The work package for block and structural brick walls in- cludes the block or brick, reinforcement, mortar, grout, in- sulation (such as perlite) used to fill the ungrouted block cavities, and imbeds and anchor bolts used to connect the building components to the wall. The block and brick walls are treated as a sheet good. When calculating the number of blocks, the estimator must separate standard blocks from bond beam blocks and other specialty shapes. The vertical rebar is treated as a counted item; the horizontal rebar is treated as a linear good. The mortar and grout are treated as quantity-from-quantity goods. The best way to determine the quantities of mortar and grout is based on past experience. Finally, anchor bolts and imbeds are treated as counted items. Steel imbeds and anchor bolts through structural steel are often provided by the struc- tural steel supplier and need to be delivered before the structural steel so they can be installed by the mason. Anchor bolts not through the structural steel also need to be provided so they can be installed by the mason. The quantity takeoff for a block or structural brick wall is shown in the following example.
EXAMPLE 6-1
Determine the number of blocks, the rebar, mortar, and grout needed to construct a 100-foot-long by 10-foot-high block wall con- structed of 7 5>8-inch-high by 7 5>8-inch-wide by 15 5>8-long blocks. The mortar joint is 3>8 inch thick. The wall is horizontally reinforced by bond beams at 4 feet on center containing two #4 bars. The wall is vertically reinforced with #5 rebar at 32 inches on center. All rebar is to be lapped 30 bar diameters. The rebar for the bond beam is to be delivered to the site in 20-foot lengths, and the vertical rebar is to be delivered cut to the required lengths. Allow 5 cubic feet of mortar and 17 cubic feet of grout per 100 square feet of block wall. Anchor bolts are placed in the top of the wall at 32 inches on center. How many of the blocks need to be bond beam blocks? Solution: Using Eq. (4-14) to find the number of rows, we get the following:
Using Eq. (4-17) to get the number of columns, we get the following:
Using Eq. (4-18), we calculate the number of blocks as follows:
Three bond beams are required: one at 4 feet, one at 8 feet, and one at 10 feet. The number of bond beam blocks is calculated using Eq. (4-18) as follows:
The project requires a total of 1,125 blocks of which 225 are bond beam blocks. For the bond beams, six 100-foot-long #4 bars are
Number⫽ (3 rows)(75 columns) ⫽ 225 blocks Number⫽ (15 rows)(75 columns) ⫽ 1,125 blocks NumberColumns⫽ (100 ft) (12 in/ft) (15 5>8 in ⫹ 3>8 in) ⫽75 columns NumberRows⫽ (10 ft) (12 in/ft) (7 5>8 in ⫹ 3>8 in)⫽ 15 rows
required for a total length of 600 feet. The lap for the #4 rebar is 30 bar diameters, or 15 inches (30⫻ 0.5 in). The number of 20- foot bars is calculated using Eq. (4-6) as follows:
The number of vertical bars is calculated using Eq. (4-1) as follows:
The required lap on the vertical bar is 18.75 inches (30⫻ 0.625 in). Each of these vertical bars will be ordered in the following incre- ments: 5 feet 7 inches long for the first 4 feet of the wall and 5 feet 11 inches long for the remaining 6 feet of the wall. If we ordered 5-foot 7-inch-long bars for the second four feet of the wall and 1-foot 11-inch-long bars for the last two feet of the wall, the last bar will lap the second to last bar 19 of its 23-inch length. It is more economical and is just as easy to replace the last two bars with a single bar. The wall will require 39 #5 rebar 5 feet 7 inches long and 39 #5 rebar 5 feet 11 inches long. The area of the wall is calculated as follows:
The number of cubic yards of mortar needed is calculated as follows:
The number of cubic yards of grout needed is calculated as follows:
The number of anchor bolts is calculated using Eq. (4-1) as follows:
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The estimator must take openings into account when estimating block walls. Openings reduce the number of blocks needed and may require the use of special blocks around the openings. Additional rebar is often placed around the opening as shown in Figure 6-2. The blocks above the opening are often supported by multiple bond beams. To allow the bond beams to provide a finished sur- face, a lintel block with a flat bottom, as shown in Figure 6-3, may be used for the bottom bond beam. Other specialty blocks, such as the bullnose block shown in Figure 6-3, may be used on the sides of the opening.
When estimating block, the estimator must determine the additional reinforcing for the opening, the specialty blocks needed, and the quantity of standard block that can be deducted for the opening. Block waste around the open- ing is greater than for other areas of the wall; therefore, the estimator cannot determine the number of standard blocks to be deducted by simply deducting the area of the opening and the specialty blocks. Many estimators do not deduct any blocks for small openings and deduct only half of the area for medium-sized openings. In addition to accounting for the opening, support for the bond beam needs to be provided
Number⫽ (100 ft) (12 in/ft) 32 in ⫹ 1 ⫽ 39 each Volume⫽ (1,000 ft2)a17 ft 3 100 ft2ba 1 yd3 27 ft3b ⫽ 6.3 yd 3 Volume⫽ (1,000 ft2)a 5 ft 3 100 ft2ba 1 yd3 27 ft3b ⫽ 1.9 yd 3 Area⫽ (100 ft)(10 ft) ⫽ 1,000 ft2 Number⫽ (100 ft) (12 in/ft) 32 in ⫹ 1 ⫽ 39 each Number⫽ 600 ft (20 ft⫺ 1.25 ft) ⫽ 32 each
FIGURE 6-2 Reinforcing around an Opening
FIGURE 6-3 Specialty Blocks
until the grout in the beam has cured. The following exam- ple looks at how to take openings into account when esti- mating block and structural brick walls.
EXAMPLE 6-2
Determine the number of specialty blocks needed, additional rebar required, and the number of standard blocks that can be de- ducted when building a wall with the opening shown in Figure 6- 2. The wall is constructed of 7 5>8-inch-high by 7 5>8-inch-wide by 15 5>8-inch-long blocks with a 3>8-inch mortar joint. The blocks at the top and bottom of the opening are to be the lintel block shown in Figure 6-3, with the blocks at the bottom placed upside down to provide a smooth surface. Bullnose blocks are to be provided at the sides of the opening. A 2⫻ 8 wood frame with a center support will be provided to support the bond beam until the grout has cured.
Solution: Lintel blocks are needed at the top and bottom of the opening. The number of lintel blocks needed for the top of the opening is calculated by dividing the width of the opening by the length of the block including one mortar joint as follows:
Blocks⫽ 40 in
The number of blocks will be rounded up to three blocks. Three lintel blocks are needed at the top and three at the bottom for a total of six. Bullnose blocks are needed at both sides. The number of bull- nose blocks needed for one of the sides of the opening is calculated by dividing the height of the opening by the height of the block in- cluding one mortar joint as follows:
Twelve bullnose blocks are needed.
The horizontal #6 rebar above and below the opening extends about a block and a half (about 24 in) beyond the opening in both di- rections; therefore, three #6 bars 7 foot 4 inches (2 ft⫹ 3 ft 4 in ⫹ 2 ft) long are needed. Bond beam blocks are needed for each of these bars. The number of bond beam blocks that are needed for one bar is calculated by dividing the length of the bar by the length of the block including one mortar joint as follows:
Blocks⫽(15 5>8 in ⫹ 3>8 in) ⫽88 in 5.5 blocks Blocks⫽ (4 ft) (12 in/ft)
(7 5>8 in ⫹ 3>8 in) ⫽6 blocks
Six bond beam blocks are needed for each bar for a total of 18 blocks. Six of these blocks are replaced with lintel blocks; therefore, 12 bond beam blocks are needed.
The vertical rebar to the sides of the opening extends about two blocks above and one block below the opening: therefore, six #6 bars 6 feet (16 in ⫹ 4 ft ⫹ 8 in) long are needed.
The number of standard blocks that can be deducted for the opening is determined by multiplying the number of full blocks that can fit in the width of the opening and the number of full blocks that can fit in the height of the opening. In this case two full blocks can fit in the width of the opening and six full blocks can fit in the height of the opening. The number of standard blocks that can be deducted is 12 (6⫻ 2). The bond beam blocks, bullnose blocks, and lintel blocks will replace standard blocks. A total of 42 (12⫹ 12 ⫹ 12 ⫹ 6) standard blocks may be deducted from the es- timate for the opening.
Two 3-foot 4-inch-long 2⫻ 8s are needed for the top and bot- tom of the opening. Three 3-foot 9-inch-long (4 ft⫺ 1 1>2 in ⫺ 1 1>2 in) 2 ⫻ 8s are needed for the sides and center of the opening. Order three 8-foot-long 2 ⫻ 8s. 䊏
A B C 1 Wall Length 100 ft 2 - in 3 Wall Height 10 ft 4 - in 5 Block Length 15.625 in 6 Block Height 7.625 in 7 Joint Thickness 0.375 in
8 Bond Beam Spacing 48 in
9 Number of Horizontal Bars per Bond Beam 2 ea
10 Splice Length for Bond Beam Rebar 15.00 in
11 Order Length of Horizontal Rebar 20.00 ft
12 Vertical Rebar Spacing 32 in
13 Splice Length for Vertical Rebar 18.75 in
14 Mortar 5 cft/100 sft 15 Grout 17 cft/100 sft 16 17 Rows 15 ea 18 Columns 75 ea 19 Bond Beams 3 ea 20 Standard Blocks 900 ea
21 Bond Beam Blocks 225 ea
22 Horizontal Rebar 32 ea
23 Length of Vertical Rebar (1) 67 in
24 Vertical Rebar (1) 39 ea
25 Length of Vertical Rebar (2) 71 in
26 Vertical Rebar (2) 39 ea
27 Mortar 1.9 cyd
28 Grout 6.3 cyd
EXCEL QUICK TIP 6-1 Block Wall
The numbers of standard blocks, bond beam blocks, bars of horizontal rebar, and bars of vertical rebar needed for a
block wall are set up in a spreadsheet by entering the data and formatting the cells as follows: