NBSIR 74-621

Stability and Strength of Home

Playground Equipment

Bal M. Mahajan

Product Systems Section

Product Systems Division

Final Report

8/74 - 10/74

Prepared for Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland 20016

NBSIR 74-621

STABILITY AND STRENGTH OF HOME

PLAYGROUND EQUIPMENT

Bal M. Mahajan

Product Systems Section

Product Engineering Division

Final Report

8/74 - 10/74

Prepared for Consumer Product Safety Com mission

5401 WestDard Avenue

Bethesda, Maryland 20016

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

Introduction

This study was conducted as a part of the Home Playground Equipment

Project for the Consumer Product Safety Commission (CPSC) . The project

consisted of two study programs, the first dealing mainly with home

swing sets, and the second dealing with other items of home playground

equipment. The overall objective of the project was to develop criteria

and test methods, along with the necessary data, for preparing a safety

standard for home playground equipment.

The first study program was completed by the end of July 1974, and

its findings were presented in an interim report entitled "Recommendations for a Safety Standard for Home Playground Equipment - Swing Sets"

(NBS Report No. NBSIR 74-563) V- This interim report provided some necessary data and suggested criteria and test methods for formulating

a safety standard for home swing sets.

Work on the second study program of the Home Playground Equipment

Project was started in the beginning of August 1974. The Consumer

Product Safety Commission had expressed concern about the stability

and strength of tl\e equipment. Therefore, the first subtask of this

study was to conduct stability and strength tests on samples of various

playground items. The objectives of these tests were to determine

whether or not the equipment could withstand the tipping moments and

loads expected with the equipment in use.

However, CPSC decided to follow Section 7 of the Consumer Product

Safety Act, and the study program was terminated in its early stages, near the end of October 1974. At that time, the NBS investigator was asked to prepare a report describing the work done to date.

When the program was terminated, the investigator had completed

the first series of stability and strength tests on samples of a few

home playground items and was in the process of analyzing the preliminary test data. Hence, this report deals mainly with the preliminary

stability and strength tests performed on a restricted sample. It

describes test procedures and presents test results.

Items of Home Playground Equipment Tested

Nine different items of home playground equipment, randomly selected,

were purchased from local retailers. Tliese included a A-climber (figure 1) , a climbing tower (figure 2), a dome climber (figure 3), a tangle tower

(figure 4) , a play center (figure 5) , a gym set or swing set (figure 6) , a free-standing slide (figure 7) , a space rocker (figure 8) , a merry-goround (figures 9A and 9) . These items were assembled and installed in
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accordance with the written instructions provided by the manufacturers.

The equipment, for which anchoring was recommended by the manufacturers,

was anchored to the ground by utilizing steel ground anchors.

Stability Tests

If the moment required to tip over an item of playground equipment

is greater tlian the tipping moment likely to be experienced by the

equipment during use, then the equipment may be considered to have

adequate stability.

Tests were performed on some items to determine if they had

adequate stability. To generate the moment necessary for tipping the

equipment over, a member near the top was subjected to a pull force,

F, acting in a direction parallel to the ground and perpendicular to a tipping axis. The tipping axes of a typical item are shown in figure 25.

Tlie magnitude of the force, F, required to tip was measured. The

tipping moment generated by F may be calculated, if desired, by multiplying F by the perpendicular distance between the line of action of F and the ground. Stability may be determined by comparing the moment

required to tip over the equipment witl) the tipping moment likely to be

experienced by the equipment when it is in use.

Test Procedures

A steel cable was used to apply the force, F, to the equipment

under test. One end of the cable was attached to the selected member

of the equipment, and the other end of the cable was connected to a force gage (figure 25) . The equipment was pulled either manually,

where possible, or with the aid of a tow truck. The pull force was increased gradually until the equipment was about to tip over. The

force, F, required to start the tipping of the equipment was read on the force gage and recorded.

The A-climber, climbing tower, tangle tower, and free-standing

slide were tested for tipping about more than one tipping-axis of the

equipment. All the stability tests were conducted with the equipment

installed in accordance with the written instructions provided by the

manufacturers . .

.

. •

Test Results '

The results of stability tests are given in figures 26-31. These

figures show tlie equipment tested, the member (or members in case of

m.ore than one test) subjected to pull force, the direction of applied

force, F, and the magnitude of force, F (or forces Fj, F-^,, etc.)

required to initiate tipping.
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Strength Tests

Tests were performed by statically loading components of some

items of home playground equipment with estimated test loads to determine if the tested equipment had adequate strength. The estimated

test load for a component is obtained by multiplying the expected load

by a safety factor (reference 1). The expected load for a component

is the maximum load likely to be carried by the component when the

equipment is in use. If the equipment does not suffer structural failure

when subjected to estimated test loads, the equipment may be considered

to have adequate strength.

The estimated test loads, for those components which were tested,

are given with other test data. Calculations leading to these values

are not given in this report. Samples of such calculations may be

found in reference 1, where the estimated test loads for home swing

set components were calculated. The estimated test loads used in these

tests, being dependent upon subjective judgment to a certain degree,

may be debatable.

Test Procedures

Several block weights, each weighing 50 pounds (22.7 kg), were

used to load the components to be tested. In some tests, when the com- ponent to be loaded was wide enough, the block weights were placed

directly on the component (figures 20-22). In other tests, when the

component to be loaded was narrow, the block weights were placed on an aluminum platform suspended from a support mounted on the component

(figures 12-19). The support used for suspending the platform was approximately 4 in (100 mm) long, and was constructed by cutting a 2.5 in (64 mm) outside diameter 0.25 in (6.4 mm) thick steel pipe along

its axis. The platform suspension system (figure 11) weighed approximately 20 pounds (9.1 kg).

Procedures for testing various items of home playground equipment

are given ebelow.

A. Selected components of the A-climber, climbing tower, dome

climber, tangle tower, play center, gym set, and slide were

tested one at a time. Tested components were randomly selected

from those components of the equipment which are likely to be

occupied by children when the equipment is in use.

The component to be tested was gradually loaded as follows:

the component was, loaded with an initial load of 100 pounds

(45.4 kg) when the block weights were placed directly on the

component, and 120 pounds (54.4 kg) when the block weights

were placed on the platform suspended from the component. The

component loaded with this initial load was kept under surveillance for 10 minutes to observe any structural failure of the

component or of the component's support system (i.e. connecting

bolts, nuts, hinges, etc.); if no observable failure occurred.
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an additional block weiglit was added to the initial weights to

increase the magnitude of the load applied to the component

by 50 pounds (22.7 kg). The component under testing now subjected to this increased load was observed for another 10

minutes for any structural failure; if no observable failure

occurred, the applied load was increased by another 50 pounds

(22.7 kg). This process of gradually increasing the load

applied to the component under testing, by 50 pounds (22.7 kg)

at 10 minute intervals, was continued until either the component

failed or the magnitude of load applied to the component

equaled or exceeded that of the estimated test load.

In all of the tests, when the equipment was tested by loading

its components one at a time, tlie procedure of gradual loading

of the component under test was followed.

The equipment components which were loaded for these tests are indicated in figures 1-7.

B. The gym set which had already been tested by procedure A, a space rocker, and a merry-go-round were also tested as follows.

Tliose components of the equipment which were designed for

occupancy (mainly seats) were loaded simultaneously witli

estimated test loads. The equipment thus loaded was kept

under surveillance for up to lu minutes to observe if any part

of the equipment failed.

The equipment components which were loaded for these tests are indicated in figures 8 - 10.

Test Results

The results of the strength tests, indicating whether failure of

any part of the tested equipment occurred or not, are given in figures

1-10. Components of the equipmient loaded, applied load, and estimated

test loads are also shown in these figures. Photographs of some items

of the equipment under testing are shown in figures 12-22. Figure 23

shows the status of the play center after it was tested, and figure 24

shows the status of the gym set after it was tested by loading all o'f the

swinging units simultaneously.

Test results indicate that all tested equipment, with the exception

of two items, showed some' sort of structural failure when subjected to

estimated loads. The two exceptions among the nine items tested were

the free standing slide and the space rocker.
Reference

Mahajan, Bal M. , "Recommendations for a Safety Standard for Home

Playground Equipment - Swing Sets," NBS Report No. NBSIR 74-563.

Figure 1. A-Climber

Strength Test Data

Location of

Component Loaded Estimated Load Applied Load Observations

lb. kg lb. kg

1 30C 136 320 14o No failure

2 300 136 320 14S No failure

3 300 136 120 54 No failure

170 77 Bar bent
Location of

Component Loaded

Figure 2. Climbing Tower

Strength Test Data

Estimated Load Applied Load Observations

lb. kg , lb. kg

1 220 100 220 100 No failure

2

' 220 100 170 77 No failure

220 100 Bar bent

3 220 100 220 100 No failure

4 220 100 220 100 No failure
Figure 3. Dome Climber

Location of

Component Loaded

Strength Test Data

Estimated Load Applied Load Observations

lb.

400

220

220

kg

ISl

100

lb.

170

220

170

220

170

220

kg

77

100

77

100

77

100

No failure

All bars connected at

point 1 caved in

No failure

Bar bent

No failure

Bar bent
Figure 4. Tangle Tower

Strength Test Data

Location of

Component Loaded Estimatec Load Applied Load Observations

lb. kg lb. kg

1 • • 350 156 420 191 No failure

2 350 156 220

270

100

122

No failure

Bar bent and upper

assembly pulled down

3 350 156 420 191 No failure

4 350 156 420 191 No failure
Figure 5. Play Center

Strength Test Data

Location of

Component Loaded Estimated Load Applied Load Observations

lb. kg lb. kg

1 150 68 150 68 No failure

2 150 68 150 68 No failure

3 150 68 150 68 No failure

4 150 68 150 68 No failure

5 150 68 150 68 No failure

6 150 68 150 68 No failure

7 200 91 200 91 No failure

8 200 91 170 77 No failure

220 ]00 Bar bent

9 200 91 220 100 No failure

10 200 91 170 77 No failure

220 100 Bar bent

11 150 68 100 45 No failure

150 68 Canop)' torn
Figure 6. Gym Set

; . /, Strength Test Data

Location of

Component Loaded Estimatec Load Applied Load Observations

lb. kg lb. kg

1 and 2 were loaded 1 300 136 300 136 No fai lure

simultaneous ly 2 300 136 300 136 No fai lure

3 and 4 were loaded 3 150 68 150 68 No failure

simultaneous ly 4 150 68 150 68 No failure

5 400 181 400 181 No failure

6 200 91 200 91 No fai lure

7 200 91 • 200 91 No fai lure

8 200 91 220 100 No fai lure

9 300 136 170 77 No failure

220 100 Bar bent
V

Figure 7. Free Standing Slide

Strength Test Data

Location of

Component Loaded Estimated Load Applied Load Observations

lb. kg lb. kg

1 200 91 200 91 No failure

2 200 91 200 91 No f ai lure

3 200 91 200 91 No fai lure
Figure 8. Space Rocker

Strength Test Data

Location of

Component Loaded Applied Load* Observations _ _

1 • 200 91 All four seats were loaded

2 200 91 simultaneously. No failure,

3 200 91

4 200 91

*The applied load was the estimated load.
Figure 9. Merry- Go- Round

Strength Test Data

Location of

Component Loaded Applied Load Observations

lb. kg

1 150 68 All four seats were loaded

2 150 68 simultaneously. Pivot at "A" and

3 150 68 seat support bars near the pivot

4 150 68 f ai led

Figure 9A. Merry-Go-Round
Figure 10. Gym Set

Strength Test Data

The equipment was loaded with a total load of 1250 lb. (567 kg)

to test the strength of the top bar. The locations of components which

were loaded and the respective magnitude of applied load is indicated

in the figure above.

As soon as the last block weight was placed on the equipment, the

equipment collapsed (figure 24)
Figure 11. Loading Platform Suspension System.
Figure 12. A-climber under test.
Figure 13. A- climber under test.
Figure 14. A-climber under test.
Figure 15. Climbing tower under test.
Figure 16. Dome climber under test.
Figure 17. Dome climber under test.
Figure 18. Tangle tower under test.
Figure 19. Gym set under test.
Figure 20. Free standing slide under test.
Figure 21. Free standing slide under test.
Figure 22. Space rocker under testing.
Figure 23. Play center after loading test.
Figure 24. Gym set after loading all of the

seats simultaneously (figure 10).
Lines AB, BC, CD, and DA are the possible

tipping axes (T.A.) for this equipment

Figure 25. The tipping axes of a typical home playground

item, and schematic set-up for applying the

pull force, F, to the equipment under stability

tests.
Figure 26. The A-frame's stability test

Force to start tipping

F^ = 24 lb. (107 N)

F^ = 43 lb. (191 N)
Figure 27. Climber tower's stability test.

Force to start tipping

F = 23 lb. (102 N)
Figure 28. Dome climber's stability test.

. Force to start tipping

F = 48 lb. (214 N)
Figure 29. Tangle tower's stability test.

Force to start tipping.

= 30 lb. (134 N)

^2 = 36 lb. (160 N3

^3 " 24 lb. (107 N)
Figure 30. Gym set's stability test.

Force to start tipping

F = 225 lb. (1000 N)
Figure 31. Free standing slide's stability test.

Force to start tipping . F^ = 5 lb. (22 N)

F^ = 21 lb. (93 N)

F^ = 34 lb. (151 N)
NBS-l HA (HE V. 7-7J)

U .S. Dt PT . OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. I'UIU.U A rui\ OK Ki:i'()K 1 NO. NBSIR 74-621

2. Cniv't Act<.s.sii>n No.

3. Ki c ipii nt 's Ai <. c.ssii>n No.

4. 11 ! l.t-; AND SUli i n i. Scability and Strength of Home Playground

Equipment

5. Publ it .It ion Date December 1974

6. Performing Or^.uuzjtion C!odc 446.04

7. AUTHOR(S)

Bal M. Mahajan

8. Performing Or^an. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Projcct/Ta.sk/Work Unit .No. 4460506

n. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Slreet, City, State, ZIP)

Consumer Product Safety Commission

Bethesda, Maryland 20016

13. Type of Report &i Period Covered

Final

8/74 - in/74

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary ol most si^ilicant information. If document includes a si^ificant

bibliography or literature survey, mention it here.)

Stability tests were performed on some items of home playground equipment

to measure the magnitude of the force, applied to generate tipping moment,

required to start the tipping of the equipment.

Strength tests were conducted by loading certain components of home

playground equipment with estimated loads to determine if the tested equipment had adequate strength.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Home playground equipment; stability; strength; test; testing; tipping

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