|
92
<br />Cuardraile varying from a triple tubu-
<br />lar beam to a simple I-beam or wooden
<br />post design were analyzed for effec-
<br />tive restraint of haulage vehicles.
<br />The choice of a particular guardrail
<br />design depends on the vehicle's size,
<br />velocity, and angle of approach. In-
<br />stallation costs of guardrail limit
<br />their application to situations where
<br />there may not be enough room for berm
<br />construction, or where [he installa-
<br />tion may be considered permanent,
<br />such that higher initial cost can be
<br />
<br />justified on the basis of lower mainte-
<br />nance costs.
<br />A guardrail system was considered safe
<br />if its maximum rail deflection did not
<br />exceed half the width of the vehicle
<br />track (axle). For systems with shallow
<br />embedded posts, the barrier damage was
<br />more extensive than for those with ex-
<br />treme post depth. Table 1 is a summary
<br />of guardrail design concepts. Design
<br />specifications for table 1 are available
<br />from the work cited in footnote 4.
<br />BARRIERS
<br />A barrier is a berm with a near-
<br />vertical face constructed of material
<br />that is capable of absorbing the kinetic
<br />energy of a runaway vehicle by the
<br />displacement of the berm itself, and the
<br />reaction between the berm and the road
<br />surface. There are two major types of
<br />barriers: (1) A rigid barrier made of
<br />TABLE 1. - Summary of maximum approach conditions of rear-dump mine haulage
<br />trucks for guardrail design concepts
<br />GROSS VEHICLE WEIGHT
<br />35-TON CAPACITY
<br />!0 mph at 14"..... 100 A
<br />20 mph at 28°.... 500 B, H
<br />30 mph at 36°.... 1,000 C, I
<br />35 mph at 62°..... 2,000 D
<br /> Ap proach I CSL' ConfiQUra
<br /> 541,000-LB GVW, 170-TON CAPACITY
<br />10 mph at 7°. ... 100 A
<br />20 mph at 13°.... 500 B, H
<br />30 mph a[ 16°.... 1,000 C, I
<br />30 mph at 29°.... 2,000 D
<br />35 mph at 35°..... 3,000 E, F
<br />35 mph at 46°.... 4,000 J, K
<br />10 mph at 8°...... 100 A 35 mph at 58°..... 5,000 J, K
<br />20 mph at 17°.... 500 B, H
<br />30 mph at 21°.... 1,000 C, I
<br />35 mph at 33°..... 2,000 D
<br />35 mph at 47°..... 3,000 E, F
<br />35 mph at 65°..... 4,000 J, K
<br />SCSI = Collision severity index, an empirically derived relationship commonly used
<br />for guardrail evaluation. It provides a numerical comparison of the demands placed
<br />on a barrier system as a function of the vehicle's mass, mass moment of inertia, im-
<br />pact speed, and approach angle.
<br />ZConfigurations are defined as follows:
<br />Double 3-tube guardrail with 60-in-high
<br />wood posts--
<br />A 72 in deep, 12 in wide.
<br />B 120 in deep, 12 in wide.
<br />C 144 in deep, 12 in wide.
<br />D 168 in deep, 14 in wide.
<br />E 120 in deep (with 10-ft by 28-in
<br />soil plate), 14 in wide.
<br />F 120 in deep (wide soil backup mass
<br />of 5 tons per foot), 14 in wide.
<br />Single, wide, multiflange guardrail with
<br />60-in-high poets--
<br />H 72 in deep, 12 in wide.
<br />I 120 in deep, 12 in wide.
<br />J 168 in deep, 14 in wide.
<br />Single, wide, multiflange guardrail with
<br />60-in-high concrete posts--
<br />K 120 in deep, 20 in wide.
<br />
|