How to Structurally Design a Concrete Slab Culvert? RC Slab Deck Design Using the FORTRAN-95 Program

Table of Contents

1 Introduction

1.1 Motivations

1.2 Problem Statement

1.3 Objective

1.3.1 Specific Objective

1.4 Scopes and Limitations

1.4.1 Scopes

1.4.2 Limitations

1.5 Methodology for the Design & Program Development

1.5.1 AASHTO LRFD Method

1.5.2 Design Methodology

1.5.3 Writing the FORTRAN Code and Testing

1.6 Substructure of slab Culvert

2 Literature Review

2.1 Overview

2.2 Slab Culvert Structure Usage in Ethiopia

2.3 Concrete Slab Culvert

2.3.1 At Grade Slab Culvert Typical Drawing

2.3.2 At Fill Slab Culvert Typical Drawings

2.4 Reinforced Concrete Slab Culvert Deck

2.5 Construction Material Strength of Slab Culvert Deck

2.5.1 Concrete

2.5.2 Steel Reinforcement Bar

2.5.2.3 Fatigue Strength

2.6 Types of Culvert

2.7 Design Problems of Slab Culverts

2.8 Considerations for the Design of Concrete Slab Culvert Deck

2.8.1 Design Method

2.8.2 Design Philosophy

2.8.3 Loadings of Slab Culvert

2.8.4 Ultimate Limit States

2.8.5 Serviceability Limit States

2.8.6 Fatigue Limit States

2.9 Substructure Design of Slab Culvert

2.10 ERA Slab Culvert Design Practice

2.10.1 Concrete Slab Culvert Deck Design Practice

2.10.2 Substructure Design Practice

3 Analysis and Design

3.1 Definition of Slab Culvert Design

3.2 Dimensioning of Culverts

3.2.1 Span Determination of Slab Culvert [S]

3.2.2 Deck Width Determination of Slab Culvert [RW,TSW]

3.2.3 Edge Beam Dimensions

3.2.4 Minimum Deck Thickness

3.2.5 Fill Height of the Deck [H]

3.2.6 Post and Railing Dimensions

3.3 Live Load Interior and Edge Strip Width Computation (EI, EE)

3.3.1 Interior Strip Width

3.3.2 Edge Strip Width

3.4 Loadings and Combinations

3.4.1 Permanent load

3.4.2 Temporary Load

3.4.3 Analysis for Design Moment and Shear in the Interior Strip

3.4.4 Analysis for Design Moment and Shear in the Edge Strip

3.4.5 Absolute Maximum Design Moment and Shear force of the Slab Deck

3.4.6 Calculation of Bending Moment and Shear Force Resistance

3.5 Design of Slab Culvert

3.5.1 Thickness check for Limit State

3.5.2 Reinforcement Bar Design

3.6 Fatigue Limit State Check

3.6.1 Investigation of Main Reinforcement Bar Stress for Fatigue Limit State

3.6.2 Allowed Stress of Main Reinforcement Bar for Fatigue Limit State

4 Program Development

4.1 General

4.2 Programming Development Process

4.3 Algorithm for Slab Culvert Deck Design

4.4 Input and Output

4.4.1 Input Data

4.4.2 Output Data

5. Results and Discussions

5.1 Concrete Slab Culvert Deck Design Input

5.2 Concrete Slab Culvert Deck Design Output

5.2.1 At grade Slab Culvert Deck Output

5.2.2 At Fill Slab Culvert Deck Output

5.3 Discussions on the Design Results

5.3.1 At Grade Slab Culvert Output

5.3.2 At Fill Slab Culvert Output

5.3.3 Distribution Reinforcement Bar

5.3.4 Temperature & Shrinkage Reinforcement Bar

6 Conclusion and Recommendation

6.1 Conclusion

6.2 Recommendation

Research Objectives and Themes

The primary goal of this research is to achieve a higher degree of standardization and uniformity in the structural design of reinforced concrete slab culvert decks across Ethiopia. By developing a FORTRAN-based computer program compliant with AASHTO LRFD specifications, the study aims to assist engineers in performing accurate, efficient, and consistent designs, thereby reducing human errors and optimizing construction costs.

• Development of an automated structural design program for slab culvert decks.
• Evaluation and comparison of design outputs with existing national standards (ERA 2002).
• Implementation of AASHTO LRFD bridge design provisions in a localized context.
• Analysis of critical design parameters, including deck thickness and reinforcement spacing.
• Improvement of design efficiency for both at-grade and at-fill slab culvert configurations.

Excerpt from the Book

Summary of Chapters

1 Introduction: Discusses the motivation for standardizing slab culvert design in Ethiopia and outlines the research objective, scope, and specific methodology used.

2 Literature Review: Provides background information on slab culvert usage, design practices, construction materials, and relevant load calculations as per standard codes.

3 Analysis and Design: Details the mathematical and structural logic applied to the design, including span determination, loading combinations, and limit state checks.

4 Program Development: Explains the algorithmic approach and programming steps taken to implement the design logic within the FORTRAN environment.

5 Results and Discussions: Compares the design outputs produced by the developed program against traditional ERA design manual suggestions to validate efficiency and accuracy.

6 Conclusion and Recommendation: Summarizes the study's findings and suggests that the program should be adopted nationally to improve design consistency and reduce engineering time.

Keywords

Slab Culvert, FORTRAN, AASHTO LRFD, Structural Design, Reinforcement, Deflection, Limit State, Interior Strip, Edge Strip, Load Combination, Ethiopia, Highway Engineering, Concrete Design, Fatigue, Standardization

Frequently Asked Questions

What is the fundamental objective of this thesis?

The thesis aims to standardize the superstructure design of slab culverts in Ethiopia by developing a computer program that ensures uniformity, improves accuracy, and reduces design time using AASHTO LRFD standards.

Which structural components of the culvert are primarily addressed?

The work focuses specifically on the design of the reinforced concrete deck (superstructure), including edge beam design and reinforcement calculation for both at-grade and at-fill configurations.

What is the primary methodology adopted for the structural design?

The study uses the Load and Resistance Factor Design (LRFD) method, which evaluates performance under strength, serviceability, and fatigue limit states as defined by the AASHTO code.

Why was the FORTRAN language selected for this development?

FORTRAN 95 was chosen due to its extensive use in scientific, numerical, and engineering fields for complex calculations and algorithm development.

How does the program validate its design results?

The program's performance is validated by comparing its outputs (such as slab thickness and reinforcement requirements) against the existing Ethiopian Roads Authority (ERA) 2002 design manual.

What is the significance of the "at-grade" vs. "at-fill" classification?

This classification determines the loading and geometric constraints on the slab culvert; the program iterates input variables for each case to determine optimal deck thickness and reinforcement layouts.

Does the program account for skewed culverts?

Yes, the program allows for the design of skewed culverts by providing a conservative calculation method for skew angles up to 25 degrees, beyond which the effect is deemed negligible.

How is the "camber" height determined in the design?

Camber height is computed by the program to counteract long-term dead load deflection, ensuring the structure maintains expected performance levels throughout its design service life.