SECTION IV. REINFORCED BRICK MASONRY
APPLICATIONS AND MATERIALS
9-113. When added strength is needed, brick walls, columns, beams, and foundations are reinforced the same as in concrete construction.
9-114. Because brick masonry in tension has low strength compared with its compressive strength, it is reinforced with steel when subject to tensile stresses. Like concrete construction, the reinforcing steel is placed in either the horizontal or vertical mortar joints of beams, columns, walls, and footings. Reinforced brick structures can resist earthquakes that would severely damage nonreinforced brick structures. The design of such structures by qualified engineers is similar to that of reinforced concrete structures.
9-115. Materials used for reinforced brick are--
Brick. The same brick is used for reinforced brick masonry as for ordinary brick masonry. However, it should have a compressive strength of at least 2,500 pounds per square inch.
Steel. The reinforcing steel is the same as that in reinforced concrete and is fabricated and stored the same way. Do not use high-grade steel except in emergencies, because masonry construction requires many sharp bends.
Mortar. Use Type N mortar for its high strength.
Wire. Use 18-gage, soft-annealed iron wire to tie the reinforcing steel.
9-116. Reinforcing steel can be placed in both horizontal and vertical mortar joints.
LAYING REINFORCED BRICK
9-117. Lay the brick the same way as ordinary brick masonry, with mortar joints 1/8 inch thicker than the diameter of the reinforcing bar. This provides 1/16 inch of mortar between the brick surface and the bar. Thus, large steel bars require mortar joints thicker than 1/2 inch.
PLACING THE STEEL
9-118. Embed all reinforcing steel firmly in mortar.
Horizontal bars. Lay horizontal bars in the mortar bed, and then push them down into position. Spread more mortar on top of the bars, smooth it out until you produce a second bed joint of the proper thickness. Lay the next course in this mortar bed, following the same procedure as laying brick without reinforcing steel.
Stirrups. Most stirrups are Z-shaped as shown in Figure 9-44 to fit the mortar joints. Insert the lower leg under--and contacting--the horizontal bars, which requires a thicker joint at that point.
Vertical bars. Hold vertical bars in the vertical mortar joints with wood templets having holes drilled at the proper bar spacing, or by wiring them to horizontal bars. Then lay the brick up around the vertical bars.
Spacing. The minimum center-to-center spacing between parallel bars is 1-1/2 times the bar diameter.
Figure 9-44. Reinforced brick-masonry beam construction
9-119. Reinforced brick-masonry walls, columns, and footings need no formwork. However, reinforced brick beams and lintels--which act as beams--require formwork for the same reason that reinforced concrete beams do.
The form consists only of support for the underside of the beam, no side formwork. The form for the beam underside is the same and is supported the same as that for concrete beams.
When a beam joins a wall or another beam, cut the form short by 1/4 inch, and fill the gap with mortar. This allows the lumber to swell and makes form removal easy.
Wait at least 10 days before removing the form from the beam underside.
BEAMS AND LINTEL CONSTRUCTION
9-120. Lintels are placed above the windows and doors to carry the weight of the wall above them. Lintels can be made of steel, precast reinforced concrete beams, or wood.
9-121. Beam width and depth depend upon brick dimensions, mortar joint thickness, and the load that the beam will support. However, beam width usually equals the wall thickness, that is 4, 8, 12, or 16 inches. Beam depth should not exceed approximately three times its width.
BEAM CONSTRUCTION PROCEDURES
9-122. The following procedures will be used in beam construction:
Step 1. Lay the first course on the form using full head joints, but no bed joint (see Figure 9-44).
Step 2. Spread a mortar bed about 1/8 inch thicker than the diameter of the horizontal reinforcing bars on the first course, and embed the bars.
Step 3. Slip the legs of any stirrups under the horizontal bars as shown in Figure 9-44. Be sure to center the stirrup in the vertical mortar joint.
Step 4. After properly positioning the stirrups and the horizontal bars, spread more mortar on the bed joints if necessary, and smooth its surface. Then lay the remaining courses in the normal way.
Step 5. Lay all bricks for one course before proceeding to the next course to ensure a continuous bond between the mortar and steel bars. Often, three or four bricklayers must work on one beam to spread the bed-joint mortar for the entire course, place the reinforcing steel, and lay the brick before the mortar sets.
9-123. The steel bars should be 3/8 inch in diameter, or less if you must maintain a 1/2-inch mortar joint. Place the bars in the first and fourth mortar joints above the opening (see Figure 9-45). They should extend 15 inches into the brick wall on each side of the opening. Table 9-7 below gives the number and diameter of bars required for different width wall openings. See paragraph 9-56 for how to place the wall above a window or door opening.
Figure 9-45. Reinforced brick-masonry lintel construction
Table 9-7. Quantities of bars required for lintels
9-124. Footings are the enlargements at the lower end of a foundation wall, pier, or column and are required to distribute the load equally.
9-125. Large footings usually require reinforcing steel because they develop tensile stresses. As in all brick foundations, lay the first course in a mortar bed about 1 inch thick, spread on the subgrade.
9-126. Figure 9-46 shows a typical wall footing with steel dowels extending above it to tie the footing and wall together. The number 3 bars running parallel to the wall prevent perpendicular cracks from forming.
Figure 9-46. Reinforced brick-masonry-wall footing construction
9-127. Reinforced brick-column footings are usually square or rectangular as shown in Figure 9-47. The dowels not only anchor the column to the footing, but transfer stress from one to the other. Note that both layers of horizontal steel are in the first mortar joint, which is accepted practice for small bars. When using large bars, place one layer in the second mortar joint, and reduce the bar spacing in this joint.
Figure 9-47. Reinforced brick-masonry-column footing construction
COLUMNS AND WALLS
9-128. Load-carrying capacity increases when brick columns and walls have steel reinforcement.
9-129. At least 1 1/2 inches of mortar or brick should cover the reinforcing bars. Install 3/8-inch diameter steel hoops or ties at every course (see Figure 9-48) to bold bars in place. Use circular hoops whenever possible. Lap-weld their ends, or bend them around the reinforcing bars as shown in Figure 9-48.
Holding steel in place. When the column footing is complete, tie the reinforcing steel to the dowels projecting from the footing. Slip the necessary number of hoops over the dowels and fasten them temporarily some distance above the course being laid, but within your reach. You do not need to wire the hoops to the dowels. Hold the tops of the dowels in position either with a wood templet or by tying them securely to a hoop near the top of the column.
Laying the brick. Lay the brick as described in paragraph 9-20. Place the hoops in a full mortar bed, and smooth it out before laying the next course. You can use brick bats in the column core or wherever it is inconvenient or impossible to use full-size bricks. After laying each course, fill the core and any space around the reinforcing bars with mortar. Then push any necessary bats into the mortar until they are completely embedded. Now spread the next mortar bed and repeat the procedure.
Figure 9-48. Reinforced brick-masonry-column construction
9-130. Reinforce brick masonry walls with both horizontal and vertical bars. Place the bars as described in paragraph 9-117. Then wire the vertical stirrups to the dowels projecting out of the wall footing.
Constructing corner leads. Place the reinforcing bars in corner leads as shown in Figure 9-49 below. Use the same size bars as in the rest of the wall, and let them extend 15 inches. The horizontal bars in the remaining wall should overlap the corner bars by the same 15 inches. As for beams, you must lay all brick in one course between the corner leads before laying any other brick, because you must embed the entire bar in mortar at one time.
Laying the remaining wall. As you lay the remaining brick, fill all spaces around the reinforcing bars with mortar.
Figure 9-49. Corner lead for reinforced brick masonry wall
SECTION V. STRUCTURAL CLAY-TILE MASONRY
STRUCTURAL CLAY TILE
9-131. Structural clay tile is either a hollow or cored burned-clay masonry unit having cores that are parallel either in the vertical or horizontal direction. The manufacturing process and the type of clay used are the same as it is for brick.
9-132. Hollow masonry units made from burned clay or shale are usually called simply clay tile. Figure 9-50 shows several common types and sizes. These stretcher units are made by forcing a plastic clay through special dyes, then cutting the tiles to size and burning them the same way as brick. The amount of burning depends upon the tile grade.
Figure 9-50. Corner lead for reinforced brick masonry wall
9-133. The hollow spaces in the tile are called cells, the external wall is called a shell, and the partitions between cells are called webs. The shell should be at least 3/4 inch thick and the web 1/2 inch thick.
9-134. Side-construction tile has horizontal cells, whereas end-construction tile has vertical cells. Neither is better than the other, and both are available in the types described below.
9-135. The two basic categories of structural clay tile--load-bearing and nonload-bearing--differ in their characteristics. Load-bearing structural clay tile further subdivides into three categories: load-bearing wall tile, structural facing tile, and ceramic glazed structural facing tile. Nonload-bearing structural clay tile further subdivides into three categories: nonload-bearing partition and furring tile, fireproofing tile, and screen tile.
9-136. Load-bearing tile has three types, divided by use: wall, facing, and glazed facing. Load-bearing wall tile includes--
Wall tile for constructing exposed or faced load-bearing walls. This tile carries the entire load, including the facing of stucco, plaster, stone, or other material.
Back-up tile for backing up combination walls of brick or other masonry in which both the facing and the backing support the wall load. Headers bond the facing or outer tier to the backing tile. The inside face is scored so that you can plaster it without lath.
9-137. The ASTM covers two grades of wall and back-up tile based on weather resistance. Grade LB is suitable for general construction that is not exposed to weathering, or exposed to weathering but protected by at least 3 inches of facing. Grade LBX can be used in masonry exposed to weathering with no facing material.
Structural facing tile is divided into two classes, based on the thickness of the face shell: standard and special duty. The ASTM grades each of these classes by factors affecting appearance.
- Type FTX is suitable for both exterior and interior walls and partitions. It has an excellent appearance and is easy to clean.
- Type FTS, although inferior in quality to Type FTX, is suitable for both exterior and interior walls where some surface finish defects are not objectionable.
Ceramic glazed structural facing tile has an exposed surface of either a ceramic or salt glaze, or a clay coating. Use this tile where you need a stainproof, easily cleaned surface. It is available in many colors and produces a durable wall having a pleasing appearance. Ceramic glazed facing tile is divided into two types and two grades:
- Type I is suitable for general use where only one finished face will be exposed.
- Type II is suitable for use where the two opposite finished faces will be exposed.
- Grade S (select) is suitable for use with comparatively narrow mortar joints.
- Grade SS (select sized or ground edge) is suitable for uses requiring very small variations in face dimensions.
9-138. Nonload-bearing tile include three types:
Nonload-bearing partition and furring tile.
- Partition tile is suitable for constructing nonload-bearing interior partitions or for backing nonload-bearing combination walls.
- Furring tile is suitable for lining the wall interiors to provide both a plaster base and an air space between plaster and the wall.
Fireproofing tile protects structural members including steel girders, columns, and beams.
Screen tile is available in a large variety of patterns, sizes, and shapes, and in a limited number of colors. The surfaces may be smooth, scored, combed, or roughened. Screen tile is divided into two types and three grades:
- Type STX has an excellent appearance and minimum size variation.
- Type STA varies more in size.
- Grade SE has high resistance to weathering, freezing, and thawing.
- Grade ME has moderate resistance to weathering.
- Grade NE is suitable for interior use only.
9-139. Besides the standard units shown in Figure 9-50 above you can order special clay tile units to use at windows, door openings, and at corners. Consult a manufacturer's catalog for any special units you need.
QUANTITIES OF MATERIALS REQUIRED
9-140. Tables 9-8 and 9-9 below give the number of structural clay tiles--both side construction and end construction--and the amount of mortar required for walls of different thickness covering varying areas.
Table 9-8. Quantities of materials required for side construction of hollow clay-tile walls
Table 9-9. Quantities of materials required for end construction of hollow clay-tile walls
PHYSICAL CHARACTERISTICS OF STRUCTURAL CLAY TILE
9-141. The compressive strength of an individual clay tile depends on its ingredients and the method of manufacture, plus the thickness of its shell and webs. You can predict that tile masonry will have a minimum compressive strength of 300 pounds per square inch based on the cross section. Tile masonry has low tensile strength--in most cases less than 10 percent of its compressive strength. Other physical properties are--
Abrasion resistance. Like brick, the abrasion resistance of clay tile depends mainly on its compressive strength. The stronger the tile, the greater its resistance to wear, but abrasion resistance decreases as the amount of absorbed water increases.
Weather resistance. Structural clay facing tile has excellent resistance to weathering. Freezing and thawing produces almost no deterioration. Tile absorbing up to 16 percent of its weight of water satisfactorily resists freezing and thawing effects. When masonry is exposed to weather, use only portland-cement-lime mortar or mortar prepared from masonry cement.
Heat- and sound-insulating properties. Because of the dead air space in its cells, clay tile has better heat-insulating qualities than solid unit walls. Its sound penetration-resistance compares favorable with that of solid masonry walls, but is somewhat less.
Fire resistance. Structural clay-tile walls have much less fire resistance than solid masonry walls. However, you can improve it by plastering the wall surface. Partition walls 6 inches thick will resist a fire for one hour, if the fire's temperature does not exceed 1,700oFF within that hour.
Weight. Structural clay-tile weighs about 125 pounds per cubic foot. However, because hollow cell size varies, actual tile weight depends on the manufacturer and the type. A 6-inch tile wall weighs approximately 30 pounds per square foot, whereas a 12-inch tile wall weighs approximately 45 pounds per square feet.
CONSTRUCTION DETAILS AND METHODS
9-142. Refer to the paragraphs listed to obtain specific information applicable to structural clay-tile construction:
Tools and equipment (paragraphs 7-4 and 7-5).
Finishing joints (paragraph 9-37).
Bricklayer's duties (paragraph 9-38).
Bricktender's duties (paragraph 9-39).
Watertight walls (paragraph 9-67).
Maintaining and repairing brick walls (paragraph 9-90)
Cleaning new brick and removing efflorescence (paragraph 9-95).
Cleaning old brick (paragraph 9-96).
Freeze protection (paragraph 9-105).
9-143. The three practical uses for structural tile are discussed below.
Exterior walls. You can use structural clay tile for either load bearing or nonload-bearing exterior walls. It is suitable for both below-grade and above-grade construction.
Partition walls. Nonload-bearing partition walls ranging from 4 to 12 inches thick are often built of structural clay tile. They are easy to construct, lightweight, and have good heat- and sound-insulating properties.
Backing for brick walls. Structural clay tile can be used as a backing unit for a brick wall.
9-144. The general procedure for making mortar joints for structural clay tile is the same as for brick. Mortar joints for end-construction units are described as follows:
Bed joint. To make a bed joint, spread 1 inch of mortar on the bed tile shells, but not on the webs (see view 1 of Figure 9-51 below). Spread the mortar about 3 feet ahead of laying the tile. Because the head joints in clay-tile masonry are staggered, the position of a tile in one course does not match the tile underneath it. Therefore, the webs do not make contact, and any mortar you spread on them is useless.
Head joint. Form the head joint by spreading plenty of mortar along each tile edge, as shown in view 2 of Figure 9-51. Because a clay tile unit is heavy, use both hands to push it into the mortar bed until it is properly positioned. The mortar joint should be about 1/2 inch thick, depending upon the type of construction. Use enough mortar that it squeezes out of the joints, and then cut the excess off with a trowel. The head joint need not be solid like a head joint in brick masonry, unless it is subject to weather.
Closure joints. Use the procedure described in paragraph 9-33 for making closure joints in brick masonry.
Figure 9-51. Laying end-construction clay tile
9-145. Mortar joints for side-construction units are described as follows:
Bed joint. Spread the mortar about 1 inch thick, approximately 3 feet ahead of laying the tile. You need not make a furrow as you must for brick bed joints.
Head joint. Use one of the two following methods:
- Method A. Spread as much mortar on both edges of the tile as will adhere (see view 1 of Figure 9-52). Then push the tile into the mortar bed against the tile already laid until it is properly positioned. Cut off the excess mortar.
- Method B. Spread as much mortar as will adhere on the interior shell of the bed tile and on the exterior shell of the unit you are placing (see view 2 or Figure 9-52). Then push the tile into place and cut off the excess mortar.
Mortar joint thickness. Make the mortar joints about 1/2 inch thick, depending upon the type of construction.
Figure 9-52. Laying side-construction clay
LAYING AN 8-INCH BRICK WALL WITH A 4-INCH HOLLOW-TILE BACKING
9-146. When laying an 8-inch brick wall with a 4-inch structural hollow-tile backing, the brick wall has six stretcher courses between the header courses. The side-construction backing tile is 4 by 5 by 12 inches in size. The 5-inch tile height equals the height of two brick courses plus a 1/2-inch mortar joint.
Lay the tile bed joint so that the top of the tile is level with every second brick course. Therefore, the thickness of the tile bed joint depends upon the thickness of the brick bed joint.
LAYING OUT THE WALL
9-147. Lay out the first brick course temporarily without mortar, as described in paragraph 9-44. This determines the number of bricks in one course.
LAYING THE CORNER LEADS
9-148. As shown in view 1 of Figure 9-53, the first brick course in the corner lead is the same as the first course of the corner lead for a solid 8-inch brick wall, except that you lay one more brick next to brick (p) as shown in step 5 of Figure 9-22. Lay all the bricks for the corner lead before laying any tile. Then lay the first tile course as shown in view 2 of Figure 9-53. Complete the corner lead as shown in view 3, Figure 9-53.
Figure 9-53. Laying a corner lead with hollow-tile backing
LAYING AN 8-INCH STRUCTURAL CLAY-TILE WALL
9-149. Use 8- by 5- by 12-inch side-construction tile in a half-lap bond to construct an 8-inch structural clay-tile wall. You can insert a 2- by 5- by 8-inch soap at the corners as shown in Figure 9-54 below. A soap is a thin end-construction tile.
Figure 9-54. Constructing the corner lead of an 8-inch structural clat-tile wall
LAYING OUT THE WALL
9-150. Follow the procedure described in paragraph 9-43.
LAYING THE CORNER LEADS
9-151. Lay tiles a and b first (see Figure 9-54), and check their level as you lay them. To avoid exposing open cells on the wall face, use either end-construction tile for corner tiles b, g, and h, or a soap as shown in Figure 9-54. Lay tile b so that it projects 6 inch from the inside corner, as shown, to start the half-lap bond. Now lay tiles c and d, and check their level as you lay them. Next, lay tiles e and f, and check their level. Lay the remainder of the corner tile, and check the level of each as you lay it. After erecting the leads, lay the wall between them using a line.
|David L. Heiserman, Editor||
Copyright © SweetHaven
Revised: June 06, 2015