Chapter IV – Structural Design Table of Contents

1 Chapter IV _____ Structural Design Chapter IV Structural Design Table of Contents Section 1: General Guidelines Section 2: Bridge Division Operating Policies and Procedures Section 3: Standard Specifications for Highway Bridges Section 4: LRFD Bridge Design Specifications Section 5: Railroad Structures Section 6: Appendices SECTION IV-01 _____ General Guidelines Page 1 Guidelines This Chapter contains NDDOT Bridge Division policies and procedures for the Design , evaluation, and rehabilitation of structures on the North Dakota State Highway System.

2 Use of this Chapter does not relieve the Design engineer of responsibility for the Design of a bridge or Structural component. Although Bridge Division policy is presented here for numerous situations, content of the Chapter is not intended to be exhaustive. Therefore, use of this Chapter must be tempered with sound engineering judgment. The basis for these guidelines is found in the current editions of the following reference publications: 1. AASHTO LRFD Bridge Design Specifications 2. Standard Specifications for Highway Bridges (AASHTO) 3.

3 Standard Specifications for Road and Bridge Construction (NDDOT) Those policies unique to the Standard Specifications for Highway Bridges are located in Section 3 and those policies unique to the LRFD Bridge Design Specifications are located in Section 4. Guidelines in Section 2 pertain to both specifications. Prior to the beginning of a Design , all applicable files in filenet and the plans of the existing structure shall be researched. The environmental documents must also be reviewed. Other items that shall be considered are the need for agreements or permits.

4 Once all of these have been studied, a Preliminary Engineering meeting shall be scheduled with the Bridge Engineer. Persons in attendance shall include the Bridge Engineer, Assistant Bridge Engineer, section leader, designer of the project, and others as appropriate. See Appendix IV-06 D for Preliminary Engineering meeting discussion items. Bridge information determined from the Preliminary Engineering meeting shall be shared with the Design Division so that right of way limits can be established. The primary Design method for structures shall be Load & Resistance Factor Design (LRFD).

5 Details on the LRFD Design method can be found in reference publication 1 above. An HL-93 loading shall be used for the live load. In rehabilitating existing structures, the Design method shall be Load Factor Design (LFD) with Working Stress Design (WSD) being used for designing piling. An HS 25 loading shall be used for the live load when practical in rehabilitating structures; otherwise an HS 20 loading shall be used. The National Bridge Inspection Program requires that every bridge in the state be rated for Inventory and Operating loadings.

6 The ratings shall be according to the AASHTO Manual for Maintenance Inspection of Bridges using an HS truck and WSD method except for NHS routes, new structures, and rehabilitated bridges, which shall be rated with the LRFR or LFD method. The Structural Management Section (Bridge) will rate the IV-02 _____ Bridge Division Operating Policies and Procedures Page 2 General Policies and Procedures General Policies and Procedures Alternate Designs The use of alternate designs can be discussed at the Preliminary Engineering meeting and a decision made whether or not alternate designs will be prepared.

7 Plan Sheet Authorship Initials of both the designer and detailer shall be placed on each plan sheet. The plan sheets shall be sealed by a registered Professional Engineer in accordance with Section I-12 of this manual. Structural Plan Sheet Sequence The bridge and box culvert plan sheets are located in Section 170 of the plans. The general sequence of the bridge plan sheets is as follows (this is a guide only): Bridge Layout Notes Screeds, Quantities and Miscellaneous Piling Layout and Bearing Elevations Abutment Underdrain and Excavation Abutments Piers Beams/Girders Slab Layout Diaphragms Endwalls Slab Section Reinforcing Bar List Approach Slabs The general sequence of the box culvert plan sheets is as follows (this is a guide only).

8 Box Culvert Layout Notes Excavation and Foundation Fill Barrel Section and Wing Floor Wall and Parapet Roof Reinforcing Bar List Bent Bar and Bar Cutting SECTION IV-02 _____ Bridge Division Operating Policies and Procedures Page 3 General Policies and Procedures Standard Set of Plans Examples of typical bridge and box culvert plan sets can be found on the Plan Preparation Guide at: Structure Numbers All structures are identified by their structure number. The structure numbers for structures on the State Highway System are determined by the highway the structure is on, and the location of the structure on that highway as indicated by the Reference Point of the center of the structure.

9 For example, Structure Number means that the structure is located on US Highway 2 at Reference Point The Planning/Asset Management Division is responsible for the establishment and maintenance of the reference point system. All reference point designations are extended to three decimal places. The structure number is permanent and does not change due to replacement, regrading, or other factors which might cause minor changes in the structure location reference point. All plan sheets shall contain the structure number, as well as all Design records and any other records pertaining to each individual structure.

10 New structure numbers are assigned by the Structural Management section leader. Structural Code Number The Structural code number, as shown below, shall be put on the upper right corner of the Structural layout sheet. The Structural code number is used when Structural items are paid for separate from roadway items. The Structural code number is required when there is major work such as a new bridge or bridge widening. The Structural code number is not required when there is minor work such as approach slabs or rail retrofit.