More Detail: Structural Repairs and Retrofits

Structural Repairs & Retrofits for Existing Mid-Rise Office Buildings in North Texas

Structural work in existing mid-rise office buildings requires a specialized understanding of building age, construction methods, local soil conditions, and the cumulative effects of decades of occupancy and modifications. In North Texas, most mid-rise buildings (4–12 stories) utilize reinforced concrete frames, structural steel with composite decks, or hybrid systems. Local environmental conditions—especially expansive clay soils, extreme heat, and occasional freeze events—impose significant structural stresses over time.

This page details the primary structural systems found in North Texas mid-rise properties, the types of repairs and retrofits commonly required, and the technical considerations that guide safe, compliant construction.

1. STRUCTURAL SYSTEM TYPES COMMON IN NORTH TEXAS MID-RISE BUILDINGS

Understanding the original building system is essential before performing repairs or retrofits. The majority of commercial buildings constructed from the 1980s–2000s in the DFW area fall into these categories:

A. Reinforced Concrete Frame Construction

Typical in mid-rise office and municipal buildings.

Characteristics:

• Cast-in-place columns, beams, and slabs
• Drop panels or waffle slabs in older structures
• Thickened slab bands
• Often includes shear walls or moment frames

Repair Implications:

Concrete frame buildings often experience cracking due to soil movement or long-term loading changes.

B. Structural Steel with Composite Deck

Another common type, especially for buildings built after 1990.

Characteristics:

• Steel beams and girders
• Composite metal deck with concrete topping slab
• Wide-open floor plates with fewer columns
• Lightweight partitions

Repair Implications:

Structural repairs often involve reinforcing beams or modifying penetrations through metal decks during TI work.

C. Post-Tensioned Concrete Slabs

Slightly less common but present in many North Texas mid-rises.

Characteristics:

• Steel tendons tensioned after concrete placement
• Allows thinner slabs and wider spans

Special Considerations:

Any slab modification requires GPR scanning to avoid cutting tendons. Cutting a tendon can cause catastrophic slab failure.

D. Foundation Types

North Texas’s expansive clay soils heavily influence foundation design.

Common Foundations:

• Drilled piers with grade beams
• Shallow strip or spread footings (older buildings)
• Mat foundations (rare but present in some heavier mid-rises)

Soil Challenges:

• Seasonal expansion and contraction
• Differential settlement across large floor plates
• Moisture variability due to landscaping or drainage issues

2. COMMON STRUCTURAL ISSUES IN NORTH TEXAS MID-RISE OFFICE BUILDINGS

Years of service, shifting soils, and equipment loads create predictable structural issues:

A. Concrete Cracking & Slab Movement

Causes:

• Soil heave or settlement
• Shrinkage from age
• Overloads or tenant modifications
• Improper drainage around foundations

Repair Types:

• Epoxy injection for structural cracks
• Polyurethane injection for non-structural cracks
• Carbon-fiber reinforcement (CFRP) for beams, slabs, or columns
• Slab stabilization through pressure grouting

B. Column and Beam Deterioration

Although uncommon in young concrete buildings, spalling can occur due to:

• Water intrusion
• Rebar corrosion
• Poor original cover depth

Repairs involve chipping away weak concrete, treating rebar, and patching with structural grout or repair mortar.

C. Structural Steel Issues

Steel members can be damaged by:

• Corrosion from roof or façade leaks
• Overloading from new rooftop equipment
• Deck cutouts for MEP systems
• Fire damage

Repairs include steel plating, sister beams, or welding reinforcement.

D. Parking Garage Structural Degradation

Many mid-rise buildings include structured parking.

Common Issues:

• Concrete spalling from water and deicing salts
• Joint sealant failure
• Surface delamination
• Corrosion at embedded steel connections

These areas often require:

• Concrete patching
• Joint replacement
• Traffic coatings
• Structural reinforcement

3. STRUCTURAL RETROFITS FOR MODERN USE

Changing tenant needs often require structural upgrades.

A. Increased Floor Load Requirements

New tenants may require:

• High-density filing systems
• Data centers or server rooms
• Heavy specialty equipment
• Large conference room assemblies

Retrofit options include:

• Adding steel beams beneath the slab
• CFRP strengthening of slab bottoms
• Adding columns or jacketing existing ones
• Reinforcing slab openings

B. Rooftop Equipment Additions

Adding mechanical units, generators, or telecom equipment requires:

• Load analysis of roof framing
• Reinforcement of beams or joists
• Curb support modifications
• Vibration and seismic anchorage

North Texas buildings often receive new HVAC units to handle modern cooling loads.

C. Stair and Elevator Shaft Modifications

Modernizations may include:

• Enlarging elevator cabs
• Adding new stair access
• Cutting new slab openings (requires engineering and scanning)
• Reinforcing shaft walls

Cutting any slab in a post-tensioned building requires extreme caution.

D. Window Wall and Curtainwall Retrofits

Structural attachment often requires:

• New anchor supports
• Reinforcement of spandrel beams
• Removal and replacement of deteriorated embeds

4. BUILDING ENVELOPE STRUCTURAL REPAIRS

Structural work also extends into envelope systems when supports degrade:

A. Masonry Façade Repair

Common problems include:

• Cracked brick due to movement
• Failed shelf angles
• Water intrusion behind brick

Repairs may require:

• Angle replacement
• Repointing mortar
• Installing new flashing systems

B. EIFS and Stucco Repairs

These lightweight systems are sensitive to moisture and backing failures.

Repairs include:

• Removing damaged foam
• Reinforcing substrate
• Installing proper drainage planes

C. Curtainwall Issues

Glass and aluminum systems may require:

• New anchors
• Mullion reinforcements
• Glazing replacements
• Sealant and gasket upgrades

5. SEISMIC & WIND RETROFITS

While North Texas has low seismic activity, wind exposure is significant.

Retrofits May Include:

• Improved anchorage of equipment
• Reinforcement of parapets
• Strengthening façade attachments
• Upgrading roof connections
• Enhancing lateral load paths

Buildings in open areas (e.g., Las Colinas, Plano Legacy corridor) face higher wind demands.

6. WATER INTRUSION & STRUCTURAL IMPACTS

Water infiltration through roofs, façades, or foundations can degrade structural components.

Repairs may include:

• Replacing corroded structural steel
• Reinforcing decks or beams
• Rebuilding weakened masonry
• Installing new waterproofing membranes

Water-damaged areas must be fully dried to prevent mold or long-term deterioration.

7. WORKING IN OCCUPIED MID-RISE BUILDINGS

Structural repairs often occur during active operations.

Requirements:

• Noise control
• Vibration monitoring
• Night or weekend slab cutting
• Temporary shoring without blocking egress
• Clear tenant communication

Safety is the top priority, especially for overhead structural work.

8. ENGINEERING, PERMITTING & INSPECTIONS

All structural work must be engineered and sealed by a Texas-licensed structural engineer.

Typical Process:

1. Structural assessment
2. GPR scanning of slabs
3. Load calculations
4. Engineering drawings
5. City permit submission
6. On-site inspections
7. Final sign-off

Cities like Dallas, Plano, and Frisco have stringent requirements for structural drawings and special inspections.