exceed those prescribed in Table of the IBC Engineering Analysis with Validation Testing: For this method, the allowable capacity shall be based on the least of all applicable limit states predicted by engineering analysis. The engineering analysis shall predict allowable capacity based on the governing limit state (limit state with the lowest allowable capacity). The validation testing shall be conducted to account for the upper and lower bounds (extreme values) of the design parameters that affect the structural performance of each screw foundation component to be evaluated. These design parameters may include geometrical dimensions/properties, material mechanical properties (including the portion of the supported structures connected to the top connection device, screw foundations

6 and surrounding soil strata), applied loading (load combinations) during field installation and at service, as applicable, and the support conditions. Unless noted otherwise, validation testing shall be conducted on a minimum of three replicate specimens for each combination of applicable design parameters, provided all test results are within 15 percent of the average. Otherwise, the allowable capacity shall be based solely on tests per Section Unless noted otherwise, the tested allowable capacity, based on the average of three replicate test results, shall be greater than or equal to the allowable capacity predicted by the proposed analysis and design provisions. As a minimum, the tested allowable capacity shall be taken as the least of 0.6 times the resistance based on tested yield strength (P y) and 0.5 times the resistance based on tested maximum strength (P max). To determine P y, yield strength, defined in ASTM E6, such as specified offset yield strength (usually an offset strain of 0.2%) or specified extension under load yield strength (usually a strain of 0.5 %) may be used, as applicable. Maximum tested strength, P max, is the peak tested strength. Testing shall be conducted in accordance with the applicable test method/requirements prescribed in Section 4.0, as applicable, or a test plan, which shall be submitted to ICC-ES prior to commencement of testing Direct Measurement (Based Solely on Tests): Where load testing only is used to establish P1, P2, P3 or P4, and the number of samples is not specified, the allowable capacity shall be reported as the average allowable strength determined in accordance with Section 4.0 from tests conducted on at least five replicate specimens, provided all test results are within 15 percent of the average. Otherwise, the allowable capacity from testing only shall be based on the least test result. For direct measurement of screw foundation system capacities (P1, P2, or P3), testing shall be conducted in accordance with the applicable test procedure described in Section 4.0. Yield strength, defined in ASTM E6, such as specified offset yield strength (usually an offset strain of 0.2%) or specified extension under load yield strength (usually a strain of 0.5%) may be used, as applicable. Maximum tested strength, P max, is the peak tested strength. The allowable capacity shall be taken as 0.6 times the resistance based on yield strength (P y) or 0.5 times the maximum strength (P max), whichever yields the lowest value. For direct measurement of soil capacity P4, testing shall be conducted in accordance with Section 4.4. For determination of allowable soil capacity, a factor of safety equal to 2 or greater shall be applied to the maximum measured soil capacity Empirical Design with Verification Testing: The proposed empirical design (empirical equations) predicts screw foundation capacities (axial compression, axial tension, and lateral capacity, as applicable) based on the applicable design parameters of the screw foundation systems (including shaft, threads and soils), such as geometrical dimensions/properties, material mechanical properties (including screw foundations and surrounding soil strata), applied loading (load combinations), shaft top restraint conditions, and the affected soil strata (strength and deformation properties). The soil bearing strata of the tested SFSs shall be relatively uniform within the affected soil zone. For example, site variability category of low 5 described in the Commentary Section C of the AASHTO LRFD Bridge Design Specification would be deemed adequate for this purpose. No groundwater table or questionable soil or expansive soil shall be within the affected soil zone of the test specimens. The purpose of the verification testing is to provide a correlation between the capacities predicted by the empirical equations and the test results. The verification of the proposed empirical equations shall be based on full-scale load test results and a statistical data analysis approach, which shall confirm that with a 90 percent confidence, within the range of the applicable design parameters, 85 percent of the tested capacities shall be equal to or greater than the predicted capacities. The factor of safety shall be at least 2.0. A test plan proposal, including the proposed empirical equations, test procedures, number of replicate tests for each combination of design parameters, the range of each design parameter, a statistical approach for data analysis, shall be submitted to ICC-ES prior to commencing verification testing. The empirical equation predicted capacities are used for preliminary design purpose. For final design, SFS capacity shall be verified through the performance of SFS load tests as prescribed by the registered design professional. The registered design professional shall establish an SFS test program, which, at a minimum, shall identify test procedures, number of tests, and conditions of acceptance, considering the variation of SFS shaft configuration, thread configuration, site conditions, and the supported loading. Section of the AASHTO LRFD Bridge Design Specifications can be used as a guide for this purpose. 3.8 Corrosion: Screw foundation systems and devices shall be hot dipped galvanized. Loss in steel thickness due to corrosion shall be accounted for in determining structural capacities by reducing the thickness of all screw foundation components, including fasteners, by the sacrificial thickness over a period, t, of 50 years. The design thickness, T d, of screw foundation components used in capacity calculations and testing shall be computed by (Eq-1). For the purposes of design calculations and fabrication of test specimens, the thickness of each component shall be reduced by 1 / 2 T s on each side, for a net reduction in thickness of T s. (Eq-1) where T n is either the design wall thickness for HSS, as prescribed in AISC 360, Section B4.2 (AISC , B3.12), if applicable, or nominal thickness and T s is sacrificial thickness (t = 50 years). For zinc-coated steel: T s = 25 t 0.65 = 318 μm (0.013 in) T d base steel thickness For validation of Engineering Design or for determination of allowable capacity through testing only, test specimens shall be constructed using steel thickness equal to T d. Alternatively, unaltered test specimens may be used and the resulting allowable strength shall be reduced by multiplying the result by a scaling factor that takes into account corrosion and the observed failure mode. Thus, a tension failure result shall be scaled by the area of the fracture surface, while a flexural failure would be scaled by the reduced section modulus. The testing laboratory shall determine the appropriate scaling method and identify the failure mode.

7 Corrosion loss shall be accounted for regardless of whether devices are below or above ground. All screw foundation components shall be galvanically isolated from building structural steel, or any other metal building components, unless the supported structures are zinccoated also. 3.9 P1 Top Connection Capacity: Screw shafts shall be mechanically connected to the supported structures by the top connection devices, described in Section At a minimum, evaluation of P1 shall include determination of the strength of connection between the supported structure (limited to steel or wood materials only) and the top connection devices, the internal strength of the top connection devices themselves, and the strength of connection between the top connection devices and the top portion of screw foundation shafts. The loading transfer between the supported structure and the top connection device is limited to vertical (tension and compression) and horizontal (shear) loads. For structures assigned to SDC A or B and Site Classes A through D, no bending moment transfer is allowed at this interface except that a bending moment due to applied axial load acting with an eccentricity of 5 percent of the shaft maximum diameter must be considered. For structures assigned to SDC C through F and Site Classes E and F, additional requirements prescribed in Section 3.13 of this criteria, including bending moments, must be satisfied. Among all applicable limit states, the governing limit state (with lowest strength) shall determine the top connection capacity, P1. Top connections may be evaluated for compression, tension, and lateral (shear and/or bending) strengths, or a combination thereof Capacity Determination: Top connection capacities shall be determined based on Conventional Design per Section or Engineering Analysis with Validation Testing in accordance with Section For the purpose of evaluation under this criteria, the supported structure is assumed to provide neither lateral nor rotational bracing for the top of the screw foundation shaft, so that the top of the shaft is essentially a free connection. For all combinations of top connection devices, supported structures (types of materials, geometric configurations, range of material strengths) and the screw foundation shafts, connection details shall be prescriptively specified Test Requirements: Tests shall not be required for evaluation of screw foundation top connection capacities provided all analysis is accomplished using Conventional Design as set forth in Section The minimum number of replicate test specimens shall be three for validation tests. Tests, if required, shall be conducted in each load direction (axial compression, axial tension, and lateral) on each top connection (considering combination of configurations and strengths of the supported structures, connection devices, and the screw shafts) that recognition is sought unless an engineering evaluation is provided, which can justify the use of tested data from a limited number of top connections, to predict the capacities of the untested top connections. Where tests are required for evaluation of lateral resistance, tests shall be conducted to verify lateral resistance in all directions for which lateral resistance is being claimed. If testing is required (see Section 4.1), a test plan proposal shall be submitted to ICC-ES prior to commencement of testing P2 Shaft Capacity: At a minimum, screw foundation shaft capacities shall be evaluated for torsion, axial compression, axial tension, and lateral resistance (shear and bending). Shafts may also be evaluated for combined lateral and axial loading, as applicable Tension: Shaft tension capacities shall be determined based on Conventional Design per Section or Engineering Analysis with Validation Testing in accordance with Section Shaft evaluation for tension shall include yielding on the gross section and fracture on the net section, and capacity of the welded connection between shaft segments, as applicable. Evaluation shall account for tapered shaft configuration (non-uniform cross sections) which has reduced cross sectional properties. The shaft tension capacities along with the corresponding locations along the shaft length shall be provided in a table or graphical format. If testing is required (see Section 4.2.1), a test plan proposal shall be submitted to ICC-ES prior to commencement of testing Compression: Shaft compression capacities shall be determined based on Conventional Design per Section or Engineering Analysis with Validation Testing per Section Shaft evaluation for compression shall include buckling resistance (per Section 3.7.2) and yielding on the gross section (per Section 3.7.1, if applicable). Tapered shaft configuration shall be accounted for in shaft capacity evaluation. Evaluation of shaft axial compression load resistance shall include a simultaneously applied bending moment based on a minimum eccentricity described in Section 3.9. Engineering analysis shall comply with Sections and Testing shall comply with Section Total Unsupported (unbraced) Length: The total unsupported shaft lengths shall include the length of the shaft in air, water, or in fluid soils (actual unbraced length) and an unbraced embedment length, specified in Section In accordance with IBC Sections and , screw foundation shafts shall be classified as columns and designed as such in accordance the IBC provisions from their top down to the point where adequate lateral support is provided per Section The unbraced embedment length can differ from that prescribed in IBC Section , provided it is substantiated by evidence, including analysis and/or test data, such that a screw foundation shaft, designed as a column resisting axial compression, considering the total unbraced length (summation of actual unbraced length and the unbraced embedment length), non-uniform cross section, an appropriate effective length factor and a minimum eccentricity described in Section 3.9, will have an equal axial compression capacity, comparing to that of the same shaft accounting for the lateral resistance afforded by the soil surrounding the shaft. The unbraced embedment lengths can be grouped together into one or several lengths, provided a justifying analysis is provided which considers the range of the applicable parameters, such as axial compression load, actual unbraced length, shaft geometric properties (diameter and moment of inertia) and mechanical properties, and the surrounding soil properties (strength and stiffness) Buckling Resistance: Effective lengths shall be determined using the total unsupported length defined in Section In the context of this criteria, the screw shaft foundations, having the top portion

8 exposed above ground, are laterally supported by surrounding soils when subjected to axial compression loads; while the shaft specimens tested in a laboratory for axial compression are fixed (with respect to translation and rotation) at one end (close to the tip) and are free (with respect to translation and rotation) at other end (at shaft top). The Engineering Analysis shall determine the shaft buckling resistance to axial compression loads plus a simultaneously applied bending moment at top per Section The analysis shall account for all applicable design parameters described in Section 3.7.2, especially the soil strength and deformation properties, embedment length and uniformity of soil strata. An equivalent slenderness ratio (see Section 1.4.4) shall be determined such that the buckling resistances of screw foundations afforded by surrounding soils are identical to those of specimens used in axial compression tests conducted in a laboratory. Slenderness ratio limitations as specified by the AISC referenced standards do not apply Torsion: Torsion resistance shall be determined using either Engineering Analysis with Validation Testing in accordance with Section or solely on tests per Section The shaft torsional capacities, which vary along the shaft length, shall be equal to or greater than the corresponding applied maximum torque during field installations. Engineering Analysis shall comply with Section Torsion testing shall be conducted in accordance with Sections and Engineering Analysis with Validation Testing: The engineering analysis shall be accordance with Section 3.7.2, and shall consider the maximum installation torque that can be applied to the specific screw foundation during field installations. The analysis shall account for the applicable range of the design parameters, such as shaft geometries (including tapered shaft configuration and threads), shaft material properties, unbraced length and soil conditions Torsion Tests (on Combined Shaft and Screw Threads): Torsion resistance shall be determined by testing in accordance with Section A minimum number of replicate test specimens, described in Sections and for validation testing and solely on tests, respectively, shall be used for each combination of shaft configurations, material (shaft and thread) strength and thread configurations. The 85 percent of the mean maximum torque, measured from testing of each combination of shaft and thread, shall be reported as the maximum allowable installation torque for the said combination of shaft and thread. Torsional strength need not be evaluated for corrosion losses. The shaft torsional capacities along with the corresponding locations along the shaft length shall be provided in a table or graphical format Lateral Resistance: Shaft lateral capacities shall be determined using Conventional Design per Section or Engineering Analysis with Validation Testing per Section Shaft evaluation for lateral resistance shall include bending and lateral shear resistance, accounting for tapered shaft configuration and the welded connection between shaft segments, as applicable. The shaft lateral capacities along with the corresponding locations along the shaft length shall be provided in a table or graphical format. If testing (see 7 Sections and 4.2.5) is required, a test plan proposal shall be submitted to ICC-ES prior to commencement of testing Elastic Shortening or Lengthening: Methods (equations) shall be provided for estimation of elastic shortening/lengthening of the shaft under the allowable axial load. These methods shall be based upon Conventional Design per section 3.7.1, accounting for tapered shaft configuration Shaft Capacity due to Combined Stresses: Shaft evaluation shall include capacity due to combined stresses, including combined axial compression/tension and bending, as applicable, using a conventional design per Section Screw Thread Capacity: Screw thread capacities shall be based on Engineering Analysis with Validation Testing per Section or solely on tests per Section Threads shall be evaluated for torsional resistance, and applicable limit states due to applied axial tension and compression loading including thread flexure, thread shear, weld flexure, and weld shear. The evaluation shall consider the variation of thread configurations Lateral Capacity: The determination of the lateral capacity, based on the screw threads, is not permitted. The lateral capacity of a screw foundation system is based on the resistance of the shaft only and is not significantly affected by the presence of screw threads Torsion Capacity: Torsion resistance of screw threads shall be determined based on Engineering Analysis with Validation Testing per Section or solely on tests per Section Thread torsion resistance shall be determined in conjunction with shaft torsion. Testing shall be conducted in accordance with Section A minimum of three specimens for each screw thread configuration shall be tested. The failure of screw thread shall not be the governing limit state out of the applicable limit states prescribed in Section The allowable capacity of the screw thread in torsion shall be considered acceptable provided it exceeds the tested maximum torque of the shaft Axial Capacity: Thread axial capacities shall be based on Engineering Analysis with Validation Testing per Section or solely on tests per Section The welded connection between threads and shaft shall not be the governing limit state. Each thread configuration, for which evaluation is being sought, shall be tested. Thread testing (for limit states related to threads and thread welded connection to shaft, such as thread bending, thread shear, weld flexure, and weld shear strength) shall be conducted in accordance with Section The total axial capacity of threads on a shaft shall be the summation of axial capacity of each thread of the shaft P4 Soil Capacity: At a minimum, soil capacity for screw foundation systems shall be based solely on tests per Section As an option, for the purpose of preliminary design, soil capacity for the screw foundation system can be based on Empirical Design with Verification Testing per Section Soil capacity includes the axial tension, axial compression, and lateral resistance of a screw foundation embedded in ground. For each test site, geotechnical investigations shall be conducted in accordance with IBC Section and reported in accordance with IBC Section

9 Axial Capacity Based Solely on Tests: Determination of Axial Capacity P4: At least three replicate specimens of each type of screw foundation shall be tested in each load direction (axial tension and compression) for which recognition is sought for a given site (soil) condition. Variations in shaft geometry and material strengths, maximum allowable installation torque, as well as thread configurations, shall constitute a different type of specimen. Three separate tests, which correspond to the upper bound, intermediate range and the lower bound of the capacity (lower of P2 and P3), shall be conducted for axial tension and axial compression, respectively, on the products for which recognition is sought. Test specimens shall consist of complete components of a screw foundation system. All tests shall be conducted in accordance with Section The maximum load for each test (on three replicate specimens) installed in similar soil conditions (see AASHTO LRFD Bridge Specification Commentary Section C for guidance) at the same test site shall be determined based on the average of the maximum loads of the three replicate specimens, provided all test results are within 15 percent of the average. Otherwise, the maximum load shall be based on the least test result of the three replicate specimens. The allowable axial soil capacity, P4, shall be determined by using the maximum load from each test (on three replicate specimens) divided by a factor of safety of at least 2.0. The soil capacity, P4, to be recognized in the evaluation report, shall be limited to the soil conditions, shaft configurations and thread configurations that have been verified through the verification tests. The evaluation report shall contain a statement that axial soil capacity in soils conditions that are substantially different from actual test sites (see Section ) included in the evaluation shall be determined by a registered professional engineer on a case-by-case basis Condition of Acceptance for Axial Verification Tests: For all screw foundation systems, fullscale field installation and load tests, described in Section , shall be conducted to verify the maximum allowable installation torque determined in accordance with Section The tests shall be regarded as a successful verification of installation, provided the maximum allowable installation torque is achieved during installation without significant damage to the screw foundation shaft or threads. The SFS shall be extracted from the ground and visually inspected to verify the requirement for lack of damage Lateral Capacity Based Solely on Tests: A minimum of three replicate specimens of each type of screw foundation shaft (each shaft configuration) shall be tested in cohesive (firm clay soil) and non-cohesive soil, respectively. Test specimens shall consist of complete components of a screw foundation system. All tests shall be conducted in accordance with Section The allowable lateral load for each specimen shall be based on the deflection criteria set forth in Section The allowable load for each test (on three replicate specimens), P4, installed in similar soil conditions (see AASHTO LRFD Bridge Specification Commentary Section C for guidance), shall be determined based on the average of the allowable loads of the three replicate specimens, provided all test results are within 15 percent of the average. Otherwise, the allowable load shall be 8 based on the least test result of the three replicate specimens. Allowable soil (lateral) capacity, P4, based on test data for different specimens in different soil conditions shall be tabulated in the evaluation report. The evaluation report shall contain a statement that soil capacity for lateral resistance in soil conditions that are substantially different from those at actual test sites (see Section ) included in the evaluation shall be determined by a registered professional engineer on a case-by-case basis Capacity-based Empirical Design with Verification Testing: Verification testing and test data analysis shall be in accordance with Section Tests conducted per Sections and may be included in the verification testing to substantiate the proposed empirical design (equations). All tests shall be conducted in accordance with Section The empirical equation predicted capacities are used for preliminary design purposes. For final design, SFS capacity shall be verified through the performance of SFS load tests as prescribed by the registered design professional. The registered design professional shall establish an SFS test program which, at a minimum, shall identify test procedures, number of tests, and conditions of acceptance, considering the variation of SFS shaft configuration, thread configuration, site conditions, and the supported loading. Section of the AASHTO Specifications can be used as a guide for this purpose Test Requirements: Axial compressive, tensile, and lateral allowable load capacity shall be verified through field load tests as required in Section Tests for axial compression and tension soil capacity shall be conducted in accordance with Section 4.4.1, and tests for lateral resistance shall be conducted in accordance with Section Tension and compression verification load tests are required to be conducted at the facility or field station of a testing laboratory complying with Section Special Seismic Requirements: General: Structures assigned to Seismic Design Categories (SDCs) C through F supported by screw foundation systems, and screw foundation systems installed on Site Class E or F sites, as determined in accordance with 2012 IBC Section (2009 IBC Section ), shall comply with the additional requirements prescribed in Section through Requirements for Top Connections: The strength of top connections shall comply with IBC Section Specifically, the strength of top connections shall be designed to resist axial and shear forces, and moments resulting from the seismic load effects including overstrength factor in accordance with Section or of ASCE 7; or shall be capable of developing the full axial, bending and shear nominal strength of the screw shaft and screw threads. Where the supported vertical lateral force-resisting elements are columns, the top connection flexural strength shall exceed the column flexural strength Requirements for Screw Shafts: Within the Shaft Seismic Flexural Length described in Section , the shafts shall be uniform in cross section, and shall comply with the limiting width-to-thickness ratios for compression elements for moderately ductile members prescribed in Table D1.1 of AISC , including footnote e for round hollow structure sections (HSSs). In order to comply with this provision, an analysis and