PCD FINAL Flashcards
(29 cards)
In this stage the cross-section is defined and Pe and Ap are estimated.
Preliminary
The values of e (at the critical section), Pe , Ap and the stresses in concrete at transfer and under service loads are calculated. The stresses are checked with the allowable values. The section is modified if required.
Final:
Two Stages of Design
Preliminary AND Final
In this type of members, no tensile stress is allowed in concrete at transfer or under service loads
TYPE 1
In these members, tensile stress is within the cracking stress of concrete.
TYPE 2
3: Here, the tensile stress is such that the crack width is within the allowable limit.
TYPE 3
the stress at the bottom should be limited to fcc,all , where fcc,all is the allowable compressive stress in concrete at transfer
✓At transfer,
the stress at the top should be limited to fcc,all , where fcc,all is the allowable compressive stress in concrete under service loads.
✓At service,
defined as the zone for placing the CGS of the tendons such that C always lies within the kern zone
limiting zone
The strength of each material corresponds to the
ultimate strength
2 TYPES OF SHEAR STRESS
➢ Flexural Shear Stress
➢ Torsional Shear Stress
These cracks form at the bottom near the midspan and propagate upwards.
Flexural cracks:
These cracks form near the neutral axis close to the support and propagate inclined to the beam axis.
Web shear cracks:
These cracks form at the bottom due to flexure and propagate due to both flexure and shear.
Flexure shear cracks:
In this mode, an inclined crack propagates rapidly due to inadequate shear reinforcement.
Diagonal tension failure
There is crushing of the concrete near the compression flange above the tip of the inclined crack.
Shear compression failure
Due to inadequate anchorage of the longitudinal bars, the diagonal cracks propagate horizontally along the bars.
Shear tension failure
The concrete in the web crushes due to inadequate web thickness.
Web crushing failure
For deep beams, the web may buckle and subsequently crush. There can be anchorage failure or failure of the bearing.
Arch rib failure
This is generated due to loading eccentric to the centroidal
Equilibrium torsion:
The analysis for axial load and flexure are based on the following principles of mechanics.
1) Equilibrium of internal and external forces
2) Compatibility of strains in concrete and steel
3) Constitutive relationships of materials.
This is generated by twisting, to maintain compatibility in deformation with the connected member. This type of torsion generates in a primary beam supporting secondary beams.
Compatibility torsion:
