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Section 4: Design – Bridges and Structures

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Overview

The TxDOT district office project development staff is the primary contact point for the local government (LG) on bridge projects and structural elements on other projects. TxDOT’s Bridge Division develops policy, standards, manuals and guidelines for the design, construction, maintenance and inspection of the state bridge system, and administers the federal bridge funding programs in Texas. The Local Government Project Management Guide (LGPM Guide) describes the administrative process for these programs. The Bridge Project Development Manual provides information pertaining to policies and guidelines for development of bridge projects.

TxDOT performs routine inspections on all publicly owned vehicular bridges at regular intervals not to exceed 24 months, or not to exceed 48 months when adhering to Federal Highway Administration (FHWA) approval criteria. Bridges requiring an underwater inspection are inspected at regular intervals not to exceed 60 months, or not to exceed 72 months when adhering to FHWA underwater criteria. Fracture critical members are inspected at regular intervals not to exceed 24 months. If the structure is owned by a LG, it is the responsibility of the LG to provide traffic control during bridge inspection operations. TxDOT will provide all equipment and engineering expertise necessary for performing bridge inspections.

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Bridge Design

General

Bridge design is defined as the steps used to develop a project in compliance with both geometric design criteria and construction quality standards. State and federal regulations require TxDOT manuals, procedures, standards and guidelines to be followed for all bridges designed and subsequently built on the state highway system and national highway system (NHS). FHWA has accepted TxDOT’s Roadway Design Manual and TxDOT’s Load and Resistance Factor Design (LRFD) Bridge Design Manual as complying with federal regulations. Bridges off the state highway system built with no state or federal funds may be designed in accordance with standards adopted by the LG.

Federal Requirements

  1. 23 CFR 625.4 – Prescribes standards, policies and specifications to be used for all projects on the NHS. 23 CFR 625.4(b) lists specific references for bridges and structures.

State Requirements

  1. 43 TAC §§5.59, 15.56, 26.33 and 27.56 – Requires projects to be designed in accordance with TxDOT manuals, procedures, standards and guidelines.

Required Practices

In general, the LG must follow the TxDOT guidelines provided in TxDOT manuals for bridge design. The LGPM Guide provides a description of the required practices and the responsibilities of the LG and TxDOT district related to bridge design.

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Bridge Layouts

General

Bridge layouts depict proposed features of a structure and are used to obtain early approval before beginning detailed bridge design. A checklist of information to be shown on bridge layouts and samples of bridge layouts are contained in TxDOT’s Bridge Detailing Guide.

Federal Requirements

  1. There are no federal statutes requiring development or submission of bridge layouts.

State Requirements

  1. 43 TAC § 15.56 – Requires preliminary design information for RMA, toll and pass-through financed projects to be sent to TxDOT for review and approval when the design is approximately 30 percent complete.

Required Practices

The LG must submit all bridge layouts to TxDOT for approval at the 30 percent complete stage of design, according to guidance contained in TxDOT manuals. The specific manuals and required practices are described in the LGPM Guide.

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Design of Other Structures

General

State and federal regulations require TxDOT manuals, procedures, standards and guidelines be followed for all other types of structures designed and subsequently built on the state highway system. Common types of structures include retaining walls, sound walls, culverts, junction boxes, manholes, signs, light and signal poles, etc. Other structures off the state highway system built with no state or federal funds may be designed in accordance with standards adopted by the LG.

Federal Requirements

  1. 23 CFR 625.4 – Prescribes standards, policies and specifications to be used for all projects on the NHS. 23 CFR625.4(b) lists specific references for bridges and structures.

State Requirements

  1. 43 TAC § 15.56 – Requires projects be designed in accordance with TxDOT manuals, procedures, standards and guidelines.

Required Practices

The LGPM Guide describes the required practices and responsibilies of the LG and TxDOT related to the design of other structures under the oversight of TxDOT.

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Geotechnical

General

Geotechnical studies are performed primarily for pavement design and structures (i.e., bridges, retaining walls, etc.), and for excavation and embankment stability evaluation. TxDOT practices are contained in TxDOT’s Geotechnical Manual.

Federal Requirements

  1. There are no federal statutes for geotechnical matters.

State Requirements

  1. 43 TAC §§5.59, 15.56, 26.33 and 27.56 – Requires projects to be designed in accordance with TxDOT manuals, procedures, standards and guidelines. For RMA, toll and pass-through financed projects, the preliminary design information must be sent to TxDOT for review and approval when the design is approximately 30 percent complete.

Required Practices

The LG is responsible for conducting geotechnical studies in accordance with TxDOT’s Geotechnical Manual. The required practices are described in the LGPM Guide.

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Scour

General

Scour is the result of the erosive action of flowing water excavating and carrying away material from the bed and banks of streams. Potential scour can be a significant factor in the analysis of a stream crossing system. The design of a crossing system involves an acceptable balance between a crossing that is economical and provides the required traffic service and one that provides a sufficient water opening that will not cause upstream damage due to backwater nor damage at the crossing from scour. TxDOT practices are contained in TxDOT’s Geotechnical Manual.

Federal Requirement

  1. 23 CFR Part 650, Subpart C – Sets national standards for the proper safety inspection and evaluation of all highway bridges. Some bridges are identified as scour-critical.

State Requirement

  1. 43 TAC §§5.59, 15.56, 26.33 and 27.56 – Requires projects to be designed in accordance with TxDOT manuals, procedures, standards and guidelines. For RMA, toll and pass-through financed projects, the preliminary design information must be sent to TxDOT for review and approval when the design is approximately 30 percent complete.

Required Practices

The LG is responsible for performing scour analyses in accordance with TxDOT guidelines. The required practices are included in the LGPM Guide.

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