The timber floor not spanning on the masonry wall but properly anchored to the wall gives:
🔬 Understanding Wall Restraint
For a masonry wall to be stable, especially against buckling, it needs support at its top and bottom. This support is described by two types of restraint, which are critical for calculating the wall's effective height and slenderness ratio.
Lateral Restraint: This prevents the wall from moving sideways (in or out, perpendicular to its plane). It provides positional stability.
Rotational Restraint: This prevents the top of the wall from rotating or tilting. It provides rotational stability, creating a "fixed" connection.
⚖️ Detailed Analysis of the Scenario
The question describes a specific situation: a timber floor whose joists run parallel to the wall, but are "properly anchored" to it. Let's analyze what type of restraint this provides.
(a) Lateral restraint but not rotational restraint
Why it's correct:
• Presence of Lateral Restraint: The floor system, acting as a large, stiff horizontal plane (a diaphragm), is connected to the wall by anchors. These anchors effectively tie the wall to the floor, preventing it from moving in or out. This is the definition of lateral restraint.
• Absence of Rotational Restraint: A timber floor is relatively flexible. The connection made by simple metal anchors is not rigid enough to prevent the top of the wall from rotating. The connection acts like a hinge or pin, which allows rotation but prevents movement. To provide rotational restraint, a much more rigid connection is needed, such as when a concrete slab is cast directly onto the top of the wall.
(b) Rotational restraint but not lateral restraint
Why it's incorrect: This is the opposite of the actual condition. The anchors provide lateral restraint, but the flexible nature of the connection prevents rotational restraint.
(c) Both lateral and rotational restraints
Why it's incorrect: This describes a "fixed" support condition, which is typically only achieved with a rigid connection like a reinforced concrete slab bearing on the wall.
(d) Neither lateral nor rotational restraint
Why it's incorrect: This would describe a "free" end, like the top of a freestanding cantilever wall. The presence of anchors explicitly provides lateral support.
💡 Study Tips for Wall Supports
- Anchor = Lateral Support: If a wall is anchored to a floor or roof, it always has lateral support.
- Concrete = Rotational Support: A reinforced concrete slab bearing on a wall provides a rigid, "fixed" connection, offering both lateral and rotational restraint.
- Timber = No Rotational Support: A timber floor, even when anchored, provides a flexible, "hinged" connection, offering only lateral restraint.