Contribution of Steel Casing to Single Shaft Foundation Structural Resistance (2018) / Chapter Skim
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5 1.1. Introduction The use of drilled shafts for bridge foundations is a well-established technology.
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6 Contribution of Steel Casing to Single Shaft Foundation Structural resistance Guide Specifications for LRFD Seismic Bridge Design (2014) based on the findings of this study.
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Background 7 shaft. In this report, AASHTO LRFD Bridge Design Specifications is referred to as AASHTO BDS, AASHTO Guide Specifications for LRFD Seismic Bridge Design is referred to as AASHTO SGS, and Drilled Shafts: Construction Procedures and LRFD Design Methods is referred to as FHWA (Brown et al.
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8 Contribution of Steel Casing to Single Shaft Foundation Structural resistance 1.3.1. Requirements for Specific Design Parameters This section summarizes the findings from a comparison of AASHTO, FHWA, and DOTs design requirements on five key structural design parameters for drilled shafts (used in Table A.1 of Appendix A, where data is presented for the 11 states having significant differences in requirements from AASHTO and FHWA)
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Background 9 3. The approach in Section 8.4.9 of South Carolina DOT Seismic Design Specifications for Highway Bridges (2008)
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10 Contribution of Steel Casing to Single Shaft Foundation Structural resistance based on experiments on specimens that exhibited satisfactory performance (i.e., "no anchorage failure and damage in the shafts was limited to a local cone failure and splitting cracks near the column-shaft interface") when designed following this rule.
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Background 11 • Texas DOT requires 30 in. for specific girder bridges.
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12 Contribution of Steel Casing to Single Shaft Foundation Structural resistance In Type II designs, the drilled shaft is sized to have a greater moment resistance than the column it supports to ensure that plastic hinging develops in the column above the shaft. One advantage of this approach is that it allows inspection of the plastic hinge following an earthquake (which would not be easily achievable for Type I designs where hinging is below ground level)
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Figure 1.2. Washington State DOT Type II shaft construction details (WSDOT Bridge Design Manual 2012)
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14 Contribution of Steel Casing to Single Shaft Foundation Structural resistance For expediency in this report, the Canadian Highway Bridge Design Code is shortened to Canadian Code, the Design of Composite Steel and Concrete Structures–Part 2: General Rules and Rules for Bridges is shortened to Eurocode, and the Concrete Structures Standard of New Zealand is termed the New Zealand Code.
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Background 15 Section 1.4.1 describes the minimum requirement of tube diameter (D) to thickness (t)
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16 Contribution of Steel Casing to Single Shaft Foundation Structural resistance considered both highly or moderately ductile (depending on their expected plastic hinge rotations) , while a Type II shaft could only be considered moderately ductile.
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Background 17 1.4.2. Effective Flexural Stiffness The effective stiffness of a CFST member is used for calculating its global buckling capacity, its period (used in dynamic analysis of its response)
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18 Contribution of Steel Casing to Single Shaft Foundation Structural resistance on circular CFST and comparing various code provisions. Results showed that of all stiffness values calculated in accordance with American code provisions, the ACI provisions provided the best estimates of effective stiffness for flexural members, but that for members subjected to combined bending and compression it underestimated the stiffness.
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Background 19 The coefficient of 0.95 is larger than the 0.85 used for the Whitney stress block calculation in order to take advantage of enhanced confinement of concrete due to presence of steel tubes. Figure 1.4 compares the AISC and ACI models.
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