TILT UP CONCRETE BUILDINGS. SOME QUESTIONS ANSWERED.
THE UNIBUILD LIGHTWEIGHT, FOAM CONCRETE STRUCTURAL WALLS.
Listed below are frequently asked questions that correspond to questions listed in a recent Tilt-up Concrete Association (TCA) newsletter.
1. What is the typical thickness of a UNIBUILD lightweight panel?
4” thick, to exceed the 3.6” minimum code thickness for two-hour fire- resistive exterior bearing walls.
2. What is the minimum size building that is economical?
Since the site area is not a function of the shop-cast wall sections, there is no minimum building size where the UNIBUILD lightweight panel is not economical.
3. What is the minimum height building that is economical?
Since the wall thickness is not a function of wall height, there is no minimum height where the UNIBUILD lightweight panel is not economical.
4. What is the maximum height panel that is economical?
UNIBUILD lightweight panels can be used economically up to 60 or 70 feet, since the 4” thickness remains constant. The closely spaced columns within become an “exterior” frame for tall buildings.
5. What is the maximum length (width) that UNIBUILD lightweight panels are economical?
8’0”. Based upon the 8’0” modular roof system, basic 8’0” internal structural columns may be connected to form 16’ or 24’ lengths.
6. Are there any limits to the number or locations of openings?
No. The only limit (economically) is when the “shear wall” building becomes a “frame” building, as the area of opening exceeds the solid area of walls.
7. Are there any limits to the size of the openings?
No. Openings wider than 8’ simply take the place of an 8’ wall section.
8. What size crane is needed to place the UNIBUILD lightweight walls.
Since the UNIBUILD lightweight wall panel is less than half the weight of conventional tilt-up panels, any 10 to 20 ton crane can efficiently place each wall section.
9. Are there any site conditions that limit a tilt-up building using UNIBUILD lightweight wall panels?
NO. Any site that is accessible to a small crane can utilize the economical UNIBUILD lightweight panel for the building walls. The property line walls of any tilt-up building can be tricky when placed immediately adjacent to neighboring buildings but are less of a challenge with the UNIBUILD lightweight panel sections.
10. What holds the tilt-up wall sections in place?
The roof, floor(s) and adjacent sections. The roof structure acts as a diaphragm to support the wall sections horizontally at the top and a slab edge beam anchors them to the foundation. In addition, the continuous ledger beam at the edge of the roof serves as a continuity tie to anchor adjacent wall sections to each other.
11. With the 8’0” wide UNIBUILD lightweight wall panels, how is the in-plane lateral force load path handled?
Overturning forces on wall sections are resisted by hold down anchorage to the foundation/floor system as well as anchorage to the adjacent sections.
12. Does the UNIBUILD lightweight panel building provide better seismic performance than the conventional tilt-up concrete building?
Yes. Seismic forces on the low-rise structure are directly proportional to the mass of the structure. So the lighter walls of the UNIBUILD lightweight panel building have a lighter reduced response to ground shaking than the massive walls of conventional tilt-up building.
13. Can the UNIBUILD lightweight wall panel be insulated?
Yes. In addition to the high thermal efficiency of cellular concrete and since the interior face of the panel is the mould face of the casting bed, the modular insulation and the finished material becomes an integral part of the UNIBUILD lightweight panel for a very thermal efficient wall.
14. What is the real cost savings of a UNIBUILD lightweight wall panel building verses a conventional tilt-up?
Since the exterior bearing walls are the most expensive element of the building shell, utilizing less expensive walls will have a significant effect on the total cost. On a typical building, the total savings is 8 to 12 %.
(By Breiholz Qazi Engineering, Inc. Civil and Structural Engineering, Seismic Hazard Reduction, Architecture).- California, USA.
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