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Advanced Building Systems
General Repairs
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General Repairs
Parts of a Building
A.  Foundation
Foundation is the basement walls that your building sits on.  Needs to be big enough to support weight of the building.  Sits on footing (made of poured concrete) to spread out the weight and prevent sinking.
  1. Joists - are the base of the floor for your first floor and all subsequent floors.  They are laid 16" on center.  You need to be careful about how much of a load will be put on them.  Sometimes you place a third foundation wall (load bearing wall) or lally columns to lessen the stress.
  2. Floors will be placed on top of the joists (4 X 8 foot plywood) which can be covered with tiles, or other types of flooring materials.
  3. On the roof, make sure to place insulation between the joists and the floor to keep the weather out.

In laying floors or walls, one must take in to consideration whether they are level or plumb (straight) 90 degree angles from one another.  LEVEL refers to horizontal items (floors, roofs) and PLUMB refers to vertical items (walls and foundations).


Multiple Dwellings roofs are flat as opposed to private dwellings which are usually pitched.  Flat roofs are slightly pitched to allow water to flow toward a drain.


  1. 3 Ply Built Up - 2 levels of tar paper + 1 Capsheet (guaranteed 2 - 5 years)

        a.  HOT- Use hot tar to adhere paper + capsheet

        b.  Cold - Use roofing cement to adhere tar

  2.  Modified Bitumen - 1 layer of 28-30 pound tar paper and 2nd layer - heated material that is melted and connects the two layers to each other to form a skin-like surface with no seams with a guaranteed lasting between 12-15 years.

Do not apply more than 2 sets of roofs.  If the roof is still leaking after applying another set, replace the entire roof down to the bare plywood and start over again.

CONCRETE - is a mixture of Portland Cement, Water and Aggregate (sand, pebbles, rocks).  When you place concrete down you must place joists (for expansion) so as to not crack it once the concrete is set or dried. 

  1. Concrete needs to be cured slowly - keep watering it to make a secure stable bond.  It takes about 30 days to dry for the strongest bond.
  2. When placed on wall should use a wire mesh to hold concrete on the wall.
  3. On the ground you use ribar metal bars to add support.
  4. Before the concrete has cured you want to roughen the surface with a broom to prevent it from being too slick when wet.  This roughening gives you traction.


1-1. Concrete is the type of construction material most widely used by both military and civilian personnel. Part one covers the physical characteristics, properties, and ingredients of concrete; the form design and construction principles; construction procedures with emphasis on concrete placement, finishing, and curing techniques; and the proportions of ingredients.

General Concrete Mixing Procedures

1-2. Concrete is produced by mixing a paste of cement and water with various inert materials. The most commonly used inert materials are sand and gravel or crushed stone. A chemical process begins as soon as the cement and water are combined. Different amounts of certain materials will effect the desirable properties of workability, nonsegregation, and uniformity of the mix. There are numerous advantages and some limitations for using concrete as a building material.



1-3. Concrete is a mixture of aggregate, and often controlled amounts of entrained air, held together by a hardened paste made from cement and water. Although there are other kinds of cement, the word cement in common usage refers to portland cement. A chemical reaction between the portland cement and water--not drying of the mixture--causes concrete to harden to a stone-like condition. This reaction is called hydration. Hydration gives off heat, known as the heat of hydration. Because hydration--not air drying--hardens concrete, freshly placed concrete submerged underwater will harden. When correctly proportioned, concrete is at first a plastic mass molded into nearly any size or shape. Upon hydration of the cement by the water, concrete becomes stone-like in strength, durability, and hardness.


1-4. Portland cement is the most commonly used modern hydraulic cement. In this case, the word hydraulic is the cement's characteristic of holding aggregate together by using water or other low-viscosity fluids. Portland cement is a carefully proportioned and specially processed chemical combination of lime, silica, iron oxide, and alumina. It was named after the Isle of Portland in the English Channel.


1-5. Unless tests or experience indicates that a particular water source is satisfactory, water should be free from acids, alkalis, oils, and organic impurities. The basic ratio of cement to water determines the concrete's strength; generally, the less water in the mix, the stronger, more durable and watertight the concrete. The concrete should be workable but not too stiff to use. Too much water dilutes the cement paste (binder), resulting in weak and porous concrete. Concrete quality varies widely, depending on the characteristics of its ingredients and the proportions of the mix.


1-6. Inert filler materials (usually sand and stone or gravel) make up between 60 and 80 percent of the volume of normal concrete. In air-entrained concrete, the air content ranges up to about 8 percent of the volume. Aggregate is often washed when impurities are found that can retard cement hydration or deteriorate the concrete's quality. All aggregate is screened to ensure proper size gradation, because concrete differs from other cement-water-aggregate mixtures in the size of its aggregate. For example, when cement is mixed with water and aggregates passing the number 4 sieve (16 openings per square inch), it is called mortar, stucco, or cement plaster. When cement is mixed with coarse aggregate (CA) of more than 1/4 inch plus fine aggregate (FA) and water, the product is concrete. The aggregate's physical and chemical properties also affect concrete properties; aggregate size, shape, and grade influence the amount of water required. For example, limestone aggregate requires more water than similar size marble aggregate. Aggregate surface texture influences the bond between the aggregate and the cement paste. In properly mixed concrete, the paste surrounds each aggregate particle and fills all spaces between the particles. The elastic properties of the aggregate influence the elastic properties of the concrete and the paste's resistance to shrinkage. Reactions between the cement paste and the aggregate can either improve or harm the bond between the two and consequently, the concrete's quality.


1-7. These substances are added to the concrete mixture to accelerate or retard the initial set, improve workability, reduce water requirements, increase strength, or otherwise alter concrete properties. They usually cause a chemical reaction within the concrete. Admixtures are normally classified into accelerators, retardants, air-entraining agents, workability agents, dampproofing and permeability-reducing agents, pozzolans, color pigments, and miscellaneous materials. Many admixtures fall into more than one classification.


1-8. Concrete has a great variety of applications; it not only meets structural demands but lends itself readily to architectural treatment. In buildings, concrete is used for footings, foundations, columns, beams, girders, wall slabs, and roof units--in short, all important building elements. Other important concrete applications are in road pavements, airport runways, bridges, dams, irrigation canals, water-diversion structures, sewage-treatment plants, and water-distribution pipelines. A great deal of concrete is used in manufacturing masonry units such as concrete blocks and concrete bricks.


1-9. Concrete and cement are among the most important construction materials. Concrete is fireproof, watertight, economical, and easy to make. It offers surface continuity (absence of joints) and solidity; it will bond with other materials. Concrete is usually locally available worldwide.


1-10. Certain limitations of concrete cause cracking and other structural weaknesses that detract from the appearance, serviceability, and useful life of concrete structures. Listed below are some principal limitations and disadvantages of concrete.

Low Tensile Strength

1-11. Concrete members subject to tensile stress must be reinforced with steel bars or mesh to prevent cracking and failure.

Thermal Movements

1-12. During setting and hardening, the heat of hydration raises the concrete temperature and then it gradually cools. These temperature changes can cause severe thermal strains and early cracking. In addition, hardened concrete expands and contracts with changes in temperature (at roughly the same rate as steel); therefore, expansion and contraction joints must be provided in many types of concrete structures to prevent failures.

Drying Shrinkage and Moisture Movements

1-13. Concrete shrinks as it dries and as it hardens. It expands and contracts with wetting and drying. These movements require that control joints be provided at intervals to avoid unsightly cracks. To prevent drying shrinkage in newly placed concrete, its surface is kept moist continuously during the curing process. Moisture is applied when the concrete is hard enough so as not to damage the concrete's surface.


1-14. Concrete deforms gradually (creeps) under load. This deformation does not recover completely when the load is removed.


1-15. Even the best quality concrete is not entirely impervious to moisture. Concrete normally contains soluble compounds that are leached out in varying amounts by water, unless properly constructed joints allow water to enter the mass. Impermeability is particularly important in reinforced concrete--the concrete must prevent water from reaching the steel reinforcement.


1-16. The unit of measure for concrete is cubic foot (cu ft). Thus, a standard sack of portland cement weighs 94 pounds and equals 1 loose cubic foot. FAs and CAs are measured by loose volume, whereas water is measured by the gallon. Concrete is usually referred to by cubic yards (cu yd)



1-17. Plastic Concrete is a concrete in a relatively fluid state that is readily molded by hand, like a lump of modeling clay. A plastic mix keeps all the grains of sand and the pieces of gravel or stone encased and held in place (homogeneous). The degree of plasticity influences the quality and character of the finished product. Significant changes in the mix proportions affect plasticity. Desirable properties of plastic concrete are listed below.


1-18. Workability is the relative ease or difficulty of placing and consolidating concrete in the form. It is largely determined by the proportions of FAs and CAs added to a given quantity of paste. One characteristic of workability is consistency, which is measured by the slump test (see Appendix B). A specific amount of slump is necessary to obtain the workability required by the intended conditions and method of placement. A very stiff mix has a low slump and is desirable for many uses, although difficult to place in heavily reinforced sections. A more fluid mix is necessary when placing concrete around reinforcing steel.


1-19. Plastic concrete must be homogeneous and carefully handled to keep segregation to a minimum. For example, plastic concrete should not drop (free fall) more than 3 to 5 feet nor be transported over long distances without proper agitation.


1-20. The uniformity of plastic concrete affects both its economy and strength. It is determined by how accurate the ingredients are proportioned and mixed according to specifications. Each separate batch of concrete must be proportioned and mixed exactly the same to ensure that the total structural mass has uniform structural properties.


1-21. Hardened Concrete is the end product of any concrete design. The essential properties that it must have are strength, durability, and watertightness.


1-22. The concrete's ability to resist a load in compression, flexure, or shear is a measure of its strength. Concrete strength is largely determined by the ratio of water to cement in the mixture (pounds of water to pounds of cement). A sack of cement requires about 2 1/2 gallons of water for hydration. Additional water allows for workability, but too much water (a high water:cement [W/C] ratio) reduces the concrete's strength. The amount of water in economical concrete mixes ranges from 4 gallons minimum to 7 gallons maximum per sack.


1-23. Climate and weather exposure affect durability. Thus, the concrete's ability to resist the effects of wind, frost, snow, ice, abrasion, and the chemical reaction of soils or salts are a measure of its durability. As the W/C ratio increases, durability decreases correspondingly. Durability should be a strong consideration for concrete structures expected to last longer than five years. Air-entrained concrete (see paragraph 2-55) has improved freeze-thaw durability.


1-24. Tests show that the watertightness of a cement paste depends on the W/C ratio and the extent of the chemical-reaction process between the cement and water. The Corps of Engineers specifications for watertightness limit the maximum amount of water in concrete mixtures to 5.5 gallons per sack of cement (W/C = 0.48) for concrete exposed to fresh water and 5 gallons per sack (W/C = 0.44) for concrete exposed to saltwater. The watertightness of air-entrained concrete is superior to that of nonair-entrained concrete.


Form Design and Construction

4-1. An inherent property of concrete is that it can be transformed into any shape. The wet mixture is placed in forms constructed of wood, metal or other suitable material to harden or set. The form must be assembled with quality workmanship, holding to close dimensional tolerances. Formwork should be strong enough to support the concrete's weight and rigid enough to maintain its position and appearance. In addition, formwork must be tight enough to prevent the water seepage and designed to permit ready removal. Because the formwork for a concrete structure constitutes a considerable item in the cost of the completed structure, particular care should be exercised in its design. It is desirable to maintain a repetition of identical units so that the forms may be removed and reused at other locations with a minimum amount of labor.



4-2. Formwork holds concrete until it sets, produces the desired shapes, and develops a desired surface finish. Forms also protect concrete, aid in curing, and support any reinforcing bars or conduit embedded within the concrete. Because formwork can represent up to one-third of a concrete structure's total cost, this phase of a project is very important. The nature of the structure, availability of equipment and form materials, anticipated reuse of the forms, and familiarity with construction methods all influence the formwork design. To design forms, you must know the strength of the forming materials and the loads they support. You must also consider the concrete's final shape, dimensions, and surface finish.


4-3. Forms must be tight, rigid, and strong. Loose forms permit either loss of cement, resulting in honeycomb, or loss of water causing sand to streak. Brace forms enough to align them and to strengthen them enough to hold the concrete. Take special care in bracing and tying down forms used for such configurations as retaining walls that are wide at the bottom and taper toward the top. The concrete in this and other types of construction, such as the first pour for walls and columns, tends to lift the form above its proper elevation. To reuse forms, make them easy to remove and replace without damage.


4-4. Forms are generally made from four materials--wood, metal, earth, and fiber.


4-5. Wood materials are the most common form materials by far, because they are economical, easy to produce and handle, and can adapt to many shapes. For added economy, you can reuse form lumber for roofing, bracing, and similar purposes. Soft wood, such as pine, fir, and spruce, makes the best and most economical form lumber because it is light, easy to work with, and available almost everywhere. Form lumber must be straight, structurally sound, strong, and only partially seasoned. Kiln-dried lumber tends to swell when soaked with water from the concrete. If the form is tightly jointed, the swelling can cause bulging and distortion. When using green lumber, either allow for shrinkage or keep the forms wet until the concrete is in place. Lumber that contacts concrete should be finished at least on one side and on both edges. The edges can be square, shiplap, or tongue and groove. The last finish makes a more watertight joint and helps prevent warping. Use plywood identified for use in concrete forms for wall and floor forms if it is made with waterproof glue. Plywood is more warp-resistant and can be reused more often than lumber. It is available in thickness of 1/4, 3/8, 9/16, 5/8, and 3/4 inch, and in widths up to 48 inches. The 5/8 and 3/4 inch thicknesses are more economical because the thinner sections require solid backing to prevent deflection. However, the 1/4 inch thickness is useful for curved surfaces. Although longer lengths are available, 8-foot plywood is the most common.


4-6. Metal materials are used for added strength or when a construction will be duplicated at more than one location. They are initially more expensive than wood forms but are more economical in the long run if reused often enough. Steel forms are common for large, unbroken surfaces such as retaining walls, tunnels, pavements, curbs, and side­walks. They are especially useful for sidewalks, curbs, pavements, and precast-concrete operations because you can use them many times.


4-7. Earth materials are acceptable in subsurface construction if the soil is stable enough to retain the desired concrete shape. The advantages of earth forms are that they require less wood construction and resist settling better than other types of forms. Their obvious disadvantages are rough surface finish and the requirement for more excavation. Therefore, earth forms are generally restricted to footings and foundations.


4-8. Fiber forms are prefabricated and are filled with waterproofed cardboard and other fiber materials. Successive layers of fiber are first glued together and then molded to the desired shape. Fiber forms are ideal for round concrete columns and other applications where preformed shapes are feasible because they require no form fab­rication at the job site and thus save considerable time.


4-9. Forms are assembled and used to make walls. Figure 4-1 shows the basic parts of a wood form for panel walls.

Figure 4-1. Wood form for a concrete panel wall


4-10. Sheathing forms the ver­tical surfaces of a concrete wall but runs horizontally itself. The sheathing edges and the side that contacts the concrete should be finished as smooth as possible, especially for an exposed final concrete surface. The sheathing must also be watertight. Sheathing made from tongue-and-groove lumber gives the smoothest and most watertight concrete surface. Plywood or fiber-based hardboard can also be used.


4-11. The weight of the plastic concrete will cause the sheathing to bulge if it's not reinforced by studs. Therefore, vertical studs add rigidity to the wall form. The studs are made from single 2 by 4s or 2 by 6s.


4-12. Wales reinforce the studs when they extend upward more than 4 or 5 feet. They should be made from doubled 2 by 4s or 2 by 6s, and are lapped at the form corners to add rigidity. Double wales not only reinforce the studs but also tie prefabricated panels together and keep them aligned.


4-13. Although braces are neither part of the form design nor considered as providing any additional strength, they help stabilize the form. The most common brace is a combination of a diagonal member and a horizontal member nailed to a stake at one end and to a stud or wale at the other end. The diagonal member makes a 20- to 60-degree angle with the horizontal member. To add more bracing, place vertical members (strongbacks) behind the wales or in the angle formed by intersecting wales.


4-14. Spreaders are small pieces of wood placed between the sheathing panels to maintain the proper wall thickness between them. They are cut to the same length as the wall thickness. Spreaders can be removed easily before the concrete hardens since friction, not fasteners, hold them in place. Attach a wire securely through the spreaders, as shown in Figure 4-1 to pull them out when the fresh concrete exerts enough pressure against the sheathing to permit removal.


4-15. Tie wires secure the formwork against the lateral pressure of the plastic concrete. They always have double strands.


4-16. Tie-rods sometimes replaces tie wires in the same function because working with rods are easier.


4-17. Figure 4-2 shows the basic parts of a wood form for a concrete column.

Figure 4-2. Form for a concrete column and footing


4-18. Sheathing runs vertically in column forms to reduce the number of saw cuts. Nail the corner joints firmly to ensure watertightness.


4-19. A yoke is a horizontal re­inforcement in the form of a rectangle that wraps around a column to prevent the plastic concrete from distorting the form. It serves the same purpose as a stud in a wall form. You can lock yokes in place using the sheathing-, scab-, or bolt-type yoke lock. The small horizontal dimensions of a column do not require vertical reinforcement.


4-20. Battens are narrow strips of boards that are placed directly over the joints to fasten several pieces of vertical sheathing together.


4-21. Footing forms are shown in Figure 4-2 and are discussed in paragraph 4-49.



4-22. Forms are the molds that hold the plastic concrete and support it until it hardens. They must keep deflections within acceptable limits, meet dimensional tolerances, prevent paste leakage, and produce a final product that meet appearance needs. Therefore, strength, rigidity, and watertightness are the most important form design considerations. In addition, forms must support all weights and stresses to which they are subject, including the dead load (DL) of the forms; the weight of people, equipment, and materials that transfers to the forms; and any impact due to vibration. Although these factors vary with each project, do not neglect any of them when designing a form. Ease of erection and removal are other important factors in economical form design. Sometimes you may want to consider using platforms and ramp structures that are independent of the formwork because they prevent form displacement due to loading, as well as impact shock from workers and equipment.


4-23. Concrete is in a plastic state when placed in the designed form; therefore, it exerts hydrostatic pressure on the form. The basis of form design is to offset the maximum pressure developed by the concrete during placing. The pressure depends on the rate of placing and the ambient temperature. The rate of placing affects pressure because it determines how much hydrostatic head builds up in the form. The hydrostatic head continues to increase until the concrete takes its initial set, usually in about 90 minutes. However, because the initial set takes more time at low ambient temperatures, consider the ambient temperature at the time of placement. Knowing these two factors (rate of placement and ambient temperature) plus the specified type of form material, calculate a tentative design.


4-24. It is best to design forms following a step-by-step procedure. Use the following steps to design a wood form for a concrete wall.

Step 1. Determine the materials needed for sheathing, studs, wales, braces, and tie wires or tie-rods.

Step 2. Determine the mixer output by dividing the mixer yield by the batch time. Batch time includes loading all ingredients, mixing, and unloading. If you will use more than one mixer, multiply the mixer output by the number of mixers.

Step 3. Determine the area enclosed by the form.

Plan area (sq ft) = Length (L) x Width (W)

Step 4. Determine the rate (vertical feet per hour) of placing (R) the concrete in the form by dividing the mixer output by the plan area.

NOTE: If using wood for an economical design, try to keep R < 5 feet per hour.

Step 5. Estimate the placing temperature of the concrete.

Step 6. Determine the maximum concrete pressure (MCP) using the rate of placing (see Figure 4-3 or the formula above the figure). Draw a vertical line from the rate of placing until it intersects the correct concrete-temperature line. Read left horizontally from the point of intersection to the left margin of the graph and determine the MCP in 100 pounds per square foot.

Figure 4-3. MCP graph

Step 7. Find the maximum stud spacing (MSS) in inches. Use Table 4-1 for board sheathing orTable 4-2 for plywood sheathing. Refer to the column headed maximum concrete pressure (MCP) and find the value you have for the MCP. If the value falls between two values in the column, round up to the nearest given value. Move right to the column identified by the sheathing thickness. (Always use the strong way for plywood when possible). This number is the MSS in inches.

Table 4-1. Maximum stud (joist) spacing for board sheathing

Maximum Concrete
Pressure, in
Pounds per Square
Nominal Thickness of S4S Boards, in Inches
1 1 1/4 1 1/2 2
75 30 37 44 50
100 28 34 41 47
125 26 33 39 44
150 25 31 37 42
175 24 30 35 41
200 23 29 34 39
300 21 26 31 35
400 18 24 29 33
500 16 22 27 31
600 15 20 25 30
700 14 18 23 28
800 13 17 22 26
900 12 16 20 24
1,000 12 15 19 23
1,100 11 15 18 22
1,200 11 14 18 22
1,400 10 13 16 20
1,600 9 12 15 18
1,800 9 12 14 17
2,000 8 11 14 16
2,200 8 10 13 16
2,400 7 10 12 15
2,600 7 10 12 14
2,800 7 9 12 14
3,000 7 9 11 13

Table 4-2. Maximum stud (joist) spacing for plywood sheathing, in inches

in Pounds
Strong Way - 5-Ply Sanded
Face, Grain Perpendicular to
the Stud
Weak Way - 5-Ply Sanded Face,
Grain Parallel to the Stud
1/2 5/8 3/4 1
(7 ply)
1/2 5/8 3/4 1
(7 ply)
75 20 24 26 31 13 18 23 30
100 18 22 24 29 12 17 22 28
125 17 20 23 28 11 15 20 27
150 16 19 22 27 11 15 19 25
175 15 18 21 26 10 14 18 24
200 15 17 20 25 10 13 17 24
300 13 15 17 22 8 12 15 21
400 12 14 16 20 8 11 14 19
500 11 13 15 19 7 10 13 18
600 10 12 14 17 6 9 12 17
700 10 11 13 16 6 9 11 16
800 9 10 12 15 5 8 11 15
900 9 10 11 14 4 8 9 15
1,000 8 9 10 13 4 7 9 14
1,100 7 9 10 12 4 6 8 12
1,200 7 8 10 11 - 6 7 11
1,300 6 8 9 11 - 5 7 11
1,400 6 7 9 10 - 5 6 10
1,500 5 7 9 9 - 5 6 9
1,600 5 6 8 9 - 4 5 9
1,700 5 6 8 8 - 4 5 8
1,800 4 6 8 8 - 4 5 8
1,900 4 5 8 7 - 4 4 7
2,000 4 5 7 7 - - 4 7
2,200 4 5 6 6     4 6
2,400 - 4 5 6     4 6
2,600 - 4 5 5     - 5
2,800 - 4 4 5     - 5
3,000 - - 4 5     - 5

Step 8. Determine the uniform load on a stud (ULS) by multiplying the MCP by the stud spacing divided by 12 inches per foot.


MCP = maximum concrete pressure, in pounds per square foot

MSS = maximum stud spacing

ULS = uniform load stud, in pounds per linear foot

Step 9. Determine the maximum wale spacing (MWS) using Table 4-3. Refer to the column headed uniform load and find the value for the ULS. If the value falls between two values in the column, round it up to the nearest given value. Move right to the column identified by the size of the stud you are using. This number is the MWS in inches.

Table 4-3. Maximum spacing, in inches, for whales, ties, stringers, and 4" x 4 or larger shores where member to be supported is a SINGLE menber

Uniform Load in
Pounds per
Linear Foot
Supported Members Size (S4S)*
2 x 4 2 x 6 3 x 6 4 x 4 4 x 6
100 60 95 120 92 131
125 54 85 440 80 124
150 49 77 100 75 118
175 45 72 93 70 110
200 42 67 87 65 102
225 40 62 82 61 97
250 38 60 77 58 92
275 36 57 74 55 87
300 35 55 71 53 84
350 32 50 65 49 77
400 30 47 61 46 72
450 28 44 58 43 68
500 27 41 55 41 65
600 24 38 50 37 59
700 22 36 46 35 55
800 21 33 43 32 51
900 20 31 41 30 48
1,000 19 30 38 29 46
1,200 17 27 35 27 42
1,400 16 25 33 25 39
1,600 15 23 31 23 36
1,800 14 22 29 22 34
2,000 13 21 27 21 32
2,200 13 20 26 20 31
2,400 12 19 25 19 30
2,600 12 19 24 18 28
2,800 11 18 23 17 27
3,000 11 17 22 17 26
3,400 10 16 21 16 25
3,800 10 15 20 15 23
4,500 9 14 18 13 21
*S4S indicates surfaced four sides.

Step 10. Determine the uniform load on a wale (ULW) by multiplying the MCP by the MWS and dividing by 12 inches per foot.


MCP = maximum concrete pressure, in pounds per square foot

MWS = maximum wale spacing, in inches, divided by 12 inches per foot

ULW = uniform load on wale, in pounds per linear foot

Step 11. Determine the tie spacing based on the ULW using Table 4-3 or Table 4-4 (depending on type of wale, either single or double). Refer to the column headed Uniform Load and find the value for the ULW. If the value falls between two values in the column, round it up to the nearest given value. Move right to the column identified by the size of wale you are using. This number is the maximum tie spacing, in inches, based on wale size.

Table 4-4. Maximum spacing, in inches, for ties and 4" x 4" or larger shores where member to be supported is a double member

Load, in
Pounds per
Linear Foot
Supporting Member Size (S4S)
2 x 4 2 x 6 3 x 6 4 x 4 4 x 6
100 85 126 143 222 156
125 76 119 135 105 147
150 70 110 129 100 141
175 64 102 124 96 135
200 60 95 120 92 131
225 57 89 116 87 127
250 54 85 109 82 124
275 51 84 104 78 121
300 49 77 100 75 118
350 46 72 93 70 110
400 43 67 87 65 102
450 40 63 82 61 97
500 38 60 77 58 92
600 35 55 71 53 81
700 32 51 65 49 77
800 30 47 61 46 72
900 28 44 58 43 68
1,000 27 43 55 41 65
1,200 25 39 50 38 59
1,400 23 36 46 35 55
1,600 21 34 43 33 51
1,800 20 32 41 31 48
2,000 19 30 39 29 46
2,200 18 29 37 28 44
2,400 17 27 36 27 42
2,600 17 26 34 26 40
2,800 16 25 33 25 39
3,000 15 24 32 24 38
3,400 14 23 30 22 35
3,800 14 21 28 21 33
4,500 12 20 25 19 30

Step 12. Determine the tie spacing based on the tie strength by dividing the tie breaking strength by the ULW. If the breaking strength of the tie is unknown, use Table 4-5 to find the breaking loads for a double-strand wire and tie-rods (found in the Army supply system).


Tie wire or tie-rod = strength = average breaking load (see Table 4-5)

ULW = uniform load on wales, in pounds per square foot

NOTE: If the result does not equal a whole number, round the value down to the next whole number.

Table 4-5. Average breaking load of tie material, in pounds

Steel Wire
Size of Wire Gage
Minimum Breaking
Double Strand, in
8 1,700
9 1,420
10 1,170
11 930
Size of Wire Gage
Minimum Breaking
12 1/2 950
13* 660
13 1/2 950
14 650
15 1/2 850
Description Minimum Breaking
Load, in Pounds
Snap ties 3,000
Pencil roads 3,000
*Single-strand barbwire

Step 13. Select the smaller of the tie spacing as determined in steps 11 and 12.

Step 14. Install tie wires at the intersection of studs and wales. Reduce the stud spacing (step 7) or the tie spacing (step 13) to conform with this requirement. tie-rods may be placed along the wales at the spacing (determined in step 13) without adjusting the studs. Place the first tie at one-half the maximum tie spacing from the end of the wale.

Step 15. Determine the number of studs on one side of a form by dividing the form length by the MSS. Add one to this number and round up to the next integer. The first and last studs must be placed at the ends of the form, even though the spacing between the last two studs may be less than the maximum allowable spacing.

NOTE: The length of the form is in feet. The stud spacing is in inches.

Step 16. Determine the number of wales for one side of a form by dividing the form height by the MWS, and round up to the next integer. Place the first wale one-half of the maximum space up from the bottom and place the remaining wales at the MWS.

Step 17. Determine the time required to place the concrete by dividing the height of the form by the rate of placing.


4-25. Design a form for a concrete wall 40 feet long, 2 feet thick, and 10 feet high. An M919 concrete mobile mixer is available and the crew can produce and place a cubic yard of concrete every 10 minutes. The concrete placing temperature is estimated at 70 F. The form materials are 2 by 4s, 1-inch board sheathing, and number 9 black annealed wire. The solution steps are as follows:

Step 1. Lay out available materials.

Studs: 2 x 4 (single)

Wales: 2 x 4 (double)

Sheathing: 1-inch board

Ties: Number 9 wire

Step 2. Calculate the production rate.

Step 3. Calculate the plan area of the form.

Step 4. Calculate the rate of placing.

Step 5. Determine the concrete-placing temperature.

Temperature = 70o

Step 6. Determine the MCP (refer to Figure 4-3).

MCP = 400 pounds per square foot

Step 7. Determine the MSS (refer to Table 4-1).

MSS = 18 inches

Step 8. Calculate the ULS.

Step 9. Determine the MWS (refer to Table 4-3).

MWS = 24 inches

Step 10. Calculate the ULW.

Step 11. Determine the tie-wire spacing based on wale size (refer to Table 4-4).

Tie-wire spacing = 30 inches.

Step 12. Determine the tie-wire spacing based on wire strength (referring to Table 4-5, breaking strength of number 9 wire = 1,420 pounds).

Step 13. Determine the maximum tie spacing.

Tie spacing = 21 inches

Step 14. Reduce the tie spacing to 18 inches since the maximum tie spacing is greater than MSS; tie at the intersection of each stud and double wale.

Step 15. Calculate number of studs per side.

Step 16. Calculate the number of double wales per side.

Step 17. Estimate the time required to place concrete.


4-26. Design the form for a concrete wall 40 feet long, 2 feet thick, and 10 feet high. An M919 concrete mobile mixer is available and the crew can produce and place a cubic yard of concrete every 7 minutes. The concrete placing temperature is estimated to be 70 F. The materials for constructing the form are 2 by 4s, 3/4-inch thick plywood, and 3,000-pound (breaking strength) snap ties. The following steps will be used:

Step 1. Lay out available needed materials.

Studs: 2 x 4 (single)

Wales: 2 x 4 (doubled)

Sheathing: 3/4-inch plywood (strong)

Ties: Snap ties (3,000 pounds)

Step 2. Calculate the production rate.

Step 3. Calculate the plan area of form.

Step 4. Calculate rate the of placing.

Step 5. Determine the concrete placing temperature.

Temperature = 70 F

Step 6. Determine the MCP (refer to Figure 4-3).

MCP = 500 pounds per square foot

Step 7. Determine the MSS (refer to Table 4-2).

MSS = 15 inches

Step 8. Determine the ULS.

Step 9. Determine the MWS (refer to Table 4-3 using 700 pounds per foot load).

MWS = 22 inches

Step 10. Determine the ULW.

Step 11. Determine the tie spacing based on wale size (refer to Table 4-4, using 1,000 pounds per load).

Tie spacing = 27 inches

Step 12. Determine the tie spacing based on tie-rod strength (refer to Table 4-5).

Step 13. Determine the maximum tie spacing.

Tie spacing = 27 inches

Step 14. Insert the first tie-rod one-half the spacing from the end and one full spacing thereafter. Because tie-rods are being used, it is not necessary to adjust the tie/stud spacing.

Step 15. Calculate the number of studs per side.

Step 16. Calculate the number of double wales per side.

Step 17. Estimate the time required to place concrete.


4-27. Braces are used against wall forms to keep them in place and in alignment and to protect them from mishaps due to external forces (wind, personnel, equipment, vibration, accidents). An equivalent force due to all of these forces (the resultant force) is assumed to be acting uniformly along the top edge of the form in a horizontal plane. For most military applications, this force is assumed to be 12.5 times the wall height, in feet. As this force can act in both directions, braces to be used should be equally strong in tension as in compression, or braces should be used on both sides of the wall forms. The design procedure is based on using a single row of braces and assumes that strong, straight, seasoned lumber will be used and that the braces are properly secured against the wall forms and the ground (both ends are secured). Once we know the height of the wall to be built and have selected a material (2 inches or greater) for the braces, we need to determine the maximum safe spacing of these braces (center-to-center) that will keep the formwork aligned.


4-28. The following terms are used in bracing for a form wall. See Figure 4-4.

  • LB = total length, in feet, of the brace member from end connection to end connection.
  • Lmax = the maximum allowable unsupported length of the brace, in feet, due to buckling and bending.
  • For all 2-inch material, Lmax = 6 1/4 feet; for all 4-inch material, L max = 14 1/2 feet.
  • L = the actual unsupported length, in feet, of the brace used.
  • h = the overall height, in feet, of the wall form.
  • y = the point of application of the brace on the wall form, measured in feet from the base of the form.
  • 0 = the angle, in degrees, that the brace makes with the horizontal shoe brace. For the best effect, the angle should be between 20 and 60 degrees.
  • J = a factor to be applied which includes all constant values (material properties and assumed wind force). It is measured in feet4, see Table 4-6.
  • Smax = the maximum safe spacing of braces (feet), center-to-center, to support the walls against external forces.

  • cos = cosine: the ratio of the distance from the stake to the wall (x) divided by the length of the brace (LB.)
  • sin = sine: the ratio of the height of the brace (y) divided by the length of the brace (LB.)

Figure 4-4. Elements of diagonal bracing

Table 4-6. J factor

Material, in Inches J, In Feet4
2 x 4 2,360
2 x 6 3,710
2 x 8 4,890
2 x 10 6,240
2 x 12 7,590
4 x 4 30,010


4-29. The design procedure can best be explained by the example problem that follows:

Step 1. Determine the spacing of braces for a wall 10 feet high. Use 2-by 6- inch by 10-foot material, attached 6 feet from the bottom of the form. The following selected materials are given:

  • J = 3,710 feet4 (from Table 4-6)
  • Lmax = 6 1/4 feet (because of the 2-inch material)
  • LB = 10 feet
  • h = 10 feet (from example problem)
  • y = 6 feet (from example problem)

Step 2. Determine the angle of placement, 0.

0 = sin-1 (.600) = 37o

Step 3. Determine the L which is the actual unsupported length of brace. Since the Lmax for all 2-inch material is 6 1/4 feet and the brace in this problem is 10 feet long, we will have to use something to support the braces (usually a 1 by 4 or a 1 by 6). The best position for this support would be in the middle of the brace, thus giving L = 5 feet.

Step 4. Determine the Smax from the formula.

4-30. Using 2- by 6- inches by 10-feet brace applied to the top edge of the wall form at y = 6 feet, place these braces no further apart than 7 feet. After the braces are properly installed, connect all braces to each other at the center so deflection does not occur.

NOTE: This procedure determines the maximum safe spacing of braces. There is no doctrine that states the braces must be placed 7 feet apart--they can be less.


4-31. To fully understand the procedure, the following points lend insight to the formula.

  • Derivation of the formula has a safety factor of 3.
  • For older or green lumber, reduce Smax according to judgment.
  • For maximum support, attach braces to the top edge of the forms (or as closely as practicable). Also, better support will be achieved when 0 = 45o
  • Remember to use intermediate supports whenever the length of the brace (LB) is greater than Lmax.
  • Whenever there are choices of material, the larger size will always carry greater loads.
  • To prevent overloading the brace, place supports a minimum of 2 feet apart for all 2-inch material and 5 feet apart for all 4-inch material. This is necessary to prevent crushing of the brace.


4-32. There may be instances where a concrete slab will have to be placed above the ground such as bunker and culvert roofs. Carefully consider the design of the formwork because of the danger of failure caused by the weight of plastic concrete and the live load (LL) of equipment and personnel on the forms. The overhead slab form design method employs some of the same figures used in the wall-form design procedure.


4-33. The following terms are used in the form design (see Figure 4-5).

  • Sheathing. Shapes and holds the concrete. Plywood or solid sheet metal is best for use.
  • Joists. Supports the sheathing against deflection. Performs the same function as studs in a wall form. Use 2-, 3-, or 4-inch thick lumber.
  • Stringers. Supports the joists against deflection. Performs the same function as wales in a wall form. Use 2-inch thick or larger lumber. Stringers do not have to be doubled as wales are.
  • Shores. Supports the stringers against deflection. Performs the same functions as ties in a wall form and also supports the concrete at the desired elevation above the ground. Lumber at least as large as the stringer should be used, but never use lumber smaller than 4 by 4s.
  • Lateral bracing. Bracing may be required between adjacent shores to keep shores from bending under load. Use 1 by 6s or larger material for bracing material.
  • Cross bracing. Cross bracing will always be required to support the formwork materials.
  • Wedges. Wood or metal shims used to adjust shore height
  • Mudsill. Board which supports shores and distributes the load. Use 2-inch thick or larger lumber.

Figure 4-5. Typical overhead slab forms


4-34. Use the following steps in determining form design:

Step 1. Lay out and specify the materials you will be using for the construction of the overhead roof slab. It is important that anyone using your design will know exactly the materials to use for each of the structural members.

Step 2. Determine the maximum total load (TL) the formwork will have to support.

The LL of materials, personnel, and equipment is estimated to be 50 pounds per square foot unless the formwork will support engine-powered concrete buggies or other power equipment. In this case, a LL of 75 pounds per square foot will be used. The LL is added with the DL of the concrete to obtain the maximum TL. The concrete's DL is obtained using the concrete's unit weight of 150 pounds per cubic foot. The formulas are--

TL = LL + DL

LL = 50 lb/sq ft, or 75 lb/sq ft with power equipment

Step 3. Determine the maximum joist spacing. Use Table 4-1, or Table 4-2 and determine the joist spacing based on the sheathing material used. This is the same procedure used in determining the MSS for wall-form design. Use the maximum TL in place of the MCP.

Step 4. Calculate the uniform load on the joists (ULJ). The same procedure is used as determining uniform loads on structural members in wall-form design.

Step 5. Determine the maximum stringer spacing. Use Table 4-3 and the ULJ calculated in step 4. Round this load up to the next higher load located in the left column of the table. Read right to the column containing the lumber material used as the joist. This is the member to be supported by the stringer. The value at this intersection is the on-center (OC) spacing of the stringer.

Step 6. Calculate the uniform load on the stringer (ULSstr).

Step 7. Determine the maximum shore spacing the following two ways:

  • Determine the maximum shore spacing based on the stringer strength. Use Table 4-3 orTable 4-4 (depending on the type of stringer) and the ULSstr, rounded to the next higher load shown in the left column of the table. Read right to the stringer material column. This intersection is the maximum OC spacing of the shore required to ensure the stringer is properly supported.
  • Determine the maximum shore spacing based on the allowable load. This determination is dependent on both the shore strength and the end bearing of the stringer on the shore. Using Tables 4-7 and Table 4-8, select the allowable load on the shore both ways as follows:

(NOTE: The unsupported length is equal to the height above the sill--sheathing thickness, joist thickness, and stringer thickness. This length is then rounded up to the next higher table value.)

Table 4-7. Allowable load (in pounds) on wood shores, based on shore strength

Nominal Lumber
Size, in Inches
4 x 4 4 x 6 6 x 6
Length, in Feet
4 9,900 9,200 15,300 14,400 23,700 22,700
5 9,900 9,200 15,300 14,400 23,700 22,700
6 9,900 9,200 15,300 14,400 23,700 22,700
7 8,100 7,000 12,500 11,000 23,700 22,700
8 6,200 5,400 9,600 8,400 23,700 22,700
9 4,900 4,200 7,600 6,700 23,700 22,700
10 4,000 3,400 6,100 5,000 23,000 21,000
11 3,300 2,800 5,100 4,500 19,000 17,300
12 2,700 2,400 4,300 3,700 16,000 14,600
13 2,300 2,000 3,600 3,200 13,600 12,400
    l/d = 50   l/d = 50    
14 2,000 1,700 3,100 2,800 11,700 10,700
  l/d = 50   l/d = 50      
15 1,800   2,700   10,200 9,300
          9,000 8,200
          7,900 7,300
          7,100 6,500
          6,400 5,800
          5,700 5,200


1. The above table values are based on wood members with the following characteristics strength:
Compression parallel to gram = 750 psi.
E = 1,100,000 psi.
2. R indicates rough lumber.

Table 4-8. Allowable load on specified shores, in pounds, based on bearing stresses where the maximum shore area is in contact with the supported member

Nominal Lumber
Size, in Inches
4 x 4 4 x 6 6 x 6
C ^ of
250 3,300 3,100 5100 4800 7900 7600
350 4600 4300 7100 6700 11100 10600
385 5100 4700 7800 7400 12200 11600
400 5300 4900 8200 7700 12700 12100


1. When the compression perpendicular to the grain of the member being supported is unknown, assume the most critical C is ^ to the grain.
2. R indicates rough lumber.
3. S4S indicates surfaced on four sides.

- First, determine the allowable load based on the shore strength. Select the shore material dimensions and determine the unsupported length in feet of the shore. See Table 4-7. The allowable load for shore is given in pounds at the intersection. Read down the left column to the unsupported length of the shore, then read right to the column of the size material used as the shore.

- Second, determine the allowable load based on end bearing area. Select the size of the shore material and the compression C perpendicular (^) to the grain of the stringer. If the C ^ to the grain is unknown, use the lowest value provided in Table 4-8. Read down the left column to the C ^ to the grain of the stringer material and then right of the column of the shore material. The allowable load between the stringer and the shore will be in pounds.

- Compare the two loads just determined and select the lower as the maximum allowable load on the shore to be used in the formula below.

Calculate shore spacing by the following formula:

Step 8. Determine the most critical shore spacing. Compare the shore spacing based on the stringer strength in step 7, with the shore spacing based on the allowable load in step 7. Select the smaller of the two spacings.

Step 9. Check the shore bracing.

Verify that the unbraced length (l) of the shore (in inches) divided by the least dimension (d) of the shore does not exceed 50. If l/d exceeds 50, the lateral and cross bracing must be provided. Table 4-7 indicates the l/d > 50 shore lengths and can be used if the shore material is sound and unspliced. It is good engineering practice to provide both lateral and diagonal bracing to all shore members if material is available.


4-35. Design the form for the roof of a concrete water tank to be 6 inches thick, 20 feet wide, and 30 feet long. The slab will be constructed 8 feet above the floor (to the bottom of the slab). Available materials are 3/4-inch plywood and 4 by 4 (S4S) (surfaced on four sides) lumber. Mechanical buggies will be used to place concrete. Use the following steps in design:

Step 1. Lay out available materials for construction.

Sheathing: 3/4-inch plywood (strong way)
Joists: 4 x 4 (S4S)
Shores: 4 x 4 (S4S)
Stringers: 4 x 4 (S4S)

Step 2. Determine the maximum TL.

LL = personnel and equipment = 75 lb/sq ft

TL = DL + LL

TL = 75 lb/sq ft + 75 lb/sq ft

TL = 150 lb/sq ft

Step 3. Determine the maximum joist spacing using Table 4-2.

3/4-inch plywood (strong way) and TL = 150 pounds per square foot

Joist spacing = 22 inches

Step 4. Calculate the ULJ.

Step 5. Determine the maximum stringer spacing using Table 4-3.

Load = 275 pounds per foot

Joist material = 4 x 4

Maximum stringer spacing = 55 inches

Step 6. Calculate the ULSstr.

Step 7. Determine the maximum shore spacing based on stringer strength. Use the maximum shore spacing shown in Table 4-3 single member stringers.

  • Load = 687.5 pounds per foot (round up to 700 pounds per foot)
  • Stringer material = 4 x 4 (S4S)
  • Maximum shore spacing = 35 inches, based on stringer strength

Step 8. Determine shore spacing based on allowable load. This determination is based on both the shore strength and end bearing stresses of the stringer to the shore. Determine both ways as follows:

  • Allowable loads based on shore strength are shown in Table 4-7.

Unsupported length = 8 feet - 3/4 inch - 3 1/2 inches - 3 1/2 inches = 7 feet 4 1/4 inches (round up to 8 feet).

For an 8-foot 4 by 4 (S4S), the allowable load = 5,400 pounds, based on shore strength.

  • For an allowable load based on end bearing stresses see Table 4-8. Since we do not know what species of wood we are using, we must assume the worst case. Therefore, the (C ^) to the grain = 250, and the allowable load for a 4 by 4 (S4S) = 3,100 pounds based on end bearing stresses.

Select the most critical of the two loads determined.

Since the (C ^) is less than the allowable load on the shore perpendicular to the grain (II), 3,100 pounds is the critical load.

Calculate the shore spacing as follows:

Step 9. Select the most critical shore spacing. The spacing determined in step 7 is less than the spacing determined in step 8; therefore, the shore spacing to be used is 35 inches.

Step 10. Check shore deflection.

Unsupported length = 8 feet - 3/4 inch - 3 1/2 inch - 3 1/2 inches

= 7 feet 4 1/4 inches

= 88.25 inches

d = least dimension of 4 x 4 (S4S) lumber = 3.5 inches

NOTE: Lateral bracing is not required. Cross bracing is always required.

4-36. Summary of materials needed for construction.

Sheathing: 3/4-inch plywood (strong way)
Joists: 4 x 4 (S4S) lumber spaced 22 inches OC
Stringer: 4 x 4 (S4S) lumber spaced 55 inches OC
Shores: 4 x 4 (S4S) lumber spaced 35 inches OC
Lateral braces: not required


4-37. Concrete slabs on grade are the most often constructed concrete projects by engineer units. Many slabs that are constructed fail because the thickness of the slab is not adequate. In other cases, the slab thickness is so excessive that materials and personnel are wasted in the construction. Use the following procedure, tables, and figures for the design of concrete slab thickness in the field to eliminate possible failure or wasted materials.


4-38. The following three points apply to the design thickness:

  • The minimum slab thickness will be 4 inches for class 1, 2, and 3 floors, as listed in Table 4-9.
  • Only the load area and the flexural strength required will be considered using this method. Whenever the loaded area exceeds 80 square inches, the soil-bearing capacity must be considered. When the load will be applied at the edges of the concrete slab, either thicken the edge by 50 percent and taper back to normal slab thickness at a slope of not more than 1 in 10 or use a grade beam to support the edge.
  • The controlling factor in determining the thickness of a floor on ground is the heaviest concentrated load the slab will carry. The load is usually the wheel load plus impact loading caused by the vehicle.

Table 4-9. Concrete floor classifications

Class Usual Traffic Use Special Consideration Concrete Finishing
1 Light foot Residential or tile-covered Grade for drainage; make plane for tile Medium steel trowel
2 Foot

Offices, churches, schools, hospitals

Ornamental residential

Nonslip aggregate; mix in surface

Color shake, special

Steel trowel; special finish for nonslip

Steel trowel, color, exposed aggregate; wash if aggregate is to be exposed

3 Light foot and pneumatic wheels Drives, garage floors, sidewalks for residences Crown; pitch joints
Air entrainment
Float, trowel, and broom
4 Foot and pneumatic wheels* Light industrial commercial Careful curing Hard steel trowel and brush for nonslip
5 Foot and wheel abrasive wear* Single-course industrial, integral topping Careful curing Special hard aggregate float and trowel
6 Foot and steel-tire vehicles - severe abrasion Bonded two-course, heavy industrial Base Textured surface and bond Surface leveled by screeding
Top Special aggregate and/or mineral or metallic surface treatment Special disc-type power floats with repeated steel troweling
7 Same as classes 3, 4, 5, 6 Unbonded topping Mesh reinforcing; bond breaker on old concrete surface; minimum thickness 2 1/2 inches  
*Under abrasive conditions on floor surface, the exposure will be much more severe and a higher quality surface will be required for class 4 and 5; for a class 6, two-course floor, a mineral or metallic aggregate monolithic surface treatment is recommended.


4-39. Use the following steps in design procedures for concrete slabs.

Step 1. Determine the floor classification. Use Table 4-9 with the usual traffic and use of the slab.

Step 2. Determine the minimum compressive strength. Using Table 4-10, read down the class of floors column until you find the floor classification selected. Read to the right and select the f 'c in psi. Note that this table gives the recommended slump range for the plastic concrete.

Table 4-10. Recommended slumps and compressive strengths

Class of Floors Slump Range, in inches Minimum Compressive
Strength, f 'c in Pounds
per Square Inch*Use
1 2-4 3,000
2 2-4 3,500
3 2-4 3,500
4 1-3 4,000
5 1-3 4,500
6 base 2-4 3,500
6 topping** 0-1 5,000 - 8,000
7 1-3 4,000

NOTE: These recommendations are specially for concrete made with normal-weight aggregate. For structural slabs, the requirements of ACI 318 and the contract documents should be met.

*Refer to the minimum compressive strength of cylinders made and tested according to applicable ASTM standards for 28 days. The average of any five consecutive strength tests of continuously moist-cured specimens representing each class of concrete should be equal to or greater than the specified strength.

**The cement content of the heavy-duty floor topping depends upon the severity of the abrasion. The minimum is 846 pounds per cubic yard.

Step 3. Determine the allowable flexural tensile stress f 't after the concrete f 'c is determined. Use the formula:

Step 4. Determine the equivalent static load (ESL). The expected impact loading is needed for this step. The impact loading is 25 percent more than the static load (SL) for the vehicles.

ESL = (1 + 25%) x SL

Step 5. Evaluate and correct the ESL if f 't is not equal to 300 psi. When calculating the allowable flexural tensile f 'c in step 4 above, an f 't was determined. If this f 't is not equal to 300 psi, then the ESL must be corrected based on a ratio between the standard (300 psi) and the actual f 't. This correction is necessary so that the standard thickness (see Figure 4-6) may be used to determine the required slab thickness. The procedure for correction is as follows:

Figure 4-6. Maximum wheel loads for industrial floors

Step 6. Determine the slab thickness. Using Figure 4-6, read up the left side until the TL is the same as the design CESL from 5 above. Read to the right until the loaded area (in square inches) for the slab design is intersected. The slab thickness can then be determined by interpolating between the slanted slab thickness lines on the figure. Round up to the next 1/4 inch.

Step 7. Determine the minimum cement content and recommended air content for structures subjected to freeze-thaw cycles, depending upon the maximum size of CA to be used.

4-42. The slab thickness design procedure is now complete, and with the accumulated information you should proceed to the mix design procedure as detailed in Chapter 3 of this manual.


4-40. Slab construction is often spoiled by improper construction practices that can be easily prevented. Forms for slabs on grades are relatively simple to construct. See Section III of this chapter. The following practices should always be employed for ensuring that the slab will hold up under service load.

  • Always use nonfrost susceptible (free-draining) material under the slab. Material such as silts and very fine sand expands under frost action if groundwater is present. Removing these types of soil and replacing them with a free-draining material (gravel or coarse sand) to one-half of the expected frost penetration, (in addition to providing adequate drainage at the edges of the structure), will prevent frost heave.
  • Always use some form of steel reinforcement. Welded-wire mesh is very desirable for preventing excessive cracking and preventing widening of cracks that do develop.
  • Always keep the slab moist and protect it from excessive heat and freezing for the required curing time. This will ensure the concrete is cured properly.


4-41. Determine the slab thickness for the floor of a wheeled-vehicle shop. The total weight on one wheel is 7,500 pounds and the loaded area equals 40 square inches. The surface will be exposed to foot and wheel traffic. Abrasive wear is expected. The maximum-size aggregate will be 1 inch.

Step 1. Determine the floor classification, see Class 5, Table 4-9.

Step 2. Determine the minimum compressive strength from Table 4-10.

Step 3. Determine the allowable flexural tensile stress.

Step 4. Determine the ESL.

ESL = (1 +.25) x SL
  = 1.25 x 7,500 = 9375 lbs

Step 5. Evaluate and correct the ESL if f 't 300 psi

Step 6. Determine the slab thickness from Figure 4-6.

Loaded area = 40 sq in

Slab thickness = 6.6 in

NOTE: Always round up to the next higher 1/4-inch thickness for convenience. Therefore, the thickness is rounded up to 6 3/4-inches.

4-42.The minimum cement content per cubic yard from, Table 4-11, with 1-inch maximum-size aggregate (MSA) is 520 pounds. Because the structure is a vehicle-shop floor, the air content may be less than the table allowance. The slab design information is now:

f 'c = 4,500 psi

Slab thickness = 6 3/4 inches

Minimum cement content = 520 lb/cu yd

Air content = 6%

Table 4-11. Minimum cement contents and percentages of entrained air

Maximum Size of
Coarse Aggregate
Minimum Cement
Content, in Pounds
per Cubic Yard
Air Content for
Shown in
1 1/2 470 5 + 1
1 520 6 + 1
3/4 540 6 + 1
1/2 590 7 1/2 + 1
3/8 610 7 1/2 + 1

NOTES: These mixtures are specially for concrete made with normal-weight aggregate; different mixtures may be needed for lightweight aggregate concrete. For structural slabs, the requirements of ACI 318 and the contract document must be met.

*Smaller percentages of entrained air can be used for concrete floors that will not be exposed to freezing and thawing or deicing. This may improve the workability of the concrete and the finish product.


4-43. Use the following steps in determining design procedures of a wood form for a concrete column.

Step 1. Determine the materials you will use for sheathing, yokes, and battens. The standard materials for column forms are 2 by 4s and 1-inch sheathing.

Step 2. Determine the column height.

Step 3. Determine the largest cross-sectional column dimension.

Step 4. Determine the maximum yoke spacing by referring to Table 4-12. First, find the column height in feet in the first column. Then move right horizontally to the column heading of the largest cross-sectional dimension in inches of the column you are constructing. The center-to-center spacing between the second yoke and the base yoke is the lowest value in the interval that falls partly in the correct column height line. You can obtain all subsequent yoke spacing by reading up this column to the top. These are maximum yoke spacing; you can place yokes closer together. Adjust final spacing to be at the top of the column.

Table 4-12. Column yoke spacing using 2 by 4s and 1-inch cheathing


4-44. Determine the yoke spacing for a 9-foot column whose largest cross-sectional dimension is 36 inches. Construction materials are 2 by 4s and 1-inch sheathing.

Solution Steps:

Step 1. Lay out materials available.

2 x 4s and 1-inch sheathing

Step 2. Determine column height.

9 feet

Step 3. Determine the largest cross-sectional dimension.

36 inches

Step 4 and Step 5. Determine the maximum yoke spacing, refer to Table 4-12. Starting from the base, the yokes are: 8, 8, 10, 11, 12, 15, 17, 17, and 10-inches. The spacing between the top two yokes are reduced due to the limits of the column height. Adjust the final spacing to be at the top of the column.



4-45. The portion of a structure that extends above the ground level is called the superstructure. The portion below ground level is called the substructure. The parts of the substructure that distribute building loads to the ground are called foundations. Footings are installed at the base of the foundations to spread the loads over a larger ground area to prevent the structure from sinking into the ground. Forms for large footings such as bearing wall footings, column footings, and pier footings are called foundation forms. Footings or foundations are relatively low in height since their primary function is to distribute building loads. Because the concrete in a footing is shallow, pressure on the form is relatively low. Therefore, it is generally not necessary to base a form design on strength and rigidity.


4-46. Whenever possible, excavate the earth and use it as a mold for concrete footings. Thoroughly moisten the earth before placing the concrete. If this is not possible, you must construct a form. Because most footings are rectangular or square, it is easier to erect the four sides of the form in panels. The following steps and figures helps explain this process:

Step 1. Build the first pair of opposing panels (see [a] in Figure 4-7 to the footing width. Nail vertical cleats to the exterior sides of the sheathing. Use 2-inch dressed lumber for the cleats and space them 2 1/2 inches from each end of the exterior sides of the (a) panels and on 2-foot centers between the ends. Use forming nails driving them only part way for easy removal of the forms.

Figure 4-7. Typical foundation

Step 2. Nail two cleats to the ends of the interior sides of the second pair of panels (see [b] in Figure 4-7). The space between them should equal the footing length, plus twice the sheathing thickness. Nail cleats on the exterior sides of the (b) panels, spaced on 2-foot centers. Erect the panels into either a rectangle or a square, and hold them in place with form nails. Make sure all reinforcing bars are in place.

Step 3. Drill small holes on each side of the center cleat on each panel less than 1/2 inch in diameter to prevent paste leakage. Pass number 8 or number 9 black annealed iron wire through these holes and wrap it around the center cleats of opposing panels to hold them together as shown in Figure 4-7.

Step 4. Mark the top of the footing on the interior side of the panels with grade nails. For forms 4 feet square or larger, drive stakes against the sheathing as shown in Figure 4-7. Both the stakes and the 1- by 6-inch tie braces nailed across the top of the form keep it from spreading apart. If a footing is less than 1 foot deep and 2 feet square, you can construct the form from 1-inch sheathing without cleats. Simply make the side panels higher than the footing depth, and mark the top of the footing on the interior sides of the panels with grade nails. Cut and nail the lumber for the sides of the form as shown in Figure 4-8.

Figure 4-8. Small footing form


4-47. It is best to place the footing and a small pier at the same time. A pier is a vertical member, either rectangular or round, that supports the concentrated loads of an arch or bridge super­structure. The form that is build for this type of construction is shown in Figure 4-9 below. The footing form should look like the one in Figure 4-7. You must provide support for the pier form while not interfering with concrete placement in the footing form. This can be accomplished by first nailing 2 by 4s or 4 by 4s across the footing form, as shown in Figure 4-9, that serve as both supports and tie braces. Nail the pier form to these support pieces.

Figure 4-9. Footing and pier form


4-48. Figure 4-10 below shows footing formwork for a bearing wall and Figure 4-11 shows bracing methods for a bearing wall footing. A bearing wall, also called a load-bearing wall, is an exterior wall that serves not only as an enclosure, but also transmits structural loads to the foundation. The form sides are 2 inch lumber whose width equals the footing depth. Stakes hold the sides in place while spreaders maintain the correct distance between them. The short braces at each stake hold the form in line.

Figure 4-10. Typical footing form

Figure 4-11. Methods of bracing bering wall footing form


4-49. Square column forms are made from wood whereas round column forms are made from steel or cardboard impregnated with waterproofing compound. Figure 4-2 shows an assembled column and footing form. After constructing the footing form follow the steps below:

Step 1. Build the column form sides in units first and then nail the yokes to them.

Step 2. Determine the yoke spacing from Table 4-1 according to the procedure described in paragraph 4-43.

Step 3. Erect the column form as a unit after assembling the steel reinforcement and tying it to the dowels in the footing.

Step 4. Place reinforcing steel in columns as described in Chapter 6. The column form should have a clean-out hole in the bottom to remove construction debris. Be sure to nail the pieces of lumber that you remove for the clean-out hole to the form. This way you can replace them exactly before placing concrete in the column.


4-50. A panel wall is an exterior or curtain wall made up of a number of units that enclose a structure below the roof line. It is built only strong enough to carry its own weight and withstand wind pressure on its exterior face.


4-51. Panel-wall units should be constructed in lengths of about 10 feet for easy handling. The sheathing is normally a 1-inch (13/16-inch dressed) tongue-and-groove lumber or 3/4-inch plywood. Make the panels by first nailing the sheathing to the studs. Then connect the panels as shown in Figure 4-12 below. Figure 4-13 below shows the form details at the wall corner. When placing concrete panel-walls and columns at the same time, construct the wall form as shown in Figure 4-14. Make the wall form shorter than the clear distance between the column forms to allow for a wood strip that acts as a wedge. When stripping the forms, remove the wedge first to facilitate form removal.

Figure 4-12. Method of connecting panel wall unit form together

Figure 4-13. Detail at corner of panel wall form

Figure 4-14. Form for panel walls and columns


4-52. Spreaders keep the sides of the wall form at the proper distance from each other until you place the concrete. Tie wires or tie-rods hold the sides firmly in place so that the weight of the freshly placed concrete does not push them apart. Figures 4-15 and 4-16 below show the installation of tie wires and tie-rods. Use the following steps to install them:

Figure 4-15. Detail at corner of panel wall form

Figure 4-16. tie-rod and spreader for wall form

Step 1. Use tie wires (see Figure 4-15 above) only for low walls or when tie-rods are not available. Number 8 or number 9 black annealed iron wire is recommended, but you can use barbwire in an emergency.

Step 2. Space the individual ties the same as the stud spacing but never more than 3 feet apart.

Step 3. Place a spreader near the location of each tie wire or tie-rod, as shown in view 2 of Figure 4-15. Form each tie by looping a wire around the wale on one form side, bringing, it through the form and looping it around the wale on the opposite form side.

Step 4. Make the wire taut by inserting a nail between the two strands and twisting. When using the wedge method shown in view 1 of Figure 4-15, twist the ends of the wire strands around a nail driven part way into the point of a wedge. Remove the nail and drive the wedge until it draws the wire taunt.

Step 5. Use pull wires to remove the spreaders as you fill the form so that they are not embedded in the concrete. Figure 4-17 below shows an easy way to remove spreaders. Loop a wire around the bottom spreader and pass it through off-center holes drilled in each succeeding spreader.

Figure 4-17. Removing wood spreader

Step 6. Pull on the wire to remove one spreader after another as the concrete level rises in the form. Use tie-rods if rust stains are unacceptable or if the wall units must be held in an exact position.

Step 7. Space spreaders as shown in Figure 4-17 the same as studs. After stripping the form, break off the rod at the notch located slightly inside the concrete surface. For a better appearance, grout in the tie-rod holes with a mortar mix.


4-53. Various types of stair forms, including prefabricated ones, can be used. A design based on strength is not necessary for moderate-width stairs joining typical floors. Figure 4-18 below shows one way to construct forms for stair widths up to and including 3 feet. Make the sloping wood platform that serves as the form for the underside of the steps from 1-inch tongue-and groove-sheathing. The platform should extend about 12 inches beyond each side of the stairs to support the stringer bracing blocks. Support the back of the platform with 4 by 4 posts. Space the 2 by 6 cleats nailed to the post supports on 4-foot centers. The post supports should rest on wedges for easy adjustment and removal. Cut the 2 by 12 planks for the side stringers to fit the tread and risers. Bevel the 2 by 12 risers as shown.

Figure 4-18. Stairway form


4-54. When possible, use standard steel pavement forms that can be set fast and accurately. They contain the concrete and provide a traction surface for form-riding equipment. These steel plate sections are 10 feet long and are normally available in slab thicknesses of 6, 7, 8, 9, 10, and 12 inches. The usual base plate width is 8 inches. Locking plates rigidly join the end sections. Three 1-inch diameter steel stakes per 10-foot section of form are required.

After driving the stakes, set the form true to line, them grade and clamp it to the stakes using special splines and wedges. Set the forms on the subgrade ahead of the paver and leave them in place for at least 24 hours after placing the concrete. Oil the forms immediately after setting them and before depositing the concrete. After oiling the form completely, wipe the top side or traction edge free from oil. Remove the forms as soon as practical, then clean, oil, and stack them in neat piles ready for reuse.


4-55. Make sure that any oil or other form coating that is used on forms does not soften or stain the concrete surface, prevent the wet surfaces from water curing, or hinder the proper functioning of sealing compounds used for curing. If standard form oil or other form coating is not obtainable, wet the forms to prevent sticking. Use water only in a emergency.


4-56. Before placing concrete in wood forms, treat the forms with a suitable oil or other coating material to prevent the concrete from sticking to them. The oil should penetrate the wood and prevent water absorption, making it environmentally safe. Almost any light-bodied petroleum oil meets these specifications. On plywood, shellac works better than oil in preventing moisture from raising the grain and detracting from the finished concrete surface. Several commercial lacquers and similar products are also available for this purpose. A coat of paint or sealing compound helps to preserve the wood if you plan to reuse wood forms repeatedly. Sometimes lumber contains enough tannin or other organic substance to soften the surface concrete. To prevent this condition, treat the form surfaces with whitewash or limewater before applying the form oil or other coating.


4-57. Oil steel column and wall forms before erecting them. You can oil all other steel forms when convenient but before reinforcing steel is in place. Use specially compounded petroleum oils, not oils intended for wood forms. Synthetic castor oil and some marine engine oils are typical examples of compound oils that give good results on steel forms.


4-58. The successful use of form oil depends on the method of application and the condition of the forms. Forms should be clean and have smooth surfaces. Therefore, do not clean forms with wire brushes which can mar their surfaces and cause concrete to stick. Apply the oil or coating with a brush, spray, or swab. Cover the form surfaces evenly, but do not allow the oil or coating to contact construction joint surfaces or any reinforcing steel in the formwork. Remove all excess oil.


4-59. Fuel oil, asphalt paint, varnish, and boiled linseed oil are also suitable coatings for forms. Plain fuel oil is too thin to use during warm weather, but mixing one part petroleum grease to three parts of fuel oil provides enough thickness.


4-60. Safety precaution should be practiced at all times. When work is progressing on elevated forms, take precautions to protect both workers on scaffolds and ground personnel.


4-61. Protruding nails are the main source of formwork accidents. Observe the following safety precautions during construction:

  • Inspect tools frequently--particularly hammers.
  • Place mudsills under shoring that rests on the ground.
  • Observe the weather, do not attempt to raise large form panels in heavy wind gusts, either by hand or by crane.
  • Brace all shoring to prevent possible formwork collapse.


4-62. Observe of the following safety precaution when stripping forms:

  • Permit only those workers actually stripping forms in the immediate work area. Do not remove forms until the concrete sets.
  • Pile stripped forms immediately to avoid congestion, exposed nails, and other hazards.
  • Take caution when cutting wires under tension to avoid backlash. See Chapter 5, Section XI.


4-63. Even when all formwork is adequately designed, many form failures occur because of some human error or improper supervision.


4-64. The following items are the most common construction deficiencies in wall-form failures and should be considered by supervisory personnel when working with concrete:

  • Failure to control the rate of placing concrete vertically without regard to drop in temperature.
  • Failure to sufficiently nail members.
  • Failure to allow for lateral pressures and forces.
  • Failure to tighten or secure form ties.
  • Use of old, damaged, or weathered form materials.
  • Use of undersized form material.
  • Failure to sufficiently allow for eccentric loading due to placement sequences.


4-65. The Following Are common Construction Deficiencies In Overhead slab Failure:

  • Failure to adequately diagonally brace the shores.
  • Failure to stabilize soil under mudsills.
  • Failure to allow for lateral pressures on formwork.
  • Failure to plumb shoring thus inducing lateral loading as well as reducing vertical load capacity.
  • Failure to correct deficiencies where locking devices on metal shoring are not locked, inoperative, or missing.
  • Failure to prevent vibration from adjacent moving loads or load carriers.
  • Failure to prevent premature removal of supports especially under long continuous sections.
  • Lack of allowance in design for such special loads as winds, power buggies, or placing equipment.
  • Failure to provide adequate reshoring.
  • Failure to sufficiently allow for eccentric loading due to placement sequence.


4-66. The following are miscellaneous causes of form failure:

  • Failure to inspect formwork during and after concrete placement to detect abnormal deflections or other signs of imminent failure which could be corrected.
  • Failure to prevent form damage in excavated area caused by embankment failure.
  • Lack of proper supervision and field inspection.
  • Failure to ensure adequate anchorage against uplift due to battered form faces.

4-67. This list is not all inclusive; there are many reasons why forms fail. It is the responsibility of the form designer to ensure that the concrete will not fail when the designs are properly interpreted and constructed. It is the responsibility of the builder to make sure that the design is correctly constructed and that proper techniques are followed.



4-68. Concrete structures are subjected to internal and external stresses caused by volume shrinkage during hydration, differential movement due to temperature changes, and differential movement caused by different loading conditions. These stresses can cause cracking, and scaling of concrete surfaces and in extreme cases result in failure of the concrete structure. These stresses can be controlled by the proper placement of joints in the structure. Three basic types of joints will be addressed--the isolation joint, the control joint, and the construction joint.


4-69. Isolation joints are used to separate or isolate adjacent structural members. An example would be the joint that separates the floor slab from a column (to allow for differential movement in the vertical plane due to loading conditions or uneven settlement). Isolation joints are sometimes referred to as expansion or contraction joints to allow for differential movement as a result of temperature changes (as in two adjacent slabs). All isolation joints extend completely through the member and do not have any load transfer devices built into them. See Figures 4-19, 4-20, and 4-21 below.

Figure 4-19. Typical isolation and control joints

Figure 4-20. Joints at colums and walls

Figure 4-21. Expansion/contraction joint for a bridge


4-70. Movement in the plane of a concrete slab is caused by drying shrinkage and thermal contraction. Some shrinkage is expected and can be tolerated depending on the design and exposure of the particular structural elements. In a slab the shrinkage occurs more rapidly at the exposed surfaces and causes upward curling at the edges. If the slab is restrained from curling, cracking will occur wherever the restraint imposes stress greater than the tensile strength. Control joints (see Figure 4-22 below) are cut into the concrete slab to create a plane of weakness that forces cracking (if it happens) to occur at a designated place rather than randomly. These joints run in both directions at right angles to each other. Control joints in interior slabs are typically cut 1/3 to 1/4, of the slab thickness and then filled with lead or joint filler, see Table 4-13 for suggested control joint spacing. Temperature steel (welded wire fabric) may be used to restrict crack width for sidewalks, driveways, and tooled joints spaced at intervals equal to the width of the slab but not more than 20 ft (6 meters) apart. Surface irregularities along the plane of the cracks are usually sufficient to transfer loads across the joint in slabs on grade, the joint should be 3/4 to 1-in deep.

Figure 4-22. Control joint

Table 4-13. Spacing of Control joints

Slab Thickness, in Inches Less Than 3/4 inch Aggregate Spacing, in Feet Larger Than 3/4 inch Aggregate Spacing, in Feet Slump Less Than 4 Inches Spacing, in Feet
5 10* 13 15
6 12 15 18
7 14 18 21
8 16 20 24
9 18 23 27
10 20 25 30
NOTE: Spacing also applies to the distances from the control joints to the parallel isolation joints or to the parallel construction joints.


4-71. Construction joints (see Figures 4-23 through 4-26 below) are made where the concrete placement operations end for the day or where one structural element will be cast against previously placed concrete. These joints allow some load to be transferred from one structural element to another through the use of keys or (for some slabs and pavement) dowels. Note that the construction joint extends entirely through the concrete element.

Figure 4-23. Keyed, wall construction joint (perspective view)

Figure 4-24. Keyed, wall construction joint (plan view)

Figure 4-25. Construction joint between wall and footing showing keyway

Figure 4-26. Types of construction joints


4-72. The anchor bolt (see Figure 4-27 below) is used to anchor either machinery or structural steel. The diameter of the sleeve should be at least 1 inch larger than the bolt. The sleeve allows the bolt to shift to compensate for any small positioning error. The pipe sleeves are packed with grease to keep concrete out during paving operations. Do not use the sleeve if machinery mounts are on a raised base that is 4 or more inches above the floor. Instead set the anchor bolts in the floor so they extend above the base. Place the machine--blocked up on scrap steel and leveled--and tighten the anchor bolts. Finally pour the base by packing the concrete into place from the sides.

Figure 4-27. Anchor bolt with pipe sleeve


4-73. The hooked anchor bolt (see Figure 4-28) and the suspended anchor bolt (see Figure 4-29 below) are both used to fasten a wood sill to either a concrete or masonry wall. Be careful not to disturb suspended bolt alignment when placing the concrete. Make the bolt holes in the board 1/16 inches larger than the bolt to permit adjustment.

Figure 4-28. Hooked anchor bolt

Figure 4-29. Suspended anchor bolt


4-74. (See Figure 4-30). A templet is used to hold anchor bolts in place while placing concrete. When using sleeves in a templet adjust them so that the top of the sleeve is level with the top of the finished concrete.

Figure 4-30. Anchor bolts held in place by a templet