us army engineer course - design forms for an overhead concrete slab

SUBCOURSE EDITIONEN5153 A

DESIGN FORMS FOR AN OVERHEADCONCRETE SLAB

DESIGN FORMS FOR THE OVERHEAD CONCRETE SLAB

Subcourse EN5153

EDITION A

United States Army Engineer SchoolFort Leonard Wood, Missouri 65473

2 Credit Hours

Edition Date: August 1995

SUBCOURSE OVERVIEW

This subcourse addresses the principles of designing forms for an overhead concrete slab. As an engineercarpenter, you must understand the basic principles concerning the design of overhead concrete slabs that willsupport the weight of concrete placed in/on them.

There are no prerequisites for this subcourse.

The lesson in this subcourse reflects the doctrine which was current at the time it was prepared. In your ownwork situation, always refer to the latest official publications.

Unless otherwise stated, the masculine gender of singular pronouns is used to refer to both men and women.

TERMINAL LEARNING OBJECTIVE:

ACTION: You will describe procedures to design wooden forms for an overhead concrete slab.

CONDITION: You will be given the material contained in this subcourse.

STANDARD: To demonstrate competency of this task you must achieve a minimum of 70 percent on thesubcourse examination.

i EN5153

TABLE OF CONTENTS

Section Page

Subcourse Overview............................................................................................................................................... i

Grading and Certification Instructions................................................................................................................. iii

Lesson: Design Forms for the Overhead Concrete Slab.....................................................................................1-1

Part A: Select Proper Materials............................................................................................................ 1-2

Part B: Determine the Total Unit Load on the Floor Form.................................................................. 1-4

Part C: Determine the Maximum Joist Spacing................................................................................... 1-6

Part D: Determine the Uniform Load on a Joist...................................................................................1-9

Part E: Determine the Maximum Stringer Spacing............................................................................ 1-10

Part F: Determine the Uniform Load on the Stringer.........................................................................1-12

Part G: Determine the Maximum Shore Spacing............................................................................... 1-13

Practice Exercise..................................................................................................................................1-15

Answer Key and Feedback.................................................................................................................. 1-18

Appendix A: List of Common Acronyms.........................................................................................................A-1

Appendix B: Recommended Reading List........................................................................................................B-1

Student Inquiry Sheet

EN5153 ii

LESSON

DESIGN FORMS FOR AN OVERHEAD CONCRETE SLAB

Critical Task: 051-199-4014

OVERVIEW

LESSON DESCRIPTION:

In this lesson, you will learn to design forms for an overhead concrete slab.

TERMINAL LEARNING OBJECTIVE:

ACTION: You will describe procedures to design wooden forms for an overhead concrete slab.

CONDITION: You will be given subcourse booklet EN5153.

STANDARD: Complete the lesson and the practical exercise.

REFERENCES: The material contained in this lesson was derived from Field Manuals (FMs) 5-34, 5-426,and 5-742; Soldier Training Publications (STPs) 5-12B24-SM-TG; and 5-51B12-SM-TG.

INTRODUCTION

As a carpenter, one of your concerns is to ensure that the forms you design will support the weight of concreteplaced in or on them. This lesson shows you how to properly design these forms.

1-1 EN5153

PART A: SELECT PROPER MATERIALS

You will need to specify the materials you use for constructing the overhead roof slab when designing forms.Anyone using your design must know exactly which materials to use for each of the structural members as shownin Figure 1-1.

Sheathing. Sheathing is the first covering of boards or of waterproof materials on the outside wall of a framestructure or on a timber roof. Sheathing shapes and holds the concrete. Plywood or solid sheet metal is the bestchoice of material to use. The materials to be used are normally 1- by 4- or 1- by 6-inch boards and 5/8- or 3/4-inch plywood.

Joist. A joist is any small timber or metal beam that is ranged parallel from wall to wall in a structure to supporta floor or ceiling. Joists support the sheathing to prevent movement. When possible, use 2- by 4-inch, 2- by 6-inch, or 4- by 4-inch material.

Stringer. A stringer is a long horizontal timber connecting uprights in a frame or supporting a floor. Stringerssupport the joists and prevent movement. When possible use material at least 2 inches thick.

Shore. A shore is a piece of lumber at least as great in size as the stringer. It is used to support or brace thestringer. A shore performs the same function as ties perform in a wall form; it also supports the concrete at thedesired elevation above ground. Use lumber at least as large as the stringer, but never smaller than 4- by 4-inchlumber.

Lateral Bracing. Lateral bracing may be required between adjacent shores to keep shores from bending underthe load. When possible use 1- by 6-inches or larger material for bracing material. Cross or "X" bracing of sometype will always be required to support the formwork materials.

EN5153 1-2

Figure 1-1. Elements of supported slab formwork

1-3 EN5153

PART B: DETERMINE THE TOTAL UNIT LOADON THE FLOOR FORM

You will need to understand the following terms and formulas to determine the total unit load on floor forms:

Determine total unit load (TL) by summing the result for dead load and live load. TL is measured in pounds persquare feet (psf).

Dead load (DL). Dead load is the weight of ordinary concrete and is estimated at 150 pounds per cubic foot(lb/cu ft).

To determine DL, use this formula:

Live Load (LL). You must also consider an additional live load of construction workers and materials. This LLis generally 50 psf. However, if you use powered concrete buggies, the LL would be 75 psf.

Now that you know how to determine DL and LL it is time to determine TL.

To determine TL, use this formula:

TL = DL + LL

EXAMPLE:

Determine the TL on the form if the slab thickness is 5 inches and you are using nonpowered equipment.

TL = DL + LL

TL = (150 x 0.42) + 50

TL = 63 + 50

TL = 113 psf

EN5153 1-4

Work the following problem to see how well you understand the concepts you have just reviewed.

PROBLEM-1:

Determine the TL load on the form if the slab thickness is 4 inches and you are using a powered concrete buggy.

A. 50

B. 75

C. 125

D. 150

See page 1-14 for the solution to this problem.

1-5 EN5153

PART C: DETERMINE THE MAXIMUM JOIST SPACING

Joist spacing depends on the type of sheathing used-boards or plywood. Joist spacing, like stud spacing, is foundby using either Table 1-1 for board sheathing or Table 1-2 for plywood sheathing. Be sure to use the correct one.

NOTE: All plywood sheathing problems and practice exercises will be using the Strong Way column inTable 1-2.

Table 1-1. Maximum stud or joist spacing for support of board sheathing

To find the maximum joist space using Table 1-1 or 1-2-

Find the TL in the left column. If the value is not listed, round up the load to the next value on the table;for example, for 138 psf use 150 psf.

Move across the row to the column headed by the sheathing thickness. The intersecting number is themaximum joist spacing.

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Table 1-2. Maximum stud or joistspacing for support of plywood sheathing

EXAMPLE:

Determine the maximum joist spacing if the TL is 150 psf and the plywood sheathing is 5/8-inch material.

19 inches

1-7 EN5153

Work this problem to see how well you understand the concept you have just reviewed.

PROBLEM-2:

Determine the maximum joist spacing if the sheathing is 3/4-inch plywood and the TL is 125 psf.

A. 20

B. 22

C. 23

D. 24


EN5153 1-8

PART D: DETERMINE THE UNIFORM LOAD ON A JOIST

The uniform load on a joist is calculated the same way as the uniform load on structural members in wall-formdesigns. The unit of measurement is pounds per linear foot (lb/lin ft).

To determine uniform load on a joist, use this formula and the procedures following:

Use the actual TL, not the rounded up figure, to obtain the maximum joist spacing.

Divide before multiplying.

Round up your answer to the next whole number.

EXAMPLE:

Determine the uniform load on the joist if the TL is 133 psf and the maximum joist spacing is 28 inches.

Work this problem to see how well you understand this concept you just reviewed.

PROBLEM-3:

Determine the uniform load on the joist if the TL is 113 and the joist spacing is 44 inches.

A. 410

B. 414

C. 424

D. 426


1-9 EN5153

PART E: DETERMINE THE MAXIMUM STRINGER SPACING

To find the maximum stinger spacing, use Table 1-3 and the following procedures:

Find the uniform load on the joist in the left column. If the value is not listed, round up the load to thenext value on the table; for example, if the value is 113 lb/lin ft, use 125.

Move across the row to either the single or double-members section. Then locate the joist size that youwill be using. The intersecting number is the maximum spacing of the stringers.

Table 1-3. Maximum safe spacing of supporting members (wales, ties stringers, 4- by 4-inch and larger shores)

EN5153 1-10

EXAMPLE:

Determine the maximum spacing of single stringers if you use 4-by-4 joists and a uniform load of the joists of200 lb/lin ft.

65 inches

Work this problem to see how well you understand the concepts you have just reviewed.

PROBLEM-4:

Determine the maximum single-stringer spacing if the uniform load on the joist is 165 lb/lin ft and you are using2-by-4 material.

A. 45

B. 49

C. 77

D. 85


1-11 EN5153

PART F: DETERMINE THE UNIFORM LOAD ONTHE STRINGER

To determine uniform load on a stringer, use this formula:

EXAMPLE:

Determine the uniform load on the stringer if the TL is 350 and the maximum stringer spacing is 50 inches.

Work the following problem to see how well you understand the concept you just reviewed.

PROBLEM-5:

Determine the uniform load on the stringer if the TL is 250 psf and the maximum stringer spacing is 85 inches.

A. 1,250

B. 1,540

C. 1,680

D. 1,770


EN5153 1-12

PART G: DETERMINE THE MAXIMUM SHORE SPACING

The maximum shore spacing is based on the stringer strength. To find the maximum shore spacing, use Table 1-3, page 1-10, and the procedures following:

Find the uniform load on the stringer in the left column. If the value is not listed, round up the load tothe next value on the table; for example, if the value is 113 lb/lin ft, use 125.

Move across the row to the column headed by the stringer size, depending on whether single stringers ordouble stringers will be used. The intersecting number is the maximum spacing of the shores.

EXAMPLE:

Determine the maximum shore spacing if the uniform load on the stringers is 825 lb/lin ft and the single stringersare 4 by 6 inches.

48 inches

Work the following problem to see how well you understand of the concept you just reviewed.

PROBLEM-6:

Determine the maximum shore spacing if the uniform load on the stringer is 720 lb/lin ft and the single stringersare 4 by 6 inches.

A. 48

B. 51

C. 56

D. 80


1-13 EN5153

LESSON PROBLEMS

ANSWER KEY AND FEEDBACK

Problem Correct Answer

1. C. 125 psf (page 1-4)

2. C. 23 psf (page 1-7)

3. B. 414 lb/lin ft (page 1-9)

4. A. 45 inches (page 1-10)

5. D. 1,770 lb/lin ft (page 1-12)

6. B. 51 inches (page 1-13)

EN5153 1-14

PRACTICE EXERCISE

The following items will test your knowledge of the material covered in this lesson. Circle your answer for eachitem on the practice exercise page. When you have completed the exercise, check your answers with the key thatfollows. If you answer any item incorrectly, study again that part which contains the portion involved.

1. Determine the TL on the form, in psf, if it has a 6-inch-thick slab and you use nonpowered equipment.

A. 50

B. 110

C. 125

D. 150

2. Determine the maximum joist spacing if the sheathing thickness is 1 1/2-inch boards and the total unit load is125 psf.

A. 33

B. 37

C. 39

D. 41

EN5153 1-15

3. Determine the uniform load on the joist if the total unit load is 150 psf and the joist spacing is 22 inches.

A. 150

B. 260

C. 275

D. 330

4. Determine the maximum single-stringer spacing if the uniform load on the joist is 900 lb/lin ft and you areusing 4-by-6 material.

A. 46

B. 48

C. 51

D. 68

EN5153 1-16

5. Determine the uniform load on the stringer if the TL is 125 psf and the maximum stringer spacing is 54inches.

A. 125

B. 563

C. 660

D. 762

6. Determine the maximum shore spacing if the uniform load on the stringer is 560 lb/lin ft and the doublestringer are 4 by 4 inches.

A. 37

B. 53

C. 63

D. 71

1-17 EN5153

PRACTICE EXERCISE

ANSWER KEY AND FEEDBACK

Item Correct Answer

1. C. 125 (page 1-4)

2. C. 39 (page 1-6)

3. C. 275 (page 1-9)

4. B. 48 (page 1-10)

5. B. 563 (page 1-12)

6. B. 53 (page 1-13)

EN5153 1-18

us army engineer course - design forms for an overhead concrete slab

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