Effects of Creep

• Understand what are effects of creep and how time-dependent deformation impacts different concrete structures
• Identify the primary structural consequences including increased deflection, crack formation, and stress redistribution
• Analyze how creep affects reinforced concrete beams through progressive bending and crack widening
• Compare beneficial versus detrimental effects of creep in determinate and indeterminate structures
• Evaluate the relationship between creep and column buckling in slender reinforced concrete elements
• Apply knowledge of differential creep effects to predict problems in high-rise building components
• Recognize how creep leads to prestress loss in concrete beams without high-tensile steel reinforcement
• Explore the connection between creep-induced stress relief and crack prevention in continuous structures

Understanding What are Effects of Creep in Structural Engineering

What are effects of creep represents one of the most critical long-term considerations in concrete structure design. Creep, the time-dependent deformation of concrete under sustained loading, produces both immediate and progressive structural changes that engineers must account for throughout a building's lifespan. These effects manifest differently depending on the structural element type, loading conditions, and overall structural system.

Primary Structural Consequences and Types of Effects of Creep

The types of effects of creep can be categorized into deformation-related and stress-related phenomena. Deformation effects include increased deflections in beams and slabs, which often exceed initial design predictions. For example, the parking garage at Logan International Airport required retrofitting due to excessive creep-induced sagging that compromised clearance requirements. Stress-related effects involve redistribution of forces within structures, sometimes beneficial in continuous systems but potentially harmful in statically determinate elements.

In reinforced concrete beams, creep amplifies deflections beyond elastic predictions, potentially causing serviceability issues. The Empire State Building's floor beams, designed in an era with limited creep understanding, required structural modifications to address long-term deflection problems. Additionally, existing cracks widen as creep concentrates stresses, while new cracks may form in previously uncracked regions.

Critical Applications in Different Structural Systems

Column behavior under creep presents unique challenges, particularly in slender elements subject to eccentric loading. The Willis Tower (formerly Sears Tower) incorporates special design provisions to prevent creep-induced buckling in its perimeter columns. When creep increases lateral deflections, the resulting secondary moments can trigger sudden buckling failure, making this effect especially dangerous in high-rise construction.

Indeterminate structures often benefit from creep through stress redistribution. Continuous concrete bridges experience stress relief at supports as creep allows moment redistribution to less critical sections. However, mass concrete applications like Hoover Dam face increased interior cracking risks as creep prevents stress relief through structural continuity.

Practical Implications for Modern Construction

High-rise buildings present complex creep scenarios involving differential effects between interior and exterior columns. One World Trade Center's design specifically addresses these issues through careful material selection and construction sequencing. Differential creep causes partition wall cracking, elevator misalignment, and cladding system failures when rigid connections cannot accommodate the gradual movements.

Prestressed concrete applications face unique vulnerabilities, particularly when using conventional steel reinforcement instead of high-tensile materials. The gradual loss of prestressing force through creep can lead to sudden failure once the concrete cracks, making this effect critical for bridge girders and parking structures throughout the United States.