In this episode, we talk to Missy McMullen, Design Engineer at Lane Supply Inc., about barrier cables in parking garages, what they are, how they work, and how they can benefit the industry as we know it.
Here Are Some of the Questions We Ask Missy in This Episode:
- Tell us more about your career and what you work on at Lane Supply, Inc.?
- Tell us what parking garage barrier cables are, what materials they are made of, and what different kinds are available?
- How did these cables come about and how are they used by engineers?
- Are the barrier cables tested for car and truck impacts?
- How are the designs made for these potential accidents?
- Are there any regional standard differences in barrier cable design?
- Do parking garages have retrofits for barrier cables?
- If the concrete is not strong enough to withstand the forces, is there a solution that can be implemented?
- What is it about your career that has been different or beneficial that you think gives you different opportunities than standard design engineering?
- Are there any personal challenges that you have experienced in your career?
- One of your hobbies is fire breathing; can you elaborate on that?
Here Are Some of the Key Points Discussed About Barriers Cable in Parking Garages:
- Parking garage barrier cable typically looks like metal strands that run around any open floor of a parking garage. The materials they are made of are generally cheaper to use than other barrier types, such as concrete barrier walls, making them more cost-effective. Future changes can be easier to make to them than a concrete wall.
- There is a lot that goes into designing parking garage barrier cable systems when dealing with accidents, like working out the force that is applied to the cables as well as the leading edge in proximity to the structure.
- They are typically made out of high strength and low relaxation 7-wire sphere cable that is used for post- or pre-tensioning. The steel is also galvanized to prolong its longevity.
- Barrier cable use started in the 1960s but only became more popular in the 1990s when Departments of Transportation started using them along highways. The International Building Code has a section that details what forces a barrier cable system needs to extend from vehicular impact. Not all barrier cables are rated for vehicular impact and are for pedestrian protection only.
- Within the International Building Code, it says that a barrier cable system needs to be able to withstand 5,000 lbs. of force, moving at 5 mph, over a 12′ by 12′ area. This is to replicate a car that is approaching a barrier cable that is not braking properly. Many barrier cable systems have four to five cables across the middle of the design that are higher rated for a higher power because this is the portion of the cable system that is intended to resist vehicular impact.
- A design cannot be made for every circumstance or scenario. There is no design that would be able to withstand the force of a vehicle hitting a barrier cable system at full speed. Making the designs according to standard will be able to protect most scenarios.
- Barrier cable design does not have any significant difference depending on the location that they are installed. All the designs follow the same guidelines and standards.
- Retrofitting barrier cables is more common than installing new barrier cable systems into new parking garages.
- If a car runs into your barrier cables, the cables elongate and are put into tension, the termination forces are anchored into the concrete, and the concrete needs to resist all the breakout force.
- There are mitigating factors that you can incorporate into your design if the concrete is not strong enough to withstand the forces. Things like deepening the embedment, using full-through penetration, or adding additional connection points that will spread the pulling force over a larger area can be used with weaker concrete.
- Many college students have tunnel vision and they are convinced that they will become one kind of engineer and nothing else. You do not need to have expectations of where you are going to be 20 years from now. When you go into the field of engineering, you realize that the number of doors that can open for you are far greater and far more diverse than engineering school teaches you.
More Details in This Episode…
About Missy McMullen
Missy is a structural engineer who lives in Fort Worth, Texas. She earned both her B.S. and M.S. in Civil Engineering from South Dakota State University before moving to the Dallas-Fort Worth area in 2014. She gained five years of experience with Structural Technologies/VSL working on the contracting side as a Project Engineer, and she has spent the past 1½ years working as a Design Engineer for Lane Supply, Inc., a canopy design and construction firm in Arlington, Texas. In her spare time, she enjoys spending time with her cat, crafting with friends, hula hooping, and fire breathing.
Please leave your comments or questions in the section below on the design and installation of barrier cables.
To your success,
Mathew Picardal, P.E. & Alexis Clark, P.E., M.ASCE
Hosts of The Structural Engineering Podcast