FIELD WORK NO. 5
LAYING OF A COMPOUND CURVE USING TRANSIT AND TAPE
To be able to lay a compound curve by incremental chords and deflection angle method. To master the skill in leveling, orienting, and using transit effectively. To work cooperatively with one’s group mates and efficiently perform the required task. MATERIALS/INSTRUMENTS:
2 range poles
50 meter tape
The professor gives the following data:
Forward Tangent Direction: N45⁰E
Station of PC: 10+ 003
Compute the elements of the compound curve given the data above. Set the transit at PC. Level and orient the transit at the magnetic south while vernier A is at zero reading. Sight the location of vertex V1 following the given direction of the back tangent T1 and mark the location on the ground at a distance T1 from PC. Set the horizontal vernier to zero again and start locating intermediate points of the curve until your reach PCC using incremental chord lengths and their deflection angle from the backward tangent. Upon reaching PCC, transfer the instrument at PCC.
Again level the instrument and with the telescope inverted position, sight the V1. After locating V1, plunge the telescope into normal position and locate V2 which is along the line from V1 to PCC, and at a computed distance T2 from PCC. Mark V2 with chalk.
Once again, set the horizontal vernier A at zero reading while sighting the position of V2. Using the incremental chord lengths and their deflection angles, lay intermediate points of the second curve on the ground until you reach PT.
Methods of radius-estimating of horizontal curves:
Many groups, including transportation agencies, accident investigators and transportation researchers, would find an accurate, quick and safe method to estimate the radius of horizontal curves particularly useful. The radius estimating methods were as follows: Basic ball bank indicator (BBI)
Advanced Basic ball bank indicator
Global Positioning System (GPS) unit
Speed advisory plate and
Vehicle yaw rate
But in this research, you will only have a glimpse of the last three methods. Plan sheet method:
The plan sheet method determines the radius of a curve by using information provided onas-built plan sheets, which are accessible at local transportation offices. Plan sheets contain information such as location of PC and PT, deflection angle and tangent length for all horizontal curves. The information provided on plan sheets is usually the as built information. From this information, each curve radius was calculated. The required information found on the plan sheets was the location of the start of the curve (PC), the end of the curve (PT) and the degrees of turn of the curve (_). This information was input into the following curve radius-estimation equation and the radius of the curve was calculated as follows (Carlson et al., 2005):
Advisory speed plate method
Advisory speeds for curves have been determined in the field by making several trial runs through the curve at different speeds in a test-vehicle equipped with a ball-bank indicator. The ball-bank reading indicates overturning forces on the vehicle and is a combined measure of the centrifugal force, vehicle roll and super elevation. The generally accepted criteria for setting advisory speeds are ball-bank readings of 14 deg for speeds below 20 mph, 12 deg for speeds between 20 and 35 mph and 10deg for speeds of 35 mph or greater.4 These criteria are based on tests conducted in the 1930s that were intended to represent the 85-90th-percentile curve speed.5. Another method used to determine the advisory speed is using the nomograph in the Traffic Control Devices Handbook (TCDH) which utilizes the following standard curve formula:
A friction factor of 0.16 is assumed in the...
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