Assignment:-Continuous Prestressed Concrete Beam Design
A cast in-place 3-span prestressed concrete T-beam is to be designed. The T-beam concsists of an 8-in thick reinforced concrete deck slab integrally cast onto rectangular girders that have webs 48-in deep by 15-in wide. The spans are to be 90,, 120, 90 ft.
Adopt the following properties:
-f’c = 6ksi
-fpu=270ksi, dt=0.5in
-k=0.005/ft, mu=0.2. Up to 19 tendons can be bundled into a 3.0-in dia. duct.
Design:
1. One T-girder to balance self-weight, where the slab is 8-ft wide.
2. Use end-to end continuous prestress, with a load balancing approach. Attempt to minimize the tendon force by maximizing the drape. Balance as closely as practicable the dead load only by assuming 15% time-dependent losses.
3. Check stresses and losses. For this, draw stress-blocks at critical locations of maximum positive and negative moments in each soan.
4. Determine the ultimate moment capacity of the designed section at key positive negative and positive moment locations.
5. Determine the maximum uniformly distributed live load that can be carried over the span based on achieving U=1.2D + 1.6L
-Service load conditions. For this check allowable stresses, including temperature stress effects as per AAASHTO and also deflection limits (L/800).
-Ultimate load conditions without moment-redistributuion (an elastic solution).
-Ultimate load with moment redistribution permitted. Note you may need to add additional mild steel at the interior support regions to improve section ductility.
6. Based on the resulting shear force distribution, design the shear reinforcement.