ONLINE EXCLUSIVE
SIDEBAR TO INSIGHT: THOUGHTS FROM A TORNADO VETERAN
WHAT ARE THE ADVANTAGES PRECAST CONCRETE OFFERS IN PROTECTING STRUCTURES AGAINST THE ELEMENTS/CLIMATE CHANGE? ROBERT SHADE We meet the ICC 500 Debris Impact Resistance Test In 2016, we sent samples to Texas Tech University for debrisimpact-resistance testing: two 4-in.-thick and four 6-in.-thick precast, prestressed concrete panels using 5000 psi concrete tested per ICC 500-14 with a 15-lb wooden 2 × 4-in. projectile propelled at 100 mph. We had the joints between the panels tested as well as the wall panels themselves.
The following wall panels types passed the impact testing: • 6-in.-thick precast concrete panel with only one layer of 4 × 4 W4.0 × W4.0 WWM centered in the thickness • 6-in.-thick prestressed concrete panel concentrically prestressed in one direction with only 250-psi compression and no reinforcement (only concrete and prestressed strands) • 4-in.-thick precast concrete panel with only one layer of 4 × 4 W4.0 × W4.0 WWM centered in the thickness • 4-in.-thick prestressed concrete panel concentrically prestressed in one direction with only 250-psi compression and no reinforcement (only concrete and prestressed strands)
Some joints that are not used in precast concrete shelter construction failed the impact testing. Testing at the center of a 1⅛-in.-wide caulked joint (a standard ¾-in.-wide joint plus ⅜-in. PCI tolerance) using various types of caulk. Precast concrete wall panels that were 6 in. thick with standard polyurethane caulked joints each on face (without any additional armoring) passed the tornado debris impact testing. We currently arrange our standard ¾-in.-wide joint between precast concrete wall panels with a continuous 1-in.-diameter steel armoring rod, or use ship-lapped joints to meet ICC-500-14 joint armoring requirements for joints larger than ⅜ in. The results of our testing have been shared with the ICC-500 code committee, and a code change proposal submitted by PCI to increase the joint width between precast concrete wall panels in storm shelters to ¾ in. plus ⅜-in. industry tolerance was recently approved with modifications by the ICC 500 committee. If this ICC 500 code change makes it through the public comment process without modification, the change could be incorporated into the 2021 IBC through adoption of the most current ICC 500 standard.
WE MEET THE TYPICAL ICC 500 COMPONENT AND CLADDING WIND LOADS Roof down pressure = +125 lb/ft2 (max.)*
With very little add to the standard reinforcing in our designs for handling our products, our 48-in.-deep precast, prestressed concrete double tee can span up to 115 ft.
Roof down pressure = +125 lb/ft2 (max.)*
With the weight of our products and a 4-in. topping applied on the roof or the use of a pretopped double tee (using a 4-in. deck), long open spaces are achieved.
Roof down pressure = +125 lb/ft2 (max.)*
With the weight of our products and the use of standard connections to connect our products, a shear wall can be created with ease.
* These are very rough numbers that are typically conservative for the preliminary product design of double tees and walls.
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