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algorembrant/
RBC

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RecrBeam Calculator

A professional desktop application for calculating the Nominal Moment Strength (Mn) of rectangular reinforced concrete beams per ACI 318 provisions.

Features

Native Windows desktop application (no browser/localhost required)
Professional dark theme UI
Real-time calculations as you type
Unit system toggle: Imperial (psi, in) / SI (MPa, mm)
Visual diagrams: Cross Section, Strain Distribution, Stress Block & Forces
Step-by-step equations: Detailed calculation breakdown with OK/NG indicators
Minimum steel area check per ACI 318

Installation

Prerequisites

Python 3.9 or higher
pip (Python package manager)

Setup

Clone the repository

bash
1git clone https://github.com/algorembrant/RecrBeam-Calculator.git 2cd RecrBeam-Calculator
Create a virtual environment (recommended)

python -m venv .venv
Activate the virtual environment

Windows (PowerShell):

.\.venv\Scripts\Activate.ps1

Windows (Command Prompt):

.venv\Scripts\activate.bat

macOS/Linux:

source .venv/bin/activate
Install dependencies

pip install -r requirements.txt

Usage

Run the Application

python app.py

The application will launch as a native desktop window.

Input Parameters

Parameter	Description	Imperial	SI
fc'	Concrete compressive strength	psi	MPa
fy	Steel yield strength	psi	MPa
Es	Modulus of elasticity	psi	MPa
Beta1	Stress block factor	-	-
ecu	Ultimate concrete strain	-	-
b	Beam width	in	mm
h	Total beam depth	in	mm
d	Effective depth	in	mm
n	Number of bars	-	-
Ab	Bar area (each)	in2	mm2

Default Values (Example 4-1)

Imperial:

fc' = 4000 psi, fy = 60,000 psi
b = 12 in, h = 20 in, d = 17.5 in
4 bars at 0.79 in2 each (No. 8 bars)

SI:

fc' = 20 MPa, fy = 420 MPa
b = 250 mm, h = 565 mm, d = 500 mm
3 bars at 510 mm2 each

Project Structure

RecrBeam-Calculator/
├── app.py              # Main desktop application (CustomTkinter)
├── calculator.py       # Beam calculation engine
├── test_calculator.py  # Unit tests
├── requirements.txt    # Python dependencies
├── README.md           # This file
├── LICENSE             # MIT License
├── MATLAB/
│   └── app.m           # Original MATLAB implementation
└── Dump/
    └── example_4_1.tex # LaTeX documentation

Theory

Based on ACI 318 provisions for nominal moment strength:

Key Equations

Stress block depth:

a = (As * fy) / (0.85 * fc' * b)

Neutral axis depth:

c = a / Beta1

Nominal moment strength:

Mn = As * fy * (d - a/2)

Minimum steel area (Imperial):

As,min = max(3*sqrt(fc')/fy * b*d, 200/fy * b*d)

Running Tests

python -m unittest test_calculator -v

Dependencies

CustomTkinter - Modern UI framework
Matplotlib - Diagram plotting
NumPy - Numerical operations

License

MIT License - see LICENSE

References

ACI 318-19: Building Code Requirements for Structural Concrete
Example 4-1 and 4-1M from ACI 318 Design Handbook

Citation

If you use this software in your research or project, please cite it as:

bibtex

@software{recrbeam_calculator,
  author       = {algorembrant},
  title        = {RecrBeam Calculator: Nominal Moment Strength Calculator for Rectangular Beams},
  year         = {2026},
  publisher    = {GitHub},
  url          = {https://github.com/algorembrant/RecrBeam-Calculator},
  note         = {Based on ACI 318 provisions}
}

algorembrant/RBC