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- To: <seaint(--nospam--at)seaint.org>
- Subject: big box remodeling
- From: "Bob Freeman" <robert.freeman(--nospam--at)idsse.com>
- Date: Thu, 30 Aug 2007 12:47:33 -0700
Concrete tilt-up is a unique structural animal to me.
Quick panel erection during construction suggests very little re-bar from the footing to the concrete tilt-up wall panel at the base. Shear wall design and damage from earthquake events like Northridge have changed dramatically the structural design for ‘big box stores’.
Dowels from the panel into the slab are the primary base shear reinforcement for in-plane seismic forces. The weight of the slab-on grade is supporting the tilt-up concrete wall during an earthquake for in-plane forces. This is more prevalent in recently designed tilt-ups and in seismic Zone 4. Not as much when I worked on them in the 1970’s. Other types of construction normally carry the in-plane forces directly into concrete footings. Older tilt-ups should be evaluated by a structural engineer (like IDS) for seismic response when a major upgrade is being done for architectural items. IDS reviewed a tilt-up after the Northridge earthquake that was destroyed when the tilt-up concrete walls fell outward, and the furniture inside the building held up the roof structure. This was a failure of ‘out-of-plane’ resistance elements. Also very common in old big box stores. Your clients would do well to review these items as well as others which have caused severe damage.
Integrated Design Services, Inc.
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