Brickwork in Circular and Flat Arches
Arches are not just architectural marvels; they are engineering feats that bear the weight of structures and transmit forces. The art of constructing arches requires skilled workmanship and attention to detail.
In this article, we will delve into the world of brickwork in circular and flat arches, exploring the specifications of bricks, centering and shuttering techniques, and the step-by-step process of constructing these arches.
Specification of Bricks for Arches:
When it comes to arch construction, the choice of bricks plays a vital role. Here are some specifications to consider:
- Gauged and Plain Arches: Gauged arches use cut or molded bricks, while plain arches utilize uncut bricks.
- Skew Bricks: The brick forming the skew of an arch should be dressed or cut to provide proper radials to the end voussoirs.
- Defect-Free Dressing: Defects in brick dressing should not be allowed. Mortar or the use of chips and bats should not be employed to compensate for any defects.
- Curvature Adaptation: Bricks in the spandrel wall, where they meet the arch’s extrude, should be cut to fit the curvature of the arch.
- Pre-Soaking: Before use, bricks for arch construction should be soaked in water for a sufficient period to ensure water penetrates the entire depth of the bricks.
Centering and Shuttering for Arches:
To ensure the stability and structural integrity of arches during construction, centering and shuttering are essential. Consider the following points:
- Load-Bearing Capacity: The centering and shuttering system must be strong enough to bear the dead load of the arch and any live loads occurring during construction.
- Secure Fastening: Shuttering should be securely tightened using hardwood wedges or sandboxes. This ensures ease of removal without transmitting jerks to the arch.
- Approved Sequence: The engineer’s approval should be obtained for the sequence of easing the shuttering.
- Optimal Timing: Shuttering should be removed within 48 hours after filling the spandrel and loading the arch.
Construction of Circular Arches:
Circular arches possess timeless elegance. Here are the steps involved in their construction:
- Choice of Arch Type: Circular arches can be either plain arches built in half-brick concentric rings or gauged arches constructed with cut or molded bricks.
- Simultaneous Construction: Work on the arch progresses simultaneously from both ends, meeting and being keyed in the center.
- Precise Brick Placement: Bricks should be flush with mortar, firmly pressed into position, and squeezed to create thin and compact joints.
- Mortar Joints: All joints should be filled with mortar, with a minimum thickness of 5 mm and a maximum of 15 mm.
- Loading the Haunches: After completing the arch, the haunches (the sides adjacent to the spandrels) should be loaded by filling the spandrels up to the crown level of the arch.
- Pointing the Arch Face: If the arch face is to be pointed instead of plastered, face bricks should be cut or molded to maintain joints no more than 5 mm thick. Radial joints to the full depth of the arch should be used.
- Ensuring Break Joints: The voussoirs (individual wedge-shaped units forming the arch) should break joints to the full depth of the arch for stability.
Construction of Flat Arches:
Flat arches offer a different aesthetic appeal while still providing load-bearing capacity. Here’s how they are constructed:
- Gauged Arches: Flat arches are built using gauged bricks, cut or molded to the required shape.
- Horizontal Extrudes: The extrudes (the outer edges of the arch) must be kept horizontal, while the intrudes (the inner part) should have a slight camber of 1 in 100 of the span.
- Determining the Center: The center of the arch, from which joints radiate, is determined by the intersection point of two lines drawn from the ends of the arch at the springing level and at a 60-degree angle to the horizontal.
- Radial Joints and Break Joints: Bricks in flat arches should have radial joints to the full depth of the arch, with voussoirs breaking joints with each other.
- Optimal Mortar Thickness: The thickness of mortar joints in flat arches should not exceed 5 mm.
- Relieving Arches: Flat arches, although primarily used for appearance, should be combined with relieving arches and lintels to support the load of the wall above.
The construction of arches, whether circular or flat, requires meticulous attention to detail and skilled craftsmanship. By adhering to the specifications of bricks, employing proper centering and shuttering techniques, and following the step-by-step construction process, architects and builders can create breathtaking arches that stand the test of time.