In this episode, we talk to Mark Kaiser, S.E., a senior associate at RLG Consulting Engineers, about tilt-up construction and shelter designs. He elaborates on the difference between tilt-up and precast and also talks about what he thinks the future holds for shelter design.
Here Are Some of the Questions We Ask Mark:
- What is the difference between tilt-up and precast?
- Is tilt-up construction cheaper than pre-engineered steel buildings?
- Can you please elaborate on your involvement in tornado storm shelter design?
- What would you say the future holds for tornado storm shelter design?
- Can you talk about one challenging project that you have worked on that benefited your career as an engineer?
- What can engineers do to be better communicators, and what benefits do you see from improved communication?
- What advice would you give structural engineers considering doing work in tilt-up construction?
Here Are Some of the Key Points Discussed About Tilt-up Construction:
- Tilt-up construction is where the exterior wall is cast on-site, face-side down on a casting bed. The reinforcing and embed plates lifting inserts are laid out, and the concrete is poured. When the concrete reaches around 75% of its strength, a crane then lifts the panels, tilting them up off the ground, and places them in their final place. It is then temporarily braced to withstand construction loads. The interior steel frame of the building is erected and tied in with either the roof or floors diaphragm.
- Tilt-up walls make construction a lot faster than conventional construction methods because when you cast your exterior wall, it includes the gravity system, lateral system, and perimeter. Once it is in place, you need to do the interior steel frame, and you are good to go.
- For construction purposes, the lifting and rigging engineer looks at the lifting loads and the temporary wind force that will be placed on the panels while they are being hoisted up by the crane. They determine how the panels should be lifted and if additional reinforcement is needed to lift the panels into place.
- Precast and tilt-up construction are similar. Precast means that the panels are made at a particular plant and then shipped to the site. This method has size constraints because you have a limit to the width and weight that can be transported to your job site. Tilt-up is made on-site and is better for making larger panels. The site plan needs to include enough room to cast the panels on-site, and then lift them into place.
- Architects have been getting creative and pushing the boundaries with tilt-up construction in terms of their vision for the building. This can be done with precast, but it is not as creative as a process. Precast has many pieces and joints, which lends itself to needing more long-term maintenance. There are a lot fewer joints and pieces that you need to worry about in tilt-up construction.
- Pre-engineered steel buildings are limited to single-floor structures. Tilt-up construction buildings can be used for up to six-story structures. A pre-engineered building will always be cheaper than tilt-up buildings, but you will be limited in the kind of building you can build.
- Because of the 2015 IBC, it has now a code requirement that any essential facilities and group E occupancy must have storm shelters as part of the construction if you fall into a 250 mph wind zone. The 2014 ICC 500 standards for tornado and hurricane storm shelters give you a wind map that illustrates where that wind zone is. Tilt-up projects can serve as a storm shelter if they are constructed properly. A precast approach can also be used for storm shelters.
- Sections of existing structures can be transformed into storm shelters. We are building buildings that are providing life safety. They are designed to not fall and save the lives of the occupants in the structure. The storm shelter section of the project will cost more to do, but it is only a small area of the entire project. Masonry can be used, but it has height limits that need to be abided by before switching to an insulated concrete form. Tilt-up construction can also be used provided you have the space to make the walls. A composite steel roof is used and designed to withstand vertical or collapse loading.
- There are things to consider when designing a tornado storm shelter. The ICC 500 provides modifications to your live load. The ASCE 710 provides modifications to the calculations of wind forces. These calculations can also be used in areas of less than 250 mph wind zones. The design must be in line with the wind category exposure C. Pressure differentials need to be considered. The position of the structure on the site plan needs consideration. The storm shelter must be able to handle structures collapsing around and on top of it to protect the occupants.
- The ICC 500 is in the process of being updated. They are trying to give engineers a lot more direction and uniformity in what they are doing. The products that can be used will give more freedom to the designers and architects, like impact resistance windows that can be used in a storm shelter.
- Structural engineering can be challenging, especially when you need to preserve a historic façade. You do things like coping with bracing schemes that are not too intrusive with the existing façade, keeping the walls and foundation systems in place, working closely with neighboring properties, and ensuring you give your client the best possible product.
- One of the best forms of communication for structural engineers is to pick up the phone and call. Establish relationships with the architect. Working through problems with anyone involved in a project is always better on the phone or face to face. There is nothing better than talking it out, working it out, and getting to know the people. Getting to know your clients and the people you work with is especially important. People want to deal more with people they know and trust.
- If you want to start moving your career toward tilt-up construction, you must get out of your comfort zone — especially when it comes to communication. Always be learning because there are always new approach designs. Be open to new ideas, new concepts, and new ways of doing things.
More Details in This Episode…
With more than 15 years in the structural engineering industry, Mr. Kaiser’s broad range of project experience includes providing professional services on a variety of commercial, educational, and residential projects. Through his years of experience, he has accrued an extensive knowledge of seismic design, tornado storm shelter design, existing building renovation, and construction practices overall. Project experience includes high-rise concrete structures, multistory tilt-wall office buildings, public and private educational projects with ICC 500 compliant storm shelters, and historic façade preservation.
About the Hosts
Mathew is a licensed engineer, practicing on structural projects in California, with an undergraduate degree from Cal Poly Pomona and an M.S. in Structural Engineering from UC San Diego. He has designed and managed various types of building structures, including residential wood apartment buildings, commercial steel buildings, and concrete parking structures and towers. He also hosts the new YouTube channel “Structural Engineering Life,” through which he promotes the structural engineering profession to engineering students who are not familiar with the industry perspective.
Cara Green, EIT, works in Hilti’s North American headquarters as the Structural Engineering Trade Manager for the U.S. and Canada. She is currently an EIT in Texas and received her bachelor’s in civil engineering from the University of Alabama in Huntsville.
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Please leave your comments or questions in the section below about tilt-up construction and tornado storm shelter design.
To your success,
Mathew Picardal, P.E. & Cara Green, EIT
Hosts of The Structural Engineering Podcast