AASHTO HS-25 Testing Protocol
3 The AASHTO HS-25 testing protocol represents the loading of a 25 ton (50,000 lbs ) semi-truck would exert onto a highway bridge. Since there is no specification for compression strength of man-hole adjustment rings, this testing protocol will be used. MGA Research in Troy Michigan is an accredited testing laboratory which performed the independent testing for Underground Technologies. MGA contract was to test various manhole chimney structures with specified AASHTO HS-25 testing protocol. The test would apply time step loading to the manhole chimney structures, measure deflection and inspect part integrity at each load. The test is to prove that the man-hole construction will pass the AASHTO HS-25 and consequently the HS-20 testing protocol.
Load Calculations:
When investigating the free body diagram of the protocol; for HS-25 the load is determined by using 40,000 lbs times a factor of 0.4, thus the loads are calculated.

 

 

 

2 See MGA Report

Static Load: 6,000 lbs. on a 10 x 20 patch

Dynamic Load: 1.3 times the static load; 20,800 lbs. This load simulates the load of the tire patch dropping one foot on to the manhole cover.

Load (lbs)/Sample (in)

VE7314- ( 5.5G & 1.5F)

VE7315- ( 1.5G & 1.5F)

VE7316- ( 2R)

5,000

0.04154

0.02617

0.02441

10,000

0.06733

0.04242

0.03608

16,000 Static Test

0.09487

0.05829

0.04669

20,800 Dynamic

0.12699

0.07137

0.05634

40,000 Destructive

0.40555

0.11799

0.12722
The results table shows the deflection relative to the load step. The deflections were low at the specified AASHTO HS-25 Dynamic load (20,800 lbs.) with no permanent set to the Grade or Finish Ring. All rings rebounded to original state. The permanent set or deflection occurred at the 40,000 lb. destructive test. The permanent deflection was measured at 1/32” for the Grade and Finish rings. Although localized bucking phenomena occurred at the 40,000 lb. load, the test samples remained intact with no cracking of the exterior seal.