Fundamentals of Steel Bridge Design, Part 2 (Self-Paced)

Lesson 5 briefly reviews live load placement for critical shear locations, reminds the user how to compute live load distribution factors for shear, but focuses mostly on the calculation of shear resistance of webs and the design of transverse shear and bearing stiffeners. Various example calculations are included.

Lesson 6 is the first of five lessons dealing with the design of steel-bridge flexural members. The discussions in these lessons will focus primarily on the design of I-section flexural members. This first lesson deals with important fundamental calculations that are employed for the design of these members. These calculations and concepts will be employed throughout the remaining four lessons of this course dealing with the design of I-section flexural members. Topics to be covered in this lesson include a discussion on the distinction between composite and non-composite members/sections. This topic will also cover the distinction between unshored and shored construction of steel bridges. The computation of elastic section properties and elastic stresses in composite sections will be discussed next, which covers extremely important concepts that will be commonly utilized in the design of these members. The computation of plastic section properties will then be described. These computations are employed in the design of specific classifications of sections in flexural members. The fundamentals of torsion, including the calculation of flange lateral bending moments and stresses in I-section flexural members, will be described next. Finally, the calculation of two important flange-stress reduction factors employed in the computation of the nominal flexural resistance of these members will be described, followed by a brief discussion on the design of tension flanges of flexural members with holes.

Lesson 7 is the second of five lessons dealing with the design of steel-bridge I-section flexural members. This lesson deals with the flexural design requirements for constructability, the service limit state, the fatigue limit state, and the fracture limit state. Topics to be covered in this lesson related to the design for constructability include a general discussion on constructability as a primary objective of bridge design in the BDS, the sequential deck placement analysis, the design for deck overhang loads, the design for wind loads during construction, and the specific design verifications that are required to ensure satisfactory performance of the noncomposite steel I-girder under the combination of the preceding force effects. Next, design for the service limit state will be covered. The specific performance requirements for a steel I-girder bridge under service conditions will be described. Design requirements to control live-load deflections will then be reviewed.

Lesson 8 is the third of five lessons dealing with the design of steel-bridge I-section flexural members. This lesson deals with the flexural design requirements for noncomposite I-sections during construction and at the strength limit state and composite I-sections in negative bending (i.e., composite I-sections in negative bending regions of continuous spans) at the strength limit state. The flexural design requirements for composite I-sections in positive bending (i.e., composite I-sections in simple spans and in positive bending regions of continuous spans) at the strength limit state will be covered in Lesson 9. Topics to be covered in this lesson include: 1) an introduction to the flexural resistance components for determining the resistance of noncomposite I-sections during construction and at the strength limit state, and composite I-sections subject to negative bending at the strength limit state; 2) the section classifications for noncomposite I-sections and composite I-sections in negative bending, which determine the maximum potential flexural resistance, Fmax or Mmax, of the section and also which design provisions in the AASHTO LRFD Specification may be used to determine the nominal flexural resistance of the section; 3) the distinction between discrete and continuous bracing of a flange; 4) the computation of the nominal flexural resistance for discretely and continuously braced flanges (subject to compression or tension); and 5) the checking of the flexural resistance of the section for the combined effects of I-girder major-axis bending, minor-axis bending, and torsion (i.e., flange lateral bending) due to any source using the so-called ‘one-third rule equations’. Lastly, the application of the various requirements to a noncomposite I-section in positive bending during construction and to composite I-sections in negative bending at the strength limit state within critical unbraced lengths of a straight I-girder bridge will be illustrated using excerpts from NSBA Steel Bridge Design Handbook Design Example 1. Portions of this lesson, namely the discussion on the determination of the nominal lateral-torsional buckling (LTB) resistance of a discretely braced compression flange, refer for informational purposes to new provisions for LTB that will be appearing in the 10th Edition AASHTO LRFD BDS when released. More detailed discussion on the background of the design provisions described in this lesson may be found in Section 6.3.5 of Chapter 4 of the NSBA Steel Bridge Design Handbook.