The objective of cranked bars is to provide reinforcements at the bottom in the central point and reinforcements at the top adjacent to the edges both employing the same bars.
Beams generally have maximum sagging bending moment at mid span and maximum hogging moment at supports. Hence the area of bottom reinforcement bars is maximum at mid span and reduces towards supports. To resist the hogging moment at supports, maximum steel is required at top at supports.
To gain economic advantages, part of the bottom reinforcement bars is compressed at a specific distance from the support.
Usually, cranked bars are bent up at 45 degrees. These bars also facilitate to withstand shear force, in the bent up portion. Shear force becomes extreme at supports and here optimal shear resistance is necessary.
Benefits of providing crank bars in slabs
1.To withstand Hogging (Negative Bending Moment) at supports.
2.To get rid of the risk of the failure of the slabs.
3.To experience the shear force. The shear force is always larger at the sections of supports.
4.The strength of slab is raised significantly with crank bars.v
Pile integrity test (PIT) is low strain impact integrity test, is a common non-destructive test method for the
-Evaluation of pile cross-sectional area and length, the pile integrity and continuity, as well as consistency of the pile material.
-Forensic evaluations on existing piles, or quality assurance in the new construction.
The integrity test is applicable to driven concrete piles and cast-in-place piles.
Low strain impact integrity testing provides acceleration or velocity and force (optional) data on slender structural elements. Sonic Echo (SE) and Impulse Response (IR) are employed for the integrity test on deep foundation and piles.
The PIT method works best for column type foundations, such as piles and drilled shafts. Continue reading How to Perform Pile Integrity Test?
The rise in water level upstream of bridge as a result of obstruction to the natural flow caused by the construction of the bridge & its approaches.
Afflux can be estimated by using several empirical equations e.g. IRC:89 (1985) Nagler (1918), Rhebock (1921), Yarnel (1934), Rao (1997) etc.
IRC-SP 13 recommends use of wier /orifice formula for computing flow with known afflux or vice versa. For shallow channels with wide flood planes (as observed in most of the rivers across the bridges on this roadway a rough first approximation of finding afflux can be obtained from the following expression, (Bradley 1970).
h *1 = 3( 1- M) V2n2/2 g
Qb =is that portion of the total discharge Q in the approach channel within a width equal to the projected length of the bridge
Vn2 = Q/An2
An2 =is the gross area of waterway under the bridge opening below normal stream depth corresponding to design flood discharge. Continue reading How is afflux calculated in bridge design?