Question 1

How does creep affect reinforced concrete beams?

Accepted Answer

Creep causes reinforced concrete beams to experience increased deflection under prolonged stress. This additional deflection can further bend the beam, widen existing cracks, and form new cracks. Understanding creep is vital for beam design, as engineers must often implement additional design measures to accommodate these gradual deformations and maintain structural integrity.

Question 2

Why can creep cause column buckling in slender reinforced concrete columns?

Accepted Answer

In slender reinforced concrete columns under eccentric loads, creep induces deflection that compromises stability. This deflection can trigger column buckling, a critical failure mode. The combination of eccentric loading and gradual creep deformation creates conditions where the column loses its load-carrying capacity, making slender columns particularly vulnerable to this phenomenon.

Question 3

Can creep be beneficial in concrete structures?

Accepted Answer

Yes, creep can be beneficial in indeterminate structures like column-beam junctions. Stress concentrations induced by shrinkage, temperature variations, or support movements can be relieved by creep, resulting in fewer cracks. This stress mitigation effect demonstrates that creep's impact varies depending on structural configuration and loading conditions.

Question 4

What problems does creep cause in mass concrete structures like dams?

Accepted Answer

In mass concrete structures such as dams, creep increases the chances of crack formation in the interior. Constraints during temperature cycles from hydration heat and subsequent cooling, combined with creep deformation, create conditions that promote cracking. This makes creep a significant concern in massive concrete design and maintenance planning.

Question 5

How does differential creep affect high-rise buildings?

Accepted Answer

In high-rise buildings, outer and inner columns may experience differential creep, causing shifts in connecting partition panels and resulting in cracks within these panels. Additionally, external cladding rigidly affixed to columns undergoing creep is prone to developing cracks. These differential movements create stress concentrations that compromise both partition and cladding integrity.

Question 6

What happens to prestressed concrete beams when they undergo creep?

Accepted Answer

Prestressed concrete beams made without high-tensile steel tend to lose their prestressing forces over time due to creep, potentially leading to failure. This prestress loss was once so significant it prompted the introduction of high-tensile steel to counter the effects. Creep-induced force loss remains a critical consideration in prestressed concrete design for bridges and other applications.

Question 7

What design provisions are necessary to accommodate creep in concrete structures?

Accepted Answer

Provisions for accommodating potential movement and stress changes due to creep are essential in concrete structure design and maintenance. Engineers must account for increased deflection in beams, potential buckling in slender columns, differential movements in high-rise buildings, and prestress loss in prestressed elements. Understanding types of non structural cracks in concrete helps identify creep-related damage patterns.

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