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Post-Tension Repair
Post Tension Cable (PT cable) reinforced structures use steel cables as strengthening components. These cables are tensioned prior to removal of the forms during original construction. Repair of the concrete in PT cable reinforced slabs is somewhat different that in conventionally reinforced slabs. The main reason is that the PT cables are under great loads and snap similar to a stretched rubber band if disturbed further. Hitting a cable with disregard for safety can damage the cable. The failure of the cable can damage adjacent property or personnel.

The actual repair of cable is usually done by splicing in a piece in the area of damage and then re-tensioning the cable. This requires a hydraulic ram with technician, even if this on the 15th floor balcony.

Post tension cable repairs is not something that novices should attempt. Lindman has experience in each of our offices, and has some of the leading technicians in the industry. It is another part of our complete restoration package for your restoration project.



Carbon Fiber Strengthening
Engineers have been designing structures using concrete since the middle ages, and steel since the 1800's. In the last 50 years we have stretched the application and strength of the two materials with technology and combining these materials in concert. The last significant new technology advance was the invention of post tension and pre-stressing of concrete in the second half of the 1900's.

In the last decade, a new technology developed for the space program, is now being applied to the retrofitting and strengthening of concrete structures. The technology to strengthen concrete structures externally with carbon fiber cloth or strips has introduced a whole new tool to engineers. In the past, steel beams typically had to be installed underneath slabs to increase capacity of existing slabs. These beams reduced head room between floors, and provided no flexibility in retrofits with mechanical and electric components suspended from the existing ceilings. In some cases, carbon fiber strengthening can be designed to be installed around much of the existing utilities.

The design of carbon fiber reinforcing is also new, with new design criteria evolving as the carbon fiber is manufactured in new sizes and strengths. The design programs are also cutting edge with expensive design software that also must be updated with each design criteria change. Because of this, many engineers prefer to simply specify the added strength required, and use Lindman for the carbon fiber design as part of our shop drawings. We have done this on dozens of projects, and can provide this turnkey approach on yours.



Strengthening
Typical elevated concrete slab construction relies on either rebar, external post tensioning cables, or some combination to achieve the desired strength. If either the original construction was faulty, or the desired loading of the slab changes, the structure may be strengthened.

The two options for adding strength are by internal or external modification. Internal requires removing much of the existing concrete to interlace additional rebar or post-tensioned cable with the existing. External modification is typically adding the strengthening materials under the existing slab. This is usually cheaper, but may reduce the usable headroom substantially.

External strengthening methods include adding structural steel beams, post tension cables and newer composite materials such as carbon fiber cloth or strips. These can be used in combination using each material where it has the best application. Working with an experienced structural engineering and strengthening contractor who is certified to install the latest high strength materials will lead to the most cost effective strengthening project.

See Carbon Fiber Strengthening
See Structural Steel



Soil Stabilization
Lindman frequently has to deal with poor bearing capacity of existing soils when repairing plazas, garages and building perimeters. It is common that A) soil shifted and settled, leading to failures in the structure above, or B) the added load of new planters and landscaping would overload the existing footers. We have installed numerous types of pin, auger and grouted piles to provide the needed bearing capacities on existing structures. This is another example of the Lindman's complete restoration package.


Structural Steel
The addition of structural steel had been the most popular way to increase loading to an existing deck until the introduction of composites in the late 1990’s. The requirement for strengthening of existing concrete decks is common during Plaza Renovations projects as additional planters and structures increase the dead load on existing structures.

Lindman has installed structural steel beams on the underside of structures, and installed steel brackets at column heads as part of strengthening projects in the past. Even with the advent of carbon fiber, there are many applications which require steel strengthening components, including some parts of blast proofing.

In some applications, structural steel can be used to replace the capacity lost by failed post tension cables. Steel can also be used as part of external post tension retrofits.

See Strengthening
See Carbon Fiber Strengthening
See Blast Proofing









VALENTE-LINDMAN LLC
New York Region
4 Cliff Drive
Englewood, NJ 07631

Voice: 201-816-0606
Fax: 201-816-1313



C.A. LINDMAN Inc.
Mid-Atlantic Region
10401 Guilford Road
Jessup, MD 20794

Voice: 301-470-4700
Fax: 301-470-4708



C.A. LINDMAN Inc.
Southern Region
1911 NW 18th St.,
Units 1 & 2
Pompano Beach, FL 33069

Voice: 954-971-3220
Fax: 954-971-3221



Carolina Restoration and Waterproofing, Inc.
Southeastern Region
P. O. Box 1007
Creedmoor, NC 27522

Voice: 919-528-6400
Fax: 919-528-4170