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MGB 13-22 BAYS WITHOUT LRS
(where water level or any obstructions are at least 2.7m below bank heights)

STEP 1. Measure the AR gap (see MGB Design, Step 1).

STEP 2. Select a bridge.

Using column (a) of Table 10, choose a bridge whose AR gap range brackets the AR gap measured. Always select the smallest range possible to avoid wasting assets. For example, if the AR gap measured 34.2m, choose the AR gap range of 32.3m to 34.6m, even though the range of 34.1m to 36.4m also meets the criteria. Read the bay configuration column (c). Check the MLC of the bridge column (d) to ensure that it meets what is specified by the tasking authority.

STEP 3. Read the bridge length column (b).

STEP 4. Read the R distance column (f).

STEP 5. Read and note the nose construction column (e).

STEP 6. Identify key construction points.

These are constant for any DS bridge construction 13 through 22 bays without LRS (Figure 7).

O peg -- Marks the clear distance behind the capsill roller beam required to construct the bridge. It is positioned by measuring the R distance, Table 10, column (f), behind the CRB peg.

Bearing Check. The minimum/maximum bearings for any DS bridge 2E + 13 through 2E + 22 bays are shown in Table 11.

• Bridge length is obtained from column (b) of Table 10.
• The AR gap was measured by you in the first step of this design procedure.
• An assumption of 0.9m is made at this point in the calculation sequence because we know that this is the minimum acceptable bearing allowed on the far bank.

If the near bank bearing is within acceptable limits, you do not have to adjust the position of the F peg. Its final position will be the initial value that you assumed of 0.9m from the A peg. The F' peg will be located at a distance equal to the near bank bearing measured from the A' peg on the near bank.

If the near bank bearing is greater than the maximum allowable (2.3m), you must do one of the following:

Move the F peg further away from its present assumed location to a point where the amount of bearing on near bank is less than or equal to 2.3m, and greater than or equal to 1.4m. This will allow the F' peg to be placed at a suitable distance from the A' peg.

Crib up the near bank end of bridge until the maximum allowable bearing is not exceeded.

Dig out the soil from the near bank until the maximum allowable bearing is not exceeded.

Physically locate the key construction points (Figure 8) on the ground and take elevations relative to the CRB peg.

Place the key construction point elevations on the baseline, Figure 8.

STEP 7. Slope check.

Ensure that the difference in elevation between the F' and F pegs does not exceed one-tenth of the total bridge length, if it does, you will have to crib up, undertake a major construction project, or choose another site. Note that the elevation of the F' peg cannot be lower than the elevation of the CRB peg or the bridge will not receive full bearing. In these cases, the normal procedure is to crib up or fill in until the elevation of the F' peg is at least as high as the CRB peg. Otherwise, you would have to remove the soil next to the bank to the level of the F' peg. This same rule applies to the F peg.

Calculate the far bank height (H) and the near bank tall clearance (G) relative to the baseline using these formulas:

STEP 9. RULE 1

Use an LNCG setting to give adequate nose clearance (N) and tall clearance (T). See Table 10.

Choose a setting from column (h), (i), or (j) which gives an N greater than H. If none of the three choices meet the criteria, choose the highest value available.

Check to see if the T value from column (g) is greater than G.

If N is not greater than H, proceed to RULE 2, or if T is not greater than G, proceed to RULE 2.

If N is greater than H and T is greater than G, the LNCG setting chosen has adequate nose clearance and the bridge selected has adequate tail clearance.

STEP 10. RULE 2

Raise both the capsill roller beam (CRB) and rear roller beam (RRB) by 0.253m to increase nose clearance (N) and tail clearance (T).

N RULE 2 = Value obtained from column (k).

T RULE 2 = Value obtained from column (l).

If N RULE 2 is not greater than H and T RULE 2 is greater than G, proceed to RULE 3a.

If N RULE 2 is greater than H and T RULE 2 is not greater than G, proceed to RULE 3b.

If N RULE 2 is greater than H and T RULE 2 is greater than G, the bridge has adequate nose and tail clearance for launching.

STEP 11. RULE 3

Lowering the RRB. If there is ample tall clearance, some increase in N can be obtained by keeping the CRB in its highest position and lowering the RRB to its lowest position. The mathematical equation for this process is shown under column (m).

N RULE 3a = N RULE 2 + Value N calculated from the equation shown under column (m).

STEP 12. RULE 3b

Lowering the CRB. If there is ample nose clearance, some increase in T can be obtained by keeping the RRB in its highest position and lowering the CRB to its lowest position. The mathematical equation for this process is shown under column (n).

T RULE 3b = T RULE 2 + Value calculated from the equation shown under column (n).

STEP 13. Loads required.

From Table 12, determine the the truck and trailer loads required for the bridge.

STEP 14. From Table 13, extract the following information:

Construction time______________________

Manpower requirements_________________

STEP 15. Final design:

2E + _____________________bays

LNCG setting __________________

CRB setting ____________________

RRB setting ____________________

Bearing: NB ________FB _________

Truck and trailer loads ____________

Manpower required ______________

Time to construct ________________