RCC Columns – Purpose of Lateral Ties under Axial Compression In a reinforced concrete rectangular column subjected to predominantly axial compression, what is the primary function of providing lateral ties?

Introduction / Context:
Lateral ties (transverse reinforcement) in RC columns are crucial for maintaining the stability of longitudinal bars and the integrity of the concrete core. While ties contribute to several beneficial effects, it is important to identify their primary role in columns predominantly under axial compression, as this influences detailing and spacing decisions in design and construction.

Given Data / Assumptions:

• Member: RC rectangular column under axial compression (non-seismic context).
• Transverse reinforcement: closed ties with 135° or 90° hooks per detailing practice.
• Main bars: subjected to compression and potential out-of-straightness imperfections.

Concept / Approach:

Longitudinal bars in compression can bow outward between tie points and buckle prematurely if not restrained. Ties provide lateral support at intervals, effectively reducing the unsupported length of the bars and preventing bar instability. Although ties also confine the concrete (enhancing ductility and strength, especially in seismic detailing), in basic axial load scenarios the dominant immediate purpose is to prevent buckling of longitudinal steel and to hold the cage in position during concreting.

Step-by-Step Solution:

Verification / Alternative check:

Experimental observations show columns with inadequate ties experience early bar buckling after cover spalling, while well-tied columns retain load-carrying capacity significantly longer.

Why Other Options Are Wrong:

• Provide adequate shear capacity: Shear in columns is mainly resisted by the concrete and longitudinal steel; ties assist but are not primarily detailed for shear in axial-dominant columns.
• Provide adequate confinement to concrete: True and very important in ductile detailing, but the single most immediate function in non-seismic axial compression is bar buckling prevention.
• Reduce axial deformation: Ties do not significantly change axial elastic shortening.

Common Pitfalls:

Assuming confinement is the only role; neglecting tie anchorage quality and spacing limits, which directly influence bar stability.

Final Answer:

Avoid the buckling of the longitudinal steel under compression