SHM - making of an exhibition model
In this blog post, I'll guide you through the process of constructing a Structural Health Monitoring (SHM) model using the co.brick observe system. This model will showcase the system's capabilities for overseeing industrial structures. I'll use a warehouse hall as a practical example to demonstrate how straightforward it is to begin monitoring any facility.
My aim is to provide a detailed explanation that empowers anyone interested in this field, regardless of their technical background, to replicate this model. Whether you're a seasoned engineer or a curious handyman, let's embark on this building journey together!
Preparing materials | Photo by author.
Building a model with IoT sensors involves working with electrical components and potentially using pre-owned machinery. Misassembly, damage, or hidden defects in these machines can lead to electric shock, mechanical injury, or other hazards. This project should not be attempted by children or anyone lacking the proper knowledge and skills to handle electrical systems and machinery safely. Anyone who undertakes this project does so at their own risk. The author and co.brick are not responsible for any injury, damage, or loss resulting from the use or misuse of the information provided. Always prioritize safety and consult a professional if unsure.
Initial planning and design
My initial goal was to develop a simplified model of a warehouse hall, mirroring a real-world structure. This model would be equipped with sensors to monitor its condition by measuring various physical parameters.
For the demonstration, I selected six sensors:
- Two load sensors mounted on the roof beams to measure roof loads.
- Two basic sensors: a digital thermometer and a digital hygrometer.
- A light sensor.
- A three-axis accelerometer to detect any vibrations in the structure.
It is important to note that in the model, the beam is discontinuous, whereas in a real-world structure, the roof integrity remains unaffected by the sensors. Sensors can be integrated into a structure's design (for example, by embedding them in reinforced concrete) or added after completion without compromising its structural integrity.
I started by finding a suitable photo of the warehouse hall's framework. Next, I needed to determine the types and sizes of angles, channels, I-beams, and other materials available. With a clear concept and understanding of the available materials, we could proceed to more detailed planning.
Initial framework design | Photo by author.
Creating the 3D model
To enhance user-friendliness, the co.brick observe system allows for the loading of a 3D model of the monitored object. Therefore, the first step in the process was to create a detailed 3D model of the entire structure using appropriate software. I utilized readily available elements for modeling, which simplified the process. Creating this 3D model also enabled me to more accurately estimate the required materials.
3D model - design | Photo by author.
3D model - observe view | Screenshot by author.
Material preparation and assembly
Once we gathered the necessary components, we began the meticulous process of cutting the I-beams and angles to the specified lengths.
One of the design challenges arose from aesthetic considerations: we wanted the bolts securing the vertical beams to be centrally placed. This required drilling precise holes in the middle of the I-beam's 1mm-thick wall.
After several unsuccessful attempts at drilling the holes manually, I realized that the drill was consistently deviating. To address this issue, I utilized a small CNC milling machine and a 3D-printed mount, which ensured the required accuracy and repeatability.
For the base, I chose an MDF board and attached angle brackets to it, creating a foundation for the rest of the framework and securing everything to the base. Drilling into the base was straightforward, using a caliper and a drill.
Designing and printing the connectors for the roof beams and vertical beams was an iterative process. The 3D model of the entire structure was invaluable in this task. However, I overlooked some details during the project, and selecting the correct dimensional tolerances for printing was crucial. I aimed for elements that would slide into the connectors without screws but fit snugly enough to maintain the structure's stability.
To enhance rigidity, I added side flat bars to both walls after connecting the beams vertically. This allowed the structure to stand independently and provided substantial stability.
The two vertical beams, cut diagonally at the top and stepped at the base, posed the most significant challenge in cutting. These beams are located on one of the narrower walls and are complemented by a horizontal flat bar, forming a wall with an entrance gate.
Challenges during assembly | Photo by author.
Drilling holes | Photo by author.
Assembling the frame | Photo by author.
Tension sensors with TPU connector | Photo by author.
Final assembly and sensor installation
Creating the roof ridge connectors also required numerous printing iterations and design approaches. Ensuring adequate material strength while accommodating the T-beam was challenging. The T-beam needed to remain fixed along its axis and contribute to rigidity. Eventually, we developed a functional connector and printed it from TPU (Thermoplastic polyurethane), a rubber-like material that offers more flexibility than the PET-G (Polyethylene terephthalate glycol-modified) used for other elements.
With the structure completed, we could proceed with sensor installation. Each sensor was housed in a custom-designed enclosure, and all sensors were mounted using the same method — sliding onto the I-beam. Careful consideration of dimensional tolerances was again crucial during this stage.
Electronics preparation | Photo by author.
Test - octopus assembly | Photo by author.
Electronics preparation
With the model framework in place and the sensors prepared, we turned our attention to the electronics. Each sensor was equipped with a suitable JST XH connector, featuring the correct number of pins. This modular approach ensures that changes or repairs can be made without disassembling the entire system. For aesthetic purposes, the connecting wires were arranged as a ribbon cable and organized using simple, 3D-printed clips. All sensor ribbons converged at a central point within the model, where an STM32 microcontroller, specifically a Blackpill board, manages the readings. Upon startup, the controller initializes all sensors and transmits readings at predefined intervals via the built-in USB port, which is recognized as a serial port by systems.
The microcontroller board was housed within two brick-patterned wall palettes, matching the company's brand colors. A contrasting co.brick observe system logo was added to the main wall. This solution effectively concealed the electronics while allowing for convenient wire routing.
A Raspberry Pi 4 single-board computer (RPi) provided internet connectivity and communication with the co.brick observe system. The RPi was connected to the STM32 board via a USB cable and ran a Linux operating system with containerized applications. One application handled reading serial port data, parsing it, and publishing it as Prometheus software metrics. Another container read these metrics and forwarded them to the co.brick observe system. Off-the-shelf enclosures were used for the Raspberry Pi, with a printed spacer added to ensure port accessibility. The RPi and STM32 were mounted beneath the model using screws, facilitating easy maintenance when necessary.
Final framework | Photo by author.
co.brick observe - integrated | Screenshot by author.
Components used
Materials
| Element | Quantity | Length | Total |
|---|---|---|---|
| I-beam | 10 | 200mm | 2000mm |
| I-beam | 10 | 144mm | 1440mm |
| I-beam | 2 | 226mm | 452mm |
| Total: | 3892mm | ||
| Tee | 1 | 498mm | 498mm |
| Total: | 498mm | ||
| Angle | 2 | 498mm | 996mm |
| Angle | 2 | 271mm | 542mm |
| Total: | 1538 | ||
| Flat bar | 2 | 498mm | 996mm |
| Flat bar | 3 | 298mm | 894 |
| Total: | 1890 | ||
| MDF board 8mm | 1 | 400mm x 600mm | 400mm x 600mm |
| M3 screws | 1box | 8mm | 1 box |
Hardware
- Raspberry Pi 4
- Bluepill STM32F103C8T6 ARM Cortex-32
- HX711 strain gauge + 1kg strain gauge beam
- 3-axis ADXL34 accelerometer
- Temperature and humidity sensor DHT22
- LEDs, photoresistor (light measurement), wires, plugs
- 5V 3A power supply
Cost
The total cost of materials and components was around 200$ including Raspberry Pi 4 and 3d printer filament. Beside that, I spent around 50 hours on the project.
Summary
Although the software development and integration for this SHM model were relatively smooth sailing, the physical assembly and modeling proved to be quite the adventure. From cutting and securing beams to designing and printing intricate connectors, the mechanical components presented a significant challenge. But with careful planning, experimentation, and a good dose of problem-solving, we managed to overcome these hurdles and create a functional and visually appealing model.
It was a lot of fun building this project, and I encourage anyone interested in IoT or IIoT to explore the co.brick observe system. It’s a fantastic tool for professionals and hobbyists alike. So, come take a look and see how it can elevate your projects!