Missing Horizontal Bars and Short Starter Laps
A 3.0 m high × 5.0 m long reinforced CHB wall is being built along a warehouse boundary. The drawing specifies 150 mm CHB, 10 mm vertical deformed bars at 600 mm on center, lapped 40 bar diameters with starter bars from the footing, and 10 mm horizontal bars every third course, all embedded in grout. A 1.5 m wide gate opening is topped by a precast lintel. The mason cuts the starter bars so only 300 mm projects above the footing, arguing that the vertical bars can simply be tied to them. He omits the horizontal bars because the wall is 'only 3 m high.' The lintel is placed with 75 mm bearing on each side of the opening. The inspector arrives when the wall is 1.2 m high and the gate lintel is already set. No bar spacing or lap records exist.
1. Assess the omission of the horizontal bars. Is the mason's 'only 3 m high' argument valid?
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The horizontal bars are a specified structural and crack-control element, not an optional extra. A 3.0 m high free-standing wall is exposed to wind on one face; horizontal bars tie the wall to the columns, distribute lateral load, and control shrinkage and temperature cracking. Omitting every third-course bar leaves the wall unreinforced horizontally, so it behaves as a series of stacked blocks. 'Only 3 m high' is not a justification: 3 m is tall for a 150 mm CHB boundary wall, and the gate opening creates a stress concentration. The inspector should issue a nonconformance. The wall may need to be demolished and rebuilt, or the bars installed by cutting chases and grouting-but that is difficult and must be approved by the designer. The omission cannot be accepted based on height alone.
2. The starter bars project only 300 mm and are not lapped. Explain the anchorage requirement and the likely consequence.
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Starter bars must develop the vertical bars. For a 10 mm deformed bar in tension, a common lap is about 40 bar diameters, or 400 mm, and the starter must extend that length above the footing; 300 mm is short. If the vertical bar is merely tied to a 300 mm stub, the lap is insufficient and the wall can separate from the footing under lateral or seismic load. The bars are also supposed to be lapped, not butted. The inspector should reject the detail. Remedial options include exposing the starter, adding an approved mechanical coupler or epoxy-anchored dowel designed for the load, and extending the vertical bar to the required lap; any repair needs designer approval and inspection. The mason's argument that tying is enough ignores anchorage.
3. The lintel over the 1.5 m gate opening has only 75 mm bearing on each side. Is that adequate, and what should be done?
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75 mm bearing is generally too small for a 1.5 m lintel. Precast lintels typically need at least 150 mm bearing on each side so the load spreads into the masonry and the bearing stress stays low. With only 75 mm, the lintel can crush the block or rotate, and the opening may crack. The lintel should be removed and replaced with one long enough to give at least 150 mm bearing each side, or the opening should be detailed with a bearing pad or lintel designed for the shorter bearing. Because the gate is already set, the inspector should stop work and require correction before further courses are laid. The designer should confirm the lintel capacity and bearing.